METHOD FOR DETERMINING COMPLETION OF CHARGE OF LITHIUM ION SECONDARY BATTERY, METHOD FOR DETERMINING TERMINATION OF DISCHARGE OF LITHIUM ION SECONDARY BATTERY, CHARGE CONTROL CIRCUIT, DISCHARGE CONTROL CIRCUIT, AND POWER SUPPLY

1 . A method for determining completion of charge of a lithium ion secondary battery including one lithium compound having an olivine crystal structure as a positive electrode active material, and a graphite material as a negative electrode active material, the method comprising:

(S 1 ) charging the battery by an amount of electricity Xc in time Ti 1 ;

(S 2 ) stopping the charging for time Yc after completion of (S 1 ), and measuring a battery voltage Vi 1 after the time Yc has passed;

(S 3 ) charging the battery by the amount of electricity Xc in the time Ti 1 after completion of (S 2 );

(S 4 ) stopping the charging for the time Yc after completion of (S 3 ), and measuring a battery voltage Vi 2 after the time Yc has passed; and

comparing Vi 2 −Vi 1 with a predetermined voltage difference Vi 3 to determine that the charge has been completed when Vi 2 −Vi 1 >Vi 3 , or determine that the charge has not been completed when Vi 2 −Vi 1 <Vi 3 .

2 . The method for determining completion of charge of the lithium ion secondary battery of claim 1 , wherein

a minimum distance between layers of carbon planes of the graphite material is equal to or smaller than 0.355 nm when it is determined that the charge has been completed.

3 . A method for determining termination of discharge of a lithium ion secondary battery including one lithium compound having an olivine crystal structure as a positive electrode active material, and a graphite material as a negative electrode active material, the method comprising:

(P 1 ) discharging the battery by an amount of electricity Xd in time To 1 ;

(P 2 ) stopping the discharging for time Yd after completion of (P 1 ), and measuring a battery voltage Vo 1 after the time Yd has passed;

(P 3 ) discharging the battery by the amount of electricity Xd in the time To 1 after completion of (P 2 );

(P 4 ) stopping the discharging for the time Yd after completion of (P 3 ), and measuring a battery voltage Vo 2 after the time Yd has passed; and

comparing Vo 1 −Vo 2 with a predetermined voltage difference Vo 3 to determine that the discharge has been terminated when Vo 1 −Vo 2 >Vo 3 , or determine that the discharge has not been terminated when Vo 1 −Vo 2 ≦Vo 3 .

4 . The method for determining termination of discharge of the lithium ion secondary battery of claim 3 , wherein

a minimum distance between layers of carbon planes of the graphite material is equal to or larger than 0.338 nm when it is determined that the discharge has been terminated.

5 . A charge control circuit for a lithium ion secondary battery including one lithium compound having an olivine crystal structure as a positive electrode active material, and a graphite material as a negative electrode active material, the charge control circuit comprising:

a voltage measurement section for measuring a battery voltage;

a cycle execution section for performing multiple cycles, each cycle including charge and a stop of the charge as one cycle;

a voltage difference detection section for detecting a difference between a battery voltage after a stop of charge of one of the cycles and a battery voltage after a stop of charge of a cycle subsequent to the one of the cycles;

a determination section for determining whether the voltage difference detected by the voltage difference detection section is larger or smaller than a set value; and

a control section for stopping the charge when the voltage difference is larger than the set value, and continuing the charge when the voltage difference is smaller than the set value.

6 . The charge control circuit of claim 5 , wherein

the control section controls the charge such that a minimum distance between layers of carbon planes of the graphite material is equal to or smaller than 0.355 nm.

7 . A discharge control circuit for a lithium ion secondary battery including one lithium compound having an olivine crystal structure as a positive electrode active material, and a graphite material as a negative electrode active material, the discharge control circuit comprising:

a voltage measurement section for measuring a battery voltage;

a cycle execution section for performing multiple cycles, each cycle including discharge and a stop of the discharge as one cycle;

a voltage difference detection section for detecting a difference between a battery voltage after a stop of discharge of one of the cycles and a battery voltage after a stop of discharge of a cycle subsequent to the one of the cycles;

a determination section for determining whether the voltage difference detected by the voltage difference detection section is larger or smaller than a set value; and

a control section for stopping the discharge when the voltage difference is larger than the set value, and continuing the discharge when the voltage difference is smaller than the set value.

8 . The discharge control circuit of claim 7 , wherein

the control section controls the discharge such that a minimum distance between layers of carbon planes of the graphite material is equal to or larger than 0.338 nm.

9 . A power supply, comprising:

a lithium ion secondary battery including one lithium compound having an olivine crystal structure as a positive electrode active material, and a graphite material as a negative electrode active material; and

at least one of the charge control circuit of claim 5 or claim 6 , or the discharge control circuit of claim 7 or claim 8 .

10 . The power supply of claim 9 , wherein

the lithium compound is any one of LiFePO 4 , LiMnPO 4 , LiCoPO 4 , LiCuPO 4 , LiNiPO 4 , LiVPO 4 , or a lithium compound having an olivine crystal structure in which some of transition metal elements of the LiFePO 4 , LiMnPO 4 , LiCoPO 4 , LiCuPO 4 , LiNiPO 4 , LiVPO 4 are substituted with another element.