Battery system

Abstract

The invention relates to a battery system. The present invention addresses the problem of improving the calculation accuracy of a battery internal pressure. A battery ECU acquires an internal void volume (Vc0), which is the volume of gas that can be retained in a case of a single battery, calculates a gas generation amount (Vgo) generated in the case, and calculates a gas pressure (Pg) in the case on the basis of the gas generation amount (Vgo) and the internal void volume (Vco). The electrolyte vapor pressure (Pe) is calculated from the battery temperature, and the electrolyte vapor pressure (Pe) and the gas pressure (Pg) are added to calculate the battery internal pressure (P), which is the pressure inside the case.

Description

Technical Field

[0001] This invention relates to a battery system. Background Technology

[0002] Japanese Patent Application Publication No. 2015-141790 (Patent Document 1) discloses a method for judging the time-related deterioration of battery components using the internal pressure of the battery (battery internal pressure).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2015-141790 Summary of the Invention

[0004] In Patent Document 1, the amount of gas generated inside the battery is calculated based on the battery's historical temperature and state of charge (SOC). Furthermore, the internal pressure of the battery is calculated based on the amount of gas generated, and the amount of internal pressure damage is determined based on the internal pressure.

[0005] In Patent Document 1, the vapor pressure of the electrolyte was not considered when calculating the internal pressure of the battery. Therefore, there is a concern that the accuracy of the battery internal pressure calculation may be compromised.

[0006] The purpose of this invention is to improve the accuracy of battery internal pressure calculation.

[0007] The battery system of the present invention is a battery system comprising an electrode body and an electrolyte housed within a casing, and a control device. The control device calculates the pressure inside the casing, i.e., the battery internal pressure P, based on the amount of gas generated within the casing, Vgo; the volume of gas that can be retained within the casing, i.e., the internal void volume, Vc0; and the vapor pressure of the electrolyte, i.e., the electrolyte vapor pressure Pe.

[0008] Based on this structure, the internal pressure P of the battery can be calculated by considering the electrolyte vapor pressure Pe, thus improving the accuracy of the calculation of the internal pressure P.

[0009] Preferably, the control device can calculate the electrolyte vapor pressure Pe based on the battery temperature TB.

[0010] Based on this structure, the electrolyte vapor pressure Pe can be calculated from the battery temperature TB, thus making it easy to determine the electrolyte vapor pressure Pe.

[0011] Preferably, the control device can calculate the gas pressure Pg inside the casing based on the gas generation amount Vgo and the internal void volume Vc0, and calculate the battery internal pressure P by adding the electrolyte vapor pressure Pe to the gas pressure Pg.

[0012] Based on this structure, the internal pressure P of the battery is obtained by adding the electrolyte vapor pressure Pe to the gas pressure Pg inside the casing, thus enabling high-precision calculation of the internal pressure P of the battery.

[0013] Preferably, the control device can calculate the cumulative damage amount ΣDp, which is an indicator of the time-related deterioration of the components constituting the battery, based on the battery internal pressure P, and issue an alarm when the cumulative damage amount ΣDp exceeds a threshold.

[0014] Based on this structure, the cumulative damage ΣDp is calculated based on the highly accurate internal battery pressure P, thus enabling appropriate inference of the time-related degradation of the components constituting the battery and appropriate alerts.

[0015] Invention Effects

[0016] According to the present invention, the calculation accuracy of the battery internal pressure P can be improved. Attached Figure Description

[0017] Figure 1 This is an overall structural diagram of an electric vehicle equipped with the battery system described in this embodiment.

[0018] Figure 2 This is a flowchart illustrating an example of the battery internal pressure calculation process performed in the battery ECU.

[0019] Figure 3 (A) and (B) are diagrams illustrating the calculation method for the gas generation rate A1.

[0020] Figure 4 This is a graph showing the relationship between electrolyte vapor pressure Pe and temperature TB.

[0021] Figure 5 This is a flowchart illustrating an example of damage inference processing performed in the control ECU. Detailed Implementation

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, identical or corresponding parts in the drawings will be labeled with the same symbols, and their descriptions will not be repeated.

[0023] Figure 1This is an overall structural diagram of an electric vehicle 1 equipped with the battery system B according to this embodiment. In this embodiment, the electric vehicle 1 is, for example, an electric car. The electric vehicle 1 may be a plug-in hybrid vehicle equipped with an internal combustion engine and a battery. The electric vehicle 1 includes a motor generator (MG) 10 as a rotary motor, a power transmission gear 20, a drive wheel 30, a power control unit (PCU) 40, a system main relay (SMR) 50, a battery 100, a monitoring unit 200, a battery ECU (electronic control unit) 300, and a control ECU 500. The battery ECU 300 and the control ECU 500 are examples of the "control device" of the present invention.

[0024] MG10 is, for example, an embedded permanent magnet synchronous motor (IPM motor), which functions as both an electric motor and a generator. The output torque of MG10 is transmitted to the drive wheel 30 via a power transmission gear 20, which includes a reducer and a differential device.

[0025] When the electric vehicle 1 brakes, the MG10 is driven by the drive wheel 30, and the MG10 functions as a generator. Thus, the MG10 also functions as a braking device for regenerative braking, converting the kinetic energy of the electric vehicle 1 into electrical energy. The regenerative electricity generated by the regenerative braking force in the MG10 is stored in the battery 100.

[0026] PCU40 is a power conversion device that bidirectionally converts power between MG10 and battery 100. PCU40 includes, for example, an inverter and a converter that operate according to control signals from control ECU500.

[0027] SMR50 is electrically connected to the power line connecting battery 100 and PCU40. When SMR50 is closed (ON) according to a control signal from control ECU500, power can be transferred between battery 100 and PCU40. On the other hand, when SMR50 is open (OFF) according to a control signal from control ECU500, the electrical connection between battery 100 and PCU40 is disconnected.

[0028] Battery 100 stores the power used to drive MG10. Battery 100 is a rechargeable DC power source (secondary battery) and is a battery pack consisting of multiple individual cells (battery units) 110 connected in series. Individual cell 110 is equivalent to the "battery" of this invention. Individual cell 110 may be, for example, composed of lithium-ion batteries.

[0029] The single cell 110 can be, for example, a prismatic cell 110a. The prismatic cell 110a houses the electrode 112a inside a casing 111a made of a cuboid frame, and seals in electrolyte. Alternatively, the single cell 110 can be a laminated cell (pouch cell) 110b. The laminated cell 110b seals the electrode 112b and electrolyte inside a casing 111b made of a laminated film. Both the prismatic cell 110a and the laminated cell 110b include components such as a discharge valve (safety valve) to expel gas to the outside when the internal pressure rises due to gas generated inside the battery (inside the casing); and a current cut-off mechanism to cut off the current when the battery overheats abnormally.

[0030] The monitoring unit 200 includes a voltage sensor 210, a current sensor 220, and a temperature sensor 230. The voltage sensor 210 detects the voltage VB of the individual battery cell 110. The current sensor 220 detects the current IB input to and output to the battery 100 (individual battery cell 110). Furthermore, when the battery 100 is discharging, the current IB becomes negative (-), and when the battery 100 is charging, the current IB becomes positive (+). The temperature sensor 230 detects the temperature TB of the battery 100 (individual battery cell 110).

[0031] Electric vehicle 1 includes a charging interface 60, and battery 100 can be externally charged using charging equipment (Electric Vehicle Supply Equipment (EVSE)) 400. The charging interface 60 is configured to connect to a connector 420 at the front end of a charging cable 410 provided on the EVSE 400. The charging interface 60 is electrically connected to a power line connected to battery 100 via charging circuit 70. In this embodiment, when SMR 50 is closed, charging interface 60 is connected to battery 100, enabling external charging. Furthermore, charging circuit 70 may include a charging relay. Alternatively, the charging interface 60 (charging circuit 70) may be connected to the power line between battery 100 and SMR 50 via the charging relay, allowing external charging of battery 100 by closing the charging relay.

[0032] The battery ECU 300 includes a central processing unit (CPU) 301 and a memory 302. The memory 302 includes RAM (e.g., Static Random Access Memory (SRAM)) and non-volatile memory (e.g., Electrically Erasable Programmable Read-Only Memory (EEPROM)). In RAM, if power to the RAM is stopped (power to the battery ECU 300 is disconnected), the stored data is lost.

[0033] Even when power is cut off (power to battery ECU 300 is disconnected), the data stored in the non-volatile memory will not be lost. Battery ECU 300 uses signals received from monitoring unit 200 to estimate the SOC of battery 100 (single cell 110) and outputs this information to control ECU 500. Furthermore, battery ECU 300 estimates the degradation level of battery 100 and outputs this information to control ECU 500. Battery ECU 300 and control ECU 500 can be connected, for example, via a Controller Area Network (CAN). In this embodiment, battery system B consists of battery 100, monitoring unit 200, battery ECU 300, and control ECU 500.

[0034] The control ECU 500 includes a CPU 501 and a memory 502. Like the memory 302, the memory 502 includes RAM and non-volatile memory. The control ECU 500 controls various devices to achieve a desired state for the electric vehicle 1 based on signals received from the battery ECU 300, signals from various sensors (not shown) (e.g., throttle opening signal, vehicle speed signal, etc.), mappings stored in the memory 502, and other information.

[0035] Figure 2 This is a flowchart illustrating an example of the battery internal pressure calculation process performed in the battery ECU 300. In this flowchart, the calculation is performed for each individual battery cell 110 at each specified period when the power switch (ignition switch) 250 is turned on and the battery system B is in the ON state, and when the battery 100 is externally charged by the EVSE 400.

[0036] In step 10 (hereinafter referred to as "S"), it is determined whether the flag F is 1. When the electric vehicle 1 is shipped and when the battery 100 is replaced, the flag F is set to "0". If the flag F is 0 and is determined negatively, proceed to S11; if the flag F is 1 and is determined positively, proceed to S12.

[0037] In S11, the internal void volume Vc0 is obtained. The internal void volume Vc0 is the volume of gas that can be retained inside the casing of the single cell 110. The internal void volume Vc0 is the volume obtained by subtracting the volume of the electrode body and the electrolyte volume Ve0 from the volume inside the casing of the single cell 110. The electrolyte volume Ve0 is the amount of electrolyte injected into the casing during the electrolyte injection process of the single cell 110.

[0038] Process history information is recorded in the two-dimensional code printed on the surface of the casing of the individual battery cell 110. When assembling the battery 100 (battery pack), the internal void volume Vc0 can be read from this two-dimensional code and stored in the memory 302. In this case, in S11, the internal void volume Vc0 is read from the memory 302. Alternatively, the process history information of the individual battery cell 110 can be stored on a server (not shown). When the electric vehicle 1 is started, the internal void volume Vc0 is obtained from the server through communication between the electric vehicle 1 (battery ECU 300) and the server.

[0039] In S12, the amount of gas generated, Vgo, is calculated. During the charging and discharging of the single-cell battery 110, gas is generated along with reactions such as electrolyte decomposition. In S12, this amount of gas generated is calculated as the amount of gas generated, Vgo. In this embodiment, the amount of gas generated, Vgo, is calculated based on the gas generation rate, A1. Figure 3 This is a diagram illustrating the calculation method for the gas generation rate A1. Figure 3 (A) represents the relationship between the natural logarithm (ln(gas generation rate A1)) of the gas generation rate A1 [cc / √time] in the single cell 110 and the reciprocal of the temperature TB (1000 / TB in this embodiment). Figure 3 (A) is known as the Arrhenius diagram (Arrhenius formula), obtained through experiments or simulations using a single cell 110. For example... Figure 3 As shown in (A), the gas generation rate A1 can be approximated as a straight line that increases with each state of charge (SOC) as temperature TB increases (the reciprocal of temperature TB decreases) and as SOC increases. For example, the gas generation rate A1 is based on... Figure 3 The relationship between (A) is calculated using the following formula (1).

[0040] A1=ln(k1×exp(k2×1000 / TB))……(1)

[0041] k1 is Figure 3 The value of the intercept on the vertical axis of (A), k2 is the slope of the line, set for each SOC. Temperature TB is the value detected by temperature sensor 230, and SOC is the current SOC.

[0042] Figure 3 (B) represents the calculation diagram of the gas generation rate A1. Figure 3 (B) is based on Figure 3 The relationship between gas generation rate A1, temperature TB, and SOC, shown in (A), is used to plot the gas generation rate A1. The gas generation rate A1 can be plotted using temperature TB and SOC as parameters, based on... Figure 3 The mapping of (B) is used to calculate.

[0043] The amount of gas produced, Vgo, is calculated using the following formula (2) based on the gas production rate, A1.

[0044] Vgon = Vgon-1 + (A1) 2 / (2×Vgon-1))×dt……(2)

[0045] Vgon represents the current gas production amount Vgo (current value), and Vgon-1 represents the previous gas production amount Vgo (previous value). dt represents the elapsed time from the previous calculation to the current calculation, equivalent to... Figure 2 The flowchart shows the calculation cycle. In S12, if the gas production amount Vgo is calculated, the current value is used as the previous value (Vgon-1) and stored in the non-volatile memory of memory 302, and then the process proceeds to S13. The initial value of Vgon-1 can be "0" or a specified value can be set.

[0046] In S13, the gas pressure Pg is calculated. The gas pressure Pg is the pressure of the gas generated inside the single cell 110 (casing). The gas pressure Pg is calculated using the following formula (3).

[0047] Pg=Vgo / Vc0……(3)

[0048] Vgo is the gas production amount Vgo calculated in S12 (this value Vgon), which is equivalent to the amount of gas currently present inside the shell. Vc0 is the internal void volume Vc0 obtained in S11.

[0049] In the following S14, the electrolyte vapor pressure Pe is calculated. Figure 4 This is a graph showing the relationship between the electrolyte vapor pressure Pe and temperature TB. (Example) Figure 4 As shown, the electrolyte vapor pressure Pe is proportional to the temperature TB as an exponential function. The electrolyte vapor pressure Pe is calculated using the following equation (4).

[0050] Pe=k3×exp(k4×TB)……(4)

[0051] k3 and k4 are constants. k3 and k4 are determined experimentally using the electrolyte encapsulated in the single cell 110. Figure 4 The relationship and according to Figure 4Use a chart to set it.

[0052] In S15, the battery internal pressure P is calculated. The battery internal pressure P is calculated using the following formula (5).

[0053] P = Pg + Pe……(5)

[0054] Pg is the gas pressure calculated in S13, and Pe is the electrolyte vapor pressure calculated in S14. The internal battery pressure P is the value obtained by adding the electrolyte vapor pressure Pe and the gas pressure Pg. If S15 is processed, the current routine ends.

[0055] Figure 5 This is a flowchart illustrating an example of damage estimation processing performed by the control ECU 500. In the flowchart, the process is performed for each individual cell 110 according to a predetermined period when the power switch 250 is turned on and the battery system B is in the on state, and when the EVSE 400 externally charges the battery 100. In S20, the damage amount Dp of the individual cell 110 is calculated. The calculation of the damage amount Dp is substantially the same as the calculation method described in Patent Document 1. Based on temperature TB and... Figure 2 The damage amount Dp is calculated using the battery internal pressure P calculated in the battery internal pressure calculation process. In this embodiment, the damage amount Dp is a factor that affects the creep fracture of the components (constituent components) constituting the single cell 110, for example, the current cut-off mechanism is taken as a constituent component.

[0056] The damage amount Dp is stored in memory 502 as a mapping with temperature TB and battery internal pressure P as parameters. For example, the larger the temperature TB, the larger the battery internal pressure P, so it is set to a larger value. In S20, the damage amount Dp is calculated based on temperature TB and battery internal pressure P.

[0057] In the subsequent S21, the cumulative damage ΣDp is calculated by accumulating the damage amount Dp calculated in S20 (ΣDp=ΣDpn-1+Dp: ΣDpn-1 is the previous value of ΣDp).

[0058] In step S22, determine if the cumulative damage ΣDp is above the threshold S. If the cumulative damage ΣDp is above the threshold S (ΣDp≥S), proceed to step S23. If the cumulative damage ΣDp is less than the threshold S (ΣDp<S), proceed to step S23. If the cumulative damage ΣDp is less than S (ΣDp<S), end the current routine.

[0059] In S23, the Malfunction Indicator Lamp (MIL) 260 is illuminated to issue an alarm and the current routine is terminated.

[0060] According to this embodiment, the battery internal pressure P, which is the pressure inside the casing, is calculated based on the amount of gas generated within the casing of the single cell 110, the internal void volume Vc0, which is the volume of gas that can be retained within the casing, and the electrolyte vapor pressure Pe, which is the vapor pressure of the electrolyte. By taking the electrolyte vapor pressure Pe into account when calculating the battery internal pressure P, the calculation accuracy of the battery internal pressure P can be improved.

[0061] According to this embodiment, Figure 4 Based on the relationship, the electrolyte vapor pressure Pe can be easily calculated from the battery temperature TB.

[0062] According to this embodiment, the gas pressure Pg inside the casing is calculated based on the gas generation amount Vgo and the internal void volume Vc0, and the battery internal pressure P is obtained by adding the electrolyte vapor pressure Pe to the gas pressure Pg. By adding the electrolyte vapor pressure Pe to the gas pressure Pg inside the casing, the battery internal pressure P can be calculated with high accuracy.

[0063] In this embodiment, the cumulative damage amount ΣDp is calculated based on the battery internal pressure P, and the MIL260 is activated when the cumulative damage amount ΣDp exceeds a threshold S. Since the cumulative damage ΣDp is calculated based on the highly accurate battery internal pressure P, the time-related degradation of the components constituting the single cell 110 can be appropriately inferred, thereby enabling appropriate alarms.

[0064] In the above embodiment, battery internal pressure calculation processing is performed in the battery ECU300. Figure 2 Damage inference processing is performed in the control ECU500. Figure 5 However, these processes can be performed in either the battery ECU 300 or the control ECU 500, or the battery ECU 300 and the control ECU 500 can work together to perform the processes.

[0065] It should be considered that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the invention is set forth in the claims, not in the description of the above embodiments, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0066] Symbol Explanation

[0067] 1-Electric vehicle, 10-Electric generator (MG), 20-Drive transmission gear, 30-Drive wheel, 40-PCU, 50-SMR, 60-Charging interface, 70-Charging circuit, 100-Battery, 110-Single cell, 111a, 111b-Housing, 112a, 112b-Electrode, 200-Monitoring unit, 210-Voltage sensor, 220-Current sensor, 230-Temperature sensor, 300-Battery ECU, 301-CPU, 302-Memory, 400-EVSE, 420-Connector, 500-Control ECU, 501-CPU, 502-Memory, B-Battery system.

Claims

1. A battery system comprising: a battery that houses an electrode body and an electrolyte solution in a case; and a control device, the battery system being characterized in that the control device calculates an internal pressure in the case, based on a generation amount of gas generated in the case, a volume in which the gas can be retained in the case, i.e., an internal void volume, and a vapor pressure of the electrolyte solution, i.e., an electrolyte vapor pressure.

2. The battery system according to claim 1, characterized in that the control device calculates the electrolyte vapor pressure based on a temperature of the battery.

3. The battery system according to claim 2, characterized in that the control device calculates a gas pressure in the case based on the generation amount of the gas and the internal void volume, and calculates the internal pressure by adding the electrolyte vapor pressure to the gas pressure.

4. The battery system according to any one of claims 1 to 3, characterized in that the control device performs the following process: calculating, based on the internal pressure, an accumulated damage amount that corresponds to an index of deterioration over time of components that constitute the battery, and when the accumulated damage amount exceeds a threshold value, performing an alarm. ​ ​ ​ ​ ​ ​ ​ ​ ​

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