Method for controlling lithium-ion secondary battery

Abstract

To provide a battery control method that can determine an SOC use range of a lithium-ion secondary battery, not limited to situations where a long charge / discharge time can be ensured.SOLUTION: A control method for a lithium-ion secondary battery equipped with a negative electrode including graphite and an active metal material includes controlling the charging and discharging of the lithium-ion secondary battery, calculating the difference between charge transfer resistance of the lithium-ion secondary battery during discharge and the charge transfer resistance of the lithium-ion secondary battery during charging, and on the basis of the difference, determining a use range (SOC use range) of the state of charge (SOC) of the lithium-ion secondary battery.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a control method for determining the SOC usage range of a lithium ion secondary battery. [Background technology]

[0002] Conventionally, a charge / discharge control method that changes the voltage range for charging / discharging according to the deterioration state of a lithium-ion secondary battery is known (Patent Document 1). The charge / discharge control method described in Patent Document 1 acquires battery information related to the charge / discharge state of the lithium-ion battery, calculates a Q-dV / dQ curve that indicates the relationship between the discharge capacity Q of the lithium-ion battery and dV / dQ that indicates the ratio of the change amount dV of the battery voltage V to the change amount dQ of the discharge capacity Q based on the battery information, and judges the deterioration state of the lithium-ion battery based on the Q-dV / dQ curve. Then, based on the judgment result of the deterioration state, changes the voltage range for charging / discharging the lithium-ion battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 025402 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned charge / discharge control method requires discharging at a low rate in order to obtain the Q-dV / dQ curve, and therefore has the problem that the voltage range for charging and discharging cannot be changed unless a long discharge time can be secured.

[0005] The problem to be solved by the present invention is to provide a control method capable of determining the SOC usage range of a lithium ion secondary battery, not limited to situations where a long charge / discharge time can be ensured. [Means for solving the problem]

[0006] The present invention solves the above problem by calculating the difference between the charge transfer resistance when a lithium ion secondary battery is discharged and the charge transfer resistance when the lithium ion secondary battery is charged, and determining the usage range of the state of charge (SOC) of the lithium ion secondary battery (SOC usage range) based on this difference. Effect of the Invention

[0007] According to the present invention, the SOC usage range of a lithium ion secondary battery can be determined not only in situations where a long charge / discharge time can be ensured. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing a battery control system for a secondary battery according to this embodiment. [Diagram 2] FIG. 2 shows a perspective view of the secondary battery before assembly and a plan view of the secondary battery. [Diagram 3] FIG. 3 is a graph showing the characteristics of the capacity retention rate versus the number of cycles of a secondary battery. [Figure 4] FIG. 4 is a graph showing the capacity retention rate when the SOC usage range is set to 50 to 100% and the capacity retention rate when the SOC usage range is set to 0 to 100% for a secondary battery including a Gr / SiO negative electrode. [Diagram 5] FIG. 5 is a Nyquist plot showing AC impedance characteristics. [Figure 6] FIG. 6 is a Bode plot showing AC impedance characteristics. [Figure 7] FIG. 7 is a graph showing the characteristics of the imaginary component ratio (Z"_d / Z"_c) at 1 Hz versus SOC. [Figure 8] FIG. 8(a) is a graph showing the characteristics of the phase difference (θ_d, θ_c) of AC impedance at 1 Hz versus SOC, and FIG. 8(b) is a graph showing the characteristics of the phase difference ratio (θ_d / θ_c) versus SOC. [Figure 9]FIG. 9 is a flowchart showing a procedure of a control process in the system for determining the SOC use range. [Figure 10] FIG. 10 is a flowchart showing a sub-flow of the control process in step S2 shown in FIG. [Figure 11] FIG. 11 is a flowchart showing a procedure of a control process in a system for determining an SOC usage range in a battery control system for a secondary battery according to another embodiment of the present invention. [Figure 12] FIG. 12 is a graph for explaining the relationship between the magnitude of the SOC estimated in the control process of step 32 shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] First Embodiment An embodiment of a control device and control method for determining the SOC usage range of a lithium-ion secondary battery according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a battery control system including an embodiment of a battery control device according to the present invention. As shown in FIG. 1, the battery control system according to this embodiment is a system for controlling charging and discharging of a secondary battery 2 and determining the SOC usage range of the secondary battery 2. The battery control system includes a battery control device 1 and a secondary battery 2. Note that the battery control device 1 may include a charging device and the like that are not shown in FIG. 1.

[0010] The battery control device 1 includes a controller 10, a voltage sensor 11, a current sensor 12, and a DCDC converter 13. The controller 10 is a battery control unit (BCU). The controller 10 manages the state of the secondary battery 2 based on the detected voltage detected by the voltage sensor 11 and / or the detected current detected by the current sensor 12, and determines the SOC usage range of the secondary battery 2 according to the state of the secondary battery 2. The controller 10 is composed of a memory such as a ROM or a RAM, a processor such as a CPU, and the like.

[0011] The voltage sensor 11 is a sensor for detecting the voltage between the terminals of the secondary battery 2. The voltage sensor 11 is connected between the wiring connected to the positive and negative electrodes of the secondary battery 2. The current sensor 12 is a sensor for detecting the input / output current of the secondary battery 2. The current sensor 12 is connected to the wiring connected to the positive or negative electrode of the secondary battery 2. The voltage sensor 11 and the current sensor 12 detect the state of the battery, and output the detected values ​​to the controller 10.

[0012] The DCDC converter 13 is a power conversion device that converts the voltage input from the secondary battery 2 to a predetermined voltage and outputs power to a load such as a motor. The DCDC converter 13 is also a power conversion device that converts the voltage input from a load such as a motor or a charging device to a predetermined voltage and outputs power to the secondary battery 2. The DCDC converter 13 is controlled by the controller 10. The secondary battery 2 is connected to the input side of the DCDC converter 13, and a load is connected to the output side of the DCDC converter 13. The load is a power grid or the like. That is, the secondary battery 2 is connected to the load via the DCDC converter 13.

[0013] The secondary battery 2 is, for example, a lithium ion secondary battery. In this type of secondary battery 2, an example can be one that uses, as the negative electrode active material, an active material having a plurality of charge / discharge regions in which the charge / discharge potential changes stepwise with the insertion / extraction of lithium ions. As such an active material, a graphite-based active material containing a graphite structure is suitable. Therefore, in the embodiment shown below, the present invention will be described by exemplifying a lithium ion secondary battery having a negative electrode containing graphite and a metal active material. In the following description, the structure and materials of the secondary battery 2 in the case of an electrolyte lithium ion secondary battery will be described, but the secondary battery 2 may be an all-solid-state lithium ion secondary battery. In addition, in the following, a laminated battery (laminated cell) will be described as an example of the secondary battery 2, but the secondary battery 2 may be a square battery (square cell) or a cylindrical battery (cylindrical cell).

[0014] 2 shows a perspective view of the secondary battery 2 before assembly and a plan view of the secondary battery 2. As shown in Fig. 2(a), the secondary battery 2 includes a positive electrode layer 21, a negative electrode layer 22, a separator 23, a positive electrode tab 24 connected to the positive electrode layer 21, a negative electrode tab 25 connected to the negative electrode layer 22, an upper exterior member 26, and a lower exterior member 27. The power generating element constituted by the positive electrode layer 21, the negative electrode layer 22, and the separator 23, the positive electrode tab 24, and the negative electrode tab 25 are housed in a sealed state by the upper exterior member 26 and the lower exterior member 27.

[0015] The positive electrode layer 21 is formed by preparing a slurry by adding a positive electrode active material, a conductive agent such as carbon black, a binder such as polyvinylidene fluoride, and an organic solvent such as N-methyl-2-pyrrolidone, applying the slurry to a main surface of a positive electrode side current collector, which is a metal foil such as aluminum, and then drying and pressing. The positive electrode active material is not particularly limited, and examples thereof include lithium composite oxides such as lithium nickel oxide (LiNiO2), lithium manganate (LiMn2O4), and lithium cobalt oxide (LiCoO2), LiFePO4, and LiMnPO4.

[0016] The negative electrode active material layer constituting the negative electrode layer 22 is formed by mixing a negative electrode active material, which is a mixture of at least two types of active materials, graphite (carbon) and a metal, with a water-based binder such as styrene butadiene rubber, and water as a solvent to prepare a slurry, which is applied to a main surface of a portion of the negative electrode side current collector, which is a metal foil such as copper, and then drying and pressing. Examples of metals contained in the negative electrode active material include metals mainly composed of Si, Sn, Sb, Pb, Al, Ge, etc., or compounds of metals of these main elements.

[0017] The separator 23 prevents a short circuit between the above-mentioned positive electrode layer 21 and negative electrode layer 22, and may have a function of retaining an electrolyte. This separator is, for example, a microporous film made of polyolefin such as polyethylene (PE) or polypropylene (PP), and when an overcurrent flows, the pores in the layer are blocked by the heat generated, thereby having a function of cutting off the current.

[0018] The electrolyte solution contained in the secondary battery 2 is a liquid in which a lithium salt such as lithium fluoroborate (LiBF4) or lithium hexafluorophosphate (LiPF6) is dissolved as a solute in an organic liquid solvent. Examples of the organic liquid solvent constituting the electrolyte solution include ester-based solvents such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl formate (MF), methyl acetate (MA), and methyl propionate (MP), and these can be used in combination.

[0019] The positive electrode tab 24 and the negative electrode tab 25 may be made of aluminum foil, aluminum alloy foil, copper foil, nickel foil, etc. The positive electrode tab 24 is joined to the current collector of the positive electrode layer 21, and the negative electrode tab 25 is joined to the negative electrode layer 22.

[0020] As shown in FIG. 2(a), the positive electrode layer 21 and the negative electrode layer 22 are laminated with a separator 23 interposed therebetween, and a power generating element is formed by these. Then, the power generating element is housed in an upper exterior member 26 and a lower exterior member 27 so that the surfaces of the positive electrode layer 21 and the negative electrode layer 22 are covered. The upper exterior member 26 and the lower exterior member 27 are formed of a flexible material such as a resin film such as polyethylene or polypropylene, or a resin-metal thin film laminate material in which both sides of a metal foil such as aluminum are laminated with a resin such as polyethylene or polypropylene. Then, an electrolyte is injected into the battery, and the periphery of the exterior members 26 and 27 is heat-sealed and sealed in a state in which the positive electrode tab 24 and the negative electrode tab 25 are led out to the outside, thereby forming the secondary battery 2.

[0021] The secondary battery 2 is electrically connected to a charging device. The charging device connected to the secondary battery 2 is, for example, a device for charging the secondary battery 2 mounted on an electric vehicle or a hybrid vehicle. The secondary battery 2 mounted on the vehicle is charged by removing the charging cable of the charging device, attaching a charging gun at the end of the charging cable to a connector of a charging port of the vehicle, and operating a charging start switch. The controller 10 manages the state of charge (State of Charge: SOC) of the secondary battery 2 and controls the DCDC converter 13 and the charging device so that the state of charge of the secondary battery 2 becomes a target state of charge.

[0022] The secondary battery 2 is electrically connected to a load such as a motor. The load is a device that operates using the power of the secondary battery 2, such as a motor that serves as a drive source for the vehicle, and auxiliary devices such as an air conditioner and lights. Discharging of the secondary battery 2 is executed under the control of the controller 10 in response to a system request or an external power request. The system request corresponds to a command from an on-board computer such as an ECU while the vehicle is running. With regard to a power request from the outside, for example, when an air conditioner is operated by a timer setting in response to a command from an external device such as a mobile terminal before the vehicle starts running so that the interior of the vehicle is at an appropriate temperature when the vehicle starts running, the command from the external device corresponds to a power request from the outside.

[0023] Furthermore, the secondary battery 2 installed in an electric vehicle or a hybrid vehicle may be used for Vehicle Grid Integration (VGI). VGI is a technology in which an electric vehicle or a hybrid vehicle equipped with a secondary battery 2 is connected to a power grid, and the power stored in the secondary battery 2 is supplied to the power grid (load) via the power grid.

[0024] Next, the deterioration characteristics and the SOC range of the lithium ion secondary battery 2 will be described. When a mixture of graphite and a metal active material is used in the negative electrode as in this embodiment, when the secondary battery 2 is charged and discharged in the SOC range in which the contribution of the metal active material is large, deterioration of the metal active material is promoted. FIG. 3 is a graph showing the characteristics of the capacity maintenance rate versus the number of cycles of the secondary battery 2. The number of cycles is the number of times that charging and discharging are performed between 0% and 100% SOC. The capacity maintenance rate represents the degree of deterioration when the battery capacity of the secondary battery 2 in the initial state is set to 1.0. In FIG. 3, graph a shows the characteristics of the secondary battery 2 equipped with a negative electrode (hereinafter also referred to as a Gr negative electrode) that does not contain a metal active material but contains graphite as the negative electrode active material. Graph b shows the characteristics of the secondary battery 2 equipped with a negative electrode (hereinafter also referred to as a Gr / SiO negative electrode) that contains a mixture of graphite and a metal as the negative electrode active material. The metal active material is a metal compound (SiO) containing Si as the main element. 3, with an increase in the number of cycles, the capacity retention rate of the secondary battery 2 including the Gr / SiO negative electrode becomes lower than that of the secondary battery 2 including the Gr negative electrode. In other words, the battery capacity of the secondary battery 2 including the Gr / SiO negative electrode decreases more quickly.

[0025] The graph in FIG. 4 shows the capacity retention rate when the SOC usage range is 50 to 100% and the capacity retention rate when the SOC usage range is 0 to 100% for the secondary battery 2 having a Gr / SiO negative electrode. The characteristics when the SOC usage range is 50 to 100% have a cycle number of about 100, and the characteristics when the SOC usage range is 0 to 100% have a cycle number of about 50. The SOC usage range is a range in which the secondary battery 2 can be used, expressed in terms of SOC, and the secondary battery 2 is charged and discharged so that the SOC of the secondary battery 2 falls within the SOC usage range. As shown in FIG. 4, when the SOC usage range is 50 to 100%, the capacity retention rate when the SOC usage range is 50 to 100% is larger than the capacity retention rate when the SOC usage range is 0 to 100%, even if the cycle number is about twice as many as when the SOC usage range is 0 to 100%. That is, the secondary battery 2 including the Gr / SiO negative electrode can suppress a decrease in battery capacity by avoiding charging and discharging at a low SOC.

[0026] In this way, when the secondary battery 2 having the Gr / SiO negative electrode is charged and discharged in a low SOC range, the contribution of the metal active material becomes large, and deterioration is accelerated. Therefore, in order to suppress deterioration of the secondary battery 2, it is necessary to charge and discharge in an SOC range in which the contribution of the metal active material is small. In addition, since the SOC range in which the contribution of the metal active material is small changes depending on the deterioration state of the secondary battery 2, it is necessary to detect the SOC range.

[0027] In contrast, in this embodiment, the charge transfer resistance during discharge of the lithium ion secondary battery (hereinafter, the discharge charge transfer resistance (R d ) and the charge transfer resistance during charging of a lithium-ion secondary battery (hereinafter referred to as the charging charge transfer resistance (R cThe difference between the SOC and the SOC of the battery is calculated, and the SOC range is determined based on the difference. This makes it possible to detect the SOC range in which the contribution of the metal active material is large, and to avoid charging and discharging in that SOC range. Note that the charge transfer resistance corresponds to the reaction resistance. In this embodiment, specifically, the imaginary component of the AC impedance during discharge (hereinafter referred to as the discharge imaginary component (Z")) is used as an index representing the difference in charge transfer resistance. _d ) and the imaginary component of the AC impedance during charging (hereinafter referred to as the charging imaginary component (Z” _c In other words, the discharge charge transfer resistance (R_ d ) and charge transfer resistance (R_ c The difference between this and the imaginary discharge component (Z” _d ) and the imaginary component of the charge (Z” _c ) and the ratio (Z” _d / Z” _c、 Z” _c / Z” _d ) and the difference (Z” _d -Z” _c , Z.” _c -Z” _d The following is an evaluation result of the correlation between the imaginary component of the AC impedance during charging and discharging and the SOC range. In the following explanation, the discharge charge transfer resistance (R d ) and charge transfer resistance (R_ c The imaginary component ratio (Z” _d / Z” _c ) is calculated.

[0028] <Creating a prototype (example)> The negative electrode layer was created by mixing graphite carbon (Gr) and silicon oxide (SiO) in a mass ratio of 95:5 as the negative electrode active material, using styrene butadiene rubber (SBR) as the binder, forming a slurry, and applying it on copper foil. The positive electrode layer was created by using lithium nickel oxide (NCA) as the positive electrode active material, carbon black as a conductive assistant, and PVDF as the binder, forming a slurry, and applying it on aluminum foil. A polyethylene (PE) film was used as the separator. The electrolyte was a mixture of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) with lithium hexafluorophosphate (LiPF6) dissolved in it. The negative electrode layer, separator, and positive electrode layer were sandwiched between aluminum laminates, the electrolyte was injected into the inside, and the laminate was sealed to create a test cell (prototype).

[0029] <Evaluation of secondary batteries> Next, the secondary battery was evaluated by EIS measurement using the fabricated prototype. FIG. 5 is a Nyquist plot showing the AC impedance characteristics, and FIG. 6 is a Bode plot showing the AC impedance characteristics. The vertical axis of FIG. 5 represents the imaginary component (Z") of the AC impedance, and the horizontal axis of FIG. 5 represents the real component (Z') of the AC impedance. The vertical axis of FIG. 6 represents the imaginary component (Z") of the AC impedance, and the horizontal axis of FIG. 6 represents the frequency. Graphs a, c, and e of FIG. 5 and FIG. 6 show the imaginary component (Z") of the AC impedance during discharge of secondary battery 2 having a Gr / SiO negative electrode. _d ) characteristics. On the other hand, graphs b, d, and f show the imaginary component (Z″ ) of the AC impedance during charging of the secondary battery 2 having the Gr / SiO negative electrode. _c ) characteristics. Also, the diameter (R d ,R_ c ) indicates the magnitude of the charge transfer resistance. Graphs a to f in Fig. 5 and Fig. 6 were calculated according to the following procedure.

[0030] (1) First, the secondary battery 2 was discharged to 2.5 V at 0.2 C, and then charged to a voltage equivalent to SOC 10% at 0.2 C. After the voltage of the secondary battery 2 reached a voltage equivalent to SOC 10%, it was switched to constant voltage charging, and charging was terminated when the current value decreased to 0.01 C.

[0031] (2) Next, EIS (Electro-chemical Impedance Spectroscopy) measurement was performed according to the following procedure. First, charging of the secondary battery 2 was started at 0.1C, and EIS measurement was performed during the charging (hereinafter, also referred to as charging EIS measurement) to measure the AC impedance during charging. At this time, the frequency was changed from 5Hz to 1Hz, and the AC impedance was measured at eight points, and the current amplitude was set to 0.1C. After the charging EIS measurement was completed, charging was stopped. Next, discharging was performed for the same charging time and at the same current value as the charging EIS measurement, and the SOC was returned to before the charging EIS measurement. Next, discharging was started at 0.1C, and EIS measurement was performed during discharging under the same conditions as the charging EIS measurement (hereinafter, also referred to as discharging EIS measurement), to measure the AC impedance during discharging. After the discharging EIS measurement was completed, discharging was stopped. Next, charging was performed for the same discharging time and at the same current value as the discharging EIS measurement, and the SOC was returned to before the discharging EIS measurement. Graph b was obtained by plotting the AC impedances obtained by the above-mentioned charge EIS measurement. Similarly, graph a was obtained by plotting the AC impedances obtained by the discharge EIS measurement.

[0032] (3) Next, the secondary battery 2 was charged at 0.2 C to a voltage equivalent to SOC 30%. After the voltage of the secondary battery 2 reached a voltage equivalent to SOC 30%, it was switched to constant voltage charging, and charging was terminated when the current value decreased to 0.01 C.

[0033] (4) Next, under the same conditions as in (2) above, charge EIS measurement and discharge EIS measurement were performed. Graph d was obtained by plotting the AC impedance obtained in this charge EIS measurement. Similarly, graph c was obtained by plotting the AC impedance obtained in the discharge EIS measurement.

[0034] (5) Next, the secondary battery 2 was charged at 0.2 C to a voltage equivalent to SOC 50%. After the voltage of the secondary battery 2 reached a voltage equivalent to SOC 50%, the charging was switched to constant voltage charging, and the charging was terminated when the current value decreased to 0.01 C.

[0035] (6) Next, under the same conditions as in (2) above, charge EIS measurement and discharge EIS measurement were performed. Graph f was obtained by plotting the AC impedance obtained in this charge EIS measurement. Similarly, graph e was obtained by plotting the AC impedance obtained in the discharge EIS measurement.

[0036] As shown in Figs. 5 and 6 obtained as described above, in the secondary battery 2 including the Gr / SiO negative electrode, when the SOC is 30% (see graphs c and d) and 50% (see graphs e and f), the discharge imaginary component (Z" _d ) and the imaginary component of the charge (Z” _c On the other hand, when the SOC is 10% (see graphs a and b), the difference between the discharge imaginary component (Z” _d ) and the imaginary component of the charge (Z” _c In other words, in the SOC range where Gr contributes to charging and discharging, the discharge imaginary component (Z” _d ) and the imaginary component of the charge (Z” _c ) is small. Therefore, although not shown in the figure, the discharge charge transfer resistance R_ d and the charge transfer resistance R_ c On the other hand, in the SOC range where SiO contributes greatly to charging and discharging, the discharge imaginary component (Z _d ) and the imaginary component of the charge (Z” _c ) is large. Therefore, as shown in Figure 5, the discharge charge transfer resistance R d and the charge transfer resistance R_ c The difference is also getting larger.

[0037] In addition, as shown in FIG. 6, in the secondary battery 2 having the Gr / SiO negative electrode, when the SOC is 30% (see graphs c and d) and 50% (see graphs e and f), the discharge imaginary component (Z″ _d ) than the imaginary component (Z” _c On the other hand, when the SOC is 10% (see graphs a and b), the discharge imaginary component (Z” _d ) than the imaginary component (Z” _c In other words, in the SOC range where Gr contributes to charging and discharging, the discharge imaginary component (Z” _d ) than the imaginary component (Z” _c On the other hand, in the SOC range where SiO contributes greatly to charging and discharging, the discharge imaginary component (Z” _d ) than the imaginary component (Z” _c ) has become smaller.

[0038] Figure 7 shows the imaginary component ratio (Z” at 1 Hz) versus SOC. _d / Z” _c The vertical axis of FIG. 7 shows the imaginary component ratio (Z” _d / Z” _c ) and the horizontal axis of FIG. 7 represents SOC. As shown in FIG. 7, in the secondary battery 2 having the Gr / SiO negative electrode, the smaller the SOC value, the smaller the imaginary component ratio (Z″ _d / Z” _c ) is getting larger. And the imaginary component ratio (Z” _d / Z” _c When the secondary battery 2 is charged and discharged within the SOC range in which the imaginary component ratio (Z") is greater than the imaginary component ratio threshold (for example, 1.0), the secondary battery 2 is charged and discharged within the SOC range in which the contribution of SiO is large, and deterioration of the metal active material is accelerated. _d / Z” _c ) and calculate the imaginary component ratio (Z” _d / Z” _cThe range of SOC in which Z” is less than the imaginary component ratio threshold (for example, 1.0) is determined as the SOC usage range. This makes it possible to detect the SOC range in which the contribution of the metal active material is large, and to avoid charging and discharging in that SOC range. In addition, the imaginary component ratio is Z” _d / Z” _c Not limited to Z” _c / Z” _d Also, the SOC range can be determined by the imaginary component difference (Z” _d -Z” _c , Z.” _d -Z” _c ) may also be used.

[0039] Alternatively, the phase of the AC impedance during charging and discharging can be used as an index showing the difference in charge transfer resistance. difference θ(θ=tan -1 (-Z″ / Z′)) may be used. FIG. 8(a) shows the phase of AC impedance with respect to SOC. difference (θ_ d , θ_ c ) and Fig. 8(b) is a graph showing the characteristics of the phase at 1 Hz against the SOC. difference Ratio(θ_ d / θ_ c ) is a graph showing the characteristics of the phase difference The horizontal axis of FIG. 8(a) represents frequency. The vertical axis of FIG. 8(b) represents phase. difference Ratio(θ_ d / θ_ c ) and the horizontal axis of FIG. 8(b) represents SOC. Graphs a, c, and e in FIG. 8(a) represent the phase of AC impedance during discharge of the secondary battery 2 having the Gr / SiO negative electrode. difference (θ_ d ) characteristics. On the other hand, graphs b, d, and f show the phase angle (θ_ c ) characteristics. In the following, (θ_ d ) discharge phase difference , (θ_ c ) charging phase difference It is also sometimes called.

[0040] In this case, in the SOC range in which Gr contributes to charging and discharging, the discharge phase difference (θ_ d ) than the charging phase difference (θ_ c On the other hand, in the SOC range where SiO contributes greatly to charging and discharging, the discharge phase difference (θ_ d ) than the charging phase difference (θ_ c ) is smaller. Therefore, as shown in Fig. 8(b), the phase at 1 Hz difference Ratio(θ_ d / θ_ c ) and calculate the calculated phase difference Ratio(θ_ d / θ_ c ) is the phase difference By determining the range of SOC below a threshold value (for example, 1.0) as the range of SOC use, it is possible to detect the range of SOC in which the contribution of the metal active material is large, and to avoid charging and discharging in that SOC range. difference The ratio is θ_ d / θ_ c Not limited to θ_ c / θ_ d In addition, the SOC range may be determined based on the phase difference Instead of a ratio, Charging phase difference and discharging phase difference Difference with (θ_ c -θ_ d , θ_ d -θ_ c ) may also be used.

[0041] In this embodiment, the controller 10 (see FIG. 1) calculates the imaginary component (Z″) of the AC impedance during charging and discharging as the difference in charge transfer resistance during charging and discharging of the secondary battery 2. _c , Z.” _d ) and calculate the imaginary component ratio (Z” _d / Z” _c ) is used to determine the SOC usage range of the secondary battery 2. Hereinafter, a method for determining such an SOC usage range will be described.

[0042] 9 is a flowchart showing the procedure of the control process in the system for determining the SOC usage range. The upper limit value (upper SOC) of the SOC usage range is preset, and is set to, for example, 100% or 80%. The upper SOC limit may be changed depending on the specification, use, and deterioration level of the secondary battery 2.

[0043] In step S1, the controller 10 turns on a switch (not shown) connected between the secondary battery 2 and the power grid, thereby connecting the secondary battery 2 to the power grid.

[0044] In step S2, the controller 10 calculates the discharge imaginary component (Z" _d ) and the imaginary component of the charge (Z” _c FIG. 10 is a flowchart showing a sub-flow of the control process in step S2. The controller 10 executes the control process in steps S21 to S29 shown in FIG. 10 to calculate the discharge imaginary component (Z″ _d ) and the imaginary component of the charge (Z” _c ) is calculated. In addition to the control processes of steps S21 to , the controller 10 detects the voltage and current of the secondary battery 2 at a predetermined cycle using the voltage sensor 11 and current sensor 12. The shorter the detection cycle (sample rate), the higher the accuracy, and is set to 1 second (1 Hz), for example. The battery temperature may be any temperature, but it is preferable that the change in battery temperature is as small as possible while the control flows of Figs. 9 and 10 are being executed.

[0045] As shown in FIG. 10, in this embodiment, although not limited to this, the discharge imaginary component (Z″ _d ) and the imaginary component of the charge (Z” _c Specifically, first, in step S21, the secondary battery 2 is charged. Next, in step S22, the AC impedance during charging is measured to calculate the imaginary axis component value of the AC impedance (charge imaginary component (Z" _c Next, in step S23, the measurement of the AC impedance is ended and charging is stopped.

[0046] The AC signal applied to measure the AC impedance may be an AC current or an AC voltage. The frequency of the AC signal is preferably in a frequency band in which the charge and discharge reaction of SiO appears, and may be, for example, 5 Hz or less. The waveform of the AC signal may be, for example, a sine wave that is generally used in EIS measurement. Alternatively, the waveform of the AC signal may be a square wave. In this embodiment, the secondary battery 2 is charged with a charging current Ic for a time tc. This charging current Ic may be any value, but is set to, for example, 0.1 C to ensure sufficient accuracy. The larger the value of this charging current and the value of the discharging current, the larger the charging imaginary component (Z" _c ) and the discharge imaginary component (Z” _d ) is easily captured. Conversely, the smaller the value of the charging current and the value of the discharging current (described later), the smaller the change in SOC during EIS measurement can be. The amplitude of the AC current or AC voltage may be any value, but is set to, for example, 0.1 C or more to ensure sufficient accuracy. The time tc may be any value required for EIS measurement. The battery voltage may be measured for multiple cells together or may be measured for each cell, but EIS measurement can be performed with higher accuracy by measuring the battery voltage for each cell.

[0047] In step S24, the controller 10 discharges the secondary battery at a current Ic for a time tc, thereby returning the SOC of the secondary battery to the value before the start of charging in step S21.

[0048] In step S25, the controller 10 discharges the secondary battery 2. In this embodiment, the secondary battery is discharged at a discharge current Id for a time td. The discharge current Id may be any value, but in order to ensure sufficient accuracy, it is set to, for example, the same value as the charging current Ic. Next, in step S26, the AC impedance during discharging is measured to obtain the imaginary axis component value of the AC impedance (discharge imaginary component (Z" _d) is calculated. Next, in step S27, the measurement of the AC impedance is ended and the discharge is stopped. Next, in step S28, the controller 10 charges the secondary battery at a current Id for a time td. This returns the SOC of the secondary battery to the value before the discharge started in step S25.

[0049] In this embodiment, since it is sufficient to perform EIS measurement during charging and discharging at one frequency, the SOC usage range can be determined in a short time. Note that EIS measurement during charging and discharging may be performed at multiple frequencies.

[0050] Returning to Figure 9, from the above calculation results, the imaginary component ratio (Z _d / Z” _c After calculating the imaginary component ratio (Z″), in step S3, the controller 10 _d / Z” _c ) is compared with the imaginary component ratio threshold, and the imaginary component ratio (Z” _d / Z” _c ) is less than the imaginary component ratio threshold. The imaginary component ratio threshold is a threshold for setting the lower limit of the SOC usage range, and is set in advance. The imaginary component ratio threshold may be set according to an allowable deterioration rate and / or an allowable deterioration degree depending on the use of the secondary battery 2, etc. The imaginary component ratio threshold may be set according to the specifications of the negative electrode active material (metal active material ratio, type of metal used in the metal active material, etc.). The imaginary component ratio threshold may also be set according to the detection accuracy of the voltage and / or current of the secondary battery 2, etc. In the present embodiment, the imaginary component ratio threshold is set to 1.0, for example.

[0051] Calculated imaginary component ratio (Z” _d / Z” _c If the calculated imaginary component ratio (Z″) is lower than the imaginary component ratio threshold (1.0), the controller 10 executes the control process of steps S4 to S8. _d / Z” _c If the imaginary component ratio threshold (1.0) is equal to or greater than the imaginary component ratio threshold, the controller 10 executes the control process of steps S9 to S13.

[0052] In step S4, the controller 10 discharges the secondary battery 2. The imaginary component ratio (Z" _d / Z” _c If the imaginary component ratio threshold (Z") is lower than the imaginary component ratio threshold (1.0), the SOC of the secondary battery 2 is higher than the lower limit of the SOC usage range, so the SOC is lowered to determine the lower limit of the SOC usage range corresponding to the imaginary component ratio threshold (1.0). In step S5, the controller 10 stops discharging. In step S6, the controller 10 calculates the discharge imaginary component (Z") _d ) and the imaginary component of the charge (Z” _c ) is calculated. _d ) and the imaginary component of the charge (Z” _c ) is calculated in the same manner as in the control process of step S2.

[0053] In step S7, the controller 10 calculates the imaginary component ratio (Z _d / Z” _c ) is compared with the imaginary component ratio threshold (1.0), and the imaginary component ratio (Z” _d / Z” _c Determine whether the imaginary component ratio (Z” _d / Z” _c If the imaginary component ratio threshold (Z") is lower than the imaginary component ratio threshold (1.0), the controller 10 returns the control process flow to step S4 and discharges the secondary battery 2. That is, by repeatedly executing the control processes of steps S4 to S7, the imaginary component ratio (Z") is adjusted so that the SOC approaches the lower limit of the SOC usage range from the high SOC side. _d / Z” _c ) approach the imaginary component ratio threshold (1.0).

[0054] Imaginary component ratio (Z” _d / Z” _c If the imaginary component ratio (Z″) is equal to or greater than the imaginary component ratio threshold (1.0), then in step S8, the controller 10 determines the current SOC to be the lower limit (lower limit SOC) of the SOC usage range. _d / Z” _cThe SOC when the imaginary component ratio threshold (1.0) is reached is determined as the lower limit SOC of the SOC usage range.

[0055] In step S9, the controller 10 charges the secondary battery 2. The imaginary component ratio (Z" _d / Z” _c If the imaginary component ratio threshold (1.0) is greater than the imaginary component ratio threshold (1.0), the SOC of the secondary battery 2 is equal to or lower than the lower limit of the SOC usage range, so the SOC is increased to determine the lower limit of the SOC usage range corresponding to the imaginary component ratio threshold (1.0). Since the charging in the control process of step S9 is outside the SOC usage range, the charging current is reduced so as not to accelerate deterioration of the secondary battery 2. For example, the charging current rate may be set to 0.5 C or less. In step S10, the controller 10 stops charging. In step S11, the controller 10 calculates the discharge imaginary component (Z") _d ) and the imaginary component of the charge (Z” _c ) is calculated. _d ) and the imaginary component of the charge (Z” _c ) is calculated in the same manner as in the control process of step S2.

[0056] In step S11, the controller 10 calculates the imaginary component ratio (Z _d / Z” _c ) is compared with the imaginary component ratio threshold (1.0), and the imaginary component ratio (Z” _d / Z” _c Determine whether the imaginary component ratio (Z” _d / Z” _c If the imaginary component ratio (Z") is equal to or greater than the imaginary component ratio threshold (1.0), the controller 10 returns the control process flow to step S9 and charges the secondary battery 2. That is, by repeatedly executing the control processes of steps S9 to S12, the imaginary component ratio (Z") is adjusted so that the SOC approaches the lower limit of the SOC usage range from the low SOC side. _d / Z” _c ) approach the imaginary component ratio threshold (1.0).

[0057] Imaginary component ratio (Z” _d / Z”_c If the imaginary component ratio (Z″) is less than the imaginary component ratio threshold (1.0), in step S13, the controller 10 determines the current SOC to be the lower limit value (lower limit SOC) of the SOC usage range. _d / Z” _c The SOC at which the imaginary component ratio (Z”) reaches the imaginary component ratio threshold (1.0) is determined as the lower limit SOC of the SOC usage range. Then, the controller 10 ends the flow of control processing for determining the SOC usage range. As a result, the controller 10 _d / Z” _c ) to determine the SOC range of use.

[0058] Then, the controller 10 sets the SOC use range determined by the control processing in steps S8 and S13 based on the calculated imaginary component ratio (Z _d / Z” _c ) and stored in memory. During normal use of the secondary battery 2, the controller 10 controls the charging and / or discharging of the secondary battery 2 so that the SOC falls within the SOC usage range stored in the memory. Note that the SOC usage range of the secondary battery 2 is a target range for suppressing the deterioration rate of the secondary battery 2, and the secondary battery 2 may be charged or discharged outside the SOC usage range. Furthermore, in order to determine the SOC usage range of the secondary battery 2, charging or discharging may be performed outside the SOC usage range determined previously.

[0059] In order to increase the battery capacity of a lithium-ion secondary battery, a mixture of graphite and a metal active material is used in the negative electrode as a negative electrode active material. However, when charging and discharging are performed in a range of SOC in which the contribution of the metal active material of the negative electrode is large, deterioration is promoted. In this embodiment, the range of SOC in which the contribution of the metal active material of the negative electrode is large can be detected with high accuracy and in a short time. Then, the SOC range in which the SOC is used is determined while avoiding the range of SOC in which the contribution of the metal active material of the negative electrode is large, so that charging and discharging are performed in a range of SOC in which the deterioration of the metal active material is small. As a result, the decrease in the capacity retention rate can be suppressed and the cycle characteristics can be improved.

[0060] As described above, in this embodiment, the charge and discharge of the secondary battery 2 is controlled, and the discharge charge transfer resistance (R d ) and the charge transfer resistance (R_ c ) and calculate the difference between them, and determine the SOC range based on that difference. d ) and the charge transfer resistance (R_ c The difference between this and the imaginary component ratio (Z” _d / Z” _c ) This allows the range of SOC to which the metal active material of the negative electrode contributes to be grasped in a short time, and charging and discharging within that range can be avoided. In other words, the SOC usage range of the secondary battery 2 can be determined not only in situations where a long charging and discharging time can be secured. In addition, the SOC usage range is set to avoid the SOC range in which the contribution of the metal active material of the negative electrode is large. Then, during normal use of the secondary battery 2, charging and discharging are performed within the SOC usage range, and therefore it is possible to suppress the capacity reduction of the lithium-ion secondary battery that is caused by the deterioration of the metal active material of the negative electrode.

[0061] In addition, SiO has different overvoltages on the charge side and the discharge side. The difference in overvoltage during charging and discharging is divided into IR (electrolyte resistance, electric resistance of active material, etc.) and overvoltages other than IR (charge transfer resistance, diffusion resistance, etc.). In this embodiment, since the overvoltages other than IR can be measured by EIS, the SiO contribution range can be accurately determined even if IR changes due to deterioration, etc. As a result, the SOC usage range to which SiO contributes can be grasped more accurately, and the lower limit of the SOC usage range can be expanded to the vicinity of the SOC usage range to which SiO contributes, and the SOC usage range can be further expanded.

[0062] In this embodiment, the SOC range where the contribution of the metal active material is large is detected from the difference between the discharge charge transfer resistance (R_d) and the charge charge transfer resistance (R_c). However, as another method, it can also be detected from the difference in the DC resistance at the end of charging and the end of discharging, or the difference in the voltage change after charging and discharging are stopped. The difference in the DC resistance at the end of charging and the end of discharging, or the difference in the voltage change after charging and discharging are stopped, includes reaction resistance, liquid resistance, and ion transport resistance as resistance elements, but the difference between the discharge charge transfer resistance (R_d) and the charge charge transfer resistance (R_c) is calculated from the reaction resistance. In other words, the method of detection from the difference between the discharge charge transfer resistance (R_d) and the charge charge transfer resistance (R_c) can improve detection accuracy by reducing the number of resistance elements that affect the detection value.

[0063] In this embodiment, the discharge charge transfer resistance (R d ) and the charge transfer resistance (R_ c ) and the value indicating the difference (imaginary component ratio (Z” _d / Z” _c ) is less than the imaginary component ratio threshold. This makes it possible to control charging and discharging while avoiding the SOC range in which the contribution of the metal active material in the negative electrode is large. As a result, it is possible to suppress the capacity reduction of the lithium ion secondary battery due to the deterioration of the metal active material in the negative electrode.

[0064] In this embodiment, the metal active material of the negative electrode contains Si. This allows the battery to be charged and discharged while avoiding the SOC range in which the contribution of the metal active material of the negative electrode is large when Si is used as the metal active material to increase the battery capacity, thereby suppressing the capacity reduction of the lithium ion secondary battery due to the degradation of Si.

[0065] In this embodiment, the SOC range is determined while the secondary battery 2 is connected to the power grid. As a result, while the secondary battery 2 is connected to the power grid, the SOC range in which the contribution of the negative electrode metal active material is large is detected, and charging and discharging can be performed in the lowest possible SOC range while avoiding the SOC range in which the contribution of the negative electrode metal active material is large. As a result, the SOC range can be set to an optimal range while suppressing both the deterioration of the metal active material and the storage deterioration that accelerates with increasing SOC.

[0066] In this embodiment, the SOC is moved from the high SOC side toward the lower limit of the SOC usage range by repeatedly executing the control process of steps S4 to S7 shown in Fig. 7. At this time, the shorter the discharge time in the control process of step S4, the more finely the discharge capacity is divided, so that the time required to determine the SOC usage range becomes longer, but the accuracy becomes higher.

[0067] In this embodiment, the discharge in the control process of step S4 may be divided by SOC instead of time. For example, the discharge is divided for each SOC (1%), and the imaginary component (Z" _d , Z.” _c ) is calculated to determine the SOC usage range. In other words, the SOC usage range is adjusted per unit of SOC (1%). Therefore, even if there is an error in the calculation accuracy of the SOC usage range, the SOC range in which the contribution of the metal active material is large can be suppressed to less than SOC (1%) due to that error.

[0068] In this embodiment, after the control process of step S8, charging may be performed for an amount equivalent to a predetermined SOC, and the SOC after charging may be determined as the lower limit of the SOC use range. The predetermined SOC may be set to, for example, 5%. In a modified example of this embodiment, the predetermined SOC may be set to 1%. This allows the lower limit of the SOC use range to be determined to an SOC that has a margin equivalent to the predetermined SOC relative to the range of SOC in which the contribution of the metal active material is large, thereby suppressing the capacity reduction of the lithium ion secondary battery due to the deterioration of the metal active material in the negative electrode.

[0069] In this embodiment, the SOC is brought closer to the lower limit of the SOC usage range from the low SOC side by repeatedly executing the control process of steps S9 to S12 shown in Fig. 9. At this time, the shorter the charging time in the control process of step S9, the more finely the charging capacity is divided, so that the time required to determine the SOC usage range becomes longer but the accuracy becomes higher.

[0070] In this embodiment, the charging in the control process of step S9 may be divided by SOC instead of time. For example, the charging may be divided for each SOC (1%), and the imaginary component (Z" _d , Z.” _c ) is calculated to determine the SOC usage range. In other words, the SOC usage range is adjusted per unit of SOC (1%). Therefore, even if there is an error in the calculation accuracy of the SOC usage range, the SOC range in which the contribution of the metal active material is large can be suppressed to less than SOC (1%) due to that error.

[0071] In this embodiment, after the control process of step S13, charging may be performed for an amount equivalent to a predetermined SOC, and the SOC after charging may be determined as the lower limit of the SOC use range. The predetermined SOC may be set to, for example, 5%. In a modified example of this embodiment, the predetermined SOC may be set to 1%. This allows the lower limit of the SOC use range to be determined to an SOC that has a margin equivalent to the predetermined SOC relative to the range of SOC in which the contribution of the metal active material is large, thereby suppressing the capacity reduction of the lithium ion secondary battery due to the deterioration of the metal active material in the negative electrode.

[0072] In a modified example of this embodiment, in the control process of step S3, the imaginary component ratio (Z _d / Z” _c If the imaginary component ratio (Z") is equal to or greater than the imaginary component ratio threshold (1.0), the controller 10 charges the secondary battery 2 and _d / Z” _c After the imaginary component ratio threshold (1.0) is reached, the control process of steps S4 to S8 may be executed to determine the SOC usage range.

[0073] In this embodiment, the controller 10 calculates the charge transfer resistance (R c ) and discharge charge transfer resistance (R d The value that indicates the difference between the imaginary component ratio (Z” _d / Z” _c ), but also the imaginary component difference (Z” _d -Z” _c Or Z” _c -Z” _d The controller 10 may also determine the discharge imaginary component (Z" _d ) and the imaginary component of the charge (Z” _c ) and the difference (Z” _d -Z” _c Or Z” _c -Z” _d ) and calculate the calculated difference (Z” _d -Z” _c Or Z” _c -Z” _d ) may determine the SOC usage range of the secondary battery 2. Specifically, in the control flow of step S3, the controller 10 determines the discharge imaginary component (Z" _d ) and the imaginary component of the charge (Z” _c ) and the difference between the imaginary component (Z” _d -Z” _c Or Z” _c -Z” _d Then, in steps S3, S7, and S12, the imaginary component ratio (Z _d / Z” _c ), the controller 10 uses the calculated imaginary component difference (Z″ _d -Z” _c Or Z” _c -Z” _d The imaginary component difference threshold is a threshold that is set in advance, similar to the imaginary component ratio threshold. Then, in steps S8 and S13, the controller 10 compares the calculated imaginary component difference (Z" _d -Z” _c Or Z” _c -Z” _d The SOC when the imaginary component difference threshold is reached is determined as the lower limit SOC of the SOC usage range.

[0074] In this manner, in this embodiment, the charging charge transfer resistance (R c ) and discharge charge transfer resistance (R d ) is the value that indicates the difference between the imaginary component (Z” _d -Z” _c Or Z” _c -Z” _d ) and calculate the imaginary component difference (Z” _d -Z” _c Or Z” _c -Z” _d ) may be used to determine the SOC range of the secondary battery 2. This allows the SOC range to be understood in a short time, and charging and discharging within that range to be avoided. In other words, the SOC range of the secondary battery 2 can be determined not only in situations where a long charging and discharging time can be secured. In addition, the SOC range is set to avoid the SOC range in which the negative electrode metal active material has a high degree of contribution. During normal use of the secondary battery 2, charging and discharging are performed within the SOC range, and therefore it is possible to suppress the capacity reduction of the lithium ion secondary battery due to the deterioration of the negative electrode metal active material.

[0075] The range of SOC usage is determined by the imaginary component ratio (Z” _d / Z” _c ) may be calculated, and the initial value of the SOC usage range may be determined from the calculation result. The SiO contribution capacity is calculated from the theoretical capacity of SiO (mAh / g) and the amount of SiO used (g), and the SOC range in which SiO mainly contributes before deterioration can be calculated from the calculated SiO contribution capacity and the battery capacity of the secondary battery 2 before deterioration. For example, if SiO contribution capacity / battery capacity=15%, the SOC range (0 to 15%) is the SOC range in which the contribution of SiO is large. Then, the range (e.g., 15 to 100%) that avoids the SOC range (0 to 15%) is the SOC usage range.

[0076] In the above example, the imaginary component ratio (Z” _d / Z” _c ) is calculated as the imaginary component ratio threshold, and after the deterioration of the secondary battery 2, the imaginary component ratio (Z _d / Z” _c) is set as the lower limit SOC of the SOC usage range. This allows charging and discharging to be performed while avoiding the SOC range in which the contribution of the negative electrode metal active material is large, even before and after deterioration of the secondary battery 2.

[0077] The battery control system according to this embodiment can be applied to the following cases other than VGI. As an example, in an electric vehicle using a secondary battery 2, an alarm threshold is set to sound a battery remaining capacity alarm for an SOC that is several percent higher than the lower limit of the SOC usage range. Then, when the SOC of the secondary battery 2 falls to the alarm threshold during normal driving, an alarm is output to prompt the user to charge the battery early.

[0078] As another example, when the SOC of the secondary battery 2 falls to the lower limit SOC of the SOC use range, the discharge current of the secondary battery 2 may be suppressed, for example, by limiting the output torque of the motor. Note that such output limitation does not necessarily need to be applied all the time, and when limited conditions are met, such as when a high acceleration performance is required (for example, when a torque equivalent to full throttle is required), the output limitation may be released and the secondary battery 2 may be used below the lower limit SOC of the SOC use range. This reduces the frequency of use within the SOC range in which the contribution of the metal active material of the negative electrode is large, and deterioration of the secondary battery 2 can be suppressed.

[0079] As yet another example, the present invention can be applied to a case where the secondary battery 2 is used as a stationary power source, or a case where a vehicle equipped with the secondary battery 2 is used as an external power source for indoor or outdoor use. In this case, an alarm may be set according to the lower limit SOC of the lower limit SOC usage range, as described above.

[0080] Second Embodiment Next, a battery control system according to a second embodiment will be described. In the second embodiment, a part of the control process for determining the SOC usage range is changed in order to make the time required for determining the SOC usage range even shorter than in the first embodiment. Note that, except for the differences from the determination system according to the first embodiment in the points described below, the second embodiment has the same configuration as the first embodiment, performs the same control as the first embodiment, and operates in the same manner as the first embodiment, and the description of the first embodiment will be used as appropriate.

[0081] In this embodiment, the controller 10 determines the SOC usage range at a predetermined timing, such as when charging or discharging the secondary battery 2 is completed. When determining the SOC usage range, the controller 10 also determines the imaginary component ratio (Z" _d / Z” _c In order to calculate the SOC ratio (Z"), a predetermined SOC range including a lower limit SOC of the SOC use range is set. The predetermined SOC range (hereinafter referred to as the lower limit SOC determination range) is a range expanded by a predetermined SOC (e.g., ±5%) on both the positive and negative sides of the lower limit SOC of the SOC use range. Then, when the current SOC is outside the lower limit SOC determination range, the controller 10 charges or discharges the secondary battery 2 so that the SOC of the secondary battery 2 is included within the lower limit SOC determination range. Then, after the SOC of the secondary battery 2 falls within the lower limit SOC determination range, the controller 10 calculates the imaginary component ratio (Z" _d / Z” _c ) and calculate the imaginary component ratio (Z” _d / Z” _c ) to determine the SOC range of use.

[0082] Below, discharge charge transfer resistance (R_ d ) and charge transfer resistance (R_ c The imaginary component ratio (Z” _d / Z” _c ) and calculate the imaginary component ratio (Z” _d / Z” _c) will be described. FIG. 11 is a flowchart showing the procedure of the control process in the system for determining the SOC usage range. In step S31, the controller 10 connects the secondary battery 2 to the power grid. In step S32, the controller 10 estimates the SOC of the secondary battery 2. The SOC may be estimated, for example, by map calculation using a map showing the correlation between the open circuit voltage (OCV) and the SOC. The map is stored in the memory of the controller 10, and the open circuit voltage (SOC) corresponds to the battery voltage immediately before the secondary battery 2 is connected to the power grid.

[0083] In step S33, the controller 10 compares the estimated SOC with the lower limit SOC of the previously determined SOC use range (SOC _0 ) plus the specified SOC (5%) (SOC _0 +5%), the estimated SOC was calculated as "SOC _0 +5%". SOC _0 +5% corresponds to the upper limit of the lower SOC determination range.

[0084] The estimated SOC is the upper limit of the lower SOC determination range (SOC _0 If the SOC is greater than the upper limit (SOC +5%), the controller 10 determines in step S34 that the SOC is equal to or lower than the upper limit (SOC _0 Discharge the secondary battery 2 until the SOC reaches the upper limit (SOC _0 After reaching +5%), the controller 10 stops discharging in step S35. Next, in step S36, the controller 10 calculates the discharge imaginary component (Z″ _d ) and the imaginary component of the charge (Z” _c ) is calculated. _d ) and the imaginary component of the charge (Z” _c The calculation method of the imaginary component ratio (Z″) is the same as the calculation method in the control process of step S2 in the first embodiment. In step S37, the controller 10 calculates the imaginary component ratio (Z″ _d / Z” _c ) is compared with the imaginary component ratio threshold (1.0), and the imaginary component ratio (Z” _d / Z” _cDetermine whether the imaginary component ratio (Z” _d / Z” _c If the imaginary component ratio threshold (1.0) is lower than the imaginary component ratio threshold (1.0), the controller 10 discharges the secondary battery 2 in step S38. Next, in step S39, the controller 10 stops discharging the secondary battery 2. Then, the controller 10 executes the control processes of steps S36 and S37 again.

[0085] On the other hand, the imaginary component ratio (Z _d / Z” _c If the imaginary component ratio threshold (1.0) is equal to or greater than the imaginary component ratio threshold (1.0), then in step S40, the controller 10 determines the current SOC to be the lower limit value (lower limit SOC) of the SOC usage range.

[0086] In the control process of the comparison judgment in step S33, if the estimated SOC is equal to or lower than the upper limit value of the lower limit SOC determination range (SOC _0 +5%) or less, in step S41, the controller 10 compares the estimated SOC with the lower limit SOC (SOC _0 ) minus the specified SOC (5%) (SOC _0 -5%), the estimated SOC was calculated as "SOC _0 -5%". _0 -5% corresponds to the lower limit of the lower SOC determination range.

[0087] The estimated SOC is the lower limit of the SOC determination range (SOC _0 If the SOC is smaller than the lower limit (SOC −5%), in step S42, the controller 10 _0 Charge the secondary battery 2 until the SOC reaches the lower limit (SOC _0 After the charge reaches -5%), the controller 10 stops charging in step S43. Next, in step S44, the discharge imaginary component (Z" _d ) and the imaginary component of the charge (Z” _c ) is calculated. _d ) and the imaginary component of the charge (Z” _cThe calculation method of the imaginary component ratio (Z" is the same as the calculation method in the control process of step S2 in the first embodiment. _d / Z” _c ) is compared with the imaginary component ratio threshold (1.0), and the imaginary component ratio (Z” _d / Z” _c Determine whether the imaginary component ratio (Z” _d / Z” _c If the imaginary component ratio threshold (1.0) is higher than the imaginary component ratio threshold (1.0), the controller 10 charges the secondary battery 2 in step S46. Next, in step S47, charging of the secondary battery is stopped. Then, the controller 10 executes the control processing of steps S44 and S45 again.

[0088] On the other hand, the imaginary component ratio (Z _d / Z” _c If the imaginary component ratio threshold (1.0) is equal to or smaller than the imaginary component ratio threshold (1.0), then in step S48, the controller 10 determines the current SOC to be the lower limit value (lower limit SOC) of the SOC usage range.

[0089] In the control process of the comparison judgment in step S41, the estimated SOC is equal to the lower limit value of the lower limit SOC determination range (SOC _0 If it is determined that the SOC is equal to or greater than -5%, that is, if the estimated SOC is within the lower limit SOC determination range, in step S49, the controller 10 calculates the discharge imaginary component (Z" _d ) and the imaginary component of the charge (Z” _c ) is calculated. _d ) and the imaginary component of the charge (Z” _c ) is calculated in the same manner as in the control process of step S2 in the first embodiment.

[0090] In step S50, the controller 10 calculates the imaginary component ratio (Z _d / Z” _c ) is compared with the imaginary component ratio threshold (1.0) to calculate the imaginary component ratio (Z _d / Z” _c Determine whether the imaginary component ratio (Z”_d / Z” _c If the imaginary component ratio threshold (1.0) is less than the imaginary component ratio threshold (1.0), in step S51, the controller 10 discharges the secondary battery 2. Then, the controller 10 executes the control process of steps S52 to S57. The control process of steps S52 to S57 is similar to the control process of steps S35 to S40.

[0091] In the comparison judgment in step S50, the imaginary component ratio (Z _d / Z” _c If it is determined that the imaginary component ratio threshold (1.0) is equal to or greater than the imaginary component ratio threshold (1.0), then in step S58, the controller 10 charges the secondary battery 2. Then, the controller 10 executes the control process of steps S59 to S64. The control process of steps S59 to S64 is similar to the control process of steps S43 to S48.

[0092] Then, the controller 10 sets the SOC use range determined by the control processing in steps S40, S48, S57, and S64 based on the calculated imaginary component ratio (Z _d / Z” _c ) and stores it in memory. During normal use of the secondary battery 2, the controller 10 controls the charging and discharging of the secondary battery 2 so that the SOC falls within the SOC usage range stored in memory.

[0093] FIG. 12 is a graph for explaining the relationship between the magnitude of the SOC estimated in the control process of step S32 and the charging and discharging of the secondary battery 2. As shown in FIG. 12, the lower limit SOC determination range is set to a predetermined SOC (±5%) width centered on the lower limit value of the previously determined SOC use range. When the estimated SOC exceeds the upper limit value of the lower limit SOC determination range (SOC _0 +5%), the secondary battery 2 is discharged, and the SOC approaches the lower limit SOC determination range from the high SOC side (see arrow H in FIG. 12). On the other hand, when the estimated SOC is closer to the lower limit of the lower limit SOC determination range (SOC _0-5%), the secondary battery 2 is charged, and the SOC approaches the lower limit SOC determination range from the low SOC side (see arrow L in FIG. 12). Then, in this embodiment, after the SOC falls within the lower limit SOC determination range, the imaginary component ratio (Z″ _d / Z” _c ) is calculated, and the imaginary component ratio (Z” _d / Z” _c ) is used to determine the current SOC use range. This makes it possible to reduce the number of times the control loop of steps S36 to S39 and the control loop of steps S53 to S56 are repeated.

[0094] As described above, in this embodiment, the discharge charge transfer resistance (R d ) and charge transfer resistance (R_ c ) and the value indicating the difference (imaginary component ratio (Z” _d / Z” _c )) and the determined SOC use range are stored in a memory in association with each other, and charging and / or discharging of the secondary battery 2 is controlled so that the SOC falls within a predetermined SOC range including the lower limit value of the previously determined SOC use range, and after the SOC falls within the lower limit SOC determination range, the discharge charge transfer resistance (R d ) and charge transfer resistance (R_ c ) and the value indicating the difference (imaginary component ratio (Z” _d / Z” _c ) is calculated. Then, the discharge charge transfer resistance (R_ d ) and charge transfer resistance (R_ c ) and the value indicating the difference (imaginary component ratio (Z” _d / Z” _c )) is used to determine the current SOC range. This allows the charge / discharge to be controlled by avoiding, as much as possible, the SOC range in which the contribution of the negative electrode metal active material is high. As a result, it is possible to suppress the capacity reduction of the lithium-ion secondary battery that accompanies the deterioration of the negative electrode metal active material.

[0095] In this embodiment, the lower limit SOC determination range is set to have a predetermined SOC width (e.g., ±5%) around the lower limit of the previously determined SOC range, but the SOC width can be set to any value. If the SOC width is too large, the number of control loops of steps S36 to S39 and steps S53 to S56 may increase. Also, if the SOC width is too small, the calculated imaginary component ratio (Z" _d / Z” _c ) may repeatedly become larger and smaller than the imaginary component ratio threshold, and may not converge to the imaginary component ratio threshold. Therefore, it is preferable to set the SOC width to about twice the SOC estimation error.

[0096] In this embodiment, the controller 10 calculates the imaginary component of the discharge (Z _d ) and the imaginary component of the charge (Z” _c ) to the imaginary component difference (Z” _d -Z” _c Or Z” _c -Z” _d ) and calculate the imaginary component difference (Z” _d -Z” _c Or Z” _c -Z” _d In steps S36, S44, S49, S53, and S60, the controller 10 determines the SOC usage range of the secondary battery 2 based on the resistance ratio (R _d / R _c ), instead of the resistance difference (R _d -R _c or R _c -R _d In steps S36, S42, S46, S49, S53, and S60, the controller 10 calculates the calculated imaginary component difference (Z" _d -Z” _c Or Z” _c -Z” _d The imaginary component difference threshold is a threshold that is set in advance, similar to the imaginary component ratio threshold. Then, in steps S37, S45, S50, S54, and S61, the controller 10 compares the calculated imaginary component difference (Z" _d -Z” _c Or Z”_c -Z” _d The SOC when the imaginary component difference threshold is reached is determined as the lower limit SOC of the SOC usage range.

[0097] Although the embodiments of the present invention have been described above, these embodiments are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design modifications and equivalents that fall within the technical scope of the present invention. [Explanation of symbols]

[0098] 1...Judgment device 2…Secondary battery 10…Controller 11…Voltage sensor 12...Current sensor 13...DCDC converter 21...Positive electrode layer 22...Negative electrode layer 23…Separator 24…Positive electrode tab 25…Negative electrode tab 26…Upper exterior member 27…Lower exterior member

Claims

1. A method for controlling a lithium ion secondary battery having a negative electrode containing graphite and a metal active material, comprising: Controlling charging and discharging of the lithium ion secondary battery; Calculating the difference between the charge transfer resistance during discharge of the lithium ion secondary battery and the charge transfer resistance during charging of the lithium ion secondary battery; determining a usage range (SOC usage range) of the state of charge (SOC) of the lithium ion secondary battery based on the difference; Calculating an imaginary component (Z″ _d ) or a phase difference (θ _d ) in the AC impedance of the lithium ion secondary battery during discharge; Calculating an imaginary component (Z″ _c ) or a phase difference (θ _c ) in the AC impedance during charging of the lithium ion secondary battery; The method includes controlling charging and / or discharging the lithium ion secondary battery within the SOC usage range in which the ratio of imaginary components (Z″ _d / Z″ _c ) or the ratio of phase differences (θ _d / θ _c ) is less than a predetermined threshold value.

2. 2. The control method according to claim 1, The control method, wherein the metal active material contains Si.

3. 3. The control method according to claim 1, A control method for determining the SOC usage range in a state where the lithium ion secondary battery is connected to a power grid.

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