Charging method, charging equipment, and integrated circuit

Details Charging method, charging equipment, and integrated circuit Charging method, charging equipment, and integrated circuit

1998-08-10

2000-09-26

Wong, Peter S.

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

With charging

320130, H02J 700

Patent

active

061247006

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a charging method and charging equipment for secondary batteries and an integrated circuit used for its charging control, and more particularly to a charging method and charging equipment suitable for applying to secondary batteries which require constant-voltage charging such as lithium ion batteries or the like and an integrated circuit used for its charging control.


BACKGROUND ART

Conventionally, for secondary batteries which are able to be charged and require constant-voltage charging, lithium ion batteries are developed. This lithium ion battery is charged with the characteristics shown, for example, in FIG. 1. FIG. 1 is a characteristic diagram of charging current/voltage vs. elapsed time of a general lithium ion battery, in which charging is carried out with a charging current I set as a constant current from the initiation of charging until the battery voltage reaches a specified potential. Carrying out this constant-current charging increases a battery voltage V and when it exceeds a specified value, charging is changed over to constant-voltage charging. In this event, for example, voltage V.sub.1 corresponding to battery voltage when the lithium ion battery is fully charged (that is, 100% charged) is supplied. Carrying out this constant-voltage charging charges the lithium ion battery, causes the battery voltage to rise to voltage V.sub.1, but as this charging takes place, the charging current I decreases. Now, when this charging current I decreases to a specified value, it is judged that the lithium ion battery is 100% charged (or charged nearly to 100%), and supply of charging current is stopped.
Charging in this way allows the lithium ion battery to be efficiently charged to 100%.
Now, the lithium ion battery charged to 100% in this way may sometimes have the characteristics deteriorated by the charging condition thereafter. That is, if the voltage V.sub.1 corresponding to battery voltage when the lithium ion battery is fully charged is constantly applied to the 100% charged lithium ion battery from the charging equipment as charging voltage and small-power charging is repeatedly carried out, the charging condition can be maintained to nearly 100% condition even when there is self-discharge. However, when such nearly 100% condition continues, the lithium ion battery becomes characteristics which tends to gradually reduce the chargeable capacity, and eventually deteriorates the characteristics as a secondary battery.
In order to prevent characteristics deterioration due to the continuation of the 100% charged condition, for example, stopping charging at about 90% of the charging capacity is assumed, but this results in inconvenience that the capacity prepared as a secondary battery is not effectively utilized.
When temperature of the battery itself rises, the lithium ion battery has a disadvantage that the chargeable capacity decreases and battery characteristics rapidly deteriorate, and it also has a disadvantage that it is not preferable to be charged to the full charging level with the battery temperature increased at the time of charging under the same conditions as those free of temperature rise.
As described above, it is when there remains scarcely charged voltage in the lithium ion battery to carry out constant-current charging at first and then change over to constant-voltage charging to charge the battery, and when any voltage remains in the battery, it is necessary to carry out constant-voltage charging with the charging current reduced, thereby preventing deterioration of characteristics as a secondary battery resulting from rapid charging by large current.
Consequently, before charging is started, the condition of the battery to be charged must be detected and the remaining voltage must be detected. In order to detect this remaining voltage, charging is carried out with a small current called pre-charging at the start of charging, the battery voltage, etc. at that time is detected, and the remaining voltage of the battery is detec

REFERENCES:
patent: 5355073 (1994-10-01), Nguyen
patent: 5391974 (1995-02-01), Shiojima et al.
patent: 5408170 (1995-04-01), Umetsu et al.
patent: 5465039 (1995-11-01), Narita et al.
patent: 5637981 (1997-06-01), Nagai et al.
patent: 5977749 (1999-11-01), Kim

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