JP2015018713A - Nonaqueous electrolytic solution and lithium-ion secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution which achieves a lithium-ion secondary battery having a positive electrode potential higher than that of a conventional one, being excellent in cycle characteristics, and generating little gas, and to provide a lithium-ion secondary battery using the nonaqueous electrolytic solution.SOLUTION: The nonaqueous electrolytic solution contains a nonaqueous solvent, an electrolyte, and a phosphonic acid compound represented by formula (1). (In the formula (1), R1 represents an optionally substituted C1-C20 organic group; R2 is one selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted C1-C10 organic group; and R3 represents a hydrogen atom or an alkali metal atom.)

Description

  The present invention relates to a non-aqueous electrolyte and a lithium ion secondary battery using the non-aqueous electrolyte.

  Lithium ion secondary batteries are widely used as power sources for mobile electronic devices such as mobile phones because they have excellent characteristics such as high energy density and high durability. In recent years, they are also used as power sources for automobiles such as electric vehicles. Has been.

  Although lithium-ion batteries are widely used, users of mobile electronic devices and electric vehicles still demand higher battery energy density. In order to respond to this, attempts to improve the energy density of the battery are actively made, and in particular, attention has been paid to the expansion of the charging depth of the positive electrode active material and the development of a high potential positive electrode.

According to Patent Document 1, when lithium-cobalt composite oxide (LiCoO ₂ ) is charged until the positive electrode potential becomes 4.3 V of lithium reference, the charging capacity is about 155 mAh / g, whereas it is 4.5 V. When it is charged until it becomes, it becomes 190 mAh / g or more. Thus, by raising the potential of the positive electrode during full charge, the utilization factor of the positive electrode active material is improved, and as a result, the energy density of the battery can be increased.

  In the lithium ion secondary battery, an electrolytic solution in which a lithium electrolyte is dissolved in a nonaqueous solvent is used. As the non-aqueous solvent, a carbonate solvent obtained by mixing cyclic carbonates such as ethylene carbonate and propylene carbonate and chain carbonates such as dimethyl carbonate and ethyl methyl carbonate in a specific ratio is employed. Carbonate solvent is widely used because it has both sufficient oxidation resistance and reduction resistance in a conventional battery (positive electrode potential at full charge: about 4.3 V lithium standard) and excellent lithium ion conductivity. It came. However, in a battery having a higher positive electrode potential than the conventional battery, since the carbonate solvent is decomposed, deposition of decomposition products and gas generation inside the battery occur, resulting in deterioration of battery characteristics such as cycle characteristics.

  In order to solve the above problem, Patent Document 2 proposes to improve the oxidation resistance of the electrolytic solution by fluorinating a non-aqueous solvent. Specifically, the oxidation resistance of the electrolytic solution is improved by using fluorinated ester and fluorinated ether at a high concentration of 50% by volume in total. Further, in Patent Document 3, it is possible to reduce the amount of gas generated inside the battery and improve cycle characteristics by containing a specific organophosphorus carboxylic acid ester such as triethylphosphonoacetate in a non-aqueous solvent. Proposed.

International Publication No. 2008-114739 International Publication No. 2012-132976 International Publication No. 2008-123038

  However, when the fluorinated non-aqueous solvent disclosed in Patent Document 2 is used, the solubility of the lithium electrolyte in the non-aqueous solvent is lowered and the ionic conductivity of the electrolytic solution is greatly lowered. There is a problem that the input / output characteristics of the device are impaired.

  In addition, when the organophosphorus carboxylic acid ester disclosed in Patent Document 3 is contained in a non-aqueous solvent, according to the results of studies by the present inventors, the amount of gas generated in a battery having a higher positive electrode potential than that of the prior art is reduced. The effect is not enough.

  As described above, the conventional technology does not show a solution for sufficiently suppressing cycle deterioration and gas generation in a lithium ion secondary battery having a high positive electrode potential.

  The present invention has been made in view of the above circumstances, and has a positive electrode potential higher than that of the prior art, has excellent cycle characteristics, and further realizes a lithium ion secondary battery with less gas generation. And it aims at providing the lithium ion secondary battery using this non-aqueous electrolyte.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above-mentioned problems can be solved by containing one or more specific phosphonic acid compounds in the non-aqueous electrolyte, and the present invention has been completed. It came to do.

That is, the present invention is as follows.
[1]
A nonaqueous solvent, an electrolyte, and a phosphonic acid compound represented by the following formula (1):
Non-aqueous electrolyte.
(In formula (1), R1 represents an optionally substituted organic group having 1 to 20 carbon atoms, and R2 represents a hydrogen atom, an alkali metal atom, and optionally substituted 1 to 10 carbon atoms. (It is a kind selected from the group consisting of organic groups, and R3 represents a hydrogen atom or an alkali metal atom.)
[2]
The non-aqueous electrolyte according to [1], wherein the phosphonic acid compound includes a compound in which R2 is a hydrogen atom or an alkali metal atom.
[3]
The nonaqueous electrolytic solution according to [1] or [2], wherein the phosphonic acid compound includes a compound represented by the following formula (2).
(In Formula (2), R4 represents a kind selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 6 carbon atoms, and R5 may be substituted. Represents a good alkylene group having 1 to 10 carbon atoms, R6 is a kind selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 10 carbon atoms; It is a hydrogen atom or an alkali metal atom.)
[4]
The non-aqueous solution according to any one of [1] to [3], wherein the phosphonic acid compound is contained in an amount of 0.00001 mass% to 10 mass% with respect to a total amount of 100 mass% of the nonaqueous electrolytic solution. Electrolytic solution.
[5]
The nonaqueous solvent according to any one of [1] to [4], wherein the nonaqueous solvent contains one or more cyclic carbonates selected from the group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and vinylene carbonate. Non-aqueous electrolyte.
[6]
Any one of [1] to [5] above, wherein the electrolyte contains one or more selected from the group consisting of LiPF ₆ , LiBF ₄ , LiB (C ₂ O ₄ ) ₂ , and LiBF ₂ (C ₂ O ₄ ). The non-aqueous electrolyte according to any one of the above.
[7]
A positive electrode, a negative electrode, and the nonaqueous electrolytic solution according to any one of [1] to [6] above,
A lithium ion secondary battery in which a potential of the positive electrode when fully charged is 4.4 V or more and 5.5 V or less based on lithium.

  According to the present invention, there is provided a non-aqueous electrolyte that has a higher positive electrode potential than the conventional one, has excellent cycle characteristics, and generates less gas, and uses the non-aqueous electrolyte. A lithium ion secondary battery can be provided.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. However, the present invention is not limited to this, and various modifications can be made without departing from the gist thereof. Is possible.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution according to this embodiment contains a nonaqueous solvent, an electrolyte, and a phosphonic acid compound represented by the following formula (1).
(In the formula, R 1 represents an optionally substituted organic group having 1 to 20 carbon atoms, and R 2 represents a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 10 carbon atoms. And R3 represents a hydrogen atom or an alkali metal atom.)

[Phosphonic acid compound]
By containing the phosphonic acid compound represented by the formula (1), the non-aqueous electrolyte according to the present embodiment has a higher positive electrode potential than the conventional one and is excellent in cycle characteristics. Fewer lithium ion secondary batteries can be realized. When the non-aqueous electrolyte according to the present embodiment is used, the reason why the cycle characteristics of the lithium ion secondary battery are improved and the gas generation is suppressed even when the positive electrode potential is higher than before is not always clear. Although the phosphonic acid compound reacts with the surface of the positive electrode active material and / or the negative electrode active material inside the battery to form a film on the surface of the active material, and by suppressing the decomposition of the nonaqueous solvent by this film, As a result, it is considered that cycle deterioration and gas generation of the lithium ion secondary battery are suppressed. However, the reason is not limited to this.

  In formula (1), R1 represents the C1-C20 organic group which may be substituted. Although it does not specifically limit as an organic group represented by R1, For example, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group etc. are mentioned. These organic groups may have a substituent as necessary, or may have different elements such as boron, silicon, nitrogen, phosphorus, sulfur, fluorine, chlorine, and bromine. As the substituent, methyl group, ethyl group, propyl group, butyl group, pentyl group, trifluoromethyl group, trifluoroethyl group, cyano group, nitro group, hydroxy group, carboxy group, sulfo group, phosphono group, ether group , Sulfide groups, carbonyl groups, and sulfonyl groups. Among these, a fluorine atom, a hydroxy group, a carboxy group, a sulfo group, and a phosphono group are preferable, and a carboxy group and a phosphono group are more preferable.

  Moreover, carbon number of the organic group represented by R1 is 1-20, 1-15 are preferable, 1-10 are more preferable, and 1-6 are more preferable. When the number of carbon atoms is 1 or more, good cycle performance can be ensured. Moreover, when the number of carbon atoms is 20 or less, good ionic conductivity of the electrolytic solution can be ensured.

  In formula (1), R2 represents a kind selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 10 carbon atoms.

  Although it does not specifically limit as an alkali metal atom, For example, Li, Na, K, Rb, Cs is mentioned. Among these, from the viewpoint of improving cycle performance, Li, Na, and K are preferable, and Li and Na are more preferable.

  Although it does not specifically limit as an organic group represented by R2, For example, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group etc. are mentioned. Here, these organic groups may have different elements such as boron, silicon, nitrogen, phosphorus, sulfur, fluorine, chlorine, bromine, cyano group, nitro group, hydroxy group, carboxy group, sulfo group, phosphono group. A substituent such as a group, an ether group, a sulfide group, a carbonyl group, or a sulfonyl group.

  Carbon number of the organic group represented by R2 is 1-10, 1-6 are preferable, and 1-3 are more preferable.

  R2 is preferably a hydrogen atom, an alkali metal atom, an alkyl group, an alkenyl group, or an alkynyl group, more preferably a hydrogen atom, an alkali metal atom, an alkenyl group, or an alkynyl group, from a viewpoint of suppressing gas generation, a hydrogen atom or an alkali metal atom Is more preferable. When the phosphonic acid compound contains a compound in which R2 is a hydrogen atom or an alkali metal atom, gas generation tends to be further suppressed.

  R3 represents a hydrogen atom or an alkali metal atom.

  The phosphonic acid compound preferably contains a phosphonic acid compound represented by the following formula (2). By using the phosphonic acid compound represented by the formula (2), it is possible to realize a lithium ion secondary battery that has a higher positive electrode potential than the conventional one, is excellent in cycle characteristics, and generates less gas. it can.

(In the formula, R4 represents one selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 6 carbon atoms, and R5 represents an optionally substituted carbon number. 1 to 10 represents an alkylene group, R6 is one selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 10 carbon atoms, and R7 is a hydrogen atom or (It is an alkali metal atom.)

  In formula (2), R4 represents a kind selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 6 carbon atoms.

  Although it does not specifically limit as an alkali metal atom, For example, Li, Na, K, Rb, Cs can be used. Among these, Li, Na, and K are preferable, and Li and Na are more preferable.

  Although it does not specifically limit as an organic group represented by R4, For example, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, a phenyl group etc. are mentioned. 1-6 are preferable, as for carbon number of the organic group represented by R4, 1-5 are more preferable, and 1-3 are more preferable. The organic group represented by R4 may have a different element such as boron, silicon, nitrogen, phosphorus, sulfur, fluorine, chlorine, or bromine.

  R4 is preferably a hydrogen atom, an alkali metal atom, an alkyl group, an alkenyl group or an alkynyl group, more preferably a hydrogen atom, an alkali metal atom, an alkenyl group or an alkynyl group, and even more preferably a hydrogen atom or an alkali metal atom.

  In formula (2), R5 represents an optionally substituted alkylene group having 1 to 10 carbon atoms. The alkylene group represented by R5 is not particularly limited, and examples thereof include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a hepsylene group, an octylene group, a nonylene group, and a decylene group. . Even if the alkylene group represented by R5 has a halogen atom such as fluorine, chlorine, bromine, etc., a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a trifluoromethyl group, a trifluoroethyl group, etc. It may have a substituent. 1-10 are preferable, as for carbon number of R5, 1-8 are more preferable, 1-6 are more preferable, and 1-3 are more preferable.

  In formula (2), R6 represents a kind selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 10 carbon atoms.

  Although it does not specifically limit as an alkali metal atom, For example, Li, Na, K, Rb, Cs is mentioned. From the viewpoint of improving cycle performance, Li, Na, and K are preferable, and Li and Na are more preferable.

  Although it does not specifically limit as an organic group represented by R6, For example, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group etc. are mentioned. Here, the organic group represented by R6 may be a cyano group, a nitro group, a hydroxy group, a carboxy group, a sulfo group, even if it has a different element such as boron, silicon, nitrogen, phosphorus, sulfur, fluorine, chlorine, or bromine. Group, phosphono group, ether group, sulfide group, carbonyl group, sulfonyl group and the like. As carbon number of the organic group represented by R6, 1-10 are preferable, 1-6 are more preferable, and 1-3 are more preferable. R6 is preferably a hydrogen atom, an alkali metal atom, an alkyl group, an alkenyl group or an alkynyl group, more preferably a hydrogen atom, an alkali metal atom, an alkenyl group or an alkynyl group, from a viewpoint of suppressing gas generation, a hydrogen atom or an alkali metal atom Is more preferable.

  R7 represents a hydrogen atom or an alkali metal atom.

  In addition, the phosphonic acid compound represented by Formula (1) and Formula (2) can be identified by conventionally well-known methods, such as NMR, FTIR, and MASS.

  Specific examples of the phosphonic acid compound represented by the formula (1) and / or the formula (2) include the following compounds.

  The phosphonic acid compound represented by Formula (1) and / or Formula (2) may be used individually by 1 type, or may use 2 or more types together.

[Nonaqueous solvent]
The nonaqueous electrolytic solution according to this embodiment contains a nonaqueous solvent. The non-aqueous solvent is not particularly limited, but an aprotic polar solvent is preferable. The aprotic polar solvent is not particularly limited. For example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate. Cyclic carbonates such as trifluoromethylethylene carbonate, fluoroethylene carbonate and 4,5-difluoroethylene carbonate; lactones such as γ-butyrolactone and γ-valerolactone; cyclic sulfones such as sulfolane; cyclic ethers such as tetrahydrofuran and dioxane; , Dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate Chain carbonates such as boronate, dibutyl carbonate, ethylpropyl carbonate and methyl trifluoroethyl carbonate; Nitriles such as acetonitrile and propionitrile; Chain ethers such as dimethyl ether and dimethoxyethane; Chain carboxyls such as methyl acetate and methyl propionate Examples include acid esters. A non-aqueous solvent may be used individually by 1 type, or may use 2 or more types together.

  As the non-aqueous solvent, it is preferable to use a carbonate solvent obtained by mixing a cyclic carbonate and a chain carbonate at a specific ratio. When mixing the cyclic carbonate and the chain carbonate, the mixing ratio of the cyclic carbonate and the chain carbonate is preferably 1:10 to 5: 1, more preferably 1: 5 to 3: 1, and more preferably 1: 4 to 1: 4. 2: 1 is more preferred. When the mixing ratio is within the above range, the ionic conductivity tends to be further improved.

  The cyclic carbonate is not particularly limited, but for example, ethylene carbonate, propylene carbonate, and one or more cyclic carbonates selected from the group consisting of fluoroethylene carbonate and vinylene carbonate are preferable. Among these, ethylene carbonate and propylene carbonate are more preferable. preferable. By using such a cyclic carbonate, the cycle characteristics tend to be more excellent.

  Although it does not specifically limit as a chain carbonate, For example, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate are preferable.

  In addition, the non-aqueous solvent can further contain other solvents such as acetonitrile and ether as necessary.

〔Electrolytes〕
The nonaqueous electrolytic solution according to this embodiment contains an electrolyte. As an electrolyte, an arbitrary electrolyte may be used alone or in combination of two or more. The electrolyte is not particularly limited, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiSbF 6, LiFSO 3, LiCF 3 SO 3, LiN (SO 2 F) 2, LiN (SO 2 F) 2, LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ CF ₂ CF ₃ ), LiPO ₂ F ₂ , Li ₂ PO ₃ F, LiPF ₃ ( C ₃ F ₇ ) ₃ , LiB (CF ₃ ) ₄ , LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiB (CN) ₄ , LiP (C ₂ O ₄ ) ₃ , LiPF ₂ (C ₂ O ₄ ) ₂ and LiPF ₄ (C ₂ O ₄ ).

Among these, the electrolyte preferably contains one or more selected from the group consisting of LiPF ₆ , LiBF ₄ , LiB (C ₂ O ₄ ) ₂ , and LiBF ₂ (C ₂ O ₄ ), and among these, LiPF ₆ LiBF ₄ is more preferable. By using such an electrolyte, the input / output characteristics tend to be further improved.

  The concentration of the electrolyte is preferably from 0.5 mol / L to 1.8 mol / L, more preferably from 0.8 mol / L to 1.5 mol / L, and even more preferably from 1 mol / L to 1.2 mol / L. It is as follows. When the concentration of the electrolyte is within the above range, the input / output characteristics tend to be further improved.

  Since the phosphonic acid compound according to the present embodiment has a high affinity with the active material, the decomposition of the nonaqueous solvent can be sufficiently suppressed even in a small amount. The content of the phosphonic acid compound in the non-aqueous electrolyte is preferably 0.00001% by mass or more, more preferably 0.0001% by mass or more, and 0.001% by mass with respect to 100% by mass of the total amount of the non-aqueous electrolyte. % Or more is more preferable. When the content of the phosphonic acid compound is 0.00001% by mass or more, the battery characteristics tend to be further improved by forming the film. On the other hand, the content of the phosphonic acid compound is preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 5% by mass or less with respect to 100% by mass of the total amount of the non-aqueous electrolyte. When the content of the phosphonic acid compound is 15% by mass or less, the input / output characteristics of the battery tend to be sufficiently maintained.

  The nonaqueous electrolytic solution according to the present embodiment is suitably used as an electrolytic solution for a nonaqueous storage device. Here, “non-aqueous electricity storage device” is a general term for electricity storage devices that do not use an aqueous solution as the electrolyte in the electricity storage device, and specifically includes lithium ion secondary batteries, sodium ion secondary batteries, lithium ion capacitors. Etc. Among these, from the viewpoint of practicality, a lithium ion secondary battery and a lithium ion capacitor are preferable, and a lithium ion secondary battery is more preferable.

[Lithium ion secondary battery]
The lithium ion secondary battery according to the present embodiment includes a positive electrode, a negative electrode, and the non-aqueous electrolyte, and a potential of the positive electrode when fully charged is 4.4 V or more and 5.5 V or less on a lithium basis. . Here, “the potential when the positive electrode is fully charged” refers to a value obtained by adding the potential of the negative electrode when fully charged to the charging voltage. For example, when graphite having a fully charged potential of about 0.05 V based on lithium is used alone as the negative electrode active material, if the battery comprising the positive electrode and the graphite negative electrode is fully charged at a charging voltage of 4.35 V, the potential of the positive electrode is lithium. The reference is about 4.4V. The potential of the positive electrode when fully charged can be easily specified using a triode cell. Specifically, when a three-electrode cell having a fully charged positive electrode as a working electrode, lithium metal as a reference electrode, and a fully charged negative electrode as a counter electrode is produced, the potential difference between the working electrode and the reference electrode is “full”. The potential of the positive electrode in the charged state ”.

[Positive electrode]
In order for the potential of the positive electrode when fully charged to reach 4.4 V or higher with respect to the lithium, the positive electrode is a positive electrode active material that occludes and releases lithium ions at a potential of 4.4 V or higher with respect to the lithium. It is preferable to contain in combination.

Occluding lithium ions in lithium reference 4.4V or more potential as the cathode active material that emits, from the viewpoint of structural stability of the positive electrode active material, preferably of the formula _LiMn 2-x _Ma x _{O 4} [Ma is a transition metal 1 or more selected from the group consisting of: 0.2 ≦ x ≦ 0.7. Spinel oxide represented _by], Li 2 MCO ₃ and LiMdO ₂ [Mc and Md represents one or more members selected from the group consisting of independently transition metal. And a compound oxide of the formula zLi ₂ McO _3- (1-z) LiMdO ₂ [0.1 ≦ z ≦ 0.9. LiMb _1-y Fe _y PO ₄ [Mb represents one or more selected from the group consisting of Mn or Co, and 0 ≦ y ≦ 0.9. And Li ₂ MePO ₄ F [Me represents one or more selected from the group consisting of transition metals. ] One or more types of positive electrode active materials selected from the group consisting of fluorinated olivine type positive electrode active materials.

As a spinel type oxide represented by the formula LiMn _2−x Ma _x O ₄ , from the viewpoint of structural stability, a composition represented by LiMn _2−x Ni _x O ₄ [0.2 ≦ x ≦ 0.7] is used. It is preferable to have LiMn _2-x Ni _x O ₄ [0.3 ≦ x ≦ 0.6], more preferably LiMn _1.5 Ni _0.5 O ₄ or LiMn _1.6 More preferably, it has a composition represented by Ni _0.4 O ₄ . Here, the spinel type oxide represented by the above formula LiMn _2−x Ma _x O ₄ is 10 mol% or less with respect to the number of moles of Mn atoms from the viewpoint of stability of the positive electrode active material, electron conductivity, and the like. In addition to the above structure, a transition metal or a transition metal oxide can be further contained within the above range.

As the Li-excess layered oxide positive electrode active material represented by the formula zLi ₂ McO ₃ — (1-z) LiMdO ₂ , from the viewpoint of stability, Mc of Li ₂ McO ₃ is Mn, and zLi ₂ MnO ₃ — ( 1-z) LiNi _a Mn _b Co _c O ₂ [0.3 ≦ z ≦ 0.7, a + b + c = 1, 0.2 ≦ a ≦ 0.6, 0.2 ≦ b ≦ 0.6, 0.05 ≦ c ≦ 0.4] is preferable. Among them, it has a composition of 0.4 ≦ z ≦ 0.6, a + b + c = 1, 0.3 ≦ a ≦ 0.4, 0.3 ≦ b ≦ 0.4, 0.2 ≦ c ≦ 0.3. It is more preferable.

As the olivine-type positive electrode active material represented by LiMb _1-y Fe _y PO ₄ , LiMn _1-y Fe _y PO ₄ [0.05 ≦ y ≦ 0.8], LiCo from the viewpoint of stability and electronic conductivity. It is preferable to have a composition represented by _1-y Fe _y PO ₄ [0.05 ≦ y ≦ 0.8].

The fluoride olivine-type positive electrode active material represented by Li ₂ MePO ₄ F, in terms of _{stability, Li 2 FePO 4 F, Li} 2 MnPO 4 F, to have a composition represented by Li 2 CoPO ₄ F preferred .

  A positive electrode for constituting a lithium ion secondary battery was prepared by adding an appropriate amount of a conductive additive such as acetylene black and a binder such as polyvinylidene fluoride to the above positive electrode active material, and preparing a positive electrode mixture. Is applied to a current collecting material such as an aluminum foil and then pressed, and then the positive electrode mixture layer is fixed onto the current collecting material. However, the method for manufacturing the positive electrode is not limited to the above-described examples.

[Negative electrode]
As a negative electrode active material that can be used for a negative electrode for constituting a lithium ion secondary battery, lithium or a compound capable of occluding and releasing lithium ions can be used. For example, alloy compounds such as Al, Si, and Sn, metal oxides such as CuO and CoO, lithium-containing compounds such as lithium titanate, and carbon materials can be used as the negative electrode active material. As the negative electrode active material in the lithium ion secondary battery according to this embodiment, a carbon material capable of occluding and releasing lithium ions at a low potential is preferable from the viewpoint of the energy density of the battery. Such a carbon material is not particularly limited. For example, hard carbon, soft carbon, artificial graphite, natural graphite, pyrolytic carbon, coke, glassy carbon, a fired body of an organic polymer compound, firing of an organic natural product Body, carbon fiber, mesocarbon microbeads, carbon black. Although it does not specifically limit as coke, For example, pitch coke, needle coke, and petroleum coke are mentioned. In addition, a fired body of an organic polymer compound refers to a carbon material obtained by firing a polymer material such as a phenol resin at an appropriate temperature, and a fired body of an organic natural product refers to a naturally derived material such as coffee husk. Refers to carbonized by firing at an appropriate temperature.

  When a carbon material is used for the negative electrode active material, the interlayer distance d002 of the (002) plane of the carbon material is preferably 0.37 nm or less, more preferably 0.35 nm or less, and further preferably 0.34 nm or less. It is. The lower limit of d002 is not particularly limited, but is theoretically about 0.335 nm.

  Further, the size of the crystallite in the c-axis direction of the carbon material is preferably 3 nm or more, more preferably 8 nm or more, and further preferably 25 nm or more. The upper limit of the crystallite is not particularly limited, but is usually about 200 nm. The average particle diameter of the carbon material is preferably 3 μm or more and 15 μm or less, more preferably 5 μm or more and 13 μm or less. Moreover, the purity is 99.9% or more.

  A negative electrode for constituting a lithium ion secondary battery was prepared by adding an appropriate amount of a thickener such as carboxymethyl cellulose and a binder such as styrene butadiene rubber to the above negative electrode active material, and preparing a negative electrode mixture. Is applied to a current collecting material such as a copper foil and then pressed, and then the negative electrode mixture layer is fixed on the current collecting material. However, the manufacturing method of the negative electrode is not limited to the above-described examples.

[Separator]
The lithium ion secondary battery in the present embodiment preferably includes a separator between the positive electrode and the negative electrode from the viewpoint of providing safety such as prevention of short circuit between the positive and negative electrodes. A separator in particular is not restrict | limited, The various separator employ | adopted with a conventionally well-known lithium ion secondary battery can be used. Such a separator is not particularly limited, but, for example, a microporous film or a nonwoven fabric formed by molding a resin represented by a polyolefin resin such as polyethylene or polypropylene; a polyester resin such as polyethylene terephthalate; or a polyamide resin such as polyaramid Etc. are preferably used. From the viewpoint of imparting safety, the thickness of the separator is preferably 5 μm or more, and more preferably 10 μm or more. Moreover, the thickness of a separator becomes like this. Preferably it is 30 micrometers or less, More preferably, it is 20 micrometers or less. When the thickness of the separator is 30 μm or less, the input / output characteristics of the battery tend to be further improved.

  The lithium ion secondary battery according to the present embodiment, for example, after the above positive electrode and negative electrode are overlapped via a separator and wound as necessary to form a laminated electrode body or a wound electrode body, This is loaded into the exterior body, the positive and negative electrodes and the positive and negative electrode terminals of the exterior body are connected via a lead body, and the nonaqueous electrolyte according to the present embodiment is injected into the exterior body, and then the exterior body is sealed. It is made to stop. As a battery outer package, a metal can container, a laminate container made of a metal foil laminate film, or the like can be suitably used. The shape of the lithium ion secondary battery is not particularly limited. For example, a cylindrical shape, a square shape, a coin shape, a flat shape, a sheet shape, or the like is adopted.

  The lithium ion secondary battery according to the present embodiment has high energy density and excellent practical durability. Therefore, the lithium ion secondary battery is widely used not only as a power source for mobile electronic devices such as mobile phones but also as a power source for various devices. can do.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples, unless the summary is exceeded.

[Example 1]
1: Manufacture of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (manufactured by Nippon Chemical Industry Co., Ltd.) as a positive electrode active material, acetylene black powder (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent, binder As a dispersion solvent, a polyvinylidene fluoride solution (manufactured by Kureha Co., Ltd.) is mixed at a solid content mass ratio of 90: 6: 4, and N-methyl-2-pyrrolidone is added as a dispersion solvent to a solid content of 40% by mass. Further mixing was performed to prepare a slurry solution. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was removed by drying, followed by rolling with a roll press to obtain a positive electrode.

2: Manufacture of negative electrode Graphite powder (manufactured by Osaka Gas Chemical Co., Ltd.) and graphite powder (manufactured by TIMCAL) as a negative electrode active material, and styrene-butadiene rubber and carboxymethylcellulose aqueous solution as a binder, The mixture was mixed at a solid content mass ratio of 8, water was added as a dispersion solvent so as to have a solid content of 45 mass%, and further mixed to prepare a slurry solution. This slurry-like solution was applied to one side of a copper foil having a thickness of 18 μm, and after removing the solvent by drying, it was rolled with a roll press to obtain a negative electrode.

3: Preparation of non-aqueous electrolyte solution Hexyl was used for a solution containing 1 mol / L of LiPF ₆ in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2. 0.1% by mass of phosphonic acid was added to obtain an electrolytic solution.

4: Production of test battery The positive electrode and the negative electrode produced as described above were placed on both sides of a separator (thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm) made of a polypropylene microporous film. A laminated body was produced. The obtained laminate was inserted into a bag made of a laminate film in which both surfaces of an aluminum foil (thickness 40 μm) were covered with a resin layer while projecting positive and negative terminals, and then prepared as described above. A water electrolyte was poured into the bag and vacuum sealed to produce a sheet-like lithium ion secondary battery.

5: Evaluation of test battery 5-1: Initial charge / discharge After charging the obtained sheet-like lithium ion secondary battery in a 25 ° C. environment at a constant current of 0.05 C until reaching a voltage of 4.35 V, The battery was charged at a constant voltage of 4.35V for 2 hours and discharged to 3.0V at a constant current of 0.2C. This was repeated for 3 cycles. Note that 1C represents a current value for discharging the reference capacity of the battery in one hour, and 0.05C represents a current value of 1/20.

5-2: Cycle test After charging the sheet-like lithium ion secondary battery after the initial charge and discharge until reaching a voltage of 4.35 V at a constant current of 1 C in an environment of 50 ° C., 1 at a constant voltage of 4.35 V The battery was charged for a period of time and discharged to 3.0 V at a constant current of 1C. The above series of charging / discharging was regarded as one cycle, and this was carried out for 100 cycles, and the capacity retention rate (%) was measured after 100 cycles. As a result, the capacity retention rate (%) after 100 cycles was as high as 82%. The capacity retention rate (%) after 100 cycles was obtained by the following formula.
Capacity maintenance rate after 100 cycles (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100

5-3: Gas generation test After the first charge / discharge sheet-like lithium ion secondary battery is immersed in a water bath and measured for volume, it reaches a voltage of 4.35 V at a constant current of 1 C in an environment of 50 ° C. The battery was continuously charged at a constant voltage of 4.35 V for one week and discharged to 3.0 V at a constant current of 1 C.

  After the battery was cooled to room temperature, the volume was measured by immersing in a water bath, and the amount of generated gas (mL) after continuous charge was determined from the volume change of the battery before and after continuous charge. As a result, the amount of generated gas (mL) after continuous charging was as low as 0.25 mL.

[Example 2]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet-like battery was produced in the same manner as in Example 1 except that octylphosphonic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. . As a result, the capacity retention rate (%) after 100 cycles was as high as 81%, and the amount of generated gas (mL) after continuous charging was as low as 0.29 mL.

[Example 3]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet-like battery was produced in the same manner as in Example 1 except that decylphosphonic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. . As a result, the capacity retention rate (%) after 100 cycles was as high as 80%, and the amount of generated gas (mL) after continuous charging was as low as 0.36 mL.

[Example 4]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet-like battery was produced in the same manner as in Example 1 except that tetradecylphosphonic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. It was. As a result, the capacity retention rate (%) after 100 cycles was as high as 78%, and the amount of generated gas (mL) after continuous charging was as low as 0.41 mL.

[Example 5]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet battery was produced in the same manner as in Example 1 except that phosphonoacetic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. As a result, the capacity retention rate (%) after 100 cycles was as high as 86%, and the amount of generated gas (mL) after continuous charging was as low as 0.22 mL.

[Example 6]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet-like battery was produced in the same manner as in Example 1 except that 6-phosphonohexanoic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. Went. As a result, the capacity retention rate (%) after 100 cycles was as high as 85%, and the amount of generated gas (mL) after continuous charging was as low as 0.26 mL.

[Example 7]
A sheet battery was prepared in the same manner as in Example 1 except that 1H, 1H, 2H, 2H-perfluorohexylphosphonic acid was used in place of hexylphosphonic acid in the preparation of the nonaqueous electrolytic solution of Example 1. A cycle test and a gas generation test were conducted. As a result, the capacity retention rate (%) after 100 cycles was as high as 80%, and the amount of generated gas (mL) after continuous charging was as low as 0.30 mL.

[Example 8]
A sheet-like battery was produced in the same manner as in Example 1 except that 0.01% by mass of phosphonoacetic acid was added instead of adding 0.1% by mass of hexylphosphonic acid in the preparation of the nonaqueous electrolytic solution of Example 1. Then, a cycle test and a gas generation test were performed. As a result, the capacity retention rate (%) after 100 cycles was as high as 82%, and the amount of generated gas (mL) after continuous charging was as low as 0.35 mL.

[Example 9]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet was obtained in the same manner as in Example 1 except that 0.01% by mass of 6-phosphonohexanoic acid was added instead of 0.1% by mass of hexylphosphonic acid. A cell battery was prepared and subjected to a cycle test and a gas generation test. As a result, the capacity retention rate (%) after 100 cycles was as high as 82%, and the amount of generated gas (mL) after continuous charging was as low as 0.38 mL.

[Example 10]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet-like battery was produced in the same manner as in Example 1 except that 1% by mass of phosphonoacetic acid was added instead of adding 0.1% by mass of hexylphosphonic acid. A cycle test and a gas generation test were conducted. As a result, the capacity retention rate (%) after 100 cycles was as high as 78%, and the amount of generated gas (mL) after continuous charging was as low as 0.20 mL.

[Comparative Example 1]
Example 1 except that a solution containing 1 mol / L of LiPF ₆ in a mixed solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 2 was used as a non-aqueous electrolyte. In the same manner as above, a sheet-like battery was produced and subjected to a cycle test and a gas generation test. As a result, the capacity retention rate (%) after 100 cycles was as low as 76%, and the amount of generated gas (mL) after continuous charging was as large as 0.54 mL.

[Comparative Example 2]
In the preparation of the nonaqueous electrolytic solution of Example 1, a sheet-like battery was produced in the same manner as in Example 1 except that triethylphosphonoacetate was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. It was. As a result, the capacity retention rate (%) after 100 cycles was as low as 77%, and the amount of generated gas (mL) after continuous charging was as large as 0.42 mL.

  The results obtained in Examples 1 to 10 and Comparative Examples 1 and 2 are shown in Table 1. From Table 1, all the lithium ion secondary batteries of Examples 1 to 10 were added with triethylphosphonoacetate described in Comparative Example 1 and Non-Patent Document 3 using a non-aqueous electrolyte containing no phosphonic acid compound. As compared with Comparative Example 2 using the nonaqueous electrolytic solution, it was revealed that the cycle characteristics were improved and the gas generation amount was greatly reduced. From the above, it was shown that the effect of the present invention is a unique effect when a phosphonic acid compound is contained in the nonaqueous electrolytic solution.

[Example 11]
1: Manufacture of positive electrode active material Nickel sulfate and manganese sulfate at a molar ratio of transition metal element of 1: 3 are dissolved in water and mixed with nickel-manganese so that the total concentration of metal ions is 2 mol / L. An aqueous solution was prepared. Subsequently, this nickel-manganese mixed aqueous solution was dropped into 3000 mL of a 2 mol / L sodium carbonate aqueous solution heated to 70 ° C. at an addition rate of 12.5 mL / min for 120 minutes. At the time of dropping, air with a flow rate of 200 mL / min was blown into the aqueous solution while stirring. As a result, a precipitated substance was generated, and the obtained precipitated substance was sufficiently washed with distilled water and dried to obtain a nickel manganese compound. The obtained nickel-manganese compound and lithium carbonate having a particle size of 2 μm were weighed so that the molar ratio of lithium: nickel: manganese was 1: 0.5: 1.5, and obtained after dry-mixing for 1 hour. The obtained mixture was baked at 1000 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material represented by LiNi _0.5 Mn _1.5 O ₄ .

2: Production of positive electrode A positive electrode active material obtained as described above, an acetylene black powder (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent, and a polyvinylidene fluoride solution (manufactured by Kureha Co., Ltd.) as a binder, The mixture was mixed at a solid content mass ratio of 6: 6, N-methyl-2-pyrrolidone as a dispersion solvent was added so as to have a solid content of 40% by mass, and further mixed to prepare a slurry solution. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was removed by drying, followed by rolling with a roll press to obtain a positive electrode.

3: Production of negative electrode Graphite powder (manufactured by Osaka Gas Chemical Co., Ltd.) and graphite powder (manufactured by TIMCAL) as a negative electrode active material, and styrene-butadiene rubber and carboxymethylcellulose aqueous solution as a binder, 90: 10: 1.5: 1. The mixture was mixed at a solid content mass ratio of 8, water was added as a dispersion solvent so as to have a solid content of 45 mass%, and further mixed to prepare a slurry solution. This slurry-like solution was applied to one side of a copper foil having a thickness of 18 μm, and after removing the solvent by drying, it was rolled with a roll press to obtain a negative electrode.

4: Preparation of non-aqueous electrolyte solution Hexyl was added to a solution containing 1 mol / L of LiPF ₆ in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2. 0.1% by mass of phosphonic acid was added to obtain an electrolytic solution.

5: Production of test battery The positive electrode and the negative electrode produced as described above were placed on both sides of a separator (thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm) made of a polypropylene microporous film. A laminated body was produced. The obtained laminate was inserted into a bag made of a laminate film in which both surfaces of an aluminum foil (thickness 40 μm) were covered with a resin layer while projecting positive and negative terminals, and then prepared as described above. A water electrolyte was poured into the bag and vacuum sealed to produce a sheet-like lithium ion secondary battery.

6: Evaluation of test battery 6-1: Initial charge / discharge After charging the obtained sheet-like lithium ion secondary battery in a 25 ° C. environment at a constant current of 0.05 C until reaching a voltage of 4.8 V, The battery was charged at a constant voltage of 4.8 V for 2 hours and discharged to 3.0 V at a constant current of 0.2C. This was repeated for 3 cycles. Note that 1C represents a current value for discharging the reference capacity of the battery in one hour, and 0.05C represents a current value of 1/20.

6-2: Cycle test After charging the sheet-like lithium ion secondary battery after initial charge and discharge until reaching a voltage of 4.8 V at a constant current of 1 C in an environment of 50 ° C., 1 at a constant voltage of 4.8 V The battery was charged for a period of time and discharged to 3.0 V at a constant current of 1C. The above series of charging / discharging was regarded as one cycle, and this was carried out for 100 cycles, and the capacity retention rate (%) was measured after 100 cycles. As a result, the capacity retention rate (%) after 100 cycles was as high as 51%. The capacity retention rate (%) after 100 cycles was obtained by the following formula.
Capacity maintenance rate after 100 cycles (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100

5-3: Gas generation test After the first charge / discharge sheet-like lithium ion secondary battery is immersed in a water bath and measured for volume, it reaches a voltage of 4.8 V at a constant current of 1 C in an environment of 50 ° C. The battery was continuously charged at a constant voltage of 4.8 V for one week and discharged to 3.0 V at a constant current of 1 C.

  After the battery was cooled to room temperature, the volume was measured by immersing in a water bath, and the amount of generated gas (mL) after continuous charge was determined from the volume change of the battery before and after continuous charge. As a result, the amount of generated gas (mL) after continuous charging was as small as 2.21 mL.

[Example 12]
In the preparation of the nonaqueous electrolytic solution of Example 11, a sheet-like battery was produced in the same manner as in Example 11 except that octylphosphonic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. . As a result, the capacity retention rate (%) after 100 cycles was as high as 49%, and the amount of generated gas (mL) after continuous charging was as small as 2.36 mL.

[Example 13]
In the preparation of the nonaqueous electrolytic solution of Example 11, a sheet-like battery was produced in the same manner as in Example 11 except that decylphosphonic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. . As a result, the capacity retention rate (%) after 100 cycles was as high as 47%, and the amount of generated gas (mL) after continuous charging was as low as 2.87 mL.

[Example 14]
In the preparation of the nonaqueous electrolytic solution of Example 11, a sheet-like battery was produced in the same manner as in Example 11 except that phosphonoacetic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. As a result, the capacity retention rate (%) after 100 cycles was as high as 55%, and the amount of generated gas (mL) after continuous charging was as low as 1.75 mL.

[Example 15]
In the preparation of the nonaqueous electrolytic solution of Example 11, a sheet-like battery was produced in the same manner as in Example 11 except that 6-phosphonohexanoic acid was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. Went. As a result, the capacity retention rate (%) after 100 cycles was as high as 57%, and the amount of generated gas (mL) after continuous charging was as low as 1.89 mL.

[Example 16]
A sheet-like battery was produced in the same manner as in Example 11 except that 0.01% by mass of phosphonoacetic acid was added instead of adding 0.1% by mass of hexylphosphonic acid in the preparation of the nonaqueous electrolytic solution of Example 11. Then, a cycle test and a gas generation test were performed. As a result, the capacity retention rate (%) after 100 cycles was as high as 49%, and the amount of generated gas (mL) after continuous charging was as low as 2.92 mL.

[Example 17]
In the preparation of the nonaqueous electrolytic solution of Example 11, a sheet was obtained in the same manner as in Example 11 except that 0.01% by mass of 6-phosphonohexanoic acid was added instead of 0.1% by mass of hexylphosphonic acid. A cell battery was prepared and subjected to a cycle test and a gas generation test. As a result, the capacity retention rate (%) after 100 cycles was as high as 51%, and the amount of generated gas (mL) after continuous charging was as small as 3.09 mL.

[Example 18]
A sheet battery was prepared in the same manner as in Example 11 except that 1% by mass of phosphonoacetic acid was used in place of 1% by mass of hexylphosphonic acid in the preparation of the nonaqueous electrolytic solution of Example 11, and the cycle test and gas were performed. A developmental test was performed. As a result, the capacity retention rate (%) after 100 cycles was as high as 44%, and the amount of generated gas (mL) after continuous charging was as low as 1.67 mL.

[Comparative Example 3]
Example 11 except that a solution containing 1 mol / L of LiPF ₆ in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 was used as a nonaqueous electrolytic solution. In the same manner as above, a sheet-like battery was produced and subjected to a cycle test and a gas generation test. As a result, the capacity retention rate (%) after 100 cycles was as low as 32%, and the amount of generated gas (mL) after continuous charging was as large as 4.32 mL.

[Comparative Example 4]
In the preparation of the nonaqueous electrolytic solution of Example 11, a sheet-like battery was produced in the same manner as in Example 11 except that triethylphosphonoacetate was used instead of hexylphosphonic acid, and a cycle test and a gas generation test were performed. It was. As a result, the capacity retention rate (%) after 100 cycles was as low as 42%, and the amount of generated gas (mL) after continuous charging was as large as 3.43 mL.

  Table 2 shows the results obtained in Examples 11 to 18 and Comparative Examples 3 to 4. From Table 2, all of the lithium ion secondary batteries of Examples 11 to 18 were added with triethylphosphonoacetate described in Comparative Example 3 and Non-Patent Document 3 using a non-aqueous electrolyte containing no phosphonic acid compound. As compared with Comparative Example 4 using the non-aqueous electrolyte, it was revealed that the cycle characteristics were improved and the gas generation amount was greatly reduced. From the above, it was shown that the effect of the present invention is a unique effect when a phosphonic acid compound is contained in the nonaqueous electrolytic solution.

  The lithium ion secondary battery using the non-aqueous electrolyte of the present invention has industrial applicability to various consumer equipment power supplies and automobile power supplies.

Claims (7)

A nonaqueous solvent, an electrolyte, and a phosphonic acid compound represented by the following formula (1):
Non-aqueous electrolyte.
(In formula (1), R1 represents an optionally substituted organic group having 1 to 20 carbon atoms, and R2 represents a hydrogen atom, an alkali metal atom, and optionally substituted 1 to 10 carbon atoms. (It is a kind selected from the group consisting of organic groups, and R3 represents a hydrogen atom or an alkali metal atom.)   The non-aqueous electrolyte according to claim 1, wherein the phosphonic acid compound includes a compound in which R 2 is a hydrogen atom or an alkali metal atom. The non-aqueous electrolyte according to claim 1 or 2, wherein the phosphonic acid compound contains a compound represented by the following formula (2).
(In Formula (2), R4 represents a kind selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 6 carbon atoms, and R5 may be substituted. Represents a good alkylene group having 1 to 10 carbon atoms, R6 is a kind selected from the group consisting of a hydrogen atom, an alkali metal atom, and an optionally substituted organic group having 1 to 10 carbon atoms; It is a hydrogen atom or an alkali metal atom.)   The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the phosphonic acid compound is contained in an amount of 0.00001% by mass to 10% by mass with respect to 100% by mass of the total amount of the non-aqueous electrolyte.   The nonaqueous electrolysis according to any one of claims 1 to 4, wherein the nonaqueous solvent contains one or more cyclic carbonates selected from the group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and vinylene carbonate. liquid. 6. The electrolyte according to claim 1, wherein the electrolyte contains one or more selected from the group consisting of LiPF ₆ , LiBF ₄ , LiB (C ₂ O ₄ ) ₂ , and LiBF ₂ (C ₂ O ₄ ). The non-aqueous electrolyte described in 1. A positive electrode, a negative electrode, and the non-aqueous electrolyte according to any one of claims 1 to 6,
A lithium ion secondary battery in which a potential of the positive electrode when fully charged is 4.4 V or more and 5.5 V or less based on lithium.