Battery management device and battery management method

Abstract

Provided are a battery management device and a battery management method, the battery management device according to the present disclosure is provided with: an AC signal supply unit for supplying an AC signal to a lithium ion secondary battery; an impedance detection unit that detects the value of the real part of the AC impedance from the lithium ion secondary battery to which the AC signal has been supplied; a swell amount calculation unit that calculates the swell amount of a battery cell in the lithium ion secondary battery on the basis of the difference between the current value and the initial value of the real part of the detected AC impedance; and a control unit that performs control so that the upper limit value of the charging rate of the lithium ion secondary battery decreases as the calculated swell amount increases.

Description

Technical Field

[0001] This disclosure relates to battery management devices and battery management methods. Background Technology

[0002] As disclosed in Patent Document 1, the inventors developed a method that uses a high-frequency signal to detect the real part of the AC impedance of a lithium-ion secondary battery and calculates the amount of Li deposited 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.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2022-108602. Summary of the Invention

[0004] However, it is known that during repeated charging and discharging in lithium-ion secondary batteries, the individual cells constituting the battery pack will expand. For example, when the battery pack is constrained by a belt, if the expansion of the individual cells continues, adverse conditions such as belt breakage may occur. Therefore, efforts are being made to suppress the expansion of the individual cells. However, methods for non-destructively detecting the expansion of individual cells in lithium-ion secondary batteries are not yet known.

[0005] This disclosure is made in view of the following circumstances, providing a battery management device capable of non-destructively detecting and suppressing the expansion of individual cells in a lithium-ion secondary battery.

[0006] The battery management device disclosed herein includes: an AC signal supply unit that supplies an AC signal to a lithium-ion secondary battery; an impedance detection unit that detects the real part of the AC impedance from the lithium-ion secondary battery to which the AC signal is supplied; an expansion calculation unit that calculates the expansion amount of a single cell in the lithium-ion secondary battery based on the difference between the current value and an initial value of the detected real part of the AC impedance; and a control unit that controls the battery in such a way that as the calculated expansion amount increases, the upper limit of the charging rate of the lithium-ion secondary battery is reduced.

[0007] In the battery management device disclosed herein, the expansion amount of a single cell in a lithium-ion secondary battery is calculated based on the difference between the current value and the initial value of the real part of the detected AC impedance. The greater the calculated expansion amount, the lower the upper limit of the charging rate of the lithium-ion secondary battery. With this structure, the expansion of single cells in a lithium-ion secondary battery can be detected non-destructively, and the expansion of single cells can be suppressed.

[0008] According to this disclosure, a battery management device is provided that can detect the expansion of individual cells in a lithium-ion secondary battery in a non-destructive manner and suppress the expansion of individual cells. The above and other objects, features and advantages of this disclosure will become more fully understood through the following detailed description and accompanying drawings. Attached Figure Description

[0009] Figure 1 This is a block diagram illustrating a structural example of the battery management system according to the first embodiment. Figure 2 This is a flowchart illustrating the battery management method according to the first embodiment. Figure 3 This is a diagram showing the control mode performed by the control unit 14 relative to the upper limit of the SOC of the expansion amount. Figure 4 This is a block diagram illustrating a structural example of the battery management system according to the second embodiment. Figure 5 This is a graph showing the relationship between the state of the secondary battery 20 (SOH) and the change in the real part Z of the AC impedance (the difference between the detected value and the initial value) when a second AC signal of 1 MHz is supplied to the secondary battery 20. Figure 6 This is a graph showing 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 7 This is a graph showing 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. Detailed Implementation

[0010] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. In addition, for clarity of description, the following description and drawings have been appropriately simplified.

[0011] (First Implementation) Figure 1 This is a block diagram illustrating an example of the structure of the battery management system according to the first embodiment. For example... Figure 1 As shown, the battery management system includes a battery management device 10 and a secondary battery 20 managed by the battery management device 10.

[0012] <Structure of Secondary Battery 20> First, the secondary battery 20, which is the object of management, will be explained. The secondary battery 20 is a lithium-ion secondary battery, consisting of a battery pack formed by stacked battery cells and a casing housing the battery pack. Each battery cell has a positive electrode, a negative electrode, and an ion-conducting medium located between the positive and negative electrodes to conduct charge-carrying ions. A separator may also be provided between the positive and negative electrodes. The separator is made of resins such as polyethylene and polypropylene.

[0013] Positive electrode active materials can be, for example, sulfides containing transition metal elements, or oxides containing lithium and transition metal elements. Specifically, the positive electrode active material can have the basic formula Li... (1-x) MnO2 (where 0 < x < 1), Li (1-x) Lithium-manganese composite oxides such as Mn2O4; with the basic formula Li (1-x) Lithium-cobalt composite oxides such as CoO2; the basic formula is Li (1-x) Lithium-nickel composite oxides such as NiO2; or those with the basic formula Li (1-x) Ni a Co b Mn c Lithium-nickel-cobalt-manganese composite oxides, such as O2 (where a+b+c=1), etc. Furthermore, the positive electrode active material can also be a substance containing other elements in the above basic formula. The current collector of the positive electrode, for example, is Al (aluminum).

[0014] The negative electrode active material can be, for example, a lithium-containing composite oxide or a carbon material. Specifically, the negative electrode active material can be an inorganic compound such as lithium, lithium alloys, or tin compounds; a carbon material capable of absorbing and releasing lithium ions; a composite oxide containing multiple elements; or a conductive polymer. Examples of carbon materials used as negative electrode active materials include coke, glassy carbon, graphite, non-graphitizable carbon, pyrolytic carbon, or carbon fibers, but artificial graphite and natural graphite are preferred. Additionally, examples of composite oxides used as negative electrode active materials include lithium-titanium composite oxides and lithium-vanadium composite oxides. The current collector of the negative electrode can be, for example, Cu (copper).

[0015] Ion-conducting media are used as electrolytes, for example, by dissolving a supporting salt. The supporting salt may be a lithium salt such as LiPF6 or LiBF4. The solvent for the electrolyte may be any one or a mixture of several of the following: carbonates, esters, ethers, nitriles, furans, sulfolane, and dioxolane. Examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butyl carbonate, and chloroethylene carbonate; and chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl n-butyl carbonate, methyl tert-butyl carbonate, diisopropyl carbonate, and tert-butyl isopropyl carbonate. Alternatively, the ion-conducting medium may also be a solid ion-conducting polymer, an inorganic solid electrolyte, a mixture of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder.

[0016] <Structure of Battery Management Device 10> Next, the battery management device 10 that manages the secondary battery 20 will be described. like Figure 1As shown, the battery management device 10 includes an AC signal supply unit 11, an impedance detection unit 12, an expansion calculation unit 13, a control unit 14, and a storage unit 15, and manages the charging of the secondary battery 20, which is the object of management. The battery management device 10 calculates the expansion amount in the secondary battery 20, and performs feedback control on the upper limit of the charging rate (SOC: State of Charge) of the secondary battery 20 based on the calculation result.

[0017] Here, as hardware, the battery management device 10 includes a storage unit 15 such as RAM (random access memory) and ROM (read-only memory) storing various programs and data, as well as an arithmetic unit such as a CPU (central processing unit) not shown. That is, the battery management device 10 has the function of a computer, performing various processes based on the aforementioned programs.

[0018] Therefore, in Figure 1 The functional blocks constituting the AC signal supply unit 11, impedance detection unit 12, expansion calculation unit 13, and control unit 14 of the battery management device 10 can be implemented in hardware by a CPU (central processing unit), memory, and other circuits; and in software by a program loaded into memory. That is, each of the above functional blocks can be implemented in various forms by computer hardware, software, or a combination thereof.

[0019] The AC signal supply unit 11 supplies an AC signal (first AC signal) to the secondary battery 20 for detecting the amount of expansion. For example, the AC signal supply unit 11 supplies an AC signal with a frequency of 500 to 1500 Hz to the secondary battery 20. The frequency of this AC signal is preferably 700 to 1000 Hz.

[0020] The impedance detection unit 12 detects the real part Z of the AC impedance from the secondary battery 20, which has been supplied with a first AC signal. The greater the expansion, the wider the electrode spacing in each battery cell, and the higher the electrolyte resistance, thus increasing the real part Z of the AC impedance detected by the impedance detection unit 12.

[0021] The expansion calculation unit 13 calculates the expansion amount in the secondary battery 20 based on the value of the real part Z of the AC impedance detected by the impedance detection unit 12 when the first AC signal is supplied to the secondary battery 20. More specifically, the expansion calculation unit 13 calculates the expansion amount in the secondary battery 20 based on the difference between the current value and the initial value of the real part Z of the AC impedance detected by the impedance detection unit 12 when the first AC signal is supplied to the secondary battery 20.

[0022] The smaller the value of the real part Z of the detected AC impedance and the smaller the difference from the initial value, the smaller the expansion amount calculation unit 13 calculates the expansion amount. On the other hand, the larger the value of the real part Z of the detected AC impedance and the larger the difference from the initial value, the larger the expansion amount calculation unit 13 calculates the expansion amount.

[0023] It should be noted that, for example, the storage unit 15 stores the initial value of the real part Z of the AC impedance when a first AC signal is supplied to the secondary battery 20, which is the object of management. In addition, the storage unit 15 may also store mapping information, which represents the relationship between the difference (change) and the expansion amount of the real part Z of the AC impedance when a first AC signal is supplied to each type of secondary battery.

[0024] This mapping information may be obtained through preliminary experiments, but it can also be updated appropriately based on information detected when a first AC signal is supplied to the secondary battery 20 under management. When using the mapping information, the expansion calculation unit 13 extracts the expansion amount corresponding to the real part Z of the AC impedance detected by the impedance detection unit 12 when the first AC signal is supplied to the secondary battery 20 from the mapping information stored in the storage unit 15.

[0025] The control unit 14 controls the upper limit of the SOC of the secondary battery 20 based on the expansion amount calculated by the expansion amount calculation unit 13. Specifically, the control unit controls the expansion amount calculated by the expansion amount calculation unit 13 as follows: the more the expansion amount increases, the more necessary it is to suppress the expansion, and therefore the upper limit of the SOC is lowered.

[0026] For example, the control unit 14 controls the expansion amount calculated by the expansion amount calculation unit 13 as follows: as the expansion amount increases, the initial upper limit of SOC is set to 100%, and the upper limit of SOC is gradually reduced to 95%, 90%, etc. Details regarding the control unit 14's control of the upper limit of SOC will be discussed later. Figure 3 Please provide an explanation.

[0027] As described above, in the battery management device 10 according to this embodiment, the expansion amount in the secondary battery 20 is calculated based on the value of the real part Z of the AC impedance detected when a first AC signal is supplied to the secondary battery 20. The greater the calculated expansion amount, the lower the upper limit of the SOC. Therefore, the expansion of the individual battery cells in the secondary battery 20 can be suppressed. That is, in the battery management device 10 of this embodiment, the expansion of the battery cells in the secondary battery 20 can be detected in a non-destructive manner, and the more the expansion increases, the lower the upper limit of SOC, thereby suppressing the expansion of the battery cells.

[0028] <Battery Management Methods> Next, we will refer to Figure 2 The operation of the battery management method, i.e., the battery management device 10, involved in this embodiment will be explained. Figure 2 This is a flowchart illustrating the battery management method according to the first embodiment. First, the AC signal supply unit 11 supplies an AC signal (first AC signal) to the secondary battery 20 for detecting the amount of expansion (step S101).

[0029] Next, the impedance detection unit 12 detects the value of the real part Z of the AC impedance from the secondary battery 20, which has been supplied with the first AC signal (step S102). Next, the expansion calculation unit 13 calculates the expansion amount in the secondary battery 20 based on the value of the real part Z of the detected AC impedance, i.e., the difference between the current value and the initial value (step S103).

[0030] For example, the expansion amount calculation unit 13 extracts the expansion amount corresponding to the difference between the current value and the initial value of the real part Z of the detected AC impedance from the mapping information stored in the storage unit 15. Specifically, the smaller the difference between the current value and the initial value of the real part Z of the detected AC impedance, the smaller the expansion amount calculation unit 13 calculates; the larger the difference between the current value and the initial value of the real part Z of the detected AC impedance, the larger the expansion amount calculation unit 13 calculates.

[0031] Finally, the control unit 14 controls the upper limit of the SOC of the secondary battery 20 based on the expansion amount calculated by the expansion amount calculation unit 13. Specifically, the control unit 14 controls the expansion amount calculated by the expansion amount calculation unit 13 as follows: the more the expansion amount increases, the more necessary it is to suppress the expansion, and therefore the upper limit of the SOC is lowered (step S104).

[0032] Here, Figure 3 This is a diagram showing the control mode performed by the control unit 14 relative to the upper limit of the SOC of the expansion amount. Figure 3 The horizontal axis represents the expansion amount, and the vertical axis represents the upper limit of SOC (%). Figure 3 The “prohibited area” shown means that the use of the secondary battery 20 is prohibited when the expansion exceeds a predetermined baseline value.

[0033] like Figure 3 As shown, both control mode 1 and control mode 2 reduce the upper limit of SOC as the expansion amount increases. like Figure 3 As shown by the solid line, in control mode 1, the control unit 14 linearly reduces the upper limit of the SOC relative to the calculated expansion amount. Furthermore, when the expansion amount reaches a predetermined reference value, the control unit 14 outputs an alarm prohibiting the use of the secondary battery 20.

[0034] On the other hand, such as Figure 3 As shown by the dashed line, in control mode 2, the control unit 14 controls as follows: in order to prevent the calculated expansion amount from reaching the reference value, the upper limit of SOC is increased relative to the increase in expansion amount as the expansion amount approaches the reference value.

[0035] It should be noted that the upper limit control mode of the SOC relative to the expansion amount performed by the control unit 14 is not limited to... Figure 3 The control modes shown are 1 and 2. That is, the control unit 14 can achieve the following in various ways: the more the expansion amount increases, the lower the upper limit of the SOC becomes.

[0036] As described above, in the battery management method of this embodiment, the expansion amount in the secondary battery 20 is calculated based on the value of the real part Z of the AC impedance detected when a first AC signal is supplied to the secondary battery 20. The greater the calculated expansion amount, the lower the upper limit of the SOC. Therefore, the expansion of the individual battery cells in the secondary battery 20 can be suppressed. That is, in the battery management method of this embodiment, the expansion of the battery cells in the secondary battery 20 can be detected in a non-destructive manner, and the more the expansion increases, the lower the upper limit of SOC, thereby suppressing the expansion of the battery cells.

[0037] (Second Implementation) Next, refer to Figure 4 The battery management device 10 according to the second embodiment will be described. Figure 4 This is a block diagram illustrating a structural example of the battery management system according to the second embodiment. Figure 4 As shown, the battery management device 10 according to this embodiment has Figure 1 In addition to the AC signal supply unit 11, impedance detection unit 12, expansion calculation unit 13, control unit 14 and storage unit 15 shown, it also includes a Li deposition calculation unit 16.

[0038] In the secondary battery 20, due to repeated charging, metallic Li will deposit on the electrode surface of each cell. The more the charging power is increased to accelerate the charging speed, the more Li deposition will develop, thus deteriorating the state of health (SOH) of the secondary battery 20.

[0039] It should be noted that the SOH of the secondary battery 20 refers to the percentage of the current full charge capacity when the initial full charge capacity of the secondary battery 20 is set to 100%. Therefore, it is desirable to set a high permissible charging power Pa for the secondary battery 20 that can suppress Li precipitation and charge efficiently with the shortest possible charging time.

[0040] In this embodiment, the AC signal supply unit 11 supplies the secondary battery 20 with a first AC signal for detecting the amount of expansion, and a second AC signal with a frequency of 0.1 MHz or higher for detecting the amount of Li deposition. Preferably, the second AC signal is a high-frequency signal that, compared to the value of the real part Z of the AC impedance detected when the first AC signal is supplied to the secondary battery 20, can detect a value of more than 10 times the real part of the AC impedance due to the skin effect. Specifically, the frequency of the second AC signal is preferably 0.5 MHz or higher.

[0041] When a second AC signal of this frequency is supplied to the secondary battery 20, the diffusion, reaction, and movement of lithium ions in each cell of the secondary battery 20 cannot be followed. Therefore, the displacement current of the second AC signal flows along the electrode surface of each cell, where Li is easily deposited, due to the skin effect.

[0042] The less Li deposited, the lower the conductivity of the electrode surface of each cell, and therefore the larger the real part Z of the AC impedance. On the other hand, the more Li deposited, the higher the conductivity of the electrode surface of each cell, and therefore the smaller the real part Z of the AC impedance. Therefore, based on the change in the real part Z of the AC impedance detected from the secondary battery 20 after being supplied with a second AC signal (the difference between the detected value and the initial value), the amount of Li deposited in the secondary battery 20 can be calculated. Furthermore, based on the amount of Li deposited, the SOH of the secondary battery 20 can also be estimated.

[0043] Here, Figure 5 This is a graph showing the relationship between the state of the secondary battery 20 (SOH) and the change in the real part Z of the AC impedance (the difference between the detected value and the initial value) when a second AC signal of 1 MHz is supplied to the secondary battery 20.

[0044] like Figure 5 As indicated by the middle triangle marking, under normal charging conditions with relatively low charging power, even with repeated charging, the amount of Li deposited is minimal. Therefore, even if SOH deteriorates due to other factors, the change in the real part Z of the AC impedance will remain small. That is, the detected value of the real part Z of the AC impedance remains high.

[0045] On the other hand, such as Figure 5 As indicated by the circular markings, under rapid charging conditions with high charging power, the amount of Li deposited increases with repeated charging. Consequently, the degradation of SOH (Sodium Oxide Hydrochloride) progresses, and the change in the real part Z of the AC impedance increases. That is, the detected value of the real part Z of the AC impedance decreases.

[0046] Here, Figure 6 and Figure 7This is a graph showing 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 6 The figure shows 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 7 The value of the real part Z of the AC impedance is shown when an AC signal of 100kHz to 100MHz is supplied to the secondary battery 20.

[0047] like Figure 6 As shown, when an AC signal with a frequency around 1 kHz, similar to the first AC signal used to detect the expansion, is supplied to the secondary battery 20, the real part Z of the AC impedance reaches its minimum value. This impedance component represents the ohmic resistance component. Furthermore, as... Figure 6 and Figure 7 As shown, the higher the frequency of the AC signal supplied to the secondary battery 20, the more concentrated the current flow will be on the electrode surface of each battery cell due to the skin effect, and therefore the larger the value of the real part Z of the AC impedance will be.

[0048] Therefore, the AC signal supply unit 11 supplies the secondary battery 20 with a high-frequency second AC signal that can detect the real part Z of the AC impedance that is sufficiently high than the ohmic resistance component.

[0049] The impedance detection unit 12 detects the real part Z of the AC impedance from the secondary battery 20 supplied with a first AC signal, and also detects the real part Z of the AC impedance from the secondary battery 20 supplied with a second AC signal. As mentioned above, the displacement current of the second AC signal supplied to the secondary battery 20 from the AC signal supply unit 11 flows on the electrode surface (Li deposition region) of each cell in the secondary battery 20 due to the skin effect. Therefore, the impedance detection unit 12 can detect the real part Z of the AC impedance corresponding to the amount of Li deposition.

[0050] The Li deposition calculation unit 16 calculates the amount of Li deposited in the secondary battery 20 based on the difference between the current value and the initial value of the real part Z of the AC impedance detected by the impedance detection unit 12 when the second AC signal is supplied to the secondary battery 20. More specifically, the larger the value of the real part Z of the detected AC impedance and the smaller the difference from the initial value, the smaller the Li deposition calculation unit 16 calculates the Li deposition amount. On the other hand, the smaller the value of the real part Z of the detected AC impedance and the larger the difference from the initial value, the larger the Li deposition calculation unit 16 calculates the Li deposition amount.

[0051] It should be noted that, for example, the storage unit 15 stores the initial value of the real part Z of the AC impedance when a second AC signal is supplied to the secondary battery 20, which is being managed. Furthermore, the storage unit 15 may also store mapping information, which represents the relationship between the current value (detected value) of the real part Z of the AC impedance when a second AC signal is supplied to each type of secondary battery and the initial value (change amount), and the amount of Li deposition.

[0052] This mapping information can be obtained, for example, through prior experiments, but it can also be updated appropriately based on information detected when a second AC signal is supplied to the secondary battery 20, which is the object of management. When using the mapping information, the Li deposition calculation unit 16 extracts the Li deposition amount corresponding to the real part Z of the AC impedance detected by the impedance detection unit 12 when the second AC signal is supplied to the secondary battery 20 from the mapping information stored in the storage unit 15.

[0053] The control unit 14 controls the allowable charging power Pa to the secondary battery 20 based on the Li deposition amount calculated by the Li deposition amount calculation unit 16. Specifically, the control unit 14 controls the charging power Pa to be lowered as follows: the more the Li deposition amount calculated by the Li deposition amount calculation unit 16 increases, the more necessary it is to suppress the development of Li deposition, and therefore the lower the allowable charging power Pa is.

[0054] For example, the control unit 14 controls the process as follows: as the amount of Li deposition calculated by the Li deposition amount calculation unit 16 increases, the initial allowable charging power Pa0 is set to 100%, and the allowable charging power Pa is gradually reduced to 95%, 90%, etc. It should be noted that the allowable charging power, i.e. the initial allowable charging power Pa0, of the new secondary battery 20 is preset according to each type of secondary battery 20, for example, and stored in the storage unit 15. The other structures are the same as in the first embodiment, so detailed descriptions are omitted.

[0055] In the battery management device 10 according to this embodiment, similarly to the first embodiment, the expansion amount in the secondary battery 20 is calculated based on the value of the real part Z of the AC impedance detected when a first AC signal is supplied to the secondary battery 20. The greater the calculated expansion amount, the lower the upper limit of the SOC. Therefore, the expansion of the individual battery cells in the secondary battery 20 can be suppressed. That is, in the battery management device 10 of this embodiment, the expansion of the battery cells in the secondary battery 20 can be detected in a non-destructive manner. The more the expansion increases, the lower the upper limit of the SOC is, thereby suppressing the expansion of the battery cells.

[0056] Furthermore, in the battery management device 10 according to this embodiment, the amount of Li deposition in the secondary battery 20 is calculated based on the value of the real part Z of the AC impedance detected when a second AC signal is supplied to the secondary battery 20. Moreover, the more the calculated amount of Li deposition increases, the lower the allowable charging power Pa becomes, thereby suppressing the development of Li deposition. Therefore, regarding the allowable charging power Pa0 at the start of use of the secondary battery 20, it is possible to set it to a higher level to prevent Li deposition from developing, in products where the range is within ±3σ rather than the conventional ±6σ range, and the charging time can also be shortened. In other words, with the battery management device 10 according to this embodiment, the allowable charging power Pa can be set to an appropriate value based on the amount of Li deposition, without setting the initial allowable charging power Pa0 of the secondary battery 20 too low, thus enabling efficient charging of the secondary battery 20.

[0057] (Third implementation method) Next, the battery management device 10 according to the third embodiment will be described. It should be noted that the battery management device 10 involved in the third embodiment and Figure 4 The battery management device 10 involved in the second embodiment shown is the same.

[0058] In the second embodiment, the real part of the AC impedance detected when a second AC signal for detecting the amount of Li deposition is supplied to the secondary battery decreases as Li deposition progresses, but increases with expansion. Therefore, if expansion occurs, the Li deposition calculation unit 16 cannot accurately calculate the amount of Li deposition based on the difference between the current value and the initial value (second change ΔR2) of the real part of the AC impedance detected when the second AC signal is supplied.

[0059] Therefore, in the battery management device 10 according to the variation of the second embodiment, the Li deposition calculation unit 16 obtains not only the real part of the AC impedance detected when the second AC signal is supplied, but also the real part of the AC impedance detected when the first AC signal is supplied. Furthermore, the Li deposition calculation unit 16 corrects the second change ΔR2 using the difference between the current value and the initial value (first change ΔR1) of the real part of the AC impedance detected when the first AC signal is supplied.

[0060] The correction for the second change ΔR2 is explained below. The second change ΔR2 is the sum of the change ΔR2s based on expansion and the change ΔR2p based on Li precipitation, and the following equation (1) holds. ΔR2=ΔR2s+ΔR2p・・・(1)

[0061] On the other hand, the real part of the AC impedance detected when the first AC signal is supplied increases with expansion, but does not change due to Li deposition. That is, the first change ΔR1 is only caused by expansion and not by Li deposition.

[0062] Here, the first change ΔR1 and the change based on expansion in equation (1) are both changes in the real part of the AC impedance caused by expansion, and therefore have a one-to-one correspondence. Therefore, the change based on expansion in equation (1) ΔR2s can be used as a function F(ΔR1) of the first change ΔR1, and is expressed by the following equation (2). ΔR2s=F(ΔR1)・・・(2) The correspondence of equation (2) is obtained in advance through experiments, etc., and stored in the storage unit 15 as mapping information, for example.

[0063] Substituting equation (2) into equation (1) and rearranging the terms, we obtain equation (3) regarding the change ΔR2p based on Li precipitation in equation (1). ΔR2p=ΔR2-F(ΔR1)・・・(3)

[0064] As shown in equation (3), in the battery management device 10 of this embodiment, the second change amount ΔR2 is corrected using the first change amount ΔR1. Furthermore, the amount of Li deposition is calculated using the net change amount ΔR2p based on Li deposition obtained through this correction. Therefore, compared to the battery management device 10 of the second embodiment, which is used as is without correcting the second change amount ΔR2, the battery management device 10 of this embodiment can more accurately calculate the amount of Li deposition. The other structures are the same as in the second embodiment, so detailed descriptions are omitted.

[0065] As can be seen from the above disclosure, the embodiments of this disclosure can be modified in various ways. Such modifications should not be considered as departing from the spirit and scope of this disclosure, and all such modifications that are obvious to those skilled in the art are intended to be included within the scope of protection of the claims.

Claims

1. A battery management device, comprising: The AC signal supply unit supplies AC signals to the lithium-ion secondary batteries. The impedance detection unit detects the real part of the AC impedance from the lithium-ion secondary battery that has been supplied with the AC signal. The expansion calculation unit calculates the expansion amount of the individual cells in the lithium-ion secondary battery based on the difference between the current value and the initial value of the detected real part of the AC impedance; and The control unit controls the battery in such a way that the higher the calculated expansion amount, the lower the upper limit of the charging rate of the lithium-ion secondary battery.

2. The battery management device according to claim 1, wherein, The AC signal supply unit supplies the lithium-ion secondary battery with a first AC signal with a frequency of 500 to 1500 Hz and a second AC signal with a frequency of 0.1 MHz or higher. The expansion calculation unit calculates the expansion amount based on a first change, which is the difference between the current value and the initial value of the real part of the AC impedance detected using the first AC signal. The battery management device further includes a Li deposition calculation unit, which calculates the amount of Li deposited in the lithium-ion secondary battery based on a second change, wherein the second change is the difference between the current value and the initial value of the real part of the AC impedance detected using the second AC signal. The control unit controls the lithium-ion secondary battery in such a way that as the calculated amount of Li deposition increases, the allowable charging power of the battery is reduced.

3. The battery management device according to claim 2, wherein, The Li precipitation calculation unit uses the first change to correct the second change and calculates the Li precipitation amount.

4. A battery management method comprising the following steps: Supplying AC signals to lithium-ion secondary batteries; The real part of the AC impedance is detected from the lithium-ion secondary battery that has been supplied with the AC signal; The expansion amount of the battery cell in the lithium-ion secondary battery is calculated based on the difference between the current value and the initial value of the real part of the detected AC impedance. as well as The greater the calculated expansion of the battery cell, the lower the upper limit of the charging rate of the lithium-ion secondary battery.

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