CN-122025881-A - Battery system

Abstract

The invention aims to inhibit degradation of a lithium iron phosphate ion battery. The battery system includes an auxiliary battery that is a lithium ion secondary battery having a positive electrode including lithium iron phosphate and a negative electrode including graphite, a voltage sensor that detects a voltage of the auxiliary battery, a DC/DC converter configured to discharge the auxiliary battery, and an ECU that controls the DC/DC converter so that discharge of the auxiliary battery ends when an SOC of the auxiliary battery reaches a discharge end SOC. When the voltage detected by the voltage sensor is lower than the threshold voltage, the ECU acquires the SOC of the auxiliary battery, and sets the discharge end SOC according to the acquired SOC.

Inventors

• MATSUMURA KAZUYOSHI

Assignees

• 丰田自动车株式会社

Dates

Publication Date

20260512

Application Date

20251028

Priority Date

20241111

Claims (5)

1. 1. A battery system, comprising: A secondary battery which is a lithium ion secondary battery having a positive electrode containing lithium iron phosphate and a negative electrode containing graphite; a voltage sensor that detects a voltage of the battery; a power converter configured to discharge the storage battery, and A control device that controls the power converter so that discharge of the battery ends when the SOC of the battery reaches a discharge end SOC, The control device acquires the SOC of the battery when the voltage detected by the voltage sensor is lower than a threshold voltage, and sets the discharge end SOC based on the acquired SOC.
2. 2. The battery system of claim 1, wherein the battery system comprises a battery module, The threshold voltage is higher than the voltage in the case where the order structure of the negative electrode is 3L.
3. 3. The battery system of claim 2, wherein the battery system comprises a battery module, The threshold voltage is 3.20V or more and 3.28V or less.
4. 4. The battery system according to any one of claim 1 to 3, wherein, The control device sets an SOC higher than the acquired SOC by an error amount of the acquired SOC as the discharge end SOC.
5. 5. The battery system according to any one of claims 1 to 3, further comprising: a temperature sensor that detects a temperature of the battery, The control device sets the discharge end SOC when the temperature detected by the temperature sensor exceeds a threshold temperature and the voltage detected by the voltage sensor is lower than the threshold voltage.

Description

Battery system Technical Field The present invention relates to a battery system, and more particularly, to a battery system including a lithium iron phosphate battery. Background The control circuit of the battery module disclosed in international publication No. 2015/080285 (patent document 1) is configured to control charge and discharge of the lithium ion secondary battery based on a discharge termination voltage of the lithium ion secondary battery. Patent document 1 International publication No. 2015/080285 Disclosure of Invention As an auxiliary battery mounted on a vehicle, a lithium iron phosphate battery is sometimes used. In this case, the lithium iron phosphate battery preferably employs a combination of a positive electrode including lithium iron phosphate and a negative electrode including graphite from the viewpoint of stably supplying and maintaining a voltage required for an auxiliary load. Like other secondary batteries, lithium iron phosphate batteries also deteriorate due to repeated charge and discharge. In particular, in the case of using a lithium iron phosphate battery as an auxiliary battery, a scenario in which the lithium iron phosphate battery discharges (i.e., supplies power to an auxiliary load) may frequently occur, and thus the number of charge-discharge cycles required for the lithium iron phosphate battery may become large. It is preferable to suppress degradation of the lithium iron phosphate battery. The present invention has been made to solve the above problems, and an object of the present invention is to suppress degradation of a lithium iron phosphate battery. (1) The battery system according to one aspect of the present invention includes a battery that is a lithium ion secondary battery having a positive electrode including lithium iron phosphate and a negative electrode including graphite, a voltage sensor that detects a voltage of the battery, a power converter configured to discharge the battery, and a control device that controls the power converter so that discharge of the battery ends when an SOC of the battery reaches a discharge end SOC. The control device acquires the SOC of the battery when the voltage detected by the voltage sensor is lower than the threshold voltage, and sets the discharge end SOC based on the acquired SOC. (2) The threshold voltage is higher than the voltage in the case where the order structure of the negative electrode is 3L. (3) The threshold voltage is 3.20V or more and 3.28V or less. In the configurations of (1) to (3) above, the control device sets the discharge end SOC instead of the discharge end voltage of the battery. The threshold voltage is higher than the voltage (3.20V or more and 3.28V or less) in the case where the order structure of the negative electrode is 3L. Therefore, the discharge end SOC is set to an SOC corresponding to a voltage at which the step structure of the negative electrode does not transition to step 3L. The details will be described later, whereby a large volume change of the anode can be suppressed. Therefore, according to the structures (1) to (3) described above, deterioration of the battery due to the change in volume of the negative electrode can be suppressed. (4) The control device sets an SOC higher than the acquired SOC by an error amount of the acquired SOC as a discharge end SOC. In the configuration of (4) above, the control device sets the discharge end SOC to be higher than the SOC error amount in consideration of the SOC error. That is, the battery is discharged by the SOC error amount. Thus, even if SOC errors occur, the order structure of the graphite anode does not reach the order 3L. Therefore, according to the structure of (4) above, deterioration of the battery can be suppressed more reliably. (5) The battery system further includes a temperature sensor that detects the temperature of the battery. The control device sets the discharge end SOC when the temperature detected by the temperature sensor exceeds a threshold temperature and the voltage detected by the voltage sensor is lower than a threshold voltage. In the configuration of (5) above, the control device determines whether or not the temperature of the battery detected by the temperature sensor exceeds a threshold temperature. In the low temperature range, the resistance of the battery increases, and the voltage drop associated with the discharge increases, and as a result, the voltage detection accuracy may decrease. According to the configuration of (5) above, voltage detection is performed in a state where the temperature of the battery exceeds the threshold temperature. Therefore, it is possible to accurately determine whether or not the voltage of the battery detected by the voltage sensor is lower than the threshold voltage. Effects of the invention According to the present invention, deterioration of the lithium iron phosphate battery can be suppressed. Drawings Fig. 1 is a block diagram showing the structure of a