JP2001217001A - Additive for non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an additive for a non-aqueous electrolyte secondary battery, which can give superior self fire-extinguishing and fire retardance and excellent low temperature discharging characteristics to the non-aqueous electrolyte as well as small surface resistance of the electrolyte, while keeping the necessary battery properties, by adding to the non-aqueous electrolyte of the secondary battery. SOLUTION: This is an additive for a non-aqueous electrolyte secondary battery having non-aqueous electrolyte containing supporting salt and organic solvent, which is added in the non-aqueous electrolyte and contains at least a phosphagen derivative inside it. It is a desirable state and manner that the above organic solvent is made of a non-protonic organic solvent and that, in particular, the non-protonic organic solvent contains a cyclic or chain (aliphatic) ester compound and further, that the added amount of the additive in the above non-aqueous electrolyte is 20 to 90 volume % and 30 to 90 volume %, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte which can be suitably added to a non-aqueous electrolyte in a non-aqueous electrolyte secondary battery, and which can impart self-extinguishing properties or flame retardancy to the non-aqueous electrolyte. The present invention relates to an additive for a liquid secondary battery.

[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. It has been commercialized. For example, more than half of notebook computers and mobile phones are driven by non-aqueous electrolyte secondary batteries.

As a material for forming the negative electrode of the nonaqueous electrolyte secondary battery, carbon (hard carbon, soft carbon) is frequently used. Various organic solvents have been used as electrolytes for the purpose of increasing the driving voltage. or,
For non-aqueous electrolyte secondary batteries for cameras, alkali metals (particularly lithium metals and lithium alloys) are used as negative electrode materials
In order to reduce the danger of violent reaction with water, an aprotic organic solvent such as an ester organic solvent is usually used as the electrolytic solution.

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 develop a non-aqueous electrolyte secondary battery having a fundamentally high safety, not a safety measure by providing ancillary parts such as a safety valve as described above. Have been.

[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. That is, the present invention, by adding to the non-aqueous electrolyte in a non-aqueous electrolyte secondary battery, while maintaining the battery characteristics and the like required as a battery, the non-aqueous electrolyte has excellent self-extinguishing properties or flame retardancy It is an object of the present invention to provide an additive for a non-aqueous electrolyte secondary battery which can provide excellent low-temperature discharge characteristics and can reduce the interfacial resistance of the non-aqueous electrolyte.

[0010]

Means for solving the above problems are as follows. <1> A non-aqueous electrolyte in a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte containing a supporting salt and an organic solvent, wherein the non-aqueous electrolyte contains at least a phosphazene derivative. It is an additive for a liquid secondary battery.

<2> The additive for a non-aqueous electrolyte secondary battery according to <1>, wherein the organic solvent is an aprotic organic solvent. <3> The additive for a non-aqueous electrolyte secondary battery according to <2>, wherein the aprotic organic solvent contains a cyclic or chain ester compound.

<4> The amount of addition in the non-aqueous electrolyte is 2
The additive for a nonaqueous electrolyte secondary battery according to any one of <1> to <3>, which is 0 to 90% by volume. <5> The additive for a non-aqueous electrolyte secondary battery according to any one of <1> to <3>, wherein the additive amount in the non-aqueous electrolyte is 30 to 90% by volume.

<6> The above-mentioned <1> to <3>, wherein the supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the amount added in the nonaqueous electrolyte is 1.5 to 2.5% by volume. The additive for a non-aqueous electrolyte secondary battery according to any one of the above. <7> The supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the amount added in the non-aqueous electrolyte is
<1> is more than 2.5% by volume and 90% by volume or less.
The additive for a nonaqueous electrolyte secondary battery according to any one of <1> to <3>. <8> The additive for a nonaqueous electrolyte secondary battery according to any one of <1> to <7>, wherein the phosphazene derivative has a substituent containing a halogen element in a molecular structure. <9> The additive for a nonaqueous electrolyte secondary battery according to <8>, wherein the content of the halogen element in the phosphazene derivative is 2 to 80% by weight.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The additive for a non-aqueous electrolyte secondary battery of the present invention is added to a non-aqueous electrolyte in a non-aqueous electrolyte secondary battery.

<Non-Aqueous Electrolyte Secondary Battery> The non-aqueous electrolyte secondary battery has a positive electrode, a negative electrode, and a non-aqueous electrolyte, and may have other members as necessary.

[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 may be appropriately selected from known shapes as 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. For example, a material containing lithium, specifically, lithium metal itself, an alloy of lithium, aluminum, indium, lead, or zinc, a carbon material such as graphite doped with lithium, and the like are preferable. Among them, a carbon material such as graphite is preferable in terms of 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] The non-aqueous electrolyte contains a supporting salt and an organic solvent.

-Supporting salt- As the supporting salt, for example, a supporting salt serving as an ion source of lithium ions is preferable. Examples of the lithium ion ion source include LiClO ₄ , LiBF ₄ , L
iPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC
_{4 F 9 SO 3, Li (} CF 3 SO 2) 2 N, Li (C 2 F 5 SO
₂₎ lithium salts such as ₂ N are preferably exemplified. They are,
One type may be used alone, or two or more types may be used in combination.

The compounding amount of the supporting salt with respect to the non-aqueous electrolyte is preferably 0.2 to 1 mol, more preferably 0.5 to 1 mol, per 1 kg of the non-aqueous 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.

-Organic solvent- As the organic solvent, an aprotic organic solvent is particularly preferred 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. Also,
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 is not particularly limited, but may be an ether compound, an ester compound or the like from the viewpoint of reducing the viscosity of the non-aqueous electrolyte. Specifically, 1,2-dimethoxyethane, tetrahydrofuran,
Preferable examples include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, methyl ethyl carbonate, and ethyl methyl carbonate. Among these, cyclic ester compounds such as ethylene carbonate, propylene carbonate, and γ-butyrolactone, and chain ester compounds such as 1,2-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, but it is preferable to use two or more in combination.

The viscosity of the aprotic organic solvent at 25 ° C. is not particularly limited, but may be 10 mPa · s.
(10 cP) or less is preferable.

In the non-aqueous electrolyte, the supporting salt is L
Including iPF ₆ , the organic solvent is particularly preferable when the solvent contains ethylene carbonate. In this case, even if the additive amount of the non-aqueous electrolyte secondary battery additive of the present invention is small, excellent self-extinguishing property or It can exhibit a flame retardant effect.

[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 current short circuit due to contact between the two 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 described above is not particularly limited, and various known forms such as a coin type, a button type, a paper type, a square type or a spiral type cylindrical battery are preferable. It is listed. 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. .

<Additive for Non-Aqueous Electrolyte Secondary Battery> The additive for a non-aqueous electrolyte secondary battery of the present invention contains a phosphazene derivative and, if necessary, other components.

The reason why the additive for a non-aqueous electrolyte secondary battery of the present invention contains a phosphazene derivative is as follows. Conventionally, in an 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 during a short circuit, etc. When heat is generated, the gas is vaporized and decomposed to generate gas, or the generated gas and heat may cause the battery to burst or ignite, which is highly dangerous.

On the other hand, by adding the additive for a nonaqueous electrolyte secondary battery of the present invention containing a phosphazene derivative to these conventional nonaqueous electrolytes, nitrogen gas and halogen gas derived from the phosphazene derivative are added. By such actions, self-extinguishing property or flame retardancy is imparted to the non-aqueous electrolyte, and the above-described danger can be reduced.
Further, since phosphorus has an effect of suppressing chain decomposition of a polymer material constituting a battery, self-extinguishing property or flame retardancy can be effectively provided.

The additive amount of the non-aqueous electrolyte secondary battery of the present invention in the non-aqueous electrolyte may be such that the non-aqueous electrolyte secondary battery is added to the non-aqueous electrolyte secondary battery. According to the effect obtained by the above, two types of a first addition amount capable of providing the non-aqueous electrolyte with self-extinguishing property and a second addition amount capable of providing the non-aqueous electrolyte with flame retardancy The addition amount is suitably mentioned.

The first amount is preferably 20 to 90% by volume, more preferably 40 to 75% by volume. If the amount is less than 20% by volume, sufficient self-extinguishing properties may not be provided.
In some cases, the viscosity of the non-aqueous electrolyte increases, and the conductivity may extremely decrease.

However, in the non-aqueous electrolyte, when the supporting salt contains LiPF ₆ and the organic solvent contains ethylene carbonate, the first addition amount is as follows:
1.5-2.5% by volume is preferred. 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 second addition amount is preferably from 30 to 90% by volume, and more preferably from 40 to 60% by volume. If the addition amount is less than 30% by volume, sufficient flame retardancy may not be imparted. On the other hand, if it exceeds 90% by volume, the viscosity of the non-aqueous electrolyte increases, and good electrical conductivity cannot be maintained. is there.

However, in the case where the supporting salt contains LiPF ₆ and the organic solvent contains ethylene carbonate in the non-aqueous electrolyte, the second addition amount is as follows:
More than 2.5% by volume, preferably 90% by volume or less, more preferably 3% by volume or more and 90% by volume or less. Incidentally, in the present invention, the flame retardant, in the following flame retardancy evaluation method,
This refers to the property in which the ignited flame does not reach the 25 mm line, and ignition is not recognized even for falling objects.

--- Evaluation method of self-extinguishing property and flame retardancy-- The evaluation of the self-extinguishing property and flame retardancy was carried out 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 phosphazene derivative preferably has a substituent containing a halogen element in the molecular structure. When the molecular structure has a substituent containing a halogen element, the halogen gas derived from the phosphazene derivative enables the self-extinguishing or flame-retardant effect to be more effectively exerted. Become. Therefore, the same effect as described above can be obtained with a smaller amount of addition. Specifically, when the phosphazene derivative has a substituent containing a halogen element in the molecular structure,
As said 1st addition amount, 10-90 volume% is preferable and 20-75 volume% is more preferable. In addition, the second
Is preferably 20 to 90% by volume, more preferably 30 to 60% by volume.

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

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. When the content is less than 2% by weight, the effect of including the halogen element may not be remarkably exhibited. On the other hand, when the content is more than 80% by weight, the viscosity increases. The conductivity may decrease. As the halogen element, in particular, fluorine, chlorine,
Bromine and the like are preferred.

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, but for example, 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.

General formula (2) (PNR ⁴ ₂ ) _{n In} the general 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 groups.

In the general formula (1), X represents at least one of elements selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen, and sulfur from the viewpoint of harmfulness, environment, and the like. 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). The element of selenium is particularly preferable because the flame retardancy of the nonaqueous electrolyte is remarkably improved. These may be of the same type or different from each other in the same organic group. In the general formula (3), Z is, for example, CH
₂ groups, CHR (R represents an alkyl group, an alkoxyl group, a phenyl group, etc .; the same applies hereinafter), an NR group, oxygen, sulfur, selenium, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum ,
Including elements such as thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, nickel, etc. Of these, in addition to the CH ₂ group, CHR group, and NR group, the elements of oxygen, sulfur, and selenium are preferable. In particular, when the element is sulfur or selenium, the flame retardancy of the non-aqueous electrolyte is remarkably improved, which is preferable.

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
Synthesis of additives for non-aqueous electrolyte secondary batteries having more suitable viscosity, solubility suitable for addition and mixing, and the like by appropriately selecting R ⁹ , Y ^{1 to} Y ³ , Y ^{5 to} Y ⁹ , and Z Becomes possible.
These phosphazene derivatives may be used alone or in combination of two or more.

The flash point of the phosphazene derivative is not particularly limited.
C. or higher, and more preferably 150 C. or higher.

According to the additive for a non-aqueous electrolyte secondary battery of the present invention described above, by adding it to the non-aqueous electrolyte, the non-aqueous electrolyte has excellent self-extinguishing properties or flame retardancy,
Low-temperature discharge characteristics can be imparted, and the interface resistance of the non-aqueous electrolyte can be reduced. Further, since the nonaqueous electrolyte secondary battery is added to the conventional nonaqueous electrolyte, a highly safe nonaqueous electrolyte secondary battery can be easily manufactured. Further, the obtained non-aqueous electrolyte secondary battery also has excellent battery characteristics equivalent to ordinary batteries.

[0057]

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. (Example 1) [Preparation of non-aqueous electrolyte] A mixed solvent of ethylene carbonate and diethyl carbonate (mixing ratio (volume ratio): ethylene carbonate / diethyl carbonate = 1/1) (aprotic organic solvent) in 80 ml, The phosphazene derivative (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)), and Y ^{1 to} Y ³ and Y ⁵化合物 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)) (for non-aqueous electrolyte secondary batteries (Additive) (20% by volume).
LiBF ₄ (supporting 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-mentioned “Method for evaluating self-extinguishing property and flame retardancy”. Was. Table 1 shows the results.

-Evaluation of Flame Retardancy- The case where the ignited flame did not reach the 25 mm line of the apparatus and no ignition was observed even on a falling object from the net was evaluated as having flame retardancy. -Evaluation of self-extinguishing property-The ignited flame extinguishes between 25 to 100 mm line,
In addition, a case where ignition was not recognized even on a falling object from the net fall 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 binder (binder resin) were added to 100 parts of LiCoO ₂ , and an organic solvent was added. (50/50 volume% mixed solvent of ethyl acetate and ethanol), and then roll-rolled to produce a thin layered positive electrode sheet having a thickness of 100 μm and a width of 40 mm. Then, the obtained positive electrode sheet 2
Using a sheet, conductive adhesive was applied to the surface, thickness 25
A 150-μm thick lithium metal foil is overlapped and wound up with a 25-μm-thick separator (microporous film: polypropylene) interposed between the aluminum foil (current collector) with a thickness of 25 μm. did. 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 / Evaluation of Battery Characteristics, etc.> For the obtained batteries, the initial battery characteristics (voltage, internal resistance) were measured and evaluated at 20 ° C., and then the following evaluation methods were used.
The charge / discharge cycle performance was measured and evaluated. Table 1 shows the results.

-Evaluation of charge / discharge cycle performance- Upper limit voltage 4.5V, lower limit voltage 3.0V, discharge current 100
Charge and discharge were repeated up to 50 cycles under the conditions of mA and a charging current of 50 mA. The charge / discharge capacity at this time was compared with the charge / discharge capacity at the initial stage, and the capacity reduction rate after 50 cycles was calculated. The same measurement and measurement were performed for a total of three batteries.
The calculated values were averaged, and the results were used to evaluate the charge / discharge cycle performance.

<Evaluation of Low-Temperature Discharge Characteristics (Measurement of Low-Temperature Discharge Capacity)> Regarding the obtained battery, except that the temperature at the time of discharging was set to low temperature (−10 ° C., −20 ° C.), The charge and discharge were repeated up to 50 cycles under the same conditions as in “Evaluation of”. The discharge capacity at low temperature at this time is
The discharge capacity reduction rate was calculated from the following equation by comparing with the discharge capacity measured at 20 ° C. For a total of three batteries,
In the same manner, measurement and calculation were performed, and the average value was taken to evaluate the low-temperature discharge characteristics. 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, the phosphazene derivative (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 ,
And the compound in which R ^{5 to} R ⁶ are all ethoxy groups and Z is oxygen)) (the additive for the non-aqueous electrolyte secondary battery) in the non-aqueous electrolyte is 80% by volume. A non-aqueous electrolyte was prepared and evaluated for self-extinguishing or flame retardancy in the same manner as in Example 1, except for the change. A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the initial battery characteristics (voltage and internal resistance), charge / discharge cycle performance, and low-temperature discharge characteristics were measured and evaluated. Table 1 shows the results.

Example 3 In “Preparation of Nonaqueous Electrolyte” in Example 1, the additive for a nonaqueous electrolyte secondary battery was a phosphazene derivative (a chain EO-type phosphazene derivative (the above-described general formula (1))). In the above, X is the structure of the organic group (A) represented by the general formula (3), 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 Z is oxygen.)) (Additive for non-aqueous electrolyte secondary battery) Replaces hydrogen element in ethoxy group with fluorine element ( A non-aqueous electrolyte was prepared and evaluated for self-extinguishing or flame retardancy in the same manner as in Example 1, except that the compound was replaced with a compound containing 15% by weight of a fluorine element in a phosphazene derivative. A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the initial battery characteristics (voltage and internal resistance), charge / discharge cycle performance, and low-temperature discharge characteristics were measured and evaluated. Table 1 shows the results.

Example 4 In “Preparation of Nonaqueous Electrolyte” in Example 1, a mixed solvent of ethylene carbonate and diethyl carbonate (mixing ratio (volume ratio): ethylene carbonate / diethyl carbonate = 1/1) ( 80 ml of the aprotic organic solvent was changed to 97 ml, and the phosphazene derivative (chain EO-type phosphazene derivative (in the above general formula (1), X represents the structure of the organic group (A) represented by the general formula (3)) Wherein 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 Certain compound)) (additive for non-aqueous electrolyte secondary battery) 20 ml (20% by volume)
Was replaced with 3 ml (3% by volume) and LiBF ₄ (supporting salt) was replaced with LiPF ₆ (supporting salt), except that a non-aqueous electrolyte solution was prepared in the same manner as in Example 1 and self-extinguishing or flame retardant. Was evaluated. A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the initial battery characteristics (voltage and internal resistance), charge / discharge cycle performance, and low-temperature discharge characteristics were measured and evaluated. Table 1 shows the results.

(Comparative Example 1) In “Preparation of Nonaqueous Electrolyte Solution” of Example 1, a phosphazene derivative (a chain EO-type phosphazene derivative (in the above general formula (1), X is represented by the general 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 ,
And a compound in which R ^{5 to} R ⁶ are all ethoxy groups and Z is oxygen)) (a non-aqueous electrolyte secondary battery additive) and a mixed solvent of ethylene carbonate and diethyl carbonate ( Aprotic organic solvent) is 100 m
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that the amount was changed to 1, and the self-extinguishing property or the flame retardancy was evaluated. Further, a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the initial battery characteristics (voltage, internal resistance), charge / discharge cycle performance,
The low-temperature discharge characteristics were measured and evaluated. Table 1 shows the results.

[0069]

[Table 1]

In Examples 1 to 3, the non-aqueous electrolyte has excellent self-extinguishing properties and flame retardancy. When the additive for a non-aqueous electrolyte secondary battery of the present invention is used, safety is improved. It turns out that it is excellent. In particular, in Examples 3 and 4, it can be seen that excellent flame retardancy can be imparted even when the amount of the additive for a non-aqueous electrolyte secondary battery is small.

[0071]

According to the present invention, by adding to a non-aqueous electrolyte in a non-aqueous electrolyte secondary battery, self-extinguishing excellent in a non-aqueous electrolyte can be maintained while maintaining battery characteristics required for the battery. It is possible to provide an additive for a non-aqueous electrolyte secondary battery, which can impart non-aqueous electrolyte with excellent low-temperature discharge characteristics and a low interface resistance.

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Claims (9)

[Claims] 1. A non-aqueous electrolyte secondary battery having a non-aqueous electrolyte containing a supporting salt and an organic solvent, wherein the non-aqueous electrolyte is added to the non-aqueous electrolyte and contains at least a phosphazene derivative. Additive for liquid secondary batteries. 2. The additive for a non-aqueous electrolyte secondary battery according to claim 1, wherein the organic solvent is an aprotic organic solvent. 3. The additive for a non-aqueous electrolyte secondary battery according to claim 2, wherein the aprotic organic solvent contains a cyclic or chain ester compound. 4. The amount of addition in the non-aqueous electrolyte is 20 to 9
The additive for a non-aqueous electrolyte secondary battery according to claim 1, wherein the additive is 0% by volume. 5. The amount of the non-aqueous electrolyte solution added is 30 to 9
The additive for a non-aqueous electrolyte secondary battery according to claim 1, wherein the additive is 0% by volume. 6. The method according to claim 1, wherein the supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the amount added in the non-aqueous electrolyte is 1.5 to 2.5% by volume. The additive for a non-aqueous electrolyte secondary battery according to the above. 7. The method according to claim 1, wherein the supporting salt contains LiPF ₆ , the organic solvent contains ethylene carbonate, and the amount added in the non-aqueous electrolyte is more than 2.5% by volume and 90% by volume or less. The additive for a non-aqueous electrolyte secondary battery according to any one of the above. 8. The additive for a non-aqueous electrolyte secondary battery according to claim 1, wherein the phosphazene derivative has a substituent containing a halogen element in a molecular structure. 9. The additive for a non-aqueous electrolyte secondary battery according to claim 8, wherein the content of the halogen element in the phosphazene derivative is 2 to 80% by weight.