SOC target setting system and secondary battery system

Abstract

To provide an SOC target setting system capable of suppressing degradation specific to a secondary battery including an electrode having a plateau potential.SOLUTION: An SOC target setting system 1 includes: a threshold determination section 4 to determine at least one of a threshold at least at one end of a plateau range indicating a plateau voltage and a threshold of an SOC corresponding to an upper limit and a lower limit of an SOC range where a secondary battery 20 is used, among SOCs in the secondary battery 20 having the plateau voltage; and an SOC target setting section 7 to set a second SOC value so that at least one of the thresholds exists between a first SOC value that is the SOC at the start of charging / discharging of the secondary battery 20 and the second SOC value that becomes a target value to perform charging / discharging from the first SOC value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a SOC target setting system and a secondary battery system. [Background technology]

[0002] In recent years, secondary batteries such as lithium-ion batteries have been increasingly used as power sources for households such as smart houses, industrial facilities such as commercial facilities and office buildings, and driving power sources for mobility. The performance of secondary batteries deteriorates due to repeated charging and discharging, storage in high-temperature environments, and other factors. Depending on the state of deterioration, the lifespan of secondary batteries can be significantly reduced. Therefore, a control method for suppressing the degree of deterioration of secondary batteries is required.

[0003] The electrode active material used in secondary batteries can be selected not only based on product specifications, applications, and price, but also from the perspective of the environment and safety. For example, typical positive electrode active materials for lithium-ion batteries include LiMn2O4 (LMO), LiNiCoAlO2 (NCA), LiCoO2 (LCO), and LiNi x Mn y Co z Examples include NMC (Non-Crystalline Metallic Compound) and LiFePO4 (LFP). Traditionally, NMC was the main material due to its high energy density, but because it uses the rare metal Co, LFP is increasingly being adopted due to its cost and environmental protection. Graphite and hard carbon were the main negative electrode active materials, but since it is difficult to obtain a uniform battery voltage with hard carbon, graphite is now being used.

[0004] Patent Document 1 describes, "A lithium ion secondary battery system in which, when it is detected or estimated that the starting battery voltage, the ending battery voltage, the starting SOC or the ending SOC of a charge / discharge cycle of a lithium ion secondary battery are characteristic points that appear on a Q-dV / dQ curve, the starting battery voltage, the ending battery voltage, the starting SOC or the ending SOC of the charge / discharge cycle of the lithium ion secondary battery are set to a battery voltage or SOC that avoids the characteristic points that appear on the Q-dV / dQ curve." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-196805 Summary of the Invention [Problem to be solved by the invention]

[0006] The method described in Patent Document 1 suppresses deterioration due to expansion and contraction of the active material by avoiding characteristic points that appear on the Q-dV / dQ curve of a lithium-ion secondary battery (paragraph 0018). However, the method described in Patent Document 1 cannot suppress deterioration specific to secondary batteries that use active materials with plateau potential. The plateau potential here refers to the potential at which the electrode potential becomes constant regardless of the charge / discharge index (SOC) of the secondary battery. The problem to be solved by the present disclosure is to provide an SOC target setting system and a secondary battery system that can suppress deterioration that is specific to secondary batteries that include electrodes with plateau potentials. [Means for solving the problem]

[0007] The SOC target setting system of the present disclosure includes a threshold determination unit that determines at least one of a threshold value representing at least one end of a plateau range indicating the plateau potential or the plateau voltage of a charge / discharge indicator that indicates the degree of charge / discharge of at least one of a positive electrode having a plateau potential, a negative electrode having a plateau potential, or a secondary battery having a plateau voltage, and a threshold value of the charge / discharge indicator that corresponds to an upper limit and a lower limit of a range of the charge / discharge indicator in which the secondary battery is used, and an SOC target setting unit that sets the second charge / discharge index value so that at least one threshold exists between a first charge / discharge index value that is the charge / discharge indicator at the start of charge / discharge of the secondary battery and a second charge / discharge index value that is a target value for charging / discharging from the first charge / discharge index value. Other solutions will be described later in the description of the present invention. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide an SOC target setting system and a secondary battery system that are capable of suppressing deterioration that is specific to secondary batteries that include electrodes with plateau potentials. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram of an SOC target setting system and a secondary battery system according to the present disclosure. [Figure 2] 1 is a block diagram showing a hardware configuration of a SOC target setting system according to the present disclosure. [Figure 3] 1 is a graph showing the positive electrode potential, the negative electrode potential, and the open circuit voltage of a secondary battery as a function of SOC. [Figure 4] 1 is a flowchart illustrating a method for setting an SOC target according to the present disclosure. [Figure 5] 1 shows the results of cycle tests for Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, modes for carrying out the present disclosure (hereinafter referred to as "embodiments") will be described with reference to the drawings. In the following description of one embodiment, other embodiments applicable to the one embodiment will also be described as appropriate. The present disclosure is not limited to the one embodiment described below, and different embodiments can be combined with each other or modified as desired without significantly impairing the effects of the present disclosure. Furthermore, the same components will be given the same reference numerals, and redundant descriptions will be omitted. Furthermore, components having the same functions will be given the same names. The contents shown are merely schematic, and for convenience of illustration, changes may be made from the actual configuration within the scope of not significantly impairing the effects of the present disclosure, and some components may be omitted or modified between drawings. Furthermore, the same embodiment does not necessarily have to include all of the configurations.

[0011] FIG. 1 is a block diagram of an SOC target setting system 1 and a secondary battery system 10 according to the present disclosure. The SOC target setting system 1 according to the present disclosure is a system that sets a second SOC value (an example of a second charge / discharge index value) that is a charge / discharge target for a secondary battery 20 having a plateau voltage. As described above, the plateau voltage is a voltage at which the voltage (closed circuit voltage) of the secondary battery 20 becomes constant, regardless of the charge / discharge index of the secondary battery 20. The charge / discharge index is an index that indicates the degree of charge / discharge of the secondary battery (the degree of the charged state, the degree of the discharged state), and is, for example, at least one of the SOC, the charge capacity, and the discharge capacity. Hereinafter, the range of the charge / discharge index that indicates the plateau voltage is referred to as the plateau range. The SOC (State of Charge) is an index that normalizes the charge capacity and the discharge capacity, and therefore, the SOC has a corresponding relationship with the charge capacity and the discharge capacity. Therefore, in the following description, the SOC is exemplified as the charge / discharge index, but the charge / discharge index may be at least one of the charge capacity and the discharge capacity.

[0012] When a secondary battery 20 having a plateau voltage is used mainly within the plateau range (especially within a narrow range), deterioration accelerates. The acceleration of deterioration is due to uneven distribution of the battery reaction. Therefore, in the present disclosure, the usage amount of the secondary battery 20 within the plateau range is calculated. If the usage amount exceeds a predetermined value, it is determined that deterioration will accelerate. If it is determined that deterioration will accelerate, the SOC of the secondary battery 20 is adjusted, for example, to a second SOC value at which the closed circuit voltage of the secondary battery 20 changes. This makes it possible to suppress acceleration of deterioration of the secondary battery 20 due to, for example, long-term use within the plateau range, and slow down the rate of deterioration.

[0013] The secondary battery system 10 includes a secondary battery 20, a load 30, a measurement unit 40, and an SOC target setting system 1. The secondary battery 20 is, for example, a lithium ion battery, and may be, for example, a battery cell, a battery module, or a battery pack. The secondary battery 20 is connected to the load 30, the measurement unit 40, and the SOC target setting system 1.

[0014] The secondary battery 20 includes a positive electrode (not shown) having a plateau potential and a negative electrode (not shown) having a plateau potential. The plateau potential is a potential at which the potentials of the positive electrode and negative electrode become constant, regardless of the charge / discharge index of the secondary battery 20. The plateau range indicating the plateau potential among the charge / discharge indexes usually coincides with the plateau range based on the voltage of the secondary battery 20. The positive electrode and negative electrode have plateau potentials, and thus the secondary battery 20 has a plateau voltage.

[0015] Whether an electrode has a plateau potential or not depends on the active material that constitutes the electrode. Positive electrode active materials that exhibit a plateau potential include, for example, active materials having an olivine structure (e.g., LiFePO4 (LFP), LiMn x Fe 1-x PO4), active materials with spinel structure (e.g., LiMn2O4 (LMO), LiNi 0.5 Mn 1.5 Examples of negative electrode active materials that exert a plateau potential include graphite, Li4Ti5O 12 etc.

[0016] The load 30 is, for example, a demand end for power. The demand end is, for example, a home, a store, a factory, a motor mounted on a mobility vehicle, etc. The secondary battery 20 is also connected to a power supply source (not shown), for example, a power transmission line, a generator, a solar panel, etc.

[0017] The measurement unit 40 is, for example, a sensor that measures the voltage, current, and temperature of the secondary battery 20. The measurement unit 40 is, for example, a voltmeter, an ammeter, a thermometer, etc. The voltage of the secondary battery 20 is, for example, a closed-circuit voltage, but it may also be an open-circuit voltage. When the secondary battery 20 is, for example, constantly used (charged and discharged), the closed-circuit voltage can be used as the voltage of the secondary battery 20. When the secondary battery 20 is not used (not charged or discharged), the open-circuit voltage of the secondary battery 20 can be measured when it is not in use and used, and the open-circuit voltage can be used as the voltage of the secondary battery 20. Note that the closed-circuit voltage is the sum of the open-circuit voltage and the overvoltage. Therefore, when measuring the closed-circuit voltage, it is preferable to keep the overvoltage close to zero.

[0018] The SOC target setting system 1 includes a measuring unit 2, a storage unit 3, a threshold determining unit 4, a usage amount calculating unit 5, a determining unit 6, an SOC target setting unit 7, and a charge / discharge control unit 8. The functional units constituting the SOC target setting system 1 may be configured by the same control device, or at least one functional unit may be configured independently of the other functional units. In the latter case, for example, some functional units may be arranged together with the secondary battery 20, and the remaining functional units may be arranged by being stored in a server located remotely away from the secondary battery 20.

[0019] FIG. 2 is a block diagram showing the hardware configuration of the SOC target setting system 1 of the present disclosure. As an example, FIG. 2 illustrates a case where the SOC target setting system 1 is configured by a single device. For example, the SOC target setting system 1 includes a central processing unit (CPU) 1001, a random access memory (RAM) 1002, a read-only memory (ROM) 1003, an interface (I / F) 1004, a bus 1005, and the like. The CPU 1001, RAM 1002, ROM 1003, and I / F 1004 are connected via the bus 1005, for example. The SOC target setting system 1 (SOC target setting device) is realized by loading a predetermined control program (e.g., the SOC target setting method of the present disclosure) stored in the ROM 1003 into the RAM 1002 and executing the program by the CPU 1001. Signals and information are exchanged between the SOC target setting system 1 and various devices (e.g., servers), external networks, and the like, in terms of hardware, via the I / F 1004.

[0020] 1, the measurement unit 2 is a functional unit that measures the time when performing the control of the present disclosure. For example, the measurement unit 2 measures the time during charging and discharging of the secondary battery 20, the standby time, etc.

[0021] The storage unit 3 is a functional unit that stores values ​​and conditions calculated by the SOC target setting system 1 and the secondary battery system 10, values ​​and conditions used, etc. Specifically, for example, the storage unit 3 stores various predetermined values, thresholds, threshold history, usage amount, a usage plan for the secondary battery 20, a first SOC value, a second SOC value, a control history, etc.

[0022] The threshold determination unit 4 is a functional unit that determines the thresholds used in the SOC target setting system 1. The determined threshold is at least one of two thresholds. The first threshold is a value that is at least one end of a plateau range in at least one of the positive electrode, the negative electrode, or the secondary battery 20. The positive electrode and the negative electrode have plateau potentials as described above, and the secondary battery 20 equipped with these has a plateau voltage. As described above, the plateau range is the range of charge / discharge indicators that indicate the plateau potential or plateau voltage among the charge / discharge indicators that indicate the degree of charge / discharge of the secondary battery 20.

[0023] The second threshold value is an SOC value corresponding to the upper and lower limits of the SOC range in which the secondary battery 20 is used. The second threshold value can be determined as a value arbitrarily set according to, for example, a usage plan for the secondary battery 20 (for example, a planned SOC range, an SOC range allowed by specifications, etc.), a usage environment for the secondary battery 20, etc. On the other hand, the first threshold value can be determined as follows.

[0024] The threshold determination unit 4 A function of the SOC and the open circuit voltage (OCV) of the secondary battery 20 (e.g., an SOC-OCV curve), A function of the SOC of the secondary battery 20 and a value (dOCV / dSOC) obtained by differentiating the open circuit voltage of the secondary battery 20 with respect to the SOC (for example, an SOC-dOCV / dSOC curve); A function (e.g., an SOC-OCP curve) of the SOC of the secondary battery 20 and the open circuit potential (OCP) of at least one of the positive and negative electrodes provided in the secondary battery 20; A function (e.g., an SOC-dOCP / dSOC curve) of the SOC of the secondary battery 20 in at least one of the positive and negative electrodes provided in the secondary battery 20 and a value (dOCP / dSOC) obtained by differentiating the open circuit potential of the electrode with respect to the SOC; The threshold value is determined using at least one of the functions listed below. The threshold value can be determined using these functions.

[0025] The threshold is the boundary between the plateau range of SOC corresponding to the plateau potential and the non-plateau range of SOC corresponding to the non-plateau potential, which is a potential other than the plateau potential. Therefore, the threshold can be determined by using each of the above functions.

[0026] The threshold determination unit 4 sets the threshold using at least one of the inflection points of each of the above functions or the amount of change in the electrode potential or open-circuit voltage per unit amount of SOC (i.e., the rate of change in potential or voltage per unit amount of SOC). Among these, the inflection points are the boundaries between the plateau range and the non-plateau range, where the trends of the electrode potential and open-circuit voltage change. Therefore, the threshold can be determined by grasping the trend change based on the inflection points. Furthermore, as will be described in detail later with reference to FIG. 4, the amount of change in potential or voltage per unit amount of SOC (i.e., the rate of change) differs between the plateau range and the non-plateau range. For example, the rate of change is relatively small in the plateau range, but relatively large in the non-plateau range. Therefore, the threshold can be determined based on the amount of change in potential or voltage per unit amount of SOC.

[0027] Usually, the open circuit voltage and closed circuit voltage of the secondary battery 20 can be easily measured, but it is difficult to directly measure the potential of the electrodes that constitute the secondary battery 20. Therefore, for example, the SOC-OCP curve can be calculated from the open circuit voltage of the secondary battery 20.

[0028] For example, the following method can be used to obtain (separate) the SOC-OCP curves of the positive and negative electrodes from the SOC-OCV curve. First, the actual measured value of the SOC-OCV curve of the secondary battery 20 is obtained. Then, the calculated value of the SOC-OCP curve of the positive electrode and the calculated value of the SOC-OCP curve of the negative electrode are obtained in advance. Then, since the difference between the positive electrode OCP and the negative electrode OCP is the OCV of the secondary battery, the calculated value of the SOC-OCV curve of the secondary battery 20 is also obtained from these two calculated values. Finally, a graph of the calculated values ​​of the SOC-OCV curve of the secondary battery 20 is fitted to a graph of the actual measured values ​​of the SOC-OCV curve of the secondary battery 20, and the SOC-OCP curves of the positive and negative electrodes at this time can be used to represent the state of the positive and negative electrodes of the secondary battery 20.

[0029] FIG. 3 is a graph showing the SOC as a function of the positive electrode potential, negative electrode potential, and open circuit voltage of the secondary battery 20. The horizontal axis represents the SOC (%) of the secondary battery 20, and the vertical axis represents the OCV (V) of the secondary battery 20 and the OCP (V) of the positive and negative electrodes. The OCP of the positive and negative electrodes is the potential relative to lithium. FIG. 3 is a graph showing the SOC-OCP curves of the positive and negative electrodes obtained from the SOC-OCV curve according to the above-described method, and is a graph actually obtained in the examples described below. The solid line represents the SOC-OCV curve of the secondary battery 20 (measured values ​​and calculated values), the dotted line represents the SOC-OCP curve of the positive electrode (calculated values), and the dashed line represents the SOC-OCP curve of the negative electrode (calculated values). In the example of the present disclosure, there are six SOC thresholds: T1, T2, T3, T4, T5, and T6.

[0030] The ranges from threshold T1 to T2, from threshold T3 to T4, and from threshold T5 to T6 are plateau ranges. In these ranges, the OCV of the secondary battery 20 and the OCP of the positive and negative electrodes hardly change. The size (width) of the SOC range from threshold T1 to T2 is ΔSOC p1 The size of the SOC range from threshold T3 to T4 is ΔSOC p2 The size of the SOC range from threshold T5 to T6 is ΔSOC p3 is.

[0031] On the other hand, the ranges from SOC 0% to less than threshold T1, from threshold T2 to T3, from threshold T4 to T5, and from threshold T6 to SOC 100% are non-plateau ranges. In these ranges, the OCV of the secondary battery 20 and the OCP of the positive and negative electrodes change significantly. The magnitude of the SOC range from SOC 0% to less than threshold T1 is ΔSOC n1 The size of the SOC range from threshold T2 to threshold T3 is ΔSOC n2 The size of the SOC range from threshold T4 to threshold T5 is ΔSOC n3 The size of the SOC range from the threshold T5 to SOC100% is ΔSOC n4 is.

[0032] As described above, when a secondary battery 20 having a plateau voltage is used a lot in the plateau range (for example, charging and discharging in the plateau range are repeated), deterioration of the secondary battery 20 accelerates. Therefore, when it is determined that the usage is high, the secondary battery 20 is charged and discharged from an SOC corresponding to the plateau range to an SOC corresponding to the non-plateau range. This forcibly changes the voltage of the secondary battery 20, thereby mitigating the acceleration of deterioration.

[0033] Returning to FIG. 1 , whether to use the potentials of the positive and negative electrodes or the voltage of the secondary battery 20 to determine the threshold value may be determined based on, for example, the availability of data necessary for processing, processing time limitations, accuracy, etc. Furthermore, although analyzing the SOC-OCV curve of the secondary battery 20 (e.g., the fitting described above) takes time, measuring the SOC-OCV curve of the secondary battery 20 can secondarily diagnose the state of deterioration of the secondary battery 20. For example, the state of deterioration of the secondary battery 20 can be diagnosed based on the shape of the SOC-OCV curve of the secondary battery 20. Specifically, for example, by evaluating the degree of deviation of the measured SOC-OCV curve from the SOC-OCV curve in the initial state, the state of deterioration can be diagnosed based on the magnitude of the deviation. Furthermore, by calculating the SOC-OCP curves of the positive and negative electrodes from the measured SOC-OCV curve, the state of the positive and negative electrodes can also be diagnosed. On the other hand, using the closed-circuit voltage of the secondary battery 20 allows for simple and quick processing.

[0034] In another embodiment, instead of or in addition to the above functions, the threshold value determining unit 4 uses A function of the SOC and the closed circuit voltage of the secondary battery 20 (for example, an SOC-CCV curve) obtained by flowing a current such that the open circuit voltage and the closed circuit voltage of the secondary battery 20 are considered to be equal, or A function of the SOC, obtained by passing a current such that the open circuit voltage and closed circuit voltage of the secondary battery 20 are considered to be equal, and the value obtained by differentiating the closed circuit voltage of the secondary battery 20 with respect to the SOC (for example, an SOC-dCCV / dSOC curve) The threshold value is determined using at least one of the functions above. The closed circuit voltage is the sum of the open circuit voltage and the overvoltage. The smaller the current, the smaller the overvoltage. Therefore, by flowing a current (for example, 1 C, but not limited to this) that makes the open circuit voltage and the closed circuit voltage of the secondary battery 20 considered to be equal, the difference between the open circuit voltage and the closed circuit voltage is reduced, and the open circuit voltage can be calculated with high accuracy from the actually measured closed circuit voltage.

[0035] Furthermore, in addition to or instead of passing a current such that the open circuit voltage and closed circuit voltage of the secondary battery 20 are considered to be equal, a step of calculating the overvoltage using an equivalent circuit model or the like may be performed. This process can reduce the influence of overvoltage that may occur in the secondary battery 20 and improve the accuracy of determining the threshold value.

[0036] The threshold value may be set as a fixed value when the secondary battery 20 starts operating, or may be determined at any timing during operation. The SOC values ​​at both ends of the plateau range for the SOC of the secondary battery 20 change in a complex manner as the secondary battery 20 deteriorates. Therefore, it is preferable to determine the threshold value during operation of the secondary battery 20. Furthermore, the threshold value determined during operation of the secondary battery 20 may be updated relative to the previously determined threshold value.

[0037] The usage amount calculation unit 5 is a functional unit that calculates the usage amount that indicates the extent to which the secondary battery 20 has been used in the plateau range. The usage amount is the usage amount of the secondary battery 20. The calculated usage amount is used for comparison with a predetermined value at which the deterioration of the secondary battery 20 is thought to accelerate, as will be described in detail later.

[0038] The usage amount calculation unit 5 calculates the accumulated current capacity (Ah) of the secondary battery 20, the accumulated power amount (Wh) of the secondary battery 20, the accumulated usage time of the secondary battery 20, the time series data of the voltage or SOC of the secondary battery 20, or the magnitude of the non-plateau range of the secondary battery 20 (ΔSOC n1 , ΔSOC n2 , ΔSOC n3 , ΔSOC n4 The usage amount is calculated using at least one of the following: the rate of change of the voltage or SOC of the secondary battery 20, the closed circuit voltage (Vc) and the SOC (SOCc) of the secondary battery 20 when the secondary battery 20 switches between charging and discharging. The usage amount of the secondary battery 20 can be calculated by using at least one of these. In particular, if the closed circuit voltage (Vc) of the secondary battery 20 when the secondary battery 20 switches between charging and discharging is a plateau voltage or if the SOC (SOCc) is in a plateau range, it can be determined that the usage amount is high.

[0039] When the cumulative current carrying capacity and cumulative power amount are used, the usage amount calculation unit 5 calculates the capacity from the time integral of the current in each plateau range of the secondary battery 20, and calculates the power amount from the time integral of the product (W) of the current and voltage. The usage amount can then be calculated by accumulating the calculated capacities and power amounts. When the cumulative usage time is used, the usage amount calculation unit 5 calculates the sum of the usage time within each plateau range of the secondary battery 20. The calculated sum can then be used as the cumulative usage time. The time range for calculating the usage amount starts from the time when the SOC of the secondary battery 20 was last at a non-plateau voltage, and the end point can be set arbitrarily. The calculated usage amount is used by the determination unit 6, which will be described later.

[0040] When the closed circuit voltage (Vc) and the SOC (SOCc) are used, the usage amount calculation unit 5 calculates the cumulative usage time during which Vc or SOCc is within the plateau range of the secondary battery 20, starting from the time when Vc or SOCc was last in the non-plateau range of the secondary battery 20. The calculated cumulative usage time is used by the determination unit 6, which will be described later, as the usage amount.

[0041] In addition, when the rate of change in the size of the non-plateau range of the secondary battery 20 is used, the usage amount calculation unit 5 calculates ΔSOC n1 ~ΔSOC n4 (Fig. 3) (the length in the horizontal axis direction in Fig. 3). n1 ~ΔSOC n4 For each of these, the rate of change relative to a predetermined reference value (for example, an initial value) is calculated. The calculated rate of change is used by the determination unit 6, which will be described later, as the amount of use. The rate of change gradually increases as the secondary battery 20 is used in its plateau range. Therefore, the amount of use can be determined based on the rate of change.

[0042] The determination unit 6 is a functional unit that determines whether or not the deterioration of the secondary battery 20 will accelerate by comparing the usage calculated by the usage calculation unit 5 with a predetermined value at which the deterioration of the secondary battery 20 is thought to accelerate. When the usage calculated by the usage calculation unit 5 exceeds the predetermined value, the determination unit 6 determines that the deterioration of the secondary battery 20 will accelerate.

[0043] The predetermined value at which the deterioration of the secondary battery 20 is considered to be accelerated may be, for example, a fixed value determined in advance during the design of the SOC target setting system 1, or may be a set value arbitrarily set by the user of the target determination system 1. For example, the deterioration rate of the secondary battery 20 differs based on the usage environment (temperature, location of use, etc.) of the secondary battery 20. For example, use in a high-temperature region will accelerate the deterioration rate more than specifications in a low-temperature region. Therefore, in a high-temperature region, deterioration is considered to be accelerated even with a relatively small amount of usage. For this reason, it is preferable that the predetermined value is relatively small. Therefore, the user can arbitrarily set the predetermined value based on, for example, the usage environment of the secondary battery 20.

[0044] The SOC target setting unit 7 is a functional unit that sets the second SOC value so that at least one threshold exists between a first SOC value (an example of a first charge / discharge index value; SOCs) that is the SOC at the start of charge / discharge of the secondary battery 20 and a second SOC value (an example of a second charge / discharge index value; SOCe) that is a target value for charging / discharging from the first SOC value. Here, "between" also includes "matching." Therefore, the SOC target setting unit 7 sets the second SOC value that allows the secondary battery 20 to be charged / discharged so as to straddle at least one threshold. In other words, the SOC target setting unit 7 sets the second SOC value so that the secondary battery 20 is charged / discharged in both a plateau range and a non-plateau range (e.g., a non-plateau range adjacent to the plateau range). The threshold is the boundary between the plateau range and the non-plateau range, as described above. Therefore, by charging / discharging the secondary battery 20 so as to straddle the threshold, the closed circuit voltage of the secondary battery 20 can be varied, and acceleration of deterioration of the secondary battery 20 can be suppressed.

[0045] As mentioned above, the number of thresholds that can be present must be at least one. However, the more thresholds there are, the greater the fluctuation range of potential and voltage can be, and the more effective it is at suppressing accelerated degradation. On the other hand, the fewer thresholds there are, the shorter the time required for charging and discharging can be.

[0046] The second SOC value is set when (or after) the determining unit 6 determines that deterioration of the secondary battery 20 is accelerating. The determination that deterioration is accelerating occurs when the usage amount of the secondary battery 20 in the plateau range exceeds a predetermined value. Therefore, when the second SOC value is set, the first SOC value is in any of the ranges of thresholds T1 to T2, thresholds T3 to T4, and thresholds T5 to T6 shown in FIG. 3.

[0047] The SOC target setting unit 7 sets the second SOC value within a plateau range other than the plateau range including the first SOC value (i.e., a plateau range not including the first SOC value) so that the difference from the first SOC value is smaller than a predetermined value. Because the potential and voltage do not change within the plateau range, charging and discharging within the plateau range is unlikely to contribute to suppressing accelerated deterioration. Therefore, by setting the second SOC value within a plateau range not including the first SOC value so that the second SOC value is smaller than a predetermined value determined based on a usage plan for the secondary battery 20, the closed circuit voltage can be varied.

[0048] For example, the second SOC value can be set to the SOC within a plateau range that does not include the first SOC value, with the smallest difference from the first SOC value (i.e., the same as the threshold value). However, the second SOC value to be set is not limited to this example. Furthermore, the second SOC value can be set to any plateau range that does not include the first SOC value. Therefore, for example, in FIG. 3, if the first SOC value is between thresholds T3 and T4, the second SOC value is set to threshold T2 within the range from threshold T1 to T2, and the second SOC value is set to threshold T5 within the range from threshold T5 to T6.

[0049] In another embodiment, when the first SOC value is in the plateau range, the SOC target setting unit 7 sets the second SOC value to a non-plateau range adjacent to the plateau range in which the first SOC value exists, but at a value other than the threshold value on the first SOC value side. This allows charge / discharge control to be performed beyond the threshold into the adjacent non-plateau range, thereby allowing the potential and voltage to fluctuate. Furthermore, because charge / discharge is performed up to the non-plateau range adjacent to the plateau range in which the first SOC value exists, the charge / discharge time can be shortened.

[0050] In another embodiment, the SOC target setting unit 7 sets the second SOC value to a non-plateau range, which is an SOC range other than the plateau range. In the non-plateau range, the potential and voltage fluctuate more than the fluctuation range (0 or nearly 0) in the plateau range. Therefore, by setting the second SOC value in the non-plateau range (particularly a range other than the threshold value on the first SOC value side), the voltage and potential can be fluctuated during charging and discharging.

[0051] In this case, the SOC target setting unit 7 preferably sets the second SOC value so that the difference between the second SOC value and the first SOC value is greater than a predetermined value. The predetermined value here is a value that can effectively suppress the acceleration of deterioration. The larger the difference, the greater the fluctuation range of the voltage and potential. Therefore, based on the usage plan for the secondary battery 20, the difference is set to be greater than the predetermined value within a range that does not have a significant impact on the usage plan. This makes it possible to increase the fluctuation range of the voltage and potential, thereby enhancing the effect of suppressing the acceleration of deterioration.

[0052] Preferably, the second SOC value is set for each non-plateau range. For example, consider a case where there is a plan for using the secondary battery 20 after the charge / discharge control of the present disclosure, and the minimum SOC of the secondary battery 20 is scheduled to be 20%. In FIG. 3, when the first SOC value is in the range from threshold T3 to T4, the second SOC value is not set to be equal to or lower than threshold T1. Furthermore, in the range from threshold T2 to T3, the second SOC value is set to 20%, in the range from threshold T4 to T5, the second SOC value is set to threshold T5, and the second SOC value is set to 100% above threshold T6 (SOC 99%).

[0053] In another embodiment, when the first SOC value is in either the plateau range or the non-plateau range, the SOC target setting unit 7 sets the second SOC value to the other range adjacent to the range in which the first SOC value is present, but not to the threshold. In this manner, when the first SOC value is in, for example, a plateau range, the second SOC value is set to the non-plateau range adjacent to the plateau range. Furthermore, when the first SOC value is in, for example, a non-plateau range, the second SOC value is set to the plateau range adjacent to the non-plateau range. This allows the potential and voltage to be varied whether the first SOC value is in the plateau range or the non-plateau range.

[0054] When there are multiple settings for the second SOC value, the SOC target setting unit 7 selects (adopts) the smallest second SOC value among the second SOC values ​​based on the usage plan for the secondary battery 20. This reduces the time required to reach the second SOC value, particularly when charging the secondary battery 20 to the second SOC value. If, for some reason, it is not possible to select the smallest second SOC value among the second SOC values, it is preferable to select a second SOC value that ensures that the difference between the first SOC value and the second SOC value is large enough to achieve the effect of suppressing accelerated deterioration according to the present disclosure.

[0055] For example, when the secondary battery 20 is scheduled to be used after mitigating accelerated degradation using the SOC target setting system 1, it is preferable to charge the secondary battery 20 among charging and discharging (charging or discharging) for mitigating accelerated degradation. This allows the SOC to be relatively high after processing for mitigating accelerated degradation, and the secondary battery 20 can be used promptly after processing. However, for example, in the case of a stationary secondary battery 20 for a smart grid or the like, discharging can also be performed when power demand is low, for example, at night.

[0056] The charge / discharge control unit 8 is a functional unit that charges / discharges (at least one of charging and discharging) the secondary battery 20 from the first SOC value to the second SOC value. Charging / discharging until the second SOC value is reached is performed when the usage calculated by the usage calculation unit 5 exceeds a predetermined value, as described above. By providing the charge / discharge control unit 8, the potential and voltage can be varied to suppress the acceleration of deterioration of the secondary battery 20. Examples of charging methods include charging from an external charger and increasing the amount of regenerative charging accepted. Examples of discharging methods include increasing the amount of assistance to a drive unit such as a motor, and discharging to an auxiliary device such as an air conditioner.

[0057] The charge / discharge current value is preferably low within a range that has little effect on the usage plan of the secondary battery 20. The reason is that a large current may cause deterioration of the secondary battery 20 and may cause the charge / discharge to end before the desired second SOC value is reached due to an overvoltage of the secondary battery 20. Specifically, for example, a current value at which the open circuit voltage and closed circuit voltage of the secondary battery 20 are considered to be equal is preferred, and is, for example, a current of 1 C or less, although not limited to this value.

[0058] In another embodiment, the charge / discharge control unit 8 also carries out charging / discharging at a constant voltage after the second SOC value is reached by charging / discharging, thereby reducing the influence of overvoltage.

[0059] When the charge / discharge control unit 8 reaches the second SOC value through charging / discharging, the usage calculation unit 5 sets the usage to zero. Alternatively, the usage calculation unit 5 sets the usage of the secondary battery 20 to a usage that is less than the usage when the second SOC value is reached, based on time-series data of the closed-circuit voltage or SOC of the secondary battery 20 during charging / discharging. By charging / discharging to the second SOC value, the acceleration of deterioration is alleviated, and the deterioration rate returns to the normal deterioration rate. Therefore, by setting the usage to zero, subsequent charge / discharge control can be performed at an appropriate time. Furthermore, the greater the difference between the first SOC value and the second SOC value, the greater the effect of suppressing the acceleration of deterioration. Therefore, by reducing the usage based on time-series data of the closed-circuit voltage or SOC, subsequent charge / discharge control can be performed at an appropriate time. For example, when the fluctuation range of the closed-circuit voltage or SOC is large, the effect of suppressing the acceleration of deterioration is considered to be large. Therefore, in this case, the amount of reduction can be relatively large.

[0060] Fig. 4 is a flowchart showing the SOC target setting method of the present disclosure. The flowchart shown in Fig. 4 can be executed using the SOC target setting system 1 and secondary battery system 10 shown in Fig. 1. Therefore, Fig. 4 will be described with reference to Fig. 1 as appropriate. The SOC target setting method of the present disclosure includes steps S1 to S6.

[0061] The threshold determination unit 4 determines a threshold (step S1: threshold determination step). Step S1 is a step of determining at least one of a threshold that is at least one end of the plateau range of the SOC of at least one of the positive electrode, the negative electrode, or the secondary battery 20, and an SOC threshold that corresponds to the upper and lower limits of the SOC range in which the secondary battery 20 is used. The threshold determination can be performed according to the method described in the threshold determination unit 4.

[0062] The usage calculation unit 5 calculates the usage of the secondary battery 20 in the plateau range (step S2). The calculation of the usage can be performed according to the method explained for the usage calculation unit 5. The determination unit 6 determines whether the usage calculated in step S2 is equal to or greater than a predetermined value (step S3). The determination can be performed according to the method explained for the determination unit 6. If it is determined that the usage is not equal to or greater than the predetermined value (No), the flow ends.

[0063] On the other hand, if it is determined that the SOC is equal to or greater than the predetermined value (Yes), the SOC target setting unit 7 sets a second SOC value (step S4, SOC target setting step). Step S4 is a step of setting the second SOC value so that there is at least one threshold between the first SOC value, which is the SOC at the start of charging / discharging of the secondary battery 20, and the second SOC value, which is the target value for charging / discharging from the first SOC value. The setting can be performed according to the method described for the SOC target setting unit 7.

[0064] In the example of the present disclosure, a plurality of second SOC values ​​are set. Therefore, the SOC target setting unit 7 selects one specific second SOC value from the plurality of second SOC values ​​(step S5). The selection can be performed according to the method described for the SOC target setting unit 7. Finally, the charge / discharge control unit 8 charges and discharges the secondary battery 20 so that the selected second SOC value is reached (step S6). As a result, the acceleration of deterioration of the secondary battery 20 is mitigated. [Example]

[0065] Example 1 A 1.1A (1C) cycle degradation test was performed using a commercially available LiFePO4 / graphite 18650-type cylindrical lithium-ion secondary battery (secondary battery 20). Before the test, the SOC-OCV curve of secondary battery 20 and the SOC-OCP curves of the positive and negative electrodes were obtained. The SOC-OCP curves of the positive and negative electrodes were separated from the SOC-OCV curve of secondary battery 20. The results are shown in Figure 3. The SOCs at which the change per unit SOC (i.e., the rate of change) exceeded 0.001 V in the SOC-OCP curves of the positive and negative electrodes were defined as the two ends of the plateau range (thresholds T1, T2, T3, T4, T5, and T6). The thresholds were T1 = 10%, T2 = 16%, T3 = 36%, T4 = 66%, T5 = 75%, and T6 = 99%.

[0066] In actual operation of the secondary battery 20, a margin may be provided for the lower operating limit of the SOC in anticipation of the risk of running out of power. Therefore, in the present disclosure, the second SOC value on the low SOC side is set to T1, which is the upper limit of the non-plateau range, and the second SOC value on the high SOC side is set to 90% of the plateau range. In addition, the predetermined value of the cumulative usage time, which is the usage amount of the secondary battery 20 in the plateau range, is set to ΔSOC 0, which is the widest plateau range. p2 The charge / discharge time corresponding to 30% of the capacity was set to 18 minutes. The first SOC value was set to an SOC equal to or lower than a threshold value T3.

[0067] <Comparative Example 1> Using the same secondary battery 20 as in Example 1, charging and discharging were repeated at SOC = 45% to 55% based on the threshold set in Example 1 so that the SOC range used was only the plateau range of the secondary battery 20.

[0068] <Result> FIG. 5 shows the results of cycle tests for Example 1 and Comparative Example 1. The cumulative charge / discharge capacity (Ah, horizontal axis) is plotted against the capacity retention rate (%; vertical axis), where the battery capacity of secondary battery 20 at the start of the test is taken as 100%. As shown in FIG. 5, at the same cumulative charge / discharge capacity, Example 1, to which the present disclosure was applied, showed an improved capacity retention rate compared to Comparative Example 1. This is thought to be because, although the deterioration of secondary battery 20 accelerated when used in the plateau range, the application of the present disclosure mitigated this acceleration, making the deterioration rate slower than that of Comparative Example 1. Therefore, it was confirmed that the present disclosure can suppress accelerated deterioration, which is a type of deterioration specific to secondary batteries. [Explanation of symbols]

[0069] 1. SOC goal setting system 10 Secondary battery system 2. Measurement section 20 Secondary battery 3 Storage section 30 Load 4. Threshold determination unit 40 Measurement section 5 Usage amount calculation part 6 Judgment section 7 SOC goal setting department 8. Charge / discharge control unit

Claims

1. a threshold value determination unit that determines at least one of a threshold value that is at least one end of a plateau range that indicates the plateau potential or the plateau voltage of a charge / discharge index that indicates the degree of charge / discharge of at least one of a positive electrode having a plateau potential, a negative electrode having a plateau potential, or a secondary battery having a plateau voltage, and a threshold value of the charge / discharge index that corresponds to an upper limit and a lower limit of a range of the charge / discharge index in which the secondary battery is used; an SOC target setting unit that sets the second charge / discharge index value so that at least one threshold value exists between a first charge / discharge index value that is the charge / discharge index at the start of charge / discharge of the secondary battery and a second charge / discharge index value that is a target value for performing charge / discharge from the first charge / discharge index value.

1. An SOC target setting system comprising:

2. 2. The SOC target setting system according to claim 1, a usage amount calculation unit that calculates a usage amount that indicates the extent to which the secondary battery has been used in the plateau range; a charge / discharge control unit that charges / discharges the secondary battery until the usage amount calculated by the usage amount calculation unit exceeds a predetermined value, and Equipped with 1. An SOC target setting system comprising:

3. 2. The SOC target setting system according to claim 1, The threshold value determination unit A function of the charge / discharge index and an open circuit voltage of the secondary battery, a function of the charge / discharge index and a value obtained by differentiating an open circuit voltage of the secondary battery by the charge / discharge index, a function of the charge / discharge index of the secondary battery and an open circuit potential of at least one of the positive electrode and the negative electrode; a function of the charge / discharge index of the secondary battery in at least one of the positive electrode and the negative electrode and a value obtained by differentiating the open circuit potential of the electrode by the charge / discharge index; determining the threshold value using at least one function of 1. An SOC target setting system comprising:

4. 4. The SOC target setting system according to claim 3, The threshold value determination unit determines the threshold value using an inflection point of the function, or at least one of a change in the potential of the electrode or the open circuit voltage per unit amount of the charge / discharge index.

1. An SOC target setting system comprising:

5. 2. The SOC target setting system according to claim 1, The threshold value determination unit A function of the charge / discharge index and the closed circuit voltage of the secondary battery, obtained by flowing a current such that the open circuit voltage and the closed circuit voltage of the secondary battery are considered to be equal, or A function of the charge / discharge index, obtained by flowing a current such that the open circuit voltage and closed circuit voltage of the secondary battery are considered to be equal, and a value obtained by differentiating the closed circuit voltage of the secondary battery by the charge / discharge index. determining the threshold value using at least one function of 1. An SOC target setting system comprising:

6. 2. The SOC target setting system according to claim 1, the SOC target setting system includes a usage amount calculation unit that calculates a usage amount that indicates a degree to which the secondary battery has been used in the plateau range, The usage amount calculation unit calculates the usage amount using at least one of the accumulated current capacity of the secondary battery, the accumulated power amount of the secondary battery, the accumulated usage time of the secondary battery, time series data of the voltage of the secondary battery or the charge / discharge index, or the rate of change of the size of the non-plateau range of the secondary battery.

1. An SOC target setting system comprising:

7. 2. The SOC target setting system according to claim 1, The SOC target setting unit sets the second charge / discharge index value to a plateau range other than a plateau range including the first charge / discharge index value so that a difference between the second charge / discharge index value and the first charge / discharge index value is smaller than a predetermined value.

1. An SOC target setting system comprising:

8. 2. The SOC target setting system according to claim 1, The SOC target setting unit sets the second charge / discharge index value to a non-plateau range, which is a range of the charge / discharge index other than the plateau range.

1. An SOC target setting system comprising:

9. 9. The SOC target setting system according to claim 8, The SOC target setting unit sets the second charge / discharge index value so that a difference between the second charge / discharge index value and the first charge / discharge index value is greater than a predetermined value.

1. An SOC target setting system comprising:

10. 2. The SOC target setting system according to claim 1, When the first charge / discharge index value is in one of a plateau range and a non-plateau range, the SOC target setting unit sets the second charge / discharge index value to another range adjacent to the range in which the first charge / discharge index value is in, other than the threshold value.

1. An SOC target setting system comprising:

11. 2. The SOC target setting system according to claim 1, When there are a plurality of set values ​​of the second charge / discharge index value, the SOC target setting unit selects the smallest second charge / discharge index value from among the second charge / discharge index values ​​based on a usage plan of the secondary battery.

1. An SOC target setting system comprising:

12. 2. The SOC target setting system according to claim 1, a charge / discharge control unit that charges / discharges the secondary battery until the second charge / discharge index value is reached, and that charges / discharges the secondary battery at a constant voltage after the second charge / discharge index value is reached by charging / discharging; 1. An SOC target setting system comprising:

13. 2. The SOC target setting system according to claim 1, The SOC target setting system includes: a usage amount calculation unit that calculates a usage amount that indicates the extent to which the secondary battery has been used in the plateau range; a charge / discharge control unit that charges / discharges the secondary battery until the second charge / discharge index value is reached; When the second charge / discharge index value is reached by charging / discharging by the charge / discharge control unit, the usage amount calculation unit sets the usage amount to 0 or to a usage amount that is reduced from the usage amount when the second charge / discharge index value is reached based on time series data of the closed circuit voltage of the secondary battery during charging / discharging or the charge / discharge index.

1. An SOC target setting system comprising:

14. a secondary battery including a positive electrode having a plateau potential and a negative electrode having a plateau potential; an SOC target setting system; The SOC target setting system includes: a threshold value determination unit that determines at least one of a threshold value that is at least one end of a plateau range that indicates the plateau potential or the plateau voltage of a charge / discharge index that indicates the degree of charge / discharge of at least one of the positive electrode, the negative electrode, or the secondary battery having a plateau voltage, and a threshold value of the charge / discharge index that corresponds to an upper limit and a lower limit of a range of the charge / discharge index in which the secondary battery is used; an SOC target setting unit that sets the second charge / discharge index value so that at least one threshold value exists between a first charge / discharge index value that is the charge / discharge index at the start of charge / discharge of the secondary battery and a second charge / discharge index value that is a target value for performing charge / discharge from the first charge / discharge index value. A secondary battery system characterized by:

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