JP5239119B2 - Non-aqueous electrolyte battery electrolyte and non-aqueous electrolyte battery - Google Patents

Description

  The present invention relates to an electrolyte for a non-aqueous electrolyte battery that imparts excellent durability to a non-aqueous electrolyte battery, and a non-aqueous electrolyte battery using the same.

  In recent years, information-related equipment, communication equipment, such as personal computers, video cameras, digital still cameras, mobile phones, and other small-sized, high energy density power storage systems, electric vehicles, hybrid vehicles, fuel cell vehicle auxiliary power supplies, power storage, etc. Large-scale, power storage systems for power applications are attracting attention. As one candidate, non-aqueous electrolyte batteries such as lithium ion batteries, lithium batteries, and lithium ion capacitors have been actively developed.

  Many of these non-aqueous electrolyte batteries have already been put into practical use, but they are not satisfactory in various applications in terms of durability, and are particularly long-lasting for automobiles due to large deterioration at 45 ° C. or higher. There is a problem in applications that are used in places with high temperatures.

Generally, in these non-aqueous electrolyte batteries, a non-aqueous electrolyte or a non-aqueous electrolyte quasi-solidified with a gelling agent is used as an ionic conductor. The structure is as follows. As a solvent, one or several kinds of mixed solvents selected from aprotic ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc. are used, and lithium as a solute. Salts, that is, LiPF ₆ , LiBF ₄ , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, and the like are used.

  So far, optimization of various battery components including positive electrode and negative electrode active materials has been studied as means for improving durability such as cycle characteristics and high-temperature storage stability of non-aqueous electrolyte batteries. Non-aqueous electrolyte-related technology is no exception, and it has been proposed to suppress degradation due to decomposition of the electrolyte on the surface of an active positive electrode or negative electrode with various additives. For example, JP 2000-123867 A (Patent Document 1) proposes to improve battery characteristics by adding vinylene carbonate to an electrolytic solution. In this method, the electrode is coated with a polymer film by polymerization of vinylene carbonate to prevent decomposition on the surface of the electrolytic solution. However, since lithium ions are difficult to pass through this film, the internal resistance increases. It has become.

In Japanese Patent No. 3439085 (Patent Document 2) and Japanese Patent Application Laid-Open No. 2004-31079 (Patent Document 3), the effect of a film formed on the electrode interface when monofluorophosphate or difluorophosphate is added to the electrolytic solution. Describes that high temperature cycle characteristics and input / output characteristics are improved. However, these effects are not yet sufficient, and the solubility of monofluorophosphate and difluorophosphate is low, so there is a risk of precipitation depending on the concentration, solvent composition, and temperature conditions. The problem is that if the amount is reduced, the effect cannot be obtained.
JP 2000-123867 A Japanese Patent No. 3439085 JP 2004-31079 A

  The present invention improves the durability of this type of nonaqueous electrolyte battery, such as cycle characteristics, high temperature storage stability, etc., and is an excellent electrolyte solution for a nonaqueous electrolyte battery that suppresses an increase in internal resistance so that it can be used for power applications. And a non-aqueous electrolyte battery.

  As a result of intensive studies in view of such problems, the present inventors have conducted electrolysis for a nonaqueous electrolyte battery comprising a positive electrode, a negative electrode made of lithium or a negative electrode material capable of occluding and releasing lithium, a nonaqueous organic solvent, and a solute. A non-aqueous electrolyte battery that can improve cycle characteristics, high-temperature storage stability, etc. by using an electrolyte for a non-aqueous electrolyte battery to which a specific compound group is added. As a result, the present inventors have found an electrolytic solution for use, and further a non-aqueous electrolyte battery using the electrolytic solution.

That is, the present invention provides at least one selected from the group consisting of fluoroethylene carbonate, chloroethylene carbonate, and difluoroethylene carbonate as an additive in an electrolyte for a non-aqueous electrolyte battery comprising a non-aqueous organic solvent and a solute. One compound and at least one compound selected from a second compound group consisting of a monofluorophosphate and a difluorophosphate, and the amount of the first compound group added to the electrolyte for a non-aqueous electrolyte battery In the range of 0.1 to 10.0% by weight (for fluoroethylene carbonate and difluoroethylene carbonate, excluding the range of 0.1 to 5.0% by weight). Non-aqueous electrolyte battery for power use, characterized by being in the range of 0.01 to 2.0% by weight with respect to the electrolyte for water electrolyte battery In the electrolytic solution, and further, the counter cation of the second compound group, a lithium ion, sodium ion, potassium ion, characterized in that at least one of the counter cation selected from tetraalkylammonium ions, solute, LiPF ₆ , LiBF ₄ , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, at least one solute selected from the group consisting of non-aqueous electrolysis for power applications An electrolyte for a liquid battery, comprising at least a positive electrode, a negative electrode made of lithium or a negative electrode material capable of occluding and releasing lithium, and a non-aqueous electrolyte battery electrolyte made of a nonaqueous organic solvent and a solute A non-aqueous electrolyte battery for power use, comprising the electrolyte solution for non-aqueous electrolyte battery for power use described above. It is intended to provide.

  The reason why these non-aqueous electrolyte battery electrolytes are effective is not clear, but is presumed as follows. At least one compound selected from the group consisting of fluoroethylene carbonate, chloroethylene carbonate, and difluoroethylene carbonate used as the first compound group forms a film having high lithium ion conductivity by decomposing on the negative electrode, This film suppresses the direct contact between the negative electrode active material and the nonaqueous organic solvent or solute, thereby preventing the decomposition and the deterioration of the battery. However, since a film cannot be formed on the positive electrode, the problem of deterioration on the positive electrode remains. At this time, when at least one compound selected from the group consisting of monofluorophosphate and difluorophosphate used as the second compound group coexists, these second compound groups are not present on the negative electrode but on the positive electrode. Since it is decomposed and forms a film on the positive electrode, the disadvantage of the first compound group can be compensated, and the first compound group and the second compound group each show durability that cannot be achieved independently.

  The non-aqueous electrolyte battery electrolyte of the present invention contains a first compound group, a second compound group, a non-aqueous organic solvent, and a solute. If necessary, other commonly known additives can be used in combination.

  Hereafter, each component of the electrolyte solution for nonaqueous electrolyte batteries of this invention is demonstrated in detail.

  The first compound group used in the present invention is a compound consisting of the group consisting of fluoroethylene carbonate, chloroethylene carbonate, and difluoroethylene carbonate. A specific structural formula is shown below. As for difluoroethylene carbonate, isomers at different positions to which fluorine is bonded are present, but those at any position behave in the same manner.

  The added amount of the first compound group is 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1.0% by weight or more, with respect to the electrolyte for nonaqueous electrolyte batteries, It is 50.0% by weight or less, preferably 10.0% by weight or less, more preferably 5.0% by weight or less. If the amount is less than 0.1% by weight, the effects of improving durability such as cycle characteristics and high-temperature storage stability of the nonaqueous electrolyte battery and suppressing the increase in internal resistance cannot be sufficiently obtained. If the weight percentage is exceeded, the viscosity of the electrolyte solution increases, causing problems that the properties at low temperatures are impaired and it is not economical.

  Next, the second compound group used in the present invention is a compound consisting of a group consisting of a monofluorophosphate and a difluorophosphate, and each salt has an anion portion having a structure shown below.

  As the counter cation to be combined with these anions, there is no particular limitation on the type of the counter cation as long as it does not impair the performance of the non-aqueous electrolyte battery electrolyte and non-aqueous electrolyte battery of the present invention, and various types can be selected. it can.

  Specific examples include metal cations such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, barium, silver, copper, and iron, and onium cations such as tetraalkylammonium, tetraalkylphosphonium, and imidazolium derivatives. However, lithium ion, sodium ion, potassium ion, and tetraalkylammonium ion are preferable from the viewpoint of helping ion conduction in the nonaqueous electrolyte battery.

  The lower limit of the addition amount of the second compound group is 0.01% by weight or more, preferably 0.03% by weight or more, and more preferably 0.05% by weight or more with respect to the electrolyte for nonaqueous electrolyte batteries. The upper limit is 10.0% by weight or less, preferably 3.0% by weight or less, more preferably 2.0% by weight or less. If it is less than 0.01% by weight, the effect of improving durability such as cycle characteristics and high-temperature storage stability of the non-aqueous electrolyte battery cannot be obtained sufficiently. On the other hand, if it exceeds 10.0% by weight, the non-aqueous electrolyte battery is exceeded. There is a possibility that the ionic conduction of the electrolyte for electrolyte will be lowered and the internal resistance will be increased.

  The addition ratio of the first compound group and the second compound group is not particularly limited, but the molar ratio of “first compound group / second compound group” in the electrolyte for non-aqueous electrolyte batteries is the lower limit. It is 0.1 or more, preferably 1.0 or more, and the upper limit is 500 or less, preferably 100 or less. If the range of the molar ratio is less than 0.1, the durability improving effect cannot be obtained sufficiently, and if it exceeds 500, the durability improving effect cannot be sufficiently obtained, such being undesirable.

  The kind of nonaqueous organic solvent used for the electrolyte solution for nonaqueous electrolyte batteries of the present invention is not particularly limited, and any nonaqueous organic solvent can be used. Specific examples include cyclic carbonates such as propylene carbonate, ethylene carbonate, and butylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone, methyl acetate, and propion. Examples include chain esters such as methyl acid, cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and dioxane, chain ethers such as dimethoxyethane and diethyl ether, and sulfur-containing nonaqueous organic solvents such as dimethyl sulfoxide and sulfolane. . Moreover, the nonaqueous organic solvent used for this invention may be used individually by 1 type, and may mix and use two or more types by arbitrary combinations and a ratio according to a use.

The kind of solute used for the electrolyte solution for non-aqueous electrolyte batteries of the present invention is not particularly limited, and any lithium salt can be used. Specific examples include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiPF ₃ (C ₃ F ₇ ) ₃ , LiB (CF ₃ ) ₄ , LiBF ₃ (C ₂ F ₅ ) and the like An electrolyte lithium salt is mentioned. One kind of these solutes may be used alone, or two or more kinds of solutes may be mixed and used in any combination and ratio according to the application. Among these, LiPF ₆ , LiBF ₄ , (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) ₂ NLi are preferable in view of energy density, output characteristics, life, etc. as a battery.

  The concentration of these solutes is not particularly limited, but the lower limit is 0.5 mol / L or more, preferably 0.7 mol / L or more, more preferably 0.9 mol / L or more, and the upper limit is 2.5 mol / L. / L or less, preferably 2.2 mol / L or less, more preferably 2.0 mol / L or less. When the concentration is less than 0.5 mol / L, the ionic conductivity is decreased, thereby reducing the cycle characteristics and output characteristics of the nonaqueous electrolyte battery. On the other hand, when the concentration exceeds 2.5 mol / L, the electrolyte solution for the nonaqueous electrolyte battery is reduced. If the viscosity increases, the ionic conduction may be lowered, and the cycle characteristics and output characteristics of the nonaqueous electrolyte battery may be degraded.

  The above is the description of the basic configuration of the electrolyte solution for a non-aqueous electrolyte battery of the present invention, but generally used for the electrolyte solution for a non-aqueous electrolyte battery of the present invention as long as the gist of the present invention is not impaired. You may add another additive in arbitrary ratios. Specific examples include cyclohexylbenzene, biphenyl, t-butylbenzene, vinylene carbonate, vinyl ethylene carbonate, difluoroanisole, propane sultone, dimethyl vinylene carbonate, and the like, which have an overcharge prevention effect, a negative electrode film formation effect, and a positive electrode protection effect. Is mentioned. Moreover, it is also possible to use the non-aqueous electrolyte battery electrolyte in a quasi-solid state with a gelling agent or a crosslinked polymer as used in a non-aqueous electrolyte battery called a lithium polymer battery.

  Next, the configuration of the nonaqueous electrolyte battery of the present invention will be described. The non-aqueous electrolyte battery according to the present invention is characterized by using the above-described electrolyte for a non-aqueous electrolyte battery according to the present invention, and the other components are those used in general non-aqueous electrolyte batteries. Is used. That is, it comprises a positive electrode and a negative electrode capable of inserting and extracting lithium, a current collector, a separator, a container and the like.

  Although it does not specifically limit as a negative electrode material, The lithium metal which can occlude / release lithium, the alloy and intermetallic compound of lithium and another metal, various carbon materials, artificial graphite, natural graphite, metal oxide, metal nitride , Activated carbon, conductive polymer and the like are used.

The positive electrode material is not particularly limited, but in the case of a lithium battery and a lithium ion battery, for example, lithium-containing transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and those lithium-containing transition metals A mixture of a plurality of transition metals of a composite oxide, a transition metal of the lithium-containing transition metal composite oxide partially substituted with another metal, oxidation of TiO ₂ , V ₂ O ₅ , MoO _3, etc. , Sulfides such as TiS ₂ and FeS, or conductive polymers such as polyacetylene, polyparaphenylene, polyaniline, and polypyrrole, activated carbon, polymers that generate radicals, and carbon materials are used.

  By adding acetylene black, ketjen black, carbon fiber, graphite as a conductive material, polytetrafluoroethylene, polyvinylidene fluoride, SBR resin, etc. as a binder to the positive electrode or negative electrode material, and forming into a sheet shape Use an electrode sheet.

  As a separator for preventing contact between the positive electrode and the negative electrode, a nonwoven fabric or a porous sheet made of polypropylene, polyethylene, paper, glass fiber, or the like is used.

  A non-aqueous electrolyte battery having a coin shape, a cylindrical shape, a square shape, an aluminum laminate sheet type or the like is assembled from each of the above elements.

  The electrolyte solution for non-aqueous electrolyte battery of the present invention improves the film characteristics of the electrode, improves the durability of the non-aqueous electrolyte battery using the same at high temperature, and suppresses the increase in resistance. Can also be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by this Example.

Reference example 1
LiPF ₆ is 1.2 mol / L as a solute in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 2, 1.0% by weight of fluoroethylene carbonate from the first compound group, and difluorophosphorus from the second compound group. An electrolyte solution for a non-aqueous electrolyte battery was prepared so that the lithium acid was 1.0% by weight.

Using this electrolytic solution, a cell was prepared using LiCoO ₂ as a positive electrode material and graphite as a negative electrode material, and a battery charge / discharge test was actually performed. The test cell was produced as follows.

To 90 parts by weight of LiCoO ₂ powder, 5 parts by weight of polyvinylidene fluoride (PVDF) as a binder and 5 parts by weight of acetylene black as a conductive material were mixed, and N-methylpyrrolidone was further added to form a paste. The paste was applied on an aluminum foil and dried to obtain a test positive electrode body. Further, 90 parts by weight of graphite powder was mixed with 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone was further added to form a slurry. This slurry was applied on a copper foil and dried at 150 ° C. for 12 hours to obtain a test negative electrode body. Then, an electrolytic solution was immersed in a polyethylene separator to assemble a 50 mAh cell with an aluminum laminate exterior.

A charge / discharge test was conducted at an ambient temperature of 60 ° C. using the cell produced by the above method. Both charging and discharging were performed at a current density of 0.35 mA / cm ^2. After charging reached 4.2 V, 4.2 V was maintained for 1 hour, and discharging was performed up to 3.0 V, and the charge / discharge cycle was repeated. Then, the degree of deterioration of the cell was evaluated by the discharge capacity retention rate after 500 cycles and the cell resistance value at room temperature after 500 cycles. The capacity retention rate is expressed as a percentage of the discharge capacity after 500 cycles with respect to the initial discharge capacity. The results are shown in Table 1.

Reference example 2
A charge / discharge test was conducted in the same manner except that the fluoroethylene carbonate concentration used in Reference Example 1 was 0.5 wt% and the lithium difluorophosphate concentration was 2.0 wt%.

Example 3
A charge / discharge test was carried out in the same manner except that the fluoroethylene carbonate concentration used in Reference Example 1 was 10.0% by weight and the lithium difluorophosphate concentration was 0.01% by weight.

Comparative Example 1
A charge / discharge test was carried out in the same manner as in Reference Example 1 except that fluoroethylene carbonate and lithium difluorophosphate were not used.

Comparative Example 2
A charge / discharge test was conducted in the same manner as in Reference Example 1 except that lithium difluorophosphate was not used.

Comparative Example 3
A charge / discharge test was conducted in the same manner as in Reference Example 1 except that fluoroethylene carbonate was not used.

Example 4
A charge / discharge test was carried out in the same manner as in Reference Example 1 except that the first compound group used in Reference Example 1 was changed to chloroethylene carbonate and the concentration was changed to 1.0% by weight.

Comparative Example 4
The charge / discharge test was conducted in the same manner except that the first compound group used in Reference Example 1 was changed to chloroethylene carbonate, the concentration thereof was 1.0% by weight, and the second compound group was not used. Carried out.

Reference Example 5
The same procedure was performed except that the first compound group used in Reference Example 1 was changed to difluoroethylene carbonate, its concentration was 5.0% by weight, and the lithium difluorophosphate concentration was 0.5% by weight. A charge / discharge test was conducted.

Comparative Example 5
The charge / discharge test was conducted in the same manner except that the first compound group used in Reference Example 1 was changed to difluoroethylene carbonate, its concentration was 5.0% by weight, and the second compound group was not used. Carried out.

Reference Example 6
Except that the fluoroethylene carbonate concentration used in Reference Example 1 was 5.0% by weight, that the second compound group was triethylmethylammonium monofluorophosphate, and that the concentration was 0.03% by weight. A charge / discharge test was conducted in the same manner.

Comparative Example 6
Except that the first compound group used in Reference Example 1 was not used, that the second compound group was changed to triethylmethylammonium monofluorophosphate, and the concentration was 0.03% by weight. The charge / discharge test was conducted.

Reference Example 7
The same procedure was performed except that the fluoroethylene carbonate concentration used in Reference Example 1 was 0.1% by weight, the second compound group was changed to sodium difluorophosphate, and the concentration was 1.0% by weight. A charge / discharge test was conducted.

Comparative Example 7
A charge / discharge test was performed in the same manner except that the first compound group used in Reference Example 1 was not used and that the second compound group was changed to sodium difluorophosphate.

Example 8
The first compound group used in Reference Example 1 was changed to chloroethylene carbonate, the concentration was changed to 0.5% by weight, the second compound group was changed to potassium difluorophosphate, and the concentration was changed to 0.03. Charge / discharge was carried out in the same manner except that the weight ratio was changed to LiBF ₄ and the solvent was a mixed solvent of ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1: 1: 1: 1. The test was conducted.

Comparing the above results, it can be seen that both the capacity retention ratio and the resistance value are superior when the first compound group and the second compound group are used alone rather than individually.

Claims (4)

In an electrolyte for a non-aqueous electrolyte battery comprising a non-aqueous organic solvent and a solute, at least one compound selected from the first compound group consisting of fluoroethylene carbonate, chloroethylene carbonate, and difluoroethylene carbonate as an additive; It contains at least one compound selected from the second compound group consisting of a fluorophosphate and a difluorophosphate, and the added amount of the first compound group is 0.1 to 0.1% of the electrolyte for a nonaqueous electrolyte battery. It is in the range of 10.0% by weight (excluding the range of 0.1 to 5.0% by weight for fluoroethylene carbonate and difluoroethylene carbonate) , and the added amount of the second compound group is for a non-aqueous electrolyte battery. An electrolyte for a non-aqueous electrolyte battery for power use, characterized by being in the range of 0.01 to 2.0% by weight with respect to the electrolyte. The non-aqueous electrolysis for power use according to claim 1, wherein the counter cation of the second compound group is at least one counter cation selected from lithium ion, sodium ion, potassium ion, and tetraalkylammonium ion. Liquid battery electrolyte. The solute is at least one solute selected from the group consisting of LiPF ₆ , LiBF ₄ , (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) ₂ NLi. The electrolyte solution for non-aqueous electrolyte batteries for power use according to 1. A nonaqueous electrolyte battery comprising at least a positive electrode, a negative electrode made of lithium or a negative electrode material capable of occluding and releasing lithium, and a nonaqueous electrolyte battery electrolyte comprising a nonaqueous organic solvent and a solute. A non-aqueous electrolyte battery for power use, comprising the electrolyte solution for non-aqueous electrolyte battery for power use according to any one of 1 to 3.