LITHIUM SECONDARY BATTERY AND CONTROL SYSTEM THEREFOR, AND METHOD FOR DETECTING STATE OF LITHIUM SECONDARY BATTERY

• US 20150200425A1
• Filed: 03/27/2015
• Published: 07/16/2015
• Est. Priority Date: 08/04/2010
• Status: Active Grant

• Current Assignee: Envision AESC Energy Devices Ltd.
• Original Assignee: NEC Energy Devices, Ltd. (Envision Group /TX/), NEC Corporation
• Inventors: IRIYAMA, Jiro, KAJITA, Tetsuya, KAWASAKI, Daisuke, KASAHARA, Ryuichi, NUMATA, Tatsuji
• Granted Patent: US 9,768,476 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G06F 17/15 Correlation function computation including computation of convolution operations arithmetic circuits for sum of products per se, e.g. multiply-accumulators G06F7/5443; digital filters, e.g. FIR, IIR, adaptive filters H03H17/00
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H01M 4/485 of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy H01M4/505, H01M4/525 take precedence
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• 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

Abstract

There is provided a control system for a lithium secondary battery that can quantitatively sense a deterioration state inherent in a lithium secondary battery using silicon oxide as a negative electrode active material, that is, the nonuniform reaction state of a negative electrode. A control system for a lithium secondary battery including a positive electrode, a negative electrode using silicon oxide as a negative electrode active material, and a lithium reference electrode having a reference potential with respect to the negative electrode includes measurement means for measuring a voltage V of the negative electrode with respect to the lithium reference electrode and a discharge capacity Q of the lithium secondary battery during discharge of the lithium secondary battery; generation means for generating a V-dQ/dV curve representing a relationship between dQ/dV, which is a proportion of an amount of change dQ in the discharge capacity Q to an amount of change dV in the voltage V, and the voltage V; calculation means for calculating an intensity ratio of two peaks appearing on the V-dQ/dV curve for two voltage values in the voltage V; and sensing means for sensing a state of the negative electrode utilizing the intensity ratio.

Claims

1. A control system for a lithium secondary battery comprising a positive electrode and a negative electrode using silicon oxide as a negative electrode active material, the control system comprising:

measurement means for measuring a voltage V of the negative electrode with respect to a lithium reference electrode and a discharge capacity Q of the lithium secondary battery during discharge of the lithium secondary battery;

generation means for generating a V-dQ/dV curve representing a relationship between dQ/dV, which is a proportion of an amount of change dQ in the discharge capacity Q to an amount of change dV in the voltage V, and the voltage V;

calculation means for calculating an intensity ratio of two peaks appearing on the V-dQ/dV curve for two voltage values in the voltage V; and

sensing means for sensing a state of the negative electrode utilizing the intensity ratio, wherein

the discharge curve of a half cell comprising the positive electrode and a metal lithium negative electrode is previously measured, and the measurement means obtains the voltage V of the negative electrode with respect to the lithium reference electrode by calculation from the difference between the discharge curve of the lithium secondary battery and the discharge curve of the half cell.

2. The control system for a lithium secondary battery according to claim 1, wherein

the two voltage values are redox potentials of the silicon oxide.

3. The control system for a lithium secondary battery according to claim 1, wherein

the two voltage values are approximately 0.3 V and approximately 0.5 V.

4. The control system for a lithium secondary battery according to claim 1, further comprising:

charge and discharge control means for repeatedly charging and discharging the lithium secondary battery, wherein

the measurement means measures the voltage V and the discharge capacity Q during first discharge and during second discharge performed after the first discharge respectively,

the generation means generates the V-dQ/dV curve, each time the voltage V and the discharge capacity Q are measured, based on the voltage V and the discharge capacity Q,

the calculation means calculates, each time the V-dQ/dV curve is generated, an intensity ratio of two peaks appearing on the V-dQ/dV curve for the two voltage values, and

the sensing means compares the intensity ratios calculated by the calculation means with each other, and senses the state of the negative electrode from a result of the comparison.

5. The control system for a lithium secondary battery according to claim 4, wherein

the sensing means senses that a degree of uniformity of lithium concentration in the negative electrode becomes equal to or less than a predetermined value when a difference between the intensity ratio calculated based on the voltage V and the discharge capacity Q during the second discharge and the intensity ratio calculated based on the voltage V and the discharge capacity Q during the first discharge is equal to or more than a predetermined threshold.

6. The control system for a lithium secondary battery according to claim 5, wherein

the sensing means further comprises information transmission means for transmitting, when the sensing means senses that the difference between the intensity ratio calculated based on the voltage V and the discharge capacity Q during the second discharge and the intensity ratio calculated based on the voltage V and the discharge capacity Q during the first discharge becomes equal to or more than a predetermined threshold, the information to the charge and discharge control means, and

the charge and discharge control means receiving the transmission executes means for improving the degree of uniformity of the lithium concentration in the negative electrode.

7. The control system for a lithium secondary battery according to claim 5, wherein

the predetermined threshold is 5 to 20%.

8. The control system for a lithium secondary battery according to claim 7, wherein

the means for improving the degree of uniformity of the lithium concentration in the negative electrode is charge and discharge with microcurrent.

9. The control system for a lithium secondary battery according to claim 8, wherein an amount of the microcurrent is 0.01 C to 0.1 C.

10. A lithium secondary battery comprising a positive electrode and a negative electrode using silicon oxide as a negative electrode active material, the lithium secondary battery comprising:

a charge and discharge control portion for repeatedly charging and discharging the lithium secondary battery;

a measurement portion for measuring a voltage V of the negative electrode with respect to a lithium reference electrode and a discharge capacity Q of the lithium secondary battery during discharge of the lithium secondary battery;

a generation portion for generating a V-dQ/dV curve representing a relationship between dQ/dV, which is a proportion of an amount of change dQ in the discharge capacity Q to an amount of change dV in the voltage V, and the voltage V;

a peak intensity ratio calculation portion for calculating an intensity ratio of two peaks appearing on the V-dQ/dV curve for two voltage values in the voltage V;

a peak intensity ratio comparison portion for sensing a state of the negative electrode utilizing the intensity ratio; and

an information transmission portion for transmitting, when the comparison portion senses that a difference between the intensity ratio of the two peaks appearing on the V-dQ/dV curve for the two voltage values in the voltage V becomes equal to or more than a predetermined threshold, the information to the charge and discharge control portion, wherein

the charge and discharge control portion receiving the transmission executes means for improving a degree of uniformity of lithium concentration in the negative electrode, and wherein

the discharge curve of a half cell comprising the positive electrode and a metal lithium negative electrode is previously measured, and the measurement portion obtains the voltage V of the negative electrode with respect to the lithium reference electrode by calculation from the difference between the discharge curve of the lithium secondary battery and the discharge curve of the half cell.

11. The lithium secondary battery according to claim 10, wherein the two voltage values are redox potentials of the silicon oxide.

12. The lithium secondary battery according to claim 10, wherein

the two voltage values are approximately 0.3 V and approximately 0.5 V.

13. The lithium secondary battery according to claim 10, wherein

the measurement portion measures the voltage V and the discharge capacity Q during first discharge and during second discharge performed after the first discharge respectively,

the generation portion generates the V-dQ/dV curve, each time the voltage V and the discharge capacity Q are measured, based on the voltage V and the discharge capacity Q,

the peak intensity ratio calculation portion calculates, each time the V-dQ/dV curve is generated, an intensity ratio of two peaks appearing on the V-dQ/dV curve for the two voltage values, and

the peak intensity ratio comparison portion compares the intensity ratios calculated by the calculation portion with each other, and senses the state of the negative electrode from a result of the comparison.

14. The lithium secondary battery according to claim 13, wherein

the comparison portion senses that the degree of uniformity of the lithium concentration in the negative electrode becomes equal to or less than a predetermined value when a difference between the intensity ratio calculated based on the voltage V and the discharge capacity Q during the second discharge and the intensity ratio calculated based on the voltage V and the discharge capacity Q during the first discharge is equal to or more than a predetermined threshold.

15. The lithium secondary battery according to claim 14, wherein the predetermined threshold is 5 to 20%.

16. The lithium secondary battery according to claim 15, wherein

the charge and discharge control portion receiving the transmission performs charge and discharge with microcurrent.

17. The lithium secondary battery according to claim 16, wherein an amount of the microcurrent is 0.01 C to 0.1 C.

18. A method for detecting a state of a lithium secondary battery comprising a positive electrode and a negative electrode using silicon oxide as a negative electrode active material, the method comprising:

a measurement step of measuring a voltage V of the negative electrode with respect to a lithium reference electrode and a discharge capacity Q of the lithium secondary battery during discharge of the lithium secondary battery;

a generation step of generating a V-dQ/dV curve representing a relationship between dQ/dV, which is a proportion of an amount of change dQ in the discharge capacity Q to an amount of change dV in the voltage V, and the voltage V;

a calculation step of calculating an intensity ratio of two peaks appearing on the V-dQ/dV curve for two voltage values in the voltage V; and

a sensing step of sensing a state of the negative electrode utilizing the intensity ratio, wherein

the discharge curve of a half cell comprising the positive electrode and a metal lithium negative electrode is previously measured, and in the measurement step, the voltage V of the negative electrode with respect to the lithium reference electrode is obtained by calculation from the difference between the discharge curve of the lithium secondary battery and the discharge curve of the half cell.

19. The method for detecting a state of a lithium secondary battery according to claim 18, wherein

the two voltage values are redox potentials of the silicon oxide.

20. The method for detecting a state of a lithium secondary battery according to claim 18, wherein

the two voltage values are approximately 0.3 V and approximately 0.5 V.