Battery management device and battery management system

Abstract

To provide a battery management device and battery management system that can achieve efficient charging of lithium-ion secondary batteries. [Solution] The battery management device according to this disclosure comprises: 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 value of the AC impedance from the lithium-ion secondary battery to which the high-frequency signal has been supplied; a calculation unit that calculates the amount of Li deposited in the lithium-ion secondary battery from the detected real value of the AC impedance; and a control unit that reduces the allowable charging power for the lithium-ion secondary battery as the calculated amount of Li deposited increases.

Description

Technical Field

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

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0006] This disclosure is made in view of the above background and aims to provide a battery management device and battery management system that can achieve efficient charging of lithium-ion secondary batteries. [Means for solving the problem]

[0007] The battery management device according to this disclosure comprises: 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 value 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 deposited in the lithium-ion secondary battery from the detected real value of the AC impedance; and a control unit that lowers the allowable charging power for the lithium-ion secondary battery as the calculated amount of Li deposited increases. The battery management device according to this disclosure calculates the amount of Li deposited in the lithium-ion secondary battery from the real value of the AC impedance detected from the lithium-ion secondary battery to which the high-frequency signal is supplied, and feedback-controls the allowable charging power for the lithium-ion secondary battery based on the calculated result. As a result, the battery management device according to this disclosure can set the allowable charging power for the lithium-ion secondary battery to an appropriate value according to the amount of Li deposited without setting it excessively low, thereby enabling efficient charging of the lithium-ion secondary battery. [Effects of the Invention]

[0008] This disclosure provides a battery management device and a battery management system that can achieve efficient charging of lithium-ion secondary batteries. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing an example configuration of a battery management system according to Embodiment 1. [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 showing the operation of the battery management device according to Embodiment 1. [Figure 6] This is a block diagram showing an example configuration of a battery management system according to Embodiment 2. [Modes for carrying out the invention]

[0010] 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.

[0011] <Embodiment 1> Figure 1 is a block diagram showing an example configuration of a battery management system 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.

[0012] 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.

[0013] 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.

[0014] 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 (where 0 < x < 1) or 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. In addition, for the positive electrode active material, a substance containing other elements in the above basic composition formula may be used. For the current collector of the positive electrode, for example, Al (aluminum), etc., is used.

[0015] For the negative electrode active material, for example, a composite oxide containing lithium, a carbon material, etc., are used. Specifically, for 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., are used. Examples of the carbon material used for the negative electrode active material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, or carbon fibers, etc., and graphites such as artificial graphite and natural graphite are preferred. In addition, examples of the composite oxide used for the negative electrode active material include a lithium titanium composite oxide and a lithium vanadium composite oxide, etc. For the current collector of the negative electrode, for example, Cu (copper), etc., is used.

[0016] 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 several 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.

[0017] The battery management device 10 performs charging management of the secondary battery 20 to be managed. For example, the battery management device 10 nondestructively detects the amount of Li precipitation in the secondary battery 20 and feedback-controls the allowable charging power (the upper limit value of the charging power) Pa for the secondary battery 20 based on the detection result.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 on the Li metal due to inductive coupling and electric field coupling. Therefore, for example, the less Li is deposited, the lower the electrical conductivity of the electrode surface of each cell, and the larger the real part Z of the AC impedance. Conversely, the more Li is deposited, the higher the electrical conductivity of the electrode surface of each cell, and the smaller the real part Z of the AC impedance. 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 conductive parts of the current collector foil and 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, so the value of the real part Z decreases. 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. If the amount of Li deposited is known, it is also possible to estimate the SOH of the secondary battery 20.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 sufficiently high real part Z value of the AC impedance is detected 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. Alternatively, the high-frequency signal supply unit 11 supplies a high-frequency signal to the secondary battery 20 such that, compared to the real part Z value of the AC impedance detected when a 1 kHz AC signal is supplied to the secondary battery 20, a real part value of the AC impedance is detected by the skin effect at least 10 times higher. 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.

[0026] The calculation unit 13 calculates the amount of Li deposited in the secondary battery 20 from 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 deposited in the secondary battery 20 based on the difference between the current value of the real part Z of the AC impedance detected by the impedance detection unit 12 and the initial value of the real part Z of the AC impedance of the secondary battery 20. Information on the initial value of the real part Z of the AC impedance of the secondary battery 20 being managed is stored, for example, in the storage unit 15.

[0027] For example, the calculation unit 13 calculates a smaller Li deposition amount the larger the real part Z value of the detected AC impedance, and calculates a larger Li deposition amount the smaller the real part Z value of the detected AC impedance.

[0028] The memory unit 15 may also store information on the initial value of the real part Z of the AC impedance for each type of secondary battery. Furthermore, the memory unit 15 may store map information representing the relationship between the current value (detected value) and the difference (change amount) between the initial value and the amount of Li deposition of the real part Z of the AC impedance for each type of secondary battery. This map information is, for example, information obtained in advance through experiments, but may be updated as appropriate based on information detected from the secondary battery 20 under management. In this case, the calculation unit 13 extracts the amount of Li deposition corresponding to the value of the real part Z of the AC impedance detected by the impedance detection unit 12 from the map information stored in the memory unit 15.

[0029] The control unit 14 controls the allowable charging power Pa for 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 control unit 14 controls the allowable charging power Pa to remain at its current level or to increase it, as the progress of Li deposition is suppressed. If the calculated amount of Li deposition is large, the control unit 14 controls the allowable charging power Pa to decrease it, as it is necessary to suppress the progress of Li deposition. The control unit 14 may also switch the allowable charging power Pa in stages, for example, from the initial value of 100% to 95%, 90%, etc., according to the calculated amount of Li deposition.

[0030] As a result, the battery management device 10 according to this disclosure can set the highest possible allowable charging power Pa for the secondary battery 20, enabling efficient charging in the shortest possible charging time while suppressing Li deposition. In other words, the battery management device 10 according to this disclosure can set the allowable charging power Pa for the secondary battery 20 to an appropriate value according to the amount of Li deposition, without setting it excessively low, thereby enabling efficient charging of the secondary battery 20.

[0031] (Operation of battery management device 10) Next, we will explain the operation of the battery management device 10 using Figure 5. Figure 5 is a flowchart showing the operation of the battery management device 10.

[0032] 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).

[0033] Subsequently, the battery management device 10 calculates the amount of Li deposited in the secondary battery 20 from 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 map information stored in the storage unit 15. Basically, the larger the detected value of the real part Z of the AC impedance, the smaller the value of Li deposited that the battery management device 10 calculates, and the smaller the detected value of the real part Z of the AC impedance, the larger the value of Li deposited that the battery management device 10 calculates.

[0034] Subsequently, the battery management device 10 controls the allowable charging power Pa for the secondary battery 20 based on the calculated amount of Li deposition (step S104). For example, if the calculated amount of Li deposition is small, the battery management device 10 maintains the allowable charging power Pa at its current level or controls it to be higher, as the progress of Li deposition is suppressed. If the calculated amount of Li deposition is large, it is necessary to suppress the progress of Li deposition, so the battery management device 10 controls it to be lowered.

[0035] Thus, the battery management device 10 according to this disclosure can set the allowable charging power Pa of the secondary battery 20 to the highest possible value, which allows for 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 according to the amount of Li deposition, without setting it excessively low, thereby enabling efficient charging of the secondary battery 20.

[0036] In this disclosure, an example is described in which the impedance detection unit 12 detects the real part Z of the AC impedance from the secondary battery 20 at any arbitrary timing, and the calculation unit 13 calculates the amount of Li deposited in the secondary battery 20 based on the real part Z of the AC impedance detected at any arbitrary timing, but the disclosure is not limited to this example.

[0037] For example, the impedance detection unit 12 periodically detects the real part Z of the AC impedance from the secondary battery 20 at a measurement interval T1 specified by the control unit 14, and the calculation unit 13 calculates the change in Li deposition per measurement interval T1 based on the real part Z of the AC impedance detected periodically at the measurement interval T1. In this case, the control unit 14 controls the system so that the larger the increase in Li deposition per measurement interval T1, the lower the allowable charging power Pa for the secondary battery 20. The control unit 14 may be configured to change the measurement interval T1 to any length. For example, the control unit 14 shortens the measurement interval T1 in environments where Li deposition is likely to occur, such as when rapid charging is performed, and lengthens the measurement interval T1 in environments where Li deposition is unlikely, such as when charging is performed with a power significantly lower than the allowable charging power.

[0038] Furthermore, the control unit 14 may, when the amount of Li deposited in the secondary battery 20 reaches a first predetermined amount, forcibly discharge the secondary battery 20 to dissolve the deposited lithium. In this case, for example, if the amount of Li deposited in the secondary battery 20 after dissolving the deposited lithium becomes less than or equal to a second predetermined amount (less than the first predetermined amount), the control unit 14 may maintain the allowable charging power Pa as it is, and if it is more than the second predetermined amount, it may control the system to lower the allowable charging power Pa.

[0039] Furthermore, when the secondary battery 20 is installed in a hybrid vehicle such as a Hybrid Electric Vehicle (HEV) or a Plug-in Hybrid Electric Vehicle (PHEV), and the control unit 14 forcibly discharges the secondary battery 20 to dissolve the deposited lithium, the control unit 14 may switch the hybrid vehicle from being driven by the secondary battery 20 to being driven by gasoline.

[0040] <Embodiment 2> Figure 6 is a block diagram showing an example configuration of the battery management system 100 according to Embodiment 2. The battery management system 100 comprises n battery management devices 10, each corresponding to n (where n is an integer of 2 or more) 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 will also be referred to as secondary batteries 20_1 to 20_n, and the n battery management devices 10 will also be referred to as battery management devices 10_1 to 10_n.

[0041] The secondary batteries 20_1 to 20_n are installed in vehicles 30_1 to 30_n, respectively. The battery management devices 10_1 to 10_n are also installed in vehicles 30_1 to 30_n together with the secondary batteries 20_1 to 20_n. All of the vehicles 30_1 to 30_n are electric vehicles or hybrid vehicles powered by secondary batteries.

[0042] 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 updates the allowable charging power settings for each of the secondary batteries 20_1 to 20_n using a trained model generated by machine learning using the allowable charging power settings.

[0043] For example, if a predetermined number of secondary batteries 20 managed by a predetermined number of battery management devices 10_1 to 10_n have a lower-than-expected allowable charging power set for them after a predetermined period of use, the initial value of the allowable charging power may be too high. In such a case, the control device 40 controls all secondary batteries 20_1 to 20_n managed by battery management devices 10_1 to 10_n to lower the allowable charging power. This suppresses the progression of Li deposition in each secondary battery 20_1 to 20_n. The control device 40 may also set the initial value of the allowable charging power set for newly shipped secondary batteries 20 to a low value, similar to the case of secondary batteries 20_1 to 20_n.

[0044] 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.

[0045] The program described above includes, when loaded into a computer, a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored in a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include Random-Access Memory (RAM), Read-Only Memory (ROM), flash memory, Solid-State Drive (SSD), or other memory technologies, CD-ROM, Digital Versatile Disc (DVD), Blu-ray® disc, or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically, or otherwise propagating signals.

[0046] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be made as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate. [Explanation of Symbols]

[0047] 1. Battery Management System 10 Battery management device 10_1~10_n Battery management device 11. High-frequency signal supply unit 12 Impedance detection unit 13 Calculation Section 14 Control Unit 15 Storage section 20 Secondary battery 20_1~20_n Secondary battery 30_1~30_n Vehicles 40 Control device 50 Networks 100 Battery Management System

Claims

1. A high-frequency signal supply unit that supplies high-frequency signals of 0.1 MHz or higher to a lithium-ion secondary battery, An impedance detection unit that detects the real part value of the AC impedance from a lithium-ion secondary battery to which the aforementioned high-frequency signal is supplied, A calculation unit that calculates the amount of Li deposited in the lithium-ion secondary battery from the real value of the detected AC impedance, A control unit that reduces the allowable charging power for the lithium-ion secondary battery as the calculated amount of Li deposited increases, A battery management device equipped with this device.

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

3. The impedance detection unit detects the real part value of the AC impedance from the lithium-ion secondary battery at a specified measurement interval. The calculation unit calculates the amount of change in Li deposition per specified measurement interval based on the real value of the AC impedance detected at the specified measurement interval. The control unit reduces the allowable charging power for the lithium-ion secondary battery as the amount of Li deposition per specified measurement interval increases. The battery management device according to claim 1.

4. When the amount of Li deposited in the lithium-ion secondary battery reaches a first predetermined amount, the control unit forcibly discharges the lithium-ion secondary battery to dissolve the deposited Li, and when the amount of Li deposited in the lithium-ion secondary battery after dissolving the Li becomes less than or equal to a second predetermined amount (less than the first predetermined amount), it maintains the allowable charging power for the lithium-ion secondary battery without reducing it. The battery management device according to claim 1.

5. A plurality of battery management devices according to claim 1 for managing a plurality of lithium-ion secondary batteries installed in each of a plurality of vehicles, A control device that learns the allowable charging power settings set for each of the plurality of lithium-ion secondary batteries and updates the allowable charging power settings for each of the plurality of lithium-ion secondary batteries based on the learning results, A battery management system equipped with this feature.

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