Method and apparatus for determining the state of charge of a lithium-ion battery

• US 6,586,130 B1
• Filed: 11/22/2000
• Issued: 07/01/2003
• Est. Priority Date: 11/22/2000
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Palanisamy, Thirumalai G., Guiheen, James V., Singh, Harmohan
• Primary Examiner(s): Kalafut, Stephen
• Assistant Examiner(s): Alejandro, Raymond
• Application Number:
  US09/721,003
• Time in Patent Office: 951 Days
• Field of Search: 429/90, 429/91, 429/92, 429/93, 429/61, 429/62, 429/50, 429/52, 320/148, 320/149, 320/124, 320/125, 320/134, 320/136, 320/DIG.10, 320/DIG.18, 320/DIG.21
• US Class Current: 429/50
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

Computer-assisted methods for determining the state of charge of a specific lithium ion battery, without the need for charging and discharging the battery, by utilizing look-up tables or algorithms which store the relationships of state of charge to open-circuit voltage or to ramp-peak current, or to both for that type of specific lithium-ion battery to determine the state of charge for that specific lithium-ion battery.

Claims

1. A method for creating a look-up table of ramp-current versus state of charge for a lithium-ion battery, said method comprising the steps of:

(a) bringing the battery to a first present state of charge;

(b) applying a monotonically increasing current to said battery from a power supply, where there is a dependence of current increase with time;

(c) recording said dependence of current increase with time;

(d) increasing said monotonically increasing current to said battery until the current reaches a value defined as the ramp-peak current at the first present state of charge for said lithium-ion battery where either

(i) a measured voltage for said battery reaches a predetermined maximum, or

(ii) said monotonically increasing current equals a maximum current rating of the power supply;

(e) recording said ramp-peak current at the present state of charge;

(f) repeating said steps (a), (b), (c), (d), and (e) for additional present states of charge, said recording step (e) recording said ramp-peak currents for the additional states of charge for said battery; and

(g) creating the look-up table of ramp-peak current versus state of charge for the lithium-ion battery using the first and additional present states of charge for said battery.

2. The method in accordance with claim 1 wherein said monotonically increasing current is an electrical current increasing from 0 amps to 20 amps in 60 seconds.

3. The method in accordance with claim 1 wherein the first and additional present states of charge for said battery are 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%.

4. The method in accordance with claim, 1 further comprising the steps of:

checking the look-up table for ramp-current versus state of charge for duplicate ramp-current values; and

repeating the steps of claim 1 for the states of charge with duplicate ramp-peak current values, except wherein the monotonically increasing current to said battery from said power supply has a different dependence of current increase with time.

5. The method in accordance with claim 1 wherein all the steps of claim 10 are repeated at a set of predetermined temperatures.

6. The method in accordance with claim 5 wherein the set of predetermined temperatures consists of −

30°

C., 0°

C., +20°

C., and +50°

C.