JP7363311B2 - Control method, control device, and computer program - Google Patents

Description

The present invention relates to a control method, a control device, and a computer program for suppressing deterioration of a power storage element.

Electric storage elements are used that can store electrical energy and supply energy when needed. Energy storage elements are applied to mobile devices, power supplies, transportation equipment including automobiles and railways, and industrial equipment including aviation, space, and construction equipment. It is important to constantly know the storage capacity of the storage element so that you can use the stored energy as much as you need when you need it. It is known that power storage elements mainly deteriorate chemically depending on time and frequency of use. Therefore, the amount of energy that can be used decreases depending on the time and frequency of use. It is important to understand the state of deterioration of power storage elements in order to use energy as needed and when it is needed. Techniques for estimating deterioration of power storage elements have been developed so far.

BACKGROUND ART Lithium ion secondary batteries (hereinafter referred to as batteries) as power storage elements that use SiO as a negative electrode active material are known. When SiO is used as the negative electrode active material, the capacity of the negative electrode increases, so the capacity of the battery can be increased.

The lithium ion conductivity of SiO increases as the amount of doped lithium increases, and there is a problem in that the amount of lithium doped in the negative electrode tends to be localized due to charging and discharging. When charging and discharging are repeated in a state where the amount of lithium doped is uneven, the volume change in the portion where the amount of doping is large becomes large, and that portion peels off from the current collector, resulting in a decrease in battery capacity.
In Patent Document 1, dQ/dV, which is the ratio of the change dQ in the discharge capacity Q to the change dV in the potential V of the negative electrode with respect to the lithium reference electrode, and V-dQ/dV, which indicates the relationship between the potential V, are generated, A method is disclosed in which the intensity ratio of two peaks on V-dQ/dV is calculated and the state of the negative electrode is detected based on the intensity ratio.
Patent Document 2 discloses that when discharging a non-aqueous electrolyte using a silicon oxide containing lithium as a negative electrode active material, the discharge is controlled so that the negative electrode voltage with respect to a lithium reference electrode does not exceed 0.6 V. A discharge control method is disclosed.

Patent No. 5682955 Patent No. 4088993

On the other hand, the inventors of the present application have discovered that when a battery including a Si-based negative electrode is repeatedly charged and discharged within a predetermined SOC (state of charge) range, a decrease in battery voltage occurs due to a temporary decrease in battery capacity. I found out.
As a result of investigating the cause of the temporary decrease in battery capacity, the inventors of the present application found that a crystalline Li ₁₅ Si ₄ phase was generated that caused a temporary decrease in battery voltage in a storage element containing a Si-based negative electrode. I discovered that this was a factor. When charging and discharging are repeated within a predetermined SOC range and the discharge is shallow, there are parts of the negative electrode where Li remains and parts where no Li remains, and if charging is performed in this state, the parts where Li remains will be charged first. As the charging depth increases, crystalline Li ₁₅ Si ₄ is produced. In a Si-based negative electrode, charging and discharging are thought to proceed in an amorphous phase, but the crystalline Li ₁₅ Si ₄ phase does not contribute to the charging and discharging process (inflow and outflow of Li ions). Therefore, the battery capacity decreases due to the formation of crystalline Li ₁₅ Si ₄ phase. In order to prevent the battery capacity from decreasing, it is necessary to control the generation of the crystalline Li ₁₅ Si ₄ phase, or to perform a process to eliminate the generated crystalline Li ₁₅ Si ₄ phase to recover the battery capacity. . In other words, the decrease in battery capacity caused by the formation of the crystalline Li ₁₅ Si ₄ phase can be restored by the recovery process, and the transient decrease in battery voltage can be resolved.
In Patent Documents 1 and 2, solving the transient battery voltage drop is not an issue.

An object of the present invention is to provide a control method, a control device, and a computer program for preventing a temporary (transient) battery voltage drop phenomenon of a power storage element from occurring. Another object of the present invention is to provide a control method, a control device, and a computer program that eliminate a temporary (transient) drop in battery voltage of a power storage element.

In a control method according to one embodiment of the present invention, a power storage element having a Si-based negative electrode is discharged so that the negative electrode potential is nobler (higher) than the negative electrode potential in a region where a temporary decrease in battery voltage occurs.

A control device according to one embodiment of the present invention includes a control unit that discharges a power storage element having a Si-based negative electrode so that the negative electrode potential is nobler (higher) than the negative electrode potential in a region where a transient battery voltage drop occurs. Be prepared.

A computer program according to one embodiment of the present invention includes a process of discharging a power storage element having a Si-based negative electrode so that the negative electrode potential is nobler (higher) than the negative electrode potential of a region where a transient battery voltage drop occurs. have the computer execute it.

In the present invention, it is possible to prevent a temporary voltage drop phenomenon of a power storage element from occurring. Further, when a temporary voltage drop in the power storage element occurs, the voltage drop can be eliminated.

It 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. 2 is a graph showing the results of determining the relationship between discharge capacity and battery voltage when the lower limit of SOC is 25% (SOC range of curve d in FIG. 1). Repeat charging and discharging in each of the SOC ranges a to f in FIG. This is a DOD (depth of discharge)-OCV curve when discharging from a fully charged state after 100 cycles. These are SOC-OCV curves and DOD-OCV curves after completely discharging each battery shown in FIG. 3 after 100 cycles of charging and discharging, and after repeating 100 cycles of charging and discharging. It is a graph showing the results of determining the DOD-OCP of the negative electrode after 50 cycles of charging and discharging when the lower limit of SOC is 10% and 25%, respectively (SOC ranges a and d in FIG. 1). . It is a graph showing the relationship between specific capacity and negative electrode potential. 1 is a block diagram showing the configuration of a charging/discharging system and a server according to Embodiment 1. FIG. It is a perspective view of a battery module. FIG. 2 is a block diagram showing the configuration of a BMU. 5 is a flowchart showing a reset discharge processing procedure in the BMU as a control device according to the first embodiment. 7 is a flowchart illustrating a reset discharge processing procedure in a BMU of Modification 1. FIG. It is a block diagram showing the composition of the charging and discharging system of modification 2. 12 is a flowchart illustrating a reset discharge processing procedure in a BMU of Modification 2. FIG. FIG. 3 is a block diagram showing the configuration of a charging/discharging system and a server according to Modification 3. FIG. 12 is a flowchart illustrating a reset discharge and charge processing procedure of Modification 3. FIG. 1 is a schematic diagram showing an example of the configuration of a power storage element refresh system. 7 is a flowchart showing a discharge processing procedure in a BMU as a control device according to a second embodiment.

(Summary of embodiment)
In the control method according to the embodiment, a power storage element having a Si-based negative electrode is discharged so that the negative electrode potential becomes nobler than the negative electrode potential in a region where a temporary decrease in battery voltage occurs.
Further, when a predetermined condition is satisfied, discharge is performed while controlling the voltage so that the negative electrode potential is nobler than the negative electrode potential in the region. Hereinafter, this discharge will be referred to as reset discharge.

Here, the Si-based negative electrode refers to a negative electrode containing Si or a compound of Si as an active material. Examples of the compound include oxides, nitrides, alloys, and the like.
Examples of cases where the predetermined condition is satisfied include a case where a predetermined time has elapsed, a case where the SOH (State of Health) becomes equal to or less than a threshold value, and the like. The predetermined time is set as the elapsed time when, for example, a curve showing the change in the capacity retention rate over time is obtained for each rate and the lower limit SOC, and the capacity retention rate becomes equal to or less than a threshold value, and it is necessary to perform a reset discharge.

According to the above configuration, by discharging so as not to generate a crystalline Li ₁₅ Si ₄ phase at the negative electrode, which causes a transient voltage drop in the power storage element, it is possible to suppress a transient voltage drop. Furthermore, by performing reset discharge when predetermined conditions are met, _{the four} Li ₁₅ Si phases disappear, thereby eliminating the transient voltage drop. As described above, it is possible to suppress a decrease in the capacity of the power storage element. The decrease in output is suppressed, and the accuracy of SOC detection is also good.

In the above control method, the negative electrode potential may be discharged to be 0.5 V vs. Li/Li ⁺ or more.

According to the above configuration, the formation of the crystalline Li ₁₅ Si ₄ phase is effectively suppressed or eliminated.

In the above-described control method, the negative electrode potential may be discharged so as to be 0.5 V vs. Li/Li ⁺ or more and 0.6 V vs. Li/Li ⁺ or less.

According to the above configuration, the formation of the crystalline Li ₁₅ Si ₄ phase is effectively suppressed or eliminated, and the deterioration of the Si-based active material is suppressed.

In the above-mentioned control method, for each of the power storage device modules in the power storage device including a plurality of power storage device modules each having a Si-based negative electrode connected in series, the negative electrode potential is more noble than the negative electrode potential in the region. You may discharge it so that

According to the above configuration, only the power storage element module in which a temporary voltage drop has occurred can be discharged to suppress or eliminate the voltage drop.

The control device according to the embodiment includes a control unit that discharges so that the negative electrode potential becomes nobler than the negative electrode potential in a region where a transient voltage drop of a power storage element having a Si-based negative electrode occurs.

According to the above configuration, since the generation of crystalline Li ₁₅ Si ₄ phase in the negative electrode, which causes a transient voltage drop in the electricity storage element due to the discharge, is suppressed, the transient voltage drop can be suppressed. . Further, by performing reset discharge when predetermined conditions are met, the Li ₁₅ Si ₄ phase disappears, so it is possible to eliminate a transient voltage drop and suppress a decrease in the capacity of the power storage element. The decrease in output is suppressed, and the accuracy of SOC detection is also good.

A computer program according to an embodiment includes a computer program that performs a process of discharging a power storage element having a Si-based negative electrode so that the absolute value of the negative electrode potential becomes larger than the absolute value of the negative electrode potential of a region in which a transient voltage drop occurs. have it executed.

According to the above configuration, it is possible to suppress or eliminate a transient voltage drop, and it is possible to suppress a decrease in the capacity of the power storage element. The decrease in output is suppressed, and the accuracy of SOC detection is also good.

Hereinafter, a method for controlling discharge will be specifically explained. Hereinafter, a case will be described in which a lithium ion secondary battery (battery) is used as the power storage element.
FIG. 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. In FIG. 1, the horizontal axis is the number of cycles, and the vertical axis is the capacity retention rate (%). NCM is Li _x (Ni _{s Cou Mnt} ) O ₂ (0≦s<1, 0≦t<1, 0≦u<1, s+t+u=1, 0<x≦1.1, s, u are at the same time In the case of NCM111, s=t=u.
Figure 1 shows the SOC ranges of 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%. The relationship between the number of cycles when charging and discharging is repeated and the capacity retention rate is shown.

The charge/discharge cycle conditions are as follows.
Test temperature: 25℃
Charging: CC (constant current) charging to 4.2V at 1CmA, then CV (constant voltage) charging, stopping charging when the current reaches 0.05CmA Discharging: CC discharge at 1CmA, corresponding to each SOC Discharge is stopped by voltage From FIG. 1, it can be seen that in the case of the curves in the SOC range of d and e, the capacity retention rate decreases greatly. That is, when the lower limit of SOC is 25 to 40%, the capacity retention rate decreases more than when discharging is performed until the SOC reaches 20% or less.
The present inventors have found that by discharging so that the negative electrode potential becomes 0.5 V vs. Li/Li ⁺ or higher at the 50th cycle, the capacity retention rate improves in all curves a to f above. I found out. As shown in FIG. 1, the capacity retention rate is improved by performing the above-described discharge at the 50th cycle. After the decrease in capacity retention rate is resolved, by repeating charging and discharging, the capacity retention rate of the curves d and e decreases again. Therefore, deep discharge (reset discharge) may be repeated at predetermined timing.

FIG. 2 is a graph showing the results of determining the relationship between discharge capacity and battery voltage for the case d where the lower limit of SOC is 25%.
In FIG. 2, the horizontal axis is discharge capacity (mAh), and the vertical axis is battery voltage (V). The discharge curve h shows the relationship between the discharge capacity and the battery voltage at the time of capacity confirmation (when discharging from SOC 100% to 0%). Discharge curves i, j, k, l, and m show the relationship between discharge capacity and battery voltage when charging and discharging are repeated 1, 10, 20, 30, and 40 times in the range of SOC 25 to 100%. show. The discharge curve n shows the relationship between the discharge capacity and the battery voltage when charging and discharging is repeated 50 times in the range of SOC 25 to 100% and then 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 3.5V.

Figure 3 shows how the SOC is filled in each of the SOC ranges a to f in Figure 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%). The DOD-OCV curve is shown when discharging is repeated and the battery is discharged from a fully charged state after 100 cycles.
In FIG. 3, the horizontal axis is DOD (%) and the vertical axis is battery voltage (V).
From FIG. 3, in the case of the curves d and e, where the lower limit of SOC is 25% and 40%, respectively, in the voltage range of 3.1 to 3.7V, especially in the voltage range of 3.2 to 3.5V, the other It can be seen that the voltage for the same DOD is lower than when charging and discharging are repeated in the SOC range of .

FIG. 4 shows the SOC-OCV curve and the DOD-OCV curve after each battery in FIG. 3 which has been repeatedly charged and discharged for 100 cycles is fully discharged and then further charged and discharged for 100 cycles. In FIG. 4, the upper side is the SOC-OCV curve, and the lower side is the DOD-OCV curve.
In FIG. 4, the horizontal axis is SOC (DOD) (%), and the vertical axis is battery voltage (V).
From FIG. 4, in the case of the curves d and e, by performing the above-mentioned reset discharge, both the SOC-OCV curve and the DOD-OCV curve overlap with the curves of other SOC ranges, and the phenomenon of capacity decrease occurs. I see that it has been resolved.

FIG. 5 is a graph showing the results of determining the DOD-OCP of the negative electrode after 50 cycles of charging and discharging in cases a and d, in which 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 ⁺ ).
From FIG. 5, in the region where the DOD is 50% or more, in the case of the DOD-OCP curve of d, the negative electrode potential for the same DOD is larger than that of the DOD-OCP curve of a, and has an upwardly convex shape. When the negative electrode potential becomes higher with the same DOD, the battery voltage decreases.

FIG. 6 is a graph showing the relationship between specific capacity and negative electrode potential.
In FIG. 6, the horizontal axis is specific capacity (mAh/g), and the vertical axis is negative electrode potential (V vs. Li/Li ⁺ ).
When a Si-based negative electrode is deeply charged to a potential of 0.05 V vs. Li/Li ⁺ or less, a crystalline Li ₁₅ Si ₄ phase is formed. When a discharge is performed in a state where this phase is generated, a potential flattening region shown in Fig. 5 appears in the range of approximately 0.4V vs. Li/Li ⁺ due to the coexistence reaction of the two phases, the crystalline phase and the amorphous phase. . When a potential plateau appears, the discharge potential of the negative electrode increases, and therefore the discharge voltage of the battery decreases.

In a battery having a Si-based negative electrode, when charging and discharging are repeated within a predetermined SOC range, a decrease in battery voltage occurs due to a temporary decrease in battery capacity. The SOC range in which a transient voltage drop occurs varies depending on the content of the Si-based compound. At a ratio of 20% SiO/80% Gr, the above phenomenon occurs when the lower limit of SOC is about 25% or more. When the content of SiO is small, the above phenomenon occurs under conditions where the lower limit SOC is lower, and a voltage change occurs in a lower voltage region.
If the negative electrode potential is not discharged until it reaches 0.5 V vs. Li/Li ⁺ or higher, the amount of crystalline Li ₁₅ Si ₄ phase accumulated gradually increases, so the discharge voltage gradually decreases as the number of cycles increases. do. Once the negative electrode potential is discharged to 0.5V vs. Li/Li ⁺ or higher, the Li ₁₅ Si ₄ phase completely disappears, so the DOD-OCV curve is reset to its original state as shown in Figure 4. be done.
Although the detailed reason is not clear, it is thought that deep discharging eliminates the imbalance in the amount of lithium doped in the mixture, making it difficult to form crystalline Li ₁₅ Si ₄ during subsequent charging.

Reset discharge is performed when SOH such as capacity retention rate becomes below a threshold value. Alternatively, the time during which the SOH becomes equal to or less than the threshold value is determined by experiment for each charging rate and charge/discharge range (SOC range), and the test is performed each time the time period elapses.
In the reset discharge, as shown in FIG. 5, when the negative electrode potential becomes 0.5 V vs. Li/Li ⁺ or more, the difference in DOD at the same potential of the curves a and d becomes small, so the negative electrode potential becomes 0. It is preferable to perform this so that the voltage is .5V vs. Li/Li ⁺ or more.
It is more preferable to carry out the reset discharge so that the negative electrode potential becomes 0.5 V vs. Li/Li ⁺ or more and 0.6 V vs. Li/Li ⁺ or less. When a deep discharge exceeding 0.6V vs. Li/Li ⁺ is performed, the Si-based negative electrode deteriorates.
The reset discharge is preferably performed so that the battery voltage is equal to or lower than the voltage corresponding to the negative electrode potential of 0.5 V vs. Li/Li ⁺ .
It is more preferable to perform the reset discharge so that the voltage is greater than or equal to (the voltage corresponding to the negative electrode potential of 0.6 V vs. Li/Li ⁺ ) and less than (the voltage corresponding to the negative electrode potential of 0.5 V vs. Li/Li ⁺ ).

(Embodiment 1)
Hereinafter, a case where the electricity storage element is a lithium ion secondary battery will be described.
FIG. 7 is a block diagram showing the configuration of the charging/discharging 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, a voltage sensor 5, a current sensor 6, and a control device 7.

In the battery module 3, a plurality of lithium ion secondary batteries (hereinafter referred to as cells) 2 as power storage elements are connected in series. The control device 7 controls the entire charging/discharging system 1 .
The server 9 includes a communication section 92 and a control section 91.
The control device 7 includes a control section 71, a display section 72, and a communication section 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.
The 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.

The control units 71 and 91 are configured with, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and control the operations of the control device 7 and the server 9.
The communication units 73 and 92 have a 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, or the like. The control unit 71 performs control to display required information on the display unit 72.

In this embodiment, either the BMU 4, the control device 7, or the server 9 functions as the control device of the present invention. Note that if the server 9 does not function as a control device, the charging/discharging system 1 may not be connected to the server 9.
Although FIG. 7 shows a case where one set of battery modules 3 is provided, a plurality of sets of battery modules 3 may be connected in series.
BMU4 may be a battery ECU.

The voltage sensor 5 is connected in parallel to the battery module 3 and outputs a detection result according to the overall voltage of the battery module 3. The voltage sensor 5 is connected to a positive terminal 23 and a negative terminal 26 of each cell 2, which will be described later, and measures the voltage V ₁ between the terminals 23 and 26 of each cell 2, and calculates the voltage V ₁ of each cell 2. A voltage V between a negative lead 33 and a positive lead 34 of the battery module 3, which will be described later, is detected as a total value.
The current sensor 6 is connected in series to the battery module 3 and outputs a detection result according to the current of the battery module 3.

FIG. 8 is a perspective view of the battery module 3.
The battery module 3 includes a rectangular parallelepiped-shaped case 31 and a plurality of cells 2 housed in the case 31.

The cell 2 includes a rectangular parallelepiped case body 21, a cover plate 22, terminals 23 and 26 provided on the cover plate 22, a rupture valve 24, and an electrode body 25. The electrode body 25 is formed by laminating a positive electrode plate, a separator, and a negative electrode plate, and is housed in the case body 21.
The electrode body 25 may be obtained by winding a positive electrode plate and a negative electrode plate into a flat shape with a separator in between.

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

The positive electrode active material used in the positive electrode active material layer is, for example, Li _x (Ni _s Mn _{t Cou} M _v )O ₂ (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 0 at the same time). The positive electrode active material has a layered rock salt crystal structure. The above a may satisfy 0.5≦a≦1. In this case, transition metal sites contain a large amount of Ni.
The positive electrode active material is preferably NCM, where v=0 and represented by Li _x (Ni _{s Cou Mnt} )O ₂ (s+t+u=1). As the NCM, the above-mentioned NCM11 may be used, and NCM523 (s:t:u=5:2:3), NCM622 (s:t:u=6:2:2), NCM811 (s:t :u=8:1:1) etc. may be used.
The positive electrode active material may be NCA, where M is Al, t=0, and is represented by Li _x (Ni _{s Cou} Al _v )O ₂ (s+u+v=1).
Note that in NCM or NCA, the metals other than Li and Ni are not limited to two kinds of metals, and may be made of three or more kinds of metals. For example, small amounts of Ti, Nb, B, W, Zr, Ti, Mg, etc. may be included.

Examples of the positive electrode active material include LiMeO ₂ -Li ₂ MnO ₃ solid solution, Li ₂ O-LiMeO ₂ solid solution, Li ₃ NbO ₄ -LiMeO ₂ solid solution, Li ₄ WO ₅ -LiMeO ₂ solid solution, Li ₄ TeO ₅ -LiMeO ₂ solid solution. , Li ₃ SbO ₄ --LiFeO ₂ solid solution, Li ₂ RuO ₃ --LiMeO ₂ solid solution, Li ₂ RuO ₃ --Li ₂ MeO ₃ solid solution, and other Li-excess type active materials may be used.
The positive electrode active material is not limited to the above case.

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 the compound include oxides, nitrides, alloys, and the like. The negative electrode active material can include 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.), easily graphitizable carbon, and the like. Graphite is preferred as the carbon material. The ratio of the Si-based active material to the total mass of the active material is preferably 5 to 20% by mass.

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

FIG. 9 is a block diagram showing the configuration of the BMU 4. The BMU 4 includes a control section 41 , a storage section 42 , a clock section 46 , an input section 47 , and a communication section 48 . These units are communicably connected to each other via a bus.

The control section 41 has the same configuration as the control section 71.
The control unit 41 functions as a processing unit that executes reset discharge processing by reading and executing a discharge program 43 to be described later.
The clock section 46 clocks the timing at which reset discharge is performed.
The input unit 47 receives input of detection results from the voltage sensor 5 and the current sensor 6.

The storage unit 42 is constituted by, for example, a hard disk drive (HDD), 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 in a computer-readable recording medium 50 such as a CD-ROM, DVD-ROM, or USB memory, and is stored in the storage unit 42 by being installed in the BMU 4. Alternatively, the discharge program 43 may be acquired from an external computer (not shown) connected to a communication network and stored in the storage unit 42.

The storage unit 42 also stores charging/discharging history data 44 . The charging/discharging history is the operation history of the battery module 3, and includes information indicating the period during which the battery module 3 was charged or discharged (period of use), information regarding charging or discharging performed by the battery module 3 during the period of use, etc. This is information that includes. The information indicating the period of use of the battery module 3 is information including information indicating the start and end points of charging or discharging, the cumulative period of use during which the battery module 3 was used, and the like. The information regarding charging or discharging performed by the battery module 3 is information indicating the voltage, rate, etc. at the time of charging or discharging performed by the battery module 3.
The storage unit 42 also stores a reset discharge time table (hereinafter referred to as a table) 45 in which reset discharge times determined in advance through experiments are set for each rate and lower limit SOC. A curve showing a change in the capacity retention rate over time is obtained for each rate and lower limit SOC, and the reset discharge time when the capacity retention rate becomes equal to or less than the threshold value and it is necessary to perform a reset discharge is stored in the table 45.
Note that although the capacity maintenance rate is used as the SOH, it is not limited to this case.

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

The control unit 41 determines whether or not to end the discharge (S3). The control unit 41 determines whether the negative electrode potential has become 0.5 V vs. Li/Li ⁺ or more. The control unit 41 may determine whether the battery voltage has become lower than the voltage corresponding to the negative electrode potential of 0.5V vs. Li/Li ⁺ . If the control unit 41 determines that the negative electrode potential has become 0.5 V vs. Li/Li ⁺ or higher, or if it determines that the battery voltage has become lower than the voltage corresponding to the negative electrode potential of 0.5 V vs. Li/ ^{Li +} , the control unit 41 starts discharging. It is determined that the process is finished (S3: YES), and the process is finished. The control unit 41 controls the negative electrode potential within the range of 0.5V vs. Li/Li ⁺ or more and 0.6V vs. Li/Li ⁺ or less, or the battery voltage (voltage corresponding to the negative electrode potential of 0.6V vs. Li/Li ^+). ) or more (a voltage corresponding to the negative electrode potential of 0.5 V vs. Li/Li ⁺ ) or less, it is preferable to terminate the discharge within a range. If the control unit 41 does not end the discharge (S3: NO), the control unit 41 repeats the determination process.
The above reset discharge process is performed every time the reset discharge time elapses.

According to this embodiment, as described above, the crystalline Li ₁₅ Si ₄ phase at the negative electrode, which causes a transient voltage drop in the battery module 3, disappears, so the transient voltage drop is eliminated. do. Therefore, a decrease in the capacity of the battery module 3 can be suppressed. A decrease in the output of the battery module 3 is suppressed, and the accuracy of SOC detection is also good.
Although the case where the control section 41 of the BMU 4 performs the reset discharge has been described, the reset discharge may be performed by the control section 71 or the control section 91.

(Modification 1)
FIG. 11 is a flowchart showing a reset discharge processing procedure in the BMU 4 of the first modification. In the first modification, the SOH of the battery module 3 is calculated, and it is determined 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 a threshold value a (%) (S12). When 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 less than or equal to the threshold value a (S12: YES), it starts discharging (S13).

The control unit 41 determines whether or not to end the discharge (S14). The determination as to whether or not to end the discharge is performed in the same manner as the process in the flowchart of FIG.
If the control unit 41 does not end the discharge (S14: NO), the control unit 41 repeats the determination process. When the control unit 41 ends the discharge (S14: YES), it ends the process.
In Modification 1, each time it is determined that the SOH is equal to or less than the threshold value a, a reset discharge can be performed to eliminate the voltage drop.

(Modification 2)
FIG. 12 is a block diagram showing the configuration of a charging/discharging system (power storage device) 1 of a second modification. In the charging/discharging system 1 of the second modification, battery modules 35, 36, and 37 are connected in parallel.
Each battery module 3 includes a CMU (Cell Monitoring Unit) 14. The CMU 14 includes a voltage sensor that detects the voltage of each cell 2 of the battery module 3. BMU4 acquires the voltage of cell 2 detected by each CMU14. A switch (not shown) is connected to each battery module 35, 36, 37, and the BMU 4 can control charging and discharging of each battery module 35, 36, 37 by turning on/off the switch.

FIG. 13 is a flowchart showing a reset discharge processing procedure in the BMU 4 of the second modification.
First, the control unit 41 calculates, for example, the 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). When 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 end the discharge (S24). The determination as to whether or not to end the discharge is performed in the same manner as the process in the flowchart of FIG.
If the control unit 41 does not end the discharge (S24: NO), the control unit 41 repeats the determination process. When the control unit 41 ends the discharge (S24: YES), it ends the process.

(Modification 3)
In modification 3, the control unit 81 of the charger 8 performs reset discharge.
FIG. 14 is a block diagram showing the configuration of the charging/discharging system 1 and the server 9 of Modification 3. In FIG. 14, the same parts as those in FIG. 7 are given the same reference numerals, and detailed explanations are omitted.
Charger 8 is connected to battery module 3 via terminals 15 and 16.
Charger 8 includes a control section 81 , a power supply section 82 , a power supply section 83 , a communication section 84 , a storage section 85 , and an operation section 87 .
The control section 81 has the same configuration as the control section 71.
The power supply section 83 has a current supply terminal that supplies the amount of current (charging current) controlled by the control section 81 to the battery module 3 . The power supply unit 82 of the charger 8 is connected to an external power supply, and supplies the battery module 3 with the amount of current instructed by the control unit 81 via the power supply unit 83. The power supply unit 82 may include a secondary battery.
The storage unit 85 stores a program 86 for performing reset discharge and then charging. The program 86 is provided stored in a computer-readable recording medium 52 such as a CD-ROM, DVD-ROM, or USB memory, and is stored in the storage unit 85 by being installed in the charger 8. Alternatively, the program 86 may be acquired from an external computer (not shown) connected to a communication network and stored in the storage section 85.
The control unit 81 reads the program 86, performs reset discharge, and then executes charging processing.

FIG. 15 is a flowchart showing the reset discharge and charge processing procedure of Modification 3.
The control unit 81 acquires the charging/discharging history of the battery module 3 from the BMU 4 (S31). The control unit 81 determines whether the reset discharge time has elapsed (S32). When 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 end the discharge (S34). The determination as to whether or not to end the discharge is performed in the same manner as the process in the flowchart of FIG.
If the control unit 81 does not end the discharge (S34: NO), the control unit 81 repeats the determination process.

When the control unit 41 ends discharging (S34: YES), it starts charging (S35).
The control unit 81 determines whether or not to end charging (S36). The control unit 81 determines whether or not the operator's input to stop charging is received through the operation unit 87, and determines whether or not charging is to be ended. Alternatively, the control unit 81 determines whether to end charging, for example, based on whether the SOC has reached 100%. When the control unit 81 determines that charging is not to be completed (S36: NO), the determination process is repeated.
If the control unit 81 determines to end the charging (S36: YES), it ends the process.

According to the third modification, the battery module 3 is reset-discharged and then charged by the charger 8, so that the battery module 3 maintains a good battery capacity.

FIG. 16 is a schematic diagram showing an example of the configuration of a power storage element refresh system.
The power storage element refresh system includes a server 9, performs reset discharge to the power storage element, and refreshes the power storage element. Server 9 has a similar configuration to server 9 in FIG.
The power storage element is mounted on buses, trucks, taxis, drones, ships, motorcycles, and the like as electric vehicles provided for the logistics/transportation service 100. The power storage element is mounted on a motorbike, a car, a bicycle, a drone, a mobile device such as a smartphone, etc. as an electric mobile object provided for the power storage element exchange/charging service 200. The power storage element is mounted on a motorbike, a car, a bicycle, etc. as an electric mobile body provided for the sharing service 300. The power storage element is used in power generation equipment and power demand equipment that are subject to the stationary power storage element operation monitoring service 400.

The logistics/transportation service 100 , the power storage element exchange/charging service 200 , the sharing service 300 , and the stationary power storage element operation monitoring service 400 include a control device 13 . The control device 13 includes a control section 131 and a communication section 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-described moving body, power generation facility, and power demand facility are equipped with the above-described charging/discharging system 1, and the control device 7 or BMU 4 is connected to the control device 13 when performing reset discharge of the power storage element. The power storage element is a battery module 3. The control device 7 may be connected to the server 9 via the network 10 without using the control device 13.

The logistics/transportation service 100 performs logistics/transportation services using mobile objects. When the reset discharge time has elapsed or when the SOH becomes equal to or less than the threshold value, the power storage element of the moving body performs reset discharge by the BMU 4 according to the flowchart of FIG. 10 or FIG. 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 power storage element. The error in SOC detection also becomes smaller. Charger 8 may be connected to the moving object, and charging may be performed after reset discharge is performed on the power storage element according to the flowchart of FIG. 15.

The power storage element exchange/charging service 200 replaces the power storage element with a new power storage element when a user brings a mobile body or a mobile device to a service base. If the reset discharge time has elapsed for the old energy storage element, or if the SOH is below the threshold, the BMU 4, control device 7, control device 13, or server 9 performs reset discharge as described above. and refreshes the power storage element.

When charging a moving object or mobile device brought by a user, 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.

In the sharing service 300, when the reset discharge time has elapsed or when the SOH becomes equal to or less than the threshold value, the power storage element of the sharing mobile body is reset discharged and then charged.

In the stationary power storage element operation monitoring service 400, if the reset discharge time has elapsed or the SOH has fallen below a threshold value, the power storage element of the power generation equipment or power demand equipment is reset discharged and then charged. Ru.
The discharge control method of the present invention is also applicable to MaaS businesses other than the above-described logistics/transportation service 100, power storage element exchange/charging service 200, sharing service 300, and stationary power storage element operation monitoring service 400.

(Embodiment 2)
FIG. 17 is a flowchart showing a discharge processing procedure in the BMU 4 as the control device of the second embodiment. In the second embodiment, when discharging, the control unit 41 always discharges to a depth at which no temporary drop in battery voltage occurs.
The control unit 41 first determines whether or not discharging is in progress (S41). The control unit 41 determines whether the battery is being discharged, for example, by determining whether the battery voltage is decreasing or determining whether the current is negative. If the controller 41 is not discharging (S41: NO), it ends the process.

If the controller 41 is discharging (S41: YES), the controller 41 determines whether or not to end the discharging (S42). The control unit 41 determines whether the negative electrode potential has become 0.5 V vs. Li/Li ⁺ or higher. The control unit 41 may determine whether the battery voltage has become lower than the voltage corresponding to the negative electrode potential of 0.5V vs. Li/Li ⁺ . The control unit 41 terminates discharging when the negative electrode potential becomes 0.5 V vs. Li/Li ⁺ or more, or when the battery voltage becomes less than the voltage corresponding to the negative electrode potential of 0.5 V vs. Li/Li ⁺ . It is determined (S42: YES) and the process is ended. The control unit 41 controls the negative electrode potential within the range of 0.5V vs. Li/Li ⁺ or more and 0.6V vs. Li/Li ⁺ or less, or the battery voltage (voltage corresponding to the negative electrode potential of 0.6V vs. Li/Li ^+). ) or more (the voltage corresponding to the negative electrode potential of 0.5 V vs. Li/Li ⁺ ) or less, it is preferable to terminate the discharge. If the control unit 41 does not end 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 section 71, the control section 81, or the control section 91.

According to the present embodiment, by discharging to a region where the crystalline Li ₁₅ Si ₄ phase does not occur in the negative electrode, which causes a transient voltage drop in the battery module 3, the transient voltage drop can be suppressed. can be suppressed to
Electric mobile objects in the logistics/transportation service 100 of the first embodiment, electric mobile objects and mobile devices in the power storage element exchange/charging service 200, electric mobile objects in the sharing service 300, stationary power storage element operation monitoring service 400, etc. Even in power storage elements used in power generation equipment and power demand equipment, it is possible to discharge to the above region and suppress a transient voltage drop.

The embodiments described above are not restrictive. The scope of the present invention is intended to include all changes within the meaning and scope equivalent to the claims.

For example, the control method according to the present invention is not limited to application to charging and discharging systems for moving objects, 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. Applicable.
The power storage element is not limited to a lithium ion secondary battery. The power storage element may be another secondary battery having a Si-based negative electrode, a primary battery, or an electrochemical cell such as a capacitor.

1 Charging/discharging system 2 Battery (storage element)
3 Battery module (power storage element)
4 BMU
41, 71, 81, 91, 131 Control section 42, 85 Storage section 43 Discharge program 44 History data 45 Reset discharge time table 46 Timing section 47 Input section 48, 73, 84, 92, 132 Communication section 7 Control device 72 Display section 8 Charger 86 Program 9 Server 10 Network

Claims (7)

A control method for discharging a power storage element having a Si-based negative electrode so that the negative electrode potential becomes nobler than the negative electrode potential in a region where a transient voltage drop occurs. The control method according to claim 1, wherein the discharge is performed so that the negative electrode potential becomes 0.5 V vs. Li/Li ⁺ or more. 3. The control method according to claim 2, wherein discharging is performed so that the negative electrode potential is 0.5 V vs. Li/Li ⁺ or more and 0.6 V vs. Li/Li ⁺ or less. Discharging each of the power storage element modules in a power storage device including a plurality of power storage element modules each having a Si-based negative electrode connected in series so that the negative electrode potential is nobler than the negative electrode potential in the region. , The control method according to any one of claims 1 to 3. 5. The control method according to claim 1, wherein when a predetermined condition is met, the discharge is performed while controlling the voltage so that the negative electrode potential is nobler than the negative electrode potential in the region. A control device including a control unit that discharges a negative electrode potential to be nobler than a negative electrode potential in a region where a transient voltage drop occurs in a power storage element having a Si-based negative electrode. A computer program that causes a computer to perform a process of discharging a power storage element having a Si-based negative electrode so that the negative electrode potential becomes nobler than the negative electrode potential in a region where a transient voltage drop occurs.

Images