Battery System and Method for System State of Charge Determination

• US 20100225325A1
• Filed: 03/03/2009
• Published: 09/09/2010
• Est. Priority Date: 03/03/2009
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Ahmed, Jasim, Christensen, John F.
• Granted Patent: US 9,030,169 B2
• Time in Patent Office: Days
• US Class Current: 324/426
• CPC Class Codes: G01R 31/378 specially adapted for the type of battery or accumulator
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A battery system and method of providing a state of charge of for the system in one embodiment includes at least one first cell, the at least one first cell having a first battery chemistry exhibiting a first open circuit potential, and at least one second cell in series connection with the at least one first cell, the at least one second cell having a second battery chemistry exhibiting a second open circuit potential, wherein the at least one first cell exhibits an open circuit potential with a center slope that is greater than the center slope of the open circuit potential exhibited by the at least one second cell.

Claims

1. A battery system comprising:

at least one first cell, the at least one first cell having a first battery chemistry and exhibiting a first open circuit potential curve; and

at least one second cell in series connection with the at least one first cell, the at least one second cell having a second battery chemistry and exhibiting a second open circuit potential,

wherein the at least one first cell exhibits an open circuit potential curve with a slope that is greater than the slope of the open circuit potential curve exhibited by the at least one second cell over a range of about 40 percent state of charge to about 60 percent state of charge.

2. The battery system of claim 1, further comprising:

a coulomb counter in parallel connection with the series connected at least one first cell and at least one second cell.

3. The battery system of claim 1, further comprising:

a voltmeter in parallel connection with the at least one first cell.

4. The battery system of claim 1, wherein either:

at least one of an energy density, a specific power, a specific energy, a power density, and a projected lifetime, of the at least one second cell is greater than an energy density, a specific power, a specific energy, a power density, a cost savings, and a projected lifetime, of the at least one first cell;

or

a cost of the at least one second cell is less than a cost of the at least one first cell.

5. The battery system of claim 1, further comprising:

at least one third cell in series connection with the at least one first cell, the at least one third cell having a third battery chemistry different from the second battery chemistry and exhibiting a third open circuit potential curve,

wherein the at least one first cell exhibits an open circuit potential curve with a slope that is greater than the slope of the open circuit potential curve exhibited by the at least one third cell over a range of about 20 percent state of charge to about 80 percent state of charge.

6. The battery system of claim 1, wherein:

the at least one first cell consists of a first number of first cells;

the at least one second cell consists of a second number of second cells; and

the second number is larger than the first number.

7. The battery system of claim 1, wherein:

the first battery chemistry comprises Li_xC₆/Li_yCoO₂.

8. The battery system of claim 7, wherein:

the second battery chemistry comprises Li_4+xTi₅O₁₂/Li_yFePO₄.

9. The battery system of claim 1, wherein the at least one first cell exhibits an open circuit potential curve with a slope that is greater than the slope of the open circuit potential curve exhibited by the at least one second cell over a range of about 20 percent state of charge to about 80 percent state of charge.

10. A method of determining the state of charge (SOC) of a battery system comprising:

providing a battery system with at least one first battery cell and at least one second battery cell, wherein the at least one first battery cell exhibits an open circuit potential curve with a slope that is greater than the slope of the open circuit potential curve exhibited by the at least one second battery cell over a range of about 40 percent SOC to about 60 percent SOC;

associating each of a plurality of first battery cell voltages with one of a plurality of SOC conditions;

storing the associated plurality of first battery cell voltages and plurality of SOC conditions;

obtaining the voltage of the first battery cell;

comparing the obtained voltage with the stored plurality of first battery cell voltages; and

determining the SOC of the battery system based upon the comparison.

11. The method of claim 10, wherein obtaining comprises:

placing the battery system in an open circuit condition.

12. The method of claim 10, wherein obtaining comprises:

determining that a battery system discharge rate is below a predetermined threshold.

13. The method of claim 10, wherein determining the SOC comprises;

monitoring discharge of the battery system using a coulomb counter.

14. A battery system comprising:

at least one first cell, the at least one first cell exhibiting a first open circuit potential curve over a first range of state of charge (SOC) conditions; and

at least one second cell in series connection with the at least one first cell, the at least one second cell exhibiting a second open circuit potential over the first range of SOC conditions,

wherein the slope of the first open circuit potential curve is substantially zero and the slope of the second open circuit potential curve is positive.

15. The battery system of claim 14, wherein the first range of SOC conditions extends from about 40 percent SOC to about 60 percent SOC.

16. The battery system of claim 15, wherein the first range of SOC conditions extends from about 20 percent SOC to about 80 percent SOC.

17. The battery system of claim 14, wherein:

the at least one first cell has a first battery chemistry; and

the at least one second cell has a second battery chemistry, the second battery chemistry different from the first battery chemistry.

18. The battery system of claim 17, further comprising at least one third cell, wherein:

the at least one second cell exhibits a third open circuit potential curve over the second range of SOC conditions;

the at least one third cell exhibits a fourth open circuit potential curve over the second range of SOC conditions; and

the slope of the fifth open circuit potential curve is positive over the second range of SOC conditions and the slope of the third open circuit potential curve is substantially less positive than the slope of the fifth open circuit potential curve over the second range of SOC conditions.

19. The battery system of claim 18, further comprising:

a voltmeter in configured to provide selective parallel connection with the at least one second cell and the at least one third cell.

20. The battery system of claim 14, further comprising:

a voltmeter in parallel connection with the at least one second cell.