JP2022191743A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide a non-aqueous electrolyte secondary battery with high capacity and excellent cycle characteristics by suppressing heterogeneous reactions in a negative electrode.SOLUTION: A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, the negative electrode includes a negative electrode active material layer containing negative electrode active material particles, the negative electrode active material particles are a material containing an element capable of forming an alloy with lithium, and the thickness of the negative electrode active material layer is set to be two times or less the mode particle size of the negative electrode active material particles.SELECTED DRAWING: Figure 1

Description

The present invention relates to non-aqueous electrolyte secondary batteries.

Lithium-ion secondary batteries are widely used as power sources for smartphones and other mobile terminals because they have higher voltage and capacity than nickel-metal hydride batteries and nickel-cadmium batteries. In recent years, as mobile terminals have become smaller and lighter, there has been a demand for higher capacity lithium-ion secondary batteries that serve as power sources. Alloy negative electrode materials such as silicon (Si) and silicon oxide (SiO) are attracting attention as electrode materials for increasing the capacity. In particular, the theoretical discharge capacity of Si is 4210 mAh/g, which is known to be 11 times higher than that of graphite, which is a conventional material.

In general, the negative electrode material has a low potential during charging, and reductive decomposition of the electrolyte occurs. At that time, gases such as carbon dioxide and hydrogen are generated. Also, a decomposition product of the electrolyte is formed on the surface of the active material. The generated gas increases the internal resistance of the lithium ion secondary battery in order to widen the distance between the electrodes. Since the decomposition product of the electrolytic solution has the effect of alleviating the reaction between the active material and the electrolytic solution, reductive decomposition of the electrolytic solution is suppressed. On the other hand, excessive electrolyte decomposition is not preferable because the internal resistance of the electrode increases and the irreversible capacity increases.

JP 2018-81927 A

When Si or SiO is used as the negative electrode active material, the volume change during charge/discharge cycles is large, and the volume change is up to four times before and after charging. Therefore, when the charge-discharge cycle is repeated, peeling of the conductive aid and the binder occurs, and the conductive path between the negative electrode active materials is likely to be lost. If the conductive path is lost, a potential distribution occurs between the negative electrode active materials and the reaction becomes non-uniform. Due to such a non-uniform reaction, the amount of lithium ions occluded by the negative electrode active material also becomes non-uniform, resulting in non-uniform expansion and reaction for each negative electrode active material. This non-uniform expansion accelerates disconnection of conductive paths and decomposition of the electrolyte, leading to further deterioration of capacity.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having high capacity and excellent cycle characteristics by suppressing heterogeneous reactions.

A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, the negative electrode having a negative electrode active material layer containing negative electrode active material particles, and the negative electrode active material particles containing lithium and The material contains an element capable of forming an alloy, and the thickness of the negative electrode active material layer is two times or less the mode particle diameter of the negative electrode active material particles.

By using the negative electrode according to the present invention, the cycle characteristics of the lithium ion secondary battery are improved.

The mode particle size of the negative electrode active material particles according to the present invention is preferably 0.1 μm or more and 100 μm or less.

By using the negative electrode according to the present invention, the cycle characteristics of the lithium ion secondary battery are improved.

The element capable of forming an alloy with lithium according to the present invention is preferably at least one element selected from silicon and tin.

By using the negative electrode according to the present invention, the capacity of the lithium ion secondary battery is increased.

The material containing an element capable of forming an alloy with lithium according to the present invention is a simple substance of at least one element selected from silicon and tin, an alloy containing the element, or an oxide of the element. can be

By using the negative electrode according to the present invention, the cycle characteristics of the lithium ion secondary battery are improved.

The thickness of the negative electrode active material layer according to the present invention is preferably 4 μm or more and 200 μm or less.

By using the negative electrode according to the present invention, the cycle characteristics of the lithium ion secondary battery are improved.

It is preferable that the content of the element capable of forming an alloy with lithium in the negative electrode active material layer according to the present invention is 60% by mass or more and 95% by mass or less.

By using the negative electrode according to the present invention, the cycle characteristics of the lithium ion secondary battery are improved.

ADVANTAGE OF THE INVENTION According to this invention, the negative electrode for lithium ion secondary batteries which has sufficient cycling characteristics can be provided.

1 is a schematic cross-sectional view of a lithium ion secondary battery according to one embodiment of the present invention; FIG.

Preferred embodiments of the present invention will now be described in detail with reference to the drawings as the case may be. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and overlapping descriptions are omitted. Also, the dimensional ratios in the drawings are not limited to the illustrated ratios.

(lithium ion secondary battery)
FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to this embodiment. As shown in FIG. 1, the lithium ion secondary battery 100 mainly includes a laminate 30, a case 50 that accommodates the laminate 30 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 30. ing.

In the laminate 30, a pair of the positive electrode 10 and the negative electrode 20 are arranged facing each other with the separator 18 interposed therebetween. The positive electrode 10 has a positive electrode active material layer 14 provided on a plate-like (film-like) positive electrode current collector 12 . The negative electrode 20 has a negative electrode active material layer 24 provided on a plate-like (film-like) negative electrode current collector 22 . The main surface of the positive electrode active material layer 14 and the main surface of the negative electrode active material layer 24 are in contact with the main surface of the separator 18 respectively. Leads 60 and 62 are connected to ends of the positive electrode current collector 12 and the negative electrode current collector 22 , respectively, and the ends of the leads 60 and 62 extend to the outside of the case 50 .

Hereinafter, the positive electrode 10 and the negative electrode 20 are collectively referred to as the electrodes 10 and 20, the positive electrode current collector 12 and the negative electrode current collector 22 are collectively referred to as the current collectors 12 and 22, and the positive electrode active material layer 14 and the negative electrode The active material layers 24 may be collectively referred to as active material layers 14 and 24 . First, the electrodes 10 and 20 are specifically described.

(Positive electrode current collector)
The positive electrode current collector 12 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as aluminum (Al), an alloy thereof, stainless steel, or the like can be used.

(Positive electrode active material layer)
The positive electrode active material layer 14 is mainly composed of a positive electrode active material, a binder, and a necessary amount of conductive aid.

(Positive electrode active material)
As the positive electrode active material, lithium ion absorption and release, lithium ion desorption and insertion (intercalation), or doping and dedoping of lithium ions and counter anions of the lithium ions (for example, PF ₆ ⁻ ) are used. is not particularly limited as long as it is possible to reversibly proceed, and known electrode active materials can be used. For example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and general formula: LiNi _x Co _y Mnz MaO ₂ (x+y+ _z +a=1, 0≦x≦ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn and Cr). oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine-type LiMPO ₄ (where M is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr, or VO ), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), _{LiNixCoyAlzO2} (0.9< _x + _y + _z <1.1), and other composite metal oxides.

(positive electrode binder)
The binder binds the positive electrode active materials together and also binds the positive electrode active material and the current collector 12 . Any binder can be used as long as it allows the above-described bonding, and examples thereof include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Furthermore, in addition to the above, binders such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, and polyamide-imide resin may be used. Alternatively, an electronically conductive polymer or an ionically conductive polymer may be used as the binder. Examples of the electron-conducting conductive polymer include polyacetylene. In this case, it is not necessary to add a conductive additive because the binder also exhibits the function of the conductive additive particles. As the ion-conducting conductive polymer, for example, one having ion conductivity such as lithium ion can be used. , polyphosphazene, etc.) and a lithium salt such as LiClO ₄ , LiBF ₄ , LiPF ₆ or an alkali metal salt mainly composed of lithium, and the like. Polymerization initiators used for complexing include, for example, photopolymerization initiators and thermal polymerization initiators compatible with the above monomers.

The content of the binder in the positive electrode active material layer 14 is also not particularly limited, but when it is added, it is preferably 0.5 to 5% by mass with respect to the mass of the positive electrode active material.

(Positive electrode conductive aid)
The conductive aid is not particularly limited as long as it improves the conductivity of the positive electrode active material layer 14, and known conductive aids can be used. Examples thereof include carbon-based materials such as graphite and carbon black, metal fine powders such as copper, nickel, stainless steel and iron, mixtures of carbon materials and metal fine powders, and conductive oxides such as ITO.

Although the content of the binder in the positive electrode active material layer 14 is not particularly limited, it is preferably 1 to 10% by mass based on the sum of the mass of the positive electrode active material, conductive aid and binder. By setting the contents of the positive electrode active material and the binder within the above ranges, it is possible to suppress the tendency of the obtained positive electrode active material layer 14 to fail to form a strong positive electrode active material layer due to an excessively small amount of the binder. In addition, it is possible to suppress the tendency that the amount of binder that does not contribute to the electric capacity increases, making it difficult to obtain a sufficient volumetric energy density.

The content of the conductive aid in the positive electrode active material layer 14 is also not particularly limited, but when it is added, it is preferably 0.5 to 5% by mass with respect to the mass of the positive electrode active material.

(Negative electrode current collector)
The negative electrode current collector 22 may be a conductive plate material, and for example, a thin metal plate (metal foil) made of copper (Cu), nickel (Ni), stainless steel, or an alloy thereof can be used.

(Negative electrode active material layer)
The negative electrode active material layer 24 is mainly composed of negative electrode active material particles, a binder, and an appropriate amount of conductive aid. Moreover, the thickness of the negative electrode active material layer is not more than twice the mode particle size of the negative electrode active material particles.

By setting the thickness of the negative electrode active material layer to be not more than twice the mode particle diameter of the negative electrode active material particles, the number of mode particles in the thickness direction of the electrode is two, and the negative electrode active material particles always come into contact with each other in the thickness direction. It becomes a form with a part where it is. Due to this form, lithium ions are diffused between the negative electrode active material particles. Therefore, generation of potential difference between particles is suppressed, and non-uniform reaction of each particle is suppressed.

(Negative electrode active material)
The mode particle size of the negative electrode active material particles is preferably 0.1 to 100 μm. Within this range, a sufficient electric capacity can be ensured even if the thickness of the negative electrode active material is less than or equal to twice the mode particle diameter of the negative electrode active material particles. If the particle size is smaller than this range, the size of the crystal structure is insufficient, and the reaction potential becomes unstable. I don't like it. In addition, active material particles with small particle diameters are not preferable because the proportion of the binder present in the electrode is uneven, resulting in non-uniform reaction. Further, when an active material having a particle size larger than the range is used, lithium ions in the vicinity of the center of the active material particles become difficult to detach, resulting in an increase in the amount of dead lithium, which is not preferable.

The element capable of forming an alloy with lithium is preferably at least one selected from Si and tin (Sn). This is because these elements have particularly large electric capacities and can produce lithium ion batteries with high energy densities.

Also, the material containing an element capable of forming an alloy with lithium may be in any of crystalline, low-crystalline and amorphous states. In addition, as this material, simple substances of elements capable of forming alloys with lithium, alloys containing those elements, oxides or nitrides of those elements, and the like can be used. Examples include Si, Sn, SiO, tin oxide (SnO), solid solutions of Si, Sn, etc. and other metals, intermetallic compounds, and the like. The Si-containing material may be, for example, an n-type or p-type semiconductor doped with boron (B) or phosphorus (P) to reduce electrical resistance.

The thickness of the negative electrode active material layer is determined by the mode particle diameter of the active material particles, and the thickness is preferably 4 μm or more. Within this range, the supported amount of the electrode material is appropriate, and the necessary battery capacity can be secured. Moreover, the thickness of the negative electrode active material layer is preferably 200 μm or less in order to facilitate preparation of the active material particles and application thereof.

The electrical resistance of the negative electrode active material layer is determined by the blending amount of the conductive aid and binder other than the active material. If the active material is less than 60% by mass, the amount of conductive aid and binder becomes excessive. Mixing an excessive amount of binder is not preferable because the electrical resistance in the electrode increases. Moreover, if an excessive amount of the conductive aid is blended, the coatability of the electrode deteriorates, which is not preferable. Moreover, it is not preferable because the capacity per unit weight of the electrode is lowered. On the other hand, when the active material is more than 95% by mass, the amounts of conductive aid and binder in the active material layer are relatively reduced. A decrease in the amount of the conductive aid added is not preferable because the electrical resistance of the electrode increases. Moreover, if the amount of the binder is reduced, the active material and current collector binder deteriorate, which is not preferable.

(Negative electrode binder and negative electrode conductive aid)
In addition to the materials used for the positive electrode 10 described above, an acrylic resin such as PAA can also be used for the binder and the conductive aid. In addition, the content of the binder and the conductive aid is also adjusted as appropriate when the magnitude of the volume change of the negative electrode active material and the adhesion with the foil must be taken into account, and the content is the same as the content in the positive electrode 10 described above. should be adopted. When added, the amount of the binder to be added is preferably 2 to 20% by mass with respect to the mass of the negative electrode active material. The amount of the conductive aid added is preferably 0.5 to 5% by mass with respect to the mass of the negative electrode active material.

With the components described above, the electrodes 10, 20 can be fabricated by commonly used methods. For example, a paint containing an active material (positive electrode active material or negative electrode active material), a binder (positive electrode binder or negative electrode binder), a solvent, and a conductive agent (positive electrode conductive agent or negative electrode conductive agent) is applied on the current collector. It can be produced by coating and removing the solvent in the coating applied on the current collector.

Examples of solvents that can be used include N-methyl-2-pyrrolidone, N,N-dimethylformamide, and water.

The coating method is not particularly limited, and a method that is commonly employed in the production of electrodes can be used. For example, a slit die coating method and a doctor blade method can be used.

The method of removing the solvent in the paint applied on the current collectors 12 and 22 is not particularly limited, and the current collectors 12 and 22 coated with the paint are dried in an atmosphere of, for example, 80°C to 150°C. All you have to do is

Then, the electrodes on which the active material layers 14 and 24 are formed in this manner may be subjected to press treatment using, for example, a roll press apparatus, if necessary. The linear pressure of the roll press can be, for example, 10 to 50 kgf/cm.

Next, other constituent elements of the lithium ion secondary battery 100 will be described.

(separator)
The separator is not particularly limited as long as it is stable with respect to the electrolytic solution and has excellent liquid retention properties.

(Electrolytes)
The electrolyte is contained inside the positive electrode active material layer 14 , the negative electrode active material layer 24 and the separator 18 . The electrolyte is not particularly limited, and for example, in the present embodiment, an electrolytic solution containing a lithium salt (electrolyte aqueous solution, electrolytic solution using an organic solvent) can be used. However, since the electrolyte aqueous solution has a low electrochemical decomposition voltage, the withstand voltage at the time of charging is limited to a low level, so an electrolyte solution using an organic solvent (non-aqueous electrolyte solution) is preferable. As the electrolytic solution, one obtained by dissolving a lithium salt in a non-aqueous solvent (organic solvent) is preferably used. The lithium salt is not particularly limited, and lithium salts used as electrolytes for lithium ion secondary batteries can be used. For example, lithium salts include inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , LiBETI, LiFSI and LiBOB, and organic acid anion salts such as LiCF ₃ SO ₃ and (CF ₃ SO ₂ ) ₂ NLi. can be done.

Examples of the organic solvent include aprotic high dielectric constant solvents such as ethylene carbonate and propylene carbonate, and aprotic low viscosity solvents such as dimethyl carbonate, ethylmethyl carbonate, acetic acid esters and propionic acid esters. Solvents can be mentioned. It is desirable to use these aprotic high dielectric constant solvents and aprotic low viscosity solvents together in a proper mixing ratio. Additionally, ionic liquids with imidazolium, ammonium, and pyridinium type cations can be used. Counter anions are not particularly limited, but include BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and} the like. The ionic liquid can be used by mixing with the aforementioned organic solvent.

The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 2.0M from the viewpoint of electrical conductivity. The conductivity of this electrolyte at a temperature of 25° C. is preferably 0.01 S/m or more, and is adjusted by the type or concentration of the electrolyte salt.

When the electrolyte is a solid electrolyte or a gel electrolyte, it is possible to contain poly(vinylidene fluoride) or the like as a polymer material.

Furthermore, various additives may be added to the electrolytic solution of the present embodiment as necessary. Examples of additives include vinylene carbonate, methylvinylene carbonate, etc. for the purpose of improving cycle life, biphenyl, alkylbiphenyl, etc. for the purpose of overcharge prevention, various carbonate compounds for the purpose of deacidification and dehydration, and various Carboxylic anhydrides, various nitrogen-containing and sulfur-containing compounds can be mentioned.

(Case)
The case 50 seals the laminate 30 and the electrolytic solution therein. The case 50 is not particularly limited as long as it can prevent the leakage of the electrolytic solution to the outside and the intrusion of moisture into the inside of the lithium ion secondary battery 100 from the outside. For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with polymer films 54 from both sides can be used. As the metal foil 52, for example, an aluminum foil can be used, and as the polymer film 54, a film such as polypropylene can be used. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point, such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). etc. are preferred.

(lead)
Leads 60 and 62 are made of a conductive material such as aluminum. The leads 60 and 62 are welded to the positive electrode current collector 12 and the negative electrode current collector 22, respectively, by a known method, and the separator 18 is placed between the positive electrode active material layer 14 of the positive electrode 10 and the negative electrode active material layer 24 of the negative electrode 20. are inserted into the case 50 together with the electrolytic solution, and the entrance of the case 50 is sealed.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, the lithium ion secondary battery is not limited to the shape shown in FIG. It may be a type or the like.

EXAMPLES The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1]
(Preparation of positive electrode)
96% by weight of _{LiNixCoyAlzO2} (0.9< _x + _y + _z <1.1) as a positive electrode active material, 2% by weight of carbon black as a conductive aid, and 0.5% by weight of graphite; 1.5% by weight of PVDF as a binder and a solvent of N-methyl-2-pyrrolidone were mixed and dispersed to prepare a pasty positive electrode slurry. Then, using a comma roll coater, this positive electrode slurry was evenly coated on both sides of a 20 μm thick Al foil to form a positive electrode active material layer. Next, the N-methyl-2-pyrrolidone solvent in the positive electrode active material was dried in a drying furnace under an air atmosphere at 110°C. The coating amount of the positive electrode active material was 22.0 mg/cm ² . The thickness of the coating film of the positive electrode active material layer applied on both sides of the Al foil was adjusted to be substantially the same thickness. The positive electrode having the positive electrode active material formed thereon was press-bonded to both sides of the positive electrode current collector using a roll press to prepare a positive electrode such that the density of the positive electrode active material layer was 3.6 g/cm ³ . . A positive electrode sheet was thus obtained.

(Preparation of negative electrode)
As a negative electrode active material, 80% by weight of Si powder, 10% by weight of acetylene black, 10% by weight of polyamideimide resin, and a solvent of N-methyl-2-pyrrolidone are mixed and dispersed to prepare a slurry for forming a negative electrode active material layer. was prepared. This slurry was applied to one surface of a copper foil having a thickness of 10 μm so that the coating amount of the negative electrode active material was 3.3 mg/cm ² , and dried at 100° C. to form a negative electrode active material layer. The negative electrode with the negative electrode active material formed thereon is pressed against both sides of the negative electrode current collector by a roll press to fabricate a negative electrode so that the density of the negative electrode active material layer is 1.5 g/cm ³ . did. A negative electrode sheet was thus obtained.

(Production of lithium ion secondary battery for evaluation)
Using the positive electrode and negative electrode prepared above, a separator made of a polyethylene microporous film is sandwiched between them, put in an aluminum laminate pack, and a 1M _LiPF6 solution (solvent: EC /DEC = 3/7 (volume ratio)) was injected and vacuum-sealed to produce a lithium ion secondary battery for evaluation.

[Examples 2 to 5]
A negative electrode was fabricated in the same manner as in Example 1 except that the negative electrode active material used was changed to Sn, SiO, SnO, and Al.
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the above negative electrode active material was used, and the cycle characteristics were evaluated.

[Examples 6 to 14]
The particle size of the negative electrode active material used was changed from 0.05 μm to 150 μm, and the thickness of the negative electrode active material layer was made twice the particle size of each negative electrode active material. A negative electrode was prepared in the same manner.
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the above negative electrode active material was used, and the cycle characteristics were evaluated.

[Examples 15 to 22]
The amount of the negative electrode active material added is 50% by weight to 99% by weight with respect to the total weight of the negative electrode active material layer-constituting member, and the total weight % of the negative electrode active material layer-constituting member is adjusted according to the amount of each negative electrode active material added. and half of the weight% difference between the amount of the active material added and the weight% of the acetylene black, and half of the weight% difference between the total weight% of the negative electrode active material layer constituent member and the amount of the active material added is the weight% of the polyamideimide resin. did.
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the slurry produced in the above mixing ratio was used, and the cycle characteristics were evaluated.

[Examples 23-26]
After making the thickness of the negative electrode active material layer twice the particle diameter of each negative electrode active material, a negative electrode was produced in the same manner as in Example 1.
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the above negative electrode active material was used, and the cycle characteristics were evaluated.

[Example 27]
The particle size of the negative electrode active material is 0.08 μm, the thickness of the negative electrode active material layer is twice the particle size of the negative electrode active material, the active material is Al, and the amount of the active material added is 50% by weight. A negative electrode was prepared in the same manner as in Example 1.
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the above negative electrode active material was used, and the cycle characteristics were evaluated.

[Comparative Examples 1 to 3]
In Comparative Examples 1 to 3, a lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the thickness of the negative electrode active material layer was not less than twice the particle size of the negative electrode active material, and the cycle characteristics were measured. was evaluated.

<Method for evaluating cycle characteristics>
The cycle characteristics of the lithium ion secondary batteries for evaluation produced in Examples and Comparative Examples were measured using a secondary battery charge/discharge test device (manufactured by Hokuto Denko Co., Ltd.). A charge/discharge cycle of constant current and constant voltage charging to 4.2 V at 0.5 C and constant current discharging to 2.5 V at 1 C was repeated for 500 cycles, and the capacity retention rate after 500 cycles was measured to evaluate cycle characteristics.

Table 1 shows the particle size, active material, thickness of the negative electrode active material layer, active material addition amount/energy density, and capacity retention rate of Examples 1 to 26 and Comparative Examples 1 to 3.

Examples 1 to 27 showed high cycle retention rates. In the batteries of Comparative Examples 1 to 3, when the thickness of the active material layer was not twice the particle size of the active material particles, the cycle retention rate was significantly lowered.

By using the lithium ion secondary battery of the present invention, it is possible to provide a lithium ion secondary battery with an improved capacity retention rate.

DESCRIPTION OF SYMBOLS 10... Positive electrode, 12... Positive electrode collector, 14... Positive electrode active material layer, 18... Separator, 20... Negative electrode, 22... Negative electrode collector, 24... Negative electrode active material layer, 30... Laminated body, 50... Case, 52 ... metal foil, 54 ... polymer film, 60, 62 ... leads, 100 ... lithium ion secondary battery.

Claims (6)

including a positive electrode, a negative electrode and a non-aqueous electrolyte,
The negative electrode has a negative electrode active material layer containing negative electrode active material particles,
The negative electrode active material particles are a material containing an element capable of forming an alloy with lithium,
A non-aqueous electrolyte secondary battery, wherein the thickness of the negative electrode active material layer is two times or less the mode particle size of the negative electrode active material particles. 2. The non-aqueous electrolyte secondary battery in accordance with claim 1, wherein said negative electrode active material particles have a mode particle size of 0.1 to 100 [mu]m. 3. The non-aqueous electrolyte secondary battery in accordance with claim 1, wherein said element capable of forming an alloy with lithium is at least one element selected from silicon and tin. Claims 1 to 3, wherein said material containing an element capable of forming an alloy with lithium is a simple substance of at least one element selected from silicon and tin, an alloy containing said element, or an oxide of said element. The non-aqueous electrolyte secondary battery according to any one of 1. 5. The non-aqueous electrolyte secondary battery in accordance with claim 1, wherein said negative electrode active material layer has a thickness of 4 μm or more and 200 μm or less. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the content of the element capable of forming an alloy with lithium in the negative electrode active material layer is 60% by mass or more and 95% by mass or less. .

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