JPWO2015046172A1 - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

Provided is a non-aqueous electrolyte secondary battery in which the amount of metal elution from a positive electrode is reduced, thermal runaway is difficult to occur, thermal stability is high, and flame retardancy is high. A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a specific lithium transition metal composite oxide containing Mn, and the non-aqueous electrolyte is a lithium salt And at least one fluorine-containing solvent (α) selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound, and a fluorine-containing chain carbonate compound, and a liquid composition And a non-aqueous electrolyte secondary battery comprising a cyclic carboxylic acid ester compound.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery excellent in safety.

Non-aqueous electrolyte secondary batteries having a positive electrode, a negative electrode, and a non-aqueous electrolyte are widely used in portable electronic devices such as mobile phones and notebook computers. As a positive electrode of a non-aqueous electrolyte secondary battery using a lithium salt as an electrolyte, for example, a positive electrode using LiCoO ₂ is known. However, Co is expensive and expensive. Therefore, a positive electrode containing Mn, which is relatively inexpensive compared to Co, has attracted attention.

  However, the Mn-based positive electrode has a problem of a large amount of metal elution. When the amount of elution of metal from the positive electrode is large, there is a problem that the crystal structure is partially collapsed and battery characteristics are deteriorated, and a negative electrode dendrite is formed, thereby causing a short circuit and thermal runaway. As a method for suppressing metal elution, a method of adding an additive to the positive electrode, a method of coating the surface of the positive electrode, and the like are known (see Patent Documents 1 and 2 and Non-Patent Document 1). Insufficient.

As the non-aqueous electrolyte, carbonate solvents such as ethylene carbonate and dimethyl carbonate have been widely used. However, since the carbonate-based solvent is flammable, there is a risk of ignition due to heat generation of the battery.
As a method for enhancing the flame retardancy, it has been proposed to use a fluorine-containing solvent. For example, as a non-aqueous electrolyte solution for obtaining a non-aqueous electrolyte secondary battery that is flame-retardant and has good battery characteristics (cycle characteristics, discharge capacity), a fluorinated solvent, a non-fluorinated cyclic carbonate, and a non-fluorine Non-aqueous electrolytes containing a cyclic ester and a lithium salt are known (see Patent Documents 3 and 4).

  However, in Patent Documents 3 and 4, battery evaluation combined with a Mn-based positive electrode is not performed at all, and an effect on problems peculiar to the Mn-based positive electrode cannot be estimated. In addition, the amount of metal elution when combining the non-aqueous electrolyte and the Mn-based positive electrode has not been studied, and the effect of reducing the metal elution amount from the Mn-based positive electrode is still insufficient. .

JP 2003-128421 A International Publication No. 2012/081518 JP 2008-192504 A JP 2010-86914 A

Journal of Electroanalytical Chemistry, 2008, Volume 624, p197-204.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the amount of metal elution from a positive electrode is reduced, thermal runaway is hardly caused, thermal stability is excellent, and flame retardancy is high.

The present invention achieves the above-mentioned problems, and the gist thereof is as follows.
[1] A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode is at least one lithium transition metal selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3): Containing complex oxides,
The non-aqueous electrolyte includes a lithium salt and a liquid composition, and the liquid composition is at least one selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound, and a fluorine-containing chain carbonate compound. A non-aqueous electrolyte secondary battery comprising a seed fluorine-containing solvent (α) and a cyclic carboxylic acid ester compound.
^{_{Li (Li a Mn b Me 1}} c) O d F e ··· (1)
_{Li f Ni g Co h Mn i} Me 2 j O 2 ··· (2)
Li _{(1 + p)} Mn _(2-pq) Me ³ _p O ₄ (3)
(In the formula (1), Me ¹ is at least one element selected from the group consisting of Co, Ni, Cr, Fe, Al, Ti, Zr and Mg, and 0.09 <a <0.3, 0.4 ≦ b / (b + c) ≦ 0.8, a + b + c = 1, 1.9 <d <2.1, and 0 ≦ e ≦ 0.1.
In formula (2), Me ² is at least one element selected from the group consisting of Cr, Fe, Al, Ti, Zr and Mg, and 0.90 ≦ f ≦ 1.10, 0.20 ≦ g ≦ 0.50, 0.10 ≦ h ≦ 0.50, 0.20 ≦ i ≦ 0.50, 0 ≦ j ≦ 0.05, and f + g + h + i + j = 2.
In formula (3), Me ³ is at least one element selected from the group consisting of Co, Ni, Cr, Fe, Zn, Cu, Al, and Mg, and 0 ≦ p ≦ 0.20, 0 ≦ q <1.00. )
[2] The non-aqueous electrolyte secondary battery according to [1], wherein a ratio of the mass of the fluorinated solvent (α) to the total mass of the non-aqueous electrolyte is 30 to 80 mass%.
[3] The liquid composition is at least selected from the group consisting of a saturated cyclic carbonate compound, a saturated chain carbonate compound having no fluorine atom, a saturated cyclic sulfone compound (excluding a lithium salt), and a phosphate ester compound. The nonaqueous electrolyte secondary battery according to [1] or [2], further including one kind of compound (β).
[4] The nonaqueous electrolyte secondary battery according to [3], wherein a ratio of a mass of the saturated chain carbonate compound having no fluorine atom to a total mass of the nonaqueous electrolyte is 30% by mass or less. .
[5] The ratio of the total mass of the mass of the saturated cyclic carbonate compound and the mass of the saturated chain carbonate compound having no fluorine atom to the total mass of the nonaqueous electrolytic solution is 30% by mass or less. 3] or the nonaqueous electrolyte secondary battery according to [4].
[6] N _A / N _Li which is a ratio of the total number of moles (N _A ) of the cyclic carboxylic acid ester compound to the total number of moles (N _Li ) of lithium atoms derived from the lithium salt is 1.5 to 7.0. And
Wherein for _{N Li,} said _{N A,} the compound is the ratio of the sum of the total number of moles _{(N B)} of _{(β) (N A + N} B) / N Li is 3.0 to 7.0, The nonaqueous electrolyte secondary battery according to any one of [3] to [5].
[7] The nonaqueous electrolytic solution according to any one of [1] to [6], wherein a ratio of the mass of the cyclic carboxylic acid ester compound to the total mass of the nonaqueous electrolytic solution is 4 to 50% by mass. Secondary battery.
[8] The nonaqueous electrolyte secondary battery according to any one of [1] to [7], wherein the fluorine-containing solvent (α) includes the fluorine-containing ether compound.
[9] The nonaqueous electrolyte secondary battery according to [8], wherein the fluorine-containing ether compound is at least one selected from the group consisting of compounds represented by the following formula (4).
R ¹ —O—R ² (4)
(In the formula, R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a fluorinated alkyl group having 1 to 10 carbon atoms, or 3 carbon atoms. -10 fluorinated cycloalkyl group, 1 to 10 carbon atoms having 1 or more etheric oxygen atoms, or 2 to 10 carbon atoms having 1 or more etheric oxygen atoms. And one or both of R ¹ and R ² is a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or a carbon number having one or more etheric oxygen atoms. 2-10 fluorinated alkyl groups.)
[10] The compound represented by the formula (4) is CF ₃ CH ₂ OCF ₂ CHF ₂ , CF ₃ CH ₂ OCF ₂ CHFCF ₃ , CHF ₂ CF ₂ CH ₂ OCF ₂ CHF ₂ , or CH ₃ CH ₂ CH _2. The non-aqueous electrolyte secondary according to [9] above, comprising at least one selected from the group consisting of OCF ₂ CHF ₂ , CH ₃ CH ₂ OCF ₂ CHF ₂ , and CHF ₂ CF ₂ CH ₂ OCF ₂ CHFCF ₃ battery.
[11] The non-cyclic material according to any one of [1] to [10], wherein the cyclic carboxylic acid ester compound is at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and ε-caprolactone. Water electrolyte secondary battery.
[12] The nonaqueous electrolyte secondary battery according to any one of [1] to [11], wherein an open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is 4.35 V or more.
[13] The lithium salt includes LiPF _6, a nonaqueous electrolyte secondary battery according to any one of [1] to [12].

  The non-aqueous electrolyte secondary battery of the present invention has a reduced amount of metal elution from the positive electrode, is unlikely to cause thermal runaway, has excellent thermal stability, and has high flame retardancy.

In the present specification, a compound represented by the formula (1) is referred to as a compound (1). The same applies to compounds represented by other formulas.
The following definitions of terms apply throughout this specification and the claims.
The “non-aqueous electrolyte” is an electrolyte that does not substantially contain water, and even if water is included, the water content of the secondary battery using the non-aqueous electrolyte does not deteriorate in performance. It means an electrolyte solution in a range of amounts. The amount of water that can be contained in the non-aqueous electrolyte is preferably 500 ppm by mass or less, more preferably 100 ppm by mass or less, and particularly preferably 50 ppm by mass or less with respect to the total mass of the non-aqueous electrolyte. The lower limit of the moisture content is 0 mass ppm.
Other compounds (other solvents, additives, etc.) other than lithium salt, fluorine-containing solvent (α), cyclic carboxylic acid ester compound and compound (β) are defined as “other components”, and lithium salt and liquid composition Differentiated from things.
The “fluorinated ether compound” means a chain or cyclic compound having an ether bond and having a fluorine atom.
“Fluorine-containing chain carboxylic acid ester compound” means a chain compound having an ester bond in a chain structure, no ring structure containing an ester bond, and having a fluorine atom.

The “fluorine-containing chain carbonate compound” is a fluorine atom having a carbonate bond represented by —O—C (═O) —O— in the chain structure, having no ring structure containing a carbonate bond. Means a chain-like compound having
The “fluorinated alkane compound” means a compound in which one or more hydrogen atoms of an alkane are substituted with fluorine atoms, and hydrogen atoms remain.
The “cyclic carboxylic acid ester compound” means a cyclic compound having an ester bond as a part of the ring skeleton.
The “saturated cyclic carbonate compound” is a ring skeleton composed of a carbon atom and an oxygen atom, having a carbonate bond represented by —O—C (═O) —O— as a part of the ring skeleton, It means a cyclic compound having no carbon unsaturated bond.
The “saturated chain carbonate compound having no fluorine atom” has a carbonate bond represented by —O—C (═O) —O— in the chain structure and has a ring structure including the carbonate bond. It means a chain compound having no fluorine atom and no carbon-carbon unsaturated bond.
“Fluorinated” and “fluorinated” mean that some or all of the hydrogen atoms bonded to the carbon atom are replaced by fluorine atoms.
The “fluorinated alkyl group” means a group in which part or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms. Among the partially fluorinated groups are hydrogen atoms and fluorine atoms.
“Carbon-carbon unsaturated bond” means a carbon-carbon double bond or a carbon-carbon triple bond.

<Positive electrode>
Examples of the positive electrode of the nonaqueous electrolytic solution of the present invention include an electrode in which a positive electrode layer containing a positive electrode active material, a conductivity-imparting agent, and a binder is formed on a current collector.

[Positive electrode active material]
The positive electrode of the non-aqueous electrolyte secondary battery of the present invention has at least one lithium transition metal composite oxide (hereinafter referred to as the following compound (1), the following compound (2) and the following compound (3)). Compound oxide (I)). That is, the composite oxide (I) is used as the positive electrode active material in the positive electrode of the nonaqueous electrolyte secondary battery of the present invention.
By combining the positive electrode containing the composite oxide (I) with a non-aqueous electrolyte described later, the amount of metal elution from the positive electrode is reduced, thermal runaway is unlikely to occur, and non-aqueous water having excellent thermal stability It becomes an electrolyte secondary battery.

^{_{Li (Li a Mn b Me 1}} c) O d F e ··· (1)
_{Li f Ni g Co h Mn i} Me 2 j O 2 ··· (2)
Li _{(1 + p)} Mn _(2-pq) Me ³ _p O ₄ (3)

In the above formula (1), Me ¹ is at least one element selected from the group consisting of Co, Ni, Cr, Fe, Al, Ti, Zr and Mg, and 0.09 <a <0. 3, 0.4 ≦ b / (b + c) ≦ 0.8, a + b + c = 1, 1.9 <d <2.1, 0 ≦ e ≦ 0.1.
In the formula (2), Me ² is at least one element selected from the group consisting of Cr, Fe, Al, Ti, Zr and Mg, and 0.90 ≦ f ≦ 1.10, 0.20 ≦ g ≦ 0.50, 0.10 ≦ h ≦ 0.50, 0.20 ≦ i ≦ 0.50, 0 ≦ j ≦ 0.05, and f + g + h + i + j = 2.
In the formula (3), Me ³ is at least one element selected from the group consisting of Co, Ni, Cr, Fe, Zn, Cu, Al, and Mg, and 0 ≦ p ≦ 0.20, 0 ≦ q <1.00.

(Compound (1))
The compound (1) is a solid solution having a lithium excess phase, and is a lithium-rich lithium transition metal composite oxide.
Me ¹ in the compound (1) is preferably Co, Ni, and Cr, and particularly preferably Co and Ni from the viewpoint that the battery voltage can be increased and the battery capacity per unit mass can be increased.
From the viewpoint of increasing the battery capacity per unit mass, a is preferably 0.1 <a <0.25.
b / (b + c) is more preferably 0.55 ≦ b / (b + c) ≦ 0.75 from the viewpoint that the battery capacity per unit mass is increased.
d is a value determined according to a, b, c, and e, and 1.9 <d <2.1.
e indicates the ratio of F. When F does not exist, e is 0. When e is larger than 0, the safety of the positive electrode active material is improved. When e is 0, a decrease in discharge capacity tends to be suppressed.

Specific examples of the compound (1) include the following compounds.
Li (Li _0.13 Ni _0.26 Co _0.09 Mn _0.52 ) O ₂ ,
Li (Li _0.13 Ni _0.22 Co _0.09 Mn _0.56 ) O ₂ ,
Li (Li _0.13 Ni _0.17 Co _0.17 Mn _0.53 ) O ₂ ,
Li (Li _0.15 Ni _0.17 Co _0.13 Mn _0.55 ) O ₂ ,
Li (Li _0.16 Ni _0.17 Co _0.08 Mn _0.59 ) O ₂ ,
Li (Li _0.17 Ni _0.17 Co _0.17 Mn _0.49 ) O ₂ ,
_{Li (Li 0.17 Ni 0.21 Co 0.08} Mn 0.54) O 2,
Li (Li _0.17 Ni _0.14 Co _0.14 Mn _0.55 ) O ₂ ,
Li (Li _0.18 Ni _0.12 Co _0.12 Mn _0.58 ) O ₂ ,
Li (Li _0.18 Ni _0.16 Co _0.12 Mn _0.54 ) O ₂ ,
Li (Li _0.20 Ni _0.12 Co _0.08 Mn _0.60 ) O ₂ ,
Li (Li _0.20 Ni _0.16 Co _0.08 Mn _0.56 ) O ₂ ,
Li (Li _0.20 Ni _0.13 Co _0.13 Mn _0.54 ) O ₂ ,
Li (Li _0.22 Ni _0.12 Co _0.12 Mn _0.54 ) O ₂ ,
Li (Li _0.23 Ni _0.12 Co _0.08 Mn _0.57 ) O ₂ ,
Li (Li _0.16 Ni _0.17 Co _0.08 Mn _0.59 ) O ₂ ,
Li (Li _0.170 Ni _0.160 Co _0.125 Mn _0.545 ) O ₂ ,
Li (Li _0.17 Ni _0.17 Co _0.17 Mn _0.49 ) O ₂ ,
_{Li (Li 0.17 Ni 0.19 Co 0.15} Mn 0.66) O 2,
_{Li (Li 0.17 Ni 0.21 Co 0.08} Mn 0.54) O 2,
Li (Li _0.17 Ni _0.14 Co _0.14 Mn _0.55 ) O ₂ ,
Li (Li _0.18 Ni _0.12 Co _0.12 Mn _0.58 ) O ₂ ,
Li (Li _0.18 Ni _0.16 Co _0.12 Mn _0.54 ) O ₂ ,
Li (Li _0.20 Ni _0.12 Co _0.08 Mn _0.60 ) O ₂ ,
Li (Li _0.20 Ni _0.16 Co _0.08 Mn _0.56 ) O ₂ ,
_{Li (Li 0.20 Ni 0.13 Co 0.13} Mn 0.54) O 2 and the like.

(Compound (2))
Compound (2) is a lithium ternary composite oxide.
Me ² in the compound (2) is preferably Al, Ti, Zr and Mg from the viewpoint of improving safety and cycle characteristics.
f is preferably 0.95 ≦ f ≦ 1.10 because the amount of free alkali is not too high and the discharge capacity and discharge rate characteristics are improved.
g is preferably 0.25 ≦ g ≦ 0.50 from the viewpoint that the balance between safety and battery characteristics tends to be improved.
h is preferably 0.20 ≦ h ≦ 0.45 from the viewpoint that the balance between safety and battery characteristics tends to be improved.
i is preferably 0.20 ≦ i ≦ 0.35 from the viewpoint that the balance between safety and battery characteristics tends to be improved.
j is preferably 0 ≦ j ≦ 0.02 from the viewpoint that the balance between safety and battery characteristics tends to be improved.

Specific examples of the compound (2) include the following compounds.
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ,
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ,
LiNi _0.45 Co _0.1 Mn _0.45 O ₂ ,
LiNi _0.47 Co _0.2 Mn _0.3 Al _0.03 O ₂ ,
LiNi _0.48 Co _0.2 Mn _0.3 Mg _0.02 O ₂ ,
LiNi _0.49 Co _0.2 Mn _0.3 Zr _0.01 O ₂ etc.

(Compound (3))
Compound (3) is a lithium transition metal composite oxide having a spinel structure as a base.
In the compound (3), Me ³ is preferably Co, Ni, Al, and Mg from the viewpoint that the cycle characteristics are improved, a high battery potential is obtained, or the stability of the active material is improved.
p is preferably 0 ≦ p ≦ 0.10 because good discharge capacity and discharge rate characteristics are easily obtained.
q is preferably 0 ≦ q ≦ 0.5 from the viewpoint that a high discharge capacity and battery potential can be easily obtained and the deterioration of the active material is easily suppressed.

Specific examples of the compound (3) include the following compounds.
LiMn ₂ O ₄ ,
LiMn _1.5 Ni _0.5 O ₄ ,
LiMn _1.8 Co _0.2 O ₄ ,
LiMn _1.8 Al _0.2 O ₄ etc.

  The composite oxide (I) may be only the compound (1), only the compound (2), or only the compound (3). As the composite oxide (I), any two or more of the compounds (1) to (3) may be used in combination. When any two or more of compounds (1) to (3) are used in combination, the ratio can be determined as appropriate.

The positive electrode of the nonaqueous electrolyte secondary battery of the present invention may contain other positive electrode active materials other than the composite oxide (I) as long as the effects of the present invention are not impaired.
Examples of other positive electrode active materials include lithium transition metal composite oxides (LiCoO ₂ , LiNiO ₂ etc.) other than the composite oxide (I), transition metal oxides, olivine-type metal lithium salts, and the like.

  The total ratio of the composite oxide (I) in the positive electrode of the nonaqueous electrolyte secondary battery of the present invention is preferably 50% by mass or more and 100% by mass or less, and 80% by mass with respect to 100% by mass of the total amount of the positive electrode active material. % To 99.5% by mass is more preferable. If the total ratio of the composite oxide (I) is at least the lower limit value, the battery characteristics can be improved without impairing the high stability of the positive electrode active material containing Mn and the availability of relatively inexpensive raw materials. . If the total ratio of the composite oxide (I) is less than or equal to the upper limit value, battery characteristics having characteristics (high safety, high voltage, etc.) of the positive electrode active material containing a metal other than Mn can be obtained.

A substance having a composition different from that of the substance constituting the main cathode active material may be attached to the surface of the cathode active material. Surface adhesion substances include oxides (aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide), sulfate (lithium sulfate, sodium sulfate, potassium sulfate, sulfuric acid) Magnesium, calcium sulfate, aluminum sulfate, etc.), carbonates (lithium carbonate, calcium carbonate, magnesium carbonate, etc.) and the like.
The amount of the surface adhesion substance with respect to the positive electrode active material is preferably 0.1 mass ppm or more and 20 mass% or less, more preferably 1 mass ppm or more and 10 mass% or less, and particularly preferably 10 massppm or more and 5 mass% or less. The surface adhering substance can suppress the oxidation reaction of the nonaqueous electrolytic solution on the surface of the positive electrode active material, and can improve the battery life.

[Conductivity imparting agent]
Examples of the conductivity-imparting agent include carbon materials, metal substances (such as Al), and conductive oxide powders.

[Binder]
Examples of the binder include a resin binder (such as polyvinylidene fluoride) and a rubber-based binder (such as hydrocarbon rubber and fluororubber).

[Current collector]
Examples of the current collector include a metal thin film mainly composed of Al or the like.

<Negative electrode>
The negative electrode is not particularly limited. Examples of the negative electrode include an electrode in which a negative electrode layer containing a powdered negative electrode active material, a conductivity-imparting agent, and a binder is formed on a current collector. The conductivity imparting agent may not be included. In addition, when a negative electrode active material can maintain a shape by itself (for example, when it is a lithium metal thin film), a negative electrode can be formed only with a negative electrode active material.

[Negative electrode active material]
Examples of the negative electrode active material include one or more selected from the group consisting of a lithium metal, a lithium alloy, and a carbon material capable of inserting and extracting lithium ions.
Examples of the lithium alloy include a Li—Al alloy, a Li—Pb alloy, and a Li—Sn alloy. Examples of the carbon material include graphite, coke, and hard carbon.

[Conductivity imparting agent, binder]
As the binder for the negative electrode and the conductivity-imparting agent, the same materials as those for the positive electrode can be used.

[Current collector]
Examples of the current collector include a metal thin film mainly composed of Cu or the like.

<Non-aqueous electrolyte>
The non-aqueous electrolyte includes a lithium salt and a liquid composition, and includes other components as necessary.
The lower limit of the ionic conductivity at 25 ° C. of the nonaqueous electrolytic solution is preferably 0.4 S / m. A secondary battery using a non-aqueous electrolyte having an ionic conductivity at 25 ° C. of less than 0.4 S / m has poor output characteristics and poor practicality. If the non-aqueous electrolyte has an ionic conductivity at 25 ° C. of 0.4 S / m or more, the secondary battery has good output characteristics.

[Lithium salt]
Lithium salt is an electrolyte that dissociates in a non-aqueous electrolyte and supplies lithium ions. Examples of the lithium salt include Li ₂ PO ₃ F, LiPO ₂ F ₂ , LiPF ₆ , the following compound (A) (where k is an integer of 1 to 5), FSO ₂ N (Li) SO ₂ F, CF ₃ SO ₂ N (Li) SO ₂ CF ₃ , CF ₃ CF ₂ SO ₂ N (Li) SO ₂ CF ₂ CF ₃ , CF ₃ CFHSO ₂ N (Li) SO ₂ CFHCF ₃ , LiClO ₄ , the following compound (B) , The following compound (C), the following compound (D), the following compound (E), LiBF _{4 and the} like.

The lithium salt contained in the non-aqueous electrolyte preferably contains LiPF ₆ and more preferably LiPF ₆ only.
LiPF ₆ can exhibit high ionic conductivity when dissolved in a solvent having a high solubility, but compared to other lithium salts such as CF ₃ CF ₂ SO ₂ N (Li) SO ₂ CF ₂ CF _3. It is difficult to dissolve in a fluorine-containing solvent. However, the combined use with a cyclic carboxylic acid ester compound improves the solubility of LiPF _{6 in} a fluorine-containing solvent. When LiPF ₆ is uniformly dissolved in the fluorine-containing solvent, it becomes easy to obtain a nonaqueous electrolytic solution having practically sufficient ionic conductivity. In addition, LiPF ₆ is likely to be thermally decomposed and easily reduce the thermal stability of the battery. However, the inclusion of the cyclic carboxylic acid ester compound makes it difficult for the battery to run out of heat in a non-aqueous electrolyte using LiPF ₆ .

  Examples of the compound (A) include the following compound (A-1) to compound (A-4). From the viewpoint of easily obtaining a nonaqueous electrolytic solution having high ionic conductivity, the compound (A) preferably includes a compound (A-2) in which k is 2, and only a compound (A-2) in which k is 2 More preferably, it consists of.

[Liquid composition]
The liquid composition contains a fluorine-containing solvent (α) and a cyclic carboxylic acid ester compound, and may contain a compound (β) as necessary. That is, the liquid composition in the present invention comprises only the fluorinated solvent (α) and the cyclic carboxylic acid ester compound, or comprises the fluorinated solvent (α), the cyclic carboxylic acid ester compound and the compound (β), One of them.
A metal from the positive electrode can be obtained by combining a non-aqueous electrolyte containing a lithium salt and a liquid composition containing a fluorine-containing solvent (α) and a cyclic carboxylic acid ester compound with the positive electrode containing the composite oxide (I) described above. Thus, a non-aqueous electrolyte secondary battery having excellent thermal stability can be obtained.

(Fluorine-containing solvent (α))
The fluorine-containing solvent (α) contains at least one selected from the group consisting of fluorine-containing ether compounds, fluorine-containing chain carboxylic acid ester compounds, and fluorine-containing chain carbonate compounds, and other fluorine-containing compounds (if necessary) However, the fluorine-containing cyclic carbonate compound may be excluded). Fluorine-containing ether compounds, fluorine-containing chain carboxylic acid ester compounds, and fluorine-containing chain carbonate compounds have similar characteristics in terms of chemical stability due to introduction of fluorine atoms, compatibility with other compounds, and the like. Yes, it can be treated as an equivalent compound.
The fluorine-containing solvent (α) is a solvent having a fluorine atom in the molecule and is excellent in flame retardancy. A fluorine-containing solvent ((alpha)) may be used individually by 1 type, and may use 2 or more types together. When the number of fluorine-containing solvents (α) is two or more, the ratio can be arbitrarily determined.

Fluorine-containing ether compound:
The fluorine-containing solvent (α) preferably contains a fluorine-containing ether compound from the viewpoint of the solubility of the lithium salt, the flame retardancy, and the ionic conductivity of the nonaqueous electrolytic solution. As the fluorine-containing ether compound, the following compound (4) is preferable from the viewpoint of the solubility of the lithium salt, flame retardancy, and the ionic conductivity of the non-aqueous electrolyte. A fluorine-containing ether compound may be used individually by 1 type, and may use 2 or more types together. When the compound (4) is included, the compound (4) may be used alone or in combination of two or more. When the number of fluorine-containing ether compounds is two or more, the ratio can be arbitrarily determined.

R ¹ —O—R ² (4)
However, R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a fluorinated alkyl group having 1 to 10 carbon atoms, or a fluorine having 3 to 10 carbon atoms. A cycloalkyl group, a C 2-10 alkyl group having one or more etheric oxygen atoms, or a C 2-10 fluorinated alkyl group having one or more etheric oxygen atoms, R ^One or both of ¹ and R ² are fluorinated alkyl groups having 1 to 10 carbon atoms, fluorinated cycloalkyl groups having 3 to 10 carbon atoms, or 2 to 10 carbon atoms having one or more etheric oxygen atoms. A fluorinated alkyl group;

Examples of the alkyl group and the alkyl group having an etheric oxygen atom in the compound (4) include groups each having a linear structure, a branched structure, or a partially cyclic structure (for example, a cycloalkylalkyl group).
One or both of R ¹ and R ² is a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or 2 to 10 carbon atoms having one or more etheric oxygen atoms. Of the fluorinated alkyl group. When one or both of R ¹ and R ² are these groups, the solubility and flame retardancy of the lithium salt in the non-aqueous electrolyte are further improved. R ¹ and R ² may be the same or different.

Compound (4) is a compound (4-A) in which R ¹ and R ² are both fluorinated alkyl groups having 1 to 10 carbon atoms from the viewpoint of excellent solubility of the lithium salt in the liquid composition, A compound (4-B) in which R ¹ is a fluorinated alkyl group having 2 to 10 carbon atoms having one or more etheric oxygen atoms, and R ² is a fluorinated alkyl group having 1 to 10 carbon atoms; Compound (4-C) in which ¹ is a fluorinated alkyl group having 1 to 10 carbon atoms and R ² is an alkyl group having 1 to 10 carbon atoms is preferred, and compound (4-A) and compound (4-C) Is more preferable, and the compound (4-A) is particularly preferable.

When the total number of carbon atoms of the compound (4) is too small, the boiling point is too low, and when it is too large, the viscosity is increased to 4 to 10, and 4 to 8 is more preferable.
When the molecular weight of the compound (4) is too small, the boiling point is too low, and when it is too large, the viscosity is preferably 150 to 800, more preferably 150 to 500, and particularly preferably 200 to 500.
When the compound (4) has an etheric oxygen atom, the number of etheric oxygen atoms in the compound (4) is preferably 1 to 4, more preferably 1 or 2, and still more preferably 1. The number of etheric oxygen atoms in the compound (4) affects flammability.
50 mass% or more is preferable and, as for fluorine content in a compound (4), 60 mass% or more is more preferable. When the fluorine content in the compound (4) is high, the flame retardancy is excellent. The fluorine content is the ratio of the total mass of fluorine atoms to the molecular weight. Although the upper limit of fluorine content is not specifically limited, Usually, it is 80 mass% or less.

The compound (4) is preferably a compound in which both R ¹ and R ² are alkyl groups in which some of the hydrogen atoms of the alkyl group are fluorinated, from the viewpoint of excellent solubility of the lithium salt in the liquid composition. A compound in which one or both ends of R ¹ and R ² are —CF ₂ H is more preferable.

  Specific examples of compound (4-A) and compound (4-B), and specific examples of fluorine-containing ether compounds other than compound (4-A) and compound (4-B) include, for example, International Publication No. 2009 / And the compounds described in No. 133899.

As the compound (4), CF ₃ CH ₂ OCF ₂ CHF ₂ , CF ₃ CH ₂ has excellent solubility in a liquid composition of lithium salt, excellent flame retardancy, low viscosity, and low boiling point. The group consisting of OCF ₂ CHFCF ₃ , CHF ₂ CF ₂ CH ₂ OCF ₂ CHF ₂ , CH ₃ CH ₂ CH ₂ OCF ₂ CHF ₂ , CH ₃ CH ₂ OCF ₂ CHF ₂ , and CHF ₂ CF ₂ CH ₂ OCF ₂ CHFCF ₃ At least one selected from is preferred. In particular, at least one selected from the group consisting of CF ₃ CH ₂ OCF ₂ CHF ₂ , CHF ₂ CF ₂ CH ₂ OCF ₂ CHF ₂ and CHF ₂ CF ₂ CH ₂ OCF ₂ CHFCF ₃ is preferable.

Fluorine-containing chain carboxylic acid ester compound:
The fluorine-containing chain carboxylic acid ester compound preferably contains the following compound (5), and more preferably consists only of the compound (5), from the viewpoints of viscosity and boiling point. A fluorine-containing chain carboxylic acid ester compound may be used individually by 1 type, and may use 2 or more types together. When the compound (5) is included, the compound (5) may be used alone or in combination of two or more. When the number of fluorine-containing chain carboxylic acid ester compounds is two or more, the ratio can be arbitrarily determined.

However, R < ³ > and R < ⁴ > is respectively independently a C1-C3 alkyl group or a C1-C3 fluorinated alkyl group, and one or both of R < ³ > and R < ⁴ > are C1-C1 ~ 3 fluorinated alkyl groups.

Examples of the alkyl group and the fluorinated alkyl group in the compound (5) include a linear structure or a branched structure, respectively.
One or both of R ³ and R ⁴ is a fluorinated alkyl group having 1 to 3 carbon atoms. By making one or both of R ³ and R ⁴ a fluorinated alkyl group having 1 to 3 carbon atoms, the oxidation resistance and flame retardancy of the compound (5) are improved. R ³ and R ⁴ may be the same or different.

R ³ is preferably a methyl group, an ethyl group, a difluoromethyl group, a trifluoromethyl group, a tetrafluoroethyl group, or a pentafluoroethyl group from the viewpoint of viscosity, boiling point, or availability of the compound, a difluoromethyl group, or A trifluoromethyl group is more preferred.
R ⁴ is a methyl group, an ethyl group, a trifluoromethyl group, a 2-fluoroethyl group, a 2,2-difluoroethyl group, or a 2,2,2- A trifluoroethyl group is preferable, a methyl group, an ethyl group, or a 2,2,2-trifluoroethyl group is more preferable, and a methyl group or an ethyl group is still more preferable.

When the total number of carbon atoms of the compound (5) is too small, the boiling point is too low, and when it is too large, the viscosity is increased, preferably 3 to 7, more preferably 3 to 6, and still more preferably 3 to 5.
When the molecular weight of the compound (5) is too small, the boiling point is too low, and when it is too large, the viscosity is preferably 100 to 300, more preferably 100 to 250, and particularly preferably 100 to 200.
The fluorine content in the compound (5) is preferably 25% by mass or more, and more preferably 30% by mass or more from the viewpoint of improving flame retardancy. Although the upper limit of fluorine content is not specifically limited, Usually, it is 55 mass% or less.

  Specific examples of the compound (5) include acetic acid (2,2,2-trifluoroethyl), methyl difluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate and the like. From the viewpoint of availability and battery performance such as cycle characteristics, methyl difluoroacetate or ethyl trifluoroacetate is preferable.

Fluorine-containing chain carbonate compound:
The fluorine-containing chain carbonate compound preferably contains the following compound (6), more preferably only the compound (6), from the viewpoints of viscosity and boiling point. A fluorine-containing chain carbonate compound may be used individually by 1 type, and may use 2 or more types together. When the compound (6) is included, the compound (6) may be used alone or in combination of two or more. When the number of fluorine-containing chain carbonate compounds is two or more, the ratio can be arbitrarily determined.

However, R ⁵ and R ⁶ are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms, and one or both of R ⁵ and R ^{6 have} 1 carbon atom. ~ 3 fluorinated alkyl groups.

Examples of the alkyl group and the fluorinated alkyl group in the compound (6) include a linear structure or a branched structure, respectively.
One or both of R ⁵ and R ⁶ is a fluorinated alkyl group having 1 to 3 carbon atoms. By making one or both of R ⁵ and R ⁶ a fluorinated alkyl group having 1 to 3 carbon atoms, the solubility and flame retardancy of the lithium salt are improved. R ⁵ and R ⁶ may be the same or different.

The compound (6) is preferably a compound in which both R ⁵ and R ⁶ are fluorinated alkyl groups having 1 to 3 carbon atoms from the viewpoint of viscosity, boiling point, or availability of the compound. R ⁵ and R ⁶ are preferably CF ₃ CH ₂ — or CHF ₂ CF ₂ CH ₂ —.

When the total carbon number of the compound (6) is too small, the boiling point is too low, and when it is too large, the viscosity is increased to 4 to 7, and 4 or 5 is more preferable.
When the molecular weight of the compound (6) is too small, the boiling point is too low, and when it is too large, the viscosity is preferably from 180 to 400, more preferably from 200 to 350, and particularly preferably from 210 to 300.
The fluorine content in the compound (6) is preferably 25% by mass or more and more preferably 30% by mass or more from the viewpoint of improving the flame retardancy. Although the upper limit of fluorine content is not specifically limited, Usually, it is 50 mass% or less.

  Specific examples of the compound (6) include bis (2,2,2-trifluoroethyl) carbonate, bis (2,2,3,3-tetrafluoropropyl) carbonate, and the like. Bis (2,2,2-trifluoroethyl) carbonate is preferred from the viewpoint of battery performance such as viscosity, availability, and output characteristics.

Other fluorine-containing solvents:
The fluorine-containing solvent (α) may contain a fluorine-containing alkane compound as another fluorine-containing solvent. When the fluorine-containing alkane compound is contained, the vapor pressure of the non-aqueous electrolyte is suppressed, and the flame retardancy is further improved.

As the fluorine-containing alkane compound, a fluorine-containing alkane compound having 4 to 12 carbon atoms is preferable. If the fluorine-containing alkane compound has 4 or more carbon atoms, the vapor pressure of the non-aqueous electrolyte is lowered. When the fluorine-containing alkane compound has 12 or less carbon atoms, the lithium salt has good solubility.
The fluorine content in the fluorine-containing alkane compound is preferably 50 to 80% by mass. If the fluorine content in the fluorine-containing alkane compound is 50% by mass or more, the flame retardancy is excellent. If the fluorine content in the fluorine-containing alkane compound is 80% by mass or less, the solubility of the lithium salt is easily maintained.

The fluorinated alkane compounds, compounds of the linear structure is preferable, for _{example, n-C 4 F 9 CH} 2 CH 3, n-C 6 F 13 CH 2 CH 3, n-C 6 F 13 H, n-C ₈ F ₁₇ H and the like. A fluorine-containing alkane compound may be used individually by 1 type, and may use 2 or more types together.

(Cyclic carboxylic acid ester compound)
The liquid composition contains a cyclic carboxylic acid ester compound. By including the cyclic carboxylic acid ester compound, the lithium salt is uniformly dissolved in the fluorine-containing solvent (α). In addition, the inclusion of the cyclic carboxylic acid ester compound makes it difficult for the non-aqueous electrolyte, the positive electrode, and the negative electrode to react with each other, making it difficult for thermal runaway in the secondary battery to occur. The cyclic carboxylic acid ester compound may be one kind or two or more kinds.

As the cyclic carboxylic acid ester compound, a saturated cyclic carboxylic acid ester compound having no carbon-carbon unsaturated bond in the molecule is preferable from the viewpoint of stability to the redox reaction.
The ring structure in the cyclic carboxylic acid ester compound is preferably a 4- to 10-membered ring and more preferably a 4- to 7-membered ring from the viewpoints of structural stability and viscosity. From the viewpoint of easy availability, a 5- to 6-membered ring is more preferable and a 5-membered ring is particularly preferable. Moreover, 4-8 are preferable and, as for the total carbon number of a cyclic carboxylic acid ester compound, 4-6 are more preferable from an easy point. In addition, the cyclic carboxylic acid ester compound is preferably composed of only a carbon atom, a hydrogen atom and an oxygen atom, and the portion other than the ester bond represented by the —C (═O) —O— bond contained in the ring structure is included. More preferably, it consists only of carbon atoms and hydrogen atoms.

The ring structure of the cyclic carboxylic acid ester compound is preferably a ring structure having one ester bond from the viewpoint of viscosity.
The cyclic carboxylic acid ester compound may be a compound in which one or more hydrogen atoms of the alkylene group are substituted with a substituent. Examples of the substituent include a fluorine atom, a chlorine atom, an alkyl group, and a fluorinated alkyl group. The carbon number of the alkyl group is preferably 1 or 2, and the carbon number of the fluorinated alkyl group is preferably 1 or 2.

  The cyclic carboxylic acid ester compound preferably includes the following compound (7), and more preferably comprises only the compound (7), from the viewpoints of stability to redox reaction, structural stability, and viscosity.

However, R ^{7 to} R ¹² are each independently a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or one or more etheric oxygens It is a C2-C3 alkyl group having an atom. n is an integer of 1 to 3. R ^{7 to} R ¹² may be the same or different.

R ^{7 to} R ¹² are preferably a hydrogen atom, a methyl group, an ethyl group, or a fluorine atom from the viewpoint of stability to redox reaction, viscosity, and availability of the compound, and a hydrogen atom, a methyl group, or an ethyl group Is more preferable.
n is preferably 1 to 3, and more preferably 1 from the viewpoint of viscosity and availability of the compound.

Examples of the compound (7) include cyclic ester compounds such as γ-butyrolactone, γ-valerolactone, γ-hexanolactone, δ-valerolactone, and ε-caprolactone, and carbon atoms forming the ring of the cyclic ester compound. 1 or more of the hydrogen atoms bonded to the carbon atom have a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or one or more etheric oxygen atoms Examples thereof include compounds substituted with 2 to 3 alkyl groups.
As the compound (7), at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone and ε-caprolactone is preferable because it is easily available and has a high effect of suppressing thermal runaway, and γ-butyrolactone is preferable. Is more preferable.

(Compound (β))
Since the liquid composition has excellent lithium salt solubility and ionic conductivity, a saturated cyclic carbonate compound, a saturated chain carbonate compound having no fluorine atom (hereinafter also referred to as a non-fluorine-based saturated chain carbonate compound), It is preferable to further contain at least one compound (β) selected from the group consisting of saturated cyclic sulfone compounds (excluding lithium salts) and phosphate ester compounds.

Examples of the saturated cyclic carbonate compound include propylene carbonate (PC), ethylene carbonate (EC), 4-fluoro-1,3-dioxolan-2-one (FEC) and the like.
Examples of the non-fluorinated saturated chain carbonate compound include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like.
Examples of the saturated cyclic sulfone compound include sulfolane and 3-methylsulfolane.
Examples of the phosphate ester compound include trimethyl phosphate, triethyl phosphate, and tris phosphate (2,2,2-trifluoroethyl).

  The liquid composition preferably contains a non-fluorinated saturated chain carbonate compound. When the non-fluorinated saturated chain carbonate compound is included, the viscosity of the non-aqueous electrolyte can be lowered, and the lithium ion diffusion coefficient in the non-aqueous electrolyte and the ionic conductivity of the non-aqueous electrolyte are easily increased.

[Other ingredients]
The non-aqueous electrolyte is a compound other than the lithium salt, the fluorine-containing solvent (α), the cyclic carboxylic acid ester compound, and the compound (β) as necessary, as long as the effects of the present invention are not impaired. , Additives, etc.).

(Other solvents)
The nonaqueous electrolytic solution may contain a solvent other than the fluorine-containing solvent (α), the cyclic carboxylic acid ester compound and the compound (β).

(Additive)
In order to improve the function of the non-aqueous electrolyte, the non-aqueous electrolyte may contain conventionally known additives as necessary. Examples of the additive include an overcharge inhibitor, a dehydrating agent, a deoxidizing agent, a property improving aid, and a surfactant.

Overcharge prevention agent:
Examples of the overcharge inhibitor include aromatic compounds (biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, etc.), aromatic Partially fluorinated compounds (2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, etc.), fluorine-containing anisole compounds (2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole) All) and the like. An overcharge inhibitor may be used individually by 1 type, and may use 2 or more types together.

Dehydrating agent:
Examples of the dehydrating agent include molecular sieves, mirabilite, magnesium sulfate, calcium hydride, sodium hydride, potassium hydride, lithium aluminum hydride and the like. As the liquid composition or other solvent used for the non-aqueous electrolyte, those obtained by rectification after dehydration with a dehydrating agent are preferable. Moreover, what performed only the dehydration by the said dehydrating agent without performing rectification may be used.

Property improvement aids:
The characteristic improving aid is for improving capacity maintenance characteristics and cycle characteristics after high temperature storage. Examples of the property improving aid include unsaturated carbonate compounds (vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 4-ethynyl-1,3-dioxolan-2-one, etc.), sulfur-containing compounds (ethylene sulfite). 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolene, dimethyl sulfone, diphenyl sulfone, methyl phenyl sulfone, dibutyl disulfide, dicyclohexyl disulfide, tetramethyl thiuram monosulfide, N, N-dimethyl Methanesulfonamide, N, N-diethylmethanesulfonamide, etc.), hydrocarbon compounds (heptane, octane, cycloheptane, etc.), fluorine-containing aromatic compounds (fluorobenzene, difluorobenzene, hexafur) Robenzen etc.) and the like. A characteristic improvement adjuvant may be used individually by 1 type, and may use 2 or more types together.

Surfactant:
The surfactant assists the impregnation of the non-aqueous electrolyte into the electrode mixture or separator. As the surfactant, any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant may be used. An activator is preferred. As the surfactant, a fluorine-containing surfactant is preferable from the viewpoint of high oxidation resistance and good cycle characteristics and rate characteristics. Only one surfactant may be used, or two or more surfactants may be used.

[Ratio of each component]
(Ratio of lithium salt)
The upper limit value of the lithium salt content in the non-aqueous electrolyte is not particularly limited, but is preferably 1.5 mol / L, more preferably 1.4 mol / L, and still more preferably 1.3 mol / L. The lower limit of the content of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is preferably 0.7 mol / L, more preferably 0.8 mol / L, and still more preferably 0.9 mol / L.
When converted to a mass standard, the ratio of the mass of the lithium salt to the total mass of the non-aqueous electrolyte is preferably 5 to 20% by mass, more preferably 7 to 17% by mass, and still more preferably 9 to 14% by mass.
If the ratio of lithium salt is more than the said lower limit, the ionic conductivity of a non-aqueous electrolyte will become high. If the proportion of the lithium salt is not more than the above upper limit value, the lithium salt is easily dissolved uniformly in the liquid composition, and the lithium salt does not precipitate even under low temperature conditions. Further, lithium ions are easily diffused into the non-aqueous electrolyte, and the lithium ion diffusion coefficient is increased.

The nonaqueous electrolytic solution of the present invention preferably contains at least LiPF ₆ as a lithium salt. The molar ratio of LiPF ₆ to the total number of moles of lithium salt contained in the non-aqueous electrolyte is preferably 40 to 100 mol%, more preferably 50 to 100 mol%, still more preferably 65 to 100 mol%, and more preferably 80 to 100 mol%. Particularly preferred. When the molar ratio of LiPF ₆ with respect to the total number of moles of lithium salt is equal to or more than the lower limit value, a nonaqueous electrolytic solution having excellent ion conductivity and high practicality is obtained.

(Ratio of fluorine-containing solvent (α))
The ratio of the mass of the fluorinated solvent (α) to the total mass of the nonaqueous electrolytic solution is not particularly limited, but the lower limit of the mass ratio of the fluorinated solvent (α) to the total mass of the nonaqueous electrolytic solution is 30% by mass. Is preferable, 40 mass% is more preferable, and 45 mass% is still more preferable. The upper limit of the proportion of the fluorinated solvent (α) is preferably 80% by mass, more preferably 75% by mass, still more preferably 73% by mass, and particularly preferably 70% by mass.
If the ratio of the fluorine-containing solvent (α) is at least the lower limit, the non-aqueous electrolyte has excellent flame retardancy, small positive electrode reactivity and negative electrode reactivity, hardly causes thermal runaway, and has high voltage resistance. Have. Moreover, it can suppress that a metal component elutes from an electrode. When the proportion of the fluorinated solvent (α) is not more than the above upper limit value, the lithium salt is uniformly dissolved and the lithium salt is unlikely to precipitate at a low temperature.

The ratio of the mass of the fluorinated solvent (α) to the total mass of the liquid composition is preferably 30 to 90 mass%, more preferably 35 to 85 mass%, still more preferably 40 to 80 mass%, and more preferably 45 to 75 mass%. Is particularly preferred.
If the ratio of the fluorine-containing solvent (α) is at least the lower limit, the non-aqueous electrolyte has excellent flame retardancy, small positive electrode reactivity and negative electrode reactivity, hardly causes thermal runaway, and has high voltage resistance. Have. When the proportion of the fluorinated solvent (α) is not more than the above upper limit value, the lithium salt is uniformly dissolved and the lithium salt is unlikely to precipitate at a low temperature.

The fluorine-containing solvent (α) preferably contains a fluorine-containing ether compound from the viewpoint of the solubility of the lithium salt, the flame retardancy of the non-aqueous electrolyte, and the ionic conductivity.
The ratio of the mass of the fluorinated ether compound to the total mass of the fluorinated solvent (α) is preferably 25 to 100 mass%, more preferably 30 to 100 mass%, further preferably 50 to 100 mass%, and 60 to 100 mass%. % Is particularly preferable, and 70 to 100% by mass is most preferable. The fluorine-containing solvent (α) is most preferably composed of only a fluorine-containing ether compound.

  The ratio of the mass of the fluorinated ether compound to the total mass of the non-aqueous electrolyte is preferably 10 to 80% by mass. The lower limit of the proportion of the fluorine-containing ether compound is more preferably 20% by mass, further preferably 30% by mass, and particularly preferably 45% by mass. Further, the upper limit of the ratio of the fluorine-containing ether compound is more preferably 75% by mass, still more preferably 73% by mass, and particularly preferably 70% by mass.

  When the fluorine-containing solvent (α) contains a fluorine-containing chain carboxylic acid ester compound, the ratio of the mass of the fluorine-containing chain carboxylic acid ester compound to the total mass of the fluorine-containing solvent (α) is 0.01 to 50% by mass. Is preferable, 0.01-40 mass% is more preferable, 0.01-30 mass% is still more preferable, 0.01-20 mass% is especially preferable.

  When the fluorine-containing solvent (α) contains a fluorine-containing chain carbonate compound, the ratio of the mass of the fluorine-containing chain carbonate compound to the total mass of the fluorine-containing solvent (α) is preferably 0.01 to 50% by mass, 0 0.01-40 mass% is more preferable, 0.01-30 mass% is still more preferable, and 0.01-20 mass% is especially preferable.

When the fluorinated solvent (α) contains a fluorinated alkane compound, the ratio of the mass of the fluorinated alkane compound to the total mass of the nonaqueous electrolytic solution is preferably from 0.01 to 5 mass%.
If the ratio of a fluorine-containing alkane compound is 0.01 mass% or more, it will be excellent in the flame retardance of a non-aqueous electrolyte. When the proportion of the fluorinated alkane is 5% by mass or less, the solubility of the lithium salt is easily maintained.

  When the fluorine-containing solvent (α) is used in combination with one or more fluorine-containing ether compounds and one or more fluorine-containing chain carboxylic acid esters, fluorine-containing chain carbonate compounds, and fluorine-containing alkane compounds, the ratio thereof is arbitrary. I can decide.

(Ratio of cyclic carboxylic acid ester compound)
The ratio of the mass of the cyclic carboxylic acid ester compound to the total mass of the nonaqueous electrolytic solution is preferably 4 to 50 mass%, more preferably 7 to 45 mass%, still more preferably 10 to 40 mass%, and more preferably 15 to 35 mass%. Is particularly preferred.
If the ratio of the cyclic carboxylic acid ester compound is equal to or more than the lower limit, the non-aqueous electrolyte uniformly dissolves the lithium salt, and the reactivity between the non-aqueous electrolyte and the positive and negative electrodes is small, causing thermal runaway. Hateful. If the ratio of the cyclic carboxylic acid ester compound is not more than the above upper limit value, the non-aqueous electrolyte is excellent in flame retardancy.
The ratio of the mass of the cyclic carboxylic acid ester to the total mass of the liquid composition is preferably 4 to 60% by mass, more preferably 7 to 50% by mass, still more preferably 10 to 45% by mass, and particularly preferably 15 to 40% by mass. preferable.
When the ratio of the cyclic carboxylic acid ester is not less than the lower limit, the liquid composition has excellent solubility, small positive electrode reactivity and negative electrode reactivity, hardly causes thermal runaway, and has high voltage resistance. If the ratio of cyclic carboxylic acid ester is below the said upper limit, a liquid composition will be excellent in a flame retardance.

Contained in the nonaqueous electrolytic solution, the ratio N _{A /} N _Li of the total number of moles N _A cyclic carboxylic acid ester compound to the total number of moles N _Li of lithium atoms from the lithium salt is not particularly limited, 1.5 7.0 is preferred. The lower limit value of the N _A / N _Li is more preferably 2, more preferably 2.5, and particularly preferably 3. Moreover, 6.5 is preferable, as for the upper limit of said N _A / N _Li , 6 is more preferable, 5 is still more preferable, 4.5 is especially preferable, and 4.2 is the most preferable.
If N _A / N _Li is within the above range, the reactivity between the non-aqueous electrolyte and the positive and negative electrodes can be reduced while dissolving the lithium salt uniformly to obtain sufficient ionic conductivity for the following reasons. The thermal runaway of the secondary battery can be suppressed.

When a non-aqueous electrolyte is used for a secondary battery, the cyclic carboxylic acid ester compound forms a stable film on the electrode active material, particularly in the positive electrode, and the reaction between the electrode and the non-aqueous electrolyte is suppressed by the film. In connection with this, it is estimated that thermal runaway is suppressed.
If N _A / N _Li is equal to or greater than the lower limit, the non-aqueous electrolyte contains a sufficient amount of the cyclic carboxylic acid ester compound, so that the coating is sufficiently formed and the reaction between the electrode and the non-aqueous electrolyte is suppressed. It is considered that a sufficient effect of suppressing thermal runaway can be obtained by sufficiently exhibiting the effect. In addition, the cyclic carboxylic acid ester compound has a high affinity with the lithium salt, and is considered to promote the dissolution of the lithium salt in a solvent. When N _A / N _Li is equal to or higher than the lower limit, the lithium salt is sufficiently dissolved in the solvent, and an electrolytic solution having practically sufficient ionic conductivity is easily obtained.
Note that fluorine-containing compounds such as fluorine-containing ether compounds, fluorine-containing chain carboxylic acid ester compounds, and fluorine-containing chain carbonate compounds are considered to have low affinity with lithium salts, and promote dissolution of lithium salts in solvents. The effect of doing this tends to be very small.

The film formed on the electrode active material is considered to be easily dissolved in a highly polar solvent, and even if a film is formed in a solvent having a high polarity, the film formation is likely to be insufficient. Presumed.
If N _A / N _Li is not more than the above upper limit, the content of the cyclic carboxylic acid ester compound in the non-aqueous electrolyte does not become excessive, and the polarity of the entire non-aqueous electrolyte is within an appropriate range, It is considered that dissolution of the film formed on the electrode active material hardly occurs. By maintaining a sufficient coating on the electrode active material, an exothermic reaction between the electrode and the non-aqueous electrolyte is unlikely to occur, and thermal runaway is unlikely to occur.
Note that fluorine-containing compounds such as a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound, and a fluorine-containing chain carbonate compound are low in polarity, and thus the effect of dissolving the coating is considered to be very low. Moreover, the flame retardance of a non-aqueous electrolyte improves also by reducing content of the highly flammable cyclic carboxylic acid ester compound.

(Ratio of compound (β))
When the liquid composition contains the compound (β), the ratio of the mass of the compound (β) to the total mass of the nonaqueous electrolytic solution is preferably 0.01 to 30% by mass, and more preferably 0.1 to 20% by mass. .
If the ratio of a compound ((beta)) is below the said upper limit, it will be easy to suppress reaction with a compound ((beta)) and an electrode, and the nonaqueous electrolyte solution excellent in stability will be obtained. Moreover, since content of a fluorine-containing solvent ((alpha)) can be increased, the nonaqueous electrolyte solution excellent in the flame retardance is easy to be obtained.

When the liquid composition contains a saturated cyclic carbonate compound, the ratio of the mass of the saturated cyclic carbonate compound to the total mass of the nonaqueous electrolytic solution is preferably 0.01 to 20% by mass, more preferably 0.01 to 15% by mass. 0.01 to 10% by mass is more preferable, and 0.01 to 5% by mass is particularly preferable.
If the ratio of a saturated cyclic carbonate compound is below the said upper limit, a saturated cyclic carbonate compound and an electrode will be hard to react, a nonaqueous electrolyte solution is excellent in stability, and is excellent in a flame retardance.

When the liquid composition contains a non-fluorinated saturated chain carbonate compound, the ratio of the mass of the non-fluorinated saturated chain carbonate compound to the total mass of the non-aqueous electrolyte is preferably 0.01 to 30% by mass, and 01-20 mass% is more preferable, and 0.01-15 mass% is still more preferable.
If the proportion of the non-fluorinated saturated chain carbonate compound is less than or equal to the above upper limit, the non-fluorinated saturated chain carbonate compound and the electrode are less likely to react, and the non-aqueous electrolyte is excellent in stability and flame retardancy. .

When the liquid composition contains a saturated cyclic carbonate compound and a non-fluorinated saturated chain carbonate compound, the ratio of the total mass of the saturated cyclic carbonate compound and the non-fluorinated saturated chain carbonate compound to the total mass of the non-aqueous electrolyte is: 0.01-30 mass% is preferable, 0.01-20 mass% is more preferable, 0.01-15 mass% is still more preferable.
If the ratio of the total mass is equal to or less than the upper limit, even when a saturated cyclic carbonate compound and a non-fluorinated saturated chain carbonate compound are used, The dissolution of the coating can be suppressed, the reactivity between them and the electrode can be kept low, and it is easy to obtain a non-aqueous electrolyte with excellent stability. Moreover, it is easy to set it as the non-aqueous electrolyte which has the outstanding flame retardance by restraining content of a combustible compound low.

When the liquid composition contains a saturated cyclic sulfone compound, the ratio of the mass of the saturated cyclic sulfone compound to the total mass of the non-aqueous electrolyte is preferably 0.01 to 20% by mass, more preferably 0.01 to 15% by mass. 0.01 to 10% by mass is more preferable, and 0.01 to 5% by mass is particularly preferable.
If the ratio of the saturated cyclic sulfone compound is not more than the above upper limit value, the saturated cyclic sulfone compound and the electrode are unlikely to react with each other, and the non-aqueous electrolyte is excellent in stability and flame retardancy.

When the liquid composition contains a phosphate ester compound, the mass ratio of the phosphate ester compound to the total mass of the non-aqueous electrolyte is preferably 0.01 to 5 mass%.
When the proportion of the phosphate ester compound is equal to or less than the upper limit, the phosphate ester compound and the electrode are difficult to react, and the non-aqueous electrolyte is excellent in stability and flame retardancy.

When the liquid composition contains the compound (β), the ratio of the mass of the cyclic carboxylic acid ester compound to the total mass of the cyclic carboxylic acid ester compound and the compound (β) is preferably 30 to 100% by mass, and 35 to 100% by mass. Is more preferable, 40-100 mass% is still more preferable, 45-100 mass% is still more preferable, 50-100 mass% is especially preferable.
When the ratio of the cyclic carboxylic acid ester compound is within the above range, the reactivity between the non-aqueous electrolyte, the positive electrode, and the negative electrode can be reduced, and thermal runaway of the secondary battery can be suppressed.

If liquid composition comprising the compound (beta), to the total mole number N _Li of lithium atoms from the lithium salt, the total number of moles N _A and the compound of the cyclic carboxylic acid ester compound with total number of moles N _B of (beta) The sum ratio (N _A + N _B ) / N _Li is preferably 3.0 to 7.0. The lower limit of the _{(N A + N B) /} N Li is more preferably 3.2, 3.5 is more preferable. Further, the upper limit of _{(N A + N B) /} N Li is more preferably 6.8, more preferably 6.5.

The compound (β) has a high affinity with the lithium salt similarly to the cyclic carboxylic acid ester compound, and is considered to have an effect of promoting dissolution of the lithium salt in a solvent. _{(N A + N B) /} N Li said lower limit value or more, that the total amount of the cyclic carboxylic acid ester compound is considered to have a high dissolution promotion effect of the lithium salt with the compound (beta) is constant for the amount of the lithium salt If so, the ionic conductivity of the non-aqueous electrolyte is improved by improving the solubility of the lithium salt in the fluorine-containing solvent (α), and in particular, a lithium salt such as LiPF ₆ that is difficult to dissolve in the fluorine-based solvent is used. Even in this case, it can be dissolved in a fluorine-based solvent, and practically sufficient ionic conductivity is easily obtained.

When the polarity of the solvent is high, the film of the cyclic carboxylic acid ester compound formed on the electrode active material is dissolved, and the film formation tends to be insufficient. Since the compound (β) is also highly polar, it is considered that it exhibits an action of dissolving the film. _{(N A + N B) /} N Li is less than the upper limit, i.e., the total amount of the compound cyclic carboxylic acid ester compound showing the effect of dissolving the coating (beta) is equal to or less constant with respect to the lithium salt, It is considered that the solubility of the film is low and the film formation is less likely to be insufficient. As a result, it is estimated that the reactivity between the non-aqueous electrolyte, the positive electrode, and the negative electrode becomes smaller, and thermal runaway of the secondary battery is less likely to occur.
In addition, the presence of a highly polar solvent causes the metal component to elute from the electrode and causes deterioration of battery characteristics. If (N _A + N _B ) / N _Li is not more than the above upper limit value, it is presumed that the remarkable elution of the metal component is suppressed and the battery characteristics are hardly lowered.
Furthermore, the flame retardancy of the non-aqueous electrolyte is improved by reducing the content of the highly flammable cyclic carboxylic acid ester compound and the compound (β) in the non-aqueous electrolyte.

In particular, by using a lithium salt containing LiPF ₆ and controlling N _A / N _Li and (N _A + N _B ) / N _Li within the above ranges, practically sufficient ion conductivity and thermal runaway can be achieved. It is easy to obtain a non-aqueous electrolyte that has excellent stability that does not easily occur.

(Ratio of other ingredients)
When the nonaqueous electrolytic solution contains another solvent, the ratio of the total mass of the other solvent and the compound (β) to the total mass of the nonaqueous electrolytic solution is preferably 0.01 to 30 mass, and preferably 0.1 to 20 The mass% is more preferable. If the ratio of the total mass of the other solvent and the compound (β) is less than or equal to the above upper limit value, it is easy to suppress the reaction between the other solvent and the compound (β) and the electrode, and the nonaqueous electrolyte solution is excellent in stability. Is obtained. Moreover, since content of a fluorine-containing solvent ((alpha)) can be increased, the nonaqueous electrolyte solution excellent in the flame retardance is easy to be obtained.

  When the non-aqueous electrolyte contains a nitrile compound as another solvent, the ratio of the mass of the nitrile compound to the total mass of the non-aqueous electrolyte is less reactive with the positive electrode and the negative electrode, and is less likely to cause thermal runaway 10 mass% or less is preferable from the point which becomes easy to obtain a liquid, 5 mass% or less is more preferable, and 3 mass% or less is still more preferable.

  When the nonaqueous electrolyte contains an ether compound having no fluorine atom as another solvent, the ratio of the mass of the ether compound having no fluorine atom to the total mass of the nonaqueous electrolyte is more reactive with the positive electrode and the negative electrode. From the viewpoint that it is easy to obtain a nonaqueous electrolyte solution that is low and hardly causes thermal runaway, it is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

When the non-aqueous electrolyte contains an overcharge inhibitor, the mass ratio of the overcharge inhibitor to the total mass of the non-aqueous electrolyte is preferably 0.01 to 5% by mass.
When the ratio of the overcharge inhibitor is within the above range, it becomes easier to suppress the secondary battery from bursting and firing due to overcharge, and the secondary battery can be used more stably.

  When the non-aqueous electrolyte contains a property improving aid, the ratio of the mass of the property improving aid to the total mass of the non-aqueous electrolyte is preferably 0.01 to 5% by mass.

  When the non-aqueous electrolyte contains a surfactant, the ratio of the mass of the surfactant to the total mass of the non-aqueous electrolyte is preferably 0.05 to 5% by mass, more preferably 0.05 to 3% by mass, 0.05-2 mass% is still more preferable.

[Separator]
A separator is interposed between the positive electrode and the negative electrode to prevent a short circuit. An example of the separator is a porous film. A non-aqueous electrolyte is used by impregnating the porous membrane. Moreover, you may use as a gel electrolyte what impregnated the porous film with the nonaqueous electrolyte solution, and was made to gelatinize.

As the porous film, one that is stable with respect to the non-aqueous electrolyte and excellent in liquid retention can be used. As a porous film, a porous sheet or a nonwoven fabric is preferable.
Examples of porous membrane materials include fluororesins (polyvinylidene fluoride, polytetrafluoroethylene, copolymers of ethylene and tetrafluoroethylene, etc.), polyimides, polyolefins (polyethylene, polypropylene, etc.), oxidation resistance, air permeability From the viewpoint of availability, polyolefin is preferred.

[Battery exterior]
Examples of the material for the battery outer package include nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a resin material, and a film material.

[shape]
The shape of the nonaqueous electrolyte secondary battery of the present invention may be selected according to the application, and may be any shape such as a coin shape, a cylindrical shape, a square shape, and a laminate shape. Moreover, the shape of a positive electrode and a negative electrode can be suitably selected according to the shape of a secondary battery.

[Charging voltage]
The open circuit voltage in the fully charged state per pair of positive electrode and negative electrode of the nonaqueous electrolyte secondary battery of the present invention is preferably 4.2 V or higher, more preferably 4.3 V or higher from the viewpoint of obtaining a high battery capacity. 4.35V or more is more preferable.

[Function and effect]
In the non-aqueous electrolyte secondary battery of the present invention described above, a specific positive electrode including the composite oxide (I), a specific non-aqueous electrolysis including a fluorine-containing solvent (α) and a cyclic carboxylic acid ester compound Since the liquid is combined, elution of the metal from the positive electrode is reduced. Furthermore, since the non-aqueous electrolyte containing the fluorine-containing solvent (α) and the cyclic carboxylic acid ester compound has high flame retardancy and excellent thermal stability, the non-aqueous electrolyte secondary battery of the present invention has a thermal runaway. Is hard to get up.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description. Examples 1, 2, 4 to 9 and 11 to 14 are examples, examples 3, 10 and 15 are comparative examples, and example 16 is a reference example. The abbreviations below are as follows.
(Lithium salt)
LPF: LiPF ₆ .

(Fluorine-containing solvent (α))
AE3000: CF ₃ CH ₂ OCF ₂ CHF ₂ (trade name: AE-3000, manufactured by Asahi Glass Co., Ltd.),
_{HFE5510: CHF 2 CF 2 CH 2} OCF 2 CHFCF 3,
_{HFE458: CHF 2 CF 2 CH 2} OCF 2 CHF 2.

(Cyclic carboxylic acid ester compound)
GBL: γ-butyrolactone.

(Compound (β))
EC: ethylene carbonate,
EMC: ethyl methyl carbonate,
DMC: dimethyl carbonate.

[Metal dissolution evaluation]
1. Metal dissolution test (A)
The evaluation cell is installed in a thermostatic chamber maintained at 25 ° C., connected to a charger / discharger, and constant current charging is performed up to 3.4 V (cell voltage, the same shall apply hereinafter) at a constant current corresponding to 0.02 C. After the charging, the battery was charged to 4.2 V with a constant current corresponding to 0.2 C, and the constant voltage charging was continued until the charging current reached a current value of 0.02 C. Next, the battery was discharged to 3.0 V at a constant current corresponding to 0.2C. In the second cycle, after a pause of 10 minutes, constant current charging was performed to 4.2 V with a constant current corresponding to 0.2 C, and then constant voltage charging was performed until the charging current reached a current value of 0.02 C. After 10 minutes of rest, constant current discharge was performed at a current value of 0.2 C until 3.0 V was reached. The 3rd to 10th cycles were performed in the same manner as the second cycle. In the eleventh cycle, after a pause of 10 minutes, after performing constant current charging to 4.2 V with a constant current corresponding to 1 C, constant voltage charging is performed until the charging current reaches a current value of 0.02 C, After a pause of 10 minutes, constant current discharge was performed at a current value of 1 C until 3.0V was reached. Thereafter, a total of 200 charge / discharge cycles were performed in the same manner. 1C means the amount of current that discharges the reference capacity of the battery in one hour.
Next, the negative electrode was collected from the evaluation cell, washed with dimethyl carbonate, and then vacuum dried to obtain an evaluation sample. The prepared negative electrode sample surface is observed by atmospheric non-exposed X-ray photoelectron spectroscopic analysis (measuring device: ULVAC-PHI 5500, using transfer vessel), and the amount of Mn elution from the positive electrode is determined by determining the amount of Mn deposited. evaluated.

2. Metal dissolution test (B)
The evaluation cell is placed in a thermostatic chamber maintained at 25 ° C., and charged and discharged five times at a constant current corresponding to 0.2 C by the same method as the fifth cycle of the metal elution evaluation test (A). It was. Thereafter, the evaluation cell was moved into a thermostat kept at 50 ° C., connected to a charger / discharger, and charged with constant current up to 4.2 V at a constant current corresponding to 0.2 C. Charging was continued for 120 hours. Then, it discharged to 3.0V with the constant current equivalent to 0.2C.
Subsequently, the elution amount of Mn was evaluated by the same analysis method as the metal elution evaluation test (A).

3. Metal dissolution test (C)
Except for changing the charging potential to 4.35 V, the elution amount of Mn was evaluated in the same manner as the metal elution test (B).

[Thermal stability evaluation]
1. Thermal stability test (D)
The following charging / discharging cycle was implemented about the cell for evaluation. In cycles 1 to 4, constant current charging was performed up to 4.2 V at a current corresponding to 0.5 C, and constant voltage charging was performed until the charging current reached a current value of 0.02 C. Then, constant current discharge was performed to 3.0V with the electric current equivalent to 0.2C. In cycle 5, constant current charging was performed up to 4.2V at a current corresponding to 0.5C, and constant voltage charging was performed until the charging current reached a current value of 0.02C.
Thereafter, the obtained evaluation cell for a charged state was decomposed under an argon atmosphere to obtain a charged positive electrode. The obtained positive electrode was washed three times with dimethyl carbonate (2 mL), vacuum-dried, then punched out to a diameter of 5 mm, placed in a sealed container made of SUS, and further, the nonaqueous electrolyte solution in each example (in the evaluation cell). 2 μL of the same non-aqueous electrolyte solution) was sealed and used as an evaluation sample. About each obtained evaluation sample, it measured by the temperature range of 50-350 degreeC, and the temperature increase rate of 5 degree-C / min with the differential scanning calorimeter (DSC-6000 by SII nanotechnology company).
The evaluation was performed based on the following criteria, with the temperature at the top of the exothermic peak appearing at the lowest temperature among the exothermic peaks exceeding 1 mW based on the calorific value at 70 ° C. in the above measurement. It was.
(Excellent): Exothermic peak temperature is 300 ° C. or higher.
○ (good): Exothermic peak temperature is 250 ° C. or higher and lower than 300 ° C.
Δ (defect): Exothermic peak temperature is 200 ° C. or higher and lower than 250 ° C.
X (very poor): Exothermic peak temperature is less than 200 ° C.

2. Thermal stability test (E)
The thermal stability was evaluated in the same manner as the thermal stability test (D) except that the charging potential was changed to 4.5V.

[Example 1]
(Manufacture of positive electrode)
Nickel sulfate (II) hexahydrate, cobalt sulfate (II) heptahydrate, manganese sulfate (II) pentahydrate, and Ni: Co: Mn = 20: 15: 65 (molar ratio) The raw material solution was obtained by dissolving in distilled water so that the total concentration of Ni, Co, and Mn was 1.5 mol / L. Ammonium sulfate was dissolved in distilled water to a concentration of 0.75 mol / L to obtain an aqueous ammonium sulfate solution. Sodium carbonate was dissolved in distilled water to a concentration of 1.5 mol / L to obtain an aqueous sodium carbonate solution.

Subsequently, distilled water is put into a 2 L (liter) baffled glass reaction vessel, heated to 30 ° C. with a mantle heater, and the raw material is stirred while stirring the solution in the reaction vessel with a two-stage inclined paddle type stirring blade. The solution was added at a rate of 5.0 g / min and an aqueous ammonium sulfate solution at a rate of 0.5 g / min over 24 hours to precipitate a coprecipitate compound (composite carbonate) containing Ni, Co and Mn. During the addition of the raw material solution, sodium carbonate was added so as to keep the pH in the reaction vessel at 8.0. Further, the liquid was continuously extracted so that the amount of the liquid in the reaction tank did not exceed 2 L.
The obtained coprecipitated compound was washed by repeated filtration in pressure and dispersion in distilled water to remove impurity ions, and then dried at 120 ° C. for 15 hours.
When the contents of Ni, Co, and Mn of the coprecipitation compound were measured by ICP (high frequency inductively coupled plasma), they were 9.6% by mass, 7.5% by mass, and 30.7% by mass, respectively (moles). Ratio Ni: Co: Mn = 0.193: 0.150: 0.657).

Next, the coprecipitation compound and lithium carbonate are mixed so that the ratio of Li to the transition metal element (X) made of Ni, Co, and Mn (Li / X) is 1.41, and in an oxygen-containing atmosphere, It baked at 850 degreeC for 16 hours, and the positive electrode active material (henceforth a compound (1-1)) consisting of lithium containing complex oxide was obtained.
The composition of the compound (1-1) _{was (Li 0.170 Ni 0.160 Co 0.125 Mn} 0.545) O 2. The volume-based D50 particle size of the compound (1-1) measured with a laser scattering particle size distribution measuring device was 10.8 μm, and the specific surface area measured using the nitrogen adsorption BET method was 7.0 m ² / g. .

  The compound (1-1) (10.0 g) obtained above and carbon black (trade name “Denka Black”, 1.25 g, manufactured by Denki Kagaku Kogyo Co., Ltd.) are mixed together, and a rotation and revolution stirrer (Sinky The process of stirring for 1 minute at a rotational speed of 2000 rpm was performed three times using a product manufactured by Awatori Nertaro AR-E310). Next, N-methyl-2-pyrrolidone (10.0 g) was added, and the step of stirring for 3 minutes at a rotational speed of 2000 rpm using the stirrer was performed three times. Next, N-methyl-2-pyrrolidone (2.2 g) was added, and the step of stirring for 3 minutes at a rotational speed of 2000 rpm using the stirrer was performed three times. Furthermore, an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride (11% by mass, 10.3 g) was added, and the mixture was stirred for 1 minute at a rotational speed of 2000 rpm using the stirrer to obtain a slurry. The slurry was applied to an aluminum foil having a thickness of 20 μm to a thickness of 200 μm, dried, and then punched into a circle having a diameter of 18 mm to obtain an evaluation electrode (positive electrode).

(Manufacture of negative electrode)
Artificial graphite (9.1 g) and carbon black (0.80 g, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material were mixed and stirred for 1 minute at a rotational speed of 2000 rpm using the stirrer. Subsequently, 2 mass% carboxymethylcellulose aqueous solution (9.0g) was added, and also the process of stirring for 5 minutes at the rotation speed of 2000 rpm was performed twice using the said stirrer. Thereafter, a styrene-butadiene rubber aqueous dispersion latex binder (0.26 g) adjusted to a solid content concentration of 40% by mass was added, and the mixture was stirred for 5 minutes at a rotational speed of 2000 rpm using the agitator. Got.
The slurry was applied to a thickness of 150 μm on a copper foil having a thickness of 20 μm, dried, and then punched into a circle having a diameter of 19 mm to form a negative electrode.

(Preparation of non-aqueous electrolyte)
LPF (0.152 g), which is a lithium salt, is diffused into AE3000 (1.02 g), which is a fluorine-containing solvent (α), and then mixed with GBL (0.344 g), which is a cyclic carboxylic acid ester compound, to add non- A water electrolyte was prepared.

(Manufacture of evaluation cells)
A polyolefin microporous membrane was present as a separator between the positive electrode and the negative electrode, and 0.5 mL of the non-aqueous electrolyte was added thereto to produce an evaluation cell.

[Examples 2 and 3]
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the composition of the liquid composition was changed as shown in Table 1. Further, an evaluation cell was produced in the same manner as in Example 1 except that the nonaqueous electrolytic solution was used.

[Example 4]
An evaluation cell was produced in the same manner as in Example 1 except that the positive electrode produced by the following method was used.
(Manufacture of positive electrode)
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (manufactured by AGC Seimi Chemical Co., Ltd., trade name “Selion L”, 32.0 g, hereinafter referred to as compound (2-1)) and carbon black (electric Chemical Industrial Co., Ltd., trade name “Denka Black”, 0.80 g) was mixed, and the process of stirring for 1 minute at a rotational speed of 2000 rpm was performed 3 times using the stirrer. Next, N-methyl-2-pyrrolidone (7.50 g) was added, and the step of stirring for 3 minutes at a rotation speed of 2000 rpm using the stirrer was performed three times. Next, N-methyl-2-pyrrolidone (1.0 g) was added, and the step of stirring for 3 minutes at a rotational speed of 2000 rpm using the stirrer was performed three times. Furthermore, an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride (11% by mass, 7.45 g) was added, and the mixture was stirred for 1 minute at a rotational speed of 2000 rpm using the stirrer to obtain a slurry. The slurry was applied to an aluminum foil having a thickness of 20 μm to a thickness of 150 μm, dried, and then punched into a circle having a diameter of 18 mm to obtain an evaluation electrode (positive electrode).

[Examples 5 to 10]
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the composition of the liquid composition was changed as shown in Table 1. Further, an evaluation cell was produced in the same manner as in Example 1 except that the positive electrode produced in the same manner as in Example 4 and the non-aqueous electrolyte were used.

[Example 11]
An evaluation cell was produced in the same manner as in Example 1 except that the positive electrode produced by the following method was used.
(Manufacture of positive electrode)
LiMn ₂ O ₄ (manufactured by Merck, 32.0 g, hereinafter referred to as compound (3-1)) and carbon black (manufactured by Denki Kagaku Kogyo, trade name “Denka Black”, 0.80 g) are mixed. Then, the step of stirring for 1 minute at a rotational speed of 2000 rpm using the agitator was performed three times. Next, N-methyl-2-pyrrolidone (7.50 g) was added, and the step of stirring for 3 minutes at a rotation speed of 2000 rpm using the stirrer was performed three times. Then, N-methyl-2-pyrrolidone (1.0 g) was added, and the step of stirring for 3 minutes at a rotational speed of 2000 rpm using the stirrer was performed three times. Furthermore, an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride (11% by mass, 7.45 g) was added, and the mixture was stirred for 1 minute at a rotational speed of 2000 rpm using the stirrer to obtain a slurry. The slurry was applied to an aluminum foil having a thickness of 20 μm to a thickness of 150 μm, dried, and then punched into a circle having a diameter of 18 mm to obtain an evaluation electrode (positive electrode).

[Examples 12 to 15]
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the composition of the liquid composition was changed as shown in Table 2. Further, an evaluation cell was produced in the same manner as in Example 1 except that the positive electrode produced in the same manner as in Example 7 and the non-aqueous electrolyte were used.

[Example 16]
An evaluation cell was produced in the same manner as in Example 1 except that the positive electrode produced by the following method was used.
(Manufacture of positive electrode)
LiCoO ₂ (manufactured by AGC Seimi Chemical Co., 32.0 g, hereinafter referred to as compound (9)) and carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name “Denka Black”, 0.80 g) are mixed, The step of stirring for 1 minute at a rotation speed of 2000 rpm using the agitator was performed three times. Then, N-methyl-2-pyrrolidone (7.50 g) was added, and the step of stirring for 3 minutes at a rotational speed of 2000 rpm using the stirrer was performed three times. Then, N-methyl-2-pyrrolidone (1.0 g) was added, and the step of stirring for 3 minutes at a rotational speed of 2000 rpm using the stirrer was performed three times. Furthermore, an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride (11% by mass, 7.45 g) was added, and the mixture was stirred for 1 minute at a rotational speed of 2000 rpm using the stirrer to obtain a slurry. The slurry was applied to an aluminum foil having a thickness of 20 μm to a thickness of 150 μm, dried, and then punched into a circle having a diameter of 18 mm to obtain an evaluation electrode (positive electrode).

  Tables 1 and 2 show the results of metal elution evaluation and thermal stability evaluation in each example. In the metal elution evaluation in Examples 1 to 15 of Table 1 and Table 2, “0” means that no Mn elution is observed, and “+” means that Mn elution is observed. In Example 16, “0” means that no Co elution is observed, and “+” means that Co elution is observed. In addition, the greater the number of “+”, the greater the elution amount of Mn or Co. “/” Means not implemented.

As shown in Tables 1 and 2, in Examples 1 and 2 in which the positive electrode containing the compound (1-1) and the nonaqueous electrolytic solution containing the fluorine-containing solvent (α) and the cyclic carboxylic acid ester compound were combined, Compared with Example 3 in which EC and EMC were used for the non-aqueous electrolyte, the elution amount of Mn was reduced. In Examples 1 and 2, the thermal stability was also superior to that in Example 3.
In Examples 4 and 6 in which the positive electrode containing the compound (2-1) and the nonaqueous electrolytic solution containing the fluorinated solvent (α) and the cyclic carboxylic acid ester compound were combined, EC and EMC were used as the nonaqueous electrolytic solution. Compared to Example 10, the elution amount of Mn was reduced. Moreover, in Examples 4-9, compared with Example 10, it was excellent also in thermal stability.
Example 8 in which (N _A + N _B ) / N _Li exceeds 7, and the mass ratio of the fluorinated solvent (α) to the total mass of the nonaqueous electrolyte is less than 30%, and the mass ratio of the saturated chain carbonate compound is Although Example 9 which is 30% or more was superior in thermal stability to Example 10, elution of Mn was confirmed. _{(N A + N B) /} N Li is not less than 7, the mass ratio of the fluorine-containing solvent (alpha) is more than 30%, mass fraction of saturated linear carbonate is considered to be more preferable to be 30% or less.
In Examples 11 to 14 in which the positive electrode including the compound (3-1) and the nonaqueous electrolytic solution including the fluorinated solvent (α) and the cyclic carboxylic acid ester compound were combined, EC and EMC were used as the nonaqueous electrolytic solution. Compared with Example 15, the elution amount of Mn was reduced. Moreover, in Examples 11-13, compared with Example 15, thermal stability was also excellent.
Example 14 in which the mass ratio of the fluorine-containing solvent (α) to the total mass of the non-aqueous electrolyte is less than 30% and the mass ratio of the saturated chain carbonate compound is 30% or more is Mn as compared with Examples 11-13. In this case, it is considered more preferable that the mass ratio of the fluorine-containing solvent (α) is 30% or more and the mass ratio of the saturated chain carbonate is 30% or less.

As shown in Table 2, Example 16 using the positive electrode of the compound (9) not containing Mn, and EC and EMC in the non-aqueous electrolyte were Example 3, Example 10 using a positive electrode active material containing Mn, and Compared with Example 15, the amount of metal elution was relatively small, and the positive electrode active material containing Mn was confirmed to have a large problem of metal elution.
It has been found that the present invention is effective in suppressing elution of Mn, which is particularly eluted as compared with other metal species.

  The lithium ion secondary battery of the present invention includes a mobile phone, a portable game machine, a digital camera, a digital video camera, an electric tool, a notebook computer, a portable information terminal, a portable music player, an electric vehicle, a hybrid vehicle, a train, an aircraft, an artificial It can be applied in the fields of satellites, submarines, ships, uninterruptible power supplies, robots, power storage systems, etc. In particular, it is useful as a large-sized secondary battery in the fields of electric vehicles, hybrid vehicles, trains, aircraft, artificial satellites, submarines, ships, uninterruptible power supplies, robots, power storage systems, and the like.

  The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2013-197588 filed on September 24, 2013 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims (13)

A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode is at least one lithium transition metal selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3): Containing complex oxides,
The non-aqueous electrolyte includes a lithium salt and a liquid composition,
The liquid composition comprises at least one fluorine-containing solvent (α) selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound, a cyclic carboxylic acid ester compound, A non-aqueous electrolyte secondary battery comprising:
^{_{Li (Li a Mn b Me 1}} c) O d F e ··· (1)
_{Li f Ni g Co h Mn i} Me 2 j O 2 ··· (2)
Li _{(1 + p)} Mn _(2-pq) Me ³ _p O ₄ (3)
(In the formula (1), Me ¹ is at least one element selected from the group consisting of Co, Ni, Cr, Fe, Al, Ti, Zr and Mg, and 0.09 <a <0.3, 0.4 ≦ b / (b + c) ≦ 0.8, a + b + c = 1, 1.9 <d <2.1, and 0 ≦ e ≦ 0.1.
In formula (2), Me ² is at least one element selected from the group consisting of Cr, Fe, Al, Ti, Zr and Mg, and 0.90 ≦ f ≦ 1.10, 0.20 ≦ g ≦ 0.50, 0.10 ≦ h ≦ 0.50, 0.20 ≦ i ≦ 0.50, 0 ≦ j ≦ 0.05, and f + g + h + i + j = 2.
In formula (3), Me ³ is at least one element selected from the group consisting of Co, Ni, Cr, Fe, Zn, Cu, Al, and Mg, and 0 ≦ p ≦ 0.20, 0 ≦ q <1.00. )   The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio of the mass of the fluorinated solvent (α) to the total mass of the nonaqueous electrolyte is 30 to 80 mass%.   The liquid composition is at least one selected from the group consisting of a saturated cyclic carbonate compound, a saturated chain carbonate compound having no fluorine atom, a saturated cyclic sulfone compound (excluding a lithium salt) and a phosphate ester compound. The nonaqueous electrolyte secondary battery according to claim 1 or 2, further comprising a compound (β).   The nonaqueous electrolyte secondary battery according to claim 3, wherein the ratio of the mass of the saturated chain carbonate compound having no fluorine atom to the total mass of the nonaqueous electrolyte is 30% by mass or less.   The ratio of the total mass of the mass of the saturated cyclic carbonate compound and the mass of the saturated chain carbonate compound having no fluorine atom with respect to the total mass of the nonaqueous electrolytic solution is 30% by mass or less. A nonaqueous electrolyte secondary battery according to 1. N _A / N _Li which is the ratio of the total number of moles of the cyclic carboxylic acid ester compound (N _A ) to the total number of moles of lithium atoms derived from the lithium salt (N _Li ) is 1.5 to 7.0,
Wherein for _{N Li,} said _{N A,} the compound is the ratio of the sum of the total number of moles _{(N B)} of _{(β) (N A + N} B) / N Li is 3.0 to 7.0, The non-aqueous electrolyte secondary battery according to any one of claims 3 to 5.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein a ratio of the mass of the cyclic carboxylic acid ester compound to the total mass of the nonaqueous electrolyte solution is 4 to 50 mass%.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the fluorine-containing solvent (α) contains the fluorine-containing ether compound. The nonaqueous electrolyte secondary battery according to claim 8, wherein the fluorine-containing ether compound is at least one selected from the group consisting of compounds represented by the following formula (4).
R ¹ —O—R ² (4)
(In the formula, R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a fluorinated alkyl group having 1 to 10 carbon atoms, or 3 carbon atoms. -10 fluorinated cycloalkyl group, 1 to 10 carbon atoms having 1 or more etheric oxygen atoms, or 2 to 10 carbon atoms having 1 or more etheric oxygen atoms. And one or both of R ¹ and R ² is a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or a carbon number having one or more etheric oxygen atoms. 2-10 fluorinated alkyl groups.) The compound represented by the formula (4) is CF ₃ CH ₂ OCF ₂ CHF ₂ , CF ₃ CH ₂ OCF ₂ CHFCF ₃ , CHF ₂ CF ₂ CH ₂ OCF ₂ CHF ₂ , CH ₃ CH ₂ CH ₂ OCF ₂ CHF The non-aqueous electrolyte secondary battery according to claim 9, comprising at least one selected from the group consisting of ₂ , CH ₃ CH ₂ OCF ₂ CHF ₂ , and CHF ₂ CF ₂ CH ₂ OCF ₂ CHFCF ₃ .   The non-aqueous electrolyte solution 2 according to any one of claims 1 to 10, wherein the cyclic carboxylic acid ester compound is at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and ε-caprolactone. Next battery.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 11, wherein an open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is 4.35V or more. The lithium salt includes LiPF _6, a nonaqueous electrolyte secondary battery according to any one of claims 1 to 12.