Battery system and deterioration state estimation method

Abstract

This battery system comprises: a battery cell 21 having a solid electrolyte and a negative electrode that contains lithium; a load mechanism that applies a load to the battery cell 21; a measurement unit that measures the cell voltage of the battery cell 21, the cell temperature of the battery cell 21, the contact pressure applied to the battery cell 21, and the displacement of the battery cell 21; and an estimation device that estimates the deterioration state of the battery cell 21. The measurement unit measures the cell voltage when the charging of the battery cell 21 is completed or when the discharging of the battery cell 21 is completed. The estimation device: calculates a cell thickness change rate, which expresses the rate of change in the thickness of the battery cell 21 after completion of the charging of the battery cell 21 or after completion of the discharging of the battery cell 21, on the basis of the measured value for the displacement of the battery cell 21; calculates the amount of reversible lithium in the battery cell 21 on the basis of the cell temperature, the contact pressure, and the cell thickness change rate; compares the calculated amount of reversible lithium with the amount of reversible lithium initially in the battery cell 21 in a state in which the voltage conditions have been made to correspond to the cell voltage measured by the measurement unit; and estimates the deterioration state of the battery cell 21 from the comparison results.

Description

Battery system and degradation state estimation method

[0001] The present invention relates to a battery system and a method for estimating a state of deterioration.

[0002] Methods for estimating the degradation state of an all-solid-state metal lithium secondary battery have been known. For example, the estimation method described in Patent Document 1 includes measuring the open circuit voltage of the all-solid-state metal lithium secondary battery and the pressure and / or dimensions in the stacking direction of the all-solid-state metal lithium secondary battery at the open circuit voltage, and estimating the degradation state of the all-solid-state metal lithium secondary battery based on the increase in the measured pressure and / or dimensions from the initial pressure and / or dimensions at the open circuit voltage.

[0003] JP 2020-148592 A

[0004] The open circuit voltage of an all-solid-state secondary battery requires time to stabilize after charging or discharging of the secondary battery is completed. Therefore, in order to improve the accuracy of estimating the degradation state, the above estimation method must wait until the open circuit voltage stabilizes, which results in a problem of taking a long time to estimate the degradation state.

[0005] The problem to be solved by the present invention is to provide a battery system and a degradation state estimation method that can estimate the degradation state in a short time.

[0006] The present invention solves the above problem by calculating the rate of change in cell thickness after the end of charging or discharging of a battery cell, calculating the amount of reversible lithium in the battery cell based on the cell temperature, surface pressure, and rate of change in cell thickness, matching the measured cell voltage with the voltage of the battery cell in its initial state, comparing the amount of reversible lithium in the battery cell in its initial state with the calculated amount of reversible lithium, and estimating the state of deterioration of the battery cell from the comparison result.

[0007] According to the present invention, the deterioration state can be estimated in a short time.

[0008] Fig. 1 is a block diagram showing a battery system according to an embodiment of the present invention. Fig. 2 is a cross-sectional view of a battery cell, where (a) shows the cross-section of the battery cell in an initial state, and (b) and (c) show the cross-sections of the battery cell after degradation. Fig. 3 is a graph showing the temporal characteristics of thickness change after charging of a battery cell. Fig. 4 is a graph showing the temporal characteristics of thickness change after charging of a battery cell. Fig. 5 is a flowchart showing the steps of a degradation state estimation method according to an embodiment of the present invention.

[0009] 1, the battery system 1 includes a controller 10, a battery module 20, a voltage sensor 30, a temperature sensor 40, a load sensor 50, and a displacement sensor 60. The battery system 1 is installed in a vehicle. The controller 10 in this embodiment corresponds to an example of an "estimation device" in the present invention, and the voltage sensor 30, the temperature sensor 40, the load sensor 50, and the displacement sensor 60 correspond to an example of a "measurement unit" in the present invention.

[0010] The controller 10 is a battery control unit (BCU). The controller 10 is composed of a memory such as a ROM or a RAM, a processor such as a CPU, etc. The controller 10 manages the state of the battery module 20 based on the voltage detected by the voltage sensor 30, etc., and controls the charge / discharge current for charging or discharging the battery module 20. The controller 10 also estimates the deterioration state (degree of deterioration) of the battery cells 21 included in the battery module 20 based on the measurements of the voltage sensor 30, temperature sensor 40, load sensor 50, and displacement sensor 60.

[0011] The battery module 20 includes a plurality of battery cells 21 and a load mechanism. The battery module 20 may be mounted on, for example, an electric vehicle or a hybrid vehicle and used for vehicle grid integration (VGI). VGI is a technology in which an electric vehicle or a hybrid vehicle equipped with a battery module 2 is connected to a power grid and power stored in the battery module 20 is supplied to a system (load) such as a motor via a power grid.

[0012] The battery cells 21 are solid-state batteries and are electrically connected to a charging device. The charging device connected to the battery cells 21 is, for example, a device for charging the battery modules 2 mounted on an electric vehicle or a hybrid vehicle. Charging the mounted battery modules 2 is performed by removing the charging cable from the charging device, attaching the charging gun at the end of the charging cable to the connector of the vehicle's charging port, and then operating the charging start switch. The controller 10 manages the state of charge (SOC) of the battery cells 21 included in the battery modules 20 and controls each charging device so that the state of charge of the battery modules 20 reaches a target state of charge.

[0013] Each battery cell 21 included in the battery module 20 has at least a positive electrode, a solid electrolyte, and a negative electrode. The positive electrode contains at least a positive electrode active material capable of absorbing and releasing an alkali metal, such as lithium (Li), sodium (Na), or potassium (K). The positive electrode contains a positive electrode active material containing sulfur, but is not limited thereto. Examples of the solid electrolyte include a sulfide solid electrolyte or an oxide solid electrolyte. The negative electrode may contain lithium, such as lithium metal or a lithium alloy. The battery cell 21 is sealed in an exterior member with a tab connected to a laminate including the positive electrode, solid electrolyte, and negative electrode. The battery cell 21 is formed in a flat shape. The stacked battery cells 21 are connected to each other by bus bars. The multiple battery cells 21 are stacked along the y direction, and the surface along the xz plane is the main surface of the battery cell 21 and corresponds to the stacking surface. In the battery cell 21 shown in FIG. 1 , tabs protrude from both sides, but a structure in which only one side protrudes is sufficient.

[0014] The fixing plates 22 to 24 and the elastic body 25 are a mechanism for applying a load to the multiple battery cells 21. The fixing plates 22 to 24 are multiple cell pressure plates that apply pressure to the battery module 2 by pressing the battery module 2 in the stacking direction of the battery cells 21 included in the battery module 2. The fixing plates 22 to 24 are provided on the top and bottom surfaces of the stack of battery cells 21, and are also provided on the outside of the stack of battery cells 21 via a load sensor 50. The fixing plates 22 and 23 provided on the top and bottom surfaces of the battery module 2 are end plates that sandwich the stack of battery cells 21 from the stacking direction of the battery cells 21 and apply pressure to the battery cells 21.

[0015] The elastic bodies 25 are installed between the multiple battery cells 21 and are capable of absorbing displacement caused by charging and discharging the battery module 2. The fixing plates 22-24 are connected to each other so that pressure can be applied to the battery cells 21 by narrowing the distance between them. For example, when the multiple battery cells 21 are charged and their thickness increases, the pressure applied to the battery cells 21 increases. The fixing plates 22-24 and the elastic bodies 25 correspond to the "loading mechanism" of the present invention. The number of fixing plates 22-24 may be two, or four or more. The elastic bodies 25 do not necessarily have to be provided on each main surface of each battery cell 21. The mechanism for applying a load to the multiple battery cells 21 may be, in addition to the mechanism having the fixing plates 22-24 and the elastic bodies 25 shown in FIG. 1 , a mechanism such as binding the multiple battery cells 21 with rubber bands may also be used.

[0016] The voltage sensor 30 measures the voltage (cell voltage) of the battery cell 21. The voltage sensor 30 is a sensor for measuring the voltage between the terminals of the battery cell 21. The voltage sensor 30 is connected between the wiring connected to the positive and negative electrodes of the battery module 20. The temperature sensor 40 measures the temperature (cell temperature) of the battery cell 21. The temperature sensor 40 is installed in the battery module 20. The load sensor 50 measures the pressure (surface pressure) applied to the battery cell 21. The displacement sensor 60 measures the displacement of the battery cell 21. The displacement of the battery cell 21 corresponds to the amount of deformation of the battery cell 21 due to charging or discharging. The displacement sensor 60 measures the displacement of the battery cell 21 not only during charging or discharging of the battery module 20, but also after charging or discharging is completed. The measured values ​​of the voltage sensor 30, temperature sensor 40, load sensor 50, and displacement sensor 60 are output to the controller 10.

[0017] Next, a deterioration model of the battery cell 21 will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view of the battery cell 21, where (a) shows the cross-section of the battery cell 21 in an initial state, and (b) and (c) show cross-sections of the battery cell 21 after deterioration. (c) is in a more deteriorated state than (b). Note that (a) to (c) show a state of charge (SOC) of the battery cell 21 of 100%.

[0018] The battery cell 21 in the initial state has a positive electrode current collector layer 21 a, a positive electrode active material layer 21 b, a solid electrolyte layer 21 c, a metallic lithium layer 21 d, and a negative electrode current collector layer 21 e. As shown in Fig. 2, the positive electrode current collector layer 21 a, the positive electrode active material layer 21 b, the solid electrolyte layer 21 c, the metallic lithium layer 21 d, and the negative electrode current collector layer 21 e are stacked in this order.

[0019] When the battery cell 21 in the initial state is charged, lithium ions move from the positive electrode active material layer 21b through the solid electrolyte layer 21c to the negative electrode current collector layer 21e and precipitate between the solid electrolyte layer 21c and the negative electrode current collector layer 21e, forming a metallic lithium layer 21d, and the battery cell 21 assumes the state shown in FIG. 2(a).

[0020] As the deterioration of the battery cell 21 progresses, the metallic lithium contained in the metallic lithium layer 21d changes to H ２ O, O ２ , N ２ , CO２ The lithium ion reacts with trace amounts of other components, such as lithium hydroxide, lithium oxide, lithium nitride, and lithium carbonate, to form a deactivated LiM layer 21f. The deactivated LiM layer 21f is an irreversible layer that does not contribute to charging and discharging of the negative electrode. As shown in FIGS. 2(b) and 2(c), as the deterioration of the battery cell 21 progresses, the thickness of the deactivated LiM layer 21f increases. When the battery cell 21 deteriorates, the overall thickness of the battery cell 21 increases by the amount of the deactivated LiM layer 21f formed, compared to the battery cell 21 before deterioration. Therefore, when comparing battery cells 21 at the same SOC (100% SOC in the example of FIG. 2), the overall thickness of the battery cell 21 increases as the deterioration state increases.

[0021] Because the battery cells 21 are restrained by a load mechanism including the fixing plates 22 to 24 and the elastic body 25, the surface pressure of the battery cells 21 increases as the overall thickness of the battery cells 21 increases. That is, when compared at the same SOC (SOC 100% in the example of FIG. 2 ), the more deteriorated the state of the battery cells 21, the greater the overall thickness of the battery cells 21 and the greater the surface pressure of the battery cells 21. Note that in the example of FIG. 2 , the deterioration state and surface pressure are explained with the same SOC after charging, but when the surface pressure of the battery cells 21 after charging is the same, the SOC decreases as the state of deterioration of the battery cells 21 increases.

[0022] As described above, when a battery cell 21 in a highly deteriorated state is charged, the surface pressure of the battery cell 21 after charging increases. The surface pressure of the battery cell 21 after charging is determined by the thicknesses of the metallic lithium layer 21d and the deactivated LiM layer 21f. The remaining capacity of the battery cell 21 is determined by the metallic lithium layer 21d. Therefore, to estimate the deterioration state of the battery cell 21, it is advisable to calculate the amount of lithium in the metallic lithium layer (reversible lithium amount). The reversible lithium amount corresponds to the thickness of the metallic lithium layer 21d. In the battery system 1 of this embodiment, the reversible lithium amount, which is the amount of lithium that contributes to the charging and discharging of the battery cell 21, is calculated, and the deterioration state of the battery cell 21 is estimated based on the calculated reversible lithium amount.

[0023] The following describes the process of calculating / estimating the deterioration state of the battery cells 21 by the controller 10. The controller 10 has at least a calculation function for calculating the rate of change in the thickness (cell thickness) of the battery cells 21 (hereinafter also referred to as the "cell thickness change rate") and an estimation function for estimating the deterioration state of the battery cells 21. The cell thickness change rate indicates the amount of change in the thickness of the battery cells 21 per unit time. The controller 10 may have a function block (control unit) for executing various functions including the function of calculating the cell thickness change rate and the function of estimating the deterioration state. The controller 10 stores programs for realizing the various functions in memory and executes the programs to perform the calculation process and estimation process.

[0024] The controller 10 calculates the cell thickness change rate of the battery cell 21 after the end of charging or discharging based on the measured value of the displacement of the battery cell 21 thickness measured by the displacement sensor 60. The end of charging or discharging is, for example, the time from the end of charging or discharging until several seconds or several tens of seconds have passed. The cell thickness change rate will now be described with reference to Figs. 3 and 4. Fig. 3 is a graph showing the temporal characteristics of the thickness change after the end of charging of the battery cell 21. Fig. 4 shows the change rate of the thickness of the battery cell 21 immediately after charging (time t ０ From t １ 3 and 4, the horizontal axis represents time, and the vertical axis represents the change (amount of reduction) in cell thickness. The vertical axis represents the amount of reduction in cell thickness, based on the thickness of the battery cell 21 at the end of charging, with a larger value representing a larger reduction in cell thickness. Of graphs a to c, graph a represents the characteristics when the surface pressure is the highest, and graph c represents the characteristics when the surface pressure is the lowest.

[0025] As shown in Figure 3, after the battery cell 21 is charged to a high SOC, creep deformation causes creep strain, reducing the thickness of the battery cell 21. Because the battery cell 21 is subjected to pressure from the loading mechanism even after charging, creep deformation causes strain in the metallic lithium. The cell thickness decreases by the amount of this strain. Also, as shown in Figure 3, the higher the surface pressure, the greater the change in cell thickness after charging is completed. Furthermore, the cell thickness changes most significantly immediately after charging is completed, and then becomes constant over time (the change in cell thickness stabilizes).

[0026] Immediately after the end of charging, time t ０ From time t １ The cell thickness changes as shown in the graph in Figure 4. As with Figure 3, the greater the surface pressure, the greater the amount of cell thickness reduction, but the greater the surface pressure, the faster the rise in the graph (the rise in the change in cell thickness) from the end of charging. The dotted lines in graphs a to c correspond to the rate of change in cell thickness immediately after charging. The rate of change in cell thickness shown in graphs a to c is the amount of reduction in cell thickness per given time (unit time) from the end of charging. As shown by the dotted lines in graphs a to c, the greater the surface pressure, the greater the rate of change in cell thickness.

[0027] As shown in Fig. 2, a characteristic of the battery cell 21 after charging to a high SOC is that the higher the state of degradation, the greater the overall thickness of the battery cell 21 and the greater the surface pressure of the battery cell 21. As shown in Fig. 4, the cell thickness change rate has a correlation with the surface pressure of the battery cell 21. Therefore, by utilizing the correlation between the state of degradation of the battery cell 21 and the surface pressure of the battery cell 21 after charging, and between the cell thickness change rate and the surface pressure of the battery cell 21 after charging, the state of degradation can be estimated from the cell thickness change rate.

[0028] The controller 10 calculates the amount of reversible lithium in the battery cell 21 based on the cell temperature measured by the temperature sensor 40, the surface pressure measured by the load sensor 50, and the cell thickness change rate calculated by the calculation function. The controller 10 matches the cell voltage measured by the voltage sensor 30 with the voltage of the battery cell in its initial state, and compares the calculated amount of reversible lithium with the amount of reversible lithium in the battery cell in its initial state. The controller 10 then estimates the deterioration state of the battery cell 21 based on the comparison result of the amount of reversible lithium. The amount of reversible lithium is determined by the remaining capacity of the battery cell 21. Therefore, the deterioration state can be estimated by comparing the amount of reversible lithium in the battery cell 21 in its initial state with the amount of reversible lithium in the current battery cell 21 when a voltage condition is satisfied between the battery cell 21 in its initial state and the battery cell 21 after completion of charging or discharging. The voltage condition is that the voltage of the battery cell in its initial state corresponds to the cell voltage of the battery cell 21 after completion of charging or discharging. The voltages corresponding to each other may be in a state where the voltage difference is equal to or less than a predetermined voltage difference.

[0029] In the initial state of the battery cell 21, the reversible lithium amount is determined by the materials and battery structure used in the battery cell 21, and varies depending on the deterioration state of the battery cell 21. Furthermore, as the battery cell 21 deteriorates, the overall cell thickness or surface pressure of the battery cell 21 increases after charging, increasing the rate of cell thickness change. As described above, the change in cell thickness (or surface pressure) after charging is caused by creep deformation. When the metallic lithium layer is compressed in the perpendicular direction (the direction normal to the main surface of the battery cell 21), the rate of creep deformation is also proportional to the surface pressure and / or temperature. In this embodiment, utilizing these battery characteristics, the controller 10 calculates the reversible lithium amount of the battery cell 21 based on the cell temperature, surface pressure, and cell thickness change rate of the battery cell 21.

[0030] Specifically, the surface pressure and cell temperature at the end of charging or discharging, and the rate of change in cell thickness after charging or discharging are acquired in advance as experimental data for the battery cell 21. The experimental data is acquired for each target voltage (target SOC) for charging or discharging. The target voltage (target SOC) is the voltage (SOC) at the end of charging or discharging. The controller 10 may store the acquired experimental data as a table for calculating the amount of reversible lithium. The calculation table indicates the characteristics of the battery cell 21 using parameters, and the parameters are represented by the amount of reversible lithium, cell temperature, surface pressure, and rate of change in cell thickness. A table may also be prepared for each target voltage (target SOC).

[0031] The controller 10 charges or discharges the current battery cell 21 to a predetermined target voltage. At the end of charging or discharging, the controller 10 acquires measured values ​​of the cell temperature and surface pressure from the temperature sensor 40 and the load sensor 50. The controller 10 extracts a table corresponding to the target voltage. This matches the cell voltage at the end of charging or discharging with the voltage in the referenced table, thereby making the voltage conditions the same. After charging is completed, the controller 10 calculates the cell thickness change rate using the measured value of the displacement sensor 60. The controller 10 references the extracted table and calculates the reversible lithium amount by identifying on the table the reversible lithium amount corresponding to the cell temperature at the end of charging, the surface pressure at the end of charging, and the cell thickness change rate after charging.

[0032] The controller 10 compares the reversible lithium amount of the battery cell 21 in the initial state with the calculated reversible lithium amount. When making the comparison, the voltage conditions of the battery cell 21 in the initial state and the current battery cell 21 are matched (considered to be the same). The controller 10 then estimates the degradation state of the current battery cell 21 from the amount of decrease in the reversible lithium amount of the current battery cell 21 relative to the amount of reversible lithium of the battery cell 21 in the initial state. The controller 10 is not limited to the amount of decrease in the reversible lithium amount, and may instead use the rate of decrease.

[0033] Next, a degradation state estimation method according to this embodiment will be described. Fig. 5 is a flowchart showing the procedure of the degradation state estimation method. The following control flow is executed when charging or discharging of the battery cell 21 is completed.

[0034] First, in step S1, the temperature sensor 40, the load sensor 50, and the displacement sensor 60 measure the cell temperature, the surface pressure of the battery cell 21, and the displacement of the battery cell 21 while a load is applied to the battery cell 21 by the loading mechanism. The controller 10 acquires the measured values ​​of each sensor. In step S2, the controller 10 measures the cell voltage at the end of charging or discharging using the voltage sensor 30. In step S3, the controller 10 calculates the cell thickness change rate after the end of charging or discharging of the battery cell 21 based on the measured displacement of the battery cell 21. In step S4, the controller 10 calculates the reversible lithium amount of the battery cell 21 based on the cell temperature, the surface pressure, and the cell thickness change rate. In step S5, the controller 10 compares the reversible lithium amount of the battery cell in the initial state with the calculated reversible lithium amount while matching the cell voltage measured in the control process of step S2 with the voltage conditions, and estimates the deterioration state of the battery cell 21 from the comparison result. Then, the controller 10 ends the control flow shown in FIG.

[0035] As described above, the battery system or degradation state estimation method according to this embodiment calculates the cell thickness change rate after the end of charging or discharging of the battery cell 21 based on the measured displacement of the battery cell 21, calculates the amount of reversible lithium in the battery cell 21 based on the cell temperature, surface pressure, and cell thickness change rate, compares the amount of reversible lithium in the battery cell 21 in the initial state with the calculated amount of reversible lithium while matching the cell voltage measured by the voltage sensor 30 with the voltage conditions, and estimates the degradation state of the battery cell 21 from the comparison result. This makes it possible to estimate the degradation state at any voltage. Furthermore, the degradation state can be estimated in a short time.

[0036] Incidentally, as a characteristic of a battery cell 21 after charging to a high SOC, the higher the state of degradation, the greater the overall thickness of the battery cell 21 and the greater the surface pressure of the battery cell 21 (see FIG. 2 ). Therefore, one method for estimating the state of degradation is to estimate the thickness or surface pressure after charging. However, the thickness or surface pressure of the battery cell 21 also fluctuates due to creep deformation of lithium metal. During charging of the battery cell 21, the surface pressure of the battery cell 21 increases over the charging time, reaches a peak at the end of charging, and then decreases over time after charging ends. It may take several hours for the surface pressure to stabilize after charging ends. In other words, the method of estimating the state of degradation based on the thickness or surface pressure after charging ends requires a long time to estimate the state of degradation.

[0037] On the other hand, in this embodiment, the deterioration state is estimated from the rate of change of cell thickness, and since the rate of change of cell thickness can be calculated in a short time from the end of charging or discharging, the deterioration state can also be estimated in a short time.

[0038] In this embodiment, the controller 10 may estimate the state of degradation when the cell voltage of the battery cell 21 at the end of charging or discharging is equal to or greater than a predetermined voltage threshold. In the control flow shown in FIG. 5 , the controller 10 first executes the control flow for measuring the cell voltage (the control flow of step S2), and if the measured cell voltage is equal to or greater than the predetermined voltage threshold, executes the control flow of steps S1, S3, and S5. Alternatively, if the measured cell voltage is less than the predetermined voltage threshold, the controller 10 may terminate the control flow without executing the control flow of steps S1, S3, and S5. That is, the controller 10 avoids estimating the state of degradation when the voltage (SOC) is low at the end of charging or discharging, and instead estimates the state of degradation when the voltage (SOC) is high. When the metallic lithium layer is thick (i.e., when the SOC is high), the cell thickness change rate increases, improving the accuracy of the state of degradation estimation and enabling estimation in a short time.

[0039] In this embodiment, the controller 10 may also estimate the state of deterioration when the battery cell 21 is in a fully charged state. For example, when the battery cell 21 is charged with the target voltage of the battery cell 21 set to the fully charged voltage, the controller 10 may execute the control flow of steps S1 and S3 to S5 of the control flow shown in Fig. 5 without executing the control flow for measuring the cell voltage (the control flow of step S2). This allows the state of deterioration to be estimated without measuring the cell voltage at the end of charging or discharging.

[0040] In this embodiment, the controller 10 may estimate the state of degradation when the cell temperature at the end of charging or discharging of the battery cell is equal to or higher than a predetermined temperature threshold. For example, the controller 10 may execute a control flow (step S1) for measuring the cell temperature, and if the measured cell temperature is equal to or higher than the predetermined temperature threshold, execute the control flow of steps S2 to S5. Alternatively, if the measured cell temperature is lower than the predetermined temperature threshold, the controller 10 may end the control flow without executing the control flow of steps S2 to S5. The temperature threshold is a preset threshold, and is set to, for example, the lower limit of the usable temperature of the battery cell 21. Because the cell thickness change rate also varies depending on the cell temperature, it is preferable to use the same cell temperature when estimating the state of degradation. That is, the controller 10 avoids estimating the state of degradation when the cell temperature is low at the end of charging or discharging, and instead estimates the state of degradation when the cell temperature is high. As a result, the cell thickness change rate increases when the cell temperature is high, improving the accuracy of the state of degradation estimation and enabling estimation in a short time.

[0041] Furthermore, in this embodiment, the controller 10 calculates the cell thickness change rate based on the measured value of the displacement of the battery cell 21 measured by the displacement sensor 60 within a predetermined time from the end of charging or discharging of the battery cell 21. As a result, the cell thickness change rate increases immediately after the end of charging or discharging, improving the accuracy of estimating the degradation state and enabling estimation in a short time.

[0042] The control flow shown in FIG. 5 is an example, and the controller 10 does not necessarily have to execute all of the control flow, and does not necessarily have to execute the control flow in the order shown in FIG.

[0043] REFERENCE SIGNS LIST 1... battery system 2... battery module 10... controller 22 to 24... fixing plate 25... elastic body 30... voltage sensor 40... temperature sensor 50... load sensor 60... displacement sensor

Claims

1. A battery cell having a solid electrolyte and a lithium-containing negative electrode, A load mechanism for applying a load to the aforementioned battery cell, A measuring unit for measuring the cell voltage of the battery cell, the cell temperature of the battery cell, the surface pressure of the battery cell, and the thickness displacement of the battery cell, The system includes an estimation device for estimating the degradation state of the battery cell, The measurement unit measures the cell voltage at the end of charging or discharging of the battery cell. The estimation device is, Based on the measured displacement of the battery cell, the cell thickness change rate, which indicates the rate of change in the thickness of the battery cell after charging or discharging is completed, is calculated. Based on the cell temperature, surface pressure, and cell thickness change rate, the reversible lithium amount of the battery cell is calculated. The cell voltage measured by the measurement unit is correlated with the voltage of the battery cell in its initial state, and the reversible lithium amount of the battery cell in its initial state is compared with the calculated reversible lithium amount. A battery system that estimates the degradation state of the battery cells based on the comparison results.

2. In the battery system according to claim 1, The estimation device is a battery system that estimates the degradation state when the cell voltage at the end of charging or discharging is above a predetermined voltage threshold.

3. In the battery system according to claim 1, The estimation device is a battery system that estimates the degradation state when the battery cell is fully charged.

4. In the battery system according to any one of claims 1 to 3, The estimation device is a battery system that estimates the degradation state when the cell temperature at the end of charging or discharging of the battery cell is above a predetermined temperature threshold.

5. In the battery system according to any one of claims 1 to 3, The estimation device is, A battery system that calculates the cell thickness change rate based on the measured value of the displacement of the battery cell, which is measured by the measuring unit within a predetermined time from the end of charging or discharging of the battery cell.

6. In a degradation state estimation method for estimating the degradation state of a battery cell having a solid electrolyte and a lithium-containing negative electrode, With a load applied to the battery cell by the load mechanism, the cell temperature, surface pressure, and displacement of the battery cell are measured. The cell voltage of the aforementioned battery cell is measured at the end of charging or discharging of the aforementioned battery cell. Based on the measured displacement of the battery cell, the cell thickness change rate, which indicates the rate of change in the thickness of the battery cell after the end of charging or discharging of the battery cell, is calculated. Based on the cell temperature, surface pressure, and cell thickness change rate, the reversible lithium amount of the battery cell is calculated. A method for estimating the degradation state of a battery cell, which involves comparing the initial state of the reversible lithium amount of the battery cell with the calculated reversible lithium amount, while the measured cell voltage and voltage conditions are associated, and estimating the degradation state of the battery cell from the comparison result.

Images