JP2005243620A - Nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To concurrently achieve output and cycle characteristics of a nonaqueous electrolyte battery having an electrolyte with high flame resistance. <P>SOLUTION: The nonaqueous electrolyte battery comprises a positive electrode 2; a negative electrode 4 containing an active substance in which the operation potential of the negative electrode is noble by 0.5 V or more against the potential of metal lithium; and an electrolyte containing a metal salt composed of at least either an alkali metal salt or an alkali earth metal salt, a fused salt and phosphate ester and fulfilling a formula (1): 0.5≤(M<SB>2</SB>/M<SB>1</SB>)≤1, wherein M<SB>1</SB>is the molar number of the metal salt and M<SB>2</SB>is the molar number of the phosphate ester. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a secondary battery provided with a nonaqueous electrolyte.

  In recent years, the market for portable information devices such as mobile phones and small personal computers has been rapidly expanding, and as these devices have become smaller and lighter, power supplies have been required to be smaller and lighter. I came. For these portable devices, lithium ion secondary batteries having a high energy density are frequently used, and research is still ongoing. In recent years, with the development of technology, various devices such as digital audio devices and POS terminals have been downsized. When it becomes portable due to the miniaturization, a built-in battery capable of omitting the power cord is required instead of the conventional AC power supply, and uses for secondary batteries are being expanded. In addition, improvement in characteristics is always required for information devices such as personal computers and mobile phones that have conventionally used secondary batteries. Against this background, secondary batteries are required to improve not only the capacity as before but also various characteristics. Among them, the stability at the time of unsteady use such as overcharge, long-term storage, and maintenance of characteristics at high temperatures are increasing in importance. Conventionally, lead-acid batteries, nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, and the like have been used as secondary batteries, but these have problems in terms of small size and light weight. On the other hand, non-aqueous electrolyte secondary batteries are small and light and have a large capacity, so that they have been used for digital cameras, video cameras, and the like as well as the above personal computers and mobile phones.

As this type of non-aqueous electrolyte secondary battery, a lithium-containing cobalt composite oxide or a lithium-containing nickel composite oxide is used as the positive electrode material, and a carbon-based material such as graphite or coke is used as the negative electrode active material. One using an organic solvent in which a lithium salt such as LiPF ₆ or LiBF ₄ is dissolved is known. The positive electrode and the negative electrode are molded into a sheet shape, and a separator that holds the electrolytic solution is disposed between them to electrically insulate the positive and negative electrodes, and these are housed in various shaped containers to form a battery.

  The non-aqueous electrolyte secondary battery as described above undergoes a chemical reaction different from the original charge / discharge during overcharge or the like, and becomes thermally unstable, and the electrolyte contains a combustible organic solvent as a main component. Therefore, the safety of the battery may be impaired by the combustion.

  In order to solve such problems, it has been studied to change the composition of the electrolytic solution. In conventional organic solvent electrolytes, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and the like have been used as solvents. These flash points are 152 ° C., 31 ° C., 24 ° C., and 98 ° C. in order, and among these, attempts are made to improve the safety of the battery by using only ethylene carbonate, γ-butyrolactone, etc. having a relatively high flash point. Has been. However, there have been reports of cases exceeding 100 ° C in passenger cars in the summer, and it was not sufficient.

  As another trial, studies have been made to improve safety by using a molten salt that exhibits a liquid state at normal temperature without a flash point as an electrolyte. For example, a lithium metal oxide is used for the positive electrode, a lithium metal, a lithium alloy, or a carbonaceous material that absorbs and releases lithium ions is used for the negative electrode, and a molten salt composed of a lithium salt, an aluminum halide, and a quaternary ammonium halide is used. A non-aqueous electrolyte secondary battery used as an electrolyte is disclosed as, for example, Patent Document 1 as a secondary battery excellent in safety. In addition, a non-aqueous solution using a positive electrode, a negative electrode containing a carbonaceous material that occludes / releases lithium ions, a fluoride anion of an element selected from boron, phosphorus, and sulfur, a quaternary ammonium ion, and a lithium salt. An electrolyte secondary battery is disclosed, for example, in Patent Document 2 as a secondary battery having excellent safety and improved cycle life and discharge capacity. However, since these molten salts have high viscosity and low ionic conductivity, the output characteristics are extremely low, and in addition, there is a problem that impregnation into positive and negative electrodes and separators is difficult.

  In order to solve this problem, addition of conventionally used non-aqueous solvents such as diethyl carbonate and ethylene carbonate has also been studied. However, even if the molten salt is nonflammable, the safety may be impaired by adding flammable ethylene carbonate.

  On the other hand, Patent Document 3 discloses a flame retardant non-aqueous electrolyte having flame retardancy without impairing battery characteristics such as charge / discharge efficiency, energy density, output density, and life. This flame-retardant non-aqueous electrolyte contains an electrolyte (A), a non-aqueous solvent (B), and a quaternary salt (C) of a compound (c) having an asymmetric chemical structure having a nitrogen-containing conjugated structure. . Examples of the electrolyte (A) include lithium tetrafluoroborate, lithium hexafluorophosphate, lithium salt of sulfonylimide having a specific structural formula, lithium salt of sulfonylmethide having a specific structural formula, and the like. Yes. Examples of the non-aqueous solvent (B) include cyclic carbonate esters, chain carbonate esters, and phosphate esters. In addition, as the quaternary salt (C), a compound having an imidazolium cation having a specific structural formula is used.

Examples of Patent Document 3 include 19% by weight of lithium bistrifluoromethanesulfonylimide (TFSILi), 10% by weight of trimethyl phosphate (TMP), and 1-methyl-3-ethylimidazolium / bistrifluoromethanesulfonylimide. A lithium secondary battery including a non-aqueous electrolyte composed of 71% by weight of salt (MEITFSI) and a negative electrode composed of graphite is described. Patent Document 3 describes that this lithium secondary battery exhibits excellent charge / discharge characteristics.
JP-A-4-349365 JP 11-86905 A JP 11-329495 A

  An object of the present invention is to achieve both output characteristics and cycle characteristics of a nonaqueous electrolyte battery including an electrolyte having high flame retardancy.

A nonaqueous electrolyte battery according to the present invention comprises a positive electrode,
A negative electrode containing an active material having a negative electrode operating potential nobler than 0.5 V with respect to a metallic lithium potential;
It comprises a metal salt comprising at least one of an alkali metal salt and an alkaline earth metal salt, a molten salt and a phosphate ester, and an electrolyte satisfying the following formula (1).

0.5 ≦ (M ₂ / M ₁ ) ≦ 1 (1)
However, M ₁ is at the number of moles of the metal salt, M ₂ is the number of moles of the phosphoric acid ester.

  According to the present invention, it is possible to achieve both output characteristics and cycle characteristics of a nonaqueous electrolyte battery including an electrolyte with high flame retardancy.

  In the nonaqueous electrolyte battery according to the present invention, an electrolyte containing a metal salt composed of at least one of an alkali metal salt and an alkaline earth metal salt, a molten salt, and a phosphate ester is used. And the thermal safety of the battery can be dramatically improved. Furthermore, the phosphate ester can reduce the viscosity of the electrolyte without impairing the flame retardancy of the electrolyte, and can improve the impregnation property of the electrolyte due to the surface active effect. As a result, a non-aqueous electrolyte battery having excellent output characteristics and capacity characteristics and high safety can be realized. In the case of a secondary battery, the charge / discharge cycle characteristics can also be improved.

  A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte containing a metal salt composed of at least one of an alkali metal salt and an alkaline earth metal salt, a molten salt, and a phosphate ester. .

  Hereinafter, the positive electrode, the negative electrode, and the electrolyte will be described.

1) Positive electrode The positive electrode contains a positive electrode active material, and can further contain a material having electronic conductivity such as carbon, and a binder for forming a sheet-like or pellet-like shape. It is also possible to use a base material such as a metal as a current collector in contact with the current collector.

Examples of the positive electrode active material include materials capable of occluding and releasing alkali metal ions such as lithium and sodium and alkaline earth metal ions such as calcium. Since a large battery capacity can be obtained, metal oxides capable of inserting and extracting lithium ions having a small weight per charge are desirable, and various oxides such as lithium-containing cobalt composite oxides, lithium-containing nickel-cobalt composite oxides are desirable. Products, lithium-containing nickel composite oxides, lithium-manganese composite oxides, vanadium oxides containing lithium, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, a lithium composite oxide containing at least one metal element selected from the group consisting of cobalt, manganese, and nickel is desirable, and in particular, a lithium-containing material having a charge / discharge potential of 3.8 V or more with respect to the lithium metal potential. Cobalt composite oxide, lithium-containing nickel-cobalt composite oxide, lithium-containing manganese composite oxide, and the like are more desirable because high battery capacity can be realized. Further, since it suppress the decomposition reaction of the molten salt in the cathode surface at room temperature or _{higher, LiCo x Ni y Mn z O} 2 (x + y + z = 1,0 <x ≦ 0.5,0 ≦ y <1,0 ≦ z < The positive electrode active material represented by 1) is desirable.

  As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer, styrene-butadiene rubber, or the like can be used.

  As the current collector, a metal foil such as aluminum, stainless steel, or titanium, a thin plate or mesh, a wire mesh, or the like can be used.

  The positive electrode active material and the conductive material can be pelletized or formed into a sheet by adding the binder and kneading and rolling. Alternatively, after dissolving and suspending in a solvent such as toluene and N-methylpyrrolidone (NMP) to form a slurry, it can be applied onto the current collector and dried to form a sheet.

2) Negative electrode The negative electrode contains a negative electrode active material and is formed into a pellet shape, a thin plate shape, or a sheet shape using a conductive agent, a binder, or the like.

  Like the positive electrode, the negative electrode active material can occlude and release alkali metal ions such as lithium and sodium, and alkaline earth metal ions such as calcium, and occlude and release the same kind of metal ions as the positive electrode at a base potential lower than the combined positive electrode. Yes. It is desirable to store and release lithium ions because a high battery capacity can be obtained. Those having such characteristics include lithium metals such as artificial graphite, natural graphite, carbonaceous materials such as non-graphitizable carbon and graphitizable low-temperature calcined carbon, lithium titanate, iron sulfide, cobalt oxide, lithium aluminum alloy, tin oxide Such as things. Furthermore, an active material whose negative electrode operating potential is nobler than 0.5 V with respect to the potential of metallic lithium is desirable. By selecting such an active material, deterioration due to side reactions of the molten salt and phosphate ester on the surface of the negative electrode active material can be suppressed, so that the cycle characteristics and storage characteristics of the secondary battery can be improved. From this point, lithium titanate and iron sulfide are most desirable as the negative electrode active material. Two or more negative electrode active materials can be mixed and used. Various shapes such as scales, fibers, and spheres are possible.

Examples of lithium titanate include Li _{4 + x} Ti ₅ O ₁₂ (x is 0 ≦ x ≦ 3), Li ₂ Ti ₃ O _{7, and the} like.

  As described above, in order to suppress the decomposition reaction of the phosphate ester, it is desirable that the negative electrode operating potential be higher by 0.5 V or more than the potential of metallic lithium. By making this potential difference 0.5V or more and 3V or less, it is possible to suppress the decomposition reaction of the phosphate ester and obtain a high battery voltage. A more preferable range is 0.5 V or more and 2 V or less.

  Examples of the active material having a negative electrode working potential whose potential difference from lithium metal is less than 0.5 V include graphite-based carbonaceous materials. Since the graphite-based carbonaceous material causes a lithium occlusion / release reaction near 0 V with respect to the lithium metal potential, the decomposition reaction of the phosphate ester proceeds in parallel with the charge / discharge reaction, that is, the lithium occlusion / release reaction. For this reason, as shown in the Example mentioned later, an output characteristic and charging / discharging cycle life become low.

  As the conductive material, a material having electronic conductivity such as carbon or metal can be used. Shapes such as powder and fibrous powder are desirable.

  As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), styrene-butadiene rubber, carboxymethyl cellulose (CMC), or the like can be used. As the current collector, a metal foil such as copper, stainless steel, nickel or the like, a thin plate or mesh, a wire net, or the like can be used.

  The negative electrode active material and the conductive material can be pelletized or formed into a sheet by adding the binder and kneading and rolling. Alternatively, after dissolving and suspending in water, a solvent such as N-methylpyrrolidone (NMP) to form a slurry, it can be applied onto the current collector and dried to form a sheet.

3) Electrolyte The electrolyte includes a metal salt composed of at least one of an alkali metal salt and an alkaline earth metal salt, a molten salt, and a phosphate ester.

  The molten salt is preferably one that exhibits a molten state near room temperature in order to operate the battery at a normal temperature. The cation forming the molten salt is not particularly limited, and examples thereof include aromatic quaternary ammonium ions and aliphatic quaternary ammonium ions. The kind of cation in molten salt can be made into 1 type, or 2 or more types.

  Examples of aromatic quaternary ammonium ions include 1-ethyl-3-methylimidazolium, 1-methyl-3-propylimidazolium, 1-methyl-3-isopropylimidazolium, and 1-butyl-3-methylimidazole. 1-ethyl-2,3-dimethylimidazolium, 1-ethyl-3,4-dimethylimidazolium, N-propylpyridinium, N-butylpyridinium, N-tert-butylpyridinium, N-tert-pentylpyridinium, etc. Can be mentioned.

  Examples of aliphatic quaternary ammonium ions include N-butyl-N, N, N-trimethylammonium, N-ethyl-N, N-dimethyl-N-propylammonium, N-butyl-N-ethyl-N, N-dimethylammonium, N-butyl-N, N-dimethyl-N-propylammonium, N-methyl-N-propylpyrrolidinium ion, N-butyl-N-methylpyrrolidinium ion, N-methyl-N-pentylpyrrole Dinium, N-propoxyethyl-N-methylpyrrolidinium, N-methyl-N-propylpiperidinium, N-methyl-N-isopropylpiperidinium, N-butyl-N-methylpiperidinium, N- Isobutyl-N-methylpiperidinium, N-sec-butyl-N-methylpiperidinium, N-methoxyethyl N- methyl-piperidinium, etc. N- ethoxyethyl -N- methylpiperidinium and the like.

  Among the above-mentioned aliphatic quaternary ammonium ions, the nitrogen-containing 5-membered pyrrolidinium ion and the nitrogen-containing 6-membered piperidinium ion have high resistance to reduction, and by suppressing side reactions, they can be stored and cycled. Improvement is desirable.

  In addition, it is more preferable to use a cation having an imidazolium structure among aromatic quaternary ammonium ions, because a molten salt having a low viscosity can be obtained and a high battery output characteristic can be obtained when used as an electrolyte. Furthermore, when an active material having an operating potential nobler than 0.5 V with respect to the metal lithium potential is used as the negative electrode active material, side reactions on the negative electrode are suppressed even with a molten salt containing a cation having the imidazolium structure, A nonaqueous electrolyte secondary battery excellent in storage and cycle characteristics can be obtained.

The anion forming the molten salt is not particularly limited, but includes tetrafluoroborate anion (BF ₄ ⁻ ), hexafluorophosphate anion (PF ₆ ⁻ ), hexafluoromethanesulfonate anion, bistrifluoromethane. One or more of sulfonylamide anion (TFSI), dicyanamide anion (DCA) and the like can be used.

As the alkali metal salt, lithium salt, sodium salt and the like, and as the alkaline earth metal salt, calcium salt and the like can be used. Lithium salts are desirable because large battery capacities can be obtained. Examples of the lithium salt include lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium hexafluoromethanesulfonate, lithium bistrifluoromethanesulfonylamide (LiTFSI), lithium bispentafluoroethanesulfonylamide ( One or more of LiBETI) and dicyanamide lithium (LiDCA) can be used.

  The metal salt concentration comprising at least one of the alkali metal salt and the alkaline earth metal salt is preferably 0.1 to 2.5 mol / L. If the metal salt concentration is less than 0.1 mol / L, sufficient ionic conductivity cannot be obtained, and the discharge capacity may be reduced. On the other hand, when the metal salt concentration exceeds 2.5 mol / L, the viscosity of the molten salt is greatly increased, so that the impregnation property with respect to the positive and negative electrode active materials may be reduced and the discharge capacity may be reduced. Even at 0 ° C. or lower, salt precipitation does not occur, and 0.5 to 1.8 mol / L is more desirable in order to maintain sufficient ionic conductivity.

  The phosphate ester is not particularly limited, and trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, and the like can be used. The type of phosphate ester used may be one type or two or more types. A low molecular weight is desirable because of its low viscosity and high flame retardant effect, and trimethyl phosphate having the lowest molecular weight and high flame retardant effect is most desirable.

When the number of moles of a metal salt composed of at least one of an alkali metal salt and an alkaline earth metal salt is M ₁ and the number of moles of a phosphate ester is M ₂ , the present inventors have a molar ratio (M ₂ / M ₁ ) is 0.5 or more and 1 or less, that is, M ₁ : M ₂ is 1: 0.5 to 1: 1, and is a potential more noble than the metal lithium potential and the potential difference from the metal lithium potential It has been found that by providing a negative electrode containing an active material that provides a negative electrode operating potential of 0.5 V or more, both output characteristics and room temperature and high temperature cycle characteristics can be achieved. This means that, when the negative electrode is used at a molar ratio (M ₂ / M ₁ ) in the above specific range, an increase in internal resistance and a decrease in capacity due to the decomposition of phosphate ester on the negative electrode are suppressed over a long period and a long cycle. It is because it can do. Although the details of this reason are not clear, when the molar ratio (M ₂ / M ₁ ) exceeds 1, that is, when the number of moles of the phosphate ester is larger than the number of moles of the metal salt, the phosphate ester that is more reactive is not It is speculated that the decomposition of the phosphate ester proceeds because it occurs in the water electrolyte. A more desirable molar ratio (M ₂ / M ₁ ) is 0.8 or more and 1 or less. By setting it as such a composition, the balance of a viscosity fall and reactivity suppression can be balanced, and a high battery output characteristic and long-term stability can be reconciled.

Further, in a secondary battery comprising a negative electrode containing an active material having the negative electrode operating potential and a non-aqueous electrolyte having a molar ratio (M ₂ / M ₁ ) of 0.5 or more and 1 or less, an imidazolium structure It is desirable to use a molten salt containing a cationic component having This is because a non-aqueous electrolyte having both high ionic conductivity and excellent electrochemical stability can be obtained.

Furthermore, in a secondary battery comprising a negative electrode containing an active material having the negative electrode operating potential and a non-aqueous electrolyte having a molar ratio (M ₂ / M ₁ ) of 0.5 or more and 1 or less, It is desirable to use a molten salt that provides acid ions. Thereby, the ionic conductivity of a nonaqueous electrolyte can be improved.

  In order to obtain as high a flame retardance as possible, the electrolyte preferably contains no organic solvent other than phosphate ester. However, other organic solvents may be included in order to suppress side reactions in the battery and improve the affinity for separators and the like. However, the amount added is preferably 10% by weight or less in order to maintain flame retardancy. In order to avoid the possibility of combustion when electrolyte leaks from the inside of the battery, it is desirable to add as little other organic solvent as possible, and the flash point of the electrolyte after mixing the other organic solvent is An addition amount that does not decrease by 10 ° C. or more from the flash point is more desirable. In addition, when adding other organic solvent for chemical reaction control in the battery, such as suppression of side reactions, it is desirable that more than half of the added amount is consumed after the battery configuration or after the completion of the initial charge / discharge, The addition amount is preferably 3% by weight or less.

  Carbon dioxide may be contained in the electrolyte. Since carbon dioxide is a non-flammable gas, side reactions on the negative electrode surface can be suppressed without impairing flame retardancy, and an increase in internal impedance and an improvement in cycle characteristics can be obtained.

  The nonaqueous electrolyte battery according to the present invention can have various forms such as a cylindrical shape, a square shape, a thin shape, and a coin shape. An example of the coin-type non-aqueous electrolyte battery is shown in FIG.

  A pellet-shaped positive electrode 2 is accommodated in a metal positive electrode container 1 that also serves as a positive electrode terminal. The separator 3 is laminated on the positive electrode 2. The pellet-shaped negative electrode 4 is laminated on the separator 3. The nonaqueous electrolyte is impregnated in the positive electrode 2, the separator 3, and the negative electrode 4. The metal negative electrode container 5 also serving as the negative electrode terminal is caulked and fixed to the positive electrode container 1 via an insulating gasket 6 with the inner surface being in contact with the negative electrode 4.

  As said separator 3, a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, a cellulose porous sheet etc. can be used, for example.

  The positive electrode container 1 and the negative electrode container 5 are made of, for example, stainless steel or iron.

  The insulating gasket 6 can be made of, for example, polypropylene, polyethylene, vinyl chloride, polycarbonate, Teflon (registered trademark), or the like.

  In addition, although FIG. 1 mentioned above demonstrated the example using a coin-type container, it is also possible to use containers of various shapes, such as a cylindrical shape and a square shape, and a laminated film bag.

[Example]
Hereinafter, examples of the present invention will be described in detail with reference to the drawings. The following examples employ the battery structure shown in FIG.

(Example 1)
On an aluminum foil having a thickness of 20 μm, 90% by weight of lithium cobalt oxide (LiCoO ₂ ) powder, 2% by weight of acetylene black, 3% by weight of graphite and 5% by weight of polyvinylidene fluoride as a binder were slurried using N-methylpyrrolidone as a solvent After applying, drying, and rolling. The obtained positive electrode sheet was cut into a circle having a diameter of 15 mm to produce a positive electrode. The positive electrode weight was 17.8 mg. The charge / discharge potential of the obtained positive electrode was about 4.0 to 4.3 V with respect to the lithium metal potential.

90% by weight of Li _4/3 Ti _5/3 O ₄ powder as a negative electrode active material, 5% by weight of artificial graphite and 5% by weight of polyvinylidene fluoride (PVdF) as a conductive material were added to an N-methylpyrrolidone (NMP) solution. The obtained slurry was applied to an aluminum foil having a thickness of 20 μm, dried, and then rolled. The obtained negative electrode sheet was cut into a circle having a diameter of 16 mm to obtain a negative electrode. The negative electrode weight was 15.5 mg. The operating potential of this negative electrode was about 1.4 to 1.6 V noble with respect to the metal lithium potential.

  A polypropylene nonwoven fabric was used for the separator.

An electrolyte in which 0.5 mol / L of lithium tetrafluoroborate (LiBF ₄ ) is dissolved in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI · BF ₄ ) is mixed with trimethyl phosphate (TMP) in a molar ratio. A nonaqueous electrolyte was prepared by adding (M ₂ / M ₁ ) to 1.0. M ₁ is the number of moles of LiBF ₄ and M ₂ is the number of moles of TMP.

  A positive electrode was housed in a coin-type positive electrode container, and a negative electrode was placed on the positive electrode via a separator, and then a nonaqueous electrolyte was added to perform vacuum impregnation. Thereafter, a coin-type nonaqueous electrolyte secondary battery was produced by caulking and fixing the coin-type negative electrode container via an insulating gasket. The reference capacity calculated from the amount of active material contained in the electrode was 1.25 mAh.

(Examples 2-3 and Reference Examples 6-9)
Except for changing the types of molten salt, lithium salt and phosphate ester and the molar ratio (M ₂ / M ₁ ) as shown in Table 1 below, the structure is the same as that described in Example 1 above. A coin-type non-aqueous electrolyte secondary battery was produced.

  In Table 1, EMI · TFSI is 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonylamide, 14P5 · TFSI is N-butyl-N-methylpyrrolidinium bistrifluoromethanesulfonylamide, 13P6 · TFSI is N-methyl-N-propylpiperidinium bistrifluoromethanesulfonylamide, LiTFSI is lithium bistrifluoromethanesulfonylamide, and TEP is triethyl phosphate.

(Comparative Example 1)
By dissolving tetrafluoroboric acid 1-ethyl-3-methylimidazolium lithium tetrafluoroborate 0.5 mol / L to _{(EMI · BF 4) (LiBF} 4), except that to prepare a non-aqueous electrolyte Example In the same manner as in Example 1, a nonaqueous electrolyte secondary battery was produced.

(Comparative Example 2)
5% by weight of nonafluoromethoxybutylene was dissolved in an electrolyte prepared by dissolving 0.5 mol / L of lithium tetrafluoroborate (LiBF ₄ ) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI · BF ₄ ). And a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a nonaqueous electrolyte was prepared.

(Comparative Example 3)
Except for preparing non-aqueous electrolyte by dissolving 0.5 mol / L lithium bistrifluoromethanesulfonylamide (LiTFSI) in N-butyl-N-methylpyrrolidinium bistrifluoromethanesulfonylamide (14P5.TFSI) A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

(Comparative Example 4)
An electrolyte prepared by dissolving 0.5 mol / L lithium bistrifluoromethanesulfonylamide (LiTFSI) in N-methyl-N-propylpiperidinium bistrifluoromethanesulfonylamide (13P6.TFSI) was mixed with 5% by weight of nonafluoromethoxy. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that butylene was added to prepare a nonaqueous electrolyte.

(Comparative Example 5)
Example except that 0.5 mol / L lithium bistrifluoromethanesulfonylamide (LiTFSI) was dissolved in 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonylamide (EMI.TFSI) to prepare a nonaqueous electrolyte. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery was produced.

<Evaluation of output characteristics>
About the obtained non-aqueous electrolyte secondary batteries of Examples 1 to 3, Comparative Examples 1 to 5 and Reference Examples 6 to 9, with a constant current of up to 2.8 V at 0.2 CmA, after reaching 2.8 V The battery was charged at a constant voltage until 2.8 V was maintained and the total time was 10 hours. Thereafter, a constant current discharge of 0.1 CmA was performed. The battery was charged again under the above conditions, and a constant current discharge of 0.2 CmA was performed. Thereafter, after charging under the same conditions, constant current discharge of 0.4 CmA and 0.8 CmA was performed. The discharge capacity obtained by the above evaluation is shown in FIG.

<Evaluation of cycle characteristics>
About the nonaqueous electrolyte secondary battery of the said Examples 1-3, the comparative examples 1-5, and the reference examples 6-9, cycle evaluation was performed after the said evaluation. The charging was performed at a constant current of 0.2 CmA as described above, with a constant current of up to 2.8 V, and after reaching 2.8 V, the battery was maintained at 2.8 V and kept at a constant voltage until the total time reached 10 hours. Discharging was performed at a constant current until it reached 1.5 V at 0.2 CmA. The open circuit time between charging and discharging was 30 minutes. The transition of the discharge capacity obtained by the above cycle evaluation is shown in FIG. In FIG. 3, it represents with the maintenance rate which made the discharge capacity of each battery at the time of a cycle evaluation start 100%.

Example 4
Except for setting the molar ratio (M ₂ / M ₁ ) between the molar number M _{1 of} LiBF ₄ and the molar number M _{2 of} TMP to 0.8, non-water is the same as described in Example 1 above. An electrolyte secondary battery was produced.

(Example 5)
Except for setting the molar ratio (M ₂ / M ₁ ) between the molar number M _{1 of} LiBF ₄ and the molar number M _{2 of} TMP to 0.5, non-water is the same as described in Example 1 above. An electrolyte secondary battery was produced.

(Comparative Example 10)
A slurry of 87% by weight of graphite powder, 10% by weight of artificial graphite having an average particle diameter of 5 μm, 1% by weight of carboxymethylcellulose, and 2% by weight of styrene-butadiene rubber was slurried using water as a solvent. After apply | coating the obtained slurry on copper foil, the negative electrode sheet was produced by drying.

The obtained negative electrode sheet was cut into a circle having a diameter of 16 mm to obtain a negative electrode. The negative electrode weight was 26.3 mg. The operating potential of this negative electrode was 0 to 0.2 V (0 to 0.2 V vs. Li / Li ⁺ ) with respect to the metal lithium potential.

After 1.2 mol / L lithium bistrifluoromethanesulfonylamide (LiTFSI) was dissolved in 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonylamide (EMI • TFSI), trimethyl phosphate (TMP) was added at a molar ratio. A nonaqueous electrolyte was prepared by adding (M ₂ / M ₁ ) to 1.1. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except for the nonaqueous electrolyte and the negative electrode.

  For the obtained secondary batteries of Examples 4 and 5 and Comparative Example 10, output characteristics and cycle characteristics were evaluated under the same conditions as described above.

Further, the secondary batteries of Examples 4 and 5 and Comparative Example 10 and the secondary batteries of Examples 1 to 3, Comparative Examples 1 to 5, and Reference Examples 6 to 9 described above were subjected to a high temperature cycle under the conditions described below. A characteristic test was carried out. First, in a constant temperature bath at 60 ° C., charge at a constant current of 0.2 CmA up to 2.8 V, and after reaching 2.8 V, hold 2.8 V and charge at a constant voltage until the total time reaches 10 hours. Went. Thereafter, constant current discharge of 0.2 CmA was performed. This charging / discharging is repeated 20 cycles, and the discharge capacity at the 20th cycle is shown in Tables 2 to 4 below.

In order to reduce the influence of the above-mentioned secondary battery due to the difference in the type of the molten salt, the second group mainly includes the first group in which the molten salt is EMI · BF ₄ and the secondary battery in which the molten salt is EMI · TFSI. The group was divided into a third group mainly composed of secondary batteries having molten salts other than the above two types. For the secondary batteries of Examples 1, 2, 5 and Comparative Examples 1, 2 and Reference Examples 6 and 7 of the first group, the output characteristics are shown in FIG. 4, the cycle characteristics are shown in FIG. 5, and the high temperature cycle characteristics are shown in Table 2. It was shown to. Regarding the secondary batteries of Example 4, Comparative Examples 2, 5, 10 and Reference Example 8 of the second group, the output characteristics are shown in FIG. 6, the cycle characteristics are shown in FIG. 7, and the high temperature cycle characteristics are shown in Table 3. For the secondary batteries of Examples 1, 3, 4 and Comparative Examples 3, 4 and Reference Example 9 of the third group, the output characteristics are shown in FIG. 8, the cycle characteristics are shown in FIG. 9, and the high temperature cycle characteristics are shown in Table 4. It was.

  First, the first group will be described. From FIG. 4, the secondary batteries of Examples 1, 2, and 5 and Reference Examples 6 and 7 using phosphate esters are at any discharge rate of 0.1 C, 0.2 C, 0.4 C, and 0.8 C. However, it is possible to obtain a larger discharge capacity than the secondary battery of Comparative Example 1 that does not contain a phosphate ester, and the output characteristics are excellent. Moreover, a high capacity can be obtained as compared with the secondary battery of Comparative Example 2 containing nonflammable nonafluoromethoxybutylene which is a kind of an alternative chlorofluorocarbon solvent.

Comparing Examples 1 and 5 and Reference Examples 6 and 7 in which the type of the organic solvent is TMP, the secondary battery of Example 1 having a molar ratio (M ₂ / M ₁ ) of 0.8 to 1 has a discharge rate. Of the discharge capacity when increasing the value to 0.1 C, 0.2 C, 0.4 C, and 0.8 C, the molar ratio (M ₂ / M ₁ ) is 0.5. Compared to the secondary battery of Reference Example 6 in which (M ₂ / M ₁ ) is less than 0.5 and Reference Example 7 in which the molar ratio (M ₂ / M ₁ ) is more than 1, the output characteristics are particularly excellent. I understand that. Also, in the secondary battery of Example 2 using TEP, which has a higher molecular weight than TMP and is difficult to evaporate, as an organic solvent, 0.1 C and 0.2 C compared to the secondary batteries of Reference Examples 6 and 7. A significant increase in the discharge capacity was observed.

From FIG. 5, the secondary batteries of Examples 1, 2 and 5 and Reference Examples 6 and 7 using phosphoric acid esters maintained the discharge capacity at the 30th cycle as compared with the secondary batteries of Comparative Examples 1 and 2. It can be seen that the rate is high. Comparing Examples 1 and 5 and Reference Examples 6 and 7 in which the type of organic solvent is TMP, the secondary battery of Example 1 having a molar ratio (M ₂ / M ₁ ) of 0.8 to 1 is 30 cycles. It can be understood that the discharge capacity retention rate of the eye is about 95.4%, which is larger than the secondary batteries of Example 5 and Reference Examples 6 and 7, and the cycle characteristics are particularly excellent.

Furthermore, as shown in Table 2, the secondary batteries of Examples 2 and 5 having a molar ratio (M ₂ / M ₁ ) of 0.5 to ₁ have cycle characteristics at 60 ° C. of those of Comparative Examples 1 and 2. Not only the secondary battery but also the secondary batteries of Reference Examples 6 and 7 whose molar ratio (M ₂ / M ₁ ) is out of the above range are excellent.

Therefore, from FIG. 4, FIG. 5, and Table 2, by making the molar ratio (M ₂ / M ₁ ) in the range of 0.5 to 1, the output characteristics are improved as compared with the case where no phosphate ester is added. It was found that excellent cycle characteristics can be realized at both room temperature and high temperature.

The second group will be described. From FIG. 6, the secondary batteries of Example 4 and Reference Example 8 using the phosphoric acid ester showed the phosphoric acid ester at any discharge rate of 0.1 C, 0.2 C, 0.4 C, and 0.8 C. A larger discharge capacity can be obtained than the secondary battery of Comparative Example 5 which does not contain, and the output characteristics are excellent. Moreover, a high capacity can be obtained as compared with the secondary battery of Comparative Example 2 containing nonafluoromethoxybutylene. The secondary battery of Comparative Example 10 has a negative electrode containing graphite and a molar ratio (M ₂ / M ₁ ) as in the lithium secondary battery described in Patent Document 3 (Japanese Patent Laid-Open No. 11-329495) described above. And more than one non-aqueous electrolyte. According to the secondary battery of Comparative Example 10, deterioration progressed during the evaluation, the discharge capacity at 0.1 C was as low as 0.20 mAh, and almost no discharge was possible at 0.4 C and 0.8 C.

From FIG. 7, the secondary battery of Example 4 having a molar ratio (M ₂ / M ₁ ) of 0.5 to ₁ is not limited to the secondary batteries of Comparative Examples 2 and 5, but the molar ratio (M ₂ / M _1). ) Is higher than 1, the secondary battery of Reference Example 8 shows that the discharge capacity retention rate at the 30th cycle is high. Further, in the secondary battery of Comparative Example 10, rapid deterioration occurred at the beginning of the cycle.

Furthermore, as shown in Table 3, the secondary battery of Example 4 having a molar ratio (M ₂ / M ₁ ) of 0.5 to ₁ has a cycle characteristic at 60 ° C. that is the secondary battery of Comparative Examples 2 and 5. It is superior to the battery and the secondary battery of Reference Example 8. Note that according to the secondary battery of Comparative Example 10, almost no discharge was possible from the first cycle, as in the case of room temperature.

Therefore, from FIG. 6, FIG. 7 and Table 3, even when the type of the molten salt is changed from EMI · BF ₄ to EMI · TFSI, the molar ratio (M ₂ / M ₁ ) is in the range of 0.5 to 1. Thus, it was found that excellent cycle characteristics can be realized at both room temperature and high temperature while improving the output characteristics as compared with the case where no phosphate ester is added.

  Finally, the third group will be described. From FIG. 8, the secondary batteries of Examples 1, 3, 4 and Reference Example 9 using phosphoric acid esters were obtained at any discharge rate of 0.1 C, 0.2 C, 0.4 C and 0.8 C. A discharge capacity larger than that of the secondary battery of Comparative Example 3 that does not contain a phosphate ester can be obtained, and the output characteristics are excellent. Moreover, a high capacity can be obtained as compared with the secondary battery of Comparative Example 4 containing nonafluoromethoxybutylene.

Comparing Examples 1 and 3 having a molar ratio (M ₂ / M ₁ ) of 1, the secondary battery of Example 1 having a molten salt whose anion component is BF ₄ is a molten salt whose anion component is TFSI. Compared to the secondary battery of Example 3 provided with a large discharge capacity at any discharge rate of 0.2C, 0.4C and 0.8C, the improvement of the output characteristics, the anion component of the molten salt It can be seen that is preferably BF ₄ .

  From FIG. 9, the secondary batteries of Examples 1, 3, 4 and Reference Example 9 using phosphoric acid esters have a discharge capacity maintenance rate at the 30th cycle as compared with the secondary batteries of Comparative Examples 3-4. I understand that it is expensive.

Comparing Examples 1 and 3 having a molar ratio (M ₂ / M ₁ ) of 1, the secondary battery of Example 1 having a molten salt whose anion component is BF ₄ is a molten salt whose anion component is TFSI. Compared with the secondary battery of Example 3 provided with the above, it can be seen that the discharge capacity retention rate at the 30th cycle is high, and it is desirable that the anion component of the molten salt is BF ₄ in order to improve cycle characteristics.

Further, as shown in Table 4, the secondary batteries of Examples 1, 3, and 4 having a molar ratio (M ₂ / M ₁ ) of 0.5 to ₁ have cycle characteristics at 60 ° C. of Comparative Example 3, In addition to being higher than the secondary battery of _No. 4, the molar ratio (M ₂ / M ₁ ) was superior to the secondary battery of Reference Example 9 having a molar ratio (M ₂ / M ₁ ) exceeding 1.

Comparing Examples 1 and 3 having a molar ratio (M ₂ / M ₁ ) of 1, the secondary battery of Example 1 having a molten salt whose anion component is BF ₄ is a molten salt whose anion component is TFSI. As compared with the secondary battery of Example 3 having the above, it is excellent in cycle characteristics at 60 ° C., and it is found that the anion component of the molten salt is preferably BF ₄ in order to improve high temperature cycle characteristics. .

Therefore, from FIG. 8, FIG. 9, and Table 4, even when molten salts other than EMI.BF ₄ and EMI.TFSI are used, the molar ratio (M ₂ / M ₁ ) is in the range of 0.5 to 1. Thus, it was found that excellent cycle characteristics can be realized at both room temperature and high temperature while improving the output characteristics as compared with the case where no phosphate ester is added.

  As described above, according to the present invention, it is possible to achieve both output characteristics and cycle characteristics of a nonaqueous electrolyte battery including an electrolyte with high flame retardancy.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

Sectional drawing which shows the coin-type nonaqueous electrolyte battery which is an example of the nonaqueous electrolyte battery which concerns on this invention. The characteristic view showing the discharge rate dependence about the nonaqueous electrolyte secondary battery of Examples 1-3, Reference Examples 6-9, and Comparative Examples 1-5. The characteristic view showing the cycle characteristic about the nonaqueous electrolyte secondary battery of Examples 1-3, Reference Examples 6-9, and Comparative Examples 1-5. The characteristic view showing the discharge rate dependence about the nonaqueous electrolyte secondary battery of Examples 1, 2, 5, Reference Examples 6, 7, and Comparative Examples 1-2. The characteristic view showing the cycle characteristic about the nonaqueous electrolyte secondary battery of Examples 1, 2, 5, Reference Examples 6, 7, and Comparative Examples 1-2. The characteristic view showing the discharge rate dependence about the nonaqueous electrolyte secondary battery of Example 4, Reference Example 8, and Comparative Examples 5 and 10. The characteristic view showing the cycle characteristic about the nonaqueous electrolyte secondary battery of Example 4, Reference Example 8, and Comparative Examples 2, 5, and 10. The characteristic view showing the discharge rate dependence about the nonaqueous electrolyte secondary battery of Examples 1, 3, 4, Reference Example 9, and Comparative Examples 3, 4. The characteristic view showing the cycle characteristics about the nonaqueous electrolyte secondary battery of Examples 1, 3, 4, Reference Example 9, and Comparative Examples 3, 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Positive electrode container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Negative electrode container, 6 ... Insulating gasket.

Claims (8)

A positive electrode;
A negative electrode containing an active material having a negative electrode operating potential nobler than 0.5 V with respect to a metallic lithium potential;
A non-aqueous electrolyte battery comprising a metal salt comprising at least one of an alkali metal salt and an alkaline earth metal salt, a molten salt, and a phosphate ester, and satisfying the following formula (1): .
0.5 ≦ (M ₂ / M ₁ ) ≦ 1 (1)
However, M ₁ is at the number of moles of the metal salt, M ₂ is the number of moles of the phosphoric acid ester.   The nonaqueous electrolyte battery according to claim 1, wherein the cation of the molten salt has an imidazolium structure.   The nonaqueous electrolyte battery according to claim 1, wherein the cation of the molten salt has an imidazolium structure, and the anion is a tetrafluoroborate anion.   The nonaqueous electrolyte battery according to claim 1, wherein the anion of the molten salt is a tetrafluoroborate anion, and the metal salt includes lithium tetrafluoroborate. 5. The non-aqueous electrolyte battery according to claim 1, wherein the (M ₂ / M ₁ ) satisfies 0.8 ≦ (M ₂ / M ₁ ) ≦ 1.   The non-aqueous electrolyte battery according to claim 1, wherein the negative electrode active material has a negative electrode operating potential of 0.5 V or more and 3 V or less with respect to a metallic lithium potential.   The non-aqueous electrolyte battery according to claim 1, wherein the negative electrode active material contains lithium titanate and / or iron sulfide. The non-aqueous solution according to claim 7, wherein the lithium titanate has a composition represented by Li _{4 + x} Ti ₅ O ₁₂ (x is −1 ≦ x ≦ 3) or Li ₂ Ti ₃ O _7. Electrolyte battery.

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