Battery management device

Abstract

The present invention relates to a battery management device. The battery management device according to the present disclosure includes a high-frequency signal supply unit that applies a high-frequency signal having a frequency of 0.1 MHz or more to a lithium-ion secondary battery; a storage unit that stores a real part of an alternating-current impedance of the lithium-ion secondary battery to which the high-frequency signal is applied at a first time point as a reference value for each battery temperature; an impedance detection unit that detects the real part of the alternating-current impedance of the lithium-ion secondary battery to which the high-frequency signal is applied at a second time point after the first time point at a certain battery temperature; and a determination unit that determines whether or not lithium deposition is present in the lithium-ion secondary battery based on the reference value at the battery temperature and the detected real part of the alternating-current impedance.

Description

Technical Field

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

[0002] There is a need to suppress the deposition of metallic lithium (Li) in lithium-ion secondary batteries (hereinafter, Li deposition) in order to prevent performance degradation. However, a non-destructive method for detecting Li deposition in lithium-ion secondary batteries is currently unknown.

[0003] In response, 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 deposition in the lithium-ion secondary battery based on the difference between the current value of the real part of the AC impedance and the initial value, as disclosed in Japanese Unexamined Patent Application Publication No. 2022-108602 (JP 2022-108602A). Summary of the Invention

[0004] Currently, from the perspective of suppressing Li deposition, the higher the charging power, the more intense the Li deposition becomes, and therefore, an allowable charging power is set for each type of lithium-ion secondary battery. Here, even for the same type of battery, the rate of Li deposition acceleration in lithium-ion secondary batteries varies among products (e.g., standard deviation σ). In conventional lithium-ion secondary batteries, for example, in products within the ±6σ range, the allowable charging power for each type is set (fixed) excessively low to suppress Li deposition acceleration, resulting in the problem of long charging times.

[0005] Therefore, the inventors have developed a technique for reducing the permissible charging power based on the amount of Li deposition calculated using the technique disclosed in JP 2022-108602 A. According to this technique, for example, in products within a range of ±3σ, the permissible charging power at the start of use can be set high enough that Li deposition is not aggravated, and the charging time can also be shortened. In the technique developed by the inventors, it is desirable to further improve the detection accuracy of Li deposition.

[0006] This disclosure is made in view of the above circumstances, and the purpose of this disclosure is to provide a battery management device that can improve the detection accuracy of Li precipitation.

[0007] The battery management device according to this disclosure includes: a high-frequency signal supply unit that applies a high-frequency signal with a frequency of 0.1 MHz or higher to a lithium-ion secondary battery; a storage unit that stores, for each battery temperature, the real part of the AC impedance of the lithium-ion secondary battery to which the high-frequency signal is applied at a first time point as a reference value; an impedance detection unit that detects the real part of the AC impedance of the lithium-ion secondary battery to which the high-frequency signal is applied at a second time point after the first time point at a certain battery temperature; and a determination unit that determines whether lithium deposition exists in the lithium-ion secondary battery based on the reference value at the battery temperature and the detected real part of the AC impedance.

[0008] This disclosure provides a battery management device that can improve the detection accuracy of Li precipitation. Attached Figure Description

[0009] 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 reference numerals denote like elements, and wherein:

[0010] Figure 1 This is a block diagram illustrating a configuration example of a battery management system according to this disclosure;

[0011] Figure 2 This is a graph showing 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 1MHz high-frequency signal is supplied to the secondary battery.

[0012] 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;

[0013] 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; and

[0014] Figure 5 This is a flowchart illustrating the operation of a battery management device according to the present disclosure. Detailed Implementation

[0015] The following describes specific embodiments of the application of the present invention in detail with reference to the accompanying drawings. However, it should be noted that the present invention is not limited to the following embodiments. Furthermore, for clarity, the following description and drawings have been appropriately simplified.

[0016] First Embodiment

[0017] Figure 1 This is a block diagram illustrating a configuration example of the battery management system 1 according to the first embodiment. For example... Figure 1As shown in the figure, 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 is configured to include a cell stack consisting of multiple stacked battery cells and a housing that contains the cell stack.

[0019] Each cell includes a cathode, an anode, and an ion transport medium disposed between the cathode and anode to conduct charge-carrying ions. A separator may also be provided between the cathode and anode. The separator is made of a resin such as polyethylene or polypropylene.

[0020] For cathode active materials, for example, sulfides containing transition metal elements, oxides containing lithium, and transition metal elements are used. Specifically, for cathode active materials, materials containing lithium such as Li are used. (1-x) MnO2 (where 0) <x<1)、Li (1-x) Lithium-manganese composite oxides with basic compositions such as Mn2O4, and those possessing properties such as Li (1-x) Lithium-cobalt composite oxides with basic compositions such as CoO2, and those possessing properties such as Li (1-x) Lithium-nickel composite oxides with basic compositions such as NiO2 or containing Li (1-x) Ni a Co b Mn c Lithium-nickel-cobalt-manganese composite oxides with a basic composition such as O2 (where a+b+c=1). Note that for cathode active materials, substances with the above basic composition containing other elements can be used. For example, aluminum (Al) is used in cathode current collectors.

[0021] For anode active materials, for example, composite oxides containing lithium, carbon materials, etc., are used. Specifically, for anode active materials, inorganic compounds such as lithium, lithium alloys, tin compounds, etc., carbon materials capable of absorbing and releasing lithium ions, composite oxides containing multiple elements, conductive polymers, etc., are used. Examples of carbon materials used for anode active materials include coke, glassy carbon, graphite, non-graphitizable carbon, pyrolytic carbon, carbon fibers, etc., with graphite—such as artificial graphite, natural graphite, etc.—being preferred. Furthermore, examples of composite oxides used for anode active materials include lithium-titanium composite oxides, lithium-vanadium composite oxides, etc. Copper (Cu), for example, is used in anode current collectors.

[0022] For example, ion-conducting media are used as electrolyte solutions by dissolving supporting salts. For example, lithium salts such as LiPF6 and LiBF4 are used. For the solvent used in the electrolyte solution, for example, any one of carbonates, esters, ethers, nitriles, furans, sulfolane, and dioxolane, or mixtures of several of these, are used. Examples of carbonates include cyclic carbonates—such as ethylene carbonate, propylene carbonate, vinylene carbonate, butyl carbonate, ethylene chloride carbonate, etc.—and chain carbonates—such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl n-butyl carbonate, methyl tert-butyl carbonate, diisopropyl carbonate, tert-butyl carbonate, etc. 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 on the secondary battery 20 to be managed. For example, the battery management device 10 non-destructively detects whether Li precipitation exists in the secondary battery 20, and performs feedback control of the allowable charging power (upper limit of charging power) Pa of the secondary battery 20 based on the detection result.

[0024] The battery management device 10 includes a high-frequency signal supply unit 11, an impedance detection unit 12, a determination unit 13, a control unit 14, a storage unit 15, a temperature detection unit 16, and a generation unit 17.

[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 of the secondary battery 20 from which the high-frequency signal is applied.

[0026] Currently, in the secondary battery 20, metallic Li precipitates on the electrode surfaces of the individual cells due to repeated charging. The more intense the Li precipitation, the higher the charging power required to increase the charging speed, leading to a deterioration in the state of health (SOH) of the secondary battery 20. Note that the SOH of the secondary battery 20 refers to the percentage of its current capacity, with an initial capacity of 100%. Therefore, it is desirable to configure the secondary battery 20 to allow for efficient charging in the shortest possible charging time while suppressing Li precipitation, with a maximum permissible charging power (Pa).

[0027] Now, when a high-frequency AC signal (high-frequency signal) is supplied to the secondary battery 20, causing the diffusion, reaction, and movement of lithium ions in each cell to fall behind, the current of the high-frequency signal flows along the edge of the conductor in each cell due to the skin effect. In other words, due to the skin effect, the current of the high-frequency signal flows through the electrode surface of each cell in which Li is easily deposited. Moreover, even when the Li metal is disconnected from the anode and in a floating state after Li deposition, current still flows through the Li metal due to inductive and capacitive coupling. Therefore, when no Li is deposited from the initial state, the real part Z of the AC impedance does not change, and the more Li is deposited, the higher the conductivity of the electrode surface in each cell becomes, and therefore the smaller the real part Z of the AC impedance becomes. Now, a large current is concentrated on the Li metal, which has high conductivity, and therefore the magnetic field changes around the Li deposition region, which is accompanied by the generation of eddy currents. Such eddy currents cause losses in the current collector foil and the conductive parts of the electrodes, but reduce the overall losses in the battery. Therefore, the greater the amount of Li deposited, the greater the change in the magnetic field, and thus the greater the eddy current, resulting in a smaller real part Z. Therefore, the amount of Li deposited in the secondary cell 20 can be calculated based on the real part Z of the AC impedance detected from the secondary cell 20 supplying the high-frequency signal. Once the amount of Li deposited is known, 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 1MHz high-frequency signal is supplied to the secondary battery 20. 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, and therefore, even when the SOH deteriorates due to other factors (i.e., the detected value of the real part Z of the AC impedance remains high), the change in the real part Z of the AC impedance remains small. Conversely, as... Figure 2 As indicated by the circle, under fast charging with high charging power, Li deposition increases with repeated charging, and therefore, the degradation of SOH is exacerbated 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 when Li deposition is the dominant cause of battery degradation, the amount of Li deposition can originate from SOH. Alternatively, SOH can originate from the amount of Li deposition.

[0029] Figure 3 and Figure 4 This 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 3The value of the real part Z of the AC impedance is shown when an AC signal ranging from 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 ranging from 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 indicates a minimum value. The impedance component at this time represents the ohmic resistance component. Furthermore, as... Figure 3 and Figure 4 As shown, as the frequency of the AC signal supplied to the secondary battery 20 increases, the skin effect causes the current to concentrate on the electrode surface of each cell, and thus the value of the real part Z of the AC impedance increases.

[0031] Therefore, the high-frequency signal supply unit 11 supplies an AC signal (i.e., a high-frequency signal) to the secondary battery 20, which has a high frequency that allows detection of the real part Z of the AC impedance, which 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. 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. As a result, due to the skin effect, the current of the high-frequency signal flows through the electrode surface (Li deposition region) of each cell in the secondary battery 20. This allows the impedance detection unit 12 to detect the real part Z of the AC impedance based on the amount of Li deposition.

[0032] Temperature detection unit 16 detects the battery temperature of secondary battery 20. For example, temperature detection unit 16 uses one or more thermistors T1 to detect the battery temperature of one or more battery cells constituting secondary battery 20. Temperature detection unit 16 can calculate the resistance value of each battery cell based on the cell voltage of each battery cell. Then, temperature detection unit 16 can calculate the difference between the heat generated by each battery cell and the heat generated by the battery cell to which the thermistor T1 is attached, based on the difference between the calculated resistance value for each battery cell and the resistance value of the battery cell to which the thermistor T1 is attached, and estimate the temperature of each battery cell based on the calculation results.

[0033] Storage unit 15 stores information about the real part Z of the AC impedance of the secondary battery 20 for each battery temperature. The real part Z of the AC impedance of the secondary battery 20 is measured at a certain time point (referred to as the first time point) for multiple battery temperatures, and the measurement result is stored in storage unit 15 as a reference value. The reference value can be measured in advance before the secondary battery 20 starts operating, or it can be measured while the secondary battery 20 is in operation.

[0034] The battery management device 10 may include a generation unit 17 that generates information indicating a reference value for the temperature of each battery. The generation unit 17 may, for example, monitor the battery temperature detected by the temperature detection unit 16, and when a new battery temperature is detected, generate the reference value indicating the temperature of each battery by acquiring the real part Z of the AC impedance detected at that time.

[0035] For example, when the secondary battery 20 is an on-board battery installed in a vehicle, the battery temperature of the secondary battery 20 can change depending on the vehicle's condition. The generation unit 17 can automatically collect the real part Z of the AC impedance of the secondary battery 20 for various battery temperatures. The real part Z of the AC impedance can be detected by the impedance detection unit 12 when the vehicle is moving or stationary.

[0036] When measuring a reference value before the secondary battery 20 begins operation, the operator can, for example, measure the real part Z of the AC impedance while changing the battery temperature of the new secondary battery 20, and store the measurement result in the storage unit 15 via an input interface (omitted in the figure). Alternatively, the generation unit 17 can perform control to change the battery temperature of the new secondary battery 20, while associating the battery temperature detected by the temperature detection unit 16 with the measured value of the real part Z of the AC impedance detected by the impedance detection unit 12.

[0037] The determining unit 13 obtains the real part Z of the AC impedance of the secondary battery 20 at a second time point after the first time point, where a high-frequency signal is applied, from the impedance detection unit 12. The determining unit 13 then obtains the battery temperature at the second time point from the temperature detection unit 16 and obtains the real part Z of the AC impedance corresponding to the battery temperature from the storage unit 15. The determining unit 13 then determines whether Li deposition exists in the secondary battery 20 based on the difference between the reference value obtained from the storage unit 15 and the real part Z of the AC impedance obtained from the impedance detection unit 12. For example, the determining unit 13 can subtract the value of the real part Z of the AC impedance from the reference value, and determine the presence of Li deposition in the secondary battery 20 if the subtraction result is greater than a threshold. The determining unit 13 can perform another calculation besides subtraction (e.g., ratio calculation, etc.) between the real part Z of the AC impedance and the reference value.

[0038] The control unit 14 controls the allowable charging power Pa of the secondary battery 20 based on the determination result from the determination unit 13. For example, when it is determined that there is no Li deposition, the aggravation of Li deposition is suppressed, and accordingly, the control unit 14 controls the allowable charging power Pa to maintain the current level or higher. When it is determined that Li deposition exists, it is necessary to suppress the aggravation of Li deposition, and therefore the control unit 14 controls the allowable charging power Pa to be lower. Note that the control unit 14 may switch the allowable charging power Pa in stages depending on the determination result of the presence or absence of Li deposition.

[0039] Therefore, the battery management device 10 according to this disclosure can set the highest possible allowable charging power Pa for the secondary battery 20, thereby achieving 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 of the secondary battery 20 to an appropriate value, rather than setting it excessively low, depending on the presence or absence of Li deposition, thereby achieving efficient charging of the secondary battery 20.

[0040] The battery management device 10 can determine with high precision whether Li precipitation exists in the secondary battery 20 by using the real part Z of the AC impedance previously detected at the same temperature as a reference value.

[0041] Operation of battery management device 10

[0042] Next, we will refer to Figure 5 An example describing the operation of the battery management device 10. Figure 5 This is a flowchart illustrating the operation of the battery management device 10. It is assumed that the storage unit 15 of the battery management device 10 stores a reference value of the real part Z of the AC impedance for each battery temperature of the secondary battery 20.

[0043] First, the battery management device 10 supplies a high-frequency AC signal (high-frequency signal) to the secondary battery 20, causing the diffusion, reaction, and movement of lithium ions in each battery cell to be unable to keep up (step S101). For example, the battery management device 10 supplies a high-frequency signal of 0.1 MHz or higher to the secondary battery 20. Then, the battery management device 10 detects the value of the real part Z of the AC impedance from the secondary battery 20 from which the high-frequency signal has been supplied (step S102).

[0044] Subsequently, the battery management device 10 acquires the battery temperature of the secondary battery 20 (step S103). Note that step S103 can be performed before step S101.

[0045] Subsequently, the battery management device 10 determines whether Li deposition exists in the secondary battery 20 based on the reference value of the real part Z of the AC impedance corresponding to the battery temperature obtained in step S103 and the value of the real part Z of the AC impedance detected in step S102 (step S104).

[0046] When Li deposition occurs in the secondary battery 20 (Yes in step S104), the battery management device 10 controls the allowable charging power Pa to be reduced because it is necessary to suppress the aggravation of Li deposition (step S105). When no Li deposition occurs in the secondary battery 20 (No in step S104), the battery management device 10 maintains the allowable charging power Pa in the current state. Alternatively, the battery management device 10 may perform control to increase the allowable charging power Pa.

[0047] In this way, the battery management device 10 according to this disclosure can set the highest possible allowable charging power Pa for the secondary battery 20, thereby achieving efficient charging in the shortest possible charging time while suppressing Li deposition. That is, the battery management device 10 according to this disclosure can set the allowable charging power Pa of the secondary battery 20 to an appropriate value depending on the amount of Li deposition, without setting it excessively low, thereby achieving efficient charging of the secondary battery 20. The battery management device 10 can determine with high precision whether Li deposition exists in the secondary battery 20 by using the real part Z of the AC impedance previously detected at the same temperature as a reference value.

[0048] Furthermore, this disclosure can be achieved by having the central processing unit (CPU) execute a computer program for some or all of the processing of the battery management device 10.

[0049] The program described above includes a set of instructions (or software code) for causing a computer to perform one or more functions described in the embodiments when the program is loaded onto the computer. The program may be stored in a non-transitory computer-readable medium or tangible storage medium. By way of example, and not limitation, computer-readable media or tangible storage media include random access memory (RAM), read-only memory (ROM), flash memory, solid-state drives (SSDs) and other memory technologies, optical disc read-only memory (CD-ROM), digital versatile disc (DVD), Blu-ray disc (registered trademark) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage, and other magnetic storage devices. The program may be transmitted on a transient computer-readable medium or communication medium. By way of example, and not limitation, transient computer-readable media or communication media include electrical, optical, acoustic signals, or other forms of propagation signals.

[0050] Although the present disclosure has been described above by way of embodiments, the present disclosure is not limited to the embodiments described above. Within the scope of the present disclosure, various modifications to the configuration and details of the present disclosure can be made that will be understood by those skilled in the art. Furthermore, each embodiment can be appropriately combined with other embodiments.

Claims

1. A battery management device, comprising: A high-frequency signal supply unit applies a high-frequency signal with a frequency of 0.1 MHz or higher to the lithium-ion secondary battery; The storage unit stores the real part of the AC impedance of the lithium-ion secondary battery to which the high-frequency signal was applied at the first time point as a reference value for each battery temperature. An impedance detection unit detects the real part of the AC impedance of the lithium-ion secondary battery at a second time point after the first time point, when the high-frequency signal is applied, at a certain battery temperature. as well as A determining unit determines whether lithium deposition exists in the lithium-ion secondary battery based on the reference value at the battery temperature and the real part of the detected AC impedance.

2. The battery management device according to claim 1, wherein, The determining unit determines whether lithium deposition exists based on the difference between the real part of the detected AC impedance and the reference value.

3. The battery management device according to claim 1, further comprising: A generation unit monitors the battery temperature of the lithium-ion secondary battery at the first time point and generates information representing reference values ​​for each battery temperature.

4. The battery management device according to claim 3, wherein, At the first time point, the lithium-ion secondary battery was installed in the vehicle, and The reference value is detected when the vehicle is moving or stopped.

5. The battery management device according to claim 1, wherein, The lithium-ion secondary battery at the first time point is a new lithium-ion battery.

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