Battery Management Device

Abstract

To provide a battery management device capable of improving the detection accuracy of lithium deposition. [Solution] The battery management device according to this disclosure includes a high-frequency signal supply unit that applies a high-frequency signal of 0.1 MHz or higher to a lithium-ion secondary battery; a storage unit that stores the actual value of the AC impedance of the lithium-ion secondary battery to which the high-frequency signal was applied at a first time point, as a reference value for each battery temperature; an impedance detection unit that detects the actual value of the impedance of the lithium-ion secondary battery to which the high-frequency signal was 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 Li has precipitated in the lithium-ion secondary battery based on the detected actual value of the impedance and the reference value at the battery temperature.

Description

Technical Field

[0001] The present disclosure relates to a battery management device.

Background Art

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

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

Prior Art Documents

Patent Documents

[0007] This disclosure is made in view of the above background and aims to provide a battery management device capable of improving the detection accuracy of Li deposition. [Means for solving the problem]

[0008] The battery management device according to this disclosure includes: a high-frequency signal supply unit that applies a high-frequency signal of 0.1 MHz or higher to a lithium-ion secondary battery; a storage unit that stores the actual value of the AC impedance of the lithium-ion secondary battery to which the high-frequency signal was applied at a first time point, as a reference value for each battery temperature; an impedance detection unit that detects the actual value of the AC impedance of the lithium-ion secondary battery to which the high-frequency signal was applied at a certain battery temperature at a second time point after the first time point; and a determination unit that determines whether or not Li has precipitated in the lithium-ion secondary battery based on the detected actual value of the AC impedance and the reference value at the battery temperature. [Effects of the Invention]

[0009] This disclosure provides a battery management device capable of improving the detection accuracy of Li deposition. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram showing an example configuration of the battery management system related to this disclosure. [Figure 2] This figure shows the relationship between the State of Health (SOH) of a secondary battery and the change in the real part Z of the AC impedance when a 1 MHz high-frequency signal is supplied to the secondary battery. [Figure 3]This diagram shows the relationship between the frequency of the AC signal supplied to the secondary battery and the real part of the AC impedance detected from the secondary battery. [Figure 4] This diagram shows the relationship between the frequency of the AC signal supplied to the secondary battery and the real part of the AC impedance detected from the secondary battery. [Figure 5] This is a flowchart illustrating the operation of the battery management device related to this disclosure. [Modes for carrying out the invention]

[0011] The following describes specific embodiments to which the present invention is applied, with reference to the drawings. However, the present invention is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings have been simplified as appropriate.

[0012] <Embodiment 1> Figure 1 is a block diagram showing an example configuration of the battery management system 1 according to Embodiment 1. As shown in Figure 1, the battery management system 1 comprises a battery management device 10 and a secondary battery 20 managed by the battery management device 10.

[0013] The secondary battery 20 is a lithium-ion secondary battery and is composed of a cell stack consisting of multiple stacked battery cells and a case that houses the cell stack.

[0014] Each battery cell comprises a positive electrode, a negative electrode, and an ion transport medium provided between the positive and negative electrodes for conducting carrier ions. A separator may be further provided between the positive and negative electrodes. The separator is made of a resin such as polyethylene or polypropylene.

[0015] For example, positive electrode active materials include sulfides containing transition metal elements and oxides containing lithium and transition metal elements. Specifically, positive electrode active materials have the basic composition formula Li (1-x) MnO2 (but 0 <x<1)やLi (1-x)A lithium manganese composite oxide such as Mn2O4, with a basic composition formula of Li (1-x) A lithium cobalt composite oxide such as CoO2, with a basic composition formula of Li (1-x) A lithium nickel composite oxide such as NiO2, or a basic composition formula of Li (1-x) Ni a Co b Mn c O2 (where a + b + c = 1), etc., such as a lithium nickel cobalt manganese composite oxide, is used. Note that as the positive electrode active material, a substance containing other elements in the above basic composition formula may also be used. For the current collector of the positive electrode, for example, Al (aluminum), etc., is used.

[0016] For the negative electrode active material, for example, a composite oxide containing lithium, a carbon material, etc., is used. Specifically, as the negative electrode active material, lithium, a lithium alloy, an inorganic compound such as a tin compound, a carbon material capable of occluding and releasing lithium ions, a composite oxide containing a plurality of elements, or a conductive polymer, etc., is used. Examples of the carbon material used for the negative electrode active material include cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, or carbon fibers, etc., and graphites such as artificial graphite and natural graphite are preferred. Also, examples of the composite oxide used for the negative electrode active material include a lithium titanium composite oxide, a lithium vanadium composite oxide, etc. For the current collector of the negative electrode, for example, Cu (copper), etc., is used.

[0017] The ionic conduction medium is used as an electrolytic solution, for example, by dissolving a supporting salt. Lithium salts such as LiPF6 and LiBF4 are used as the supporting salt. As the solvent of the electrolytic solution, for example, any one of carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, or a mixture of some of them, is used. Examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, and chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate. Alternatively, the ionic conduction medium may be a solid ionic conductive polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder, etc.

[0018] The battery management device 10 performs charge management of the secondary battery 20 to be managed. For example, the battery management device 10 non-destructively detects the presence or absence of Li precipitation in the secondary battery 20, and feedback-controls the allowable charge power (the upper limit value of the charge power) Pa for the secondary battery 20 based on the detection result.

[0019] 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.

[0020] The high-frequency signal supply unit 11 supplies a high-frequency signal to the secondary battery 20. The impedance detection unit 12 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.

[0021] Incidentally, in the secondary battery 20, metallic Li is deposited on the electrode surface of each battery cell as charging is repeated. Li deposition progresses as the charging power is increased to speed up the charging process, degrading the State of Health (SOH) of the secondary battery 20. The SOH of the secondary battery 20 is the ratio of the current capacity to the initial capacity of the secondary battery 20, which is set to 100%. Therefore, it is desirable to set the allowable charging power Pa of the secondary battery 20 to be as high as possible, which allows for efficient charging in the shortest possible charging time while suppressing Li deposition.

[0022] Here, if an AC signal (high-frequency signal) with a frequency too high for the diffusion, reaction, and movement of lithium ions in each cell of the secondary battery 20 is supplied to the secondary battery 20, the current of the high-frequency signal flows along the edges of the conductors of each cell due to the skin effect. In other words, the current of the high-frequency signal flows along the electrode surface of each cell where Li is easily deposited due to the skin effect. Furthermore, even when the Li metal is electrically disconnected from the negative electrode and becomes a floating state after Li deposition, current flows over the Li metal due to inductive coupling and electric field coupling. Therefore, the value of the real part Z of the AC impedance does not change when no Li is deposited compared to the initial state, and as the amount of Li deposition increases, the electrical conductivity of the electrode surface of each cell increases, so the value of the real part Z of the AC impedance decreases. Here, since a lot of current concentrates in the highly conductive Li metal, the magnetic field changes around the Li deposition region, and eddy currents are generated as a result. These eddy currents cause losses in the current collector foil and the conductive parts of the electrodes, but reduce the overall loss of the battery. Therefore, as the amount of Li deposited increases, the change in the magnetic field becomes larger, and consequently the eddy currents increase, resulting in a smaller value for the real part Z. For this reason, the amount of Li deposited in the secondary battery 20 can be calculated from the value of the real part Z of the AC impedance detected from the secondary battery 20 to which a high-frequency signal is supplied. Once the amount of Li deposited is known, it is also possible to estimate the SOH of the secondary battery 20.

[0023] Figure 2 shows the relationship between the State of Health (SOH) of the secondary battery 20 and the change in the real part Z of the AC impedance (the difference between the detected value and the initial value) when a 1 MHz high-frequency signal is supplied to the secondary battery 20. As indicated by the triangles in Figure 2, in the case of normal charging with low charging power, even if charging is repeated, the amount of Li deposition is small, so even if the deterioration of SOH progresses due to other factors, the change in the real part Z of the AC impedance remains small (i.e., the detected value of the real part Z of the AC impedance is maintained at a high value). In contrast, as indicated by the circles in Figure 2, in the case of rapid charging with high charging power, the amount of Li deposition increases with repeated charging, and consequently, the deterioration of SOH progresses, and the change in the real part Z of the AC impedance becomes large (i.e., the detected value of the real part Z of the AC impedance becomes low). Note that if battery degradation due to Li deposition is the dominant factor among the factors of battery degradation, the amount of Li deposition can be derived from SOH. Alternatively, SOH can be derived from the amount of Li deposition.

[0024] Figures 3 and 4 show the relationship between the frequency of the AC signal supplied to the secondary battery 20 and the real part of the AC impedance detected from the secondary battery 20. Figure 3 shows the value of the real part Z of the AC impedance when an AC signal from 1 kHz to 100 kHz is supplied to the secondary battery 20. Figure 4 shows the value of the real part Z of the AC impedance when an AC signal from 100 kHz to 100 MHz is supplied to the secondary battery 20.

[0025] As shown in Figure 3, when an AC signal near 1 kHz is supplied to the secondary battery 20, the real part Z of the AC impedance is at its minimum value. The impedance component at this time represents the ohmic resistance component. Furthermore, as shown in Figures 3 and 4, as the frequency of the AC signal supplied to the secondary battery 20 increases, the real part Z of the AC impedance increases because the current flow concentrates on the electrode surface of each cell due to the skin effect.

[0026] Therefore, the high-frequency signal supply unit 11 supplies a high-frequency AC signal (i.e., a high-frequency signal) to the secondary battery 20 such that a value of the real part Z of the AC impedance is detected that is sufficiently high compared to the ohmic resistance component. For example, the high-frequency signal supply unit 11 supplies a high-frequency signal of 0.1 MHz or higher to the secondary battery 20. In the examples of Figures 3 and 4, the high-frequency signal supply unit 11 supplies a high-frequency signal of 0.5 MHz or higher to the secondary battery 20. As a result, the current of the high-frequency signal flows through the electrode surface (Li deposition region) of each battery cell of the secondary battery 20 due to the skin effect. As a result, the impedance detection unit 12 can detect the real part Z of the AC impedance according to the amount of Li deposition.

[0027] The temperature detection unit 16 detects the battery temperature of the secondary battery 20. For example, the temperature detection unit 16 detects the battery temperature of one or more of the multiple battery cells constituting the secondary battery 20 using one or more thermistors T1. The temperature detection unit 16 may also calculate the resistance value of each of the multiple battery cells from the cell voltage of each of the multiple battery cells. Then, the temperature detection unit 16 may calculate the difference between the heat generated by each of the multiple battery cells and the heat generated by the battery cell to which the thermistor T1 is attached, from the difference between the calculated resistance values ​​of each of the multiple battery cells and the resistance value of the battery cell to which the thermistor T1 is attached, and estimate the temperature of each of the multiple battery cells from the calculation result.

[0028] The memory unit 15 stores reference values ​​for the real part Z of the AC impedance of the secondary battery 20 for each battery temperature. The value of the real part Z of the AC impedance of the secondary battery 20 is measured for multiple battery temperatures at a certain point in time (referred to as the first point in time), and the measurement results are stored in the memory unit 15 as reference values. The reference values ​​may be measured in advance before starting operation of the secondary battery 20, or they may be measured during operation of the secondary battery 20.

[0029] The battery management device 10 may include a generation unit 17 that generates information representing a reference value for each battery temperature. 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, it may acquire the real part Z of the AC impedance detected at that time to generate information indicating a reference value for each battery temperature.

[0030] For example, if the secondary battery 20 is an on-board battery installed in a vehicle, the battery temperature of the secondary battery 20 may change depending on the vehicle's condition. The generation unit 17 can automatically collect the actual value Z of the AC impedance of the secondary battery 20 for various battery temperatures. The actual value Z of the AC impedance may be detected by the impedance detection unit 12 while the vehicle is running or stopped.

[0031] When measuring reference values ​​before starting operation of the secondary battery 20, for example, an operator may measure the actual AC impedance Z while changing the battery temperature of a new secondary battery 20 and store the measurement results in the storage unit 15 via an input interface (not shown). Alternatively, the generation unit 17 may control the battery temperature of the new secondary battery 20 and associate the battery temperature detected by the temperature detection unit 16 with the measured value of the actual AC impedance Z detected by the impedance detection unit 12.

[0032] The determination unit 13 obtains the real part Z of the AC impedance of the secondary battery 20 to which the high-frequency signal was applied at a second time point following the first time point, from the impedance detection unit 12. The determination 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 determination unit 13 then determines whether or not Li has been deposited in the secondary battery 20 based on the difference between the reference value obtained from the storage unit 15 and the value of the AC impedance Z obtained from the impedance detection unit 12. The determination unit 13 may, for example, subtract the value of the real part Z of the AC impedance from the reference value, and if the subtraction result is greater than a threshold, it may determine that Li has been deposited in the secondary battery 20. The determination unit 13 may also perform other calculations (for example, calculation of a ratio) other than subtraction between the reference value and the real part Z of the AC impedance.

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

[0034] As a result, the battery management device 10 according to this disclosure can set the highest possible allowable charging power Pa for the secondary battery 20, enabling efficient charging in the shortest possible charging time while suppressing Li deposition. In other words, the battery management device 10 according to this disclosure can set the allowable charging power Pa for the secondary battery 20 to an appropriate value depending on whether or not Li deposition occurs, without setting it excessively low, thereby enabling efficient charging of the secondary battery 20.

[0035] The battery management device 10 can determine with high accuracy whether or not Li has deposited in the secondary battery 20 by using the real part Z of the AC impedance detected at the same temperature in the past as a reference value.

[0036] (Operation of battery management device 10) Next, an example of the operation of the battery management device 10 will be explained using Figure 5. Figure 5 is a flowchart showing the operation of the battery management device 10. Assume that the memory unit 15 of the battery management device 10 stores reference values ​​for the real part Z of the AC impedance of the secondary battery 20 for each battery temperature.

[0037] First, the battery management device 10 supplies the secondary battery 20 with an AC signal (high-frequency signal) of such a high frequency that the diffusion, reaction, and movement of lithium ions in each battery cell cannot keep up (step S101). For example, the battery management device 10 supplies the secondary battery 20 with a high-frequency signal of 0.1 MHz or higher. Then, the battery management device 10 detects the value of the real part Z of the AC impedance from the secondary battery 20 to which the high-frequency signal has been supplied (step S102).

[0038] Subsequently, the battery management device 10 obtains the battery temperature of the secondary battery 20 (step S103). Note that step S103 may be performed before step S101.

[0039] Subsequently, the battery management device 10 determines whether or not Li has precipitated 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).

[0040] If Li is deposited in the secondary battery 20 (YES in step S104), the battery management device 10 needs to suppress the progression of Li deposition, and therefore controls the allowable charging power Pa to be lowered (step S105). If Li is not deposited in the secondary battery 20 (NO in step S104), the battery management device 10 maintains the allowable charging power Pa as it is. Alternatively, the battery management device 10 may control the allowable charging power Pa to be higher.

[0041] Thus, the battery management device 10 according to this disclosure can set the highest possible allowable charging power Pa for the secondary battery 20, enabling efficient charging in the shortest possible charging time while suppressing Li deposition. In other words, the battery management device 10 according to this disclosure can set the allowable charging power Pa for the secondary battery 20 to an appropriate value according to the amount of Li deposition, without setting it excessively low, thereby enabling efficient charging of the secondary battery 20. The battery management device 10 can determine with high accuracy whether or not Li has been deposited in the secondary battery 20 by using the real part Z of the AC impedance detected at the same temperature in the past as a reference value.

[0042] Furthermore, this disclosure can be realized by having a Central Processing Unit (CPU) execute a computer program to perform some or all of the processing of the battery management device 10.

[0043] When the above program is loaded into a computer, it includes a set of instructions (or software code) for causing the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium includes Random-Access Memory (RAM), Read-Only Memory (ROM), flash memory, Solid-State Drive (SSD) or other memory technologies, CD-ROM, Digital Versatile Disc (DVD), Blu-ray (registered trademark) disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted on a transitory computer-readable medium or a communication medium. By way of example and not limitation, the transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0044] As described above, the present disclosure has been described with reference to the embodiments, but the present disclosure is not limited to the above-described embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. And each embodiment can be combined with other embodiments as appropriate.

Description of Reference Numerals

[0045] 1 Battery management system 10 Battery management device 11 High-frequency signal supply unit 12 Impedance detection unit 13 Determination unit 14 Control unit 15 Storage unit 16 Temperature detection unit 17 Generation unit 20 Secondary battery T1 Thermistor

Claims

1. A high-frequency signal supply unit that applies a high-frequency signal of 0.1 MHz or higher to a lithium-ion secondary battery, A storage unit that stores 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 for each battery temperature, An impedance detection unit that detects the actual AC impedance of the lithium-ion secondary battery to which the high-frequency signal is applied at a certain battery temperature at a second time point after the first time point, A determination unit that determines whether or not Li has precipitated in the lithium-ion secondary battery based on the detected AC impedance and the reference value at the battery temperature. A battery management device.

2. The determination unit determines whether or not Li has precipitated based on the difference between the actual value of the detected AC impedance and the reference value. The battery management device according to claim 1.

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

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

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

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