JP2016219275A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-capacity lithium ion secondary battery which exhibits superior charge and discharge cycle characteristics.SOLUTION: Provided is a lithium ion secondary battery comprising an outer sheath, a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte solution which are at least encased in the outer sheath. The negative electrode includes, as a negative electrode active material, a material S including SiO, graphite A having an average particle diameter of over 15 up to 25 μm, and graphite B having an average particle diameter of 8-15 μm, and including graphite particles of which the surface is covered with amorphous carbon. The mix mass%(A+B) of the graphite A and the graphite B included as the negative electrode active material is 20% to less than 99%, and the mass ratio (A/B) of the graphite A to the graphite B is 0.5-4.5. The positive electrode includes, as a positive electrode active material, a metal oxide including Li and a metal M other than Li. When the lithium ion secondary battery is discharged in a particular condition, the mole ratio (Li/M) of Li to the metal M other than Li included in the positive electrode active material is 0.9-1.05.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lithium ion secondary battery having a high capacity and excellent cycle characteristics and storage properties.

  Lithium ion secondary batteries, which are one type of electrochemical element, are considered to be applied to portable devices, automobiles, electric tools, electric chairs, household and commercial power storage systems because of their high energy density. Yes. In particular, as a portable device, it is widely used as a power source for a mobile phone, a smartphone, or a tablet PC.

  In addition, lithium ion secondary batteries are required to improve various battery characteristics as well as to increase the capacity in accordance with the spread of applied devices. Since it is a secondary battery especially, the improvement of a charging / discharging cycling characteristic is calculated | required strongly.

Usually, a carbon material such as graphite capable of inserting and removing lithium (Li) ions is widely used as a negative electrode active material of a lithium ion secondary battery. On the other hand, Si or Sn, or a material containing these elements, has been studied as a material capable of inserting and desorbing more Li ions. In particular, the compound SiO _x having a structure in which Si fine particles are dispersed in SiO ₂ has attracted attention. ing. Further, since these materials have low conductivity, a structure in which the surface of particles is covered with a conductor such as carbon has been proposed (Patent Documents 1 and 2).

The conventional SiO _x found in Patent Documents 1 and 2 has a tendency that the battery characteristics are remarkably lowered when the charge and discharge cycle is repeated due to the volume change accompanying the charge and discharge. Therefore, the negative electrode mixture layer has a low density (1.4 g / cm ³ or less), and as the negative electrode active material, carbon-coated SiO (all negative electrodes) in addition to artificial graphite of 15 μm to 20 μm and pitch-coated graphite of 10 μm or less. A proposal has been made to improve load characteristics and cycle characteristics due to a large current using 1 to 10% by weight based on the total weight of the active material (Patent Document 3).

In addition, since SiO _x has a relatively high irreversible capacity, it is desirable to introduce, for example, metal Li as a Li source in advance to the negative electrode side. However, in the method of attaching a metal Li foil to the negative electrode, variation in the introduction of Li occurs and the negative electrode Since there is a possibility that lithium dendrite is precipitated on the top, a method using a Li-containing layer formed by a vapor phase method as a Li source has been proposed (Patent Document 4).

JP 2004-47404 A Japanese Patent Laid-Open No. 2005-259697 Japanese Patent No. 5302456 JP 2007-242590 A

  In the configuration of Patent Document 3, numerical values are only shown for the discharge capacity at the 300th cycle, and no mention is made of the capacity retention rate in the repetition of the charge / discharge cycle, so the effect of improving the cycle characteristics is unclear. . In the configuration of Patent Document 4, although the initial charge and discharge efficiency is improved by introducing Li in advance, there is still room for improvement in the reaction uniformity of Li introduction.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a lithium ion secondary battery having high capacity and excellent cycle characteristics.

  The present invention relates to a lithium ion secondary battery in which a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are loaded in at least an outer package, wherein the negative electrode is a support comprising a metal foil and a negative electrode mixture layer mainly composed of a negative electrode active material. The negative electrode active material is a compound SiOx containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5). ), Graphite A having an average particle diameter of more than 15 μm and not more than 25 μm, graphite having an average particle diameter of 8 μm to 15 μm, and the surface of the graphite particles coated with amorphous carbon When B is included and the total of all the negative electrode active materials contained in the negative electrode is 100 mass%, the mixed mass% (A + B) of graphite A and graphite B contained as the negative electrode active material is 20% or more and 99. Less than% The positive electrode active material when the mass ratio (A / B) of graphite A to graphite B is 0.5 or more and 4.5 or less, and discharge is performed at a discharge current rate of 0.1 C until the voltage reaches 2.0 V. Is a lithium ion secondary battery having a molar ratio (Li / M) of Li and a metal M other than Li of 0.9 to 1.05.

  According to the present invention, it is possible to provide a lithium ion secondary battery having a high capacity and excellent cycle characteristics.

It is a top view which represents typically an example of the positive electrode which concerns on the lithium ion secondary battery of this invention. It is a top view which represents typically an example of the negative electrode which concerns on the lithium ion secondary battery of this invention. It is a top view which represents typically an example of the lithium ion secondary battery of this invention. It is the II sectional view taken on the line of FIG. It is a top view which represents typically the middle stage of preparation of an example of the lithium ion secondary battery of this invention.

  As the negative electrode according to the lithium ion secondary battery of the present invention, one having a structure in which a negative electrode mixture layer containing a negative electrode active material, a binder or the like is provided on one side or both sides of a current collector is used.

The negative electrode active material in the present invention includes a material S composed of a compound SiO _x containing Si and O as constituent elements, graphite A having an average particle diameter of more than 15 μm and 25 μm or less, and an average particle diameter of 8 μm or more and 15 μm or less. In addition, there are mother particles made of graphite and graphite B whose surfaces are coated with amorphous carbon.

The material S containing SiO _x exhibits a capacity of 1000 mAh / g or more, and is characterized by significantly exceeding 372 mAh / g, which is called the theoretical capacity of graphite. On the other hand, compared with the charge / discharge efficiency (90% or more) of general graphite, the material S containing SiO _x often has an initial charge / discharge efficiency of less than 80%, and the irreversible capacity increases, so there is a problem in cycle characteristics. there were. Therefore, it is desired to introduce a Li source into the negative electrode in advance.

  As a method of introducing Li into the negative electrode active material, a lithium metal foil is attached to the negative electrode mixture layer, a Li vapor deposition layer is formed, particulate lithium is included, and the Li source and electrochemical are formed after forming the negative electrode mixture layer. When adopting the method of introducing Li through contact (short circuit) and the method of charging or discharging the negative electrode and Li source arranged so as not to be short-circuited by external connection, the charge / discharge efficiency and the initial capacity are slightly improved. Although there was an effect, there was still room for improvement in terms of cycle characteristics. The cause is presumed that, in the negative electrode mixture layer, a place where the introduction of Li progressed and a place where the progress did not proceed, and the reaction became non-uniform. Therefore, as a result of various studies, when Li ions are introduced into the negative electrode, the charge / discharge efficiency, the initial capacity, and the cycle characteristics are greatly improved by using the material S in combination with graphite A and graphite B described later. I found out.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, the SiO _x to SiO ₂ matrix of amorphous Si (e.g., microcrystalline Si) is include the dispersed structure, the SiO ₂ of the amorphous, dispersed therein It is only necessary that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

The material S containing SiO _x is preferably a composite that is combined with a carbon material. For example, the surface of the SiO _x is preferably covered with the carbon material. Usually, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. If complexes complexed with carbon material SiO _x, for example, simply than with a material obtained by mixing a conductive material such as SiO _x and the carbon material, good conductive network in the negative electrode Formed.

That is, the specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, whereas the specific resistance value of the carbon material exemplified above is usually 10 ^{−5 to} 10 kΩcm. And the conductivity of SiO _x can be improved.

The complex with the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, granulated material or the like between the SiO _x and the carbon material can be cited.

Preferred examples of the carbon material that can be used for forming a composite with the SiO _x include carbon materials such as low crystalline carbon, carbon nanotubes, and vapor grown carbon fibers.

Details of the carbon material include at least selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. One material is preferred. A fibrous or coiled carbon material is preferable in that it easily forms a conductive network and has a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention, and the SiO _x particles expand and contract. However, it is preferable in that it has a property of easily maintaining contact with the particles.

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable as a material used when the composite with SiO _x is a granulated body. The fibrous carbon material has a thin thread shape and high flexibility so that it can follow the expansion and contraction of SiO _x that accompanies charging / discharging of the battery, and because of its large bulk density, it has a large amount of SiO _x particles. It is because it can have the following junction point. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used.

When a composite of SiO _x and a carbon material is used for the negative electrode, the ratio of SiO _x and the carbon material is SiO _x : 100 parts by weight from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. On the other hand, the carbon material is preferably 5 parts by weight or more, and more preferably 10 parts by weight or more. In the composite, if the ratio of the carbon material to be composited with SiO _x is too large, the amount of SiO _x in the negative electrode mixture layer may be reduced, and the effect of increasing the capacity may be reduced. The carbon material is preferably 50 parts by weight or less and more preferably 40 parts by weight or less with respect to SiO _x : 100 parts by weight.

The composite of the above SiO _x and carbon material can be obtained by, for example, the following method.

When the surface of SiO _x is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon gas are heated in the gas phase, and are generated by thermal decomposition of the hydrocarbon gas. Carbon is deposited on the surface of the particles. Thus, according to the vapor deposition (CVD) method, a hydrocarbon-based gas spreads to every corner of the SiO _x particle, and a thin and uniform film (carbon material) containing a conductive carbon material on the surface of the particle. Since the coating layer) can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon material.

In the production of SiO _x coated with the carbon material, the processing temperature (atmosphere temperature) of the CVD method varies depending on the type of hydrocarbon-based gas, but usually 600 to 1200 ° C. is suitable. It is preferable that it is higher than ℃, and more preferable that it is higher than 800 ℃. This is because the higher the treatment temperature, the fewer impurities remain and the formation of a coating layer containing carbon having high conductivity.

  As the liquid source of the hydrocarbon gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

Further, when a granulated body of SiO _x and a carbon material is prepared, a dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, sprayed and dried to obtain a granulated body including a plurality of particles. Make it. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. In addition to the above method, a granulated body of SiO _x and a carbon material can be produced also by a granulating method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

In the above-described negative electrode, from the viewpoint of satisfactorily ensuring the effect of the high capacity by using a SiO _x, the content of the complex of the SiO _x and the carbon material in the anode active material is 0.01 wt% or more Preferably, it is 1% by weight or more, more preferably 3% by weight or more. Further, from the viewpoint of better avoiding the problem due to the volume change of SiO _x accompanying charge / discharge, the content of the composite of SiO _x and the carbon material in the negative electrode active material is preferably 20% by weight or less. 15% by weight or less is more preferable.

  If the average particle size of the material S is too small, the dispersibility of the material S may be reduced, and the effects of the present invention may not be sufficiently obtained, and the material S has a large volume change associated with charging / discharging of the battery. If the average particle diameter is too large, the material S is likely to collapse due to expansion / contraction (this phenomenon leads to capacity degradation of the material S), and therefore it is preferably 0.1 μm or more and 10 μm or less.

  The content ratio of the material S to the total negative electrode active material in the negative electrode mixture layer is preferably 1% or more, more preferably 10% by mass or more, and most preferably 50% by mass or more. . As described above, the material S is a material that can achieve a dramatic increase in capacity as compared with graphite. Therefore, if the material S is contained in a small amount in the negative electrode active material, an effect of improving the battery capacity can be obtained. On the other hand, the material S is preferably 10% by mass or more based on the total amount of the negative electrode active material in order to achieve a dramatic increase in battery capacity. The content of the material S may be adjusted in accordance with various battery uses and required characteristics. In order to exhibit the effect of introducing Li by graphite A and graphite B described later (by electrochemical contact between Li and the negative electrode), the ratio of the material S is less than 99% by mass, preferably 90% by mass or less. More preferably, it is 80 mass% or less.

Examples of the graphite A include natural graphite and artificial graphite which are used as a negative electrode active material of a normal lithium ion secondary battery. As artificial graphite, for example, a coke or organic material fired at 2800 ° C. or higher, or a natural graphite and the coke or organic material mixed and heat-treated at 2800 ° C. or higher, and further coke or organic material at 2800 ° C. or higher. The natural graphite is coated on the surface of the natural graphite. The R value, which is the peak intensity ratio appearing at 1340-1370 cm ⁻¹ with respect to the peak intensity appearing at 1570-1590 cm ⁻¹ in the argon ion laser Raman spectrum, is Graphite that is 0.05 to 0.2 can be used. If the average particle diameter is in the above range, two or more kinds of graphite may be used in combination with the graphite A.

Graphite B is composed of graphite particles serving as mother particles and amorphous carbon covering the surface. Specifically, it is graphite in which the R value, which is a peak intensity ratio appearing at 1340 to 1370 cm ⁻¹ with respect to the peak intensity appearing at 1570 to 1590 cm ⁻¹ in the argon ion laser Raman spectrum, is 0.1 to 0.7. The R value is more preferably 0.3 or more in order to ensure a sufficient coating amount of amorphous carbon. Moreover, since an irreversible capacity | capacitance will increase if there is too much coating amount of amorphous carbon, R value is 0.6 or less. Such graphite B uses, for example, natural graphite having d ₀₀₂ of 0.338 nm or less or graphite obtained by spherically shaping artificial graphite as a base material (base particle), and the surface thereof is coated with an organic compound. It can be obtained by calcining at 0 ° C., pulverizing, and sizing through a sieve. The organic compound covering the base material includes aromatic hydrocarbons; tars or pitches obtained by polycondensation of aromatic hydrocarbons under heat and pressure; tars mainly composed of a mixture of aromatic hydrocarbons. , Pitch or asphalt; In order to coat the base material with the organic compound, a method of impregnating and kneading the base material into the organic compound can be employed. Alternatively, graphite B can be produced by a vapor phase method in which a hydrocarbon gas such as propane or acetylene is carbonized by pyrolysis and deposited on the surface of graphite having d ₀₀₂ of 0.338 nm or less.

  Furthermore, the graphite B has high Li ion acceptability (for example, it can be quantified by the ratio of the constant current charge capacity to the total charge capacity). Therefore, the lithium ion secondary battery of the present invention using graphite B together has good acceptability of Li ions and good charge / discharge cycle characteristics. As described above, when the Li source is introduced into the negative electrode containing the material S by electrochemical contact (short circuit), if the graphite B is used in combination, the uneven introduction of Li can be suppressed. We thought that the characteristics could be improved.

However, it has been found that sufficient improvement in battery characteristics cannot be obtained only by using graphite B alone. Because graphite B is based on graphite activated in a spherical shape as described above, graphite B alone cannot provide sufficient contact between the particles, which causes unevenness in the introduction of Li, and the negative electrode. It is presumed that the overall Li ion acceptability was not improved and the battery characteristics were not greatly improved. Accordingly, it has been found that the battery characteristics are significantly improved by using graphite A having an average particle size higher than that of graphite B, specifically, more than 15 μm and not more than 25 μm in combination with graphite B. Specifically, the total content of graphite A and graphite B in the total negative electrode active material contained in the negative electrode is 20% by mass or more and less than 99% by mass, and the graphite with respect to graphite B in the total negative electrode active material contained in the negative electrode The content ratio (A / B) of A is 0.5 or more and 4.5 or less. By using graphite A and graphite B together in this way, the number of places where the contact of graphite B cannot be secured is reduced, that is, the introduction of Li ions into the negative electrode is reduced, so that Li ions are used rather than graphite B alone. This is presumed to be due to the increased acceptability of.
Furthermore, reducing the unevenness at the time of introducing Li also leads to a uniform charge / discharge reaction thereafter, and it has also been clarified that the cycle characteristics are dramatically improved as compared with the case of using only graphite B.

  In addition, when the particle diameter of graphite A is too small, the specific surface area is excessively increased (the irreversible capacity is increased), so that the particle diameter is preferably not too small. Therefore, in the present invention, graphite A having an average particle diameter of more than 15 μm is used. In addition, if the particle size of graphite B is too small, the coating amount of amorphous carbon covering the surface varies, and there are reasons that the features of graphite B cannot be fully exhibited. It is preferable not to be too small. Therefore, in the present invention, graphite B having an average particle diameter of 8 μm or more is used.

As used herein, graphite (graphite A, graphite B, and other graphite), material S, and other various average particle sizes may be measured by, for example, a laser scattering particle size distribution meter (for example, Microtrack particle size distribution measurement manufactured by Nikkiso Co., Ltd.). Using an apparatus “HRA9320”), in which the integrated volume is determined from particles having a small particle size distribution measured by dispersing graphite in a medium that does not dissolve or swell graphite, Value (D _50% ) is the median diameter.

The specific surface area of graphite A and graphite B (according to the BET method. The specific surface area of other materials is also the same. An example of the apparatus is “Bell Soap Mini” manufactured by Bell Japan Co., Ltd.) is preferably 1.0 m ² / g or more. Moreover, it is preferable that it is 5.0 m < ² > / g or less.

  The crystallite size in the c-axis direction: Lc in the crystal structures of graphite A and graphite B is preferably 3 nm or more, more preferably 8 nm or more, and further preferably 25 nm or more. This is because, within this range, insertion / extraction of lithium ions becomes easier. The upper limit value of Lc of graphite is not particularly limited, but is usually about 200 nm.

  In addition, the negative electrode active material includes a negative electrode active material other than graphite A and graphite B (for example, graphite A, which is the same type as graphite A and has an average particle diameter of less than 15 μm or more than 25 μm. And graphite not corresponding to graphite B), Si or Sn alone, alloys containing Si or Sn, oxides containing Si or Sn (though not applicable to material S) do not impair the effects of the present invention. It can also be used to the extent.

  As the binder related to the negative electrode mixture layer, for example, a material that is electrochemically inactive with respect to Li in the working potential range of the negative electrode and does not affect other substances as much as possible is selected. Specifically, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), methylcellulose, polyimide, polyamideimide, polyacrylic acid, and derivatives and co-polymers thereof. A polymer etc. are mentioned as a suitable thing. These binders may use only 1 type and may use 2 or more types together.

  A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), carbon It is possible to use one or more materials such as fiber, metal powder (powder of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative (described in JP-A-59-20971). it can. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

  The negative electrode is prepared, for example, by preparing a negative electrode mixture-containing composition in which a negative electrode active material and a binder and, if necessary, a conductive additive are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. (However, the binder may be dissolved in a solvent), which is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the manufacturing method of the negative electrode is not limited to the above method, and may be manufactured by other manufacturing methods.

The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per side of the current collector, and the density of the negative electrode mixture layer (from the mass and thickness of the negative electrode mixture layer per unit area laminated on the current collector) (Calculated) is preferably 1.0 g / cm ³ or more, more preferably 1.2 g / cm ³ or more in order to increase the capacity of the battery. In addition, if the density of the negative electrode mixture layer is too high, adverse effects such as a decrease in the permeability of the non-aqueous electrolyte solution occur, so 1.6 g / cm ³ or less is desirable. Moreover, as a composition of a negative mix layer, it is preferable that the quantity of a negative electrode active material is 80-99 mass%, for example, it is preferable that the quantity of a binder is 0.5-10 mass%, and a conductive support agent. When using, it is preferable that the quantity is 1-10 mass%.

  As a support (current collector) for supporting the current collector of the negative electrode and the negative electrode mixture layer, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used. In the negative electrode support, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is 4 μm in order to ensure mechanical strength. desirable.

  As a method for introducing Li into the negative electrode active material described above, for example, a metal Li foil is attached to the negative electrode mixture layer, the Li source is brought into contact with the negative electrode mixture layer, and then a non-aqueous electrolyte is injected to form the negative electrode When adopting a technique for introducing Li into the mixture layer, a copper foil is used as the support, and when the negative electrode mixture layer is provided on both sides of the copper foil, the Li source is arranged on the negative electrode mixture layer on both sides. Need arises. On the other hand, when a metal foil having a through-hole penetrating from one surface of the copper foil to the other surface is used as the support (current collector), the negative electrode mixture layer provided on both surfaces passes through the through-hole. Since they are electrically connected, if a Li source is arranged on one of the surfaces, Li ions move from one negative electrode mixture layer to the other negative electrode mixture layer through a through hole, Li is to be introduced into the negative electrode mixture layer, and the work of arranging the Li source can be simplified.

  When a metal foil having a plurality of through holes penetrating from one surface to the other surface is used as a support (current collector) for the negative electrode mixture layer, the upper limit of the thickness is preferably 30 μm, In order to ensure strength, the lower limit is preferably 4 μm. Further, the size of the through hole is preferably 0.05 mm or more for the purpose of making the introduction of Li uniform. However, if the size of the through hole is too large, 1 mm or less is desirable because the mechanical strength cannot be maintained. Furthermore, the pitch between the through holes is desirably about 1 to 5 mm.

  As a method for introducing Li into the negative electrode mixture layer, as described above, a Li foil is attached to the negative electrode mixture layer, particulate Li is included in the negative electrode mixture layer, or Li is deposited on the negative electrode surface. In a state where the Li source and the negative electrode are in contact with each other by various known methods, such as charging and discharging with a nonaqueous electrolyte solution, or arranging so that the negative electrode and the Li source are not in contact with each other, nonaqueous electrolysis For example, a method of filling the liquid and charging / discharging by external connection can be used.

The present invention provides a porous layer (hereinafter simply referred to as a porous layer) containing an insulating material that does not react with Li on the negative electrode mixture layer (the surface of the negative electrode mixture layer opposite to the negative electrode current collector). Can be provided). By providing such a porous layer, it is possible to prevent the Li source disposed inside the battery from reacting rapidly with the negative electrode and contribute to uniform introduction of Li into the negative electrode.
Such a porous layer is preferably a layer containing, for example, an insulating material that does not react with L i and having pores that allow a nonaqueous electrolyte (electrolytic solution) to pass through. Examples of the insulating material for the porous layer include various inorganic oxides and organic fine particles. As the inorganic fine particles, chalcogenites (oxides, sulfides, etc.), hydroxides, nitrides, carbides, silicides and the like of metal elements or nonmetal elements are preferable.

As the metal element or non-metal element chalcogenite, an oxide is preferable, and an oxide which is not easily reduced is more preferable. As such an oxide, _{e.g., MgO, CaO, SrO, BaO} , ZrO 2, ZnO, B 2 O 3, Al 2 O 3, Ga 2 O 3, In 2 O 3, SiO 2, As 4 O 6 , Sb ₂ O _{5 and the} like. Moreover, the metal element hydroxide which comprises the said oxide may be sufficient, and AlOOH (boehmite) etc. can also be used. Among these, ZnO, Al ₂ O ₃ , AlOOH, Ga ₂ O ₃ , SiO ₂ , and ZrO ₂ are particularly preferable. The oxide or hydroxide may be a single compound or a complex compound.

Examples of the nitride of the metal element or non-metal element include aluminum nitride (AlN) and BN, and examples of the carbide or silicide of the metal element or non-metal element include SiC, which have high insulation and chemical properties. It is preferable in that it is stable.
Among the insulating materials for forming the porous layer, the organic fine particles are preferably those that do not flow into a film or decompose at a temperature of 300 ° C. or lower. For example, polytetrafluoroethylene Fine particles of fluororesin such as (PTFE) or a crosslinked latex can be used.

  The particle size of the insulating material is, for example, 0.1 μm or more, more preferably 0.2 μm or more, and preferably 10 μm or less, more preferably 5 μm or less.

  The porous layer preferably contains an electron conductive material in addition to an insulating material that does not react with Li. This is because the diffusion of Li proceeds smoothly by reducing the electrical resistance between the negative electrode mixture layer and the Li-containing layer. Examples of the electron conductive material for forming the porous layer include carbon materials such as carbon particles and carbon fibers; metal materials such as metal particles and metal fibers; metal oxides; Among these, carbon particles and metal particles having low reactivity with Li are preferable.

  As the carbon material to be contained in the porous layer, for example, a known carbon material that is used as a conductive additive in an electrode constituting a battery can be used. Specifically, carbon such as carbon black (thermal black, furnace black, channel black, lamp black, ketjen black, acetylene black, etc.), graphite (natural graphite such as flake graphite, earth graphite, and artificial graphite) Examples include particles and carbon fibers.

  Among the above carbon materials, the combined use of carbon black and graphite is particularly preferable from the viewpoint of dispersibility with a binder described later. Further, as the carbon black, ketjen black and acetylene black are particularly preferable.

  The particle size of the carbon particles is, for example, 0.01 μm or more, more preferably 0.02 μm or more, and preferably 10 μm or less, more preferably 5 μm or less.

  Among the electron conductive materials for forming the porous layer, the metal particles and the metal fibers are preferably made of a metal element that is low in reactivity with Li and hardly forms an alloy with Li. Specific metal elements constituting the metal particles and metal fibers include, for example, Ti, Fe, Ni, Cu, Mo, Ta, and W.

  In the case of metal particles, the shape is not particularly limited, and may be any shape such as a lump shape, a needle shape, a column shape, or a plate shape. In addition, the metal particles and the metal fibers are preferably those whose surfaces are not so oxidized, and those that are excessively oxidized may be subjected to a heat treatment in a reducing atmosphere in advance and then subjected to porous layer formation. desirable.

The particle size of the metal particles is, for example, 0.02 μm or more, more preferably 0.1 μm or more, and preferably 10 μm or less, more preferably 5 μm or less.
As a combination of an insulating material that does not react with Li and an electron conductive material, for example, a combination of aluminum oxide (Al ₂ O ₃ ) or boehmite and a carbon material is particularly preferable.

  In forming the porous layer, it is preferable to use a binder for the purpose of binding an insulating material or an electron conductive material that does not react with Li. As the binder, for example, various materials exemplified as the binder for the negative electrode mixture layer can be used.

  In the porous layer, when the total of the insulating material that does not react with Li and the material having electron conductivity is 100% by mass, the ratio of the material having electron conductivity is, for example, 2.5% by mass or more. More preferably, it is 5% by mass or more and 96% by mass or less, more preferably 95% by mass or less. In other words, the ratio of the insulating material that does not react with Li is, for example, 4% by mass. More preferably, it is 5% by mass or more, 97.5% by mass or less, and more preferably 95% by mass or less.

  Further, when a binder is used for forming the porous layer, when the total of the insulating material that does not react with Li, the material that has electronic conductivity, and the binder is 100% by mass, the insulating that does not react with Li The ratio of the total amount of the conductive material and the material having electron conductivity is 40% by mass or more, more preferably 50% by mass or more, and 96% by mass or less, more preferably 94% by mass or less. Desirably, in other words, the binder ratio is, for example, 4% by mass or more, more preferably 6% by mass or more, and 60% by mass or less, more preferably 50% by mass or less.

  The thickness of the porous layer is, for example, 2 μm or more, more preferably 3 μm or more, and preferably 10 μm or less, more preferably 8 μm or less. If the porous layer has such a thickness, the direct reaction between the material S of the negative electrode mixture layer and the Li of the Li-containing layer can be controlled more efficiently, thereby increasing the capacity of the battery and improving the battery characteristics. It can be achieved more reliably. That is, if the thickness of the porous layer becomes too thin relative to the surface roughness of the negative electrode mixture layer, for example, it becomes difficult to cover the entire surface of the negative electrode mixture layer without pinholes, thereby forming a porous layer. On the other hand, if the porous layer is too thick, it leads to a decrease in battery capacity. Therefore, it is preferable to form it as thin and uniform as possible.

  In addition, since the affinity between the negative electrode and the nonaqueous electrolyte is improved by providing the porous layer, an effect of facilitating the introduction of the nonaqueous electrolyte into the battery can be expected.

  The porous layer is, for example, a paste obtained by sufficiently kneading a mixture containing an insulating material that does not react with Li, an electron conductive material, and a binder with an appropriate solvent (dispersion medium). Or a slurry-like composition (coating material) is applied onto the negative electrode mixture layer, and the solvent (dispersion medium) is removed by drying or the like to form a predetermined thickness.

  For the positive electrode according to the lithium ion secondary battery of the present invention, for example, a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder is used on one or both sides of the positive electrode current collector. be able to.

The positive electrode active material used for the positive electrode is not particularly limited, and a generally usable active material such as a lithium-containing transition metal oxide may be used. Specific examples of the lithium-containing transition metal oxide include, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O _2. , etc. _{Li x Ni 1-y M y} O 2, Li x Mn y Ni z Co 1-y-z O 2, Li x Mn 2 O 4, Li x Mn 2-y M y O 4 are exemplified. However, in each of the above structural formulas, M is at least one metal element selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Mo, Al, Ti, Ge, and Cr. 0 ≦ x ≦ 1.1, 0 <y ≦ 1.0, and 0 <z <1.0.

  As a conductive support agent used for the said positive electrode, what is chemically stable should just be in a battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metal powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives, etc. You may use independently and may use 2 or more types together. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

  Moreover, PVDF, P (VDF-CTFE), polytetrafluoroethylene (PTFE), SBR, etc. can be used for the binder which concerns on a positive mix layer.

The positive electrode is prepared, for example, as a paste-like or slurry-like positive electrode mixture-containing composition in which the above-described positive electrode active material, conductive additive and binder are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). (However, the binder may be dissolved in a solvent.) After applying this to one or both sides of the current collector and drying, it can be produced through a process of calendering if necessary. . The manufacturing method of a positive electrode is not necessarily restricted to said method, It can also manufacture with another manufacturing method.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector. Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 65-95 mass%, for example, it is preferable that the quantity of a binder is 1-15 mass%, and the quantity of a conductive support agent. Is preferably 3 to 20% by mass.

The current collector can be the same as that used for the positive electrode of a conventionally known lithium ion secondary battery, such as aluminum foil, punching metal, net, expanded metal, etc. The thickness is preferably 5 to 30 μm.
When the method of introducing Li to the negative electrode mixture layer by contacting the Li source described above is used, a metal foil having a plurality of through holes penetrating the negative electrode current collector from one surface to the other surface, and Also for the positive electrode current collector, by using a metal foil having a plurality of through holes penetrating from one surface to the other surface, Li is transferred to the entire inside of the battery through the through holes of the negative electrode current collector and the positive electrode current collector. Since it moves, it becomes unnecessary to contact Li source with all the negative electrodes, and it can improve working efficiency.
When a metal foil having a plurality of through holes penetrating from one surface to the other surface is used as the positive electrode current collector, the upper limit of the thickness is preferably 30 μm, and the lower limit is in order to ensure mechanical strength. It is desirable to be 4 μm. Further, the size of the through hole is preferably 0.05 mm or more for the purpose of making the movement of Li uniform. However, if the size of the through hole is too large, 1 mm or less is desirable because the mechanical strength cannot be maintained. Furthermore, the pitch between the through holes is desirably about 1 to 5 mm.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a positive electrode as needed.

  The separator is preferably a porous film composed of polyolefin such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester such as polyethylene terephthalate and copolymer polyester; In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator has a melting point, that is, a thermoplastic resin having a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 ° C. in accordance with JIS K 7121 as a component. Preferably, it is a single layer porous film mainly composed of polyethylene or a laminated porous film comprising a porous film such as a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. Is preferred. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is desirable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More desirable.

  As such a resin porous membrane, for example, a porous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known lithium ion secondary battery or the like, that is, a solvent extraction method, a dry type Alternatively, an ion-permeable porous film manufactured by a wet stretching method or the like can be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

Moreover, as a characteristic of the separator, a Gurley value represented by the number of seconds in which 100 ml of air permeates the membrane under a pressure of 0.879 g / mm ² is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  As the separator, a laminated separator having a porous layer (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher may be used. . The separator has both shutdown characteristics, heat resistance (heat shrinkage resistance), and high mechanical strength. It has also been found that cycle characteristics can be further improved by using a laminated separator. The reason is not clear, but the high mechanical strength of this separator shows high resistance to negative electrode expansion / contraction associated with the charge / discharge cycle. The reason is that it can be maintained.

  In this specification, “heat-resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

  The porous layer (I) according to the separator is mainly for ensuring a shutdown function, and when the battery reaches or exceeds the melting point of the thermoplastic resin that is the main component of the porous layer (I), The thermoplastic resin related to the porous layer (I) melts and closes the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

  The thermoplastic resin that is the main component of the porous layer (I) is a resin having a melting point, that is, a melting temperature of 140 ° C. or less measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. Specific examples include polyethylene. In addition, as the form of the porous layer (I), a microporous film usually used as a battery separator or a base material such as a nonwoven fabric is coated with a dispersion containing polyethylene particles and dried. Examples thereof include sheet-like materials such as those obtained. Here, among the total volume of the constituent components of the porous layer (I) [the total volume excluding the pores. The same applies to the volume content of the constituent components of the porous layer (I) and the porous layer (II) relating to the separator. ], The volume content of the thermoplastic resin as a main component is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous layer (I) is formed of the polyethylene microporous film, the volume content of the thermoplastic resin is 100% by volume.

  The porous layer (II) according to the separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the battery rises, and has a heat resistance temperature of 150 ° C. or higher. The function is secured by. In other words, when the battery becomes hot, even if the porous layer (I) shrinks, the porous layer (II) which does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally shrunk. It is possible to prevent a short circuit due to the contact of. Moreover, since this heat-resistant porous layer (II) acts as a skeleton of the separator, the thermal contraction of the porous layer (I), that is, the thermal contraction of the entire separator itself can be suppressed.

  The filler related to the porous layer (II) has a heat-resistant temperature of 150 ° C. or higher, is stable with respect to the electrolyte solution of the battery, and is electrochemically stable that is not easily oxidized or reduced in the battery operating voltage range. If present, inorganic particles or organic particles may be used, but fine particles are preferable from the viewpoint of dispersion and the like, and inorganic oxide particles, more specifically, alumina, silica, and boehmite are preferable. Alumina, silica, and boehmite have high oxidation resistance, and the particle size and shape can be adjusted to the desired numerical values, making it easy to accurately control the porosity of the porous layer (II). It becomes. In addition, the filler whose heat-resistant temperature is 150 degreeC or more may use the thing of the said illustration individually by 1 type, and may use 2 or more types together, for example.

  As the non-aqueous electrolyte according to the non-aqueous secondary battery of the present invention, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Examples thereof include sulfites such as glycol sulfite, and these may be used as a mixture of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause a side reaction such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF _{6 and} other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used. be able to.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  In addition, in the non-aqueous electrolyte, vinylene carbonate, vinyl ethylene carbonate, acid anhydride, sulfonic acid ester, for the purpose of improving the safety such as further improvement of charge / discharge cycle characteristics and high temperature storage property and prevention of overcharge, Additives (including these derivatives) such as dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene, phosphonoacetate compounds, 1,3-dioxane as appropriate It can also be added.

  Further, as the non-aqueous electrolyte, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer can be used.

  In the lithium ion secondary battery of the present invention, the negative electrode and the positive electrode are a laminated body (laminated electrode body) superposed via a separator, or a wound body (winding electrode) obtained by further winding the laminated body in a spiral shape. Body). In the case of a laminated electrode body, even if the volume of the negative electrode changes due to charging / discharging of the battery, the battery characteristics are more favorably maintained because it is easier to maintain the distance from the positive electrode. . For these reasons, it is more preferable to use a laminated electrode body in the lithium ion secondary battery of the present invention.

  It is preferable to use a metal laminate film outer package for the outer package according to the lithium ion secondary battery of the present invention. Since the metal laminate film outer package is easier to deform than, for example, a metal outer can, the negative electrode mixture layer and the negative electrode current collector are hardly broken even if the negative electrode expands due to battery charging. It is.

  As the metal laminate film constituting the metal laminate film exterior body, for example, a metal laminate film having a three-layer structure composed of exterior resin layer / metal layer / interior resin layer is used.

  The metal layer in the metal laminate film is an aluminum film, a stainless steel film or the like, and the interior resin layer is a heat-sealing resin (for example, a modified polyolefin ionomer that develops heat-fusibility at a temperature of about 110 to 165 ° C.). A structured film may be mentioned. Examples of the exterior resin layer of the metal laminate film include a nylon film (such as nylon 66 film) and a polyester film (such as polyethylene terephthalate film).

In the metal laminate film, the thickness of the metal layer is preferably 10 to 150 μm, the thickness of the interior resin layer is preferably 20 to 100 μm, and the thickness of the exterior resin layer is preferably 20 to 100 μm.

  The shape of the exterior body is not particularly limited. For example, the shape of the exterior body may be a polygon such as a triangle, a quadrangle, a pentagon, a hexagon, a heptagon, and an octagon in plan view. A square (rectangular or square) is common. The size of the exterior body is not particularly limited, and can be various sizes such as a so-called thin shape and large size.

  The metal laminate film exterior body may be configured by folding a single metal laminate film in two, or may be configured by stacking two metal laminate films.

  When the planar shape of the exterior body is a polygon, the side from which the positive external terminal is drawn out and the side from which the negative external terminal is drawn out may be the same side or different sides.

  The width of the heat fusion part in the outer package is preferably 5 to 20 mm.

When the lithium ion secondary battery of the present invention is discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, Li contained in the positive electrode active material and a metal M other than Li (Co, Mg) , Zr, Ni, Mn, Ti, etc.) is a molar ratio (Li / M) of 0.9 to 1.05.
As described above, when a negative electrode active material having a high irreversible capacity such as SiO _x is used for the negative electrode, Li in the positive electrode active material is consumed at the time of initial charge, and there is a problem that charge / discharge cycle characteristics are remarkably deteriorated. Therefore, as described above, if Li is introduced into the negative electrode in advance, the irreversible capacity of the negative electrode active material can be compensated, and the consumption loss of Li contained in the positive electrode active material is greatly reduced. Therefore, the capacity of the battery can be increased, and the charge / discharge cycle characteristics can be greatly improved.
The above (Li / M) of 0.9 to 1.05 is obtained by adding Li to the negative electrode mixture layer containing the above-described material S and graphites A and B in an appropriate amount and in an appropriate ratio and having high acceptability of Li ions. It can be realized by introducing. In order to introduce Li into the negative electrode mixture layer, a method of bringing the negative electrode into contact with a Li source, for example, sticking a Li foil to the negative electrode mixture layer, including particulate Li in the negative electrode mixture layer, In a state where the Li source and the negative electrode are brought into contact with each other by various methods such as depositing Li on the surface, charging and discharging with a nonaqueous electrolyte solution, and so as not to contact the negative electrode and the Li source Examples of the method include arranging, filling with a non-aqueous electrolyte, and charging and discharging by external connection.

  The composition analysis of the lithium-containing composite oxide can be performed as follows using an ICP (Inductive Coupled Plasma) method. First, 0.2 g of the positive electrode active material to be measured is collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water and an ICP analyzer “ICP-757” manufactured by JARRELASH was used. The composition is analyzed by a calibration curve method. The composition amount can be derived from the obtained results.

  The lithium ion secondary battery of the present invention can be used with a charging upper limit voltage of about 4.2 V as in the case of the conventional lithium ion secondary battery. However, the charging upper limit voltage is higher than 4.4 V. It is possible to set and use as described above. With this, it is possible to stably exhibit excellent characteristics even when repeatedly used over a long period of time while increasing the capacity. In addition, it is preferable that the upper limit voltage of charge of a lithium ion secondary battery is 4.5V or less.

  The lithium ion secondary battery of the present invention can be applied to the same applications as conventionally known lithium ion secondary batteries.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. Table 1 shows the physical properties of the composites obtained by coating the graphite and SiO surfaces used in the examples with carbon materials. Graphite A-1, A-2, and A-3 are graphite A having an average particle diameter defined in claim 1 of more than 15 μm and 25 μm or less, and graphite a-1 and graphite a-2 are defined in the claims. It is graphite which has an average particle diameter other than the above. Graphite B-1 and Graphite B-2 are graphite B having an average particle diameter of 8 μm or more and 15 μm or less as defined in claim 1, and the surface of the graphite particles is coated with amorphous carbon. -1 is graphite having an average particle diameter other than those specified in the claims.

Example 1
<Preparation of positive electrode>
LiCoO _{2 as} positive electrode active material: 96.5 parts by mass, NMP solution containing P (VDF-CTFE) as a binder at a concentration of 10% by mass: 20 parts by mass, and acetylene black as a conductive auxiliary agent: 1. 5 parts by mass was kneaded using a biaxial kneader, and NMP was further added to adjust the viscosity to prepare a positive electrode mixture-containing paste. This paste is applied to one or both sides of an aluminum foil having a thickness of 15 μm, vacuum-dried at 120 ° C. for 12 hours to form a positive electrode mixture layer on one or both sides of the aluminum foil, and subjected to a press treatment. A belt-like positive electrode was obtained. In addition, when applying the positive electrode mixture-containing paste to the aluminum foil, a part of the aluminum foil is exposed, and the positive electrode mixture-containing paste is applied to both sides of the aluminum foil. The applied part was also made into the application part. The thickness of the positive electrode mixture layer of the obtained positive electrode (the thickness per one side when the positive electrode mixture layer was formed on both surfaces of the aluminum foil) was 55 μm.

  Exposure of aluminum foil (positive electrode current collector) to form a strip-shaped positive electrode with a positive electrode mixture layer formed on one side of the aluminum foil and a strip-shaped positive electrode with a positive electrode mixture layer formed on both sides of the aluminum foil as tabs Punch out with a Thomson blade so that a part of the part protrudes and the formation part of the positive electrode mixture layer becomes a substantially square shape with four corners curved, and the positive electrode mixture layer is formed on one side of the positive electrode current collector And a positive electrode for a battery having a positive electrode mixture layer on both surfaces of a positive electrode current collector. FIG. 1 is a plan view schematically showing the battery positive electrode (however, in order to facilitate understanding of the structure of the positive electrode, the size of the positive electrode shown in FIG. 1 does not necessarily match the actual one). Not) The positive electrode 10 has a shape having a tab portion 13 punched out so that a part of the exposed portion of the positive electrode current collector 12 protrudes, and the shape of the formation portion of the positive electrode mixture layer 11 is a substantially rectangular shape with four corners curved. In the figure, the lengths a, b and c were 5 mm, 30 mm and 2 mm, respectively.

<Production of negative electrode>
Graphite A-1 shown in Table 1 (graphite whose surface is not coated with amorphous carbon): 25% by mass, and graphite B-1 (the surface of the mother particles made of graphite, using pitch as the carbon source) Graphite coated with amorphous carbon: 25% by mass, and composite Si-1 having an SiO surface coated with a carbon material (average particle diameter of 8 μm, specific surface area of 7.9 m ² / g, carbon in the composite) The amount of the material was 20% by mass): 50% by mass was mixed with a V-type blender for 12 hours to obtain a negative electrode active material.
After adding 100 parts by mass of polyacrylic acid to 500 parts by mass of ion-exchanged water and stirring and dissolving, NaOH: 70 parts by mass was added and stirred and dissolved until the pH became 7 or less. Further, ion exchange water was added to prepare a 5% by mass aqueous solution of sodium salt of polyacrylic acid. The negative electrode active material, a 1% by weight aqueous solution of CMC, and carbon black were added to this aqueous solution and mixed by stirring to obtain a negative electrode mixture paste. The composition ratio (mass ratio) of negative electrode active material: carbon black: sodium salt of polyacrylic acid: CMC in this paste was 94: 1.5: 3: 1.5.

The negative electrode mixture paste is applied to both sides of a copper foil having a thickness of 6 μm and dried to form a negative electrode mixture layer on both sides of the copper foil, and press treatment is performed to set the density of the negative electrode mixture layer to 1. After adjusting to 4 g / cm ³ , it was cut into a predetermined size to obtain a strip-shaped negative electrode. In addition, when apply | coating the negative mix containing paste to copper foil, a part of copper foil was exposed and the back surface also made the application part the part made into the application part on the surface. The thickness of the negative electrode mixture layer of the obtained negative electrode (thickness per one side of the copper foil as the negative electrode current collector) was 65 μm.

  In order to make the strip-shaped negative electrode into a tab portion, a part of the exposed portion of the copper foil (negative electrode current collector) protrudes, and the negative electrode mixture layer forming portion has a substantially square shape with four corners curved. Then, a negative electrode for a battery having a negative electrode mixture layer on both surfaces of the negative electrode current collector was obtained. FIG. 2 is a plan view schematically showing the battery negative electrode (however, in order to facilitate understanding of the structure of the negative electrode, the size of the negative electrode shown in FIG. 2 does not necessarily match the actual size). Not) The negative electrode 20 has a shape having a tab portion 23 punched out so that a part of the exposed portion of the negative electrode current collector 22 protrudes, and the shape of the formation portion of the negative electrode mixture layer 21 is a substantially rectangular shape with four corners curved. In the figure, the lengths of d, e, and f were 6 mm, 31 mm, and 2 mm, respectively.

  A Li foil having a thickness of 30 μm was punched out, and the Li foil was pasted on the surface having the negative electrode mixture layer of the negative electrode prepared as described above in the amounts shown in Table 2. This operation was performed in a glove box with an argon gas atmosphere.

<Battery assembly>
Two positive electrodes for a battery with a positive electrode mixture layer formed on one side of the positive electrode current collector, 14 positive electrodes for a battery with a positive electrode mixture layer formed on both sides of the positive electrode current collector, and a negative electrode mixture on both sides of the negative electrode current collector A laminated electrode body was formed using 15 battery negative electrodes on which the agent layer was formed. In the laminated electrode body, the upper and lower ends are arranged as the positive electrode for a battery in which a positive electrode mixture layer is formed on one surface of the positive electrode current collector, and the respective current collectors are arranged to face the outside, and the negative electrode current collector is interposed therebetween. The negative electrode for a battery having a negative electrode mixture layer formed on both sides thereof and the positive electrode for a battery having a positive electrode mixture layer formed on both sides of the positive electrode current collector are alternately arranged, and a PE made between each positive electrode and each negative electrode. A separator (thickness: 16 μm) was interposed, and the tab portions between the positive electrodes and the tab portions between the negative electrodes were welded to prepare a laminated electrode body. And the said laminated electrode body is inserted in the said hollow of the aluminum laminate film of thickness: 0.15mm, width: 34mm, and height: 50mm which formed the hollow so that the said laminated electrode body might be accommodated, and said and above An aluminum laminate film of the same size was placed and three sides of both aluminum laminate films were heat-welded. Then, from the remaining one side of both aluminum laminate films, LiPF ₆ was dissolved at a concentration of 1 mol / l in a non-aqueous electrolyte (a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7), and vinylene carbonate was further added. The solution added in an amount of 3% by mass) was injected. Thereafter, the remaining one side of both aluminum laminate films was vacuum-sealed to produce a lithium ion secondary battery having the appearance shown in FIG. 3 and the cross-sectional structure shown in FIG.

  Here, FIG. 3 and FIG. 4 will be described. FIG. 3 is a plan view schematically showing a lithium ion secondary battery, and FIG. 4 is a cross-sectional view taken along the line II of FIG. The nonaqueous secondary battery 100 includes a laminated electrode body 102 constituted by laminating a positive electrode and a negative electrode with a separator in an aluminum laminated film outer package 101 constituted by two aluminum laminated films, and a nonaqueous electrolytic solution. (Not shown) is housed, and the aluminum laminate film outer package 101 is sealed by heat-sealing the upper and lower aluminum laminate films at the outer peripheral portion thereof. In FIG. 4, in order to avoid the complexity of the drawing, the layers constituting the aluminum laminate film outer package 101 and the positive electrode, the negative electrode, and the separator constituting the laminated electrode body are not shown separately. .

Each positive electrode of the laminated electrode body 102 is integrated by welding the tab portions together, and the integrated product of the welded tab portions is connected to the positive electrode external terminal 103 in the battery 100, although not shown. The negative electrodes of the laminated electrode body 102 are also integrated by welding the tab portions together, and the integrated product of the welded tab portions is connected to the negative electrode external terminal 104 in the battery 100. The positive electrode external terminal 103 and the negative electrode external terminal 104 are drawn out to the outside of the aluminum laminate film exterior body 101 so that they can be connected to an external device or the like.
The lithium ion secondary battery produced as described above was stored in a constant temperature bath at 60 ° C. for 24 hours.

(Examples 2 to 16)
A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the negative electrode active material obtained by mixing the material S and graphite shown in Table 1 at a mass ratio shown in Table 2 was used.

(Example 17)
A copper foil having a through-hole penetrating the negative electrode mixture paste prepared in Example 1 from one surface to the other surface (thickness is 10 μm, diameter of the through-hole is 0.3 mm, and the pitch between the through-holes is 2 mm) and drying to form a negative electrode mixture layer on both sides of the copper foil, and after pressing to adjust the density of the negative electrode mixture layer to 1.4 g / cm ³ , a predetermined size is obtained. This was cut to obtain a strip-shaped negative electrode. A 30 μm-thick Li foil was punched out, and the amount of Li foil shown in Table 2 was attached to one side of the negative electrode mixture layer. Thereafter, a lithium ion secondary battery was produced in the same manner as in Example 1.

(Example 18)
Modified polybutyl acrylate resin binder: 3 parts by mass, boehmite powder (average particle diameter: 1 μm): 97 parts by mass, and water: 100 parts by mass were mixed to prepare an insulating layer forming slurry. This slurry was applied to one side of a 12 μm thick polyethylene microporous membrane for lithium ion batteries; porous layer (I) and dried. A separator having a porous layer (II) mainly composed of boehmite on one surface of the porous layer (I) was obtained. The thickness of the porous layer (II) was 3 μm. Using this separator, a lithium ion secondary battery was obtained in the same manner as in Example 1.

(Example 19)
As a positive electrode active material, LiCoO ₂ (80 parts by mass) and Li _1.02 Ni _0.5 Co _0.2 Mn _0.3 O ₂ (20 parts by mass) and P (VDF-CTFE) as a binder are N- 20 parts by mass of a solution dissolved in methyl-2-pyrrolidone (NMP), 1 part by mass of artificial graphite and 1 part by mass of ketjen black, which are conductive assistants, are kneaded using a biaxial kneader, and further NMP Was added to adjust the viscosity to prepare a positive electrode mixture-containing paste. Using this paste, a positive electrode was produced in the same manner as in Example 1. Thereafter, a lithium ion secondary battery was obtained in the same manner as in Example 1.

(Example 20)
A negative electrode was obtained in the same manner as in Example 1 except that a 30 μm thick Li foil was not attached to the negative electrode mixture layer. Hereinafter, in the same manner as in Example 1, a positive electrode, a separator, and a negative electrode were interposed, and a tab portion between the positive electrodes and a tab portion between the negative electrodes were welded to produce a laminated electrode body. And the said laminated electrode body was inserted in the said hollow of the aluminum laminate film of thickness: 0.15mm, width: 68mm, and height: 50mm which formed the hollow so that the said laminated electrode body might be accommodated, and the said laminated electrode body On the lateral side, a lithium counter electrode 106 in which a metal lithium foil having a thickness of 0.5 mm, a width of 10 mm, and a height of 40 mm is bonded to a nickel mesh welded to a nickel lithium counter electrode terminal 105 is disposed as shown in FIG. did. An aluminum laminate film of the same size as above was placed thereon, and three sides of both aluminum laminate films were thermally welded. At this time, the laminated electrode body 102 and the lithium counter electrode 106 were not in physical contact within the laminated film. Then, a nonaqueous electrolytic solution was injected so as to reach the laminated electrode body 102 and the lithium counter electrode 106, and a lithium ion secondary battery having an appearance shown in FIG. 5 was produced.
The produced lithium ion secondary battery was allowed to stand in a constant temperature bath at 25 ° C. for 5 hours, and then the negative electrode external terminal 104 and the lithium counter electrode terminal 105 were electrically connected via a charging / discharging device. Was discharged at a constant current of 0.01 V, followed by constant voltage discharge at 0.01 V, and then charged at a current rate of 0.1 C until the voltage reached 1.5 V.
Thereafter, the laminate film was cut in order to cut off the lithium counter electrode portion, and the cut portion was thermally welded to obtain the lithium ion secondary battery having the cross-sectional structure shown in FIG. 4 with the appearance shown in FIG.

(Example 21)
Polyvinylidene fluoride (PVDF): 6 parts by mass, boehmite powder (average particle diameter 1 μm): 80 parts by mass, graphite (average particle diameter 2 μm): 14 parts by mass, N-methyl-2-pyrrolidone (NMP): 100 parts by mass was mixed to prepare a porous layer forming slurry. This slurry was applied to both sides of the negative electrode mixture layer of the negative electrode prepared in Example 1 and dried. A negative electrode in which a porous layer mainly composed of boehmite was formed on both surfaces of the negative electrode mixture layer was obtained. The porous layer had a thickness of 3 μm. A lithium ion secondary battery was obtained in the same manner as in Example 1 except that this negative electrode was used.

(Comparative Example 1)
Graphite A-1 shown in Table 1 (graphite whose surface is not coated with amorphous carbon): 50% by mass, and graphite B-1 (the surface of the mother particles made of graphite, using pitch as the carbon source) Graphite coated with amorphous carbon): 50% by mass was mixed with a V-type blender for 12 hours to obtain a negative electrode active material. Using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1. Moreover, the lithium ion secondary battery was produced like Example 1 in the state which does not stick Li foil to the negative mix layer of a negative electrode.

(Comparative Example 2)
A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the Li foil was not attached to the negative electrode mixture layer of the negative electrode.

(Comparative Examples 3 to 7)
A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the negative electrode active material obtained by mixing the material S and graphite shown in Table 1 at a mass ratio shown in Table 2 was used.

  The following battery characteristic evaluation was performed about each lithium ion secondary battery of the Example and comparative example which are shown to Tables 1-3. Table 4 shows the evaluation results of each battery.

<Measurement of Li content in positive electrode active material>
Lithium ion secondary batteries stored for 24 hours in a constant temperature bath at 60 ° C. are left in a constant temperature bath at 25 ° C. for 5 hours, and then each battery is charged with a constant current up to 4.4 V at a current value of 0.2 C. Subsequently, the battery is charged at a constant voltage of 4.4 V (the total charging time of the constant current charging and the constant voltage charging is 2.5 hours), and then the voltage reaches 2.0 V at a discharge current rate of 0.1 C. Discharged. Thereafter, the aluminum laminate was disassembled in the glove box, and only the positive electrode was taken out. After the taken-out positive electrode was washed with diethyl carbonate, the positive electrode mixture layer was scraped out, and by the ICP method described above, the composition ratio of metals other than Li and Li; Li / M (Li; Li amount, M; metal amount other than Li) ) Was calculated.

<Evaluation of initial discharge capacity and charge / discharge cycle characteristics>
The lithium ion secondary batteries of Examples and Comparative Examples (separate from those for Li / M calculation described above) were allowed to stand in a thermostatic bath at 25 ° C. for 5 hours, and then 0.5 C of each battery was used. Constant current charge to 4.4V in current value, followed by constant voltage charge at 4.4V (total charge time of constant current charge and constant voltage charge is 2.5 hours), then 0.2C constant current Was discharged to 2.0 V (Comparative Example 1 was 2.75 V), and the initial discharge capacity was determined. Next, each battery was charged with a constant current up to 4.4 V at a current value of 1 C, subsequently charged with a constant voltage of 4.4 V until the current value reached 0.05 C, and then 2. with a current value of 1 C. A series of operations for discharging to 0 V (2.75 V in Comparative Example 1) was taken as one cycle, and this was cycled 500 times. And about each battery, the constant current-constant voltage charge and the constant current discharge were performed on the same conditions as the time of the said first time discharge capacity measurement, and the discharge capacity was calculated | required. Then, the cycle capacity retention rate was calculated by expressing the value obtained by dividing these discharge capacities by the initial discharge capacity as a percentage. The initial discharge capacity is shown as a ratio when the discharge capacity of Comparative Example 1 is 100%.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Positive electrode mixture layer 12 Positive electrode collector 13 Tab part 20 Negative electrode 21 Negative electrode mixture layer 22 Negative electrode collector 23 Tab part 100 Nonaqueous secondary battery 101 Metal laminate film exterior body 102 Laminated electrode body 103 Positive electrode external terminal 104 Negative electrode external terminal 105 Lithium counter electrode terminal

Claims (7)

In a lithium ion secondary battery in which a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution are loaded in at least an outer package,
The negative electrode is provided with a negative electrode mixture layer mainly composed of a negative electrode active material on at least one surface of a support made of a metal foil,
The negative electrode active material includes a material S containing a compound SiOx containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5), and the average particle size is Containing graphite A exceeding 15 μm and not more than 25 μm, and graphite B having an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles coated with amorphous carbon,
When the total of all negative electrode active materials contained in the negative electrode is 100% by mass, the mixed mass% (A + B) of graphite A and graphite B contained as the negative electrode active material is 20% or more and less than 99%, The mass ratio of graphite A to graphite B (A / B) is 0.5 or more and 4.5 or less,
The positive electrode is a metal oxide composed of a metal M other than Li and Li as a positive electrode active material,
When discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, the molar ratio (Li / M) between Li and the metal M other than Li contained in the positive electrode active material is 0.9 to 1 .05, a lithium ion secondary battery.   When the total of all the negative electrode active materials contained in the negative electrode is 100% by mass, the content of the material S contained as the negative electrode active material is at least 10% by mass, and graphite A contained as the negative electrode active material and The lithium ion secondary battery according to claim 1, wherein a mixed mass% (A + B) of graphite B is 90% or less.   The lithium ion secondary battery according to claim 1, wherein the support made of the metal foil has a through hole penetrating from one surface to the other surface.   The lithium ion secondary battery according to claim 1, further comprising a porous layer formed on the negative electrode mixture layer and containing an insulating material that does not react with Li.   The separator has a porous film (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C or higher. The lithium ion secondary battery in any one of 1-4.   The lithium ion secondary battery according to any one of claims 1 to 5, wherein the exterior body is a metal laminate film exterior body.   The lithium ion secondary battery according to claim 1, wherein the positive electrode and the negative electrode form an electrode body laminated via the separator.

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