Secondary battery and method for using secondary battery

1. A secondary battery comprising at least:

a positive electrode;

a negative electrode;

a separation layer that spatially separates the positive electrode and the negative electrode; and

an ion conductor that is held between the positive electrode and the negative electrode and has a function of conducting ions between the positive electrode and the negative electrode,

wherein, in an initial stage of using the secondary battery, the secondary battery has

a characteristic of a potential decrease rate of the positive electrode immediately before completion of full discharging being larger than a potential increase rate of the negative electrode immediately before the completion of full discharging and

a characteristic of a potential increase rate of the positive electrode immediately before completion of full charging being larger than a potential decrease rate of the negative electrode immediately before the completion of full charging, and

the secondary battery is continuously used until a state in which the potential decrease rate of the positive electrode immediately before the completion of full discharging becomes smaller than the potential increase rate of the negative electrode immediately before the completion of full discharging,

wherein the secondary battery is produced by at least a method selected from a group consisting of Method 1 to 4 below:

wherein Method 1 comprises using a first positive electrode, as the positive electrode, having a larger irreversible capacity than that of a first negative electrode, as the negative electrode, on which a treatment that removes some of conduction ions has been carried out,

wherein Method 2 comprises using a second negative electrode, as the negative electrode, including a negative electrode active material having an irreversible capacity that is smaller than an irreversible capacity of a second positive electrode, as the positive electrode, and a material having an irreversible capacity,

wherein Method 3 comprises using a third negative electrode, as the negative electrode, having a larger irreversible capacity than that of a third positive electrode, as the positive electrode, on which a treatment that adds conduction ions has been carried out,

wherein Method 4 comprises using a fourth positive electrode, as the positive electrode, having a smaller irreversible capacity than that of a fourth negative electrode, as the negative electrode, on which the treatment that adds conduction ions has been carried out.

2. The secondary battery according to claim 1 ,

wherein, in the initial stage of using the secondary battery,

when discharging is carried out with a constant current of 1/20 C, a ratio (ΔV 2 /ΔV 1 ) of an absolute value (ΔV 2 ) of an amount of a potential changed per 10 mAh/g of the positive electrode immediately before the completion of full discharging to an absolute value (ΔV 1 ) of an amount of a potential changed per 10 mAh/g of the negative electrode immediately before the completion of full discharging satisfies a relationship ΔV 2 /ΔV 1 >1.

3. The secondary battery according to claim 1 ,

wherein, in the initial stage of using the secondary battery,

when charging is carried out with a constant current of 1/20 C, a ratio (ΔV 4 /ΔV 3 ) of an absolute value (ΔV 4 ) of an amount of a potential changed per 10 mAh/g of the positive electrode immediately before the completion of full charging to an absolute value (ΔV 3 ) of an amount of a potential changed per 10 mAh/g of the negative electrode immediately before the completion of full charging satisfies a relationship ΔV 4 /ΔV 3 >1.

4. The secondary battery according to claim 1 ,

wherein the secondary battery is continuously used until a state in which, when discharging is carried out with a constant current of 1/20 C, the ratio (ΔV 2 /ΔV 1 ) of an absolute value (ΔV 2 ) of an amount of a potential changed per 10 mAh/g of the positive electrode immediately before the completion of full discharging to an absolute value (ΔV 1 ) of an amount of a potential changed per 10 mAh/g of the negative electrode immediately before the completion of full discharging satisfies a relationship ΔV 2 /ΔV 1 <1.

5. The secondary battery according to claim 1 ,

wherein, in the initial stage of using the secondary battery, excess conduction ions are present in the negative electrode at the time of completing full discharging.

6. The secondary battery according to claim 5 ,

wherein, in a period of time of the secondary battery being used, when the conduction ions that contribute to charging and discharging decrease, the decreased conduction ions are compensated for by the excess conduction ions in the negative electrode.

7. The secondary battery according to claim 1 ,

wherein the secondary battery is a lithium ion secondary battery.

8. A method for using a secondary battery including at least a positive electrode, a negative electrode, a separation layer that spatially separates the positive electrode and the negative electrode, and an ion conductor that is held between the positive electrode and the negative electrode and has a function of conducting ions between the positive electrode and the negative electrode,

wherein, in an initial stage of using the secondary battery,

the secondary battery is used under a condition of a potential decrease rate of the positive electrode immediately before completion of full discharging being larger than a potential increase rate of the negative electrode immediately before the completion of full discharging and is used under a condition of a potential increase rate of the positive electrode immediately before completion of full charging being larger than a potential decrease rate of the negative electrode immediately before the completion of full charging, and

the secondary battery is continuously used until a state in which the potential decrease rate of the positive electrode immediately before the completion of full discharging becomes smaller than the potential increase rate of the negative electrode immediately before the completion of full discharging,

wherein the secondary battery is produced by at least a method selected from a group consisting of Method 1 to 4 below:

wherein Method 1 comprises using a first positive electrode, as the positive electrode, having a larger irreversible capacity than that of a first negative electrode, as the negative electrode, on which a treatment that removes some of conduction ions has been carried out,

wherein Method 2 comprises using a second negative electrode, as the negative electrode, including a negative electrode active material having an irreversible capacity that is smaller than an irreversible capacity of a second positive electrode, as the positive electrode, and a material having an irreversible capacity,

wherein Method 3 comprises using a third negative electrode, as the negative electrode, having a larger irreversible capacity than that of a third positive electrode, as the positive electrode, on which a treatment that adds conduction ions has been carried out,

wherein Method 4 comprises using a fourth positive electrode, as the positive electrode, having a smaller irreversible capacity than that of a fourth negative electrode, as the negative electrode, on which the treatment that adds conduction ions has been carried out.

9. The method for using a secondary battery according to claim 8 ,

wherein, in the initial stage of using the secondary battery,

the secondary battery is used under a condition in which, when discharging is carried out with a constant current of 1/20 C, a ratio (ΔV 2 /ΔV 1 ) of an absolute value (ΔV 2 ) of an amount of a potential changed per 10 mAh/g of the positive electrode immediately before the completion of full discharging to an absolute value (ΔV 1 ) of an amount of a potential changed per 10 mAh/g of the negative electrode immediately before the completion of full discharging satisfies a relationship ΔV 2 /ΔV 1 >1.

10. The method for using a secondary battery according to claim 8 ,

wherein, in the initial stage of using the secondary battery,

the secondary battery is used under a condition in which, when charging is carried out with a constant current of 1/20 C, a ratio (ΔV 4 /ΔV 3 ) of an absolute value (ΔV 4 ) of an amount of a potential changed per 10 mAh/g of the positive electrode immediately before the completion of full charging to an absolute value (ΔV 3 ) of an amount of a potential changed per 10 mAh/g of the negative electrode immediately before the completion of full charging satisfies a relationship ΔV 4 /ΔV 3 >1.

11. The method for using a secondary battery according to claim 8 ,

wherein the secondary battery is continuously used until a state in which, when discharging is carried out with a constant current of 1/20 C, the ratio (ΔV 2 /ΔV 1 ) of an absolute value (ΔV 2 ) of an amount of a potential changed per 10 mAh/g of the positive electrode immediately before the completion of full discharging to an absolute value (ΔV 1 ) of an amount of a potential changed per 10 mAh/g of the negative electrode immediately before the completion of full discharging satisfies a relationship ΔV 2 /ΔV 1 <1.

12. The method for using a secondary battery according to claim 8 ,

wherein, in the initial stage of using the secondary battery, excess conduction ions are present in the negative electrode at the time of completing full discharging.

13. The method for using a secondary battery according to claim 12 ,

wherein, in a period of time of the secondary battery being used, when the conduction ions that contribute to charging and discharging decrease, the decreased conduction ions are compensated for by the excess conduction ions in the negative electrode.

14. The method for using a secondary battery according to claim 8 ,

wherein the secondary battery is a lithium ion secondary battery.