Charging method and charger for non-aqueous electrolyte secondary battery

A charger for a non-aqueous electrolyte secondary battery which comprises a positive electrode including a lithium-containing composite oxide as an active material, a negative electrode including an alloy-formable negative electrode active material, and a non-aqueous electrolyte, the charger comprising:

• a voltage detection unit for detecting a voltage of the secondary battery;
• a state-of-charge detection unit for detecting a state of charge of the secondary battery on the basis of the detected voltage;
• a current supply circuit for supplying a current from an external or internal DC power supply to the secondary battery with changing a value of the current stepwise;
• a switch for switching an electrically connected state between the secondary battery and the current supply circuit;
• a judgment unit for comparing the detected state of charge with a predetermined value X, a predetermined value Y, and a predetermined value Z satisfying Y>Z>X, to make judgment on the detected state of charge;
• and
• a control unit for controlling the switch and the current supply circuit on the basis of the judgment of the judgment unit, in such a manner that
• (i) when the detected state of charge is equal to or higher than the predetermined value Y, performing constant-voltage charging or terminating charging,
• (ii) when the detected state of charge is equal to or higher than the predetermined value X and lower than the predetermined value Z, performing constant-current charging at a current value A until the detected state of charge reaches a predetermined state of charge,
• (iii) when the detected state of charge is lower than the predetermined value X, performing constant-current charging at a current value B, and
• (iv) when the detected state of charge is equal to or higher than the predetermined value Z and lower than the predetermined value Y, performing constant-current charging at a current value C satisfying B<C<A.