Method for controlling a lithium ion secondary battery

Abstract

To provide a battery control method that determines 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 metal active material, after the charging and discharging of the lithium ion secondary battery 2 is controlled and the discharging of the lithium ion secondary battery 2 is started, a DC resistance value (R_d) is calculated from a discharge current value at the time when a predetermined time elapses, and after the charging of the lithium ion battery is started, a DC resistance value (R_c) is calculated from a charging current value at the time when the predetermined time elapses, and an SOC usage range of the lithium ion secondary battery is determined on the basis of a difference between the DC resistance value (R_d) and the DC resistance value (R_c).SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] This invention relates to a control method for determining the State of Charge (SOC) usage range of a lithium-ion secondary battery. [Background technology]

[0002] A conventional charge-discharge control method is known that changes the voltage range for charging and discharging according to the degradation state of a lithium-ion secondary battery (Patent Document 1). In the charge-discharge control method described in Patent Document 1, battery information regarding the charge-discharge state of a lithium-ion battery is acquired, and based on the battery information, a Q-dV / dQ curve is calculated that shows the relationship between the discharge capacity Q of the lithium-ion battery and dV / dQ, which is the ratio of the change in battery voltage dV to the change in discharge capacity Q dQ, and the degradation state of the lithium-ion battery is determined based on the Q-dV / dQ curve. Then, based on the result of the degradation state determination, the voltage range for charging and discharging the lithium-ion battery is changed. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2015 / 025402 [Overview of the project] [Problems that the invention aims to solve]

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

[0005] The problem that this invention aims to solve is to provide a control method that can determine the state of charge (SOC) usage range of a lithium-ion secondary battery, not limited to situations where a long charge-discharge time can be secured. [Means for solving the problem]

[0006] This invention relates to the DC resistance value (R) calculated from the discharge current value at a predetermined time after the start of discharge of a lithium-ion secondary battery. _d The DC resistance value (R) is calculated from the charging current value at a predetermined time after the lithium-ion secondary battery has started to charge. _c ) calculate the DC resistance value (R _d ) and DC resistance value (R _c The above problem is solved by determining the SOC usage range of lithium-ion secondary batteries based on the differences with ). [Effects of the Invention]

[0007] According to the present invention, the State of Charge (SOC) usage range of a lithium-ion secondary battery can be determined not only in situations where a long charge-discharge time can be secured, but also in other situations. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a block diagram showing the battery control system of a secondary battery according to this embodiment. [Figure 2] Figure 2 shows a perspective view of the secondary battery before assembly, and a plan view of the secondary battery. [Figure 3] Figure 3 is a graph showing the characteristics of the capacity retention rate of a secondary battery with respect to the number of cycles. [Figure 4] Figure 4 is a graph showing the capacity retention rate for a secondary battery equipped with a Gr / SiO negative electrode when the SOC usage range is 50-100% and when the SOC usage range is 0-100%. [Figure 5] Figure 5 is a graph showing the characteristics of the DC resistance values ​​(R_d, R_c) with respect to the State of Coffee (SOC). [Figure 6] Figure 6 is a graph showing the characteristics of the resistance ratio (R_d / R_c) of the DC resistance value relative to the SOC. [Figure 7] Figure 7 is a flowchart showing the control processing procedure in the system for determining the SOC usage range. [Figure 8]Figure 8 is a flowchart showing the subflow of the control process in step S2 shown in Figure 7. [Figure 9] Figure 9 is a flowchart showing the control process procedure in a system for determining the SOC usage range in a battery control system for a secondary battery according to another embodiment of the present invention. [Figure 10] Figure 10 is a graph illustrating the relationship between the size of the State of Cycle (SOC) estimated in the control process of step 32 shown in Figure 9 and the charging and discharging of the secondary battery 2. [Figure 11] Figure 11 is a graph showing the measurement results in the embodiment, and is a graph showing the measurement results of voltage change and the characteristics of charge and discharge current. [Figure 12] Figure 12 is a graph showing the measurement results of DC resistance values ​​(R_d, R_c) relative to SOC. [Figure 13] Figure 13 is a graph showing the measurement results of the resistance ratio (R_d / R_c) of the DC resistance value relative to the SOC. [Figure 14] Figure 14 is a graph showing the measurement results of the resistance difference (R_d - R_c) of the DC resistance value relative to the SOC. [Modes for carrying out the invention]

[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. Figure 1 is a block diagram showing a battery control system including one embodiment of the battery control device according to the present invention. As shown in Figure 1, the battery control system according to this embodiment is a system for controlling the charging and discharging of a secondary battery 2 and determining the SOC usage range of the secondary battery 2. The battery control system comprises 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, which are not shown in Figure 1.

[0010] The battery control device 1 comprises a controller 10, a voltage sensor 11, a current sensor 12, and a DC-DC converter 13. The controller 10 is a battery control unit (BCU). Based on the detected voltage detected by the voltage sensor 11 and / or the detected current detected by the current sensor 12, the controller 10 manages the state of the secondary battery 2 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 memory such as ROM or RAM, and a processor such as a CPU.

[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 terminals of the secondary battery 2. The current sensor 12 is a sensor for detecting the input and output current of the secondary battery 2. The current sensor 12 is connected to the wiring connected to either the positive or negative terminal 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 DC-DC converter 13 is a power conversion device that converts the voltage input from the secondary battery 2 into a predetermined voltage and outputs power to a load such as a motor. The DC-DC converter 13 also converts the voltage input from a load such as a motor or a charging device into a predetermined voltage and outputs power to the secondary battery 2. The DC-DC converter 13 is controlled by the controller 10. The secondary battery 2 is connected to the input side of the DC-DC converter 13, and the load is connected to the output side of the DC-DC converter 13. The load is a power grid, etc. In other words, the secondary battery 2 is connected to the load via the DC-DC converter 13.

[0013] The secondary battery 2 is, for example, a lithium-ion secondary battery. An example of this type of secondary battery 2 is one in which an active material having multiple charge-discharge regions in which the charge-discharge potential changes in steps with the insertion and removal of lithium ions is used as the negative electrode active material. As such an active material having multiple charge-discharge regions in which the charge-discharge potential changes in steps with the insertion and removal of lithium ions, a graphite-based active material containing a graphite structure is preferred. Therefore, in the embodiments shown below, the present invention will be explained using a lithium-ion secondary battery having a negative electrode containing graphite and a metal active material as an example. In the following description, the structure and materials of the secondary battery 2 when it is an electrolyte lithium-ion secondary battery will be described, but the secondary battery 2 may also be an all-solid-state lithium-ion secondary battery. Furthermore, in the following description, a laminate-type battery (laminated cell) will be used as an example of the secondary battery 2, but the secondary battery 2 may also be a prismatic battery (prismatic cell) or a cylindrical battery (cylindrical cell).

[0014] Figure 2 shows a perspective view of the secondary battery 2 before assembly and a plan view of the secondary battery 2. As shown in Figure 2(a), the secondary battery 2 comprises 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 casing member 26, and a lower casing member 27. The power generation element, consisting of 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 casing member 26 and the lower casing 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 portion of the main surface of the positive electrode current collector, which is a metal foil such as aluminum, drying it, and pressing it. The positive electrode active material is not particularly limited, but examples include lithium composite oxides such as lithium nickelate (LiNiO2), lithium manganeseate (LiMn2O4), and lithium cobaltate (LiCoO2), as well as 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 graphite (carbon) and at least two other active materials, with a water-based binder such as styrene-butadiene rubber and water as a solvent, to prepare a slurry, which is then applied to a portion of the main surface of the negative electrode side current collector 104a, which is a metal foil such as copper, and then drying and pressing it. The metals contained in the negative electrode active material include metals whose main elements are Si, Sn, Sb, Pb, Al, Ge, etc., or compounds of these main elements.

[0017] The separator 23 prevents short circuits between the positive electrode layer 21 and the negative electrode layer 22 as described above, and may also have a function of holding the electrolyte. This separator is a microporous membrane made of, for example, polyethylene (PE) or polyolefin such as polypropylene (PP), and when an overcurrent flows, the heat generated closes the pores in the layer, thus interrupting the current.

[0018] The electrolyte contained in secondary battery 2 is a liquid obtained by dissolving lithium salts such as lithium borofluoride (LiBF4) and lithium hexafluoride phosphate (LiPF6) as solutes in an organic liquid solvent. Examples of organic liquid solvents that make up the electrolyte 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 mixtures.

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

[0020] As shown in Figure 2(a), the positive electrode layer 21 and the negative electrode layer 22 are stacked with a separator 23 in between, forming a power generation element. The power generation element is then housed in the upper casing member 26 and the lower casing member 27 so as to cover the surfaces of the positive electrode layer 21 and the negative electrode layer 22. The upper casing member 26 and the lower casing member 27 are made of flexible materials, such as a resin film of polyethylene or polypropylene, or a resin-metal thin film laminate material in which both sides of a metal foil of aluminum or other metal are laminated with a resin of polyethylene or polypropylene. The secondary battery 2 is then constructed by injecting electrolyte into the battery, leading the positive electrode tab 24 and the negative electrode tab 25 to the outside, and then sealing the periphery of the casing members 26 and 27 by heat fusion.

[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 installed in an electric vehicle or a hybrid vehicle. Charging the vehicle-mounted secondary battery 2 is performed by taking out the charging cable from the charging device, attaching the charging gun at the end of the charging cable to the connector of the vehicle's charging port, and then operating the charging start switch. The controller 10 manages the charge state (State of Charge: SOC) of the secondary battery 2 and controls the DC-DC converter 13 and the charging device, respectively, so that the charge state of the secondary battery 2 reaches the target charge state.

[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, and includes the motor that is the drive source of the vehicle, and auxiliary equipment such as an air conditioner and lights. Discharging of the secondary battery 2 is performed under the control of the controller 10 in response to a system request or an external power request. A system request corresponds to a command from an on-board computer such as an ECU while the vehicle is running. Regarding an external power request, for example, if the air conditioner is operated before the vehicle starts running by setting a timer based on a command from an external device such as a mobile terminal, so that the interior of the vehicle reaches an appropriate temperature when the vehicle starts running, the command from the external device corresponds to an external power request.

[0023] Furthermore, the secondary battery 2 installed in electric vehicles and hybrid vehicles may be used for Vehicle Grid Integration (VGI). VGI is a technology that connects electric vehicles and hybrid vehicles equipped with the secondary battery 2 to the grid and supplies the power stored in the secondary battery 2 to the grid (load) via the power network.

[0024] Next, the degradation characteristics and SOC usage range of the lithium-ion secondary battery 2 will be described. In this embodiment, when a mixture of graphite and metal active material is used as the negative electrode, the degradation of the metal active material is accelerated when the secondary battery 2 is charged and discharged in the SOC usage range in which the contribution of the metal active material is large. Figure 3 is a graph showing the characteristics of the capacity retention rate with respect to the number of cycles of the secondary battery 2. The number of cycles is the number of times the SOC has been charged and discharged between 0% and 100%. The capacity retention rate represents the degree of degradation when the battery capacity of the secondary battery 2 in its initial state is set to 1.0. In Figure 3, graph a shows the characteristics of the secondary battery 2 equipped with a negative electrode containing graphite without a metal active material (hereinafter also referred to as the Gr negative electrode). Graph b shows the characteristics of the secondary battery 2 equipped with a negative electrode containing a mixture of graphite and metal (hereinafter also referred to as the Gr / SiO negative electrode). The metal active material is a metal compound (SiO) with Si as the main element. As shown in Figure 3, as the number of cycles increases, the capacity retention rate of secondary battery 2 equipped with a Gr / SiO anode becomes lower than that of secondary battery 2 equipped with a Gr anode. In other words, secondary battery 2 equipped with a Gr / SiO anode experiences a faster decrease in battery capacity.

[0025] The graph in Figure 4 shows the capacity retention rate for a secondary battery 2 equipped with a Gr / SiO negative electrode when the SOC usage range is 50-100% and when the SOC usage range is 0-100%. The characteristics when the SOC usage range is 50-100% are based on approximately 100 cycles, while the characteristics when the SOC usage range is 0-100% are based on approximately 50 cycles. The SOC usage range is the range in which the secondary battery 2 can be used, expressed in terms of SOC. The secondary battery 2 is charged and discharged so that its SOC remains within this range. As shown in Figure 4, when the SOC usage range is 50-100%, even if the number of cycles is approximately doubled compared to when the SOC usage range is 0-100%, the capacity retention rate when the SOC usage range is 50-100% is greater than the capacity retention rate when the SOC usage range is 0-100%. In other words, secondary battery 2 equipped with a Gr / SiO negative electrode can suppress the decrease in battery capacity by avoiding charging and discharging at low SOC.

[0026] Thus, when a secondary battery 2 equipped with a Gr / SiO negative electrode is charged and discharged within a low SOC usage range, the contribution of the metal active material increases, accelerating degradation. Therefore, to suppress the degradation of secondary battery 2, it is necessary to charge and discharge within an SOC usage range where the contribution of the metal active material is small. Furthermore, since the SOC usage range in which the contribution of the metal active material is small changes depending on the degradation state of secondary battery 2, it is necessary to detect the SOC usage range.

[0027] Figure 5 shows the DC resistance value (R) relative to the SOC in secondary battery 2. _d , R _c These are graphs showing the characteristics (characteristics indicating the SOC sensitivity of the DC resistance value). Graphs a and b show the characteristics of the discharge resistance value and charge resistance value of secondary battery 2 equipped with a Gr / SiO negative electrode, respectively. Graphs c and d show the discharge resistance value (R _d ) and charging resistance value (R _c The characteristics of each component are shown below. Note that the mass ratio of Gr to SiO in the Gr / SiO negative electrode is assumed to be 95:5.

[0028] As shown in Fig. 5, in the secondary battery 2 equipped with a Gr / SiO negative electrode, when the SOC is greater than 20%, the resistance difference between the discharge resistance value (R _d ) and the charge resistance value (R _c ) is small. When the SOC is 20% or less, the discharge resistance value (R _d ) is larger than the charge resistance value (R _c ), and the resistance difference between the discharge resistance value (R _d ) and the charge resistance value (R _c ) becomes large. On the other hand, in the secondary battery 2 equipped with a Gr negative electrode, regardless of the magnitude of the SOC, the discharge resistance value (R _d ) and the charge resistance value (R _c ) are almost the same. In the secondary battery 2 equipped with a Gr / SiO negative electrode, when the SOC becomes 20% or less, the contribution degree of SiO increases, and it appears as the difference in the magnitudes of the discharge resistance value (R _d ) and the charge resistance value (R _c ). On the other hand, when the SOC is greater than 20%, the contribution degree of Gr increases, and the discharge resistance value (R _d ) and the charge resistance value (R _c ) become almost the same value. That is, in the SOC range where SiO greatly contributes to charge and discharge, the difference in the DC resistance values during charging and discharging is larger compared to the SOC range where Gr contributes.

[0029] When the vertical axis of the graph shown in Fig. 5 is the resistance ratio (R _d ) of the discharge resistance value (R _c ) and the charge resistance value (R _d / R _c ), the characteristics (characteristics showing the SOC sensitivity of the resistance ratio (R _d / R _c )) are shown in Fig. 6. The horizontal axis of Fig. 6 is the SOC as in Fig. 5. Graph a shows the resistance ratio of the secondary battery 2 equipped with a Gr / SiO negative electrode, and graph b shows the resistance ratio of the secondary battery 2 equipped with a Gr negative electrode. As shown in Fig. 6, in the secondary battery 2 equipped with a Gr / SiO negative electrode, the resistance ratio (R _d / R _c ) becomes 1.05 or more in the range of SOC (20%) or less. And the resistance ratio (R _d / R _cIf the secondary battery 2 is charged and discharged within the operating range of SOC where the resistance ratio (R) is above the threshold (1.05), the secondary battery 2 will be charged and discharged within the operating range of SOC where the contribution of SiO is large, thus accelerating the degradation of the metal active material. In other words, the resistance ratio (R) _d / R _c ) is calculated, and the calculated resistance ratio (R _d / R _c The range of SOC in which the resistance ratio is below the threshold is determined as the SOC usage range. This allows for the detection of SOC ranges where the contribution of metal actives is large, and enables avoidance of charging and discharging within that SOC range.

[0030] In this embodiment, after the charging and discharging of the secondary battery 2 is started, the controller 10 calculates the DC resistance value (R) from the discharge current value and charging current value at a predetermined time after the time has elapsed. _d ) and DC resistance value during charging (R _c Calculate the DC resistance value (R) for each of them. _d ) and DC resistance value (R _c The difference between this value and the calculated difference value is calculated, and the SOC usage range of secondary battery 2 is determined based on this calculated difference value. Below, the DC resistance value (R _d ) and DC resistance value (R _c The resistance ratio (R) is a value that shows the difference from ). _d / R _c ) calculate the resistance ratio (R _d / R _c Based on the above, the method for determining the SOC usage range will be explained. Figure 7 is a flowchart showing the control processing procedure in the system for determining the SOC usage range. Note that the DC resistance value (R _d ) and DC resistance value (R _c The difference from ) is the DC resistance value (R _d ) and DC resistance value (R _c This is the difference in value from the resistance ratio (R _d / R _c ) and resistance difference (R _d -R _c , R _c -R _d It is represented by ). In the following explanation, the DC resistance value (R _d ) and DC resistance value (R _c The value that shows the difference from ) is the resistance ratio (R_d / R _c ) is calculated. Note that the upper limit of the SOC usage range (upper SOC) is set in advance, for example, to 100% or 80%. The upper SOC may be changed depending on the specifications, application, and degree of degradation of secondary battery 2. Also, the resistance ratio is R _d / R _c Not limited to R _c / R _d But that's fine.

[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 determines the discharge resistance value (R _d ) and charging resistance value (R _c The controller calculates the discharge resistance value (R). Figure 8 is a flowchart of the subflow of the control process in step S2. The controller 10 executes the control processes in steps S21 to S27 shown in Figure 8, thereby calculating the discharge resistance value (R). _d ) and charging resistance value (R _c The controller 10 calculates the voltage and current of the secondary battery 2 at predetermined intervals using the voltage sensor 11 and the current sensor 12, separate from the control processing in steps S21 to S27. The shorter the detection period (sample rate), the higher the accuracy, but it is set to, for example, 1 second (1 Hz). The battery temperature can be any temperature, but it is preferable that the change in battery temperature be as small as possible while executing the control flow in Figures 7 and 8.

[0033] In step S21, after connecting to the power grid, the controller 10 puts the secondary battery 2 into a dormant state by prohibiting charging and discharging for at least one minute. If the secondary battery is already in a dormant state for at least one minute before connecting to the power grid, the dormant period after connecting to the power grid in step S1 may be omitted. Note that setting the dormant period to at least one minute is just an example; the dormant period could be, for example, 10 seconds or more. After the dormant period has elapsed, in step S22, the controller 10 discharges the secondary battery 2 with a constant current. The discharge current value can be any value, but to ensure sufficient accuracy, it is set to, for example, 0.5C. The discharge time can also be any time, but it is set to, for example, 3 seconds.

[0034] In step S23, the controller 10 determines the battery voltage (V) 1 second before the start of discharge. _d (-1)) Battery voltage (V) 3 seconds after discharge begins _d (3)), and discharge current (I _d ) From this, the discharge resistance value (R _d Calculate the discharge resistance (R). _d ) is calculated using the formula [(V _d (-1)-V _d (3)) / I _d It is calculated by [ ]. That is, after the discharge starts, the controller 10 calculates the DC resistance value (R) from the current value of the discharge current (discharge current value) at a predetermined time after the discharge has started. _d The voltage is then calculated. Note that the closer the voltage detection timing is to the discharge start timing, the smaller the voltage variation immediately before discharge. For example, the battery voltage one second before the discharge start can ensure sufficient accuracy.

[0035] In step S24, the controller 10 stops the discharge of the secondary battery 2 and, after stopping, puts the secondary battery 2 into a dormant state for a predetermined rest period (e.g., 10 seconds). The longer the rest period after discharge, the smaller the variation in the detected voltage. For example, if the rest period is set to about 10 seconds, sufficient accuracy can be ensured.

[0036] After a predetermined rest time (e.g., 10 seconds) has elapsed, at step S25, the controller 10 charges the secondary battery 2 with a constant current. The current value of the charging current may be an arbitrary value, but is set to, for example, 0.5C in order to ensure sufficient accuracy. Also, the charging time may be an arbitrary time, but is set to, for example, 3 seconds.

[0037] At step S26, the controller 10 calculates the charging resistance (R _c (-1)), the battery voltage (V _c (3)) 3 seconds after the start of charging, and the charging current (I _c ). The charging resistance (R<映 _c ) is calculated from the battery voltage (V _c )(3) - V _c (-1)) / I _c using the calculation formula [(V _c (3) - V _c (-1)) / I

[0038] At step S27, the controller 10 calculates the resistance ratio (R _d ) of the calculated discharge resistance value (R _c ) to the charging resistance value (R _d [[ID=(32]] / R _c ). The resistance ratio (R _d / R _c ) is expressed as the ratio of the discharge resistance value (R _c ) to the charging resistance value (R _d ). As described above, the controller 10 calculates the resistance ratio (R _d / R _c ) by executing the control processes of steps S21 to S27 (step S2). In the control processes of steps S21 to S27, discharging is performed first and charging is performed later, but the order of discharging and charging may be reversed.

[0039] In step S2, the resistance ratio (R_d / R _c ) After calculating, in step S3, the controller 10 calculates the resistance ratio (R _d / R _c ) and compares it with the resistance ratio threshold value, and determines whether the resistance ratio (R _d / R _c ) is less than the resistance ratio threshold value. The resistance ratio threshold value is a threshold value for setting the lower limit value of the SOC usage range and is preset. The resistance ratio threshold value may be set according to the allowable deterioration rate and / or the allowable degree of deterioration, etc., depending on the usage purpose of the secondary battery 2. The resistance ratio threshold value 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 for the metal active material, etc.). Also, the resistance ratio threshold value may be set according to the detection accuracy of the voltage and / or current of the secondary battery 2. In this embodiment, as an example, the resistance ratio threshold value is set to 1.05.

[0040] When the calculated resistance ratio (R _d / R _c ) is lower than the resistance ratio threshold value (1.05), the controller 10 executes the control processes of steps S4 to S7. On the other hand, when the calculated resistance ratio (R _d / R _c ) is greater than or equal to the resistance ratio threshold value (1.05), the controller 10 executes the control processes of steps S8 to S11.

[0041] In step S4, the controller 10 discharges the secondary battery 2. When the resistance ratio (R _d / R _c ) of the secondary battery 2 is lower than the resistance ratio threshold value (1.05), since the SOC of the secondary battery 2 is higher than the lower limit value of the SOC usage range, in order to determine the lower limit value of the SOC usage range corresponding to the resistance ratio threshold value (1.05), the SOC is decreased. In step S5, the controller 10 calculates the discharge resistance value (R _d ) and the charge resistance value (R _c ). The calculation methods of the discharge resistance value (R _d ) and the charge resistance value (R _c ) are the same as the calculation methods in the control process of step S2.

[0042] In step S6, the controller 10 has a resistance ratio (R _d / R _c ) is compared with the resistance ratio threshold (1.05), and the resistance ratio (R _d / R _c Determine whether the resistance ratio (R) is equal to or greater than the resistance ratio threshold (1.05). _d / R _c If the resistance ratio (R) is lower than the resistance ratio threshold (1.05), 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 in steps S4 to S6, the resistance ratio (R) is adjusted so that the SOC approaches the lower limit of the SOC usage range from the high SOC side. _d / R _c Bring the resistance ratio threshold (1.05) closer to the threshold.

[0043] Resistance ratio (R _d / R _c If the resistance ratio (R) is greater than or equal to the resistance ratio threshold (1.05), in step S7, the controller 10 determines the current SOC to the lower limit of the SOC usage range (lower limit SOC). In other words, the controller 10 determines the resistance ratio (R) _d / R _c The SOC at which the resistance ratio threshold (1.05) is reached is determined as the lower limit of the SOC usage range.

[0044] In step S8, the controller 10 charges the secondary battery 2. The resistance ratio of the secondary battery 2 (R _d / R _c If the discharge resistance value (R) is greater than or equal to the resistance ratio threshold (1.05), the SOC of secondary battery 2 is less than or equal to the lower limit of the SOC usage range. Therefore, to determine the lower limit of the SOC usage range corresponding to the resistance ratio threshold (1.05), the SOC is increased. 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 the degradation of secondary battery 2. For example, the charging current rate should be set to 0.5C or less. In step S9, the controller 10 determines the discharge resistance value (R) _d ) and charging resistance value (R _c Calculate the discharge resistance value (R). _d ) and charging resistance value (R _cThe method for calculating ) is the same as the calculation method in the control process of step S2.

[0045] In step S10, the controller 10 has a resistance ratio (R _d / R _c ) is compared with the resistance ratio threshold (1.05), and the resistance ratio (R _d / R _c Determine whether the resistance ratio (R) is less than the resistance ratio threshold (1.05). _d / R _c If the resistance ratio (R) is greater than or equal to the resistance ratio threshold (1.05), the controller 10 returns the control process flow to step S8 and charges the secondary battery 2. In other words, by repeatedly executing the control processes in steps S8 to S10, the resistance ratio (R) is adjusted so that the SOC approaches the lower limit of the SOC usage range from the low SOC side. _d / R _c Bring the resistance ratio threshold (1.05) closer to the threshold.

[0046] Resistance ratio (R _d / R _c If the resistance ratio (R) is less than the resistance ratio threshold (1.05), in step S11, the controller 10 determines the current SOC to be the lower limit of the SOC usage range (lower limit SOC). In other words, the controller 10 determines the resistance ratio (R) _d / R _c The controller determines the SOC when the resistance ratio (R) reaches the resistance ratio threshold (1.05) as the lower limit of the SOC usage range. Then, the controller 10 terminates the control processing flow for determining the SOC usage range. As a result, the controller 10 determines the resistance ratio (R) _d / R _c The scope of SOC usage is determined based on the above.

[0047] Then, the controller 10 determines the SOC usage range determined by the control processing in steps S7 and S11, and calculates the resistance ratio (R _d / R _cThe SOC is stored in memory in correspondence with the SOC usage range stored in memory. When the secondary battery 2 is in normal use, 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 the controller 10 determines a new SOC usage range, it refers to the memory and stores the resistance ratio (R) corresponding to the lower limit SOC of the SOC usage range. _d / R _c The resistance ratio threshold is set, and the control processes of steps S1 to S11 are executed. Note that the SOC usage range of the secondary battery 2 is a target range for suppressing the degradation rate of the secondary battery 2, and the secondary battery 2 may be charged and discharged outside the SOC usage range. In addition, 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.

[0048] Incidentally, to increase the battery capacity of lithium-ion secondary batteries, a mixture of graphite and a metal active material is used as the negative electrode active material. However, if charging and discharging are performed in the state of charge (SOC) range where the contribution of the metal active material in the negative electrode is large, degradation is accelerated. In this embodiment, the SOC range where the contribution of the metal active material in the negative electrode is large can be detected with high accuracy and in a short time. Then, the SOC usage range is determined while avoiding the SOC range where the contribution of the metal active material in the negative electrode is large, so charging and discharging are performed in the SOC range where the degradation of the metal active material is small. As a result, the decrease in capacity retention rate can be suppressed and the cycle characteristics can be improved.

[0049] As described above, in this embodiment, the charging and discharging of the secondary battery 2 is controlled, and after the discharge of the secondary battery 2 is started, the DC resistance value (R) is calculated from the current value of the discharge current at a predetermined time after the current has elapsed. _d ) is calculated, and after charging of secondary battery 2 is started, the DC resistance value (R) is calculated from the current value of the charging current at a predetermined time elapsed. _c ) calculate the DC resistance value (R _d ) and DC resistance value (R _c Based on the difference with ), the SOC usage range of secondary battery 2 is determined. Note that the DC resistance value (R _d ) and DC resistance value (R _c The difference from ) is the resistance ratio (R _d / R _cThis corresponds to ). This makes it possible to quickly determine the range of SOC to which the negative electrode's metal active material contributes and to avoid charging and discharging within that range. In other words, the SOC usage range of secondary battery 2 can be determined not only in situations where long charging and discharging times can be secured. Furthermore, the SOC usage range is set to avoid the range of SOC to which the negative electrode's metal active material contributes greatly. Then, during normal use of secondary battery 2, charging and discharging occur within the SOC usage range, so the decrease in the capacity of the lithium-ion secondary battery due to the deterioration of the negative electrode's metal active material can be suppressed.

[0050] Furthermore, in this embodiment, the DC resistance value (R _d ) and DC resistance value (R _c The value that shows the difference from (resistance ratio (R) _d / R _c The charging and / or discharging of the secondary battery 2 is controlled within the SOC usage range where the value corresponding to () is below the resistance ratio threshold. This allows charging and discharging to be controlled while avoiding the SOC range in which the contribution of the negative electrode metal active material is large. As a result, the decrease in the capacity of the lithium-ion secondary battery due to the degradation of the negative electrode metal active material can be suppressed.

[0051] Furthermore, in this embodiment, the negative electrode metal active material contains Si. This allows charging and discharging to avoid the state of charge (SOC) range where the negative electrode metal active material contributes significantly when Si is used as the metal active material to increase battery capacity, thereby suppressing the decrease in lithium-ion secondary battery capacity due to Si degradation.

[0052] In this embodiment, the SOC usage range is determined while the secondary battery 2 is connected to the power grid. This allows the detection of the SOC range in which the negative electrode's metal active material contributes significantly while the secondary battery 2 is connected to the power grid, and enables charging and discharging while avoiding the SOC range in which the negative electrode's metal active material contributes significantly. As a result, the SOC usage range can be set to an optimal range while suppressing both degradation and storage degradation of the metal active material.

[0053] In this embodiment, the control processes shown in steps S4 to S6 in Figure 7 are repeatedly executed to bring the SOC closer to the lower limit of the SOC usage range from the high SOC side. At this time, the shorter the discharge time in the control process of step S4, the finer the intervals between discharge capacities become, so the time required to determine the SOC usage range increases, but the accuracy increases.

[0054] Furthermore, in this embodiment, the discharge in the control process of step S4 may be divided by SOC instead of time. For example, the discharge may be divided at SOC (1%) intervals, and the DC resistance value (R _d , R _c The SOC (State of Charge) is calculated, and the SOC usage range is determined. In other words, the SOC usage range is adjusted to SOC (1%) per unit. Therefore, even if there is an error in the accuracy of calculating the SOC usage range, that error can suppress the range of SOC where the contribution of the metal active material is large to less than SOC (1%).

[0055] Furthermore, in this embodiment, after the control processing in step S6, the battery may be charged by a predetermined amount equivalent to SOC, and the SOC after charging may be determined as the lower limit of the SOC usage range. The predetermined SOC is set to, for example, 5%. In a modified version of this embodiment, the predetermined SOC may be set to 1%. This allows the SOC to be set as the lower limit of the SOC usage range with a margin equivalent to the predetermined SOC relative to the SOC range in which the metal active material has a large contribution, thereby suppressing the decrease in the capacity of the lithium-ion secondary battery due to the deterioration of the metal active material of the negative electrode.

[0056] In this embodiment, the control processes shown in steps S8 to S10 in Figure 7 are repeatedly executed to bring the SOC closer to the lower limit of the SOC usage range from the low SOC side. At this time, the shorter the charging time in the control process of step S4, the finer the increments of the charging capacity become, so the time required to determine the SOC usage range increases, but the accuracy increases.

[0057] Furthermore, in this embodiment, the charging in the control process of step S8 may be divided by SOC instead of time. For example, the charging may be divided at SOC (1%) intervals, and the DC resistance value (R _d , R _c The SOC (State of Charge) is calculated, and the SOC usage range is determined. In other words, the SOC usage range is adjusted to SOC (1%) per unit. Therefore, even if there is an error in the accuracy of calculating the SOC usage range, that error can suppress the range of SOC where the contribution of the metal active material is large to less than SOC (1%).

[0058] Furthermore, in this embodiment, after the control processing in step S10, the battery may be charged by a predetermined amount equivalent to SOC, and the SOC after charging may be determined as the lower limit of the SOC usage range. The predetermined SOC is set to, for example, 5%. In a modified version of this embodiment, the predetermined SOC may be set to 1%. This allows the SOC to be set as the lower limit of the SOC usage range with a margin equivalent to the predetermined SOC relative to the SOC range in which the metal active material has a large contribution, thereby suppressing the decrease in the capacity of the lithium-ion secondary battery due to the deterioration of the metal active material of the negative electrode.

[0059] Furthermore, as a modified example of this embodiment, in the control process of step S3, the resistance ratio (R _d / R _c If the resistance ratio (R) is greater than or equal to the resistance ratio threshold (1.05), the controller 10 charges the secondary battery 2 and adjusts the resistance ratio (R _d / R _c After the resistance ratio falls below the threshold (1.05), the control processes in steps S4 to S7 may be executed to determine the SOC usage range.

[0060] In this embodiment, the controller 10 has a DC resistance value (R _d ) and DC resistance value (R _c The value showing the difference from ) is the resistance ratio (R _d / R _c ) is not limited to the resistance difference (R _d -R _c or R _c -R _d ) is also acceptable. Controller 10 controls the DC resistance value (R _d) and DC resistance value (R _c ) from the resistance difference (R _d -R _c or R _c -R _d ) is calculated, and the calculated resistance difference (R _d -R _c or R _c -R _d The SOC usage range of the secondary battery 2 may be determined based on the following. Specifically, in the control flow of step S27 among the subflows of the control processing in step S2, the controller 10 determines the discharge resistance value (R _d ) and charging resistance value (R _c The difference between this and the resistance difference (R _d -R _c or R _c -R _d ) is calculated as follows. In steps S3, S6, and S10, the resistance ratio (R _d / R _c Instead of ) the controller 10 calculates the resistance difference (R _d -R _c or R _c -R _d The controller compares the calculated resistance difference (R) with the resistance difference threshold. The resistance difference threshold is a preset threshold, similar to the resistance ratio threshold. Then, in steps S7 and S11, the controller 10 calculates the resistance difference (R) and compares it with the resistance difference threshold. _d -R _c or R _c -R _d The SOC at which the resistance difference threshold is reached is determined as the lower limit SOC of the SOC usage range.

[0061] Thus, in this embodiment, the DC resistance value (R _d ) and DC resistance value (R _c The value that shows the difference from ) is the DC resistance value (R _d ) and DC resistance value (R _c The resistance difference (R) _d -R _c or R _c -R _d ) is calculated, and the calculated resistance difference (R _d -R _c or R _c -R _dBased on this, the SOC usage range of secondary battery 2 is determined. This allows for quick identification of the SOC range to which the negative electrode's metal active material contributes, and enables avoidance of charging and discharging within that range. In other words, the SOC usage range of secondary battery 2 can be determined not only in situations where long charging and discharging times can be secured. Furthermore, the SOC usage range is set to avoid the SOC range in which the negative electrode's metal active material contributes significantly. During normal use of secondary battery 2, charging and discharging occur within the SOC usage range, thus suppressing the decrease in lithium-ion secondary battery capacity due to the degradation of the negative electrode's metal active material.

[0062] Note that the SOC usage range is the resistance ratio (R) before degradation. _d / R _c Alternatively, the initial value of the SOC usage range can be determined by calculating the theoretical capacity of SiO (mAh / g) and the amount of SiO used (g). The SiO contribution capacity can then be calculated from the calculated SiO contribution capacity and the battery capacity of secondary battery 2 before degradation. This allows for the calculation of the SOC range in which SiO primarily contributes before degradation. For example, if SiO contribution capacity / battery capacity = 15%, then the SOC range (0-15%) will be the SOC range in which SiO contributes most significantly. The range excluding this SOC range (0-15%) (for example, 15-100%) will then be the SOC usage range.

[0063] Furthermore, in the above example, the resistance ratio (R) equivalent to 15% of the SOC before degradation. _d / R _c The resistance ratio threshold is calculated as ) and after the secondary battery 2 has deteriorated, the resistance ratio (R _d / R _c The SOC at which the resistance ratio threshold is set is defined as the lower limit of the SOC usage range. This allows charging and discharging to be performed while avoiding the SOC range where the contribution of the negative electrode's metal active material is large, even before and after the degradation of the secondary battery 2.

[0064] In addition to VGI, the battery control system according to this embodiment can be applied in the following ways. For example, in an electric vehicle using secondary battery 2, an alarm threshold is set to sound a battery level alarm when the SOC is several percent higher than the lower limit of the SOC usage range. Then, during normal driving, if the SOC of secondary battery 2 falls to the alarm threshold, an alarm is output to prompt the user to charge the battery early.

[0065] As another example, if the State of Charge (SOC) of secondary battery 2 falls to the lower limit of the SOC usage range, the discharge current of secondary battery 2 may be reduced by limiting the motor's output torque. However, such output limitations do not necessarily need to be applied at all times. For example, in situations where high acceleration performance is required (e.g., when torque equivalent to full throttle is required), the output limitation may be removed and secondary battery 2 may be used at or below the lower limit of the SOC usage range when specific conditions are met. This reduces the frequency of use within the SOC range where the contribution of the negative electrode's metal active material is large, thereby suppressing the degradation of secondary battery 2.

[0066] Further examples include cases where the secondary battery 2 is used as a stationary power source, or where a vehicle equipped with the secondary battery 2 is used as an external power source for indoor or outdoor use. In these cases, as described above, alarm settings may be made according to the lower limit of the lower limit of the SOC usage range.

[0067] ≪Second Embodiment≫ Next, a battery control system according to the second embodiment will be described. In the second embodiment, in order to further reduce the time required to determine the SOC usage range compared to the first embodiment, a part of the control process for determining the SOC usage range has been modified. Except for the differences from the determination system according to the first embodiment described below, the second embodiment has the same configuration as the first embodiment, implements 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 appropriately referenced.

[0068] In this embodiment, the controller 10 determines the SOC usage range at a predetermined timing, such as when the charging and discharging of the secondary battery 2 is completed. Furthermore, when the controller 10 determines the SOC usage range, it considers the resistance ratio (R) to be close to the lower limit SOC of the SOC usage range when the SOC of the secondary battery 2 is close to that value. _d / R _c To calculate the SOC, a predetermined SOC range is set, including the lower limit SOC of the SOC usage range. The predetermined SOC range (hereinafter referred to as the lower limit SOC determination range) is a range that is expanded by a predetermined amount of SOC (for example, ±5%) on both the positive and negative sides relative to the lower limit SOC of the SOC usage range. If 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 falls within the lower limit SOC determination range. After the SOC of the secondary battery 2 is within the lower limit SOC determination range, the controller 10 sets the charge / discharge current value (I _d , I _c ) detects the resistance ratio (R _d / R _c ) calculate the resistance ratio (R _d / R _c The scope of SOC usage is determined based on the above.

[0069] Below are the DC resistance values ​​(R _d ) and DC resistance value (R _c The resistance ratio (R) is a value that shows the difference from ). _d / R _c ) is calculated, and the calculated resistance ratio (R _d / R _c The control process for determining the SOC usage range based on the above will be explained. Figure 9 is a flowchart showing the procedure for 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 can be estimated, for example, by a map calculation using a map that shows 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 connecting the secondary battery 2 to the power grid.

[0070] In step S33, the controller 10 uses the estimated SOC and the previously determined lower limit SOC of the SOC usage range (SOC _0 ) plus a predetermined SOC (5%) (SOC _0 Compared to +5%), the estimated SOC is "SOC _0 Determine whether it is greater than "+5%" or not. SOC _0 +5% corresponds to the upper limit of the lower bound SOC determination range.

[0071] The estimated SOC is the upper limit of the lower limit SOC determination range (SOC _0 If the SOC is greater than +5%, in step S34 the controller 10 will set the SOC to the upper limit (SOC _0 Discharge secondary battery 2 until it reaches +5%. (SOC) _0 After reaching +5%), in step S35, the controller 10 determines the discharge resistance value (R _d ) and charging resistance value (R _c Calculate the discharge resistance value (R). _d ) and charging resistance value (R _c The method for calculating the resistance ratio (R) is the same as the method for calculating it in the control process of step S2 in the first embodiment. In step S36, the controller 10 calculates the resistance ratio (R _d / R _c ) is compared with the resistance ratio threshold (1.05), and the resistance ratio (R _d / R _c Determine whether the resistance ratio (R) is equal to or greater than the resistance ratio threshold (1.05). _d / R _c If the resistance ratio is lower than the resistance ratio threshold (1.05), in step S37, the controller 10 discharges the secondary battery 2. Then, the controller 10 executes the control process in step S35.

[0072] Resistance ratio (R _d / R _c If the resistance ratio (R) is greater than or equal to the resistance ratio threshold (1.05), in step S38, the controller 10 determines the current SOC to the lower limit of the SOC usage range (lower limit SOC). In other words, the controller 10 determines the resistance ratio (R) _d / R _cThe SOC at which the resistance ratio threshold (1.05) is reached is determined as the lower limit of the SOC usage range.

[0073] In the comparison and determination control process of step S33, the estimated SOC is the upper limit of the lower limit SOC determination range (SOC _0 If it is determined to be less than or equal to +5%), in step S39, the controller 10 will determine the estimated SOC and the lower limit SOC of the previously determined SOC usage range (SOC _0 (SOC) is the value obtained by subtracting a predetermined SOC (5%) from the original value. _0 Compared to -5%, the estimated SOC is "SOC _0 Determine whether it is less than -5% or not. SOC _0 -5% corresponds to the lower limit of the lower limit of the SOC determination range.

[0074] The estimated SOC is the lower limit of the lower limit of the SOC determination range (SOC _0 If it is less than -5%, in step S40 the controller 10 will set the SOC to the upper limit (SOC _0 Charge secondary battery 2 until the SOC reaches -5%. _0 After reaching -5%, in step S41, the controller 10 determines the discharge resistance value (R _d ) and charging resistance value (R _c Calculate the discharge resistance value (R). _d ) and charging resistance value (R _c The method for calculating the resistance ratio (R) is the same as the method for calculating it in the control process of step S2 in the first embodiment. In step S42, the controller 10 calculates the resistance ratio (R _d / R _c ) is compared with the resistance ratio threshold (1.05), and the resistance ratio (R _d / R _c Determine whether the resistance ratio (R) is below the resistance ratio threshold (1.05). _d / R _c If the resistance ratio is higher than the resistance ratio threshold (1.05), in step S43, the controller 10 charges the secondary battery 2. Then, the controller 10 executes the control process in step S41.

[0075] Resistance ratio (R_d / R _c If the resistance ratio (R) is less than or equal to the resistance ratio threshold (1.05), in step S44, the controller 10 determines the current SOC to be the lower limit of the SOC usage range (lower limit SOC). In other words, the controller 10 determines the resistance ratio (R) _d / R _c The SOC at which the resistance ratio threshold (1.05) is reached is determined as the lower limit of the SOC usage range.

[0076] In the comparison and determination control process of step S39, the estimated SOC is the lower limit of the lower limit SOC determination range (SOC _0 If it is determined to be -5% or more, that is, if the estimated SOC is within the lower limit SOC determination range, in step S45 the controller 10 determines the discharge resistance value (R _d ) and charging resistance value (R _c Calculate the discharge resistance value (R). _d ) and charging resistance value (R _c The method for calculating ) is the same as the calculation method in the control process of step S2 in the first embodiment.

[0077] In step S46, the controller 10 calculates the resistance ratio (R _d / R _c The resistance ratio (R) is compared with the resistance ratio threshold (1.05) and the calculated resistance ratio (R _d / R _c Determine whether the resistance ratio (R) is less than the resistance ratio threshold (1.05). _d / R _c If the resistance ratio is less than the threshold (1.05), in step S47, the controller 10 discharges the secondary battery 2. Then, the controller 10 executes the control processes in steps S48 to S51. The control processes in steps S48 to S51 are the same as the control processes in steps S35 to S38.

[0078] In the comparison and determination in step S46, the resistance ratio (R) is determined in the control process. _d / R _cIf it is determined that the resistance ratio is greater than or equal to the threshold (1.05), in step S52, the controller 10 charges the secondary battery 2. Then, the controller 10 executes the control processes in steps S53 to S56. The control processes in steps S53 to S56 are the same as the control processes in steps S41 to S44.

[0079] Then, the controller 10 determines the SOC usage range determined by the control processing in steps S38, S44, S51, and S56, and calculates the resistance ratio (R _d / R _c The controller 10 stores the SOC in memory in correspondence with the SOC usage range stored in memory. When the secondary battery 2 is in normal use, 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 the controller 10 determines a new SOC usage range, it refers to the memory and stores the resistance ratio (R) corresponding to the lower limit SOC of the SOC usage range. _d / R _c The resistance ratio threshold is set, and the control processing from steps 31 to S56 is executed.

[0080] Figure 10 is a graph illustrating the relationship between the size of the State of Coffee (SOC) estimated in the control process of step 32 and the charging and discharging of the secondary battery 2. As shown in Figure 10, the lower limit SOC determination range is set to a predetermined SOC (±5%) range centered on the lower limit of the previously determined SOC usage range. The estimated SOC is set to the upper limit of the lower limit SOC determination range (SOC _0 If it is greater than +5%), secondary battery 2 will discharge, and the SOC will approach the lower limit of the SOC determination range from the high SOC side (see arrow H in Figure 10). On the other hand, if the estimated SOC is greater than the lower limit of the lower limit of the SOC determination range (SOC _0 If it is less than -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 Figure 10). Then, in this embodiment, after the SOC is within the lower limit SOC determination range, the resistance ratio (R _d / R _c The resistance ratio (R) is calculated and calculated. _d / R _cThe SOC usage range is determined based on the above. This reduces the number of repetitions of the control loops in steps S35-S37 and S41-S43.

[0081] As described above, in this embodiment, the DC resistance value (R _d ) and DC resistance value (R _c The value that shows the difference from (resistance ratio (R) _d / R _c The system of occupancy range (R) determined to be equivalent to the above is stored in memory in association with the above, and the charging and / or discharging of the secondary battery 2 is controlled so that the SOC falls within a predetermined SOC range that includes the lower limit of the previously determined SOC range, and after the SOC falls within the lower limit of the determined SOC range, the DC resistance value (R) is stored in memory in association with the above, and the charging and / or discharging of the secondary battery 2 is controlled so that the SOC falls within a predetermined SOC range that includes the lower limit of the determined SOC range. _d ) and DC resistance value (R _c The value that shows the difference from (resistance ratio (R) _d / R _c The DC resistance value (R) is calculated after the SOC falls within the lower limit of the SOC determination range. _d ) and DC resistance value (R _c The value that shows the difference from (resistance ratio (R) _d / R _c The SOC usage range is determined based on the following criteria. This allows for controlling charging and discharging while avoiding as much as possible the SOC range in which the negative electrode's metal active material contributes significantly. As a result, the decrease in lithium-ion secondary battery capacity due to the degradation of the negative electrode's metal active material can be suppressed.

[0082] In this embodiment, the lower limit SOC determination range was set to have a predetermined SOC width (e.g., ±5%) centered on the lower limit of the SOC usage range determined previously, 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 calculated resistance ratio (R _d / R _cThe value may repeatedly exceed or fall below the resistance ratio threshold, and may not converge to the resistance ratio threshold. Therefore, it is preferable to set the width of the SOC to about twice the estimation error of the SOC.

[0083] In this embodiment, the controller 10 has a DC resistance value (R _d ) and DC resistance value (R _c ) from the resistance difference (R _d -R _c or R _c -R _d ) is calculated, and the calculated resistance difference (R _d -R _c or R _c -R _d The SOC usage range of the secondary battery 2 may be determined based on the following. In steps S35, S41, S45, S48, and S53, the controller 10 determines the resistance ratio (R _d / R _c Instead of ), the resistance difference (R _d -R _c or R _c -R _d The controller calculates the calculated resistance difference (R). In steps S36, S42, S46, S49, and S54, the controller 10 calculates the resistance difference (R). _d -R _c or R _c -R _d The controller compares the calculated resistance difference (R) with the resistance difference threshold. The resistance difference threshold is a preset threshold, similar to the resistance ratio threshold. Then, in steps S38, S44, S53, and S56, the controller 10 calculates the resistance difference (R) and compares it with the resistance difference threshold. _d -R _c or R _c -R _d The SOC at which the resistance difference threshold is reached is determined as the lower limit SOC of the SOC usage range.

[0084] While embodiments of the present invention have been described above, these embodiments are provided to facilitate understanding of the present invention and are not intended to limit it. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention. [Examples]

[0085] The present invention will be described below based on more detailed examples, but the present invention is not limited to these examples.

[0086] <Creation of a prototype (example)> A 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, and applying the resulting slurry onto copper foil. A positive electrode layer was created by using lithium nickelate (NCA) as the positive electrode active material, carbon black as the conductive additive, and PVDF as the binder, and applying the resulting slurry onto aluminum foil. A polyethylene (PE) film was used as the separator. A solution of lithium hexafluoride phosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) was used as the electrolyte. A test cell (prototype) was created by layering the negative electrode layer, separator, and positive electrode layer, sandwiching them between aluminum laminates, injecting the electrolyte into the interior, and sealing the area around the laminates.

[0087] <Evaluation of Examples> (1) The prototype underwent the following charge and discharge procedure to adjust the State of Charge (SOC). First, the battery was discharged at a discharge current of 0.2C until the battery voltage reached 2.5V. After discharge, it was charged at a charge current of 0.2C until it reached a target voltage corresponding to a 10% SOC. After reaching the target voltage corresponding to a 10% SOC, the charging was switched to constant voltage charging, and charging was terminated when the charge current dropped to 0.01C. (2)(1) The voltage change of the prototype after SOC adjustment was measured in the following manner. First, after more than 1 minute had elapsed since the end of charging, charge and discharge control was performed in the following order: discharge for 10 seconds at a discharge current value (0.5C), pause for 10 seconds, charge for 10 seconds at a charge current value (0.5C), and pause for 10 seconds. During the control, the voltage change was recorded. In addition, the absolute value of the voltage difference (ΔV) between the voltage 1 second before the start of discharge and the voltage 3 seconds after the start of discharge was recorded. _d) and the absolute value of the voltage difference (ΔV) between the voltage 1 second before charging starts and the voltage 3 seconds after charging starts. _c The voltage difference (ΔV) was calculated. _d ) divided by the charging current value gives the DC resistance value (R _d ) is calculated, and the calculated voltage difference (ΔV _c ) divided by the discharge current value gives the DC resistance value (R _c ) was calculated. (3) The prototypes measured in (2) were charged with a charging current of 0.2C until they reached a target voltage corresponding to 20% SOC. After reaching the target voltage corresponding to 20% SOC, constant voltage charging was performed until the current value decreased to 0.01C (SOC adjustment). (4) Record the voltage change in the same manner as in (2), and the voltage difference (ΔV _d , ΔV _c ) is calculated, and further, the DC resistance value (R _d , R _c ) was calculated. (5) From (4) onward, the SOC adjustment in (3) is performed with the target voltages corresponding to SOC 30%, 40%, and 50%, and the voltage change measurement in (4) (voltage difference (ΔV) _d , ΔV _c ) and DC resistance value (R _d , R _c The calculation of (including) was performed.

[0088] <Evaluation results of the examples> After adjusting the SOC to 10%, plotting the voltage change measured in (2) yielded the measurement results shown in the graph in Figure 11. 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 calculated DC resistance value (R) was obtained for each SOC (10%, 20%, 30%, 40%, 50%). _d , R _c When the values ​​were plotted, the measurement results shown in the graphs in Figures 12 to 14 were obtained. In Figures 12 to 14, the horizontal axis is the same for SOC, and the vertical axis is the DC resistance value (R). _d , R _c ), DC resistance value (R _d , R _c ) Resistance ratio (R _d / R _c), and DC resistance value (R _d , R _c ) difference (R _d -R _c These represent the following: As shown in Figures 13 and 14, in the range where SOC is 20% or less, the DC resistance value (R _d , R _c ) Resistance ratio (R _d / R _c ) and difference (R _d -R _c It can be confirmed that the value is larger compared to the value in the range where the SOC is greater than 20%. In other words, in the examples, it was confirmed that in the SOC range where SiO contributes significantly to charging and discharging, the difference in DC resistance values ​​during charging and discharging is larger compared to the SOC range where Gr contributes. [Explanation of symbols]

[0089] 1...Judgment device 2…Secondary battery 10…Controller 11…Voltage sensor 12...Current sensor 13…DC-DC converter 21…Positive electrode layer 22... Negative electrode layer 23... Separator 24…Positive electrode tab 25... Negative electrode tab 26… Upper exterior components 27…Lower exterior components

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; After starting discharging the lithium ion secondary battery, the DC resistance value (R ＿ｄ ) is calculated, After the charging of the lithium ion secondary battery is started, the DC resistance value (R ＿ｃ ) is calculated, The DC resistance value (R ＿ｄ ) and the DC resistance value (R ＿ｃ 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 a difference between the actual state of charge (SOC) and the actual state of charge (SOC usable range).

2. 2. The control method according to claim 1, The DC resistance value (R ＿ｄ ) and the DC resistance value (R ＿ｃ 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 SOC and the actual SOC is less than a predetermined threshold value.

3. 3. The control method according to claim 1 or 2, The DC resistance value (R ＿ｄ ) and the DC resistance value (R ＿ｃ ) and the determined SOC use range are stored in a memory in association with each other; controlling charging and / or discharging of the lithium ion secondary battery so that the SOC falls within a predetermined SOC range including a previously determined lower limit value of the SOC use range; After the SOC falls within the predetermined SOC range, the DC resistance value (R ＿ｄ ) and the DC resistance value (R ＿ｃ ) and calculate the difference value, The DC resistance value (R ＿ｄ ) and the DC resistance value (R ＿ｃ A control method for determining the current SOC usage range based on a value indicating the difference between the SOC and the actual SOC.

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

5. 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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