Battery management device and battery management system

Abstract

The invention provides a battery management device and a battery management system. A battery management device according to the present disclosure includes: a high-frequency signal supply unit that supplies a high-frequency signal having 0.1 MHz or more to a lithium ion secondary battery; an impedance detection unit that detects a value of a real part of AC impedance from the lithium ion secondary battery to which the high-frequency signal is supplied; a calculation unit that calculates an amount of Li deposition in the lithium ion secondary battery from a detected value of a real part of the AC impedance; and a control unit that reduces the allowable charging power of the lithium ion secondary battery as the calculated Li deposition amount increases.

Description

Technical Field

[0001] This disclosure relates to a battery management device and a battery management system. Background Technology

[0002] To prevent performance degradation in lithium-ion secondary batteries, it is desirable to limit the deposition of lithium (Li) metal (hereinafter referred to as Li deposition) in them. However, a non-destructive technique for detecting Li deposition in lithium-ion secondary batteries is currently unknown.

[0003] In response, as disclosed in Japanese Unexamined Patent Application Publication No. 2022-108602 (JP 2022-108602 A), the inventors have developed a technique 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 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. Summary of the Invention

[0004] Li deposition progresses with increasing charging power, and therefore, from the perspective of limiting Li deposition, a permissible charging power is set for each product type of lithium-ion secondary battery. The rate of Li deposition progression in lithium-ion secondary batteries varies (e.g., standard deviation σ) even within the same product type, depending on the individual product. In conventional lithium-ion secondary batteries, for example, in products encompassing the ±6σ range, the permissible charging power for each product type is set (fixed) to an excessively low value, preventing Li deposition from progressing, thus resulting in long charging times.

[0005] This disclosure is made in view of the foregoing, and the purpose of this disclosure is to provide a battery management device and a battery management system that enable efficient charging of lithium-ion secondary batteries.

[0006] The battery management device according to this disclosure includes: a high-frequency signal supply unit that supplies a high-frequency signal of 0.1 MHz or higher 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 high-frequency signal is supplied; a calculation unit that calculates the amount of Li deposition in the lithium-ion secondary battery based on the detected value of the real part of the AC impedance; and a control unit that decreases the allowable charging power of the lithium-ion secondary battery as the calculated amount of Li deposition increases. The battery management device according to this disclosure calculates the amount of Li deposition in the lithium-ion secondary battery based on the real part of the AC impedance detected from the lithium-ion secondary battery to which the high-frequency signal is supplied, and performs feedback control of the allowable charging power of the lithium-ion secondary battery based on the calculation result. Therefore, the battery management device according to this disclosure can set the allowable charging power of the lithium-ion secondary battery to an appropriate value based on the amount of Li deposition, rather than setting it to an excessively low value, thus achieving efficient charging of the lithium-ion secondary battery.

[0007] This disclosure provides a battery management device and a battery management system that enable efficient charging of lithium-ion secondary batteries. Attached Figure Description

[0008] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein like symbols denote like elements, and wherein:

[0009] Figure 1 This is a block diagram illustrating an exemplary configuration of the battery management system according to Embodiment 1;

[0010] Figure 2 This is a graph showing the relationship between the state of harmonics (SOH) of a secondary battery and the change in the real part of the alternating impedance (Z) when a high-frequency signal of 1 MHz is supplied to the secondary battery.

[0011] Figure 3 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;

[0012] Figure 4 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;

[0013] Figure 5 This is a flowchart illustrating the operation of the battery management device according to Embodiment 1; and

[0014] Figure 6 This is a block diagram illustrating an exemplary configuration of the battery management system according to Embodiment 2. Detailed Implementation

[0015] Specific embodiments of the invention will now be described in detail with reference to the accompanying drawings. However, the invention is not limited to the following embodiments. Furthermore, the following description and drawings have been appropriately simplified for illustrative purposes.

[0016] Example 1

[0017] Figure 1 This is a block diagram illustrating an exemplary configuration of the battery management system according to Embodiment 1. Figure 1 As shown, the battery management system 1 includes a battery management device 10 and a secondary battery 20 managed by the battery management device 10.

[0018] The secondary battery 20 is a lithium-ion secondary battery, and consists of a cell stack in which multiple battery cells are stacked and a casing that houses the cell stack.

[0019] Each battery cell includes a positive electrode, a negative electrode, and an ion-conducting medium disposed between the positive and negative electrodes to conduct current-carrying ions. A separator may also be provided between the positive and negative electrodes. For the separator, resins such as polyethylene and polypropylene are used.

[0020] For positive electrode active materials, for example, sulfides containing transition metal elements or oxides containing lithium and transition metal elements are used. Specifically, for positive electrode active materials, Li-containing oxides are used. (1-x) MnO2(0 <x<1)、Li (1-x) Lithium manganese composite oxides with basic compositions such as Mn2O4, and those possessing Li (1-x) Lithium cobalt composite oxides with basic composition such as CoO2, and possessing Li (1-x) Lithium-nickel composite oxides with basic composition such as NiO2, and possessing Li (1-x) Ni a Co b Mn c Lithium-nickel-cobalt-manganese composite oxides, etc., are based on the fundamental composition of O2 (a+b+c=1). For the positive electrode active material, a substance containing another element in the above-mentioned fundamental composition formula can be used. For the current collector of the positive electrode, aluminum (Al) is used, for example.

[0021] For the negative electrode active material, lithium-containing composite oxides or carbon materials are used, for example. Specifically, inorganic compounds (such as lithium, lithium alloys, and tin compounds), carbon materials capable of storing and releasing lithium ions, composite oxides containing multiple elements, conductive polymers, etc., are used as negative electrode active materials. Examples of carbon materials used for negative electrode active materials include coke, glassy carbon, graphite, non-graphitizable carbon, pyrolytic carbon, carbon fibers, etc., with graphite (such as artificial graphite and natural graphite) being preferred. Furthermore, lithium-titanium composite oxides and lithium-vanadium composite oxides are used as composite oxides for negative electrode active materials. For the current collector of the negative electrode, copper (Cu) is used, for example.

[0022] Ion-conducting media are used as electrolyte solutions, for example, by dissolving supporting salts. Supporting salts, for example, are lithium salts, such as LiPF6 and LiBF4. Solvents for the electrolyte solution, for example, are carbonates, esters, ethers, nitriles, furans, sulfolane, dioxolane, or mixtures of some of these. As carbonates, cyclic carbonates exist (such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate), as well as 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, for ion-conducting media, solid ion-conducting polymers, inorganic solid electrolytes, mixtures of organic polymer electrolytes and inorganic solid electrolytes, inorganic solid powders bound by organic binders, etc., can be used.

[0023] The battery management device 10 performs charging management for the secondary battery 20, which is the object of management. For example, the battery management device 10 detects the amount of Li deposited in the secondary battery 20 in a non-destructive manner, and performs feedback control on the allowable charging power (the upper limit of the charging power) Pa of the secondary battery 20 based on the detection results.

[0024] The battery management device 10 includes a high-frequency signal supply unit 11, an impedance detection unit 12, a calculation unit 13, a control unit 14, and a storage unit 15.

[0025] The high-frequency signal supply unit 11 supplies a high-frequency signal to the secondary battery 20. The impedance detection unit 12 detects the real part Z of the AC impedance from the secondary battery 20 that has been supplied with a high-frequency signal.

[0026] In the secondary battery 20, Li metal is deposited on the electrode surface of each cell through repeated charging. As the charging power increases to improve the charging speed, Li deposition progresses, deteriorating the state of health (SOH) of the secondary battery 20. The SOH of the secondary battery 20 is the ratio of its current capacity to its initial capacity of 100%. Therefore, for the secondary battery 20, it is desirable to set a maximum permissible charging power Pa that allows for efficient charging within the shortest possible charging time while limiting Li deposition.

[0027] When an alternating current signal (a high-frequency signal) is supplied to the secondary battery 20 (the high frequency of which prevents the diffusion, reaction, and movement of lithium ions in each cell of the secondary battery 20 from occurring), the current of the high-frequency signal flows along the edge of the electrical conductor of each cell due to the skin effect. In other words, due to the skin effect, the current of the high-frequency signal flows on the electrode surface of each cell where Li is easily deposited. Furthermore, similarly, when the Li metal is electrically disconnected from the negative electrode and becomes floating after Li deposition, current flows on the Li metal due to inductive and electric field connections. Therefore, for example, with a smaller amount of Li deposition, the conductivity of the electrode surface of each cell is lower, and thus the real part Z of the alternating current impedance is larger. With a larger amount of Li deposition, the conductivity of the electrode surface of each cell is higher, and therefore the real part Z of the alternating current impedance is smaller. A large amount of current is concentrated on the Li metal with high conductivity, and therefore the magnetic field changes around the Li deposition area, causing eddy currents to be generated. Eddy currents cause losses at the conductive parts of the current collector foil and electrodes, but reduce the overall battery loss. Therefore, with a larger Li deposition amount, the magnetic field changes more significantly, resulting in a higher eddy current and a smaller real part Z. Thus, the Li deposition amount in the secondary cell 20 can be calculated based on the real part Z of the AC impedance detected from the secondary cell 20 supplied with a high-frequency signal. When the Li deposition amount is detected, the state of harmonics (SOH) of the secondary cell 20 can also be estimated.

[0028] Figure 2 This is a graph showing the relationship between the state of harmonics (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 high-frequency signal of 1 MHz is supplied to the secondary battery 20. (See graph for example.) Figure 2 As indicated by the triangle markings, under normal charging conditions with low charging power, the amount of Li deposition is small even during repeated charging. Therefore, even when the degradation of SOH progresses due to other reasons, 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 remains high). On the other hand, as... Figure 2As indicated by the circles, under high-power fast charging, the amount of Li deposition increases with repeated charging, and thus the degradation of the State of Harmonic Effect (SOH) progresses, resulting in a large change in the real part Z of the AC impedance (i.e., a low detected value of the real part Z of the AC impedance). When the battery degradation is primarily due to Li deposition (one of the causes of battery degradation), the amount of Li deposition can be derived from the SOH. Alternatively, the SOH can be derived from the amount of Li deposition.

[0029] Figure 3 and Figure 4 Each of these 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 3 The value of the real part Z of the AC impedance is shown when an AC signal of 1 kHz to 100 kHz is supplied to the secondary battery 20. Figure 4 The value of the real part Z of the AC impedance is shown when an AC signal of 100 kHz to 100 MHz is supplied to the secondary battery 20.

[0030] like Figure 3 As shown, when an AC signal of approximately 1 kHz is supplied to the secondary battery 20, the real part Z of the AC impedance becomes minimum. In this case, the impedance component is the ohmic resistance component. Furthermore, as... Figure 3 and Figure 4 As shown, when the frequency of the AC signal supplied to the secondary battery 20 is high, due to the skin effect, the current flow is concentrated on the electrode surface of each cell, and therefore, the real part Z of the AC impedance is large.

[0031] Therefore, the high-frequency signal supply unit 11 supplies the secondary battery 20 with an AC signal of a high frequency (i.e., a high-frequency signal), which allows the detection of the real part Z of the AC impedance sufficiently higher than the ohmic resistance component. For example, the high-frequency signal supply unit 11 supplies the secondary battery 20 with a high-frequency signal of 0.1 MHz or higher. Alternatively, the high-frequency signal supply unit 11 supplies the secondary battery 20 with a high-frequency signal such that, due to the skin effect, the detected value of the real part Z of the AC impedance is 10 times or greater than the value of the real part Z of the AC impedance detected when an AC signal of 1 kHz is supplied to the secondary battery 20. Figure 3 and Figure 4 In the example, the high-frequency signal supply unit 11 supplies a high-frequency signal of 0.5 MHz or higher to the secondary battery 20. Therefore, due to the skin effect, the current used for the high-frequency signal flows on the electrode surface (Li deposition region) of each cell in the secondary battery 20. Consequently, the impedance detection unit 12 can detect the real part Z of the AC impedance corresponding to the amount of Li deposition.

[0032] The calculation unit 13 calculates the amount of Li deposition 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. More specifically, the calculation unit 13 calculates the amount of Li deposition 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. For example, information about the initial value of the real part Z of the AC impedance of the secondary battery 20, which is the subject of management, is stored in the storage unit 15.

[0033] For example, the calculation unit 13 calculates the amount of Li deposition such that the value of the amount of Li deposition decreases as the detected value of the real part Z of the AC impedance increases, and increases as the detected value of the real part Z of the AC impedance decreases.

[0034] Storage unit 15 can store information about the initial value of the real part Z of the AC impedance for each type of secondary battery. Additionally, storage unit 15 can also store mapping information representing the relationship between the difference (change) between the current value (detected value) and the initial value of the real part Z of the AC impedance for each type of secondary battery and the amount of Li deposition. The mapping information is, for example, information previously obtained through experiments and can be updated as appropriate using information detected from the secondary battery 20, which is the object of management. In this case, calculation unit 13 extracts the amount of Li deposition corresponding to the value of the real part Z of the AC impedance detected by impedance detection unit 12 from the mapping information stored in storage unit 15.

[0035] The control unit 14 controls the allowable charging power Pa of the secondary battery 20 based on the amount of Li deposition calculated by the calculation unit 13. For example, if the calculated amount of Li deposition is small, the progress of Li deposition is limited, so the control unit 14 controls the allowable charging power Pa to remain at its current value or increase it. As the calculated amount of Li deposition increases, it is necessary to limit the progress of Li deposition, and therefore, the control unit 14 controls the allowable charging power Pa to decrease. For example, the control unit 14 can switch the allowable charging power Pa in stages from 100% as an initial value to 95%, 90%, or others, depending on the calculated amount of Li deposition.

[0036] Therefore, the battery management device 10 according to this disclosure can set a maximum permissible charging power Pa for the secondary battery 20, which allows for efficient charging in the shortest possible charging time while limiting Li deposition. In other words, the battery management device 10 according to this disclosure can set the permissible charging power Pa of the secondary battery 20 to an appropriate value based on the amount of Li deposition, rather than setting it to an excessively low value, thus achieving efficient charging of the secondary battery 20.

[0037] Operation of battery management device 10

[0038] Subsequently, will be used Figure 5 Describe the operation of the battery management device 10. Figure 5 This is a flowchart illustrating the operation of the battery management device 10.

[0039] First, the battery management device 10 supplies the secondary battery 20 with an AC signal (high-frequency signal) of such high frequency that the diffusion, reaction, and movement of lithium ions in each battery cell cannot occur (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 is supplied (step S102).

[0040] Subsequently, the battery management device 10 calculates the amount of Li deposited in the secondary battery 20 based on the detected value of the real part Z of the AC impedance (step S103). For example, the battery management device 10 extracts the amount of Li deposited corresponding to the detected value of the real part Z of the AC impedance from the mapping information stored in the storage cell 15. Basically, the battery management device 10 calculates the amount of Li deposited such that the value of the Li deposited decreases as the detected value of the real part Z of the AC impedance increases, and increases as the detected value of the real part Z of the AC impedance decreases.

[0041] Subsequently, the battery management device 10 controls the allowable charging power Pa of the secondary battery 20 based on the calculated Li deposition amount (step S104). For example, if the calculated Li deposition amount is small, the progress of Li deposition is limited, therefore, the battery management device 10 performs control to keep the allowable charging power Pa at its current value or increase it. As the calculated Li deposition amount is larger, it is necessary to limit the progress of Li deposition, therefore, the battery management device 10 performs control to reduce the allowable charging power Pa.

[0042] In this way, the battery management device 10 according to the present disclosure can set a maximum permissible charging power Pa for the secondary battery 20, which allows for efficient charging in the shortest possible charging time while limiting Li deposition. That is, the battery management device 10 according to the present disclosure can set the permissible charging power Pa of the secondary battery 20 to an appropriate value based on the amount of Li deposition, rather than setting it to an excessively low value, thus achieving efficient charging of the secondary battery 20.

[0043] An example has been described in which the impedance detection unit 12 detects the real part Z of the AC impedance from the secondary battery 20 at any time and the calculation unit 13 calculates the amount of Li deposition in the secondary battery 20 based on the real part Z of the AC impedance detected at any time, but this disclosure is not limited thereto.

[0044] For example, the impedance detection unit 12 can periodically detect the real part Z of the AC impedance from the secondary battery 20 at measurement intervals T1 specified by the control unit 14, and the calculation unit 13 can detect the change in Li deposition during the measurement interval T1 based on the value of the real part Z of the AC impedance periodically detected at the measurement interval T1. In this case, the control unit 14 performs control such that as the increase in Li deposition during the measurement interval T1 is large, the allowable charging power Pa of the secondary battery 20 decreases. The control unit 14 can be configured to change the measurement interval T1 to an arbitrary length. For example, the control unit 14 can shorten the measurement interval T1 in an environment where Li deposition is easy, as exemplified by an environment where fast charging is performed, and extend the measurement interval T1 in an environment where Li deposition is difficult, as exemplified by an environment where charging is performed with an electrical power sufficiently lower than the allowable charging power.

[0045] Furthermore, when the amount of Li deposited in the secondary battery 20 reaches a first predetermined amount, the control unit 14 can dissolve the deposited lithium by forcibly discharging the secondary battery 20. In this case, for example, when the amount of Li deposited in the secondary battery 20 after the deposited lithium has dissolved is less than or equal to a second predetermined amount less than the first predetermined amount, the control unit 14 can maintain the allowable charging power Pa at its current value, and when the amount of deposited lithium is greater than the second predetermined amount, the control unit 14 can perform control to reduce the allowable charging power Pa.

[0046] Furthermore, when the secondary battery 20 is installed in a hybrid vehicle (such as a hybrid electric vehicle (HEV) and a plug-in hybrid electric vehicle (PHEV)) and the control unit 14 dissolves the deposited lithium by forcibly discharging the secondary battery 20, the control unit 14 can switch the hybrid vehicle from driving using the secondary battery 20 to driving using gasoline.

[0047] Example 2

[0048] Figure 6 This is a block diagram illustrating an exemplary configuration of a battery management system 100 according to Embodiment 2. The battery management system 100 includes n (n is an integer of 2 or greater) battery management devices 10 (which are configured to correspond to n secondary batteries 20), a control device 40, and a network 50. The n battery management devices 10 and the control device 40 are configured to communicate with each other via the network 50. Hereinafter, the n secondary batteries 20 are also referred to as secondary batteries 20_1 to 20_n, and the n battery management devices 10 are also referred to as battery management devices 10_1 to 10_n.

[0049] Secondary batteries 20_1 to 20_n are respectively installed on vehicles 30_1 to 30_n. Furthermore, battery management devices 10_1 to 10_n are respectively installed on vehicles 30_1 to 30_n along with secondary batteries 20_1 to 20_n. Each of vehicles 30_1 to 30_n is a battery-electric vehicle or a hybrid vehicle powered by the secondary batteries.

[0050] The control device 40 learns the allowable charging power settings for each of the secondary batteries 20_1 to 20_n managed by the battery management devices 10_1 to 10_n, and updates the allowable charging power settings for each of the secondary batteries 20_1 to 20_n based on the learning results. In other words, the control device 40 uses a learned model generated by machine learning (which uses the allowable charging power settings) to update the allowable charging power settings for each of the secondary batteries 20_1 to 20_n.

[0051] For example, if, after a predetermined usage period, a lower-than-expected allowable charging power is set for a predetermined number or more secondary batteries 20 managed by battery management devices 10_1 to 10_n, there is a possibility that the initial value of the allowable charging power is too high. In this case, the control device 40 performs control to reduce the allowable charging power for all secondary batteries 20_1 to 20_n managed by battery management devices 10_1 to 10_n. Therefore, Li deposition in each of the secondary batteries 20_1 to 20_n is limited. Similar to secondary batteries 20_1 to 20_n, the control device 40 can set the initial value of the allowable charging power set for newly transported secondary batteries 20 to a low value.

[0052] In this disclosure, some or all of the processing of the battery management device 10 can be implemented by having the central processing unit (CPU) execute a computer program.

[0053] The program described above includes commands (or software code) for causing a computer to perform one or more functions described in the embodiments when the program is read by the computer. The program may be stored in a non-transitory computer-readable medium or tangible storage medium. As a non-limiting example, the computer-readable medium or tangible storage medium includes random access memory (RAM), read-only memory (ROM), flash memory, solid-state drives (SSDs), other memory technologies, CD-ROMs, digital versatile discs (DVDs), Blu-ray discs, other optical disc storage devices, magnetic cartridges, magnetic tapes, disk drives, or other magnetic storage devices. The program may be transmitted on a transient computer-readable medium or communication medium. As a non-limiting example, the transient computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagation signals.

[0054] The present disclosure has been described above with reference to embodiments. The present disclosure is not limited to the embodiments described above. Various changes that will be understood by those skilled in the art can be made to the configurations and details of the present disclosure within its scope. Furthermore, each embodiment may be combined with other embodiments where appropriate.

Claims

1. A battery management device, comprising: A high-frequency signal supply unit that supplies a high-frequency signal of 0.1 MHz or higher to the lithium-ion secondary battery; An impedance detection unit detects the real part of the AC impedance from the lithium-ion secondary battery to which the high-frequency signal is supplied; The calculation unit calculates the amount of Li deposited in the lithium-ion secondary battery based on the detected value of the real part of the AC impedance; as well as A control unit that reduces the allowable charging power of the lithium-ion secondary battery as the calculated amount of Li deposition increases.

2. The battery management device of claim 1, wherein, The high-frequency signal supplied by the high-frequency signal supply unit has a frequency such that, due to the skin effect, the detected value of the real part of the AC impedance is 10 times or more the value of the real part of the AC impedance detected when an AC signal of 1 kHz is supplied to the lithium-ion secondary battery.

3. The battery management device according to claim 1, wherein: The impedance detection unit detects the real part of the AC impedance from the lithium-ion secondary battery at specified measurement intervals; The calculation unit calculates the change in Li deposition during the specified measurement interval based on the value of the real part of the AC impedance detected at the specified measurement interval. and The control unit reduces the permissible charging power of the lithium-ion secondary battery as the amount of Li deposition increases during the specified measurement interval.

4. The battery management device of claim 1, wherein, When the amount of Li deposited in the lithium-ion secondary battery reaches a first predetermined amount, the control unit dissolves the deposited Li by forcibly discharging the lithium-ion secondary battery. When the amount of Li deposited in the lithium-ion secondary battery becomes less than or equal to a second predetermined amount after the Li is dissolved, the control unit maintains the allowable charging power of the lithium-ion secondary battery without reducing it, wherein the second predetermined amount is less than the first predetermined amount.

5. A battery management system, comprising: Multiple battery management devices according to claim 1, each of which manages multiple lithium-ion secondary batteries installed in multiple vehicles; as well as A control device that learns the allowable charging power settings for each lithium-ion secondary battery in the lithium-ion secondary battery, and updates the allowable charging power settings for each lithium-ion secondary battery in the lithium-ion secondary battery based on the learning results.

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