JP6397642B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention has excellent cycle characteristics when silicon oxide (SiOx, 0.5 ≦ x <1.6) is mixed with a graphite material as a negative electrode active material as means for increasing the capacity of a nonaqueous electrolyte secondary battery. The present invention also relates to a non-aqueous electrolyte secondary battery.

Carbon materials such as graphite and amorphous carbon are widely used as negative electrode active materials used in non-aqueous electrolyte secondary batteries. However, when a negative electrode active material made of a carbon material is used, lithium can only be inserted up to the composition of LiC ₆ and the theoretical capacity is 372 mAh / g, which is an obstacle to increasing the capacity of the battery. Yes. Therefore, a nonaqueous electrolyte secondary battery using silicon or silicon alloy or silicon oxide alloyed with lithium as a negative electrode active material having high energy density per mass and volume has been developed. For example, since silicon can insert lithium up to the composition of Li _4.4 Si, the theoretical capacity is 4200 mAh / g, and a larger capacity than when a carbon material is used as the negative electrode active material can be expected.

  As specific examples thereof, the following Patent Document 1 discloses a material containing silicon and oxygen as constituent elements as a negative electrode active material (provided that the element ratio x of oxygen to silicon is 0.5 ≦ x ≦ 1.5). And a non-aqueous electrolyte secondary battery using a material containing graphite. In this non-aqueous electrolyte secondary battery, when the total of the material containing silicon and oxygen as constituent elements and graphite is 100% by mass, the ratio of the material containing silicon and oxygen as constituent elements is 3 to 20% by mass. An active material is used.

JP 2010-212228 A

  According to the non-aqueous electrolyte secondary battery disclosed in Patent Document 1, it is possible to suppress deterioration of battery characteristics due to the volume change while using silicon oxide having a high capacity and a large volume change accompanying charge / discharge. Therefore, good battery characteristics can be ensured without greatly changing the configuration of the conventional nonaqueous electrolyte secondary battery.

  However, when a material containing silicon or a silicon alloy or silicon oxide is used as the negative electrode active material, the negative electrode active material undergoes large expansion / contraction along with the charge / discharge cycle, and the negative electrode active material is pulverized. Or fall off the conductive network. As a result, there is a problem that the capacity retention rate (cycle characteristics) of the battery is lowered. Therefore, it is desired to develop a non-aqueous electrolyte secondary battery having a larger negative electrode capacity and a good capacity retention ratio.

According to the nonaqueous electrolyte secondary battery of one embodiment of the present invention,
A positive electrode plate having a positive electrode mixture layer containing a positive electrode active material capable of occluding and releasing lithium ions;
A negative electrode plate having a negative electrode mixture layer containing a negative electrode active material capable of occluding and releasing lithium ions;
A separator, a non-aqueous electrolyte,
With
The negative electrode active material is
It is a mixture of graphite material and silicon oxide represented by SiOx (0.5 ≦ x <1.6),
The fracture strength ratio Ss / Sg, which is the ratio of the fracture strength Ss of the single particle of silicon oxide and the fracture strength Sg of the single particle of the graphite material, is 60 to 90.
A non-aqueous electrolyte secondary battery is provided.

  In the nonaqueous electrolyte secondary battery of one embodiment of the present invention, not only graphite but also silicon oxide represented by SiOx (0.5 ≦ x <1.6) is included as the negative electrode active material. The silicon oxide represented by SiOx has a larger volume change due to charging / discharging than the graphite material, but a theoretical capacity value is larger than that of the graphite material. Therefore, according to the nonaqueous electrolyte secondary battery of the present invention, the battery capacity can be made larger than that of the nonaqueous electrolyte secondary battery using the negative electrode active material made of only the graphite material.

  In addition, the negative electrode active material used in the non-aqueous electrolyte secondary battery of one embodiment of the present invention includes the single-particle fracture strength Ss of silicon oxide represented by SiOx and the single-particle fracture strength Sg of graphite material. Is selected such that the fracture strength ratio Ss / Sg is 60 to 90. This indicates that a relatively soft graphite material in the negative electrode active material is selected.

  Therefore, in the nonaqueous electrolyte secondary battery of one embodiment of the present invention, even if the expansion / contraction of silicon oxide accompanying charge / discharge is larger than that of the graphite material, the expansion / contraction is absorbed by the soft graphite material. Thus, according to the nonaqueous electrolyte secondary battery of one embodiment of the present invention, a nonaqueous electrolyte secondary battery exhibiting a good capacity retention rate can be obtained.

  When the fracture strength ratio Ss / Sg is less than 60, the fracture strength Sg of the graphite material becomes too high, and the graphite material cannot absorb the expansion / contraction of silicon oxide, so that the capacity retention rate is lowered. When the fracture strength ratio Ss / Sg exceeds 90, the graphite material is too crushed and the conductive network structure with the silicon oxide cannot be maintained, and the capacity retention rate similarly decreases. A more preferable breaking strength ratio Ss / Sg is 64 to 84.

It is a perspective view of a laminate type nonaqueous electrolyte secondary battery common to each experimental example. It is a graph which shows the relationship between a fracture strength ratio (Ss / Sg) and a capacity | capacitance maintenance factor when the silicon oxide content rate in a negative electrode active material is 3 mass%.

  Hereinafter, the form for implementing this invention is demonstrated in detail using each experiment example. However, each experimental example shown below is illustrated in order to embody the technical idea of the present invention, and is not intended to limit the present invention to these experimental examples. The present invention can also be applied to various modifications made without departing from the technical idea shown in the claims.

First, the configuration of the nonaqueous electrolyte secondary battery common to each experimental example will be specifically described.
[Production of positive electrode plate]
The positive electrode plate was produced as follows. During the synthesis of cobalt carbonate (CoCO ₃ ), 0.1 mol% of zirconium and 1 mol% of magnesium and aluminum are co-precipitated with respect to cobalt, respectively, and are subjected to a thermal decomposition reaction. Tricobalt oxide was obtained. This was mixed with lithium carbonate (Li ₂ CO ₃ ) as a lithium source and calcined at 850 ° C. for 20 hours to obtain a zirconium / magnesium / aluminum-containing lithium cobalt composite oxide (LiCo _0.979 Zr _0.001 Mg _{0. 01} Al _0.01 O ₂ ) was obtained.

  95 parts by mass of the zirconium-magnesium-aluminum-containing lithium cobalt composite oxide powder synthesized as described above as the positive electrode active material, 2.5 parts by mass of the carbon material powder as the conductive agent, and polyvinylidene fluoride as the binder (PVdF) powder was mixed so that it might become 2.5 mass parts, this was mixed with the N-methylpyrrolidone (NMP) solvent, and the positive mix slurry was prepared. This positive electrode mixture slurry was applied to both surfaces of an aluminum positive electrode core having a thickness of 15 μm by a doctor blade method. Then, after drying and removing NMP, it rolled using the compression roller, it cut | judged to predetermined size, and produced the positive electrode plate which has a positive mix layer on both surfaces of the positive electrode core body made from aluminum.

[Production of negative electrode plate]
(Preparation of silicon oxide negative electrode active material)
Metallic silicon and separately prepared silicon dioxide were mixed and subjected to heat treatment under reduced pressure to obtain silicon oxide having a composition of SiO (corresponding to x = 1 in SiOx). Next, the silicon oxide was pulverized and classified to adjust the particle size, and then the temperature was raised to about 1000 ° C., and the surfaces of the particles were coated with a carbon material by a CVD method in an argon atmosphere. At that time, the coating amount of the carbon material was set to 5 mass% of the total amount of silicon oxide including the carbon material. This was crushed and classified, and a negative electrode active material made of silicon oxide having a surface coated with a carbon material represented by SiO and an average particle size of 10 μm was prepared.

(Preparation of graphite negative electrode active material)
As the graphite material, artificial graphite (I), natural graphite (II), and composite graphite (III) of artificial graphite and natural graphite were used. Artificial graphite (I) was prepared by molding coke as a main raw material, firing it, pulverizing to a predetermined size, and sieving. Natural graphite (II) was prepared by spheroidizing and sieving scaly natural graphite as a main raw material.

  Composite graphite (III) is a mixture of coke, an artificial graphite precursor, and spheroidized natural graphite having the same particle size as that of the artificial graphite, and thereafter the same as in the case of artificial graphite (I). did. The fracture strength of the composite graphite (III) was adjusted by changing the content ratio of the spheroidized natural graphite to the coke which is an artificial graphite precursor. Whether or not the raw material of the composite graphite (III) was uniformly composited and existed as a single particle (aggregate) was confirmed by performing SEM (scanning electron microscope) observation.

In addition, the average particle diameter of silicon oxide and graphite material is obtained by using a laser diffraction particle size distribution analyzer (SALD-2000A manufactured by Shimadzu Corporation), using water as a dispersion medium, and a refractive index of 1.70-0.01i. It was. The average particle size was a particle size (D ₅₀ ) at which the cumulative particle amount on a volume basis was 50%.

(Measurement of fracture strength ratio)
The fracture strength ratio between the silicon oxide represented by SiO and the graphite material was determined by the ratio Ss / Sg of the fracture strength Ss of the single particle of the silicon oxide material to the fracture strength Sg of the single particle of the graphite material. The breaking strength of single particles was measured as follows using a micro compression tester (MCT-W201) manufactured by Shimadzu Corporation as a measuring device.
(1) A sample is spread | dispersed on the lower pressurization plate (SKS flat plate) of a measuring apparatus.
(2) Select particles having a target size close to the average particle size with an optical microscope.
(3) A diamond flat indenter having a diameter of 50 μm is used as the upper pressurizer, and only one particle is present between the upper pressurizer and the lower pressurization plate.
(4) The upper pressurizer is slowly lowered, and a load is applied at a constant acceleration from the time when it comes into contact with the sample (the lowering speed changes).
(5) The relationship between the load and the amount of deformation of the sample is measured, and the point at which the amount of deformation of the sample suddenly changes (the inflection point of the load-deformation amount profile) is taken as the breaking point. The fracture strength is calculated based on the following formula. The breaking strength is determined by averaging five measurements.
St = 2.8P / πd ²
St: Breaking strength [N / mm ² or MPa]
P: Load [N]
d: Particle diameter [mm]

(Formation of negative electrode mixture layer)
The silicon oxide represented by SiO prepared as described above and graphite having an average particle diameter of 22 μm were weighed and mixed so as to have the blending ratio shown in Table 1 below, and used as the negative electrode active material. Subsequently, the negative electrode active material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a binder are in a mass ratio of 97.0: 1.5: 1.5. Thus, the mixture was mixed in water to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both surfaces of a negative electrode core made of a copper foil having a thickness of 8 μm by a doctor blade method. Subsequently, after drying this and removing a water | moisture content, it rolled to the predetermined thickness using the compression roller, it cut | judged to the predetermined size, and produced the negative electrode plate which has a negative mix layer on both surfaces of a negative electrode core.

[Preparation of non-aqueous electrolyte]
Ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) were mixed at a volume ratio of 30:60:10 at 25 ° C., and then lithium hexafluorophosphate (LIPF ₆ ) Was dissolved to a concentration of 1 mol / L. Furthermore, vinylene carbonate (VC) is added and dissolved so that 2.0 mass% and fluoroethylene carbonate (FEC) are 1.0 mass% with respect to the whole non-aqueous electrolyte, and a non-aqueous electrolyte is prepared. did.

[Production of battery]
The positive electrode plate and the negative electrode plate prepared as described above are wound through a separator made of a polyethylene microporous film, and a cylindrical wound electrode body is produced by attaching a polypropylene tape to the outermost periphery. A flat wound electrode body (not shown) was produced by pressing. Next, the positive electrode current collector tab was attached to the positive electrode plate, and the negative electrode current collector tab was attached to the negative electrode plate by welding.

  Here, the configuration of a laminate type nonaqueous electrolyte secondary battery common to each experimental example will be described with reference to FIG. Prepare a sheet-like aluminum laminate material consisting of a five-layer structure of resin layer (polypropylene) / adhesive layer / aluminum alloy layer / adhesive layer / resin layer (polypropylene) and fold this aluminum laminate material to form the bottom. Then, a laminate outer package 11 having a cup-shaped electrode body storage space was produced. Next, in the glove box under an argon atmosphere, the flat wound electrode body is accommodated in the laminate outer package 11 together with the non-aqueous electrolyte, and the flat wound coil body 12 is welded from the welding sealing portion 12 of the laminate outer package 11. The positive electrode current collecting tab 13 and the negative electrode current collecting tab 14 respectively connected to the positive electrode plate and the negative electrode plate of the rotating electrode body were protruded.

  Thereafter, the laminate exterior body 11 was depressurized to impregnate the separator with a non-aqueous electrolyte, and the opening of the laminate exterior body 11 was sealed with the welded sealing portion 12. In the laminate outer package 11, between the positive electrode current collection tab 13 and the negative electrode current collection tab 14 and the laminate outer package 11, between the positive electrode current collection tab 13 and the negative electrode current collection tab 14 and the laminate outer package 11. In order to improve adhesion and prevent a short circuit between the positive electrode current collector tab 13 and the negative electrode current collector tab 14 and the aluminum alloy layer constituting the laminate outer package 11, a positive electrode current collector tab resin 15 and a negative electrode current collector tab resin 16 respectively. Arranged. The obtained laminate type nonaqueous electrolyte secondary battery 10 common to each experimental example has a height of 62 mm, a width of 35 mm, and a thickness of 3.6 mm (excluding the size of the welded sealing portion 12), and the design capacity is the end of charging. It is 800 mAh at a voltage of 4.4V.

Next, the different configurations of the nonaqueous electrolyte secondary battery of each experimental example will be described.
[Experimental Examples 1-6]
In the battery of Experimental Example 1, a negative electrode active material that did not contain silicon oxide represented by SiO and consisted only of composite graphite was used. In the batteries of Experimental Examples 2 to 6, the content rate of silicon oxide represented by SiO is constant at 3% by mass, and the fracture strength ratio (Ss / Sg) is 57 (Experimental Example 2), 65 (Experimental Example 3), 79 (Experimental example 4), 84 (Experimental example 5) and 93 (Experimental example 6).

[Experimental Examples 7 to 10]
In the batteries of Experimental Examples 7 to 10, the content rate of silicon oxide represented by SiO is constant at 5% by mass, and the fracture strength ratio (Ss / Sg) is 57 (Experimental Example 7), 65 (Experimental Example 8), 79 (Experimental Example 9) and 84 (Experimental Example 10).

[Experimental Examples 11 to 13]
In the batteries of Experimental Examples 11 and 12, the content of silicon oxide represented by SiO is constant at 10% by mass, and the fracture strength ratio (Ss / Sg) is 57 (Experimental Example 11) and 79 (Experimental Example 12). Changed. Furthermore, in the battery of Experimental Example 13, the content of silicon oxide represented by SiO was 15 mass%, and the fracture strength ratio (Ss / Sg) was 79.

[Measurement of 25 ° C cycle capacity maintenance rate]
Each nonaqueous electrolyte secondary battery of Experimental Examples 1 to 13 was charged at 25 ° C. with a constant current of 1 It = 800 mA until the battery voltage reached 4.4 V, and then the current was 40 mA at a constant voltage of 4.4 V. Charged until converged. Next, the battery was discharged at a constant current of 1 It = 800 mA until the battery voltage reached 2.5 V, and the current flowing at that time was determined as the discharge capacity of the first cycle. This charge / discharge cycle was repeated, the discharge capacity at the 300th cycle was determined, and the capacity retention rate after 300 cycles was determined by the following formula.
Capacity maintenance rate after 300 cycles (%)
= (Discharge capacity at 300th cycle / Discharge capacity at 1st cycle) × 100

  The measurement results of the capacity retention rate after 300 cycles of Experimental Examples 1 to 13 are the same as the types of graphite in the negative electrode active material, the content of silicon oxide represented by SiO in the negative electrode active material, and the fracture strength ratio (Ss / Sg). Table 1 summarizes the results. Furthermore, FIG. 2 is a graph in which the horizontal axis represents the fracture strength ratio (Ss / Sg) and the vertical axis represents the capacity retention rate, with the measurement results of Experimental Examples 2 to 6 having a silicon oxide content of 3 mass%. Indicated.

  From the measurement results of Experimental Examples 1 to 5 shown in Table 1, the following can be understood. That is, when the content of silicon oxide in the negative electrode active material is 3% by mass, a battery having a fracture strength ratio (Ss / Sg) of 65 to 84 (Experimental Examples 3 to 5) is composed of only graphite. A better capacity retention rate than the battery of Experimental Example 1 is obtained. However, in the case of the batteries having the fracture strength ratios of 57 (Experimental Example 2) and 93 (Experimental Example 6), the capacity retention rate is lower than that of the battery of Experimental Example 1.

  Here, referring to the graph of FIG. 2, when the content of silicon oxide in the negative electrode active material is 3 mass%, if the fracture strength ratio is 60 to 90, at least the negative electrode active material is an experimental example consisting of only graphite. It can be seen that a capacity retention rate equivalent to or better than that of the battery 1 is obtained. It is recognized that a more preferable fracture strength ratio is 65 to 84. Within this range, it can be seen that a better result of the capacity retention rate than that of the battery of Example 1 can be obtained.

  When the content of silicon oxide in the negative electrode active material is 5% by mass, a battery with a fracture strength ratio of 65 to 84 (Experimental Examples 8 to 10) has a better capacity maintenance ratio than the battery of Experimental Example 1. ing. However, in the case of a battery having a fracture strength ratio of 57 (Experimental Example 7), the capacity retention rate is lower than that of the battery of Experimental Example 1.

  When the content rate of silicon oxide in the negative electrode active material is 10% by mass, the battery with a fracture strength ratio of 79 (Experimental Example 12) has a better capacity retention rate than the battery of Experimental Example 1. On the other hand, in the case of a battery having a fracture strength ratio of 57 (Experimental Example 11), the capacity retention rate is lower than that of the battery of Experimental Example 1. When the content of silicon oxide in the negative electrode active material is 15% by mass, the capacity retention rate is lower than that of the battery of Experimental Example 1, even if the battery has a fracture strength ratio of 79 (Experimental Example 13).

  Considering the measurement results of the above Experimental Examples 1 to 13 comprehensively, the fracture strength ratio is 60 to 90 within the range of 3 to 10% by mass in which the content of silicon oxide in the negative electrode active material is actually measured. If it is in the range, it can be seen that an excellent capacity retention rate equal to or higher than that in the case where the negative electrode active material is composed only of graphite can be achieved. Further, when extrapolating the results of Experimental Example 3 in which the fracture strength ratio is 79 and the content of silicon oxide in the negative electrode mixture is 3% by mass and Experimental Example 9 in which the content is 5% by mass is extrapolated, at least in the negative electrode active material If the silicon oxide content is 1% by mass or more, it is considered that the effect of improving the capacity retention rate is exhibited. Therefore, it is thought that the content rate of the silicon oxide in a preferable negative electrode active material is 1-10 mass%.

In each experimental example, a silicon oxide having a composition of SiO (corresponding to x = 1 in SiOx) was used. However, if it is within the range of 0.5 ≦ x <1.6, the same good effect is obtained. Play. When x is less than 0.5, since the Si component increases, the expansion / contraction associated with charging / discharging increases, so the capacity retention rate decreases. When x is 1.6 or more, since the SiO ₂ component increases, the effect of increasing the negative electrode capacity decreases.

  In each experimental example, graphite having an average particle diameter of 22 μm was used. However, if the average particle diameter of graphite is in the range of 18 to 22 μm, the same effect can be obtained. Similarly, an example in which the addition amount of CMC and the addition amount of SBR in the negative electrode mixture was 1.5% by mass of the total negative electrode mixture, respectively, was within the range of 0.5 to 2% by mass, respectively. The same effect is obtained. Similarly, an example in which the addition amount of VC is 2.0 mass% and the addition amount of FEC is 1.0 mass% with respect to the total amount of the non-electrolytic solution is shown, but the addition amount of VC is 1 to 5 mass%, FEC If the addition amount is in the range of 0.5 to 5% by mass, the same effect is obtained. Further, an example in which the coating amount of the carbon material covering the surface of the silicon oxide represented by SiO is 5% by mass of the total amount of silicon oxide including the carbon material is shown. If the content is less than or equal to mass%, the same good effect is obtained.

Further, in each experimental example, an example in which a zirconium-magnesium-aluminum-containing lithium cobalt composite oxide having a composition of LiCo _0.979 Zr _0.001 Mg _0.01 Al _0.01 O ₂ was used as the positive electrode active material. Indicated. However, in the present invention, not only compounds having different contents of different metal elements such as zirconium, magnesium and aluminum but also compounds capable of reversibly occluding and releasing lithium ions are used. be able to. As a compound capable of reversibly occluding and releasing lithium ions, for example, a lithium transition metal composite oxide represented by LiMO ₂ (where M is at least one of Co, Ni, and Mn) (Ie, LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiCo _x Mn _y Ni _z O ₂ (x + y + z = 1), etc.), LiMn _One kind of ₂ O ₄ , LiFePO ₄ or the like, or a mixture of plural kinds thereof can be used.

  Examples of the nonaqueous solvent in the nonaqueous electrolytic solution that can be used in the nonaqueous electrolyte secondary battery of the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and fluorine. Cyclic carbonate ester; cyclic carboxylic acid ester such as γ-butyrolactone (γ-BL), γ-valerolactone (γ-VL); dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) Chain carbonates such as methylpropyl carbonate (MPC) and dibutyl carbonate (DBC); fluorinated chain carbonates; chains such as methyl pivalate, ethyl pivalate, methyl isobutyrate, and methyl propionate Carboxylic acid ester; N, N′-dimethylform Bromide or, N- methyl oxazolidone amide compound, dimethylsulfoxide or the like; may be used tetrafluoroboric acid 1-ethyl-3- ambient temperature molten salt such as methyl imidazolium and the like; sulfur compounds such as sulfolane. Moreover, you may make it use these in mixture of 2 or more types.

As the electrolyte salt dissolved in the non-aqueous solvent in the non-aqueous electrolyte that can be used in the non-aqueous electrolyte secondary battery of the present invention, a lithium salt generally used as an electrolyte salt in the non-aqueous electrolyte secondary battery can be used. . Examples of such lithium salt include lithium hexafluorophosphate (LiPF ₆ ), LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ( _{CF 3 SO 2) (C 4} F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Li 2 B 10 Cl 10, Li 2 B ₁₂ Cl ₁₂ or the like can be used singly or as a mixture of a plurality of them. Among these, LiPF ₆ is particularly preferable. The amount of electrolyte salt dissolved in the non-aqueous solvent is preferably 0.8 to 1.5 mol / L.

  In the non-aqueous electrolyte solution of the non-aqueous electrolyte secondary battery of the present invention, for example, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), succinic anhydride (SUCAH), maleic anhydride as an electrode stabilizing compound. Acid (MAAH), glycolic anhydride, ethylene sulfite (ES), divinyl sulfone (VS), vinyl acetate (VA), vinyl pivalate (VP), catechol carbonate, biphenyl (BP), etc. may be added. . Two or more of these compounds may be appropriately mixed and used.

DESCRIPTION OF SYMBOLS 10 ... Laminate type nonaqueous electrolyte secondary battery 11 ... Laminate exterior body 12 ... Welding sealing part 13 ... Positive electrode current collection tab 14 ... Negative electrode current collection tab 15 ... Positive electrode current collection tab resin 16 ... Negative electrode current collection tab resin

Claims (2)

A positive electrode plate having a positive electrode mixture layer containing a positive electrode active material capable of occluding and releasing lithium ions;
A negative electrode plate having a negative electrode mixture layer containing a negative electrode active material capable of occluding and releasing lithium ions;
A separator, a non-aqueous electrolyte,
With
The negative electrode active material is
It is a mixture of graphite material and silicon oxide represented by SiOx (0.5 ≦ x <1.6),
The breaking strength ratio Ss / Sg, which is the ratio of the breaking strength Sg single particles of fracture strength Ss of single particles of silicon oxide the graphite material Ri 60-90 der,
The content ratio of the silicon oxide in the negative electrode active material is 1 to 10% by mass with respect to the total negative electrode active material.
Non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte 2 according to claim 1, wherein a fracture strength ratio Ss / Sg, which is a ratio of a fracture strength Ss of the single particle of silicon oxide and a fracture strength Sg of the single particle of the graphite material, is 64 to 84. Next battery.

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