All-solid-state battery systems and vehicles

Abstract

To suppress variations in the power storage amount between cells when a plurality of all solid batteries (cells) are connected and used as a battery assembly.SOLUTION: An all solid battery system has a battery assembly consisting of a plurality of cells connected together, and a control unit that executes charge control and discharge control of the battery assembly. Each of a plurality of cells is an all solid battery. The control unit is configured to execute an equalization process to bring power storage amount between cells closer to equality in the plateau region in the relationship between the voltage and power storage amount of the battery assembly in the charge or discharge control of the battery assembly.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a all-solid-state battery system and a vehicle including the all-solid-state battery system.

Background Art

[0002] In recent years, research and development of all-solid-state batteries have been underway. For example, Japanese Patent Application Laid-Open No. 2022-133689 (Patent Document 1) discloses a technique for calculating the remaining battery capacity based on the Li occupancy state in the thickness direction of the electrode layer of an all-solid-state battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the technique described in Patent Document 1, the stored electricity amount (remaining battery capacity) of an all-solid-state battery can be calculated. However, when a plurality of all-solid-state batteries (cells) are connected and used as a battery pack, there is a possibility that the stored electricity amounts vary among the cells.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to suppress variations in the stored electricity amounts among cells when a plurality of all-solid-state batteries (cells) are connected and used as a battery pack.

Means for Solving the Problems

[0006] A solid-state battery system according to one embodiment of the present disclosure comprises a battery pack composed of a plurality of connected cells, and a control device that performs charging and discharging control of the battery pack. Each of the plurality of cells is a solid-state battery. The control device is configured to perform an equalization process in the charging or discharging control of the battery pack to bring the amount of stored energy between cells closer to equal in a plateau region in the relationship between the voltage and stored energy of the battery pack. [Effects of the Invention]

[0007] According to this disclosure, when multiple solid-state batteries (cells) are connected and used as a battery pack, it becomes possible to suppress variations in the amount of stored energy between cells. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows the schematic configuration of a vehicle according to an embodiment of the present disclosure. [Figure 2] This figure shows the components included in the battery pack shown in Figure 1. [Figure 3] This flowchart shows the charging control process performed by the control device according to the embodiment of this disclosure. [Figure 4] This flowchart shows the discharge control process performed by the control device according to the embodiment of this disclosure. [Figure 5] Figure 3 is a flowchart showing a modified example of the charging control. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0010] Figure 1 is a diagram showing the schematic configuration of a vehicle according to this embodiment. Referring to Figure 1, Vehicle 1 is configured to perform charging using power supplied from outside the vehicle (external power source) (hereinafter also referred to as "external charging"). Vehicle 1 is a four-wheeled BEV (battery electric vehicle). The external charging performed by Vehicle 1 is contact charging (plug-in charging) using power supplied from EVSE (Electric Vehicle Supply Equipment). However, Vehicle 1 may be other xEVs (electric vehicles), such as a plug-in hybrid vehicle. The number of wheels is also arbitrary, and may be 3 wheels or 5 or more wheels. External charging may be contactless charging.

[0011] Vehicle 1 comprises a charging unit 10, a battery pack 20, a drive unit 30, drive wheels 40, a power conversion circuit 50, on-board equipment 60, and an ECU (Electronic Control Unit) 100. The charging unit 10 includes an inlet 11, a power conversion circuit 12, and a CHR (charging relay) 13. The power conversion circuit 12 includes, for example, at least one of a DC / DC converter and an inverter. The battery pack 20 includes a battery 21 and a thermal management device 22 that regulates the temperature of the battery 21. The thermal management device 22 includes, for example, at least one of an electric heater and a cooling device. The drive unit 30 includes a PCU (Power Control Unit) 31 and an MG (motor generator) 32. The PCU 31 drives the MG 32 using power supplied from the battery 21. The MG 32 rotates the drive wheels 40. In this way, vehicle 1 is configured to be electrically powered. The battery 21 also supplies power to the on-board equipment 60. The in-vehicle equipment 60 includes an air conditioning system that provides air conditioning inside the vehicle 1. Power from the battery 21 is supplied to the in-vehicle equipment 60 via the power conversion circuit 50. The power conversion circuit 50 includes, for example, at least one of a DC / DC converter and an inverter. The ECU 100 controls the charging unit 10, the battery pack 20, the drive unit 30, and the power conversion circuit 50.

[0012] The ECU 100 includes a processor 101, RAM (Random Access Memory) 102, and a storage device 103. For example, a CPU (Central Processing Unit) can be used as the processor 101. The storage device 103 is configured to store stored information. In addition to the program, the storage device 103 stores information used by the program (e.g., maps, mathematical formulas, and various parameters). In this embodiment, the processor 101 executes the program stored in the storage device 103, thereby executing various controls in the ECU 100 (e.g., the controls shown in Figures 3 and 4, described later). However, the various controls in the ECU 100 may be executed by hardware (electronic circuits) rather than software. The number of processors in the ECU 100 is arbitrary and may be multiple.

[0013] The ECU 100 is configured to communicate with an HMI (Human Machine Interface) 80 located inside or outside the vehicle 1. The HMI 80 includes an input device and a notification device (e.g., a display device and a speaker). The HMI 80 may be a terminal mounted in the vehicle 1 (e.g., a navigation system) or a mobile terminal that can be carried by the user (e.g., a smartphone or wearable device).

[0014] The storage device 103 stores battery information relating to the battery 21. The battery information includes data showing the change in the voltage of the battery 21 as the amount of charge in the battery 21 increases during charging (hereinafter referred to as the "charging curve") and data showing the change in the voltage of the battery 21 as the amount of charge in the battery 21 decreases during discharging (hereinafter referred to as the "discharge curve"). The charging curve and the discharge curve are measured in advance and stored in the storage device 103. Each of the charging curve and the discharge curve shows the relationship between the voltage and the amount of charge in the battery 21. The "voltage" in each curve is, for example, the OCV (open circuit voltage). The amount of charge in the battery 21 is expressed, for example, as SOC (State of Charge). SOC is the ratio of the current amount of charge to the amount of charge in a fully charged state, expressed, for example, as 0 to 100%. The ECU 100 may sequentially update the charging curve and discharging curve in the storage device 103 using the measured data (e.g., voltage and SOC) obtained during the control of the battery 21 described later (Figures 3 and 4).

[0015] Although not shown in Figure 1, the battery pack 20 also includes a Battery Management System (BMS) that monitors the status of the battery 21. The BMS includes various sensors for detecting the status of the battery 21. The internal configuration of the battery pack 20 will be explained below using Figure 2.

[0016] Figure 2 shows the components included in the battery pack 20. Referring to Figure 2, the battery 21 is a battery pack composed of N cells 2-1 to 2-N connected together. N is a natural number greater than or equal to 2, and may be greater than or equal to 100 or greater than or equal to 100. Cells 2-1 to 2-N are connected in series. However, the connection configuration of cells in a battery pack is not limited to series and may include parallel connections. In this embodiment, since cells 2-1 to 2-N shown in Figure 2 have the same configuration, they will be referred to as "cell 2" below unless otherwise distinguished. Cell 2 is an all-solid-state secondary battery that constitutes the battery pack.

[0017] Cell 2 includes a positive electrode current collector 201, a positive electrode layer 202, an electrolyte layer 203, a negative electrode layer 204, and a negative electrode current collector 205. The positive electrode current collector 201 is configured to collect current from the positive electrode layer 202. Examples of materials for the positive electrode current collector 201 include SUS (Steel Use Stainless), aluminum, nickel, iron, titanium, and carbon. The negative electrode current collector 205 is configured to collect current from the negative electrode layer 204. Examples of materials for the negative electrode current collector 205 include SUS, copper, nickel, and carbon. The shape of Cell 2 may be, for example, a rectangular parallelepiped shape (square shape), a laminate shape, a cylindrical shape, a button shape, a coin shape, or a flat shape.

[0018] In Cell 2, which is a all-solid-state battery, the electrolyte layer 203 contains a solid electrolyte. The electrolyte layer 203 is located between the positive electrode layer 202 and the negative electrode layer 204. The thickness of the electrolyte layer 203 is, for example, 0.1 μm or more and 1000 μm or less. Examples of solid electrolytes include inorganic solid electrolytes (such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc.), and organic polymer electrolytes (such as polymer electrolytes). Examples of sulfide solid electrolytes include solid electrolytes containing Li element, X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S element. The sulfide solid electrolyte may further contain at least one of O element and halogen element. The sulfide solid electrolyte may be glass (amorphous) or glass-ceramics. Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-SiS2, Li2S-GeS2, and Li2S-P2S5-GeS2.

[0019] The positive electrode layer 202 is a layer containing at least a positive electrode active material. The thickness of the positive electrode layer 202 is, for example, 0.1 μm or more and 1000 μm or less. Further, the positive electrode layer 202 may contain at least one of an electrolyte, a conductive material (such as a carbon material, metal particles, a conductive polymer, etc.), and a binder, if necessary.

[0020] The positive electrode active material is, for example, an oxide active material. Examples of oxide active materials include rock salt layered active materials (LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., spinel-type active materials (LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5 Examples of positive electrode active materials include olivine-type active materials (such as O4), LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4). A coating layer containing a Li ion-conducting oxide may be formed on the surface of the oxide active material. Such a coating layer can suppress the reaction between the oxide active material and the solid electrolyte (especially the sulfide solid electrolyte). An example of a Li ion-conducting oxide is LiNbO3. The thickness of the coating layer is, for example, 1 nm to 30 nm. However, the positive electrode active material is not limited to the above oxide active materials. For example, Li2S may be used as the positive electrode active material.

[0021] The negative electrode layer 204 is a layer containing at least a negative electrode active material. The thickness of the negative electrode layer 204 is, for example, 0.1 μm to 1000 μm. The proportion of the negative electrode active material in the negative electrode layer 204 is, for example, 20% by weight to 80% by weight. The negative electrode layer 204 may optionally contain at least one of an electrolyte, a conductive material (carbon material, metal particles, conductive polymer, etc.), and a binder.

[0022] In this embodiment, the negative electrode active material has a silicon clathrate II type crystalline phase. For example, a silicon clathrate II type crystalline phase can be generated by reacting a Na source (e.g., metallic Na, NaH, or a metallic Na dispersion in which metallic Na particles are dispersed in oil) and a Si source (e.g., porous Si having voids inside primary particles) to obtain an Na-Si alloy, and then heating the Na-Si alloy to reduce the amount of Na in the Na-Si alloy. In the silicon clathrate II type crystalline phase, polyhedra (cages) containing pentagons or hexagons are formed by multiple Si elements. These polyhedra have spaces inside that can encapsulate metal ions, such as Li ions. The negative electrode active material may have minute voids with a pore diameter of 100 nm or less. The porosity may be, for example, 4% to 40%. By inserting metal ions into these spaces, volume changes due to charging and discharging can be suppressed. Note that general Si has a diamond type crystalline phase.

[0023] The structure and materials of cell 2 are not limited to those described above and can be changed as appropriate. The battery pack 20 may further include a restraining jig that applies restraining pressure along the stacking direction of cells 2-1 to 2-N. Restraining pressure (for example, a restraining pressure of 0.1 MPa to 100 MPa) may be applied to form good ion conduction paths and electron conduction paths.

[0024] The battery pack 20 further includes a current sensor 25 for detecting the current flowing through the battery 21 (battery pack), and voltage sensors 23-1 to 23-N and temperature sensors 24-1 to 24-N corresponding to cells 2-1 to 2-N, respectively. The detection results from each sensor are input to the ECU 100. Each sensor functions as a BMS. Based on the signals from each sensor, the ECU 100 can obtain the current of the battery 21 and the voltage and temperature of each cell of the battery 21. The ECU 100 can also calculate the SOC for each cell from the detection results from each sensor. Regarding the parameters detected for each cell in the battery 21 (e.g., voltage, temperature, and SOC), a representative value (e.g., mean or median) of the detected value for each cell may be considered as the detected value for the battery 21. The configuration of the BMS can be changed as appropriate. For example, the number of current sensors and temperature sensors may be one for multiple cells, rather than one per cell.

[0025] Incidentally, when multiple solid-state batteries (cells) are connected and used as a battery pack, variations in the amount of charge stored between cells tend to occur. Therefore, the ECU100 according to this embodiment suppresses variations in the amount of charge stored between cells by performing the charge control shown in Figure 3 and the discharge control shown in Figure 4, as described below.

[0026] Figure 3 is a flowchart showing the charging control process performed by the ECU 100. Each step in the flowchart is simply denoted as "S". The process shown in this flowchart starts, for example, when the conditions for starting plug-in charging are met. Specifically, when the connector of the EVSE (external power supply) charging cable is connected to the inlet 11 of the vehicle 1, the conditions for starting plug-in charging are met, and the following processing flow (S11, S12 and S21~S24) may start.

[0027] Referring to Figure 3, in S11, the ECU 100 obtains the current State of Charge (SOC) of the battery 21 and determines whether the obtained SOC belongs to a plateau region of the charging curve L1. Specifically, the ECU 100 reads the charging curve L1 from the storage device 103 and recognizes the plateau region of the charging curve L1. A plateau region is a region where the charging curve or discharge curve becomes flat. In a plateau region, the change in voltage (slope of the curve) with respect to the change in the amount of stored energy becomes smaller than the reference change. The plateau voltage is the battery voltage in the plateau region.

[0028] In the charging curve L1 shown in Figure 3, the first SOC range from 0% to value P11 (plateau region A) and the second SOC range from value P12 to value P13 (plateau region B) each correspond to a plateau region. In this embodiment, values ​​P11, P12, and P13 are 30%, 60%, and 80%, respectively, and the widths of the first SOC range and the second SOC range are 30% and 20%, respectively. However, the values ​​P11, P12, and P13 are not limited to those above and may vary depending on the characteristics of the cell (all-solid-state battery) used. The width of the first SOC range is preferably 5% or more, and more preferably 15% or more. Each of the cells 2-1 to 2-N constituting the battery 21 according to this embodiment is an all-solid-state battery equipped with an electrode layer (specifically, a negative electrode layer) containing silicon clathrate. These all-solid-state batteries tend to have a clear plateau region in the low SOC range in both the charging and discharging curves, and more specifically, a plateau region in at least a portion of the SOC range between 0% and 30%.

[0029] In this embodiment, if the State of Charge (SOC) of the battery 21 when the plug-in charging start condition is met falls within either the first SOC range (0-30%) or the second SOC range (60-80%), S11 is determined to be YES. If the SOC does not fall within either the first or second SOC range, S11 is determined to be NO. As a method for measuring the SOC, a known method such as the current integration method can be used.

[0030] If YES is determined in S11, the ECU 100 performs an equalization process for the battery 21 in the following S12. The equalization process is a process that brings the amount of stored charge between cells closer to equal. In this embodiment, the ECU 100 controls the charging unit 10 in S12 to match the SOC of each of cells 2-1 to 2-N (Figure 2). Specifically, in the plateau region, the ECU 100 controls the charging of the battery 21 (external charging) at a voltage lower than the normal charging (S21) described later (hereinafter referred to as the "first equalization voltage"). The first equalization voltage is a voltage lower than the reference voltage (S21) described later, and may be half or less of the reference voltage. The ECU 100 may adjust (step down) the voltage using the power conversion circuit 12. As a result of the above equalization process, voltage variations between cells and potential variations within cells (for example, potential variations due to reaction unevenness) are reduced for the battery 21. In all-solid-state batteries that do not contain an electrolyte, ion conduction paths between solid electrolytes are difficult to form in the thickness direction, and the resistance to ion movement in the thickness direction is high, which can easily lead to uneven reactions.

[0031] Once the equalization process is complete, the process proceeds to S21. The ECU 100 may determine whether the equalization process is complete based on the state of each cell of the battery 21 (e.g., SOC). Alternatively, the ECU 100 may determine that the equalization process is complete when a predetermined time has elapsed since the start of the equalization process. Furthermore, if the SOC of the battery 21 moves out of the plateau region during the equalization process, the ECU 100 may stop the equalization process and proceed to S21. In addition, if NO is determined in S11, the process also proceeds to S21.

[0032] In S21, the ECU 100 performs external charging (plug-in charging) of the battery 21 at a predetermined reference voltage. The reference voltage may be determined according to the specifications (e.g., rated voltage) of the EVSE connected to the vehicle 1. The ECU 100 controls the charging unit 10 so that the battery 21 is charged by the power supplied from the EVSE.

[0033] Next, in S22, the ECU 100 determines whether or not to terminate charging based on whether or not the charging termination condition has been met. The charging termination condition is met, for example, when the State of Charge (SOC) of the battery 21 reaches a target value. The target value may be automatically set by the ECU 100 or EVSE, or it may be set by the user. The target value may be 100% (the SOC value indicating full charge). The charging termination condition is also met when the charging cable is disconnected from the inlet 11. The charging termination condition can be changed as appropriate. For example, the charging termination condition may be met when a predetermined time has elapsed since the start of external charging (S21). Alternatively, the charging termination condition may be met in response to a charging stop instruction from the user.

[0034] If the charging termination condition is not met (NO in S22), the process proceeds to S23. In S23, the ECU 100 determines whether the SOC of the battery 21 has entered the plateau region of the charging curve L1 due to the above charging (S21). In this embodiment, if the SOC of the battery 21 rises due to the above charging and reaches the value P12, it is determined to be YES in S23, and the process proceeds to S24. In S24, the ECU 100 performs an equalization process for the battery 21 (for example, the low-voltage charging described above). The equalization process in S24 may be the same as or different from the equalization process in S12. Once the equalization process in S24 is completed, the process returns to S21. Also, if it is determined to be NO in S23, the process returns to S21. If the equalization process in S24 has been completed, it is determined to be NO in S23.

[0035] As long as the result is NO in both S22 and S23, external charging of the battery 21 at the reference voltage (S21) is continuously performed. When the charging termination condition is met (YES in S22), the processing flow shown in Figure 3 ends.

[0036] The equalization process is not limited to the low-voltage charging described above. The equalization process in S12 and S24 may, for example, be a process to stop charging the battery 21. In the plateau region, stopping charging causes the voltage of each cell constituting the battery 21 to approach the plateau voltage. For example, after the vehicle 1 has finished running using the power of the battery 21 (electric driving), if the condition for starting plug-in charging is met (YES in S11) while the State of Charge (SOC) of the battery 21 is in the plateau region, the ECU 100 may wait in the plateau region in S12 without charging or discharging the battery 21, and then start plug-in charging of the battery 21 (S21). Alternatively, in the charging control of the battery 21, the ECU 100 may stop charging the battery 21 as an equalization process when the amount of charge stored in the battery 21 is in the plateau region, and then resume charging the battery 21 after the equalization process is completed. Specifically, when charging control is started, the State of Charge (SOC) of battery 21 is not in the plateau region (NO in S11), and when the SOC of battery 21 rises due to plug-in charging (S21) and comes into the plateau region (YES in S23), the ECU 100 may stop charging battery 21 in S24. Then, after the equalization process is completed, the ECU 100 may resume plug-in charging of battery 21 (S21). The equalization process may also be discharge (see S121 in Figure 5), which will be described later.

[0037] Figure 4 is a flowchart showing the discharge control process performed by the ECU 100. The process shown in this flowchart is started, for example, when the discharge start condition for the battery 21 is met in a stationary vehicle 1. Specifically, in a stationary vehicle 1, when the State of Charge (SOC) of the battery 21 is higher than a lower limit (for example, a value P21 described later) and the user performs an ON operation (operation request) of an in-vehicle device 60 (for example, an air conditioner), the discharge start condition for the battery 21 is met, and the following processing flow (S31-S33 and S341, S342) may be started.

[0038] Referring to Figure 4, in S31, the ECU 100 performs a discharge of the battery 21. Specifically, the ECU 100 controls the power conversion circuit 50 so that power to operate the in-vehicle equipment 60 is supplied from the battery 21 to the in-vehicle equipment 60. In other words, in S31, the ECU 100 performs discharge control of the battery 21 using the drive voltage of the in-vehicle equipment 60. Hereafter, the in-vehicle equipment 60 that receives power from the battery 21 will be referred to as the "target equipment".

[0039] Next, in S32, the ECU100 determines whether or not to terminate the discharge based on whether or not the discharge termination condition has been met. The discharge termination condition is met, for example, when the user performs the OFF operation (stop request) of the target equipment. The discharge termination condition is also met when vehicle 1 starts moving. Note that the discharge termination condition can be changed as appropriate.

[0040] If the discharge termination condition is not met (NO in S32), the process proceeds to S33. In S33, the ECU 100 determines whether the State of Charge (SOC) of the battery 21 has entered the plateau region (in this embodiment, plateau region C shown below) located on the lowest SOC side of the plateau region of the discharge curve L2 due to the discharge (S31).

[0041] More specifically, the ECU 100 reads the discharge curve L2 from the storage device 103 and recognizes the plateau region of the discharge curve L2. In the discharge curve L2 shown in Figure 4, the third SOC range from 0% to value P21 (plateau region C) and the fourth SOC range from value P22 to value P23 (plateau region D) each correspond to a plateau region. In this embodiment, values ​​P21, P22, and P23 are 30%, 55%, and 75%, respectively, and the widths of the third SOC range and the fourth SOC range are 30% and 20%, respectively. However, the values ​​P21, P22, and P23 are not limited to those above and may vary depending on the characteristics of the cell (all-solid-state battery) used. The width of the third SOC range is preferably 5% or more, and more preferably 15% or more.

[0042] If the State of Charge (SOC) of battery 21 is higher than the value P21, the result is determined to be NO in S33. In this embodiment, as long as the result is determined to be NO in both S32 and S33, power supply from battery 21 to the target device (S31) is continuously performed. When the SOC of battery 21 decreases due to this discharge (S31) and reaches the value P21, the result is determined to be YES in S33, and the process proceeds to S341.

[0043] In S341, the ECU 100 notifies the user of the cessation of discharge. Specifically, the ECU 100 controls the HMI 80 to notify the user of the cessation of the target device, for example. The HMI 80 may provide the notification by display or sound. Subsequently, in S342, the ECU 100 performs an equalization process for the battery 21. Specifically, in plateau region C, the ECU 100 controls the discharge of the battery 21 at a voltage lower than the drive voltage of the in-vehicle device 60 (S31) (hereinafter referred to as the "second equalization voltage"). As a result, the power supply from the battery 21 to the target device is stopped. The second equalization voltage is a voltage lower than the discharge voltage in S31. In S342, low-voltage discharge of the battery 21 is performed. The ECU 100 may adjust (step down) the voltage by, for example, the power conversion circuit 50. The discharged power may be consumed by a power load (not shown) included in the in-vehicle equipment 60, or it may be stored in an auxiliary battery (not shown). The equalization process in S342 reduces voltage variations between cells and potential variations within cells in the battery 21. In the low SOC plateau region (plateau region close to over-discharge), the mitigation (equalization) of these variations is particularly promoted.

[0044] Once the equalization process in S342 is completed, the processing flow shown in Figure 4 ends. The processing flow shown in Figure 4 also ends if the discharge termination condition is met (YES in S32). In the discharge control shown in Figure 4 above, the equalization process of the battery 21 is not performed in plateau region D so as not to excessively reduce user convenience. However, this is not limited to this, and the ECU 100 may perform the equalization process of the battery 21 not only in plateau region C but also in plateau region D. Furthermore, the discharge control of the battery 21 is not limited to discharge control for operating the in-vehicle equipment 60, but may also be discharge control for supplying power to the outside of the vehicle.

[0045] As described above, the vehicle 1 according to this embodiment is equipped with a solid-state battery system. This solid-state battery system includes a battery 21 and an ECU 100 (control unit) that performs charging and discharging control of the battery 21. The battery 21 is a battery pack composed of multiple cells connected together. Each of the multiple cells is a solid-state battery. The ECU 100 is configured to perform an equalization process (S12, S24 in Figure 3 and S342 in Figure 4) in the charging or discharging control of the battery 21, which brings the amount of charge stored between cells closer to equal in the plateau region (flat region) of the relationship between the voltage and the amount of charge stored in the battery 21. In the plateau region, the voltage of each cell (solid-state battery) that makes up the battery pack tends to approach the plateau voltage. Therefore, equalization of the amount of charge stored between cells is promoted in the plateau region. According to the above configuration, when multiple solid-state batteries (cells) are connected and used as a battery pack, variations in the amount of charge stored between cells are suppressed.

[0046] The charge curve and discharge curve of the battery 21 according to the above embodiment each have multiple spaced-out plateau regions. However, it is not limited to this, and each of the charge curve and discharge curve may have only one plateau region. For example, the charge curve of the battery 21 may have plateau region A shown in Figure 3 as the sole plateau region. Even with such a battery 21, the variation in the amount of charge stored between cells can be suppressed by the charge control shown in Figure 3. Furthermore, the discharge curve of the battery 21 may have plateau region C shown in Figure 4 as the sole plateau region. Even with such a battery 21, the variation in the amount of charge stored between cells can be suppressed by the discharge control shown in Figure 4.

[0047] The processing flows shown in Figures 3 and 4 can be modified as appropriate. For example, the order of processing may be changed or unnecessary steps may be omitted depending on the purpose. Also, the content of any of the processing steps may be changed. For example, the ECU 100 may perform the charging control shown in Figure 5, which will be described below, instead of the charging control shown in Figure 3.

[0048] Figure 5 is a flowchart showing a modified version of the charging control shown in Figure 3. The battery 21 (all-solid-state battery) in this modified version has the characteristics shown by the charging curve L1A. The charging curve L1A has a plateau region A as its only plateau region. The plateau region A in Figure 5 is the same as the plateau region A shown in Figure 3. However, the ECU 100 recognizes the plateau region A as being divided into multiple sections (specifically, sections A1 and A2). The plateau region A of the charging curve L1A shown in Figure 5 includes a first section (section A1) from 0% to value P10, and a second section (section A2) from value P10 to value P11. Values ​​P10 and P11 are stored in the memory device 103 in advance along with the charging curve L1A. Value P10 is smaller than value P11. Value P10 is an SOC value near 0%, for example, an SOC value selected from the range of greater than 0% and less than or equal to 15%.

[0049] Referring to Figure 5, in S111, the ECU 100 obtains the current SOC of battery 21 and determines whether the obtained SOC belongs to plateau region A (0% to value P11) of the charging curve L1A. If the SOC of battery 21 belongs to plateau region A of the charging curve L1A (YES in S111), the ECU 100 then determines in S112 whether the SOC of battery 21 belongs to category A1 (0% to value P10). If the SOC of battery 21 belongs to category A1 (YES in S112), the ECU 100 performs the first equalization process of battery 21 in S121. If the SOC of battery 21 belongs to a category other than category A1 (category A2) (NO in S112), the ECU 100 performs the second equalization process of battery 21 in S122.

[0050] The first equalization process is the discharge of the battery 21. Specifically, in S121, the ECU 100 controls the power conversion circuit 50 so that the battery 21 is discharged until its State of Charge (SOC) is 0% or less. The discharged power may be consumed by a power load (not shown) included in the in-vehicle equipment 60, or it may be stored in an auxiliary battery (not shown).

[0051] The second equalization process is the low-voltage charging described above, that is, external charging of the battery 21 at the first equalization voltage (see S12 in Figure 3). In other words, in S122, the charging control of the battery 21 is performed at a lower voltage than normal charging (S21).

[0052] If the equalization process is completed in either S121 or S122, the process proceeds to S21. Also, if NO is determined in S111, the process proceeds to S21. In S21, the ECU 100 performs external charging (plug-in charging) of the battery 21. Subsequently, in S22, the ECU 100 decides whether to terminate charging based on whether the charging termination condition has been met. S21 and S22 in Figure 5 are the same as S21 and S22 in Figure 3, so the explanation will not be repeated. As long as the charging termination condition is not met (NO in S22), plug-in charging in S21 is continuously performed. Then, when the charging termination condition is met (YES in S22), the process flow shown in Figure 5 ends.

[0053] In the above modified example, different equalization processes are performed for each plateau region classified according to the amount of stored energy. This makes it possible to more effectively suppress variations in the amount of stored energy between cells. Figure 5 illustrates the charge control, but different equalization processes may also be performed for each plateau region in the discharge control.

[0054] The ECU 100 may adjust the temperature of the battery 21 using the thermal management device 22 during the equalization process (S12, S24 in Figure 3, S342 in Figure 4, and S121, S122 in Figure 5). The ECU 100 may adjust the battery temperature to a temperature range that promotes equalization.

[0055] In the above embodiments and modifications, the ECU 100 determines whether the charge or discharge state of the battery 21 falls into a plateau region based on the State of Charge (S11, S23 in Figure 3, S33 in Figure 4, and S111 in Figure 5). However, it is not limited to this, and the ECU 100 may determine whether the charge or discharge state of the battery 21 falls into a plateau region using the OCV of the battery 21 in addition to or instead of the State of Charge (SOC) of the battery 21. The ECU 100 may estimate the OCV of the battery 21 based on the terminal voltage, current, and internal resistance of the battery 21 while continuing to charge the battery 21. Alternatively, the ECU 100 may temporarily stop charging the battery 21 and measure the voltage (OCV) of the battery 21 when no current is flowing. Furthermore, the ECU 100 may consider the voltage of the battery 21 when a small current is flowing as the OCV of the battery 21.

[0056] The applications of all-solid-state battery systems are not limited to vehicles. All-solid-state battery systems may also be used in applications other than vehicles (e.g., stationary applications).

[0057] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The technical scope provided herein is defined by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0058] 1 vehicle, 2 cells, 10 charging units, 11 inlets, 12 power conversion circuits, 20 battery packs, 21 batteries, 50 power conversion circuits, 60 on-board equipment, 100 ECUs.

Claims

1. A solid-state battery system comprising a battery pack composed of multiple connected cells and a control device, Each of the aforementioned plurality of cells is an all-solid-state battery, The control device, in controlling the charging of the battery pack, Determine whether the amount of charge stored in the battery pack falls within a plateau region in the relationship between the voltage and the amount of charge stored in the battery pack. If it is determined that the amount of charge stored in the battery pack falls within the plateau region, an equalization process is performed to make the amount of charge stored between the cells more uniform by controlling the charging of the battery pack at a voltage lower than the reference voltage, and after the equalization process is completed, the charging of the battery pack is controlled at the reference voltage. A solid-state battery system configured to control the charging of the battery pack at the reference voltage without performing the equalization process if it is determined that the amount of charge stored in the battery pack does not fall within the plateau region.

2. A solid-state battery system comprising a battery pack composed of multiple connected cells and a control device, Each of the aforementioned plurality of cells is an all-solid-state battery, The control device, in controlling the charging of the battery pack, Determine whether the amount of charge stored in the battery pack falls within a plateau region in the relationship between the voltage and the amount of charge stored in the battery pack. If it is determined that the amount of charge stored in the battery pack falls within the plateau region, the charging of the battery pack is stopped as an equalization process to bring the amount of charge stored between the cells closer to being equal, and the charging of the battery pack is resumed after the equalization process is completed. A solid-state battery system configured to charge the battery pack without performing the equalization process if it is determined that the amount of charge stored in the battery pack does not fall within the plateau region.

3. A solid-state battery system comprising a battery pack composed of multiple connected cells and a control device, Each of the aforementioned plurality of cells is an all-solid-state battery, The control device is In order to supply power from the battery pack to the target device, the discharge control of the battery pack is performed using the drive voltage of the target device, and it is determined whether the amount of charge stored in the battery pack has entered a plateau region in the relationship between the voltage and the amount of charge stored in the battery pack due to the discharge. If it is determined that the amount of charge stored in the battery pack has entered the plateau region due to the discharge of the battery pack, then, as an equalization process to make the amount of charge stored between the cells more uniform, the discharge control of the battery pack is performed at a voltage lower than the drive voltage. A solid-state battery system configured to continue controlling the discharge of the battery pack at the drive voltage without performing the equalization process if it is determined that the amount of charge stored in the battery pack has not entered the plateau region due to the discharge of the battery pack.

4. Each of the aforementioned plurality of cells comprises an electrode layer containing silicon clathrate, The all-solid-state battery system according to any one of claims 1 to 3, wherein the battery pack has a plateau region in at least a portion of the range in which the State of Charge (SOC), which indicates the ratio of the current amount of stored energy to the amount of stored energy when fully charged, is 0% or more and 30% or less.

5. A vehicle comprising the all-solid-state battery system described in any one of claims 1 to 3.

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