Battery management device, battery management method, and program

Abstract

To provide a battery management device, a battery management method, and a control program that enable efficient and low-cost charging of lithium-ion secondary batteries. [Solution] The battery management device according to this disclosure includes a high-frequency signal supply unit that applies a high-frequency signal of 0.1 MHz or higher to a first battery cell having a low battery temperature among a plurality of battery cells constituting a lithium-ion secondary battery; an impedance detection unit that detects the actual AC impedance of the first battery cell to which the high-frequency signal has been applied; and a determination unit that determines whether or not Li has been deposited in the lithium-ion secondary battery based on the actual AC impedance of the first battery cell.

Description

Technical Field

[0001] The present disclosure relates to a battery management device, a battery management method, and a program.

Background Art

[0002] In order to prevent deterioration of the performance of a lithium-ion secondary battery, it is required to suppress the precipitation of metallic Li (lithium) in the lithium-ion secondary battery (hereinafter referred to as Li precipitation). However, a method for non-destructively detecting Li precipitation in a lithium-ion secondary battery has not been known.

[0003] On the other hand, as disclosed in Patent Document 1, the inventors have developed a method for detecting the real part of the AC impedance of a lithium-ion secondary battery using a high-frequency signal and calculating the amount of Li precipitation in the lithium-ion secondary battery based on the difference between the current value and the initial value of the real part of the AC impedance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, since Li precipitation progresses as the charging power increases, an allowable charging power is set for each type of lithium-ion secondary battery from the viewpoint of suppressing Li precipitation. Here, the progress rate of Li precipitation in a lithium-ion secondary battery has variations (for example, standard deviation σ) for each individual product even within the same type. In conventional lithium-ion secondary batteries, for example, the allowable charging power for each type has been set (fixed) too low so that Li precipitation does not progress in products included in the range of ±6σ, resulting in a problem of longer charging time.

[0006] Therefore, the inventors developed a method to reduce the allowable charging power depending on the presence or absence of Li deposition detected using the method disclosed in Patent Document 1. This method allows the allowable charging power at the start of use to be set high enough to prevent Li deposition from progressing, and also shortens the charging time.

[0007] However, if a circuit is provided to apply a high-frequency signal to each of the multiple battery cells that make up a lithium-ion secondary battery, the number of circuits and the cost will increase.

[0008] This disclosure is made in view of the above background and aims to provide a battery management device, a battery management method, and a control program that can achieve efficient charging of lithium-ion secondary batteries at low cost. [Means for solving the problem]

[0009] The battery management device according to this disclosure includes a high-frequency signal supply unit that applies a high-frequency signal of 0.1 MHz or higher to a first battery cell having a low battery temperature among a plurality of battery cells constituting a lithium-ion secondary battery; an impedance detection unit that detects the actual AC impedance of the first battery cell to which the high-frequency signal is applied; and a determination unit that determines whether or not Li has been deposited in the lithium-ion secondary battery based on the actual AC impedance of the first battery cell.

[0010] The battery management method according to this disclosure involves applying a high-frequency signal of 0.1 MHz or higher to a first battery cell having a low battery temperature among a plurality of battery cells constituting a lithium-ion secondary battery, detecting the real portion of the AC impedance of the first battery cell to which the high-frequency signal is applied, and determining whether or not Li has been deposited in the lithium-ion secondary battery based on the real portion of the AC impedance of the first battery cell.

[0011] The program according to this disclosure causes a computer to perform the following processes: applying a high-frequency signal with a frequency of 0.1 MHz or higher to a first battery cell having a low battery temperature among a plurality of battery cells constituting a lithium-ion secondary battery; detecting the real part of the AC impedance of the first battery cell to which the high-frequency signal is applied; and determining whether or not Li has been deposited in the lithium-ion secondary battery based on the real part of the AC impedance of the first battery cell. [Effects of the Invention]

[0012] This disclosure provides a battery management device, a battery management method, and a control program that enable efficient charging of lithium-ion secondary batteries. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram showing an example configuration of the battery management system related to this disclosure. [Figure 2] This figure shows the relationship between the State of Health (SOH) of a secondary battery and the change in the real part Z of the AC impedance when a 1 MHz high-frequency signal is supplied to the secondary battery. [Figure 3] This diagram shows the relationship between the frequency of the AC signal supplied to the secondary battery and the real part of the AC impedance detected from the secondary battery. [Figure 4] This diagram shows the relationship between the frequency of the AC signal supplied to the secondary battery and the real part of the AC impedance detected from the secondary battery. [Figure 5] This is a flowchart illustrating the operation of the battery management device related to this disclosure. [Figure 6] This is a block diagram showing an example configuration of the battery management system related to this disclosure. [Figure 7] This is a block diagram showing an example configuration of the battery management system related to this disclosure. [Figure 8] This is a flowchart illustrating the operation of the battery management device related to this disclosure. [Figure 9] This is a block diagram showing an example configuration of the battery management system related to this disclosure.

Mode for Carrying Out the Invention

[0014] Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings are simplified as appropriate.

[0015] <Embodiment 1> FIG. 1 is a block diagram showing a configuration example of a battery management system 1 according to Embodiment 1. As shown in FIG. 1, the battery management system 1 includes a battery management device 10 and a secondary battery 20 managed by the battery management device 10.

[0016] The secondary battery 20 is a lithium-ion secondary battery and is composed of a cell stack composed of a plurality of stacked battery cells and a case for housing the cell stack.

[0017] Each battery cell includes a positive electrode, a negative electrode, and an ion transmission medium provided between the positive electrode and the negative electrode for conducting carrier ions. A separator may be further provided between the positive electrode and the negative electrode. Resins such as polyethylene and polypropylene are used for the separator.

[0018] For the positive electrode active material, for example, sulfides containing transition metal elements, oxides containing lithium and transition metal elements, etc. are used. Specifically, for the positive electrode active material, the basic composition formula is Li (1-x) MnO2 (where 0 < x < 1) or Li (1-x) Mn2O4 and other lithium manganese composite oxides, the basic composition formula is Li (1-x) CoO2 and other lithium cobalt composite oxides, the basic composition formula is Li (1-x) NiO2 and other lithium nickel composite oxides, or the basic composition formula is Li (1-x) Ni a Co b Mn cLithium nickel cobalt manganese composite oxides such as O2 (where a+b+c=1) are used. Note that the positive electrode active material may include other elements in addition to the basic composition formula described above. For the positive electrode current collector, for example, aluminum (Al) is used.

[0019] For example, composite oxides containing lithium or carbon materials are used as the negative electrode active material. Specifically, the negative electrode active material may be an inorganic compound such as lithium, lithium alloys, or tin compounds, a carbon material capable of intercalating and deintercalating lithium ions, a composite oxide containing multiple elements, or a conductive polymer. Examples of carbon materials used for the negative electrode active material include coke, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, or carbon fibers, but graphites such as artificial graphite or natural graphite are preferred. Examples of composite oxides used for the negative electrode active material include lithium titanium composite oxide and lithium vanadium composite oxide. For the current collector of the negative electrode, for example, Cu (copper) is used.

[0020] The ion-conducting medium is used as an electrolyte, for example, by dissolving a supporting salt. Lithium salts such as LiPF6 and LiBF4 are used as supporting salts. The solvent for the electrolyte is one or a mixture of several of the following: carbonates, esters, ethers, nitriles, furans, sulforanes, and dioxolanes. Examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, and linear carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate. Alternatively, the ion-conducting medium may be a solid ion-conducting polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound together by an organic binder.

[0021] The battery management device 10 manages the charging of the secondary battery 20 under management. For example, the battery management device 10 non-destructively detects the presence or absence of Li deposition in the secondary battery 20 and provides feedback control of the allowable charging power (upper limit of charging power) Pa for the secondary battery 20 based on the detection result.

[0022] The battery management device 10 comprises a high-frequency signal supply unit 11, an impedance detection unit 12, a determination unit 13, a control unit 14, and a storage unit 15.

[0023] The high-frequency signal supply unit 11 supplies a high-frequency signal to a first battery cell among the multiple battery cells constituting the secondary battery 20. The first cell has the lowest battery temperature among the multiple battery cells constituting the secondary battery 20. For example, the battery temperature of the first cell may be the lowest among the battery temperatures of the multiple battery cells. The battery temperature of the first cell may be lower than the representative value (e.g., mean, median) of the battery temperatures of the multiple battery cells.

[0024] The first battery cell may be predetermined by experiment or simulation. For example, from the standpoint of heat dissipation, the battery temperature of the outer battery cell closer to the case may be lower. Also, the battery temperature of the battery cell located away from heat sources in the environment where the secondary battery 20 is placed, or heat sources inside the case of the secondary battery 20, may be lower. The secondary battery 20 can be used in vehicle drive systems, household energy supply systems, and the like.

[0025] Incidentally, in the secondary battery 20, metallic Li is deposited on the electrode surface of each battery cell as charging is repeated. Li deposition progresses as the charging power is increased to speed up the charging process, degrading the State of Health (SOH) of the secondary battery 20. The SOH of the secondary battery 20 is the ratio of the current capacity to the initial capacity of the secondary battery 20, which is set to 100%. Therefore, it is desirable to set the allowable charging power Pa of the secondary battery 20 to be as high as possible, which allows for efficient charging in the shortest possible charging time while suppressing Li deposition.

[0026] Here, if an AC signal (high-frequency signal) with a frequency too high for the diffusion, reaction, and movement of lithium ions in each cell of the secondary battery 20 is supplied to the secondary battery 20, the current of the high-frequency signal flows along the edges of the conductors of each cell due to the skin effect. In other words, the current of the high-frequency signal flows along the electrode surface of each cell where Li is easily deposited due to the skin effect. Furthermore, even when the Li metal is electrically disconnected from the negative electrode and becomes a floating state after Li deposition, current flows over the Li metal due to inductive coupling and electric field coupling. Therefore, the value of the real part Z of the AC impedance does not change when no Li is deposited compared to the initial state, and as the amount of Li deposition increases, the electrical conductivity of the electrode surface of each cell increases, so the value of the real part Z of the AC impedance decreases. Here, since a lot of current concentrates in the highly conductive Li metal, the magnetic field changes around the Li deposition region, and eddy currents are generated as a result. These eddy currents cause losses in the current collector foil and the conductive parts of the electrodes, but reduce the overall loss of the battery. Therefore, as the amount of Li deposited increases, the change in the magnetic field becomes larger, and consequently the eddy currents increase, resulting in a smaller value for the real part Z. For this reason, the amount of Li deposited in the secondary battery 20 can be calculated from the value of the real part Z of the AC impedance detected from the secondary battery 20 to which a high-frequency signal is supplied. Once the amount of Li deposited is known, it is also possible to estimate the SOH of the secondary battery 20.

[0027] Figure 2 shows the relationship between the State of Health (SOH) of the secondary battery 20 and the change in the real part Z of the AC impedance (the difference between the detected value and the initial value) when a 1 MHz high-frequency signal is supplied to the secondary battery 20. As indicated by the triangles in Figure 2, in the case of normal charging with low charging power, even if charging is repeated, the amount of Li deposition is small, so even if the deterioration of SOH progresses due to other factors, the change in the real part Z of the AC impedance remains small (i.e., the detected value of the real part Z of the AC impedance is maintained at a high value). In contrast, as indicated by the circles in Figure 2, in the case of rapid charging with high charging power, the amount of Li deposition increases with repeated charging, and consequently, the deterioration of SOH progresses, and the change in the real part Z of the AC impedance becomes large (i.e., the detected value of the real part Z of the AC impedance becomes low). Note that if battery degradation due to Li deposition is the dominant factor among the factors of battery degradation, the amount of Li deposition can be derived from SOH. Alternatively, SOH can be derived from the amount of Li deposition.

[0028] Figures 3 and 4 show the relationship between the frequency of the AC signal supplied to the secondary battery 20 and the real part of the AC impedance detected from the secondary battery 20. Figure 3 shows the value of the real part Z of the AC impedance when an AC signal from 1 kHz to 100 kHz is supplied to the secondary battery 20. Figure 4 shows the value of the real part Z of the AC impedance when an AC signal from 100 kHz to 100 MHz is supplied to the secondary battery 20.

[0029] As shown in Figure 3, when an AC signal near 1 kHz is supplied to the secondary battery 20, the real part Z of the AC impedance is at its minimum value. The impedance component at this time represents the ohmic resistance component. Furthermore, as shown in Figures 3 and 4, as the frequency of the AC signal supplied to the secondary battery 20 increases, the real part Z of the AC impedance increases because the current flow concentrates on the electrode surface of each cell due to the skin effect.

[0030] Therefore, the high-frequency signal supply unit 11 supplies a high-frequency AC signal (i.e., a high-frequency signal) to the secondary battery 20 such that a value of the real part Z of the AC impedance is detected that is sufficiently high compared to the ohmic resistance component. For example, the high-frequency signal supply unit 11 supplies a high-frequency signal of 0.1 MHz or higher to the secondary battery 20. In the examples of Figures 3 and 4, the high-frequency signal supply unit 11 supplies a high-frequency signal of 0.5 MHz or higher to the secondary battery 20. As a result, the current of the high-frequency signal flows through the electrode surface (Li deposition region) of each battery cell of the secondary battery 20 due to the skin effect. As a result, the impedance detection unit 12 can detect the real part Z of the AC impedance according to the amount of Li deposition.

[0031] The determination unit 13 determines whether or not Li has been deposited in the first battery cell of the secondary battery 20 based on the value of the real part Z of the AC impedance detected by the impedance detection unit 12. More specifically, the determination unit 13 determines whether or not Li has been deposited in the secondary battery 20 based on the difference between the current value of the real part Z of the AC impedance detected by the impedance detection unit 12 and the initial value of the real part Z of the AC impedance of the secondary battery 20. Information on the initial value of the real part Z of the AC impedance of the secondary battery 20 being managed is stored, for example, in the storage unit 15. The determination unit 13 may, for example, subtract the value of the real part Z of the AC impedance from the initial value, and if the subtraction result is greater than a threshold, it may determine that Li has been deposited in the secondary battery 20. The determination unit 13 may also perform other calculations (for example, calculation of a ratio) other than subtraction on the initial value and the real part Z of the AC impedance.

[0032] The memory unit 15 may also store information about the initial value of the real part Z of the AC impedance for each type of secondary battery. The initial value of the real part Z of the AC impedance may be updated during operation of the secondary battery 20. The memory unit 15 may include memory such as RAM (Random Access Memory).

[0033] The control unit 14 controls the allowable charging power Pa for the secondary battery 20 based on the determination result from the determination unit 13. For example, if the control unit 14 determines that no Li has been deposited, it maintains the allowable charging power Pa at its current level or controls it to be higher, since the progression of Li deposition is being suppressed. If the control unit 14 determines that Li has been deposited, it controls the allowable charging power Pa to be lowered, as it is necessary to suppress the progression of Li deposition. The control unit 14 may also switch the allowable charging power Pa in stages depending on the determination result of whether or not Li deposition has occurred.

[0034] As a result, the battery management device 10 according to this disclosure can set the highest possible allowable charging power Pa for the secondary battery 20, enabling efficient charging in the shortest possible charging time while suppressing Li deposition. In other words, the battery management device 10 according to this disclosure can set the allowable charging power Pa for the secondary battery 20 to an appropriate value according to the amount of Li deposition, without setting it excessively low, thereby enabling efficient charging of the secondary battery 20.

[0035] The functions of the determination unit 13 and the control unit 14 may be realized, for example, by loading a program into memory and having the processor execute it. Alternatively, the determination unit 13 and the control unit 14 may be realized by hardware such as semiconductor chips or electronic circuits. At least a portion of the high-frequency signal supply unit 11 and the impedance detection unit 12 may be composed of electronic circuits such as resonant circuits or peak hold circuits. However, a portion of the functions of the high-frequency signal supply unit 11 and the impedance detection unit 12 may be performed by the processor. For example, the processor may apply a high-frequency signal to the first battery cell and detect the actual AC impedance of the first battery cell by transmitting control signals to the electronic circuits constituting the high-frequency signal supply unit 11 and the impedance detection unit 12.

[0036] When Li is deposited in the secondary battery 20, it is thought that Li is deposited sequentially starting from the battery cells with relatively lower battery temperatures. The battery management device 10 controls the allowable charging power Pa based on the real part Z of the AC impedance of the first battery cell, thereby reducing the number and cost of circuits required for efficient charging.

[0037] (Operation of battery management device 10) Next, an example of the operation of the battery management device 10 will be explained using Figure 5. Figure 5 is a flowchart showing the operation of the battery management device 10.

[0038] First, the battery management device 10 supplies the first battery cells of the secondary battery 20 with an AC signal (high-frequency signal) of such a high frequency that the diffusion, reaction, and movement of lithium ions in each battery cell cannot keep up (step S101). For example, the battery management device 10 supplies the secondary battery 20 with a high-frequency signal of 0.1 MHz or higher. Then, the battery management device 10 detects the value of the real part Z of the AC impedance from the secondary battery 20 to which the high-frequency signal has been supplied (step S102).

[0039] Subsequently, the battery management device 10 determines whether or not Li has been deposited in the first battery cell of the secondary battery 20 based on the value of the real part Z of the detected AC impedance (step S103). Basically, the battery management device 10 determines that Li has been deposited in the first battery cell if the value of the real part Z of the detected AC impedance is smaller than the initial value.

[0040] If Li is deposited in the first battery cell (YES in step S103), the battery management device 10 needs to suppress the progression of Li deposition, so it controls the allowable charging power Pa to be lowered (step S104). If Li is not deposited in the first battery cell (NO in step S103), the battery management device 10 maintains the allowable charging power Pa as it is because the progression of Li deposition is suppressed. Alternatively, the battery management device 10 may control the allowable charging power Pa to be higher.

[0041] Thus, the battery management device 10 according to this disclosure can set the highest possible allowable charging power Pa for the secondary battery 20, enabling efficient charging in the shortest possible charging time while suppressing Li deposition. Since the battery management device 10 can perform charging control based on the real part Z of the AC impedance of a single battery cell, it can reduce the process of detecting the real part Z of the AC impedance of each of multiple battery cells.

[0042] <Modification 1 of Embodiment 1> Figure 6 is a block diagram showing an example configuration of the battery management system 1 according to a modified example 1 of Embodiment 1. Comparing Figure 1 and Figure 6, the battery management device 10 shown in Figure 6 further includes a temperature detection unit 16 and a multiplexer 17. The function of the temperature detection unit 16 may be realized by a processor executing a program, or it may be realized by hardware such as a semiconductor chip or electronic circuit.

[0043] The temperature detection unit 16 detects the battery temperature of each battery cell of the secondary battery 20. For example, the temperature detection unit 16 detects the battery temperature of one or more battery cells among the multiple battery cells constituting the secondary battery 20 using one or more thermistors T1. The temperature detection unit 16 also calculates the resistance value of each of the multiple battery cells from the cell voltage of each of the multiple battery cells. Then, the temperature detection unit 16 calculates the difference between the heat generated by each of the multiple battery cells and the heat generated by the battery cell to which the thermistor T1 is attached, from the difference between the calculated resistance value of each of the multiple battery cells and the resistance value of the battery cell to which the thermistor T1 is attached, and estimates the battery temperature of each of the multiple battery cells from the calculation result. A thermistor T1 may be attached to each of the multiple battery cells, and the temperature detection unit 16 may detect the battery temperature measured using the thermistor T1.

[0044] The temperature detection unit 16 sets the battery cell with the lowest battery temperature as the first battery cell based on the battery temperature of each battery cell. The first battery cell may be a battery cell with a relatively low battery temperature among the battery cells to which thermistor T1 is attached. Thermistor T1 does not need to be attached to all battery cells that make up the secondary battery 20. The temperature detection unit 16 may output a selection signal to the multiplexer 17 corresponding to the battery cell set as the first battery cell.

[0045] The multiplexer 17 switches the battery cells connected to the high-frequency signal supply unit 11 and the impedance detection unit 12 from among the multiple battery cells constituting the secondary battery 20. The multiple battery cells in the secondary battery 20 may be connected in series with each other, or in parallel with each other. The multiple battery cells may be connected in both series and parallel. The multiplexer 17 may connect the battery cell corresponding to the selection signal received from the temperature detection unit 16, i.e., the first battery cell, to the high-frequency signal supply unit 11 and the impedance detection unit 12. Note that if the high-frequency signal supply unit 11 is configured to supply high-frequency signals to multiple battery cells, only the battery cell connected to the impedance detection unit 12 may be switched.

[0046] Referring again to Figure 5, the modified battery management device 10 of Embodiment 1, for example, sets a first battery cell based on the battery temperature of each battery cell and switches the connection destination of the high-frequency signal supply unit 11 and the impedance detection unit 12 before step S101.

[0047] According to a modified version of Embodiment 1, the first battery cell can be appropriately configured, and the accuracy of determining whether or not Li deposition is present can be improved.

[0048] <Embodiment 2> Figure 7 is a block diagram showing an example configuration of the battery management system 1a according to Embodiment 2. Comparing Figure 1 and Figure 7, the battery management device 10 has been replaced by the battery management device 10a. In the battery management device 10a, the high-frequency signal supply unit 11 has been replaced by the high-frequency signal supply unit 11a, the impedance detection unit 12 has been replaced by the impedance detection unit 12a, and the determination unit 13 has been replaced by the determination unit 13a. The battery management device 10a also includes a temperature detection unit 16, which has already been described with reference to Figure 6.

[0049] The secondary battery 20 comprises multiple battery cells, including the first battery cell described above and a second battery cell having a higher battery temperature than the first battery cell. The first and second battery cells may be pre-set according to the results of simulations or experiments. Alternatively, the first and second battery cells may be set based on measurement results from thermistor T1.

[0050] The high-frequency signal supply unit 11a includes high-frequency signal supply units 111 and 112. High-frequency signal supply unit 111 applies a high-frequency signal to the first battery cell, and high-frequency signal supply unit 112 applies a high-frequency signal to the second battery cell. Alternatively, one high-frequency signal supply unit 11 may be configured to supply high-frequency signals to both the first and second battery cells.

[0051] The impedance detection unit 12a includes impedance detection units 121 and 122. The impedance detection unit 121 detects the actual part Z1 of the AC impedance of the first battery cell, and the impedance detection unit 122 detects the actual part Z2 of the AC impedance of the second battery cell.

[0052] The determination unit 13a determines whether or not Li has been deposited in the secondary battery 20 based on the actual part Z1 of the AC impedance of the first battery cell and the actual part Z2 of the AC impedance of the second battery cell. The following describes the flow of the determination method by the determination unit 13a.

[0053] After detecting the real part Z1 of the AC impedance of the first battery cell, the determination unit 13a stores the degree of change (e.g., decrease, increase) of the real part Z1 of the AC impedance from its initial value in the storage unit 15, corresponding to the battery temperature of the first battery cell. This allows the determination unit 13a to generate first impedance information indicating the degree of change (also referred to as the first degree of change) of the real part Z1 of the AC impedance for each battery temperature of the first battery cell. In a similar manner, the determination unit 13a can generate second impedance information indicating the degree of change (also referred to as the second degree of change) of the real part Z2 of the AC impedance from its initial value for each battery temperature of the second battery cell. If the values ​​of the real parts Z1 and Z2 of the AC impedance are smaller than their initial values, the absolute values ​​of the first and second degrees of change are also referred to as the first and second decreases, respectively. If the values ​​of the real parts Z1 and Z2 of the AC impedance are larger than their initial values, the first and second degrees of change are also referred to as the first and second increases, respectively.

[0054] The initial value of the real part Z1 of the AC impedance may be the same as or different from the initial value of the real part Z2 of the AC impedance. The initial values ​​of the real parts Z1 and Z2 of the AC impedance may be stored in the memory unit 15. The initial values ​​may be stored for each battery temperature, or an initial value that is independent of the battery temperature may be stored. The values ​​of the real parts Z1 and Z2 of the AC impedance may be larger or smaller than the initial value that is independent of the battery temperature.

[0055] The determination unit 13a refers to the first impedance information and the second impedance information and determines whether or not Li has precipitated in the secondary battery 20 based on the first and second degrees of change detected at the same battery temperature. Specifically, the determination unit 13a may determine that Li has precipitated in the secondary battery 20 if the first degree of decrease is greater than the second degree of decrease, or if the first degree of increase is less than the second degree of increase. The determination unit 13a may also determine that Li has precipitated if the first degree of decrease at one battery temperature is greater than the second degree of decrease, or if the first degree of increase at one battery temperature is less than the second degree of increase. The determination unit 13a may also determine that Li has precipitated if the first degree of decrease tends to be greater than the second degree of decrease at multiple battery temperatures, or if the first degree of increase tends to be less than the second degree of increase at multiple battery temperatures. The case where the first degree of decline is greater than the second degree of decline includes the case where the first degree of decline is greater than or equal to a threshold value than the second degree of decline. The case where the first degree of increase is less than the second degree of increase includes the case where the second degree of increase is greater than or equal to a threshold value than the first degree of decline.

[0056] To elaborate, the ease with which Li precipitates may depend on the state of the secondary battery 20, and the battery management device 10a improves the accuracy of determining whether or not Li precipitates by comparing the actual values ​​Z1 and Z2 of the AC impedance. This also reduces the influence of errors in the impedance detection unit 12. However, since the values ​​of AC impedance Z1 and Z2 also depend on the battery temperature, the determination unit 13a makes its determination based on the actual values ​​Z1 and Z2 of the AC impedance at the same battery temperature. At one point in time, the battery temperature of the first battery cell is lower than the battery temperature of the second battery cell, but since the battery temperatures of the first and second battery cells change over time during the operation of the secondary battery 20, the battery temperatures of the first and second battery cells may be the same at different points in time.

[0057] The control unit 14 controls the allowable charging power Pa for the secondary battery 20 based on the determination result from the determination unit 13a, similar to the first embodiment.

[0058] The battery management device 10a can improve the accuracy of determining whether or not Li deposition is present by using the real part Z of the AC impedance of two battery cells. Furthermore, if the number of battery cells constituting the secondary battery 20 is three or more, it may be possible to reduce the number of electronic circuits constituting the impedance detection unit 12.

[0059] (Operation of battery management device 10a) Next, an example of the operation of the battery management device 10a will be explained using Figure 8. Figure 8 is a flowchart showing the operation of the battery management device 10a.

[0060] First, the battery management device 10a generates first impedance information based on the value of the real part Z1 of the AC impedance of the first battery cell (step S201). Similarly, the battery management device 10a generates second impedance information based on the value of the real part Z2 of the AC impedance of the second battery cell (step S202). The order of steps S201 and S202 may be reversed.

[0061] Next, the battery management device 10a determines whether or not Li has deposited in the secondary battery 20 based on the first impedance information generated in step S201 and the second impedance information generated in step S202 (step S203). Step S204 is the same as step S104 in Figure 5, so its explanation is omitted.

[0062] Thus, the battery management device 10 according to this disclosure can improve the accuracy of determining whether or not Li deposition is present, and further improve the charging efficiency of the secondary battery 20.

[0063] <Modification 1 of Embodiment 2> Similar to the first modification of Embodiment 1, the battery management device 10a may set the first and second battery cells using the measurement results of the thermistor T1. The battery management device 10a may also include both a multiplexer for switching the connection destination of the high-frequency signal supply unit 111 and the impedance detection unit 121 between multiple cells, and a multiplexer for switching the connection destination of the high-frequency signal supply unit 112 and the impedance detection unit 122 between multiple cells.

[0064] According to Modification 1 of Embodiment 2, the first battery cell and the second battery cell can be appropriately set, and the presence or absence of Li deposition can be determined with high accuracy.

[0065] <Modification 2 of Embodiment 2> Figure 9 is a block diagram showing an example configuration of a battery management system according to a modified example 2 of Embodiment 2. Comparing Figure 7 and Figure 9, the two high-frequency signal supply units 111 and 112 are replaced by one high-frequency signal supply unit 11, and the two impedance detection units 121 and 122 are replaced by one impedance detection unit 12. Furthermore, the battery management device 10a shown in Figure 9 further includes a multiplexer 17.

[0066] The multiplexer 17 switches the connection destination of the high-frequency signal supply unit 11 and the impedance detection unit 12 between the first battery cell and the second battery cell. If the high-frequency signal supply unit 11 is configured to apply a high-frequency signal to multiple battery cells, only the connection destination of the impedance detection unit 12 may be switched.

[0067] In the modified example 2 of Embodiment 2, the number of electronic circuits constituting the high-frequency signal supply unit 11 and the impedance detection unit 12 can be reduced while improving the accuracy of determining whether or not Li deposition is present.

[0068] Furthermore, this disclosure can be realized by having a Central Processing Unit (CPU) execute a computer program to perform some or all of the processing of the battery management device 10.

[0069] The program described above includes, when loaded into a computer, a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored in a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include Random-Access Memory (RAM), Read-Only Memory (ROM), flash memory, Solid-State Drive (SSD), or other memory technologies, CD-ROM, Digital Versatile Disc (DVD), Blu-ray® disc, or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically, or otherwise propagating signals.

[0070] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be made as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate. [Explanation of Symbols]

[0071] 1. 1a Battery Management System 10, 10a battery management device 11, 11a, 111, 112 High-frequency signal supply section 12, 12a, 121, 122 Impedance detection unit 13, 13a Judgment section 14 Control Unit 15 Storage section 16 Temperature detection unit 17 Multiplexer 20 Secondary battery T1 Thermistor

Claims

1. A high-frequency signal supply unit that applies a high-frequency signal of 0.1 MHz or higher to a first battery cell having a low battery temperature among multiple battery cells constituting a lithium-ion secondary battery, An impedance detection unit for detecting the real portion of the AC impedance of the first battery cell to which the high-frequency signal is applied, A determination unit that determines whether or not Li has been deposited in the lithium-ion secondary battery based on the actual AC impedance of the first battery cell. A battery management device.

2. The high-frequency signal supply unit further applies the high-frequency signal to a second battery cell among the plurality of battery cells that has a higher battery temperature than the first battery cell. The impedance detection unit further detects the actual impedance of the second battery cell, The determination unit determines whether or not Li has precipitated in the lithium-ion secondary battery based on the actual values ​​of the AC impedance of the first battery cell and the AC impedance of the second battery cell, which are detected at the same battery temperature. The battery management device according to claim 1.

3. The determination unit determines whether or not Li has precipitated in the lithium-ion secondary battery based on the degree of change in the real part of the AC impedance of the first battery cell at a certain battery temperature and the degree of change in the AC impedance of the second battery cell at the same battery temperature. The battery management device according to claim 2.

4. A multiplexer switches the connection destination of the electronic circuit, which functions as the impedance detection unit, between the first battery cell and the second battery cell. The battery management device according to claim 2, comprising:

5. A temperature detection unit detects the battery temperature of each of the plurality of battery cells and sets the first battery cell based on the detection result. A battery management device according to claim 1 or 2, comprising:

6. A high-frequency signal of 0.1 MHz or higher is applied to a first battery cell, which has a low battery temperature, among the multiple battery cells constituting the lithium-ion secondary battery. The real portion of the AC impedance of the first battery cell to which the high-frequency signal is applied is detected. Based on the real part of the AC impedance of the first battery cell, it is determined whether or not Li has been deposited in the lithium-ion secondary battery. How to manage batteries.

7. A process of applying a high-frequency signal of 0.1 MHz or higher to a first battery cell having a low battery temperature among multiple battery cells constituting a lithium-ion secondary battery, A process for detecting the real part of the AC impedance of the first battery cell to which the high-frequency signal is applied, A process to determine whether or not Li has been deposited in the lithium-ion secondary battery based on the actual value of the AC impedance of the first battery cell. A program that causes a computer to execute something.

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