JP6652814B2 - Lithium battery and method of manufacturing the same - Google Patents

Description

  The present invention relates to a lithium battery and a method for manufacturing the same.

Hitherto, Ni—Mn spinels such as LiNi _0.5 Mn _1.5 O ₄ have been proposed as a positive electrode active material for lithium batteries (see Non-Patent Document 1). Since the Ni-Mn spinel can insert and desorb Li ⁺ at about 4.6 to 4.8 V (vs. Li ⁺ / Li), a battery with an average voltage of about 4.6 V when combined with a graphite negative electrode Can be configured. However, a lithium battery using Ni-Mn spinel has a high positive electrode potential. Therefore, when a conventional lithium battery electrolyte solvent, such as ethylene carbonate, is used, oxidative decomposition occurs at the positive electrode and durability may be poor. . Therefore, it has been proposed to use a fluorine-substituted solvent having high acid resistance (see Non-Patent Document 2).

Although not related to a lithium battery, a fluorinated aryl group or a fluorinated aryl group is contained in a 1,2-dimethoxyethane solvent containing a lithium salt such as LiF, LiCl, LiBr, LiI, CF ₃ COOLi, and C ₂ F ₅ COOLi. It has been studied to add a borate compound having an alkyl (see Non-Patent Document 3). By doing so, the degree of dissociation of the lithium salt can be increased, and the ionic conductivity of the solution can be increased.

Q. Zhong et al., J. Electrochem. Soc., 144, 1, (1997) 205-213. Z. Zhang et al., Energy Environ. Sci., 2013, 6, 1806-1810. H. S. Lee et al., J. Electrochem. Soc., 145, 8, (1998) 2813-2818.

  However, although the lithium battery of Non-Patent Document 2 is said to exhibit high durability by using a fluorine-substituted solvent, gas generation in the battery may not be sufficiently suppressed, and gas generation in the battery may not be sufficient. It has been desired to further suppress. Non-Patent Document 3 merely examines the improvement of the dissociation degree of a lithium salt and the improvement of the ionic conductivity of a solution by adding a borate compound.

  The present invention has been made to solve such a problem, and has as its main object to further suppress gas generation in a lithium battery.

In order to achieve the above-mentioned object, the present inventors have intensively studied. In a lithium battery provided with a positive electrode active material having a Li insertion / desorption potential of 4.4 V or more (vs. Li ⁺ / Li), an electrolytic solution containing a carbonate-based solvent, a supporting salt, and a predetermined amount of a predetermined borate compound It has been found that the use of is able to further suppress the generation of gas in the lithium battery, and the present invention has been completed.

That is, the lithium battery of the present invention is:
A positive electrode including a positive electrode active material having a Li insertion / desorption potential of 4.4 V or more based on lithium;
A negative electrode containing a negative electrode active material;
Interposed between the positive electrode and the negative electrode, a carbonate-based solvent, a supporting salt, and a borate compound having a structure in which three hydrogens of orthoboric acid are substituted with a fluorinated alkyl group, including the borate compound. An electrolyte contained in a range of 0.01 mol / L or more and 0.4 mol / L or less;
It is provided with.

The method for producing a lithium battery of the present invention comprises:
Between a positive electrode containing a positive electrode active material having a Li insertion / desorption potential of 4.4 V or more based on lithium and a negative electrode containing a negative electrode active material, a carbonate-based solvent, a supporting salt, and three hydrogens of orthoboric acid are formed. A borate compound having a structure substituted with a fluorinated alkyl group, and the electrolyte solution containing the borate compound in a range of 0.01 mol / L or more and 0.4 mol / L or less is injected.

According to the lithium battery and the method for manufacturing the same, gas generation in the lithium battery can be further suppressed. The reason why these effects can be obtained is presumed as follows. For example, even when a borate compound that is a Lewis base interacts with a carbonate-based solvent having a lone electron pair, even when a positive electrode containing a positive electrode active material having a Li insertion / desorption potential of 4.4 V or more on a lithium basis is used. It is considered that the oxidative decomposition of the carbonate-based solvent on the positive electrode can be suppressed. H ⁺ generated by the oxidative decomposition of the carbonate-based solvent may move to the negative electrode and generate hydrogen gas. However, by suppressing the oxidative decomposition of the carbonate-based solvent, gas generation in the lithium battery is suppressed as a result. It is considered possible.

FIG. 2 is a schematic diagram illustrating an example of a lithium battery 10.

  The lithium battery of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution interposed between the positive electrode and the negative electrode and conducting lithium ions.

The positive electrode of the lithium battery of the present invention contains a positive electrode active material having a Li insertion / desorption potential of 4.4 V or more based on lithium. Examples of the positive electrode active material include spinel-type lithium nickel manganese oxide, olivine-type lithium cobalt phosphate, olivine-type lithium nickel phosphate, and the like. The spinel type lithium-nickel-manganese oxide, for _{example, Li a Ni b Mn c Me} d O e (Me is Mn, a transition metal element other than Ni, is at least one element selected from Al and alkaline earth metal , A to e are 0.9 ≦ a ≦ 1.2, 0.45 ≦ b ≦ 0.55, 1.45 ≦ c ≦ 1.55, 0 ≦ d ≦ 5.00, 3.8 ≦ e ≦ 4 .2) and the like. The transition metal as Me can be, for example, V, Ti, Cr, Fe, Co, Cu, or the like. The olivine-type lithium phosphate cobalt is like LiCoPO _4, and the like LiNiPO ₄ as olivine-type lithium nickel phosphate. As the positive electrode active material, among those described above, a spinel type lithium nickel manganese oxide is preferable, and LiNi _0.5 Mn _1.5 O ₄ is more preferable. Note that, in the present invention, the substance represented by each chemical formula is not limited to those having a stoichiometric composition, and some of the elements may be excessive, defective, or replaced with another element. Good.

  This positive electrode is prepared by mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode material, coating and drying the surface of the current collector, and, if necessary, It may be formed by compression to increase the density. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale graphite, flake graphite) or artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fiber, and one or a mixture of two or more of metals (copper, nickel, aluminum, silver, gold, and the like) can be used. Among these, carbon black and acetylene black are preferable as the conductive material from the viewpoints of electron conductivity and coatability. The binder plays a role of binding the active material particles and the conductive material particles. For example, a binder resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a fluorine-containing resin such as fluororubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Further, an aqueous dispersion of a cellulose-based or styrene-butadiene rubber (SBR) as an aqueous binder can also be used. Examples of the solvent in which the positive electrode active material, the conductive material, and the binder are dispersed include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylene triamine, N, N-dimethylaminopropylamine And organic solvents such as ethylene oxide and tetrahydrofuran. Further, a dispersant, a thickener, and the like may be added to water, and the active material may be slurried with a latex such as SBR. As the thickener, for example, polysaccharides such as carboxymethylcellulose and methylcellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as an applicator roll, screen coating, a doctor blade method, spin coating, and a bar coater, and any of these can be used to obtain an arbitrary thickness and shape. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, etc., and aluminum and copper for the purpose of improving adhesion, conductivity and oxidation resistance. The surface of which has been treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the current collector include a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foam, and a formed body of a fiber group. The thickness of the current collector is, for example, 1 to 500 μm.

The negative electrode of the lithium battery of the present invention contains a negative electrode active material. Examples of negative electrode active materials include lithium, lithium alloys, carbonaceous materials capable of absorbing and releasing lithium ions, silicon, silicon compounds, tin, tin compounds, composite oxides containing multiple elements, and conductive polymers. Can be Examples of the carbonaceous material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. As a carbonaceous material, graphite such as artificial graphite and natural graphite has an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and self-discharges when a lithium salt is used as a supporting salt. This is preferable because the irreversible capacity during charging can be reduced and the irreversible capacity during charging can be reduced. Examples of the composite oxide include a lithium titanium composite oxide (eg, LiTi ₂ O ₄ ) and a lithium vanadium composite oxide (eg, LiV ₂ O ₅ ). As the negative electrode active material, a carbonaceous material, silicon, tin, lithium titanium composite oxide and the like are preferable.

  The negative electrode may be formed, for example, by adhering a negative electrode active material and a current collector, or by mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent, and then forming a paste-like negative electrode. The material may be coated on the surface of the current collector and dried, and may be compressed and formed as necessary to increase the electrode density. As the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. The current collector of the negative electrode includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as adhesiveness, conductivity and reduction resistance improvement. For the purpose, for example, one obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver, or the like can be used. For these, the surface can be oxidized. The shape of the current collector can be the same as that of the positive electrode.

  The electrolytic solution of the lithium battery of the present invention contains a carbonate-based solvent, a supporting salt, and a borate compound.

  Examples of the carbonate-based solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, and dicarbonate. Chain carbonates such as -i-propyl carbonate and t-butyl-i-propyl carbonate; Further, the carbonate-based solvent may be one in which at least one hydrogen atom in each of the above-described carbonate-based solvents is substituted with a fluorine atom. As the carbonate-based solvent, one type may be used alone, or two or more types may be used in combination. The carbonate-based solvent preferably contains both a cyclic carbonate and a chain carbonate. Further, the carbonate-based solvent preferably contains a fluorinated carbonate in which at least one hydrogen atom has been replaced with a fluorine atom. It is thought that the one containing fluorinated carbonate can further improve the durability of the lithium battery. The carbonate-based solvent includes fluorinated ethylene carbonate in which at least one hydrogen atom of ethylene carbonate is substituted with a fluorine atom, and fluorinated ethyl methyl carbonate in which at least one hydrogen atom of ethyl methyl carbonate is substituted with a fluorine atom. More preferred.

As the supporting salt, for _{example, LiPF 6, LiClO 4, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiN (FSO 2) 2, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) ₃ , lithium salts such as LiSiF ₆ , LiAlF ₄ , LiSCN, LiCl, LiF, LiBr, LiI, and LiAlCl ₄ . Among them, LiPF ₆ and LiFSI (the above-described LiN (FSO ₂ ) ₂ ) are preferable. The concentration of the supporting salt in the electrolytic solution is preferably 0.1 mol / L or more and 5 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration of the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when the concentration is 5 mol / L or less, the electrolyte can be further stabilized.

The borate compound has a structure in which three hydrogens of orthoboric acid (B (OH) ₃ ) are substituted with a fluorinated alkyl group. The fluorinated alkyl group may have a structure in which one or more of hydrogens included in the alkyl group is substituted with fluorine, may have a structure in which some hydrogens are substituted with fluorine, or may have a structure in which all hydrogens are substituted with fluorine. A substituted structure may be used. It is more preferable that the fluorinated alkyl group has a structure in which at least one or more of the hydrogens bonded to carbon at the terminal of the alkyl group are substituted with fluorine. The alkyl group may be linear or branched, and preferably has 1 to 9 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group and a nonyl group. Further, these alkyl groups may have a substituent. This borate compound may be represented by the following formula (1).

In the formula (1), a fluorinated alkyl _{group, C x1 H y1 F z1,} C x2 H y2 F z2 and C _x3 H _y3 F _z3, may be all the same, two one same but different Or all may be different. Each of x1, x2 and x3 may be 1 or more and 9 or less, but is preferably 6 or less, more preferably 5 or less, still more preferably 4 or less, and still more preferably 1 or more and 2 or less. Each of y1, y2 and y3 may be 0 or more and 18 or less, preferably 12 or less, more preferably 7 or less, still more preferably 3 or less, and still more preferably 0 or more and 2 or less. Each of z1, z2 and z3 may be 1 or more and 19 or less, preferably 13 or less, more preferably 11 or less, still more preferably 7 or less, and still more preferably 1 or more and 5 or less. The borate compound is (2,2,2-trifluoroethyl) borate in which x1, x2, and x3 are all 2, y1, y2, and y3 are all 2, and z1, z2, and z3 are all 3. Is more preferred.

  The electrolyte solution contains a borate compound in a range of 0.01 mol / L or more and 0.4 mol / L or less. Of these, 0.02 mol / L or more is preferable, and 0.03 mol / L or more is more preferable. Further, it is preferably at most 0.3 mol / L, more preferably at most 0.2 mol / L. Within such a range, gas generation in the lithium battery can be further suppressed, and high-temperature durability can be further improved. When the concentration is 0.4 mol / L or less, an increase in negative electrode resistance can be suppressed, and an increase in resistance as a battery can be suppressed.

  The lithium battery of the present invention may include a separator between the positive electrode and the negative electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium battery.For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin microporous membrane of an olefin-based resin such as polyethylene or polypropylene Is mentioned. These may be used alone or in combination of two or more.

  The shape of the lithium battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a stacked type, a cylindrical type, a flat type, and a square type. Further, the present invention may be applied to a large vehicle used for an electric vehicle or the like. FIG. 1 is a schematic diagram showing an example of the lithium battery of the present invention. The lithium battery 10 includes a positive electrode sheet 13 in which a positive electrode active material 12 is formed on a current collector 11, a negative electrode sheet 18 in which a negative electrode active material 17 is formed on a surface of a current collector 14, a positive electrode sheet 13 and a negative electrode sheet 18. And a separator 20 provided between the positive electrode sheet 13 and the negative electrode sheet 18. In this lithium battery 10, a separator 19 is sandwiched between a positive electrode sheet 13 and a negative electrode sheet 18, these are wound and inserted into a cylindrical case 22, and connected to a positive electrode terminal 24 connected to the positive electrode sheet 13 and a negative electrode sheet 18. And the formed negative electrode terminal 26. Here, the positive electrode active material 12 has a Li insertion / desorption potential of 4.4 V or more based on lithium. The electrolytic solution 20 includes a carbonate-based solvent, a supporting salt, and a borate compound having a structure in which three hydrogens of orthoboric acid are substituted with a fluorinated alkyl group, and the borate compound is 0.01 mol / L or more. It is contained in a range of 0.4 mol / L or less.

  In the method for manufacturing a lithium battery according to the present invention, an electrolyte is injected between the positive electrode and the negative electrode. The positive electrode only needs to include a positive electrode active material having a Li insertion / desorption potential of 4.4 V or more on a lithium basis, and the above-described positive electrode of a lithium battery or the like can be used. The negative electrode only needs to include a negative electrode active material, and the above-described negative electrode of a lithium battery or the like can be used. The electrolytic solution includes a carbonate-based solvent, a supporting salt, and a borate compound having a structure in which three hydrogens of orthoboric acid are substituted with a fluorinated alkyl group, wherein the borate compound is contained in an amount of 0.01 mol / L to 0.1 mol / L. What is necessary is just to contain in the range of 4 mol / L or less, and the above-mentioned electrolyte of a lithium battery or the like can be used. The lithium battery of the present invention is not limited to one manufactured by such a manufacturing method, but may be any one manufactured by a manufacturing method that allows an electrolytic solution to be interposed between a positive electrode and a negative electrode. For example, a positive electrode or a negative electrode may be arranged in the electrolytic solution, or a lithium battery may be manufactured using the positive electrode or the negative electrode impregnated with the electrolytic solution in advance. If the concentration of the borate compound in the electrolyte used in the production of the lithium battery is in the range of 0.01 mol / L or more and 0.4 mol / L or less, the concentration of the borate compound in the electrolyte changes during subsequent charging and discharging. It is also considered that gas generation in the lithium battery can be suppressed.

According to the lithium battery and the method for manufacturing the same of the present invention described above, gas generation in the lithium battery can be further suppressed. The reason why these effects can be obtained is presumed as follows. For example, in the lithium battery of Non-Patent Document 2 described above, acid resistance can be increased by using a fluorinated ethylene carbonate solvent (hereinafter, also referred to as FEC), and the Li insertion / desorption potential is 4.6 to lithium based. The durability of a lithium battery using a 4.8 V positive electrode can be increased. However, in the lithium battery of Non-Patent Document 2, it is considered that FEC is oxidized and decomposed at the positive electrode to generate CO ₂ and HF, H ⁺ moves to the negative electrode, and is reduced at the negative electrode to generate hydrogen gas. On the other hand, in the lithium battery of the present invention, since a proper amount of a borate compound having a structure in which three hydrogens of orthoboric acid are substituted with a fluorinated alkyl group is included, it is considered that such a side reaction on the positive electrode can be suppressed. . More specifically, for example, a borate compound that is a Lewis base interacts with a carbonate-based solvent having a lone pair of electrons, thereby suppressing oxidative decomposition of the carbonate-based solvent on the positive electrode. It is thought that gas generation in the inside can be suppressed. In addition, according to the lithium battery of the present invention, since a side reaction on the positive electrode can be suppressed, it is considered that a decrease in battery capacity due to a capacity shift between the positive electrode and the negative electrode due to the side reaction can be suppressed.

  It should be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  Hereinafter, an example in which the lithium battery of the present invention is specifically manufactured will be described as an example.

[Example 1]
(Production of battery)
In a mixed solvent containing monofluoroethylene carbonate (MFEC) and methyl-2,2,2-trifluoroethyl carbonate (MTFEC) in a volume ratio of MFEC: FTFEC = 3: 7, LiPF ₆ was added at a concentration of 1.1 M. A mixed solution containing a concentration was prepared. 3.08 g (0.05 mol / L) of tris (2,2,2-trifluoroethyl) borate (manufactured by Aldrich) was added to 100 mL of the mixed solution to prepare an electrolytic solution.

90% by mass of LiNi _0.5 Mn _1.5 O ₄ as a positive electrode active material, 8% by mass of carbon black as a conductive material, and 2% by mass of polyvinylidene fluoride as a binder, and N as a dispersion medium -Methyl-2-pyrrolidone was added and dispersed in an appropriate amount to obtain a slurry-like positive electrode mixture. The slurry-like positive electrode mixture was applied to both sides of a 15-μm-thick aluminum foil current collector, dried, and then densified by a roll press to obtain a positive electrode sheet. The amount of the positive electrode active material attached was 6.0 mg / cm ² per side.

98% by mass of amorphous coated graphite as a negative electrode active material, 1% by mass of styrene butadiene rubber as a binder, and 1% by mass of sodium carboxymethylcellulose as a thickener, and an appropriate amount of water is added. To obtain a slurry negative electrode mixture. This slurry negative electrode mixture was applied to both surfaces of a 10 μm thick copper foil current collector, dried, and then densified by a roll press to obtain a negative electrode sheet. The amount of the negative electrode active material attached was 4.0 mg / cm ² per side.

  A positive electrode current collector tab lead was welded to the positive electrode sheet to form a positive electrode, and a negative electrode current collector tab lead was welded to the negative electrode sheet to form a negative electrode. A 20 μm-thick microporous membrane separator having a three-layer structure of polypropylene / polyethylene / polypropylene was sandwiched between these positive electrode and negative electrode, and wound to produce a roll electrode body. This roll electrode body was inserted into a nickel-plated iron cylindrical battery case composed of an outer can and a cap. The positive electrode current collecting tab lead was welded to the positive electrode current collecting tab arranged on the cap side of the battery case, and the negative electrode current collecting tab lead was welded to the negative electrode current collecting tab arranged on the bottom of the outer can. Then, the electrolytic solution was impregnated in the battery case, and the cap was caulked to close the battery case, thereby producing a cylindrical battery.

(Battery conditioning)
Activated charging and discharging were performed at 20 ° C. using the obtained battery. In the first cycle, the battery was charged up to an upper limit voltage of 4.9 V at a constant current of 0.3 mA / cm ² (corresponding to 0.3 C) by a constant current method. Thereafter, the battery was discharged to a lower limit voltage of 3.5 V at a current density of 0.3 mA / cm ² by a constant current method. In the second cycle, a constant current-constant voltage method was used, and a constant current charge was performed at 0.3 mA / cm ² , and after reaching 4.9 V, a constant voltage charge was performed at 4.9 V for one hour. Thereafter, the battery was discharged to a lower limit voltage of 3.5 V at a current density of 0.3 mA / cm ² by a constant current method. The discharge capacity at this time was defined as Cini.

(High temperature cycle endurance test of batteries)
Using the battery after conditioning, a constant current charge / discharge test was performed at an environmental temperature of 60 ° C. and a current corresponding to 2 C. The upper limit voltage was 4.9 V, the lower limit voltage was 3.5 V, and the number of cycles was 200. After 200 cycles, the battery was charged at a constant current of 0.3 mA / cm ² at a constant current-constant voltage method at an environmental temperature of 20 ° C., and after reaching 4.9 V, was charged at a constant voltage of 4.9 V for 1 hour. went. Thereafter, the battery was discharged to a lower limit voltage of 3.5 V at a current density of 0.3 mA / cm ² by a constant current method. The discharge capacity at this time was C200, and C200 / Cini was the capacity retention ratio.

(Gas measurement)
After conditioning, before and after the high-temperature cycle durability test, the gas amount was measured as follows. The battery was discharged to 3.5 V and sealed in a Teflon-sealed container with a syringe connected to it. The battery was opened with a needle, and the valve was opened to open the valve. The amount of gas generated in the battery was measured from the volume.

[Example 2]
Example 1 was the same as Example 1 except that an electrolytic solution having a tris (2,2,2-trifluoroethyl) borate concentration of 0.1 mol / L was used.

[Example 3]
Example 1 was the same as Example 1 except that LiTi ₂ O ₄ was used as the negative electrode active material and the upper limit voltage was 3.4 V and the lower limit voltage was 2.0 V in the conditioning and the high-temperature cycle durability test.

[Example 4]
Using an electrolytic solution having a concentration of tris (2,2,2-trifluoroethyl) borate of 0.1 mol / L, using LiTi ₂ O ₄ as a negative electrode active material, and setting an upper limit voltage of 3 in conditioning and a high temperature cycle durability test. Example 4 was the same as Example 1 except that the voltage was 0.4 V and the lower limit voltage was 2.0 V.

[Comparative Example 1]
Example 1 was repeated except that a mixed solution containing no tris (2,2,2-trifluoroethyl) borate was used as the electrolyte.

[Comparative Example 2]
Example 1 was repeated except that an electrolytic solution having a concentration of tris (2,2,2-trifluoroethyl) borate of 0.5 mol / L was used.

[Comparative Example 3]
A mixed solution containing no tris (2,2,2-trifluoroethyl) borate is used as an electrolyte, LiTi ₂ O ₄ is used as a negative electrode active material, and the upper limit voltage is 3.4 V and the lower limit is lower limit in conditioning and high temperature cycle durability test. It was the same as Example 1 except that the voltage was 2.0 V.

[Experimental result]
Table 1 summarizes the experimental results. In Table 1, the gas amount was a relative gas amount when the initial gas amount in Comparative Example 1 was 1. Comparison of Comparative Example 1, Example 1 and Example 2 using graphite for the negative electrode shows that by adding tris (2,2,2-trifluoroethyl) borate, the initial gas amount and the post-durability gas amount are reduced. Was confirmed. In addition, the capacity retention of the high-temperature cycle durability test was also improved. When the gas components after the durability test were analyzed, it was found that CO ₂ and H _{2 in} Examples 1 and ₂ were smaller than those in Comparative Example 1. Thus, the addition of tris (2,2,2-trifluoroethyl) borate suppresses the decomposition of the solvent on the positive electrode, reduces the amount of CO ₂ generated, and the amount of HF generated by the oxidative decomposition of the solvent. It was considered that the generation of H ₂ on the negative electrode was also suppressed and the amount of generated H ₂ was reduced due to the decrease in H ₂ .

The same effect was obtained when LiTi ₂ O ₄ was used instead of graphite for the negative electrode. From this, it was found that the type of the negative electrode was not particularly limited.

  On the other hand, in Comparative Example 2 in which tris (2,2,2-trifluoroethyl) borate was added at 0.5 mol / L, although the initial gas amount decreased, the gas amount after endurance and the capacity retention rate in the high-temperature endurance test Got worse. In Comparative Example 2, the battery resistance after durability increased. The reason for this is that, for example, when the proportion of tris (2,2,2-trifluoroethyl) borate in the electrolyte is high, some new reaction occurs and a film-like substance is formed on the electrode surface, and the Li ion It was speculated that this would block the passage of traffic.

  It is to be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  The present invention can be used in the field of the battery industry.

  Reference Signs List 10 lithium battery, 11 current collector, 12 positive electrode active material, 13 positive electrode sheet, 14 current collector, 17 negative electrode active material, 18 negative electrode sheet, 19 separator, 20 electrolyte, 22 cylindrical case, 24 positive electrode terminal, 26 negative electrode terminal .

Claims (8)

A positive electrode including a positive electrode active material having a Li insertion / desorption potential of 4.4 V or more based on lithium;
A negative electrode containing a negative electrode active material;
Interposed between the positive electrode and the negative electrode, a carbonate-based solvent containing a fluorinated chain carbonate, a supporting salt, and a borate compound having a structure in which three hydrogens of orthoboric acid are substituted with a fluorinated alkyl group, An electrolytic solution containing the borate compound in a range of 0.01 mol / L or more and 0.2 mol / L or less ;
With lithium battery. The lithium battery according to claim 1, wherein the borate compound is represented by Formula (1).
  The lithium battery according to claim 1, wherein the borate compound is (2,2,2-trifluoroethyl) borate. 4. The lithium battery according to claim 1, wherein the positive electrode active material includes LiNi _0.5 Mn _1.5 O _{4. 5} .   The lithium battery according to any one of claims 1 to 4, wherein the negative electrode active material includes one or more selected from the group consisting of a carbonaceous material, silicon, tin, and a lithium-titanium composite oxide.   The lithium battery according to any one of claims 1 to 5, wherein the carbonate-based solvent includes a fluorinated carbonate in which at least one hydrogen atom is substituted with a fluorine atom. The lithium battery according to claim 1, wherein the supporting salt includes one or more of LiPF ₆ and LiFSI. A positive electrode containing a positive electrode active material having a Li insertion / elimination potential of 4.4 V or more on a lithium basis, and a negative electrode containing a negative electrode active material, a carbonate-based solvent containing a fluorinated chain carbonate, a supporting salt, A borate compound having a structure in which three hydrogens of orthoboric acid are substituted with a fluorinated alkyl group, and injecting an electrolytic solution containing the borate compound in a range of 0.01 mol / L to 0.2 mol / L. To manufacture a lithium battery.