JP5601536B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

Nonaqueous electrolyte secondary batteries are widely used as power sources for portable electronic devices and the like because of their large electromotive force and high energy density.
Conventionally, in a nonaqueous electrolyte secondary battery, a carbon material has been widely used as a negative electrode active material since lithium dendrite precipitation can be prevented. However, when a carbon material is used as the negative electrode active material, it is difficult to increase the discharge capacity as a battery by 10% or more because the discharge capacity cannot be increased beyond the theoretical capacity (372 mAh / g). There was a problem.

  Therefore, in order to increase the discharge capacity and increase the energy density of the battery, attempts have been made to use a metal that can be alloyed with lithium as an active material. An example of such a metal is silicon (see, for example, Patent Document 1).

  Silicon has a diamond-type crystal structure in which tetrahedrons formed by coordination of four atoms to each atom are continuous, and can store a very large amount of lithium ions.

  However, silicon has a large volume expansion associated with occlusion of lithium ions, and is easily pulverized by repeated charge and discharge. By this pulverization, a portion where the conductive path is interrupted is generated, and the current collection efficiency is lowered. For this reason, when the charge-discharge cycle progresses, the capacity rapidly decreases and the cycle life becomes short. For these reasons, when silicon is used as the negative electrode active material, it has been difficult to improve the capacity retention after 50 cycles, for example, by 20% or more.

Japanese Patent Laid-Open No. 7-29602

  The present invention has been completed based on the above circumstances, and an object thereof is to provide a nonaqueous electrolyte secondary battery having a high energy density and excellent cycle characteristics.

As means for achieving the above object, the invention of claim 1 is a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte. wherein said negative electrode active material, and particles composed of silicon Si, silicon oxides SiO X _(where, 0 <X ≦ 2) and particles consisting of, viewed contains composite particles composed of a carbon material, and the silicon Si The ratio of the silicon Si to the total of the silicon oxide SiO _X is 20 wt% or more and 80 wt% or less .

When the negative electrode active material includes particles made of Si and particles made of SiO _X (where 0 <X ≦ 2), a non-aqueous electrolyte secondary battery having a high energy density can be obtained. This is because particles made of Si and particles made of SiO 2 _X can occlude a large amount of lithium ions by forming a solid solution or an intermetallic compound with lithium ions.
Further, since Si has a larger discharge capacity than SiO _X , it is not preferable that the Si ratio is less than 20% by weight because the discharge capacity decreases. On the other hand, SiO _X has a smaller volume expansion due to charging / discharging than Si, and is excellent in cycle characteristics. Therefore, if the ratio of Si exceeds 80% by weight, cycle characteristics deteriorate, which is not preferable. Accordingly, the ratio of Si to the total of Si and SiO _X is preferably 20% by weight or more and 80% by weight or less.

As a reference example, in a non-aqueous electrolyte secondary battery, the particles composed of silicon Si and the silicon oxide SiO _X (where 0 <X ≦ 2) are composed of silicon Si and silicon oxide SiO _X (where 0 <X ≦ 2), the secondary particles do not contain the carbon material, and the average interplanar spacing d (002) of the carbon material is 0.3354 nm or more and 0. It is good also as being 35 nm or less .

  The negative electrode active material is Si and SiO. _X However, a high energy density non-aqueous electrolyte secondary battery can be obtained by including particles including (0 <X ≦ 2). This is because Si and SiO _X This is because the particles containing can form a large amount of lithium ions by forming a solid solution or an intermetallic compound with lithium ions.

  SiO _X (However, 0 <X ≦ 2) can be preferably used as the negative electrode active material because X shows a high discharge capacity when X is 2 or less. The reason is considered as follows. A silicon oxide having a ratio of oxygen atoms to silicon atoms of 2 or less is considered to form a skeletal structure including bonds between silicon atoms in addition to bonds between silicon atoms and oxygen atoms. In such a structure, it is considered that there are very many sites that can occlude lithium ions. For this reason, it is considered that lithium ions can be easily stored and released in large quantities. Furthermore, SiO _X Since the volume expansion is suppressed by including, it is considered that the cycle characteristics are improved as compared with the case where only Si is used as the negative electrode active material.

Furthermore, a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be obtained by mixing the negative electrode active material and the carbon material. This is because the conductive path is maintained by the carbon material even if the particles made of Si, the particles made of SiO _X , or the particles containing Si and SiO _X are pulverized along with charge and discharge. This is because the decrease is suppressed.

When the ratio of the carbon material constituting the composite particles (hereinafter referred to as carbon material A) to the entire negative electrode active material is less than 3% by weight, particles made of Si, SiO particles consisting of _X, and Si and could not be prevented disconnection of the conductive path caused by the pulverization of the particles comprising an SiO _X, since the cycle characteristics are deteriorated unfavorably. On the other hand, if it exceeds 60% by weight, the discharge capacity decreases, which is not preferable. Therefore, the ratio of the carbon material to the whole negative electrode active material is preferably 3% by weight or more and 60% by weight or less.

  Since d (002) of the most crystalline graphite material is 0.3354 nm, d (002) of the carbon material A used for the negative electrode active material is preferably 0.3354 nm or more. On the other hand, if it exceeds 0.35 nm, the conductivity of the carbon material A itself is lowered, which is not preferable. From the above, the average interplanar distance d (002) is preferably 0.3354 nm or more and 0.35 nm or less. For example, d (002) can be measured using CuKα rays using an X-Ray Diffractometer, RINT2000, manufactured by Rigaku Corporation.

By selecting the carbon material A constituting the composite particles from the group consisting of natural graphite, artificial graphite, acetylene black, and vapor-grown carbon fiber, cycle characteristics can be improved. This is because the high conductivity of the carbon material, particles composed of Si, from it is easy to maintain a conductive path of particles comprising particles consisting of SiO _X, and Si and a SiO _X. The above carbon materials may be used alone or in combination of two or more.

By coating the surface of the composite particles with a carbon material (hereinafter, the carbon material covering the surface of the composite particles is referred to as carbon material B), a nonaqueous electrolyte secondary battery with improved cycle characteristics can be obtained. . The reason is considered as follows. For the particles composed of Si exposed on the surface of the composite particles, the particles composed of SiO _X , and the particles containing Si and SiO _X , the cycle characteristics are deteriorated by the fine powder generated by repeated charge and discharge dropping off from the composite particles. There is a case. By covering the composite particles with the carbon material B, the conductive path is maintained even for the particles made of Si, the particles made of SiO _X , and the particles containing Si and SiO _X exposed on the surface of the composite particles. Therefore, it is considered that the cycle characteristics are improved.

In addition, when the surface of the composite particle is not covered with a carbon material, the reactivity with lithium ions is higher on the particles made of Si, the particles made of SiO _X , and the particles containing Si and SiO _X compared to others. In some cases, so-called reaction unevenness occurs in which the reaction of occluding and releasing lithium ions proceeds intensively in the highly reactive portion. Then, in the highly reactive part, the volume of the negative electrode active material expands due to occlusion of lithium ions, whereas in the low reactive part, the volume expansion of the negative electrode active material becomes small. Due to the occurrence of such unevenness of volume fluctuation, the shape of the particles made of Si, the particles made of SiO _X , and the particles containing Si and SiO _X are broken, resulting in isolated portions from the surroundings, and the conduction path is interrupted. Sometimes it is done.

By the surface of the composite particle is covered with the carbon material B having conductivity, the reaction unevenness as described above is alleviated, comprising particles consisting of Si, particles made of SiO _X, and Si and a SiO _X particles And lithium ions react uniformly. As a result, since the particles made of Si, the particles made of SiO _X , and the particles containing Si and SiO _X are uniformly expanded in volume, isolation is prevented and the conductive path is maintained, resulting in excellent cycle characteristics. A nonaqueous electrolyte secondary battery can be obtained.

When the ratio of the entire carbon material (the total of the carbon material A and the carbon material B) to the entire negative electrode active material is less than 30% by weight, particles composed of Si, particles composed of SiO _X , and When fine particles of particles containing Si and SiO _X are generated, the conductive path cannot be maintained, and as a result, cycle characteristics deteriorate, which is not preferable. If it exceeds 80% by weight, the ratio of the particles composed of Si, the particles composed of SiO _x , and the particles containing Si and SiO _x decreases, resulting in a decrease in discharge capacity. Therefore, the ratio of all the carbon materials to the whole negative electrode active material is preferably 30% by weight or more and 80% by weight or less.

When the ratio of the carbon material B covering the surface of the composite particle to the whole negative electrode active material is less than 0.5% by weight, the surface of the composite particle cannot be sufficiently covered, so that the cycle characteristics are deteriorated. Therefore, it is not preferable. If it exceeds 40.0% by weight, the ratio of the particles composed of Si, the particles composed of SiO _x , and the particles containing Si and SiO _x decreases, resulting in a decrease in discharge capacity. Therefore, the ratio of the carbon material B covering the surface of the composite particles to the whole negative electrode active material is preferably 0.5% by weight or more and 40.0% by weight or less.

When the BET specific surface area of the negative electrode active material exceeds 10.0 m ² / g, the binding property of the binder decreases. For this reason, an expansion | swelling and shrinkage | contraction of the negative electrode active material accompanying charging / discharging generate | occur | produces a clearance gap between negative electrode active materials, As a result of disconnecting the electrical contact of negative electrode active materials, it is unpreferable since cycling characteristics fall. Therefore, the BET specific surface area of the negative electrode active material is preferably 10.0 m ² / g or less.

  According to the present invention, a nonaqueous electrolyte secondary battery having a high energy density and excellent cycle characteristics can be obtained. That is, compared with a conventional battery using a carbon material as a negative electrode active material, the discharge capacity can be increased by 10% or more, and compared with a battery using a composite of silicon and carbon as a negative electrode active material. The capacity retention rate can be improved by 20% or more.

The schematic diagram which shows the cross section of the negative electrode active material which concerns on invention of Example 1 The schematic diagram which shows the cross section of the negative electrode active material which concerns on invention of Example 2 Schematic showing the cross section of the negative electrode active material according to Reference Example 2 Schematic showing the cross section of the negative electrode active material according to Reference Example 3 The longitudinal cross-sectional view of the square nonaqueous electrolyte secondary battery of one Embodiment of this invention

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 5 is a schematic cross-sectional view of a prismatic nonaqueous electrolyte secondary battery according to an embodiment of the present invention. This rectangular nonaqueous electrolyte secondary battery 21 includes a positive electrode 23 formed by applying a positive electrode mixture to a positive electrode current collector made of aluminum foil, and a negative electrode formed by applying a negative electrode mixture to a negative electrode current collector made of copper foil. A flat wound electrode group 22 wound around a separator 25 and a nonaqueous electrolyte solution are housed in a battery case 26.

  A battery lid 27 provided with a safety valve 28 is attached to the battery case 26 by laser welding, a negative electrode terminal 29 is connected to the negative electrode 24 via a negative electrode lead 31, and a positive electrode 23 is connected to the battery lid 27 via a positive electrode lead 30. It is connected.

As the positive electrode active material, a compound that can reversibly insert and desorb lithium ions can be used. Examples of such compounds include the following substances. As the inorganic compound, a composition formula Li _x MO ₂ (M is one or more transition metals, 0 ≦ x ≦ 1), or a composition formula Li _y M ₂ O ₄ (M is one or more kinds). Transition metals, lithium transition metal composite oxides represented by 0 ≦ y ≦ 2), oxides having tunnel-like vacancies, layered metal chalcogenides, and the like can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS _{2 and the} like. . Examples of the organic compound include conductive polymers such as polyaniline. Furthermore, the above various positive electrode active materials may be mixed and used regardless of whether they are inorganic compounds or organic compounds.

  A positive electrode plate is manufactured by preparing a positive electrode mixture by mixing the positive electrode active material, a conductive agent, and a binder, and coating the positive electrode mixture on a positive electrode current collector made of a metal foil. be able to.

  The kind in particular of electrically conductive agent is not restrict | limited, A metal or a nonmetal may be sufficient. Examples of the metal conductive agent include materials composed of metal elements such as Cu and Ni. Examples of the nonmetallic conductive agent include carbon materials such as graphite, carbon black, acetylene black, and ketjen black.

  The type of the binder is not particularly limited as long as it is a material that is stable with respect to the solvent and the electrolyte used in manufacturing the electrode. Specifically, cellulose, carboxymethyl cellulose, styrene-butadiene rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber, syndiotactic 1,2-polybutadiene, ethylene-vinyl acetate copolymer, propylene-α-olefin (carbon (Equation 2-12) Copolymers, polyvinylidene fluoride, polytetrafluoroethylene, polytetrafluoroethylene-ethylene copolymers and the like can be used.

  Examples of the positive electrode current collector include Al, Ta, Nb, Ti, Hf, Zr, Zn, W, Bi, and alloys containing these metals. Since these metals form a passive film on the surface by anodic oxidation in the electrolytic solution, it is possible to effectively prevent the nonaqueous electrolyte from being oxidatively decomposed at the contact portion between the positive electrode current collector and the electrolytic solution. it can. As a result, the cycle characteristics of the non-aqueous secondary battery can be effectively improved.

FIG. 1 is a schematic diagram showing a cross section of a negative electrode active material according to the invention of claim 1. The negative electrode active material includes composite particles 10 composed of particles 11 made of Si, particles 12 made of SiO _X (where 0 <X ≦ 2), and a carbon material A13.

Composite particles 10 described above, the particles 11 made of Si, and the particles 12 made of SiO _X, and carbon materials A13, can be obtained by milling with a mill. At this time, although it may be in the air, milling is preferably performed in an inert atmosphere such as argon or nitrogen. Examples of the mill include ball mill, vibration mill, sanitary ball mill, tube mill, jet mill, rod mill, hammer mill, roller mill, disk mill, attritor mill, planetary ball mill, impact mill and the like. Further, a mechanical alloy method may be used. The milling temperature can be performed in the range of 10 ° C to 300 ° C. The milling time can be in the range of 30 seconds to 48 hours.

  Moreover, in this invention, as shown in FIG. 2, what coated the carbon material B14 on the surface of the said composite particle 10 can also be used as a negative electrode active material.

FIG. 3 is a schematic diagram showing a cross section of the negative electrode active material according to Reference Example 2 . The negative electrode active material includes composite particles 16 composed of particles 15 containing Si and SiO _X (where 0 <X ≦ 2) and a carbon material A13.

The composite particle 16 can be obtained by the same method as the composite particle 10 shown in FIG. 1 with the particle 15 containing Si and SiO _X and the carbon material A13.
As Reference Example 3, as shown in FIG. 4, the composite particle 16 whose surface is coated with the carbon material B14 can be used as the negative electrode active material.

  In order to coat the surface of the composite particles 10 and 16 with the carbon material B14, a method in which an organic compound is coated on the surfaces of the composite particles 10 and 16 and then firing, a chemical vapor deposition (CVD) method, or the like can be used. .

In the CVD method, an organic compound such as methane, acetylene, benzene, and toluene can be used as a reaction gas. The reaction temperature can be in the range of 700 ° C to 1300 ° C. The reaction time can be 30 to 72 hours. According to the CVD method, the carbon material can be coated at a lower reaction temperature than the method of firing the coated organic compound. Thus, it preferred because perform the coating process at a temperature lower than the melting point of the particles 15 containing the particles 11, made of SiO _X particles 12, and Si and SiO _X consisting of Si.

Whether or not the carbon material B14 is coated on the surface of the composite particle 10 can be confirmed by performing Raman spectroscopic analysis. Since Raman spectroscopic analysis analyzes the surface portion of the sample, when the carbon material B14 is entirely coated on the surface of the composite particle 10, an R value (intensity) indicating the crystallinity of the carbon material B14 coated on the surface. the ratio peak intensity of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1) is, be measured anywhere in the anode active material particles will exhibit a constant value. For example, this Raman spectroscopic analysis
T64000 manufactured by JOBIN, YVON can be used.

Particles made of Si, particles made of SiO _X (where 0 <X ≦ 2), particles containing Si and SiO _X (where 0 <X ≦ 2) are washed with an acid such as hydrofluoric acid or sulfuric acid. And those reduced with hydrogen can also be used.

The ratio of the carbon material A13 and the carbon material B14 to the whole negative electrode active material can be measured by performing thermogravimetric analysis. For example, when thermogravimetric measurement is performed at 10 ± 2 ° C./min, weight loss of the carbon material A13 and the carbon material B14 is observed in the range of 30 ° C. to 1000 ° C. In the vicinity of 580 ° C., a decrease in the weight of the carbon material B 14 having a relatively low crystallinity coated on the surface of the composite particle 10 is observed. Next, in the vicinity of 610 ° C., the particles 11 made of Si and the SiO _X The weight loss of the carbon material A13 milled together with the particles 12 and the particles 15 containing Si and SiO _X is observed. Weight loss of the particle 11, made of SiO _X particles 12 and Si and particles 15 containing a SiO _X, made of Si is observed in the vicinity 1500 ° C. to 2000 ° C.. From this result, the weight ratio of each material can be measured. For this thermogravimetric analysis, for example, SSC / 5200 manufactured by Seiko Instruments Inc. can be used.

  The specific surface area of the negative electrode active material is, for example, made by Shimadzu Corporation, Micromeritex, Jenimi 2370, using liquid nitrogen, by a constant temperature gas adsorption method by a dynamic constant pressure method with a pressure measurement range of 0-126.6 KPa, It can be analyzed by the BET method. Further, GEMINI-PC1 can be used as data processing software.

  The material of the negative electrode current collector is preferably a metal such as copper, nickel, and stainless steel. Among these, it is preferable to use a copper foil because it is easy to process into a thin film and is inexpensive.

  The manufacturing method in particular of a negative electrode plate is not restrict | limited, It can manufacture by the method similar to the manufacturing method of said positive electrode.

  Examples of the non-aqueous solvent for the non-aqueous electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, γ-valerolactone, methyl acetate, methyl propionate, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, dimethoxyethane, dimethoxymethane, ethylene methyl phosphate, ethyl ethylene phosphate, trimethyl phosphate, triethyl phosphate and the like can be used. Only one kind of these organic solvents may be selected and used, or two or more kinds may be used in combination.

As a solute of the non-aqueous electrolyte, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN Examples thereof include fluorine-containing organic lithium salts such as (CF ₃ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ . Only one type of these solutes may be selected and used, or two or more types may be used in combination.

  As the electrolyte, a solid or gel electrolyte can be used in addition to the electrolyte solution. Examples of such an electrolyte include an inorganic solid electrolyte, polyethylene oxide, polypropylene oxide, and derivatives thereof.

  As the separator, an insulating polyethylene microporous membrane, polypropylene microporous membrane, polyethylene nonwoven fabric, polypropylene nonwoven fabric and the like impregnated with an electrolytic solution can be used.

Hereinafter, the present invention will be described in detail based on examples. In addition, this invention is not limited at all by the following Example.
<Example 1>
A negative electrode active material was prepared by preparing composite particles by treating 30 parts by weight of Si, 30 parts by weight of SiO ₂ and 40 parts by weight of artificial graphite in a nitrogen atmosphere at 25 ° C. for 30 minutes with a ball mill.

A negative electrode paste was prepared by mixing 95% by weight of the negative electrode active material, 3% by weight of SBR, and 2% by weight of CMC in water. This negative electrode paste was applied onto a copper foil having a thickness of 15 μm so that the application weight was 1.15 mg / cm ² and the amount of the negative electrode active material stored in the battery was 2 g, and then dried at 150 ° C. The water was evaporated. This operation was performed on both sides of the copper foil, and both sides were compression molded with a roll press. Thus, the negative electrode plate provided with the negative mix layer on both surfaces was produced.

A positive electrode paste was prepared by dispersing 90% by weight of lithium cobaltate as a positive electrode active material, 5% by weight of acetylene black as a conductive agent, and 5% by weight of PVDF as a binder in NMP. This positive electrode paste is applied onto an aluminum foil having a thickness of 20 μm so that the application weight is 2.5 mg / cm ² and the amount of the positive electrode active material stored in the battery is 5.3 g, and then dried at 150 ° C. As a result, NMP was evaporated. The above operation was performed on both sides of the aluminum foil, and both sides were compression molded with a roll press. In this way, a positive electrode plate having a positive electrode mixture layer on both sides was produced.

The positive electrode plate and the negative electrode plate thus produced were stacked with a polyethylene separator, which is a continuous porous body having a thickness of 20 μm and a porosity of 40%, interposed between them to produce a wound power generation element. The power generation element was inserted into a container having a height of 48 mm, a width of 30 mm, and a thickness of 4.2 mm, and then a nonaqueous electrolyte was injected into the battery to produce a rectangular nonaqueous electrolyte secondary battery. As this nonaqueous electrolytic solution, a solution obtained by dissolving 1 mol / l LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 1 was used.

<Example 2>
For Example 2, 20 parts by weight of Si, 20 parts by weight of SiO ₂ and 40 parts by weight of artificial graphite were treated as a negative electrode active material by a ball mill in a nitrogen atmosphere at 25 ° C. for 30 minutes to prepare composite particles. Thereafter, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the surface of the composite particles was coated with a carbon material by a method of thermally decomposing methane at 900 ° C. (CVD). .

<Example 3>
For Example 3, except for using SiO instead of SiO ₂ was used to fabricate a non-aqueous electrolyte secondary battery in the same manner as in Example 2.

<Comparative Examples 1 to 4>
A negative electrode active material was prepared in the same manner as in Example 2 except that the raw materials shown in Table 1 were used, and a nonaqueous electrolyte secondary battery was produced using this.

<Measurement>
(Raman spectroscopy)
About the negative electrode active material prepared as mentioned above, the Raman spectroscopic analysis was performed by the above-mentioned method, and R value was measured. The R value was about 0.8 regardless of which part of the negative electrode active material particles was measured. This R value indicates 0 when the crystallinity of the sample is high, and increases as the crystallinity decreases. Since the R value was about 0.8, it was confirmed that the particles were uniformly coated with the carbon material having a relatively low crystallinity deposited by the CVD method.

(Thermogravimetric analysis)
The negative electrode active material prepared as described above was subjected to thermogravimetric analysis by the above-described method, and the weight ratio of each material was measured.

(XRD)
The negative electrode active material prepared as described above was subjected to X-ray diffraction by the method described above, and the average interplanar spacing d (002) of the carbon material was measured from the diffraction angle (2θ) of the X-ray diffraction pattern of CuKα rays.

(BET specific surface area)
About the negative electrode active material prepared as mentioned above, the BET specific surface area measurement was performed by the above-mentioned method.

(Charge / discharge characteristics)
The non-aqueous electrolyte secondary battery produced as described above was charged to 4.2 V at a current of 1 CmA at 25 ° C., and then charged for 2 hours at a constant voltage of 4.2 V, and then at a current of 1 CmA. The battery was discharged to 0V. This charging / discharging process was made into 1 cycle, and the 500-cycle charging / discharging test was done. The ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle (expressed as a percentage) was defined as the cycle capacity retention rate.

<Result>
Various measurement results regarding the above-described Examples and Comparative Examples are summarized in Table 1.
Examples 1 to 3 have a higher capacity retention rate than Comparative Example 1 that does not contain SiO _X , and a larger discharge capacity than Comparative Example 2 that does not contain Si. And the capacity | capacitance retention is high compared with the comparative example 3 which does not contain a carbon material in a composite particle. Furthermore, the discharge capacity is large as compared with Comparative Example 4 that does not contain Si and SiO _X.
When Example 1 is compared with Examples 2 and 3 in which composite particles are coated with a carbon material, Example 2 is superior in capacity retention.

<Examples 4 to 7 and Reference Example 1 >
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that the ratio of Si to the total amount of Si and SiO ₂ was as shown in Table 2.

Various measurement results regarding the above-mentioned examples are summarized in Table 2 together with the results of Example 2 and Comparative Examples 1 and 2.
In Examples 2 and 4 to 7 in which the ratio of the particles made of Si to the total of the particles made of Si and the particles made of SiO _X is 20 wt% or more and 80 wt% or less, the ratio of the particles made of Si is Compared with the reference example 1 which is 10 weight%, discharge capacity is large.

<Examples 8 to 13 >
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that the amount of artificial graphite mixed with Si and SiO ₂ was changed to the ratio shown in Table 3.

Table 3 summarizes various measurement results regarding the above examples.
Examples 9 to 12 in which the ratio of the artificial graphite to the whole negative electrode active material is 3% by weight or more and 60% by weight or less have a higher capacity retention than Example 8 in which the ratio of the artificial graphite is 1% by weight. On the other hand, compared with Example 13 in which the proportion of artificial graphite is 70% by weight, Examples 9 to 12 have a larger discharge capacity.

Examples 10 to 12 in which the ratio of the total carbon material to the whole negative electrode active material is 30% by weight or more and 80% by weight or less are Example 8 in which the ratio of the total carbon material is 21% by weight and 23% by weight, respectively. Compared to 9 , the capacity retention rate is high. Compared with Example 13 in which the proportion of the total carbon material is 90% by weight, Examples 10 to 12 have a large discharge capacity and a high capacity retention rate.

<Examples 14 to 16 >
As a carbon material to be mixed with Si and SiO ₂ , natural graphite was used in Example 14 , acetylene black was used in Example 15 , and vapor grown carbon fiber was used in Example 16 , instead of artificial graphite. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 2.

Various measurement results regarding the above-mentioned example are summarized in Table 4 together with the result of Example 2.
In Examples 2, 14 , and 16 in which the average surface distance d (002) is 0.3354 nm or more and 0.35 nm or less, the discharge capacity is larger than that in Example 15 in which d (002) is 0.37 nm, and the capacity The retention rate is also excellent.

<Examples 17 to 19 >
When the carbon material was coated by the CVD method, the negative electrode active material having the value shown in Table 5 as the amount of carbon coated on the surface of the composite particles was prepared by appropriately changing the reaction conditions. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that this negative electrode active material was used.

Various measurement results regarding the above-mentioned example are summarized in Table 5 together with the result of Example 2.
In Examples 2, 17 and 18 , in which the ratio of the carbon material covering the surface of the composite particles with respect to the whole negative electrode active material is 0.5 wt% or more and 40.0 wt% or less, the ratio of the carbon material is 60 wt% % and is compared to example 19, the discharge capacity is large, the capacity retention rate is high.

<Examples 20 to 22 >
A negative electrode active material having a BET specific surface area shown in Table 6 was prepared using Si, SiO ₂ , and artificial graphite having a predetermined specific surface area. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that this negative electrode active material was used.

Various measurement results regarding the above-mentioned example are summarized in Table 6 together with the result of Example 2.
In Examples 2, 20 and 21 , in which the negative electrode active material has a BET specific surface area of 10.0 m ² / g or less, the discharge capacity is large and the capacity retention rate is higher than that of Example 22 in which the BET specific surface area is 20 m ² / g. Is also expensive.

< Reference Example 2 >
By preparing composite particles by treating 60 parts by weight of particles containing Si and SiO ₂ at a weight ratio of 1: 1 and 40 parts by weight of artificial graphite in a nitrogen atmosphere at 25 ° C. for 30 minutes in a ball mill, An active material was prepared. A nonaqueous electrolyte secondary battery of Reference Example 2 was produced in the same manner as Example 1 except for the negative electrode active material.

< Reference Example 3 >
As a negative electrode active material, 40 parts by weight of particles containing Si and SiO ₂ at a weight ratio of 1: 1 and 40 parts by weight of artificial graphite were treated in a nitrogen atmosphere at 25 ° C. for 30 minutes by a ball mill to prepare composite particles. Then, the nonaqueous electrolyte of Reference Example 3 was used in the same manner as Reference Example 2 except that the composite particles were coated with a carbon material by a method of thermally decomposing methane at 900 ° C. (CVD). A secondary battery was produced.

< Reference Example 4 >
A nonaqueous electrolyte secondary battery of Reference Example 4 was produced in the same manner as Reference Example 3 , except that SiO was used instead of SiO ₂ .

For the negative electrode active materials of Reference Examples 2 to 4 , the Raman spectroscopic analysis, thermogravimetric analysis, XRD, and BET specific surface area were measured in the same manner as in Example 1. The charge / discharge characteristics of the nonaqueous electrolyte secondary batteries of Reference Examples 2 to 4 were measured in the same manner as in Example 1. The results are shown in Table 7. For comparison, Table 7 also shows data of Comparative Examples 1 to 4 shown in Table 1.

<Result>
Reference Examples 2 to 4 have a higher capacity retention rate than Comparative Example 1 that does not contain SiO _X , and a larger discharge capacity than Comparative Example 2 that does not contain Si. And the capacity | capacitance retention is high compared with the comparative example 3 which does not contain a carbon material in a composite particle. Furthermore, the discharge capacity is large as compared with Comparative Example 4 that does not contain Si and SiO _X.
When Reference Example 2 is compared with Reference Examples 3 and 4 in which composite particles are coated with a carbon material, Reference Examples 3 and 4 have excellent capacity retention.

< Reference Examples 5 to 9 >
Nonaqueous electrolyte secondary batteries of Reference Examples 5 to 9 were produced in the same manner as Reference Example 3 except that the ratio of Si in the particles containing Si and SiO ₂ was as shown in Table 8.
Various measurement results for Reference Examples 5 to 9 are summarized in Table 8 together with the results of Reference Example 3 and Comparative Examples 1 and 2.

In Reference Example 3 and 6 to 9 in which the proportion of Si in the particles containing Si and SiO ₂ is 20 wt% or more and 80 wt% or less, compared to Reference Example 5 in which the proportion of Si is 10 wt%, Large discharge capacity.

< Reference Examples 10 to 15 >
The nonaqueous electrolyte secondary batteries of Reference Examples 10 to 15 were manufactured in the same manner as Reference Example 3 except that the amount of artificial graphite mixed with particles containing Si and SiO ₂ was changed to the ratio shown in Table 9. Produced.
Various measurement results on to 1 5 Reference Example 10 are summarized in Table 9.

Reference Examples 11 to 14 in which the proportion of artificial graphite with respect to the whole negative electrode active material is 3 wt% or more and 60 wt% or less have a higher capacity retention than Reference Example 10 in which the proportion of artificial graphite is 1 wt%. On the other hand, compared with Reference Example 15 in which the proportion of artificial graphite is 70% by weight, Reference Examples 11 to 14 have a larger discharge capacity.

Further, to no Example 12 or less 30 wt% to 60 wt% fraction of the total carbon material to the entire negative electrode active material 14, 21 wt% fraction of the total carbon material respectively, Example 10 is 23 wt%, Compared to 11 , the capacity retention rate is high. Compared with Reference Example 15 in which the proportion of the entire carbon material is 90% by weight, Reference Examples 12 to 14 have a large discharge capacity and a high capacity retention rate.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.

  In the above-described embodiment, the prismatic nonaqueous electrolyte secondary battery 21 has been described. However, the battery structure is not particularly limited, and may be a cylindrical shape, a bag shape, a lithium polymer battery, or the like.

10, 16 ... Composite particles 11 ... Si particles 12 ... SiO _X particles 13 ... Carbon material A
14 ... Carbon material B
15 ... Particles containing Si and SiO _X

Claims (1)

In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte, the negative electrode active material comprises particles made of silicon Si, silicon oxide SiO _X (Provided that the ratio of the silicon Si to the total of the silicon Si and the silicon oxide SiO _X is 20% by weight, including composite particles composed of particles composed of 0 <X ≦ 2) and a carbon material. A nonaqueous electrolyte secondary battery characterized by being 80 wt% or less.

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