JP2001217005A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery that has excellent self fire-extinguishing and fire retardance and deterioration resistance as well as low surface resistance of non-aqueous electrolyte and excellent electrochemical stability, and low temperature discharging characteristics, while keeping the long term stability and safety necessary for a battery. SOLUTION: The non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, supporting salt, organic solvent and non-aqueous electrolyte containing phosphagen derivative. The above phosphagen derivative has an electric potential window in the range of a lower limit of less than +0.5 V and an upper limit of more than +4.5 V, and the electric potential window of the above organic solvent has a wider range than that of the phosphagen derivative. It is a desirable state and manner that the electric potential window of phosphagen derivative is in the range less than +0 V of lower limit and more than +5 V of upper limit, and that viscosity of the phosphagen derivative is less than 100 m Pa.s (100 cP) at 25 deg.C and that the flashing point of the phosphagen derivative is more than 100 deg.C, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a self-extinguishing or flame-retardant, deteriorating, and long-term stable and safe element similar to conventional non-aqueous electrolyte secondary batteries. The present invention relates to a non-aqueous electrolyte secondary battery having excellent electrochemical stability.

[0002]

2. Description of the Related Art Conventionally, in particular, AVs of personal computers, VTRs, etc.
・ Ni-Cd batteries have been the mainstream for memory backup of information devices and secondary batteries for their driving power supply. In recent years, non-aqueous electrolyte secondary batteries have attracted much attention as an alternative to nickel-cadmium batteries because they have the advantages of high voltage and high energy density and exhibit excellent self-discharge properties. Attempts have been made, some of which have been commercialized. For example, more than half of notebook computers and mobile phones are driven by non-aqueous electrolyte secondary batteries.

In these non-aqueous electrolyte secondary batteries,
Carbon is often used as a material for forming the negative electrode, but various organic solvents are used as an electrolyte for the purpose of reducing the risk of lithium being generated on the surface and increasing the driving voltage. Also, since non-aqueous electrolyte secondary batteries for cameras use an alkali metal (particularly, lithium metal or lithium alloy) as a negative electrode material,
As the electrolyte, an aprotic organic solvent such as an ester organic solvent is usually used.

However, these non-aqueous electrolyte secondary batteries are:
Although having high performance, there were the following problems in safety. First, when an alkali metal (particularly, lithium metal or lithium alloy) used as a negative electrode material of a non-aqueous electrolyte secondary battery is used, the alkali metal has a very high activity against moisture, For example, when moisture enters due to incomplete sealing of the battery or the like, there is a problem in that there is a high risk that the anode material and water react with each other to generate hydrogen or ignite.

Also, lithium metal has a low melting point (about 170
° C), so if a large current suddenly flows, such as during a short circuit,
There is a problem in that a very dangerous situation such as abnormal heat generation of the battery and melting of the battery is caused. Furthermore, as the battery generates heat, the electrolyte based on the above-mentioned organic solvent is vaporized.
There has been a problem that the gas is decomposed to generate gas, and the generated gas causes the battery to burst or ignite.

In order to solve the above problem, for example, in a cylindrical battery, when the battery temperature rises when the battery is short-circuited or overcharged and the internal pressure of the battery rises, the safety valve is activated and the electrode terminals are simultaneously broken. Thereby, in the cylindrical battery,
A technique has been proposed in which a battery is provided with a mechanism for suppressing the flow of an excessive current of a predetermined amount or more (Nikkan Kogyo Shimbun,
"Electronic Technology", Vol. 39, No. 9, 1997).

However, it is not reliable that the mechanism always operates normally. If the mechanism does not operate normally,
There is a concern that heat generation due to an excessive current may increase and a dangerous state such as ignition may be caused.

In order to solve the above-mentioned problem, it is necessary to provide not only safety measures by providing ancillary parts such as a safety valve as described above but also a fundamentally high safety and a conventional non-aqueous electrolyte secondary battery. There is a demand for the development of a non-aqueous electrolyte secondary battery having the same excellent stability, excellent deterioration resistance, and excellent electrochemical stability.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems or to meet various demands and achieve the following objects. In other words, the present invention is excellent in self-extinguishing property or flame retardancy, excellent in deterioration resistance, low in interfacial resistance of non-aqueous electrolyte, and electrochemically, while maintaining long-term stability and safety required as a battery. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent stability and low-temperature discharge characteristics.

[0010]

Means for solving the above problems are as follows: <1> It contains a positive electrode, a negative electrode, a supporting salt, an organic solvent, and a phosphazene derivative. A non-aqueous electrolyte, wherein the potential window of the phosphazene derivative is in a range of lower limit +0.5 V or less and an upper limit +4.5 V or more, and the potential window of the organic solvent is A non-aqueous electrolyte secondary battery characterized by having a range wider than the potential window.

<2> The potential window of the phosphazene derivative is
The nonaqueous electrolyte secondary battery according to <1>, wherein the lower limit is 0 V or less and the upper limit is +5 V or more. <3> The viscosity of the phosphazene derivative at 25 ° C.
<1> which is 100 mPa · s (100 cP) or less
Or the non-aqueous electrolyte secondary battery according to <2>.

<4> The flash point of the phosphazene derivative is
The nonaqueous electrolyte secondary battery according to any one of <1> to <3>, which is at least 100 ° C. <5> The nonaqueous electrolyte secondary battery according to any one of <1> to <4>, wherein the phosphazene derivative has a substituent containing a halogen element in a molecular structure.

<6> The non-aqueous electrolyte secondary battery according to any one of <1> to <5>, wherein the organic solvent contains an aprotic organic solvent. <7> The non-aqueous electrolyte secondary battery according to <6>, wherein the aprotic organic solvent contains a cyclic ester compound or a chain ester compound. <8> The nonaqueous electrolyte secondary battery according to <7>, wherein the cyclic ester compound is at least one of ethylene carbonate, propylene carbonate, and γ-butyrolactone.

<9> The non-aqueous electrolyte secondary battery according to <7>, wherein the chain ester compound is diethyl carbonate. <10> The above <6>, wherein the viscosity of the aprotic organic solvent at 25 ° C. is 10 mPa · s (10 cP) or less.
To the non-aqueous electrolyte secondary battery according to any one of <9> to <9>.

<11> The method according to <1>, wherein the supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the content of the phosphazene derivative in the nonaqueous electrolyte is 1.5 to 2.5% by volume. The nonaqueous electrolyte secondary battery according to any one of <10>. <12> The supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the content of the phosphazene derivative in the nonaqueous electrolyte exceeds 2.5% by volume.
> The non-aqueous electrolyte secondary battery according to any one of <10>.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The nonaqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, a nonaqueous electrolyte containing a supporting salt, an organic solvent, and a phosphazene derivative. The potential window of the phosphazene derivative is within a predetermined range, and is wider than the potential window of the organic solvent.

In the non-aqueous electrolyte secondary battery according to the present invention, the potential window refers to a voltage range in which an electrochemical reaction does not occur. Here, a Li / Li ⁺ contrast value is used as a reference electrode. ing. In the non-aqueous electrolyte according to the present invention, the potential window of the phosphazene derivative is +0.5 V even if the lower limit is large and +4 V even if the upper limit is small.
It is necessary to be in the range of 5 V, and it is preferable that the lower limit is 0 V at most and the upper limit is +5 V at least. The lower limit of the potential window of the phosphazene derivative is more preferably in the range of -0.5 to 0 V, and the upper limit is more preferably in the range of +5 V to +8.5 V. In addition, if within the above numerical range,
A potential window in a numerical range by a combination of any upper limit and any lower limit may be used.

When the lower limit value of the potential window exceeds +0.5 V, or when the upper limit value of the potential window is less than +4.5 V, the potential window becomes narrower, and the potential of the nonaqueous electrolyte secondary battery is reduced. During charging and discharging, the non-aqueous electrolyte itself undergoes electrolysis, shortening the life of the non-aqueous electrolyte secondary battery, and causing the explosion of the non-aqueous electrolyte secondary battery due to the generated gas. This is undesirable. On the other hand, if the lower limit and the upper limit of the potential window are within the numerical range, the non-aqueous electrolyte is
The non-aqueous electrolyte secondary battery is stable over a long period of time, stable over a long period of time, and has no danger of explosion or the like, because it is stable with respect to the potential applied during charging and discharging.

In the present invention, the value of the potential window is:
It is a value obtained by using a cyclic voltammetry device (manufactured by Solartron) under the following measurement conditions. --Measurement conditions-- Working electrode: Pt, counter electrode: Pt, reference electrode: Li metal, supporting salt: tetraethylammonium tetrafluoroborate (manufactured by Aldrich) (addition amount: 1 mol /
l), scanning potential: 10 mV / sec.

[Positive Electrode] The material of the positive electrode is not particularly limited, and may be appropriately selected from known positive electrode materials. For example, V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ , MoO ₃ , L
Metal oxides such as iCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline are preferable. Among them, high capacity and safety are high. LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are particularly preferable because they are high in the wettability of the electrolyte. These materials may be used alone or in combination of two or more.

The shape of the positive electrode is not particularly limited, and can be appropriately selected from known shapes of electrodes. For example, a sheet shape, a column shape, a plate shape, a spiral shape, and the like can be given.

[Negative Electrode] The material of the negative electrode is not particularly limited as long as it can occlude and release lithium or lithium ions, for example, and can be appropriately selected from known negative electrode materials. Examples of the material of the negative electrode include a material containing lithium, specifically, lithium metal itself, an alloy of lithium, aluminum, indium, lead, or zinc, and a carbon material such as graphite doped with lithium. Preferably, carbon materials such as graphite are preferred among them because of their higher safety. These materials may be used alone or in combination of two or more. The shape of the negative electrode is not particularly limited, and may be appropriately selected from known shapes similar to the shape of the positive electrode.

[Non-Aqueous Electrolyte] -Supporting Salt- As the supporting salt, for example, lithium ion
And the like, as the ion source of the lithium ions.
Is, for example, LiClO_Four, LiBF_Four, LiPF ₆, L
iCF_ThreeSO_ThreeAnd LiAsF₆, LiC_FourF₉SO_Three,
Li (CF_ThreeSO_Two)_TwoN, Li (C_TwoF_FiveSO_Two)_TwoSuch as N
Lithium salts are preferred. These can be used alone
They may be used, or two or more kinds may be used in combination.

The compounding amount of the supporting salt with respect to the nonaqueous electrolyte is preferably 0.2 to 1 mol, more preferably 0.5 to 1 mol, per 1 kg of the nonaqueous electrolyte (solvent component). When the amount is less than 0.2 mol,
Insufficient conductivity of the non-aqueous electrolyte cannot be ensured, which may impair the charge / discharge characteristics of the battery.On the other hand, if it exceeds 1 mol, the viscosity of the non-aqueous electrolyte increases, Since sufficient mobility of lithium ions or the like cannot be secured, sufficient conductivity of the non-aqueous electrolyte cannot be secured as described above, and the charge / discharge characteristics of the battery may be affected.

-Phosphazene Derivative- The reason why the non-aqueous electrolyte contains a phosphazene derivative is as follows. Conventionally, in a non-aqueous electrolyte based on an aprotic organic solvent used for a non-aqueous electrolyte in a non-aqueous electrolyte secondary battery, a large current suddenly flows at the time of a short circuit, etc. When abnormal heat is generated, gas is generated by vaporization / decomposition, or the generated gas may cause rupture or ignition of the battery, which is highly dangerous.

On the other hand, if the conventional non-aqueous electrolyte contains a phosphazene derivative, the non-aqueous electrolyte can exhibit excellent self-extinguishing properties or flame retardancy due to the action of nitrogen gas or the like derived from the phosphazene derivative. Therefore, it is possible to reduce the risk as described above.

The content of the phosphazene derivative in the non-aqueous electrolyte is preferably at least 20% by volume. If the content is less than 20% by volume, the self-extinguishing property may not be sufficient. In the present invention, the self-extinguishing property means a property in which an ignited flame extinguishes on a 25 to 100 mm line in the following self-extinguishing property evaluation method, and a state in which ignition is not recognized even on a falling object. .

The content of the phosphazene derivative in the non-aqueous electrolyte is more preferably at least 30% by volume. If the content is 30% by volume or more,
The non-aqueous electrolyte can exhibit sufficient flame retardancy. In the present invention, the term "flame retardancy" refers to a property in which the ignited flame does not reach the 25 mm line and ignition of falling objects is not recognized in the following flame retardancy evaluation method.

--- Evaluation method of self-extinguishing property and flame retardancy-- The self-extinguishing property and flame retardancy are evaluated under the atmospheric environment by using a method arranged by UL (Underwriting Laboratory) standard UL94HB method. The combustion behavior of the ignited flame was measured and evaluated. At that time, ignitability, flammability, formation of carbides, and phenomena during secondary ignition were also observed. Specifically, based on the UL test standard, a non-combustible quartz fiber was impregnated with 1.0 ml of various electrolytic solutions, and was 127 mm
A test piece having a size of 12.7 mm was produced.

The upper limit of the content of the phosphazene derivative is not particularly limited, and may be 100% by volume of the non-aqueous electrolyte.
May be the phosphazene derivative.

The viscosity of the phosphazene derivative at 25 ° C. is 100 m from the viewpoint of reducing the viscosity of the non-aqueous electrolyte.
Pa · s (100 cP) or less, preferably 20 mPa · s
s (20 cP) or less is more preferable.

The flash point of the phosphazene derivative is preferably 100 ° C. or higher from the viewpoint of suppressing ignition and the like.
150 ° C. or higher is more preferable.

The phosphazene derivative preferably has a substituent containing a halogen element in the molecular structure. If the molecular structure has a substituent containing a halogen element, the halogen gas derived from the phosphazene derivative allows the phosphazene derivative to be more effectively used even in a smaller content within the numerical range of the content. ,
The non-aqueous electrolyte can exhibit self-extinguishing properties or flame retardancy.

In a compound containing a halogen element as a substituent, generation of a halogen radical may be a problem. However, in the phosphazene derivative of the present invention, the phosphorus element in the molecular structure promotes the halogen radical to stabilize it. Such a problem does not occur because phosphorus halide is formed.

Further, when the phosphazene derivative has a substituent containing a halogen element in the molecular structure, both the lower limit and the upper limit of the potential window slightly shift in the positive direction, but the potential It is presumed that there is no particular problem.

The content of the halogen element in the phosphazene derivative is preferably from 2 to 80% by weight,
-60% by weight is more preferred, and 2-50% by weight is even more preferred. If the content is less than 2% by weight, the effect obtained by incorporating halogen may not be effectively obtained. On the other hand, if the content is more than 80% by weight, the viscosity becomes high. When added, the conductivity of the non-aqueous electrolyte may decrease. As the halogen element, fluorine, chlorine, bromine and the like are preferable, and among them, fluorine is particularly preferable.

The phosphazene derivative is not particularly limited as long as it is a liquid at ordinary temperature (25 ° C.) in view of the conductivity of the non-aqueous electrolyte. For example, the phosphazene derivative may be a chain represented by the following general formula (1). Preferable examples include a phosphazene derivative and a cyclic phosphazene derivative represented by the following general formula (2).

General formula (1)

Embedded image However, in the general formula (1), R ¹ , R ² , and R
³ represents a monovalent substituent or a halogen element. X is carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic,
Represents an organic group containing at least one element selected from the group consisting of antimony, bismuth, oxygen, sulfur, selenium, tellurium, and polonium. Y ¹ , Y ² and Y
³ represents a divalent linking group, a divalent element, or a single bond.

Formula (2) (PNR ⁴ ₂ ) _{n In} the formula (2), R ⁴ represents a monovalent substituent or a halogen element. n represents 3 to 15.

In the general formula (1), R ¹ , R ² , and
R ³ is not particularly limited as long as it is a monovalent substituent or a halogen element, and examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group. Further, as the halogen element, for example, the above-mentioned halogen elements are preferably exemplified. Among these, an alkoxy group is particularly preferred in that the viscosity of the non-aqueous electrolyte can be reduced. R ^{1 to} R ³ may all be the same type of substituent, or some of them may be different types of substituents.

Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like, and an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group. Among these, as R ^{1 to} R ³ , all methoxy groups, ethoxy groups, methoxyethoxy groups, or methoxyethoxyethoxy groups are preferable, and from the viewpoints of low viscosity and high dielectric constant, all methoxy groups, ethoxyethoxy groups, or methoxyethoxyethoxy groups are preferable. Particularly preferred is a group or an ethoxy group.

Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group and a pentyl group. As the acyl group, a formyl group, an acetyl group,
Examples include a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group.

The hydrogen element in these substituents is preferably substituted by a halogen element as described above.

In the general formula (1), Y ¹ , Y ² , and
The group represented by Y ^3, for example, addition of CH ₂ group, oxygen, sulfur, selenium, nitrogen, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, Germanium, zirconium, lead, phosphorus, vanadium, arsenic,
Groups containing elements such as niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, nickel, etc., among these, a CH ₂ group, and oxygen, sulfur, selenium, nitrogen And the like are preferred. In particular, Y ¹ , Y ² , and
It is preferable that Y ³ contains elements of sulfur and selenium because the flame retardancy of the non-aqueous electrolyte is significantly improved. Y ^{1 to} Y
³ may be all the same type, or some may be different types.

In the general formula (1), X represents at least one element selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen, and sulfur from the viewpoint of harmfulness and environmental considerations. An organic group containing a seed is preferable, and an organic group having a structure represented by the following general formula (3) is more preferable.

General formula (3)

Embedded image However, in the general formula (3), R ^{5 to} R ⁹ represent a monovalent substituent or a halogen element. Y ^{5 to} Y ⁹ represent a divalent linking group, a divalent element, or a single bond, and Z represents a divalent group or a divalent element.

In the general formula (3), R ^{5 to} R ⁹ are preferably the same monovalent substituents or halogen elements as described for R ^{1 to} R ³ in the general formula (1). Can be Further, these may be of the same type within the same organic group, or some may be of different types. R ⁵ and R ⁶ , and R ⁸ and R ⁹ may combine with each other to form a ring. In the general formula (3),
Examples of the group represented by Y ^{5 to} Y ⁹ include the same divalent linking group or divalent group as described for Y ^{1 to} Y ³ in the general formula (1). In the case of a group containing an element of selenium or selenium, the flame retardancy of the non-aqueous electrolyte is significantly improved, which is particularly preferable. These may be of the same type or different from each other in the same organic group. In the general formula (3), Z represents, for example, a CH ₂ group, a CHR (R represents an alkyl group, an alkoxyl group, a phenyl group, etc .; the same applies hereinafter), an NR group, oxygen, sulfur, selenium, etc. , Boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium , Polonium, tungsten,
Examples thereof include groups containing elements such as iron, cobalt, and nickel. Among these, it is preferable to include oxygen, sulfur, and selenium in addition to CH ₂ , CHR, and NR groups. In particular, it is preferable to include the elements of sulfur and selenium, since the flame retardancy of the non-aqueous electrolyte is significantly improved.

In the general formula (3), the organic group includes
An organic group containing phosphorus as represented by the organic group (A) is particularly preferable because it can provide self-extinguishing property or flame retardancy particularly effectively. Further, when the organic group is an organic group containing sulfur as represented by the organic group (B), it is particularly preferable in terms of reducing the interface resistance of the non-aqueous electrolyte.

In the general formula (2), R ⁴ is not particularly limited as long as it is a monovalent substituent or a halogen element. Examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group and an acyl group. Group, aryl group and the like. Further, as the halogen element, for example, the above-mentioned halogen elements are preferably exemplified. Among these, an alkoxy group is particularly preferred in that the viscosity of the non-aqueous electrolyte can be reduced. Examples of the alkoxy group include a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group,
Phenoxy groups and the like. Among these, a methoxy group, an ethoxy group and a methoxyethoxy group are particularly preferred. The hydrogen element in these substituents is preferably substituted with a halogen element as described above.

In the general formulas (1) to (3), R ¹ to
By appropriately selecting R ⁹ , Y ^{1 to} Y ³ , Y ^{5 to} Y ⁹ , and Z, it is possible to synthesize a non-aqueous electrolyte having more suitable viscosity and solubility, and to obtain a non-aqueous electrolyte having a more suitable numerical range potential window. It becomes possible to produce a water electrolyte secondary battery. These phosphazene derivatives are
One type may be used alone, or two or more types may be used in combination.

-Organic solvent- As the organic solvent, an aprotic organic solvent or the like is particularly preferable from the viewpoint of safety. If the non-aqueous electrolyte contains the aprotic organic solvent, high safety can be obtained without reacting with the material of the negative electrode. Further, the viscosity of the non-aqueous electrolyte can be reduced, and optimal ionic conductivity as a non-aqueous electrolyte secondary battery can be easily achieved.

The aprotic organic solvent may be any organic solvent having a potential window wider than the potential window of the phosphazene derivative, and examples thereof include ether compounds and ester compounds. The aprotic organic solvent is not particularly limited, but examples thereof include an ether compound and an ester compound from the viewpoint of reducing the viscosity of the nonaqueous electrolyte. Specifically, 1,2-dimethoxyethane, tetrahydrofuran, dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, γ
-Valerolactone, methyl ethyl carbonate, ethyl methyl carbonate and the like are preferred. Among these, ethylene carbonate, propylene carbonate, cyclic ester compounds such as γ-butyrolactone, 1,
Chain ester compounds such as 2-dimethoxyethane, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate are preferred. In particular, a cyclic ester compound has a high relative dielectric constant and is excellent in solubility of a lithium salt or the like, and a chain ester compound has a low viscosity. Therefore, it is suitable in terms of reducing the viscosity of a nonaqueous electrolyte. is there. These may be used alone or in combination of two or more.
It is preferred to use more than one species in combination.

The viscosity of the aprotic organic solvent at 25 ° C. is 10 m from the viewpoint of reducing the viscosity of the non-aqueous electrolyte.
Pa · s (10 cP) or less is preferable.

As the non-aqueous electrolyte, phosphazene derivatives, LiP
Particularly preferred is a case where F ₆ and ethylene carbonate are contained. In this case, regardless of the above description, even if the content of the phosphazene derivative in the non-aqueous electrolyte is small, excellent self-extinguishing property or flame retardancy is obtained. Has the effect of That is, in such a case, when the content of the phosphazene derivative in the nonaqueous electrolyte is 1.5 to 2.5% by volume, the nonaqueous electrolyte has excellent self-extinguishing properties. It becomes a non-aqueous electrolyte with excellent flame retardancy.

[Other Members] As the other members, there is a separator interposed between the positive electrode and the negative electrode in a non-aqueous electrolyte secondary battery so as to prevent a short circuit of current due to contact between both electrodes. As the material of the separator, a material capable of reliably preventing contact between the two electrodes, and capable of passing or containing an electrolytic solution, for example, a nonwoven fabric made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, a thin film And the like. Among these, a polypropylene or polyethylene microporous film having a thickness of about 20 to 50 μm is particularly preferable.

As the above-mentioned other members in addition to the above-mentioned separator, well-known members usually used for batteries are preferably exemplified.

The form of the non-aqueous electrolyte secondary battery of the present invention described above is not particularly limited, and various known types such as a coin type, a button type, a paper type, a square type or a spiral type cylindrical battery, and the like can be used. A form is suitably mentioned.
In the case of the spiral structure, for example, a nonaqueous electrolyte secondary battery can be manufactured by forming a sheet-shaped positive electrode, sandwiching a current collector, and stacking and winding the negative electrode (sheet-shaped) on the current collector. .

The non-aqueous electrolyte secondary battery of the present invention described above has excellent self-extinguishing properties, flame retardancy, and deterioration resistance while maintaining the long-term stability and safety required for the battery. A non-aqueous electrolyte secondary battery having a low interfacial resistance of an aqueous electrolyte, and excellent in electrochemical stability and low-temperature discharge characteristics.

[0059]

EXAMPLES The present invention will be described below in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In each of the examples, the aprotic organic solvent used had a potential window wider than that of the phosphazene derivative used. (Example 1) [Preparation of non-aqueous electrolyte] γ-butyrolactone (aprotic organic solvent, viscosity at 25 ° C: 1.7 mPa · s)
(1.7 cP)) contains 80 ml of a phosphazene derivative (a chain EO-type phosphazene derivative (in the general formula (1), X is a structure of the organic group (A) represented by the general formula (3)); A compound in which Y ^{1 to} Y ³ and Y ^{5 to} Y ⁶ are all single bonds, R ^{1 to} R ³ and R ^{5 to} R ⁶ are all ethoxy groups, and Z is oxygen) ) (Viscosity at 25 ° C .: 5.8 mPa · s (5.8 cP), flash point: 155)
° C) (20% by volume).
F ₄ (lithium salt) was dissolved at a concentration of 0.5 mol / kg to prepare a non-aqueous electrolyte.

-Evaluation of self-extinguishing property or flame retardancy- The obtained non-aqueous electrolyte was evaluated as described below in the same manner as in the above "method of evaluating self-extinguishing property and flame retardancy". Was. Table 1 shows the results.

<Evaluation of Flame Retardancy>
The case where it did not reach the 5 mm line and no ignition was found even on a falling object from the net was evaluated as having flame retardancy. <Evaluation of self-extinguishing property> The ignited flame is 25 to 100 mm
A fire was extinguished between the lines, and a case where no ignition was recognized even for a falling object from a net drop was evaluated as having self-extinguishing properties. <Evaluation of flammability> The case where the ignited flame exceeded the 100 mm line was evaluated as having flammability.

[Preparation of Non-Aqueous Electrolyte Secondary Battery] Chemical Formula Li
Cobalt oxide represented by CoO ₂ was used as a positive electrode active material, and 10 parts of acetylene black (conductive additive) and 10 parts of Teflon (registered trademark) binder (binder resin) were added to 100 parts of LiCoO _2. And kneaded with an organic solvent (50/50 volume% mixed solvent of ethyl acetate and ethanol), and then roll-rolled to a thickness of 100 μm and a width of 40 m.
m of a positive electrode sheet in the form of a thin layer. Thereafter, using the two obtained positive electrode sheets, a 25 μm-thick aluminum foil (current collector) coated with a conductive adhesive on its surface was sandwiched, and a 25 μm-thick separator (microporous film: A 150 μm-thick carbon film (negative electrode material) was overlapped and wound up with a polypropylene electrode interposed therebetween to produce a cylindrical electrode. The length of the positive electrode of the cylindrical electrode was about 260 mm.

The non-aqueous electrolyte was injected into the cylindrical electrode and sealed to prepare an AA lithium battery.

-Measurement of Potential Window- The lower limit and the upper limit of the potential window of the phosphazene derivative used under the measurement conditions were measured using the above-described cyclic voltammetry apparatus. Table 1 shows the results.

-Evaluation of stability of battery- The obtained battery was measured for the following charge / discharge capacity.
Charge and discharge capacity (mA) at initial and after 50 cycles of charge / discharge
h / g) was measured to evaluate the stability of the battery. Table 1 shows the results.

--Measurement of charge / discharge capacity-- A charge / discharge curve at 20 ° C. was measured using a positive electrode or a negative electrode having a known weight, and the amount of charge or discharge at this time was determined by the weight of the positive electrode or the negative electrode used. It was determined by dividing. Table 1 shows the results. The theoretical capacity of the used positive electrode (LiCoO ₂ ) is 145 mAh / g, and that of the negative electrode (carbon film) is 350 mAh / g.

-Evaluation of Electrochemical Stability- The potential of the solvent (non-aqueous electrolyte) was set to 5 V on the positive electrode side and 0 V on the negative electrode side, and the degree of decomposition of the solvent (non-aqueous electrolyte) was measured by NMR, It measured by GC-MS and evaluated the electrochemical stability. Table 1 shows the results.

-Evaluation of low-temperature discharge characteristics (measurement of low-temperature discharge capacity)-Upper limit voltage 4.5 V, lower limit voltage 3.0 V, discharge current 100
Charge and discharge were repeated up to 50 cycles under the conditions of mA and a charging current of 50 mA. At this time, charging was performed at 20 ° C., and discharging was performed at low temperature (−20 ° C., −10 ° C.). At this time, the discharge capacity at a low temperature was compared with the discharge capacity at 20 ° C., and the discharge capacity reduction rate was calculated from the following equation. Table 1 shows the results. Formula: discharge capacity reduction rate = 100− (low temperature discharge capacity / discharge capacity (20 ° C.)) × 100 (%)

(Example 2) In "Preparation of non-aqueous electrolyte" in Example 1, γ-butyrolactone was changed to 20 ml, and
80 ml of phosphazene derivative (80% by volume)
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that the self-extinguishing property or the flame retardancy was evaluated. A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the potential window was measured, the stability of the battery was evaluated, the electrochemical stability was evaluated, and the low-temperature discharge characteristics were evaluated. Table 1 shows these results.
Shown in

(Example 3) In "Preparation of non-aqueous electrolyte" of Example 2, the phosphazene derivative was replaced with a phosphazene derivative (a chain EO-type phosphazene derivative (X in the above formula (1), 3) The structure of the organic group (A) represented by (3), wherein Y ^{1 to} Y ³ and Y ^{5 to} Y ⁶ are all single bonds, and R ^{1 to} R ³ and R ^{5 to} R ⁶ Are all ethoxy groups and compounds in which Z is oxygen)) in which the hydrogen element in the ethoxy group is replaced with fluorine (the content of the fluorine element in the phosphazene derivative: 12.4% by weight). Prepared a non-aqueous electrolyte in the same manner as in Example 2, and evaluated self-extinguishing properties or flame retardancy. A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 2, and the potential window was measured and evaluated, the stability of the battery was evaluated, the electrochemical stability was evaluated, and the low-temperature discharge characteristics were evaluated. . Table 1 shows the results.

(Example 4) In "Preparation of non-aqueous electrolyte" in Example 1, 80 ml of γ-butyrolactone was changed to 97 ml of ethylene carbonate, and the added amount of the phosphazene derivative was changed to 3 ml (3% by volume). A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that LiBF ₄ (lithium salt) was replaced with LiPF ₆ , and self-extinguishing or flame retardancy was evaluated. Further, a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the potential window was measured and evaluated, the stability of the battery was evaluated, the electrochemical stability was evaluated, and the low-temperature discharge characteristics were evaluated. . Table 1 shows the results.

(Comparative Example 1) In “Preparation of Nonaqueous Electrolyte Solution” in Example 1, a phosphazene derivative (a chain EO-type phosphazene derivative (in the above formula (1), X is represented by the formula (3)) a structure of the organic group (a) is, Y ¹ ~
Y ³ and Y ^{5 to} Y ⁶ are all single bonds, and R ^{1 to} R ³ ,
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that compounds in which R ^{5 to} R ⁶ were all ethoxy groups, and Z was oxygen)) were not used. The flammability was evaluated. Further, a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the potential window was measured and evaluated, the stability of the battery was evaluated, the electrochemical stability was evaluated, and the low-temperature discharge characteristics were evaluated. . Table 1 shows the results.

[0073]

[Table 1]

In Examples 1 to 4, the non-aqueous electrolyte has excellent self-extinguishing properties or flame retardancy, and the long-term stability, deterioration resistance, and electrochemical stability of the non-aqueous electrolyte secondary battery. It is also found that the low-temperature discharge characteristics are excellent.

[0075]

According to the present invention, while maintaining the long-term stability and safety required for a battery, it is excellent in self-extinguishing properties, flame retardancy, and deterioration resistance, and the interface resistance of a non-aqueous electrolyte is low. It is possible to provide a non-aqueous electrolyte secondary battery which is low and has excellent electrochemical stability and low-temperature discharge characteristics.

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Claims (12)

[Claims] A non-aqueous electrolytic solution containing a positive electrode, a negative electrode, a supporting salt, an organic solvent, and a phosphazene derivative, wherein a potential window of the phosphazene derivative has a lower limit of +0.5 V or less, A non-aqueous electrolyte secondary battery, wherein the upper limit is +4.5 V or more and the potential window of the organic solvent is wider than the potential window of the phosphazene derivative. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a potential window of the phosphazene derivative is in a range of a lower limit of 0 V or less and an upper limit of +5 V or more. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the phosphazene derivative has a viscosity at 25 ° C. of 100 mPa · s (100 cP) or less. 4. A phosphazene derivative having a flash point of 100
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the temperature is higher than or equal to ° C. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the phosphazene derivative has a substituent containing a halogen element in a molecular structure. 6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the organic solvent contains an aprotic organic solvent. 7. The non-aqueous electrolyte secondary battery according to claim 6, wherein the aprotic organic solvent contains a cyclic ester compound or a chain ester compound. 8. The non-aqueous electrolyte secondary battery according to claim 7, wherein the cyclic ester compound is at least one of ethylene carbonate, propylene carbonate, and γ-butyrolactone. 9. The non-aqueous electrolyte secondary battery according to claim 7, wherein the chain ester compound is diethyl carbonate. 10. The non-aqueous electrolyte secondary battery according to claim 6, wherein the viscosity of the aprotic organic solvent at 25 ° C. is 10 mPa · s (10 cP) or less. 11. The method according to claim 1, wherein the supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the content of the phosphazene derivative in the non-aqueous electrolyte is 1.5 to 2.5% by volume. The non-aqueous electrolyte secondary battery according to any one of the above. 12. The method according to claim 1, wherein the supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the content of the phosphazene derivative in the non-aqueous electrolyte exceeds 2.5% by volume. Non-aqueous electrolyte secondary battery.