Polyimide binder for power storage device, electrode sheet using same, and power storage device

1. A polyimide binder for energy storage device, comprising:

a polyimide produced by a process comprising subjecting an aqueous solution of a polyamic acid to an imidization reaction,

wherein the polyamic acid is produced by reacting at least one tetracarboxylic acid component selected from the group consisting of an aromatic tetracarboxylic dianhydride not containing a fluorine group, an aliphatic tetracarboxylic dianhydride, and an aromatic tetracarboxylic dianhydride containing a fluorine group and at least one diamine component selected from the group consisting of an aromatic diamine not containing a fluorine group and having a solubility in water of 25° C. of 0.1 g/L or more, an aliphatic diamine having a molecular weight of 500 or less, and an aromatic diamine containing a fluorine group, such that the polyamic acid has a repeating unit of formula (I)

wherein

A is a residue of the tetracarboxylic acid component,

B is a residue of the diamine component,

55 mol % or more of B in a total amount of the repeating unit is derived from the aliphatic diamine having a molecular weight of 500 or less, and

the polyimide has a tensile elastic modulus of from 1.5 GPa to 2.7 GPa.

2. The polyimide binder of claim 1 , wherein the aqueous solution of the polyamic acid is produced by reacting the at least one tetracarboxylic acid component and the at least one diamine component by using water as a reaction solvent in the presence of an imidazole.

3. The polyimide binder of claim 2 , wherein the tetracarboxylic acid component is at least one selected from the group consisting of 4,4′-oxydiphthalic dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 1,2,4,5-cyclohexane tetracarboxylic acid-1,2:4,5-dianhydride, and dicyclohexyl-3,3′,4,4′-tetracarboxylic dianhydride.

4. The polyimide binder of claim 2 , wherein the diamine component is at least one selected from the group consisting of p-phenylenediamine, 4,4′-diaminodiphenyl ether, trans-1,4-diaminocyclohexane, cis-1,4-diaminocyclohexane, 1,6-hexamethylenediamine, and 1,4-bis(aminomethyl)cyclohexane.

5. The polyimide binder of claim 2 , wherein the imidazole is at least one selected from the group consisting of 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, and 1-methyl-4-ethylimidazole.

6. The polyimide binder of claim 2 , wherein the reacting of the at least one tetracarboxylic acid component and the at least one diamine component is carried out such that the aqueous solution of the polyamic acid comprises the imidazole in an amount of 1.6 molar times or more relative to an amount of the tetracarboxylic acid component of the polyamic acid.

7. The polyimide binder of claim 1 , wherein the imidization reaction is performed at an imidization temperature of from 120° C. to 200° C.

8. A negative electrode sheet for energy storage device, comprising:

a copper collector having a negative electrode active material layer formed on a surface of the copper collector,

wherein the negative electrode active material layer is formed by a process comprising casting or applying a negative electrode mixture comprising the polyimide binder for energy storage device of claim 1 , a silicon-containing negative electrode active material, and a carbon material on the surface of the copper collector.

9. A positive electrode sheet for energy storage device, comprising:

an aluminum collector having a positive electrode active material layer formed on a surface of the aluminum collector,

wherein the positive electrode active material layer is formed by a process comprising casting or applying a positive electrode mixture comprising the polyimide binder for energy storage device of claim 1 , a carbon material, and a lithium transition metal oxide on the surface of the aluminum collector, and

the lithium transition metal oxide comprises a nickel atom and a manganese atom in a total amount of from 50 atomic % to 100 atomic % of all metal elements other than a lithium atom.

10. An energy storage device, comprising:

a positive electrode;

a negative electrode comprising the negative electrode sheet of claim 8 ; and

a nonaqueous electrolytic solution comprising an electrolyte salt dissolved in a nonaqueous solvent.

11. The energy storage device of claim 10 , wherein the nonaqueous electrolytic solution comprises a fluorine-containing compound.

12. The energy storage device of claim 11 , wherein the fluorine-containing compound is at least one selected from the group consisting of 4-fluoro-1,3-dioxol an-2-one, trans- or cis-4,5-difluoro-1,3-dioxol an-2-one, and vinyl sulfonyl fluoride.

13. The energy storage device of claim 10 , wherein the electrolyte salt comprises LiPF 6 and at least one lithium salt selected from the group consisting of LiPO 2 F 2 , LiSO 3 F, C 2 H 5 SO 4 Li, LiN(SO 2 F) 2 , lithium difluoro[oxalate-O,O′]borate, lithium difluorobis[oxalate-O,O′]phosphate, and lithium tetrafluoro[oxalate-O,O′]phosphate, and

the at least one lithium salt is included in an amount of from 0.001 M to 0.4 M in the nonaqueous electrolytic solution.

14. The energy storage device of claim 10 , wherein the nonaqueous electrolytic solution comprises at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, 4-ethynyl-1,3-dioxolan-2-one, hexamethylene diisocyanate, methyl phenyl carbonate, diphenyl carbonate, and 1,3-dioxane in an amount of from 0.001% by mass or more to 5% by mass.

15. An energy storage device, comprising:

a polyimide binder having a tensile elastic modulus of from 1.5 GPa to 2.7 GPa and produced by a process comprising subjecting an aqueous solution of a polyamic acid to an imidization reaction, the polyamic acid produced by reacting at least one tetracarboxylic acid component selected from the group consisting of an aromatic tetracarboxylic dianhydride not containing a fluorine group, an aliphatic tetracarboxylic dianhydride, and an aromatic tetracarboxylic dianhydride containing a fluorine group and at least one diamine component selected from the group consisting of an aromatic diamine not containing a fluorine group and having a solubility in water of 25° C. of 0.1 g/L or more, an aliphatic diamine having a molecular weight of 500 or less, and an aromatic diamine containing a fluorine group, such that the polyamic acid has a repeating unit of formula (I)

wherein

A is a residue of the tetracarboxylic acid component,

B is a residue of the diamine component, and

55 mol % or more of B in a total amount of the repeating unit is derived from the aliphatic diamine having a molecular weight of 500 or less.

16. A method for improving an electrical property of an energy storage device, comprising:

including the polyimide binder of claim 1 in the energy storage device.

17. The energy storage device of claim 11 , wherein the nonaqueous electrolytic solution comprises the fluorine-containing compound in an amount of from 0.07% by volume to 35% by volume relative to a total volume of the nonaqueous solvent.

18. The energy storage device of claim 10 , wherein the nonaqueous electrolytic solution further comprises an unsaturated bond-containing cyclic carbonate, an isocyanate compound, a phenyl carbonate compound, and a cyclic acetal compound.

19. The polyimide binder of claim 3 , wherein the diamine component of the polyamic acid is at least one selected from the group consisting of p-phenylenediamine, 4,4′-diaminodiphenyl ether, trans-1,4-diaminocyclohexane, cis-1,4-diaminocyclohexane, 1,6-hexamethylenediamine, and 1,4-bis (aminomethyl)cyclohexane.

20. The polyimide binder of claim 3 , wherein the diamine component is at least one selected from the group consisting of p-phenylenediamine, 4,4′-diaminodiphenyl ether, trans-1,4-diaminocyclohexane,cis-1,4-diaminocyclohexane, 1,6-hexamethylenediamine, and 1,4-bis(aminomethyl)cyclohexane, and

the imidazole is at least one selected from the group consisting of 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, and 1-methyl-4-ethylimidazole.