JP6097708B2 - Electrolyte and secondary battery using the same - Google Patents

Description

Detailed Description of the Invention

(Field of the Invention)
The present invention relates to a water electrolyte and a secondary battery using the same.

[Background Technology]
In recent years, with the development and popularization of mobile tools and electric motors, a high-capacity energy source has been demanded, and a typical example thereof is a (lithium) secondary battery. Currently, a lithium salt such as LiPF ₆ is used as a supporting salt for an electrolyte of a lithium secondary battery.

It is well known in the prior art that LiPF ₆ is contained as a main component as a supporting salt of the electrolytic solution. Further, according to Non-Patent Document 1 (Journal of Power Sources, Volume 196, Issue 7, 2011, Pages 3623-3632), LiFSI [lithium bis (fluorosulfonyl) imide] is the main component of the electrolyte supporting salt. In some cases, it is pointed out that it is necessary to contain LiPF ₆ at a certain ratio or more.

  On the other hand, when the amount of lithium ions in the non-aqueous electrolyte is increased, that is, when the concentration of the lithium salt is increased, the DC internal resistance increases due to the viscosity of the non-aqueous electrolyte, and the non-aqueous electrolyte secondary battery It has been pointed out that the output and the life are reduced (Patent Document 1: Patent Publication No. 2003-243029).

  Moreover, when this inventor made LiFSI the main component of the support salt of electrolyte solution, it confirmed that the positive electrode electrical power collector which consists of aluminum corroded and had a bad influence on the characteristic and lifetime of a battery.

  For this reason, without increasing the viscosity of the electrolytic solution, lithium salt, especially, imide-based lithium salt such as LiFSI may be used as the main component of the supporting salt of the electrolytic solution, and the positive electrode current collector may be corroded. There is no urgent need to develop electrolytes.

Patent Publication 2003-243029

Journal of Power Sources, Volume 196, Issue 7, 2011, Pages 3623-3632)

  The inventors of the present invention stabilize the surface of the aluminum current collector by adding a specific low molecular fluorine atom-containing organic compound to the lithium salt (particularly, an imide salt), and suppress the increase in the viscosity of the electrolytic solution. In addition, the inventors obtained knowledge that the secondary battery can be increased in capacity, output, and stability. The present invention has been made based on such knowledge.

Therefore, the non-aqueous electrolyte proposed by the present invention is
Comprising a lithium salt and an electrolyte additive,
Wherein the electrolyte additive, are those capable of dissolving the lithium salt, and has a fluorine group, are those having a structure that liberates HF or F _2, a compound or its equilibrium following Formula 1 The product is a non-aqueous electrolyte.
X ₂ CHCF ₂ -Y (Equation 1)
[In the above formula 1,
X represents an electron withdrawing group,
Y represents an electron donating group. ]

Mode for carrying out the invention

[Electrolyte / Non-aqueous electrolyte]
(Electrolyte additive)
In the present invention, the electrolyte additive added to the non-aqueous electrolyte is one that can dissolve a lithium salt, has a fluorine group, and has a structure that liberates HF or F ₂ . A compound represented by the following chemical formula 1 or an equilibrium product thereof.
X ₂ CHCF ₂ -Y (formula 1)
[In the above formula 1,
X represents an electron withdrawing group,
Y represents an electron donating group. ]

In the present invention, “having a structure that liberates HF or F ₂ ” can be explained as follows.

_{(CF 3) 2 CHCF 2 -O} -R → (CF 3) 2 C = CF-O-R
("HF group" withdrawal under basic conditions)
(CF ₃ ) ₂ CHCF ₂ —O—R → (CF ₃ ) ₂ CH—C (O) —O—R
("F ₂ group" leaving under acid conditions)

These chemical reaction formulas form a chemical equilibrium [reversible change: (→) and (←)].

In the compound represented by the above chemical formula 1 or an equilibrium product thereof, when X is an electron withdrawing group, protons are easily released from the carbon to which X is bonded under basic conditions. Moreover, when Y is an electron donating group, the intermediate from which the proton is eliminated becomes unstable and F ⁻ is easily eliminated. As a result, it appears that HF and vinyl ether are produced step by step.
When Y is an electron donating group, F ⁻ is easily detached from carbon to which Y is bonded under acid conditions. Further, when X is an electron-withdrawing group, the intermediate from which F ⁻ is eliminated becomes unstable, and as a result, when an oxide is present in the system, oxygen is withdrawn to produce an ester and a fluoride.

In lithium ion batteries, it is considered that the aluminum foil surface is fluorinated to form a protective layer stronger than a normal oxide film to prevent corrosion of the aluminum foil. The formation of such a fluorinated film is usually caused by PF ₆ ⁻ , but if a strong fluorinating agent is present in the electrolytic solution, it is considered that a protective layer is similarly formed. Further, PF ₆ ^- occurring after fluorinated membranes formed by POF ₄ ^- Fluorinated be reacted phosphoric acid compound with a strong fluorinating agents PF ₆ such as ^- because the return indirectly fluorinated membranes of the aluminum foil surface F ₂ for the formation of will be supplied. Since these reactions are performed under acid conditions, stable esters increase in the electrolyte while supplying F ₂ .
In addition, a reaction under basic conditions may occur on the negative electrode surface or the surface of a strongly basic positive electrode active material, but the formed HF and vinyl ether further react to form a solid electrolyte layer on the electrode surface called SEI. This is considered to stabilize the electrode surface and prevent deterioration of battery characteristics.

In the present invention, in the chemical formula (1), preferably, X is a compound having a fluoroalkyl group, more preferably about 1 to 10 carbon atoms, more preferably about 1 to 6 carbon atoms. A compound having a linear or branched chain (more preferably having 1 to 4 carbon atoms) and having a fluoroalkyl group in which all or part of the hydrogen atoms are substituted with fluorine atoms is exemplified.
In the chemical formula (1), Y is preferably an alkoxy group, more preferably about 1 to 10 carbon atoms, more preferably about 1 to 6 carbon atoms (more preferably carbon numbers). 1 to 4), preferably a straight or branched chain, and preferably all or most of the hydrogen atoms are not substituted by halogen atoms (preferably fluorine atoms) (substitution of about 1 to 3 is allowed) Range), compounds that are alkoxy groups.

The electron withdrawing property and electron donating property can be determined by the fluorine substitution rate of the alkyl group or alkoxy group. The higher the fluorine substitution rate, the stronger the electron withdrawing property and the weaker the electron donating property. Therefore, in order to increase the liberation of HF or F ₂ , it is desirable that all or most of hydrogen atoms in X are substituted with fluorine atoms, and in Y, all or most of the hydrogen atoms are fluorine atoms. It is desirable that it is not substituted with. Moreover, when there is too much liberation of HF or F ₂ which adversely affects the battery characteristics, the liberation of HF or F ₂ can be controlled by adjusting the fluorine substitution rate.

  According to a preferred embodiment of the present invention, the substitution rate to the fluorine atom in X is 50% or more and 100% or less, preferably the lower limit is 70% or more, more preferably the lower limit is 80% or more. The substitution rate of fluorine atoms in Y and Y is 0% or more and 80% or less, preferably the upper limit is 30% or less, and more preferably the upper limit is 20% or less.

The compound represented by the chemical formula 1 or the equilibrium product thereof is preferably any one represented by the following chemical formulas 2 to 4.
(CF ₃ ) ₂ CHCF ₂ —O—R (Chemical Formula 2)
(CF ₃ ) ₂ C═CF—O—R (Chemical Formula 3)
(CF ₃ ) ₂ CHCO—O—R (Chemical Formula 4)
[In the above formula,
O—R is the same as Y defined above, preferably O—CH ₃ . ]

(Lithium salt)
Lithium salts can be used as electrolyte salts, and various types of salts can be used. For example, an imide-based lithium salt can be used, and a compound represented by LiN (R ¹ SO ₂ ) (R ² SO ₂ ): (Chemical Formula 5) is exemplified.
In the above formula 5, R ¹ and R ² independently represent a fluorine atom or a fluoroalkyl group having 1 to 6 carbon atoms. The fluoroalkyl group may be linear, branched, cyclic, or a combination thereof, and a part of hydrogen atoms bonded to a carbon atom is substituted with a fluorine atom. Anything is acceptable. Specific examples of the fluoroalkyl group include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, a pentafluoroethyl group, a fluoropropyl group, a fluoropentyl group, and a fluorohexyl group. Groups and the like. R ¹ and R ² are preferably a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group. When ^{one of} R ¹ and R ² is a fluoroalkyl group, the other is preferably a fluorine atom (F).

Examples of the imide-based lithium salt include lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, and lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide. (Fluorosulfonyl) imide (LiFSI).
The imide-based lithium salt may be added as an appropriate amount (concentration) in the electrolytic solution.

(Other lithium salts)
In the present invention, in addition to the imide-based lithium salt, other lithium salts may be included. For example, a fluorine-containing lithium salt may be further added.

Other lithium salts include
LiPF _a (C _m F _{2m + 1} ) _6-a (0 ≦ a ≦ 6, 1 ≦ m ≦ 2) (Chemical formula 6)
LiBF _b (C _n F _{2n + 1} ) _4-b (0 ≦ b ≦ 4, 1 ≦ n ≦ 2) (Chemical formula 7)
LiAsF ₆ (Formula 8)
LiSbF ₆ (Formula 9)
It may be one or a mixture of two or more selected from the group consisting of compounds represented by:

More _{specifically, LiPF 6, LiPF 3 (C} 2 F 5) 3, LiBF 4, LiBF (CF 3) 3, LiAsF 6, LiSbF 6 are _{preferred, LiPF 6, LiBF 4, LiAsF} 6 , more preferably, LiPF ₆ and LiBF ₄ are more preferable.

  By adding these fluorine-containing lithium salts, the corrosion inhibitory effect of the positive electrode current collector is improved compared to the case where the imide-based lithium salt is used alone, and the stability of the nonaqueous electrolyte, ionic conductivity, Since mobility can be improved, it is preferable.

(Additive)
In the present invention, one or a mixture of two or more sulfonic acid esters and / or sulfone compounds may be contained as an additive. The sulfonic acid ester and / or sulfone compound reacts with the oxide film formed on the surface of the current collector during battery operation, and a film derived from the sulfonic acid ester and / or sulfone compound is formed on the positive electrode. It is possible to sufficiently suppress the corrosion of the electrode even when operating under a voltage (for example, 4 V or more).

The sulfonic acid ester is a compound represented by R ³ —S (O) ₂ —O—R ⁴ , and R ³ and R ⁴ represent a hydrocarbon group having 1 to 5 carbon atoms. The hydrocarbon group may be a chain, a branched chain, a ring, or may have two or more of these structures, and a part or all of the hydrogen atoms bonded to the carbon constituting the hydrocarbon group. May be substituted with halogen. Specific examples include an alkyl group, an aryl group, a fluoroalkyl group, and a fluoroaryl group. R ³ and R ⁴ may be the same or different, and R ³ and R ⁴ may be bonded to form a ring.

Specific examples of sulfonic acid esters include 1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,5-pentane sultone, 2,4-pentane sultone And cyclic sulfonic acid esters such as 1,4-hexane sultone and 4,6-heptane sultone, and chain sulfonic acid esters such as methyl methanesulfonate, methyl benzenesulfonate and methyl trifluoromethanesulfonate.
Among these, 1,3-propane sultone, 1,4-butane sultone, and 2,4-butane sultone are preferable, 1,3-propane sultone and 1,4-butane sultone are more preferable, and 1,3-butane sultone is more preferable. Propane sultone.

The sulfone compound is a compound having a sulfone bond (R ³ —SO ₂ —R ⁴ ) in the molecule (R ³ and R ⁴ are the same as the sulfonate ester). Specific examples of the sulfone compound include cyclic sulfone compounds such as sulfolane and 3-methylsulfolane, and chain sulfone compounds such as ethyl methyl sulfone, diphenyl sulfone, and bis (4-fluorophenyl) sulfone. Among the compounds having a sulfonyl group, sulfolane, 3-methylsulfolane, and ethylmethylsulfone are preferable, and sulfolane is more preferable.

(solvent)
When the non-aqueous electrolyte is used, the solvent is not particularly limited as long as it contains a chain or cyclic carbonate. Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate. Among these, dimethyl carbonate and ethyl methyl carbonate are preferable.

  In the present invention, other non-aqueous solvents can also be used. For example, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane; Non-aqueous solvents such as lactones such as -butyrolactone, γ-valerolactone, α-methyl-γ-butyrolactone; chain carboxylic acid esters such as methyl propionate and methyl butyrate;

(Other additives)
In the present invention, other additives for the purpose of improving cycle characteristics and safety may be contained.

  Other additives include cyclic carbonates having unsaturated bonds such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (MVC), ethyl vinylene carbonate (EVC); fluoroethylene carbonate, trifluoropropylene Carbonate compounds such as carbonate, phenylethylene carbonate and erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclohexane Carboxylic anhydrides such as pentanetetracarboxylic dianhydride and phenylsuccinic anhydride; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazo Nitrogen compounds such as dinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide; phosphates such as monofluorophosphate and difluorophosphate; heptane, octane, cycloheptane, etc. Hydrocarbon compounds; and the like.

[Secondary battery]
In the present invention, a secondary battery, preferably a lithium secondary battery,
Comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator;
A secondary battery is proposed in which the non-aqueous electrolyte comprises the electrolyte according to the present invention.

  Generally, a lithium secondary battery can conduct lithium ions by blocking electron conduction between a positive electrode made of a positive electrode active material and a positive electrode current collector, a negative electrode made of a negative electrode active material and a negative electrode current collector, and the positive electrode and the negative electrode. A non-aqueous electrolyte containing a lithium salt for conducting lithium ions is injected into the gap between the electrode and the separator material.

(Positive electrode)
The positive electrode is produced, for example, by applying a mixture of a positive electrode active material, a conductive agent and a binder on a positive electrode current collector and then drying. If necessary, a filler can be further added to the mixture.

As the positive electrode active material, a lithium-containing transition metal oxide can be desirably used. For example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO ₂ (0.5 <x <1.3), Li _x Mn ₂ O ₄ (0.5 <x <1.3), Li _x (Ni _a Co _b Mn _c ) O ₂ (0.5 < x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), Li _x Ni _1-y Co _y O ₂ (0.5 <x <1.3, 0 <y <1), Li _x Co _1-y Mn _y O ₂ (0.5 <x <1.3, 0 ≦ y <1), Li _x Ni _1-y Mn _y O ₂ (0.5 < x <1.3, 0 ≦ y <1), Li _x (Ni _a Co _b Mn _c ) O ₄ (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 < c <2, a + b + c = 2 _{, Li x Mn 2-z Ni} z O 4 (0.5 <x <1.3,0 <z <2), Li x Mn 2-z Co z O 4 (0.5 <x <1.3, Any one selected from the group consisting of 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3), and Li _x FePO ₄ (0.5 <x <1.3) Two or more mixtures can be used. In addition to the lithium-containing transition metal oxide, sulfides, selenides, halides, and the like can also be used.
Preferably, Li _x CoO ₂ (0.5 <x <1.3) and Li _x (Ni _a Co _b Mn _c ) O ₂ (0.5 <x <1.3, 0 <a <1, 0 < A mixture with b <1, 0 <c <1, a + b + c = 1) can be used as the positive electrode active material. In particular, Li _x (Ni _a Co _b Mn _c ) O ₂ (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1) is a high voltage. It is desirable in that high output characteristics can be exhibited under certain conditions.

  The positive electrode current collector is manufactured with a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel that has been surface-treated with carbon, nickel, titanium, silver, or the like is used. The positive electrode current collector can form fine irregularities on the surface to increase the adhesive strength of the positive electrode active material, and has various forms such as a film, a sheet, a wheel, a net, a porous body, a foam, and a non-woven body. Is possible.

  The conductive agent is usually added at 1 to 50% by weight based on the total weight of the mixture containing the positive electrode active material. Such a conductive agent only needs to have conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black (trade name), carbon nanotube, carbon nanofiber, channel black, furnace black, lamp black, and thermal black; carbon fiber Conductive fibers such as metal fibers, metal powders such as fluorocarbon, aluminum, and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives Is used.

  The binder is a component that promotes the binding of the active substance and the conductive agent, and the binding of the active substance to the current collector. Usually, the binder is added at 1 to 50% by weight based on the total weight of the mixture containing the positive electrode active material. For example, polyvinylidene fluoride, polyvinyl alcohol, polyimide, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer (EPDM), sulfone EPDM, styrene butylene rubber, fluororubber, various copolymers and the like.

  The filler is a component that suppresses expansion of the positive electrode, may be selectively used, and may be a fibrous material that does not induce a chemical change in the battery. Examples thereof include olefin polymers such as polyethylene and polypropylene; and fibrous substances such as glass fiber and carbon fiber.

(Negative electrode)
The negative electrode is produced, for example, by applying a mixture of a negative electrode active material, a conductive agent and a binder on a negative electrode current collector and then drying. If necessary, a filler can be further added to the mixture.

  Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, and activated carbon; Al and Si capable of alloying with lithium , Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, and the like, and compounds containing such elements; a composite material of a metal or a compound thereof and carbon and graphite materials; lithium Examples thereof include, but are not limited to, containing nitrides. Desirably, it may be one or a combination of two or more selected from the group consisting of crystalline carbon, amorphous carbon, silicon-based active material, tin-based active material, and silicon-carbon-based active material. In addition, a normal binder, a conductive material, and other additives contained in the negative electrode can be included, and specific examples and contents thereof may be added as long as they are normally added.

  The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50% by weight based on the total weight of the electrode mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene. Examples thereof include polymers (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

  The conductive material is a component for further improving the conductivity of the electrode active material, and may be added at 1 to 20% by weight based on the total weight of the electrode mixture. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black and lamp black; conductive fiber such as carbon fiber and metal fiber; carbon fluoride, aluminum, nickel powder Metal powders such as: conductive metal oxides such as zinc oxide, potassium titanate, and titanium oxide; conductive materials such as polyphenylene derivatives can be used.

  The filler is not particularly limited as long as it is selectively used as a component that suppresses expansion of the negative electrode and does not cause a chemical change in the battery and is a fibrous material. For example, an olefin polymer such as polyethylene or polypropylene; a fibrous material such as glass fiber or carbon fiber can be used.

  The negative electrode current collector is manufactured with a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, copper, steel, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like is used. The negative electrode current collector, like the positive electrode current collector, can form fine irregularities on the surface to increase the adhesion of the negative electrode active material, and can be a film, sheet, wheel, net, porous body, foam, Various forms such as non-woven fabric are possible.

(Separator)
The separator is an insulating thin film that is interposed between the positive electrode and the negative electrode and has high ion permeability and mechanical strength. Generally, the separator has a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm. As such a separator, for example, an olefin polymer such as chemically resistant and hydrophobic polypropylene; a sheet or a nonwoven fabric made of glass fiber or polyethylene is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as a separator.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte, those described in the section [Electrolyte / Non-aqueous electrolyte] are used.

(Manufacturing)
The secondary battery according to the present invention is manufactured by inserting a porous separator between a positive electrode and a negative electrode and introducing a nonaqueous electrolytic solution by a usual method. The secondary battery according to the present invention is used regardless of the outer shape, such as a cylindrical type, a square type, or a pouch type battery.

Embodiment of the Invention

  The contents of the present invention will be described in detail by the following examples and the like, but the scope of the present invention is not limited to these examples, and according to the embodiments of these examples, the present specification Those skilled in the art will understand that the present invention can be easily implemented from the matters disclosed in the above.

The octafluoroisobutyl methyl ether (OIME) represented by the chemical formula 1 is the one represented by the following chemical formula: OIME1: (CF ₃ ) ₂ CHCF ₂ —O—CH ₃ (Chemical formula 2-1)
OIME2: (CF ₃ ) ₂ C═CF—O—CH ₃ (Chemical Formula 3-1)
_{OIME3: (CF 3) 2 CHCO} -O-CH 3 ( Formula 4-1)

[Non-aqueous electrolyte performance test]
[Example 1]
A 20 μm thick aluminum foil was cut into 1 cm × 5 cm, immersed in OIME 1 under an Ar atmosphere, allowed to stand at 60 ° C. for 24 hours, washed with ethanol and dried, and surface-treated.

[Comparative Example 1]
Except not having been immersed in OIME1, it carried out similarly to Example 1, and obtained the aluminum stay which did not carry out OIME surface treatment.

(Evaluation test 1: Corrosion test)
1M LiFSI solution having a composition of ethylene carbonate: diethyl carbonate: ethyl methyl carbonate = 3: 4: 3 (weight ratio) under Ar atmosphere was used as the electrolytic solution for the aluminum stay according to Example 1 and Comparative Example 1, and the above The corrosion current of the treated aluminum foil was measured at a constant voltage of 5V.

(Evaluation result 1)
The results of the evaluation test are as shown in Table 1 below. In Example 1 (solid line), no corrosion was observed even with aging, but in Comparative Example 1 (dashed line) Corrosion was clearly seen by the change.

[Battery performance test]
(Battery manufacturing)
[Example 2-1]
(Electrolyte)
A 1M LiFSI solution having a composition of ethylene carbonate: diethyl carbonate: ethyl methyl carbonate = 3: 4: 3 (weight ratio) was used as an electrolyte in an Ar atmosphere, and 1 weight of OIME1 was used with respect to 100% by weight of the electrolyte. % Was added. The composition of the electrolytic solution is as described in Table 2.
(Positive electrode)
LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon as a conductive material are mixed in a weight ratio of 93: 4: 4, and then dispersed in N-methyl-2-pyrrolidone to produce a positive electrode slurry. did. The slurry was coated on an aluminum foil having a thickness of 15 μm, and then dried and pressed to produce a positive electrode.
(Negative electrode)
Natural graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener were mixed at a weight ratio of 96: 2: 2, and then dispersed in water to prepare a negative electrode slurry. The slurry was coated on a copper foil having a thickness of 10 μm, and then dried and pressed to produce a negative electrode.
(Secondary battery)
A 2016-size coin-type secondary battery was produced by a normal method using the positive electrode, negative electrode, and porous separator produced above, and then the electrolyte was injected to produce a battery.

[Examples 2-1 to 2-9 and Comparative examples 2-1 to 2-4]
In these Examples and Comparative Examples, in the same manner as in Example 2-1, an electrolyte solution was prepared according to the composition table shown in Table 2, and a coin-type secondary battery was manufactured. In Table 2, M is mol.

(Evaluation test 2: Battery performance)
Regarding the coin-type secondary batteries of Examples and Comparative Examples, after charging to 4.20 V, the initial capacity at 0.2 C is measured, and the cycle test is repeated with the rate test at 1 C and the charge and discharge at 1 C at 45 ° C. Went. The capacities after 100 cycles and 200 cycles were measured at 0.2 C, and the capacity remaining rate from the initial capacity was calculated and compared. The results were as shown in Table 3.

(Evaluation result 2)
The coin-type secondary battery of the example showed excellent results in the initial capacity and the discharge cycle as compared with the comparative example.

〔Comprehensive evaluation〕
According to the present invention, by using an electrolytic solution containing an additive having a structure that liberates HF or F ₂ , the electrode current collector metal surface and the electrode active material surface are stabilized, and the life characteristics of the lithium secondary battery Improved.

Claims (10)

An electrolyte,
Comprising a lithium salt and an electrolyte additive,
The lithium salt is LiFSI;
The electrolyte additive is an electrode current collector corrosion inhibitor, an electrode current collector metal surface stabilizer, or an electrode active material surface stabilizer, is capable of dissolving the lithium salt, and has a fluorine group. And an electrolyte that has a structure that liberates HF or F ₂ and is a compound represented by the following chemical formula 1 or an equilibrium product thereof.
X ₂ CHCF ₂ -Y (Equation 1)
[In Chemical Formula 1,
X is a fluoroalkyl group;
Y is an alkoxy group. ] The fluoroalkyl group is a 1 to 10 carbon atoms, having a linear or branched, and are those in which one or more hydrogen atoms are replaced all or in part by fluorine atoms,
The alkoxy group has 1 to 10 carbon atoms and has a linear or branched chain, or
The electrolyte according to claim 1, wherein the alkoxy group has 1 to 10 carbon atoms, has a straight chain or a branched chain, and a hydrogen atom is partially substituted with a fluorine atom . The electrolyte according to claim 1 or 2, wherein the compound represented by the chemical formula 1 or an equilibrium product thereof is one or two or more of the compounds represented by the following chemical formulas 2 to 4.
(CF ₃ ) ₂ CHCF ₂ —O—R (Chemical Formula 2)
(CF ₃ ) ₂ C═CF—O—R (Chemical Formula 3)
(CF ₃ ) ₂ CHCO—O—R (Chemical Formula 4)
[In the above formula,
O—R is the same as Y ( alkoxy group) as defined in claim 1 or 2. ] The electrolyte according to claim ₃ , wherein the substituent R in the chemical formulas 2 to 4 is CH ₃ . The electrolyte according to claim 1, wherein the lithium salt does not liberate HF or F ₂ in the electrolyte. Further comprising a fluorine-containing lithium salt,
The fluorine-containing lithium salt is one or a mixture of two or more selected from the group consisting of compounds represented by any one of the following (Chemical Formula 6) to (Chemical Formula 9) . The electrolyte according to any one of the above.
LiPF _a (C _m F _{2m + 1} ) _6-a (0 ≦ a ≦ 6, 1 ≦ m ≦ 2) (Chemical formula 6)
LiBF _b (C _n F _{2n + 1} ) _4-b (0 ≦ b ≦ 4, 1 ≦ n ≦ 2) (Chemical Formula 7)
LiAsF ₆ (Formula 8)
LiSbF ₆ (Formula 9) Wherein the fluorine-containing lithium _{salt, LiPF 6, LiPF 3 (C} 2 F 5) 3, LiBF 4, LiBF (CF 3) 3, LiAsF 6, or LiSbF is _6, electrolyte according to claim 6. Further comprising an additive for forming a positive electrode film,
The electrolyte according to any one of claims 1 to 7, wherein the additive for forming a positive electrode film is a sulfonate ester and / or a mixture of two or more sulfone compounds . A secondary battery,
Comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator;
A secondary battery, wherein the nonaqueous electrolytic solution comprises the electrolyte according to any one of claims 1 to 8.   The secondary battery according to claim 9, wherein the secondary battery is a lithium secondary battery.