JP6647211B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte containing a negative electrode active material containing a specific carbon material and a specific polyvalent carboxylate compound.

  With the spread of portable electronic devices such as portable personal computers, handy video cameras and information terminals in recent years, non-aqueous electrolyte secondary batteries having high voltage and high energy density have been widely used as power sources. Also, from the viewpoint of environmental issues, a battery-powered vehicle or a hybrid vehicle using electric power as a part of power has been put to practical use.

In recent years, non-aqueous electrolyte secondary batteries have been required to have higher performance from the viewpoint of higher performance of hybrid vehicles, and there is an urgent need to improve the performance. Specifically, the discharge capacity is an important characteristic so that the current, which is the energy source of the hybrid vehicle, can be sufficiently supplied. In addition, in order to enable charging in a short time, the non-aqueous electrolyte secondary battery preferably maintains a high charging capacity up to a high current density, and is required to have a high charging capacity maintenance rate.
Furthermore, a hybrid vehicle also needs to have long-term reliability, that is, less capacity degradation after long-term use than a portable electronic device.
In order to provide a non-aqueous electrolyte secondary battery suitable for such hybrid vehicles, artificial graphite which has been used as a negative electrode active material in portable electronic devices such as portable personal computers, handy video cameras, and information terminals has been used. On the other hand, in the case of a highly crystalline carbon material such as natural graphite, the distance between carbon layers is small, so that smooth insertion and removal of lithium ions is difficult, and a high charge capacity retention rate cannot be satisfied.
For this reason, attention has been focused on low-crystalline carbon materials capable of smoothly inserting and removing lithium ions.

  On the other hand, non-aqueous electrolyte secondary batteries have a negative electrode active material that undergoes reductive decomposition on the surface of the negative electrode active material made of a carbon material, regardless of whether it is high-crystalline carbon or low-crystalline carbon during initial charging. A film called SEI (Solid Electrolyte Interface) is formed on the surface. Although this film has an effect of suppressing the decomposition of the electrolyte solution in the negative electrode, there is a problem that if the stability of the film is low, reductive decomposition of the electrolyte solution occurs due to repetition of charge and discharge, causing deterioration of the battery capacity. .

For this reason, in the non-aqueous electrolyte secondary battery, various additives for the non-aqueous electrolyte have been proposed in order to improve the stability and electric characteristics of the non-aqueous electrolyte secondary battery. Such additives include 1,3-propane sultone (see, for example, Patent Document 1), vinylethylene carbonate (for example, see Patent Document 2), vinylene carbonate (for example, see Patent Document 3), 1, 3-propane sultone, butane sultone (for example, see Patent Document 4), vinylene carbonate (for example, see Patent Document 5), vinylethylene carbonate (for example, see Patent Document 6), and among others, vinylene has been proposed. Carbonate is widely used because of its great effect. It is thought that these additives form a stable film called SEI on the surface of the negative electrode, and this film covers the surface of the negative electrode, thereby suppressing the reductive decomposition of the electrolytic solution. In addition, a silylbenzene-based additive (for example, see Patent Document 8), a polyvalent carboxylic acid silyl ester-based additive (for example, see Patent Document 9), and the like are disclosed.
However, the electrolyte additives reported so far are electrolyte additives applied to highly crystalline carbon materials such as artificial graphite and natural graphite. Not detailed in the literature.
A highly crystalline carbon material such as graphite has a high potential on the surface of the negative electrode active material, and thus has high reactivity with the electrolytic solution and additives, so that SEI is easily formed. Low reactivity with the electrolyte due to low surface potential. Therefore, it is difficult to form SEI which is stable and sufficiently covers the surface.
For this reason, up to now, it was not possible to form a sufficient SEI on the surface of the active material, and it was not possible to improve the storage characteristics.

JP-A-63-102173 JP-A-4-87156 JP-A-5-74486 JP-A-10-50342 U.S. Pat. No. 5,626,981 U.S. Pat. No. 6,919,145 US Patent Publication No. 2004/0043300 US Patent Publication No. 2004/0106039 US Patent Publication No. 2015/0044551

  Accordingly, an object of the present invention is to suppress capacity deterioration in a non-aqueous electrolyte secondary battery.

  The present inventors have conducted intensive studies and as a result, have found that the above object can be achieved by using a negative electrode active material containing a specific carbon material and a non-aqueous electrolyte containing a polycarboxylic acid ester compound having a specific structure. Heading, the present invention has been completed.

The present invention provides (A) a negative electrode containing a carbon material having a true specific gravity of 1.60 to 2.20 g / cm ³ as a negative electrode active material, (B) a positive electrode containing a positive electrode active material, and (C) a lithium salt in an organic solvent. In a non-aqueous electrolyte secondary battery comprising a dissolved non-aqueous electrolyte and (D) a separation membrane,
(C) A non-aqueous electrolyte secondary battery comprising a compound represented by the following general formula (1) in a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent. .

（式中、Ｒ¹は２価の炭素原子数２〜６の不飽和炭化水素基、炭素原子数６〜１２のアリーレン基又は２価の炭素原子数３〜１２の複素環含有基を表し、Ｒ²〜Ｒ⁷はそれぞれ独立して炭素原子数１〜６のアルキル基、炭素原子数２〜６のアルケニル基又は炭素原子数２〜６のアルキニル基を表す。）

(Wherein, R ¹ represents a divalent unsaturated hydrocarbon group having 2 to 6 carbon atoms, an arylene group having 6 to 12 carbon atoms or a heterovalent group having 3 to 12 carbon atoms, R ^{2 to} R ⁷ each independently represent an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 2 to 6 carbon atoms.)

（式中、Ｒ⁸〜Ｒ¹⁵はそれぞれ独立して水素原子、炭素原子数１〜６のアルキル基、炭素原子数１〜６のアルコキシ基、フェニル基、フェノキシ基、若しくはベンジル基、又は、フッ素、塩素、臭素若しくは炭素原子数１〜６のアルキル基で置換されたフェニル基、フェノキシ基、若しくはベンジル基を表わす。）Further, the present invention provides the above non-aqueous electrolyte solution, wherein the (C) non-aqueous electrolyte solution obtained by dissolving a lithium salt in an organic solvent contains a compound represented by the following general formula (2). A secondary battery is provided.

(Wherein, R ^{8 to} R ¹⁵ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group, a phenoxy group, a benzyl group, or a fluorine atom; , A phenyl group, a phenoxy group or a benzyl group substituted with chlorine, bromine or an alkyl group having 1 to 6 carbon atoms.)

  ADVANTAGE OF THE INVENTION According to this invention, the capacity deterioration suppression of a nonaqueous electrolyte secondary battery can be implement | achieved.

FIG. 1 is a longitudinal sectional view schematically showing an example of the structure of a coin-type battery of the nonaqueous electrolyte secondary battery of the present invention. FIG. 2 is a schematic diagram showing a basic configuration of a cylindrical battery of the non-aqueous electrolyte secondary battery of the present invention. FIG. 3 is a perspective view showing the internal structure of the cylindrical battery of the nonaqueous electrolyte secondary battery of the present invention as a cross section.

Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described in detail based on preferred embodiments.
<(A) Negative electrode containing carbon material having true specific gravity of 1.60 to 2.20 g / cm ³ as negative electrode active material>
The negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a carbon material having a true specific gravity in the range of 1.60 to 2.20 g / cm ³ . The carbon material giving such a true specific gravity can be obtained by calcining coal-based and / or petroleum-based (coal-based etc.) raw coke or calcined coke of coal-based etc. alone or by mixing and firing. (In the present specification, the term "coal-based or the like" refers to "coal-based and / or petroleum-based," that is, either coal-based or petroleum-based, or a mixture of both. Good thing.) When the true specific gravity is less than 1.60 g / cm ³ , when applied to a lithium ion secondary battery, a side reaction occurs at the time of charging and discharging, which leads to a reduction in capacity and efficiency. On the other hand, when the true specific gravity exceeds 2.20 g / cm ³ , the characteristics of the input / output characteristics and the capacity retention ratio deteriorate when applied to a battery. In addition, raw coke such as coal-based is a petroleum-based and / or coal-based heavy oil, which is heated for about 24 hours at a temperature of about 400 ° C. to 700 ° C. using a coking facility such as a delayed coker. Means obtained by carrying out decomposition / polycondensation reaction. Coal-based calcined coke means calcined coke such as coal-based raw coke. Petroleum-based and / or coal-based coke calcined at about 2000C.

  If the method for obtaining the negative electrode active material for a nonaqueous electrolyte secondary battery pond in which the true specific gravity gives the above range is described in detail, first, heavy oil such as coal is converted to a coke-equipment such as a delayed coker using A raw coke such as coal-based coke is obtained by advancing the thermal decomposition / polycondensation reaction at an ultimate temperature of about 400 ° C. to 700 ° C. for about 24 hours. Thereafter, the obtained lump of raw coke such as coal is pulverized to a predetermined size. For the pulverization, an industrially used pulverizer can be used. Specific examples include atomizers, raymond mills, impeller mills, ball mills, cutter mills, jet mills, hybridizers, and oriental mills, but are not particularly limited thereto. In the pulverizing step, two or more of these devices may be used for pulverization, or one type of device may be used for pulverizing a plurality of times.

  The heavy oil such as coal used here may be a heavy oil of petroleum or a heavy oil of coal, but the heavy oil of coal is richer in aroma attribute, It is preferable to use coal-based heavy oil because it has a small amount of impurities such as S, V, and Fe and has a small volatile content.

  The negative electrode active material for a non-aqueous electrolyte secondary battery used here is a raw coke of coal type and / or petroleum type (such as coal type), or a calcined coke of coal type alone or a mixture thereof. In the process, a shape control process such as a plurality of firings and / or granulation in the process, and / or a process of modifying and coating the surface with different organic or inorganic components And / or a step of forming different metal components uniformly or dispersed on the surface.

  Further, the raw coke such as coal obtained as described above is calcined at a maximum temperature of 800 ° C. to 2000 ° C. to produce calcined coke such as coal. For the firing of raw coke such as coal, equipment such as a lead hammer furnace, a shuttle furnace, a tunnel furnace, a rotary kiln, a roller hearth kiln or a microwave capable of mass heat treatment can be used. is not. Further, these firing equipments may be either a continuous type or a batch type. Next, the obtained lump of calcined coke such as coal is pulverized to a predetermined size using a pulverizer such as an atomizer that is industrially used in the same manner as described above. The pulverized coke powder can be sized to a predetermined particle size by cutting fine powder by classification or removing coarse powder with a sieve or the like.

The firing temperature is preferably 800 ° C. or higher and 2000 ° C. or lower at the highest temperature. When the firing temperature exceeds the upper limit, the crystal growth of the coke material is excessively promoted, and it is difficult to reduce the true specific gravity to 2.20 g / cm ³ or less. If the true specific gravity exceeds 2.20 g / cm ³ , the crystal structure of coke will be oriented like graphite during firing, and the distance between crystal layers will be narrowed. The characteristics resulting from the structure of the above will be degraded. Further, when the firing temperature is lower than the lower limit, the crystal structure becomes undeveloped and the true specific gravity becomes not more than 1.60 g / cm ^3, and also, the functional groups (OH group, COOH group, etc.) derived from the raw material become on the coke surface. It remains and a side reaction occurs when the battery is charged and discharged as described above, leading to a reduction in capacity and efficiency.

The measurement of the true specific gravity is performed by a liquid phase replacement method (also called a pycnometer method). Specifically, the powder of the negative electrode active material is put into a pycnometer, a solvent liquid such as distilled water is added, and the air and the solvent liquid on the powder surface are replaced by a method such as vacuum degassing to obtain an accurate powder weight and volume. Is calculated to calculate the true specific gravity value.
(Note that the true specific gravity of a carbon material is one of the indices indicating the degree of crystallinity (graphitization). Generally, a carbon material having a true specific gravity of 2.20 g / cm ³ or more is made of highly crystalline carbon, .23 g / cm ³ or more is called graphite.)

The negative electrode is prepared by mixing a negative electrode active material containing a carbon material having a true specific gravity in the range of 1.60 to 2.20 g / cm ³ on a current collector (generally a copper foil), a conductive material, and a binder. And a formed mixture layer. True specific gravity is preferably 1.60-2.20g / cm ³ of the negative electrode active material, 2.05-2.20g / cm ³ is more preferred.

As the negative electrode active material for a non-aqueous electrolyte secondary battery, a carbon material having a true specific gravity in the range of 1.60 to 2.20 g / cm ^{3 according} to the above method may be used as it is, A carbon material having a specific gravity in the range of 1.60 to 2.20 g / cm ³ and a carbon material having a true specific gravity of 2.20 g / cm ³ or more may be mixed.
When the latter mixture is used, the mass ratio between the carbon material whose true specific gravity is in the range of 1.60 to 2.20 g / cm ³ and the carbon material whose true specific gravity is 2.20 g / cm ³ or more is determined by the above method. The carbon material having a true specific gravity in the range of 1.60 to 2.20 g / cm ³ is preferably at least 5 wt%, more preferably at least 10 wt%, based on the mixture.
If the carbon material whose true specific gravity is in the range of 1.60 to 2.20 g / cm ³ is less than 5 wt%, the capacity deterioration effect on the whole battery is reduced, and the effect of the present electrolyte additive cannot be sufficiently obtained.

  As the binder, generally, a fluorine-based resin powder such as polyvinylidene fluoride (PVDF) or a water-soluble binder such as a polyimide (PI) resin, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like. An agent is used, but is not limited thereto. The amount of the binder used for the negative electrode is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the negative electrode active material.

  Examples of the conductive material for the negative electrode include, but are not limited to, graphite fine particles, carbon black such as acetylene black and Ketjen black, amorphous carbon fine particles such as needle coke, and the like, and carbon nanofibers. The amount of the conductive material used for the negative electrode is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the negative electrode active material.

The formation of the mixture layer on the current collector is performed by preparing a slurry of the above-described negative electrode active material and the binder using a solvent, applying the slurry on the current collector (generally, a copper foil), and drying. Pressing under arbitrary conditions can be performed. The solvent used is not particularly limited, but N-methylpyrrolidone (NMP), dimethylformamdo, water, alcohol, or the like is used.
When water is used as a solvent for the negative electrode, it is preferable to use a thickener in combination. The amount of the solvent is adjusted so that the paste has such a viscosity that it can be easily applied to the current collector.
Examples of the current collector of the negative electrode include a stainless steel foil, a nickel foil, a copper foil, a nickel mesh, a copper mesh, and the like.

<(B) Positive electrode containing positive electrode active material>
As a positive electrode used in the present invention, as in a normal secondary battery, a positive electrode active material, a binder, a conductive material and the like slurried with an organic solvent or water are applied to a current collector, and dried. A sheet is used. The positive electrode active material contains a transition metal and lithium, and is preferably a material containing one type of transition metal and lithium. Examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound. May be used in combination.
As the transition metal of the lithium transition metal composite oxide, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and the like are preferable.
Specific examples of the lithium transition metal composite oxide include a lithium cobalt composite oxide such as LiCoO ₂ , a lithium nickel composite oxide such as LiNiO ₂ , and a lithium manganese composite oxide such as LiMnO ₂ , LiMn ₂ O ₄ and Li ₂ MnO _3. Products, some of the transition metal atoms that are the main components of these lithium transition metal composite oxides are converted to aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, etc. Examples thereof include those substituted with another metal.
Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.80 Co _0.17 Al _0.03 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O _{4 and the} like.
As the transition metal of the lithium-containing transition metal phosphate compound, vanadium, titanium, manganese, iron, cobalt, nickel and the like are preferable, and specific examples include iron phosphates such as LiFePO ₄ and phosphorus such as LiCoPO _4. Cobaltates, part of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds, are aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, and zirconium. And other metals such as niobium.

The binder for the positive electrode and the solvent for slurrying are the same as those used for the negative electrode. The amount of the binder used for the positive electrode is preferably 0.001 to 20 parts by mass, more preferably 0.01 to 10 parts by mass, and most preferably 0.02 to 8 parts by mass with respect to 100 parts by mass of the positive electrode active material. preferable. The amount of the solvent used for the positive electrode is preferably 30 to 300 parts by mass, more preferably 50 to 200 parts by mass, per 100 parts by mass of the positive electrode active material.
Examples of the conductive material for the positive electrode include, but are not limited to, graphite fine particles, carbon black such as acetylene black and Ketjen black, amorphous carbon fine particles such as needle coke, and the like, and carbon nanofibers.
The amount of the conductive material used for the positive electrode is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the positive electrode active material.
As the current collector of the positive electrode, aluminum, stainless steel, nickel-plated steel, or the like is usually used.

<(C) Non-aqueous electrolyte in which lithium salt is dissolved in organic solvent>
A non-aqueous electrolyte solution in which a lithium salt used in the present invention is dissolved in an organic solvent (hereinafter, simply referred to as “non-aqueous electrolyte solution”) will be described. The non-aqueous electrolyte contains the compound represented by the general formula (1). Hereinafter, this compound will be described.
The divalent unsaturated hydrocarbon group having 2 to 6 carbon atoms represented by R ¹ in the general formula (1) is particularly a divalent hydrocarbon group containing an unsaturated double bond or triple bond in the group. Specific examples include, but are not limited to, vinylene, propenylene, isopropenylene, butenylene, pentenylene, hexenylene, 1-propenylene-2,3-diyl, ethynylene, propynylene, butynylene, pentynylene, hexenylene and the like. Examples of the arylene group having 6 to 12 atoms include 1,2-phenylene, 1,3-phenylene, and 1,4-phenylene. As the divalent heterocyclic-containing group having 3 to 12 carbon atoms, The following structure is mentioned.

Examples of the alkyl group having 1 to 6 carbon atoms represented by R ^{2 to} R ⁷ in the general formula (1) include methyl, ethyl, propyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, isopentyl, cyclopentyl, and hexyl. , Cyclohexyl, etc., and the alkenyl group having 2 to 6 carbon atoms includes vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, 5-hexenyl, etc., and the alkynyl group having 2 to 6 carbon atoms. Examples include ethynyl, 2-propynyl, 2-butynyl, 3-butynyl and the like.
As R ^{2 to} R ⁷ , methyl, ethyl, propyl, butyl, and vinyl are preferable, and methyl is most preferable, since a highly durable surface structure that is hardly deteriorated can be obtained.

  Specific examples of the compound represented by the general formula (1) include bis (trimethylsilyl) acetylenedicarboxylate, bis (ethyldimethylsilyl) acetylenedicarboxylate, bis (dimethylpropylsilyl) acetylenedicarboxylate, bis (dimethyl) (Butylsilyl) acetylene dicarboxylate, bis (dimethylvinylsilyl) acetylene dicarboxylate, bis (trimethylsilyl) fumarate, bis (trimethylsilyl) maleate, bis (trimethylsilyl) phthalate, bis (trimethylsilyl) isophthalate, bis terephthalate (Trimethylsilyl), bis (trimethylsilyl) itaconate, and the like.

In the nonaqueous electrolyte, the compound represented by the general formula (1) may be used alone or in combination of two or more.
In the nonaqueous electrolytic solution of the present invention, if the content of the compound represented by the general formula (1) is too small, a sufficient effect cannot be exerted. If the content is too large, the compounding amount is appropriate. Since not only the effect of increasing the volume is not obtained but also the properties of the non-aqueous electrolyte may be adversely affected, the content of the compound represented by the general formula (1) is 0.001 in the non-aqueous electrolyte. 10 to 10% by mass is preferable, 0.01 to 8% by mass is more preferable, and 0.03 to 5% by mass is most preferable.

It is preferable that the non-aqueous electrolyte used in the present invention contains the compound represented by the general formula (2) because the effects of the present invention are remarkably exhibited. Hereinafter, the compound represented by Formula (2) will be described.
As the alkyl group having 1 to 6 carbon atoms represented by R ^{8 to} R ¹⁵ in the general formula (2), the same groups as those represented by the alkyl group having 1 to 6 carbon atoms represented by R ² can be used. And the alkoxy group having 1 to 6 carbon atoms represented by R ^{8 to} R ¹⁵ includes methoxy, ethoxy, propoxy, butoxy, isobutyloxy, s-butyloxy, t-butyloxy, pentoxy, isopentyloxy, cyclopentyloxy, Hexyloxy, cyclohexyloxy and the like can be mentioned.
Examples of the alkyl group having 1 to 6 carbon atoms for substituting the phenyl group, phenoxy group and benzyl group include the alkyl groups having 1 to 6 carbon atoms listed above.
Among the groups represented by R ^{8 to} R ¹⁰ , those which are an alkyl group having 1 to 6 carbon atoms are preferable, and among the groups represented by R ^{11 to} R ¹⁵ , a hydrogen atom or an alkyl group having 1 to 6 carbon atoms is preferable. Some are preferred.

  Specific examples of the compound represented by the general formula (2) include trimethylphenylsilane, triethylphenylsilane, 1-trimethylsilyl-4-methylbenzene, ethoxy (methyl) diphenylsilane, and monomethyltriphenylsilane.

In the non-aqueous electrolyte, the compound represented by the general formula (2) may be used alone or in combination of two or more.
When the compound represented by the general formula (2) is used, the content of the compound represented by the general formula (2) is preferably 0.001 to 20% by mass in the non-aqueous electrolyte, and 0.01 to 20% by mass. 10 mass% is more preferable, and 0.1 to 5 mass% is most preferable.

  The non-aqueous electrolytic solution used in the present invention further includes a fluorosilane compound having two or more difluorosilyl groups in a molecule, a cyclic carbonate compound having an unsaturated group, a chain carbonate compound, an unsaturated diester compound, and a cyclic sulfate. , A cyclic sulfite, a sultone, an unsaturated phosphate ester compound, a halogenated cyclic carbonate compound or an aromatic silane compound other than the compound represented by the general formula (2) can be added.

Examples of the fluorosilane compound containing two or more difluorosilyl groups in the molecule include bis (difluoromethylsilyl) methane, 1,2-bis (difluoromethylsilyl) ethane, and 1,3-bis (difluoromethylsilyl) Propane, 1,4-bis (difluoromethylsilyl) butane, 1,4- (bisdifluoromethylsilyl) benzene, tris (difluoromethylsilyl) methane, tetrakis (difluoromethylsilyl) methane and the like; Bis (difluoromethylsilyl) ethane, 1,3-bis (difluoromethylsilyl) propane, 1,4-bis (difluoromethylsilyl) butane, and tris (difluoromethylsilyl) methane are preferred,
Examples of the cyclic carbonate compound having an unsaturated group include vinylene carbonate, vinyl ethylene carbonate, propylidene carbonate, ethylene ethylidene carbonate, ethylene isopropylidene carbonate, and the like, and vinylene carbonate and vinyl ethylene carbonate are preferable.
Examples of the chain carbonate compound include dipropargyl carbonate, propargyl methyl carbonate, ethyl propargyl carbonate, bis (1-methylpropargyl) carbonate, and bis (1-dimethylpropargyl) carbonate.
Examples of the unsaturated diester compound include dimethyl maleate, diethyl maleate, dipropyl maleate, dibutyl maleate, dipentyl maleate, dihexyl maleate, diheptyl maleate, dioctyl maleate, dimethyl fumarate, diethyl fumarate, and fumaric acid. Dipropyl, dibutyl fumarate, dipentyl fumarate, dihexyl fumarate, diheptyl fumarate, dioctyl fumarate, dimethyl acetylenedicarboxylate, diethyl acetylenedicarboxylate, dipropyl acetylenedicarboxylate, dibutyl acetylenedicarboxylate, dipentyl acetylenedicarboxylate, acetylenedicarboxylic acid Dihexyl, diheptyl acetylenedicarboxylate, dioctyl acetylenedicarboxylate, and the like,
Examples of the cyclic sulfate include 1,3,2-dioxathiolane-2,2-dioxide, 1,3-propanediol cyclic sulfate, propane-1,2-cyclic sulfate, and the like.
Examples of the cyclic sulfite include ethylene sulfite, propylene sulfite, and the like,
Examples of the sultone include propane sultone, butane sultone, 1,5,2,4-dioxadithiolane-2,2,4,4-tetraoxide.
Examples of the unsaturated phosphate compound include tris (2-propynyl) phosphate and diphenyl-2-methacryloyloxyethyl phosphate. Examples of the halogenated cyclic carbonate compound include chloroethylene carbonate, dichloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and the like.
Examples of the aromatic silane compound other than the compound represented by the general formula (2) include 1,1,2,2-tetramethyl-1,2-diphenyldisilane, 1,4-bis (trimethylsilyl) benzene, 2-bis (trimethylsilyl) benzene and the like.
Among these additives, 1,2-bis (difluoromethylsilyl) ethane, 1,4-bis (difluoromethylsilyl) butane, tris (difluoromethylsilyl) methane, vinylene carbonate, vinylethylene carbonate, dipropargyl carbonate, Dimethyl acetylenedicarboxylate, diethyl acetylenedicarboxylate, propane sultone, butane sultone, tris (2-propynyl) phosphate, chloroethylene carbonate, dichloroethylene carbonate, and fluoroethylene carbonate are preferred, and 1,2-bis (difluoromethylsilyl) ethane, 1,4-bis (difluoromethylsilyl) butane, tris (difluoromethylsilyl) methane, vinylene carbonate, dipropargyl carbonate, acetylene diene Dimethyl rubonate, propane sultone, and fluoroethylene carbonate are more preferable, 1,2-bis (difluoromethylsilyl) ethane, 1,4-bis (difluoromethylsilyl) butane, tris (difluoromethylsilyl) methane, vinylene carbonate, And fluoroethylene carbonate are most preferred.

  These additives may be used alone or in a combination of two or more. In the non-aqueous electrolyte, the content of these additives is usually used in a total of 20% by mass or less in the non-aqueous electrolyte, preferably 5% by mass or less, and more preferably 3% by mass or less. .

  As the organic solvent used for the non-aqueous electrolyte, one commonly used for the non-aqueous electrolyte can be used alone or in combination of two or more. Specifically, saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, amide compounds, saturated chain carbonate compounds, chain ether compounds, cyclic ether compounds, saturated chain ester compounds, phosphorus-containing organic solvents, etc. Is mentioned.

Among the organic solvents, the saturated cyclic carbonate compound, the saturated cyclic ester compound, the sulfoxide compound, the sulfone compound and the amide compound have a high relative dielectric constant, and thus play a role of increasing the dielectric constant of the non-aqueous electrolyte. Compounds are preferred.
Examples of such a saturated cyclic carbonate compound include ethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, and 1,1, -dimethylethylene carbonate. And the like.
Examples of the saturated cyclic ester compound include γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-hexanolactone, δ-octanolactone, and the like.
Examples of the sulfoxide compound include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, and thiophene.
Examples of the sulfone compound include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also referred to as tetramethylene sulfone), 3-methylsulfolane, 3,4-dimethylsulfolane, 3,4-diphenylmethylsulfolane, and sulfolene. , 3-methylsulfolene, 3-ethylsulfolene, 3-bromomethylsulfolene, etc., and sulfolane and tetramethylsulfolane are preferred.
Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, dimethylacetamide and the like.
Among the organic solvents, the saturated chain carbonate compound, chain ether compound, cyclic ether compound and saturated chain ester compound can lower the viscosity of the non-aqueous electrolyte and increase the mobility of electrolyte ions. And battery characteristics such as output density can be improved. Further, since the viscosity is low, the performance of the non-aqueous electrolyte at a low temperature can be enhanced, and among them, a saturated chain carbonate compound is preferable.
Examples of such a saturated chain carbonate compound include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl butyl carbonate, methyl-t-butyl carbonate, diisopropyl carbonate, and t-butyl propyl carbonate. And the like.
Examples of the above chain ether compound or cyclic ether compound include dimethoxyethane (DME), ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolan, dioxane, 1,2-bis (methoxycarbonyloxy) ethane, 1,2 -Bis (ethoxycarbonyloxy) ethane, 1,2-bis (ethoxycarbonyloxy) propane, ethylene glycol bis (trifluoroethyl) ether, propylene glycol bis (trifluoroethyl) ether, ethylene glycol bis (trifluoromethyl) ether And diethylene glycol bis (trifluoroethyl) ether. Of these, dioxolan is preferred.
As the saturated chain ester compound, a monoester compound and a diester compound having a total of 2 to 8 carbon atoms in the molecule are preferable, and specific compounds include methyl formate, ethyl formate, methyl acetate, and ethyl acetate. , Propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate, ethyl trimethyl acetate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, 3 -Methyl methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, propylene glycol diacetyl and the like, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, as well as Propionic acid ethyl are preferred.
Phosphorus esters such as trimethyl phosphate, triethyl phosphate and triphenyl phosphate; phosphites such as trimethyl phosphite, triethyl phosphite and triphenyl phosphite; Phosphine oxides such as trimethylphosphine oxide, triethylphosphine oxide, and triphenylphosphine oxide; and phosphazenes.

  In addition, acetonitrile, propionitrile, nitromethane, and derivatives thereof can be used as the organic solvent.

As the lithium salt to be dissolved in the organic solvent, a conventionally known lithium salt is used. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC _{(CF 3 SO 2) 3,} LiB (CF 3 SO 3) 4, LiB (C 2 O 4) 2, LiBF 2 (C 2 O 4), LiSbF 6, LiSiF 5, LiAlF 4, LiSCN, LiClO 4, LiCl , LiF, LiBr, LiI, LiAlF ₄ , LiAlCl ₄ , and derivatives thereof, among which LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , and LiC (CF ₃ SO ₂ ) ₃ and derivatives LiCF ₃ SO _3, and LiC (CF ₃ SO ₂₎ to use at least one member selected from the group consisting of ₃ derivatives The preferred because of excellent electrical characteristics.

  The lithium salt may be dissolved in the organic solvent so that the concentration in the non-aqueous electrolyte of the present invention is 0.1 to 3.0 mol / L, particularly 0.5 to 2.0 mol / L. preferable. If the concentration of the lithium salt is less than 0.1 mol / L, a sufficient current density may not be obtained. If the concentration is more than 3.0 mol / L, the stability of the nonaqueous electrolyte may be impaired. The lithium salt may be used in combination of two or more lithium salts.

Further, a halogen-based, phosphorus-based, or other flame retardant can be appropriately added to the non-aqueous electrolyte in order to impart flame retardancy. If the added amount of the flame retardant is too small, a sufficient flame retarding effect cannot be exhibited, and if the added amount is too large, not only the effect of increasing the amount corresponding to the compounding amount cannot be obtained, but also the characteristics of the nonaqueous electrolyte. Since it may have an adverse effect, it is preferably 1 to 50% by mass, more preferably 3 to 10% by mass, based on the organic solvent constituting the non-aqueous electrolyte of the present invention.
Specific examples of the halogen-based flame retardant include di (2,2,2-trifluoroethyl) carbonate, di (2,2,3,3-tetrafluoropropyl) carbonate, and di (2,2,3,3,3). 4,4,5,5-octafluoropentyl) carbonate, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether and the like. Specific examples include trimethyl phosphate, triethyl phosphate, and the like.

<(D) Separation membrane>
In the nonaqueous electrolyte secondary battery of the present invention, a separation membrane is used between the positive electrode and the negative electrode. As the separation membrane, a commonly used polymer microporous film can be used without particular limitation. Examples of the film include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethylene oxide and polypropylene oxide. Films composed of ethers, various celluloses such as carboxymethylcellulose and hydroxypropylcellulose, high molecular compounds mainly composed of poly (meth) acrylic acid and various esters thereof, derivatives thereof, and copolymers and mixtures thereof. And the like. These films may be used alone or may be used as a multilayer film by laminating these films. Furthermore, various additives may be used for these films, and the types and contents thereof are not particularly limited. Among these films, a film made of polyethylene, polypropylene, polyvinylidene fluoride, or polysulfone is preferably used for the nonaqueous electrolyte secondary battery of the present invention.

  These films are made microporous so that the electrolyte can easily permeate and permeate the ions. There are two methods of microporization: a phase separation method, in which a solution of a polymer compound and a solvent is microphase-separated to form a film, and the solvent is extracted and removed to form a porous layer. The film is extruded to form a film, and then heat-treated, the crystals are arranged in one direction, and a “stretching method” for forming a gap between the crystals by stretching to make the crystals porous, and the like are appropriately selected depending on the film to be used.

  In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode material, the non-aqueous electrolyte and the separator are provided with a phenolic antioxidant, a phosphorus-based antioxidant, and a thioether-based antioxidant for the purpose of further improving safety. Agents, hindered amine compounds and the like may be added.

<Structure of non-aqueous electrolyte secondary battery>
The shape of the non-aqueous electrolyte secondary battery of the present invention composed of the above (A) to (D) is not particularly limited, and may be various shapes such as a coin shape, a cylindrical shape, and a square shape. Can be. FIG. 1 shows an example of a coin-type battery of the nonaqueous electrolyte secondary battery of the present invention, and FIGS. 2 and 3 show examples of a cylindrical battery.

  In the coin-type non-aqueous electrolyte secondary battery 10 shown in FIG. 1, 1 is a positive electrode, 1a is a positive electrode current collector, and 2 is a negative electrode active material containing a carbon material having a true specific gravity of 1.60 to 2.20 g / cm 3. A negative electrode 2a is a negative electrode current collector, 3 is a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent, 4 is a positive electrode case made of stainless steel, 5 is a negative electrode case made of stainless steel, 6 is a gasket made of polypropylene, 7 Is a polyethylene separation membrane.

  In the cylindrical nonaqueous electrolyte secondary battery 10 'shown in FIGS. 2 and 3, 11 is a negative electrode, 12 is a negative electrode current collector, 13 is a positive electrode, 14 is a positive electrode current collector, and 15 is a Non-aqueous electrolyte of the invention, 16 is a separation membrane, 17 is a positive electrode terminal, 18 is a negative electrode terminal, 19 is a negative electrode plate, 20 is a negative electrode lead, 21 is a positive electrode plate, 22 is a positive electrode lead, 23 is a case, 24 is an insulating plate , 25 are a gasket, 26 is a safety valve, and 27 is a PTC element.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited at all by the following examples. In the examples, “parts” and “%” are based on mass unless otherwise specified.

[Examples 1 to 14 and Comparative Examples 1 to 13 ] Production and Evaluation of Nonaqueous Electrolyte Secondary Battery In Examples and Comparative Examples, the following production procedure was used for the nonaqueous electrolyte secondary battery (lithium secondary battery). Prepared according to

<Production of each configuration>
[Production of negative electrode (A1)]
94.5 parts by mass of a carbon material having a true specific gravity of 2.01 as an active material, 1.0 part by mass of acetylene black as a conductive material, 3.0 parts by mass of styrene butadiene rubber as a binder, and 1.5 parts by mass of carboxymethyl cellulose as a thickener Parts were mixed and dispersed in 50 parts by mass of water to form a slurry. This slurry was applied to a copper negative electrode current collector, dried, and then press-molded. Thereafter, the negative electrode was cut into a predetermined size to produce a disk-shaped negative electrode A1.

[Production of negative electrode (A2)]
94.5 parts by mass of a carbon material having a true specific gravity of 2.14 as an active material, 1.0 part by mass of acetylene black as a conductive material, 3.0 parts by mass of styrene butadiene rubber as a binder, and 1.5 parts by mass of carboxymethyl cellulose as a thickener Parts were mixed and dispersed in 50 parts by mass of water to form a slurry. This slurry was applied to a copper negative electrode current collector, dried, and then press-molded. Thereafter, the negative electrode was cut into a predetermined size to produce a disk-shaped negative electrode A2.

[Production of Negative Electrode (A'1)]
96.0 parts by mass of artificial graphite having a true specific gravity of 2.23 as an active material, 1.0 part by mass of acetylene black as a conductive material, 1.5 parts by mass of styrene-butadiene rubber as a binder, and 1.5 parts by mass of carboxymethyl cellulose as a thickener Parts were mixed and dispersed in 120 parts by mass of water to form a slurry. This slurry was applied to a copper negative electrode current collector, dried, and then press-molded. Thereafter, the negative electrode was cut into a predetermined size to produce a disk-shaped negative electrode A′1.

[Production of negative electrode (A3)]
47.5 parts by mass of natural graphite having a true specific gravity of 2.23 and 47.5 parts by mass of a carbon material having a true specific gravity of 2.14 (artificial graphite / carbon material = 5/5) as an active material, and styrene butadiene rubber as a binder. 0 parts by mass and 1.5 parts by mass of carboxymethylcellulose as a thickener were mixed and dispersed in 50 parts by mass of water to form a slurry. This slurry was applied to a copper negative electrode current collector, dried, and then press-molded. Thereafter, the negative electrode was cut into a predetermined size to produce a disk-shaped negative electrode (A3).

[Production of negative electrode (A4)]
76 parts by mass of natural graphite having a true specific gravity of 2.23 and 19 parts by mass of a carbon material having a true specific gravity of 2.14 (artificial graphite / carbon material = 8/2) as an active material, and 3.0 parts by mass of styrene-butadiene rubber as a binder; 1.5 parts by mass of carboxymethyl cellulose as a thickener was mixed and dispersed in 50 parts by mass of water to form a slurry. This slurry was applied to a copper negative electrode current collector, dried, and then press-molded. Thereafter, the negative electrode was cut into a predetermined size to produce a disk-shaped negative electrode (A4).

[Production of Positive Electrode (B1)]
After mixing 88 parts by mass of LiNiMnCoO ₂ (NMC) as an active material, 5 parts by mass of acetylene black as a conductive material, and 7 parts by mass of polyvinylidene fluoride (PVDF) as a binder, the mixture was dispersed in 50 parts by mass of N-methylpyrrolidone (NMP). This was made into a slurry. This slurry was applied to an aluminum current collector, dried, and press molded. Thereafter, the positive electrode was cut into a predetermined size to produce a disk-shaped positive electrode B1.

(Preparation of electrolyte solution)
LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent consisting of 30% by volume of ethylene carbonate, 40% by volume of ethyl methyl carbonate, and 30% by volume of dimethyl carbonate to prepare an electrolyte solution A.

[Preparation of non-aqueous electrolyte (C)]
As the electrolyte additive, compounds represented by the above general formula (1) (compounds C1-1, C1-2, and C1-3 shown below) and compounds represented by the above general formula (2) (shown below) Compound C2-1) and compound C′1 shown below were dissolved in the electrolyte solution at the ratios shown in Table 1 to prepare a non-aqueous electrolyte solution (C). The numbers in parentheses in Table 1 represent the concentration (% by mass) in the non-aqueous electrolyte.

[Compound C1-1]
Bis (trimethylsilyl) fumarate
[Compound C1-2]
Bis (trimethylsilyl) itaconate
[Compound C1-3]
Thiophene-2,5-dicarboxylic acid bis (trimethylsilyl)
[Compound C2-1]
Phenyltrimethylsilane [Compound C'1]
Vinylene carbonate

[Battery assembly]
The obtained disc-shaped negative electrode (A) and disc-shaped positive electrode (B) were held in a case with a microporous polypropylene film ((D) separation membrane) having a thickness of 25 μm interposed therebetween. Then, each non-aqueous electrolyte solution was poured into the case so that the non-aqueous electrolyte solution (C) adjusted above became as shown in Table 1, and the cases were hermetically sealed and sealed. The non-aqueous electrolyte secondary batteries of Examples 1 to 14 (coin type having a diameter of 20 mm and a thickness of 3.2 mm) were manufactured.

Using a non-aqueous electrolyte secondary batteries of Examples 1 to 1 4 and Comparative Examples 1 to 1 3, by the following test methods to evaluate the capacity loss due to battery deterioration. The results are shown in Tables 1 and 2 .
After the production of the nonaqueous electrolyte secondary battery, five cycles of charge / discharge were performed at 25 ° C., and the fifth discharge capacity was defined as “capacity before storage”. Thereafter, the battery was allowed to stand in a fully charged state in a thermostat at 60 ° C for 2 weeks. After 2 weeks, 5 cycles of charge / discharge were performed at 25 ° C., and the discharge capacity at the fifth time (a total of ten times after battery production) was defined as “capacity after storage”. As shown in the following formula, the capacity loss due to battery deterioration was determined as a ratio when the “capacity before storage” was set to 100.
Capacity loss rate (%) = [1-[(capacity after storage) / (capacity before storage)]] × 100

As is clear from the results of [Table 1] and [Table 2], (A) non-aqueous electrolyte secondary using a negative electrode containing a carbon material having a true specific gravity of 1.60 to 2.20 g / cm ³ as a negative electrode active material In the battery, when the compound represented by the general formula (1) is added to the non-aqueous electrolyte, storage deterioration of the battery is suppressed, and when the compound represented by the general formula (2) is further added, Remarkably, storage deterioration is suppressed.

  As described above, the non-aqueous electrolyte secondary battery of the present invention is useful because it can maintain a stable battery capacity for a long time.

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 2 Negative electrode 2a Negative electrode collector 3 Electrolyte 4 Positive case 5 Negative case 6 Gasket 7 Separation membrane 10 Coin type non-aqueous electrolyte secondary battery 10 'Cylindrical non-aqueous electrolyte secondary Battery 11 Negative electrode 12 Negative electrode current collector 13 Positive electrode 14 Positive electrode current collector 15 Electrolyte 16 Separation film 17 Positive terminal 18 Negative terminal 19 Negative plate 20 Negative lead 21 Positive electrode 22 Positive lead 23 Case 24 Insulating plate 25 Gasket 26 Safety valve 27 PTC element

Claims (2)

As (A) the anode active material includes a carbon material true specific gravity 1.60-2.20g / cm ^3, a mixture of true specific gravity of 2.23 g / cm ³ or more graphite, true specific gravity 1.60-2 A negative electrode in which .20 g / cm ³ of a carbon raw material accounts for 5% by mass or more and 20% by mass or less of the mixture; (B) a positive electrode containing a compound containing a transition metal and lithium as a positive electrode active material; (C) a lithium salt Is dissolved in an organic solvent, and (D) a non-aqueous electrolyte secondary battery comprising a separation membrane,
(C) A non-aqueous electrolyte secondary battery comprising a compound represented by the following general formula (1) in a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent (however, as a negative electrode active material) Excluding those using a carbon material in which the surface of a composite of graphite and hard carbon is coated with a fired carbon material.
The negative electrode active material is composed of at least a mixture of graphite and calcined carbon, and the calcined carbon has a pore distribution of less than 8 mm in pore diameter of nitrogen gas by BET adsorption method of 2 × 10 ⁻⁴ CC / g or more. A carbonaceous negative electrode for a non-aqueous secondary battery, wherein the pores of 8 to 18 ° are 15 × 10 ⁻⁴ CC / g or less and the proportion of calcined carbon in the mixture of graphite and calcined carbon is 20 to 80% by weight. Excluding those that are active materials) .

(Wherein, R ¹ represents a divalent unsaturated hydrocarbon group having 2 to 6 carbon atoms, an arylene group having 6 to 12 carbon atoms or a heterovalent group having 3 to 12 carbon atoms, R ^{2 to} R ⁷ each independently represent an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 2 to 6 carbon atoms.) The non-aqueous electrolyte secondary battery according to claim 1, wherein the (C) non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent contains a compound represented by the following general formula (2). .

(Wherein, R ^{8 to} R ¹⁵ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group, a phenoxy group, a benzyl group, or a fluorine atom; , A phenyl group, a phenoxy group or a benzyl group substituted with chlorine, bromine or an alkyl group having 1 to 6 carbon atoms.)

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