Method for evaluating capacity of secondary battery using mathematical calculation of specific resistance components of equivalent circuit model fitted from impedance spectrum

• US 20040006440A1
• Filed: 07/01/2003
• Published: 01/08/2004
• Est. Priority Date: 07/02/2002
• Status: Active Grant

• Current Assignee: Korea Kumho Petrochemical Co Limited (Korea Kumho Petrochemical)
• Original Assignee: Korea Kumho Petrochemical Co Limited (Korea Kumho Petrochemical)
• Inventors: Ryu, Sang-Hyo, Kim, Dong-Hwan, Lee, Hyung-Song
• Granted Patent: US 7,062,390 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

The present invention relates to a method for evaluating an initial capacity of secondary batteries and, more specifically, to a method for evaluating an initial capacity of secondary batteries that involves mathematical operation of specific internal resistance components obtained from an equivalent circuit model of an impedance spectrum measured for a short time period instead of using direct discharge characteristics, thereby allowing selection of batteries having a different initial discharge characteristic.

Claims

1. A method for evaluating a capacity of at least one secondary battery, the method comprising:

(a) preparing the at least one secondary battery to at least one of partially charged to a voltage less than a full charge voltage and partially discharged to a voltage less than the full charge voltage;

(b) measuring an impedance spectrum for the prepared battery;

(c) mathematically operating specific internal resistance components obtained from an equivalent circuit model fitted from the impedance spectrum measured; and

(d) comparing the mathematical operation value of the resistance components with an initial discharge capacity graph to evaluate an initial discharge capacity of a unknown battery of the same group.

2. The method as claimed in claim 1, wherein the equivalent circuit model used for simulation of the impedance spectrum includes model parameters of nonlinear resistors, nonlinear capacitors and nonlinear transfer lines.

3. The method as claimed in claim 1, wherein the discharge capacity graph is a capacity correlation graph obtained from a relationship equation with the initial discharge capacity determined after a discharge performed with a discharge rate of 1.0 C.

4. The method as claimed in claim 1, wherein the secondary battery includes a lithium ion battery, a lithium polymer battery, a Ni—

Cd battery and a NiMH battery.

5. The method as claimed in claim 1, wherein the batteries are charged to a constant voltage being less than a full charge voltage to provide more than 60% of the charge capacity and less than 10% of the charging current.

6. The method as claimed in claim 5, wherein the equivalent circuit model used for simulation of the impedance spectrum includes model parameters of nonlinear resistors, nonlinear capacitors and nonlinear transfer lines.

7. The method as claimed in claim 1, wherein the batteries are discharged to a voltage level less than a full charge voltage to provide less than 10% of the discharge capacity.

8. The method as claimed in claim 7, wherein the equivalent circuit model used for simulation of the impedance spectrum includes model parameters of nonlinear resistors, nonlinear capacitors and nonlinear transfer lines.

9. The method as claimed in claim 1, wherein the impedance spectrum is measured in a frequency range of 10 mHz to 10 kHz.

10. The method as claimed in claim 9, wherein the equivalent circuit model used for simulation of the impedance spectrum includes model parameters of nonlinear resistors, nonlinear capacitors and nonlinear transfer lines.

11. The method as claimed in claim 10, wherein the internal resistance components obtained from the equivalent circuit model include resistance components and charge transfer resistance components related to a degradation of an electrolyte, a separator or a current collector.

12. The method as claimed in claim 11, wherein the discharge capacity graph is a capacity correlation graph obtained from a relationship equation with the initial discharge capacity determined after a discharge performed with a discharge rate of 1.0 C.

13. The method as claimed in claim 11, wherein the secondary battery includes a lithium ion battery, a lithium polymer battery, a Ni—

Cd battery and a NiMH battery.