JP2010010078A - Nonaqueous electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nonaqueous electrolyte having characteristics, such as battery characteristics (charge and discharge cycle characteristics, high discharge capacity or the like), nonflammability (incombustibility), and compatibility with other solvents such as hydrocarbon system carbonates with sufficient balance. <P>SOLUTION: A solvent for dissolving electrolytic salt includes: ether containing fluorine and chlorine shown in a formula 1 of HCF<SB>2</SB>CF<SB>2</SB>CH<SB>2</SB>OCF<SB>2</SB>CClFH; cyclic carbonate; and chain-like carbonate. The nonaqueous electrolyte includes electrolytic salt. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolytic solution suitable for a lithium secondary battery.

  Solvents for dissolving electrolyte salts used in non-aqueous electrolytes for lithium secondary batteries include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. . However, since these hydrocarbon carbonates have a low flash point and high combustibility, especially in large lithium secondary batteries for hybrid vehicles and distributed power supplies, the nonflammability of nonaqueous electrolytes is improved for ensuring safety. It is an important issue.

  In order to improve nonflammability (flame retardancy) without degrading the performance as a non-aqueous electrolyte, it has also been proposed to add a fluorinated solvent (Patent Documents 1 to 12), but battery characteristics (charge / discharge cycle) Nonaqueous electrolytes having good balance of properties such as properties, high discharge capacity, nonflammability (flame retardant), and compatibility with other solvent components such as hydrocarbon carbonates are expected.

Japanese Patent Application Laid-Open No. 08-037044 JP 09-097627 A Japanese Patent Laid-Open No. 11-026015 JP 2000-294281 A JP 2001-052737 A Japanese Patent Laid-Open No. 11-307123 JP-A-10-112334 International Publication No. 2006/088009 Pamphlet International Publication No. 2006/106655 Pamphlet International Publication No. 2006/106656 Pamphlet International Publication No. 2006/106657 Pamphlet International Publication No. 2008/007734 Pamphlet

  The present invention is intended to solve such conventional problems, and other solvents such as battery characteristics (charge / discharge cycle characteristics, high discharge capacity, etc.), nonflammability (flame retardant), hydrocarbon carbonates and the like. An object of the present invention is to provide a nonaqueous electrolytic solution having a good balance of compatibility and other characteristics.

As a result of intensive studies, the present inventors have found that in a non-aqueous electrolyte using both a cyclic carbonate and a chain carbonate, a specific fluorine-containing chlorinated ether in which only one terminal fluorine atom is substituted with a chlorine atom is a chain carbonate. Excellent solubility in general, and exhibits the same characteristics as HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, which has been proposed to improve nonflammability in terms of oxidation resistance, battery characteristics, and safety. The present invention has been completed.

That is, the present invention
(I) (A) formula (1): HCF fluorinated chlorine-containing ether represented by _{2 CF 2 CH 2 OCF 2 CClFH} ,
The present invention relates to (B) a cyclic carbonate, (C) a solvent for dissolving an electrolyte salt containing a chain carbonate, and (II) a non-aqueous electrolyte solution containing an electrolyte salt.

In the nonaqueous electrolytic solution of the present invention, the solvent (I) for dissolving the electrolyte salt is 10 to 60% by volume of the fluorine-containing chlorinated ether (A) and 3 of the cyclic carbonate (B) with respect to the entire solvent (I). -40% by volume and 10-60% by volume of linear carbonate (C), and LiPF ₆ , LiBF ₄ , LiN (O ₂ SCF ₃ ) ₂ and LiN (O ₂ SC ₂ F ₅ ) ₂ as electrolyte salt (II) It is preferable from a point with favorable battery characteristics to contain at least 1 sort (s) chosen from the group which consists of 0.8 mol / liter or more of density | concentration.

  Such a non-aqueous electrolyte is suitable as a non-aqueous electrolyte for a lithium secondary battery.

  The present invention also relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and the nonaqueous electrolytic solution of the present invention.

  According to the present invention, the battery characteristics (charge / discharge cycle characteristics, high discharge capacity, etc.), nonflammability (flame retardant), and compatibility with other solvents such as hydrocarbon carbonates are well balanced. A water electrolyte and a lithium secondary battery can be provided.

  The nonaqueous electrolytic solution of the present invention contains an electrolyte salt dissolving solvent (I) containing a specific component and an electrolyte salt (II).

Solvent for dissolving electrolyte salt (I)
(A) Formula (1): Fluorine-containing chlorine-containing ether represented by HCF ₂ CF ₂ CH ₂ OCF ₂ CClFH,
(B) a cyclic carbonate and (C) a chain carbonate.

  Hereinafter, each solvent component (A)-(C) is demonstrated.

(A) Fluorine-containing chlorinated ether represented by the formula (1): HCF ₂ CF ₂ CH ₂ OCF ₂ CClFH:
The fluorine-chlorine-containing ether (A) may be readily prepared by, for example, the reaction of HCF ₂ CF ₂ CH ₂ OH and chlorotrifluoroethylene.

Conventionally known HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H has good solubility in DMC and MEC, but has low solubility in DEC, which is the same chain carbonate. Was restricted. The fluorine-containing chlorinated ether (A) used in the present invention is excellent in solubility with respect to all chain carbonates including DEC, and can greatly widen the range of the formulation of the non-aqueous electrolyte.

In addition, oxidation resistance, battery characteristics (rate characteristics, cycle characteristics, etc.), and safety (overcharge safety, etc.) can be equivalent to those of HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H.

(B) Cyclic carbonate:
The non-fluorinated cyclic carbonate (B1), the fluorine-based cyclic carbonate (B2), or a combination thereof may be used. Of these, the non-fluorinated cyclic carbonate (B1) is preferable from the viewpoint that the effects of improving the solubility of the electrolyte salt (II) and improving the ion dissociation can be obtained particularly remarkably.

  As the non-fluorinated cyclic carbonate (B1), at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and vinylene carbonate (VC) has good ion dissociation, low viscosity and dielectric constant. From this point, it is preferable. Of these, vinylene carbonate is added as a film forming material on the carbon surface of the negative electrode, and the amount added is preferably 5% by volume or less.

  The fluorine-based cyclic carbonate (B2) is useful in that it provides an effect of improving nonflammability (safety).

  Examples of the fluorine-based cyclic carbonate (B2) include trifluoroethylene carbonate and 3-monofluoropropylene carbonate.

(C) Chain carbonate:
The non-fluorine chain carbonate (C1), the fluorine chain carbonate (C2), or a combination thereof may be used. Of these, the non-fluorine chain carbonate (C1) is preferable from the viewpoints of the effects of improving the battery capacity, rate characteristics, and low temperature characteristics of the electrolyte salt (II).

As the non-fluorine chain carbonate (C1), the formula (C1):
R ¹ OCOOR ²
A compound represented by the formula (wherein R ¹ and R ² are the same or different, and an alkyl group having 1 to 4 carbon atoms) is preferred from the viewpoint of low viscosity and good compatibility with other solvents.

  Specific examples include, for example, diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), methyl propyl carbonate, etc. Among them, DEC, DMC, MEC are compatible with other solvents, rate It is preferable from the viewpoint of good characteristics.

  Fluorine chain carbonate (C2) has a higher flash point than non-fluorine chain carbonate, and is useful in that it provides an effect of improving nonflammability (safety).

  Examples of the fluorine chain carbonate (C2) include 2,2,2-trifluoroethyl methyl carbonate, 2,2,2-trifluoroethyl ethyl carbonate, 3,3,2,2-tetrafluoropropyl ethyl carbonate, and the like. Can be illustrated.

  In the nonaqueous electrolytic solution of the present invention, the fluorine-containing chlorine-containing ether (A) is preferably contained in an amount of 10 to 60% by volume with respect to the entire electrolyte salt dissolving solvent (I). If the amount of fluorine-containing chlorinated ether (A) decreases, nonflammability and rate characteristics tend to decrease, and if it increases, phase separation or discharge capacity tends to decrease. From the viewpoint of good flame retardancy and rate characteristics, it is preferably contained in an amount of 10 to 40% by volume, particularly 20 to 40% by volume.

  In the nonaqueous electrolytic solution of the present invention, the cyclic carbonate (B) is preferably contained in an amount of 3 to 40% by volume with respect to the entire electrolyte salt dissolving solvent (I). When the amount of the cyclic carbonate (B) decreases, the discharge capacity and cycle characteristics tend to decrease, and when it increases, the phase separation tends to occur. From the viewpoint of good discharge capacity and cycle characteristics, it is further preferably contained in an amount of 5 to 35% by volume, particularly 8 to 30% by volume.

  In the nonaqueous electrolytic solution of the present invention, the chain carbonate (C) is preferably contained in an amount of 10 to 60% by volume with respect to the entire electrolyte salt dissolving solvent (I). When the amount of chain carbonate (C) decreases, the discharge capacity, cycle characteristics, low temperature characteristics, etc. tend to decrease. When the amount increases, the flash point of chain carbonates, especially non-fluorine chain carbonates, is low, so safety decreases. And cycle characteristics tend to decrease. From the viewpoint of good discharge capacity, rate characteristics, and low temperature characteristics, it is further preferably contained in an amount of 10 to 40% by volume, particularly 20 to 40% by volume.

In the nonaqueous electrolytic solution of the present invention, a fluorine-containing ether such as HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H may be used in combination as long as the battery characteristics do not deteriorate.

  In the present invention, hexafluorobenzene, fluorobenzene, toluene, cyclohexylbenzene and the like having an anti-overcharge action can be used as an organic solvent as necessary. In this case, the above-mentioned fluorine-containing chlorinated ether (A), cyclic carbonate The amount is preferably such that (B) and the advantages and improvements brought about by each component such as the chain carbonate (C) are not excluded. The amount can be used in the range of 0.5 to 10% by weight with respect to the entire electrolyte. In addition, monofluoroethylene carbonate having an effect of improving the cycle characteristics may be used in an amount that does not inhibit the effect of the present invention, for example, in the range of 0.1 to 10% by weight with respect to the entire electrolytic solution, and flame retardancy is improved You may use the phosphate ester which has an effect | action in the range which does not inhibit the effect of this invention, for example, 0.1 to 10 weight% with respect to the whole electrolyte solution.

  Next, the electrolyte salt (II) will be described.

Examples of the electrolyte salt (II) used in the nonaqueous electrolytic solution of the present invention include LiAsF ₆ , LiClO ₄ , LiPF ₆ , LiBF ₄ , LiN (O ₂ SCF ₃ ) ₂ , LiN (O ₂ SC ₂ F ₅ ) _2. Or a combination thereof, and LiPF ₆ , LiBF ₄ , LiN (O ₂ SCF ₃ ) ₂ , LiN (O ₂ SC ₂ F ₅ ) _2, or a combination thereof is preferable from the viewpoint of good battery characteristics, particularly LiPF. ₆ and / or LiN (O ₂ SCF ₃ ) ₂ are preferable from the viewpoint of improving the cycle life.

  The concentration of the electrolyte salt (II) is required to be 0.8 mol / liter or more, further 1.0 mol / liter or more in order to achieve the required battery characteristics. The upper limit is usually 1.5 mol / liter although it depends on the organic solvent (I) for dissolving the electrolyte salt.

  In order to further increase the capacity of the battery, a surfactant (D) may be added to the nonaqueous electrolytic solution of the present invention. The blending amount of the surfactant (D) is 5% by mass or less based on the total amount of the solvent (I) from the viewpoint of reducing the surface tension of the electrolytic solution without reducing the charge / discharge cycle characteristics, and further 3 Less than mass%, especially 0.05-2 mass% is preferable.

  As the surfactant (D), any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant may be used. However, the fluorine-containing surfactant has cycle characteristics and rate characteristics. Is preferable from the viewpoint of good.

For example, the formula (D1a):
Rf ^a COO ^- M ⁺
(Wherein, Rf ^a fluorine-containing alkyl group having 4 to 20 carbon atoms, M ⁺ unlike alkali metal cation or NHR _'3 ⁺ (R' are the same or are both H or carbon atoms of 1 to 3 alkyl Group)) and / or formula (D2a):
Rf ^a SO ₃ ^- M ⁺
(Wherein, Rf ^a fluorine-containing alkyl group having 4 to 20 carbon atoms, M ⁺ unlike alkali metal cation or NHR _'3 ⁺ (R' are the same or are both H or carbon atoms of 1 to 3 alkyl Group))-containing fluorine-containing sulfonate, and further formula (D1b):
Rf ^b COO ^- M ⁺
(In the formula, Rf ^b is a fluorine-containing ether group having 4 to 20 carbon atoms, M ⁺ is an alkali metal cation or NHR ′ ₃ ⁺ (R ′ is the same or different, both are H or alkyl having 1 to 3 carbon atoms) Group)) and / or formula (D2b):
Rf ^b SO ₃ ^- M ⁺
(In the formula, Rf ^b is a fluorine-containing ether group having 4 to 20 carbon atoms, M ⁺ is an alkali metal cation or NHR ′ ₃ ⁺ (R ′ is the same or different, both are H or alkyl having 1 to 3 carbon atoms) One or more of the fluorine-containing sulfonates represented by the group)) can be preferably exemplified.

The Rf ^a fluorine-containing alkyl group having 4 to 20 carbon atoms, and Rf ^b is a fluorine-containing ether group having 4 to 20 carbon atoms, preferably from the degree of lowering the surface tension of the electrolytic solution good points, particularly carbon The fluorine-containing alkyl group of several 4-8 is preferable from the point which is excellent in solubility.

As the M ⁺ alkali metal, Li, Na, and K are preferable, and as M ⁺ , NH ₄ ⁺ is particularly preferable.

Specific examples of the fluorine-containing carboxylate (D1a) include, for example, C ₄ F ₉ COO ^— NH ₄ ⁺ , C ₅ F ₁₁ COO ^— NH ₄ ⁺ , C ₆ F ₁₃ COO ^— NH ₄ ⁺ , C ₇ F ₁₅ COO ^{_{- NH 4 +, C 8 F}} 17 COO - NH 4 +, C 9 F 19 COO - NH 4 +,
^{_{C 4 F 9 COO - NH (}} CH 3) 3 +, C 5 F 11 COO - NH (CH 3) 3 +, C 6 F 13 COO - NH (CH 3) 3 +, C 7 F 15 COO - NH ( ^{_{CH 3) 3 +, C 8}} F 17 COO - NH (CH 3) 3 +, C 9 F 19 COO - NH (CH 3) 3 +, C 4 F 9 COO - Li +, C 5 F 11 COO - Li ⁺ , C ₆ F ₁₃ COO ^- Li ⁺ , C ₇ F ₁₅ COO ^- Li ⁺ , C ₈ F ₁₇ COO ^- Li ⁺ , C ₉ F ₁₉ COO ^- Li ⁺ , among others, solubility in the electrolyte C ₅ F ₁₁ COO ^- NH ₄ ⁺ , C ₇ F ₁₅ COO ^- NH ₄ ⁺ , C ₅ F ₁₁ COO ^- Li ⁺ , and C ₆ F ₁₃ COO ^- Li ⁺ preferable.

Specific examples of the fluorine-containing carboxylate (D1b) include C ₃ F ₇ OCF (CF ₃ ) COO ^— NH ₄ ⁺ , C ₃ F ₇ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COO ^— NH ₄ ⁺ _{, C 3 F 7 OCF (CF} 3) COO - NH (CH 3) 3 +, C 3 F 7 OCF (CF 3) CF 2 OCF (CF 3) COO - NH (CH 3) 3 +, C 3 F 7 OCF (CF ₃ ) COO ⁻ Li ⁺ , C ₃ F ₇ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COO ⁻ Li ^+, etc., among others, the solubility in the electrolyte and the effect of reducing the surface tension from the viewpoint of _{good, C 3 F 7 OC (CF} 3) FCOO - NH 4 +, C 3 F 7 OCF (CF 3) CF 2 OCF (CF 3) COO - NH 4 +, C 3 F 7 OCF (CF 3 _{^{) COO - Li +, C 3}} F 7 OCF (CF 3) CF 2 OCF (CF 3) COO - Li + is preferred .

Specific examples of the fluorine-containing sulfonate (D2a), for example, ^{_{C 4 F 9 SO 3 - NH}} 4 +, C 5 F 11 SO 3 - NH 4 +, C 6 F 13 SO 3 - NH 4 +, C 7 _{^{F 15 SO 3 - NH 4 +}} , C 8 F 17 SO 3 - NH 4 +, C 9 F 19 SO 3 - NH 4 +, C 4 F 9 SO 3 - NH (CH 3) 3 +, C 5 F 11 _{^{SO 3 - NH (CH 3)}} 3 +, C 6 F 13 SO 3 - NH (CH 3) 3 +, C 7 F 15 SO 3 - NH (CH 3) 3 +, C 8 F 17 SO 3 - NH ( CH ₃ ) ₃ ⁺ , C ₉ F ₁₉ SO ₃ ^- NH (CH ₃ ) ₃ ⁺ , C ₄ F ₉ SO ₃ ^- Li ⁺ , C ₅ F ₁₁ SO ₃ ^- Li ⁺ , C ₆ F ₁₃ SO ₃ ^- Li ⁺ , C ₇ F ₁₅ SO ₃ ^- Li ⁺ , C ₈ F ₁₇ SO ₃ ^- Li ⁺ , C ₉ F ₁₉ SO ₃ ^- Li ^+, etc. From a good point, C ₄ F ₉ SO ₃ ^- NH ₄ ⁺ , C ₆ F _{^{13 SO 3 - NH 4 +,}} C 8 F 17 SO 3 - NH 4 +, C 4 F 9 SO 3 - Li +, C 6 F 13 SO 3 - Li +, C 8 F 17 SO 3 - Li + is preferred .

Specific examples of the fluorine-containing sulfonate (D2b), for example, _{C 3 F 7 OC (CF 3} ) FCF 2 OC (CF 3) FSO 3 - NH 4 +, C 3 F 7 OC (CF 3) FCF 2 OC _{(CF 3) FCF 2 OC (} CF 3) FSO 3 - NH 4 +, HCF 2 CF 2 OCF 2 CF 2 SO 3 - NH 4 +, CF 3 CFHCF 2 OCF 2 CF 2 SO 3 - NH 4 +, C 3 _{F 7 OC (CF 3) FSO} 3 - NH 4 +, C 3 F 7 OC (CF 3) FCF 2 OC (CF 3) FSO 3 - NH (CH 3) 3 +, C 3 F 7 OC (CF 3) _{FCF 2 OC (CF 3) FCF} 2 OC (CF 3) FSO 3 - NH (CH 3) 3 +, HCF 2 CF 2 OCF 2 CF 2 SO 3 - NH (CH 3) 3 +, CF 3 CFHCF 2 OCF 2 ^{_{CF 2 SO 3 - NH (CH}} 3) 3 +, C 3 F 7 OC (CF 3) FSO 3 - NH (CH 3) 3 + _{, C 3 F 7 OC (CF} 3) FCF 2 OC (CF 3) FSO 3 - Li +, C 3 F 7 OC (CF 3) FCF 2 OC (CF 3) FCF 2 OC (CF 3) FSO 3 - Li ^{_{+, HCF 2 CF 2 OCF 2}} CF 2 SO 3 - Li +, CF 3 CFHCF 2 OCF 2 CF 2 SO 3 - Li +, C 3 F 7 OC (CF 3) FSO 3 - Li + and the like, Naka But solubility in the electrolyte, the effect of lowering surface tension in terms of _{good, C 3 F 7 OC (CF} 3) FCF 2 OC (CF 3) FSO 3 - NH 4 +, C 3 F 7 OC (CF 3 _{) FCF 2 OC (CF 3)} FSO 3 - Li +, C 3 F 7 OC (CF 3) FSO 3 - NH 4 +, C 3 F 7 OC (CF 3) FSO 3 - Li + is preferred.

  In addition, surfactants such as anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants should be added within the range that does not impair the properties of the present invention in order to improve the wettability with the electrodes. Can do.

  Since the electrolytic solution of the present invention has the above-described configuration, it is incombustible (flame retardant) and excellent in battery characteristics (charge / discharge cycle characteristics, discharge capacity). Furthermore, according to the electrolytic solution of the present invention, it can be expected that phase separation is difficult even at low temperatures, heat resistance is high, electrolyte salt solubility is high, battery capacity is improved, and rate characteristics are excellent. .

  The electrolyte solution of the present invention is suitable for a lithium secondary battery from the viewpoint of improving capacity and rate characteristics, and can provide a lithium secondary battery including a positive electrode, a negative electrode, a separator, and the electrolyte solution of the present invention.

  The positive electrode active material used for the positive electrode is not particularly limited, but at least selected from the group consisting of cobalt-based composite oxides, nickel-based composite oxides, manganese-based composite oxides, iron-based composite oxides, and vanadium-based composite oxides. When using 1 type, it is preferable from becoming a high output lithium secondary battery with a high energy density.

An example of the cobalt-based composite oxide is LiCoO ₂ , an example of the nickel-based composite oxide is LiNiO ₂ , and an example of the manganese-based composite oxide is LiMnO ₂ . LiCo _x Ni _1-x O ₂ (0 <x <1), LiCo _x Mn _1-x O ₂ (0 <x <1), LiNi _x Mn _1-x O ₂ (0 <x <1), _{LiNi x Mn 2-x O 4} (0 <x <2), CoNi represented by _{LiNi 1-xy Co x Mn y} O 2 (0 <x <1,0 <y <1,0 <x + y <1) , CoMn, NiMn, and NiCoMn composite oxides may be used. In these lithium-containing composite oxides, a part of metal elements such as Co, Ni, and Mn may be substituted with one or more metal elements such as Mg, Al, Zr, Ti, and Cr. .

In addition, examples of the iron-based composite oxide include LiFeO ₂ and LiFePO ₄ , and examples of the vanadium-based composite oxide include V ₂ O ₅ .

  As the positive electrode active material, among the above complex oxides, a nickel complex oxide or a cobalt complex oxide is preferable because the capacity can be increased. In particular, in a small lithium secondary battery, it is desirable to use a cobalt-based composite oxide from the viewpoint of high energy density and safety. In the present invention, particularly when used in a large-sized lithium secondary battery for a hybrid vehicle or a distributed power source, a high output is required, so the particles of the positive electrode active material are mainly secondary particles, and the secondary particles It is preferable to contain 0.5 to 7.0% by volume of fine particles having an average particle size of 40 μm or less and an average primary particle size of 1 μm or less.

  By containing fine particles having an average primary particle diameter of 1 μm or less, the contact area with the electrolytic solution is increased, and the diffusion of lithium ions between the electrode and the electrolytic solution can be accelerated, and the output performance can be improved. .

Examples of the negative electrode active material used for the negative electrode in the present invention include carbon materials, and also include metal oxides and metal nitrides into which lithium ions can be inserted. Examples of carbon materials include natural graphite, artificial graphite, pyrolytic carbons, cokes, mesocarbon microbeads, carbon fibers, activated carbon, and pitch-coated graphite. Metal oxides capable of inserting lithium ions include tin and Examples of the metal compound include silicon and titanium, such as tin oxide, silicon oxide, and lithium titanate. Examples of the metal nitride include Li _2.6 Co _0.4 N.

  As a combination of the positive electrode active material and the negative electrode active material, the positive electrode active material is lithium cobaltate and the negative electrode active material is graphite. The positive electrode active material is nickel-based composite oxide and the negative electrode active material is graphite. This is preferable.

  The separator that can be used in the present invention is not particularly limited, and is a microporous polyethylene film, a microporous polypropylene film, a microporous ethylene-propylene copolymer film, a microporous polypropylene / polyethylene bilayer film, a microporous polypropylene / polyethylene / Examples thereof include a polypropylene three-layer film. In addition, a film in which an aramid resin is coated on a separator made to prevent a short circuit caused by Li dentlite and improve safety, or a film in which a resin containing polyamideimide and an alumina filler is coated on a separator Etc.

  In addition, since the electrolytic solution of the present invention is nonflammable, it is particularly useful as an electrolytic solution for a hybrid lithium battery or a large lithium secondary battery for a distributed power source. It is also useful as a nonaqueous electrolytic solution such as an electrolytic solution for electrolytic capacitors and an electrolytic solution for electric double layer capacitors.

  In addition, the electrolytic solution of the present invention can be used for, for example, electrolytic capacitors, solid display elements such as electroluminescence, sensors such as current sensors, and the like.

  Next, the present invention will be specifically described based on examples, but the present invention is not limited to such examples.

In addition, each compound used in the following Examples and Comparative Examples is as follows.
Ingredient (A)
(A1): HCF ₂ CF ₂ CH ₂ OCF ₂ CClFH
(A2): HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H
Ingredient (B)
(B1): Ethylene carbonate (B2): Propylene carbonate component (C)
(C1): Dimethyl carbonate (C2): Methyl ethyl carbonate (C3): Diethyl carbonate

Example 1
The component (A) is HCF ₂ CF ₂ CH ₂ OCF ₂ CClFH (A1), the component (B) is ethylene carbonate (B1), and the component (C) is dimethyl carbonate (C1) in a 60/20/20 volume% ratio. Then, LiPF ₆ as an electrolyte salt is further added to the electrolyte salt dissolving solvent to a concentration of 1.0 mol / liter, and the mixture is sufficiently stirred at 25 ° C. to prepare the nonaqueous electrolytic solution of the present invention. did.

Example 2
A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that the mixing ratio of (A1) / (B1) / (C1) was 50/40/10 vol%.

Example 3
A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that the mixing ratio of (A1) / (B1) / (C1) was 4/50/10 vol%.

Example 4
As a component (C), methyl ethyl carbonate (C2) and diethyl carbonate (C3) are mixed 1: 2 (volume ratio), and the mixing ratio of (A1) / (B1) / ((C2) + (C3)) is set. A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that 60/10/30% by volume.

Example 5
As a component (C), methyl ethyl carbonate (C2) and diethyl carbonate (C3) are mixed 1: 2 (volume ratio), and the mixing ratio of (A1) / (B1) / ((C2) + (C3)) is set. A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that 40/30/30% by volume.

Example 6
As a component (C), methyl ethyl carbonate (C2) and diethyl carbonate (C3) are mixed 1: 2 (volume ratio), and the mixing ratio of (A1) / (B1) / ((C2) + (C3)) is set. A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that the volume was 30/40/30% by volume.

Comparative Example 1
A nonaqueous electrolytic solution for comparison was prepared in the same manner as in Example 1 except that HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (A2) was used instead of the component (A1).

Comparative Example 2
In Example 2, a nonaqueous electrolytic solution for comparison was prepared in the same manner except that HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (A2) was used instead of the component (A1).

Comparative Example 3
In Example 3, a non-aqueous electrolyte for comparison was prepared in the same manner except that HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (A2) was used instead of the component (A1).

Comparative Example 4
In Example 4, a non-aqueous electrolyte solution for comparison was prepared in the same manner except that HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (A2) was used instead of the component (A1).

Comparative Example 5
In Example 5, a nonaqueous electrolytic solution for comparison was prepared in the same manner except that HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (A2) was used instead of the component (A1).

Comparative Example 6
In Example 6, a non-aqueous electrolyte for comparison was prepared in the same manner except that HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (A2) was used instead of the component (A1).

  The following solubility tests were performed on these nonaqueous electrolyte solutions.

Solubility test Each non-aqueous electrolyte is allowed to stand at 25 ° C for 24 hours, and the solubility is judged by whether or not crystals (electrolytes) are precipitated. In the evaluation, ◯ indicates that no crystal appeared, and X indicates that a crystal appeared.
The results are shown in Table 1.

  Those in which crystals are not deposited can be used as an electrolyte because the electrolyte is dissolved. However, it cannot be used as an electrolyte when crystals are deposited. From this point of view, all of the electrolyte solutions of Examples 1 to 6 can be used as the electrolyte solution because no crystals were precipitated. On the other hand, the electrolyte solutions of Comparative Examples 1 to 6 cannot be used as the electrolyte solution because crystals are deposited.

From this result, it can be seen that HCF ₂ CF ₂ CH ₂ OCF ₂ CClFH is superior in that it can widen the degree of freedom of the composition range when preparing the electrolytic solution.

Example 7
A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that the mixing ratio of (A1) / (B1) / (C1) was 40/20/40% by volume.

Comparative Example 7
A nonaqueous electrolytic solution for comparison was prepared in the same manner as in Example 7 except that HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (A2) was used instead of the component (A1).

  For these non-aqueous electrolytes, linear sweep voltammetry (LSV) was measured by the following method. The results are shown in FIG.

LSV Measurement Method Using a closed voltammetry cell (VC-4) manufactured by BAS, using a platinum electrode as a working electrode, Li as a counter electrode and a reference electrode, 3 ml of a test electrolyte is put into a measurement cell. The cell is scanned at a rate of 5 mV / sec from a natural potential to 7.0 V using a potentio-galvanostat (1287 type manufactured by Solartron Co.) as a measuring instrument at a constant temperature of 25 ° C., and the decomposition initiation potential of the electrolytic solution is examined.

From the result of FIG. 1, the electrolytic solution of Example 7 has almost the same potential as that of the electrolytic solution of Comparative Example 7 at which the rapid rise at which the electrolytic solution begins to decompose begins. This indicates that an electrolytic solution containing component (A): HCF ₂ CF ₂ CH ₂ OCF ₂ CClFH can be sufficiently used as a practical electrolytic solution.

Example 8
A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that the mixing ratio of (A1) / (B1) / (C1) was 10/30/60% by volume.

Comparative Example 8
A nonaqueous electrolytic solution for comparison was prepared in the same manner as in Example 1 except that the component (A1) was not blended and the mixing ratio of (B1) / (C1) was 30/70% by volume.

  The following battery characteristics and overcharge characteristics were examined for these non-aqueous electrolytes, as well as each of the electrolyte solutions of Example 1, Example 4, and Comparative Example 7. The results are shown in Table 2.

Measurement of battery characteristics A cylindrical secondary battery was produced by the following method.

A positive electrode active material prepared by mixing LiCoO ₂ , carbon black, and polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name KF-1000) at 90/3/7 (mass% ratio) is dispersed in N-methyl-2-pyrrolidone. Then, the slurry is applied uniformly on a positive electrode current collector (aluminum foil having a thickness of 15 μm), dried to form a positive electrode mixture layer, and then compression-molded with a roller press and then cut. The lead body was then welded to produce a strip-shaped positive electrode.

  Separately, styrene-butadiene rubber dispersed with distilled water is added to artificial graphite powder (manufactured by Hitachi Chemical Co., Ltd., trade name MAG-D) so that the solid content becomes 6% by mass, and mixed with a disperser. After applying the slurry in a uniform manner on a negative electrode current collector (copper foil having a thickness of 10 μm), drying, forming a negative electrode mixture layer, and then compression molding with a roller press machine and cutting, It dried and welded the lead body and produced the strip | belt-shaped negative electrode.

  This belt-like positive electrode was stacked on the belt-like negative electrode with a microporous polyethylene film (separator) having a thickness of 20 μm and wound in a spiral shape to obtain a laminated electrode body having a spiral winding structure. At that time, the positive electrode current collector was wound so that the rough surface side was the outer peripheral side. Thereafter, the electrode body was filled in a bottomed cylindrical battery case having an outer diameter of 18 mm, and the positive and negative lead bodies were welded.

  Next, the electrolyte solutions prepared in Examples and Comparative Examples were injected into the battery case, and after the electrolyte solution sufficiently penetrated into the separator, etc., sealed, precharged, and aged, a cylindrical lithium secondary battery was obtained. Produced.

  The lithium secondary battery was examined for discharge capacity, rate characteristics, cycle characteristics, and safety during overcharge in the following manner. The results are shown in Table 2.

(Discharge capacity)
When the charge / discharge current is represented by C, measurement is performed under the following charge / discharge measurement conditions with 1800 mA as 1C. The evaluation is performed using an index with the result of the discharge capacity of Comparative Example 8 as 100.
Charging / Discharging Condition Charging: Holds until the charging current reaches 1 / 10C at 1.0C and 4.2V (CC / CV charging)
Discharge: 1C 3.0Vcut (CC discharge)

(Rate characteristics)
As for charging, charging is performed until the charging current becomes 1/10 C at 4.2 V at 1.0 C, and discharging is performed to 3.0 V at a current equivalent to 0.2 C, and the discharge capacity is obtained. Subsequently, the battery is charged at 1.0 C at 4.2 V until the charging current becomes 1/10 C, discharged at a current equivalent to 2 C until 3.0 V, and the discharge capacity is obtained. From the ratio of the discharge capacity at 2C and the discharge capacity at 0.2C, the rate characteristic is obtained by substituting into the following calculation formula.
Rate characteristic (%) = 2C discharge capacity (mAh) /0.2C discharge capacity (mAh) × 100

(Cycle characteristics)
As for the cycle characteristics, a charge / discharge cycle performed under the above-described charge / discharge conditions (charging at 1.0 V until the charging current becomes 1/10 C at 4.2 V and discharging to 3.0 V at a current equivalent to 1 C) is 1 The discharge capacity after the first cycle and the discharge capacity after 100 cycles are measured. For the cycle characteristics, the value obtained by the following calculation formula is used as the cycle maintenance ratio value.
Cycle maintenance ratio (%) = 100 cycle discharge capacity (mAh) / 1 cycle discharge capacity (mAh) × 100

Overcharge characteristics For the cylindrical batteries of Examples and Comparative Examples, each battery was discharged to 3.0 V at a current value equivalent to 1 CmA, overcharged at a current value equivalent to 3 CmA with 12 V as the upper limit voltage, and whether or not there was ignition or rupture. Investigate. The case where ignition or rupture occurs is marked as x, and the case where it does not occur is marked as ◯.

  From the results in Table 2, it can be seen that even when the proportions of the components (A1), (B1) and (C1) are changed, the battery characteristics and the overcharge characteristics (safety) are good. It is also shown that the battery characteristics are inferior to the overcharge characteristics unless the component (A) is blended.

Examples 9-14
A nonaqueous electrolytic solution of the present invention was prepared in the same manner as in Example 1 except that the compounds shown in Table 3 were blended in the proportions shown in Table 3 as the components (B) and (C).

  The above battery characteristics and overcharge characteristics of these electrolytes were examined. The results are shown in Table 3.

  From the results of Table 3, it can be seen that even when the component (B) and the component (C) are changed, the battery characteristics and the overcharge characteristics (safety) can be maintained satisfactorily.

Examples 15-17
In place of LiPF ₆ as the electrolyte salt, LiN (O ₂ SCF ₃ ) ₂ (Example 15), LiN (O ₂ SC ₂ F ₅ ) ₂ (Example 16) or LiBF ₄ (Example 17) was used. Prepared a non-aqueous electrolyte solution of the present invention in the same manner as in Example 1.

  The above battery characteristics and overcharge characteristics of these electrolytes were examined. The results are shown in Table 4.

  From the results in Table 4, it can be seen that even if the electrolyte salt is changed, the battery characteristics and the overcharge characteristics (safety) can be maintained well.

It is a graph which shows the result of having measured LSV about the electrolyte solution of Example 7 and Comparative Example 7. FIG.

Claims (4)

(I) (A) Formula (1): Fluorine-containing chlorine-containing ether represented by HCF ₂ CF ₂ CH ₂ OCF ₂ CClFH,
(B) A solvent for dissolving an electrolyte salt containing a cyclic carbonate and (C) a chain carbonate, and (II) a non-aqueous electrolyte solution containing an electrolyte salt. The solvent (I) for dissolving the electrolyte salt is 10 to 60% by volume of the fluorine-containing chlorinated ether (A), 3 to 40% by volume of the cyclic carbonate (B) and the chain carbonate (B) with respect to the entire solvent (I). 10) to 60% by volume of C), and at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiN (O ₂ SCF ₃ ) ₂ and LiN (O ₂ SC ₂ F ₅ ) ₂ as the electrolyte salt (II) The nonaqueous electrolytic solution for a lithium secondary battery according to claim 1, comprising: 0.8 mol / liter or more. The nonaqueous electrolytic solution according to claim 1 or 2, which is for a lithium secondary battery. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and the nonaqueous electrolytic solution according to claim 3.

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