JP4899341B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery.

  Non-aqueous electrolyte lithium ions or lithium secondary batteries are attracting attention as power sources for mobile phones and laptop computers because they can achieve high energy density.

  In this secondary battery, a carbon material, particularly graphite, has been conventionally used as the negative electrode active material. It is known that a surface film, a protective film, a film called SEI or a film is formed on the surface of the negative electrode using graphite. Since these surface films have a great influence on charge / discharge efficiency, cycle life, and safety, it is known that control of the surface film is indispensable for improving the performance of the electrode.

  In Patent Documents 1 to 3, when a carbon material such as graphite capable of occluding and releasing lithium ions is used as a negative electrode active material, a technology for suppressing the formation of a film on the negative electrode surface and improving the capacity and charge / discharge efficiency Has been reported.

  Patent Document 1 proposes a negative electrode in which a carbon material is coated with a metal thin film such as aluminum. Thereby, reductive decomposition on the carbon surface of solvent molecules solvated with lithium ions is suppressed, and deterioration of cycle life is suppressed.

  Patent Document 2 proposes a negative electrode in which a surface of a highly crystalline graphite material is coated with a lithium ion conductive solid electrolyte thin film. Thereby, it is said that the decomposition | disassembly of the solvent which arises when using a carbon material can be suppressed, and especially the lithium ion secondary battery which can use a propylene carbonate can be provided.

  In Patent Document 3, the negative electrode active material is mainly composed of a material containing highly crystalline graphite such as natural graphite or artificial graphite, and the electrolytic solution is mainly composed of cyclic carbonate and chain carbonate, and the electrolytic solution. A secondary battery containing 1,3-propane sultone and / or 1,4-butane sultone, which is a cyclic sulfonic acid ester of 0.1% by mass or more and 4% by mass or less, is disclosed. Here, 1,3-propane sultone and 1,4-butane sultone contribute to the formation of a passive film on the surface of the carbon material and have an effect of suppressing the decomposition of the electrolyte without impairing the normal reaction of the battery. It is believed that.

  Patent Documents 4 and 5 disclose techniques for improving battery safety by adding a vinylene carbonate compound to an electrolytic solution.

  In Patent Document 4, a negative electrode including a graphite-based carbonaceous material having a surface spacing of less than 3.37 mm and a carbonaceous material having a surface spacing of 3.37 mm or more, a vinylene carbonate compound and / or vinylethylene in an electrolyte solution containing a phosphate ester are disclosed. A secondary battery containing a carbonate compound has been proposed. Patent Document 5 discloses that a negative electrode including a graphite-based carbonaceous material having a surface spacing of less than 3.37 mm and a carbonaceous material having a surface spacing of 3.37 mm or more, a vinylene carbonate compound and / or vinylethylene in an electrolyte solution containing a phosphate ester. Secondary batteries each including a carbonate compound and a nitrogen-containing cyclic compound are presented. Accordingly, it is said that the battery is nonflammable and has high safety.

  In addition to these cyclic sulfonate esters and vinylene carbonate compounds, Patent Documents 6 and 7 report that similar effects can be obtained even when chain-like disulfonate esters are used.

  Patent Documents 8 and 9 disclose a method for producing a cyclic sulfonic acid ester having two sulfonyl groups, and Non-Patent Documents 1 to 4 disclose a method for producing a chain disulfonic acid ester.

  However, depending on the technique for forming a film on these negative electrodes, it may be difficult to maintain the battery with a high discharge capacity and excellent cycle characteristics. This is thought to be due to the following reasons. When a highly crystalline material such as graphite is used as the negative electrode active material, this material takes in lithium ions between carbon layers, so that the volume changes greatly by occluding and releasing lithium ions, while it is formed on the surface. The film has almost no volume change. For this reason, internal stress is generated in these layers and the interface, part of the surface film is damaged, and the dendrite suppressing function is lowered. As a result, the electrolytic solution is decomposed and the high discharge capacity and cycle characteristics are deteriorated. In addition, when graphite is used as the negative electrode active material, solvent molecules are likely to be decomposed, and the charge generated thereby acts as an irreversible capacity component, leading to a decrease in initial charge / discharge efficiency and high discharge. There was a problem that it was difficult to obtain the capacity.

  Therefore, as a method for solving these problems, a method using amorphous carbon as a negative electrode active material can be considered. Since this amorphous carbon includes a large number of voids inside, lithium ions are stored in the voids, and the volume change associated with insertion and extraction of lithium ions is smaller than that of highly crystalline substances such as graphite. For this reason, the damage of the surface film formed on the negative electrode surface accompanying the volume change of the negative electrode can be reduced. Further, since lithium ions are isotropically inserted into amorphous carbon, lithium ions move quickly into the amorphous carbon. For this reason, it is difficult to inhibit the movement of lithium ions even during discharge with a large current, and a secondary battery capable of high output can be obtained.

  Patent Documents 10 to 13 disclose a technique for improving battery characteristics such as conductivity by adding an additive into a negative electrode or an electrolyte even when amorphous carbon is used as a negative electrode active material. .

  Patent Document 10 proposes a negative electrode formed by mixing amorphous carbon and fine carbon particles and / or fine fibrous graphite. Thereby, it is supposed that charge / discharge capacity loss is reduced and charge / discharge cycle characteristics are improved.

  Patent Document 11 proposes a negative electrode formed by mixing amorphous carbon and a conductive agent having higher conductivity than amorphous carbon in a content of 2-6 mass%. As a result, the increase in battery internal resistance is suppressed and the output characteristics are excellent.

Further, Patent Document 12 discloses a carbonaceous material, a carbon fiber, and a binder that have an interplanar spacing of 3.70 mm or more, a true density of less than 1.70 g / cm ³ , and no heat generation peak at 700 ° C. or higher by suggestion thermal analysis. A negative electrode formed by applying a negative electrode composite material is proposed. Patent Document 13 each presents a negative electrode formed by mixing a carbon material having an interplanar spacing of 0.335-0.410 nm and 5-30% of vapor-grown carbon fiber. Thus, the electrode reaction is facilitated, and charge / discharge cycle characteristics and the like are improved.
Japanese Patent Laid-Open No. 5-234583 JP-A-5-275077 JP 2000-3724 A JP 2003-187865 A JP 2003-187866 A JP 2000-133304 A US Pat. No. 6,436,582 Japanese Patent Publication No. 5-44946 US Pat. No. 4,950,768 Japanese Patent No. 3239302 JP 2002-231316 A JP 7-134984 A JP 2002-334893 A J. et al. Am. Pham. Assoc. , Vol.26, pp.485-493, 1937 G. Schroeter, Lieb, Ann, Der Chemie, 418, 161-257, 1919 Biol. Aktiv. Soedin. , Pp 64-69 (1968). Armyanskii Kimicheskii Zhurnal, 21, pp 393-396 (1968).

  However, when amorphous carbon is used as the negative electrode active material, there is a problem that the conductivity is deteriorated because the true density is low. Although the techniques of Patent Documents 10 to 13 can improve the conductivity to some extent, there are cases where it is insufficient in practice. Although these techniques are insufficient, the conductivity of the negative electrode is improved to promote the decomposition of the electrolyte component and the like, and an unstable film resulting from this is formed on the electrode. As a result, problems such as deterioration of cycle characteristics have occurred.

  Therefore, the present inventor has examined a battery configuration that improves both characteristics such as improvement in conductivity of the negative electrode and improvement of cycle characteristics by forming a stable film. As a result, amorphous carbon and conductive graphite particles are contained in the negative electrode. And at least one of conductive carbon fibers and the compound of the general formula (1) (chain disulfonic acid) was found to be added to the electrolytic solution.

  That is, the present invention provides a secondary battery including a positive electrode, a negative electrode, and an electrolyte solution containing an aprotic solvent in which an electrolyte is dissolved. The negative electrode is capable of inserting and extracting lithium ions during charge and discharge. An active material layer including an amorphous carbon material and at least one of conductive graphite particles and conductive carbon fibers is provided, and the electrolytic solution includes a compound represented by the following general formula (1) The object is to provide a secondary battery.

In order to solve the above problems, the present invention has the following configuration. That is, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution containing an aprotic solvent in which an electrolyte is dissolved.
The negative electrode includes an active material layer including amorphous carbon capable of occluding and releasing lithium ions during charge and discharge, and at least one of conductive graphite particles and conductive carbon fibers,
The electrolyte solution includes a compound represented by the following general formula (1).

(However, in the said General formula (1), R < ₁ > and R < ₄ > are respectively independently a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group, a substituted or unsubstituted C1-C5. An alkoxy group, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, —SO ₂ X ₁ (wherein X ₁ is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms). alkyl group), - SY ₁ (Y ₁ is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), - COZ (Z is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms. An alkoxy group, substituted or Substituted phenoxy group, substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, polyfluoroalkyl group having 1 to 5 carbon atoms, substituted or unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, 1 to carbon atoms 5 polyfluoroalkoxy group, hydroxyl group, halogen atom, -NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and _{-NY 2 CONY 3 Y 4 (Y} 2 ~Y 4 are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), indicating the atom or a group selected from.).

In the present invention, it is preferable that the total content of the conductive graphite particles and the conductive carbon fibers in the negative electrode active material layer is 5% by mass or less.
In the present invention, it is preferable that the conductive graphite particles have (A) a BET specific surface area of 70 m ² / g or less and (B) an average particle diameter of 10 μm or less.
In the present invention, it is further preferable that the conductive graphite particles include conductive carbon black or artificial graphite.

In the present invention, it is preferable that the conductive carbon fiber has (C) an average fiber diameter of 0.05 μm or more and (D) an average fiber length of 25 μm or less.
In the present invention, it is further preferable that the conductive carbon fiber is a vapor-grown carbon fiber.
In the present invention, the content of the compound represented by the general formula (1) in the electrolytic solution is preferably 0.1 to 5.0% by mass.

  In the present invention, it is preferable that the electrolytic solution further includes a cyclic monosulfonic acid ester represented by the following general formula (2).

(However, in the general formula (2), n is 0 to 2 integer. Also, R ₅ to R ₁₀ each independently represent a hydrogen atom, a substituted or unsubstituted alkyl having 1 to 12 carbon atoms An atom or a group selected from a group, a substituted or unsubstituted fluoroalkyl group having 1 to 6 carbon atoms, and a polyfluoroalkyl group having 1 to 6 carbon atoms.

  In the present invention, it is preferable that the electrolytic solution further includes a cyclic sulfonic acid ester having two sulfonyl groups represented by the following general formula (3).

(In the above general formula (3), Q is an oxygen atom, a methylene group or a single bond, A is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a carbonyl group, a sulfinyl group, or a carbon number of 1). -5 polyfluoroalkylene group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, or a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms in which at least one C-C bond is C-O- A group having a C bond, a group in which at least one C—C bond in the C 1-5 polyfluoroalkylene group is a C—O—C bond, and a substituted or unsubstituted C 1-5 carbon atom A group selected from a group in which at least one C—C bond in a fluoroalkylene group is a C—O—C bond, B is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, Polyfluoroalkylene group prime 1-5, and a substituted or unsubstituted group selected from fluoroalkylene group having 1 to 5 carbon atoms.).

In the present invention, it is further preferable that the electrolytic solution further contains at least one of vinylene carbonate and a derivative thereof.
In the present invention, it is further preferable that the electrolyte contains a lithium salt.
The present invention further provides the lithium _{salt, LiPF 6, LiBF 4, LiAsF} 6, LiSbF 6, LiClO 4, LiAlCl 4, and _{LiN (C k F 2k + 1} SO 2) (C m F 2m + 1 SO 2) It is preferably at least one lithium salt selected from the group consisting of (k and m are each independently 1 or 2).

In the present invention, the aprotic solvent further comprises a group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers, and fluorinated derivatives thereof. It is preferably at least one organic solvent selected from the above.
In the present invention, it is preferable that the secondary battery is enclosed in a film outer package.

  In this specification, “polyfluoroalkylene group”, “polyfluoroalkyl group”, and “polyfluoroalkoxy group” are all hydrogen atoms bonded to carbon atoms of the corresponding alkylene group, alkyl group, and alkoxy group, respectively, by fluorine atoms. Represents a substituted group, and “fluoroalkylene group”, “fluoroalkyl group”, and “fluoroalkoxy group” are fluorine atoms in which part of hydrogen atoms bonded to carbon atoms of the corresponding alkylene group, alkyl group, and alkoxy group, respectively. Represents the one substituted by.

In the “substituted fluoroalkylene group”, “substituted fluoroalkyl group” and “substituted fluoroalkoxy group”, “substituted” means that at least one hydrogen atom bonded to a carbon atom is substituted with an atom or functional group other than fluorine. Represents that Examples of the atoms or functional groups other than fluorine include, for example, a halogen atom such as a chlorine atom, a bromine atom, and an iodine atom, a hydroxyl group, or an alkoxy group having 1 to 5 carbon atoms, or a group in which this is substituted with a halogen atom or a hydroxyl group. Or a group in which —SO ₂ — is introduced into these groups (for example, —OSO ₂ CH ₂ SO ₂ Cl). When this functional group contains a carbon atom, this carbon atom is not included in the number of “C1-5” in the description of “substituted or unsubstituted alkyl group having 1 to 5 carbon atoms”. And

  According to the present invention, an active material layer including an amorphous carbon material capable of occluding and releasing lithium ions and at least one of conductive graphite particles and conductive carbon fibers in a negative electrode of a secondary battery. By including the compound represented by the general formula (1) (chain disulfonic acid compound) in the electrolytic solution, the negative electrode has excellent conductivity and charge / discharge efficiency, good cycle characteristics, and capacity retention rate. It is high, and it can be set as the outstanding lithium secondary battery which can suppress the resistance raise in storage.

(Description of battery configuration according to the present invention)
FIG. 1 shows a schematic structure of an example of a battery according to the present invention. A positive electrode current collector 11, a layer 12 containing a positive electrode active material capable of occluding and releasing lithium ions, amorphous carbon capable of occluding and releasing lithium ions during charge and discharge, conductive graphite particles, and It is comprised from the layer (active material layer) 13 containing at least one of electroconductive carbon fiber, the negative electrode collector 14, the electrolyte solution 15, and the separator 16 containing this.

(Current collector)
Aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used as the positive electrode current collector 11, and copper, stainless steel, nickel, titanium, or an alloy thereof can be used as the negative electrode current collector 14. .

(Separator)
As the separator 16, a porous film such as a polyolefin such as polypropylene or polyethylene, or a fluororesin is preferably used.

(Positive electrode)
As the positive electrode active material, a commonly used lithium-containing composite oxide is used. Specifically, LiMO ₂ (M is selected from Mn, Fe, Co, and a part thereof is substituted with other cations such as Mg, Al, Ti, etc. It is also possible to use a general-purpose material such as LiMn ₂ O ₄ . Using the selected positive electrode active material, it is dispersed and kneaded in a conductive material such as conductive carbon black and a binder such as polyvinylidene fluoride (PVDF) in a solvent such as N-methyl-2-pyrrolidone (NMP). The layer 12 serving as the positive electrode can be obtained by a method such as coating on a substrate such as an aluminum foil.

(Negative electrode)
Using amorphous carbon capable of occluding and releasing lithium ions during charge and discharge, and at least one of conductive graphite particles and conductive carbon fiber, these are used as a binder such as polyvinylidene fluoride (PVDF). In addition, the layer 13 to be the negative electrode can be obtained by a method of dispersing and kneading in a solvent such as N-methyl-2-pyrrolidone (NMP) and applying the mixture onto a substrate such as a copper foil (current collector). .

  In the secondary battery of the present invention, by using amorphous carbon as a material capable of occluding and releasing lithium ions in this way, volume change due to occlusion of lithium ions can be reduced, and a chain disulfonic acid compound Can be stably formed on the negative electrode. In addition, the conductive graphite particles and the conductive carbon fibers improve the conductivity of the negative electrode, and can form a more stable film on the negative electrode surface by a synergistic action with the disulfonic acid compound. Furthermore, since conductive graphite particles and conductive carbon fibers have the same specific gravity as amorphous carbon materials, these materials (amorphous carbon materials, conductive graphite particles, conductive carbon fibers) Can be uniformly dispersed in the active material layer. As a result, it is considered that the electric field on the negative electrode surface is made uniform to enable stable film formation.

  Amorphous carbon is a carbon material that is difficult to graphitize even when heat-treated at a high temperature (eg, 3000 ° C. or higher), or a stage structure change in crystal structure due to insertion / release of lithium ions accompanying charge / discharge. The carbon material which does not show is shown. Whether the carbon material is an amorphous carbon material or a crystalline carbon material can be confirmed by measuring an X-ray diffraction spectrum. In the case of a crystalline carbon material, since it has a crystal structure, a clear (sharp) peak appears in the X-ray diffraction spectrum. In addition, when lithium ions are occluded, lithium is inserted between the carbon layers, so that the layers expand (lattice spacing increases), and the movement of the peak position and peak It can be detected as a change in shape. On the other hand, when the negative electrode active material is made of an amorphous carbon material, the X-ray diffraction spectrum is wide and does not show a clear peak shape change even when lithium ions are occluded. Therefore, whether the carbon material is an amorphous carbon material or a crystalline carbon material can be determined based on the presence or absence of a peak change in the spectrum.

  The ratio of the total content of conductive graphite particles and conductive carbon fibers in the negative electrode is not particularly limited, but is preferably 5% by mass or less in the active material layer of the negative electrode. Generally, when the conductivity of the negative electrode is improved, the decomposition of the electrolytic solution is promoted. For this reason, there is no practical problem at 5% by mass or less, but when it exceeds 5% by mass, not only more additives are required to suppress decomposition of the electrolyte solvent, but also the negative electrode capacity is reduced. It is not preferable.

  A more preferable content ratio for fully exhibiting the effects of the present invention is 0.1% by mass or more and 3% by mass or less.

  Furthermore, in this invention, what mixed the 2 or more types of electroconductive graphite particle which satisfy | fills the said conditions can be used, or what mixed 2 or more types of electroconductive carbon fibers can be used. It is also possible to use a mixture of one or more of these graphite particles and conductive carbon fibers. By using conductive graphite particles and conductive carbon fibers, the conductivity of the negative electrode can be increased more effectively, and a more stable chain disulfonic acid film can be formed on the negative electrode.

  Graphite particles can be produced by the following method. First, as a raw material for the graphite particles, a graphitizable aggregate or graphite and a graphitizable binder are used. Moreover, you may add a graphitization catalyst as needed. As aggregates that can be graphitized, various cokes such as fluid coke and needle coke can be used. As graphite, natural graphite and artificial graphite can be used. As the binder that can be graphitized, various pitches such as coal-based, petroleum-based, and artificial ones, tar, thermoplastic resin, thermosetting resin, and the like can be used. As the graphitization catalyst, iron, nickel, titanium, boron and the like, carbides thereof, oxides, nitrides, and the like can be used.

  Next, the mixture obtained by mixing the raw materials is fired. Firing is preferably performed in an atmosphere in which raw material oxidation is difficult, and the graphitization temperature is preferably 2000 ° C. or higher, more preferably 2500 ° C. or higher, and further preferably 2800 ° C. or higher. Thereafter, the graphitized product thus graphitized is pulverized. The method for pulverizing the graphitized material is not particularly limited, but known methods such as a jet mill, a vibration mill, a pin mill, and a hammer mill can be used.

In addition, the physical properties of the conductive graphite particles are not particularly limited. However, while ensuring the conductivity in the negative electrode active material layer, the effect of forming a film on the negative electrode by the additives described later, charge / discharge efficiency, and charge / discharge In order to effectively suppress the deterioration of the cycle,
(A) The BET specific surface area is preferably 70 m ² / g or less, and (B) the average particle diameter is preferably 10 μm or less.

(I) When the BET specific surface area exceeds 70 m ² / g, the area where the graphite particles come into contact with the electrolytic solution increases, so that the electrolytic solution and the like are easily decomposed, and more additives are added to suppress the decomposition. Is not preferable because it is necessary.

  (Ii) When the average particle diameter exceeds 10 μm, the pores in the negative electrode active material layer become large, it becomes difficult to maintain contact between the amorphous carbons, and it is not preferable because it is difficult to ensure conductivity.

  In order to obtain graphite particles satisfying the above characteristics (A) and (B), the kind of raw material, the composition of the raw material mixture, the firing temperature, and the pulverization method are appropriately adjusted when producing the graphite particles. Just do it.

In order to sufficiently exhibit the effects of the present invention, the conductive graphite particles preferably have a BET specific surface area of 20 m ² / g or more and 70 m ² / g or less, more preferably 30 m ² / g or more and 50 m ² / g. More preferably, it is as follows. The average particle size is more preferably 0.035 μm or more and 0.06 μm or less, and further preferably 0.04 μm or more and 0.05 μm or less. By setting it as such a BET specific surface area and an average particle diameter, the electroconductivity of a negative electrode can be improved more effectively.

  Note that the volume of the conductive negative electrode particles does not change during charge / discharge, or even if the volume changes, the amount of conductive graphite particles contained in the active material layer is very small. Almost negligible.

  Further, it is preferable to use conductive graphite particles containing conductive carbon black or artificial graphite. As the conductive carbon black, for example, ketjen black, furnace black, acetylene black, or the like can be used. Since conductive carbon black and artificial graphite have excellent conductivity, the addition of these conductivity imparting agents can further improve characteristics such as cycle characteristics and charge / discharge efficiency.

In addition, the conductive carbon fiber is not particularly limited, but while ensuring the conductivity in the negative electrode active material layer, the effect of forming a film on the negative electrode by the chain disulfonic acid compound, the charge and discharge efficiency, and the charge and discharge cycle. In order to effectively suppress deterioration,
(C) The average fiber diameter is preferably 0.05 μm or more, and (D) the average fiber length is preferably 25 μm or less.

  (I) An average fiber diameter of less than 0.05 μm is not preferable because it is difficult to maintain contact between amorphous carbon as an active material.

  (Ii) When the average fiber length exceeds 25 μm, the pores in the negative electrode active material layer become large, it becomes difficult to maintain contact between the amorphous carbons, and it is not preferable because it is difficult to ensure conductivity.

  The conductive carbon fiber for fully exhibiting the effects of the present invention preferably has an average fiber diameter of 0.05 μm to 0.2 μm, more preferably 0.1 μm to 0.15 μm. Further preferred. Further, the average fiber length is more preferably 5 μm or more and 20 μm or less, and further preferably 10 μm or more and 15 μm or less. By setting such an average fiber diameter and average fiber length, the contact area between the conductive carbon fibers and between the amorphous carbon and the conductive carbon fibers can be increased, and the conductivity of the negative electrode can be increased more effectively. .

  Vapor-grown carbon fibers are preferably used as the conductive carbon fibers. Vapor-grown carbon fiber uses organic compounds such as benzene as raw materials, organic transition metal compounds such as ferrocene as metal catalysts, and these are introduced into a high-temperature reactor together with a carrier gas to form fine carbon fibers into a substrate. It is a carbon fiber produced by being produced on top, produced in a floating state, or grown on a reactor wall. A carbon fiber having the above characteristics (C) and (D) can be obtained by appropriately adjusting the supply amount of the raw material gas, the substrate temperature and the like during the production of the carbon fiber. In addition, single-walled carbon nanotubes, multi-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanocoils, and the like can be used as the carbon fibers.

(Electrolyte)
The electrolytic solution 15 includes at least an electrolyte, an aprotic solvent, and an additive (such as a compound represented by the general formula (1)).

(Electrolytes)
As the electrolyte, in the case of a lithium secondary battery, a lithium salt is used and dissolved in an aprotic solvent. The lithium salt, lithium imide _{salt, LiPF 6, LiAsF 6, LiAlCl} 4, LiClO 4, LiBF 4, LiSbF 6 , and the like. Of these, LiPF ₆ and LiBF ₄ are particularly preferable. LiN The lithium imide salt _{(C k F 2k + 1 SO} 2) (C m F 2m + 1 SO 2) (k, m are each independently 1 or 2). These can be used alone or in combination of two or more. By including these lithium salts, a high energy density can be achieved.

(Aprotic solvent)
The aprotic electrolyte is selected from organic solvents such as cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and their fluorinated derivatives. In addition, at least one organic solvent is used. More specifically,
Cyclic carbonates: propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and derivatives thereof Chain carbonates: dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), Dipropyl carbonate (DPC) and derivatives thereof Aliphatic carboxylic acid esters: methyl formate, methyl acetate, ethyl propionate, and derivatives thereof γ-lactones: γ-butyrolactone, and derivatives thereof Cyclic ethers: Tetrahydrofuran , 2-methyltetrahydrofuran chain ethers: 1, 2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, and derivatives thereof Other: Dimethylsulfoxy Sid, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl 2-Imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylate, one or two of these The above can be mixed and used.

(Additive)
As the additive, a chain disulfonic acid ester represented by the general formula (1) is used.

(However, in the said General formula (1), R < ₁ > and R < ₄ > are respectively independently a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group, a substituted or unsubstituted C1-C5. An alkoxy group, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, —SO ₂ X ₁ (wherein X ₁ is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms). alkyl group), - SY ₁ (Y ₁ is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), - COZ (Z is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms. An alkoxy group, substituted or Substituted phenoxy group, substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, polyfluoroalkyl group having 1 to 5 carbon atoms, substituted or unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, 1 to carbon atoms 5 polyfluoroalkoxy group, hydroxyl group, halogen atom, -NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and _{-NY 2 CONY 3 Y 4 (Y} 2 ~Y 4 are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), indicating the atom or a group selected from.).

  The compound represented by the general formula (1) is an acyclic compound and does not involve a cyclization reaction during synthesis, and can be synthesized using, for example, Non-Patent Documents 1 to 4. Moreover, it can also be obtained as a by-product of the synthesis of a cyclic sulfonic acid ester having two sulfonyl groups shown in Patent Document 9. Thus, the compound represented by the general formula (1) has an advantage that an inexpensive electrolytic solution can be provided because the synthesis process is easy.

Preferred molecular structures of R ₁ and R _{4 in} the general formula (1) include ease of forming a reactive film on the electrode, stability of the compound, ease of handling, solubility in a solvent, From the viewpoints of ease of synthesis, cost, etc., each independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, and SO ₂ X ₁ (X ₁ is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms. Atoms or groups selected from the above-mentioned alkyl groups, each independently preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 5 carbon atoms, more preferably a hydrogen atom or a methyl group.

Particularly preferred embodiments of R ₁ and R ₄ is where R ₁ and R ₄ is a hydrogen atom. This is because when R ₁ and R ₄ are hydrogen atoms, the methylene moiety sandwiched between the two sulfonyl groups is activated and a reaction film on the electrode is easily formed.

In addition, in R ₂ and R ₃ , from the viewpoints of stability of the compound, ease of synthesis of the compound, solubility in a solvent, price, and the like, each independently substituted or unsubstituted alkyl having 1 to 5 carbon atoms A group, a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, a substituted or unsubstituted phenoxy group, a hydroxyl group, a halogen atom, and NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom, Or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms) is preferable, and each independently is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted group. An alkoxy group having 1 to 5 carbon atoms is more preferable, and one or both of R ₂ and R ₃ is a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms. For the same reason, the substituted or unsubstituted alkyl group having 1 to 5 carbon atoms is preferably a methyl group or ethyl group, and the substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms is a methoxy group or An ethoxy group is preferable.

  The compound of the general formula (1) has two sulfonyl groups, has a small LUMO, and has a smaller LUMO value than solvent molecules and monosulfonic acid esters in the electrolytic solution, and thus is easily reduced. For example, Compound No. 1 shown in Table 1 below. The LUMO of 1 is as small as -0.86 eV according to semiempirical molecular orbital calculation. For this reason, compound No. 1 is preceded by a solvent (LUMO: about 1.2 eV) comprising a cyclic carbonate or a chain carbonate. It is considered that 1 reduction film is formed on the negative electrode and plays a role of suppressing decomposition of the solvent molecules. In order to suppress the decomposition of the solvent molecules, it is difficult to form a highly resistant solvent molecule decomposition film on the negative electrode, so that an increase in resistance and an improvement in cycle characteristics can be expected. Moreover, it is considered that two electron-withdrawing sulfonyl groups are bonded to the carbon atom, and a film is easily formed on the electrode by the activation of the carbon atom.

  In particular, with respect to the negative electrode having the above-described structure, the compound represented by the general formula (1) effectively forms a film on the surface of the negative electrode and simultaneously forms an effective film on the surface of the positive electrode. It is considered that there is an effect of suppressing resistance increase in order to suppress the decomposition of and inhibit the deposition of resistive substances. Moreover, in order to suppress the rise in the battery internal impedance at the end of discharge, the coating is considered to be effective for improving the charge / discharge efficiency and the charge / discharge cycle.

  Further, in the secondary battery of the present invention, since amorphous carbon is used as a material capable of inserting and extracting lithium ions during charging and discharging, the volume change of the negative electrode accompanying the insertion and extraction of lithium ions is small, and the negative electrode A stable film of the compound of the general formula (1) can be formed on the top. Furthermore, by including at least one of conductive graphite particles and conductive carbon fibers in the negative electrode active material layer, the conductivity of the negative electrode is improved and the synergistic action with the compound of the general formula (1) allows It is possible to stabilize the film formed on the surface.

  Although the specific example of General formula (1) is shown below, this invention is not specifically limited to these.

  Although the compound represented by General formula (1) is not specifically limited, It is preferable that 0.1 to 5.0 mass% is contained in electrolyte solution. If it is less than 0.1% by mass, a sufficient effect may not be exhibited in forming a film by an electrochemical reaction on the electrode surface. Moreover, when it exceeds 5.0 mass%, it not only becomes difficult to melt | dissolve, but the viscosity of electrolyte solution may be enlarged. In the present invention, more preferably, a sufficient film effect can be obtained by adding in the range of 0.5% by mass to 3.0% by mass.

You may use the compound shown in General formula (1) individually or in combination of 2 or more types. When two or more types are used in combination, it is not particularly limited, but at least one of them contains a compound having an active methylene group (that is, a compound in which R ₁ and R ₄ are hydrogen) from the viewpoint of easy film formation with an electrode. Is effective. As a specific combination, the above-mentioned compound no. 1 (compound having an active methylene group) and compound no. 5 compounds.

  When two or more types of the compound of the general formula (1) are added to the electrolytic solution, the proportion of the electrolytic solution in the electrolytic solution is not particularly limited, but for the same reason as described above, the two types are combined to be 0.1% by mass or more and 5.0% by mass. The following is preferred. Further, when two or more kinds of the compound of the general formula (1) are added, the ratio of each compound to the total mass of the compound of the general formula (1) is not particularly limited, but the ratio of the smallest compound is 5 It is preferable that the ratio of the compound with the most mass% is 95 mass%.

  Furthermore, the electrolyte solution containing the compound of the general formula (1) contains at least one of a cyclic monosulfonic acid ester, a cyclic sulfonic acid ester having two sulfonyl groups, an alkanesulfonic acid anhydride, and a sulfolene compound. It is also effective to use an electrolyte solution.

  Examples of the cyclic monosulfonic acid ester include compounds represented by the following general formula (2).

(However, in the general formula (2), n is 0 to 2 integer. Also, R ₅ to R ₁₀ each independently represent a hydrogen atom, a substituted or unsubstituted alkyl having 1 to 12 carbon atoms An atom or group selected from a group, a substituted or unsubstituted fluoroalkyl group having 1 to 6 carbon atoms, and a polyfluoroalkyl group having 1 to 6 carbon atoms.
In the compound represented by the general formula (2), n is preferably 0 or 1 from the viewpoints of stability of the compound, ease of synthesis of the compound, solubility in a solvent, price, and the like, and R _{5 to} R ₁₀ Are preferably each independently an atom or group selected from a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, and a polyfluoroalkyl group having 1 to 5 carbon atoms. A hydrogen atom or a polyfluoroalkyl group having 1 to 5 carbon atoms is more preferable. More preferably, all of R _{5 to} R ₁₀ are hydrogen atoms, or one or two of R _{5 to} R ₁₀ are polyfluoroalkyl groups having 1 to 5 carbon atoms, and the other is a hydrogen atom. As said C1-C5 polyfluoroalkyl group, a trifluoromethyl group is preferable.

  Specifically, 1,3-propane sultone (1,3-PS), α-trifluoromethyl-γ-sultone, β-trifluoromethyl-γ-sultone, γ-trifluoromethyl-γ-sultone, α -Methyl-γ-sultone, α, β-di (trifluoromethyl) -γ-sultone, α, α-di (trifluoromethyl) -γ-sultone, α-undecafluoropentyl-γ-sultone, α- Examples include heptafluoropropyl-γ-sultone and 1,4-butane sultone (1,4-BS).

  Among them, 1,3-propane sultone (1,3-PS) is considered to form a decomposition film on the negative electrode of a lithium ion secondary battery. 1, 3-PS has a LUMO of 0.07 eV. It is larger than that of 1 (−0.86 eV). For example, compound no. When 1 and 1, 3-PS were added to the electrolyte and charged, first, compound No. 1 was used. It is conceivable that one substance forms a film on the negative electrode, and then 1,3-PS forms a film. At the initial stage of charging, a portion having a negative electrode surface and compound No. 1 reacts mainly, but compound no. Charge proceeds at the portion that did not react with 1 (the portion that may react with the solvent molecule) and reacted with 1,3-PS. A composite film of 1 and 1,3-PS is formed, and further resistance increase suppression effect, battery swelling expansion, and the like can be expected.

  When the compound of the general formula (2) is added to the electrolytic solution, the content in the electrolytic solution is not particularly limited, but 0.5% by mass to 10.0% by mass is contained in the electrolytic solution. Is preferred. If the amount is less than 0.5% by mass, the effect may not be sufficiently exerted on the film formation by the electrochemical reaction on the electrode surface. If it exceeds 10.0 mass%, the viscosity of the electrolytic solution may be increased. Moreover, as a ratio of the general formula (2) in the compound of the general formula (1) and the general formula (2), the total mass of the compound of the general formula (1) and the compound of the general formula (2), respectively, 10 to 90% by mass is preferable.

  Examples of the cyclic sulfonic acid ester having two sulfonyl groups include compounds represented by the following general formula (3).

(However, in the said General formula (3), Q is an oxygen atom, a methylene group, or a single bond, A is a substituted or unsubstituted C1-C5 alkylene group, a carbonyl group, a sulfinyl group, C1-C5. At least one C—C bond in the polyfluoroalkylene group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, or a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms is a C—O—C bond A group in which at least one C—C bond in the C 1-5 polyfluoroalkylene group is a C—O—C bond, and a substituted or unsubstituted C 1-5 fluoroalkylene A group selected from a group in which at least one C—C bond in the group is a C—O—C bond, B is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, carbon Number 1-5 polyfluoroalkylene group, and a substituted or unsubstituted group selected from fluoroalkylene group having 1 to 5 carbon atoms.)
In the compound represented by the general formula (3), A is a substituted or unsubstituted carbon number of 1 to 5 from the viewpoints of stability of the compound, ease of synthesis of the compound, solubility in a solvent, price, and the like. At least a C-C bond in the alkylene group, a polyfluoroalkylene group having 1 to 5 carbon atoms, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, and a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms. A group in which one site is a C—O—C bond, a group in which at least one C—C bond in a C 1-5 polyfluoroalkylene group is a C—O—C bond, and a substituted or unsubstituted group A group selected from a group in which at least one C—C bond in the fluoroalkylene group having 1 to 5 carbon atoms is a C—O—C bond is preferable. A group selected from a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a polyfluoroalkylene group having 1 to 5 carbon atoms, and a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms is more preferable. Alternatively, an unsubstituted alkylene group having 1 to 5 carbon atoms is more preferable, and a methylene group, an ethylene group, or a 2,2-propanediyl group is particularly preferable. The C1-C5 fluoroalkylene group preferably includes a methylene group and a difluoromethylene group, and more preferably includes a methylene group and a difluoromethylene group.

  For the same reason, B is preferably an alkylene group having 1 to 5 carbon atoms, more preferably a methylene group, a 1,1-ethanediyl group, or a 2,2-propanediyl group.

  The cyclic sulfonic acid ester having two of these sulfonyl groups is disclosed in Patent Document 10.

  Specific compounds represented by the general formula (3) are listed below, but are not limited thereto.

  These compounds have the same level of LUMO as the compound of the general formula (1) of the present invention and have two or more sulfonyl groups. 1 and compound no. When 21 (MMDS) is added to the electrolyte, a high ion conductive composite film is easily formed in the initial stage of charging. MMDS is considered to be a compound that easily forms a film by reacting with the negative electrode by ring opening.

  If MMDS contributes to the film formation fairly selectively on the negative electrode, compound no. In the case of the first material, the film formation probability on the negative electrode is decreased, the reaction probability on the positive electrode is increased, and the film formation on the positive electrode is achieved. As a result, suppression of solvent decomposition on the positive electrode can be expected.

  When the compound of the general formula (3) is added to the electrolytic solution, the content of the compound of the general formula (3) in the electrolytic solution is not particularly limited, but 0.5% by mass or more and 10. It is preferably contained in an amount of 0% by mass or less. If the amount is less than 0.5% by mass, the effect may not be sufficiently exerted on the film formation by the electrochemical reaction on the electrode surface. If it exceeds 10.0 mass%, the viscosity of the electrolytic solution may be increased. As a ratio of the compound of the general formula (3) in the general formula (1) and the general formula (3), 10 to 90% by mass of the total mass of the compound of the general formula (1) and the general formula (3) is preferable. . Moreover, when using the compound of General formula (2) in addition to this, 10-90 mass% of the total mass of the compound of General formula (1), General formula (2), and General formula (3) is preferable.

  In the present invention, in some cases, at least one of vinylene carbonate (VC) and its derivatives can be added to the electrolytic solution. The cycle characteristics can be further improved by adding at least one of VC and its derivatives. The LUMO of VC is 0.09 eV and is less susceptible to the reduction reaction than the compound of general formula (1). It is considered that it exists in the electrolyte for a long time without being consumed after receiving the reduction reaction in the initial charge and discharge. Therefore, it is possible to contribute to the improvement of cycle characteristics by being gradually consumed during the charge / discharge cycle. When at least one of the vinylene carbonate and its derivatives is used as an additive for an electrolytic solution, the effect can be obtained by including 0.05% by mass to 3.0% by mass in the electrolytic solution.

  When the compound of the general formula (1) and VC, the compound of the general formula (1) and other additives, and VC are further added to the electrolytic solution, the proportion of VC in the whole electrolytic solution is not particularly limited. Is preferably 0.5% by mass to 10.0% by mass. If the amount is less than 0.5% by mass, the effect may not be sufficiently exerted on the film formation by the electrochemical reaction on the electrode surface. If it exceeds 10.0 mass%, the viscosity of the electrolytic solution may be increased.

  The electrolytic solution of the present invention is brought about by adding and dissolving the compound represented by the general formula (1) in the electrolytic solution in advance. By appropriately adding other additive materials (cyclic monosulfonic acid ester, cyclic sulfonic acid ester having two sulfonyl groups, sulfolane, alkanesulfonic acid anhydride, sulfolene compound or vinylene carbonate compound) to this electrolytic solution, The electrolyte solution can be obtained.

  The shape of the secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical shape, a square shape, a coin shape, and a laminate shape. Among them, the laminate type has a shape sealed by an exterior body made of a flexible film made of a laminate of a synthetic resin and a metal foil, and cans such as a cylindrical type, a square type, and a coin type It is more susceptible to an increase in internal pressure than that enclosed in an outer package, and therefore control of the chemical reaction between the electrode and the interface between the electrolytic solution is more important. In the case of a secondary battery containing a chain disulfone compound represented by the general formula (1) according to the present invention, even in a laminate type battery, resistance increase is suppressed and battery swelling (gas generation and internal pressure increase). ) Can be suppressed. Therefore, safety and long-term reliability can be ensured even in a large-sized lithium ion secondary battery such as an automobile.

  In the lithium secondary battery according to the present invention, the negative electrode 13 and the positive electrode 12 are laminated via the separator 16 in a dry air or an inert gas atmosphere, or the laminated one is wound, and then inserted into the outer package. It is obtained by impregnating an electrolytic solution containing a compound represented by the formula (1) and then sealing the battery outer package. The effect of the present invention can be obtained by forming the film on the electrode by charging the battery before or after sealing.

(Production of battery)
(Positive electrode)
A positive electrode active material described in Tables 1 to 3 and a conductivity-imparting agent were dry-mixed and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) in which PVDF as a binder was dissolved to prepare a slurry. . Conductive carbon black was used as the conductivity imparting agent. The slurry was applied on an aluminum metal foil having a thickness of 25 μm to be the positive electrode current collector 11, and then NMP was evaporated to obtain a positive electrode sheet. The solid content ratio in the positive electrode was positive electrode active material: conductivity imparting agent: PVDF = 80: 10: 10 (mass%).

(Negative electrode)
For Examples 1 to 36 and Comparative Examples 1 to 6, 9, and 10, amorphous carbon capable of occluding and releasing lithium ions during charge and discharge, and conductive substances described in Tables 4 to 6 (conductive graphite) Particles, conductive carbon fiber) and PVDF as a binder were mixed so that the conductive substance had a ratio (mass%) shown in Tables 4 to 6, and dispersed in NMP to prepare a slurry. The slurry was applied on a 20 μm thick copper foil to be the negative electrode current collector 14, and then NMP was evaporated to obtain a negative electrode sheet. The PVDF ratio in the active material layer was 10% by mass.

  For Comparative Examples 7 and 8, negative electrodes were prepared by the same method as above except that graphite was used instead of amorphous carbon.

(Electrolyte)
The electrolyte solution 15 was prepared by dissolving 1 mol / L LiPF ₆ as an electrolyte and the additives listed in Tables 1 to 3 in the solvents listed in Tables 1 to 3.

(Battery assembly)
The positive electrode and the negative electrode were laminated via a separator 16 made of polyethylene to produce an aluminum laminated film type secondary battery (Examples 1 to 36, Comparative Examples 1 to 10). In the case of an aluminum laminate film type secondary battery, the laminate film used has a structure in which a polypropylene resin (sealing layer, thickness 70 μm), polyethylene terephthalate (20 μm), aluminum (50 μm), and polyethylene terephthalate (20 μm) are laminated in this order. Two pieces of this are cut into a predetermined size, and a concave portion having a bottom surface portion and a side surface portion that match the size of the multilayer electrode body is formed in a part thereof, and these are opposed to wrap the multilayer electrode body. Then, the periphery was thermally fused to produce a film-clad battery. Before the last side was heat-sealed and sealed, the electrolyte solution was impregnated with the laminated electrode body.

(Charge / discharge cycle test)
Constant current charging was performed at a charge rate of 1C-end-of-charge voltage of 4.2V, and then constant-current discharge was performed at a discharge rate of 1C-end-of-stop voltage of 2.5V. The charge / discharge cycle test was conducted with this as one cycle. The capacity retention rate (%) is a value obtained by dividing the discharge capacity (mAh) after 600 cycles by the discharge capacity (mAh) at the 10th cycle.

(Storage characteristics test)
Generated at room temperature (25 ° C) at a constant current and a constant voltage of 2A to a final voltage of 4.3V for 5 hours and then discharged to a final voltage of 2.5V under a constant current of 2A. The volume of the battery (initial volume) at this time was measured. After removing the gas, it was allowed to stand for 1 week, and then charged again to 4.3 V at a current value of 2 A at room temperature, and then discharged to 2.5 V at a current value of 2 A. The discharge capacity at this time was defined as the initial discharge capacity. Then, after charging for 2.5 hours to a final voltage of 4.2 V at a constant current and a constant voltage of 2 A, after discharging to a discharge depth of 50%, it was stored at 50 ° C. for 70 days, and a storage characteristic test was performed. . After storage, perform constant-current discharge at room temperature, then perform constant-current charge and constant-current discharge in this order, and let the discharge capacity at this time be the recovery capacity, (capacity recovery rate) = (recovery capacity) / (initial discharge capacity) Calculated as After measuring the recovery capacity, the volume of the battery was measured, and the difference between the volume at this time and the initial volume was calculated as the volume change amount. Further, the resistance increase rate was calculated by dividing the resistance value after storage by the resistance value at the start of storage.

(Confirmation of amorphous carbon)
In Examples 1 to 36 and Comparative Examples 1 to 6, 9, and 10, the above charge / discharge cycle test was performed, the X-ray diffraction spectra during charging and discharging were measured, and there was no change in peak due to carbon crystals. The confirmed amorphous carbon was used.

(BET specific surface area)
Using a specific surface area measuring device (SA-1000) manufactured by Shibata Rikagaku Co., the nitrogen adsorption BET one-point method was used.

(Average particle size)
Using a Horiba laser diffraction / scattering particle size distribution analyzer (LA-920), the 50% cumulative average particle size (D ₅₀ ) on a volume basis was measured. For the measurement, 1.0 g of graphite particles was added to 150 ml of pure water, and then a slurry in which this was dispersed was used as a measurement sample.

(Average fiber diameter and average fiber length)
In the case of the average fiber diameter, 100 cross-sections obtained by cutting the carbon fiber, and in the case of the average fiber length, 100 images were randomly sampled using an optical microscope. Thereafter, the image information was introduced into an image analysis apparatus (LUZEX AP) manufactured by Nicole via an interface for analysis, and the average fiber diameter and average fiber length were measured. In addition, the average fiber diameter measured the diameter of the longest part in a fiber cross section.

  In Tables 1 to 3, “No.” in the “Type and composition of additives in electrolyte solution” column is Compound No. Represents.

  "-" In Tables 4-6 represents a non-relevant item of the present invention.

  The results obtained in the charge / discharge cycle test and the storage characteristic test are shown in Tables 7 to 9 below. The resistance increase rate in the storage characteristics is a relative value when the resistance value at the start of storage is 1.

(Effect of ratio of conductivity imparting agent)
When the charge / discharge curves (FIG. 2) of the secondary battery of Example 1 and Comparative Example 1 were compared, it was confirmed that both the charge / discharge capacity and the charge / discharge efficiency were improved, and that a conductive material was necessary. . Further, comparing the results of Example 1 and Comparative Example 1, the capacity retention rate, the resistance increase rate, the capacity recovery rate, and the cell volume change amount are all improved and formed on the negative electrode by the addition of the conductive material. It was confirmed that the coated film was stabilized and the charge / discharge cycle characteristics and storage characteristics were improved.

  When the capacity retention rate, resistance increase rate, capacity recovery rate, and cell volume change amount in Examples 1 to 4 were compared with Examples 20 to 23, both the charge / discharge cycle characteristics and the storage characteristics were improved, and the negative electrode in the present invention The proportion of the conductive material in the active material layer was preferably 5% by mass or less, and more preferably 3% by mass or less.

  Further, when Examples 1, 15 to 19 and Comparative Examples 9 and 10 are compared, the capacity retention rate, resistance increase rate, capacity recovery rate, and cell volume change amount are all improved, and graphite is used as a conductive material in the negative electrode. It was confirmed that charging / discharging cycle characteristics and storage characteristics were improved by adding at least one of carbonaceous particles and carbon fibers.

(Effects of BET specific surface area and average particle diameter of graphite particles)
When the capacity retention rate, the resistance increase rate, the capacity recovery rate, and the cell volume change amount in Examples 1 and 5 to 8 were compared with Examples 24 to 26, it was confirmed that the charge / discharge cycle characteristics and the storage characteristics were improved. From these results, in the graphite particles in the present invention,
(A) It was confirmed that the BET specific surface area was 70 m ² / g or less. (B) The average particle diameter was preferably 10 μm or less.

(Effect of average fiber diameter and average fiber length of carbon fiber)
When the capacity retention rate, the resistance increase rate, the capacity recovery rate, and the cell volume change amount in Examples 15 to 19 were compared with Examples 31 to 36, the charge / discharge cycle characteristics and the storage characteristics were improved. From these results, in the carbon fiber in the present invention,
(C) It was confirmed that the average fiber diameter was 0.05 μm or more and (D) the average fiber length was 25 μm or less.

(Effect by adding compound of general formula (1))
When the capacity retention rate, the resistance increase rate, the capacity recovery rate, and the cell volume change amount in Example 1 were compared with the results of Comparative Examples 2 and 3, improvements in charge / discharge cycle characteristics and storage characteristics were confirmed. In particular, the cell volume change amount of Example 1 is smaller than that of Comparative Examples 2 and 3. This is presumably because the decomposition film of the compound (1) was formed on the electrode and the decomposition of the electrolytic solution and the accompanying gas generation could be suppressed.

When the negative electrode surface and the positive electrode surface after the cycle test of the battery shown in Example 1 were examined using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX), LiF, LiCO ₃ The existence of such was shown. Moreover, as a result of performing peak splitting of the sulfur spectrum by XPS analysis, it was confirmed that a substance having a peak near 164 eV was present in both the positive electrode and the negative electrode. In Comparative Examples 2 and 3, there is no substance having a peak in the vicinity of 164 eV in both the positive electrode and the negative electrode, and it is considered that a unique film was formed by adding the additive of the present invention.

(Effect of concentration change in electrolyte solution of compound of general formula (1))
When the capacity retention rate, the resistance increase rate, the capacity recovery rate, and the cell volume change amount in Examples 1 and 9 to 11 were compared with Examples 29 and 30, additive No. It was confirmed that both the charge / discharge cycle characteristics and the storage characteristics deteriorate at a concentration of less than 0.1% by mass and more than 5.0% by mass in the electrolyte solution of 1, and the compound of the general formula (1) The concentration in the electrolyte solution was preferably 0.1% by mass or more and 5.0% by mass or less, and a more preferable concentration range was 0.5% by mass or more and 3.0% by mass or less.

(Effects of using amorphous carbon for the negative electrode)
When the capacity retention rate, the resistance increase rate, the capacity recovery rate, and the cell volume change amount in Examples 1 and 15 were compared with Comparative Examples 7 and 8, both the cycle characteristics and the storage characteristics were improved, and these characteristics were improved. In order to keep it, it was confirmed that amorphous carbon is a suitable material.

(Effect of adding cyclic monosulfonic acid ester)
When Example 12 was compared with Example 1, it was confirmed that charge and discharge cycle characteristics and storage characteristics were improved. In particular, the improvement of the cell volume change amount is because the irreversible reaction is suppressed by the addition of 1,3-PS due to the stabilization of the film existing at the interface between the electrode surface and the electrolyte and the high ion conductivity of the film, and This is probably because the decomposition of the electrolyte and the accompanying gas generation were greatly suppressed. Moreover, when Example 12 and Comparative Example 4 are compared, it is confirmed that only 1,3-PS has no effect, and that a higher effect is exhibited by mixing with the compound represented by the general formula (1) of the present invention. did it.

(Effect of adding cyclic disulfonic acid ester (cyclic sulfonic acid ester having two sulfonyl groups))
When Example 13 was compared with Example 1, an improvement was confirmed in the resistance increase rate and the cell volume change amount. The improvement in the resistance increase rate can be achieved by adding a compound represented by the general formula (1) of the present invention and a cyclic sulfonic acid ester having two sulfonyl groups to the electrolyte solution, so that no additive system or conventional additive system can be used. This is probably because a film having a higher ion conductivity and higher stability during storage was formed. In addition, the improvement in the cell volume change amount is shown in Compound No. It is considered that a film was formed on the negative electrode due to the combined effect of No. 1 and MMDS, and the decomposition of the electrolyte and the accompanying gas generation could be greatly suppressed. Further, when Example 13 and Comparative Example 5 were compared, it was confirmed that only MMDS had no effect, and that a higher effect was exhibited by mixing with the compound represented by the general formula (1) of the present invention.

(Verification of the effects of adding VC)
When Example 14 was compared with Example 12, the charge / discharge cycle characteristics and the storage characteristics were improved. By further adding VC to the electrolytic solution containing the compound represented by the general formula (1) and the cyclic monosulfonic acid ester, the ionic conductivity is higher and the stability during storage and charge / discharge cycle is higher. This is probably because a film was formed. Further, when Example 14 and Comparative Example 6 are compared, only 1,3-PS and VC are not effective, and a higher effect is exhibited by mixing with the compound represented by the general formula (1) of the present invention. confirmed.

It is a schematic block diagram of the secondary battery which concerns on this invention. It is a figure showing the charging / discharging curve of the secondary battery of Example 1 of this invention, and Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Positive electrode collector 12 Layer containing positive electrode active material 13 Layer containing negative electrode active material 14 Negative electrode collector 15 Nonaqueous electrolyte solution 16 Porous separator

Claims (18)

In a secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution containing an aprotic solvent in which an electrolyte is dissolved,
The negative electrode includes an active material layer including amorphous carbon capable of occluding and releasing lithium ions during charge and discharge, and at least one of conductive graphite particles and conductive carbon fibers,
The secondary battery, wherein the electrolytic solution includes a compound represented by the following general formula (1).

(However, in the said General formula (1), R < ₁ > and R < ₄ > are respectively independently a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group, a substituted or unsubstituted C1-C5. An alkoxy group, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, —SO ₂ X ₁ (wherein X ₁ is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms). alkyl group), - SY ₁ (Y ₁ is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), - COZ (Z is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms. An alkoxy group, substituted or Substituted phenoxy group, substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, polyfluoroalkyl group having 1 to 5 carbon atoms, substituted or unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, 1 to carbon atoms 5 polyfluoroalkoxy group, hydroxyl group, halogen atom, -NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and _{-NY 2 CONY 3 Y 4 (Y} 2 ~Y 4 are each independently a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), indicating the atom or a group selected from.)   The secondary battery according to claim 1, wherein a total content of the conductive graphite particles and conductive carbon fibers in the active material layer of the negative electrode is 5% by mass or less. The secondary battery according to claim 1, wherein the conductive graphite particles have (A) a BET specific surface area of 70 m ² / g or less and (B) an average particle diameter of 10 μm or less. .   The secondary battery according to claim 1, wherein the conductive graphite particles include conductive carbon black or artificial graphite.   5. The conductive carbon fiber according to claim 1, wherein (C) the average fiber diameter is 0.05 μm or more and (D) the average fiber length is 25 μm or less. Next battery.   The secondary battery according to claim 1, wherein the conductive carbon fiber is a vapor-grown carbon fiber.   The secondary battery according to any one of claims 1 to 6, wherein a content of the compound represented by the general formula (1) in the electrolytic solution is 0.1 to 5.0% by mass. . The secondary battery according to any one of claims 1 to 7, wherein the electrolytic solution further includes a cyclic monosulfonic acid ester represented by the following general formula (2).

(However, in the general formula (2), n is 0 to 2 integer. Also, R ₅ to R ₁₀ each independently represent a hydrogen atom, a substituted or unsubstituted alkyl having 1 to 12 carbon atoms An atom or group selected from a group, a substituted or unsubstituted fluoroalkyl group having 1 to 6 carbon atoms, and a polyfluoroalkyl group having 1 to 6 carbon atoms. The secondary battery according to claim 1, wherein the electrolytic solution further includes a cyclic sulfonic acid ester having two sulfonyl groups represented by the following general formula (3).

(However, in the said General formula (3), Q is an oxygen atom, a methylene group, or a single bond, A is a substituted or unsubstituted C1-C5 alkylene group, a carbonyl group, a sulfinyl group, C1-C5. At least one C—C bond in the polyfluoroalkylene group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, or a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms is a C—O—C bond A group in which at least one C—C bond in the C 1-5 polyfluoroalkylene group is a C—O—C bond, and a substituted or unsubstituted C 1-5 fluoroalkylene A group selected from a group in which at least one C—C bond in the group is a C—O—C bond, B is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, carbon Number 1-5 polyfluoroalkylene group, and a substituted or unsubstituted group selected from fluoroalkylene group having 1 to 5 carbon atoms.)   The secondary battery according to any one of claims 1 to 9, wherein the electrolytic solution further contains at least one of vinylene carbonate and a derivative thereof.   The secondary battery according to any one of claims 1 to 10, wherein the electrolyte includes a lithium salt. The lithium salt is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , and LiN (C _k F _{2k + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) (k, m are The secondary battery according to claim 11, wherein the secondary battery is at least one lithium salt selected from the group consisting of 1 or 2 each independently.   The aprotic solvent is at least selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and their fluorinated derivatives. The secondary battery according to claim 1, wherein the secondary battery is an organic solvent.   The secondary battery according to claim 1, wherein the secondary battery is enclosed in a film outer package. The secondary battery according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by the following formula (4).

The secondary battery according to claim 1, wherein the conductive graphite particles have an average particle diameter of 10 μm or less. The secondary battery according to claim 1, wherein an average fiber diameter of the conductive carbon fibers is 0.05 μm or more. 18. The secondary battery according to claim 1, wherein an average fiber length of the conductive carbon fiber is 25 μm or less.

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