Method for controlling lithium-ion secondary battery

Abstract

To provide a battery control method that can determine an SOC usage range of a lithium ion secondary battery, not limited to a situation where a long charge / discharge time can be secured.SOLUTION: In a control method of a lithium ion secondary battery with a negative electrode containing graphite and a metallic active material, after the charging and discharging of a lithium ion secondary battery 2 is controlled and the discharging of the lithium ion secondary battery 2 is stopped, the amount of change in a discharge voltage after a lapse of a predetermined time is calculated, and after the charging of lithium ion secondary battery 2 is stopped, the amount of change in the charge voltage after a lapse of a predetermined time is calculated, and the SOC usage range of the lithium ion secondary battery is determined on the basis of a difference between the amount of change in the discharge voltage and the amount of change in the charge voltage.SELECTED DRAWING: Figure 7

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 is a method for preventing discharge of a lithium ion secondary battery. Later The change in discharge voltage The change from the discharge voltage before the discharge stopped The charging of the lithium-ion secondary battery was stopped. Later The change in charging voltage Change in charging voltage from before charging stopped The above problem is solved by calculating the SOC usage range of the lithium ion secondary battery and determining the SOC usage range of the lithium ion secondary battery based on the difference between the amount of change in the discharge voltage and the amount of change in the charge voltage. 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 graph showing the characteristics of the charge / discharge voltage change amount (ΔV_d, ΔV_c) versus SOC. [Figure 6] FIG. 6 is a graph showing the characteristics of the ratio of the voltage change amount (ΔV_d / ΔV_c) to the SOC. [Figure 7] FIG. 7 is a flowchart showing a procedure of a control process in the system for determining the SOC use range. [Figure 8] FIG. 8 is a flowchart showing a sub-flow of the control process in step S2 shown in FIG. [Figure 9] FIG. 9 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 10] FIG. 10 is a graph for explaining the relationship between the magnitude of the SOC estimated in the control process of step 32 shown in FIG. [Figure 11] FIG. 11 is a graph showing the measurement results in the example, and is a graph showing the measurement results of voltage change and the characteristics of charge and discharge current. [Figure 12] FIG. 12 is a graph showing the measurement results of the charge / discharge voltage change (ΔV_d, ΔV_c) versus SOC. [Figure 13] FIG. 13 is a graph showing the measurement results of the difference (ΔV_d−ΔV_c) in the amount of change in charge / discharge voltage versus SOC. [Figure 14] FIG. 14 is a graph showing the measurement results of the ratio of the amount of change in charge / discharge voltage (ΔV_d / ΔV_c) relative to the SOC. 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. It 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 having a plurality of charge / discharge regions in which the charge / discharge potential changes stepwise with the insertion / extraction of lithium ions, 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 in the case where the secondary battery 2 is 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 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 collector, which is a metal foil such as aluminum, and then drying and pressing the slurry. 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, preparing a slurry, applying the slurry to a part of the main surface of the negative electrode side current collector 104a, which is a metal foil such as copper, and 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] FIG. 5 shows the change in charge / discharge voltage (ΔV _d , ΔV _c) characteristics (characteristics showing SOC sensitivity of voltage change amount). Graphs a and b respectively show the characteristics of the discharge voltage change amount and the charge voltage change amount of the secondary battery 2 having a Gr / SiO negative electrode. Graphs c and d respectively show the characteristics of the discharge voltage change amount and the charge voltage change amount of the secondary battery 2 having a Gr negative electrode. The mass ratio of Gr to SiO in the Gr / SiO negative electrode is 95:5. The discharge current for calculating the discharge voltage change amount and the charge current for calculating the charge voltage change amount are set to the same current value. Furthermore, the discharge time for calculating the discharge voltage change amount and the charge time for calculating the charge voltage change amount are set to the same time.

[0028] As shown in FIG. 5, in the secondary battery 2 having the Gr / SiO negative electrode, when the SOC is greater than 20%, the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c ) is small, and when the SOC is 20% or less, the discharge voltage change (ΔV _d ) is the charge voltage change (ΔV _c ) and the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c On the other hand, in the secondary battery 2 having the Gr negative electrode, the difference in the amount of discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c In the secondary battery 2 with the Gr / SiO negative electrode, when the SOC becomes 20% or less, the contribution of SiO increases, and the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c On the other hand, when the SOC is greater than 20%, the contribution of Gr becomes large, and the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c In other words, in the SOC range in which SiO contributes greatly to charging and discharging, the difference in the amount of voltage change during charging and discharging is greater than in the SOC range in which Gr contributes.

[0029] The vertical axis of the graph in Fig. 5 represents the discharge voltage change (ΔV _d) and the charge voltage change (ΔV _c ) and the voltage change ratio (ΔV _d / ΔV _c ) (Ratio of voltage change (ΔV _d / ΔV _c The SOC sensitivity of the secondary battery 2 having a Gr / SiO negative electrode is shown in FIG. 6. The horizontal axis of FIG. 6 is SOC, as in FIG. 5. Graph A shows the ratio of the voltage change amount (ΔV _d / ΔV _c ), and graph b shows the ratio of the voltage change amount of the secondary battery 2 equipped with the Gr negative electrode (ΔV _d / ΔV _c 6, in the secondary battery 2 having the Gr / SiO negative electrode, the ratio of the voltage change amount (ΔV _d / ΔV _c ) is 1.1 or more in the range of SOC (20%) or less. And the ratio of voltage change (ΔV _d / ΔV _c When the secondary battery 2 is charged and discharged within the range of SOC in which the ratio of voltage changes (ΔV _d / ΔV _c ) and calculate the ratio of the calculated voltage changes (ΔV _d / ΔV _c ) is less than the voltage change threshold value is determined as the SOC usage range. This makes it possible to detect the SOC range in which the contribution of the metal active substance is large and to avoid charging and discharging in that SOC range.

[0030] In this embodiment, the controller 10 measures the change in discharge voltage (ΔV _d ) and the change in charging voltage at a predetermined time after the charging of the secondary battery 2 is stopped (ΔV _c ) and the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c ) is calculated, and the SOC usage range of the secondary battery 2 is determined based on the calculated difference. _d) and the charge voltage change (ΔV _c ) as a ratio of the voltage change (ΔV _d / ΔV _c ) and calculate the ratio of the voltage change (ΔV _d / ΔV _c ) based on the SOC usage range is determined. FIG. 7 is a flowchart showing the procedure of the control process in the system that determines the SOC usage range. _d ) and the charge voltage change (ΔV _c ) is the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c ) and the ratio of the voltage change (ΔV _d / ΔV _c ) and the difference in voltage change (ΔV _d -ΔV _c , ΔV _c -ΔV _d In the following explanation, the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c ) is the ratio of the voltage change (ΔV _d / ΔV _c The upper limit of the SOC range (upper SOC limit) 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. The ratio of the voltage change amount is ΔV _d / ΔV _c Not limited to ΔV _c / ΔV _d That's fine too.

[0031] 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.

[0032] In step S2, the controller 10 calculates the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c) is calculated. FIG. 8 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 S28 shown in FIG. 8 to calculate the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is calculated. In addition to the control processes of steps S21 to S28, 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. 7 and 8 are being executed.

[0033] In step S21, the controller 10 prohibits charging and discharging for one minute or more after connecting to the power grid, and puts the secondary battery 2 into a pause state. If the secondary battery is in a pause state for one minute or more before connecting to the power grid, the pause after connecting to the power grid in step S1 may not be provided. Note that the pause time of one minute or more is merely an example, and the pause time may be, for example, 10 seconds or more. After a predetermined pause time has elapsed, in step S22, the controller 10 discharges the secondary battery 2 with a constant current. The current value of the discharge current may be any value, but is set to, for example, 0.5 C to ensure sufficient accuracy. The discharge time may be any time, but is set to, for example, 3 seconds.

[0034] In step S23, the controller 10 stops discharging the secondary battery 2 and places the secondary battery 2 in a rest state for a predetermined rest time (e.g., 10 seconds) after the discharge is stopped. The longer the rest time after discharge is, the smaller the variation in the detected voltage will be. For example, if the rest time is set to about 10 seconds, sufficient accuracy can be ensured.

[0035] In step S24, the controller 10 measures the battery voltage (V _d (-1)) and the battery voltage 3 seconds after discharge was stopped (V _d (3)) to obtain the discharge voltage change (ΔV _d) is calculated. That is, the controller 10 calculates the amount of change in the discharge voltage at a predetermined time after the discharge is stopped, as the change from the discharge voltage before the discharge was stopped. Note that the closer the voltage detection timing is to the timing of the discharge being stopped, the smaller the variation in the voltage immediately before the discharge was stopped. For example, if the battery voltage is one second before the discharge was stopped, sufficient accuracy can be ensured.

[0036] In step S25, the controller 10 charges the secondary battery 2 with a constant current. The current value of the charging current may be any value, but is set to, for example, 0.5 C to ensure sufficient accuracy. The charging time may be any time, but is set to, for example, 3 seconds. However, the current value of the charging current is set to the same value as the current value of the discharging current set in the control process of step S23. The charging time is set to the same time as the discharging time set in the control process of step S23.

[0037] In step S26, the controller 10 stops charging the secondary battery 2 and places the secondary battery 2 in a rest state for a predetermined rest time (e.g., 10 seconds) after charging has stopped. The longer the rest time after charging, the smaller the variation in the detected voltage. For example, if the rest time is set to about 10 seconds, sufficient accuracy can be ensured.

[0038] In step S27, the controller 10 detects the battery voltage (V _c (-1)), battery voltage 3 seconds after charging stopped (V _c (3)) to calculate the charge voltage change (ΔV _c ) is calculated. That is, the controller 10 calculates the amount of change in the charging voltage at a predetermined time after charging is stopped, as the change from the charging voltage before charging was stopped. Note that the closer the voltage detection timing is to the timing of charging being stopped, the smaller the variation in voltage immediately before charging was stopped. For example, if the battery voltage is one second before charging was stopped, sufficient accuracy can be ensured.

[0039] In step S28, the controller 10 calculates the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c) and the voltage change ratio (ΔV _d / ΔV _c ) is calculated. The ratio of the voltage change (ΔV _d / ΔV _c ) is the charge voltage change (ΔV _c ) to the discharge voltage change (ΔV _d As described above, the controller 10 executes the control process of steps S21 to S28 to obtain the ratio of the voltage change amounts (ΔV _d / ΔV _c ) is calculated (step S2). Note that in the control processing of steps S21 to S28, discharging is performed first and then charging is performed, but the order of discharging and charging may be reversed.

[0040] In step S2, the ratio of the voltage changes (ΔV _d / ΔV _c After calculating the voltage change ratio (ΔV _d / ΔV _c ) is compared with a threshold value for the ratio of the voltage change amount (hereinafter referred to as the voltage change threshold value), and the ratio of the voltage change amount (ΔV _d / ΔV _c ) is less than the voltage change threshold. The ratio of the voltage change amount is a threshold for setting the lower limit of the SOC usage range, and is set in advance. The voltage change 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 voltage change threshold may be set according to the specifications of the negative electrode active material (the ratio of the metal active material, the type of metal used in the metal active material, etc.). The voltage change threshold may also be set according to the detection accuracy of the voltage and / or current of the secondary battery 2, etc. In this embodiment, the voltage change threshold is set to 1.1, for example.

[0041] The calculated voltage change ratio (ΔV _d / ΔV _c If the voltage change ratio (ΔV _d / ΔV _cIf the voltage change threshold (1.1) is equal to or greater than the voltage change threshold (1.1), the controller 10 executes the control process of steps S8 to S11.

[0042] In step S4, the controller 10 discharges the secondary battery 2. The ratio of the voltage change amount of the secondary battery 2 (ΔV _d / ΔV _c If the voltage change threshold (1.1) is lower than the voltage change threshold (1.1), 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 voltage change threshold (1.1). In step S5, the controller 10 calculates the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is calculated. _d ) and the charge voltage change (ΔV _c ) is calculated in the same manner as in the control process of step S2.

[0043] In step S6, the controller 10 calculates the ratio of the voltage changes (ΔV _d / ΔV _c ) is compared with the voltage change threshold (1.1), and the ratio of the voltage change amount (ΔV _d / ΔV _c ) is greater than or equal to the voltage change threshold (1.1). _d / ΔV _c If the voltage change threshold value (1.1) is exceeded, the controller 10 returns the control process flow to step S4 and discharges the secondary battery 2. In other words, by repeatedly executing the control processes of steps S4 to S6, the voltage change ratio (ΔV _d / ΔV _c ) approaches the voltage change threshold (1.1).

[0044] Voltage change ratio (ΔV _d / ΔV _c If the voltage change ratio (ΔV) is equal to or greater than the voltage change threshold (1.1), the controller 10 determines the current SOC to be the lower limit (lower limit SOC) of the SOC usage range in step S7._d / ΔV _c The SOC at which the voltage change threshold (1.1) is reached is determined as the lower limit SOC of the SOC usage range.

[0045] In step S8, the controller 10 charges the secondary battery 2. The ratio of the voltage change amount of the secondary battery 2 (ΔV _d / ΔV _c ) is equal to or greater than the voltage change threshold (1.1), the SOC of the secondary battery 2 is equal to or less than the lower limit of the SOC usage range, so the SOC is increased to determine the lower limit of the SOC usage range that corresponds to the voltage change threshold (1.1). Since the charging in the control process of step S8 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 is preferably set to 0.5 C or less. In step S9, the controller 10 calculates the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c ) is calculated. _d ) and the charge voltage change (ΔV _c ) is calculated in the same manner as in the control process of step S2.

[0046] In step S10, the controller 10 calculates the ratio of the voltage changes (ΔV _d / ΔV _c ) is compared with the voltage change threshold (1.1), and the ratio of the voltage change amount (ΔV _d / ΔV _c ) is less than the voltage change threshold (1.1). _d / ΔV _c If the voltage change threshold value (1.1) or more, the controller 10 returns the control process flow to step S8 and charges the secondary battery 2. That is, by repeatedly executing the control processes of steps S8 to S10, the voltage change ratio (ΔV _d / ΔV _c ) approaches the voltage change threshold (1.1).

[0047] Voltage change ratio (ΔV _d / ΔV_c If the voltage change ratio (ΔV) is less than the voltage change threshold (1.1), the controller 10 determines the current SOC as the lower limit (lower limit SOC) of the SOC usage range in step S11. _d / ΔV _c The SOC at which the ratio of the voltage changes (ΔV _d / ΔV _c ) to determine the SOC range of use.

[0048] Then, the controller 10 sets the SOC use range determined by the control processing in steps S7 and S11 based on the calculated voltage change ratio (ΔV _d / ΔV _c ) and stores it 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 memory. When determining a new SOC usage range, the controller 10 refers to the memory and calculates the ratio of the voltage change amount (ΔV _d / ΔV _c ) is set as the voltage change threshold, and the control process of steps S1 to S11 is executed. 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 and discharged outside the SOC usage range. In order to determine the SOC usage range of the secondary battery 2, charging and discharging may be performed outside the previously determined SOC usage range.

[0049] In order to increase the battery capacity of a lithium-ion secondary battery, a mixture of graphite and a metal active material is used as the 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, since the SOC use range is determined while avoiding the range of SOC in which the contribution of the metal active material of the negative electrode is large, charging and discharging are performed within the 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.

[0050] As described above, in this embodiment, the charge and discharge of the secondary battery 2 is controlled, and the amount of change in the discharge voltage at a predetermined time point after the discharge of the secondary battery 2 is stopped (ΔV _d ) is calculated, and the change in charging voltage at a predetermined time point after the charging of the secondary battery 2 is stopped (ΔV _c ) and calculate the change in discharge voltage (ΔV _d ) and the change in charging voltage (ΔV _c ) and the SOC range of the secondary battery 2 is determined based on the difference between the discharge voltage change (ΔV _d ) and the change in charging voltage (ΔV _c ) is the ratio of the voltage change (ΔV _d / ΔV _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.

[0051] In this embodiment, the change in discharge voltage (ΔV _d ) and the change in charging voltage (ΔV _c ) and the ratio of voltage change (ΔV _d / ΔV _c) is less than the voltage change 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.

[0052] 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.

[0053] In this embodiment, the SOC range is determined while the secondary battery 2 is connected to the power grid. This allows the secondary battery 2 to detect the SOC range in which the negative electrode metal active material has a large contribution while connected to the power grid, and to charge and discharge the secondary battery 2 while avoiding the SOC range in which the negative electrode metal active material has a large contribution. As a result, the SOC range can be set to an optimal range while suppressing both deterioration and storage deterioration of the metal active material.

[0054] 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 S6 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.

[0055] 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 discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _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.

[0056] In this embodiment, after the control process of step S6, 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 usage 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 usage 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.

[0057] In this embodiment, the SOC is moved from the low SOC side toward the lower limit of the SOC usage range by repeatedly executing the control process of steps S8 to S10 shown in Fig. 7. At this time, the shorter the charging time in the control process of step S4, 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.

[0058] In this embodiment, the charging in the control process of step S8 may be divided by SOC instead of time. For example, the charging is divided every SOC (1%), and the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _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.

[0059] In this embodiment, after the control process of step S10, 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.

[0060] In a modified example of this embodiment, in the control process of step S3, the ratio of the voltage change amounts (ΔV _d / ΔV _c ) is equal to or greater than the voltage change threshold (1.1), the controller 10 charges the secondary battery 2 and increases the voltage change ratio (ΔV _d / ΔV _c After the voltage change threshold (1.1) is reached, the control process of steps S4 to S7 may be executed to determine the SOC usage range.

[0061] In this embodiment, the controller 10 calculates the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is the ratio of the voltage change (ΔV _d / ΔV _c ), but also the difference in voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d The controller 10 may also calculate the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) to the difference in voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d ) and calculate the difference in the calculated voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d) may be used to determine the SOC range of the secondary battery 2. Specifically, in the control flow of step S28 of the subflow of the control process in step S2, the controller 10 determines the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is the difference in the voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d In steps S3, S6, and S10, the ratio of the voltage change amount (ΔV _d / ΔV _c ), the controller 10 calculates the difference in the voltage changes (ΔV _d -ΔV _c or ΔV _c -ΔV _d ) and the threshold value of the voltage change amount difference. The threshold value of the voltage change amount difference is a threshold value that is set in advance, similar to the voltage change threshold value. Then, in steps S7 and S11, the controller 10 compares the calculated voltage change amount difference (ΔV _d -ΔV _c or ΔV _c -ΔV _d The SOC at which the difference in the amount of voltage change reaches the threshold value is determined as the lower limit SOC of the SOC usage range.

[0062] In this manner, in this embodiment, the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is the difference between the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c ) and the difference in the voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d ) and calculate the difference in the calculated voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d) is used to determine the SOC range of the secondary battery 2. This makes it possible to quickly grasp the SOC range to which the metal active material of the negative electrode contributes, and to avoid charging and discharging within that range. 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 metal active material of the negative electrode contributes highly. 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 that is caused by the deterioration of the metal active material of the negative electrode.

[0063] The SOC range is determined by the ratio of the voltage change before and after degradation (ΔV _d / ΔV _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.

[0064] In the above example, the ratio of the voltage change equivalent to SOC 15% before deterioration (ΔV _d / ΔV _c ) is calculated as the voltage change threshold value, and after the deterioration of the secondary battery 2, the ratio of the voltage change amount (ΔV _d / ΔV _c ) is the voltage change threshold value, 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In this embodiment, the controller 10 determines the SOC use range at a predetermined timing, such as when charging or discharging the secondary battery 2 is completed. When determining the SOC use range, the controller 10 determines the voltage change ratio (ΔV _d / ΔV _c ), a predetermined SOC range including a lower limit SOC of the SOC usage 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 usage 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 detects the charge and discharge voltages, and calculates the ratio of the voltage changes (ΔV _d / ΔV _c ) and calculate the ratio of the voltage change (ΔV _d / ΔV _c ) to determine the SOC range of use.

[0070] The following is the discharge voltage change (ΔV _d ) and the charge voltage change (ΔV _c ) as a ratio of the voltage change (ΔV _d / ΔV _c ) and calculate the ratio of the calculated voltage changes (ΔV _d / ΔV _c ) will be described. FIG. 9 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.

[0071] 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.

[0072] 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 the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is calculated. _d ) and the charge voltage change (ΔV _c The method of calculating the ratio of the voltage changes (ΔV _d / ΔV _c ) is compared with the voltage change threshold (1.1), and the ratio of the voltage change amount (ΔV _d / ΔV _c ) is greater than or equal to the voltage change threshold (1.1). _d / ΔV _c If the voltage change threshold (1.1) is lower than the voltage change threshold (1.1), then in step S37, the controller 10 discharges the secondary battery 2. Then, the controller 10 executes the control process of step S35.

[0073] Voltage change ratio (ΔV _d / ΔV _c If the voltage change ratio (ΔV) is equal to or greater than the voltage change threshold (1.1), then in step S38, the controller 10 determines the current SOC to be the lower limit (lower limit SOC) of the SOC usage range._d / ΔV _c The SOC at which the voltage change threshold (1.1) is reached is determined as the lower limit SOC of the SOC usage range.

[0074] 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 S39, the controller 10 compares the estimated SOC with the lower limit SOC of the previously determined SOC use range (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.

[0075] The estimated SOC is the lower limit of the SOC determination range (SOC _0 -5%), in step S40, the controller 10 determines whether the SOC is equal to or lower than the upper limit (SOC _0 Charge the secondary battery 2 until the SOC reaches the upper limit (SOC _0 After the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is calculated. _d ) and the charge voltage change (ΔV _c ) is calculated in the same manner as in the control process in step S2 in the first embodiment. In step S42, the controller 10 calculates the ratio of the voltage changes (ΔV _d / ΔV _c ) is compared with the voltage change threshold (1.1), and the ratio of the voltage change amount (ΔV _d / ΔV _c ) is equal to or less than the voltage change threshold (1.1). _d / ΔV _cIf the voltage change threshold (1.1) is higher than the voltage change threshold (1.2), then in step S43, the controller 10 charges the secondary battery 2. Then, the controller 10 executes the control process of step S41.

[0076] Voltage change ratio (ΔV _d / ΔV _c If the voltage change ratio (ΔV) is equal to or less than the voltage change threshold (1.1), the controller 10 determines the current SOC to be the lower limit (lower limit SOC) of the SOC usage range in step S44. _d / ΔV _c The SOC at which the voltage change threshold (1.1) is reached is determined as the lower limit SOC of the SOC usage range.

[0077] In the control process of the comparison judgment in step S39, if the estimated SOC is equal to or smaller than the lower limit of the lower limit SOC determination range (SOC _0 -5%) or more, that is, if the estimated SOC is within the lower limit SOC determination range, in step S45, the controller 10 calculates the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) is calculated. _d ) and the charge voltage change (ΔV _c ) is calculated in the same manner as in the control process of step S2 in the first embodiment.

[0078] In step S46, the controller 10 calculates the ratio of the calculated voltage changes (ΔV _d / ΔV _c ) is compared with the voltage change threshold (1.1), and the calculated voltage change ratio (ΔV _d / ΔV _c ) is less than the voltage change threshold (1.1). _d / ΔV _cIf the voltage change threshold (1.1) is less than the voltage change threshold (1.1), the controller 10 discharges the secondary battery 2 in step S47. Then, the controller 10 executes the control process of steps S48 to S51. The control process of steps S48 to S51 is similar to the control process of steps S35 to S38.

[0079] In the comparison judgment of step S46, the ratio of the voltage change amount (ΔV _d / ΔV _c If it is determined that the voltage change threshold (1.1) is equal to or greater than the voltage change threshold (1.2), then in step S52, the controller 10 charges the secondary battery 2. Then, the controller 10 executes the control process of steps S53 to S56. The control process of steps S53 to S56 is similar to the control process of steps S41 to S44.

[0080] Then, the controller 10 sets the SOC use range determined by the control processing in steps S38, S44, S51, and S56 based on the calculated voltage change ratio (ΔV _d / ΔV _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. When determining a new SOC usage range, the controller 10 also refers to the memory and calculates the ratio of the voltage change amount (ΔV _d / ΔV _c ) is set as the voltage change threshold value, and the control process of steps S31 to S56 is executed.

[0081] FIG. 10 is a graph for explaining the relationship between the magnitude of the SOC estimated in the control process of step 32 and the charging and discharging of the secondary battery 2. As shown in FIG. 10, 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. 10). 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. 10). Then, in this embodiment, after the SOC falls within the lower limit SOC determination range, the ratio of the voltage change amount (ΔV _d / ΔV _c ) is calculated, and the ratio of the voltage changes (ΔV _d / ΔV _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 S35 to S37 and the control loop of steps S41 to S43 are repeated.

[0082] As described above, in this embodiment, the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) and the ratio of voltage change (ΔV _d / ΔV _c )) and the determined SOC use range are stored in a memory in association with each other, 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 voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) and the ratio of voltage change (ΔV _d / ΔV _c Then, the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) and the ratio of voltage change (ΔV _d / ΔV _c) is used to determine the current SOC range. This allows charge and 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.

[0083] In this embodiment, the lower limit SOC determination range is set to have a predetermined SOC width (for example, ±5%) around the lower limit of the previously determined SOC use range, but the SOC width can be set to any value. If the SOC width is too large, the number of control loops in steps S35 to S37 and steps S41 to S43 may increase. Also, if the SOC width is too small, the ratio of the calculated voltage changes (ΔV _d / ΔV _c ) may repeatedly become larger and smaller than the voltage change threshold, and may not converge to the voltage change threshold. Therefore, it is preferable to set the SOC width to about twice the SOC estimation error.

[0084] In this embodiment, the controller 10 calculates the discharge voltage change amount (ΔV _d ) and the charge voltage change (ΔV _c ) to the difference in voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d ) and calculate the difference in the calculated voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d In steps S35, S41, S45, S48, and S53, the controller 10 may determine the SOC usage range of the secondary battery 2 based on the ratio of the voltage change amounts (ΔV _d / ΔV _c ), the difference in voltage change (ΔV _d -ΔV _c or ΔV _c -ΔV _d In steps S36, S42, S46, S49, and S54, the controller 10 calculates the difference between the calculated voltage changes (ΔV _d -ΔV_c or ΔV _c -ΔV _d ) and a threshold value for the voltage change amount difference. The threshold value for the voltage change amount difference is a threshold value that is set in advance, similar to the current change threshold value. Then, in steps S38, S44, S53, and S56, the controller 10 compares the calculated voltage change amount difference (ΔV _d -ΔV _c or ΔV _c -ΔV _d The SOC at which the difference in the amount of voltage change reaches the threshold value is determined as the lower limit SOC of the SOC usage range.

[0085] 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. EXAMPLES

[0086] The present invention will be described below with reference to more detailed examples, but the present invention is not limited to these examples.

[0087] <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).

[0088] <Evaluation of Examples> (1) The prototype was charged and discharged as follows to adjust the SOC. First, the battery was discharged at a discharge current value (0.2C) until the battery voltage reached 2.5V. After discharging, the battery was charged at a charge current value (0.2C) until the target voltage corresponding to an SOC of 10% was reached. After reaching the target voltage corresponding to an SOC of 10%, the battery was switched to constant voltage charging, and charging was terminated when the charging current value dropped to 0.01C. (2)(1) The voltage change was measured for the prototype after SOC adjustment in the following manner. First, after more than one minute had passed since the end of charging, charge and discharge control was performed in the following order: discharge for 10 seconds at the discharge current value (0.5C), rest for 10 seconds, charge for 10 seconds at the charge current value (0.5C), and rest for 10 seconds. During this control, the voltage change was recorded. In addition, the absolute value of the voltage difference between the voltage 1 second before discharge was stopped and the voltage 3 seconds after discharge was stopped (discharge voltage change: ΔV _d ) and the absolute value of the voltage difference between the voltage 1 second before charging was stopped and the voltage 3 seconds after charging was stopped (charge voltage change: ΔV _c ) was calculated. (3) After the voltage measurement in (2), the prototype was charged at a charging current value (0.2 C) up to the target voltage corresponding to SOC 20%. After the target voltage corresponding to SOC 20% was reached, constant voltage charging was performed until the current value decreased to 0.01 C (SOC adjustment). (4) In the same manner as in (2), record the voltage change and calculate the charge / discharge voltage change (ΔV _d , ΔV _c ) was calculated. (5) After (4), set the target voltages corresponding to SOC 30%, 40%, and 50% and adjust the SOC in (3). Measure the voltage change in (4) (charge / discharge voltage change (ΔV _d , ΔV _c ) was carried out.

[0089] <Evaluation Results of Examples> After adjusting the SOC to 10%, the voltage change measured in (2) was plotted, and the measurement results shown in the graph in Figure 11 were obtained. In Figure 11, graph a represents the voltage change, and graph b represents the charge / discharge current. Using the evaluation methods (1) to (5), the charge / discharge voltage change (ΔV _d , ΔV _c ) were plotted, the measurement results shown in the graphs of Figures 12 to 14 were obtained. In Figures 12 to 14, the horizontal axis is the same as the SOC, and the vertical axis is the charge / discharge voltage change (ΔV _d , ΔV _c ), the difference in the charge / discharge voltage change (ΔV _d -ΔV _c ), and the ratio of the voltage change (ΔV _d / ΔV _c ) respectively. As shown in Fig. 13 and Fig. 14, when the SOC is in the range of 20% or less, the difference in the charge / discharge voltage change (ΔV _d -ΔV _c ) and the ratio of voltage change (ΔV _d / ΔV _c) is larger than the value in the range where the SOC is greater than 20%. That is, in the examples, it was confirmed that in the SOC range where SiO contributes greatly to charge and discharge, the difference in the amount of voltage change during charge and discharge is larger than in the SOC range where Gr contributes. In the example of Fig. 14, if the SOC usage range is SOC (20%) or more, the voltage change threshold should be set to 1.1. To further suppress deterioration, the SOC usage range can be set to 30% or more by setting the voltage change threshold to 1.03. [Explanation of symbols]

[0090] 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; A change in discharge voltage of the lithium ion secondary battery after the discharge is stopped is calculated as a change from the discharge voltage before the discharge is stopped; A change in a charging voltage after charging of the lithium ion secondary battery is stopped is calculated as a change from a charging voltage before charging is stopped; A control method for determining a usable range (SOC usable range) of the state of charge (SOC) of the lithium ion secondary battery based on the difference between the amount of change in the discharge voltage and the amount of change in the charge voltage.

2. 2. The control method according to claim 1, A control method for controlling charging and / or discharging of the lithium ion secondary battery within the SOC usage range in which a value indicating a difference between the amount of change in the discharge voltage and the amount of change in the charge voltage is less than a predetermined threshold value.

3. 3. The control method according to claim 1, a value indicating the calculated difference between the amount of change in the discharge voltage and the amount of change in the charge voltage is associated with the determined SOC usage range and stored in a memory; Controlling charging and / or discharging of the lithium ion secondary battery so that the SOC falls within a predetermined SOC range including a lower limit value of the previously determined SOC use range; After the SOC falls within the predetermined SOC range, a value indicating a difference between an amount of change in the discharge voltage and an amount of change in the charge voltage is calculated; A control method for determining the current SOC usage range based on a value indicating a difference between an amount of change in the discharge voltage and an amount of change in the charge voltage, the difference being calculated after the SOC falls within the specified SOC range.

4. In the control method according to any one of claims 1 to 3, The control method, wherein the metal active material contains Si.

5. In the control method according to any one of claims 1 to 4, 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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