JP2018056021A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery excellent in charge/discharge capacity and high-temperature cycle characteristics.SOLUTION: In a lithium ion secondary battery, a positive electrode active material layer contains a lithium-manganese-nickel composite oxide as a positive electrode active material, contains a lithium compound different from the positive electrode active material, and further contains 1.0×10-8 mol/g to 3.0×10-2 mol/g of at least one of compounds represented by formulae (1)-(3) per unit mass of the positive electrode active material layer. LiX1-OR1O-X2Li...(1) LiX1-OR1O-X2R2...(2) R2X1-OR1O-X2R3...(3) [R1 represents a 1-4C alkyl group or halogenated alkylene group; X1 and X2 each independently represent -(COO)n; n represents 0 or 1; R2 and R3 each independently represent H, a 1-10C alkyl group, a 1-10C mono- or polyhydroxyalkyl group, a 2-10C alkenyl group, a 2-10C mono- or polyhydroxyalkenyl group, a 3-6C cycloalkyl group, or an aryl group]SELECTED DRAWING: None

Description

  The present invention relates to a lithium ion secondary battery.

  With the recent development of electronic technology or increasing interest in environmental technology, various electrochemical devices have been used. In particular, there are many demands for energy saving, and there are high expectations for electrochemical devices that can contribute to this. Lithium ion secondary batteries, which are representative examples of power storage devices and also representative examples of non-aqueous electrolyte secondary batteries, have been used mainly as rechargeable batteries for portable devices. However, in recent years, batteries for hybrid vehicles and electric vehicles have been used. As a result, there is an increasing demand for higher energy density.

As a method for increasing the energy density of a lithium ion secondary battery, it is effective to use a positive electrode active material that can be driven at a high voltage. A conventional lithium ion battery using LiCoO _{2 having} a layered structure or LiMn ₂ O ₄ having a spinel structure as a positive electrode active material is charged and discharged at 4.2 V or lower (lithium reference). In contrast, a lithium ion battery using a lithium manganese nickel composite oxide (LiMn _1.5 Ni _0.5 O ₄ or the like) in which the manganese site of LiMn ₂ O ₄ is replaced with nickel or the like as a positive electrode active material is 4 It is known to charge and discharge at 5 V or higher (lithium standard) (Patent Document 1).

  A lithium ion secondary battery using lithium manganese nickel composite oxide as a positive electrode active material has a high operating voltage, and therefore, the electrolytic solution is more easily oxidatively decomposed than a lithium ion secondary battery using a conventional positive electrode active material. Therefore, improvement of durability such as cycle characteristics under a high temperature environment is required for practical use.

  Further, it is known that when a lithium manganese nickel composite oxide is synthesized, nickel-based impurities are likely to appear (Patent Document 2). The main component of this nickel-based impurity is the rock salt structure, which is electrochemically inactive. Therefore, if nickel-based impurities are present, the lithium ion storage / release reaction is inhibited, and the charge / discharge capacity or input / output characteristics Will get worse.

  Conventionally, the technique described in patent document 3 or 4 has been proposed with the aim of improving the battery performance.

  Patent Document 3 describes a method for increasing the discharge capacity by reducing impurities having a by-product rock salt structure and increasing the crystallinity of a lithium manganese nickel composite oxide having a spinel structure.

In Patent Document 4, the following general formula: Li _y Ni _0.5-x Mn _{1.5 + x} O _4-δ {wherein y is 0.9 <y ≦ 1.1, and x is Cycle characteristics or input / output characteristics of a lithium manganese nickel composite oxide in which 0 <x ≦ 0.1 and δ is δ> 0} and the oxidation state of a part of manganese is +3 Is described as improving.

JP-A-9-147867 JP 2004-303710 A International Publication No. 2012/127919 Special table 2009-505929

  However, none of the conventional techniques represented by the technique described in Patent Document 3 or 4 satisfy the cycle characteristics under a high temperature environment (hereinafter also referred to as high temperature cycle characteristics). This has become an important issue for practical use.

  For example, in Patent Document 3, the discharge capacity is increased by reducing nickel impurities, but the oxidative decomposition reaction of the electrolyte solution at the interface between the electrolyte solution and the lithium manganese nickel composite oxide cannot be suppressed. There was a problem with the characteristics.

  In Patent Document 4, the use of a lithium manganese nickel composite oxide in which the oxidation state of a part of manganese is +3 improves the cycle characteristics at room temperature, but there is a problem with the high temperature cycle characteristics.

  In view of the above situation, the problem to be solved by the present invention is to provide a lithium ion secondary battery excellent in charge / discharge capacity and high-temperature cycle characteristics.

The present inventors diligently studied to solve the above problems, and as a result of repeated experiments, by forming a high-quality coating film containing lithium ions on the positive electrode, it has a high discharge capacity and has a characteristic deterioration due to a high-temperature cycle. It was found that it can be suppressed. The present invention has been made based on such knowledge. That is, the present invention is as follows.
[1]
Positive electrode;
Negative electrode;
A separator; and a non-aqueous electrolyte containing lithium ions;
A lithium ion secondary battery comprising
The negative electrode has a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material provided on one or both surfaces of the negative electrode current collector,
The positive electrode has a positive electrode current collector, and a positive electrode active material layer including a positive electrode active material provided on one or both surfaces of the positive electrode current collector,
The positive electrode active material has the following general formula (A):
Li _{1 + a} Mn _1.5-b Ni _0.5-c M _d O _4-δ (A)
{In Formula (A), a is −0.2 ≦ a ≦ 0.2, b is −0.3 ≦ b ≦ 0.3, and c is −0.3 ≦ c ≦ 0. .3, d is 0 ≦ d ≦ 0.3, δ is −0.2 ≦ δ ≦ 0.2, M is a transition metal other than Ni and Mn, and Na, K, Mg, Ca, Zn, Sr, Ba, Al, Ga, In, Si, Ge, Sn, P, Sb, B and S are at least one element selected from the group consisting of Li, It may be substituted with hydrogen. }
And the positive electrode active material layer contains a lithium compound different from the lithium manganese nickel composite oxide, and the following formulas (1) to (3):
LiX ¹ -OR ¹ O—X ² Li (1)
{In Formula (1), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and X ¹ and X ² are each independently — (COO) _n. (Where n is 0 or 1). }
^{LiX 1 -OR 1 O-X 2} R 2 ······ (2)
{In Formula (2), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and R ² is hydrogen, an alkyl group having 1 to 10 carbon atoms, carbon A mono- or polyhydroxyalkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a mono- or polyhydroxyalkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group, X ¹ and X ² are each independently — (COO) _n (where n is 0 or 1). }
^{R 2 X 1 -OR 1 O-} X 2 R 3 ······ (3)
{In Formula (3), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and R ² and R ³ are each independently hydrogen, 10 alkyl groups, mono- or polyhydroxyalkyl groups having 1 to 10 carbon atoms, alkenyl groups having 2 to 10 carbon atoms, mono- or polyhydroxyalkenyl groups having 2 to 10 carbon atoms, cycloalkyl groups having 3 to 6 carbon atoms, Or an aryl group, and X ¹ and X ² are each independently — (COO) _n (where n is 0 or 1). }
Containing at least one compound selected from 1.0 × 10 ⁻⁸ mol / g to 3.0 × 10 ⁻² mol / g per unit mass of the positive electrode active material layer,
The lithium ion secondary battery.
[2]
The content per unit mass of the positive electrode active material layer of one or more compounds selected from the formulas (1) to (3) is A, the content per unit mass of the negative electrode active material layer is B, The lithium ion secondary battery according to [1], wherein 0.2 ≦ A / B ≦ 20.
[3]
The lithium ion secondary battery according to [1] or [2], wherein the lithium compound is at least one selected from the group consisting of lithium carbonate, lithium oxide, and lithium hydroxide.
[4]
In the said general formula (A), c is a lithium ion secondary battery of any one of [1]-[3] which is -0.1 <c <= 0.2.
[5]
In the general formula (A), the lithium ion secondary battery according to any one of [1] to [4], wherein c is −0.1 <c ≦ 0.1.
[6]
The lithium ion battery according to any one of [1] to [5], wherein the lithium manganese nickel composite oxide has a BET specific surface area of 1.0 m ² / g or less.
[7]
Any one of [1] to [6], wherein the nonaqueous electrolytic solution contains at least one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and fluoroethylene carbonate. The lithium ion secondary battery according to item.
[8]
The lithium ion secondary battery according to any one of [1] to [7], wherein the non-aqueous electrolyte contains at least one of LiPF ₆ and LiBF ₄ .

  According to the present invention, it is possible to provide a lithium ion secondary battery excellent in charge / discharge capacity and high-temperature cycle characteristics.

  Hereinafter, although an embodiment of the present invention (hereinafter referred to as “this embodiment”) will be described in detail, the present invention is not limited to this embodiment. The upper limit value and the lower limit value in each numerical range of the present embodiment can be arbitrarily combined to constitute an arbitrary numerical range.

  Generally, a lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolytic solution as main components. As the electrolytic solution, an organic solvent containing lithium ions (hereinafter also referred to as “non-aqueous electrolytic solution”) is used.

<Positive electrode>
The positive electrode in the present embodiment includes a positive electrode current collector and a positive electrode active material layer including a positive electrode active material provided on one side or both sides thereof.

It is preferable that the positive electrode in this embodiment contains a lithium compound as a positive electrode precursor before assembling a lithium ion secondary battery. As will be described later, in the present embodiment, in the step of assembling the lithium ion secondary battery, it is preferable that the negative electrode is pre-doped with lithium ions. As a pre-doping method in the present embodiment, a lithium ion secondary battery is assembled using a positive electrode precursor containing a lithium compound, a negative electrode, a separator, and a non-aqueous electrolyte solution, and then between the positive electrode precursor and the negative electrode. It is preferable to apply a voltage to. The lithium compound is preferably contained in the positive electrode active material layer formed on the positive electrode current collector of the positive electrode precursor.
In the present specification, the positive electrode before the lithium doping step is defined as “positive electrode precursor”, and the positive electrode after the lithium doping step is defined as “positive electrode”.

[Positive electrode active material layer]
The positive electrode active material layer contains a positive electrode active material containing a transition metal oxide, and may contain optional components such as a conductive filler, a binder, and a dispersion stabilizer in addition to this.

  The positive electrode active material layer of the positive electrode precursor preferably contains a lithium compound.

(Positive electrode active material)
The positive electrode active material according to the present embodiment includes a lithium manganese nickel composite oxide. The lithium manganese nickel composite oxide has the following general formula (A):
Li _{1 + a} Mn _1.5-b Ni _0.5-c M _d O _4-δ (A)
{Wherein a is −0.3 ≦ a ≦ 0.3, b is −0.3 ≦ b ≦ 0.3, and c is −0.3 ≦ c ≦ 0.3. Yes, d is 0 ≦ d ≦ 0.3, δ is −0.2 ≦ δ ≦ 0.2, M is a transition metal other than Ni and Mn, and Na, K, Mg, Ca , Zn, Sr, Ba, Al, Ga, In, Si, Ge, Sn, P, Sb, B and S is at least one element, and Li is partially substituted with hydrogen May be represented}.

The lithium manganese nickel composite oxide mainly undergoes oxidation reduction of Mn ³⁺ / Mn ⁴⁺ around 4.25 to 3.8 V (lithium reference), and Ni ²⁺ / Ni ³⁺ around 4.7 V (lithium reference). And / or Ni ³⁺ / Ni ⁴⁺ is oxidized and reduced, and lithium ions are inserted and desorbed.

  In the above general formula (A), c is preferably −0.3 ≦ c ≦ 0.3. When c is −0.3 or more, nickel-based impurities are less likely to be present, lithium ion storage / release reactions are not hindered, and charge / discharge capacity or input / output characteristics are improved. Further, when c is 0.3 or less, the ratio of redox accompanying lithium insertion / extraction due to high-potential nickel increases, and the average operating potential increases. That is, during the dope process described later, the amount of metal ion oxidation-reduction associated with insertion / extraction of lithium in the positive electrode active material decreases until the compound generated by oxidative decomposition of the lithium compound covers the positive electrode active material, Since the amount of nickel ions and manganese ions eluted from the positive electrode active material is reduced, the high-temperature cycle characteristics are improved. In the above general formula (A), c is more preferably −0.1 <c ≦ 0.2, and further preferably −0.1 <c ≦ 0.1.

The BET surface area of the lithium manganese nickel composite oxide is preferably 1.0 m ² / g or less. When the BET surface area is 1.0 m ² / g or less, the non-aqueous electrolyte solution is less likely to come into contact with the lithium manganese nickel composite oxide, and the non-aqueous electrolyte solution can be prevented from being oxidatively decomposed. The lower limit value of the BET surface area of the lithium manganese nickel composite oxide may exceed 0 m ² / g, or may be 0.3 m ² / g or more. When the BET surface area is 0.3 m ² / g or more, the input / output characteristics are improved without inhibiting the insertion / extraction of Li ions.

As the positive electrode active material in the present embodiment, only a lithium manganese nickel composite oxide may be used, or another positive electrode active material may be used in combination with the lithium manganese nickel composite oxide. Other positive electrode active materials include, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x Ni _y M _(1-y) O ₂ (wherein M is Co, Mn, Al, Fe, Mg, and And at least one element selected from the group consisting of Ti and y satisfies 0.2 <y <0.97.), Li _x Ni _1/3 Co _1/3 Mn _1/3 O ₂ , Li _x MnO ₂ , α-Li _x FeO ₂ , Li _x VO ₂ , Li _x CrO ₂ , Li _x FePO ₄ (wherein x satisfies 0 ≦ x ≦ 1) and the like. The content ratio of the other positive electrode active material is preferably 15% by mass or less, more preferably 10% by mass or less, based on the total mass of the positive electrode active material layer in the positive electrode precursor. When the content rate of other positive electrode active materials is 15 mass% or less, the energy density of a lithium ion secondary battery can be raised.

  The average particle size of the positive electrode active material is preferably 1 to 20 μm. When the average particle diameter of the positive electrode active material is 1 μm or more, the capacity per electrode volume tends to increase because the density of the active material layer is high. If the average particle size of the positive electrode active material is small, the durability may be low. However, if the average particle size is 1 μm or more, the durability is unlikely to decrease. When the average particle size of the positive electrode active material is 20 μm or less, it tends to be easily adapted to high-speed charge / discharge. The average particle diameter of the positive electrode active material is more preferably 1 to 15 μm, still more preferably 1 to 10 μm.

  The content ratio of the positive electrode active material in the positive electrode active material layer is preferably 35% by mass or more and 95% by mass or less based on the total mass of the positive electrode active material layer in the positive electrode precursor. As a minimum of the content rate of a positive electrode active material, it is more preferable that it is 45 mass% or more, and it is further more preferable that it is 55 mass% or more. As an upper limit of the content rate of a positive electrode active material, it is still more preferable that it is 90 mass% or less. When the content ratio of the positive electrode active material in the positive electrode active material layer is 35% by mass or more and 95% by mass or less, suitable charge / discharge characteristics are exhibited.

(Lithium compound)
In the present specification, the “lithium compound” means a lithium compound that is not a positive electrode active material and is not a compound of the formulas (1) to (3).

  As a lithium compound, lithium carbonate, lithium oxide, lithium hydroxide, lithium fluoride, lithium chloride, lithium oxalate, and iodide can be decomposed at the positive electrode in the lithium doping step described later and release lithium ions. Examples thereof include at least one selected from the group consisting of lithium, lithium nitride, lithium sulfide, lithium phosphide, lithium nitrate, lithium sulfate, lithium phosphate, lithium oxalate, lithium formate, and lithium acetate. The lithium compound is preferably lithium carbonate, lithium oxide, or lithium hydroxide, and more preferably lithium carbonate that can be handled in air and has low hygroscopicity. Such a lithium compound is decomposed by the application of a voltage, functions as a lithium-doped dopant source for the negative electrode, and forms pores in the positive electrode active material layer, so that it has excellent electrolyte retention and ion conduction. A positive electrode having excellent properties can be formed.

The lithium compound is preferably particulate. The average particle diameter of the particulate lithium compound is preferably 0.1 μm or more and 100 μm or less. The upper limit of the average particle diameter of the lithium compound is more preferably 50 μm or less, and still more preferably 10 μm or less. If the average particle diameter of the lithium compound is 0.1 μm or more, the volume of the vacancies remaining after the oxidation reaction of the lithium compound in the positive electrode becomes sufficiently large to hold the electrolyte solution, so that high load charge / discharge characteristics are improved. . When the average particle size of the lithium compound is 100 μm or less, the surface area of the lithium compound does not become excessively small, so that the speed of the oxidation reaction of the lithium compound can be ensured. If the average particle diameter of a lithium compound is 10 micrometers or less, since the surface area of a lithium compound increases and an oxidation rate can be improved more, it is still more preferable.
Various methods can be used for micronization of the lithium compound. For example, a pulverizer such as a ball mill, a bead mill, a ring mill, a jet mill, or a rod mill can be used.

  The content ratio of the lithium compound contained in the positive electrode active material layer in the positive electrode precursor is preferably 1% by mass or more and 50% by mass or less based on the total mass of the positive electrode active material layer in the positive electrode precursor. % To 20% by mass is more preferable. If the content ratio of the lithium compound contained in the positive electrode active material layer in the positive electrode precursor is 1% by mass or more, the negative electrode can be sufficiently doped with lithium, and if it is 50% by mass or less, the lithium compound reacts. It is preferable because the positive electrode density can be increased and the strength of the positive electrode can be maintained.

  The amount of the lithium compound contained in the positive electrode active material layer in the positive electrode is preferably 0.5% by mass or more and 50% by mass or less, more preferably 0.5% by mass, based on the total mass of the positive electrode active material layer in the positive electrode. It is 20 mass% or less. If the amount of the lithium compound contained in the positive electrode active material layer in the positive electrode is 0.5% by mass or more, a sufficient amount of the lithium compound that adsorbs an active product such as fluorine ions generated in a high load charge / discharge cycle is present. Therefore, the high load charge / discharge cycle characteristics are improved. When the amount of the lithium compound contained in the positive electrode active material layer in the positive electrode is 50% by mass or less, the energy density of the lithium ion secondary battery can be increased.

(High load charge / discharge characteristics)
When charging / discharging a lithium ion secondary battery, lithium ions in the electrolytic solution move along with charging / discharging and react with the active material. Here, the activation energies of the ion insertion reaction and desorption reaction into the active material are different. Therefore, especially when the charge / discharge load is large, ions cannot follow the change in charge / discharge. As a result, the electrolyte concentration in the bulk electrolyte solution decreases, and the resistance of the lithium ion secondary battery increases.
When a lithium compound is contained in the positive electrode precursor, good vacancies that can hold the electrolytic solution are formed inside the positive electrode by oxidizing and decomposing the lithium compound. Although not limited to theory, the positive electrode having such vacancies is supplied with ions from the electrolyte in the vacancies formed in the vicinity of the active material at any time during charge and discharge, and therefore has high load charge / discharge cycle characteristics. It is thought to improve.

(Optional component)
The positive electrode active material layer in the present embodiment may contain optional components such as a conductive filler, a binder, and a dispersion stabilizer in addition to the positive electrode active material and the lithium compound as necessary.

  The conductive filler is not particularly limited, and for example, acetylene black, ketjen black, vapor grown carbon fiber, graphite, carbon nanotube, a mixture thereof, and the like can be used. The amount of the conductive filler to be used is preferably more than 0 parts by mass and 30 parts by mass or less, more preferably more than 0 parts by mass and 25 parts by mass or less, further preferably 1 part by mass or more and 20 parts by mass with respect to 100 parts by mass of the positive electrode active material. Or less. When the mixing amount is 30 parts by mass or less, the content ratio of the positive electrode active material in the positive electrode active material layer is increased, and the energy density per volume of the positive electrode active material layer can be ensured.

  The binder is not particularly limited. For example, PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), polyimide, latex, styrene-butadiene copolymer, fluororubber, acrylic copolymer, and the like. Can be used. The amount of the binder used is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 1 part by mass or more and 15 parts by mass or less, and further preferably 1 part by mass or more and 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. Or less. When the amount of the binder is 1% by mass or more, sufficient electrode strength is exhibited. On the other hand, when the amount of the binder is 30 parts by mass or less, high input / output characteristics are exhibited without hindering the entry / exit and diffusion of ions to / from the positive electrode active material.

  Although it does not restrict | limit especially as a dispersion stabilizer, For example, PVP (polyvinyl pyrrolidone), PVA (polyvinyl alcohol), a cellulose derivative etc. can be used. The amount of the dispersion stabilizer used is preferably more than 0 parts by mass and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. When the amount of the dispersion stabilizer is 10 parts by mass or less, high input / output characteristics are exhibited without hindering the entry / exit and diffusion of ions to / from the positive electrode active material.

[Positive electrode current collector]
The material constituting the positive electrode current collector in the present embodiment is not particularly limited as long as it is a material that has high electron conductivity and does not easily deteriorate due to elution into the electrolyte solution and reaction with the electrolyte or ions. A foil is preferred. As the positive electrode current collector in the lithium ion secondary battery of the present embodiment, an aluminum foil is particularly preferable.
The metal foil may be a normal metal foil having no irregularities or through holes, or a metal foil having irregularities subjected to embossing, chemical etching, electrolytic deposition, blasting, etc., expanded metal, punching metal, A metal foil having a through-hole such as an etching foil may be used.
Although the thickness of the positive electrode current collector is not particularly limited as long as the shape and strength of the positive electrode can be sufficiently maintained, for example, 1 to 100 μm is preferable. When the positive electrode current collector has irregularities or through holes, the thickness of the positive electrode current collector is measured based on a portion where there are no irregularities or through holes.

<Negative electrode>
The negative electrode in the present embodiment includes a negative electrode current collector and a negative electrode active material layer including a negative electrode active material provided on one or both surfaces thereof.

[Negative electrode active material layer]
The negative electrode active material layer includes a negative electrode active material that can occlude and release lithium ions, and may include optional components such as a conductive filler, a binder, and a dispersion stabilizer as necessary.

(Negative electrode active material)
As the negative electrode active material, a material capable of inserting and extracting lithium ions can be used. Specific examples of the negative electrode active material include carbon materials, titanium oxide, silicon, silicon oxide, silicon alloys, silicon compounds, tin, and tin compounds. The content of the carbon material is preferably 50% by mass or more, more preferably 70% by mass or more, with respect to the total mass of the negative electrode active material. The content of the carbon material may be 100% by mass, but is preferably 90% by mass or less, for example, 80% by mass or less from the viewpoint of obtaining the effect of the combined use with other materials. Also good.

  Examples of carbon materials include non-graphitizable carbon materials; graphitizable carbon materials; carbon blacks; carbon nanoparticles; activated carbon; artificial graphite; natural graphite; graphitized mesophase carbon microspheres; graphite whiskers; Amorphous carbonaceous materials; carbonaceous materials obtained by heat-treating carbonaceous material precursors such as petroleum pitch, coal pitch, mesocarbon microbeads, coke, synthetic resin (eg phenol resin); furfuryl Examples include thermal decomposition products of alcohol resins or novolak resins; fullerenes; carbon nanophones; and composite carbon materials thereof.

  The average particle diameter of the negative electrode active material is preferably 1 μm or more and 10 μm or less, the lower limit value is more preferably 2 μm or more, further preferably 2.5 μm or more, and the upper limit value is more preferably 6 μm or less, still more preferably. Is 4 μm or less. When the average particle diameter of the negative electrode active material is 1 μm or more and 10 μm or less, good durability is maintained.

(Optional component)
In addition to the negative electrode active material, the negative electrode active material layer in the present embodiment may include optional components such as a conductive filler, a binder, and a dispersion stabilizer as necessary.

  The type of the conductive filler is not particularly limited, and examples thereof include acetylene black, ketjen black, and vapor grown carbon fiber. The amount of the conductive filler used is preferably more than 0 parts by mass and less than 30 parts by mass, more preferably more than 0 parts by mass and less than 20 parts by mass, and even more preferably more than 0 parts by mass and more than 15 parts by mass with respect to 100 parts by mass of the negative electrode active material. Or less.

  The binder is not particularly limited. For example, PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), polyimide, latex, styrene-butadiene copolymer, fluororubber, acrylic copolymer, and the like. Can be used. The amount of the binder used is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 2 parts by mass or more and 27 parts by mass or less, and still more preferably 3 parts by mass or more and 25 parts by mass with respect to 100 parts by mass of the negative electrode active material. Or less. When the amount of the binder is 1% by mass or more, sufficient electrode strength is exhibited. When the amount of the binder is 30 parts by mass or less, high input / output characteristics are exhibited without inhibiting lithium ions from entering and leaving the negative electrode active material.

  Although it does not restrict | limit especially as a dispersion stabilizer, For example, PVP (polyvinyl pyrrolidone), PVA (polyvinyl alcohol), a cellulose derivative etc. can be used. The amount of the dispersion stabilizer used is preferably 0 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the amount of the dispersion stabilizer is 10 parts by mass or less, high input / output characteristics are exhibited without inhibiting lithium ions from entering and leaving the negative electrode active material.

[Negative electrode current collector]
The material constituting the negative electrode current collector in this embodiment is preferably a metal foil that has high electron conductivity and does not deteriorate due to elution into a non-aqueous electrolyte and reaction with an electrolyte or ions. There is no restriction | limiting in particular as such metal foil, For example, aluminum foil, copper foil, nickel foil, stainless steel foil, etc. are mentioned. The negative electrode current collector in the lithium ion secondary battery of this embodiment is preferably a copper foil.
The metal foil may be a normal metal foil having no irregularities or through holes, or a metal foil having irregularities subjected to embossing, chemical etching, electrolytic deposition, blasting, etc., expanded metal, punching metal, A metal foil having a through-hole such as an etching foil may be used.
The thickness of the negative electrode current collector is not particularly limited as long as the shape and strength of the negative electrode can be sufficiently maintained, but for example, 1 to 100 μm is preferable. When the negative electrode current collector has irregularities or through holes, the thickness of the negative electrode current collector is measured based on a portion where there are no irregularities or through holes.

<Production of positive electrode precursor and negative electrode>
Each of the positive electrode precursor and the negative electrode has a positive electrode active material layer on one side or both sides of the positive electrode current collector, and a negative electrode active material layer on one side or both sides of the negative electrode current collector. Typically, the positive electrode active material layer is fixed on one surface or both surfaces of the positive electrode current collector, and the negative electrode active material layer is fixed on one surface or both surfaces of the negative electrode current collector.

  The positive electrode precursor and the negative electrode can be manufactured by an electrode manufacturing technique in a known lithium ion secondary battery, electric double layer capacitor, or the like. For example, various materials including a positive electrode active material or a negative electrode active material are dispersed or dissolved in water or an organic solvent to prepare slurry-like positive electrode coating solution and negative electrode coating solution, respectively. By coating these positive electrode coating liquid and negative electrode coating liquid on one side or both sides of the positive electrode current collector and the negative electrode current collector, respectively, a coating film is formed, and this is dried, whereby the positive electrode A precursor and a negative electrode can be obtained. You may press the obtained positive electrode precursor and / or negative electrode, and may adjust the film thickness, bulk density, etc. of a positive electrode active material layer and / or a negative electrode active material layer. Alternatively, various materials including a positive electrode active material or a negative electrode active material are mixed by a dry method without using a solvent, and the resulting mixture is press-molded, and then a positive electrode current collector or a negative electrode current collector using a conductive adhesive. A method of attaching to an electric body is also possible.

  The positive electrode coating liquid and the negative electrode coating liquid are obtained by dry blending part or all of various positive electrode active materials or various material powders containing the negative electrode active material, and then water or an organic solvent, and / or a binder or It may be prepared by adding a liquid or slurry substance in which the dispersion stabilizer is dissolved or dispersed. Also, a coating liquid is prepared by adding various material powders containing a positive electrode active material or a negative electrode active material to a liquid or slurry substance in which a binder or dispersion stabilizer is dissolved or dispersed in water or an organic solvent. May be.

  As a method of dry blending part or all of various material powders including the positive electrode active material, for example, using a ball mill or the like, the positive electrode active material and the lithium compound, and a conductive filler as necessary are pre-mixed to be conductive. Alternatively, premixing may be performed in which a conductive material is coated on a lithium compound having a low content. Thereby, a lithium compound becomes easy to decompose | disassemble with a positive electrode precursor in the lithium dope process mentioned later. When water is used as a solvent for the positive electrode coating solution, the addition of a lithium compound may make the coating solution alkaline, so a pH adjuster may be added as necessary.

  The dissolving or dispersing method is not particularly limited, but preferably a disperser such as a homodisper, a multi-axis disperser, a planetary mixer, a thin film swirl type high speed mixer or the like can be used. In order to obtain a coating liquid in a good dispersion state, it is preferable to disperse at a peripheral speed of 1 m / s to 50 m / s. A peripheral speed of 1 m / s or more is preferable because various materials can be dissolved or dispersed satisfactorily. A peripheral speed of 50 m / s or less is preferable because various materials are not easily broken by heat and shearing force due to dispersion, and reaggregation is reduced.

  Regarding the degree of dispersion of the coating liquid, the particle size measured with a particle gauge is preferably 0.1 μm or more and 100 μm or less. As the upper limit of the degree of dispersion, the particle size is more preferably 80 μm or less, and further preferably the particle size is 50 μm or less. A particle size of 0.1 μm or more means that various material powders including the positive electrode active material are not excessively crushed during the preparation of the coating liquid. Further, when the particle size is 100 μm or less, clogging during coating liquid discharge and streaking of the coating film are not generated, and coating can be performed stably.

The viscosity (ηb) of the coating solution is preferably 1,000 mPa · s or more and 20,000 mPa · s or less, more preferably 1,500 mPa · s or more and 10,000 mPa · s or less, and further preferably 1,700 mPa · s or more. 5,000 mPa · s or less. When the viscosity (ηb) of the coating liquid is 1,000 mPa · s or more, dripping during coating film formation is suppressed, and the coating film width and thickness can be controlled well. If the viscosity (ηb) of the coating liquid is 20,000 mPa · s or less, the coating liquid can be stably applied with little pressure loss in the flow path of the coating liquid when a coating machine is used, and the desired coating thickness The following can be controlled.
The TI value (thixotropic index value) of the coating solution is preferably 1.1 or more, more preferably 1.2 or more, and still more preferably 1.5 or more. When the TI value is 1.1 or more, the coating film width and thickness can be favorably controlled.

  The method for forming the coating film is not particularly limited, but preferably a coating machine such as a die coater, a comma coater, a knife coater, or a gravure coating machine can be used. The coating film may be formed by single layer coating or may be formed by multilayer coating. In the case of multilayer coating of the positive electrode precursor, the coating solution composition may be adjusted so that the lithium compound content in each layer of the coating film is different. The coating speed is preferably 0.1 m / min to 100 m / min, more preferably 0.5 m / min to 70 m / min, and further preferably 1 m / min to 50 m / min. If the coating speed is 0.1 m / min or more, the coating can be performed stably, and if it is 100 m / min or less, sufficient coating accuracy can be secured.

  The method for drying the coating film is not particularly limited, but a drying method such as hot air drying or infrared (IR) drying can be preferably used. The coating film may be dried at a single temperature or may be dried by changing the temperature in multiple stages. Moreover, you may dry combining several drying methods. The drying temperature is preferably 25 ° C. or higher and 200 ° C. or lower, more preferably 40 ° C. or higher and 180 ° C. or lower, and further preferably 50 ° C. or higher and 160 ° C. or lower. When the drying temperature is 25 ° C. or higher, the solvent in the coating film can be sufficiently volatilized. If the drying temperature is 200 ° C. or lower, the cracking of the coating due to rapid solvent volatilization, the uneven distribution of the binder due to migration, the positive electrode current collector and the negative electrode current collector, the positive electrode active material layer and the negative electrode active material layer Oxidation can be suppressed.

The method for pressing the positive electrode precursor and the negative electrode is not particularly limited, but a press such as a hydraulic press or a vacuum press can be preferably used. The film thickness, bulk density, and electrode strength of the positive electrode active material layer and the negative electrode active material layer can be adjusted by the press pressure, the gap, and the surface temperature of the press part described later.
The pressing pressure is preferably 0.5 kN / cm or more and 20 kN / cm or less, more preferably 1 kN / cm or more and 10 kN / cm or less, and further preferably 2 kN / cm or more and 7 kN / cm or less. If the pressing pressure is 0.5 kN / cm or more, the electrode strength can be sufficiently increased. When the pressing pressure is 20 kN / cm or less, the positive electrode precursor and the negative electrode are unlikely to bend or wrinkle, and can be easily adjusted to a desired film thickness and bulk density.
The gap between the press rolls can be set to an arbitrary value according to the film thickness after drying so as to have a desired film thickness and bulk density.
The press speed can be set to an arbitrary speed so that bending and wrinkles are reduced.
The surface temperature of the press part may be room temperature, or the surface of the press part may be heated if necessary. The lower limit of the surface temperature of the press part when heating is preferably the melting point of the binder used minus 60 ° C. or more, more preferably the melting point of the binder minus 45 ° C. or more, and more preferably the melting point of the binder minus 30. It is above ℃. The upper limit of the surface temperature of the press portion when heating is preferably the melting point of the binder used plus 50 ° C. or less, more preferably the melting point of the binder plus 30 ° C. or less, and more preferably the melting point of the binder plus 20 It is below ℃. For example, when PVdF (polyvinylidene fluoride: melting point 150 ° C.) is used as the binder, it is preferably pressed at 90 ° C. or higher and 200 ° C. or lower, more preferably 105 ° C. or higher and 180 ° C. or lower, and further preferably 120 ° C. or higher and 170 ° C. or lower. Heat the surface of the part. When a styrene-butadiene copolymer (melting point 100 ° C.) is used as the binder, it is preferably pressed at 40 ° C. or higher and 150 ° C. or lower, more preferably 55 ° C. or higher and 130 ° C. or lower, and further preferably 70 ° C. or higher and 120 ° C. or lower. Warm the surface of the part.
The melting point of the binder can be determined at the endothermic peak position of DSC (Differential Scanning Calorimetry). For example, using a differential scanning calorimeter “DSC7” manufactured by PerkinElmer Co., Ltd., 10 mg of sample resin is set in a measurement cell, and the temperature is increased from 30 ° C. to 250 ° C. at a temperature increase rate of 10 ° C./min in a nitrogen gas atmosphere. The temperature is raised, and the endothermic peak temperature in the temperature raising process becomes the melting point.
You may press several times, changing conditions of press pressure, a crevice, speed, and surface temperature of a press part.

  The thickness of the positive electrode active material layer is preferably 20 μm or more and 200 μm or less per side of the positive electrode current collector. The thickness of the positive electrode active material layer is more preferably 25 μm or more and 100 μm or less, more preferably 30 μm or more and 80 μm or less per side. If the thickness of the positive electrode active material layer is 20 μm or more, sufficient charge / discharge capacity can be exhibited. If the thickness of the positive electrode active material layer is 200 μm or less, the ion diffusion resistance in the electrode can be kept low. Therefore, if the thickness of the positive electrode current collector layer is 20 μm or more and 200 μm or less, sufficient output characteristics can be obtained, the cell volume can be reduced, and therefore the energy density can be increased. The thickness of the positive electrode active material layer in the case where the positive electrode current collector has through-holes and irregularities is the thickness of the positive electrode active material layer per side in the portion of the positive electrode current collector that does not have through-holes and irregularities. The average value of

  The thickness of the negative electrode active material layer is preferably 5 μm or more and 100 μm or less per side of the negative electrode current collector. The lower limit of the thickness of the negative electrode active material layer is more preferably 7 μm or more, and further preferably 10 μm or more. The upper limit of the thickness of the negative electrode active material layer is more preferably 80 μm or less, and even more preferably 60 μm or less. When the thickness of the negative electrode active material layer is 5 μm or more, streaks or the like hardly occur when the negative electrode active material layer is applied, and the coating property is excellent. When the thickness of the negative electrode active material layer is 100 μm or less, a high energy density can be expressed by reducing the cell volume. Note that the thickness of the negative electrode active material layer in the case where the negative electrode current collector has unevenness means an average value of the thickness of the negative electrode active material layer per one surface in a portion where the negative electrode current collector does not have unevenness.

The bulk density of the negative electrode active material layer is preferably 0.30 g / cm ³ or more and 1.8 g / cm ³ or less, more preferably 0.40 g / cm ³ or more and 1.5 g / cm ³ or less, and further preferably 0.45 g. / Cm ³ or more and 1.3 g / cm ³ or less. When the bulk density of the negative electrode active material layer is 0.30 g / cm ³ or more, sufficient strength can be maintained and sufficient conductivity between the negative electrode active materials can be exhibited. If the bulk density of the negative electrode active material layer is 1.8 g / cm ³ or less, vacancies capable of sufficiently diffusing ions in the negative electrode active material layer can be secured.

<Separator>
The positive electrode precursor and the negative electrode are generally laminated or wound via a separator to form an electrode laminate or an electrode winding body having a positive electrode precursor, a negative electrode, and a separator.

  As the separator, a polyethylene microporous film or a polypropylene microporous film used in a lithium ion secondary battery, a cellulose nonwoven paper used in an electric double layer capacitor, or the like can be used. A film composed of organic or inorganic fine particles may be laminated on one side or both sides of these separators. Further, organic or inorganic fine particles may be contained inside the separator.

  The thickness of the separator is preferably 5 μm or more and 35 μm or less. It is preferable that the thickness of the separator is 5 μm or more because self-discharge due to an internal micro short circuit tends to be small. It is preferable that the thickness of the separator is 35 μm or less because the output characteristics of the lithium ion secondary battery tend to be high.

  The thickness of the film composed of organic or inorganic fine particles is preferably 1 μm or more and 10 μm or less. A film composed of organic or inorganic fine particles having a thickness of 1 μm or more is preferable because self-discharge due to internal micro-shorts tends to be small. It is preferable that the film composed of organic or inorganic fine particles has a thickness of 10 μm or less because the output characteristics of the lithium ion secondary battery tend to be high.

The separator may contain an organic polymer that swells by permeation of the non-aqueous electrolyte solution, or an organic polymer may be used alone as an alternative to the separator. Although there is no restriction | limiting in particular as an organic polymer, Affinity with non-aqueous electrolyte solution is good, and what gelatinizes by making electrolyte solution osmose | permeate and swell is preferable. As the organic polymer, for example, polyethylene oxide, polyacrylonitrile, poly (vinylidene fluoride), polymethyl methacrylate, and a mixture thereof can be suitably used because they can exhibit high lithium ion conductivity when gelled.
The organic polymer can include an electrolyte within the organic polymer. Therefore, when an exterior body is damaged, there exists an effect which prevents that an electrolyte solution flows out from a lithium ion secondary battery, and it is preferable on safety.

<Manufacture of lithium ion secondary batteries>
[assembly]
In the cell assembling step, a positive electrode terminal and a negative electrode terminal are connected to a laminate formed by laminating a positive electrode precursor and a negative electrode cut into a sheet shape via a separator to produce an electrode laminate. Or a positive electrode terminal and a negative electrode terminal are connected to the winding body which laminated | stacked and wound the positive electrode precursor and the negative electrode through the separator, and an electrode winding body is produced. The shape of the electrode winding body may be a cylindrical shape or a flat shape.

  Although the connection method of a positive electrode terminal and a negative electrode terminal is not specifically limited, It can carry out by methods, such as resistance welding and ultrasonic welding.

[Exterior body]
As the exterior body, a metal can, a laminate packaging material, or the like can be used. The metal can is preferably made of aluminum. As the laminate packaging material, a film in which a metal foil and a resin film are laminated is preferable, and a laminate packaging material composed of three layers of outer layer resin film / metal foil / inner layer resin film is exemplified. The outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and a resin such as nylon or polyester can be suitably used. The metal foil is for preventing the permeation of moisture and gas, and foils of copper, aluminum, stainless steel and the like can be suitably used. The inner layer resin film protects the metal foil from the electrolyte contained therein, and melts and seals the outer body during heat sealing. Polyolefin, acid-modified polyolefin, and the like can be suitably used.

[Storage in exterior material]
The dried electrode laminate or electrode winding body is preferably housed in an exterior body typified by a metal can or a laminate packaging material, and is sealed with only one opening left. Although the sealing method of an exterior body is not specifically limited, When using a laminate packaging material, methods, such as a heat seal and an impulse seal, can be used.

[Dry]
It is preferable to remove the residual solvent by drying the electrode laminate or the electrode winding body housed in the exterior body. Although a drying method is not limited, it can dry by vacuum drying etc. The residual solvent is preferably 1.5% by mass or less based on the weight of the positive electrode active material layer or the negative electrode active material layer. When the residual solvent is more than 1.5% by mass, the solvent remains in the system, and the self-discharge characteristics and the cycle characteristics may be deteriorated.

[Non-aqueous electrolyte]
The electrolytic solution in the present embodiment is a non-aqueous electrolytic solution containing lithium ions. That is, this non-aqueous electrolyte contains a non-aqueous solvent described later. The non-aqueous electrolyte solution preferably contains 0.5 mol / L or more lithium salt based on the total volume of the non-aqueous electrolyte solution. That is, the non-aqueous electrolyte contains lithium ions as an electrolyte.

Examples of the lithium salt include (LiN (SO ₂ F) ₂ ), LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₅ ), LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₄ H), LiC (SO ₂ F) ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ , LiCF _{3 SO 3, LiC 4 F 9 SO} 3, LiPF 6, and LiBF ₄ and the like. these can be used alone or may be used in combination of two or more. The lithium salt preferably contains LiPF ₆ and / or LiBF ₄ because it can exhibit high conductivity.

  The lithium salt concentration in the non-aqueous electrolyte is preferably 0.5 mol / L or more, and more preferably in the range of 0.5 to 2.0 mol / L. If the lithium salt concentration is 0.5 mol / L or more, since the anion is sufficiently present, the battery capacity can be sufficiently increased. When the lithium salt concentration is 2.0 mol / L or less, it is possible to prevent undissolved lithium salt from precipitating in the non-aqueous electrolyte and preventing the viscosity of the non-aqueous electrolyte from becoming too high, resulting in a decrease in conductivity. This is preferable because it is difficult to reduce output characteristics.

The nonaqueous electrolytic solution in the present embodiment preferably contains a cyclic carbonate and a chain carbonate as a nonaqueous solvent. The nonaqueous electrolytic solution containing a cyclic carbonate and a chain carbonate is advantageous in that a lithium salt having a desired concentration is dissolved and a high lithium ion conductivity is exhibited. Examples of the cyclic carbonate include alkylene carbonate compounds represented by ethylene carbonate, propylene carbonate, butylene carbonate, and the like. The alkylene carbonate compound is typically unsubstituted. Examples of the chain carbonate include dialkyl carbonate compounds represented by dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, dibutyl carbonate and the like. The dialkyl carbonate compound is typically unsubstituted.
In the present embodiment, from the viewpoint of ensuring the solubility of lithium salt and high lithium ion conductivity, and containing a precursor of a compound represented by formulas (1) to (3) described later in the battery, The nonaqueous electrolytic solution preferably contains at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and fluoroethylene carbonate as an organic solvent.

  The total content of the cyclic carbonate and the chain carbonate is preferably 50% by mass or more, more preferably 65% by mass or more, still more preferably 95% by mass or less, and still more preferably, based on the total mass of the nonaqueous electrolytic solution. 90% by mass or less. When the total content of the cyclic carbonate and the chain carbonate is 50% by mass or more, a lithium salt having a desired concentration can be dissolved, and high lithium ion conductivity can be expressed. When the total concentration of the cyclic carbonate and the chain carbonate is 95% by mass or less, the electrolytic solution can further contain an additive described later.

  The non-aqueous electrolyte solution in the present embodiment may further contain an additive. The additive is not particularly limited, and examples thereof include sultone compounds, cyclic phosphazenes, acyclic fluorine-containing ethers, fluorine-containing cyclic carbonates, cyclic carbonates, cyclic carboxylic acid esters, and cyclic acid anhydrides. They can be used alone or in admixture of two or more.

[Liquid injection, impregnation, sealing process]
After the assembly process is completed, a nonaqueous electrolytic solution is injected into the electrode laminate housed in the exterior body. It is desirable that further impregnation is performed after the injection, and the positive electrode, the negative electrode, and the separator are sufficiently immersed in the nonaqueous electrolytic solution. In a state where the non-aqueous electrolyte solution is not immersed in at least a part of the positive electrode, the negative electrode, and the separator, the lithium doping proceeds in a non-uniform manner in the lithium doping step described later. It rises or the durability decreases. The impregnation method is not particularly limited. For example, after pouring a non-aqueous electrolyte, the electrode laminate is placed in a decompression chamber with the exterior material opened, and the inside of the chamber is decompressed using a vacuum pump. A method of returning the pressure to atmospheric pressure again can be used. After the impregnation, the electrode laminate can be sealed while being decompressed in a state where the exterior material is opened, and can be sealed.

[Lithium doping process]
In this embodiment, the positive electrode active material and lithium compound containing lithium ions function as a dopant source for lithium ions into the negative electrode active material. In the lithium doping step, a negative electrode active material layer is formed by applying a voltage between the positive electrode precursor and the negative electrode, decomposing the lithium compound in the positive electrode precursor to release lithium ions, and reducing lithium ions at the negative electrode It is preferable to pre-dope riotium ions.

In the lithium doping step, a gas such as CO ₂ is generated with the oxidative decomposition of the lithium compound in the positive electrode precursor. Therefore, when applying a voltage, it is preferable to provide a means for releasing the generated gas to the outside of the exterior body. As this means, for example, a method in which a voltage is applied in a state where a part of the exterior body is opened; in a state in which an appropriate gas releasing means such as a gas vent valve or a gas permeable film is previously installed in a part of the exterior body A method of applying a voltage;
Etc.

[Aging process]
It is preferable to age the electrode stack after lithium doping. In aging, the solvent in the non-aqueous electrolyte is decomposed at the negative electrode, and a lithium ion permeable solid polymer film is formed on the negative electrode surface.

  The aging method is not particularly limited. For example, a method of reacting a solvent in the electrolytic solution under a high temperature environment can be used.

[Degassing process]
It is preferable to further degas after aging to reliably remove the gas remaining in the electrolyte, the positive electrode, and the negative electrode. In a state where gas remains in at least a part of the electrolytic solution, the positive electrode, and the negative electrode, ion conduction is inhibited, and thus the resistance of the obtained lithium ion secondary battery is increased.

  The degassing method is not particularly limited. For example, a method in which the electrode stack is placed in a decompression chamber with the exterior body opened, and the interior of the chamber is decompressed using a vacuum pump can be used. . After degassing, the exterior body is sealed by sealing the exterior body, and a lithium ion secondary battery can be manufactured.

<Lithium ion secondary battery>
A lithium ion secondary battery can be manufactured by the above method. In one embodiment, the lithium ion secondary battery includes a positive electrode having a porous positive electrode active material layer having pores that are traces of decomposition and dissipation of a lithium compound contained in a positive electrode precursor, and a lithium compound. And a negative electrode having a negative electrode active material layer doped with a dopant source. The positive electrode may contain a lithium compound that has not been decomposed in the lithium doping step.

[Positive electrode]
The bulk density of the positive electrode active material layer is preferably 1.0 g / cm ³ or more, more preferably 1.2 g / cm ³ or more and 4.5 g / cm ³ or less. When the bulk density of the positive electrode active material layer is 1.2 g / cm ³ or more, a high energy density can be expressed, and downsizing of the lithium ion secondary battery can be achieved. When the bulk density of the positive electrode active material layer is 4.5 g / cm ³ or less, the electrolyte solution is sufficiently diffused in the pores in the positive electrode active material layer, and high output characteristics are obtained.

[Positive electrode active material layer after lithium doping]
In the present embodiment, the positive electrode active material layer after lithium doping has at least one compound selected from the following formulas (1) to (3) at 1.0 × 10 ⁻⁸ mol per unit mass of the positive electrode active material layer. / G to 3.0 × 10 ⁻² mol / g.
LiX ¹ -OR ¹ O—X ² Li (1)
{In Formula (1), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and X ¹ and X ² are each independently — (COO) _n. (Where n is 0 or 1). }
^{LiX 1 -OR 1 O-X 2} R 2 ······ (2)
{In Formula (2), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and R ² is hydrogen, an alkyl group having 1 to 10 carbon atoms, carbon A mono- or polyhydroxyalkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a mono- or polyhydroxyalkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group, X ¹ and X ² are each independently — (COO) _n (where n is 0 or 1). }
^{R 2 X 1 -OR 1 O-} X 2 R 3 ······ (3)
{In Formula (3), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and R ² and R ³ are each independently hydrogen, 10 alkyl groups, mono- or polyhydroxyalkyl groups having 1 to 10 carbon atoms, alkenyl groups having 2 to 10 carbon atoms, mono- or polyhydroxyalkenyl groups having 2 to 10 carbon atoms, cycloalkyl groups having 3 to 6 carbon atoms, Or an aryl group, and X ¹ and X ² are each independently — (COO) _n (where n is 0 or 1). }

Particularly preferred compounds as the compound of formula (1) are not limited, but for example, LiOC ₂ H ₄ OLi, LiOC ₃ H ₆ OLi, LiOC ₂ H ₄ OCOOLi, LiOCOOC ₃ H ₆ OLi, LiOCOOC ₂ H ₄ OCOOLi, and LiOCOOC ₃ A compound represented by H ₆ OCOOLi is given.

Particularly preferable compounds as the compound of the formula (2) are not limited, but for example, LiOC ₂ H ₄ OH, LiOC ₃ H ₆ OH, LiOC ₂ H ₄ OCOOH, LiOC ₃ H ₆ OCOOH, LiOCOOC ₂ H ₄ OCOOH, LiOCOOC ₃ H _{6 OCOOH, LiOC 2 H 4 OCH} 3, LiOC 3 H 6 OCH 3, LiOC 2 H 4 OCOOCH 3, LiOC 3 H 6 OCOOCH 3, LiOCOOC 2 H 4 OCOOCH 3, LiOCOOC 3 H 6 OCOOCH 3, LiOC 2 H 4 OC in _{2 H 5, LiOC 3 H 6} OC 2 H 5, LiOC 2 H 4 OCOOC 2 H 5, LiOC 3 H 6 OCOOC 2 H 5, LiOCOOC 2 H 4 OCOOC 2 H 5, LiOCOOC 3 H 6 OCOOC 2 H 5 It includes compounds.

Particularly preferred compounds as the compound of the formula (3) are not limited, but for example, HOC ₂ H ₄ OH, HOC ₃ H ₆ OH, HOC ₂ H ₄ OCOOH, HOC ₃ H ₆ OCOOH, HOCOOC ₂ H ₄ OCOOH, HOCOOC ₃ H _{6 OCOOH, HOC 2 H 4 OCH} 3, HOC 3 H 6 OCH 3, HOC 2 H 4 OCOOCH 3, HOC 3 H 6 OCOOCH 3, HOCOOC 2 H 4 OCOOCH 3, HOCOOC 3 H 6 OCOOCH 3, HOC 2 H 4 OC ₂ H ₅ , HOC ₃ H ₆ OC ₂ H ₅ , HOC ₂ H ₄ OCOOC ₂ H ₅ , HOC ₃ H ₆ OCOOC ₂ H ₅ , HOCOOC ₂ H ₄ OCOOC ₂ H ₅ , HOCOOC ₃ H ₆ OCOOC ₂ H ₅ , _{3 OC 2 H 4 OCH 3,} CH _{OC 3 H 6 OCH 3, CH} 3 OC 2 H 4 OCOOCH 3, CH 3 OC 3 H 6 OCOOCH 3, CH 3 OCOOC 2 H 4 OCOOCH 3, CH 3 OCOOC 3 H 6 OCOOCH 3, CH 3 OC 2 H 4 OC ₂ H ₅ , CH ₃ OC ₃ H ₆ OC ₂ H ₅ , CH ₃ OC ₂ H ₄ OCOOC ₂ H ₅ , CH ₃ OC ₃ H ₆ OCOOC ₂ H ₅ , CH ₃ OCOOC ₂ H ₄ OCOOC ₂ H ₅ , CH ₃ OCOOC ₃ H ₆ OCOOC ₂ H ₅ , C ₂ H ₅ OC ₂ H ₄ OC ₂ H ₅ , C ₂ H ₅ OC ₃ H ₆ OC ₂ H ₅ , C ₂ H ₅ OC ₂ H ₄ OCOOC ₂ H ₅ , C _{2 H 5 OC 3 H 6 OCOOC 2} H 5, C 2 H 5 OCOOC 2 H 4 OCOOC 2 H 5, and _C 2 _H 5 OCO A compound represented by C ₃ H ₆ OCOOC ₂ H ₅ and the like.

  In this embodiment, as a method for containing the compounds of the above formulas (1) to (3) in the positive electrode active material layer, for example, the compounds of formulas (1) to (3) are added to the positive electrode active material layer. A method of mixing; a method of adsorbing the compounds of formulas (1) to (3) on the positive electrode active material layer; and a method of electrochemically depositing the compounds of formulas (1) to (3) on the positive electrode active material layer. Can be mentioned.

  As a preferred method for incorporating the compounds of the formulas (1) to (3) into the positive electrode active material layer, a precursor that can be decomposed to produce these compounds is contained in a non-aqueous electrolyte, and lithium ions are added. A method in which the precursor is decomposed in the step of manufacturing a secondary battery and the compound is deposited in the positive electrode active material layer is preferable.

  The precursor that decomposes to form the compounds of formulas (1) to (3) is at least one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Of these, ethylene carbonate and propylene carbonate are preferred.

The total amount of the compounds of the formulas (1) to (3) is 1.0 × 10 ⁻⁸ mol / g or more and 5.0 × 10 ⁻⁷ mol / g or more per unit mass of the positive electrode active material layer. More preferably. When the total amount of the compounds of formulas (1) to (3) is 1.0 × 10 ⁻⁸ mol / g or more per unit mass of the positive electrode active material layer, the non-aqueous electrolyte solution is less likely to come into contact with the positive electrode active material. In addition, the oxidative decomposition of the nonaqueous electrolytic solution can be more effectively suppressed.
The total amount of the compounds of the formulas (1) to (3) is 3.0 × 10 ⁻² mol / g or less, preferably 7.0 × 10 ⁻³ mol / g per unit mass of the positive electrode active material layer. Hereinafter, it is more preferably 3.0 × 10 ⁻⁵ mol / g or less. If the total amount of the compounds of the formulas (1) to (3) is 3.0 × 10 ⁻² mol / g or less per unit mass of the positive electrode active material layer, the diffusion of lithium (Li) ions is hardly inhibited, Higher input / output characteristics can be expressed.

[Anode active material layer after lithium doping]
In the present embodiment, the negative electrode active material layer contains one or more compounds selected from the formulas (1) to (3) at 0.50 × 10 ⁻⁴ mol / g to 120 per unit mass of the negative electrode active material layer. It is preferable to contain ^x10 < ^-4 > mol / g. In the lithium doping step, the compounds of the above formulas (1) to (3) coat the negative electrode active material, so that nickel ions and manganese ions eluted from the positive electrode active material react with lithium on the surface of the negative electrode active material. It is possible to effectively suppress the deactivation of lithium.

  In this embodiment, as a method for containing the compounds of the above formulas (1) to (3) in the negative electrode active material layer, for example, the compounds of formulas (1) to (3) are added to the negative electrode active material layer. A method of mixing; a method of adsorbing the compounds of formulas (1) to (3) on the negative electrode active material layer; and a method of electrochemically depositing the compounds of formulas (1) to (3) on the negative electrode active material layer. Can be mentioned.

  As a preferred method for incorporating the compounds of the formulas (1) to (3) into the negative electrode active material layer, a precursor that can be decomposed to produce these compounds is contained in a non-aqueous electrolyte, and lithium ions are added. A method in which the precursor is decomposed in the step of manufacturing a secondary battery and the compound is deposited in the negative electrode active material layer is preferable.

  The precursor that decomposes to form the compounds of formulas (1) to (3) is at least one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Of these, ethylene carbonate and propylene carbonate are preferred.

The total amount of the compounds of formulas (1) to (3) is preferably 5.0 × 10 ⁻¹⁰ mol / g or more, more preferably 2.5 × 10 ⁻⁸ mol / g per unit mass of the negative electrode active material layer. g or more. If the total amount of the compounds of formulas (1) to (3) is 5.0 × 10 ⁻¹⁰ mol / g or more per unit mass of the negative electrode active material layer, the non-aqueous electrolyte solution is less likely to come into contact with the negative electrode active material, It can suppress more effectively that nonaqueous electrolyte solution carries out reductive decomposition.
The total amount of the compounds of formulas (1) to (3) is preferably 1.5 × 10 ⁻³ mol / g or less, more preferably 3.5 × 10 ⁻⁴ mol / g per unit mass of the negative electrode active material layer. g or less, more preferably 1.5 × 10 ⁻⁶ mol / g or less. If the total amount of the compounds of the formulas (1) to (3) is 1.5 × 10 ⁻³ mol / g or less per unit mass of the negative electrode active material layer, the diffusion of lithium (Li) ions is hardly inhibited, Higher input / output characteristics can be expressed.

  In this embodiment, the ratio A / B of the content A per unit mass of the positive electrode active material layer and the content B per unit mass of the negative electrode active material layer of the compounds of the above formulas (1) to (3) Is preferably 0.2 or more and 20 or less. A / B is more preferably 0.8 or more and 15 or less, and further preferably 1.2 or more and 12 or less. When A / B is 0.2 or more, the nonaqueous electrolytic solution is hardly oxidatively decomposed at the positive electrode interface, and does not inhibit the diffusion of Li ions at the negative electrode interface. In addition, when A / B is 20 or less, the nonaqueous electrolytic solution is difficult to undergo reductive decomposition at the negative electrode interface and does not inhibit the diffusion of Li ions at the positive electrode interface. Therefore, when A / B is 0.2 or more and 20 or less, sufficient high-temperature durability and high input / output characteristics at a wide temperature range can be achieved.

[Average particle size of lithium compound]
In general, when a lithium ion secondary battery is repeatedly stored and used, the electrolyte contained in the electrolytic solution is decomposed to generate fluorine ions. The generated fluorine ions are not preferred because they mainly form lithium fluoride at the negative electrode and increase the internal resistance of the lithium ion secondary battery. On the other hand, since the lithium compound can adsorb fluorine ions, formation of lithium fluoride at the negative electrode can be suppressed. Therefore, it is preferable that the lithium compound is present in the positive electrode active material layer because an increase in internal resistance of the lithium ion secondary battery can be suppressed.

  The average particle size of the lithium compound is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 5 μm or less. When the average particle size of the lithium compound is 0.1 μm or more, it is possible to suppress characteristic deterioration and gas generation due to high temperature storage by efficiently adsorbing fluorine ions generated by high temperature storage. When the average particle diameter of the lithium compound is 10 μm or less, the reaction area with fluorine ions generated in a high-load charge / discharge cycle increases, so that fluorine ions can be adsorbed efficiently.

  Although the measuring method of the average particle diameter of a lithium compound is not specifically limited, It can calculate from the SEM image of a positive electrode cross section, and a SEM-EDX image. As a method for forming the positive electrode cross section, BIB processing can be used in which an Ar beam is irradiated from the upper part of the positive electrode and a smooth cross section is produced along the end of the shielding plate placed immediately above the sample. When lithium carbonate is contained in the positive electrode, the distribution of carbonate ions can be obtained by measuring Raman imaging of the cross section of the positive electrode.

[Identification method of lithium compound]
Although the identification method of the lithium compound contained in a positive electrode active material is not specifically limited, For example, it can identify by the following method. It is preferable to identify a lithium compound by combining a plurality of analysis methods described below.

  When measuring SEM-EDX, Raman spectroscopy, and XPS described below, the lithium ion secondary battery is disassembled in an argon box, the positive electrode is taken out, and the electrolyte attached to the positive electrode surface is washed before measurement. Preferably it is done. As the solvent for washing the positive electrode, it is only necessary to wash away the electrolyte attached to the surface of the positive electrode. For example, carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate can be suitably used. As a cleaning method, for example, the positive electrode is immersed in a diethyl carbonate solvent 50 to 100 times the weight of the positive electrode for 10 minutes or more, and then the solvent is changed and the positive electrode is immersed again. Thereafter, the positive electrode is taken out from diethyl carbonate and vacuum-dried, and then SEM-EDX, Raman spectroscopy, and XPS analysis are performed. The conditions for vacuum drying are such that the residual amount of diethyl carbonate in the positive electrode is 1% by mass or less in the range of temperature: 0 to 200 ° C., pressure: 0 to 20 kPa, and time: 1 to 40 hours. About the residual amount of diethyl carbonate, GC / MS of the water after distilled water washing | cleaning mentioned later and liquid volume adjustment can be measured, and it can quantify based on the analytical curve created beforehand.

  In ion chromatography described later, anions can be identified by analyzing the water after washing the positive electrode with distilled water.

When a lithium compound could not be identified by the above analysis technique, other analysis techniques include ⁷ Li-solid NMR, XRD (X-ray diffraction), TOF-SIMS (time-of-flight secondary ion mass spectrometry), AES (Auger) Lithium compounds can also be identified by using electron spectroscopy, TPD / MS (heat generation gas mass spectrometry), DSC (differential scanning calorimetry), or the like.

  A method for identifying a lithium compound by SEM observation of the cross section of the positive electrode is exemplified below. For example, in the case of lithium carbonate, the lithium compound can be discriminated by carbon mapping and oxygen mapping based on the SEM-EDX image of the cross section of the positive electrode measured with an observation magnification of 1000 to 4000 times. With respect to the SEM-EDX image measurement method, it is preferable to adjust the brightness and contrast so that the brightness does not have pixels that reach the maximum brightness, and the average brightness is in the range of 40% to 60%. When each of the obtained carbon mapping and oxygen mapping is a carbon region and an oxygen region, the regions containing 50% or more of the bright portion binarized based on the average value of brightness are defined as the carbon region and the oxygen region, respectively. The overlapping portion can be identified as lithium carbonate.

[Characteristic evaluation of lithium ion secondary battery]
(Discharge capacity)
In this specification, the capacity Q (mAh) and the capacity Q ′ (mAh) are values obtained by the following method.

  First, constant-current charging is performed until a voltage of 4.9 V is reached at a current value of 0.1 C in a thermostatic chamber in which a cell corresponding to the lithium ion secondary battery is set to 25 ° C., and then a constant voltage of 4.9 V is reached. A constant voltage charge is applied for 1 hour. Thereafter, the electric capacity when constant current discharge is performed at a current value of 0.1 C up to 3.0 V is defined as Q (mAh). Here, 1C is a current value at which the battery is discharged in one hour. A value obtained by dividing the electric capacity Q (mAh) by the active material weight (g) of the positive electrode is defined as an electric capacity Q ′ (mAh / g (active material)).

(Normal temperature internal resistance)
In the present specification, the room temperature internal resistance Ra (Ω) is a value obtained by the following method.
First, constant-current charging is performed until a voltage of 4.9 V is reached at a current value of 0.1 C in a thermostatic chamber in which a cell corresponding to the lithium ion secondary battery is set to 25 ° C., and then a constant voltage of 4.9 V is applied. The applied constant voltage charge is performed for 1 hour. Subsequently, a constant current discharge is performed up to 3.0 V at a current value of 1 C to obtain a discharge curve (time-voltage). In this discharge curve, when the voltage at the discharge time = 0 seconds obtained by extrapolating from the voltage values at the discharge time of 1 second and 10 seconds by linear approximation is Eo, the drop voltage ΔE = 4.9− A value calculated by Eo and Ra = ΔE / (1C (current value A)) is a room temperature internal resistance Ra (Ω).

[Cycle test]
(Discharge capacity after 100 cycles)
In this specification, the discharge capacity Q ″ (mAh / g (active material)) after the cycle test is measured by the following method.
The cell after measuring the electric capacity Q described above was charged in a constant current until reaching 4.9 V at a current value of 0.1 C in a thermostat set at 55 ° C., and then 4.9 V Constant voltage charging for applying a constant voltage is performed for 1 hour. Thereafter, constant current discharge is performed at a current value of 0.1 C up to 3.0 V. The series of charging / discharging is defined as one cycle, and charging / discharging is further performed 99 cycles. A value obtained by dividing the electric capacity at the 100th cycle by the active material weight (g) of the positive electrode is defined as an electric capacity Q ″ (mAh / g (active material)).

(Capacity maintenance rate after 100 cycles)
A value obtained by dividing the electric capacity at the 100th cycle by the electric capacity at the first cycle is defined as a capacity retention rate (%) after 100 cycles.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and embodiment of this invention is described concretely, this invention is not limited at all by the following example and comparative example.

<Example 1>
[Synthesis of positive electrode active material]
Nickel sulfate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.) and manganese sulfate (II) pentahydrate (Wako Pure Chemical Industries, Ltd.) in a molar ratio of transition metal element of 1: 3 Were dissolved in water to prepare a nickel-manganese mixed aqueous solution so that the total concentration of metal ions was 2 mol / L. Subsequently, this nickel-manganese mixed aqueous solution was dropped into 1500 mL of a 2 mol / L sodium carbonate aqueous solution heated to 70 ° C. at an addition rate of 12.5 mL / min for 120 minutes. At the time of dropping, air with a flow rate of 200 mL / min was blown into the aqueous solution while stirring. As a result, a precipitated substance was generated, and the obtained precipitated substance was sufficiently washed with distilled water and dried to obtain a nickel manganese compound. The obtained nickel-manganese compound and lithium carbonate having a particle size of 2 μm were weighed so that the molar ratio of lithium: nickel: manganese was 1: 0.5: 1.5, and obtained after dry-mixing for 1 hour. The obtained mixture was baked at 1000 ° C. for 4 hours in an oxygen atmosphere to obtain a positive electrode active material represented by LiNi _0.5 Mn _1.5 O ₄ .
[Production of positive electrode precursor]
86.0 parts by mass of LiNi _0.5 Mn _1.5 O ₄ obtained as described above, 3.0 parts by mass of graphite powder (manufactured by TIMCAL, KS-6) as a conductive auxiliary agent and acetylene 3.0 parts by weight of black powder (manufactured by Denki Kagaku Kogyo, HS-100), 4.0 parts by weight of lithium carbonate as a lithium compound, and a polyvinylidene fluoride solution as a binder (manufactured by Kureha, L # 7208) 4.0 parts by mass and N-methyl-2-pyrrolidone as a dispersion solvent were mixed to obtain a positive electrode slurry having a solid concentration of 35% by mass. The obtained positive electrode slurry was applied to one side of an aluminum foil having a thickness of 20 μm as a positive electrode current collector, the solvent was removed by drying, and then rolled with a roll press. The rolled product was punched into a 30 mm × 50 mm rectangular shape excluding the tab portion to obtain a positive electrode precursor. The thickness of the positive electrode active material layer of the positive electrode precursor was approximately 70 μm.

[Production of negative electrode]
88.0 parts by mass of graphite powder (OMAC1.2H / SS, manufactured by Osaka Gas Chemical Co., Ltd.) and 9.5 parts by mass of graphite powder (manufactured by TIMCAL, SFG6), which is a negative electrode active material, and styrene-butadiene rubber (Binder) 1.0 part by mass of SBR, Asahi Kasei Chemicals Corporation, L-1571), 1.5 parts by mass of carboxymethylcellulose ammonium (Daicel Chemical Industries, Ltd., DN-400H), and water as a dispersion solvent were mixed. A slurry for negative electrode having a solid content concentration of 45% by mass was obtained. The obtained slurry for negative electrode was applied to and dried on one side of an 18 μm-thick electrolytic copper foil as a negative electrode current collector, and the solvent was dried and removed, followed by rolling with a roll press. The rolled product was punched into a rectangular shape of 32 mm × 52 mm excluding the tab portion to obtain a negative electrode. The thickness of the negative electrode active material layer was approximately 40 μm.

[Preparation of non-aqueous electrolyte]
LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 so as to be 1 mol / L to obtain an electrolyte solution that was a nonaqueous electrolyte. .

[Production of lithium ion secondary battery]
A laminate in which the positive electrode precursor and the negative electrode produced as described above are laminated on both sides of a separator (thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm) made of a polypropylene microporous film. After inserting the positive and negative terminals into a bag made of a laminate film in which both surfaces of an aluminum foil (thickness 40 μm) are coated with a resin layer, the non-aqueous electrolyte solution prepared above is put in a 0.5 mL bag. Then, the pressure was reduced to -90 kPa, and the operation of returning to -30 kPa was carried out twice, and then held at -95 kPa for 5 minutes. After returning to normal pressure, the pressure was reduced to -85 kPa, and then temporary sealing was performed to produce a sheet-like lithium ion secondary battery. For decompression and temporary sealing, a reduced pressure sealing device (model: M-3295) manufactured by Techny Co., Ltd. was used.

[Lithium doping process]
Using a charging / discharging device manufactured by Asuka Electronics Co., Ltd., the sheet-like lithium ion secondary battery obtained by temporary sealing reaches a voltage of 4.5 V at a current value of 0.5 A in a 45 ° C. environment. Then, the negative electrode was lithium-doped by performing 4.5 V constant voltage charging for an arbitrary time.

[Aging process]
The lithium-ion secondary battery after lithium doping was subjected to constant current discharge in a 25 ° C. environment until reaching a voltage of 3.0 V at 0.5 A, and then subjected to 3.0 V constant current discharge for 1 hour to reduce the voltage to 3 Adjusted to 0.0V. Subsequently, the lithium ion secondary battery was stored in a constant temperature bath at 60 ° C. for 5 hours.

[Degassing process]
A part of the laminate film of the lithium ion secondary battery after aging was opened in a dry air environment at a temperature of 25 ° C. and a dew point of −40 ° C. Subsequently, the step of putting the lithium ion secondary battery in the reduced pressure chamber, reducing the pressure from atmospheric pressure to −80 kPa over 3 minutes, and then returning to atmospheric pressure over 3 minutes was repeated a total of 3 times. Then, after putting a lithium ion secondary battery in the decompression sealing machine and depressurizing to -90 kPa, the laminate film was sealed by sealing at 200 ° C. for 10 seconds with a pressure of 0.1 MPa.

<Example 2>
Except for obtaining a positive electrode active material represented by LiNi _0.45 Mn _1.55 O ₄ with a transition metal element molar ratio of 9:31 during synthesis of the positive electrode active material, the same as in Example 1. Thus, a lithium ion secondary battery was obtained.

<Example 3>
Except for obtaining a positive electrode active material represented by LiNi _0.4 Mn _1.5 O ₄ with a transition metal element molar ratio of 1: 4 during the synthesis of the positive electrode active material, the same as in Example 1. Thus, a lithium ion secondary battery was obtained.

<Example 4>
Except for obtaining the positive electrode active material represented by LiNi _0.35 Mn _1.65 O ₄ with the transition metal element molar ratio of 7:33 during the synthesis of the positive electrode active material, the same as in Example 1. Thus, a lithium ion secondary battery was obtained.

<Example 5>
The same procedure as in Example 1 was performed except that the positive electrode active material represented by LiNi _0.3 Mn _1.7 O ₄ was obtained at the synthesis of the positive electrode active material at a molar ratio of the transition metal element of 3:17. Thus, a lithium ion secondary battery was obtained.

<Example 6>
The same procedure as in Example 1 was performed except that the positive electrode active material represented by LiNi _0.2 Mn _1.8 O ₄ was obtained at the synthesis of the positive electrode active material at a molar ratio of transition metal element of 2: 9. Thus, a lithium ion secondary battery was obtained.

<Example 7>
Except for obtaining a positive electrode active material represented by LiNi _0.55 Mn _1.45 O ₄ with a transition metal element molar ratio of 11:29 during the synthesis of the positive electrode active material, the same as in Example 1. Thus, a lithium ion secondary battery was obtained.

<Example 8>
The same procedure as in Example 1 was performed except that the positive electrode active material represented by LiNi _0.6 Mn _1.4 O ₄ was obtained by synthesizing the molar ratio of the transition metal element at a ratio of 3: 7 during the synthesis of the positive electrode active material. Thus, a lithium ion secondary battery was obtained.

<Example 9>
In the same manner as in Example 1, except that the positive electrode precursor was obtained by using 89.0 parts by mass of LiNi _0.5 Mn _1.5 O ₄ and 1.0 part by weight of lithium carbonate during the production of the positive electrode precursor. An ion secondary battery was obtained.

<Example 10>
In the same manner as in Example 1, except that the positive electrode precursor was obtained by using 80.0 parts by mass of LiNi _0.5 Mn _1.5 O ₄ and 10.0 parts by weight of lithium carbonate during the production of the positive electrode precursor. An ion secondary battery was obtained.

<Example 11>
In the same manner as in Example 1, except that the positive electrode precursor was obtained by producing 60.0 parts by mass of LiNi _0.5 Mn _1.5 O ₄ and 3.0 parts by weight of lithium carbonate during the production of the positive electrode precursor. An ion secondary battery was obtained.

<Example 12>
In the same manner as in Example 1, except that the positive electrode precursor was obtained by using 40.0 parts by mass of LiNi _0.5 Mn _1.5 O ₄ and 50.0 parts by weight of lithium carbonate at the time of manufacturing the positive electrode precursor. An ion secondary battery was obtained.

<Example 13>
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that the positive electrode precursor was obtained using lithium oxide as the lithium compound during the production of the positive electrode precursor.

<Example 14>
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that the positive electrode precursor was obtained using lithium hydroxide as the lithium compound during the production of the positive electrode precursor.

<Example 15>
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that during the synthesis of the positive electrode active material, the positive electrode active material was obtained by setting the firing conditions at 1000 ° C. for 8 hours.

<Example 16>
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that during the synthesis of the positive electrode active material, the positive electrode active material was obtained by setting the firing conditions at 1000 ° C. for 2 hours.

<Example 17>
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that during the synthesis of the positive electrode active material, the positive electrode active material was obtained by setting the firing conditions at 900 ° C. for 2 hours.

<Comparative Example 1>
When synthesizing the positive electrode active material, lithium carbonate (Wako Pure Chemical Industries, Ltd.) and manganese carbonate (II) n hydrate (Wako Pure Chemical Industries, Ltd.) were used at a molar ratio of lithium: manganese of 1: 2. And weighed for 1 hour. Then, the obtained mixture was baked at 1000 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material precursor represented by LiMn ₂ O ₄ .
Thereafter, a lithium ion secondary battery was obtained in the same manner as in Example 1.

<Comparative example 2>
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that the positive electrode precursor was obtained using LiCoO ₂ powder (manufactured by Nichia Corporation) as the positive electrode active material during the production of the positive electrode precursor. It was.

<Comparative Example 3>
In the same manner as in Example 1, except that LiNi _0.5 Mn _1.5 O ₄ was 90.0 parts by mass at the time of synthesis of the positive electrode active material and a positive electrode precursor was obtained without using a lithium compound, The next battery was obtained.

[Quantification of compounds of formulas (1) to (3) contained in the positive electrode active material layer]
After the lithium ion secondary batteries obtained in Examples 1 to 17 and Comparative Examples 1 to 3 were adjusted to 2.9 V, they were controlled at a dew point of −90 ° C. or less and an oxygen concentration of 1 ppm or less installed in a room at 23 ° C. Was disassembled in an argon (Ar) box, and the positive electrode was taken out. The positive electrode taken out was immersed and washed with dimethyl carbonate (DMC), and then vacuum-dried in a side box in a state in which exposure to the atmosphere was not maintained.

The positive electrode after drying was transferred from the side box to the Ar box in a state where exposure to air was not performed, and immersion extraction was performed with heavy water to obtain a positive electrode extract. The analysis of the extract was performed by (i) ion chromatography (IC) and (ii) ¹ H-NMR, the concentration A (mol / ml) of each compound in the obtained positive electrode extract, and heavy water used for extraction From the volume B (ml) and the mass C (g) of the positive electrode active material layer used for extraction, the following formula 2:
Abundance per unit mass (mol / g) = A × B ÷ C (Formula 2)
Thus, the abundance (mol / g) of each compound deposited on the positive electrode per unit mass of the positive electrode active material layer was determined.

  The mass of the positive electrode active material layer used for extraction was determined by the following method. The mixture (positive electrode active material layer) was peeled off from the current collector of the positive electrode remaining after the heavy water extraction, and the peeled mixture was washed with water and then vacuum dried. The mixture obtained by vacuum drying was washed with NMP or DMF. Subsequently, the obtained positive electrode active material layer was vacuum-dried again and weighed to examine the mass of the positive electrode active material layer used for extraction.

The positive electrode extract was put in a 3 mmφ NMR tube (PN-002 manufactured by Shigemi Co., Ltd.), and a 5 mmφ NMR tube containing deuterated chloroform containing 1,2,4,5-tetrafluorobenzene (N-5 manufactured by Japan Precision Science Co., Ltd.). ) And ¹ H NMR measurement was performed by a double tube method. Normalization was performed with a signal of 1,2,4,5-tetrafluorobenzene of 7.1 ppm (m, 2H), and an integral value of each observed compound was determined.

In addition, deuterated chloroform containing dimethyl sulfoxide of known concentration is put into a 3 mmφ NMR tube (PN-002 manufactured by Shigemi Co., Ltd.), and the same deuterated chloroform containing 1,2,4,5-tetrafluorobenzene as above. Was inserted into a 5 mmφ NMR tube (N-5 manufactured by Japan Precision Science Co., Ltd.), and ¹ H NMR measurement was performed by a double tube method. In the same manner as described above, the signal was normalized with 7.1 ppm (m, 2H) of 1,2,4,5-tetrafluorobenzene, and the integral value of 2.6 ppm (s, 6H) of dimethyl sulfoxide was obtained. From the relationship between the concentration of dimethyl sulfoxide used and the integral value, the concentration A of each compound in the positive electrode extract was determined.

Assignment of ¹ H NMR spectrum is as follows.
[About XOCH ₂ CH ₂ OX]
XOCH ₂ CH ₂ OX CH ₂ : 3.7 ppm (s, 4H)
CH ₃ OX: 3.3 ppm (s, 3H)
CH ₃ CH ₂ OX CH ₃ : 1.2 ppm (t, 3H)
CH ₃ CH ₂ OX of _{CH 2 O: 3.7ppm (q,} 2H)

As described _above, the signal (3.7 ppm) is XOCH 2 _CH 2 OX of CH _2, since the overlaps with CH 3 _CH 2 OX of CH ₂ O signals (3.7 _ppm), the CH 3 _CH 2 OX except for the CH ₂ O equivalent of _CH 3 _CH 2 OX calculated from CH ₃ signal (1.2 ppm), was calculated an amount of a compound of formula (1) to (3).
In the above, each X is — (COO) _n Li or — (COO) _n R ¹ (where n is 0 or 1, and R ¹ is an alkyl group having 1 to 4 carbon atoms, or carbon A halogenated alkyl group of 1 to 4).

  The formula contained in the positive electrode active material layer from the concentration of each compound obtained by the analysis of (i) and (ii) above, the volume of heavy water used for extraction, and the active material mass of the positive electrode used for extraction The amounts of the compounds (1) to (3) were measured and summarized in Table 1. In Comparative Example 3 in which lithium carbonate was not added to the positive electrode precursor, the compounds of the formulas (1) to (3) were scarcely present in the positive electrode active material layer. It can be seen that the compounds of the formulas (1) to (3) exist according to the 5V constant voltage charging.

[Quantification of compounds of formulas (1) to (3) contained in negative electrode active material layer]
The negative electrode active material layer was analyzed in the same manner as the analysis of the positive electrode active material layer, and the analysis results are summarized in Table 1. In the comparative example 1 which does not contain nickel, it turns out that the compound of Formula (1)-(3) hardly exists in a negative electrode active material layer.

[Measurement of discharge capacity]
About the lithium ion secondary battery obtained in Examples 1-17 and Comparative Example 3, in a thermostat set to 25 ° C., using a charge / discharge device manufactured by Asuka Electronics Co., Ltd., a current value of 0.1C Then, constant current charging was performed until 4.9 V was reached, followed by constant voltage charging for applying a constant voltage of 4.9 V for 1 hour.
About the lithium ion secondary battery obtained in Comparative Examples 1 and 2, it was 4.35 V at a current value of 0.1 C using a charge / discharge device manufactured by Asuka Electronics Co., Ltd. in a thermostat set at 25 ° C. Then, constant current charging was performed until the voltage reached, and then constant voltage charging for applying a constant voltage of 4.35 V was performed for 1 hour.
Then, about the lithium ion secondary battery obtained in Examples 1-17 and Comparative Examples 1-3, the discharge capacity Q at the time of performing a constant current discharge to the current value of 0.1C to 3.0V is shown in Table 1. Summarized in The values obtained by dividing the discharge capacity Q (mAh) by the active material weight (g) of the positive electrode are summarized in Table 1 as the discharge capacity Q ′ (mAh / g (active material)).

[Calculation of Ra]
About the lithium ion secondary battery of Examples 1-17 obtained by the said process, and the comparative example 3, 0.1C was used in the thermostat set to 25 degreeC using the charging / discharging apparatus by Asuka Electronics Co., Ltd. Charge at a constant current until it reaches 4.9V, followed by constant voltage charging for 1 hour to apply a constant voltage of 4.9V, and then discharge at a constant current to 3.0V at a current value of 5C. To obtain a discharge curve (time-voltage). In this discharge curve, Eo is the voltage at discharge time = 0 seconds obtained by extrapolation by linear approximation from the voltage values at time points of 1 second and 10 seconds, and the drop voltage ΔE = 4.9−Eo, and The internal resistance Ra was calculated from R = ΔE / (1C (current value A)) and summarized in Table 1.
About the lithium ion secondary battery of Comparative Examples 1 and 2 obtained in the above process, using a charge / discharge device manufactured by Asuka Electronics Co., Ltd. 4. Constant current charge until 4.35V is reached, followed by constant voltage charge for applying a constant voltage of 4.35V for 1 hour, followed by constant current discharge to 3.0V at a current value of 5C, A discharge curve (time-voltage) was obtained. In this discharge curve, Eo is the voltage at discharge time = 0 seconds obtained by extrapolation by linear approximation from the voltage values at the discharge time of 1 second and 10 seconds, and the drop voltage ΔE = 4.35−Eo, and The internal resistance Ra was calculated from R = ΔE / (1C (current value A)) and summarized in Table 1.

[Calculation of discharge capacity after 100 cycles]
About the lithium ion secondary battery of Examples 1-17 after the electrical capacity Q measurement, and the comparative example 3, 0.1C was used in the thermostat set to 55 degreeC using the charging / discharging apparatus by Asuka Electronics Co., Ltd. The constant current charge was performed until the current value reached 4.9 V, and then the constant voltage charge for applying the constant voltage of 4.9 V was performed for 1 hour. Thereafter, constant current discharge was performed at a current value of 0.1 C up to 3.0 V. The series of charging / discharging was made into 1 cycle, and 99 cycles were further charged / discharged. Values obtained by dividing the electric capacity at the 100th cycle by the active material weight (g) of the positive electrode are shown in Table 1 as electric capacity Q ″ (mAh / g (active material)).
About the lithium ion secondary battery of Comparative Examples 1 and 2 after measuring the electric capacity Q, using a charging / discharging device manufactured by Asuka Electronics Co., Ltd. Constant current charging was performed until 4.35V was reached, followed by constant voltage charging for which a constant voltage of 4.35V was applied for 1 hour. Thereafter, constant current discharge was performed at a current value of 0.1 C up to 3.0 V. The series of charging / discharging was made into 1 cycle, and 99 cycles were further charged / discharged. Values obtained by dividing the electric capacity at the 100th cycle by the active material weight (g) of the positive electrode are shown in Table 1 as electric capacity Q ″ (mAh / g (active material)).

[Calculation of capacity maintenance rate after 100 cycles]
For the lithium ion battery that was charged and discharged for 100 cycles, values obtained by dividing the electric capacity at the 100th cycle by the electric capacity at the first cycle are shown in Table 1 as the capacity retention rate (%) after 100 cycles.

From Table 1, the positive electrode active material has the following general formula (A):
Li _{1 + a} Mn _1.5-b Ni _0.5-c M _d O _4-δ (A)
{Wherein, a is −0.2 ≦ a ≦ 0.2, b is −0.3 ≦ b ≦ 0.3, and c is −0.3 ≦ c ≦ 0.3. Yes, d is 0 ≦ d ≦ 0.3, δ is −0.2 ≦ δ ≦ 0.2, M is a transition metal other than Ni and Mn, and Na, K, Mg, Ca , Zn, Sr, Ba, Al, Ga, In, Si, Ge, Sn, P, Sb, B and S is at least one element, and Li is partially substituted with hydrogen The amount of the compound of formulas (1) to (3) contained in the positive electrode active material layer is 1.0 × 10 ⁻⁸ mol. if / g or more 3.0 × ¹⁰ -2 mol / g or less, Q is large, Ra is small, provides a lithium ion secondary cell having excellent durability at high temperature It is found. Although not limited to theory, the reason is that the compounds of the formulas (1) to (3) contained in the positive electrode active material layer function as a good ionic conductor by being present in the form of a film on the surface of the positive electrode active material, In addition to reducing the internal resistance, it covers the reaction active sites on the positive electrode active material, reduces the amount of nickel ions and manganese ions eluted from the positive electrode active material, and improves charge / discharge capacity or high-temperature cycle characteristics. it is conceivable that.

  The lithium ion secondary battery of the present invention can be suitably used, for example, as a lithium ion secondary battery in in-vehicle applications such as electric vehicles and consumer applications such as notebook computers and mobile phones.

Claims (8)

Positive electrode;
Negative electrode;
A separator; and a non-aqueous electrolyte containing lithium ions;
A lithium ion secondary battery comprising
The negative electrode has a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material provided on one or both surfaces of the negative electrode current collector,
The positive electrode has a positive electrode current collector, and a positive electrode active material layer including a positive electrode active material provided on one or both surfaces of the positive electrode current collector,
The positive electrode active material has the following general formula (A):
Li _{1 + a} Mn _1.5-b Ni _0.5-c M _d O _4-δ (A)
{In Formula (A), a is −0.2 ≦ a ≦ 0.2, b is −0.3 ≦ b ≦ 0.3, and c is −0.3 ≦ c ≦ 0. .3, d is 0 ≦ d ≦ 0.3, δ is −0.2 ≦ δ ≦ 0.2, M is a transition metal other than Ni and Mn, and Na, K, Mg, Ca, Zn, Sr, Ba, Al, Ga, In, Si, Ge, Sn, P, Sb, B and S are at least one element selected from the group consisting of Li, It may be substituted with hydrogen. }
And the positive electrode active material layer contains a lithium compound different from the lithium manganese nickel composite oxide, and the following formulas (1) to (3):
LiX ¹ -OR ¹ O—X ² Li (1)
{In Formula (1), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and X ¹ and X ² are each independently — (COO) _n. (Where n is 0 or 1). }
^{LiX 1 -OR 1 O-X 2} R 2 ······ (2)
{In Formula (2), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and R ² is hydrogen, an alkyl group having 1 to 10 carbon atoms, carbon A mono- or polyhydroxyalkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a mono- or polyhydroxyalkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group, X ¹ and X ² are each independently — (COO) _n (where n is 0 or 1). }
^{R 2 X 1 -OR 1 O-} X 2 R 3 ······ (3)
{In Formula (3), R ¹ is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and R ² and R ³ are each independently hydrogen, 10 alkyl groups, mono- or polyhydroxyalkyl groups having 1 to 10 carbon atoms, alkenyl groups having 2 to 10 carbon atoms, mono- or polyhydroxyalkenyl groups having 2 to 10 carbon atoms, cycloalkyl groups having 3 to 6 carbon atoms, Or an aryl group, and X ¹ and X ² are each independently — (COO) _n (where n is 0 or 1). }
Containing at least one compound selected from 1.0 × 10 ⁻⁸ mol / g to 3.0 × 10 ⁻² mol / g per unit mass of the positive electrode active material layer,
The lithium ion secondary battery.   The content per unit mass of the positive electrode active material layer of one or more compounds selected from the formulas (1) to (3) is A, the content per unit mass of the negative electrode active material layer is B, The lithium ion secondary battery according to claim 1, wherein 0.2 ≦ A / B ≦ 20.   The lithium ion secondary battery according to claim 1 or 2, wherein the lithium compound is at least one selected from the group consisting of lithium carbonate, lithium oxide, and lithium hydroxide.   4. The lithium ion secondary battery according to claim 1, wherein in the general formula (A), c is −0.1 <c ≦ 0.2.   5. The lithium ion secondary battery according to claim 1, wherein in the general formula (A), c is −0.1 <c ≦ 0.1. The lithium ion battery according to any one of claims 1 to 5, wherein a BET specific surface area of the lithium manganese nickel composite oxide is 1.0 m ² / g or less.   The non-aqueous electrolyte solution contains at least one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and fluoroethylene carbonate. The lithium ion secondary battery as described. The lithium ion secondary battery according to any one of claims 1 to 7, wherein the nonaqueous electrolytic solution contains at least one of LiPF ₆ and LiBF ₄ .