Secondary battery system

Abstract

This invention provides a secondary battery system that improves the accuracy of estimating the degradation of secondary batteries. [Solution] A secondary battery system for estimating the degradation of a secondary battery, comprising: an acquisition unit that acquires the internal resistance, internal pressure, and temperature of a battery cell; a first estimation unit that estimates the degradation of the secondary battery based on the internal resistance when the temperature is below a first threshold; a second estimation unit that estimates the degradation of the secondary battery based on the internal pressure when the temperature is above a second threshold; and a third estimation unit that estimates the degradation of the secondary battery based on both the internal resistance and the internal pressure when the temperature exceeds the first threshold and is below the second threshold.

Description

Technical Field

[0001] The present disclosure relates to a secondary battery system capable of estimating deterioration of a secondary battery.

Background Art

[0002] Patent Document 1 discloses a deterioration determination device that determines deterioration of a secondary battery based on an internal resistance calculated from a voltage value and a current value of a battery cell.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a method of estimating deterioration of a secondary battery based on an internal resistance calculated from a voltage value and a current value of a battery cell as in the technology described in Patent Document 1 above, as the temperature of the battery cell increases, the absolute value of the internal resistance decreases, so there is a problem that the difference before and after deterioration becomes difficult to distinguish. Therefore, there is room for further study to improve the accuracy of the method for estimating deterioration of a secondary battery.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to provide a secondary battery system that improves the accuracy in estimating deterioration of a secondary battery.

Means for Solving the Problems

[0006] To solve the above problems, one aspect of the disclosed technology is a secondary battery system for estimating the degradation of a secondary battery, comprising: an acquisition unit that acquires the internal resistance, internal pressure, and temperature of a battery cell; a first estimation unit that estimates the degradation of the secondary battery based on the internal resistance when the temperature is below a first threshold; a second estimation unit that estimates the degradation of the secondary battery based on the internal pressure when the temperature is above a second threshold; and a third estimation unit that estimates the degradation of the secondary battery based on both the internal resistance and the internal pressure when the temperature exceeds the first threshold and is below the second threshold. [Effects of the Invention]

[0007] According to the secondary battery system described above, the degradation estimation of the secondary battery is performed using an optimal method according to the temperature of the battery cell, thereby improving the accuracy of the secondary battery degradation estimation. [Brief explanation of the drawing]

[0008] [Figure 1] Schematic diagram of a secondary battery system and secondary battery according to one embodiment of the present disclosure. [Figure 2] Flowchart of the processing flow for secondary battery degradation estimation control performed by the secondary battery system. [Modes for carrying out the invention]

[0009] The secondary battery system disclosed herein not only estimates (detects) degradation by measuring capacity and resistance using conventional cell voltage and current sensors, but also measures the increase in internal pressure due to gas generated as the energy storage device deteriorates by measuring cell pressure, and constructs a more accurate degradation estimation (detection) system by combining the results of both. The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0010] <Embodiment> [composition] Figure 1 is a diagram showing a schematic configuration of a power supply system 100 including a secondary battery system 120 according to one embodiment of the present disclosure. The power supply system 100 illustrated in Figure 1 comprises a secondary battery 110 and a secondary battery system 120. This power supply system 100 is mounted, for example, in a vehicle.

[0011] The secondary battery 110 is a rechargeable energy storage device, such as a lithium-ion battery. When installed in a vehicle, the secondary battery 110 can be used, for example, as a redundant sub-battery to back up the main battery that supplies power to the vehicle load. This secondary battery 110 includes multiple battery cells 111, an outer casing 112, a voltage / current / temperature sensor 113, and a pressure sensor 114.

[0012] Multiple battery cells 111 are typically configured as a stack of lithium-ion battery cells connected in series and / or parallel. Figure 1 shows an example of a battery stack with four battery cells 111 connected in series, but the number of battery cells 111 and their connection configuration are not limited to this.

[0013] The outer casing 112 is a housing for housing multiple battery cells 111, which constitute a battery stack. This outer casing 112 is, for example, a roughly box-shaped component formed from an insulating material such as resin.

[0014] The voltage / current / temperature sensor 113 is a device for detecting the voltage, current, and temperature of the battery cell 111. The voltage, current, and temperature values ​​detected by this voltage / current / temperature sensor 113 are output to the secondary battery system 120.

[0015] The pressure sensor 114 is a device for detecting the internal pressure of the battery cell 111. This pressure sensor 114 measures the change in internal cell pressure due to gas generated as the battery cell 111 deteriorates. It is common knowledge that as a battery deteriorates, gas is generated by chemical reactions. As the amount of gas generated increases, the internal pressure of the closed space of the battery cell 111 increases, and this change is detected by the pressure sensor 114. The internal pressure p increases as the temperature T increases according to the general equation of state "pV=nRT", making it easier to detect the difference before and after deterioration. As an example of a measurement method, the battery cell 111 is restrained at a certain pressure by a restraining member (this can be done by stacking general cells), and the reaction force caused by the expansion of the cell case due to the internal cell pressure is measured as the internal pressure.

[0016] The secondary battery system 120 is a system for controlling and managing the secondary battery 110. In particular, the secondary battery system 120 of this embodiment estimates the degradation of the secondary battery 110. This secondary battery system 120 includes an information acquisition unit 121 and a degradation estimation unit 122.

[0017] The information acquisition unit 121 acquires the voltage, current, and temperature of the battery cell 111 from the voltage / current / temperature sensor 113, and the internal pressure of the battery cell 111 from the pressure sensor 114, as the status of the secondary battery 110.

[0018] The degradation estimation unit 122 estimates (or determines) the degradation of the secondary battery 110 based on the state of the secondary battery 110 acquired by the information acquisition unit 121. In this embodiment, the degradation of the secondary battery 110 is estimated by appropriately using two methods: a degradation estimation method based on the internal resistance due to discharge of the battery cell 111, and a degradation estimation method based on the internal pressure obtained by measuring the pressure of the battery cell 111. Details of the degradation estimation control of the secondary battery 110 performed by this degradation estimation unit 122 will be described later.

[0019] Note that part or all of the secondary battery system 120 described above is typically configured as an electronic control unit (ECU: Electronic Control Unit) that includes a processor such as a microcomputer, a memory, and an input / output interface. By the processor reading and executing a program stored in the memory, part or all of each function of the information acquisition unit 121 and the deterioration estimation unit 122 described above can be realized.

[0020] [Control] Next, referring further to FIG. 2, the control executed by the secondary battery system 120 according to an embodiment of the present disclosure will be described. FIG. 2 is a flowchart for explaining the procedure of the deterioration estimation control of the secondary battery 110 executed by the information acquisition unit 121 and the deterioration estimation unit 122 of the secondary battery system 120.

[0021] The deterioration estimation control of the secondary battery 110 illustrated in FIG. 2 is started, for example, when the ignition of the vehicle is turned off (IGR-OFF) and the vehicle stops (operation ends). Note that even immediately after the ignition of the vehicle is turned on (IGR-ON), as long as the vehicle system has not started up, it is also possible to perform the deterioration estimation control of the secondary battery 110.

[0022] (Step S201) The information acquisition unit 121 acquires the state of the battery cell 111 from the secondary battery 110. The state of this battery cell 111 is the voltage, current, temperature, and internal pressure of the battery cell 111 detected by the voltage / current / temperature sensor 113 and the pressure sensor 114, respectively.

[0023] When the state of the battery cell 111 is acquired by the information acquisition unit 121, the process proceeds to step S202.

[0024] (Step S202) The degradation estimation unit 122 determines the relationship between the temperature T of the battery cell 111 of the secondary battery 110 and a preset first threshold th1 and second threshold th2. Here, the first threshold th1 is set to an arbitrary temperature (for example, 0 to 10°C) in a low temperature range where the degradation estimation method based on the internal resistance due to the discharge of the battery cell 111 is more accurate than the degradation estimation method based on the internal pressure by pressure measurement of the battery cell 111. Also, the second threshold th2 is set to an arbitrary temperature (for example, 30 to 40°C) in a high temperature range where the degradation estimation method based on the internal pressure by pressure measurement of the battery cell 111 is more accurate than the degradation estimation method based on the internal resistance due to the discharge of the battery cell 111.

[0025] When the degradation estimation unit 122 determines that the temperature T of the battery cell 111 is less than or equal to the first threshold th1 (step S202, T ≦ th1), the process proceeds to step S203. When the degradation estimation unit 122 determines that the temperature T of the battery cell 111 is greater than or equal to the second threshold th2 (step S202, th2 ≦ T), the process proceeds to step S204. When the degradation estimation unit 122 determines that the temperature T of the battery cell 111 exceeds the first threshold th1 and is less than the second threshold th2 (step S202, th1 < T < th2), the process proceeds to step S205.

[0026] (Step S203) Since the temperature T of the battery cell 111 is in the low temperature range, the degradation estimation unit 122 estimates the degradation of the secondary battery 110 using the degradation estimation method based on the internal resistance due to the discharge of the battery cell 111 (first estimation unit). For the degradation estimation, the voltage and current of the battery cell 111 acquired by the information acquisition unit 121 from the secondary battery 110 are used. In this low temperature range, the accuracy of the degradation estimation method based on the internal resistance due to the discharge of the battery cell 111 is higher than that of the degradation estimation method based on the internal pressure by pressure measurement of the battery cell 111, so only the latter degradation estimation method based on the internal resistance is implemented.

[0027] As a method for estimating the degradation of this battery cell 111 based on its internal resistance due to discharge, the degradation rate of the secondary battery 110 can be calculated by comparing the resistance and capacitance values ​​measured by well-known resistance measurement methods with the initial values. The following formulas can be used for the calculation. Resistance [Ω] = Interval capacitance [Ah or F] / Measurement current [I] Capacity [Ah or F] = Battery-specific coefficient × Interval capacity [Ah or F] Interval capacity [Ah or F] = measured current [I] × time [t] (or, battery-specific coefficient × (V1) 2 -V2 2 ))

[0028] When the degradation estimation unit 122 estimates the degradation of the secondary battery 110 using only a degradation estimation method based on the internal resistance due to discharge of the battery cell 111, the process proceeds to step S206.

[0029] (Step S204) The degradation estimation unit 122 estimates the degradation of the secondary battery 110 using a degradation estimation method based on the internal pressure obtained by pressure measurement of the battery cell 111, because the temperature T of the battery cell 111 is in the high-temperature range (second estimation unit). The internal pressure of the battery cell 111 obtained from the secondary battery 110 by the information acquisition unit 121 is used for degradation estimation. In this high-temperature range, the degradation estimation method based on the internal pressure obtained by pressure measurement of the battery cell 111 is more accurate than the degradation estimation method based on the internal resistance due to discharge of the battery cell 111, so only the latter degradation estimation method based on internal pressure is implemented. This allows for accurate performance estimation of the secondary battery 110 at the end of its degradation stage, eliminating the need for design to ensure extra cell performance, and enabling cost reduction while guaranteeing quality.

[0030] As a method for estimating degradation based on the internal pressure measured by pressure measurement of the battery cell 111, a method can be presented in which the degradation rate of the secondary battery 110 is calculated by comparing the initial internal pressure of the battery cell 111 at the same temperature with the internal pressure of the battery cell 111 at a certain point in time, and multiplying by a corresponding unique coefficient. The unique coefficient is obtained by creating a control map based on the temperature and state of charge (SOC) of the battery cell 111 in advance and storing it in an electronic control unit (ECU), and using it in the calculation. Alternatively, since the internal pressure p shows a linear correlation with temperature T according to the equation of state "pV=nRT", that equation may also be used.

[0031] When the degradation estimation unit 122 estimates the degradation of the secondary battery 110 using only a degradation estimation method based on the internal pressure obtained by measuring the pressure of the battery cell 111, the process proceeds to step S206.

[0032] (Step S205) The degradation estimation unit 122 estimates the degradation of the secondary battery 110 (third estimation unit) using both a degradation estimation method based on the internal resistance due to discharge of the battery cell 111 and a degradation estimation method based on the internal pressure obtained by measuring the pressure of the battery cell 111, since the temperature T of the battery cell 111 is in the room temperature range, which is between the low temperature range and the high temperature range. The voltage, current, and internal pressure of the battery cell 111 obtained from the secondary battery 110 by the information acquisition unit 121 are used for degradation estimation. In this room temperature range, the accuracy of the degradation estimation method based on the internal resistance due to discharge of the battery cell 111 is low, so the degradation estimation method based on the internal pressure obtained by measuring the pressure of the battery cell 111 is used in combination to ensure high accuracy. This makes it possible to accurately estimate the performance of the secondary battery 110 at the end of its degradation, eliminates the need for design to secure extra cell performance, and enables cost reduction while ensuring quality.

[0033] In the room temperature range, the absolute value of the resistance decreases in both cases of degradation estimation due to discharge and degradation estimation due to pressure, and the difference in absolute value between before and after degradation becomes small. Therefore, considering the effects of errors in the sensors used for measurement, it is expected that the accuracy will be low if only one degradation estimation is performed, so both degradation estimations are performed. Mathematical methods such as the least squares method, Kalman filter, and Bayesian estimation can be used for degradation estimation methods that use both measurement results. The advantage of performing both degradation estimations over simply performing one degradation estimation multiple times is that both measurement errors (especially degradation estimation due to discharge) are systematic errors (system errors) = bias rather than random errors, so by combining different types of measurements, the bias inherent in one measurement can be canceled out. For example, measurement errors with voltage sensors include the temperature dependence of the sensor, the effects of noise and electromagnetic interference, the linearity error of the sensor, offset error, phase error, impedance effects, magnetic hysteresis, and the effects of wiring to other equipment, and these errors are more due to bias than randomness.

[0034] When the degradation estimation unit 122 estimates the degradation of the secondary battery 110 by using a degradation estimation method based on the internal pressure obtained by measuring the pressure of the battery cell 111 and a degradation estimation method based on the internal resistance due to the discharge of the battery cell 111 in combination, the process proceeds to step S206.

[0035] (Step S206) The degradation estimation unit 122 determines the degradation rate estimated in any of steps S203 to S205 described above as the degradation rate of the secondary battery 110.

[0036] Once the degradation rate of the secondary battery 110 is determined by the degradation estimation unit 122, the degradation estimation control for the secondary battery 110 is terminated.

[0037] Furthermore, after determining the degradation rate of the secondary battery 110 in step S206, fault detection of the secondary battery 110 may be performed. If no fault is detected in the secondary battery 110 as a result of the detection, the operation of the secondary battery system 120 may be stopped and it may be put into a standby state (sleep state). On the other hand, if a fault is detected in the secondary battery 110, a fault determination may be made and measures such as illuminating a diagnostic indicator may be taken.

[0038] Alternatively, if the battery resistance is measured using a short-time pulse discharge (0.1 to 0.5 seconds) and the battery state of charge (SOC) is estimated accordingly, a battery pressure correction value may be calculated from that SOC.

[0039] <Effects and Actions> As described above, according to the secondary battery system 120 according to one embodiment of the present disclosure, the degradation of the secondary battery 110 is estimated based on the internal resistance if the temperature T of the battery cell 111 is in the low temperature range, based on the internal pressure if the temperature T is in the high temperature range, and based on both the internal resistance and internal pressure if the temperature T is in the normal temperature range.

[0040] This degradation estimation method can improve the accuracy of estimating the degradation of the secondary battery 110. Therefore, it is possible to accurately estimate the performance of the secondary battery 110 at the end of its degradation stage, eliminating the need for design to ensure extra cell performance, and enabling cost reduction while maintaining quality.

[0041] Although one embodiment of the present disclosure has been described above, the present disclosure can be understood not only as a secondary battery system, but also as a method performed by a secondary battery system comprising a processor and memory, a program for performing this method, a computer-readable non-temporary storage medium storing this program, and a vehicle equipped with the secondary battery system. [Industrial applicability]

[0042] The secondary battery system disclosed herein can be used in cases where it is desired to estimate the degradation of a secondary battery with high accuracy. [Explanation of Symbols]

[0043] 100 Power Systems 110 Secondary battery 111 battery cells 112 Outer Case 113 Voltage / Current / Temperature Sensor 114 Pressure Sensor 120 Secondary Battery Systems 121 Information Acquisition Department 122 Degradation Estimation Unit

Claims

1. A secondary battery system for estimating the degradation of secondary batteries, An acquisition unit that acquires the internal resistance, internal pressure, and temperature of a battery cell, When the temperature is below a first threshold, a first estimation unit estimates the degradation of the secondary battery based on the internal resistance, If the temperature is above a second threshold, a second estimation unit estimates the degradation of the secondary battery based on the internal pressure, The system includes a third estimation unit that estimates the degradation of the secondary battery based on both the internal resistance and the internal pressure when the temperature exceeds the first threshold and is less than the second threshold. Secondary battery system.

2. The acquisition unit acquires the internal pressure by detecting the change in internal pressure of the battery cell due to the gas generated as the battery cell deteriorates. The secondary battery system according to claim 1.

Images