JP2001217004A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery that is excellent in deterioration resistance and has low surface resistance of non-aqueous electrolyte and excellent low temperature discharging characteristics while keeping properties necessary for a battery. SOLUTION: This is a non-aqueous electrolyte secondary battery which has a positive electrode, a negative electrode, supporting salt and a non-aqueous electrolyte containing phosphagen derivative of more than 2 and less than 20 volume %. It is a desirable state and manner that the non-aqueous electrolyte contains the phosphagen derivative of more than 3 and less than 20 volume % and that the ion source of lithium ion is LiPF6 and further that the non- aqueous electrolyte contains non-protonic organic solvent and that the non- protonic organic solvent contains cyclic or chain (aliphatic) ester compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having excellent deterioration resistance.

[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.

[0004] However, although the nonaqueous electrolyte secondary battery has high performance, it is liable to be deteriorated, so that high performance cannot be maintained for a long period of time, which has been a problem. Therefore, there has been a strong demand for the development of a non-aqueous electrolyte secondary battery capable of maintaining battery characteristics such as high charge / discharge capacity for a long period without deterioration.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and achieve the following objects. That is, the present invention provides a non-aqueous electrolyte secondary battery having excellent resistance to deterioration, low interfacial resistance of the non-aqueous electrolyte, and excellent low-temperature discharge characteristics, while maintaining battery characteristics and the like required as a battery. The purpose is to do.

[0006]

Means for solving the above problems are as follows: <1> A positive electrode, a negative electrode, a supporting salt and 2% by volume or more.
A non-aqueous electrolyte solution containing less than% by volume of a phosphazene derivative. <2> The nonaqueous electrolyte secondary battery according to <1>, wherein the nonaqueous electrolyte contains 3% by volume or more and less than 20% by volume of a phosphazene derivative.

<3> The non-aqueous electrolyte secondary battery according to <1> or <2>, wherein the supporting salt is a LiPF ₆ salt. <4> The non-aqueous electrolyte secondary battery according to any one of <1> to <3>, wherein the non-aqueous electrolyte contains an aprotic organic solvent. <5> The non-aqueous electrolyte secondary battery according to <4>, wherein the aprotic organic solvent contains a cyclic or chain ester compound.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The non-aqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte, and has 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.

[0010] The shape of the positive electrode is not particularly limited, and can 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 negative electrode can, for example, occlude and release lithium or lithium ions. Therefore, the material is not particularly limited as long as it can occlude and release lithium or lithium ions, 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 2% by volume to less than 20% by volume of a phosphazene derivative, and may contain other components such as an aprotic organic solvent, if necessary. contains.

-Supporting salt- As the supporting salt, for example, a supporting salt serving as an ion source of lithium ions is preferable. The ion source of the lithium ions is not particularly limited.
O ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , and
LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂
Lithium salts such as N and Li (C ₂ F ₅ SO ₂ ) ₂ N are preferred. Among them, LiPF has a high conductivity
_Six salts are preferred. These may be used alone,
Two or more kinds may be used in combination.

The amount of the supporting salt to be mixed with 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,
In some cases, good conductivity cannot be ensured. On the other hand, when it exceeds 1 mol, the viscosity of the non-aqueous electrolyte increases, and similarly, the conductivity may decrease.

-Phosphazene derivative- The reason why the nonaqueous electrolyte contains a phosphazene derivative is as follows. In a conventional non-aqueous electrolyte secondary battery, in an ester-based electrolyte or the like used as an electrolyte, for example, LiPF _{6 as a} supporting salt is used.
A lithium ion source such as a salt becomes LiF and PF over time.
_It is considered that the corrosion progresses and deteriorates due to PF ₅ gas generated by decomposition into ₅ and hydrogen fluoride gas generated by further reaction of the generated PF ₅ gas with water or the like. In other words, the conductivity of the non-aqueous electrolyte is reduced, and the electrode material is deteriorated by the generated hydrogen fluoride gas.

On the other hand, the phosphazene derivative suppresses decomposition of the lithium ion source such as LiPF ₆ and contributes to stabilization. Therefore, when the phosphazene derivative is contained in the conventional non-aqueous electrolyte, the decomposition reaction of the non-aqueous electrolyte is suppressed, and corrosion and deterioration can be suppressed.

It is necessary that the content of the phosphazene derivative in the nonaqueous electrolyte is not less than 2% by volume and less than 20% by volume, preferably more than 2.5% by volume and not more than 20% by volume. More preferably, it is at least 3% by volume and less than 20% by volume. When the content is within the numerical range, the deterioration can be suitably suppressed.
In the present invention, the term “deterioration” refers to the above-mentioned supporting salt (for example,
Decomposition of lithium salt), and the effect of preventing the deterioration was evaluated by the following "stability evaluation method".

--Evaluation Method of Stability-- (1) First, after preparing a non-aqueous electrolyte containing a supporting salt, the moisture content is measured. Next, the concentration of hydrogen fluoride in the non-aqueous electrolyte is measured by NMR and GC-MS. Further, after visually observing the color tone of the nonaqueous electrolyte, the charge / discharge capacity is calculated by a charge / discharge test. (2) After leaving the non-aqueous electrolyte in the glove box for two months, the moisture content and the concentration of hydrogen fluoride were measured again,
The color tone is observed, the charge / discharge capacity is calculated, and the stability is evaluated based on the change in the obtained numerical value.

The phosphazene derivative is not particularly limited as long as it is a liquid at ordinary temperature (25 ° C.). For example, a chain phosphazene derivative represented by the following general formula (1) or the following general formula (2) Suitable examples include a cyclic phosphazene derivative represented by

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 including elements such as niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, nickel and the like are included. Among these, a CH ₂ group, and oxygen, sulfur, selenium, nitrogen And the like, and particularly preferred are groups containing sulfur and selenium elements. 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, 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). And selenium-containing groups are preferred. 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, C
H ₂ group, CHR (R is an alkyl group, an alkoxyl group,
Represents a phenyl group or the like. The same applies hereinafter. ) Group, NR group,
Oxygen, sulfur, selenium, 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, iron, cobalt, a group containing an element such as nickel. among these, CH ₂ group, CHR group, in addition to NR group, oxygen, sulfur, elemental selenium Preferably, the group is
Groups containing the elements sulfur and selenium are preferred.

In the general formula (3), the organic group includes
In particular, the organic group (A) can effectively impart deterioration resistance.
An organic group containing phosphorus as represented by is particularly preferable. 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 becomes possible to synthesize a nonaqueous electrolyte having more suitable viscosity, solubility suitable for mixing, and the like. 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.

-Other components- As the other components, an aprotic organic solvent 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 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 nonaqueous 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.

[Other Members] Examples of the other members include 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.

In addition to the above-mentioned separator, as the above-mentioned other members, 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, etc. 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 deterioration resistance, low interfacial resistance of the non-aqueous electrolyte, and excellent low-temperature discharge while maintaining the battery characteristics required for the battery. Has characteristics.

[0041]

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 electrolytic solution] A phosphazene derivative (chain E) was added to 49 ml of γ-butyrolactone (an aprotic organic solvent).
O-type phosphazene derivative (in the general formula (1),
X is the structure of the organic group (A) represented by the general formula (3), and Y ^{1 to} Y ³ and Y ^{5 to} Y ⁶ are all single bonds;
^{1 to} R ³ and R ^{5 to} R ⁶ are all ethoxy groups;
Is added oxygen (2% by volume)
Further, LiPF ₆ (lithium salt) is added at 0.5 mol / k.
The resultant was dissolved at a concentration of g to prepare a non-aqueous electrolyte.

-Evaluation of Deterioration- The water content of the obtained non-aqueous electrolyte immediately after the preparation of the non-aqueous electrolyte and after leaving it in a glove box for 2 months (similar to the above-mentioned "stability evaluation method") ppm), hydrogen fluoride concentration (ppm) and charge / discharge capacity (mAh / g) were measured and calculated to evaluate deterioration. At this time, the charge / discharge capacity (mAh)
/ G) was determined by measuring a charge / discharge curve using a positive electrode or a negative electrode having a known weight and dividing the obtained charge amount and discharge amount by the weight of the electrode or the negative electrode using the obtained amount. Table 1 shows the results. The color tone change of the non-aqueous electrolyte immediately after preparation of the non-aqueous electrolyte and after being left in the glove box for two months was visually observed, and no change was observed.

[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 lithium metal foil 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. Since the obtained battery used the non-aqueous electrolyte, the battery had excellent deterioration resistance while maintaining the battery characteristics required for the battery.

-Evaluation of low-temperature discharge characteristics (measurement of low-temperature discharge capacity)-With respect to the obtained nonaqueous electrolyte secondary battery, the upper limit voltage was 4.5.
Under the conditions of V, a lower limit voltage of 3.0 V, a discharge current of 100 mA, and a charging current of 50 mA, charging and discharging were repeated up to 50 cycles. At this time, charging was performed at 20 ° C. and discharging was performed at a low temperature (−
(20 ° C, -10 ° C). At this time, the discharge capacity at a low temperature was compared with the discharge capacity when charge and discharge were repeated up to 50 cycles 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, 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 a non-aqueous electrolyte solution similar to that of Example 1 except that the addition amount of R ^{5 to} R ⁶ is an ethoxy group and Z is oxygen) is changed to 20% by volume. Was prepared, and the deterioration and the low-temperature discharge characteristics were evaluated. A change in the color tone of the non-aqueous electrolyte immediately after preparation of the non-aqueous electrolyte and after being left in the glove box for 2 months was not observed. Further, when a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, the non-aqueous electrolyte secondary battery was excellent in deterioration resistance.
Table 1 shows the results.

(Comparative Example 1) In "Preparation of Nonaqueous Electrolyte Solution" 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 R ^{5 to} R ⁶ are all ethoxy groups and Z is oxygen)), and the amount of γ-butyrolactone (aprotic organic solvent) is changed to 50 ml. A non-aqueous electrolyte was prepared in the same manner as in Example 1, and the deterioration and the low-temperature discharge characteristics were evaluated. Immediately after preparation of non-aqueous electrolyte and 2
When the color tone change of the non-aqueous electrolyte solution after being left in the glove box for two months was visually observed, blackening was observed after being left in the glove box for two months.
Further, when a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, it was inferior in deterioration resistance. Table 1 shows the results.

[0048]

[Table 1]

[0049]

According to the present invention, a non-aqueous electrolyte having excellent deterioration resistance, low interfacial resistance of a non-aqueous electrolyte, and excellent low-temperature discharge characteristics while maintaining battery characteristics required for a battery. A secondary battery can be provided.

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Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode; and a non-aqueous electrolyte containing a supporting salt and 2% by volume to less than 20% by volume of a phosphazene derivative. 2. The method according to claim 1, wherein the non-aqueous electrolyte contains 3% by volume or more and 20% by volume.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery contains less than the phosphazene derivative. 3. The method according to claim 1, wherein the supporting salt is a LiPF ₆ salt.
Or the non-aqueous electrolyte secondary battery according to 2. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte contains an aprotic organic solvent. 5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the aprotic organic solvent contains a cyclic or chain ester compound.