WO2019177055A1

WO2019177055A1 - Lithium ion secondary battery

Info

Publication number: WO2019177055A1
Application number: PCT/JP2019/010365
Authority: WO
Inventors: 明秀田中; 奥村　壮文; 純川治; 敦史飯島; 篤宇根本; 克上田
Original assignee: 日立化成株式会社
Priority date: 2018-03-14
Filing date: 2019-03-13
Publication date: 2019-09-19
Also published as: JPWO2019177055A1

Abstract

The present invention provides a lithium ion secondary battery comprising: an electrode group including a positive electrode having a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, an electrolyte layer, and a negative electrode having a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector; and an outer case accommodating the electrode group, wherein the electrode group includes an ion conductive material including a solvent and a lithium salt, a total mass of the ion conductive material per unit volume of the outer case is 0.12-0.35 g/cm³, the solvent includes a solvent having a vapor pressure of 200 Pa or less at 20°C, and the amount of the solvent having a vapor pressure of 200 Pa or less at 20°C is 85 mol% or more based on the total mass of the solvent.

Description

Lithium ion secondary battery

The present invention relates to a lithium ion secondary battery.

In recent years, lithium ion secondary batteries have been actively developed. In particular, development of a battery used for an electric vehicle is in progress, and a further increase in capacity is demanded for a lithium ion secondary battery.

On the other hand, in order to increase the capacity of the lithium ion secondary battery, it is necessary to increase the safety in the battery. In particular, it is required to ensure safety (safety at the time of overcharge) when the controller or the like malfunctions and the battery voltage becomes higher than the normally used voltage.

As a method for enhancing such safety, for example, a method of replacing an electrolyte used in a lithium ion secondary battery with a liquid that is low in volatility and flame retardant from a conventional carbonate-based organic electrolyte. .

For example, Patent Document 1 discloses an electrolyte for a lithium ion secondary battery including a glyme complex composed of a glyme mixture composed of methyltriglyme and methyltetraglyme and lithium ions.

JP 2010-287481 A

However, according to the study by the present inventors, even when a low-volatile and flame-retardant liquid is used as the electrolyte, the conventional lithium ion secondary battery has sufficient safety during overcharge. In addition, it has been found that the discharge rate characteristics may deteriorate.

The present invention has been made in view of such circumstances, and a main object of the present invention is to provide a lithium ion secondary battery that is excellent in safety during overcharge and excellent in discharge rate characteristics.

When the present inventors diligently studied, in a lithium ion secondary battery having a specific configuration, a solvent that is difficult to volatilize is adopted as the solvent used in the ion conductive material, and the amount of the ion conductive material in the battery is adjusted. Thus, the inventors have found that the above-mentioned problems can be solved, and have completed the present invention.

One aspect of the present invention is a positive electrode having a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, an electrolyte layer, and a negative electrode current collector and a negative electrode mixture provided on the negative electrode current collector. An electrode group including a negative electrode having a layer, and an outer package containing the electrode group, the electrode group containing an ion conductive material containing a solvent and a lithium salt, and an ion conductive material per unit volume of the outer package The total mass is 0.12 to 0.35 g / cm ³ , the solvent contains a solvent having a vapor pressure at 20 ° C. of 200 Pa or less, and the content of the solvent having a vapor pressure at 20 ° C. of 200 Pa or less is Provided is a lithium ion secondary battery that is 85 mol% or more based on the total amount of substances in the solvent.

According to the lithium ion secondary battery, the safety during overcharge is excellent, and the discharge rate characteristic is also excellent. The reason why such an effect is achieved is not necessarily clear, but the present inventors have a range of the amount of the ion conductive material in the battery that is sufficient for charging / discharging, and the liquid during overcharging. This is considered to be within the range where withering can occur. When the liquid withering occurs, the internal resistance of the battery increases and the current can be cut off by itself. Due to the development of such a current interruption characteristic, the lithium ion secondary battery can be excellent in safety even during overcharge.

The mass of the ion conductive material per unit volume of the positive electrode mixture layer may be 0.05 to 0.50 g / cm ³ . The mass of the ion conductive material per unit volume of the negative electrode mixture layer may be 0.05 to 0.50 g / cm ³ .

The solvent whose vapor pressure in 20 degreeC is 200 Pa or less may contain the glyme represented by following General formula (1). Further, it may contain triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.
R ¹ O— (CH ₂ CH ₂ O) _m —R ² (1)
[In Formula (1), R ¹ and R ² each independently represents an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 3 to 6. ]

According to the present invention, there is provided a lithium ion secondary battery that is excellent in safety during overcharge and excellent in discharge rate characteristics.

It is a schematic cross section which shows one Embodiment of a lithium ion secondary battery. FIG. 2 is an exploded view of the lithium ion secondary battery shown in FIG. 1. It is a schematic cross section which shows other embodiment of a lithium ion secondary battery.

Hereinafter, embodiments of the present invention will be described with appropriate reference to the drawings. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including steps and the like) are not essential unless otherwise specified. The size of the component in each figure is conceptual, and the relative relationship of the size between the components is not limited to that shown in each figure.

The same applies to the numerical values and ranges thereof in this specification, and do not limit the present invention. In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical range. Good. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.

In the present specification, a lithium ion secondary battery will be described as an example of a secondary battery. However, the technical idea of the present invention is a lithium ion secondary battery, a sodium ion secondary battery, a magnesium ion secondary battery, The present invention can also be applied to an aluminum ion secondary battery.

[Lithium ion secondary battery]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a lithium ion secondary battery. The lithium ion secondary battery 100 includes a positive electrode 70 having a positive electrode current collector 10 and a positive electrode mixture layer 40 provided on the positive electrode current collector 10, an electrolyte layer 50, and a negative electrode current collector 20 and a negative electrode current collector 20. The electrode group 85 provided with the negative electrode 80 which has the negative mix layer 60 provided on the top, and the exterior body 30 which accommodates the electrode group 85 are provided. FIG. 2 is an exploded view of the lithium ion secondary battery shown in FIG. The exterior body 30 has a volume S. The positive electrode mixture layer 40 has a volume V1, and the negative electrode mixture layer 60 has a volume V2.

The electrode group 85 contains an ion conductive material containing a solvent and a lithium salt. The total mass of the ion conductive material per unit volume of the outer package 30 (total mass of the ion conductive material / volume S of the outer package 30) is 0.12 to 0.35 g / cm ³ . The solvent includes a solvent having a vapor pressure of 200 Pa or less at 20 ° C., and the content of the solvent having a vapor pressure of 20 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of the solvent.

Electrode group [positive electrode]
The positive electrode 70 includes a positive electrode current collector 10 and a positive electrode mixture layer 40 provided on the positive electrode current collector 10. The positive electrode mixture layer 40 contains a positive electrode active material and an ionic conductive material. The positive electrode mixture layer 40 may contain, as necessary, a positive electrode conductive material for imparting conductivity, a positive electrode binder for binding them, and the like.

<Positive electrode current collector>
The positive electrode current collector 10 is not particularly limited, and a positive electrode current collector generally used in a secondary battery can be used. The positive electrode current collector 10 is preferably a low-resistance conductor having heat resistance that can withstand the heating during the secondary battery manufacturing process and the operating temperature of the secondary battery. Examples of such positive electrode current collector 10 include metal foil (thickness 10 to 100 μm), perforated metal foil (thickness 10 to 100 μm, hole diameter 0.1 to 10 mm), expanded metal, foam metal plate, and glassy carbon plate. Etc. Moreover, as a metal seed | species, aluminum, stainless steel, titanium, a noble metal (for example, gold, silver, platinum) etc. are mentioned, for example.

<Positive electrode mixture layer>
First, the positive electrode mixture layer 40 is prepared by mixing a positive electrode mixture slurry obtained by mixing a positive electrode active material, a positive electrode conductive material, a positive electrode binder, a dispersion medium, etc. with a doctor blade method, a dipping method, a spray method, or the like. Apply to 10. Next, the dispersion medium of the positive electrode mixture slurry is dried, and the positive electrode active material layer is formed by pressure molding using a roll press. Next, the positive electrode mixture layer 40 can be produced by dropping an ion conductive material onto the obtained positive electrode active material layer with a micropipette or the like. In addition, the positive electrode mixture layer 40 can be stacked on the positive electrode current collector 10 by performing such a process a plurality of times.

(Positive electrode active material)
The positive electrode active material may be, for example, a lithium composite oxide containing a transition metal. Examples of the lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₃ MO ₈ (M = Fe, Co , Ni, Cu, Zn), Li _1-x M _x Mn ₂ O ₄ (M = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca, x = 0.01 to 0.1), _{_{_{LiMn 2-x M x O 2}}} (M = Co, Ni, Fe, Cr, Zn, Ta, x = 0.01 ~ 0.2), LiCo 1-x M x O 2 (M = Ni, Fe, Mn , X = 0.01 to 0.2), LiNi _1-x M _x O ₂ (M = Mn, Fe, Co, Al, Ga, Ca, Mg, x = 0.01 to 0.2), LiNi _{1 _{_{_{-x-y Mn x Co y O}}}} 2 (x = 0.1 ~ 0.8, y = 0.1 _{0.8, x + y = 0.1 ~} 0.9), LiFeO 2, LiFePO 4, LiMnPO 4 , and the like.

(Positive electrode conductive material)
The positive electrode conductive material is manufactured from conductive fibers (for example, vapor-grown carbon, carbon nanotubes, pitch (byproducts such as petroleum, coal, coal tar, etc.), carbonized at high temperature, and manufactured from acrylic fibers. Carbon fiber). Further, the positive electrode conductive material is preferably a material that has a lower electrical resistivity than the positive electrode active material and is difficult to oxidize and dissolve at the charge / discharge potential (usually 2.5 to 4.5 V) of the positive electrode. Examples of such materials include corrosion resistant metals (titanium, gold, etc.), carbides (SiC, WC, etc.), nitrides (Si ₃ N ₄ , BN, etc.), and the like. Further, the positive electrode conductive material may be a carbon material having a high specific surface area (for example, carbon black, activated carbon, etc.).

(Positive electrode binder)
Examples of the positive electrode binder include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF); and a mixture thereof.

(Dispersion medium)
Examples of the dispersion medium include water and 1-methyl-2-pyrrolidone.

(Ion conductive material)
The ion conductive material includes a solvent and a lithium salt. The solvent includes a solvent having a vapor pressure of 200 Pa or less at 20 ° C., and the content of the solvent having a vapor pressure of 20 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of the solvent.

Examples of the solvent having a vapor pressure at 20 ° C. of 200 Pa or less include glyme, ionic liquid, and cyclic carbonate represented by the following general formula (1).
R ¹ O— (CH ₂ CH ₂ O) _m —R ² (1)

In formula (1), R ¹ and R ² each independently represents an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 3 to 6. The alkyl group as R ¹ and R ² may be a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group or the like. Among these, the alkyl group is preferably a methyl group or an ethyl group.

Examples of the glyme include triethylene glycol dimethyl ether (triglyme, 20 ° C. vapor pressure: 120 Pa), tetraethylene glycol dimethyl ether (tetraglyme, 20 ° C. vapor pressure: 1 Pa), pentaethylene glycol dimethyl ether (pentag lime), hexaethylene glycol dimethyl ether. (Hexaglyme) and the like. Pentag lime and hexaglyme are similar in structure to tetraglyme and have a molecular weight greater than that of tetraglyme. From this, the 20 ° C. vapor pressure of pentag lime and hexaglyme is expected to be about the same as or lower than that of tetraglyme. You may use these individually by 1 type or in combination of 2 or more types. Among these, the glyme is preferably triglyme or tetraglyme.

It is known that ionic liquids have almost no vapor pressure unlike molecular liquids such as water and organic solvents due to strong electrostatic interaction between constituent cations and anions. Therefore, the ionic liquid is expected to have a vapor pressure of 200 Pa or less at 20 ° C.

The anion component of the ionic liquid is not particularly limited, but is an anion of a halogen such as Cl ⁻ , Br ⁻ and I ⁻ , an inorganic anion such as BF ₄ ⁻ and N (SO ₂ F) ₂ ^— , B (C ₆ H ₅ ) ₄ ⁻ , CH ₃ SO ₂ O ⁻ , CF ₃ SO ₂ O ⁻ , N (SO ₂ C ₄ F ₉ ) ₂ ⁻ , N (SO ₂ CF ₃ ) ₂ ⁻ , N (SO ₂ C ₂ F ₅ ) ₂ ⁻ Or an organic anion. The anionic component of the ionic liquid preferably contains at least one anionic component represented by the following formula (A).
N (SO ₂ C _m F _{2m + 1} ) (SO ₂ C _n F _{2n + 1} ) ⁻ (A)
[In the formula (A), m and n each independently represents an integer of 0 to 5. m and n may be the same as or different from each other, and are preferably the same as each other. ]

The cation component of the ionic liquid is preferably at least one selected from the group consisting of a chain quaternary onium cation, a piperidinium cation, a pyrrolidinium cation, a pyridinium cation, and an imidazolium cation.

The chain quaternary onium cation may be, for example, a compound represented by the following formula (2).

[In Formula (2), R ¹ to R ⁴ each independently represents a chain alkyl group having 1 to 20 carbon atoms, or a chain alkoxyalkyl group represented by R—O— (CH ₂ ) _n —. (R represents a methyl group or an ethyl group, and n represents an integer of 1 to 4), and X represents a nitrogen atom or a phosphorus atom. The number of carbon atoms of the alkyl group represented by R ¹ to R ⁴ is preferably 1 to 20, more preferably 1 to 10, and still more preferably 1 to 5. ]

The piperidinium cation may be, for example, a nitrogen-containing six-membered cyclic compound represented by the following formula (3).

[In Formula (3), R ⁵ and R ⁶ are each independently an alkyl group having 1 to 20 carbon atoms or an alkoxyalkyl group represented by R—O— (CH ₂ ) _n — (R is methyl A group or an ethyl group, and n represents an integer of 1 to 4. The number of carbon atoms of the alkyl group represented by R ⁵ and R ⁶ is preferably 1 to 20, more preferably 1 to 10, and still more preferably 1 to 5. ]

The pyrrolidinium cation may be, for example, a five-membered cyclic compound represented by the following formula (4).

[In Formula (4), R ⁷ and R ⁸ are each independently an alkyl group having 1 to 20 carbon atoms, or an alkoxyalkyl group represented by R—O— (CH ₂ ) _n — (R is methyl A group or an ethyl group, and n represents an integer of 1 to 4. The carbon number of the alkyl group represented by R ⁷ and R ⁸ is preferably 1-20, more preferably 1-10, and still more preferably 1-5. ]

The pyridinium cation may be, for example, a compound represented by the following formula (5).

[In Formula (5), R ⁹ to R ¹³ each independently represents an alkyl group having 1 to 20 carbon atoms, an alkoxyalkyl group represented by R—O— (CH ₂ ) _n — (R represents a methyl group) Or an ethyl group, and n represents an integer of 1 to 4), or a hydrogen atom. The number of carbon atoms of the alkyl group represented by R ⁹ to R ¹³ is preferably 1 to 20, more preferably 1 to 10, and still more preferably 1 to 5. ]

The imidazolium cation may be, for example, a compound represented by the following formula (6).

[In the formula (6), R ¹⁴ to R ¹⁸ are each independently an alkyl group having 1 to 20 carbon atoms, an alkoxyalkyl group represented by R—O— (CH ₂ ) _n — (R is a methyl group) Or an ethyl group, and n represents an integer of 1 to 4), or a hydrogen atom. The number of carbon atoms of the alkyl group represented by R ¹⁴ to R ¹⁸ is preferably 1 to 20, more preferably 1 to 10, and still more preferably 1 to 5. ]

Examples of the ionic liquid include N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium-bis (trifluoromethanesulfonyl) imide (DEME-TFSI), N, N-diethyl-N-methyl- N- (2-methoxyethyl) ammonium-bis (fluorosulfonyl) imide (DEME-FSI), 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (EMI-TFSI), 1-ethyl-3 -Methylimidazolidium-bis (fluorosulfonyl) imide (EMI-FSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMI-TFSI), 1-butyl-3-methylimidazolium- Bis (fluorosulfonyl) imide (BMI- SI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13-TFSI), N-methyl-N-propylpiperidinium-bis (fluorosulfonyl) imide (PP13-FSI), Examples thereof include 1-methyl-1-propylpyrrolidinium-bis (trifluoromethanesulfonyl) imide (PY13-TFSI), 1-methyl-1-propylpyrrolidinium-bis (fluorosulfonyl) imide (PY13-FSI), and the like. You may use these individually by 1 type or in combination of 2 or more types. Among these, the ionic liquid is preferably DEME-TFSI or EMI-FSI.

Examples of the cyclic carbonate include propylene carbonate (20 ° C. vapor pressure: 17 Pa), ethylene carbonate (20 ° C. vapor pressure: 21 Pa), and the like. You may use these individually by 1 type or in combination of 2 or more types. Among these, the cyclic carbonate is preferably propylene carbonate.

The content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of the solvent. The content of the solvent may be 85 to 100 mol%, 90 to 100 mol%, or 95 to 100 mol%, or may be composed only of the solvent (that is, 100 mol%). When the content of the solvent having a vapor pressure at 20 ° C. of 200 Pa or less is 85 mol% or more based on the total amount of the solvent, the discharge rate characteristics are excellent.

The solvent may include a solvent having a vapor pressure at 20 ° C. exceeding 200 Pa. Such a solvent is not particularly limited, and a solvent usually used in a lithium ion secondary battery can be used. The content of the solvent may be 0 to 15 mol%, 0 to 10 mol%, or 0 to 5 mol%, based on the total amount of the solvent.

Examples of the lithium _{_{_{salt, LiPF 6, LiBF 4, LiClO}}} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, lithium bis oxalate borate (LiBOB), lithium imide salt (e.g., lithium bis (Fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI)) and the like. These lithium salts may be used alone or in combination of two or more. Among these, the lithium salt is preferably LiTFSI.

The mass of the ion conductive material per unit volume of the positive electrode mixture layer (the mass of the ion conductive material of the positive electrode mixture layer / the volume V1 of the positive electrode mixture layer) may be 0.05 to 0.50 g / cm ^3. . The mass of the ion conductive material per unit volume of the positive electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ion conductive material per unit volume of the positive electrode mixture layer is 0.05 g / cm ³ or more, the discharge rate characteristics tend to be excellent, and when it is 0.50 g / cm ³ or less, It tends to be superior to safety.

[Negative electrode]
The negative electrode 80 includes a negative electrode current collector 20 and a negative electrode mixture layer 60 provided on the negative electrode current collector 20. The negative electrode mixture layer 60 contains a negative electrode active material and an ionic conductive material. The negative electrode mixture layer 60 may contain a negative electrode conductive material for imparting conductivity, a negative electrode binder for binding them, and the like as necessary.

<Negative electrode current collector>
The negative electrode current collector 20 is not particularly limited, and a negative electrode current collector generally used in a secondary battery can be used. Similarly to the positive electrode current collector 10, the negative electrode current collector 20 is preferably a low-resistance conductor having heat resistance that can withstand the heating during the secondary battery manufacturing process and the operating temperature of the secondary battery. Examples of the negative electrode current collector 20 include metal foil (thickness 10 to 100 μm), perforated metal foil (thickness 10 to 100 μm, hole diameter 0.1 to 10 mm), expanded metal, foam metal plate, and glassy carbon plate. Etc. Moreover, as a metal seed | species, aluminum, stainless steel, titanium, a noble metal (for example, gold, silver, platinum) etc. are mentioned, for example.

<Negative electrode mixture layer>
First, the negative electrode mixture layer 60 is obtained by mixing a negative electrode mixture slurry obtained by mixing a negative electrode active material, a negative electrode conductive material, a negative electrode binder, a dispersion medium, and the like by a doctor blade method, a dipping method, a spray method, and the like. Apply to 20. Next, the dispersion medium of the negative electrode mixture slurry is dried, and the negative electrode active material layer is formed by pressure molding using a roll press. Next, the negative electrode mixture layer 60 can be produced by dropping an ion conductive material into the obtained negative electrode active material layer with a micropipette or the like. In addition, the negative electrode mixture layer 60 can be laminated on the negative electrode current collector 20 by performing such a process a plurality of times.

(Negative electrode active material)
Examples of the negative electrode active material include carbon-based materials (eg, graphite, graphitizable carbon materials, amorphous carbon materials), conductive polymer materials (eg, polyacene, polyparaphenylene, polyaniline, polyacetylene, etc.), Examples thereof include lithium composite oxides (for example, lithium titanate: Li ₄ Ti ₅ O ₁₂ ), metallic lithium, metals that form an alloy with lithium (for example, aluminum, silicon, tin, and the like).

(Negative electrode conductive material)
The thing similar to what was illustrated with the positive electrode electrically conductive material can be used for a negative electrode electrically conductive material.

(Negative electrode binder)
The thing similar to what was illustrated with the positive electrode binder can be used for a negative electrode binder.

(Ion conductive material)
The ion conductive material may be the same as the above-described ion conductive material.

The mass of the ion conductive material per unit volume of the negative electrode mixture layer (the mass of the ion conductive material of the negative electrode mixture layer / the volume V2 of the negative electrode mixture layer) may be 0.05 to 0.50 g / cm ^3. . The mass of the ion conductive material per unit volume of the negative electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ion conductive material per unit volume of the negative electrode mixture layer is 0.05 g / cm ³ or more, the discharge rate characteristics tend to be superior, and when it is 0.50 g / cm ³ or less, Excellent safety.

[Electrolyte layer]
The electrolyte layer 50 contains an electrolyte component and an electrolyte binder. The electrolyte layer 50 can be produced, for example, by adding and mixing an electrolyte binder to the electrolyte component. The electrolyte layer 50 can also be produced by preparing a solution obtained by mixing an electrolyte component and an electrolyte binder with a dispersion medium and distilling off the dispersion medium.

<Electrolyte component>
The electrolyte component is composed of inorganic particles and an ion conductive material. That is, the electrolyte layer 50 contains an ionic conductive material. The ionic conductive material may be supported on inorganic particles. As the electrolyte component, for example, inorganic particles and an ionic conductive material are mixed at a specific volume ratio, and a dispersion medium such as methanol is added and mixed to prepare an electrolyte component slurry. Then, the electrolyte component can be obtained by dropping the slurry into a petri dish and distilling off the dispersion medium.

(Inorganic particles)
From the viewpoint of electrochemical stability, the inorganic particles are preferably insulating particles and insoluble in the above-mentioned solvent. Such inorganic particles may be, for example, silica (SiO ₂ ) particles, γ-alumina (Al ₂ O ₃ ) particles, ceria (CeO ₂ ) particles, or zirconia (ZrO ₂ ) particles. The inorganic particles may be other known metal oxide particles.

The amount of ion conductive material retained is considered to be proportional to the specific surface area of the inorganic particles. The average primary particle diameter of the inorganic particles may be 1 nm to 10 μm. When the average particle size is 10 μm or less, the inorganic particles can hold a sufficient amount of the ionic conductive material and tend to form an electrolyte layer. When the average particle size is 1 nm or more, the inter-surface force between the particles becomes too large, and the particles can be prevented from aggregating, and the electrolyte layer tends to be easily formed. The average particle size of the primary particles of the metal oxide particles may be 1 to 50 nm or 1 to 10 nm. In addition, the average particle diameter of primary particles can be calculated | required using the well-known particle size distribution measuring apparatus using a laser scattering method.

When SiO ₂ particles (average particle size: 7 nm, zeta potential: about −20 mV) are used as inorganic particles, a high heat-resistant electrolyte layer tends to be obtained.

When γ-Al ₂ O ₃ particles (average particle size: 5 nm, zeta potential: about −5 mV) are used as the inorganic particles, the number of charge / discharge cycles of the secondary battery tends to be increased. The reason for such an effect is not clear, but it is considered that lithium dendrite precipitation on the negative electrode side during the charge / discharge cycle can be suppressed by using alumina particles having high reduction resistance.

When CeO ₂ particles (zeta potential: about 30 mV) or ZrO ₂ particles (zeta potential: about 40 mV) are used as inorganic particles, a high ion conductive electrolyte layer tends to be obtained. When particles having a high zeta potential are used as the inorganic particles, it is considered that the adsorption of the ion conductive material to the particle surface is weakened, and the ion conductive material can be thermally moved relatively freely. As a result, lithium ions are likely to move from the ion conductive material, and lithium ion conduction is expected to be promoted.

The inorganic particles tend to provide an electrolyte layer having better ion conductivity by using a lithium ion conductive inorganic substance. As such an inorganic substance, for example, Li _{5 + X} La ₃ (Zr _X , A _2−X ) O ₁₂ (where A is Sc, Ti, C, Y, Nb, Hf, Ta, Al, Si, Ga) , Ge, Sn, one or more elements selected from the group consisting of 1.4 ≦ X ≦ 2), Li _{1 + Y} Al _Y Ti _{2 -Y} (PO ₄ ) ₃ (0 ≦ Y ≦ 1), Li _3Z La _{2 / 3-Z} TiO ₃ (0 ≦ Z ≦ 2/3) and the like. These tend to have high ionic conductivity at room temperature and high electrochemical stability.

<Electrolyte binder>
As the electrolyte binder, a fluorine-based resin is preferably used. Examples of the fluorine-based resin include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). By using PVDF or PTFE, the adhesion between the electrolyte layer and the electrode current collector is improved, so that the battery performance tends to be improved.

Exterior Body The exterior body 30 is a battery case that can accommodate an electrode group 85 including the positive electrode 70, the electrolyte layer 50, and the negative electrode 80. The material of the exterior body is preferably one having corrosion resistance such as aluminum, stainless steel, nickel plated steel or the like. The volume S of the exterior body can be appropriately set according to the size of the battery.

The total mass of the ion conductive material per unit volume of the exterior body (total mass of the ion conductive material / volume S of the exterior body) is 0.12 to 0.35 g / cm ³ . The total mass of the ion conductive material per unit volume of the outer package is 0.15 g / cm ³ or more, 0.18 g / cm ³ or more, 0.21 g / cm ³ or more, 0.24 g / cm ³ or more, 0.27 g. / cm ³ or more at a even better, 0.34 g / cm ³ or less, 0.33 g / cm ³ or less, 0.32 g / cm ³ or less, 0.31 g / cm ³ or less, 0.30 g / cm ³ or less There may be. When the total mass of the ion conductive material per unit volume of the outer package is 0.12 g / cm ³ or more, the discharge rate characteristics are excellent, and the total mass of the ion conductive material per unit volume of the outer package is 0.35 g / cm. ^When it is ³ or less, the safety during overcharge is excellent.

[Method for producing lithium ion secondary battery]
The lithium ion secondary battery 100 described above includes a positive electrode 70 having a positive electrode current collector 10 and a positive electrode mixture layer 40 provided on the positive electrode current collector 10, an electrolyte layer 50, and a negative electrode current collector 20 and a negative electrode current collector. The electrode group 85 including the negative electrode 80 having the negative electrode mixture layer 60 provided on the body 20 and the process of accommodating the electrode group 85 in the exterior body 30 can be manufactured by a manufacturing method. .

The positive electrode 70 includes, for example, a step of preparing a positive electrode precursor in which a positive electrode active material layer containing a positive electrode active material is provided on the positive electrode current collector 10, and a positive electrode mixture layer by adding an ionic conductive material to the positive electrode active material layer. And the step of forming 40.

The mass of the ion conductive material per unit volume of the positive electrode mixture layer 40 (the mass of the ion conductive material of the positive electrode mixture layer / the volume V1 of the positive electrode mixture layer) is 0.05 to 0.50 g / cm ^3. Good. The mass of the ion conductive material per unit volume of the positive electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ion conductive material per unit volume of the positive electrode mixture layer is 0.05 g / cm ³ or more, the discharge rate characteristics tend to be excellent, and when it is 0.50 g / cm ³ or less, It tends to be superior to safety.

The electrolyte layer 50 can be manufactured by, for example, a manufacturing method including a step of adding and mixing an electrolyte binder to an electrolyte component and a step of forming the obtained mixture into a sheet shape.

The negative electrode 80 includes, for example, a step of preparing a negative electrode precursor in which a negative electrode active material layer including a negative electrode active material is provided on the negative electrode current collector 20, and an ionic conductive material added to the negative electrode active material layer to form a negative electrode mixture layer And a step of forming 60.

The mass of the ion conductive material per unit volume of the negative electrode mixture layer 60 (the mass of the ion conductive material of the negative electrode mixture layer / the volume V2 of the negative electrode mixture layer) is 0.05 to 0.50 g / cm ^3. Good. The mass of the ion conductive material per unit volume of the negative electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ion conductive material per unit volume of the negative electrode mixture layer is 0.05 g / cm ³ or more, the discharge rate characteristics tend to be superior, and when it is 0.50 g / cm ³ or less, Excellent safety.

Subsequently, the lithium ion secondary battery 100 can be obtained by housing the obtained electrode group 85 including the positive electrode 70, the electrolyte layer 50, and the negative electrode 80 in the outer package 30. Even when the electrode group 85 is accommodated in the outer package 30, an ion conductive material is injected into the electrode group 85, and the total mass of the ion conductive material per unit volume of the outer package is adjusted to be within a predetermined range. Good. In addition, since the injected ionic conductive material is present in the gap between the outer package 30 and the electrode group 85, the ions per unit volume of the positive electrode mixture layer 40 and the negative electrode mixture layer 60 before and after the injection. It is presumed that the mass of the conductive material does not change.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the lithium ion secondary battery. The lithium ion secondary battery 200 includes a positive electrode current collector 10, a positive electrode mixture layer 40, an electrolyte layer 50, a negative electrode mixture layer 60, an interconnector 90, a positive electrode mixture layer 40, an electrolyte layer 50, a negative electrode mixture layer 60, An electrode group 85 including the interconnector 90, the positive electrode mixture layer 40, the electrolyte layer 50, the negative electrode mixture layer 60, and the negative electrode current collector 20 in this order, and the exterior body 30 are provided. As shown in FIG. 3, the lithium ion secondary battery 200 is considered to include a plurality of combinations having the positive electrode mixture layer 40, the electrolyte layer 50, and the negative electrode mixture layer 60 in this order via the interconnector 90. be able to. Among the plurality of combinations, the outermost positive electrode mixture layer 40 is connected to the positive electrode current collector 10, and the outermost negative electrode mixture layer 60 is connected to the negative electrode current collector 20.

[Interconnector]
The interconnector 90 is required to have high electron conductivity, no ionic conductivity, and the surface in contact with the negative electrode mixture layer 60 and the positive electrode mixture layer 40 do not exhibit a redox reaction depending on the respective potentials. . The interconnector 90 may be used as the positive electrode current collector 10 and the negative electrode current collector 20, and may be an aluminum foil or a SUS foil.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited thereto.

Example 1
<Preparation of ion conductive material>
LiTFSI (lithium salt) and tetraglyme (solvent (glyme represented by the general formula (1)), 20 ° C. vapor pressure: 1 Pa) are mixed at a molar ratio of 1: 1 using a magnetic stirrer in a glass bottle. Stir to prepare an ionic conductive material. Content of the solvent whose vapor pressure in 20 degreeC is 200 Pa or less was 100 mol%.

<Preparation of positive electrode>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (positive electrode active material) 81.0 parts by mass, powdered carbon (positive electrode conductive material) 3.0 parts by mass and acetylene black (positive electrode conductive material) 6.0 Part by mass was added to obtain a mixture. Separately, prepare a solution in which 10.0 parts by weight of polyvinylidene fluoride (PVDF, positive electrode binder) is dissolved in N-methyl-2-pyrrolidone (NMP, dispersion medium), add the above mixture to this, and adjust the viscosity with NMP. While mixing with a planetary mixer, a positive electrode mixture slurry was prepared. The positive electrode mixture slurry was uniformly and evenly applied to one side of a current collector (positive electrode current collector) made of SUS steel foil having a thickness of 12 μm with a coating machine. After the application, compression molding was performed with a roll press, pressurizing at 5 MPa, and punching out to Φ10 mm to obtain a positive electrode precursor having a positive electrode active material layer. The mass per unit area of the positive electrode precursor was 15 mg / cm ² .

With respect to the positive electrode active material layer of the obtained positive electrode precursor, the said ion conductive material was dripped using the micropipette, and the positive electrode which has a positive mix layer was produced. At this time, the mass of the ion conductive material per unit volume of the positive electrode mixture layer was adjusted to be 0.3 g / cm ³ . The mass of the ion conductive material dropped on the positive electrode active material layer was 0.0306 g, and the volume of the positive electrode mixture layer was 0.102 cm ³ . Moreover, the volume of the positive mix layer was calculated | required by measuring the thickness etc. of a positive mix layer using a micrometer.

<Production of negative electrode>
A solution obtained by dissolving 10.0 parts by mass of PVDF (negative electrode binder) in NMP (dispersion medium) is added to 90.0 parts by mass of graphite (negative electrode active material), and mixed with a planetary mixer while adjusting the viscosity with NMP. A negative electrode mixture slurry was prepared. The negative electrode mixture slurry was uniformly and evenly applied to one side of a current collector (negative electrode current collector) made of SUS steel foil having a thickness of 12 μm with a coating machine. After the application, compression molding was performed with a roll press, pressurizing at 5 MPa, and punching out to Φ10 mm to obtain a negative electrode precursor having a negative electrode active material layer. The mass per unit area of the negative electrode precursor was 6.8 mg / cm ² .

With respect to the negative electrode active material layer of the obtained negative electrode precursor, the said ion conductive material was dripped using the micropipette, and the negative electrode which has a negative mix layer was produced. At this time, the mass of the ion conductive material per unit volume of the negative electrode mixture layer was adjusted to 0.3 g / cm ³ . The mass of the ion conductive material dropped onto the negative electrode active material layer was 0.0225 g, and the volume of the negative electrode mixture layer was 0.075 cm ³ . The volume of the negative electrode mixture layer was determined by measuring the thickness of the negative electrode mixture layer using a micrometer.

<Preparation of electrolyte layer sheet>
The ionic conductive material and SiO ₂ nanoparticles (inorganic particles) were mixed at a volume ratio of 62:38, and methanol was added thereto and stirred for 30 minutes. Thereafter, the obtained electrolyte component slurry was spread on a petri dish, and methanol was distilled off to obtain a powdery electrolyte component. To this, polytetrafluoroethylene (PTFE, electrolyte binder) is added so as to be 5% by mass, thoroughly mixed, then stretched by pressurization, and punched to Φ16 mm, so that the electrolyte layer sheet has a thickness of about 30 μm. Obtained. The mass of the ion conductive material in the electrolyte layer sheet was 0.0506 g.

<Production of battery>
The prepared positive electrode, negative electrode, and electrolyte layer sheet are placed in a glove box filled with argon, and the negative electrode current collector, the negative electrode mixture layer, the electrolyte layer sheet, the positive electrode mixture layer, and the positive electrode current collector are placed in this glove box. They were stacked in order and accommodated in a 2032 size coin-type battery cell holder (exterior body, volume: 0.542 cm ³ ). Next, using a micropipette, the ion conductive material was injected into a coin-type battery cell holder, and the total mass of the ion conductive material per unit volume of the outer package was adjusted to 0.29 g / cm ³ . The dropped ion conductive material had a mass of 0.0535 g, and the total mass of the ion conductive material was 0.1572 g. Then, the lithium ion secondary battery of Example 1 was produced by sealing with a caulking machine.

(Example 2)
As shown in Table 1, the lithium ion secondary battery of Example 2 was prepared in the same manner as in Example 1 except that tetraglyme was changed to DEME-TFSI (solvent (ionic liquid)) in the preparation of the ion conductive material. Produced.

(Example 3)
As shown in Table 1, in the preparation of the ion conductive material, lithium ion of Example 3 was obtained in the same manner as in Example 1 except that tetraglyme was changed to propylene carbonate (cyclic carbonate, 20 ° C. vapor pressure: 17 Pa). A secondary battery was produced.

Example 4
As shown in Table 1, in the same manner as in Example 1, except that the total mass of the ionic conductive material per unit volume of the outer package was adjusted to 0.35 g / cm ³ , the lithium ion 2 of Example 4 was adjusted. A secondary battery was produced.

(Example 5)
As shown in Table 1, in the same manner as in Example 1 except that the total mass of the ionic conductive material per unit volume of the outer package was adjusted to 0.23 g / cm ³ , the lithium ion 2 of Example 5 was adjusted. A secondary battery was produced.

(Example 6)
As shown in Table 1, the mass of the ion conductive material per unit volume of the positive electrode mixture layer and the negative electrode mixture layer is 0.27 g / cm ³ , and the total mass of the ion conductive material per unit volume of the outer package is 0.18 g. A lithium ion secondary battery of Example 6 was produced in the same manner as in Example 1 except that the adjustment was made to be / cm ³ .

(Example 7)
As shown in Table 1, the mass of the ion conductive material per unit volume of the positive electrode mixture layer and the negative electrode mixture layer is 0.12 g / cm ³ , and the total mass of the ion conductive material per unit volume of the outer package is 0.12 g. A lithium ion secondary battery of Example 7 was produced in the same manner as in Example 1 except that the adjustment was made to be / cm ³ .

(Comparative Example 1)
As shown in Table 1, in the same manner as in Example 1 except that the total mass of the ion conductive material per unit volume of the outer package was adjusted to 0.59 g / cm ³ , the lithium ion 2 of Comparative Example 1 was used. A secondary battery was produced.

(Comparative Example 2)
As shown in Table 1, in the same manner as in Example 1, except that the total mass of the ion conductive material per unit volume of the outer package was adjusted to 0.41 g / cm ³ , the lithium ion 2 of Comparative Example 2 was used. A secondary battery was produced.

(Comparative Example 3)
As shown in Table 1, the mass of the ion conductive material per unit volume of the positive electrode mixture layer and the negative electrode mixture layer is 0.05 g / cm ³ , and the total mass of the ion conductive material per unit volume of the outer package is 0.09 g. A lithium ion secondary battery of Comparative Example 3 was produced in the same manner as in Example 1, except that the adjustment was made to be / cm ³ .

(Comparative Example 4)
As shown in Table 1, in the preparation of the ion conductive material, except that tetraglyme was changed to a mixed solution of tetraglyme (80 mol%) and dimethyl carbonate (20 ° C vapor pressure: 5300 Pa, 20 mol%), Examples In the same manner as in Example 1, a lithium ion secondary battery of Comparative Example 4 was produced.

<Evaluation of coin cell battery>
(Evaluation of discharge rate characteristics)
The lithium ion secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4 were charged at 0.1 C using a 1480 potentiostat (manufactured by Solartron), and 1% at SOC (Stage of Charge) 100%. After holding for a period of time, discharge was performed at 0.1 C. The upper limit potential was 4.2 V, the lower limit potential was 2.7 V, and the discharge capacity at 0.1 C was measured. Then, after charging at 0.1 C, the discharge capacity at 0.5 C was measured by holding at 100% SOC for 1 hour and discharging at 0.5 C. At this time, the value represented by the following formula was used as the discharge rate characteristic. The results are shown in Table 2.
Discharge rate characteristic (%) = [(discharge capacity at 0.5 C) / (discharge capacity at 0.1 C)] × 100

(Evaluation of overcharge characteristics)
After evaluating the 0.5C rate characteristics, the battery was further discharged at 0.1C and left for 1 hour. Thereafter, the battery was charged at 0.1 C, and the amount of voltage change after 1 hour from the time of reaching 5 V was measured. The results are shown in Table 2. In this test, the higher the value, the higher the internal resistance of the battery (that is, the better current interruption characteristics), and the better the safety.

The lithium ion secondary batteries of Examples 1 to 7 were excellent in safety during overcharging and also in discharge rate characteristics. On the other hand, the lithium ion secondary batteries of Comparative Examples 1 and 2 in which the total mass of the ion conductive material per unit volume of the outer package exceeds 0.35 g / cm ³ are excellent in discharge rate characteristics, but are safe during overcharge. Was not enough. Further, the total amount of substance content solvent of the solvent vapor pressure is less than 200Pa total weight of the ion conductive material of Comparative Example 3 and 20 ° C. less than 0.12 g / cm ³ per unit volume of the outer body The lithium ion secondary battery of Comparative Example 4, which is less than 85 mol% as a reference, is excellent in safety during overcharge, but has insufficient discharge rate characteristics. From these results, it was confirmed that the lithium secondary battery of the present invention was excellent in safety during overcharge and also in discharge rate characteristics.

The lithium ion secondary battery obtained in the present invention can be used as an electricity storage device by connecting to a cell controller or control panel and protecting it with a casing. The lithium ion secondary battery according to the present invention can be charged / discharged at a higher current, and further can suppress a decrease in power storage performance associated with the cycle. In addition, an electricity storage device using a lithium ion secondary battery can be disposed on the front surface or the bottom surface of a vehicle body as a power source for an automobile. Furthermore, the power storage device can be used as an industrial power source for balancing power supply and demand.

DESCRIPTION OF SYMBOLS 10 ... Positive electrode collector, 20 ... Negative electrode collector, 30 ... Exterior body, 40 ... Positive electrode mixture layer, 50 ... Electrolyte layer, 60 ... Negative electrode mixture layer, 70 ... Positive electrode, 80 ... Negative electrode, 85 ... Electrode group , 90 ... interconnector, 100, 200 ... lithium ion secondary battery, S ... volume (exterior body), V1 ... volume (positive electrode mixture layer), V2 ... volume (negative electrode mixture layer).

Claims

A positive electrode having a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, an electrolyte layer, and a negative electrode having a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector An electrode group comprising:
An exterior body that houses the electrode group;
With
The electrode group contains an ion conductive material containing a solvent and a lithium salt,
The total mass of the ion conductive material per unit volume of the outer package is 0.12 to 0.35 g / cm 3 ;
The solvent includes a solvent having a vapor pressure at 20 ° C. of 200 Pa or less,
The lithium ion secondary battery, wherein the content of the solvent having a vapor pressure at 20 ° C of 200 Pa or less is 85 mol% or more based on the total amount of the solvent.
The lithium ion secondary battery according to claim 1, wherein a mass of the ion conductive material per unit volume of the positive electrode mixture layer is 0.05 to 0.50 g / cm 3 .
The lithium ion secondary battery according to claim 1 or 2, wherein a mass of the ion conductive material per unit volume of the negative electrode mixture layer is 0.05 to 0.50 g / cm 3 .
The lithium ion secondary battery according to any one of claims 1 to 3, wherein the solvent having a vapor pressure at 20 ° C of 200 Pa or less contains glyme represented by the following general formula (1).
R 1 O— (CH 2 CH 2 O) m —R 2 (1)
[In Formula (1), R 1 and R 2 each independently represents an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 3 to 6. ]
The lithium ion secondary battery according to any one of claims 1 to 3, wherein the solvent having a vapor pressure of 200 Pa or less at 20 ° C contains triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.