JP2015097179A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery superior in safety and cycle characteristics.SOLUTION: A lithium ion secondary battery comprises: a negative electrode including a carbon material which lithium ions can go into and out of; a positive electrode; and an electrolyte. The electrolyte includes: 70 vol.% or more of a phosphorus compound expressed by a predetermined formula; 0.01-30 vol.% of a fluorinated carbonate compound; and metal ions having an oxidation-reduction potential at a potential higher than lithium by 1.0 V or more.

Description

  Embodiments according to the present invention relate to a secondary battery, and more particularly, to a lithium ion secondary battery.

  With the rapid market expansion of notebook PCs, mobile phones, electric cars, etc., secondary batteries with high energy density are required. However, the secondary battery has a problem in thermal stability when placed under a high temperature.

  In secondary batteries, the use of flame retardant materials is being studied to ensure safety. Patent Document 1 describes that an electrolyte solution containing a halogen-substituted phosphate compound exhibits a self-digesting action.

  In addition, in order to improve battery characteristics, development of an electrolytic solution used for a secondary battery is underway. Patent Document 2 describes a nonaqueous electrolytic solution containing a tin salt. Patent Document 3 describes an electrolytic solution containing metal ions implanted by immersing two different metals connected to an organic solvent by an electrically conductive material.

JP-A-8-88023 JP 2000-294274 A International Publication WO2011 / 102171

  However, when the electrolytic solution described in Patent Document 1 is used in a secondary battery including a carbon-containing negative electrode, the phosphoric ester compound is decomposed on the negative electrode, and the battery cannot operate or the cycle characteristics are extremely poor. There is a problem of becoming. This problem was particularly remarkable when the content of the phosphoric acid ester compound, which is a flame retardant material, is increased. The secondary battery described in Patent Document 2 has a problem in flame retardancy. Moreover, although it is described that the secondary battery described in Patent Document 3 can improve the cycle characteristics, there is a problem in characteristics at a high rate because the lithium salt concentration is high.

  The present invention relates to the following matters.

A lithium ion secondary battery comprising a negative electrode containing a carbon material capable of inserting / extracting lithium ions, a positive electrode, and an electrolyte solution,
The electrolyte is
70 vol% or more of the following formula (1):

｛式（１）中、Ｒ^１、Ｒ^２およびＲ^３は、それぞれ独立して、水素原子、アルキル基、ハロゲン化アルキル基、アルケニル基、ハロゲン化アルケニル基、アリール基、オキサアルキル基［−Ｒ⁴−Ｏ−Ｒ⁵（Ｒ⁴はアルキレン基を表し、Ｒ⁵はアルキル基またはハロゲン化アルキル基を表す）］、シクロアルキル基、ハロゲン化シクロアルキル基、シリル基、ヒドロキシ基、アルコキシ基、ハロゲン化アルコキシ基、アルケニルオキシ基、ハロゲン化アルケニルオキシ基、アリールオキシ基、オキサアルキルオキシ基［−Ｏ−Ｒ⁶−Ｏ−Ｒ⁷（Ｒ⁶はアルキレン基を表し、Ｒ⁷はアルキル基またはハロゲン化アルキル基を表す）］、シクロアルキルオキシ基、ハロゲン化シクロアルキルオキシ基またはシリルオキシ基であり、Ｒ^１、Ｒ^２およびＲ^３は、いずれか２つまたは全てが結合した環状構造を形成していてもよい。ただし、Ｒ^１、Ｒ^２およびＲ^３のうち少なくとも１つが、水素原子およびヒドロキシ基のいずれでもないものとする。｝
で表されるリン化合物と、
０．０１ｖｏｌ％以上３０ｖｏｌ％以下のフッ素化カーボネート化合物と、
リチウムに対して１．０Ｖ以上高い電位に酸化還元電位をもつ金属イオンとを含むことを特徴とする二次電池。

{In Formula (1), R ¹ , R ² and R ³ are each independently a hydrogen atom, alkyl group, halogenated alkyl group, alkenyl group, halogenated alkenyl group, aryl group, oxaalkyl group [-R ^4- O—R ⁵ (R ⁴ represents an alkylene group, R ⁵ represents an alkyl group or a halogenated alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group, a silyl group, a hydroxy group, an alkoxy group, a halogen Alkoxy group, alkenyloxy group, halogenated alkenyloxy group, aryloxy group, oxaalkyloxy group [—O—R ⁶ —O—R ⁷ (R ⁶ represents an alkylene group, R ⁷ represents an alkyl group or a halogenated group] represents an alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group or silyloxy group, R ^1, R ² Contact Fine R ³ may form either two or all bonded cyclic structures. However, at least one of R ¹ , R ² and R ³ is neither a hydrogen atom nor a hydroxy group. }
A phosphorus compound represented by:
0.01 vol% or more and 30 vol% or less of a fluorinated carbonate compound;
A secondary battery comprising a metal ion having a redox potential at a potential higher than 1.0 V with respect to lithium.

  According to this embodiment, a secondary battery excellent in safety and cycle characteristics can be provided.

FIG. 3 is a schematic cross-sectional view showing a structure of an electrode element included in a laminated laminate type secondary battery.

  Hereinafter, this embodiment will be described in detail.

  In the secondary battery according to this embodiment, an electrode element in which a positive electrode and a negative electrode are arranged to face each other, and an electrolytic solution are included in an outer package. The shape of the secondary battery may be any of a cylindrical type, a flat wound square type, a laminated square type, a coin type, a flat wound laminated type, and a laminated laminate type, and a laminated laminate type is preferable. Hereinafter, the laminated laminate type secondary battery will be described.

  FIG. 1 is a schematic cross-sectional view showing a structure of an electrode element included in a laminated laminate type secondary battery. This electrode element is formed by alternately stacking a plurality of positive electrodes c and a plurality of negative electrodes a with a separator b interposed therebetween. The positive electrode current collector e of each positive electrode c is welded to and electrically connected to each other at an end portion not covered with the positive electrode active material, and a positive electrode terminal f is welded to the welded portion. The negative electrode current collector d of each negative electrode a is welded and electrically connected to each other at an end portion not covered with the negative electrode active material, and a negative electrode terminal g is welded to the welded portion.

  Since the electrode element having such a planar laminated structure does not have a portion with a small R (a region close to the winding core of the wound structure), the electrode element associated with charge / discharge is compared with an electrode element having a wound structure. There is an advantage that it is difficult to be adversely affected by the volume change. On the other hand, in an electrode element having a wound structure, since the electrode is curved, the structure is easily distorted when a volume change occurs.

[1] Negative electrode The negative electrode is configured, for example, by binding a negative electrode active material so as to cover a negative electrode current collector with a negative electrode binder. In the present embodiment, the negative electrode includes a carbon material that can insert and desorb lithium ions as a negative electrode active material.

  As the carbon material that is the negative electrode active material, graphite such as artificial graphite and natural graphite, amorphous carbon, diamond-like carbon, carbon nanotube, or a composite of two or more of these carbon materials can be used. . Here, carbon with high crystallinity has high electrical conductivity, and is excellent in adhesiveness and voltage flatness with a positive electrode current collector made of a metal such as copper. On the other hand, since amorphous carbon having low crystallinity has a relatively small volume expansion, it has a high effect of relaxing the volume expansion of the entire negative electrode, and deterioration due to non-uniformity such as crystal grain boundaries and defects hardly occurs.

  As the binder for the negative electrode, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene, polyethylene, Polyimide, polyamideimide, or the like can be used. Among these, polyvinylidene fluoride and styrene-butadiene copolymer rubber that are easy to handle are particularly desirable. The amount of the binder for the negative electrode to be used is preferably 5 to 25 parts by mass with respect to 100 parts by mass of the negative electrode active material from the viewpoints of “sufficient binding force” and “high energy” which are in a trade-off relationship. . Moreover, when using styrene-butadiene copolymer rubber, you may use carboxymethylcellulose (CMC) together as a thickener.

  The negative electrode may contain a conductive additive for the purpose of reducing impedance. Examples of the conductive assistant that can be used for the negative electrode include carbonaceous fine particles such as graphite, carbon black, acetylene black, carbon nanotube, and carbon nanophone.

  As the negative electrode current collector, aluminum, nickel, copper, SUS, silver, and alloys thereof are preferable from the viewpoint of electrochemical stability. Examples of the shape include foil, flat plate, and mesh.

  The negative electrode can be produced by forming a negative electrode active material layer containing a negative electrode active material and a negative electrode binder on a negative electrode current collector. Examples of the method for forming the negative electrode active material layer include a doctor blade method, a die coater method, a CVD method, and a sputtering method. After forming a negative electrode active material layer in advance, a thin film of aluminum, nickel, or an alloy thereof may be formed by a method such as vapor deposition or sputtering to form a negative electrode current collector.

[2] Positive Electrode The positive electrode is formed, for example, by binding a positive electrode active material so as to cover the positive electrode current collector with a positive electrode binder.

As the positive electrode active material, a layered structure such as LiMnO ₂ , Li _x Mn ₂ O ₄ (0 <x <2), LiNi _y Mn _z O ₄ (0 <y <1, 0 <z <2, y + z = 2) or the like. Lithium manganate having a spinel structure or lithium manganate having a spinel structure, or a part thereof replaced with another metal; LiCoO ₂ , LiNiO ₂ , or a part of these transition metals replaced with another metal LiMn _a Ni _b Co _c O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ Lithium transition metal oxides in which the number of specific transition metals does not exceed half; those lithium transition metal oxides in which Li is excessive in excess of the stoichiometric composition. In particular, Li _α Ni _β Co _γ Al _δ O ₂ (1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.7, γ ≦ 0.2) or Li _α Ni _β Co _γ Mn _δ O ₂ (1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.1, γ ≧ 0.1) are preferable. A positive electrode active material can be used individually by 1 type or in combination of 2 or more types.

  As the positive electrode binder, the same binder as the negative electrode binder can be used. Among these, polyvinylidene fluoride is preferable from the viewpoint of versatility and low cost. The amount of the binder for the positive electrode to be used is preferably 2 to 15 parts by mass with respect to 100 parts by mass of the positive electrode active material from the viewpoints of “sufficient binding force” and “high energy” in a trade-off relationship. .

  As the positive electrode current collector, the same as the negative electrode current collector can be used.

  A conductive auxiliary material may be added to the positive electrode active material layer containing the positive electrode active material for the purpose of reducing impedance. Examples of the conductive auxiliary material include carbonaceous fine particles such as graphite, carbon black, and acetylene black.

[3] Electrolytic Solution The electrolytic solution used in the present embodiment is a phosphorous compound represented by the formula (1) of 70 vol% or more (in this specification, sometimes simply referred to as “phosphorous compound”); A fluorinated carbonate compound of 01 vol% or more and 30 vol% or less and a metal ion having a redox potential at a potential higher than 1.0 V with respect to lithium are included. Hereinafter, each compound contained in the electrolytic solution will be described.

When the electrolytic solution contains a phosphorus compound, flame retardancy can be enhanced, and the safety of the secondary battery can be enhanced. In this embodiment, since the phosphorus compound is contained at a high concentration of 70 vol% or more, the safety of the secondary battery is high. Furthermore, deterioration of electrolyte solution can be suppressed because electrolyte solution contains a phosphorus compound, especially phosphate ester. For example, when the electrolytic solution contains PF ₆ anion, if the electrolytic solution is placed at a high temperature, the decomposition of the PF ₆ anion proceeds and the electrolytic solution is likely to be deteriorated. Deterioration can be suppressed.

  In this embodiment, the phosphorus compound contained in electrolyte solution is represented by following formula (1).

式（１）中、Ｒ^１、Ｒ^２およびＲ^３は、それぞれ独立して、水素原子、アルキル基、ハロゲン化アルキル基、アルケニル基、ハロゲン化アルケニル基、アリール基、オキサアルキル基［−Ｒ⁴−Ｏ−Ｒ⁵（Ｒ⁴はアルキレン基を表し、Ｒ⁵はアルキル基またはハロゲン化アルキル基を表す）］、シクロアルキル基、ハロゲン化シクロアルキル基、シリル基、ヒドロキシ基、アルコキシ基、ハロゲン化アルコキシ基、アルケニルオキシ基、ハロゲン化アルケニルオキシ基、アリールオキシ基、オキサアルキルオキシ基［−Ｏ−Ｒ⁶−Ｏ−Ｒ⁷（Ｒ⁶はアルキレン基を表し、Ｒ⁷はアルキル基またはハロゲン化アルキル基を表す）］、シクロアルキルオキシ基、ハロゲン化シクロアルキルオキシ基またはシリルオキシ基であり、Ｒ^１、Ｒ^２およびＲ^３は、いずれか２つまたは全てが結合した環状構造を形成していてもよい。ただし、Ｒ^１、Ｒ^２およびＲ^３のうち少なくとも１つが、水素原子およびヒドロキシ基のいずれでもないものとする。

In formula (1), R ¹ , R ² and R ³ each independently represent a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, an aryl group, an oxaalkyl group [—R ⁴ —O—R ⁵ (R ⁴ represents an alkylene group, R ⁵ represents an alkyl group or a halogenated alkyl group)], cycloalkyl group, halogenated cycloalkyl group, silyl group, hydroxy group, alkoxy group, halogenated An alkoxy group, an alkenyloxy group, a halogenated alkenyloxy group, an aryloxy group, an oxaalkyloxy group [—O—R ⁶ —O—R ^{7, wherein} R ⁶ represents an alkylene group, R ⁷ represents an alkyl group or an alkyl halide; represents a group), a cycloalkyl group, a halogenated cycloalkyl group or silyloxy group, R ^1, R ² Oyo R ³ may also form either two or all bonded cyclic structures. However, at least one of R ¹ , R ² and R ³ is neither a hydrogen atom nor a hydroxy group.

In the formula (1), an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, an oxaalkyl group [—R ⁴ —O—R ⁵ (R ⁴ represents an alkylene group, R ⁵ represents an alkyl group or a halogen An alkyl group)], a silyl group, an alkoxy group, a halogenated alkoxy group, an alkenyloxy group, a halogenated alkenyloxy group, and an oxaalkyloxy group [—O—R ⁶ —O—R ⁷ (R ⁶ is alkylene) R ⁷ represents an alkyl group or a halogenated alkyl group)] may be linear or branched. Halogenated alkyl group, halogenated alkenyl group, halogenated alkoxy group, halogenated cycloalkyl group, halogenated alkoxy group, halogenated alkenyloxy group and halogenated cycloalkyloxy group have their corresponding unsubstituted groups. At least one of the hydrogen atoms is substituted with a halogen atom. Examples of the halogen atom contained in these include fluorine, chlorine, bromine and iodine, and fluorine is preferred. R ¹ , R ² and R ³ are each preferably a group having 10 or less carbon atoms, more preferably a group having 1 to 10 carbon atoms, and all are alkyl groups having 1 to 10 carbon atoms. More preferably.

  In the present embodiment, the phosphorus compound is preferably a compound having a P atom as a central element and having a —P—O— bond in addition to a —P═O bond, and particularly represented by the following formula (2). Phosphate ester compounds are preferred.

式（２）中、Ｒｓ、ＲｔおよびＲｕは、それぞれ独立して、水素原子、アルキル基、ハロゲン化アルキル基、アルケニル基、ハロゲン化アルケニル基、アリール基、オキサアルキル基［−Ｒ^２１−Ｏ−Ｒ^２２（Ｒ^２１はアルキレン基を表し、Ｒ^２２はアルキル基またはハロゲン化アルキル基を表す）］、シクロアルキル基、ハロゲン化シクロアルキル基、またはシリル基であり、Ｒｓ、ＲｔおよびＲｕは、いずれか２つまたは全てが結合した環状構造を形成していてもよい。ただし、Ｒｓ、ＲｔおよびＲｕのうち少なくとも１つが、水素原子ではないものとする。

In the formula (2), Rs, Rt and Ru each independently represent a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, an aryl group, an oxaalkyl group [—R ²¹ —O— R ²² (R ²¹ represents an alkylene group, R ²² represents an alkyl group or a halogenated alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group, or a silyl group, and Rs, Rt, and Ru are any of Or two or all of them may form a cyclic structure. However, at least one of Rs, Rt, and Ru is not a hydrogen atom.

In Formula (2), an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, or an oxaalkyl group [—R ²¹ —O—R ²² (R ²¹ represents an alkylene group, R ²² represents an alkyl group or Represents a halogenated alkyl group)] may be linear or branched. Examples of the halogen atom that the halogenated alkyl group, halogenated alkenyl group, and halogenated cycloalkyl group have include fluorine, chlorine, bromine, and iodine, with fluorine being preferred. Rs, Rt and Ru all preferably have 10 or less carbon atoms, and more preferably all are alkyl groups having 10 or less carbon atoms.

  Specific examples of phosphorus compounds include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, dimethyl ethyl phosphate, diethyl methyl phosphate. Alkylphosphoric acid ester compounds such as dimethyl methylphosphonate (DMMP), phosphonic acid esters such as dimethyl ethylphosphonate; aryl phosphoric acid ester compounds such as triphenyl phosphate; methylethylene phosphate, ethylethylene phosphate (EEP), phosphorus Phosphate ester compounds having a cyclic structure such as ethylbutylene acid, tri- (n) -cresyl phosphate (wherein n may be ortho, para or meta, or may be a phosphate ester compound composed of each) Tris phosphate (trifluoromethyl ), Tris phosphate (pentafluoroethyl), tris phosphate (2,2,2-trifluoroethyl), tris phosphate (2,2,3,3-tetrafluoropropyl), tris phosphate (3,3 , 3-trifluoropropyl), and halogenated alkyl phosphate compounds such as tris (2,2,3,3,3-pentafluoropropyl) phosphate. Among them, trialkyl phosphate compounds such as trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, and trioctyl phosphate are used as the phosphate ester compound. It is preferable. A phosphorus compound can be used individually by 1 type or in combination of 2 or more types.

  In the present embodiment, the content of the phosphorus compound is 70 vol% or more in the electrolytic solution, preferably 70 to 99.9 vol%, more preferably 80 vol% or more, and still more preferably 85 vol% or more. More preferably, it is 99 vol% or less, More preferably, it is 95 vol% or less.

  The fluorinated carbonate compound contained in the electrolyte solution of the secondary battery of this embodiment may be a fluorinated cyclic carbonate compound or a fluorinated chain carbonate compound. When the electrolytic solution contains the fluorinated carbonate compound, the discharge capacity of the secondary battery is increased. In this embodiment, as described later, when the electrolyte contains metal ions having a redox potential at a potential higher than 1.0 V with respect to lithium, metal is deposited on the negative electrode active material. When the compound decomposes on the metal, a film derived from the fluorinated carbonate compound is further formed on the metal film formed on the negative electrode active material, and the decomposition suppression effect of the phosphorus compound contained in the electrolytic solution is further improved. It is thought to improve.

  Examples of the fluorinated cyclic carbonate compound include the following formula (3a) or (3b):

で表される化合物が挙げられる。なお、式（３ａ）または（３ｂ）中、Ｒａ、Ｒｂ、Ｒｃ、Ｒｄ、ＲｅおよびＲｆは、それぞれ独立して、水素原子、アルキル基、ハロゲン化アルキル基、ハロゲン原子、アルケニル基、ハロゲン化アルケニル基、シアノ基、アミノ基、ニトロ基、アルコキシ基、ハロゲン化アルコキシ基、シクロアルキル基、ハロゲン化シクロアルキル基またはシリル基である。ただし、Ｒａ、Ｒｂ、ＲｃおよびＲｄのうち少なくとも１つが、フッ素原子、フッ素化アルキル基、フッ素化アルケニル基、フッ素化アルコキシ基またはフッ素化シクロアルキル基であり、ＲｅおよびＲｆのうち少なくとも１つが、フッ素原子、フッ素化アルキル基、フッ素化アルケニル基、フッ素化アルコキシ基またはフッ素化シクロアルキル基である。アルキル基、ハロゲン化アルキル基、アルケニル基、ハロゲン化アルケニル基、アルコキシ基、ハロゲン化アルコキシ基、シクロアルキル基およびハロゲン化シクロアルキル基の炭素数は１０以下が好ましく、５以下がより好ましい。ハロゲン化アルキル基、ハロゲン化アルケニル基、ハロゲン化アルコキシ基およびハロゲン化シクロアルキル基のハロゲン原子としては、フッ素、塩素、臭素、ヨウ素が挙げられる。

The compound represented by these is mentioned. In the formula (3a) or (3b), Ra, Rb, Rc, Rd, Re and Rf each independently represent a hydrogen atom, an alkyl group, a halogenated alkyl group, a halogen atom, an alkenyl group, or an alkenyl halide. Group, cyano group, amino group, nitro group, alkoxy group, halogenated alkoxy group, cycloalkyl group, halogenated cycloalkyl group or silyl group. However, at least one of Ra, Rb, Rc and Rd is a fluorine atom, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkoxy group or a fluorinated cycloalkyl group, and at least one of Re and Rf is A fluorine atom, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkoxy group or a fluorinated cycloalkyl group. The alkyl group, halogenated alkyl group, alkenyl group, halogenated alkenyl group, alkoxy group, halogenated alkoxy group, cycloalkyl group and halogenated cycloalkyl group preferably have 10 or less carbon atoms, and more preferably 5 or less. Examples of the halogen atom of the halogenated alkyl group, halogenated alkenyl group, halogenated alkoxy group and halogenated cycloalkyl group include fluorine, chlorine, bromine and iodine.

  As the fluorinated cyclic carbonate compound, a compound in which all or a part of hydrogen atoms of ethylene carbonate, propylene carbonate, vinylene carbonate or vinyl ethylene carbonate are substituted with fluorine atoms can be used. Among them, it is preferable to use a compound obtained by fluorinating a part of ethylene carbonate such as fluoroethylene carbonate, cis- or trans-difluoroethylene carbonate, and it is more preferable to use fluoroethylene carbonate.

  Examples of the fluorinated chain carbonate compound include the following formula (4):

で表される化合物が挙げられる。なお、式（４）中、ＲｙおよびＲｚは、それぞれ独立して、水素原子、アルキル基、ハロゲン化アルキル基、ハロゲン原子、アルケニル基、ハロゲン化アルケニル基、シアノ基、アミノ基、ニトロ基、アルコキシ基、ハロゲン化アルコキシ基、シクロアルキル基、ハロゲン化シクロアルキル基またはシリル基である。ただし、ＲｙおよびＲｚのうち少なくとも１つがフッ素原子、フッ素化アルキル基、フッ素化アルケニル基、フッ素化アルコキシ基またはフッ素化シクロアルキル基である。アルキル基、ハロゲン化アルキル基、アルケニル基、ハロゲン化アルケニル基、アルコキシ基、ハロゲン化アルコキシ基、シクロアルキル基およびハロゲン化シクロアルキル基の炭素数は１０以下が好ましく、５以下がより好ましい。ハロゲン化アルキル基、ハロゲン化アルケニル基、ハロゲン化アルコキシ基およびハロゲン化シクロアルキル基のハロゲン原子としては、フッ素、塩素、臭素、ヨウ素が挙げられる。

The compound represented by these is mentioned. In formula (4), Ry and Rz are each independently a hydrogen atom, alkyl group, halogenated alkyl group, halogen atom, alkenyl group, halogenated alkenyl group, cyano group, amino group, nitro group, alkoxy Group, halogenated alkoxy group, cycloalkyl group, halogenated cycloalkyl group or silyl group. However, at least one of Ry and Rz is a fluorine atom, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkoxy group, or a fluorinated cycloalkyl group. The alkyl group, halogenated alkyl group, alkenyl group, halogenated alkenyl group, alkoxy group, halogenated alkoxy group, cycloalkyl group and halogenated cycloalkyl group preferably have 10 or less carbon atoms, and more preferably 5 or less. Examples of the halogen atom of the halogenated alkyl group, halogenated alkenyl group, halogenated alkoxy group and halogenated cycloalkyl group include fluorine, chlorine, bromine and iodine.

  Examples of the fluorinated chain carbonate compound include bis (1-fluoroethyl) carbonate, bis (2-fluoroethyl) carbonate, 3-fluoropropylmethyl carbonate, and 3,3,3-trifluoropropylmethyl carbonate.

A fluorinated carbonate compound can be used individually by 1 type or in combination of 2 or more types.

  In the present embodiment, the content of the fluorinated carbonate compound is 0.01 vol% or more and 30 vol% or less, preferably 1 vol% or more, preferably 20 vol% or less, more preferably 10 vol% or less in the electrolytic solution. is there. When there is too much content of a fluorinated carbonate compound, the viscosity of electrolyte solution may go up and resistance may go up.

  In the present embodiment, the electrolytic solution includes a metal ion having an oxidation-reduction potential at a potential higher than 1.0 V with respect to lithium (sometimes simply referred to as “metal ion” in this specification). On the other hand, it is preferable to include a metal ion having a redox potential at a potential higher than 1.4V. When the electrolytic solution contains a metal ion having an oxidation-reduction potential at a potential higher than 1.0 V with respect to Li, decomposition of the phosphorus compound in the electrolytic solution can be prevented, and deterioration of cycle characteristics can be prevented. This is considered to be an effect by forming a metal film on the surface of the negative electrode containing carbon as a negative electrode active material. In addition, when the electrolytic solution contains a metal ion having a redox potential at a potential higher than 1.4 V with respect to lithium, the metal film is more easily formed, and the effect of suppressing decomposition of the phosphorus compound on the electrode Becomes larger.

As metal ions having a redox potential at a potential higher than 1.0 V with respect to Li, Be ²⁺ , Al ³⁺ , Mn ²⁺ , Cr ²⁺ , Zn ²⁺ , Ga ³⁺ , Fe ²⁺ , Cd ²⁺ , In ³⁺ , Ti ⁺ , Co ²⁺ , Sn ²⁺ , Ni ²⁺ , Pb ²⁺ , Bi ³⁺ , Cu ²⁺ , Rh ³⁺ , Ag ⁺ , Pd ²⁺ , Pt ²⁺ , Au ³⁺ , Zn ²⁺ , Fe ²⁺ , Ni ²⁺ , Cu ²⁺ , It is preferable to include one or more selected from the group consisting of Ag ⁺ and Au ³⁺ , and more preferable to include one or more selected from the group consisting of Zn ²⁺ , Fe ²⁺ , Cu ²⁺ , Ag ⁺ and Au ³⁺ . Among these, it is particularly desirable to use Ag ⁺ .

As a method of including these metal ions in the electrolytic solution, it is preferable to dissolve a salt containing these metal ions in the electrolytic solution. Examples of the counter anion of the salt containing a metal ion include SO ₄ ²⁻ , NO ₃ ⁻ , PO ₄ ³⁻ , hexafluorophosphate (PF ₆ ⁻ ), and the electrolytic solution contains LiPF ₆ as a supporting salt. it is preferably ^- PF ₆ If. Examples of the salt containing metal ions include NiSO ₄ , Ni (NO ₃ ) ₂ , AlPO ₄ , Zn ₃ (PO ₄ ) ₂ , AgPF _{6 and the} like. In particular, NiSO ₄ , Ni (NO ₃ ) ₂ , and AgPF ₆ having high solubility are preferable. The concentration of these salts contained in the electrolytic solution is preferably 0.01 wt% or more and 10 wt% or less, and more preferably 0.1 wt% or more and 5 wt% or less. If the concentration of the salt containing metal ions in the electrolyte is too high, metal accumulates on the negative electrode surface during charging, and the deposit is too much to break through the separator, causing a short circuit, or the metal film is too thick. In some cases, the carbon active material and lithium ions cannot be sufficiently reacted.

  The electrolytic solution used in the present embodiment may contain another organic solvent. Other organic solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), propane sultone (PS) ), Butane sultone (BS), Dioxothiolane-2,2-dioxide (DD), sulfolene, 3-methylsulfolene, sulfolane (SL), succinic anhydride (SUCAH), propionic anhydride, acetic anhydride, maleic anhydride, diallyl Carbonate (DAC), diphenyl disulfide (DPS), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), chloroethylene carbonate, diethyl carbonate (DEC), dimethoxyethane (DM ), Dimethoxymethane (DMM), diethoxyethane (DEE), ethoxymethoxyethane, dimethyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl butyl ether, diethyl ether, phenyl methyl ether, tetrahydrofuran (THF) ), Tetrahydropyran (THP), 1,4-dioxane (DIOX), 1,3-dioxolane (DOL), carbonate electrolyte, ether, acetonitrile, propiononitrile, γ-butyrolactone, γ-valerolactone, ionic liquid, phosphazene And aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate. Among these, ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and γ-valerolactone are preferable. Another organic solvent can be used individually by 1 type or in combination of 2 or more types.

The electrolytic solution used in the present embodiment includes a supporting salt. Specific examples of the supporting salt include LiPF ₆ , LiI, LiBr, LiCl, LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (FSO ₂ ) _2. , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ), LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO _{2), LiN} containing a five-membered ring structure _{(CF 2 SO 2) 2 (} CF 2), LiN having a six-membered ring structure _{(CF 2 SO 2) 2 (} CF 2) 2, at least one fluorine atom in LiPF ₆ Is substituted with a fluorinated alkyl group, LiPF ₅ (CF ₃ ), LiPF ₅ (C ₂ F ₅ ), LiPF ₅ (C ₃ F ₇ ), LiPF ₄ (CF ₃ ) ₂ And lithium salts such as LiPF ₄ (CF ₃ ) (C ₂ F ₅ ) and LiPF ₃ (CF ₃ ) ₃ . Further, as the supporting salt, the following formula (5):

で表される化合物を用いることもできる。なお、式（５）中、Ｒ_１、Ｒ_２およびＲ_３は、それぞれ独立して、ハロゲン原子またはフッ化アルキル基である。ハロゲン原子としては、フッ素、塩素、臭素、ヨウ素が挙げられる。フッ化アルキル基の炭素数は、１〜１０であることが好ましい。式（５）で表される化合物の具体例としては、ＬｉＣ（ＣＦ_３ＳＯ_２）_３、ＬｉＣ（Ｃ_２Ｆ_５ＳＯ_２）_３が挙げられる。支持塩は、一種を単独で、または二種以上を組み合わせて使用することができる。

The compound represented by these can also be used. In formula (5), R ₁ , R ₂ and R ₃ are each independently a halogen atom or a fluorinated alkyl group. Examples of the halogen atom include fluorine, chlorine, bromine and iodine. The fluorinated alkyl group preferably has 1 to 10 carbon atoms. Specific examples of the compound represented by the formula (5) include LiC (CF ₃ SO ₂ ) ₃ and LiC (C ₂ F ₅ SO ₂ ) ₃ . The supporting salt can be used alone or in combination of two or more.

  The concentration of the supporting salt in the electrolytic solution is preferably 0.01 M (mol / L) or more and 3 M (mol / L) or less, preferably 0.5 M (mol / L) or more and 1.5 M (mol / L) or less. More preferred.

[4] Separator As the separator, a porous film such as polypropylene or polyethylene, cellulose, polyimide, polyvinylidene, or a heat-resistant nonwoven fabric made of glass fiber can be used. Moreover, what laminated | stacked them can also be used as a separator.

[5] Exterior Body The exterior body can be appropriately selected as long as it is stable to the electrolytic solution and has a sufficient water vapor barrier property. For example, in the case of a laminated laminate type secondary battery, a laminate film made of aluminum, silica-coated polypropylene, polyethylene, or the like can be used as the outer package. In particular, it is preferable to use an aluminum laminate film from the viewpoint of suppressing volume expansion.

  Although the manufacturing method of the secondary battery which concerns on this embodiment is not specifically limited, For example, the method shown below is mentioned. A positive electrode tab and a negative electrode tab are connected to a positive electrode and a negative electrode containing a carbon material into which lithium ions can be inserted and desorbed via a positive electrode current collector and a negative electrode current collector, respectively. The positive electrode and the negative electrode are arranged opposite to each other with the separator interposed therebetween, and a stacked electrode element is manufactured. The electrode element is accommodated in the exterior body and immersed in an electrolytic solution. The secondary battery can be manufactured by sealing the exterior body so that a part of the positive electrode tab and the negative electrode tab protrudes to the outside.

  Hereinafter, the present embodiment will be specifically described by way of examples, but the present invention is not limited thereto.

Example 1
<Preparation of positive electrode>
VGCF (manufactured by Showa Denko KK) as a conductive agent is mixed with lithium manganese composite oxide-based material (LiMn ₂ O ₄ ) as a positive electrode active material, and this is dispersed in N-methylpyrrolidone (NMP) to form a slurry. Then, it was applied to an aluminum foil as a positive electrode current collector and dried. Thereafter, a positive electrode having a diameter of 12 mmφ was produced.

<Production of negative electrode>
Artificial graphite as negative electrode active material and styrene butadiene rubber as binder for negative electrode are mixed at a mass ratio of 95: 5 (artificial graphite: styrene butadiene rubber), and CMC (carboxymethylcellulose) is dissolved in 1 wt% water. A negative electrode slurry was prepared using the obtained material as a solvent. The negative electrode slurry was applied to a copper foil having a thickness of 10 μm and then dried. From this, a negative electrode of φ13 size was produced.

<Electrolyte>
As an electrolytic solution, supported by an electrolytic solvent in which triethyl phosphate (hereinafter abbreviated as TEP) and fluoroethylene carbonate (hereinafter abbreviated as FEC) were mixed at a ratio of TEP: FEC = 90: 10 (volume ratio). As the salt, LiPF ₆ was dissolved at a concentration of 1 mol / L, and further, 1 wt% of AgPF ₆ was dissolved with respect to the total mass of the electrolytic solution.

  A coin cell was fabricated using a φ12 size positive electrode and a φ13 size negative electrode using a polypropylene separator and the above electrolyte.

<Evaluation of charge / discharge>
Charge / discharge evaluation was performed using the produced coin cell. The charge / discharge evaluation was performed by charging to 4.2 V at 0.1 C and discharging to 3.0 V at 0.1 C in an environment of 25 ° C. The ratio of the discharge capacity at the second cycle to the charge capacity at the second cycle was determined, and was defined as “charge / discharge efficiency at the second cycle”. The results are shown in Table 1.

(Example 2)
As an electrolytic solution, LiPF ₆ as a supporting salt is dissolved at a concentration of 1 mol / L in an electrolytic solvent obtained by mixing TEP and FEC at TEP: FEC = 90: 10 (volume ratio), and further AgPF ₆ is dissolved in the electrolytic solution. What dissolved 2 wt% with respect to the total mass was used. A lithium ion secondary battery was prepared in the same manner as in Example 1 except for the electrolytic solution, and charge / discharge evaluation was performed. The results are shown in Table 1.

(Example 3)
As an electrolytic solution, LiPF ₆ as a supporting salt is dissolved at a concentration of 1 mol / L in an electrolytic solvent obtained by mixing TEP and FEC at TEP: FEC = 90: 10 (volume ratio), and further AgPF ₆ is dissolved in the electrolytic solution. What dissolved 5 wt% with respect to the total mass was used. A lithium ion secondary battery was prepared in the same manner as in Example 1 except for the electrolytic solution, and charge / discharge evaluation was performed. The results are shown in Table 1.

(Comparative Example 1)
As an electrolytic solution, an electrolytic solvent obtained by mixing TEP and FEC at TEP: FEC = 90: 10 (volume ratio) and further dissolving LiPF ₆ as a supporting salt at a concentration of 1 mol / L was used. A lithium ion secondary battery was prepared in the same manner as in Example 1 except for the electrolytic solution, and charge / discharge evaluation was performed. The results are shown in Table 1.

(Comparative Example 2)
As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as a supporting salt in an electrolytic solvent containing only TEP to a concentration of 1 mol / L and dissolving 2 wt% of AgPF ₆ with respect to the total mass of the electrolytic solution was used. A lithium ion secondary battery was prepared in the same manner as in Example 1 except for the electrolytic solution, and charge / discharge evaluation was performed. The results are shown in Table 1.

It was confirmed that the charge / discharge efficiency in the second cycle was improved by mixing AgPF ₆ with the electrolytic solution using phosphate ester as the main solvent (Examples 1, 2, 3 and Comparative Example 1). In the case of using an electrolytic solution containing phosphoric acid ester and AgPF _6, it was also found to improve characteristics by combination of FEC (Examples 1, 2, 3, Comparative Example 2). Since the oxidation-reduction potential of Ag is higher than lithium by 3 V or more, it can be considered that it is deposited on the carbon active material in the first charging process. Thereafter, FEC (about 1.2 V vs Li / Li ⁺ ) whose decomposition potential on graphite is higher than TEP (about 1.0 V vs Li / Li ⁺ ) decomposes on Ag deposited on the surface of the negative electrode active material, and the film As a result, it was found that the decomposition of the phosphate ester can be further suppressed. That is, it has been found that the decomposition of the phosphate ester can be further suppressed by forming a metal film on the carbon active material and an FEC decomposition product thereon.

<High temperature storage test of electrolyte>
In Example 4 and Comparative Examples 3 and 4, the electrolyte solutions described below were prepared and stored at 85 ° C. for 1 hour, and then the color change of the electrolyte solution was visually observed.

Example 4
As an electrolytic solution, LiPF ₆ as a supporting salt is dissolved at a concentration of 1 mol / L in an electrolytic solvent obtained by mixing TEP and FEC at TEP: FEC 70:30 (volume ratio), and further 1 wt% of AgPF ₆ is dissolved. Used. The results are shown in Table 2.

(Comparative Example 3)
As the electrolytic solution, a mixture of TEP: FEC at a volume ratio of 50:50 (volume ratio) was used. Further, LiPF ₆ was dissolved at a concentration of 1 mol / L as a supporting salt, and further 1 wt% of AgPF ₆ was dissolved. A thing was used. The results are shown in Table 2.

(Comparative Example 4)
As an electrolytic solution, an electrolytic solvent obtained by mixing EC and DEC at EC: DEC = 30: 70 (volume ratio) and LiPF ₆ as a supporting salt dissolved at a concentration of 1 mol / L was used. The results are shown in Table 2.

The coloration of the electrolytic solution is remarkably observed when a salt having PF ₆ as an anion is dissolved, and is considered to indicate deterioration of the electrolytic solution due to the decomposition reaction of PF ₆ . From the results of Example 4 above, it is considered that when the electrolytic solution contains TEP in an amount of 70 vol% or more, the color change is eliminated and the deterioration of the electrolytic solution is suppressed. That is, the phosphate ester compound was shown to be the effect of suppressing a decomposition reaction of PF _6.

  This embodiment can be used in all industrial fields that require a power source, and in industrial fields related to the transport, storage, and supply of electrical energy. Specifically, power supplies for mobile devices such as mobile phones and notebook computers; power supplies for transportation and transportation media such as trains, satellites, and submarines, including electric vehicles such as electric cars, hybrid cars, electric bikes, and electric assist bicycles A backup power source such as a UPS; a power storage facility for storing power generated by solar power generation, wind power generation, etc .;

a negative electrode b separator c positive electrode d negative electrode current collector e positive electrode current collector f positive electrode terminal g negative electrode terminal

Claims (6)

A lithium ion secondary battery comprising a negative electrode containing a carbon material capable of inserting / extracting lithium ions, a positive electrode, and an electrolyte solution,
The electrolyte is
70 vol% or more of the following formula (1):

{In Formula (1), R ¹ , R ² and R ³ are each independently a hydrogen atom, alkyl group, halogenated alkyl group, alkenyl group, halogenated alkenyl group, aryl group, oxaalkyl group [-R ^4- O—R ⁵ (R ⁴ represents an alkylene group, R ⁵ represents an alkyl group or a halogenated alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group, a silyl group, a hydroxy group, an alkoxy group, a halogen Alkoxy group, alkenyloxy group, halogenated alkenyloxy group, aryloxy group, oxaalkyloxy group [—O—R ⁶ —O—R ⁷ (R ⁶ represents an alkylene group, R ⁷ represents an alkyl group or a halogenated group] represents an alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group or silyloxy group, R ^1, R ² Contact Fine R ³ may form either two or all bonded cyclic structures. However, at least one of R ¹ , R ² and R ³ is neither a hydrogen atom nor a hydroxy group. }
A phosphorus compound represented by:
0.01 vol% or more and 30 vol% or less of a fluorinated carbonate compound;
A secondary battery comprising a metal ion having a redox potential at a potential higher than 1.0 V with respect to lithium. The phosphorus compound is represented by the following formula (2):

[In the formula (2), Rs, Rt and Ru are each independently a hydrogen atom, an alkyl group, a halogenated alkyl group, an alkenyl group, a halogenated alkenyl group, an aryl group, a cycloalkyl group or a halogenated cycloalkyl group. , A silyl group, or an oxaalkyl group [—R ²¹ —O—R ²² (R ²¹ represents an alkylene group, R ²² represents an alkyl group or a halogenated alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group Or Rs, Rt and Ru may form a cyclic structure in which any two or all of them are bonded. However, at least one of Rs, Rt, and Ru is not a hydrogen atom. ]
The secondary battery according to claim 1, wherein the phosphoric acid ester compound is represented by:   3. The secondary battery according to claim 1, comprising a metal ion having an oxidation-reduction potential at a potential higher by 1.4 V or more than lithium. 4. The metal ion having a redox potential at a potential higher than 1.0 V with respect to lithium is at least one selected from the group consisting of Zn ²⁺ , Fe ²⁺ , Cu ²⁺ , Ag ⁺ , and Au ^3+. The secondary battery according to any one of claims 1 to 3. The electrolyte further comprises LiPF ₆ ; and
5. The counter anion of a metal ion having an oxidation-reduction potential at a potential higher than 1.0 V with respect to lithium in the electrolyte solution is hexafluorophosphate (PF ₆ ⁻ ). The secondary battery according to any one of the above. A step of producing an electrode element by opposingly arranging a positive electrode and a negative electrode containing a carbon material capable of inserting and desorbing lithium ions;
A step of enclosing the electrode element and the electrolytic solution in an exterior body,
The electrolyte is 70 vol% or more of the following formula (1):

{In Formula (1), R ¹ , R ² and R ³ are each independently a hydrogen atom, alkyl group, halogenated alkyl group, alkenyl group, halogenated alkenyl group, aryl group, oxaalkyl group [-R ^4- O—R ⁵ (R ⁴ represents an alkylene group, R ⁵ represents an alkyl group or a halogenated alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group, a silyl group, a hydroxy group, an alkoxy group, a halogen Alkoxy group, alkenyloxy group, halogenated alkenyloxy group, aryloxy group, oxaalkyloxy group [—O—R ⁶ —O—R ⁷ (R ⁶ represents an alkylene group, R ⁷ represents an alkyl group or a halogenated group] represents an alkyl group)], a cycloalkyl group, a halogenated cycloalkyl group or silyloxy group, R ^1, R ² Contact Fine R ³ may form either two or all bonded cyclic structures. However, at least one of R ¹ , R ² and R ³ is neither a hydrogen atom nor a hydroxy group. }
A phosphorus compound represented by the formula: 0.01 vol% or more and 30 vol% or less of a fluorinated carbonate compound; and a metal ion having an oxidation-reduction potential at a potential higher by 1.0 V or more than lithium. A method for manufacturing a secondary battery.

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