JP5708244B2 - Non-aqueous electrolyte and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte and a lithium ion secondary battery using the same.

  In recent years, there is an increasing demand for miniaturization or higher energy density for mobile communication power supplies such as mobile phones and portable personal computers. Development of a power source for storing midnight power, a power source for storing power combined with solar cells and wind power generation, and the like is also progressing. Furthermore, commercialization of electric vehicles, hybrid vehicles and hybrid trains that use electric power as part of their power is also progressing.

  By the way, as a nonaqueous electrolytic solution, a solution obtained by dissolving a supporting salt (electrolyte) such as lithium hexafluorophosphate in a nonaqueous solvent such as ethylene carbonate is widely known. These non-aqueous solvents are generally volatile and flammable.

  In particular, in a relatively large lithium ion secondary battery application such as a power storage power source, the problem of heat generation is increased due to the large battery capacity, and therefore, it is desired to use a non-aqueous electrolyte solution that does not cause ignition. Yes. Therefore, research for adding flame retardants to non-aqueous electrolytes and imparting flame retardancy is underway energetically.

  (Patent Document 1) discloses a flame retardant electrolytic solution in which a specific neopentyl glycol phosphonate compound and a trialkyl phosphate compound are combined, and a nonaqueous electrolyte secondary battery containing the same.

  Further, (Patent Document 2) discloses a nonaqueous electrolytic solution containing a phosphate ester and a bisphosphonate ester and / or a host acid ester, and a lithium secondary battery using the same.

JP 2003-229173 A JP 2002-280061 A

  However, when a flame retardant is added to the non-aqueous electrolyte, there is room for improvement in that the initial capacity of the battery is reduced when the amount of the flame retardant added is increased in order to obtain sufficient flame retardancy. Moreover, in order to maintain good high rate discharge characteristics, an electrolyte system with high electrical conductivity was required.

  Accordingly, an object of the present invention is to provide a nonaqueous electrolytic solution having flame retardancy and high electrical conductivity and excellent in high rate discharge characteristics, and a lithium ion secondary battery using the same.

  In order to solve the above problems, the nonaqueous electrolytic solution of the present invention contains a nonaqueous solvent containing at least a cyclic carbonate and a chain carbonate and a supporting salt, and further contains a phosphate ester and a bisphosphonate ester. Features.

  According to the present invention, a non-aqueous electrolyte excellent in flame retardancy and electrical conductivity can be obtained, thereby realizing a lithium ion secondary battery with good high rate discharge characteristics. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a schematic exploded view of the test cell used for the charging / discharging test. 6 is a partial cross-sectional view showing a lithium ion secondary battery of Example 5. FIG.

  Hereinafter, a nonaqueous electrolytic solution according to an embodiment of the present invention and a lithium ion secondary battery using the same will be described.

  The nonaqueous electrolytic solution contains a nonaqueous solvent containing at least a cyclic carbonate and a chain carbonate and a supporting salt, and further contains a phosphate ester and a bisphosphonate ester.

  As the cyclic carbonate, for example, a simple substance such as ethylene carbonate, propylene carbonate, butylene carbonate, or a mixture thereof can be used.

  Examples of the chain carbonate include asymmetric chain carbonates such as ethyl methyl carbonate, methyl propyl carbonate, methyl butyl carbonate, and ethyl propyl carbonate, and symmetric chain carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate. These mixtures are mentioned.

  From the viewpoint of high rate discharge characteristics, ethylene carbonate and dimethyl carbonate are particularly preferably used as the cyclic carbonate and chain carbonate. Further, the mixing ratio of the cyclic carbonate such as ethylene carbonate and the chain carbonate such as dimethyl carbonate is not particularly limited, but the ratio of the chain carbonate with respect to 100 vol% of the total of the cyclic carbonate and the chain carbonate is not limited. 20 vol% or more and 65 vol% or less is preferable because the flash point of the non-aqueous electrolyte can be increased.

  As a non-aqueous solvent, vinylene carbonate can be further contained. By using vinylene carbonate, it is estimated that a stable film is formed on the surface of the negative electrode during charging. This coating has the effect of suppressing the decomposition of the non-aqueous electrolyte on the negative electrode surface.

  The content of vinylene carbonate in the nonaqueous electrolytic solution is preferably in the range of 0.5 to 5% by weight with respect to the total of the cyclic carbonate and the chain carbonate. When the content of vinylene carbonate is less than 0.5% by weight, the effect of improving the cycle characteristics is reduced, and when it exceeds 5% by weight, the vinylene carbonate is excessively decomposed to lower the charge / discharge efficiency. There is a fear.

  Furthermore, a fluorinated cyclic carbonate can be contained as the non-aqueous solvent. By using a fluorinated cyclic carbonate, it is estimated that a stable film is formed on the surface of the electrode. Examples of the fluorinated cyclic carbonate include fluoroethylene carbonate. The content of the fluorinated cyclic carbonate in the nonaqueous electrolytic solution is preferably in the range of 0.5 to 15 vol% in the mixture of the nonaqueous solvent and the supporting salt. When the content of the fluorinated cyclic carbonate is less than 0.5 vol%, the effect of improving the cycle characteristics is reduced, and when the content of the fluorinated cyclic carbonate exceeds 15 vol%, the fluorinated cyclic carbonate is excessively decomposed. Charge / discharge efficiency may be reduced.

  In addition, as a non-aqueous solvent, a simple substance or a mixture of cyclic esters such as γ-butyrolactone and γ-valerolactone, tetrahydrofuran, 1,2-dimethoxyethane, dimethyl sulfoxide, sulfolane and the like can be appropriately contained. The total content of these other solvents is preferably 30% by weight or less in the mixture of the non-aqueous solvent and the supporting salt.

As the supporting salt used in the non-aqueous electrolyte solution, for _example, be used _{LiPF 6, LiBF 4, LiClO 4} , LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiN (SO 2 CF 3) alone or a mixture of such ₂ it can. Among them, LiPF ₆ or LiBF ₄ is preferable, and LiPF ₆ is particularly preferable. Moreover, there is no restriction | limiting in particular about the density | concentration of these support salt, However, It is preferable to set it as the range of 0.8-2.0 mol / l with respect to the sum total of cyclic carbonate and cyclic carbonate.

  As the phosphate ester, any of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate and the like can be used alone or in combination. Further, tris phosphate (2,2,2-trifluoroethyl), tris phosphate (2,2,3,3-tetrafluoropropyl), tris phosphate (2,2,3,3,4,4,4) Any fluorine-containing phosphate ester such as 5,5-octafluoropentyl) may be used alone or in combination. In the present invention, conceptually, this fluorine-containing phosphate ester is also included in the phosphate ester. Among the above, trimethyl phosphate is particularly preferably used.

  The amount of the phosphate ester added is preferably 1 to 15% by weight, more preferably 1 to 10% by weight, based on 100% by weight of the total amount of the nonaqueous solvent and the supporting salt.

  As the bisphosphonic acid ester, any of tetraisopropyl methylene diphosphonate, tetraethyl methylene diphosphonate, tetraethyl ethylene diphosphonate, tetraethyl p-xylylene diphosphonate and the like can be used alone or in combination. Among these, tetraisopropyl methylene diphosphonate or tetraethyl methylene diphosphonate is particularly preferably used.

  The addition amount of the bisphosphonic acid ester is preferably 0.5 to 10% by weight, more preferably 0.5 to 8% by weight, based on 100% by weight of the total amount of the nonaqueous solvent and the supporting salt.

  In particular, the total addition amount of the phosphate ester and the bisphosphonate ester is preferably 1.5 to 5% by weight with respect to the total 100% by weight of the nonaqueous solvent and the supporting salt. When the addition amount is less than 1.5% by weight, it is difficult to obtain a fire extinguishing effect. In addition, even in the case of addition of 5% by weight and a relatively small amount, the combined use of phosphoric acid ester and bisphosphonic acid ester has good fire extinguishing properties and little adverse effect on battery characteristics. There is an effect of excellent characteristics. Further, comparing the fire extinguishing properties of phosphate ester and bisphosphonate ester, phosphate ester is more digestible, so it is desirable that the addition amount of phosphate ester be greater than or equal to the addition amount of bisphosphonate ester.

  In addition to the above-mentioned components, the non-aqueous electrolyte includes bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluoro (bisoxalato) phosphate as necessary. At least one salt selected from the group consisting of a salt and tetrafluoro (bisoxalato) phosphate may be added. By adding these salts, it is thought that a film is formed on the electrode, which leads to an improvement in battery performance. The total content of these salts is preferably 5% by weight or less in the non-aqueous electrolyte.

  In addition, as long as the gist of the present invention is not impaired, other commonly used additives may be added to the non-aqueous electrolyte at an arbitrary ratio. Specific examples include compounds having an overcharge preventing effect and a positive electrode protecting effect, such as cyclohexylbenzene, biphenyl, t-butylbenzene, and propane sultone. The content of these other additives is not particularly limited, but is preferably 10% by weight or less in the non-aqueous electrolyte in total.

Next, the configuration of the lithium ion secondary battery will be described.
For the lithium ion secondary battery, the non-aqueous electrolyte is used. As other components, a negative electrode, a positive electrode, a separator, a container, and the like that are used in a general lithium ion secondary battery can be used.

  The negative electrode active material used for the negative electrode constituting the lithium ion battery is not particularly limited as long as the material can occlude and release lithium ions. Examples thereof include artificial graphite, natural graphite, non-graphitizable carbons, metal oxides, metal nitrides, activated carbon and the like. Any of these may be used alone or in admixture of two or more.

  The positive electrode active material used for the positive electrode constituting the lithium ion battery is not particularly limited as long as it is a material capable of occluding and releasing lithium ions. For example, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide And lithium transition metal composite oxides. Any of these may be used alone or in admixture of two or more.

  After preparing the positive electrode mixture slurry and the negative electrode mixture slurry by mixing the above-described positive electrode active material and negative electrode active material with a binder, a thickener, a conductive material, a solvent, and the like, respectively, as necessary. Each can be applied to a current collector and dried to cut out a desired shape.

  As the separator constituting the lithium ion battery, for example, a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene can be used.

  By using the above components, lithium ion secondary batteries having various shapes such as a coin shape, a cylindrical shape, a square shape, and an aluminum laminate sheet shape can be assembled.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples.

Example 1
In a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 2: 3), 0.8% by weight of vinylene carbonate (VC) and 1 mol / l of LiPF ₆ as a supporting salt were dissolved. Here, the concentration of VC and supporting salt is the concentration with respect to the sum of EC and DMC (hereinafter the same). A nonaqueous electrolytic solution was prepared by adding 2% by weight of trimethyl phosphate (TMP) as a phosphate ester and 2% by weight of tetraisopropyl methylene diphosphonate (TPMDP) as a bisphosphonate. In addition, the density | concentration of phosphate ester and bisphosphonic acid ester is a density | concentration when the sum total of a nonaqueous solvent (EC, DMC, and VC) and support salt is 100 weight% (hereinafter, the same).

(Combustion test)
About the non-aqueous electrolyte obtained above, the following combustion test was implemented and the flame retardance was evaluated. First, 2 ml of non-aqueous electrolyte is immersed in glass fiber (width 20 mm x length 65 mm), exposed to the test flame for 10 seconds in the atmosphere, then the test flame is moved away, and the state of the flaming flame is visually observed. And the time to extinguish was measured. The case where the fire extinguishing time was less than 10 seconds was regarded as flame retardancy, and the case where the fire extinguishing time was 10 seconds or more was regarded as combustibility.

(Measurement of electrical conductivity)
Subsequently, the electrical conductivity of the nonaqueous electrolytic solution at 25 ° C. was measured using CM-30V manufactured by Toa Denpa Kogyo.

(Charge / discharge test of negative electrode for lithium ion secondary battery)
Next, using the non-aqueous electrolyte, a test cell was prepared using graphite as a negative electrode active material, and a charge / discharge test was performed. Artificial graphite was used as the negative electrode active material, and polyvinylidene fluoride was used as the binder. First, a solution in which a binder was dissolved at a ratio of 5% by weight in N-methyl-2-pyrrolidone was prepared. Subsequently, this solution was added to artificial graphite and kneaded (the proportion of artificial graphite in the kneaded product was 8.6% by weight), and N-methyl-2-pyrrolidone was further added to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to one side of a copper foil as a current collector and dried to form a negative electrode mixture layer. Then, it was compression-molded with a roll press and cut into a predetermined size to produce a negative electrode for a lithium ion secondary battery.

  Next, a test cell was produced using this negative electrode for a lithium ion secondary battery. FIG. 1 is a schematic exploded view of a test cell used for measurement. In FIG. 1, a counter electrode 31, a negative electrode mixture layer 32, and a reference electrode 33 are stacked in a state where insulation is maintained by sandwiching a separator 35 therebetween, and the outside is pressed by a SUS jig 36. is there. In FIG. 1, the negative electrode mixture layer 32 and the copper foil current collector 34 are separately shown, but these constitute a negative electrode as an integral member as described above. The negative electrode mixture layer 32 has a disk shape with a diameter of 15 mm. The counter electrode 31 and the reference electrode 33 are made of metallic lithium. The separator 35 is a polyethylene porous film having a thickness of 30 μm. About the test cell 30 comprised as mentioned above, said nonaqueous electrolyte was used, and the initial stage discharge capacity characteristic and cycle characteristic were evaluated with the following procedure.

  The charging conditions for the measurement were constant current and constant voltage charging, the voltage value was 5 mV, the current value was 1 mA (initial) and 30 μA (end), and the rest time was 10 minutes. The discharge conditions were a current value of 1 mA and a cut voltage of 1.5V.

  The initial discharge capacity characteristics were evaluated by calculating the discharge capacity per unit weight of artificial graphite, which is the negative electrode active material, after one cycle of charge and discharge under the above conditions. Further, as cycle characteristics, charging / discharging under the above conditions is repeated 20 cycles, and the ratio of the discharge capacity at the 20th cycle to the discharge capacity at the first cycle (initial discharge capacity) (discharge capacity at the 20th cycle / 1 cycle). The discharge capacity of the eye) was calculated and evaluated as a discharge capacity retention rate. Table 1 shows the results.

(Example 2)
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 4% by weight of trimethyl phosphate (TMP) and 1% by weight of tetraisopropyl methylene diphosphonate (TPMDP) were added, and a combustion test was performed. The electrical conductivity measurement and the charge / discharge test were carried out. The results are shown in Table 1.

(Example 3)
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 3% by weight of trimethyl phosphate (TMP) and 2% by weight of tetraisopropyl methylene diphosphonate (TPMDP) were added. Measurement of electrical conductivity and charge / discharge test were performed. The results are shown in Table 1.

Example 4
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 3% by weight of trimethyl phosphate (TMP) and 2% by weight of tetraethyl methylenediphosphonate (TEMDP) were added. Conductivity measurements and charge / discharge tests were performed. The results are shown in Table 1.

(Comparative Example 1)
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that trimethyl phosphate (TMP) and tetraisopropyl methylene diphosphonate (TPMDP) were not added, and a combustion test, electrical conductivity measurement, and charge / discharge The test was conducted. The results are shown in Table 1.

(Comparative Example 2)
In a mixed solution (volume ratio 1: 2) of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), 0.8% by weight of vinylene carbonate (VC) and 1 mol / l of LiPF ₆ were dissolved, and phosphoric acid was dissolved in this solution. A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that trimethyl (TMP) was added to 5 wt% to prepare a non-aqueous electrolyte, and a combustion test, electrical conductivity measurement and charging were performed. A discharge test was performed. The results are shown in Table 1.

(Comparative Example 3)
A nonaqueous electrolytic solution was prepared in the same manner as in Comparative Example 1 except that trimethyl phosphate (TMP) was added to 20 wt%, and a combustion test, an electrical conductivity measurement, and a charge / discharge test were performed. The results are shown in Table 1.

(Comparative Example 4)
A nonaqueous electrolytic solution was prepared in the same manner as in Comparative Example 1 except that trimethyl phosphate (TMP) was added so as to be 15% by weight, and a combustion test, an electrical conductivity measurement, and a charge / discharge test were performed. The results are shown in Table 1.

  As is clear from the results in Table 1, the nonaqueous electrolyte solutions of Examples 1 to 4 have flame retardancy, high electrical conductivity, and high initial discharge capacity. Furthermore, the capacity retention rate after the cycle test also showed a high value. On the other hand, in said Comparative Examples 1-4, it does not have a flame retardance, electrical conductivity, an initial discharge capacity, and a capacity | capacitance maintenance factor.

(Example 5)
An 18650 (diameter 18 mm × height 65 mm) type lithium ion secondary battery was produced using the non-aqueous electrolyte solution and the negative electrode of Example 1 and evaluated. FIG. 2 is a partial cross-sectional view of a lithium ion secondary battery. The positive electrode 1 and the negative electrode 2 are wound in a cylindrical shape with a separator 3 interposed therebetween so that they do not directly contact each other, thereby forming an electrode group. A positive electrode lead 7 is attached to the positive electrode 1, and a negative electrode lead 5 is attached to the negative electrode 2. The electrode group is inserted into the battery can 4, and an insulating plate 9 is installed at the bottom and top of the battery can 4 so that the electrode group does not directly contact the battery can 4. Further, a non-aqueous electrolyte is injected into the battery can 4. Note that the battery can 4 is insulated from the lid 6 via a packing 8.

In this example, the positive electrode was produced by the following method. First, LiMn ₂ O _{4 as} a positive electrode active material and graphite as a conductive material are mixed, and a binder (a solution in which polyvinylidene fluoride is dissolved in N-methyl-2-pyrrolidone) is added and kneaded. A mixture slurry was prepared. At this time, in the solid content of the positive electrode mixture slurry, the positive electrode active material was 88.5% by weight, the conductive material was 4.5% by weight, and the binder was 7% by weight.

  This positive electrode mixture slurry was applied to one surface (surface) of an aluminum foil as a current collector, and then dried at 100 ° C. By the same method, the positive electrode mixture slurry was applied to the other surface (back surface) of the aluminum foil and dried to form a positive electrode mixture layer. And after compression-molding with a roll press machine, it cut | disconnected to the predetermined | prescribed magnitude | size and welded the positive electrode lead made from the aluminum foil for taking out an electric current, and produced the positive electrode.

  The positive electrode and the negative electrode produced by the method of Example 1 were wound into a cylindrical shape with a separator sandwiched therebetween so that they were not in direct contact, and then inserted into a 18650 type battery can. Subsequently, after the current collecting tab and the lid portion of the battery can were connected, the lid portion of the battery can and the battery can were welded by laser welding to seal the battery. Finally, a non-aqueous electrolyte was injected from the injection port provided in the battery can to obtain an 18650 type battery (lithium ion secondary battery).

The characteristics of the produced lithium ion secondary battery were evaluated according to the following procedure.
First, the lithium ion secondary battery was placed in a constant temperature bath at 25 ° C. and held for 1 hour. In the initial charge and discharge, the battery was charged at a constant current and a constant voltage up to 4.2 V at a current of 0.2 C, and then discharged to 2.7 V at a current of 0.5 C. Thereafter, charging at a constant current and a constant voltage up to 4.2 V at a current of 0.5 C and discharging to 2.7 V at a current of 0.5 C were repeated 3 cycles. Next, charging was performed at a constant current and a constant voltage up to 4.2 V at a current of 0.5 C, and the discharge capacity when discharged to 2.7 V at a current of 0.2 C was defined as an initial discharge capacity, and 4 at a current of 0.5 C. The discharge capacity when charged at a constant current and a constant voltage up to 2 V and discharged to 2.7 V at a current of 1.0 C was defined as a high rate discharge capacity. The ratio of the high rate discharge capacity (1.0 C) to the initial discharge capacity (0.2 C) (high rate discharge capacity / initial discharge capacity) was calculated as the discharge capacity ratio. As a result, the discharge capacity ratio was 96%.

  Here, the charge / discharge rate of “1C” means that, when the battery is charged from a fully discharged state, 100% charge is completed in one hour, and the battery is discharged from a fully charged state. In some cases, 100% discharge is completed in one hour. That is, it means that the speed of charging or discharging is 100% per hour.

(Example 6)
A lithium ion battery was produced in the same manner as in Example 5 except that the non-aqueous electrolyte solution of Example 2 was used, and the battery performance was evaluated. As a result, the discharge capacity ratio was 95%.

(Example 7)
A lithium ion battery was produced in the same manner as in Example 5 except that the non-aqueous electrolyte solution of Example 3 was used, and the battery performance was evaluated. As a result, the discharge capacity ratio was 94%.

(Example 8)
A lithium ion battery was produced in the same manner as in Example 5 except that the nonaqueous electrolytic solution of Example 4 was used, and the battery performance was evaluated. As a result, the discharge capacity ratio was 94%.

  As explained above, according to the present invention, a flame retardant non-aqueous electrolyte and a lithium ion secondary battery excellent in high rate discharge characteristics can be obtained. Such a non-aqueous electrolyte and a lithium ion secondary battery using the non-aqueous electrolyte contribute to performance improvement of a power storage power source, an electric vehicle, and the like. Since the nonaqueous electrolytic solution of the present invention has flame retardancy and contributes to the safety of the battery, it is particularly desirable to be used for an industrial lithium ion secondary battery having a large battery capacity.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery can 5 Negative electrode lead 6 Lid part 7 Positive electrode lead 8 Packing 9 Insulating plate 30 Test cell 31 Counter electrode 32 Negative electrode mixture layer 33 Reference electrode 34 Current collector 35 Separator 36 Jig

Claims (10)

An electrolyte solution for a lithium ion secondary battery containing a non-aqueous solvent containing at least a cyclic carbonate and a chain carbonate and a supporting salt, further comprising a phosphate ester and a bisphosphonate ester , wherein the phosphate ester is phosphorous an acid trimethyl, the bisphosphonic acid ester is methylene diphosphonate tetraisopropyl or methylene diphosphonic acid tetraethyl der Ru said lithium ion secondary battery electrolyte solution. The electrolytic solution for a lithium ion secondary battery according to claim 1 , wherein the chain carbonate is dimethyl carbonate. The supporting salt is at least one lithium salt selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ and LiN (SO ₂ CF ₃ ) _2. Or 2. The electrolyte solution for lithium ion secondary batteries according to 2 . The electrolyte solution for lithium ion secondary batteries according to any one of claims 1 to 3 , further comprising vinylene carbonate as a nonaqueous solvent. The electrolyte solution for a lithium ion secondary battery according to any one of claims 1 to 4 , wherein the addition amount of the phosphate ester is 1 to 15% by weight with respect to 100% by weight in total of the nonaqueous solvent and the supporting salt. The electrolyte solution for a lithium ion secondary battery according to any one of claims 1 to 5 , wherein the addition amount of the bisphosphonic acid ester is 0.5 to 10% by weight based on 100% by weight of the total amount of the nonaqueous solvent and the supporting salt. Total amount of phosphoric acid ester and bisphosphonic acid ester, the total 100 wt% of the non-aqueous solvent and a support salt is 1.5 to 5 wt% claim 1 lithium ion secondary according to any one of 4 Secondary battery electrolyte. The electrolyte solution for a lithium ion secondary battery according to any one of claims 1 to 7 , wherein the addition amount of the phosphate ester is equal to or greater than the addition amount of the bisphosphonate ester. And at least selected from the group consisting of bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluoro (bisoxalato) phosphate and tetrafluoro (bisoxalato) phosphate. The electrolyte solution for lithium ion secondary batteries according to any one of claims 1 to 8 , comprising one kind of salt. Lithium-ion secondary battery using the lithium ion secondary battery electrolyte according to any one of claims 1-9.

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