JP2015018603A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which can ensure a high capacity by being charged with a high voltage, while withstanding repeated use required practically as an on-vehicle power supply for motor drive.SOLUTION: A nonaqueous electrolyte secondary battery has a solid-solution-based positive electrode and negative electrode and a nonaqueous electrolyte. The nonaqueous electrolyte is composed of a base electrolyte containing a specific compound (α) and a lithium salt (β), and one kind or more of compound represented by a general formula (II) (Z is an alkaline metal or an alkaline earth metal, and k is an integer of 1-5).

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, particularly a lithium ion secondary battery.

Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and notebook computers. In recent years, it is also expected to be used as an in-vehicle power source for driving a motor, which is the key to the spread of electric vehicles, in order to solve environmental and energy problems.
However, in order to obtain a practical on-vehicle power source for driving a motor, a discharge capacity capable of obtaining a sufficient travel distance is required, and a battery having a higher energy density is desired.

Currently, as a positive electrode active material for a lithium secondary battery, lithium cobalt oxide (LiCoO ₂ ), a lithium nickel compound (LiNiO ₂ ), a lithium cobalt nickel manganese composite oxide (for example, LiCo _1/3 Ni _1/3 Mn ₁₎ Layered rock salt type compounds such as _{/ 3} O ₂ ), spinel type manganese compounds (LiMn ₂ O ₄ ), olivine iron lithium compounds (LiFePO ₄ ) and the like are known. However, any of these positive electrode materials has a capacity density of less than 200 mAh / g, and a sufficient discharge capacity cannot be obtained as an in-vehicle power source for driving a motor.

A so-called solid solution positive electrode has been studied as a positive electrode material that may meet this demand. Among them, a solid solution of an electrochemically inactive layered Li ₂ MnO ₃ and an electrochemically active layered LiMO ₂ (where M is a transition metal such as Co or Ni), A composite oxide having a higher ratio of Li element to transition metal element such as Co, Mn, etc. is expected as a high-capacity positive electrode candidate material capable of exhibiting a large energy density exceeding 200 mAh / g (for example, Patent Document 1).
Patent Document 2 proposes a positive electrode material for a lithium ion battery, characterized in that an oxidation treatment is performed on a positive electrode material for a lithium ion battery using the same solid solution.

Moreover, in order to obtain a high discharge capacity, a high charging voltage is required. However, if the charging voltage is high, the non-aqueous electrolyte is decomposed and the cycle characteristics are likely to deteriorate. Therefore, a nonaqueous electrolyte mainly composed of γ-butyrolactone has been proposed as a nonaqueous electrolyte that can withstand a high charging voltage (Patent Document 3).
On the other hand, in order to improve the safety performance of a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte containing a specific cyclic bissulfonylimide salt has been proposed (Patent Document 4).

Japanese Patent No. 3539518 JP 2008-270201 A JP 2003-272704 A Japanese Patent No. 4433833

However, the solid solution positive electrode using Li ₂ MnO ₃ which is a high capacity positive electrode candidate material described in Patent Document 1 has a large discharge capacity, but if the charge / discharge potential is high, the cycle characteristics are poor. There was a problem that it deteriorated easily by repeated discharge. For this reason, even a lithium ion battery using such a solid solution positive electrode as a high-capacity positive electrode has a problem that the cycle durability under a high-capacity usage condition is poor, and it deteriorates immediately when charging / discharging at a high potential. It was.
In Patent Document 2, an attempt is made to improve the above-described degradation problem by oxidation treatment, but the charge / discharge cycle characteristics at a high potential still do not have a practically sufficient performance.

In addition, the non-aqueous electrolyte of Patent Document 3 has only been confirmed to have cycle characteristics of about 10 cycles while being able to withstand a high charge voltage, and cannot be said to withstand repeated use that is practically required. .
Moreover, in the non-aqueous electrolyte of patent document 4, it is not examined whether practically sufficient cycle characteristics can be obtained by charging and discharging at a high potential.
The present invention has been made in view of the above problems, and can be charged at a high voltage to obtain a high capacity, and can withstand repeated use that is practically required as an on-vehicle power source for driving a motor. It is an object to provide a water electrolyte secondary battery.

The present invention provides the following.
[1] A positive electrode having a compound represented by the general formula (I) as a positive electrode active material, a negative electrode, and a nonaqueous electrolytic solution,
The non-aqueous electrolyte is
One or more compounds (α) selected from the group consisting of cyclic carbonate compounds, chain carbonate compounds, cyclic ester compounds, and chain ester compounds;
LiPF ₆ , LiClO ₄ , LiBF ₄ , a compound represented by the general formula (A), a compound represented by the general formula (B), LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₃ , A base electrolyte solution including one or more lithium salts (β) selected from the group consisting of LiN (CF ₃ SO ₂ ) ₂ ;
A non-aqueous electrolyte secondary battery comprising one or more compounds represented by the general formula (II).
_{Li (Li x Mn y Me' z} ) O p F q ......... (I)

However, in the formula (I), Me ′ is at least one selected from Co, Ni, Cr, Fe, Al, Ti, Zr and Mg.
Further, 0.09 <x <0.3, y> 0, z> 0, 1.9 <p <2.1, 0 ≦ q ≦ 0.1, and 0.4 ≦ y / (y + z) ≦ 0.8, x + y + z = 1, 1.2 <(1 + x) / (y + z).
In the formula (II), Z is an alkali metal or an alkaline earth metal, and k is an integer of 1 to 5.

[2] The nonaqueous electrolyte secondary battery according to [1], wherein Z of the compound represented by the formula (II) is an alkali metal.
[3] The nonaqueous electrolyte secondary battery according to [1] or [2], wherein k of the compound represented by the formula (II) is 2.
[4] The content of the compound represented by the formula (II) in the nonaqueous electrolytic solution is 0.2 to 10.0 parts by mass with respect to 100 parts by mass of the base electrolytic solution. The non-aqueous electrolyte secondary battery according to any one of the above.
[5] The nonaqueous electrolyte secondary battery according to any one of [1] to [4], in which a ratio of the compound (α) in the base electrolyte is 50 to 99.8% by mass.
[6] The nonaqueous electrolytic solution according to any one of [1] to [5], wherein the concentration of the lithium salt (β) in the base electrolytic solution is 0.5 mol / l to 1.5 mol / l. Secondary battery.
[7] The nonaqueous electrolyte secondary battery according to any one of [1] to [6], wherein the compound represented by the formula (I) is a compound represented by the following formula (I ′).
_{Li (Li x Mn y Ni v} Co w) O p ............ (I ')
However, in the formula (I ′), 0.09 <x <0.3, 0.36 <y <0.73, 0 <v <0.32, 0 <w <0.32, 1.9 <p <2.1, x + y + v + w = 1, 1.2 <(1 + x) / (y + v + w) <1.8.
[8] The nonaqueous electrolyte secondary battery according to any one of [1] to [7], wherein the charging voltage is 4.4 V or higher.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that can be charged at a high voltage to obtain a high capacity and can withstand repeated use that is practically required.

  In the present specification, unless otherwise specified, a compound represented by the formula (I) is referred to as a compound (I), and other formulas are also shown similarly. The non-aqueous electrolyte secondary battery of the present invention has a positive electrode and a negative electrode facing each other with a separator interposed therebetween, and a non-aqueous electrolyte.

[Positive electrode]
In the positive electrode of the present invention, a compound represented by the following formula (I) or formula (I ′) is used as the positive electrode active material. The notation of the compound represented by the formula (I) or the formula (I ′) is a composition formula before performing treatment such as charge / discharge and activation. Here, the activation means removing lithium oxide (Li ₂ O) or lithium and lithium oxide from the positive electrode active material. As an ordinary activation method, there is an electrochemical activation method in which charging is performed at a voltage higher than 4.4 V or 4.6 V (a value expressed as a potential difference from the redox potential of Li ⁺ / Li). . Moreover, the activation method chemically performed by performing chemical reaction using acids, such as a sulfuric acid, hydrochloric acid, or nitric acid, is mentioned.

_{Li (Li x Mn y Me' z} ) O p F q ............ (I)
However, in the formula (I), Me ′ is at least one selected from Co, Ni, Cr, Fe, Al, Ti, Zr and Mg.
Further, x, y, z, p, and q in the formula (I) satisfy the relationships of the following formulas (I-1) to (I-8).
0.09 <x <0.3 ............ (I-1)
y> 0 ………… (I-2)
z> 0 ............ (I-3)
1.9 <p <2.1 (I-4)
0 ≦ q ≦ 0.1 …… (I-5)
0.4 ≦ y / (y + z) ≦ 0.8 (I-6)
x + y + z = 1 ………… (I-7)
1.2 <(1 + x) / (y + z) ............ (I-8)

As shown in the formula (I-8), in the compound (I), the ratio of Li exceeds 1.2 times mol with respect to the total of Mn and Me ′ which are transition metal elements.
The composition ratio of Li element to the total molar amount of the transition metal element is preferably 1.25 ≦ (1 + x) / (y + z) ≦ 1.75, and 1.35 ≦ (1 + x) / (y + z) ≦ 1.65. More preferably, 1.40 ≦ (1 + x) / (y + z) ≦ 1.55 is particularly preferable. When the composition ratio is in the above range, a positive electrode material having a high discharge capacity per unit mass can be obtained when a high charging voltage of 4.6 V or higher is applied.

Moreover, as shown to Formula (I-2), compound (I) contains Mn. Moreover, the ratio of Mn to the total amount of Mn and Me ′ is 0.4 to 0.8 as shown in Formula (I-6), and preferably 0.55 to 0.75. When the ratio of Mn is in the range of the formula (I-6), the discharge capacity becomes high.
q represents the ratio of F, but includes 0 as shown in Formula (I-5). That is, the compound (I) includes a compound in which F is not present.
p is a value determined according to x, y, z, and q, and is in a range of more than 1.9 and less than 2.1 as shown in Formula (I-4).

Among the compounds (I), the compound (I ′) represented by the following formula (I ′) is more preferable.
_{Li (Li x Mn y Ni v} Co w) O p ............ (I ')
However, x, y, v, w, and p in the formula (I ′) satisfy the relationships of the following formulas (I′-1) to (I′-7).
0.09 <x <0.3 ............ (I'-1)
0.36 <y <0.73 ............ (I'-2)
0 <v <0.32 ………… (I'-3)
0 <w <0.32 ………… (I'-4)
1.9 <p <2.1 (I'-5)
x + y + v + w = 1 …… (I′−6)
1.2 <(1 + x) / (y + v + w) <1.8 (I′−7)

As shown in the formula (I′-7), in the compound (I ′), the ratio of Li exceeds 1.2 times mol with respect to the total of transition metal elements Mn, Ni, and Co. Less than 8.
The composition ratio of the Li element to the total molar amount of the transition metal element is preferably 1.35 <(1 + x) / (y + v + w) <1.65, and 1.45 <(1 + x) / (y + v + w) <1.55. More preferred. When the composition ratio is in the above range, a positive electrode material having a high discharge capacity per unit mass can be obtained when a high charging voltage of 4.6 V or higher is applied.

As the positive electrode active material, 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 is particularly preferred.

Compound (I) or Compound (I ′) preferably has a layered rock salt type crystal structure (space group R-3m). In addition, since the ratio of Li element to transition metal element is high, XRD (X-ray diffraction) measurement using CuKα ray as an X-ray source has a peak in a range of 2θ = 20 to 25 °, similarly to layered Li ₂ MnO _3. Is observed.
Further, the compound (I) or the compound (I ′) has a metal surface containing at least one metal element selected from Al, Y, Ga, In, La, Pr, Nd, Gd, Dy, Er, and Yb. You may coat | cover with the compound containing an oxide and / or Li and a nonmetallic element (P, S, B).

  The positive electrode is formed by forming a positive electrode layer containing a positive electrode active material, a conductivity-imparting agent, and a binder on a current collector. As the conductivity-imparting agent, a carbon material, a metal substance such as Al, and a conductive oxide powder can be used. As the binder, a resin binder such as polyvinylidene fluoride and / or a rubber binder such as hydrocarbon rubber or fluorine rubber can be used. As the current collector, a metal thin film mainly composed of Al or the like can be used.

  The content of the conductivity imparting agent in the positive electrode is preferably 1 to 10% by mass of the entire positive electrode layer, and the content of the binder is also preferably about 1 to 10% by mass of the entire positive electrode layer. When the ratio between the conductivity-imparting agent and the binder is equal to or less than the preferable upper limit value, the ratio of the active material in the positive electrode layer can be sufficiently secured, and a sufficient capacity per unit mass can be obtained. If the ratio between the conductivity-imparting agent and the binder is too small, the conductivity may not be maintained, or a problem of electrode peeling may occur. The ratio of the active material in the positive electrode layer is preferably 80 to 98% by mass.

[Negative electrode]
The negative electrode is formed by forming a negative electrode layer containing a powdered negative electrode active material, a conductivity-imparting agent, and a binder on a current collector. The negative electrode active material used for the negative electrode is not particularly limited as long as lithium ions can be occluded during charging and released during discharging, and known materials can be used. Specific examples include graphite, coke, carbon materials such as hard carbon, a lithium - aluminum alloy, a lithium - lead alloy, lithium - lithium alloy such as a tin alloy, a lithium _{metal, Si, SnO 2, SnO,} TiO 2, Nb 2 A metal oxide having a base potential lower than that of the positive electrode active material, such as O ₂ SiO, can be used.
As the negative electrode binder and the conductivity-imparting agent, those equivalent to the positive electrode can be used. As the current collector, a metal thin film mainly composed of Cu or the like can be used.
In the case where the negative electrode active material can keep its shape by itself (for example, a lithium metal thin film), the negative electrode can be formed only with the negative electrode active material.

[Non-aqueous electrolyte]
A non-aqueous electrolyte is an electrolyte that does not substantially contain water, and even if it contains water, the amount of water is in a range where performance degradation of a secondary battery using the non-aqueous electrolyte is not observed. The amount of electrolyte solution. 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 50 ppm by mass or less with respect to the total mass of the non-aqueous electrolyte. It is particularly preferred. The lower limit of the moisture content is 0 mass ppm.

The nonaqueous electrolytic solution in the present invention comprises a base electrolytic solution and one or more compounds represented by the general formula (II) described later. The base electrolyte contains one or more compounds (α) and one or more lithium salts (β) described below.
The compound (α) is a compound selected from the group consisting of a cyclic carbonate compound, a chain carbonate compound, a cyclic ester compound, and a chain ester compound.
The proportion of the compound (α) in the base electrolyte is preferably 50 to 99.8% by mass, more preferably 60 to 99.5% by mass, and 70 to 99% by mass. Particularly preferred.
When the proportion of the compound (α) in the base electrolyte is at least a preferred lower limit value, the lithium salt (β) can be dissolved well. Moreover, if it is below a preferable upper limit, sufficient quantity of lithium salt ((beta)) can be contained.

A cyclic carbonate compound is a compound in which the ring skeleton has a ring structure composed of carbon atoms and oxygen atoms, and the ring structure has a carbonate bond represented by -O-C (= O) -O-.
The ring structure in the cyclic carbonate compound is preferably a 4- to 10-membered ring, more preferably a 4- to 7-membered ring, more preferably a 5- to 6-membered ring, and particularly preferably a 5-membered ring from the viewpoint of easy availability.
The ring structure of the cyclic carbonate compound is preferably a ring structure having one carbonate bond. In addition, a ring structure in which a carbonate bond is formed by linking with a linear alkylene group or vinylene group is more preferable.

In the case of a carbonate compound having a ring structure formed by linking a carbonate bond to a linear alkylene group, the linear alkylene group preferably has 1 to 7 carbon atoms, more preferably 1 to 4, more preferably 2 or 3 2 is particularly preferable. Specific examples include propylene carbonate (PC) and ethylene carbonate (EC).
Examples of the carbonate compound having a ring structure in which a carbonate bond is linked to a vinylene group include vinylene carbonate and dimethyl vinylene carbonate, and vinylene carbonate is particularly preferable.

The cyclic carbonate compound is also preferably a compound in which one or more hydrogen atoms of the linear alkylene group are substituted with a substituent. As the substituent, for example, a halogen atom, an alkyl group, a halogenated alkyl group, a vinyl group, and an allyl group are preferable. Specific examples include fluoroethylene carbonate.
When the base electrolyte contains a cyclic carbonate compound, the cyclic carbonate compound may be only one type or two or more types. The inclusion of a cyclic carbonate compound is preferable because the dielectric constant of the non-aqueous electrolyte can be increased.

The chain carbonate compound is a chain compound having no carbonate structure and having a carbonate bond represented by —O—C (═O) —O—.
The chain carbonate compound is preferably a chain monocarbonate having one carbonate bond. Examples of the chain monocarbonate include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).
When the base electrolyte contains a chain carbonate compound, the chain carbonate compound may be only one type or two or more types. It is preferable to contain a chain carbonate compound because the viscosity of the nonaqueous electrolytic solution can be reduced.

A cyclic ester compound is a compound in which the ring skeleton has a ring structure composed of a carbon atom and an oxygen atom, and the ring structure has an ester bond represented by —O—C (═O) —C—.
The cyclic ester compound is preferably a compound that does not contain a carbon-carbon unsaturated bond in the molecule. The ring structure in the cyclic ester compound is preferably a 4- to 10-membered ring, more preferably a 4- to 7-membered ring, more preferably a 5- to 6-membered ring, and particularly preferably a 5-membered ring from the viewpoint of easy availability.
The ring structure of the cyclic ester compound is preferably a ring structure having one ester bond, and more preferably a ring structure formed by linking an ester bond with a linear alkylene group. 1-7 are preferable, as for carbon number of a linear alkylene group, 1-4 are more preferable, 2 or 3 is more preferable, and 2 is especially preferable. Further, the cyclic ester compound may be a compound in which one or more hydrogen atoms of the linear alkylene group are substituted with a substituent. Examples of the substituent include a halogen atom, an alkyl group, and a halogenated alkyl group.

Specific examples include cyclic ester compounds such as γ-butyrolactone, γ-valerolactone, γ-hexanolactone, and δ-valerolactone, and one of hydrogen atoms bonded to carbon atoms forming the ring structure of the cyclic ester compound. Examples thereof include compounds in which at least one group is substituted with a halogen atom, an alkyl group, or a halogenated alkyl group. Of these, γ-butyrolactone and γ-valerolactone are preferred, and γ-butyrolactone is particularly preferred from the viewpoint of easy availability and the properties of the electrolytic solution.
When the non-aqueous electrolyte contains a cyclic ester compound, the cyclic ester compound may be only one type or two or more types. The inclusion of a cyclic ester compound is preferable because the stability of the electrolytic solution is improved.

A chain ester compound is a chain compound which does not have a ring structure and has an ester bond represented by —O—C (═O) —C—.
The chain ester compound is preferably a chain monoester having one ester bond. Examples of the chain monoester include ethyl acetate, ethyl butyrate, butyl acetate and the like.
When the base electrolyte contains a chain ester compound, the chain ester compound may be only one type or two or more types. It is preferable to include a chain ester compound because the viscosity of the electrolytic solution can be easily reduced.

The base electrolyte may contain any two or more of a cyclic carbonate compound, a chain carbonate compound, a cyclic ester compound, and a chain ester compound. You may contain all four types.
The base electrolyte solution preferably contains one or more compounds (α ′) selected from the group consisting of the following compound (1), compound (2), and compound (3).

In formulas (1) to (3), R ^{1 to} R ¹² are each independently a hydrogen atom, a halogen atom, an alkyl group, or a halogenated alkyl group, and X is an oxygen atom or CH ₂ .
When R ^{1 to} R ¹² are halogen atoms, each is preferably independently a fluorine atom or a chlorine atom. When R ^{1 to} R ¹² are alkyl groups, the alkyl group preferably has 1 to 6 carbon atoms. When R ^{1 to} R ¹² are halogenated alkyl groups, the alkyl group preferably has 1 to 6 carbon atoms, and the halogen atom is preferably a fluorine atom or a chlorine atom.

The proportion of the compound (α ′) in the base electrolyte solution, that is, the proportion of the total amount of the compound (1), the compound (2), and the compound (3) in the base electrolyte solution is 50 to 99.8 mass%. It is preferable that it is 60-99.5 mass%, and it is especially preferable that it is 70-99 mass%.
The proportion of each of the compound (1), the compound (2), and the compound (3) in the entire compound (α ′) is 5 to 100 mass% for the compound (1) and 0 to 95 mass for the compound (2). %, Compound (3) is preferably 0 to 10% by mass, compound (1) is 10 to 100% by mass, compound (2) is 0 to 90% by mass, and compound (3) is 0 to 5% by mass. It is more preferable that the compound (1) is 20 to 100% by mass, the compound (2) is 0 to 80% by mass, and the compound (3) is particularly preferably 0 to 3% by mass.

The lithium salt (β) is LiPF ₆ , LiClO ₄ , LiBF ₄ , the following compound (A), the following compound (B), LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN It is a lithium salt selected from the group consisting of (CF ₃ SO ₂ ) ₂ .

The concentration of the lithium salt (β) in the base electrolyte is preferably 0.5 mol / l to 1.5 mol / l. In terms of mass, 5 to 50% by mass is preferable, 8 to 30% by mass is more preferable, and 10 to 20% by mass is more preferable. If this concentration is too high, the viscosity increases, and if the concentration is too low, the electrical conductivity decreases.
The lithium salt (β) is preferably dissolved in the base electrolyte.

  The base electrolyte may contain a conventional solvent for non-aqueous electrolyte other than the above. For example, chain ethers such as 1,2-dimethoxymethane (DME), 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide , Formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, ethylene carbonate derivative, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, anisole, N-methylpyrrolidone, etc.

The nonaqueous electrolytic solution of the present invention contains one or more compounds represented by the formula (II).
However, in Formula (II), Z is an alkali metal or alkaline-earth metal, and k is an integer of 1-5.

In the formula (II), Z is preferably an alkali metal. k is preferably 1 to 3.
Only one type of compound (II) may be used, or two or more types may be used. In the present invention, when the nonaqueous electrolyte contains compound (II), the energy density can be maintained by suppressing the decrease in the average discharge voltage even when charging and discharging are performed at a high voltage.
The content of the compound (II) in the nonaqueous electrolytic solution is preferably 0.2 to 10.0 parts by mass, and 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the base electrolytic solution. It is more preferable.
When the content of compound (II) is at least the preferred lower limit, it becomes easy to obtain good high potential charge / discharge cycle characteristics. When the content of the compound (II) is not more than the preferable upper limit value, various characteristics of the electrolytic solution such as conductivity and low temperature characteristics can be achieved at a high level.

[Separator]
The material and shape of the porous membrane as the separator are not particularly limited as long as it is stable with respect to the non-aqueous electrolyte and has excellent liquid retention properties. Polyvinylidene fluoride, polytetrafluoroethylene, ethylene and tetrafluoroethylene A porous sheet or non-woven fabric made of a fluororesin such as a copolymer, polyimide, or a polyolefin such as polyethylene or polypropylene is preferred, and the material is preferably a polyolefin such as polyethylene or polypropylene. Moreover, you may use what impregnated these porous membranes with the nonaqueous electrolyte solution and gelatinized it as a gel electrolyte.

  The lithium secondary battery according to the present invention is, for example, laminated in a dry air or inert gas atmosphere with a negative electrode and a positive electrode laminated via a separator, or after winding the laminated one, the outer battery such as a can case A battery can be manufactured by housing, injecting an electrolytic solution, and sealing with a flexible film made of a laminate of a synthetic resin and a metal foil.

The configuration and shape of the battery is not particularly limited, and can take the form of a positive electrode facing the separator, a wound type wound with the negative electrode, a laminated type, etc., and a coin type, laminate pack, square type, etc. It can take the form of a cell, a cylindrical cell or the like.
The charging voltage of the lithium secondary battery according to the present invention is preferably 4.2 V or higher, more preferably 4.4 V or higher, and particularly preferably 4.5 V or higher. Moreover, 5.0V or less is preferable, 4.9V or less is more preferable, and 4.8V or less is especially preferable.

[Preparation of test electrolyte]
LiPF ₆ was dissolved in a carbonate-based solvent in which ethylene carbonate and diethyl carbonate were mixed in equal volumes so as to have a concentration of 1 M, and used as a test electrolyte of a reference example.
With respect to the test electrolyte solution of this reference example, a specific additive was added at a specific ratio to obtain test electrolyte solutions of Examples and Comparative Examples. Table 1 shows the types and amounts of additives in the test electrolytes of the examples and comparative examples (the test electrolyte of the reference example is 100 parts by mass).
In addition, the compound (II-1) and the compound (II-2) in Table 1 are compounds represented by the general formulas (II-1) and (II-2).

[Preparation of evaluation cell]
_{4.48 g} of Li (Li _0.2 Ni _0.128 Co _0.134 Mn _0.538 ) O ₂ as a positive electrode active material, 0.56 g of acetylene black as a conductivity-imparting agent, and polyvinylidene fluoride as a binder 4.67 g of (PVdF) was mixed in 12.55 g of N-methylpyrrolidone (NMP) solvent, and the slurry was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed into a circular shape having a diameter of 18 mm. The positive electrode was punched out. A negative electrode was prepared by punching a lithium metal foil having a thickness of 300 μm into a circle having a diameter of 19 mm. As a separator, a polyolefin microporous film having a thickness of 20 μm was present between the positive electrode and the negative electrode, and 0.5 mL of each test electrolyte was added thereto to prepare an evaluation cell.

[Charge / discharge cycle test]
The evaluation cell was connected to the charger / discharger, and in the first cycle, constant current charging was performed up to 4.6 V (potential with respect to lithium metal; the same applies hereinafter) with a current amount of 20 mA / g, and then a constant voltage of 4.6 V was applied. The battery was charged at a voltage for 23 hours, rested for 10 minutes after charging, and then discharged at a constant current of 20 mA / g until reaching 2.0V. After the second cycle, the battery was charged at a constant current of up to 4.6 V at a current amount of 200 mA / g, then charged at a constant voltage of 4.6 V for 4 hours, paused for 10 minutes after charging, and then 100 mA / g. Constant current discharge was performed until the current reached 2.0V. Then, a charge / discharge cycle test of a maximum of 80 times was performed such that the charge / discharge of the next cycle was started after a pause of 10 minutes.

If a significant decrease in the discharge capacity retention rate was observed before reaching 80 times, the charge / discharge cycle test was stopped at that time. Table 1 shows the number of cycles when the charge / discharge cycle test was stopped. Further, Table 1 shows the ratio of the discharge capacity at the time when the charge / discharge cycle test is stopped to the discharge capacity at the fifth cycle as the discharge capacity maintenance ratio when the 80 cycles are completed or when it is stopped halfway.
For the reference example and Examples 1 and 2, Table 2 shows the ratio of the average discharge voltage at the completion of 80 cycles to the average discharge voltage at the fifth cycle as the average discharge voltage maintenance ratio.
For the reference example and Examples 1 and 2, Table 3 shows the ratio of the discharge energy at the completion of 80 cycles to the discharge energy at the fifth cycle as the discharge energy maintenance rate. The discharge energy is a numerical value represented by the product of the discharge capacity and the average discharge voltage. The larger the numerical value, the larger the work that can be performed by the nonaqueous electrolyte secondary battery.

  As shown in Tables 1 and 2, in Examples 1 and 2, high values were obtained for both the discharge capacity retention ratio and the average discharge voltage at the 80th cycle. As a result, as shown in Table 3, a high discharge energy maintenance rate was obtained.

Claims (8)

A positive electrode having a compound represented by the general formula (I) as a positive electrode active material, a negative electrode, and a non-aqueous electrolyte;
The non-aqueous electrolyte is
One or more compounds (α) selected from the group consisting of cyclic carbonate compounds, chain carbonate compounds, cyclic ester compounds, and chain ester compounds;
LiPF ₆ , LiClO ₄ , LiBF ₄ , a compound represented by the general formula (A), a compound represented by the general formula (B), LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₃ , A base electrolyte solution including one or more lithium salts (β) selected from the group consisting of LiN (CF ₃ SO ₂ ) ₂ ;
A non-aqueous electrolyte secondary battery comprising one or more compounds represented by the general formula (II).
_{Li (Li x Mn y Me' z} ) O p F q ......... (I)

However, in the formula (I), Me ′ is at least one selected from Co, Ni, Cr, Fe, Al, Ti, Zr and Mg.
Further, 0.09 <x <0.3, y> 0, z> 0, 1.9 <p <2.1, 0 ≦ q ≦ 0.1, and 0.4 ≦ y / (y + z) ≦ 0.8, x + y + z = 1, 1.2 <(1 + x) / (y + z).
In the formula (II), Z is an alkali metal or an alkaline earth metal, and k is an integer of 1 to 5.   The nonaqueous electrolyte secondary battery according to claim 1, wherein Z of the compound represented by the formula (II) is an alkali metal.   The non-aqueous electrolyte secondary battery according to claim 1, wherein k of the compound represented by the formula (II) is 2.   The content of the compound represented by the formula (II) in the nonaqueous electrolytic solution is 0.2 to 10.0 parts by mass with respect to 100 parts by mass of the base electrolytic solution. The nonaqueous electrolyte secondary battery as described.   The ratio of the said compound ((alpha)) to the said base electrolyte solution is 50-99.8 mass%, The nonaqueous electrolyte secondary battery as described in any one of Claims 1-4.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein a concentration of the lithium salt (β) in the base electrolyte is 0.5 mol / l to 1.5 mol / l. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the compound represented by the formula (I) is a compound represented by the following formula (I ').
_{Li (Li x Mn y Ni v} Co w) O p ............ (I ')
However, in the formula (I ′), 0.09 <x <0.3, 0.36 <y <0.73, 0 <v <0.32, 0 <w <0.32, 1.9 <p <2.1, x + y + v + w = 1, 1.2 <(1 + x) / (y + v + w) <1.8.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein a charging voltage is used as 4.4 V or more.