RAPID CHARGE LITHIUM ION BATTERY CHARGER

• US 20080024090A1
• Filed: 08/10/2007
• Published: 01/31/2008
• Est. Priority Date: 09/30/2005
• Status: Active Grant

• Current Assignee: ICC-Nexergy, Inc
• Original Assignee: International Components Corporation (ICC-Nexergy, Inc)
• Inventors: Hua, Li, Jie, Xia, Guang, Huang, Wentink, Robert
• Granted Patent: US 7,598,709 B2
• Time in Patent Office: Days
• US Class Current: 320/148
• CPC Class Codes: H02J 7/00712 the cycle being controlled or terminated in response to electric parameters
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors

Abstract

A rapid charging circuit for a lithium ion battery. The battery charger in accordance with the present invention compensates for the voltage drops across the various resistance elements in the battery circuit by setting the charging voltage to a level to compensate for the initial resistance of the series resistances in the circuit and an additional resistance selected to take into account the anticipated increase in resistance of the various circuit elements over time. The battery charger in accordance with the present invention periodically monitors the open-circuit voltage of the battery cell and reduces the charging voltage to when the battery cell voltage reaches the optimal value. Thus, during a constant current charging mode, the battery cell is driven at a relatively optimal charging current to reduce the charging time. As such, the system is able to optimize the charging current supplied to a battery cell during a constant current mode of operation while compensating for circuit elements whose resistance may vary over time due to temperature or other factors, such as corrosion, while at the same time avoiding exceeding the maximum recommended voltage for the battery cell.

Claims

1. A method for fast charging a lithium ion battery cell having a maximum recommended battery cell voltage, the method comprising:

(a) providing a charging voltage higher than the maximum recommended battery cell voltage that has been selected to compensate for the maximum anticipated resistance over time of a battery charging circuit coupled to the battery cell;

(b) periodically measuring the battery cell voltage to determine if it has reached a predetermined value.

(c) reducing the charging voltage to a value at or near the maximum recommended battery cell voltage when said battery cell voltage is at said predetermined voltage;

(d) monitoring the charging current supplied to said battery cell after said charging voltage has been reduced; and

(e) terminating charging when said charging current drops below a predetennined value.

2. The method as recited in claim 1, wherein step (a) comprises:

(a) providing a charging voltage that has been selected to compensate for the maximum anticipated resistance in a battery charging circuit coupled to the battery cell including an internal battery cell resistance, battery terminals, and wire connected to the circuit.

3. The method as recited in claim 1, wherein step (b) includes the step of turning off the charging current to the battery cell.

4. The method as recited in claim 3, wherein step (b) includes the step of periodically turning off the charging current to the battery cell.

5. The method as recited in claim 3, wherein step (b) includes the step of turning off the charging current to the battery cell for a predetermined time period t₂ and taking one or more battery cell voltage measurements.

6. A battery charging for rapidly charging a lithium ion battery cell having a maximum recommended battery cell voltage, the battery charger comprising:

(a) a circuit for charging a battery cell at a constant current during a constant current mode of operation by way of a charging voltage that is selected to compensate for a predetermined resistance in a charging circuit connected to the battery cell, the charging circuit configured to sense the battery cell voltage and reduce the charging voltage to a value around the maximum recommended battery cell voltage when said battery cell voltage reaches a value around said maximum recommended battery cell voltage.

7. The battery charger as recited in claim 6, wherein said charging circuit is configured to turn off charging current to said battery cell when the voltage of said battery cell is being measured.

8. The battery charger as recited in claim 6, wherein said battery cell voltage is used in a feedback loop to control the charging voltage of said charging circuit.

9. A battery charger comprising:

a pair of input terminals adapted to be coupled to a source of DC voltage;

a pair of output terminals adapted to be coupled to a battery cell;

a charging circuit coupled between said input terminals and said output terminals, said at least one charging circuit comprising

a converter including a regulator, a switching device coupled between said input terminals and said output terminals and a voltage comparator, said switching device for selectively connecting and disconnecting said pair of output terminals from said charging circuit, said voltage comparator coupled to said regulator; and

a microprocessor operatively coupled to said pair of output terminals for monitoring one or more parameters of said battery cell under charge and selectively providing a signal representative of said battery cell voltage to said voltage comparator forming a first feedback loop, said said regulator being configured to control said switching device as a function of the output signal of said voltage regulator, forming a secondary feedback loop.