Battery Management Device

Abstract

To provide a battery management device that enables efficient charging of lithium-ion secondary batteries. [Solution] The battery management device according to this disclosure comprises a high-frequency signal supply unit that applies a high-frequency signal of 0.1 MHz or higher to a lithium-ion secondary battery; an impedance detection unit that detects the actual AC impedance of the lithium-ion secondary battery to which the high-frequency signal has been applied; and a control unit that controls the allowable charging power of the lithium-ion secondary battery based on the actual AC impedance and SOH (State of Health) of the lithium-ion secondary battery.

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 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, an 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) to be excessively 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 that can achieve efficient charging of lithium-ion secondary batteries. [Means for solving the problem]

[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; an impedance detection unit that detects the actual AC impedance of the lithium-ion secondary battery to which the high-frequency signal has been applied; and a control unit that controls the allowable charging power of the lithium-ion secondary battery based on the actual AC impedance and SOH (State of Health) of the lithium-ion secondary battery. [Effects of the Invention]

[0008] This disclosure provides a battery management device that enables 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 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]

[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 (but 0 <x<1)やLi (1-x) Lithium manganese composite oxides such as Mn2O4, with the basic composition formula being Li (1-x) Lithium cobalt composite oxides such as CoO2, with the basic composition formula being Li (1-x) Lithium nickel composite oxides such as NiO2, or the basic composition formula Li (1-x) Ni a Co b Mn c Lithium nickel cobalt manganese composite oxides such as O2 (where a+b+c=1) are used. Note that the positive electrode active material may include other elements in addition to the basic composition formula described above. For the positive electrode current collector, for example, aluminum (Al) is used.

[0015] As the negative electrode active material, for example, a composite oxide containing lithium, a carbon material, or the like is used. Specifically, as the negative electrode active material, an inorganic compound such as lithium, a lithium alloy, or 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, or the like, 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 preferable. Further, examples of the composite oxide used for the negative electrode active material include a lithium titanium composite oxide, a lithium vanadium composite oxide, or the like. As the current collector of the negative electrode, for example, Cu (copper) or the like is used.

[0016] The ion conduction medium is used as an electrolytic solution, for example, by dissolving a supporting salt. As the supporting salt, for example, a lithium salt such as LiPF6 or LiBF4 is used. 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 the 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, as the ion conduction medium, a solid ion 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, or the like, may be used.

[0017] The battery management device 10 performs charge management of the secondary battery 20 to be managed. For example, the battery management device 10 nondestructively detects the presence or absence of Li deposition 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.

[0018] The battery management device 10 includes a high-frequency signal supply unit 11, an impedance detection unit 12, a diagnosis 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, by repeating charging, metallic Li is deposited on the electrode surface of each battery cell. The Li deposition progresses as the charging power is increased to increase the charging speed, and deteriorates the State Of Health (SOH) of the secondary battery 20. Note that the SOH of the secondary battery 20 is the ratio of the current capacity when the initial capacity of the secondary battery 20 is set to 100%. Therefore, it is desirable to set the allowable charge power Pa as high as possible that can efficiently charge the secondary battery 20 in as short a charging time as possible 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 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.

[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 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.

[0026] The memory unit 15 stores the diagnostic results of the State of Health (SOH) of the secondary battery 20. The battery management device 10 may include a diagnostic unit 13 for diagnosing the SOH of the secondary battery 20. Alternatively, an operator may diagnose the SOH of the secondary battery 20 and store the diagnostic results in the memory unit 15 via an input interface (not shown). The method for diagnosing the SOH is not particularly limited, and various known methods can be applied. The SOH may be accurately diagnosed by charging and discharging the secondary battery 20, or it may be diagnosed by estimation using parameters related to the SOH (e.g., number of charge / discharge cycles, charging time, impedance, etc.). The diagnostic unit 13 may control the measurement of the SOH by sending control signals to a measuring instrument.

[0027] Furthermore, the memory unit 15 may store reference values ​​for the real part Z of the AC impedance of the secondary battery 20 for each State of Health (SOH). The higher the SOH, the larger the reference value of the real part Z of the AC impedance, and the lower the SOH, the smaller the reference value of the real part Z of the AC impedance. Note that the reference value does not necessarily have to be associated with the SOH.

[0028] The control unit 14 controls the allowable charging power Pa of the secondary battery 20 based on the real part Z of the AC impedance detected by the impedance detection unit 12 and the State of Health (SOH) of the secondary battery 20. Specifically, the control unit 14 may determine whether the real part of the AC impedance of the secondary battery 20 is smaller than a reference value based on SOH, and control the allowable charging power Pa based on the determination result. However, the control by the control unit 14 is not limited to controlling the allowable charging power Pa based on the determination result. For example, the control unit 14 may estimate the amount of Li deposition based on the real part of the AC impedance and control the allowable charging power Pa based on SOH and the amount of Li deposition.

[0029] For example, the control unit 14 first obtains the real part Z of the AC impedance of the secondary battery 20 to which a high-frequency signal is applied from the impedance detection unit 12. Then, the control unit 14 obtains the SOH value stored in the storage unit 15 or diagnosed by the diagnostic unit 13, and obtains a reference value corresponding to the SOH from the storage unit 15. Then, the control unit 14 determines whether or not to reduce the allowable charging power Pa in the secondary battery 20 based on the difference between the reference value obtained from the storage unit 15 and the AC impedance Z value obtained from the impedance detection unit 12. The control unit 14 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 to reduce the allowable charging power Pa. The control unit 14 may perform other calculations other than subtraction between the reference value and the real part Z of the AC impedance (for example, calculation of a ratio). Furthermore, the calculations performed by the control unit 14 are not limited to calculations using the reference value.

[0030] If the value of the real part Z of the AC impedance is greater than or equal to a reference value, the control unit 14 specifically controls the allowable charging power Pa to either remain at its current level or increase it. If the value of the real part Z of the AC impedance is less than the reference value, the control unit 14 controls the allowable charging power Pa to decrease because it is necessary to suppress the progression of Li deposition. Depending on the determination result, the control unit 14 may gradually decrease the allowable charging power Pa. Alternatively, if the real part of the AC impedance is less than a reference value not associated with the State of Health (SOH), the control unit 14 may control the allowable charging power Pa to decrease based on the SOH. For example, the lower the SOH, the greater the decrease in the allowable charging power Pa may be.

[0031] 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.

[0032] Furthermore, since the battery management device 10 controls the allowable charging power Pa based on the real part Z and SOH of the AC impedance, it reduces the possibility of setting the allowable charging power Pa lower than necessary, thereby enabling more efficient charging.

[0033] (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.

[0034] 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).

[0035] Subsequently, the battery management device 10 obtains the State of Health (SOH) of the secondary battery 20 (step S103). Note that step S103 may be performed before step S101.

[0036] Subsequently, the battery management device 10 determines whether the value of the real part Z of the AC impedance detected in step S102 is smaller than the reference value of the AC impedance corresponding to SOH obtained in step S103 (step S104).

[0037] If the real part Z of the AC impedance is less than the reference value (YES in step S104), the battery management device 10 controls the allowable charging power Pa to be lower because it is necessary to suppress the progress of Li deposition (step S105). If the real part Z of the AC impedance is greater than or equal to the reference value (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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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]

[0042] 1. Battery Management System 10 Battery management device 11. High-frequency signal supply unit 12 Impedance detection unit 13. Diagnostic Department 14 Control Unit 15 Storage section 20 Secondary battery

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, An impedance detection unit for detecting the real part of the AC impedance of the lithium-ion secondary battery to which the high-frequency signal is applied, A control unit controls the allowable charging power of the lithium-ion secondary battery based on the actual value of the AC impedance of the lithium-ion secondary battery and the State of Health (SOH). A battery management device.

2. The control unit determines whether the real part of the AC impedance is smaller than a reference value, and if the real part of the AC impedance is smaller than the reference value, it controls the allowable charging power to be lowered. The battery management device according to claim 1.

3. The aforementioned reference value is based on the SOH. The battery management device according to claim 2.

4. The control unit determines that the real part of the AC impedance is smaller than the reference value, and it gradually reduces the allowable charging power. The battery management device according to claim 2 or 3.

5. Diagnostic unit for diagnosing the SOH of the lithium-ion secondary battery. A battery management device according to claim 1 or 2, comprising:

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