Control method, control device, and computer program

Abstract

To provide a control method, a control device, and a computer program to prevent a temporary (transient) battery voltage drop phenomenon of a power storage element.SOLUTION: In a discharge control method of a power storage element 3, discharging is performed such that the negative electrode potential becomes more noble than the negative electrode potential in a region where a transient voltage drop occurs in the power storage element 3 having a Si-based negative electrode.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a control method, a control device, and a computer program for suppressing deterioration of an energy storage element. [Background technology]

[0002] Energy storage devices are used to store electrical energy and supply it when needed. Energy storage devices are used in a variety of applications, including portable devices, power supplies, transportation equipment (including automobiles and railways), and industrial equipment (including aerospace, construction, and other applications). It is important to constantly monitor the storage capacity of energy storage devices so that stored energy can be used when needed and in the amount needed. Energy storage devices are known to deteriorate primarily chemically over time and with frequency of use. Therefore, the amount of available energy decreases over time and with frequency of use. It is important to monitor the degradation status of energy storage devices in order to use energy when needed and in the amount needed. Several technologies have been developed to estimate the degradation of energy storage devices.

[0003] Lithium ion secondary batteries (hereinafter referred to as batteries) serving as energy storage devices are known to use SiO as the negative electrode active material, which increases the capacity of the negative electrode and therefore the capacity of the battery.

[0004] The lithium ion conductivity of SiO increases with the amount of doped lithium, which causes a problem that the amount of lithium doped tends to become unevenly distributed within the negative electrode during charging and discharging. When charging and discharging are repeated in a state where the amount of lithium doped is uneven, the volume of the heavily doped area increases, causing the area to peel off from the current collector, resulting in a decrease in battery capacity. Patent Document 1 discloses a method for detecting the state of the negative electrode based on the intensity ratio, which is calculated by generating V-dQ / dV, which shows the relationship between dQ / dV, which is the ratio of the change in discharge capacity Q, dQ, to the change in potential V, dV, of the negative electrode relative to a lithium reference electrode, and V-dQ / dV, which shows the relationship between the potential V and V. Patent Document 2 discloses a discharge control method for controlling the discharge of a non-aqueous electrolyte using a silicon oxide containing lithium as a negative electrode active material so that the negative electrode voltage relative to a lithium reference electrode does not exceed 0.6 V when the non-aqueous electrolyte is discharged. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5682955 [Patent Document 2] Patent No. 4088993 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, the inventors of the present application have found that in a battery containing a Si-based negative electrode, when charging and discharging are repeated within a predetermined SOC (state of charge) range, a drop in battery voltage occurs due to a temporary decrease in battery capacity. The inventors of the present invention investigated the cause of the temporary decrease in battery capacity and found that the crystalline Li 15 The formation of Si4 phase When charging and discharging are repeated within a specified SOC range and the discharge is shallow, there are areas in the negative electrode where Li remains and areas where it does not remain. When charging is performed in this state, the area where Li remains is charged first, resulting in a deeper charge depth and the formation of crystalline Li. 15 Si4 In Si-based anodes, charge and discharge are thought to proceed in the amorphous phase, but crystalline Li 15 In the Si4 phase, it contributes to the charge / discharge (Li ion ingress / egress) process. Therefore, crystalline Li 15 The formation of the Si4 phase reduces the battery capacity. To prevent battery capacity loss, crystalline Li 15 Controlling the formation of Si4 phase, or The resulting crystalline Li 15 It is necessary to carry out a process to eliminate the Si4 phase and restore the battery capacity. In other words, crystalline Li 15 The decrease in battery capacity caused by the formation of the Si4 phase can be corrected by a recovery process. This allows the battery capacity to be restored and the temporary drop in battery voltage to be eliminated. In Patent Documents 1 and 2, the solution to the transient drop in battery voltage is not an issue to be addressed.

[0007] An object of the present invention is to provide a control method, a control device, and a computer program for preventing a temporary (transient) drop in the battery voltage of an energy storage element, or to provide a control method, a control device, and a computer program for eliminating a temporary (transient) drop in the battery voltage of an energy storage element. [Means for solving the problem]

[0008] In a control method according to one aspect of the present invention, a power storage element having a Si-based negative electrode is discharged so that the negative electrode potential becomes nobler (higher) than the negative electrode potential in a region where a transient drop in battery voltage occurs.

[0009] A control device according to one embodiment of the present invention includes a control unit that discharges a negative electrode potential so that it becomes nobler (higher) than the negative electrode potential in a region where a transient drop in battery voltage occurs in an energy storage element having a Si-based negative electrode.

[0010] A computer program according to one embodiment of the present invention causes a computer to execute a process of discharging a storage element having a Si-based negative electrode so that the negative electrode potential becomes nobler (higher) than the negative electrode potential in a region where a transient drop in battery voltage occurs. [Effects of the Invention]

[0011] In the present invention, it is possible to prevent the phenomenon of temporary voltage drops in the storage elements, and even if a temporary voltage drop in the storage elements does occur, it is possible to eliminate the voltage drop. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the relationship between the number of charge / discharge cycles and the capacity retention rate of a battery containing NCM111 in the positive electrode and SiO and Gr in the negative electrode. [Figure 2] 10 is a graph showing the relationship between discharge capacity and battery voltage when the lower limit of the SOC is 25% (the SOC range of curve d in FIG. 1). [Figure 3] These are DOD (depth of discharge)-OCV curves obtained by repeatedly charging and discharging within each of the SOC ranges a to f in Figure 1 (SOC 10-100%, SOC 15-100%, SOC 20-100%, SOC 25-100%, SOC 40-100%, and SOC 60-100%) and discharging from a fully charged state after 100 cycles. [Figure 4] Each battery in FIG. 3 that had been subjected to 100 charge-discharge cycles was fully discharged, and the SOC-OCV curves and DOD-OCV curves after 100 charge-discharge cycles were shown. [Figure 5] 1 is a graph showing the results of determining the DOD-OCP of the negative electrode after 50 cycles of charge and discharge when the lower limit values ​​of the SOC are 10% and 25%, respectively (the SOC ranges of a and d in FIG. 1). [Figure 6] 1 is a graph showing the relationship between specific capacity and negative electrode potential. [Figure 7] 1 is a block diagram showing the configuration of a charge / discharge system and a server according to a first embodiment. [Figure 8] FIG. 2 is a perspective view of a battery module. [Figure 9] FIG. 2 is a block diagram showing the configuration of a BMU. [Figure 10] 10 is a flowchart showing a procedure for reset discharge in a BMU as a control device according to the first embodiment. [Figure 11] 10 is a flowchart showing a procedure for reset discharge in the BMU of the first modification. [Figure 12] FIG. 10 is a block diagram showing the configuration of a charge / discharge system according to a second modification. [Figure 13] 10 is a flowchart showing a procedure for reset discharge in a BMU according to the second modification. [Figure 14] FIG. 11 is a block diagram showing the configuration of a charge / discharge system and a server according to a third modification. [Figure 15] 10 is a flowchart showing a procedure for reset discharge and charge in Modification 3. [Figure 16] 1 is a schematic diagram showing an example of the configuration of a storage element refresh system; [Figure 17] 10 is a flowchart showing a procedure for discharging in a BMU as a control device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Outline of the embodiment) In the control method according to the embodiment, the electric storage element having a Si-based negative electrode is discharged so that the negative electrode potential becomes more noble than the negative electrode potential in the region where a transient drop in battery voltage occurs. When a predetermined condition is satisfied, the discharge is performed while controlling the voltage so that the negative electrode potential becomes more noble than the negative electrode potential in the above-mentioned region. Hereinafter, this discharge is referred to as reset discharge.

[0014] Here, the Si-based negative electrode refers to a negative electrode containing Si or a Si compound as an active material, such as an oxide, nitride, or alloy. The predetermined condition is satisfied when a predetermined time has elapsed, when the SOH (State Of Health) is below a threshold, etc. The predetermined time may be determined by, for example, the rate and the lower limit S A curve showing the change in capacity retention rate over time is obtained for each OC, and the time at which the capacity retention rate falls below a threshold and reset discharge is required is set as the elapsed time.

[0015] According to the above configuration, the crystalline Li in the negative electrode, which causes a transient voltage drop in the energy storage element, 15 By discharging in a manner that prevents the formation of the Si4 phase, it is possible to suppress a transient voltage drop. In addition, by performing a reset discharge when certain conditions are met, Li 15 The Si4 phase disappears Therefore, transient voltage drops are eliminated. As a result, the decrease in capacity of the storage element can be suppressed. The decrease in output is suppressed, and the accuracy of SOC detection is also good.

[0016] In the above-mentioned control method, the negative electrode potential is 0.5V vs. Li / Li + Discharge the battery until it reaches or exceeds the specified value. That's fine.

[0017] According to the above configuration, crystalline Li 15 The formation of Si4 phase is effectively suppressed or eliminated do.

[0018] In the above-mentioned control method, the negative electrode potential is 0.5V vs. Li / Li + More than 0.6V vs. Li / Li + It may be discharged so that:

[0019] According to the above configuration, crystalline Li 15 The formation of Si4 phase is well suppressed or well eliminated. At the same time, deterioration of the Si-based active material is suppressed.

[0020] In the above-described control method, in an energy storage device in which a plurality of energy storage element modules, each of which has a plurality of energy storage elements having a Si-based negative electrode connected in series, are connected in parallel, each energy storage element module may be discharged so that the negative electrode potential becomes more noble than the negative electrode potential in the region.

[0021] According to the above configuration, only the energy storage element module in which a temporary voltage drop occurs can be discharged, thereby suppressing or eliminating the voltage drop.

[0022] The control device according to the embodiment includes a control unit that discharges electricity so that the negative electrode potential becomes more noble than the negative electrode potential in a region where a transient voltage drop occurs in an electricity storage element having a Si-based negative electrode.

[0023] According to the above configuration, the crystalline Li in the negative electrode that causes a transient voltage drop in the energy storage element due to the above discharge 15 The generation of the Si4 phase is suppressed, so the transient voltage drop can be suppressed by performing reset discharge when predetermined conditions are satisfied, the Li 15 Si4 phase disappears Therefore, the transient voltage drop can be eliminated, and the decrease in the capacity of the energy storage element can be suppressed. The decrease in output is suppressed, and the accuracy of SOC detection is also good.

[0024] The computer program according to the embodiment causes the computer to execute a process of discharging so that the absolute value of the negative electrode potential becomes larger than the absolute value of the negative electrode potential in a region where a transient voltage drop occurs in an energy storage element having a Si-based negative electrode.

[0025] According to the above configuration, the transient voltage drop can be suppressed or eliminated, and the decrease in the capacity of the energy storage element can be suppressed. The decrease in output is suppressed, and the accuracy of SOC detection is also good.

[0026] Hereinafter, a method for controlling discharge will be specifically described. Hereinafter, a case where a lithium ion secondary battery (battery) is used as the energy storage element will be described. FIG. 1 is a graph showing the relationship between the number of charge-discharge cycles and the capacity retention rate of a battery having NCM111 in the positive electrode and SiO and Gr in the negative electrode. In FIG. 1, the horizontal axis represents the number of cycles, and the vertical axis represents the capacity retention rate (%). NCM is Li x (Ni s Co u Mn t )O2 (0 ≦ s < 1, 0 ≦ t < 1, 0 ≦ u < 1, s + t + u = 1, 0 < x ≦ 1.1, s, u are not 0 at the same time) is an active material, and in the case of NCM111, s = t = u. Figure 1 shows the relationship between the number of cycles and the capacity retention rate when charging and discharging were repeated within each SOC range: a: SOC 10-100%, b: SOC 15-100%, c: SOC 20-100%, d: SOC 25-100%, e: SOC 40-100%, and f: SOC 60-100%.

[0027] The charge-discharge cycle conditions were as follows: Test temperature: 25℃ Charging: CC (constant current) charging at 1 CmA up to 4.2V, then CV (constant voltage) charging, stopping when the current reaches 0.05 CmA Discharge: CC discharge at 1CmA, discharge stops at the voltage corresponding to each SOC 1, it can be seen that the capacity retention rate is significantly reduced in the case of the curves in the SOC ranges d and e. That is, compared to the case where the battery is discharged until the SOC reaches 20% or less, the capacity retention rate is significantly reduced when the lower limit of the SOC is 25 to 40%. The inventors found that the negative electrode potential was 0.5 V vs. Li / Li at the 50th cycle. + To be more than It was found that the capacity retention rate improved in all of the curves a to f by discharging. As shown in Figure 1, the capacity retention rate improved by performing the above-mentioned discharge at the 50th cycle. After the decrease in capacity retention rate was resolved, the capacity retention rate of the curves d and e decreased again by repeating charge and discharge. Therefore, deep discharge (reset discharge) may be repeated at a predetermined timing.

[0028] FIG. 2 is a graph showing the relationship between discharge capacity and battery voltage for the case d where the lower limit of the SOC is 25%. In Figure 2, the horizontal axis is the discharge capacity (mAh) and the vertical axis is the battery voltage (V). The discharge curve h is the relationship between the discharge capacity and the battery voltage when the capacity was confirmed (when discharging from SOC 100% to 0%). The relationship between the discharge capacity and the battery voltage is shown. Discharge curves i, j, k, l, and m show the relationship between the discharge capacity and the battery voltage when the charge / discharge cycle is repeated 1, 10, 20, 30, and 40 times within the range of SOC 25 to 100%. Discharge curve n shows the relationship between the discharge capacity and the battery voltage when the charge / discharge cycle is repeated 50 times within the range of SOC 25 to 100%, followed by discharging to SOC 0%. From FIG. 2, it can be seen that as the number of cycles increases, the discharge capacity decreases significantly in the voltage range of 3.2 to 3.5 V.

[0029] FIG. 3 shows the DOD-OCV curves obtained by repeatedly charging and discharging within each of the SOC ranges a to f in FIG. 1 (ranges of SOC 10 to 100%, SOC 15 to 100%, SOC 20 to 100%, SOC 25 to 100%, SOC 40 to 100%, and SOC 60 to 100%) and discharging from a fully charged state after 100 cycles. In FIG. 3, the horizontal axis represents DOD (%) and the vertical axis represents battery voltage (V). From Figure 3, it can be seen that in the case of curves d and e, where the lower limit values ​​of SOC are 25% and 40%, respectively, the voltage for the same DOD is lower in the voltage range of 3.1 to 3.7 V, especially in the voltage range of 3.2 to 3.5 V, compared to repeated charging and discharging in other SOC ranges.

[0030] Figure 4 shows the SOC-OCV curves and DOD-OCV curves after fully discharging and then repeating another 100 charge-discharge cycles for each battery that had been subjected to 100 charge-discharge cycles in Figure 3. In Figure 4, the upper side is the SOC-OCV curve, and the lower side is the DOD-OCV curve. In FIG. 4, the horizontal axis represents SOC (DOD) (%), and the vertical axis represents battery voltage (V). From FIG. 4, it can be seen that in the case of the curves d and e, by performing the reset discharge described above, both the SOC-OCV curve and the DOD-OCV curve overlap with the curves in other SOC ranges, and the phenomenon of capacity decrease is resolved.

[0031] FIG. 5 is a graph showing the results of determining the DOD-OCP of the negative electrode after 50 cycles of charge / discharge for the cases a and d, where the lower limit of SOC is 10% and 25%, respectively. In FIG. 5, the horizontal axis is DOD (%) and the vertical axis is OCP (V vs. Li / Li + ) 5, in the region above 50% DOD, the DOD-OCP curve d shows a larger negative electrode potential for the same DOD than the DOD-OCP curve a, forming an upward convex shape. If the negative electrode potential increases at the same DOD, the battery voltage decreases.

[0032] FIG. 6 is a graph showing the relationship between the specific capacity and the negative electrode potential. In Figure 6, the horizontal axis is the specific capacity (mAh / g) and the vertical axis is the negative electrode potential (V vs. Li / Li + ) . 0.05V vs. Li / Li for Si-based negative electrodes + Deep charging was performed to reach the following potential: In this case, crystalline Li 15 When discharge occurs in this state, the crystal The potential plateau shown in Figure 5 is approximately 0.4 V vs. Li / Li due to the coexistence of two phases, the amorphous phase and the amorphous phase. + When the potential plateau appears, the discharge potential of the negative electrode becomes high. , the discharge voltage of the battery becomes lower.

[0033] In batteries with Si-based negative electrodes, repeated charging and discharging within a certain SOC range causes a drop in battery voltage due to a temporary decrease in battery capacity. The SOC range at which a transient voltage drop occurs varies depending on the content of Si-based compounds. With a 20% SiO / 80% Gr ratio, this phenomenon occurs when the SOC lower limit is approximately 25% or higher. With a low SiO content, this phenomenon occurs at a lower SOC lower limit, resulting in voltage changes in a lower voltage range. Negative electrode potential is 0.5V vs. Li / Li + If the discharge is not continued until the 15 As the accumulation of Si4 phase increases, the discharge voltage gradually decreases with the number of cycles. Once the negative electrode potential is 0.5V vs. Li / Li + When discharged to more than Li 15 Si4 phase As a result, the DOD-OCV curve is reset to its original state, as shown in Figure 4. Although the detailed reason is unclear, deep discharge eliminates the unevenness of the amount of lithium doped in the mixture, and crystalline Li is released during subsequent charging. 15 This is thought to be because Si4 is less likely to be formed.

[0034] Reset discharge is performed when the SOH, such as capacity retention, falls below a threshold value. Alternatively, the time at which the SOH falls below the threshold value is experimentally determined for each charge rate and charge / discharge range (SOC range), and reset discharge is performed each time that time elapses. As shown in Figure 5, the reset discharge was performed when the negative electrode potential was 0.5 V vs. Li / Li + If it becomes more than Since the difference in DOD at the same potential between the curves a and d becomes smaller, the negative electrode potential becomes 0.5V vs. Li / Li + It is preferable to carry out the process so that the above value is achieved. Reset discharge occurs when the negative electrode potential is 0.5V vs. Li / Li + More than 0.6V vs. Li / Li + It is more preferable to set it so that it is less than 0.6V vs. Li / Li. + When a deep discharge exceeding Deterioration of the negative electrode progresses. The reset discharge is performed at a battery voltage of 0.5V vs. Li / Li, which is the negative electrode potential. + Voltages corresponding to It is preferable to do this so that it is facing downwards. The reset discharge is performed at a negative electrode potential of 0.6V vs. Li / Li + (voltage corresponding to the negative electrode potential) or more ( 0.5V vs. Li / Li + It is more preferable to perform this so that the voltage is equal to or lower than the voltage corresponding to the voltage.

[0035] (Embodiment 1) The following description will be given of a case where the storage element is a lithium ion secondary battery. FIG. 7 is a block diagram showing the configuration of the charge / discharge system 1 and the server 9 according to the first embodiment. The charging / discharging system 1 includes a battery module 3, a BMU (Battery Management Unit) 4, and , a voltage sensor 5, a current sensor 6, and a control device 7.

[0036] The battery module 3 has a plurality of lithium ion secondary batteries (hereinafter referred to as cells) 2 connected in series as power storage elements. The control device 7 controls the entire charge / discharge system 1. The server 9 includes a communication unit 92 and a control unit 91 . The control device 7 includes a control unit 71, a display unit 72, and a communication unit 73. The control unit 71 of the control device 7 is connected to the control unit 91 via the communication unit 73, the network 10, and the communication unit 92. A load 17 is connected to the battery module 3 via terminals 11 and 12. When charging, a charger 8 is connected to the battery module 3 as shown in FIG.

[0037] The control units 71 and 91 include, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and The controller 7 is configured with a RAM (Random Access Memory) and a Controls the operation of the server 9. The communication units 73 and 92 have the function of communicating with other devices via a network, and can send and receive required information. The display unit 72 of the control device 7 can be configured with a liquid crystal panel, an organic EL (Electro Luminescence) display panel, etc. The control unit 71 controls the display unit 72 to display required information.

[0038] In this embodiment, any one of the BMU 4, the control device 7, and the server 9 functions as a control device of the present invention. Note that if the server 9 does not function as a control device, the charging / discharging system 1 does not need to be connected to the server 9. Although FIG. 7 shows a case where one battery module 3 is provided, a plurality of battery modules 3 may be connected in series. The BMU 4 may be a battery ECU.

[0039] The voltage sensor 5 is connected in parallel to the battery module 3 and outputs a detection result corresponding to the overall voltage of the battery module 3. The voltage sensor 5 is connected to a positive electrode terminal 23 and a negative electrode terminal 26 (described later) of each cell 2, measures a voltage V1 between the terminals 23 and 26 of each cell 2, and detects a voltage V (described later) between a negative electrode lead 33 and a positive electrode lead 34 of the battery module 3, which is the sum of V1 of each cell 2. The current sensor 6 is connected in series to the battery module 3 and outputs a detection result corresponding to the current of the battery module 3.

[0040] FIG. 8 is a perspective view of the battery module 3. As shown in FIG. The battery module 3 includes a rectangular parallelepiped case 31 and a plurality of the cells 2 housed in the case 31.

[0041] The cell 2 includes a rectangular parallelepiped case body 21, a cover plate 22, and terminals 23 and 26, a burst valve 24, and an electrode assembly 25, which are provided on the cover plate 22. The electrode assembly 25 is made by stacking a positive electrode plate, a separator, and a negative electrode plate, and is housed in the case body 21. The electrode assembly 25 may be obtained by winding a positive electrode plate and a negative electrode plate together in a flat shape with a separator interposed therebetween.

[0042] The positive electrode plate is one in which an active material layer is formed on a positive electrode base foil that is a plate-shaped (sheet-shaped) or long-strip-shaped metal foil made of aluminum, aluminum alloy, or the like. The negative electrode plate is one in which an active material layer is formed on a negative electrode base foil that is a plate-shaped (sheet-shaped) or long-strip-shaped metal foil made of copper, copper alloy, or the like. The separator is a microporous sheet made of a synthetic resin.

[0043] The positive electrode active material used in the positive electrode active material layer is, for example, Li x (Ni s Mn t Co u M v )O2 (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ s < 1, 0 ≦ t < 1, 0 ≦ u < 1, s + t + u + v = 1, 0 < x ≦ 1.1, s and u are not both 0 at the same time) is a layered oxide represented by. The positive electrode active material has a layered rock salt-type crystal structure. The a may satisfy 0.5 ≦ a ≦ 1. In this case, it contains a large amount of Ni in the transition metal site. The positive electrode active material has v = 0, and Li x (Ni s Co u Mn t )O2 (s + t + u = 1) is preferably NCM represented by As NCM, NCM11 described above may be used, or NCM523 (s:t:u = 5:2:3), NCM622 (s:t:u = 6:2:2), NCM811 (s:t:u = 8:1:1), etc. with a high Ni content may also be used. The positive electrode active material may be N x (Ni s Co u Al v )O2 represented by CA (s + u + v = 1). In addition, in NCM or NCA, it is not limited to the case where the metals other than Li and Ni are each composed of two types of metals, and those composed of three or more types of metals may also be used. For example, a small amount of Ti, Nb, B, W, Zr, Ti, Mg, etc. may be included.

[0044] Examples of the positive electrode active material include LiMeO2-Li2MnO3 solid solution, Li2O-LiMeO2 solid solution, Li3NbO4-LiMeO2 solid solution, Li4WO5-LiMeO2 solid solution, Li4TeO5-LiMeO2 solid solution, Li3SbO4-LiFeO2 solid solution, Li2RuO3-Li The active material may be a Li-excess active material such as MeO2 solid solution, Li2RuO3-Li2MeO3 solid solution, etc. stomach. The positive electrode active material is not limited to the above.

[0045] The negative electrode active material used in the negative electrode active material layer is a Si-based active material. Examples of Si-based materials include Si and Si compounds. Examples of compounds include oxides, nitrides, and alloys. The negative electrode active material may contain a carbon material. Examples of carbon materials include graphite and amorphous carbon. Examples of amorphous carbon include non-graphitizable carbon (acetylene black, furnace black, ketjen black, etc.) and easily graphitizable carbon. Graphite is preferred as the carbon material. The proportion of the Si-based active material to the total mass of the active materials is preferably 5 to 20 mass%.

[0046] Adjacent terminals 23, 26 of adjacent cells 2 of the battery module 3 are electrically connected by a bus bar 32, so that the plurality of cells 2 are connected in series. The terminals 23, 26 of the cells 2 at both ends of the battery module 3 are provided with leads 34, 33 for extracting power.

[0047] 9 is a block diagram showing the configuration of the BMU 4. The BMU 4 includes a control unit 41, a storage unit 42, a timer unit 46, an input unit 47, and a communication unit 48. These units are connected to each other via a bus so that they can communicate with each other.

[0048] The control unit 41 has the same configuration as the control unit 71 . The control unit 41 functions as a processing unit that executes the reset discharge process by reading and executing a discharge program 43, which will be described later. The timer 46 times the timing for performing the reset discharge. The input unit 47 receives the input of the detection results from the voltage sensor 5 and the current sensor 6 .

[0049] The storage unit 42 is configured with, for example, a hard disk drive (HDD) or the like, and stores various programs and data. A discharge program 43 is stored in the storage unit 42. The discharge program 43 is provided in a state stored on a computer-readable recording medium 50, such as a CD-ROM, a DVD-ROM, or a USB memory, and is stored in the storage unit 42 by installing it in the BMU 4. Alternatively, the discharge program 43 may be obtained from an external computer (not shown) connected to a communication network and stored in the storage unit 42.

[0050] The memory unit 42 also stores charge / discharge history data 44. The charge / discharge history is the operating history of the battery module 3, and includes information indicating the period (usage period) during which the battery module 3 was charged or discharged, and information regarding the charging or discharging performed by the battery module 3 during the usage period. The information indicating the usage period of the battery module 3 includes information indicating the start and end points of charging or discharging, and the accumulated usage period during which the battery module 3 was used. The information regarding the charging or discharging performed by the battery module 3 includes information indicating the voltage, rate, etc. during charging or discharging performed by the battery module 3. The memory unit 42 also stores a reset discharge time table (hereinafter referred to as the table) 45 in which reset discharge times determined in advance by experiment are set for each rate and lower limit SOC. Curves showing changes in capacity retention over time are determined for each rate and lower limit SOC, and the reset discharge times when the capacity retention falls below a threshold and reset discharge is required are stored in the table 45. Although the capacity maintenance rate is used as the SOH, the present invention is not limited to this case.

[0051] FIG. 10 is a flowchart showing the procedure for reset discharge in the BMU 4 as the control device of the first embodiment. The control unit 41 determines whether or not the reset discharge time has elapsed (S1) using the timer unit 46. If the control unit 41 determines that the reset discharge time has not elapsed (S1: NO), the process ends. When the control unit 41 determines that the reset discharge time has elapsed (S1: YES), it starts discharging (S2).

[0052] The control unit 41 determines whether or not to terminate the discharge (S3). + The control unit 41 determines whether the battery voltage is equal to or greater than 0. .5V vs. Li / Li + The control unit 41 may determine whether the voltage has become equal to or lower than the voltage corresponding to the load. Electrode potential is 0.5V vs. Li / Li + If it is determined that the battery voltage is equal to or greater than 0.5 of the negative electrode potential, V vs. Li / Li + When it is judged that the voltage has fallen below the voltage corresponding to 3: YES), the process is terminated. + Over 0.6 V vs. Li / Li + Within the range below, or the battery voltage (negative electrode potential 0.6V vs. Li / Li + (voltage corresponding to the negative electrode potential) or more (0.5V vs. Li / Li + Discharge within the range below the voltage corresponding to the If the control unit 41 determines not to terminate the discharge (S3: NO), the control unit 41 repeats the determination process. The above reset discharge process is carried out every time the reset discharge time elapses.

[0053] According to this embodiment, as described above, the crystalline Li in the negative electrode, which causes a transient voltage drop in the battery module 3, 15 The Si4 phase disappears, so the transient voltage drop is resolved. This suppresses the decrease in capacity of the battery module 3. The decrease in output of the battery module 3 is suppressed, and the accuracy of SOC detection is also good. Although the case where the control unit 41 of the BMU 4 performs the reset discharge has been described, the reset discharge may be performed by the control unit 71 or the control unit 91.

[0054] (Variation 1) 11 is a flowchart showing the procedure for reset discharge in the BMU 4 of Modification 1. In Modification 1, the SOH of the battery module 3 is calculated to determine whether or not to perform reset discharge. First, the control unit 41 calculates, for example, a capacity maintenance rate as the SOH (S11). The control unit 41 determines whether the SOH is equal to or less than the threshold value a (%) (S12). If the control unit 41 determines that the SOH is not equal to or less than the threshold value a (S12: NO), the process ends. When the control unit 41 determines that the SOH is equal to or less than the threshold value a (S12: YES), the control unit 41 starts discharging (S13).

[0055] The control unit 41 determines whether or not to terminate the discharge (S14). The determination as to whether or not to terminate the discharge is performed in the same manner as the processing in the flowchart of FIG. If the control unit 41 determines not to end the discharge (S14: NO), it repeats the determination process. If the control unit 41 determines to end the discharge (S14: YES), it ends the process. In the first modification, each time it is determined that the SOH is equal to or less than the threshold value a, a reset discharge is performed to eliminate the voltage drop.

[0056] (Variation 2) 12 is a block diagram showing the configuration of a charge / discharge system (electricity storage device) 1 of Modification 2. In the charge / discharge system 1 of Modification 2, battery modules 35, 36, and 37 are connected in parallel. Each battery module 3 is equipped with a CMU (Cell Monitoring Unit) 14. The CMU 14 has a voltage sensor that detects the voltage of each cell 2 in the battery module 3. The BMU 4 acquires the voltage of the cell 2 detected by each CMU 14. A switch (not shown) is connected to each battery module 35, 36, 37, and the BMU 4 can control the charging and discharging of each battery module 35, 36, 37 by turning the switch on and off.

[0057] FIG. 13 is a flowchart showing the procedure for reset discharge in the BMU 4 of the second modification. First, the control unit 41 calculates, for example, a capacity maintenance rate as the SOH for each battery module (S21). The control unit 41 determines whether there is a battery module whose SOH is equal to or less than the threshold value a (%) (S22). If the control unit 41 determines that there is no battery module whose SOH is equal to or less than the threshold value a (S22: NO), the process ends. When the control unit 41 determines that there is a battery module whose SOH is equal to or less than the threshold value a (S22: YES), the control unit 41 starts discharging the battery module (S23). The control unit 41 determines whether or not to terminate the discharge (S24). The determination as to whether or not to terminate the discharge is performed in the same manner as the processing in the flowchart of FIG. If the control unit 41 determines not to end the discharge (S24: NO), it repeats the determination process. If the control unit 41 determines to end the discharge (S24: YES), it ends the process.

[0058] (Variation 3) In the third modification, the control unit 81 of the charger 8 performs reset discharge. Fig. 14 is a block diagram showing the configuration of the charge / discharge system 1 and the server 9 of Modification 3. In Fig. 14, the same components as those in Fig. 7 are given the same reference numerals and detailed description thereof will be omitted. The charger 8 is connected to the battery module 3 via terminals 15 and 16 . The charger 8 includes a control unit 81 , a power supply unit 82 , a power supply unit 83 , a communication unit 84 , a storage unit 85 , and an operation unit 87 . The control unit 81 has the same configuration as the control unit 71 . The power supply unit 83 has a current supply terminal that supplies the amount of current (charging current) controlled by the control unit 81 to the battery module 3. The power supply unit 82 of the charger 8 is connected to an external power source, and supplies the amount of power instructed by the control unit 81 to the battery module 3 via the power supply unit 83. The power supply unit 82 may include a secondary battery. A program 86 for performing charging after reset discharge is stored in the storage unit 85. The program 86 is provided in a state stored on a computer-readable recording medium 52, such as a CD-ROM, a DVD-ROM, or a USB memory, and is stored in the storage unit 85 by installing it in the charger 8. Alternatively, the program 86 may be obtained from an external computer (not shown) connected to a communication network and stored in the storage unit 85. The control unit 81 reads the program 86, performs reset discharge, and then executes charging processing.

[0059] FIG. 15 is a flowchart showing the procedure of reset discharge and charge in the third modification. The control unit 81 acquires the charge / discharge history of the battery module 3 from the BMU 4 (S31). The control unit 81 determines whether or not the reset discharge time has elapsed (S32). If the control unit 41 determines that the reset discharge time has not elapsed (S32: NO), the process proceeds to S35. When the control unit 41 determines that the reset discharge time has elapsed (S32: YES), it starts discharging (S33). The control unit 81 determines whether or not to terminate the discharge (S34). The determination as to whether or not to terminate the discharge is performed in the same manner as the processing in the flowchart of FIG. If the discharge is not to be ended (S34: NO), the control unit 81 repeats the determination process.

[0060] If the discharge is to be ended (S34: YES), the control unit 41 starts charging (S35). The control unit 81 determines whether to terminate charging (S36). The control unit 81 determines whether to terminate charging by determining whether an input to stop charging has been received from the operator via the operation unit 87. Alternatively, the control unit 81 determines whether to terminate charging based on, for example, whether the SOC has reached 100%. If the control unit 81 determines not to terminate charging (S36: NO), it repeats the determination process. When the control unit 81 determines that charging should be ended (S36: YES), the process ends.

[0061] According to the third modification, the battery module 3 is reset and discharged by the charger 8 before being charged, so that the battery module 3 maintains a good battery capacity.

[0062] FIG. 16 is a schematic diagram showing an example of the configuration of an energy storage element refreshing system. The energy storage element refresh system includes a server 9, and refreshes the energy storage elements by performing reset discharge on the energy storage elements. The server 9 has the same configuration as the server 9 in FIG. The energy storage elements are mounted on buses, trucks, taxis, drones, ships, motorcycles, etc., which are electric vehicles provided for the logistics and transportation service 100. The energy storage elements are mounted on motorcycles, cars, bicycles, drones, mobile devices such as smartphones, etc., which are electric vehicles provided for the energy storage element exchange and charging service 200. The energy storage elements are mounted on motorcycles, cars, bicycles, etc., which are electric vehicles provided for the sharing service 300. The energy storage elements are used in power generation facilities and power demand facilities that are the subject of the stationary energy storage element operation monitoring service 400.

[0063] The logistics and transportation service 100, the energy storage element exchange and charging service 200, the sharing service 300, and the stationary energy storage element operation monitoring service 400 each include a control device 13. The control device 13 includes a control unit 131 and a communication unit 132. The control unit 131 of the control device 13 is connected to the control unit 91 of the server 9 via the communication unit 132, the network 10, and the communication unit 92. The above-mentioned mobile body, power generation facility, and power demand facility are equipped with the above-mentioned charge / discharge system 1, and when resetting and discharging the storage element, the control device 7 or the BMU 4 is connected to the control device 13. The storage element is a battery module 3. The control device 7 may be connected to the server 9 via the network 10 without going through the control device 13.

[0064] The logistics and transportation service 100 uses a mobile object to provide the logistics and transportation service. When the reset discharge time has elapsed or when the SOH falls below the threshold, the BMU 4 performs reset discharge on the storage element of the mobile object according to the flowchart of FIG. 10 or 11 described above. The reset discharge may be performed by the control device 7, the control device 13, or the server 9. This increases the capacity and refreshes the storage element. It also reduces errors in SOC detection. The charger 8 may be connected to the mobile object, and the storage element may be reset discharged and then charged according to the flowchart of FIG. 15.

[0065] When a user brings a moving body or mobile device to a service center, the energy storage element replacement and charging service 200 replaces the energy storage element with a new energy storage element. If the reset discharge time for the old energy storage element has elapsed or if the SOH is equal to or less than the threshold, the BMU 4, the control device 7, the control device 13, or the server 9 performs reset discharge as described above to refresh the energy storage element.

[0066] When a user wants to charge a moving object or mobile device brought in, the charger 8 is connected to the power storage element, and the power storage element is reset and discharged according to the flowchart of FIG. 15 before being charged.

[0067] In the sharing service 300, when the reset discharge time has elapsed or when the SOH of the storage element of the mobile object being shared has become equal to or less than the threshold, the storage element is reset discharged and then charged.

[0068] In the stationary storage element operation monitoring service 400, when the reset discharge time for a storage element of a power generation facility or power demand facility has elapsed or when the SOH falls below a threshold, the storage element is reset and discharged before being charged. The discharge control method of the present invention is applicable to the above-mentioned logistics and transportation service 100, storage element exchange and charging service The present invention can also be applied to MaaS businesses other than the service 200, the sharing service 300, and the stationary energy storage element operation monitoring service 400.

[0069] (Embodiment 2) 17 is a flowchart showing the procedure for discharging in the BMU 4 as the control device of embodiment 2. In embodiment 2, when discharging, the control unit 41 always discharges to a depth that does not cause a temporary drop in battery voltage. The control unit 41 first determines whether or not the battery is discharging (S41). The control unit 41 determines whether or not the battery is discharging by, for example, determining whether or not the battery voltage is decreasing, or determining whether or not the current is negative. If the battery is not discharging (S41: NO), the control unit 41 ends the process.

[0070] If discharging is in progress (S41: YES), the control unit 41 determines whether or not to terminate discharging (S42). + Determine whether it is greater than or equal to The control unit 41 determines whether the battery voltage is 0.5V vs. Li / Li of the negative electrode potential. + The voltage is below the voltage corresponding to The control unit 41 may determine whether the negative electrode potential is 0.5 V vs. Li / Li. + If it exceeds When the battery voltage is 0.5V vs. Li / Li of the negative electrode potential + When the voltage drops below the voltage corresponding to The control unit 41 determines that the negative electrode potential is 0.5 V vs. Li / Li + More than 0.6V vs. Li / Li + Within the range below, or the battery voltage (negative electrode potential 0.6V vs. Li / Li+ (voltage corresponding to the negative electrode potential) or more (0.5V vs. Li / Li + It is preferable to terminate the discharge within a range equal to or less than the voltage corresponding to the voltage (S42: NO). If the control unit 41 does not terminate the discharge (S42: NO), the control unit 41 repeats the determination process. The above processing is performed at a predetermined timing. The above processing may be performed by the control unit 71, the control unit 81, or the control unit 91.

[0071] According to this embodiment, the crystalline Li in the negative electrode, which causes a transient voltage drop in the battery module 3, 15 By discharging to an area where no Si4 phase occurs, a transient voltage drop can be prevented. It can be effectively suppressed. In the electric vehicles of the logistics and transportation service 100 of embodiment 1, the electric vehicles and mobile devices of the storage element exchange and charging service 200, the electric vehicles of the sharing service 300, the power generation facilities of the stationary storage element operation monitoring service 400, and the storage elements used in power demand facilities can also be discharged to the above range, thereby suppressing transient voltage drops.

[0072] The above-described embodiments are not intended to be limiting, and the scope of the present invention is intended to include all modifications within the meaning and scope of the claims.

[0073] For example, the control method according to the present invention is not limited to application to charging and discharging systems for moving bodies, mobile devices, power generation equipment, and power demand equipment, but can also be applied to other charging and discharging systems such as regenerative power storage devices for railways. The energy storage element is not limited to a lithium-ion secondary battery, and may be another secondary battery having a Si-based negative electrode, a primary battery, or an electrochemical cell such as a capacitor. [Explanation of symbols]

[0074] 1. Charging and discharging system 2. Battery (energy storage element) 3 Battery module (energy storage element) 4 BMU 41, 71, 81, 91, 131 Control section 42, 85 Storage section 43 Discharge Program 44 Historical Data 45 Reset discharge time table 46 Timing section 47 Input section 48, 73, 84, 92, 132 Communications Department 7 Control Device 72 Display section 8 charger 86 Programs 9 Server 10 Network

Claims

1. A control method for discharging an electric storage element having a Si-based negative electrode so that the negative electrode potential becomes more noble than the negative electrode potential in a region where a transient voltage drop occurs.

2. The negative electrode potential is 0.5 V vs. Li / Li + 2. The control according to claim 1, wherein the discharge is performed so that the method.

3. The negative electrode potential is 0.5 V vs. Li / Li + Above 0.6V vs. Li / Li + The control method according to claim 2 , wherein the discharge is performed so that:

4. 4. The control method according to claim 1, wherein, in an energy storage device including a plurality of energy storage element modules connected in parallel, each of the energy storage element modules is configured to include a plurality of energy storage elements having a Si-based negative electrode connected in series, and the energy storage element modules are each ... parallel.

5. The control method according to claim 1 , wherein when a predetermined condition is satisfied, the discharge is performed while controlling the voltage so that the negative electrode potential is more noble than the negative electrode potential in the region.

6. A control device including a control unit that discharges a power storage element having a Si-based negative electrode so that the negative electrode potential becomes more noble than the negative electrode potential in a region where a transient voltage drop occurs.

7. Discharge is performed so that the negative electrode potential becomes more noble than the negative electrode potential in the region where a transient voltage drop occurs in the electric storage element having a Si-based negative electrode. A computer program that causes a computer to perform a process.

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