JP2023146966A - Nonaqueous secondary battery and production method thereof - Google Patents

Abstract

The present invention provides an acetonitrile-containing nonaqueous secondary battery that has a high capacity retention rate after a 50°C cycle test.
[Solution] A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, the non-aqueous electrolyte comprising a non-aqueous solvent containing acetonitrile, a lithium salt, and a general formula (1). a sulfone compound, the content of the sulfone compound is 0.1% by mass or more and 3% by mass or less based on the total amount of the nonaqueous electrolyte, and the ionic conductivity of the nonaqueous electrolyte at 25°C is 12 mS/cm or more, and the 10-second discharge DCIR expressed as (voltage change for 10 seconds after the start of discharge)/(discharge current value for 10 seconds after the start of discharge), (10-second discharge DCIR after storage at 85°C)/ The rate of change before and after storage at 85°C and 12 hours expressed as (10 seconds discharge DCIR before storage at 85°C) is more than 0 and 1.3 or less.

[Selection diagram] Figure 1

Description

The present invention relates to a non-aqueous secondary battery and a method for manufacturing the same.

Lithium-ion secondary batteries have been widely used in mobile devices, but in recent years, with the global trend toward electrification of automobiles, their use as a power source for electric vehicles has become mainstream. To be used as an automotive battery, a wide range of characteristics are required, including not only improved energy density and long-term cycle performance, but also high-temperature durability and low-temperature charge/discharge characteristics. Under these circumstances, several technologies have been reported that address the wide range of performance requirements mentioned above, such as by using an electrolytic solution with high ionic conductivity and adding additives to the electrolytic solution that form a stable electrode protective film. ing.

For example, Patent Document 1 discloses a nonaqueous secondary battery that operates with thick film electrodes using a highly ionic conductive acetonitrile electrolyte. Furthermore, a method for strengthening SEI (Solid Electrolyte Interface) by combining a plurality of electrode protection additives has been reported. Similarly, Patent Document 2 also reports that a specific organic lithium salt enhances SEI and suppresses decomposition of a highly ionic conductive electrolyte. Patent Document 3 describes that a nonaqueous secondary battery with excellent storage characteristics and cycle performance can be obtained by adding a sulfone additive to a nonaqueous electrolyte containing vinylene carbonate.

Moreover, Patent Document 4 shows that a non-aqueous secondary battery with excellent cycle characteristics, low-temperature performance, etc. can be obtained by adding a sulfone compound having a phenyl group to a carbonate-based electrolyte.

International Publication No. 2013/062056 International Publication No. 2012/057311 International Publication No. 2021/049648 Japanese Patent Application Publication No. 2000-133305

Although acetonitrile-containing electrolytes such as those disclosed in Patent Documents 1 to 3 have good ionic conductivity, depending on the conditions, there may be a problem with cycle characteristics after storage at a high temperature such as 50°C.

The problem with the carbonate electrolyte solution as disclosed in Patent Document 4 is that it does not have sufficient ionic conductivity because it does not contain a highly ionic conductive solvent such as acetonitrile.

An object of the present invention is to provide an acetonitrile-containing nonaqueous secondary battery that has a high capacity retention rate after a 50°C cycle test, and a method for manufacturing the same.

The present invention has been made in view of the above circumstances, and as a result of study, it has been found that the above problems can be solved by providing the following components, and the present invention has been completed.

｛式中、Ｒ_１及びＲ_２はそれぞれ独立して、ハロゲン基、又はハロゲン原子で置換されていてもよいアルキル基を示す。）で表されるスルホン化合物と、を含み、
前記スルホン化合物の含有量が前記非水系電解液の全量に対して、０．１質量%以上３質量％以下であり、
２５℃における前記非水系電解液のイオン伝導度が１２ｍＳ／ｃｍ以上３０ｍＳ／ｃｍ以下でありであり、
下記式（１－１）：
１０秒放電ＤＣＩＲ＝(放電開始後１０秒間の電圧変化)／（放電開始後１０秒間の放電電流値） ・・・式（１－１）
で表される１０秒放電ＤＣＩＲについて、８５℃及び１２時間の貯蔵前後での下記式（１－２）：
１０秒放電ＤＣＩＲ変化率＝（８５℃貯蔵後１０秒放電ＤＣＩＲ）／（８５℃貯蔵前１０秒放電ＤＣＩＲ） ・・・式（１－２）
で表される１０秒放電ＤＣＩＲ変化率が０超え１．３以下である、
非水系二次電池。
［２］
前記非水系溶媒の全量に対してビニレンカーボネートが２体積％未満である、［１］に記載の非水系二次電池。
［３］
前記非水系電解液中の非水系溶媒の全量に対して、前記アセトニトリルの含有量が２０～６０体積％である、［１］又は［２］に記載の非水系二次電池。
［４］
前記リチウム塩がリチウム含有イミド塩と六フッ化リン酸リチウム（ＬｉＰＦ_６）からなる群から選ばれる少なくとも一種である、［１］～［３］のいずれか１項に記載の非水系二次電池。
［５］
前記一般式（１）で示されるスルホン化合物としてジフェニルスルホンを含む、［１］～［４］のいずれか１項に記載の非水系二次電池。
［６］
前記正極は、正極活物質としてリチウムイオンを吸蔵及び放出することが可能な材料からなる群より選ばれる１種以上の材料を含有し、前記負極は、負極活物質としてリチウムイオンを吸蔵及び放出することが可能な材料と、金属リチウムと、からなる群より選ばれる１種以上の材料を含有する、［１］～［５］のいずれか１項に記載の非水系二次電池。
［７］
前記正極活物質がリチウムと遷移金属の複合酸化物であり、負極活物質が黒鉛である、［６］に記載の非水系二次電池。
［８］
［１］～［７］のいずれか１項に記載の非水系二次電池の製造方法であって、
１時間で設定容量を放電できる電流量を１Ｃとした時に、０．１Ｃ以上の充電速度で初回充電を行う工程を有する、非水系二次電池の製造方法。 That is, one embodiment of the present invention is as follows.
[1]
A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The non-aqueous electrolyte includes a non-aqueous solvent containing acetonitrile, a lithium salt,
General formula (1) below:

{In the formula, R ₁ and R ₂ each independently represent a halogen group or an alkyl group optionally substituted with a halogen atom. ) a sulfone compound represented by
The content of the sulfone compound is 0.1% by mass or more and 3% by mass or less with respect to the total amount of the nonaqueous electrolyte,
The ionic conductivity of the non-aqueous electrolyte at 25° C. is 12 mS/cm or more and 30 mS/cm or less,
The following formula (1-1):
10 seconds discharge DCIR = (voltage change for 10 seconds after the start of discharge) / (discharge current value for 10 seconds after the start of discharge) ...Formula (1-1)
Regarding the 10-second discharge DCIR expressed by the following formula (1-2) before and after storage at 85°C and 12 hours:
10-second discharge DCIR change rate = (10-second discharge DCIR after storage at 85°C)/(10-second discharge DCIR before storage at 85°C) ...Formula (1-2)
The 10-second discharge DCIR change rate expressed by is more than 0 and less than 1.3,
Non-aqueous secondary battery.
[2]
The nonaqueous secondary battery according to [1], wherein vinylene carbonate is less than 2% by volume based on the total amount of the nonaqueous solvent.
[3]
The non-aqueous secondary battery according to [1] or [2], wherein the content of the acetonitrile is 20 to 60% by volume with respect to the total amount of the non-aqueous solvent in the non-aqueous electrolyte.
[4]
The nonaqueous secondary battery according to any one of [1] to [3], wherein the lithium salt is at least one selected from the group consisting of a lithium-containing imide salt and lithium hexafluorophosphate (LiPF ₆ ). .
[5]
The non-aqueous secondary battery according to any one of [1] to [4], which contains diphenyl sulfone as the sulfone compound represented by the general formula (1).
[6]
The positive electrode contains one or more materials selected from the group consisting of materials capable of inserting and releasing lithium ions as a positive electrode active material, and the negative electrode contains and releasing lithium ions as a negative electrode active material. The non-aqueous secondary battery according to any one of [1] to [5], which contains one or more materials selected from the group consisting of a material capable of oxidation, and metallic lithium.
[7]
The non-aqueous secondary battery according to [6], wherein the positive electrode active material is a composite oxide of lithium and a transition metal, and the negative electrode active material is graphite.
[8]
The method for manufacturing a non-aqueous secondary battery according to any one of [1] to [7],
A method for manufacturing a non-aqueous secondary battery, comprising the step of initially charging at a charging rate of 0.1C or more, where 1C is the amount of current that can discharge a set capacity in 1 hour.

According to the present invention, it is possible to provide an acetonitrile-containing nonaqueous secondary battery with a high capacity retention rate after a 50°C cycle test, and a method for manufacturing the same.
Further, according to a preferred embodiment of the present invention, there is a sufficient negative electrode protection function even at high temperatures due to the addition of the diphenylsulfone substituted product, and the capacity retention rate at the initial stage of the cycle is stable in a 50°C cycle test after high-temperature storage. Furthermore, it is possible to provide a non-aqueous secondary battery with a high capacity retention rate and a method for manufacturing the same.

FIG. 1 is a plan view schematically showing an example of a non-aqueous secondary battery according to the present embodiment. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1.

Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "this embodiment") will be described in detail. In addition, in this specification, a numerical range described using "~" includes the numerical values described before and after it. In this specification, the upper limit value or lower limit value described in a certain numerical range in a numerical range described in a stepwise manner can be replaced with the upper limit value or lower limit value of a numerical range in another stepwise description. In this specification, the upper limit value or lower limit value described in a certain numerical range can also be replaced with the value described in the Examples. The scale, shape, and length of parts of the drawings may be exaggerated for added clarity.

｛式中、Ｒ_１及びＲ_２はそれぞれ独立して、ハロゲン基、又はハロゲン原子で置換されていてもよいアルキル基を示す。）で表されるスルホン化合物と、を含み、
スルホン化合物の含有量が非水系電解液の全量に対して、０．１質量%以上３質量％以下であり、
２５℃における非水系電解液のイオン伝導度が１２ｍＳ／ｃｍ以上３０ｍＳ／ｃｍ以下であり、
下記式（１－１）：
１０秒放電ＤＣＩＲ＝(放電開始後１０秒間の電圧変化)／（放電開始後１０秒間の放電電流値） ・・・式（１－１）
で表される１０秒放電ＤＣＩＲについて、８５℃及び１２時間の貯蔵前後での下記式（１－２）：
１０秒放電ＤＣＩＲ変化率＝（８５℃貯蔵後１０秒放電ＤＣＩＲ）/（８５℃貯蔵前１０秒放電ＤＣＩＲ） ・・・式（１－２）
で表される１０秒放電ＤＣＩＲ変化率が０超え１．３以下である、非水系二次電池である。
これによれば、５０℃サイクル試験後の容量維持率の高いアセトニトリル含有非水系二次電池を提供することができる。
＜非水系二次電池＞
本実施形態の非水系二次電池は、正極及び負極と共に上記非水系電解液を備える二次電池であり、例えば、リチウムイオン電池であってよく、より具体的には、図１に概略的に平面図を、かつ図２に概略的に断面図を示すリチウムイオン電池であってよい。図１、２に示されるリチウムイオン電池１００は、セパレータ１７０と、そのセパレータ１７０を両側から挟む正極１５０と負極１６０と、更にそれら（セパレータ１７０、正極１５０及び負極１６０）の積層体を挟む正極リード体１３０（正極１５０に接続）と、負極リード体１４０（負極１６０に接続）と、それらを収容する電池外装１１０とを備える。正極１５０とセパレータ１７０と負極１６０とを積層した積層体は、本実施形態に係る非水系電解液に含浸されている。 One aspect of this embodiment is
A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The non-aqueous electrolyte includes a non-aqueous solvent containing acetonitrile, a lithium salt,
General formula (1) below:

{In the formula, R ₁ and R ₂ each independently represent a halogen group or an alkyl group optionally substituted with a halogen atom. ) a sulfone compound represented by
The content of the sulfone compound is 0.1% by mass or more and 3% by mass or less with respect to the total amount of the nonaqueous electrolyte,
The ionic conductivity of the non-aqueous electrolyte at 25°C is 12 mS/cm or more and 30 mS/cm or less,
The following formula (1-1):
10 seconds discharge DCIR = (voltage change for 10 seconds after the start of discharge) / (discharge current value for 10 seconds after the start of discharge) ...Formula (1-1)
Regarding the 10-second discharge DCIR expressed by the following formula (1-2) before and after storage at 85°C and 12 hours:
10-second discharge DCIR change rate = (10-second discharge DCIR after storage at 85°C)/(10-second discharge DCIR before storage at 85°C) ...Formula (1-2)
This is a non-aqueous secondary battery whose 10-second discharge DCIR change rate expressed by is greater than 0 and less than or equal to 1.3.
According to this, it is possible to provide an acetonitrile-containing nonaqueous secondary battery that has a high capacity retention rate after a 50° C. cycle test.
<Nonaqueous secondary battery>
The non-aqueous secondary battery of this embodiment is a secondary battery that includes the above-mentioned non-aqueous electrolyte together with a positive electrode and a negative electrode, and may be a lithium ion battery, for example, and more specifically, as shown schematically in FIG. It may be a lithium ion battery, shown in plan view and schematically in cross-section in FIG. The lithium ion battery 100 shown in FIGS. 1 and 2 includes a separator 170, a positive electrode 150 and a negative electrode 160 sandwiching the separator 170 from both sides, and a positive electrode lead sandwiching a stack of these (separator 170, positive electrode 150, and negative electrode 160). The battery includes a body 130 (connected to the positive electrode 150), a negative electrode lead body 140 (connected to the negative electrode 160), and a battery exterior 110 that houses them. A laminate in which the positive electrode 150, the separator 170, and the negative electrode 160 are stacked is impregnated with the non-aqueous electrolyte according to this embodiment.

<1. Non-aqueous electrolyte>
The "non-aqueous electrolytic solution" in this embodiment refers to a non-aqueous electrolytic solution containing a non-aqueous solvent containing acetonitrile, a lithium salt, and a predetermined sulfone compound. Although it is preferable that the non-aqueous electrolytic solution according to the present embodiment contains as little water as possible, it may contain a very small amount of water as long as it does not hinder the problem solving of the present invention. The content of such water is 1% by mass or less of water based on the total amount of the nonaqueous electrolytic solution, and is 300 mass ppm or less, preferably 200 mass ppm or less. As for the non-aqueous electrolyte, as long as it has a configuration to achieve the problem of the present invention, for other components, the constituent materials of known non-aqueous electrolytes used in lithium ion batteries may be used as appropriate. Can be selected and applied.

<1-1. Non-aqueous solvent>
The term "non-aqueous solvent" as used in this embodiment refers to an element obtained by removing the lithium salt, a predetermined sulfone compound, and various additives from the non-aqueous electrolyte. When the non-aqueous electrolyte contains an electrode protection additive, the "non-aqueous solvent" refers to the lithium salt, the specified sulfone compound, and any additives other than the electrode protection additive contained in the non-aqueous electrolyte. It refers to the elements excluding the agent. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; aprotic solvents, and the like. Among these, aprotic solvents are preferred as the non-aqueous solvent. The non-aqueous solvent may contain solvents other than aprotic solvents as long as they do not impede the problem solving of the present invention.

The non-aqueous solvent related to the non-aqueous electrolyte of this embodiment contains acetonitrile as an aprotic solvent. When the non-aqueous solvent contains acetonitrile, the ionic conductivity of the non-aqueous electrolyte improves, so that the diffusibility of lithium ions within the battery can be improved. Therefore, when the nonaqueous electrolyte contains acetonitrile, even in a positive electrode in which the positive electrode active material layer is thickened to increase the amount of positive electrode active material filled, lithium ions have difficulty reaching the current collector during high-load discharge. Lithium ions can diffuse well into nearby areas. Thereby, it becomes possible to draw out sufficient capacity even during high-load discharge, and it is possible to obtain a non-aqueous secondary battery with excellent load characteristics.
In the case of a carbonate-based solvent that does not contain acetonitrile, the ionic conductivity is insufficient because it does not contain a highly ionic conductive solvent such as acetonitrile, and the charge/discharge rate is limited to a range that can follow the movement of lithium ions.

Moreover, when the non-aqueous solvent contains acetonitrile, the rapid charging characteristics of the non-aqueous secondary battery can be improved. In constant current (CC)-constant voltage (CV) charging of a non-aqueous secondary battery, the capacity per unit time during the CC charging period is larger than the charging capacity per unit time during the CV charging period. When acetonitrile is used as a non-aqueous solvent in a non-aqueous electrolyte, it is possible to widen the CC charging area (longer CC charging time) and increase the charging current, so it is possible to increase the charging current from the start of charging a non-aqueous secondary battery. It can significantly shorten the time it takes to reach a fully charged state.

Note that acetonitrile is easily electrochemically reductively decomposed. Therefore, when acetonitrile is used, other solvents (for example, aprotic solvents other than acetonitrile) should be used together with acetonitrile as a non-aqueous solvent, and/or electrode protection additives should be added to form a protective film on the electrode. It is preferable to add.

The content of acetonitrile in the non-aqueous solvent is preferably 10 to 60% by volume based on the total amount of the non-aqueous solvent. The upper limit of the content of acetonitrile is more preferably 50% by volume or less, and even more preferably 40% by volume or less, based on the total amount of the nonaqueous solvent. The lower limit of the content of acetonitrile is more preferably 20% by volume or more based on the total amount of the non-aqueous solvent. When the lower limit of the content of acetonitrile is within the above range, the ionic conductivity of the non-aqueous electrolyte tends to increase and the high output characteristics of the non-aqueous secondary battery can be expressed. Dissolution can be promoted. In addition, when the content of acetonitrile in the non-aqueous solvent is within the above range, the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery can be improved while maintaining the excellent performance of acetonitrile. tend to be able to do so.

Examples of aprotic solvents other than acetonitrile include cyclic carbonates, lactones, organic compounds having a sulfur atom, chain fluorinated carbonates, cyclic ethers, mononitriles other than acetonitrile, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, and short Examples include chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvent are replaced with halogen atoms.

Since acetonitrile, which is one component of the non-aqueous solvent, is easily electrochemically reductively decomposed, the non-aqueous electrolyte according to the present embodiment contains a specific sulfone compound in addition to acetonitrile in the non-aqueous solvent.

The nonaqueous solvent according to the present embodiment contains acetonitrile and a sulfone compound, and preferably further contains ethylene carbonate as a cyclic carbonate, so that vinylene carbonate is less than 2% by volume based on the total amount of the nonaqueous solvent. Even if the non-aqueous electrolyte does not contain vinylene carbonate (for example, even if the non-aqueous electrolyte does not contain vinylene carbonate), when the non-aqueous electrolyte is used in a non-aqueous secondary battery, it forms an SEI with high thermal durability and suppresses deterioration of the negative electrode. do.
In acetonitrile-containing electrolytes such as those disclosed in Patent Documents 1 to 3, SEI formation has conventionally been performed using fluoroethylene carbonate (FEC) or vinylene carbonate (VC). On the other hand, in these electrolytic solutions, SEI thermally decomposes under high temperature conditions and loses the negative electrode protection effect, so depending on the conditions, there is a possibility that the cycle characteristics after high temperature conditions become unstable. Further, if VC itself decomposes within the battery at high temperatures, there is a possibility that the battery performance will be degraded. Therefore, it is preferable that the amount of vinylene carbonate is less than 2% by volume based on the total amount of the nonaqueous solvent, and for example, it is preferable that the nonaqueous electrolyte does not contain vinylene carbonate.

Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2, 3-pentylene carbonate, cis-2,3-pentylene carbonate;

As lactones, γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

Examples of chain carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methylpropyl carbonate, methylisopropyl carbonate, dipropyl carbonate, methylbutyl carbonate, dibutyl carbonate, ethylpropyl carbonate, diisobutyl carbonate;

Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

Examples of alkoxy group-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile;

Examples of the dinitrile include malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, Dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dicyanodecane Talonitrile;

Examples of the cyclic nitrile include benzonitrile;

Examples of short chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelate, methyl caproate, ethyl acetate, and propionic acid. Ethyl, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, Propyl valerate, propyl pivalate, propyl hydroangelate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, isopropyl pivalate, isopropyl hydroangelate, caprone Isopropyl acid, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, Isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, isovaleric acid tert-butyl, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelate, and tert-butyl caproate;

Examples of chain ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

Examples of the fluorinated ether include, for example, Rf ²⁰ -OR ²¹ (wherein Rf ²⁰ represents an alkyl group containing a fluorine atom, and R ⁷ represents a monovalent organic group that may contain a fluorine atom). );

Ketones include, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

Examples of compounds in which some or all of the H atoms of the aprotic solvent are replaced with halogen atoms include, for example, compounds in which the halogen atoms are fluorine;
can be mentioned.

Here, examples of the fluorinated chain carbonate include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2, Examples include 2-trifluoroethyl carbonate and methyl 2,2,3,3-tetrafluoropropyl carbonate. The above fluorinated chain carbonate has the following general formula:
R ⁷ -O-C(O)OR ⁸
{wherein R ⁷ and R ⁸ are at least one selected from the group consisting of CH ₃ , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH(CH ₃ ) ₂ , and CH ₂ Rf ⁹ , Rf ⁹ is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R ⁷ and/or R ⁸ contain at least one fluorine atom. }
It can be expressed as

In addition, examples of fluorinated short-chain fatty acid esters include fluorinated esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Examples include short-chain fatty acid esters. The fluorinated short chain fatty acid ester has the following general formula:
R ¹⁰ -C(O)OR ¹¹
{In the formula, R ¹⁰ is CH ₃ , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH(CH ₃ ) ₂ , CF ₃ CF ₂ H, CFH ₂ , CF ₂ Rf ¹² , CFHRf ¹² , and CH ₂ at least one selected from the group consisting of Rf ¹³ , and R ¹¹ is selected from the group consisting of CH ₃ , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH(CH ₃ ) ₂ , and CH ₂ Rf ¹³ Rf ¹² is an alkyl group having 1 to 3 carbon atoms in which the hydrogen atom may be substituted with at least one fluorine atom, and Rf ¹³ is an alkyl group having at least one fluorine atom in which the hydrogen atom may be substituted. is a substituted alkyl group having 1 to 3 carbon atoms, and R ¹⁰ and/or R ¹¹ contain at least one fluorine atom, and when R ¹⁰ is CF ₂ H, R ¹¹ is not CH ₃ . }
It can be expressed as

The aprotic solvents other than acetonitrile in this embodiment may be used alone or in combination of two or more.

As the non-aqueous solvent in this embodiment, it is preferable to use acetonitrile together with one or more of a cyclic carbonate and a chain carbonate from the viewpoint of improving the stability of the non-aqueous electrolyte. From this point of view, it is more preferable to use a cyclic carbonate together with acetonitrile, and it is even more preferable to use both a cyclic carbonate and a chain carbonate together with acetonitrile as the nonaqueous solvent in this embodiment.

When using a cyclic carbonate with acetonitrile, it is particularly preferred that the cyclic carbonate comprises ethylene carbonate.

<1-2. Lithium salt>
The non-aqueous electrolyte of this embodiment preferably contains LiPF ₆ , and other lithium salts are not particularly limited. For example, the lithium salt preferably contains at least one selected from the group consisting of LiPF ₆ and lithium-containing imide salts. According to this, the effects of the present invention can be easily achieved.

The lithium-containing imide salt is a lithium salt represented by LiN(SO ₂ C _m F _2m+1 ) ₂ [where m is an integer from 0 to 8], and specifically, LiN(SO ₂ F ) ₂ and LiN(SO ₂ CF ₃ ) ₂ . It may contain only one or both of these imide salts. It may contain imide salts other than these imide salts.

In this embodiment in which the non-aqueous solvent contains acetonitrile, the saturated concentration of the lithium-containing imide salt with respect to acetonitrile is higher than the saturation concentration of LiPF ₆ , so the lithium-containing imide salt is used at a molar concentration such that LiPF ₆ ≦lithium-containing imide salt. It is preferable to include , since association and precipitation of lithium salt and acetonitrile at low temperatures can be suppressed. Further, it is preferable from the viewpoint of the amount of ions supplied that the content of the lithium-containing imide salt is 0.5 mol or more and 3 mol or less per 1 L of the nonaqueous solvent. According to an acetonitrile-containing non-aqueous electrolytic solution containing at least one of LiN(SO ₂ F) ₂ and LiN(SO ₂ CF ₃ ) ₂ , ion conduction at low temperatures such as -10°C or -30°C is possible. It is possible to effectively suppress the reduction in the rate and obtain excellent low-temperature properties. By limiting the content in this way, it is also possible to more effectively suppress the increase in resistance during high-temperature heating.

Further, the lithium salt may further contain a fluorine-containing inorganic lithium salt other than LiPF ₆ , for example, LiBF ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiSbF ₆ , Li ₂ B ₁₂ F _b H _12-b [in the formula , b is an integer of 0 to 3]. "Inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom as an anion and is soluble in acetonitrile. Furthermore, the term "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in its anion, contains a fluorine atom in its anion, and is soluble in acetonitrile. The fluorine-containing inorganic lithium salt is excellent in that it forms a passive film on the surface of the metal foil, which is the positive electrode current collector, and suppresses corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts may be used alone or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable. Among them, it is more preferable to use a fluorine-containing inorganic lithium salt having a phosphorus atom because it facilitates the release of free fluorine atoms. A typical fluorine-containing inorganic lithium salt is _LiPF6 , which dissolves to release the _PF6 anion. When a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferable because it becomes easier to trap excess free acid components that may cause battery deterioration. Particularly preferred is _LiBF4 .

The content of the fluorine-containing inorganic lithium salt in the nonaqueous electrolyte of this embodiment is not particularly limited, but it is preferably 0.01 mol or more, and 0.02 mol or more per 1 L of nonaqueous solvent. is more preferable, and even more preferably 0.03 mol or more. When the content of the fluorine-containing inorganic lithium salt is within the above range of 0.01 mol or more, the ionic conductivity tends to increase and high output characteristics can be exhibited. Further, the content of the fluorine-containing inorganic lithium salt is preferably less than 1.5 mol, more preferably less than 0.5 mol, and even more preferably less than 0.1 mol per liter of nonaqueous solvent. . When the content of the fluorine-containing inorganic lithium salt is within the above-mentioned range of less than 1.5 mol, the ionic conductivity increases and high output characteristics can be expressed, and the decrease in ionic conductivity due to the increase in viscosity at low temperatures can be suppressed. There is a tendency that the high temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery can be made even better while maintaining the excellent performance of the non-aqueous electrolyte.

The non-aqueous electrolyte of this embodiment may further contain an organic lithium salt. "Organolithium salt" refers to a lithium salt that contains a carbon atom as an anion and is soluble in acetonitrile.

Examples of the organic lithium salt include organic lithium salts having an oxalate group. Specific examples of organic lithium salts having an oxalate group include LiB(C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiPF ₄ (C ₂ O ₄ ), and LiPF ₂ (C ₂ O ₄ ) At least one lithium salt selected from the lithium salts represented by LiB(C ₂ O ₄ ) ₂ and LiBF ₂ (C ₂ O ₄ ), including organic lithium salts represented by each of ₂ ). is preferred. Moreover, it is more preferable to use one or more of these together with a fluorine-containing inorganic lithium salt. This organic lithium salt having an oxalic acid group may be added to the non-aqueous electrolyte solution or may be contained in the negative electrode (negative electrode active material layer).

The amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte is 0.005 mol per 1 L of the non-aqueous solvent of the non-aqueous electrolyte, from the viewpoint of ensuring better effects from its use. It is preferably at least 0.02 mol, more preferably at least 0.05 mol, even more preferably at least 0.05 mol. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, there is a risk of precipitation. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte is preferably less than 1.0 mol per 1 L of the non-aqueous solvent of the non-aqueous electrolyte, and 0.5 More preferably, it is less than 0.2 mol, and even more preferably less than 0.2 mol.

It is known that organic lithium salts having an oxalic acid group are poorly soluble in organic solvents with low polarity, particularly in chain carbonates. Organic lithium salts with oxalate groups may contain trace amounts of lithium oxalate, and furthermore, when mixed as a non-aqueous electrolyte, they may react with trace amounts of water contained in other raw materials. , new white precipitates of lithium oxalate may be generated. Therefore, the content of lithium oxalate in the non-aqueous electrolyte of the present embodiment is not particularly limited, but is preferably 0 to 500 ppm.

As the lithium salt in this embodiment, in addition to those listed above, a lithium salt generally used for non-aqueous secondary batteries may be added as an auxiliary. Specific examples of other lithium salts include inorganic lithium salts that do not contain fluorine atoms in their anions, such as LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiB ₁₀ Cl ₁₀ , chloroborane Li; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiC _n F _(2n+1) SO ₃ {in the formula, n≧2}, lower aliphatic carboxylic acid Li, tetraphenylborate Li _{, LiB} ( _{C 3} O ₄ H _{2 ) 2} , _{and other} organic lithium salts; and p is an integer of 1 to 8]; an organic lithium salt represented by LiBF _q (C _s F _2s+1 ) _4-q such as LiBF ₃ (CF ₃ ); and s is an integer of 1 to 8]; lithium salt combined with a polyvalent anion;
The following formula (a):
LiC ⁽ _SO2RA )( ^SO2RB )( _SO2RC ) ⁽ a ₎
{In the formula, R ^A , R ^B , and R ^C may be the same or different from each other and represent a perfluoroalkyl group having 1 to 8 carbon atoms. },
The following formula (b):
LiN(SO ₂ OR ^D ) (SO ₂ OR ^E ) (b)
{In the formula, R ^D and R ^E may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms. }, and the following formula (c)
_{LiN(SO2RF)(SO2ORG )} ^{( c} )
{In the formula, R ^F and R ^G may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms. }
Examples include organic lithium salts represented by the following, and one or more of these can be used together with a fluorine-containing inorganic lithium salt.

｛式中、Ｒ^１及びＲ^２はそれぞれ独立して、ハロゲン基、又はハロゲン原子で置換されていてもよいアルキル基を示す。）で表されるスルホン化合物を含む。 <1-3. Sulfonated compound>
In addition to the non-aqueous solvent and lithium salt described above, the non-aqueous electrolyte according to the present embodiment has the following general formula (1):

{In the formula, R ¹ and R ² each independently represent a halogen group or an alkyl group optionally substituted with a halogen atom. ) Contains sulfone compounds represented by

The sulfone compound represented by the above formula (1) forms a protective film on the surface of the negative electrode by forming a polymer through a radical polymerization reaction of the phenyl group. Substitution of a functional group to a phenyl group changes the reactivity of the sulfone. Examples of such compounds include diphenylsulfone, dichlorodiphenylsulfone, difluorodiphenylsulfone, ditolylsulfone, diethyldiphenylsulfone, di-n-butylsulfone, di-iso-butylsulfone, and the like. Among these, diphenyl sulfone is preferred from the viewpoint of having little steric hindrance and not hindering SEI construction.

The content of the sulfone compound represented by the formula (1) in this embodiment is within the range of 0.1% by mass or more and 3% by mass or less based on the total amount of the nonaqueous electrolyte. The lower limit of the content of the sulfone compound represented by the formula (1) is preferably 0.3% by mass, more preferably 0.5% by mass or more based on the total amount of the nonaqueous electrolyte. Further, the upper limit of the content of the sulfone compound is more preferably 2% by mass or less based on the total amount of the non-aqueous electrolyte from the viewpoint of suppressing internal resistance. By adjusting the content of the sulfone compound represented by the formula (1) within the above range, even better battery characteristics can be added without impairing the basic functions as a non-aqueous secondary battery. This tends to be possible, and the effects of the present invention can be easily achieved.

<Ionic conductivity>
The non-aqueous electrolyte of this embodiment has an ionic conductivity of 12 mS/cm or more at 25°C. When the ionic conductivity is 12 mS/cm or more, high output characteristics can be sufficiently exhibited. The ionic conductivity can be controlled by adjusting the various raw materials and their contents listed in the Examples Table, and the upper limit thereof may be, for example, 30 mS/cm. Ionic conductivity can be measured, for example, by the following method:
Connect a platinum electrical conductivity cell CT-58101B (trade name) manufactured by TOADKK Corporation to an electrical conductivity meter CM-41M (trade name) manufactured by TOADKK Corporation, and add the electrical conductivity cell to 5 mL of electrolyte at 25°C. It can be measured by soaking in water and checking the conductivity at that time.

<10 seconds discharge DCIR and 10 seconds discharge DCIR change rate>
The nonaqueous electrolyte of this embodiment has the following formula (1-1):
10 seconds discharge DCIR = (voltage change for 10 seconds after the start of discharge) / (discharge current value for 10 seconds after the start of discharge) ...Formula (1-1)
Regarding the 10-second discharge DCIR expressed by the following formula (1-2) before and after storage at 85°C and 12 hours:
10-second discharge DCIR change rate = (10-second discharge DCIR after storage at 85°C)/(10-second discharge DCIR before storage at 85°C) ...Formula (1-2)
The 10-second discharge DCIR change rate expressed by is greater than 0 and less than or equal to 1.3.

Here, the fact that the 10-second discharge DCIR change rate is more than 0 and less than 1.3 means that deterioration of the negative electrode can be suppressed and side reactions can be suppressed even with a thermal history of 85°C and 12 hours. do. Specific methods for measuring the 10-second discharge DCIR and the 10-second discharge DCIR change rate are as described in Examples.

<Other electrode protection additives>
Other electrode protective additives are not particularly limited as long as they do not impede the problem solving of the present invention; (However, acetonitrile and sulfone compounds are excluded). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte and non-aqueous secondary battery in this embodiment, but it also includes substances that are not directly involved in electrochemical reactions. .

Specific examples of other electrode protective additives include lactones represented by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone; - Cyclic ethers represented by dioxane; chain acid anhydrides represented by acetic anhydride, propionic anhydride, benzoic anhydride; malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride , 1,2-cyclohexanedicarboxylic anhydride, 2,3-naphthalene dicarboxylic anhydride, or cyclic acid anhydride represented by naphthalene-1,4,5,8-tetracarboxylic dianhydride; 2 different Examples include mixed acid anhydrides that have a structure in which different types of acids, such as different types of carboxylic acids, are dehydrated and condensed. These may be used alone or in combination of two or more.

The content of the electrode protection additive in the non-aqueous electrolyte in this embodiment is not particularly limited, but the content of the electrode protection additive in the total amount of the non-aqueous solvent is 0.1 to 30% by volume. The content is preferably from 0.3 to 15% by volume, and even more preferably from 0.5 to 4% by volume.

In this embodiment, the higher the content of the electrode protection additive, the more the deterioration of the non-aqueous electrolyte can be suppressed. However, the lower the content of the electrode protection additive, the better the high output characteristics of the non-aqueous secondary battery in a low-temperature environment. Therefore, by adjusting the content of the electrode protection additive within the above range, it is possible to achieve excellent performance based on the high ionic conductivity of the non-aqueous electrolyte without impairing the basic functions of a non-aqueous secondary battery. They tend to be able to maximize performance. By preparing a nonaqueous electrolyte with such a composition, it is possible to improve the cycle performance of a nonaqueous secondary battery, high output performance in a low-temperature environment, and other battery characteristics. be.

<Other optional additives>
In this embodiment, for example, sulfonic acid ester is added to the non-aqueous electrolyte for the purpose of improving the charge/discharge cycle characteristics, high-temperature storage properties, and safety (for example, preventing overcharging) of the non-aqueous secondary battery. , diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphoric acid ester [ethyl diethylphosphonoacetate (EDPA): (C ₂ H ₅ O) ₂ (P=O)-CH ₂ (C=O )OC ₂ H ₅ , tris(trifluoroethyl) phosphate (TFEP): (CF ₃ CH ₂ O) ₃ P=O, triphenyl phosphate (TPP): (C ₆ H ₅ O) ₃ P=O: (CH ₂ =CHCH ₂ O) ₃ P=O, triallyl phosphate, etc.], nitrogen-containing cyclic compounds with no steric hindrance around lone pairs [pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc. ], etc., and derivatives of these compounds, etc., may be included as appropriate. In particular, phosphoric acid esters are effective in suppressing side reactions during storage.

The content of other optional additives in this embodiment is calculated as a mass percentage with respect to the total mass of all components constituting the non-aqueous electrolyte. The content of other optional additives is not particularly limited, but is preferably in the range of 0.01% by mass or more and 10% by mass or less, and 0.02% by mass or more based on the total amount of the non-aqueous electrolyte. It is more preferably 5% by mass or less, and even more preferably 0.05% by mass or more and 3% by mass or less. By adjusting the content of other optional additives within the above range, it tends to be possible to add even better battery characteristics without impairing the basic functions of a non-aqueous secondary battery. be.

<2. Positive electrode and positive electrode current collector>
The positive electrode 150 shown in FIGS. 1 and 2 is composed of a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The positive electrode 150 is not particularly limited as long as it functions as a positive electrode for a non-aqueous secondary battery, and may be any known electrode. The positive electrode active material in the present invention is preferably a composite oxide of lithium and a transition metal, and preferably contains nickel (Ni) in a relatively high proportion.

It is preferable that the positive electrode active material layer contains a positive electrode active material, and further contains a conductive aid and a binder as necessary.

The positive electrode active material layer preferably contains, as the positive electrode active material, a material capable of intercalating and deintercalating lithium ions. The use of such materials is preferred because they tend to provide high voltages and high energy densities.

Examples of the positive electrode active material include positive electrode active materials containing at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and have the following general formula (a):
Li _p Ni _{q Cor} Mn _s M _t O _u ...(a)
{In the formula, M is aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn) , molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and 0<p<1.3, 0<q<1 .2, 0<r<1.2, 0≦s<0.5, 0≦t<0.3, 0.7≦q+r+s+t≦1.2, 1.8<u<2.2. , and p are values determined by the charging/discharging state of the battery. }
At least one kind of Li-containing metal oxide selected from the lithium (Li)-containing metal oxides represented by is suitable.

Specific examples of positive electrode active _materials include, for _example , lithium _cobalt oxide represented by _LiCoO2 ; lithium manganese oxide represented by _LiMnO2 , _LiMn2O4 , and _Li2Mn2O4 ; and Lithium manganese oxide represented by _LiNiO2 . Lithium nickel oxide; represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Co _0.2 O ₂ Li _z MO ₂ (wherein M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and includes at least one transition metal element selected from the group consisting of Ni, Mn, Co, Al, and Mg) Examples include lithium-containing composite metal oxides represented by two or more selected metal elements, and z is a number greater than 0.9 and less than 1.2.

In particular, when the Ni content ratio q of the Li-containing metal oxide expressed by the general formula (a) is 0.5<q<1.2, it is possible to reduce the amount of Co used, which is a rare metal, and to achieve high energy consumption. This is preferred because both densification and densification are achieved. Examples of such positive electrode active materials include LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.75 Co _0.15 Mn _0.15 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.85 Co _0.075 Mn _0.075 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.81 Co _0.1 Al _0.09 O ₂ , LiNi _0.85 Co _0.1 Al _0.05 O ₂ , and the like are lithium-containing composite metal oxides.

On the other hand, as the Ni content ratio increases in the positive electrode active material layer, deterioration tends to progress at lower voltages. The Li-containing metal oxide cathode active material represented by general formula (a) essentially has active sites that oxidize and degrade the non-aqueous electrolyte, but these active sites are added to protect the negative electrode. The compound may be unintentionally consumed on the positive electrode side. Among them, acid anhydrides tend to be easily affected. In particular, when acetonitrile is contained as a non-aqueous solvent, the effect of adding an acid anhydride is tremendous, so consumption of the acid anhydride on the positive electrode side is a fatal problem.

Furthermore, these additive decomposition products taken into and deposited on the positive electrode side not only cause an increase in the internal resistance of the non-aqueous secondary battery, but also accelerate the deterioration of the lithium salt. Furthermore, the protection of the negative electrode surface, which was the original purpose, becomes insufficient. In order to deactivate the active sites that essentially cause oxidative deterioration of the non-aqueous electrolyte, it is important to control Jahn-Teller distortion or coexist with a component that plays a role as a neutralizer. Therefore, it is preferable that the positive electrode active material contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

For the same reason, the surface of the positive electrode active material is preferably coated with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Further, it is more preferable that the surface of the positive electrode active material is coated with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Furthermore, the surface of the positive electrode active material is coated with at least one oxide selected from the group consisting of ZrO ₂ , TiO ₂ , Al ₂ O ₃ , NbO ₃ , and LiNbO ₂ to prevent the permeation of lithium ions. It is particularly preferable because it does not inhibit.

The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxide represented by formula (a), and is not particularly limited as long as it contains lithium. Examples of such lithium-containing compounds include composite oxides containing lithium and a transition metal element, metal chalcogenides containing lithium, metal phosphate compounds containing lithium and a transition metal element, and lithium and transition metal elements. Examples include metal silicate compounds containing. From the viewpoint of obtaining higher voltage, the lithium-containing compound is particularly composed of lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti. A metal phosphate compound containing the following is preferred.
More specifically, the lithium-containing compound is the following formula (Xa):
_Liv M ^I D ₂ (Xa)
{In the formula, D represents a chalcogen element, M ^I represents one or more transition metal elements including at least one transition metal element, and the value of v is determined by the charging/discharging state of the battery, and is from 0.05 to 1. Shows the number of 10. },
The following formula (Xb):
Li _w M ^II PO ₄ (Xb)
{In the formula, M ^II represents one or more transition metal elements including at least one transition metal element, and the value of w is determined by the charging/discharging state of the battery, and is a number from 0.05 to 1.10. show. }, and the following formula (Xc):
Li _t M ^III _u SiO ₄ (Xc)
{In the formula, M ^III represents one or more transition metal elements including at least one transition metal element, and the value of t is determined by the charging/discharging state of the battery, and is a number from 0.05 to 1.10. and u represents a number from 0 to 2. }
Examples include compounds represented by each of the following.

The lithium-containing compound represented by the above formula (Xa) has a layered structure, and the compounds represented by the above formulas (Xb) and (Xc) have an olivine structure. These lithium-containing compounds are compounds in which a part of the transition metal element is replaced with Al, Mg, or other transition metal elements, or in which these metal elements are included in the grain boundaries, for the purpose of stabilizing the structure. It may also be one in which some of the oxygen atoms are replaced with fluorine atoms or the like, or one in which at least a portion of the surface of the positive electrode active material is coated with another positive electrode active material.

As the positive electrode active material in this embodiment, only the above-described lithium-containing compound may be used, or the lithium-containing compound and other positive electrode active materials may be used together.

Examples of such other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and layered structure; sulfur; conductive polymers, and the like. Examples of metal oxides or metal chalcogenides having a tunnel structure and layered structure include MnO ₂ , FeO ₂ , FeS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , MoS ₂ , and NbSe. Examples include oxides, sulfides, and selenides of metals other than lithium, as represented by ₂ . Examples of the conductive polymer include conductive polymers typified by polyaniline, polythiophene, polyacetylene, and polypyrrole.

The above-mentioned other positive electrode active materials may be used alone or in combination of two or more, and are not particularly limited. However, since it is possible to reversibly and stably insert and release lithium ions and to achieve high energy density, the positive electrode active material layer is made of at least one transition metal element selected from Ni, Mn, and Co. It is preferable to contain.

When a lithium-containing compound and another cathode active material are used together as a cathode active material, the proportion of both used is preferably 80% by mass or more, and the proportion of the lithium-containing compound relative to the total of the cathode active material is preferably 80% by mass or more, and 85% by mass. % or more is more preferable.

Examples of the conductive aid include graphite, acetylene black, carbon black represented by Ketjen black, and carbon fiber. The content of the conductive additive is preferably 10 parts by mass or less, more preferably 1 to 5 parts by mass, based on 100 parts by mass of the positive electrode active material.

Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content of the binder is preferably 6 parts by mass or less, more preferably 0.5 to 4 parts by mass, based on 100 parts by mass of the positive electrode active material.

The positive electrode active material layer is formed by applying a positive electrode mixture-containing slurry, which is prepared by dispersing a positive electrode mixture in a solvent, in which a positive electrode active material is mixed with a conductive additive and a binder as necessary, onto a positive electrode current collector and drying (removing the solvent). ) and press as necessary. There are no particular limitations on such a solvent, and conventionally known solvents can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like.

The positive electrode current collector is made of, for example, metal foil such as aluminum foil, nickel foil, or stainless steel foil. The surface of the positive electrode current collector may be coated with carbon, or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

<3. Negative electrode and negative electrode current collector>
The negative electrode 160 shown in FIGS. 1 and 2 is composed of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode 160 can function as a negative electrode of a non-aqueous secondary battery.

The negative electrode active material layer preferably contains a negative electrode active material and, if necessary, a conductive aid and a binder.

Examples of negative electrode active materials include amorphous carbon (hard carbon), graphite (for example, artificial graphite, natural graphite, etc.), pyrolytic carbon, coke, glassy carbon, fired bodies of organic polymer compounds, mesocarbon microbeads, In addition to carbon materials such as carbon fibers, activated carbon, carbon colloids, and carbon black, metal lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, Examples include metal complexes and organic polymer compounds. One type of negative electrode active material may be used alone or two or more types may be used in combination. When the negative electrode active material is graphite, the positive electrode active material is preferably a composite oxide of lithium and a transition metal from the viewpoint of facilitating the effects of the present invention.

In the negative electrode active material layer, lithium ions are used as the negative electrode active material at a voltage of 0.4V vs. from the viewpoint of increasing the battery voltage. It is preferable to contain a material that can be occluded at a potential more base than Li/Li ⁺ .

Examples of the conductive aid include graphite, acetylene black, carbon black represented by Ketjen black, and carbon fiber. The content of the conductive additive is preferably 20 parts by mass or less, more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the negative electrode active material.

Examples of the binder include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Also included are diene rubbers such as styrene-butadiene rubber. The content of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass, based on 100 parts by mass of the negative electrode active material.

For the negative electrode active material layer, a negative electrode mixture-containing slurry in which a negative electrode mixture, which is a mixture of the negative electrode active material and a conductive aid and a binder as necessary, is dispersed in a solvent is applied to the negative electrode current collector and dried (solvent removal). It is then formed by pressing as necessary. There are no particular limitations on such a solvent, and conventionally known solvents can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like.

The negative electrode current collector is made of metal foil such as copper foil, nickel foil, stainless steel foil, etc., for example. Further, the surface of the negative electrode current collector may be coated with carbon, or may be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

<4. Separator＞
As shown in FIG. 2, the nonaqueous secondary battery 100 in this embodiment includes a separator 170 between the positive electrode 150 and the negative electrode 160 in order to prevent short circuit between the positive electrode 150 and the negative electrode 160, and to provide safety such as shutdown. It is preferable to have one. The separator 170 is not limited to one, but may be the same as those used in known non-aqueous secondary batteries, and may be an insulating thin film with high ion permeability and excellent mechanical strength. preferable. Examples of the separator 170 include woven fabrics, nonwoven fabrics, and microporous synthetic resin membranes, among which microporous synthetic resin membranes are preferred.

As the synthetic resin microporous membrane, for example, a polyolefin microporous membrane, such as a microporous membrane containing polyethylene or polypropylene as a main component, or a microporous membrane containing both of these polyolefins, is suitably used. Examples of the nonwoven fabric include porous membranes made of heat-resistant resins such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, and aramid.

The separator 170 may have a structure in which one type of microporous membrane is laminated in a single layer or a plurality of layers, or it may be in a configuration in which two or more types of microporous membranes are laminated. The separator 170 may have a single layer or a plurality of laminated layers using a mixed resin material obtained by melting and kneading two or more types of resin materials.

For the purpose of imparting functionality, inorganic particles may be present on the surface or inside the separator, and other organic layers may be further coated or laminated. Moreover, it may contain a crosslinked structure. In order to improve the safety performance of non-aqueous secondary batteries, these methods may be combined as necessary.

By using such a separator 170, it is possible to achieve good input/output characteristics and low self-discharge characteristics, which are particularly required of the above-mentioned lithium ion batteries for high output applications.

The thickness of the microporous membrane that can be used as a separator is not particularly limited, but from the viewpoint of membrane strength it is preferably 1 μm or more, and from the viewpoint of permeability it is preferably 500 μm or less. The thickness of the microporous membrane is determined from the viewpoint that it will be used in high-power applications such as safety tests, which have a relatively high calorific value and require better self-discharge characteristics than conventional ones, and from the viewpoint of being used for winding with large battery winding machines. From the viewpoint of circularity, it is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 25 μm or less. The thickness of the microporous membrane is more preferably 15 μm or more and 25 μm or less when both short-circuit resistance and output performance are important, but when both high energy density and output performance are important. More preferably, the thickness is 10 μm or more and less than 15 μm.

The porosity of the microporous membrane that can be used as a separator is preferably 30% or more and 90% or less, more preferably 35% or more and 80% or less, and 40% or more, from the viewpoint of following the rapid movement of lithium ions at high output. It is more preferably 70% or less. In addition, if priority is given to improving output performance while ensuring safety, the porosity of the microporous membrane is particularly preferably 50% or more and 70% or less, emphasizing both short-circuit resistance performance and output performance. In this case, it is particularly preferably 40% or more and less than 50%.

The air permeability of a microporous membrane that can be used as a separator is preferably 1 sec/100 cm ³ or more and 400 sec/100 cm 3 or less, and 1 sec/100 cm ³ or more and 350 sec/100 cm ³ or less, from the viewpoint of balance with membrane thickness and porosity. More preferably, it is 100 cm ³ or less. In addition, when placing emphasis on both short-circuit resistance performance and output performance, the air permeability of the microporous membrane is particularly preferably 150 seconds/100 cm ³ or more and 350 seconds/100 cm ^{3 or} less, which allows output while ensuring safety. When priority is given to improving performance, a time of 100/100 cm ³ seconds or more and less than 150 seconds/100 cm ³ is particularly preferable. On the other hand, when a nonaqueous electrolyte with low ionic conductivity is combined with a separator within the above range, the rate at which lithium ions move is determined not by the structure of the separator but by the high ionic conductivity of the nonaqueous electrolyte. Therefore, the expected input/output characteristics tend not to be obtained. Therefore, the ionic conductivity of the nonaqueous nonaqueous electrolyte is 12 mS/cm or more, preferably 15 mS/cm or more, and more preferably 20 mS/cm or more. The ionic conductivity of the nonaqueous nonaqueous electrolyte may be 30 mS/cm or less. However, the preferred values of the film thickness, air permeability and porosity of the separator, and the ionic conductivity of the non-aqueous electrolyte are not limited to the above examples.

<5. Battery exterior＞
The structure of the battery exterior 110 of the non-aqueous secondary battery 100 shown in FIGS. 1 and 2 is not particularly limited, but for example, either a battery can or a laminate film exterior may be used. As the battery can, for example, a square, square tube, cylindrical, elliptical, flat, coin-shaped, or button-shaped metal can made of steel, stainless steel, aluminum, clad material, etc. can be used. . As the laminate film exterior body, for example, a laminate film having a three-layer structure of hot melt resin/metal film/resin can be used.

The laminate film exterior body is made by stacking two sheets with the hot melt resin side facing inward, or by folding them so that the hot melt resin side faces inward, and sealing the ends with heat sealing. It can be used as an exterior body. When using a laminate film exterior, connect the positive electrode lead body 130 (or the positive electrode terminal and the lead tab connected to the positive electrode terminal) to the positive electrode current collector, and connect the negative electrode lead body 140 (or the negative electrode terminal and the negative electrode terminal) to the negative electrode current collector. (lead tab) may be connected. In this case, the laminate film exterior body is sealed with the ends of the positive electrode lead body 130 and the negative electrode lead body 140 (or the lead tabs connected to the positive and negative electrode terminals, respectively) pulled out to the outside of the exterior body. Good too.

<6. Battery manufacturing method>
The non-aqueous secondary battery 100 in this embodiment includes the above-mentioned non-aqueous electrolyte, a positive electrode 150 having a positive electrode active material layer on one or both sides of the current collector, and a negative electrode active material layer on one or both sides of the current collector. It is produced by a known method using the negative electrode 160, the battery exterior 110, and, if necessary, the separator 170.

First, a laminate consisting of a positive electrode 150, a negative electrode 160, and, if necessary, a separator 170 is formed. for example:
A mode in which a long positive electrode 150 and a negative electrode 160 are wound in a laminated state with the long separator interposed between the positive electrode 150 and the negative electrode 160 to form a laminate having a wound structure;
An embodiment in which positive electrode sheets and negative electrode sheets obtained by cutting the positive electrode 150 and negative electrode 160 into a plurality of sheets having a certain area and shape are alternately laminated with separator sheets interposed therebetween to form a laminate having a laminate structure. ;
An embodiment in which a long separator is folded in a zigzag manner, and a laminate having a laminated structure is formed in which positive electrode sheets and negative electrode sheets are alternately inserted between the zigzag-folded separators;
etc. are possible.

Next, the above-described laminate is housed in the battery exterior 110 (battery case), and the non-aqueous electrolyte according to this embodiment is injected into the battery case, and the laminate is immersed in the non-aqueous electrolyte and sealed. By doing so, the non-aqueous secondary battery according to this embodiment can be manufactured.

Alternatively, an electrolyte membrane in a gel state may be prepared in advance by impregnating a base material made of a polymeric material with a non-aqueous electrolytic solution, and the sheet-shaped positive electrode 150, negative electrode 160, and electrolyte membrane, as well as the necessary After forming a laminate having a laminate structure using the separator 170 according to the requirements, the non-aqueous secondary battery 100 can also be manufactured by housing the laminate in the battery exterior 110.

Note that the electrodes are arranged such that there is a portion where the outer peripheral edge of the negative electrode active material layer and the outer peripheral edge of the positive electrode active material layer overlap, or there is a portion where the width is too small in a non-opposing portion of the negative electrode active material layer. If so designed, there is a risk that the charge/discharge cycle characteristics of the non-aqueous secondary battery will deteriorate due to positional displacement of the electrodes during battery assembly. Therefore, in the electrode body used in the nonaqueous secondary battery, it is preferable to fix the position of the electrode in advance with tape such as polyimide tape, polyphenylene sulfide tape, polypropylene (PP) tape, adhesive, or the like.

Due to its high ionic conductivity, the non-aqueous electrolyte that uses acetonitrile, as in this embodiment, causes lithium ions released from the positive electrode to diffuse throughout the negative electrode during the first charge of the non-aqueous secondary battery. There is a possibility that it will happen. In nonaqueous secondary batteries, the area of the negative electrode active material layer is generally larger than that of the positive electrode active material layer. However, if lithium ions are diffused and occluded to a portion of the negative electrode active material layer that does not face the positive electrode active material layer, the lithium ions will remain in the negative electrode without being released during the first discharge. Therefore, the contribution of the unreleased lithium ions becomes irreversible capacity. For these reasons, a non-aqueous secondary battery using a non-aqueous electrolyte containing acetonitrile may have low initial charge/discharge efficiency.

On the other hand, if the area of the positive electrode active material layer is larger than that of the negative electrode active material layer, or if both are the same, current concentration tends to occur at the edge of the negative electrode active material layer during charging, and lithium dendrites are generated. It becomes easier.

For the above reasons, there is no particular restriction on the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other, but it should be greater than 1.0 and less than 1.1. It is preferably greater than 1.002 and less than 1.09, still more preferably greater than 1.005 and less than 1.08, and more preferably greater than 1.01 and less than 1.08. Particularly preferred. In a non-aqueous secondary battery using a non-aqueous electrolyte containing acetonitrile, by reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other, Initial charge/discharge efficiency can be improved.

Reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other means that the portion of the negative electrode active material layer that does not face the positive electrode active material layer It means to limit the area ratio of a part. As a result, of the lithium ions released from the positive electrode during the first charge, the amount of lithium ions occluded in the part of the negative electrode active material layer that does not face the positive electrode active material layer (i.e., the amount of lithium ions released from the negative electrode during the first discharge) This makes it possible to reduce as much as possible the amount of lithium ions that reach irreversible capacity. Therefore, by designing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, the load characteristics of the battery by using acetonitrile can be improved. This makes it possible to increase the initial charging and discharging efficiency of the battery while also suppressing the formation of lithium dendrites.

Here, in the manufacturing method according to the present embodiment (the manufacturing method of a non-aqueous secondary battery), initial charging is performed at a charging rate of 0.1 C or more, assuming that the amount of current that can discharge the set capacity in 1 hour is 1 C. It is preferable to have a step. The non-aqueous secondary battery 100 according to the present embodiment can function as a battery when charged for the first time, but is stabilized by partially decomposing the non-aqueous electrolyte during the first charge. Although there is no particular restriction on the method of initial charging, it is preferable that the initial charging is performed at 0.1 to 0.3C. It is also preferable that the initial charging is performed via constant voltage charging in the middle. The constant current that discharges the designed capacity in one hour is 1C. By setting a long voltage range in which the lithium salt participates in the electrochemical reaction, a stable and strong SEI is formed on the surface of the electrode (negative electrode 160), which not only has the effect of suppressing the increase in internal resistance but also increases the reaction rate. The product is not firmly immobilized only on the negative electrode 160, and in some way, a good effect is exerted on members other than the negative electrode 160, such as the positive electrode 150 and the separator 170. Therefore, it is very effective to perform the initial charging in consideration of the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte.

The non-aqueous secondary battery 100 in this embodiment can also be used as a battery pack in which a plurality of non-aqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of managing the charging and discharging state of the battery pack, the working voltage range per battery pack is preferably 2 to 5 V, more preferably 2.5 to 5 V, and preferably 2.75 V to 5 V. Particularly preferred.

Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to the above embodiments. The present invention can be modified in various ways without departing from the gist thereof.

Hereinafter, the present invention will be explained in more detail with reference to Examples. The present invention is not limited to these examples. Unless otherwise specified, Examples were performed at room temperature.

(1) Preparation of nonaqueous electrolyte Under an inert atmosphere, acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate (EC), vinylene carbonate (VC), and ethylene sulfite (ES) were added as shown in Table 1. A non-aqueous solvent was added in the indicated volume and volume so that each compound had a predetermined concentration. Furthermore, non-aqueous electrolytes (S01 to S09) were prepared by mixing 0.3 mol of lithium hexafluorophosphate (LiPF ₆ ) and 1 mol of lithium bis(fluorosulfonyl)imide to 1 L of non-aqueous solvent. did. Furthermore, electrolytic solutions (S01) to (S09) were prepared by adding sulfone compounds to the predetermined concentrations shown in Table 1. The abbreviations of additives in Table 1 have the following meanings. Moreover, the mass % of the sulfone compound in Table 1 indicates the proportion to the total amount of the non-aqueous electrolyte.
(Sulfone compound)
Diphenylsulfone: DPS
Phenyl vinyl sulfone: PVS

(2) Preparation of non-aqueous secondary battery (2-1) Preparation of positive electrode (A) Complex oxide of lithium, nickel, manganese, and cobalt (LiNi _0.8 Mn _0.1 Co _0.1 O ₂ ), (B) acetylene black powder as a conductive aid, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed at a mass ratio of 94:3:3 to obtain a positive electrode mixture. Ta.

N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture so that the solid content was 68% by mass, and the mixture was further mixed to prepare a positive electrode mixture-containing slurry. On one side of an aluminum foil with a thickness of 15 μm and a width of 280 mm, which will serve as a positive electrode current collector, the slurry containing the positive electrode mixture is applied to a coating width of 240 to 250 mm, a coating length of 125 mm, and an uncoated length of 20 mm while adjusting the basis weight. The coating was applied using a three-roll transfer coater so that the coating pattern was as follows, and the solvent was removed by drying in a hot air drying oven. The obtained electrode roll was trimmed on both sides and dried under reduced pressure at 130° C. for 8 hours. Thereafter, the positive electrode (P2) consisting of the positive electrode active material layer and the positive electrode current collector was obtained by rolling with a roll press so that the density of the positive electrode active material layer was 2.7 g/cm ³ . The basis weight excluding the positive electrode current collector was 8.4 mg/cm ² .

(2-2) Preparation of negative electrode (a) Graphite powder as a negative electrode active material, (b) Carbon black powder (Super-P) as a conductive agent, (c) Polyvinylidene fluoride (PVDF) as a binder. were mixed at a solid content mass ratio of 90:3:7 to obtain a negative electrode mixture.

Water was added as a solvent to the obtained negative electrode mixture so that the solid content was 45% by mass, and the mixture was further mixed to prepare a negative electrode mixture-containing slurry. On one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which will serve as a negative electrode current collector, the slurry containing the negative electrode mixture is applied to a coating width of 240 to 250 mm, a coating length of 125 mm, and an uncoated length of 20 mm while adjusting the basis weight. The coating was applied using a three-roll transfer coater so that the coating pattern was as follows, and the solvent was removed by drying in a hot air drying oven. The obtained electrode roll was trimmed on both sides and dried under reduced pressure at 80° C. for 12 hours. Thereafter, it was rolled using a roll press so that the density of the negative electrode active material layer was 1.3 g/cm ³ to obtain a negative electrode (N1) consisting of a negative electrode active material layer and a negative electrode current collector. The basis weight excluding the negative electrode current collector was 5.4 mg/cm ² .

(2-3) Assembling a nonaqueous secondary battery A polypropylene gasket is set in a CR2032 type battery case (SUS304/Al clad), and the positive electrode obtained as described above is placed in the center of a disk with a diameter of 15.958 mm. The blank was punched out into a shape and set with the positive electrode active material layer facing upward. A glass fiber filter paper (manufactured by Advantech, GA-100) punched out into a disk shape with a diameter of 16.156 mm was set on top of it, and 150 μL of the non-aqueous electrolyte was injected, and then the sample was obtained as described above. A negative electrode punched out into a disk shape with a diameter of 16.156 mm was set with the negative electrode active material layer facing downward. After setting the spacer and spring, I fitted the battery cap and crimped it with a crimping machine. The overflowing electrolyte was wiped off with a cloth. The laminate was held at 25° C. for 12 hours to fully absorb the nonaqueous electrolyte into the laminate to obtain a coin-type nonaqueous secondary battery.

(3) Evaluation of non-aqueous secondary battery The coin-shaped non-aqueous secondary battery obtained as described above was first subjected to an initial charge/discharge treatment according to the procedure (3-1) below. Next, each coin-type non-aqueous secondary battery was evaluated according to the procedure (3-2). Note that charging and discharging was performed using a charging/discharging device ACD-M01A (trade name) manufactured by Asuka Electronics Co., Ltd. and a program constant temperature bath IN804 (trade name) manufactured by Yamato Scientific Co., Ltd.
Here, 1C means a current value that is expected to complete discharging in one hour when a fully charged battery is discharged at a constant current.

(3-1) Charging and discharging processing of non-aqueous secondary batteries Set the ambient temperature of the non-aqueous secondary batteries to 25°C, and perform initial charging at a constant current of 0.3 mA, which corresponds to 0.1 C, to 4.2 V. After reaching the voltage, it was discharged to 3.0V at a constant current of 0.09mA corresponding to 0.03C. Thereafter, charging was performed at a constant current corresponding to 0.1C, and charging was performed at a constant voltage of 4.2V until the current attenuated to 0.025C.

(3-2) Heat storage at 85°C for 12 hours Next, the non-aqueous secondary battery was taken out from the charging/discharging device, placed in a constant temperature bath set at 85°C, and left to stand for 12 hours.

(3-3) Measurement of DCIR change rate for 10 seconds before and after storage at 85°C Regarding small non-aqueous secondary batteries subjected to the initial charge/discharge treatment by the method described in (3-1) above, 0. The battery was charged to 4.2 V with a constant current of 0.3 mA corresponding to 1 C, and the 10 second discharge DCIR at 0.3 C discharge was measured at 25°C. After storage according to the method described in (3-2), the 10-second discharge DCIR at 0.3C discharge was measured at 50°C. The rate of change before and after storage was investigated using the following formula (1-2). Note that the voltage change for 10 seconds after the start of discharge was determined from the charging/discharging voltage value obtained with a charging/discharging device ACD-M01A manufactured by Asuka Electronics Co., Ltd.
Formula (1-1): 10 seconds discharge DCIR = (voltage change for 10 seconds after the start of discharge)/(discharge current value for 10 seconds after the start of discharge)
Formula (1-2): 10-second discharge DCIR change rate = (10-second discharge DCIR after storage at 85°C)/(10-second discharge DCIR before storage at 85°C)

(3-4) Non-aqueous secondary battery [Examples 1-2 and Comparative Examples 1-5]
Using each electrolytic solution shown in Table 1, a non-aqueous secondary battery was assembled according to the ionic conductivity and above, and the initial charge/discharge treatment and 10-second DCIR change rate were measured. Here, we will discuss the interpretation of each test result.

After thermal history is applied, the resistance value of the negative electrode increases due to the decomposition of SEI, which is a negative electrode protective film, and the accompanying deterioration of the electrode. The value of DCIR for 10 seconds after thermal history is preferably less than 23Ω, more preferably less than 21Ω. The rate of change in 10-second DCIR is 1.3 or less (for example, 1.30 or less), and preferably 1.2 or less (for example, 1.20 or less). Here, the influence of side reactions will be examined by comparing the resistances of batteries using electrolytes S01, S03, S04, S06, S07, and S08 with electrolyte S05 that does not contain a sulfone compound. Table 2 shows the measurement results.

As shown in Table 2, in Examples 1 to 2 and Comparative Examples 1 to 5, it was confirmed that the acetonitrile-containing electrolyte had a high ionic conductivity of 14.0 mS/cm or more. Further, in the example in which DPS was added up to 2% by mass, the 10-second DCIR change rate was 1.15, and it was revealed that when the amount added was increased to 4% by mass, the change rate increased to 1.67. In Comparative Example 2, the 10-second DCIR change rate in the electrolytic solution without additives was 2.52, which indicates that by adding up to 2% by mass of DPS, side reactions can be suppressed while suppressing negative electrode deterioration. It was confirmed that no effect was observed. In Comparative Examples 3 and 5, it was confirmed that the 10 second DCIR change rate increased by adding vinylene carbonate. It was also confirmed from Comparative Example 4 that the combination of vinylene carbonate and ethylene sulfite had better thermal durability than the combination of vinylene carbonate and ethylene sulfite.

From the above, it is considered that in the examples, by adding an appropriate amount of the sulfone compound, the increase in negative electrode resistance due to thermal history is suppressed, and the battery operates stably.

(3-5) 50°C cycle test For non-aqueous secondary batteries that have been subjected to initial charge/discharge treatment using the method described in (3-1) above, the ambient temperature is set to 50°C, and a constant voltage of 6 mA corresponding to 2C is applied. After the current reached 4.2V, charging was performed at a constant voltage of 4.2V until the current attenuated to 0.025C, and once discharged to 3V at a current value of 0.9mA corresponding to 0.3C. Thereafter, the battery was charged in the same manner as above, and a charge/discharge test was conducted for 100 cycles in which the battery was discharged to 3V at a current value of 6 mA corresponding to 2C.

The discharge capacity of each cycle during the cycle test was calculated as the capacity retention rate, with the discharge capacity of the first cycle during the cycle test being taken as 100%.

(3-6) Nonaqueous secondary battery [Examples 3 to 5 and Comparative Examples 6 to 11]
Using each electrolytic solution shown in Table 1, a non-aqueous secondary battery was assembled as described above, and an initial charge/discharge treatment and a cycle test were performed. Here, we will discuss the interpretation of each test result.

The capacity retention rate is an index indicating the ratio of the discharge capacity in each cycle to the discharge capacity in the first cycle. In the above cycle test, charging and discharging are repeated at a higher current density than in a general cycle test, and the larger the value, the less the capacity deterioration occurs when the battery is repeatedly used for charging and discharging. Further, if the capacity retention rate increases during the cycle, this is not preferable because it suggests that the state of the electrode surface is not stable. The capacity retention rate is preferably 85% or more (e.g., 85.0% or more), more preferably 86% or more (e.g., 86.0% or more), and more preferably 87% or more (e.g., 87.0% or more). More preferably.

In Examples 3 to 5, it was confirmed that the capacity retention rate at the 100th cycle exceeded 87.0% by adding 0.5 to 2.0% by mass of DPS. On the other hand, in Comparative Example 6, it was also confirmed that the capacity retention rate decreased when the amount of DPS added was 4% by mass. In Comparative Example 7, it was confirmed that the addition of DPS improved cycle performance. In Comparative Example 8, the capacity retention rate increased at the 10th cycle and became unstable. This is because SEI was decomposed due to high-temperature storage, and power was then consumed to reform SEI in the 1st to 9th cycles. This confirms that the addition of DPS improves heat resistance. It was confirmed that Comparative Example 9 was superior in thermal stability to the composition that was considered suitable in Patent Document 3. In Comparative Example 10, as in Comparative Example 8, the capacity retention rate exceeded 100% at the 10th cycle, and instability in the initial cycle was confirmed. In Comparative Example 11, with the phenylvinylsulfone-added electrolytic solution, the electrolytic solution decomposed during the first charge, so charging and discharging could not be performed, and it is clear that the diphenylsulfone substituted product is effective in forming a thermally stable SEI. became. This is presumably due to the fact that the anion radical of the diphenylsulfone substituted product is relatively stable.

From the above results, in the example, it was confirmed that by adding a sulfone compound with a specific structure such as DPS to a nonaqueous solvent, a nonaqueous secondary battery with thermal stability and excellent cycle performance can be provided. Ta.

(3-7) Low rate initial charging/discharging For coin-type nonaqueous batteries containing electrolytes S1 to S3, initial charging at a lower rate than (3-1) was investigated (Comparative Examples 12 to 14). Set the ambient temperature of the non-aqueous secondary battery to 25°C, perform initial charging with a constant current of 0.075mA corresponding to 0.025C, and after reaching 4.2V, charge at 0.09mA equivalent to 0.03C. After reaching 3.0V by discharging at a constant current of , the battery was charged at a constant current corresponding to 0.1C until the current attenuated to 0.025C at a constant voltage of 4.2V. Thereafter, high-temperature storage and cycle tests were performed using the methods described in (3-2) and (3-4) to evaluate the respective capacity retention rates.

In Examples 3 to 5, a high capacity retention rate of 87.0% or more was obtained after 100 cycles, whereas in Comparative Examples 12 to 14, in which the initial charge was performed at 0.025C, the concentration of diphenyl sulfone was It was confirmed that the capacity retention rate at 100 cycles was 50.0% or less regardless of the conditions. Furthermore, in Comparative Examples 12 to 14, the capacity retention rate decreased even at the initial stage of the 10th cycle, suggesting that precise SEI construction was not possible during the initial charge/discharge. This is considered to be because all the diphenyl sulfone was consumed during the first low rate charge of 0.1 C or less, and defects were created in SEI as the active material expanded during the subsequent charging and discharging process.

From the above, it is considered that in the examples, by adding an appropriate amount of diphenyl sulfone and appropriate initial charging, the increase in negative electrode resistance due to heat storage is suppressed and the battery operates stably.

The nonaqueous secondary battery of the present invention can be used, for example, as a storage battery for automobiles such as hybrid cars, plug-in hybrid cars, and electric cars, as well as industrial storage batteries for power tools, drones, electric motorcycles, etc., and even as a residential electricity storage system. is also expected to be used.

100 Nonaqueous secondary battery 110 Battery exterior 120 Space of battery exterior 130 Positive electrode lead body 140 Negative electrode lead body 150 Positive electrode 160 Negative electrode 170 Separator

Claims (8)

A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The non-aqueous electrolyte includes a non-aqueous solvent containing acetonitrile, a lithium salt,
General formula (1) below:

{In the formula, R ₁ and R ₂ each independently represent a halogen group or an alkyl group optionally substituted with a halogen atom. ) a sulfone compound represented by
The content of the sulfone compound is 0.1% by mass or more and 3% by mass or less with respect to the total amount of the nonaqueous electrolyte,
The ionic conductivity of the non-aqueous electrolyte at 25° C. is 12 mS/cm or more and 30 mS/cm or less,
The following formula (1-1):
10 seconds discharge DCIR = (voltage change for 10 seconds after the start of discharge) / (discharge current value for 10 seconds after the start of discharge) ...Formula (1-1)
Regarding the 10-second discharge DCIR expressed by the following formula (1-2) before and after storage at 85°C and 12 hours:
10-second discharge DCIR change rate = (10-second discharge DCIR after storage at 85°C)/(10-second discharge DCIR before storage at 85°C) ...Formula (1-2)
The 10-second discharge DCIR change rate expressed by is more than 0 and less than 1.3,
Non-aqueous secondary battery. The nonaqueous secondary battery according to claim 1, wherein vinylene carbonate is less than 2% by volume based on the total amount of the nonaqueous solvent. The nonaqueous secondary battery according to claim 1 or 2, wherein the content of the acetonitrile is 10 to 60% by volume with respect to the total amount of the nonaqueous solvent in the nonaqueous electrolyte. The nonaqueous secondary battery according to any one of claims 1 to 3, wherein the lithium salt is at least one selected from the group consisting of a lithium-containing imide salt and lithium hexafluorophosphate (LiPF ₆ ). The non-aqueous secondary battery according to any one of claims 1 to 4, comprising diphenyl sulfone as the sulfone compound represented by the general formula (1). The positive electrode contains one or more materials selected from the group consisting of materials capable of inserting and releasing lithium ions as a positive electrode active material, and the negative electrode contains and releasing lithium ions as a negative electrode active material. The non-aqueous secondary battery according to any one of claims 1 to 5, comprising one or more materials selected from the group consisting of a material capable of oxidation, and metallic lithium. 7. The nonaqueous secondary battery according to claim 6, wherein the positive electrode active material is a composite oxide of lithium and a transition metal, and the negative electrode active material is graphite. A method for manufacturing a non-aqueous secondary battery according to any one of claims 1 to 7, comprising:
A method for manufacturing a non-aqueous secondary battery, comprising the step of initially charging at a charging rate of 0.1C or more, where 1C is the amount of current that can discharge a set capacity in 1 hour.

Images