JP2010092830A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a nonaqueous electrolyte secondary battery with high capacity and excellent in cycle characteristics, by improving an anode active material and nonaqueous electrolyte solution for using the nonaqueous electrolyte secondary battery. <P>SOLUTION: In the nonaqueous electrolyte secondary battery equipped with a cathode 11 containing a cathode active material capable of absorbing/emitting lithium ions, an anode 12 containing an anode active material capable of absorbing/emitting lithium ions, and nonaqueous electrolyte solution, the anode active material is processed with the use of a first material consisting of a graphite material and a second material of a complex body having a graphite material and silicon or silicon compound with amorphous carbon material coated and ratio of silicon in the complex body to be 17 mass% or more and 30 mass% or less, a ratio of the second material in the anode active material is made to be 5 mass% or more and 13 mass% or less, and also, cyclic carbonate derivative containing fluorine atom is added into the nonaqueous electrolyte solution. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte. In particular, the present invention is characterized in that a negative electrode active material and a non-aqueous electrolyte solution are improved to obtain a non-aqueous electrolyte secondary battery having a high capacity and greatly improved cycle characteristics. .

  In recent years, non-aqueous electrolyte secondary batteries that use non-aqueous electrolyte and charge and discharge by moving lithium ions between the positive and negative electrodes have been used as power sources for portable electronic devices and power storage. Has been.

  In such a nonaqueous electrolyte secondary battery, a graphite material is widely used as a negative electrode active material in the negative electrode.

  Here, in the case of a graphite material, the discharge potential is flat and the lithium ions are inserted and desorbed between the graphite crystal layers to be charged / discharged. There is an advantage that the volume change is small.

On the other hand, in recent years, there has been a demand for a non-aqueous electrolyte secondary battery having a higher capacity in order to cope with the multifunctional and high performance of portable electronic devices, etc. The theoretical capacity of LiC _{6 was} as small as 372 mAh / g, and there was a problem that it was not possible to sufficiently meet the above demands.

  Therefore, in recent years, it has been studied to use silicon, tin, aluminum, or the like that forms an alloy with lithium ions as a high-capacity negative electrode active material. In particular, in the case of silicon, the theoretical capacity per unit mass is about 4200 mAh. Since it is very large as / g, various studies have been made for practical use.

  However, silicon or the like that forms an alloy with lithium ions has a problem that the volume change accompanying the insertion and extraction of lithium ions is large, and the cycle characteristics of the nonaqueous electrolyte secondary battery are deteriorated.

For this reason, conventionally, as disclosed in Patent Document 1, silicon, tin, or the like that forms an alloy with lithium ions is used as the negative electrode active material, and the first made of LiB (C ₂ O ₄ ) ₂ is used.
A non-aqueous electrolyte solution containing a non-aqueous electrolyte solution containing a second electrolyte salt such as LiPF ₆ and a carbonate ester derivative having a halogen atom such as 4-fluoroethylene carbonate in a solvent. In order to improve the cycle characteristics, the non-aqueous electrolyte is prevented from reacting and decomposing with the negative electrode active material such as silicon or tin that forms an alloy with lithium ions. Has been proposed.

  However, when silicon, tin, or the like that forms an alloy with lithium ions is used as the negative electrode active material, the volume change due to charge / discharge is large as described above, and the expansion / contraction of the negative electrode active material is increased. As a result, there was a problem in that the electron conductivity in the battery decreased, the capacity decreased intermittently, and the cycle characteristics of the nonaqueous electrolyte secondary battery could not be sufficiently improved.

  In recent years, as disclosed in Patent Documents 2 to 4, the negative electrode active material is supported with silicon, aluminum, or the like that forms an alloy with lithium ions on the surface of the carbon particles, and the surface of the carbon particles is further carbonized. Using a composite carbonaceous material coated with a material, volume changes such as silicon and aluminum that accompany occlusion / release of lithium ions are absorbed by the above carbon particles to prevent a decrease in electronic conductivity between the negative electrode active materials. However, a battery that improves the cycle characteristics of a non-aqueous electrolyte secondary battery has been proposed.

  However, even when a composite carbonaceous material in which silicon, aluminum, or the like is supported on the surface of the carbon particles and the surface of the carbon particles is coated with a carbon material is used in the negative electrode active material, The non-aqueous electrolyte solution decomposes by continuously reacting with the above-mentioned silicon and aluminum contained in the composite carbonaceous material and the carbon on the surface of the composite carbonaceous material, thereby improving the cycle characteristics of the non-aqueous electrolyte secondary battery. There was a problem that it could not be improved sufficiently.

JP 2005-228565 A Japanese Patent No. 3369589 JP 2007-87956 A JP 2008-27897 A

  An object of the present invention is to solve the above problems in a non-aqueous electrolyte secondary battery.

  Then, the present inventors use a composite carbonaceous material in which the negative electrode active material carries silicon, aluminum, or the like on the surface of the carbon particles as described above, and the surface of the carbon particles is covered with a carbon material, The use of a non-aqueous electrolyte containing a cyclic carbonate derivative having a halogen atom such as 4-fluoroethylene carbonate was studied.

  However, even when the negative electrode active material and the non-aqueous electrolyte are used in combination, the non-aqueous electrolyte continuously reacts with the carbon on the surface of the composite carbonaceous material and decomposes. When charging / discharging was repeated, it was found that the carbonic acid ester derivative having a halogen atom such as 4-fluoroethylene carbonate in the non-aqueous electrolyte was consumed and the cycle characteristics were deteriorated.

  In the present invention, in order to solve such a problem, the negative electrode active material used in the nonaqueous electrolyte secondary battery is further improved, and the nonaqueous electrolyte secondary battery has a high capacity and further improved cycle characteristics. It is a problem to be able to obtain.

  In the present invention, in order to solve the above problems, a positive electrode including a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, and non-aqueous electrolysis In a non-aqueous electrolyte secondary battery comprising a liquid, a composite in which the negative electrode active material is coated with a first material made of a graphite material, and a graphite material and silicon or a silicon compound with an amorphous carbon material. And the second material having a silicon ratio of 17% by mass or more and 30% by mass or less in the composite, and the ratio of the second material in the negative electrode active material is 5% by mass or more and 13% by mass or less. The cyclic carbonate derivative having a fluorine atom is added to the non-aqueous electrolyte.

  In the nonaqueous electrolyte secondary battery according to the present invention, as described above, a composite in which the negative electrode active material is coated with the first material made of a graphite material and the graphite material and silicon or a silicon compound with an amorphous carbon material. Therefore, the packing density of the negative electrode active material is improved as compared with the case where a composite in which a graphite material and silicon or a silicon compound are coated with an amorphous carbon material is used alone. Thus, a sufficient battery capacity can be obtained, and the initial charge / discharge efficiency can be improved.

  Further, in the non-aqueous electrolyte secondary battery according to the present invention, the cyclic carbonate derivative having a fluorine atom is added to the non-aqueous electrolyte as described above. A stable film is formed on the surface of the negative electrode active material during discharge, and the nonaqueous electrolyte is suppressed from reacting and decomposing with the negative electrode active material during charge and discharge, and the nonaqueous electrolyte secondary Cycle characteristics in the battery are improved.

  In the non-aqueous electrolyte secondary battery according to the present invention, since the proportion of silicon in the composite is 17% by mass or more as a composite of the second material in the negative electrode active material, the non-aqueous electrolyte secondary battery Since the capacity of the secondary battery is further improved and the ratio of silicon in the composite is 30% by mass or less, the volume change of the composite during charging / discharging is reduced, and the charge of the nonaqueous electrolyte secondary battery is reduced. The deterioration of the discharge cycle characteristics is further prevented.

  In the nonaqueous electrolyte secondary battery according to the present invention, the ratio of the second material made of a composite in which the graphite material and silicon or a silicon compound are coated with an amorphous carbon material in the negative electrode active material described above is set. Since the content is 5% by mass or more, the capacity of the non-aqueous electrolyte secondary battery is further improved, and since the ratio of the second material is 13% by mass or less, the surface of the second material made of this composite during the charge / discharge cycle Therefore, the decomposition of the nonaqueous electrolyte solution to which the cyclic carbonate derivative having a fluorine atom is added is suppressed, and the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery are further prevented from being deteriorated. . In order to more appropriately suppress the decomposition of the nonaqueous electrolytic solution to which the cyclic carbonate derivative having a fluorine atom is added on the surface of the second material made of this composite, The ratio of the second material is preferably 10% by mass or less.

  As a result, in the present invention, a nonaqueous electrolyte secondary battery having a high capacity and excellent charge / discharge cycle characteristics can be obtained.

It is the partial cross section explanatory drawing and schematic perspective view of the flat electrode body produced in the Example and comparative example of this invention. It is a schematic plan view of the nonaqueous electrolyte secondary battery produced in said Example and comparative example.

  Next, an embodiment of the nonaqueous electrolyte secondary battery according to the present invention will be specifically described. In addition, the nonaqueous electrolyte secondary battery in this invention is not limited to what was shown to the following embodiment, In the range which does not change the summary, it can implement suitably.

  In the non-aqueous electrolyte secondary battery of the present invention, as described above, a composite in which the negative electrode active material is coated with the first material made of a graphite material and the graphite material and silicon or a silicon compound with an amorphous carbon material. The second material made of is used.

Here, as the graphite material in the first material, it is preferable to use artificial graphite or natural graphite having excellent charge / discharge characteristics and the like. Generally, the lattice spacing d002 measured by the X-ray diffraction method is used.
Is preferably 0.337 nm or less, and graphite having a c-axis direction crystallite size Lc of 30 nm or more. Moreover, as this graphite material, it is preferable to use a material having an average particle diameter (median diameter D50) in a range of 10 to 25 μm at a mass integral of 50%.

  Further, as the graphite material in the first material, it is also possible to use carbon-coated graphite in which the surface of artificial graphite or natural graphite is further coated with a carbonaceous material. Here, as a precursor of the carbonaceous material covering the surface of artificial graphite or natural graphite, a pitch material, a tar material, a resin material such as a vinyl resin, a cellulose resin, or a phenol resin is used. be able to.

  Further, in the second material comprising a composite in which a graphite material and silicon or a silicon compound are coated with an amorphous carbon material, the silicon may be any of single crystal silicon, polycrystalline silicon, and amorphous silicon. However, it is preferable to use polycrystalline silicon or amorphous silicon having a crystallite size of 60 nm or less. This is because in the case of polycrystalline silicon or amorphous silicon having a crystallite size of 60 nm or less, the orientation of the crystallite is disordered, so that cracks occur at the crystallite interface of one particle during charge and discharge. In this case, cracks are difficult to propagate, the structure of the composite is prevented from being destroyed, and the charge / discharge cycle characteristics are prevented from being deteriorated.

  In addition, as the silicon compound, a silicon alloy in which a metal element such as nickel, copper, cobalt, chromium, iron, silver, titanium, molybdenum, or tungsten and silicon are made amorphous, or silicon oxide is used. it can.

In addition, if the particle size of the silicon or silicon compound is too large, the expansion / contraction of the composite during charge / discharge increases, making it difficult to maintain the structure of the composite. Since the charge / discharge cycle characteristics of the secondary battery are degraded, it is preferable to use a silicon or silicon compound having an average particle diameter (median diameter D50) in the range of 0.1 to 10 μm at a mass integral of 50%. More preferably, a material in the range of 0.1 to 3 μm is used. In addition, when obtaining silicon or silicon compound having the above particle diameter, silicon or silicon compound can be obtained by pulverizing by dry pulverization method such as jet mill or ball mill, or wet pulverization method such as bead mill or ball mill. .

Further, as the graphite material in the composite, it is preferable to use a material excellent in charge / discharge characteristics, etc., and artificial graphite, natural graphite, graphitized mesophase spheroids, etc. can be used. It is preferable to use graphite having a measured lattice spacing d002 of 0.337 nm or less and a crystallite size Lc in the c-axis direction of 30 nm or more.

Here, if the particle size of the graphite material in the composite is too small, a side reaction occurs with the non-aqueous electrolyte during the first charge / discharge, the initial efficiency is reduced, and the capacity of the non-aqueous electrolyte secondary battery is reduced. On the other hand, if the particle size of the graphite material becomes too large, the expansion / contraction of the silicon or silicon compound during charge / discharge cannot be sufficiently relaxed, and the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery are reduced. descend. For this reason, as a graphite material in the composite, the mass integral is 50%.
It is preferable to use those having an average particle diameter (median diameter D50) in the range of 1 to 25 μm, more preferably 5 to 20 μm.

  In addition, as the amorphous carbon material in the above composite, as a precursor, a pitch material, a tar material, a resin material such as a vinyl resin, a cellulose resin, or a phenol resin is used. What was carbonized at the temperature of 700-1300 degreeC in inert gas atmosphere, such as nitrogen, argon, helium, can be used.

  In addition, as the above-mentioned composite, it is possible to use a composite obtained by attaching silicon or a silicon compound to the surface of a graphite material and coating the surface with an amorphous carbon material. Those coated with can also be used.

  Here, when the surface of the composite is coated with a carbonaceous material, as a precursor of the carbonaceous material, the pitch-based material, tar-based material, vinyl-based resin, cellulose-based resin, phenol-based resin, etc. Using a resin-based material, this is applied to the surface of the composite, and carbonized at a temperature of 700 to 1300 ° C. in an inert gas atmosphere such as nitrogen, argon, helium, etc. as described above. Can be coated with a carbonaceous material.

  In preparing a negative electrode using the negative electrode active material as described above, a negative electrode mixture containing the negative electrode active material, a conductive agent, and a binder may be applied to the surface of the negative electrode current collector. it can.

  Here, the material of the negative electrode current collector may be a conductive material excellent in reduction resistance. For example, copper, nickel, an alloy containing these, and the like can be used.

  Moreover, as said electrically conductive agent, acetylene black, graphite, carbon black etc. can be used, for example. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, EPDM, SBR, NBR, and fluororubber.

In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode active material used for the positive electrode is not particularly limited as long as it is a material that can occlude and release lithium ions and has a noble potential, and is generally used. A known positive electrode active material can be used. For example, lithium cobalt complex oxides such as LiCoO _2, lithium-nickel composite oxides such as _{LiNiO 2, LiMn 2 O 4,} LiMnO lithium-manganese composite oxides such as _{2, LiNi 1-x Co x} O 2 (0 <X <1) and other lithium / nickel / cobalt composite oxides, LiMn _1-x Co _x O ₂ (
Lithium / manganese / cobalt composite oxide such as 0 <x <1), LiNi _x Co _y Mn _z O ₂ (x + y + z = 1) and other lithium / nickel / cobalt / manganese composite oxide, LiNi _x
Li-containing transition metal oxides such as lithium / nickel / cobalt / aluminum composite oxides such as Co _y Al _z O ₂ (x + y + z = 1), manganese oxides such as MnO ₂ , vanadium oxides such as V ₂ O ₅ Such metal oxides, other oxides and sulfides can be used.

Furthermore, it is preferable that the positive electrode active material includes a lithium / nickel composite oxide containing at least nickel. When a positive electrode active material containing a lithium / nickel composite oxide is used, Li ₂ CO ₃ is generated on the surface of the positive electrode active material with a charge / discharge cycle. The produced Li ₂ CO ₃ reacts with a trace amount of H ₂ O present in the electrolytic solution to generate CO ₂ . The generated CO ₂ works well on the organic compound film formed on the surface of the second material in accordance with the charge / discharge cycle, and the cycle characteristics are further improved.

  And when producing a positive electrode using the above positive electrode active materials, for example, a positive electrode mixture containing the above positive electrode active material, a conductive agent and a binder is applied to the surface of the positive electrode current collector. be able to.

  Here, the material of the positive electrode current collector may be a conductive material excellent in oxidation resistance, and for example, aluminum, stainless steel, titanium, or the like can be used.

  Moreover, as said electrically conductive agent, acetylene black, graphite, carbon black etc. can be used, for example. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, EPDM, SBR, NBR, and fluororubber.

  Further, as the non-aqueous electrolyte in the non-aqueous electrolyte secondary battery of the present invention, a solution obtained by dissolving a solute in a generally used non-aqueous solvent can be used.

  Further, the above non-aqueous solvent is not particularly limited, and those commonly used can be used, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl A mixed solvent of a chain carbonate such as carbonate or a mixed solvent of a cyclic carbonate and an ether solvent such as 1,2-dimethoxyethane or 1,2-diethoxyethane can be used.

Further, the solute is not particularly limited, and those commonly used can be used. For example, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , L
iN (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 , a mixture thereof, or the like can be used.

  Examples of the cyclic carbonate derivative having a fluorine atom to be added to the non-aqueous electrolyte include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolane. -2-one, 4,5-difluoro-1,3-dioxolan-2-one, 4- (fluoromethyl) -1,3-dioxolan-2-one, 4- (trifluoromethyl) -1,3- Dioxolan-2-one can be used, and preferably 4-fluoro-1,3-dioxolan-2-one is used.

  When the cyclic carbonate derivative having such a fluorine atom is added to the non-aqueous electrolyte, if the amount added to the non-aqueous electrolyte is less than 0.1% by mass, the cycle of the non-aqueous electrolyte secondary battery While the effect of sufficiently improving the characteristics cannot be obtained, when the addition amount is 30% by mass or more, when stored in a charged state at a high temperature, it reacts with the negative electrode active material and decomposes, so that the battery It becomes easy to swell. For this reason, it is preferable to add such a cyclic carbonate derivative having a fluorine atom in a range of 0.1% by mass or more and less than 30% by mass with respect to the nonaqueous electrolytic solution.

  Moreover, it is preferable to add vinylene carbonate to the non-aqueous electrolyte together with the cyclic carbonate derivative having the fluorine atom.

  As described above, when vinylene carbonate is added together with the cyclic carbonate derivative having a fluorine atom to the non-aqueous electrolyte, the vinylene carbonate is decomposed, and the surface of the second material composed of the composite in the negative electrode active material is formed. A stable organic coating is formed, thereby suppressing excessive decomposition of the cyclic carbonate derivative having a fluorine atom, and the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery are further improved.

  Here, when adding vinylene carbonate to the non-aqueous electrolyte as described above, if the amount is small, the above effects cannot be obtained sufficiently, while if the amount is too large, the initial efficiency is lowered. As a result, the capacity of the non-aqueous electrolyte secondary battery decreases. For this reason, it is preferable to make the quantity of vinylene carbonate added with respect to a non-aqueous electrolyte into the range of 0.1 mass% or more and less than 10 mass%.

  Next, the non-aqueous electrolyte secondary battery according to the present invention will be specifically described with reference to examples, and in the non-aqueous electrolyte secondary battery according to this example, the cycle characteristics are improved. To clarify.

Example 1
In Example 1, a positive electrode, a negative electrode, and a non-aqueous electrolyte prepared as described below were used.

[Production of positive electrode]
In producing the positive electrode, Li ₂ CO ₃ and Co ₃ O ₄ were mixed in an Ishikawa type mortar so that the molar ratio of Li and Co was 1: 1, and then mixed in an air atmosphere. And then heat-treated at 850 ° C. for 20 hours, and then pulverized to obtain a lithium-cobalt composite oxide made of LiCoO _{2 as} the positive electrode active material.

  The mass ratio of the positive electrode active material, the conductive agent carbon, and the polyvinylidene fluoride binder is 95: 2.5: 2.5, and the dispersion medium N-methyl-2-pyrrolidone is added thereto. Were added and kneaded to prepare a positive electrode mixture slurry.

Next, this positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector made of aluminum foil, dried, and then rolled to prepare a positive electrode, and a positive electrode current collecting tab was attached to the positive electrode. The filling density of the positive electrode mixture in the positive electrode thus prepared was 3.60 g / cm ^3.
Met.

[Production of negative electrode]
In producing the negative electrode, the single crystal silicon raw material and the solvent methylnaphthalene were placed in a bead mill in a nitrogen gas atmosphere and wet pulverized, and the average particle diameter (median diameter D50) of the single crystal silicon was 0.2 μm. A single crystal silicon-containing slurry was obtained. The crystallite size of this single crystal silicon is equal to its particle size.

  Then, graphite and carbon pitch are added to and mixed with the above-mentioned single crystal silicon-containing slurry, and the mixture is carbonized and classified, and then carbon pitch is added to the resulting slurry to further carbonize the graphite and A second material composed of a composite in which silicon was coated with an amorphous carbon material was obtained. In addition, content of the silicon in the 2nd material which consists of this composite_body | complex was 20.9 mass%.

Further, as the first graphite material, the lattice spacing d002 measured by the X-ray diffraction method is 0.
. Artificial graphite having a crystallite size Lc of 116.1 nm in the c-axis direction of 3355 nm was used.

  And the 1st material which consists of said artificial graphite, and the 2nd material which consists of said composite were mixed so that mass ratio might be 88.8: 11.2, and the negative electrode active material was obtained.

  And in the aqueous solution which melt | dissolved the carboxymethylcellulose of the thickener in water, said negative electrode active material and SBR of a binder are 97.5: 1. Mass ratio of a negative electrode active material, a binder, and a thickener. 5: 1.0 was added and kneaded to prepare a negative electrode mixture slurry.

Next, the negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector made of copper foil, dried, and then rolled to produce a negative electrode. A negative electrode current collecting tab was attached to the negative electrode. The filling density of the negative electrode mixture in the negative electrode thus prepared was 1.60 g / cm ³ .

[Preparation of non-aqueous electrolyte]
In producing the non-aqueous electrolyte, lithium hexafluorophosphate LiPF ₆ is used as a solute at a concentration of 1 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7. 10.0 mass% of 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, was added to the nonaqueous electrolytic solution dissolved in the solution.

  And in producing a nonaqueous electrolyte secondary battery, as shown to FIG. 1 (A) and (B), said positive electrode 11 and the negative electrode 12 are passed through the separator 13 which consists of a microporous film made from a polypropylene. The flat electrode body 10 is manufactured by pressing it so as to face each other, and the positive electrode current collecting tab 11a and the negative electrode current collecting tab 12a provided on the positive electrode 11 and the negative electrode 12 are connected to the flat electrode body. 10 protruded.

  Next, as shown in FIG. 2, the flat electrode body 10 is housed in a battery container 20 made of an aluminum laminate film, and the non-aqueous electrolyte is added to the battery container 20. 11 and the negative electrode current collecting tab 12a provided on the negative electrode 12 are taken out to the outside, the opening of the battery container 20 is sealed, and the height is 6.2 cm and the width is 3.5 cm. A non-aqueous electrolyte secondary battery having a thickness of 3.6 mm was produced.

(Example 2)
In Example 2, in the preparation of the non-aqueous electrolyte in Example 1 above, 4-fluoro-1,3-dioxolane, which is a cyclic carbonate derivative having a fluorine atom, is used with respect to the non-aqueous electrolyte. The non-aqueous electrolyte secondary of Example 2 was added in the same manner as in Example 1 except that 10.0% by mass of 2-one was added and 2.0% by mass of vinylene carbonate was added. A battery was produced.

(Example 3)
In Example 3, as in Example 2 above, 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, was added to the non-aqueous electrolyte. While adding 10.0 mass%, what added 2.0 mass% vinylene carbonate was used.

  Further, in this Example 3, in the production of the negative electrode in Example 1 described above, the silicon content in the second material made of the above composite was made 22.8% by mass, and the artificial graphite was used. A negative electrode active material obtained by mixing the first material and the second material made of the above composite so that the mass ratio was 92.4: 7.6 was used.

  Except for these, the nonaqueous electrolyte secondary battery of Example 3 was fabricated in the same manner as in Example 1 above.

Example 4
In Example 4, as in Example 2 above, 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, was added to the non-aqueous electrolyte. While adding 10.0 mass%, what added 2.0 mass% vinylene carbonate was used.

Further, in this Example 4, in the production of the negative electrode in Example 1 described above, in obtaining the second material composed of a composite in which graphite and silicon are coated with an amorphous carbon material, the single crystal silicon described above is used. Instead of using polycrystalline silicon produced by a thermal reduction method using high-purity silane trichloride SiHCl ₃ as a raw material, the silicon content in the second material composed of the composite is 18.6% by mass, and A negative electrode active material in which a first material made of artificial graphite and a second material made of the above composite were mixed at a mass ratio of 91.5: 8.5 was used.

  Except for these, the nonaqueous electrolyte secondary battery of Example 4 was fabricated in the same manner as in Example 1 above.

(Example 5)
In Example 5, as in Example 2 above, 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, was added to the non-aqueous electrolyte. While adding 10.0 mass%, what added 2.0 mass% vinylene carbonate was used.

  Further, in this Example 5, in the production of the negative electrode in Example 1 described above, the silicon content in the second material made of the above composite was set to 22.0% by mass, and the artificial graphite was used. A negative electrode active material obtained by mixing the first material and the second material made of the above composite so that the mass ratio was 92.4: 7.6 was used.

Further, in this embodiment 5, in the preparation of the positive electrode in Example 1 above, and LiOH, composite hydroxide containing nickel _{(Ni 0.80 Co 0.15 Al 0.05 (} OH) 2) and, Lithium / nickel composite oxide obtained by mixing in an Ishikawa type mortar with a molar ratio of 1.05: 1 and then pulverizing after heat treatment at 720 ° C. for 20 hours in an oxygen atmosphere. I used it.

  A nonaqueous electrolyte secondary battery of Example 5 was made in the same manner as in Example 1 except for those described above.

(Comparative Example 1)
In Comparative Example 1, as in Example 2 above, 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, was added to the nonaqueous electrolyte solution in the manner of 10. While adding 0% by mass, 2.0% by mass of vinylene carbonate was added.

  Further, in Comparative Example 1, in the production of the negative electrode in Example 1 described above, the silicon content in the second material made of the composite was 4.0% by mass, and the artificial graphite was used. A negative electrode active material in which a first material and a second material made of the above composite were mixed so as to have a mass ratio of 45.0: 55.0 was used.

  Except for these, the nonaqueous electrolyte secondary battery of Comparative Example 1 was fabricated in the same manner as in Example 1 above.

(Comparative Example 2)
In Comparative Example 2, as in Example 2 described above, 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, was added to the non-aqueous electrolyte solution in an amount of 10. While adding 0% by mass, 2.0% by mass of vinylene carbonate was added.

  Further, in Comparative Example 2, in the production of the negative electrode in Example 1 described above, the silicon content in the second material made of the composite was set to 15.8% by mass, and the artificial graphite was used. A negative electrode active material obtained by mixing the first material and the second material composed of the above composite so that the mass ratio was 85.8: 14.2 was used.

  Except for these, a nonaqueous electrolyte secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 above.

(Comparative Example 3)
In Comparative Example 3, as in Example 2 described above, 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, was added to the nonaqueous electrolytic solution in an amount of 10. While adding 0% by mass, 2.0% by mass of vinylene carbonate was added.

  Further, in Comparative Example 3, in the production of the negative electrode in Example 1 above, the silicon content in the second material made of the composite was set to 19.0% by mass, and the artificial graphite was used. A negative electrode active material in which a first material and a second material made of the above composite were mixed so that the mass ratio was 85.5: 14.5 was used.

  Except for these, a nonaqueous electrolyte secondary battery of Comparative Example 3 was produced in the same manner as in Example 1 above.

  First, the nonaqueous electrolyte secondary batteries of Examples 1 and 2 and Comparative Example 1 manufactured as described above were charged under a room temperature condition until the battery voltage reached 4.2 V at a constant current of 800 mA. The battery is further charged with a constant voltage of 4.2 V until the current value reaches 40 mA, and then discharged with a constant current of 800 mA until the battery voltage reaches 2.75 V, and the discharge capacity Q1 of the first cycle is obtained for each. It was.

Then, each of the nonaqueous electrolyte secondary batteries of Examples 1 and 2 and Comparative Example 1 was repeatedly charged and discharged for 200 cycles in the same manner as in the first cycle, and each of the 200th cycle. The discharge capacity Q200 was determined, the capacity retention rate after 200 cycles was determined by the following formula, and the results are shown in Table 1 below. In the following table, 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, is abbreviated as FEC, and vinylene carbonate is abbreviated as VC.
Capacity maintenance rate after 200 cycles (%) = Q200 ÷ Q1 × 100

  As a result, in the case of using a nonaqueous electrolytic solution to which 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, is used, the negative electrode active material is made of a graphite material. A first material and a second material made of a composite in which a graphite material and silicon or a silicon compound are coated with an amorphous carbon material are used, and the silicon content in the composite is 17% by mass to 30% by mass. In the following, each nonaqueous electrolyte secondary battery of Examples 1 and 2 in which the ratio of the second material in the negative electrode active material is 5% by mass or more and 13% by mass or less has a silicon ratio in the above composite. Compared to the non-aqueous electrolyte secondary battery of Comparative Example 1 in which the ratio of the second material in the negative electrode active material is less than 17% by mass of 4.0% by mass and 55.0% by mass exceeding 13% by mass. Large charge / discharge cycle characteristics It was improved.

  Further, the nonaqueous electrolyte of Example 2 in which vinylene carbonate was added together with 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, to the above nonaqueous electrolytic solution. The secondary battery had further improved charge / discharge cycle characteristics as compared with the nonaqueous electrolyte secondary battery of Example 1 in which vinylene carbonate was not added to the nonaqueous electrolyte.

  Next, a nonaqueous electrolytic solution in which 10.0% by mass of 4-fluoro-1,3-dioxolan-2-one, which is a cyclic carbonate derivative having a fluorine atom, and 2.0% by mass of vinylene carbonate are added. For each of the nonaqueous electrolyte secondary batteries of Examples 2 to 5 and Comparative Examples 2 and 3 used, charging was performed at a constant current of 800 mA until the battery voltage reached 4.2 V under the room temperature conditions as described above. Further, after charging at a constant voltage of 4.2 V until the current value reaches 40 mA, each of the nonaqueous electrolyte secondary batteries of Examples 2 to 5 and Comparative Examples 2 and 3 has a battery voltage of 2. The battery was discharged until it reached 75 V, and the discharge capacity Q1 of the first cycle was determined for each.

Then, each of the nonaqueous electrolyte secondary batteries of Examples 2 to 5 and Comparative Examples 2 and 3 was repeatedly charged and discharged for 300 cycles in the same manner as in the first cycle, and 300 cycles for each. The discharge capacity Q300 of the eye was determined, the capacity retention rate after 300 cycles was determined by the following formula, and the results are shown in Table 2 below.
Capacity maintenance rate after 300 cycles (%) = Q300 ÷ Q1 × 100

  As a result, in the case of using a non-aqueous electrolyte solution in which a cyclic carbonate derivative having a fluorine atom and vinylene carbonate are used, the negative electrode active material includes a first material made of a graphite material, a graphite material and silicon or silicon. And a second material made of a composite coated with an amorphous carbon material, and the silicon content in the composite is 17% by mass to 30% by mass, and the second material in the negative electrode active material In each of the nonaqueous electrolyte secondary batteries of Examples 2 to 5 having a ratio of 5 mass% to 13 mass%, the ratio of silicon in the above composite was 15.8 mass% with a ratio of 17 mass% or less. Yes, Comparative Example 2 in which the ratio of the second material in the negative electrode active material is 14.2% by mass exceeding 13% by mass, and the ratio of silicon in the composite is 17% by mass to 30% by mass But Compared to the non-aqueous electrolyte secondary battery of Comparative Example 3 in which the ratio of the second material became 14.5 wt% of more than 13 wt% in the anode active material, the charge-discharge cycle characteristics were significantly improved.

  Moreover, when comparing the nonaqueous electrolyte secondary batteries of Examples 2 to 4, the nonaqueous electrolyte secondary batteries of Examples 3 and 4 in which the ratio of the second material in the negative electrode active material was 10% by mass or less were In addition, the charge / discharge cycle characteristics are further improved as compared with the nonaqueous electrolyte secondary battery of Example 2 in which the ratio of the second material in the negative electrode active material exceeds 10% by mass. The nonaqueous electrolyte secondary battery of Example 4 using polycrystalline silicon having a size of 60 nm or less is the nonaqueous electrolyte secondary battery of Example 3 using single crystal silicon having a crystallite size exceeding 60 nm as silicon in the composite. The charge / discharge cycle characteristics were further improved by the battery.

  Further, when comparing the non-aqueous electrolyte secondary batteries of Examples 3 and 5, the non-aqueous electrolyte secondary battery of Example 5 using a lithium-nickel composite oxide as the positive electrode active material was obtained by using lithium The charge / discharge cycle characteristics were further improved as compared with the nonaqueous electrolyte secondary battery of Example 3 using a cobalt composite oxide.

DESCRIPTION OF SYMBOLS 10 Flat electrode body 11 Positive electrode 11a Positive electrode current collection tab 12 Negative electrode 12a Negative electrode current collection tab 13 Separator 20 Battery container

Claims (7)

  In a non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte, A composite in which a negative electrode active material is coated with a first material made of a graphite material and a graphite material and silicon or a silicon compound with an amorphous carbon material, and the proportion of silicon in the composite is 17% by mass or more and 30% by mass. A second material that is less than or equal to mass%, the ratio of the second material in the negative electrode active material is set to 5 mass% or more and 13 mass% or less, and the non-aqueous electrolyte includes a cyclic atom having a fluorine atom. A non-aqueous electrolyte secondary battery comprising a carbonate ester derivative added thereto.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein vinylene carbonate is added to the nonaqueous electrolyte solution together with the cyclic carbonate derivative having a fluorine atom. battery.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the cyclic carbonate derivative having a fluorine atom is 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro. A non-aqueous electrolyte secondary battery comprising at least one selected from 1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the cyclic carbonate derivative having a fluorine atom is 0.1% by mass with respect to the nonaqueous electrolyte. A nonaqueous electrolyte secondary battery characterized by being added in a range of less than 30% by mass.   5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material contains a lithium / nickel composite oxide containing at least nickel. Secondary battery.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein a crystallite size of silicon or a silicon compound in the composite is 60 nm or less. Secondary battery. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein a ratio of the second material in the negative electrode active material is 5% by mass or more and 10% by mass or less. A non-aqueous electrolyte secondary battery.

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