Non-aqueous electrolyte secondary battery, and method of producing non-aqueous electrolyte secondary battery

1. A non-aqueous electrolyte secondary battery comprising:

an electrode array; and

an electrolyte solution,

the electrode array including:

a positive electrode, the positive electrode including a positive electrode current collector and a positive electrode composite material layer disposed on a surface of the positive electrode current collector;

a negative electrode, the negative electrode including a negative electrode current collector and a negative electrode composite material layer; and

a separator, the separator being interposed between the positive electrode and the negative electrode,

the electrode array including cellulose nanofibers,

at least one of the peel strength between the positive electrode current collector and the positive electrode composite material layer and the peel strength between the negative electrode current collector and the negative electrode composite material layer being smaller than both the peel strength between the separator and the positive electrode composite material layer and the peel strength between the separator and the negative electrode composite material layer,

the greater of the peel strength between the positive electrode current collector and the positive electrode composite material layer and the peel strength between the negative electrode current collector and the negative electrode composite material layer being at least 1.5 times greater than the smaller of the two,

the electrolyte solution containing a lithium salt and a solvent,

the separator including separator pores,

the positive electrode composite material layer including positive pores,

the negative electrode composite material layer including negative pores,

the cellulose nanofibers are disposed in the separator pores, the positive pores, and the negative pores,

the cellulose nanofibers link to inner walls of the positive pores,

the cellulose nanofibers link to inner walls of the negative pores, and

the cellulose nanofibers link to inner walls of the separator pores.

2. The non-aqueous electrolyte secondary battery according to claim 1 , further comprising an ionic liquid.

3. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the cellulose nanofiber content rate of the electrode array is not lower than 10 vol % and not higher than 30 vol % of a total pore volume of the electrode array, the total pore volume being a sum of a total volume of the separator pores, a total volume of the negative pores, and a total volume of the positive pores.

4. A method of producing the non-aqueous electrolyte secondary battery according to claim 1 , the method comprising the steps, in the sequence set forth, of:

placing the electrode array comprising the positive electrode, the negative electrode, and the separator in a casing;

impregnating the electrode array with a cellulose nanofiber solution to provide a state in which the electrode array is immersed in the cellulose nanofiber solution, the cellulose nanofiber solution containing an ionic liquid and the cellulose nanofibers dissolved in the ionic liquid;

maintaining the state in which the electrode array is immersed in the cellulose nanofiber solution for a predetermined period of time; and

after the predetermined period of time, injecting the electrolyte solution into the casing,

the cellulose nanofiber content rate of the cellulose nanofiber solution being not lower than 4 mass % of the amount of the ionic liquid.

5. The method according to claim 4 , wherein the cellulose nanofiber content rate of the cellulose nanofiber solution is lower than 20 mass % of the amount of the ionic liquid.

6. The method according to claim 4 , wherein the impregnating step comprises impregnating the positive electrode composite material layer, the negative electrode composite material layer, and the separator with the cellulose nanofiber solution.

7. The method according to claim 4 , wherein the ionic liquid is a salt in a liquid state.

8. The method according to claim 4 , wherein the ionic liquid is represented by one or more of formulae (1) to (6) below:

9. The non-aqueous electrolyte secondary battery according to claim 2 , wherein the ionic liquid is a salt in a liquid state.

10. The non-aqueous electrolyte secondary battery according to claim 2 , wherein the ionic liquid is capable of dissolving the cellulose nanofiber.

11. The non-aqueous electrolyte secondary battery according to claim 2 , wherein the ionic liquid is represented by one or more of formulae (1) to (6) below:

12. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the cellulose fibers disposed in the separator pores directly contact the cellulose fibers disposed in the positive pores.

13. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the cellulose fibers disposed in the separator pores directly contact the cellulose fibers disposed in the negative pores.

14. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the cellulose fibers disposed in the separator pores are linked directly together with each other and contact the cellulose fibers disposed in the positive pores.

15. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the cellulose fibers disposed in the separator pores are linked directly together with each other and contact the cellulose fibers disposed in the negative pores.