JP2015170542A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is superior in cycle characteristics, and includes, as a negative electrode active material, a mixture of graphite material and silicon oxide (SiOx, where 0.5≤x<1.6) to which another element is added as means for increasing the capacity of the nonaqueous electrolyte secondary battery.SOLUTION: A nonaqueous electrolyte secondary battery 10 comprises: a positive electrode plate; a negative electrode plate; a separator; and a nonaqueous electrolyte. The negative electrode plate includes a negative electrode active material consisting of a mixture of graphite material and silicon oxide expressed by SiOx (where 0.5≤x<1.6). The content of the graphite material is 92-99.5 mass% to the total mass of the negative electrode active material. The silicon oxide includes at least one element selected from Mn, V, Ti, Al and B within a range of 10-100 ppm.

Description

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

As a negative electrode active material used for a nonaqueous electrolyte secondary battery, carbonaceous materials such as graphite and amorphous carbon are widely used. 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. In this case, 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 can be expected than when a carbon material is used as the negative electrode active material.

  For example, the following Patent Document 1 includes a material containing silicon and oxygen as constituent elements as a negative electrode active material (where the element ratio x of oxygen to silicon is 0.5 ≦ x ≦ 1.5) and graphite. A non-aqueous electrolyte secondary battery using the above is disclosed. 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 mixture layer is used.

  According to the non-aqueous electrolyte secondary battery disclosed in Patent Document 1 below, it is possible to suppress deterioration in battery characteristics due to the volume change while using silicon oxide having a high capacity and a large volume change accompanying charge / discharge. Therefore, it is said that good battery characteristics can be secured 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. Thereby, since the subject that the cycling characteristics of a battery falls exists, various improvement is performed also about the physical property of a negative electrode active material in order to solve these subjects.

For example, in the following Patent Document 2, as a negative electrode material for a non-aqueous electrolyte secondary battery, a composite having a structure in which silicon is dispersed in silicon dioxide represented by SiOx (x = 0.5 to 1.6) or Element selected from La, V, Co, Mn, Ga, Ge, Sn, B, Al, Fe, Mg, Ag, As, Bi, Br, Cr, Hg, S, Te, P and Nb with respect to the mixture It is shown that at least one of these is contained at a concentration of 50 to 100,000 ppm. In Patent Document 2, a negative electrode material for a non-aqueous electrolyte secondary battery that has a carbon coating on the surface is used, and a volume average value D ₅₀ by a laser diffraction scattering particle size distribution measurement method is shown. The use of 0.01 to 50 μm is also shown.

  Patent Document 3 below discloses a lithium secondary battery using a material containing SiOx (x ≦ 1.5) containing B, Al, V or the like and a carbon material as a negative electrode active material. In this lithium secondary battery, B, Al, V, and the like are added to SiOx so as to be 50 mass% or less, preferably 10 to 30 mass%, in order to increase the amorphousness of SiOx. This patent document 3 also shows that the surface of a carbon material and SiOx containing B, Al, V, etc. is coated with the carbon material.

  Patent Document 4 listed below discloses a nonaqueous electrolyte secondary battery using a mixture of a silicon oxide and a carbon material having a content of Fe, Cr, and Ni of 250 ppm or less as a negative electrode active material for a nonaqueous electrolyte battery. ing.

JP 2010-212228 A JP 2011-192453 A Japanese Patent Laid-Open No. 2005-259697 JP 2004-349057 A

  According to the nonaqueous electrolyte secondary battery disclosed in Patent Document 2, the conductivity of the negative electrode active material in the bulk can be improved as compared with the case where no other element is contained in SiOx, and the rate characteristics In addition, a nonaqueous electrolyte secondary battery with improved cycle characteristics can be obtained. In addition, according to the nonaqueous electrolyte secondary battery disclosed in Patent Document 3, since the amorphous state of SiOx can be increased and the diffusion rate of Li atoms can be improved, other elements are incorporated into SiOx. A non-aqueous electrolyte secondary battery having superior life characteristics and high rate charge / discharge characteristics can be obtained as compared with the case where it is not contained. Furthermore, according to the nonaqueous electrolyte secondary battery disclosed in Patent Document 4, battery swelling when left at a high temperature in a charged state is suppressed as compared with the case where no other element is contained in SiOx. A nonaqueous electrolyte secondary battery can be obtained.

  As shown in the above Patent Documents 2 to 4, when a material in which other elements are added to Si or SiOx as a negative electrode active material, not only high capacity can be achieved, but also rate characteristics and cycle characteristics can be achieved. It can be seen that a non-aqueous electrolyte secondary battery can be obtained which can be improved and which is suppressed from battery swelling when left in a charged state at a high temperature. However, even in the nonaqueous electrolyte secondary batteries disclosed in Patent Documents 2 to 4, the cycle characteristics are only about 83 to 86% (see Patent Document 2) at a capacity retention rate after 200 cycles, It is still desired to improve cycle characteristics (life characteristics).

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 content ratio of the graphite material is 92% by mass or more and 99.5% by mass or less in the entire negative electrode active material,
The silicon oxide contains at least one element selected from Mn, V, Ti, Al and B in a range of 10 ppm to 100 ppm.
A non-aqueous electrolyte secondary battery is provided.

  In the nonaqueous electrolyte secondary battery of one embodiment of the present invention, the negative electrode active material contains not only graphite but also silicon oxide represented by SiOx (0.5 ≦ x <1.6). The content of is 92% by mass or more and 99.5% by mass or less in the entire negative electrode active material. The silicon oxide represented by SiOx has a volume change accompanying charge / discharge larger than that of the graphite material, but has a theoretical capacity value 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, in the silicon oxide represented by SiOx used in the nonaqueous electrolyte secondary battery of one embodiment of the present invention, at least one element selected from Mn, V, Ti, Al, and B is 10 ppm. To 100 ppm. If these elements are contained in the silicon oxide represented by SiOx, the ionic radius of these elements is larger than Si ⁴⁺ , so the distance between Si-Si bonds of the Si crystal structure or Si of the SiO ₂ crystal structure The -O bond distance becomes longer, and the rate of volume change of silicon oxide accompanying charge / discharge becomes smaller than when these elements are not added. Therefore, according to the nonaqueous electrolyte secondary battery of the present invention, the cycle characteristics are better than when no element such as Mn, V, Ti, Al, and B is added to the silicon oxide represented by SiOx. .

  In addition, when the concentration of at least one element selected from Mn, V, Ti, Al, and B in silicon oxide represented by SiOx is less than 10 ppm or exceeds 100 ppm, the cycle characteristics are all deteriorated. Further, when the content ratio of the graphite material in the negative electrode active material is less than 92% by mass in all the negative electrode active materials, that is, when the content ratio of silicon oxide represented by SiOx exceeds 8.0% by mass, charging and discharging are performed. Cycle characteristics are degraded due to the pulverization of the negative electrode active material based on the large expansion and contraction of silicon oxide and chipping from the conductive network. Further, when the content ratio of the graphite material in the negative electrode active material exceeds 99.5% by mass in all the negative electrode active materials, that is, when the content ratio of silicon oxide represented by SiOx is less than 0.5% by mass. The effect of adding silicon oxide is small, and the battery capacity is reduced.

It is a perspective view of a laminate type nonaqueous electrolyte secondary battery common to each experimental example.

  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 core having a thickness of 15 μm by a doctor blade method to form a positive electrode mixture layer on both surfaces of the positive electrode core. Then, after drying and removing NMP, it rolled using the compression roller, it cut | judged to the predetermined size, and produced the positive electrode plate.

[Production of negative electrode plate]
(Preparation of silicon oxide negative electrode active material)
Metallic silicon and the additive element were placed in an electric furnace, and high temperature treatment was performed in an argon atmosphere to obtain metallic silicon containing the additive element. This metal silicon and silicon dioxide prepared separately were mixed and subjected to heat treatment under reduced pressure to obtain silicon oxide having a composition containing additive elements 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. And this was crushed and classified, and the negative electrode active material which the surface coat | covered with a carbon material and consists of silicon oxide represented by SiO containing an additional element was prepared.

The particle diameter of the silicon oxide represented by SiO 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%.

  The amount of the additive element in the silicon oxide represented by SiO was measured by inductively coupled plasma (ICP) emission spectrometry after dissolving a silicon oxide sample represented by SiO with hydrofluoric acid.

(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 ratios shown in Tables 1 to 4 below, respectively, as a negative electrode active material. Using. Subsequently, the negative electrode active material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a binder have 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 and removing 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 in which the negative mix layer was formed on both surfaces.

[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 laminated 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 nonaqueous 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 laminate type nonaqueous electrolyte secondary battery 10 common to the obtained experimental examples 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 1-5]
In the non-aqueous electrolyte secondary batteries of Experimental Examples 1 to 5, with respect to the negative electrode active material, all of the additive elements in the silicon oxide represented by SiO are Mn, and the addition amount is 2 ppm (Experimental Example 1), 12 ppm (experimental) Examples 2), 48 ppm (Experimental Example 3), 99 ppm (Experimental Example 4) and 121 ppm (Experimental Example 5) were used. At that time, the content ratio of silicon oxide represented by SiO in the negative electrode active material was all kept constant at 5% by mass.

  The particle diameter of silicon oxide represented by SiO in the negative electrode active material was 10 μm, but the measured value was in the range of 9.1 to 10.3 μm due to the difference in the Mn content in the silicon oxide. It varied.

[Experimental Examples 6 to 9]
As the non-aqueous electrolyte secondary batteries of Experimental Examples 6 to 9, the additive elements in the silicon oxide represented by SiO for the negative electrode active material were V (Experimental Example 6), Ti (Experimental Example 7), Al (Experimental). Examples 8) and B (Experimental Example 9) were used. At that time, the content ratio of silicon oxide represented by SiO in the negative electrode active material was all kept constant at 5% by mass.

  The content ratio of the additive element in the silicon oxide in the negative electrode active material was set to 48 ppm, but the measured value varied in the range of 43 to 54 ppm due to the difference in the composition of the additive element in the silicon oxide. Similarly, the particle size of silicon oxide represented by SiO in the negative electrode active material was selected to be 10 μm, but the measured value was 9.p due to the difference in the composition of additive elements in silicon oxide represented by SiO. It fluctuated in the range of 2 to 10.3 μm.

[Experimental Examples 10 to 13]
As the non-aqueous electrolyte secondary batteries of Experimental Examples 10 to 13, the negative electrode active material was all Mn as the additive element in the silicon oxide represented by SiO, and the addition amount was kept constant at 48 ppm. The particle size of silicon oxide represented by the formula (1) was set to be constant at 10.3 μm. At that time, the content ratio of silicon oxide represented by SiO in the negative electrode active material was 0.5 mass (Experimental Example 10), 1 mass% (Experimental Example 11), 8 mass% (Experimental Example 12), and 10 mass. % (Experimental Example 13). Table 3 also shows the measurement results of Experimental Example 3 having the same configuration as the nonaqueous electrolyte secondary batteries of Experimental Examples 10 to 13 except that the content ratio of silicon oxide represented by SiO is 5 mass%. It is written together.

[Experimental Examples 14 to 17]
In the non-aqueous electrolyte secondary batteries of Experimental Examples 14 to 17, the negative electrode active material is all Mn as the additive element in the silicon oxide represented by SiO, and the addition amount is 48 ppm. What added the silicon oxide represented so that it might become 5 mass% constant was used. At that time, the particle diameter of silicon oxide represented by SiO in the negative electrode active material was 5.5 μm (Experimental Example 14), 8.2 μm (Experimental Example 15), 11.7 μm (Experimental Example 16), and 15.4 μm. (Experimental example 17) Table 4 also shows the measurement results of Experimental Example 3 having the same configuration as the non-aqueous electrolyte secondary batteries of Experimental Examples 14 to 17 except that the particle size of silicon oxide represented by SiO is 10.3 μm. It is written together.

  In Experimental Examples 14 to 17, the addition amount of the additive element in silicon oxide represented by SiO in the negative electrode active material was selected to be 48 ppm, but the particle size of silicon oxide represented by SiO Due to the difference, the measured values varied in the range of 45 to 54 ppm.

[Measurement of cycle capacity maintenance rate at 25 ° C]
Each non-aqueous electrolyte secondary battery of Experimental Examples 1 to 17 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 Experimental Examples 1 to 5 show the types and amounts of additive elements in silicon oxide represented by SiO, the content of silicon oxide represented by SiO in the negative electrode active material, and silicon oxide represented by SiO. It showed in Table 1 with the particle size of. Similarly, the measurement results of Experimental Examples 6 to 9 are shown in Table 2, the measurement results of Experimental Examples 10 to 13 are shown in Table 3 together with the measurement results of Experimental Example 3, and the measurement results of Experimental Examples 14 to 17 are the measurement results of Experimental Example 3. Table 4 also shows the results.

  From the measurement results of Experimental Examples 1 to 4 shown in Table 1, the following can be understood. That is, when the additive element in the silicon oxide represented by SiO is Mn, when the added amount of Mn is 2 ppm (Experimental Example 1) and 121 ppm (Experimental Example 5) is the highest, Even when the silicon oxide content and the silicon oxide particle size are almost the same as those in Experimental Examples 2 to 4, the capacity retention rate at the 300th cycle is as low as 72%. On the other hand, when the amount of Mn added is between 12 ppm (Experimental Example 2) and 99 ppm (Experimental Example 4), the capacity retention rate at the 300th cycle is 80.5% or more.

  Therefore, when the measurement results of Experimental Examples 2 and 4 are extrapolated, if the amount of Mn in the silicon oxide represented by SiO is within a range of 10 to 100 ppm, the capacity retention rate at the 300th cycle is 80 % Can be secured.

  From the measurement results of Experimental Examples 6 to 9 shown in Table 2, the following can be understood. That is, regardless of whether the additive element in silicon oxide represented by SiO is V, Ti, Al, or B, the content of silicon oxide and the particle size of silicon oxide in all negative electrode active materials are shown in Table 1. If it is substantially the same as in the case of Experimental Example 3, the capacity maintenance rate at the 300th cycle can be ensured to be 78% or more. Therefore, when comparing the measurement results of Experimental Examples 6 to 9 shown in Table 2 and the measurement results of Experimental Example 3 shown in Table 1, as an additive element in silicon oxide represented by SiO in the negative electrode active material, Although it is considered that at least one element selected from Mn, V, Ti, Al and B can be used, it is understood that Mn is the most preferable additive element in silicon oxide represented by SiO.

  From the measurement results of Experimental Examples 10 to 13 and Experimental Example 3 shown in Table 3, the following can be understood. That is, when the additive element in silicon oxide represented by SiO, the amount of addition, and the particle size of silicon oxide are made equal to those in Experimental Example 3, the content of silicon oxide represented by SiO in all negative electrode active materials Is within the range of 0.5 to 8% by mass, that is, the graphite material content is 92% by mass (Experimental Example 10) or more and 99.5% by mass (Experimental Example 8) or less, the capacity of the 300th cycle The maintenance rate is 78% or more.

  Therefore, considering the results shown in Tables 2 and 3 comprehensively, the additive element in the silicon oxide represented by SiO in the negative electrode active material is an element selected from Mn, V, Ti, Al and B. Even if it is at least one kind, the content of silicon oxide represented by SiO in all negative electrode active materials is 0.5 to 8% by mass, that is, the content of graphite material is 92% by mass or more and 99.5% by mass or less. If it is within the range, it is considered that the capacity maintenance rate at the 300th cycle can be secured at 78% or more. In particular, the element contained in silicon oxide is Mn, and the content of silicon oxide represented by SiO in all negative electrode active materials is within the range of 1.0 to 5.0 mass%, that is, the content of graphite material It can also be seen that if the amount is 95 to 99% by mass, better cycle characteristics can be obtained.

  The following can be understood from the measurement results of Experimental Examples 14 to 17 and Experimental Example 3 shown in Table 4. That is, if the additive element in silicon oxide represented by SiO, the amount added, and the content of silicon oxide represented by SiO in all negative electrode active materials are substantially the same as in Experimental Example 3, it is represented by SiO. When the particle size of the silicon oxide is in the range of 5.5 to 15.4 μm, the capacity retention rate at the 300th cycle can be ensured to be 79% or more.

  Therefore, extrapolating the measurement results of Experimental Examples 14 and 17, when the additive element in the silicon oxide represented by SiO is Mn and the content thereof is 48 ppm, the silicon oxide represented by SiO in the entire negative electrode active material In the case where the content of graphite is 5% by mass, that is, the content of the graphite material is 95% by mass, if the particle size of silicon oxide represented by SiO is at least in the range of 5.0 to 16 μm, 300% is obtained. It is considered that the capacity maintenance ratio at the cycle can be secured at 78% or more. In this case, it can also be seen that better cycle characteristics can be obtained if the particle size of the silicon oxide represented by SiO is in the range of 8.0 to 12 μm.

  In each experimental example, graphite having an average particle size of 22 μm was used. However, if the average particle size of graphite is in the range of 16 to 26 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. Furthermore, an example in which the coating amount of the carbon material covering the surface of the silicon oxide represented by SiO was 5% by mass of the total amount of silicon oxide including the carbon material was shown. If it does, there exists a favorable effect similarly.

In each experimental example, an example in which a lithium cobalt composite oxide added with a different metal element such as zirconium, magnesium, or aluminum was used as the positive electrode active material. However, a known lithium ion was used as the positive electrode active material. A compound that can be reversibly occluded / released can be used. 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 (5)

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 content ratio of the graphite material is 92% by mass or more and 99.5% by mass or less in the entire negative electrode active material,
The non-aqueous electrolyte secondary battery, wherein the silicon oxide contains at least one element selected from Mn, V, Ti, Al and B in a range of 10 ppm to 100 ppm.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the element contained in the silicon oxide is Mn.   The non-aqueous electrolyte secondary battery according to claim 2, wherein a content ratio of the graphite material is 95 to 99% by mass in all negative electrode active materials. The nonaqueous electrolyte secondary battery according to claim 1, wherein the silicon oxide has an average particle diameter (D ₅₀ ) of 8 to 12 μm.   The surface of the silicon oxide is coated with a carbon material, and the coating amount of the carbon material is 1% by mass or more and 5% by mass or less of the total amount of the silicon oxide including the carbon material. The nonaqueous electrolyte secondary battery according to any one of the above.

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