WO2023119947A1

WO2023119947A1 - Electrolytic solution for lithium ion secondary battery and lithium ion secondary battery

Info

Publication number: WO2023119947A1
Application number: PCT/JP2022/042308
Authority: WO
Inventors: 智梅津; 光則中本; 巧日浅; 一成本橋
Original assignee: 株式会社村田製作所
Priority date: 2021-12-23
Filing date: 2022-11-15
Publication date: 2023-06-29

Abstract

This lithium-ion secondary battery includes an electrolytic solution together with a positive electrode and a negative electrode, the electrolytic solution includes a fluorinated alcohol represented by formula (1), and the content of the fluoroalcohol in the electrolytic solution is 0.1-5.0% by weight.

Description

Electrolyte for lithium ion secondary battery and lithium ion secondary battery

This technology relates to electrolyte solutions for lithium-ion secondary batteries and lithium-ion secondary batteries.

Due to the widespread use of various electronic devices such as mobile phones, the development of lithium-ion secondary batteries is underway as a power source that is compact, lightweight, and provides high energy density.

This lithium-ion secondary battery includes an electrolyte (electrolyte for lithium-ion secondary batteries) along with a positive electrode and a negative electrode, and various studies have been made on the configuration of the lithium-ion secondary battery.

Specifically, the electrolyte of the lithium ion secondary battery contains an alcohol such as ethanol, and the content of the alcohol in the electrolyte is 0.01 ppm or more and less than 50 ppm (see, for example, Patent Document 1). ). Also, the non-aqueous electrolyte of metal hydride batteries contains alcohols such as trifluoromethanol (see, for example, Patent Document 2).

JP 2015-133236 A Japanese Patent Publication No. 2018-509743

Various studies have been conducted on the composition of lithium-ion secondary batteries, but the storage characteristics and charge-discharge characteristics of the lithium-ion secondary batteries are still insufficient, so there is room for improvement.

Therefore, there is a demand for an electrolytic solution for lithium ion secondary batteries and a lithium ion secondary battery that are capable of obtaining excellent storage characteristics and excellent charge/discharge characteristics.

An electrolyte solution for a lithium ion secondary battery according to an embodiment of the present technology includes a fluorinated alcohol represented by formula (1), and the content of the fluorinated alcohol is 0.1% by weight or more and 5.0% by weight. are as follows.

R1R2R3COH (1)
(Each of R1, R2 and R3 is a hydrogen group, an alkyl group or a fluorinated alkyl group, provided that at least one of R1, R2 and R3 is a fluorinated alkyl group. )

A lithium ion secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution has the same configuration as the electrolytic solution for a lithium ion secondary battery according to an embodiment of the present technology. It has a configuration.

According to the lithium ion secondary battery electrolyte solution or the lithium ion secondary battery of one embodiment of the present technology, the lithium ion secondary battery electrolyte solution contains a fluorinated alcohol, and the content of the fluorinated alcohol is is 0.1% by weight or more and 5.0% by weight or less, excellent storage characteristics and excellent charge/discharge characteristics can be obtained.

It should be noted that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described below.

It is a perspective view showing composition of a lithium ion secondary battery in one embodiment of this art. FIG. 2 is a cross-sectional view showing the configuration of the battery element shown in FIG. 1; FIG. 4 is a block diagram showing the configuration of an application example of a lithium ion secondary battery; FIG. 2 is a cross-sectional view showing the configuration of a test lithium-ion secondary battery;

Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. The order of explanation is as follows.

1. Electrolyte solution for lithium ion secondary battery 1-1. Configuration 1-2. Manufacturing method 1-3. Action and effect 2 . Lithium ion secondary battery 2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Modification 4. Applications of lithium-ion secondary batteries

<1. Electrolyte solution for lithium ion secondary battery>
First, an electrolyte solution for a lithium ion secondary battery (hereinafter simply referred to as "electrolyte solution") according to an embodiment of the present technology will be described.

This electrolyte is used in lithium-ion secondary batteries, which are electrochemical devices. However, the electrolytic solution may be used in electrochemical devices other than lithium ion secondary batteries. Specific examples of other electrochemical devices are capacitors and the like.

<1-1. Configuration>
The electrolytic solution is a liquid electrolyte, and is used as a medium for lithium ions in lithium ion secondary batteries.

[Fluorinated alcohol]
The electrolytic solution contains one or more of the fluorinated alcohols represented by formula (1), and the content of the fluorinated alcohol in the electrolytic solution is 0.1% by weight to 5.0% by weight, preferably 0.3% to 3.0% by weight. This fluorinated alcohol is a compound in which alcohol is fluorinated.

The reason why the electrolyte contains an appropriate amount (= 0.1 wt% to 5.0 wt%) of fluorinated alcohol is that in a lithium ion secondary battery using the electrolyte, the chemical This is because the state is easily maintained, and the discharge capacity is less likely to decrease even if charging and discharging are repeated.

Specifically, in fluorinated alcohols, the nucleophilicity is reduced because the alcohol is fluorinated. In this case, even if the electrolytic solution contains fluorinated alcohol, the fluorinated alcohol is less likely to react with other components in the electrolytic solution. Electrolyte salts and the like are less likely to deposit in the electrolytic solution. This facilitates maintaining the chemical state of the electrolyte even when the lithium ion secondary battery is stored. The deterioration of the electrolytic solution includes discoloration and the like, and specific examples of other components include electrolyte salts described later.

Moreover, fluorinated alcohols have high reducing properties. In this case, when the lithium ion secondary battery is repeatedly charged and discharged, the fluorinated alcohol rapidly reacts on the surface of the negative electrode during the initial charge, so that a good film derived from the fluorinated alcohol is formed. be done. This coating contains fluorinated alkoxide and electrochemically stable lithium fluoride (LiF), which is believed to be formed by decomposition of the fluorinated alcohol after reduction. As a result, the electrolytic solution is less likely to be decomposed on the surface of the negative electrode, and thus the discharge capacity is less likely to decrease even if charging and discharging are repeated.

Each of R1, R2 and R3 is not particularly limited as long as it is a hydrogen group (--H), an alkyl group or a fluorinated alkyl group, as described above.

The alkyl group may be linear or branched with one or more side chains. Although the number of carbon atoms in the alkyl group is not particularly limited, it is preferably 1 to 4. This is because the solubility and compatibility of the fluorinated alcohol are improved.

Specific examples of alkyl groups include methyl, ethyl, propyl and butyl groups. However, as described above, the alkyl group is not limited to a chain shape and may be branched. Thus, by way of example, a propyl group may be an n-propyl group or an isopropyl group. Further, to give another example, the butyl group may be an n-butyl group, a sec-butyl group, an isobutyl group, or a tert-butyl group.

A fluorinated alkyl group is a group in which one or more hydrogen groups in an alkyl group have been substituted with a fluorine group. The details of the alkyl group (structure, number of carbon atoms, etc.) are as described above.

Specific examples of fluorinated alkyl groups include perfluoromethyl, perfluoroethyl, perfluoropropyl and perfluorobutyl groups. However, specific examples of the fluorine alkyl group are not limited to the perfluoro group, and may be a monofluoromethyl group, a monofluoroethyl group, a monofluoropropyl group, a monofluorobutyl group, or the like.

Here, as described above, one or more of R1, R2 and R3 is a fluorinated alkyl group. This is because the fluorinated alcohol is a compound obtained by fluorinating an alcohol as described above, and thus contains one or more fluorine atoms as constituent elements. Compounds in which each of R1, R2 and R3 is either a hydrogen group or an alkyl group are thereby excluded from the fluorinated alcohols described herein.

Specifically, when at least one of R1, R2 and R3 is a fluorinated alkyl group, at least one of R1, R2 and R3 is a bulky group containing fluorine as a constituent element. . This makes it easier for the fluorinated alcohol to decompose after the reduction, thus facilitating the formation of lithium fluoride. Therefore, the chemical state of the electrolytic solution is more likely to be maintained, and the discharge capacity is less likely to decrease even if charging and discharging are repeated.

Among them, two or more of R1, R2 and R3 are preferably fluorinated alkyl groups. This is because the degree of fluorination of the fluorinated alcohol increases, so that the chemical state of the electrolytic solution is more likely to be maintained, and the discharge capacity is less likely to decrease even after repeated charging and discharging.

_Specific _examples _of fluorinated _alcohols _are _CF3CH2OH , _CF2HCH2OH _, _CFH2CH2OH _, _CF3CF2CH2OH , _CF3CFHCH2OH , _CF3CH2CH2OH _, _CF2 _HCF2CH2OH , ( _CF3 ) _2CHOH , _CF3C (CH3)HOH _, ( _CF3 ) _3COH , ₍ _CF3 ) _2C ( _CH3 )OH, ( _CF3 )C( _CH3 ) _2OH _, _{CF3CF2CF2CH2OH} _, _{CF3CF2CH2CH2OH} _, _{CF3CH2CH2CH2OH} _, _CF3CF2CH ₍ _OH ₎ _CF3 _, _CF3CF2CH ₍ _{_} _{_} OH) _CH3 _, _CF3CH2CH ( _OH ₎ _CF3 , _CF3CH2CH (OH) _CH3 and _CH3CH2CH (OH) _CF3 .

When measuring the content of the fluorinated alcohol in the electrolytic solution, the secondary battery is disassembled to collect the electrolytic solution, and then the electrolytic solution is analyzed to determine the content of the fluorinated alcohol. calculate. The method of analyzing the electrolytic solution is not particularly limited, but specifically includes inductively coupled plasma (ICP) emission spectroscopy, nuclear magnetic resonance spectroscopy (NMR), gas chromatograph mass spectrometry (GC-MS), and the like. Any one type or two or more types.

[solvent]
Note that the electrolytic solution further contains a solvent. This solvent contains one or more of non-aqueous solvents (organic solvents), and the electrolytic solution containing the non-aqueous solvent is a so-called non-aqueous electrolytic solution. Non-aqueous solvents include esters, ethers, and the like, and more specifically, carbonate compounds, carboxylic acid ester compounds, lactone compounds, and the like.

The carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates include ethylene carbonate and propylene carbonate. Specific examples of chain carbonates include dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate.

The carboxylic acid ester compound is a chain carboxylic acid ester or the like. Specific examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl trimethyl acetate, ethyl trimethyl acetate, methyl butyrate and ethyl butyrate.

Lactone-based compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

The ethers may be partially fluorinated compounds, specifically 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane and 1,1 , 2-tetrafluoroethyl 2,2,2,3,3-tetrafluoropropyl ether and the like.

Among them, the solvent preferably contains a cyclic carbonate and a chain carbonate. This is because a high battery capacity can be stably obtained in a lithium ion secondary battery. In addition, the chemical state of the electrolytic solution is easily maintained sufficiently, and the discharge capacity is less likely to decrease sufficiently even if charging and discharging are repeated.

[Electrolyte salt]
Moreover, the electrolytic solution further contains an electrolytic salt. This electrolyte salt is a light metal salt such as a lithium salt.

Specific examples of lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis(fluorosulfonyl)imide (LiN ( _FSO2 ) ₂ ), bis(trifluoromethanesulfonyl _{)imidolithium (LiN(CF3SO2)2), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3} ₎ _, _bis ₍ _oxalato )boron lithium oxide (LiB( _C2O4 ) ₂ ₎ , lithium monofluorophosphate ( _Li2PFO3 ) and lithium difluorophosphate ₍ _LiPF2O2 ₎ . This is because a high battery capacity can be obtained.

The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol/kg to 3.0 mol/kg with respect to the solvent. This is because high ionic conductivity can be obtained.

[Additive]
In addition, the electrolytic solution may further contain one or more of additives. This is because the electrochemical stability of the electrolytic solution is improved, so that the decomposition reaction of the electrolytic solution is suppressed during charging and discharging of the lithium ion secondary battery using the electrolytic solution.

The types of additives are not particularly limited, but specific examples include unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonate esters, phosphate esters, acid anhydrides, nitrile compounds and isocyanate compounds.

Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate and methyleneethylene carbonate. Specific examples of fluorinated cyclic carbonates include ethylene monofluorocarbonate and ethylene difluorocarbonate. Specific examples of sulfonate esters include propane sultone and propene sultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds include acetonitrile, valeronitrile, adiponitrile and succinonitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

<1-2. Manufacturing method>
The electrolytic solution is manufactured by a series of procedures described below. Specifically, after adding the electrolyte salt to the solvent, the fluorinated alcohol is added to the solvent. As a result, the electrolyte salt and the fluorinated alcohol are each dispersed or dissolved in the solvent to prepare an electrolytic solution.

When producing the electrolytic solution, a solvent in which the fluorinated alcohol is dissolved may be used. In this case, the content of the fluorinated alcohol in the electrolytic solution may exceed 5% by weight during the production of the electrolytic solution.

<1-3. Action and effect>
According to this electrolytic solution, the electrolytic solution contains the fluorinated alcohol, and the content of the fluorinated alcohol in the electrolytic solution is 0.1% by weight to 5.0% by weight.

In this case, as described above, the nucleophilicity of the fluorinated alcohol is lowered, so that the electrolyte is less likely to deteriorate over time, and electrolyte salts and the like are less likely to deposit in the electrolyte. Moreover, as described above, since the fluorinated alcohol has a high reducing property, a good film derived from the fluorinated alcohol is formed on the surface of the negative electrode during the initial charge.

Therefore, the chemical state of the electrolyte solution is easily maintained, and the discharge capacity is less likely to decrease even if the lithium ion secondary battery using the electrolyte solution is repeatedly charged and discharged. Charge/discharge characteristics can be obtained.

In particular, when the content of the fluorinated alcohol in the electrolytic solution is 0.3% by weight to 3.0% by weight, the chemical state of the electrolytic solution is more likely to be maintained, and lithium ions using the electrolytic solution Even if the secondary battery is repeatedly charged and discharged, the discharge capacity is less likely to decrease, so a higher effect can be obtained.

In addition, if two or more of R1, R2 and R3 shown in formula (1) are fluorinated alkyl groups, the degree of fluorination of the fluorinated alcohol increases, so that a higher effect can be obtained. .

Further, if the electrolytic solution further contains a cyclic carbonate and a chain carbonate, the chemical state of the electrolytic solution can be sufficiently maintained in a lithium-ion secondary battery using the electrolytic solution. Even if charging and discharging are repeated, the discharge capacity is less likely to decrease sufficiently, so a higher effect can be obtained.

<2. Lithium ion secondary battery>
Next, a lithium-ion secondary battery according to an embodiment of the present technology using the electrolyte solution described above will be described.

The lithium-ion secondary battery described here is a secondary battery in which battery capacity is obtained by utilizing the absorption and release of lithium. A lithium ion secondary battery can stably obtain a sufficient battery capacity by utilizing the absorption and release of lithium.

In this lithium-ion secondary battery, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of the negative electrode is set to be larger than the electrochemical capacity per unit area of the positive electrode. This is to prevent lithium metal from depositing on the surface of the negative electrode during charging.

<2-1. Configuration>
1 shows a perspective configuration of a lithium ion secondary battery, and FIG. 2 shows a cross-sectional configuration of the battery element 20 shown in FIG. However, FIG. 1 shows a state in which the exterior film 10 and the battery element 20 are separated from each other, and the cross section of the battery element 20 along the XZ plane is indicated by a broken line. In FIG. 2, only part of the battery element 20 is shown.

This lithium ion secondary battery, as shown in FIGS. 1 and 2, includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing

films

41 and 42. . The lithium-ion secondary battery described here is a laminated film-type secondary battery using a flexible or pliable exterior film 10 .

[Exterior film and sealing film]
As shown in FIG. 1, the exterior film 10 is an exterior member that houses the battery element 20, and has a sealed bag-like structure with the battery element 20 housed therein. As a result, the exterior film 10 accommodates the electrolytic solution together with the positive electrode 21 and the negative electrode 22, which will be described later.

Here, the exterior film 10 is a single film-like member and is folded in the folding direction F. The exterior film 10 is provided with a recessed portion 10U (deeply drawn portion) for housing the battery element 20 .

Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order from the inside. Outer peripheral edge portions of the fusion layer are fused together. The fusible layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one layer, two layers, or four layers or more.

The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31 , and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32 . However, one or both of the sealing

films

41 and 42 may be omitted.

The sealing film 41 is a sealing member that prevents external air from entering the exterior film 10 . The sealing film 41 contains a polymer compound such as polyolefin having adhesiveness to the positive electrode lead 31, and a specific example of the polyolefin is polypropylene.

The structure of the sealing film 42 is the same as the structure of the sealing film 41 except that it is a sealing member having adhesion to the negative electrode lead 32 . That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32 .

[Battery element]
The battery element 20 is a power generation element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution (not shown), as shown in FIGS. It is

This battery element 20 is a so-called wound electrode assembly. That is, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 interposed therebetween, and are wound around the winding axis P while facing each other with the separator 23 interposed therebetween. Note that the winding axis P is a virtual axis extending in the Y-axis direction.

The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the three-dimensional shape of the battery element 20 is flat, the shape of the cross section of the battery element 20 intersecting the winding axis P (the cross section along the XZ plane) is determined by the long axis J1 and the short axis J2. It is a defined flat shape. The long axis J1 is a virtual axis extending in the X-axis direction and having a length larger than the length of the short axis J2, and the short axis J2 extends in the Z-axis direction that intersects the X-axis direction. is a virtual axis having a length smaller than that of the long axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the cross-sectional shape of the battery element 20 is a flat, substantially elliptical shape.

(positive electrode)
The positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B, as shown in FIG.

The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A, and contains one or more of positive electrode active materials that occlude and release lithium. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22 . In addition, the positive electrode active material layer 21B may further contain one or more of other materials such as a positive electrode binder and a positive electrode conductive agent. A method for forming the positive electrode active material layer 21B is not particularly limited, but a specific example is a coating method.

The positive electrode active material contains a lithium-containing compound. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of the other element is not particularly limited as long as it is an element other than a transition metal element (excluding lithium). Specifically, it is an element belonging to Groups 2 to 15 in the long period periodic table. The type of lithium-containing compound is not particularly limited, but specific examples include oxides, phosphoric acid compounds, silicic acid compounds and boric acid compounds.

_Specific _examples _of _oxides _are _LiNiO2 _, _LiCoO2 _, _{LiCo0.98Al0.01Mg0.01O2} , _{LiNi0.5Co0.2Mn0.3O2} _, _{LiNi0.8Co0.15Al0.05O2} _, _{LiNi0.33Co0.33Mn0.33} _. _O2 , _Li _{1.2Mn0.52Co0.175Ni0.1O2} _, _Li1.15 ₍ _{Mn0.65Ni0.22Co0.13} ₎ _O2 _and _LiMn2O4 _. _{_} _{_} _Specific examples _of phosphoric acid compounds include _LiFePO4 _, _LiMnPO4 _, _{LiFe0.5Mn0.5PO4} and _{LiFe0.3Mn0.7PO4} .

The positive electrode binder contains one or more of compounds such as synthetic rubber and polymer compounds. Specific examples of synthetic rubbers include styrene-butadiene rubber, fluororubber, and ethylene propylene diene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide and carboxymethylcellulose.

The positive electrode conductive agent contains one or more of conductive materials such as carbon materials, and specific examples of the conductive materials include graphite, carbon black, acetylene black, ketjen black, carbon Such as fibers, carbon nanofibers and carbon nanotubes. However, the conductive material may be a metal material, a conductive polymer compound, or the like.

(negative electrode)
The negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B, as shown in FIG.

The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode current collector 22A contains a conductive material such as a metal material, and a specific example of the conductive material is copper.

Here, the negative electrode active material layer 22B is provided on both surfaces of the negative electrode current collector 22A, and contains one or more of negative electrode active materials that intercalate and deintercalate lithium. However, the negative electrode active material layer 22B may be provided only on one side of the negative electrode current collector 22A on the side where the negative electrode 22 faces the positive electrode 21 . In addition, the negative electrode active material layer 22B may further contain one or more of other materials such as a negative electrode binder and a negative electrode conductor. The method of forming the negative electrode active material layer 22B is not particularly limited, but specifically, it is a coating method or the like.

The negative electrode active material contains one or more of carbon materials and metal-based materials. This is because a high energy density can be obtained.

Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite. This graphite may be natural graphite, artificial graphite, or both.

A metallic material is a material containing as constituent elements one or more of metallic elements and semi-metallic elements capable of forming an alloy with lithium. , silicon and tin. This metallic material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing two or more of these phases. Specific examples of metallic materials include TiSi ₂ and SiO _x (0<x≦2, or 0.2<x<1.4).

The details of each of the negative electrode binder and the negative electrode conductive agent are the same as those of the positive electrode binder and the positive electrode conductive agent.

(separator)
The separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, as shown in FIG. Allows lithium ions to pass through. This separator 23 contains a polymer compound such as polyethylene.

(Electrolyte)
Details regarding the electrolyte are as described above. That is, the electrolytic solution contains an appropriate amount (=0.1% by weight to 5.0% by weight) of fluorinated alcohol.

[Positive lead and negative lead]
The positive electrode lead 31 is a positive electrode terminal connected to the positive electrode current collector 21A of the positive electrode 21, as shown in FIGS. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, but specifically, it is either a thin plate shape, a mesh shape, or the like.

The negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22, as shown in FIGS. The negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper. Here, the details regarding the lead-out direction and shape of the negative electrode lead 32 are the same as the details regarding the lead-out direction and shape of the positive electrode lead 31 .

<2-2. Operation>
A lithium ion secondary battery operates as described below.

During charging, in the battery element 20, lithium is released in an ionic state from the positive electrode 21, and the lithium is absorbed in the negative electrode 22 in an ionic state through the electrolyte. On the other hand, in the battery element 20, on the other hand, lithium is released in an ionic state from the negative electrode 22 in the battery element 20, and the lithium is absorbed in the positive electrode 21 in an ionic state through the electrolyte.

<2-3. Manufacturing method>
In the case of manufacturing a lithium ion secondary battery, the positive electrode 21 and the negative electrode 22 are prepared according to an example procedure described below, and an electrolytic solution is prepared. While assembling a lithium ion secondary battery using it, the stabilization process of the lithium ion secondary battery is performed.

[Preparation of positive electrode]
First, a paste-like positive electrode mixture slurry is prepared by putting a mixture (positive electrode mixture) in which a positive electrode active material, a positive electrode binder, and a positive electrode conductor are mixed together into a solvent. This solvent may be an aqueous solvent or an organic solvent. Subsequently, the cathode active material layer 21B is formed by applying the cathode mixture slurry to both surfaces of the cathode current collector 21A. Finally, the positive electrode active material layer 21B may be compression-molded using a roll press machine or the like. In this case, the positive electrode active material layer 21B may be heated, or compression molding may be repeated multiple times. As a result, the cathode active material layers 21B are formed on both surfaces of the cathode current collector 21A, so that the cathode 21 is produced.

[Preparation of negative electrode]
The negative electrode 22 is manufactured by the same procedure as the manufacturing procedure of the positive electrode 21 described above. Specifically, a paste-like negative electrode mixture slurry is prepared by adding a mixture (negative electrode mixture) in which a negative electrode active material, a negative electrode binder, and a negative electrode conductor are mixed with each other into a solvent, and then a negative electrode collection is performed. The anode active material layer 22B is formed by applying the anode mixture slurry to both surfaces of the conductor 22A. After that, the negative electrode active material layer 22B may be compression molded. As a result, the negative electrode 22 is manufactured because the negative electrode active material layers 22B are formed on both surfaces of the negative electrode current collector 22A.

[Preparation of electrolytic solution]
An electrolytic solution containing a fluorinated alcohol is prepared according to the procedure described above.

[Assembly of lithium-ion secondary battery]
First, a joining method such as welding is used to connect the positive electrode lead 31 to the positive electrode current collector 21A of the positive electrode 21, and a joining method such as welding is used to connect the negative electrode current collector 22A of the negative electrode 22 to the negative electrode. Connect lead 32 .

Subsequently, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22 and the separator 23 are wound to form a wound body (not shown). This wound body has the same structure as the battery element 20 except that the positive electrode 21, the negative electrode 22 and the separator 23 are not impregnated with the electrolytic solution. Subsequently, the wound body is molded into a flat shape by pressing the wound body using a press machine or the like.

Subsequently, after the wound body is housed inside the hollow portion 10U, the exterior films 10 (bonding layer/metal layer/surface protective layer) are folded to face each other. Subsequently, by using an adhesion method such as a heat fusion method, the outer peripheral edge portions of two sides of the fusion layers facing each other are joined to each other, so that the wound body is placed inside the bag-shaped exterior film 10. to accommodate.

Finally, after injecting the electrolytic solution into the interior of the bag-shaped exterior film 10, the outer peripheral edges of the remaining one side of the mutually facing fusion layers are bonded together using a bonding method such as a heat fusion method. Join each other. In this case, a sealing film 41 is inserted between the packaging film 10 and the positive electrode lead 31 and a sealing film 42 is inserted between the packaging film 10 and the negative electrode lead 32 .

As a result, the wound body is impregnated with the electrolytic solution, so that the battery element 20, which is the wound electrode body, is produced. Accordingly, the battery element 20 is enclosed inside the bag-shaped exterior film 10, so that the lithium ion secondary battery is assembled.

[Stabilization treatment]
The assembled lithium ion secondary battery is charged and discharged. Various conditions such as environmental temperature, number of charge/discharge times (number of cycles), and charge/discharge conditions can be arbitrarily set. As a result, films are formed on the respective surfaces of the positive electrode 21 and the negative electrode 22, so that the state of the lithium ion secondary battery is electrochemically stabilized. Thus, a lithium ion secondary battery is completed.

<2-4. Action and effect>
According to this lithium ion secondary battery, the lithium ion secondary battery is provided with an electrolytic solution, and the electrolytic solution has the structure described above. Therefore, for the reasons described above, excellent storage characteristics and excellent charge/discharge characteristics can be obtained.

Other actions and effects regarding this lithium ion secondary battery are the same as other actions and effects regarding the positive electrode 1 .

<3. Variation>
The configuration of the lithium ion secondary battery can be changed as appropriate, as described below. However, the series of variants described below may be combined with each other.

[Modification 1]
A separator 23, which is a porous membrane, was used. However, although not specifically illustrated here, a laminated separator including a polymer compound layer may be used.

Specifically, a laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both sides of the porous membrane. This is because the adhesiveness of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, so that the winding misalignment of the battery element 20 is suppressed. As a result, swelling of the lithium-ion secondary battery is suppressed even if a decomposition reaction of the electrolytic solution occurs. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. Polyvinylidene fluoride has excellent physical strength and is electrochemically stable.

One or both of the porous membrane and the polymer compound layer may contain a plurality of insulating particles. This is because the safety (heat resistance) of the lithium ion secondary battery is improved because the plurality of insulating particles promote heat dissipation when the lithium ion secondary battery generates heat. The insulating particles contain one or more of insulating materials such as inorganic materials and resin materials. Specific examples of inorganic materials are aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide and zirconium oxide. Specific examples of resin materials include acrylic resins and styrene resins.

When manufacturing a laminated separator, after preparing a precursor solution containing a polymer compound, a solvent, etc., the precursor solution is applied to one or both sides of the porous membrane. In this case, if necessary, a plurality of insulating particles may be added to the precursor solution.

Even when this laminated separator is used, the same effect can be obtained because lithium can move between the positive electrode 21 and the negative electrode 22 . In this case, especially, as described above, the safety of the lithium ion secondary battery is improved, so that a higher effect can be obtained.

[Modification 2]
An electrolytic solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer that is a gel electrolyte may be used.

In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 and the electrolyte layer interposed therebetween, and the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte layer are wound. This electrolyte layer is interposed between the positive electrode 21 and the separator 23 and interposed between the negative electrode 22 and the separator 23 .

Specifically, the electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. Polymer compounds include polyvinylidene fluoride and the like. When forming the electrolyte layer, after preparing a precursor solution containing an electrolytic solution, a polymer compound, a solvent, and the like, the precursor solution is applied to one side or both sides of each of the positive electrode 21 and the negative electrode 22 .

Even when this electrolyte layer is used, lithium can move between the positive electrode 21 and the negative electrode 22 through the electrolyte layer, so that similar effects can be obtained. In this case, especially, as described above, leakage of the electrolytic solution is prevented, so that a higher effect can be obtained.

<4. Applications of Lithium Ion Secondary Battery>
The use (application example) of the lithium ion secondary battery is not particularly limited. A lithium-ion secondary battery used as a power source may be a main power source for electronic devices and electric vehicles, or may be an auxiliary power source. A main power source is a power source that is preferentially used regardless of the presence or absence of other power sources. The auxiliary power supply may be a power supply that is used in place of the main power supply or a power supply that is switched from the main power supply.

Specific examples of lithium-ion secondary battery applications are as follows. Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios and portable information terminals. Backup power and storage devices such as memory cards. Power tools such as power drills and power saws. It is a battery pack mounted on an electronic device. Medical electronic devices such as pacemakers and hearing aids. It is an electric vehicle such as an electric vehicle (including a hybrid vehicle). A power storage system, such as a domestic or industrial battery system, that stores power for emergencies. In these uses, one lithium ion secondary battery may be used, or a plurality of lithium ion secondary batteries may be used.

The battery pack may use a single cell or an assembled battery. An electric vehicle is a vehicle that operates (runs) using a lithium-ion secondary battery as a drive power source, and may be a hybrid vehicle that also includes a drive source different from the lithium-ion secondary battery. In a home electric power storage system, electric power stored in a lithium-ion secondary battery, which is a power storage source, can be used to power home electric appliances.

Here, an example of application of the lithium-ion secondary battery will be specifically described. The configuration of the application example described below is merely an example, and can be changed as appropriate.

Fig. 3 shows the block configuration of the battery pack. The battery pack described here is a battery pack (a so-called soft pack) using one lithium-ion secondary battery, and is mounted in an electronic device such as a smart phone.

This battery pack includes a power supply 51 and a circuit board 52, as shown in FIG. This circuit board 52 is connected to the power supply 51 and includes a positive terminal 53 , a negative terminal 54 and a temperature detection terminal 55 .

The power supply 51 includes one lithium ion secondary battery. In this lithium ion secondary battery, the positive lead is connected to the positive terminal 53 and the negative lead is connected to the negative terminal 54 . The power supply 51 can be connected to the outside through the positive terminal 53 and the negative terminal 54, and thus can be charged and discharged. The circuit board 52 includes a control section 56 , a switch 57 , a PTC element 58 and a temperature detection section 59 . However, the PTC element 58 may be omitted.

The control unit 56 includes a central processing unit (CPU), memory, etc., and controls the overall operation of the battery pack. This control unit 56 detects and controls the use state of the power source 51 as necessary.

When the voltage of the power source 51 (lithium-ion secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 cuts off the switch 57 so that the charging current flows through the current path of the power source 51. avoid The overcharge detection voltage is not particularly limited, but is specifically 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but is specifically 2.40V±0.1V. is.

The switch 57 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, and the like, and switches connection/disconnection between the power supply 51 and an external device according to instructions from the control unit 56 . This switch 57 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, etc., and each of the charging current and the discharging current is detected based on the ON resistance of switch 57 .

The temperature detection unit 59 includes a temperature detection element such as a thermistor. The temperature detection unit 59 measures the temperature of the power supply 51 using the temperature detection terminal 55 and outputs the temperature measurement result to the control unit 56 . The measurement result of the temperature measured by the temperature detection unit 59 is used when the control unit 56 performs charging/discharging control at the time of abnormal heat generation and when the control unit 56 performs correction processing when calculating the remaining capacity.

An example of this technology will be explained.

<Experimental Examples 1 to 10 and Comparative Examples 1 to 7>
After producing a lithium ion secondary battery, the characteristics of the lithium ion secondary battery were evaluated as described below.

[Production of lithium ion secondary battery]
A lithium ion secondary battery (laminate film type) shown in FIGS. 1 and 2 was produced by the procedure described below.

(Preparation of positive electrode)
First, 91 parts by mass of a positive electrode active material (lithium cobalt oxide (LiCoO ₂ ), which is a lithium-containing compound (oxide)), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and a positive electrode conductor (amorphous carbon A positive electrode material mixture was obtained by mixing 6 parts by mass of Ketjen Black (powder) with each other. Subsequently, the positive electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), and the solvent was stirred to prepare a pasty positive electrode mixture slurry.

Subsequently, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 21A (aluminum foil having a thickness of 10 μm) using a coating device, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer. 21B.

Finally, after compression-molding the positive electrode active material layer 21B using a roll press, the positive electrode current collector 21A on which the positive electrode active material layer 21B was formed was cut into strips. Thus, the positive electrode 21 was produced.

(Preparation of negative electrode)
First, 94 parts by mass of a negative electrode active material (20 parts by mass of silicon oxide as a metal material and 74 parts by mass of artificial graphite as a carbon material), 1.5 parts by mass of a negative electrode binder (polyvinylidene fluoride), and a negative electrode A negative electrode mixture was prepared by mixing 2.5 parts by mass of a conductive agent (2 parts by mass of carbon nanotubes and 0.5 parts by mass of graphite) and 2 parts by mass of a thickening agent (carboxymethyl cellulose).

Subsequently, after the negative electrode mixture was put into a solvent (water, which is an aqueous solvent), the solvent was stirred to prepare a pasty negative electrode mixture slurry.

Subsequently, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 22A (copper foil having a thickness of 8 μm) using a coating device, and then the negative electrode mixture slurry is dried to form a negative electrode active material layer. 22B was formed.

Finally, the negative electrode active material layer 22B was compression-molded using a roll press, and then the negative electrode current collector 22A on which the negative electrode active material layer 22B was formed was cut into strips. Thus, the negative electrode 22 was produced.

(Preparation of electrolytic solution)
After adding an electrolyte salt (lithium hexafluorophosphate (LiPF ₆ ), which is a lithium salt) to a solvent (ethylene carbonate (EC), which is a cyclic carbonate, and ethylmethyl carbonate (EMC), which is a chain carbonate), The solvent was stirred. Mixing ratios (% by weight) of solvents are as shown in Table 1. In this case, the content of the electrolyte salt was 1 mol/kg of the solvent.

Subsequently, after the fluorinated alcohol was added to the solvent containing the electrolyte salt, the solvent was stirred. Hexafluoroisopropanol ((CF ₃ ) ₂ CHOH(HFIP)) and 2,2,2-trifluoroethanol (CF ₃ CH ₂ OH(TFE)) were used as the fluorinated alcohols. The content (% by weight) of the fluorinated alcohol in the electrolytic solution is as shown in Table 1, and the procedure for measuring the content of the fluorinated alcohol in the electrolytic solution is as described above.

As a result, an electrolytic solution containing fluorinated alcohol was prepared.

For comparison, an electrolytic solution was prepared by the same procedure except that the fluorinated alcohol was not used. For comparison, an electrolytic solution was prepared by the same procedure except that ethanol (C ₂ H ₅ OH (EA)) was used instead of the fluorinated alcohol. Furthermore, for comparison, an electrolytic solution was prepared by the same procedure except that ethanol was used instead of the cyclic carbonate.

(Assembly of lithium-ion secondary battery)
First, the positive electrode lead 31 (aluminum foil) was welded to the positive electrode collector 21A of the positive electrode 21, and the negative electrode lead 32 (copper foil) was welded to the negative electrode collector 22A.

Subsequently, after laminating the positive electrode 21 and the negative electrode 22 with each other with a separator 23 (a microporous polyethylene film having a thickness of 25 μm) interposed therebetween, the positive electrode 21, the negative electrode 22 and the separator 23 are wound to obtain a winding. A circular body was produced. Subsequently, the wound body was molded into a flat shape by pressing the wound body using a pressing machine.

Subsequently, the exterior film 10 was folded so as to sandwich the wound body housed inside the recessed portion 10U. The exterior film 10 includes a fusion layer (a polypropylene film with a thickness of 30 μm), a metal layer (aluminum foil with a thickness of 40 μm), and a surface protective layer (a nylon film with a thickness of 25 μm). was laminated in this order from the inside. Subsequently, the wound body was housed inside the bag-shaped exterior film 10 by heat-sealing the outer peripheral edge portions of two sides of the fusion layers facing each other.

Finally, after the electrolytic solution was injected into the interior of the bag-shaped exterior film 10, the outer peripheral edges of the remaining sides of the mutually facing fusion layers were heat-sealed to each other in a reduced pressure environment. In this case, a sealing film 41 (polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 was inserted between the exterior film 10 and the negative electrode lead 32. (polypropylene film with thickness = 5 μm) was inserted.

As a result, the wound body was impregnated with the electrolytic solution, and the battery element 20 was produced. Accordingly, since the battery element 20 was sealed inside the exterior film 10, a lithium ion secondary battery was assembled.

(stabilization treatment)
The lithium ion secondary battery was charged and discharged for one cycle in a normal temperature environment (temperature = 23°C). At the time of charging, constant-current charging was performed at a current of 0.1C until the voltage reached 4.4V, and then constant-voltage charging was performed at the voltage of 4.4V until the current reached 0.025C. During discharge, constant current discharge was performed at a current of 0.1C until the voltage reached 3.0V. 0.1C is a current value that can completely discharge the battery capacity (theoretical capacity) in 10 hours, and 0.025C is a current value that completely discharges the battery capacity in 40 hours.

As a result, films were formed on the surfaces of the positive electrode 21 and the negative electrode 22, and the lithium ion secondary battery was electrochemically stabilized. Thus, a lithium ion secondary battery was completed.

[Characteristic evaluation of lithium ion secondary battery]
When the storage characteristics and charge/discharge characteristics were evaluated according to the procedures described below, the results shown in Table 1 were obtained.

(storage characteristics)
Here, in order to simplify the evaluation contents, instead of using a lithium ion secondary battery produced using an electrolytic solution, the electrolytic solution was used as it was for evaluation.

Specifically, after preparing the electrolytic solution, the state of the electrolytic solution was visually observed by storing the electrolytic solution in a high-temperature environment (temperature = 40°C) (storage period = 2 weeks). As a result, it was investigated whether or not deterioration (discoloration) occurred, and whether or not deposition of electrolyte salt occurred.

(Charging and discharging characteristics)
A test lithium-ion secondary battery was used to evaluate the charge-discharge characteristics. FIG. 4 shows a cross-sectional configuration of a test (coin-type) lithium-ion secondary battery.

In the coin-type lithium ion secondary battery, as shown in FIG. 4, the test electrode 61 is housed inside the outer cup 64 and the counter electrode 62 is housed inside the outer can 65 . The test electrode 61 and the counter electrode 62 are laminated with a separator 63 interposed therebetween, and the exterior cup 64 and the exterior can 65 are crimped together with a gasket 66 interposed therebetween. The electrolytic solution is impregnated in each of the test electrode 61, counter electrode 62 and separator 63, and has the structure described above.

When producing a coin-type lithium ion secondary battery, a test electrode 61 was produced in the same manner, except that the positive electrode active material layer 21B was formed only on one side of the positive electrode current collector 21A. A counter electrode 62 was produced by the same procedure, except that the negative electrode active material layer 22B was formed only on one side of the current collector 22A. Thus, the positive electrode active material layer 21B and the negative electrode active material layer 22B were opposed to each other with the separator 63 interposed therebetween. Details of the separator 63 are the same as those of the separator 23 .

When evaluating the charge-discharge characteristics, first, the lithium-ion secondary battery is charged in a normal temperature environment (temperature = 23 ° C.) to measure the charge capacity, and then the lithium-ion secondary battery is placed in the same environment. was discharged to measure the discharge capacity (discharge capacity at the first cycle).

Next, the initial efficiency, which is an index for evaluating charge-discharge characteristics, was calculated based on the formula: initial efficiency (%) = (discharge capacity/charge capacity) x 100.

Subsequently, the discharge capacity (discharge capacity at the 150th cycle) was measured by repeatedly charging and discharging the lithium ion secondary battery until the number of cycles reached 150 in the same environment.

Finally, capacity retention rate (%) = (discharge capacity at 150th cycle/discharge capacity at 1st cycle) x 100, which is another index for evaluating charge/discharge characteristics. was calculated.

The charging/discharging conditions were the same as the charging/discharging conditions during the stabilization treatment of the lithium-ion secondary battery. However, the value of the capacity retention rate shown in Table 1 is a value normalized by setting the value of the capacity retention rate in the case of not using the fluorinated alcohol (Comparative Example 1) to 100.

[Discussion]
As shown in Table 1, each of the storage characteristics and charge/discharge characteristics varied greatly depending on the composition of the electrolytic solution. In the following, the case in which neither fluorinated alcohol nor ethanol was used (Comparative Example 1) is used as a reference for comparison.

Specifically, when the electrolyte contained an excessive amount of fluorinated alcohol (Comparative Examples 2 and 3), neither discoloration nor deposition occurred. However, the initial efficiency was significantly reduced. In addition, since the lithium ion secondary battery could not be charged and discharged for two cycles or more, the capacity retention rate could not be calculated.

Note that when the electrolytic solution contained ethanol as an additive (Comparative Example 4), precipitation did not occur, but discoloration occurred. In this case, since discoloration occurred, the initial efficiency and the capacity retention rate were not calculated.

In addition, since ethanol was used as part of the solvent, both discoloration and precipitation occurred when the electrolyte contained a large amount of ethanol (Comparative Examples 5-7). In this case, since both discoloration and precipitation occurred, the initial efficiency and capacity retention rate were not calculated.

On the other hand, when the electrolyte contains an appropriate amount (=0.1 wt% to 5.0 wt%) of fluorinated alcohol (Examples 1 to 10), both discoloration and deposition occur. didn't. In this case, although the initial efficiency slightly decreased, the capacity retention rate increased while maintaining a high initial efficiency.

In particular, when the electrolyte contained an appropriate amount of fluorinated alcohol (Examples 1 to 10), the tendencies described below were obtained.

First, when the content of the electrolytic solution is 0.3% by weight to 3.0% by weight (Examples 2 to 4, 7 to 9), the capacity retention rate is reduced while maintaining a sufficiently high initial efficiency. increased enough.

Second, when the fluorinated alcohol contained one or more fluorinated alkyl groups (Examples 1 to 10), the capacity retention rate was likely to increase while maintaining a sufficiently high initial efficiency.

Third, when the solvent of the electrolytic solution contained cyclic carbonate and chain carbonate (Examples 1 to 10), the capacity retention rate was sufficiently increased while sufficiently high initial efficiency was maintained.

[summary]
From the results shown in Table 1, when the electrolyte contains an appropriate amount (= 0.1% by weight to 5.0% by weight) of fluorinated alcohol, both discoloration and deposition do not occur, and a high The capacity retention rate increased while the initial efficiency was maintained. Therefore, excellent storage characteristics and excellent charge/discharge characteristics could be obtained in the lithium ion secondary battery.

Although the present technology has been described above while citing one embodiment and example, the configuration of this technology is not limited to the configuration described in the one embodiment and example, and can be variously modified.

Specifically, the case where the element structure of the battery element is a wound type was explained. However, since the element structure of the battery element is not particularly limited, it may be a stacked type or a folded type. In the laminated type, the positive electrode and the negative electrode are alternately laminated with a separator interposed therebetween, and in the multifold type, the positive electrode and the negative electrode are folded zigzag while facing each other with the separator interposed therebetween.

Since the effects described in this specification are merely examples, the effects of the present technology are not limited to the effects described in this specification. Accordingly, other advantages may be obtained with respect to the present technology.

Claims

an electrolyte with a positive electrode and a negative electrode;
The electrolytic solution contains a fluorinated alcohol represented by formula (1),
The content of the fluorinated alcohol in the electrolytic solution is 0.1% by weight or more and 5.0% by weight or less.
Lithium-ion secondary battery.
R1R2R3COH (1)
(Each of R1, R2 and R3 is a hydrogen group, an alkyl group or a fluorinated alkyl group, provided that at least one of R1, R2 and R3 is a fluorinated alkyl group. )
The content of the fluorinated alcohol in the electrolytic solution is 0.3% by weight or more and 3.0% by weight or less.
The lithium ion secondary battery according to claim 1.
two or more of said R1, said R2 and said R3 are said fluorinated alkyl groups;
The lithium ion secondary battery according to claim 1 or 2.
The electrolytic solution further contains a cyclic carbonate and a chain carbonate,
The lithium ion secondary battery according to any one of claims 1 to 3.
including a fluorinated alcohol represented by formula (1),
The content of the fluorinated alcohol is 0.1% by weight or more and 5.0% by weight or less.
Electrolyte for lithium-ion secondary batteries.
R1R2R3COH (1)
(Each of R1, R2 and R3 is a hydrogen group, an alkyl group or a fluorinated alkyl group, provided that at least one of R1, R2 and R3 is a fluorinated alkyl group. )