JP2022086167A - Lithium-ion secondary battery control method - Google Patents

Abstract

To provide a battery control method to determine an SOC use range of a lithium-ion secondary battery, not limited to situations where a long charge/discharge time can be ensured.SOLUTION: A control method for a secondary battery 2 equipped with a negative electrode including graphite and a metal active material includes controlling charging and discharging of the secondary battery 2, calculating a voltage response to an alternating current input or a current response to an alternating voltage input at a time of stopping charging/discharging, and determining a use range (SOC range of use) of the state of charge (SOC) of the secondary battery 2 on the basis of the difference in responsiveness between the discharge voltage response, which is the voltage response on the discharge side, and the charge voltage response, which is the voltage response on the charge side, or the discharge current response, which is the current response on the discharge side, and the charge current response, which is the current response on the charge side.SELECTED DRAWING: Figure 7

Description

The present invention relates to a control method for determining the SOC usage range of a lithium ion secondary battery.

Conventionally, a charge / discharge control method for changing a voltage range for charge / discharge according to a deterioration state of a lithium ion secondary battery has been known (Patent Document 1). In the charge / discharge control method described in Patent Document 1, battery information regarding the charge / discharge state of the lithium ion battery is acquired, and the battery voltage with respect to the discharge capacity Q of the lithium ion battery and the change amount dQ of the discharge capacity Q based on the battery information. A Q-dV / dQ curve showing the relationship with dV / dQ showing the rate of change in V dV is calculated, and the deterioration state of the lithium ion battery is determined based on the Q-dV / dQ curve. Then, based on the determination result of the deterioration state, the voltage range for charging / discharging of the lithium ion battery is changed.

International Publication No. 2015/025402

However, in the above charge / discharge control method, it is necessary to discharge at a low rate in order to obtain a Q-dV / dQ curve, so the voltage range for charge / discharge is changed unless a long discharge time can be secured. There is a problem that it cannot be done.

An object to be solved by the present invention is to provide a control method capable of determining the SOC usage range of a lithium ion secondary battery, not limited to a situation where a long charge / discharge time can be secured.

The present invention measures the voltage response to the AC current input or the current response to the AC voltage input when charging / discharging is stopped, and determines the discharge voltage response, which is the voltage response on the discharge side, and the charge voltage response, which is the voltage response on the charge side. The range of use of the charge state (SOC) of the lithium ion secondary battery based on the difference in responsiveness or the difference in responsiveness between the discharge current response, which is the current response on the discharge side, and the charge current response, which is the current response on the charge side. The above problem is solved by determining (SOC usage range).

According to the present invention, the SOC usage range of the lithium ion secondary battery can be determined not only in a situation where a long charge / discharge time can be secured.

FIG. 1 is a block diagram showing a battery control system for a secondary battery according to the present embodiment. FIG. 2 shows a perspective view of the secondary battery before assembly and a plan view of the secondary battery. FIG. 3 is a graph showing the characteristics of the capacity retention rate with respect to the number of cycles of the secondary battery. FIG. 4 shows the capacity retention rate when the SOC usage range is 50 to 100% and the capacity retention rate when the SOC usage range is 0 to 100% for the secondary battery provided with the Gr / SiO negative electrode. It is a graph which shows. FIG. 5 (a) is a graph showing the responsiveness of the voltage response to the AC current input (triangle wave), and FIG. 5 (b) is a graph showing the characteristics of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) with respect to the SOC. FIG. 6A is a graph showing the responsiveness of the voltage response to an AC current input (square wave), and FIG. 6B is a graph showing the characteristics of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) with respect to the SOC. .. FIG. 7 is a flowchart showing a procedure of control processing in the system for determining the SOC usage range in the battery control system of the secondary battery according to the first embodiment. FIG. 8 is a flowchart showing a subflow of the control process in step S2 shown in FIG. 7. FIG. 9 is a flowchart showing a procedure of control processing in the system for determining the SOC usage range in the battery control system of the secondary battery according to the second embodiment. FIG. 10 is a flowchart showing a subflow of the control process in step S2'shown in FIG. FIG. 11 is a flowchart showing a procedure of control processing in the system for determining the SOC usage range in the battery control system of the secondary battery according to the third embodiment. FIG. 12 is a graph for explaining the relationship between the SOC size estimated by the control process of step 32 shown in FIG. 11 and the charge / discharge of the secondary battery 2. FIG. 13A is a graph showing the measurement results in the examples, and is a graph showing the responsiveness of the voltage response, and FIG. 13B is a graph showing the amplitude of the voltage response to the SOC (ΔV _{_d} , ΔV _{_c} ). 13 (c) is a graph showing the measurement result of the voltage response amplitude ratio (ΔV _{_d} / ΔV _{_c} ) with respect to the SOC, and FIG. 13 (d) is the graph showing the measurement result of the voltage response with respect to the SOC. It is a graph which shows the measurement result of (ΔV _{_d} − ΔV _{_c} ).

<< First Embodiment >>
An embodiment of a control device and a control method for determining the SOC usage range of the lithium ion secondary battery according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a battery control system including an embodiment of the battery control device according to the present invention. As shown in FIG. 1, the battery control system according to the present embodiment is a system for controlling the charge / discharge of the secondary battery 2 and determining the SOC usage range of the secondary battery 2. The battery control system includes a battery control device 1 and a secondary battery 2. The battery control device 1 may include a charging device or the like (not shown in FIG. 1).

The battery control device 1 includes a controller 10, a voltage sensor 11, a current sensor 12, and a DCDC converter 13. The controller 10 is a battery control unit (BCU). The controller 10 manages the state of the secondary battery 2 based on the detected voltage detected by the voltage sensor 11 and / or the detected current detected by the current sensor 12, and according to the state of the secondary battery 2. The SOC usage range of the secondary battery 2 is determined. The controller 10 is composed of a memory such as a ROM or RAM, a processor such as a CPU, and the like.

The voltage sensor 11 is a sensor for detecting the voltage between the terminals of the secondary battery 2. The voltage sensor 11 is connected between the wiring connected to the positive electrode and the negative electrode of the secondary battery 2. The current sensor 12 is a sensor for detecting the input / output current of the secondary battery 2. The current sensor 12 is connected to the wiring connected to the positive electrode or the negative electrode of the secondary battery 2. The voltage sensor 11 and the current sensor 12 detect the state of the battery, and output the detected value to the controller 10.

The DCDC converter 13 is a power conversion device that converts the voltage input from the secondary battery 2 into a predetermined voltage and outputs the power to a load such as a motor. Further, the DCDC converter 13 is also a power conversion device that converts a voltage input from a load such as a motor or a charging device into a predetermined voltage and outputs power to the secondary battery 2. The DCDC converter 13 is controlled by the controller 10. A secondary battery 2 is connected to the input side of the DCDC converter 13, and a load is connected to the output side of the DCDC converter 13. The load is a power grid or the like. That is, the secondary battery 2 is connected to the load via the DCDC converter 13.

The secondary battery 2 is, for example, a lithium ion secondary battery. The secondary battery 2 of this type exemplifies a negative electrode active material using an active material having a plurality of charge / discharge regions in which the charge / discharge potential changes stepwise with the insertion / desorption of lithium ions. Can be done. As such an active material, a graphite-based active material containing a graphite structure is suitable. Therefore, in the embodiment shown below, the present invention will be described by exemplifying a lithium ion secondary battery including a negative electrode containing graphite and a metal active material. In the following description, the structure and materials of the secondary battery 2 to be an electrolytic solution lithium ion secondary battery will be described, but the secondary battery 2 may be an all-solid-state lithium ion secondary battery. Hereinafter, the secondary battery 2 will be described by taking a laminated battery (laminated cell) as an example. The secondary battery 2 is a square battery (square cell) or a cylindrical battery (cylinder). It may be a type cell).

FIG. 2 shows a perspective view of the secondary battery 2 before assembly and a plan view of the secondary battery 2. As shown in FIG. 2 (а), the secondary battery 2 includes a positive electrode layer 21, a negative electrode layer 22, a separator 23, a positive electrode tab 24 connected to the positive electrode layer 21, and a negative electrode connected to the negative electrode layer 22. It includes a tab 25, an upper exterior member 26, and a lower exterior member 27. The power generation element composed of the positive electrode layer 21, the negative electrode layer 22, and the separator 23, the positive electrode tab 24, and the negative electrode tab 25 are housed in a state of being sealed by the upper exterior member 26 and the lower exterior member 27.

The positive electrode layer 21 is formed by adding a positive electrode active material, a conductive agent such as carbon black, a binder such as polyvinylidene fluoride, and an organic solvent such as N-methyl-2-pyrrolidone to prepare a slurry to prepare aluminum or the like. It is formed by applying it to the main surface of a part of the positive electrode side current collector, which is the metal leaf of the above, and drying and pressing it. The positive electrode active material is not particularly limited, but is, for example, a lithium composite oxide such as lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium cobalt oxide (LiCoO ₂ ), LiFePO ₄ or LiMnPO ₄ . And so on.

The negative electrode active material layer constituting the negative electrode layer 22 includes a negative electrode active material in which at least two types of active materials of graphite (carbon) and metal are mixed, an aqueous binder such as styrene butadiene rubber, and water as a solvent. Is mixed, a slurry is prepared, applied to a part of the main surface of the negative electrode side current collector, which is a metal foil such as copper, dried and pressed. Examples of the metal contained in the negative electrode active material include metals having Si, Sn, Sb, Pb, Al, Ge and the like as main elements, and compounds of metals of these main elements.

The separator 23 prevents a short circuit between the positive electrode layer 21 and the negative electrode layer 22 described above, and may have a function of holding an electrolyte. This separator is a microporous membrane composed of, for example, polyolefins such as polyethylene (PE) and polypropylene (PP), and when an overcurrent flows, the heat generated by the separator closes the pores of the layer and causes current to flow. It also has a function of blocking.

The electrolytic solution contained in the secondary battery 2 is a liquid in which a lithium salt such as lithium borofluoride (LiBF ₄ ) or lithium hexafluorophosphate (LiPF ₆ ) is dissolved as a solute in an organic liquid solvent. Examples of the organic liquid solvent constituting the electrolytic solution include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like. Ester-based solvents such as methyl formate (MF), methyl acetate (MA), and methyl propionate (MP) can be mentioned, and these can be mixed and used.

For the positive electrode tab 24 and the negative electrode tab 25, aluminum foil, aluminum alloy foil, copper foil, nickel foil, or the like can be used. The positive electrode tab 24 is bonded to the current collector of the positive electrode layer 21, and the negative electrode tab 25 is bonded to the negative electrode layer 22.

As shown in FIG. 2 (а), the positive electrode layer 21 and the negative electrode layer 22 are laminated via the separator 23, and a power generation element is formed by these. Then, the power generation element is housed in the upper exterior member 26 and the lower exterior member 27 so that the surfaces of the positive electrode layer 21 and the negative electrode layer 22 are covered. The upper exterior member 26 and the lower exterior member 27 are flexible, for example, a resin film such as polyethylene or polypropylene, or a resin-metal thin film laminate in which both sides of a metal foil such as aluminum are laminated with a resin such as polyethylene or polypropylene. It is made of a material having. Then, the electrolytic solution is injected into the battery, and the positive electrode tab 24 and the negative electrode tab 25 are led out to the outside, and the periphery of the exterior members 26 and 27 is heat-sealed and sealed to be secondary. The battery 2 is configured.

The secondary battery 2 is electrically connected to the charging device. The charging device connected to the secondary battery 2 is, for example, a device for charging the secondary battery 2 mounted on an electric vehicle or a hybrid vehicle. Charging of the in-vehicle secondary battery 2 is performed by taking out the charging cable of the charging device, attaching the charging gun at the tip of the charging cable to the connector of the charging port of the vehicle, and then operating the charging start switch. The controller 10 controls the DCDC converter 13 and the charging device, respectively, so that the charging state of the secondary battery 2 becomes the target charging state while managing the charging state (State of Charge: SOC) of the secondary battery 2. do.

The secondary battery 2 is electrically connected to a load such as a motor. The load is a device that operates using the electric power of the secondary battery 2, and is a motor that is a drive source of the vehicle, auxiliary equipment such as an air conditioner and a light, and the like. The discharge of the secondary battery 2 is executed under the control of the controller 10 by a system request or an external power request. The system request corresponds to a command from an in-vehicle computer such as an ECU while the vehicle is running. Regarding the power request from the outside, for example, when the air conditioner is operated before the vehicle is driven by the timer setting by the command from the outside device such as the mobile terminal so that the temperature inside the vehicle becomes appropriate at the start of the vehicle running, the outside of the vehicle. The command from the device corresponds to the power request from the outside.

Further, the secondary battery 2 mounted on the electric vehicle or the hybrid vehicle may be used for the Vehicle Grid Integration (VGI). VGI is a technology for connecting an electric vehicle or a hybrid vehicle equipped with a secondary battery 2 to a grid and supplying the electric power stored in the secondary battery 2 to the grid (load) via a power grid.

Next, the deterioration characteristics of the lithium ion secondary battery 2 and the SOC usage range will be described. When a mixture of graphite and a metal active material is used for the negative electrode as in the present embodiment, when the secondary battery 2 is charged and discharged within the SOC usage range in which the contribution of the metal active material is large, the metal activity is activated. Deterioration of substances is accelerated. FIG. 3 is a graph showing the characteristics of the capacity retention rate with respect to the number of cycles of the secondary battery 2. The number of cycles is the number of times the SOC is charged and discharged between 0% and 100%. The capacity retention rate represents the degree of deterioration when the battery capacity of the secondary battery 2 in the initial state is 1.0. In FIG. 3, graph а shows the characteristics of the secondary battery 2 provided with a negative electrode (hereinafter, also referred to as Gr negative electrode) containing graphite without containing a metal active material as the negative electrode active material. Graph b shows the characteristics of the secondary battery 2 provided with a negative electrode (hereinafter, also referred to as Gr / SiO negative electrode) containing a mixture of graphite and metal as the negative electrode active material. The metal active material is a metal compound (SiO) containing Si as a main element. As shown in FIG. 3, as the number of cycles increases, the capacity retention rate of the secondary battery 2 provided with the Gr / SiO negative electrode becomes lower than the capacity retention rate of the secondary battery 2 provided with the Gr negative electrode. That is, the secondary battery 2 provided with the Gr / SiO negative electrode has a faster battery capacity.

The graph of FIG. 4 shows the capacity retention rate when the SOC usage range is 50 to 100% and the capacity when the SOC usage range is 0 to 100% with respect to the secondary battery 2 provided with the Gr / SiO negative electrode. It shows the maintenance rate. The characteristic when the SOC usage range is 50 to 100% is that the number of cycles is about 100, and the characteristic when the SOC usage range is 0 to 100% is that the number of cycles is about 50. The SOC usage range is a range in which the usable range of the secondary battery 2 is expressed by SOC, and the secondary battery 2 is charged and discharged so that the SOC of the secondary battery 2 is within the SOC usage range. As shown in FIG. 4, when the SOC usage range is set to 50 to 100%, even if the number of cycles is doubled as compared with the case where the SOC usage range is set to 0 to 100%, the SOC is used. The capacity retention rate when the usage range is 50 to 100% is larger than the capacity retention rate when the SOC usage range is 0 to 100%. That is, the secondary battery 2 provided with the Gr / SiO negative electrode can suppress a decrease in battery capacity by avoiding charging / discharging at a low SOC.

As described above, when the secondary battery 2 provided with the Gr / SiO negative electrode is charged and discharged in a low SOC usage range, the contribution of the metal active material becomes large and deterioration is promoted. Therefore, in order to suppress the deterioration of the secondary battery 2, it is necessary to charge and discharge within the SOC usage range in which the contribution of the metal active material is small. Further, since the SOC usage range in which the contribution of the metal active material is small changes according to the deterioration state of the secondary battery 2, it is necessary to detect the SOC usage range.

On the other hand, in the present embodiment, when the charging / discharging of the secondary battery 2 is stopped, the voltage response to the AC current input is measured, and the discharge voltage response, which is the voltage response on the discharge side, and the charge, which is the voltage response on the charge side, are measured. Based on the difference in responsiveness from the voltage response, the usage range (SOC usage range) of the charge state (SOC) of the lithium ion secondary battery is determined. As a result, it is possible to detect a range of SOC in which the contribution of the metal active material is large and avoid charging / discharging in the SOC range. In the present embodiment, as an index showing the difference in responsiveness between the discharge voltage response and the charge voltage response, the voltage amplitude ratio, which is the ratio between the amplitude of the discharge voltage response (ΔV _{_d} ) and the amplitude of the charge voltage response (ΔV _{_c} ). The value of (ΔV _{_d} / ΔV _{_c} ) is used. That is, the difference in responsiveness between the discharge voltage response and the charge voltage response is the difference between the values of the discharge voltage amplitude (ΔV _{_d} ) and the charge voltage amplitude (ΔV _{_c} ), and the ratios (ΔV _{_d} / ΔV _{_c,} ΔV _{_c} ). It can be indicated by / ΔV _{_d} ) or a difference (ΔV _{_d} − ΔV _{_c} , ΔV _{_c} − ΔV _{_d} ).

FIG. 5A is a graph showing the responsiveness of the voltage response to the AC current input (triangle wave). Graph a in FIG. 5A shows an input value of an alternating current to the secondary battery 2, and graph b shows a voltage response to the alternating current. However, the voltage value shown in FIG. 5A shows the difference between the voltage value generated by the alternating current and the cell voltage in the hibernation state of the secondary battery 2. The mass ratio of Gr to SiO of the Gr / SiO negative electrode is 95: 5. Further, FIG. 5A shows the responsiveness of the voltage response to the AC current input when the SOC is 10%. Specifically, when a triangular wave having a frequency of 2 Hz and a current amplitude of 4 mA is input for 5 seconds. It shows the voltage change of.

As shown in FIG. 5A, when an alternating current is input to the secondary battery 2, a voltage response to the alternating current can be obtained. _{ΔV_d} (n) (n is a positive integer, and in this example n = 4) is the value of the discharge voltage at the apex of the discharge side (downwardly convex side) in FIG. 5A, and the discharge It shows the amplitude of the voltage response. On the other hand, _{ΔV_c} (n) is the value of the discharge voltage at the apex on the charging side (upwardly convex side), and indicates the amplitude of the charging voltage response. _{ΔV_c} (n) and _{ΔV_d} (n) are values after taking the difference from the cell voltage in the hibernation state of the secondary battery 2.

As the discharge voltage amplitude ( _{ΔV_d} ), the average value of _{ΔV_d} (n) in FIG. 5 (a) can be used, and similarly, the charge voltage amplitude ( _{ΔV_c} ) is shown in FIG. 5 (a). The average value of _{ΔV_c} (n) in the medium can be used. In this example, the charge voltage amplitude ( _{ΔV_c} ) and the discharge voltage amplitude ( _{ΔV_d} ) can be calculated from _{ΔV_c} (n) and _{ΔV_d} (n) at four locations. Then, the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) can be calculated from the calculated charge voltage amplitude ( _{ΔV_c} ) and discharge voltage amplitude ( _{ΔV_d} ).

FIG. 5B is a graph showing the characteristics of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) with respect to SOC. Here, in addition to the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) in the case of SOC (10%) calculated from FIG. 5 (a) above, the voltage amplitude ratio in the case of SOC (30%, 50%) ( _{ΔV_d} / _{ΔV_c} ) is also shown. As shown in FIG. 5B, the secondary battery 2 provided with the Gr / SiO negative electrode has a tendency that the value of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) increases as the SOC value decreases. ing. That is, in the SOC range in which SiO greatly contributes to charge / discharge, the discharge voltage amplitude ( _{ΔV_d} ) is larger than the SOC range in which Gr contributes with respect to the charge voltage amplitude ( _{ΔV_c} ).

Within the usage range of SOC where the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is larger than the threshold value (1.1), when the secondary battery 2 is charged and discharged, the contribution of SiO is large within the usage range of SOC. Since the secondary battery 2 is charged and discharged, deterioration of the metal active material is promoted. That is, the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is calculated, and the SOC range in which the calculated voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is less than the voltage amplitude ratio threshold is determined as the SOC usage range. As a result, it is possible to detect a range of SOC in which the contribution of the metal active substance is large and avoid charging / discharging in the SOC range.

Note that FIGS. 5A and 5B illustrate the case where the AC current waveform is a triangular wave, but the AC current waveform is not limited to this. The above-mentioned correlation between the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) and SOC is also established, for example, when the waveform of the alternating current is a square wave. FIG. 6A is a graph showing the responsiveness of the voltage response to the AC current input (square wave), and shows the voltage change when the AC current of FIG. 5A is a square wave. Further, FIG. 6B is a graph showing the characteristics of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) with respect to the SOC.

Even in such a case, as shown in FIG. 6B, the secondary battery 2 tends to have a larger value of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) as the SOC value becomes smaller. is doing. In the case of FIG. 6 (b), the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is larger than 1.1 in the range of SOC (about 21%) or less. Then, when the secondary battery 2 is charged and discharged within the usage range of the SOC in which the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is larger than the threshold value (1.1), the SOC having a large contribution of SiO is used. Since the secondary battery 2 is charged and discharged within the range, deterioration of the metal active material is promoted. Although not shown in particular, the waveform of the alternating current may be a sine wave.

In the present embodiment, the controller 10 measures the voltage response to the AC current input when the charging / discharging of the secondary battery 2 is stopped, and the discharge voltage response which is the voltage response on the discharge side and the charge voltage which is the voltage response on the charge side. Based on the difference in responsiveness from the response, the usage range (SOC usage range) of the charge state (SOC) of the secondary battery 2 is determined. Hereinafter, a method of determining the SOC usage range will be described based on the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) calculated as a value indicating the difference in responsiveness and the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ). FIG. 7 is a flowchart showing a procedure of control processing in a system for determining an SOC usage range. The upper limit of the SOC usage range (upper limit SOC) is set in advance, and is set to, for example, 100% or 80%. The upper limit SOC may be changed depending on the specification application of the secondary battery 2, the degree of deterioration, and the like.

In step S1, the controller 10 turns on a switch (not shown) connected between the secondary battery 2 and the power grid to connect the secondary battery 2 to the power grid.

In step S2, the controller 10 calculates the charge voltage amplitude ( _{ΔV_c} ) and the discharge voltage amplitude ( _{ΔV_d} ). FIG. 8 is a flowchart showing a subflow of the control process in step S2. The controller 10 calculates the charge voltage amplitude ( _{ΔV_c} ) and the discharge voltage amplitude ( _{ΔV_d} ) by executing the control processes of steps S21 to 26 shown in FIG. In addition to the control processing in steps S21 to 26, the controller 10 uses the voltage sensor 11 and the current sensor 12 to detect the voltage and current of the secondary battery 2 in a predetermined cycle. The shorter the detection cycle (sample rate), the higher the accuracy, but it is set to, for example, 1 second (1 Hz). The battery temperature may be any temperature, but the lower the battery temperature, the larger the voltage response amplitude (ΔV), and the higher the battery temperature, the smaller the voltage response amplitude (ΔV).

In step S21, the controller 10 prohibits charging / discharging for 1 minute or more after connecting the secondary battery 2 to the power grid, and puts the secondary battery 2 into a hibernation state. If the secondary battery has been in a dormant state for 1 minute or more before being connected to the power grid, it is not necessary to provide the hibernation after connecting to the power grid in step S1. The rest time of 1 minute or more is only an example, and the rest time may be, for example, 10 seconds or more. After the pause time has elapsed, in step S22, the controller 10 stores the cell voltage V_0 (opening voltage) of the secondary battery 2 in the pause state in the memory.

In step S23, the controller 10 inputs an alternating current for n cycles (n is a positive integer) to the secondary battery 2. The alternating current input here may have the same amplitude and waveform on the discharge side and the charge side. The waveform of the alternating current may be any waveform as long as the waveforms on the charging side and the discharging side are symmetric, and may be, for example, a triangular wave, a square wave, or a sine wave. Further, the frequency of the alternating current may be any value as long as it is a value within the band in which the charge / discharge reaction of SiO appears. Further, the measurement cycle (n) may be any integer, and may be a peak value for one cycle. Further, the current value may be any value, but for example, if it is 0.1 C, sufficient accuracy can be ensured. Further, in step S23, the alternating current may be used to discharge the battery first and then charge the battery, or to charge the battery first and then discharge the battery.

Next, in step 24, the amplitude of the voltage response on the discharge side of each cycle ( _{V_d} (n)) and the amplitude of the voltage response on the charge side of each cycle ( _{V_c} (n)) are measured, and the voltage amplitude is measured. ( _{V_d} (n), _{V_c} (n)) is stored in the memory. At this time, the value of the amplitude of the voltage response may be measured for each of a plurality of cells or for each cell, but if it is measured for each cell, the accuracy can be further improved. ..

In step S25, the controller 10 calculates the mean value of each of the voltage amplitudes ( _{V_d} (n), _{V_c} (n)), thereby performing the mean value ( _{V_d} ) of the voltage response amplitude on the discharge side and the voltage response. The average value ( _{V_c} ) of the amplitude of the voltage response on the charging side is calculated. Next, in step 26, the discharge voltage amplitude ( _{ΔV_d} = V_0- _{V_d} ) and the charge voltage amplitude ( _{ΔV_c} = V_c- _{V_0} ) are calculated.

Returning to FIG. 7, after calculating the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) in step S2, the controller 10 calculates the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) in step S3. Then, the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is compared with the voltage amplitude ratio threshold, and it is determined whether or not the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is less than the voltage amplitude ratio threshold. The voltage amplitude ratio threshold value is a threshold value for setting the lower limit value of the SOC usage range, and is set in advance. The voltage amplitude ratio threshold value may be set according to the permissible deterioration rate and / or the permissible degree of deterioration depending on the intended use of the secondary battery 2. The voltage amplitude ratio threshold may be set according to the specifications of the negative electrode active material (ratio of metal active material, type of metal used for metal active material, etc.). Further, the voltage amplitude ratio threshold value may be set according to the detection accuracy of the voltage and / or the current of the secondary battery 2. In this embodiment, the voltage amplitude ratio threshold is set to 1.1 as an example.

When the calculated voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is lower than the voltage amplitude ratio threshold value (1.1), the controller 10 executes the control processing of steps S4 to S8. On the other hand, when the calculated voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is equal to or greater than the voltage amplitude ratio threshold value (1.1), the controller 10 executes the control processing of steps S9 to S13.

In step S4, the controller 10 discharges the secondary battery 2. When the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) of the secondary battery 2 is lower than the voltage amplitude ratio threshold value (1.1), the SOC of the secondary battery 2 is higher than the lower limit of the SOC usage range, so that the voltage amplitude The SOC is lowered in order to determine the lower limit of the SOC usage range corresponding to the ratio threshold (1.1). In step S5, the controller 10 stops discharging. In step S6, the controller 10 recalculates the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ). The calculation method of the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) is the same as the calculation method in the control process of step S2.

In step S7, the controller 10 compares the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) with the voltage amplitude ratio threshold value (1.1), and the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is the voltage amplitude ratio threshold value (1). .1) Determine if it is greater than or equal to. When the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is lower than the voltage amplitude ratio threshold value (1.1), the controller 10 returns the control processing flow to step S4 and discharges the secondary battery 2. That is, by repeatedly executing the control processes of steps S4 to S7, the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is set to the voltage amplitude ratio threshold value (1) so that the SOC approaches the lower limit of the SOC usage range from the high SOC side. 1. Bring it closer to 1).

When the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is equal to or greater than the voltage amplitude ratio threshold value (1.1), in step S8, the controller 10 sets the current SOC to the lower limit value (lower limit SOC) of the SOC usage range. decide. That is, the controller 10 determines the SOC when the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) reaches the voltage amplitude ratio threshold value (1.1) as the lower limit SOC of the SOC usage range.

In step S9, the controller 10 charges the secondary battery 2. When the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) of the secondary battery 2 is equal to or greater than the voltage amplitude ratio threshold value (1.1), the SOC of the secondary battery 2 is equal to or less than the lower limit of the SOC usage range. The SOC is increased in order to determine the lower limit of the SOC usage range corresponding to the voltage amplitude ratio threshold (1.1). Since the charging in the control process of step S9 is out of the SOC usage range, the charging current is reduced so that the deterioration of the secondary battery 2 is not promoted. For example, the charging current rate may be set to 0.5 C or less. In step S10, the controller 10 stops charging the secondary battery 2. Next, in step 11, the controller 10 calculates the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ). The calculation method of the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) is the same as the calculation method in the control process of step S2.

In step S12, the controller 10 compares the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) with the voltage amplitude ratio threshold value (1.1), and the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is the voltage amplitude ratio threshold value (1). It is determined whether or not it is less than 1). When the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is equal to or greater than the voltage amplitude ratio threshold value (1.1), the controller 10 returns the control processing flow to step S9 to charge the secondary battery 2. That is, by repeatedly executing the control processes of steps S9 to S12, the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is set to the voltage amplitude ratio threshold value (1) so that the SOC approaches the lower limit of the SOC usage range from the low SOC side. 1. Bring it closer to 1).

If the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is less than the voltage amplitude ratio threshold (1.1), in step S13, the controller 10 sets the current SOC to the lower limit (lower limit SOC) of the SOC usage range. decide. That is, the controller 10 determines the SOC when the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) reaches the voltage amplitude ratio threshold value (1.1) as the lower limit SOC of the SOC usage range. Then, the controller 10 ends the flow of the control process for determining the SOC usage range. As a result, the controller 10 determines the SOC usage range based on the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ).

Then, the controller 10 stores the SOC usage range determined by the control processing in steps S8 and S13 in the memory in association with the calculated voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ). The controller 10 controls charging and / or discharging of the secondary battery 2 so that the SOC is within the SOC usage range stored in the memory during normal use of the secondary battery 2. The SOC usage range of the secondary battery 2 is a target range for suppressing the deterioration rate of the secondary battery 2, and the secondary battery 2 may be charged and discharged outside the SOC usage range. Further, in order to determine the SOC usage range of the secondary battery 2, charging / discharging may be performed outside the SOC usage range previously determined.

By the way, in order to increase the battery capacity of the lithium ion secondary battery, a mixture of graphite and a metal active material is used for the negative electrode as the negative electrode active material. However, if charging and discharging are performed in the SOC range in which the contribution of the metal active material of the negative electrode is large, deterioration is promoted. In the present embodiment, the range of SOC in which the contribution of the metal active material of the negative electrode is large can be detected with high accuracy and in a short time. Then, since the SOC usage range is determined while avoiding the SOC range in which the contribution of the metal active material of the negative electrode is large, charging / discharging is performed within the SOC range in which the deterioration of the metal active material is small. As a result, it is possible to suppress a decrease in the capacity retention rate and improve the cycle characteristics.

As described above, in the present embodiment, the charging / discharging of the secondary battery 2 is controlled, and the discharge voltage amplitude ( _{ΔV_d} ) and the charging voltage amplitude ( _{ΔV_c} ) are calculated when the charging / discharging of the secondary battery 2 is stopped. The SOC usage range of the secondary battery 2 is determined based on the difference _between the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude (ΔV_c). The difference _between the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) corresponds to the voltage amplitude ratio ( _{ΔV_d} / ΔV_c). As a result, the range of SOC in which the metal active material of the negative electrode contributes can be grasped in a short time, and charging / discharging in that range can be avoided. That is, the SOC usage range of the secondary battery 2 can be determined not only in a situation where a long charge / discharge time can be secured. Further, the SOC usage range is set so as to avoid the SOC range in which the contribution of the metal active material of the negative electrode is large. Since the secondary battery 2 is charged and discharged within the SOC usage range during normal use, it is possible to suppress a decrease in the capacity of the lithium ion secondary battery due to deterioration of the metal active material of the negative electrode.

In addition, as another method, it is conceivable to detect the SOC range in which the contribution of the metal active material is large from the difference in the measured values of the EIS (Electro-chemical Impedance Spectroscopy) measurement during charging and discharging. In EIS measurement, the difference in the amplitude of the AC impedance on the charging side and the discharging side is not taken into consideration, so even if the measurement is performed in the charged / discharged stopped state, the AC impedance is only uniquely determined, and the presence or absence of the contribution of the metal active material is present. Cannot be determined. Therefore, when using EIS measurement, it is necessary to make a judgment by looking at the difference in measurement results during charging / discharging, and it is necessary to perform two measurements. On the other hand, in the present embodiment, the presence or absence of the contribution of the metal active material can be determined only by measuring the responsiveness of the voltage response at least once in the charge / discharge stop state. It is possible to discriminate the difference _between the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude (ΔV_c) in a time of / 2 or less.

Further, in the present embodiment, the value indicating the difference _between the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude (ΔV_c) (corresponding to the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} )) is less than the voltage amplitude ratio threshold. The charging and / or discharging of the secondary battery 2 is controlled within the SOC usage range. As a result, charging / discharging can be controlled while avoiding the range of SOC in which the contribution of the metal active material of the negative electrode is large. As a result, it is possible to suppress a decrease in the capacity of the lithium ion secondary battery due to deterioration of the metal active material of the negative electrode.

Further, in the present embodiment, the metal active material of the negative electrode contains Si. As a result, when Si is used as the metal active material in order to increase the battery capacity, charging and discharging can be performed while avoiding the SOC range in which the contribution of the metal active material of the negative electrode is large. It is possible to suppress a decrease in the capacity of the next battery.

Further, in the present embodiment, the SOC usage range is determined in a state where the secondary battery 2 is connected to the power grid. As a result, while the secondary battery 2 is connected to the power grid, the range of SOC in which the contribution of the metal active material of the negative electrode is large is detected, and the range of SOC in which the contribution of the metal active material of the negative electrode is large is avoided. It can be charged and discharged in the lowest possible SOC range. As a result, the SOC usage range can be set to the optimum range while suppressing both the deterioration of the metal active material and the storage deterioration that is promoted as the SOC is higher.

In this embodiment, by repeatedly executing the control processes of steps S4 to S7 shown in FIG. 7, the SOC is brought closer to the lower limit of the SOC usage range from the high SOC side. At this time, as the discharge time in the control process of step S4 is shortened, the discharge capacity is finely chopped, so that the time required to determine the SOC usage range becomes longer, but the accuracy becomes higher.

Further, in the present embodiment, the discharge in the control process of step S4 may be separated by SOC instead of time. For example, for each SOC (1%), the discharge is divided, the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) are calculated, and the SOC usage range is determined. That is, the SOC usage range is adjusted in SOC (1%) per unit. Therefore, even if there is an error in the calculation accuracy of the SOC usage range, the range of SOC in which the contribution of the metal active material is large can be suppressed to less than SOC (1%) due to the error.

Further, in the present embodiment, after the control process in step S6, the SOC may be charged by a predetermined amount equivalent to the SOC, and the SOC after charging may be determined as the lower limit value of the SOC usage range. The predetermined SOC is set to, for example, 5%. Further, in the modified example of this embodiment, the predetermined SOC may be set to 1%. As a result, the SOC with a margin equivalent to a predetermined SOC can be determined as the lower limit of the SOC usage range with respect to the SOC range in which the contribution of the metal active material is large, so that the metal active material of the negative electrode is deteriorated. It is possible to suppress the accompanying decrease in the capacity of the lithium ion secondary battery.

In this embodiment, by repeatedly executing the control processes of steps S9 to S12 shown in FIG. 7, the SOC is brought closer to the lower limit of the SOC usage range from the low SOC side. At this time, as the charging time in the control process of step S9 is shortened, the charging capacity is finely chopped, so that the time required to determine the SOC usage range becomes longer, but the accuracy becomes higher.

Further, in the present embodiment, the charging in the control process of step S9 may be separated by SOC instead of time. For example, the charge is divided for each SOC (1%), the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) are calculated, and the SOC usage range is determined. That is, the SOC usage range is adjusted in SOC (1%) per unit. Therefore, even if there is an error in the calculation accuracy of the SOC usage range, the range of SOC in which the contribution of the metal active material is large can be suppressed to less than SOC (1%) due to the error.

Further, in the present embodiment, after the control process in step S12, the SOC may be charged by a predetermined amount equivalent to the SOC, and the SOC after charging may be determined as the lower limit value of the SOC usage range. The predetermined SOC is set to, for example, 5%. Further, in the modified example of this embodiment, the predetermined SOC may be set to 1%. As a result, the SOC with a margin equivalent to a predetermined SOC can be determined as the lower limit of the SOC usage range with respect to the SOC range in which the contribution of the metal active material is large, so that the metal active material of the negative electrode is deteriorated. It is possible to suppress the accompanying decrease in the capacity of the lithium ion secondary battery.

Further, as a modification of the present embodiment, in the control process of step S3, when the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is equal to or higher than the voltage amplitude ratio threshold value (1.1), the controller 10 is secondary. After the battery 2 is charged and the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) becomes less than the voltage amplitude ratio threshold value (1.1), the control processes of steps S4 to S8 are executed to determine the SOC usage range. You may.

In the present embodiment, in the controller 10, the value indicating the difference _between the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude (ΔV_c) is not limited to the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ), and the voltage amplitude. It may be a difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ). The controller 10 calculates the voltage amplitude difference (ΔV _d − ΔV _{_c} or ΔV _{_c −} ΔV _{_d} ) from the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude (ΔV _{_c} ), and the calculated voltage amplitude difference (ΔV _{_d} −). The SOC usage range of the secondary battery 2 may be determined based on ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ). Specifically, in the control flow of step S3, the controller 10 sets the difference _{between the discharge voltage amplitude (ΔV_d) and the charge voltage amplitude (ΔV_c) as the voltage amplitude difference (ΔV _d − ΔV _c or ΔV _c − ΔV _d ) .} ). Then, in step S3, step S7, and step S12, instead of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ), the controller 10 determines the calculated voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ) and the voltage. Compare with the amplitude difference threshold. The voltage amplitude threshold value is a preset threshold value similar to the voltage amplitude ratio threshold value. Then, in step S8 and step S13, the controller 10 sets the SOC when the calculated voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ) reaches the voltage amplitude difference threshold value as the lower limit of the SOC usage range. Decide on SOC.

As described above, in the present embodiment, the voltage between the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) is used as a value indicating the difference between the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ). The amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ) is calculated, and the SOC usage range of the secondary battery 2 is determined based on the calculated voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ). decide. As a result, the range of SOC in which the metal active material of the negative electrode contributes can be grasped in a short time, and charging / discharging in that range can be avoided. That is, the SOC usage range of the secondary battery 2 can be determined not only in a situation where a long charge / discharge time can be secured. Further, the SOC usage range is set so as to avoid the SOC range in which the contribution of the metal active material of the negative electrode is high. Since the secondary battery 2 is charged and discharged within the SOC usage range during normal use, it is possible to suppress a decrease in the capacity of the lithium ion secondary battery due to deterioration of the metal active material of the negative electrode.

Further, in SiO, the overvoltage on the charging side and the overvoltage on the discharging side are different. The difference in overvoltage during charging and discharging is divided into IR (electrolyte resistance, electrical resistance of active material, etc.) and overvoltage other than IR (charge transfer resistance, diffusion resistance, etc.), but the voltage amplitude difference (ΔV _{_d} − ΔV, etc.) Since IR can be offset by calculating _{_c} or ΔV _{_c} − ΔV _{_d} ), the SiO contribution range can be accurately determined even if an IR change due to deterioration or the like occurs. As a result, the SOC usage range contributed by SiO can be grasped more accurately, so that the lower limit of the SOC usage range can be expanded to the vicinity of the SOC usage range contributed by SiO, and the SOC usage range is further expanded. be able to.

As for the SOC usage range, the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) before deterioration may be calculated, and the initial value of the SOC usage range may be determined from the calculation result. The SiO contribution capacity is calculated from the theoretical capacity (mAh / g) of SiO and the amount of SiO used (g), and from the calculated SiO contribution capacity and the battery capacity of the secondary battery 2 before deterioration, mainly SiO before deterioration. The SOC range to which is contributed can be calculated. For example, if SiO contribution capacity / battery capacity = 15%, the SOC range (0 to 15%) is the SOC range in which the contribution of SiO is large. Then, the SOC range (0 to 15%) avoided (for example, 15 to 100%) is the SOC usage range.

Further, in the above example, the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) equivalent to SOC 15% before deterioration is calculated as the voltage amplitude ratio threshold, and after the deterioration of the secondary battery 2, the voltage amplitude ratio (ΔV _{_d} / ΔV) is calculated. The SOC in which _{_c} ) is the voltage amplitude ratio threshold is defined as the lower limit SOC of the SOC usage range. As a result, even before and after the deterioration of the secondary battery 2, charging and discharging can be performed while avoiding the range of SOC in which the contribution of the metal active material of the negative electrode is large.

The battery control system according to the present embodiment has the following application examples as examples other than VGI. As an example, in an electric vehicle using a secondary battery 2, an alarm threshold for sounding a battery level alarm is set for an SOC that is several percent higher than the lower limit of the SOC usage range. Then, when the SOC of the secondary battery 2 becomes low to the threshold value for an alarm during normal driving, an alarm is output to urge the user to charge the battery at an early stage.

As another example, when the SOC of the secondary battery 2 becomes low to the lower limit SOC of the SOC usage range, the discharge current of the secondary battery 2 may be suppressed by limiting the output torque of the motor. It should be noted that such an output limit does not always have to be applied, and when a limited condition is satisfied, for example, when a large acceleration performance is required (for example, when a torque equivalent to a full throttle is required). In addition, the secondary battery 2 may be used with the output limit released and the SOC being below the lower limit of the SOC usage range. As a result, the frequency of use within the SOC range in which the contribution of the metal active material of the negative electrode is large can be reduced, and deterioration of the secondary battery 2 can be suppressed.

As yet another example, it is also applicable when the secondary battery 2 is used as a stationary power source, or when a vehicle equipped with the secondary battery 2 is used as an external power source for indoor or outdoor use. In this case, the alarm may be set according to the lower limit SOC of the lower limit SOC usage range in the same manner as described above.

<< Second Embodiment >>
Next, the battery control system according to the second embodiment will be described. In the second embodiment, the current response of the secondary battery 2 to the AC voltage input is calculated, and based on the difference in responsiveness between the discharge current response, which is the current response on the discharge side, and the charge current response, which is the current response on the charge side. To determine the SOC usage range.

FIG. 9 is a flowchart showing a procedure of control processing in the system for determining the SOC usage range in the battery control system of the secondary battery according to the second embodiment. FIG. 10 is a flowchart showing a subflow of control processing in step S2'shown in FIG. In the present embodiment, the difference in responsiveness between the discharge current response and the charge current response is the current amplitude ratio (ΔI _{_d} ), which is the ratio between the discharge current response amplitude (ΔI _{_d} ) and the charge current response amplitude (ΔI _{_c} ). The value of / _{ΔI_c} ) is used to determine the SOC usage range. In the flowchart shown in FIG. 9, steps S2, S3, S6, S7, S11, and S12 using the voltage response of the flowchart of FIG. 7 are steps S2', S3', S6', S7', S11'using the current response. , S12'has been replaced. Hereinafter, steps S2', S3', S6', S7', S11', and S12'will be described in detail. The system has the same configuration as the first embodiment except for the steps different from the determination system according to the first embodiment, performs the same control as the first embodiment, and operates in the same manner as the first embodiment. Therefore, the description of the first embodiment is appropriately incorporated.

In step S2'in FIG. 9, the amplitude of the discharge current response ( _{ΔI_d} ) and the amplitude of the charge current response ( _{ΔI_c} ) are calculated. In this step S2', the controller 10 calculates the amplitude of the discharge current response ( _{ΔI_d} ) and the amplitude of the charge current response ( _{ΔI_c} ) by executing the control process of steps S21'to 24'shown in FIG. do.

In step S21', the controller 10 prohibits charging and discharging for 1 minute or more after connecting the secondary battery 2 to the power grid, and puts the secondary battery 2 into a hibernation state. If the secondary battery has been in a dormant state for 1 minute or more before being connected to the power grid, it is not necessary to provide the hibernation after connecting to the power grid in step S1. The rest time of 1 minute or more is only an example, and the rest time may be, for example, 10 seconds or more.

In step S22', the controller 10 inputs an AC voltage for n cycles (n is a positive integer) to the secondary battery 2. The AC voltage input here may have the same amplitude and waveform on the discharge side and the charge side. The waveform of the AC voltage may be any waveform as long as the waveforms on the charging side and the discharging side are symmetric, and may be, for example, a triangular wave, a square wave, or a sine wave. Further, the measurement cycle (n) may be any integer, and may be a peak value for one cycle. Further, the frequency of the AC voltage may be any value as long as it is a value within the band in which the charging / discharging reaction of SiO appears. Further, the voltage value may be any value, but for example, if it is 0.1 C, sufficient accuracy can be ensured. Further, in step S22', the AC voltage may be used to discharge the battery first and then charge the battery, or to charge the battery first and then discharge the battery.

In step S23', the controller 10 measures the amplitude of the current response on the discharge side in each cycle ( _{I_d} (n)) and the amplitude of the current response on the charge side in each cycle (I_c ₍ n)). The current amplitude ( _{I_d} (n), I_c ₍ n)) is stored in the memory. At this time, the value of the amplitude of the current may be measured for each of a plurality of cells or for each cell, but if it is measured for each cell, the accuracy can be further improved. ..

In step S24', the controller 10 calculates the average value of each from the stored current amplitudes ( _{I_d} (n), I_c ₍ n)), whereby the average value of the amplitude of the current response on the discharge side ( _{I_d} ) and the average value (I_c ₎ of the amplitude of the current response on the charging side are calculated. In the present embodiment, the average value ( _{I_d} ) is the amplitude of the discharge current response ( _{ΔI_d} ), and the average value (I_c) is _the amplitude of the charge current response ( _{ΔI_c} ).

Returning to FIG. 9, after calculating the discharge current response amplitude (ΔI _{_d} ) and the electric current response amplitude (ΔI _{_c} ) in step S2, the controller 10 calculates the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) in step S3. do. Then, the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is compared with the current amplitude ratio threshold, and it is determined whether or not the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is less than the current amplitude ratio threshold. The current amplitude ratio threshold value is a threshold value for setting the lower limit value of the SOC usage range, and is set in advance. The current amplitude ratio threshold value may be set according to the permissible deterioration rate and / or the permissible degree of deterioration depending on the intended use of the secondary battery 2. The current amplitude ratio threshold value may be set according to the specifications of the negative electrode active material (ratio of the metal active material, the type of metal used for the metal active material, etc.). Further, the current amplitude ratio threshold value may be set according to the voltage and / or current detection accuracy of the secondary battery 2. In this embodiment, the current amplitude ratio threshold is set to 1.1 as an example.

When the calculated current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is lower than the current amplitude ratio threshold value (1.1), the controller 10 executes the control processing of steps S4 to S8. On the other hand, when the calculated current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is equal to or greater than the current amplitude ratio threshold value (1.1), the controller 10 executes the control processing of steps S9 to S13.

Steps S4 and S5 are the same as those in the first embodiment. In step S6', the discharge current response amplitude ( _{ΔI_d} ) and the electric current response amplitude ( _{ΔI_c} ) are calculated by the same method as in step S2'. Then, in step S7', the controller 10 compares the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) with the current amplitude ratio threshold value (1.1), and the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is the current amplitude ratio. It is determined whether or not it is equal to or higher than the threshold value (1.1). When the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is lower than the current amplitude ratio threshold value (1.1), the controller 10 returns the control processing flow to step S4 and discharges the secondary battery 2. That is, by repeatedly executing the control processes of steps S4 to S7', the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is set to the current amplitude ratio threshold value (ΔI _d / ΔI _c) so that the SOC approaches the lower limit of the SOC usage range from the high SOC side. 1. Bring it closer to).

When the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is equal to or greater than the current amplitude ratio threshold value (1.1), in step S8, the controller 10 sets the current SOC to the lower limit value (lower limit SOC) of the SOC usage range. decide. That is, the controller 10 determines the SOC when the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) reaches the current amplitude ratio threshold value (1.1) as the lower limit SOC of the SOC usage range.

Steps S9 and S10 are the same as those in the first embodiment. In step S11', the discharge current response amplitude ( _{ΔI_d} ) and the electric current response amplitude ( _{ΔI_c} ) are calculated by the same method as in step S2'. Then, in step S7', the controller 10 compares the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) with the current amplitude ratio threshold value (1.1), and the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is the current amplitude ratio. It is determined whether or not it is less than the threshold value (1.1). When the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is equal to or greater than the current amplitude ratio threshold value (1.1), the controller 10 returns the control processing flow to step S9 to charge the secondary battery 2. That is, by repeatedly executing the control process of steps S9 to S12', the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is set to the current amplitude ratio threshold value (ΔI _d / ΔI _c) so that the SOC approaches the lower limit of the SOC usage range from the low SOC side. 1. Bring it closer to).

If the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is less than the current amplitude ratio threshold (1.1), in step S13, the controller 10 sets the current SOC to the lower limit (lower limit SOC) of the SOC usage range. decide. That is, the controller 10 determines the SOC when the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) reaches the current amplitude ratio threshold value (1.1) as the lower limit SOC of the SOC usage range. Then, the controller 10 ends the flow of the control process for determining the SOC usage range. As a result, the controller 10 determines the SOC usage range based on the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ).

Also in the second embodiment as described above, the same effect as that of the first embodiment can be obtained. In this embodiment, an example in which the value of the current amplitude ratio (ΔI _{_d} / _{ΔI_c} ) is used as the value indicating the difference in responsiveness between the discharge current response and the charge current response has been described, but the present invention is not limited to this. For example, a current amplitude difference (ΔI _{_d} − ΔI _{_c} or ΔI _{_c} − ΔI _{_d} ) may be used as a value indicating the difference. In this case, in steps S3', S6', and S12', the controller 10 calculates the current amplitude difference (ΔI _{_d} − ΔI _{_c} or ΔI _{_c} − ΔI _{_d} ) instead of the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ). do. Then, the controller 10 compares the calculated current amplitude difference (ΔI _{_d} − ΔI _{_c} or ΔI _{_c} − ΔI _{_d} ) with the current amplitude difference threshold value. The current amplitude difference threshold is a preset threshold similar to the current amplitude ratio threshold.

<< Third Embodiment >>
Next, the battery control system according to the third embodiment will be described. In the third embodiment, in order to make the time required for determining the SOC usage range even faster than that in the first embodiment, a part of the control process for determining the SOC usage range is changed. It should be noted that the system has the same configuration as that of the first embodiment except that it is different from the determination system according to the first embodiment in the points described below, and the same control as that of the first embodiment is carried out. It operates in the same manner as the above, and the description of the first embodiment is appropriately incorporated.

In the present embodiment, the controller 10 determines the SOC usage range at a predetermined timing, for example, at the end of charging / discharging of the secondary battery 2. Further, when the controller 10 determines the SOC usage range, the SOC of the secondary battery 2 is a value close to the lower limit SOC of the SOC usage range, and the controller 10 calculates the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ). A predetermined SOC range including the lower limit SOC of the SOC usage range is set. The predetermined SOC range (hereinafter referred to as the lower limit SOC determination range) is a range extended by a predetermined SOC (for example, ± 5%) to the plus side and the minus side with respect to the lower limit SOC of the SOC usage range. Then, when the current SOC is outside the lower limit SOC determination range, the controller 10 charges or discharges the secondary battery 2 so that the SOC of the secondary battery 2 is included in the lower limit SOC determination range. Then, after the SOC of the secondary battery 2 is within the lower limit SOC determination range, the controller 10 calculates the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ), and the SOC is based on the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ). Determine the range of use.

Hereinafter, the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) is calculated as a value indicating the difference in responsiveness between the discharge voltage response and the charge voltage response, and the SOC usage range is based on the calculated voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ). The control process for determining the voltage will be described. FIG. 11 is a flowchart showing a procedure of control processing in a system for determining an SOC usage range. In step S31, the controller 10 connects the secondary battery 2 to the power grid. In step S32, the controller 10 estimates the SOC of the secondary battery 2. The SOC may be estimated by, for example, a map calculation using a map showing the correlation between the open circuit voltage (OCV) and the SOC. The map is stored in the memory in the controller 10, and the open circuit voltage (SOC) corresponds to the battery voltage immediately before connecting the secondary battery 2 to the power grid.

In step S33, the controller 10 compares the estimated SOC with the previously determined lower limit SOC (SOC _{_0} ) of the SOC usage range plus a predetermined SOC (5%) (SOC _{_0} + 5%) and estimates. It is determined whether or not the SOC is larger than "SOC _{_0} + 5%". SOC _{_0} + 5% corresponds to the upper limit of the lower limit SOC determination range.

When the estimated SOC is larger than the upper limit value (SOC _{_0} + 5%) of the lower limit SOC determination range, in step S34, the controller 10 determines the secondary battery until the SOC reaches the upper limit value (SOC _{_0} + 5%). Discharge 2 After the SOC reaches the upper limit value (SOC _{_0} + 5%), in step S35, the controller 10 stops discharging. Next, in step S36, the controller 10 calculates the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ). The calculation method of the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) is the same as the calculation method in the control process of step S2 in the first embodiment. In step S37, the controller 10 compares the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) with the voltage amplitude ratio threshold value (1.1), and the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is the voltage amplitude ratio threshold value (1). .1) Determine if it is greater than or equal to. When the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is lower than the voltage amplitude ratio threshold value (1.1), in step S38, the controller 10 discharges the secondary battery 2. Next, in step S39, the discharge of the secondary battery is stopped. Then, the controller 10 re-executes the control processing of step S36 and step S37.

On the other hand, when the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is equal to or higher than the voltage amplitude ratio threshold value (1.1), in step S40, the controller 10 sets the current SOC to the lower limit value (lower limit) of the SOC usage range. Determined to SOC).

If it is determined in the control process of the comparison determination in step S33 that the estimated SOC is equal to or less than the upper limit value (SOC _{_0} + 5%) of the lower limit SOC determination range, the controller 10 is estimated in step S41. The SOC is compared with the value obtained by subtracting the predetermined SOC (5%) from the lower limit SOC (SOC _{_0} ) of the SOC usage range determined last time (SOC _{_0-5} %), and the estimated SOC is "SOC _{_0-5} ". % ”To determine if it is smaller than. SOC _{_0-5} % corresponds to the lower limit of the lower limit SOC determination range.

If the estimated SOC is smaller than the lower limit of the lower limit SOC determination range (SOC _{_0-5} %), in step S42, the controller 10 determines the SOC until the lower limit (SOC _{_0-5} %). Next, charge the battery 2. After the SOC reaches the lower limit (SOC _{_0-5} %), in step S43, the controller 10 stops charging. Next, in step S44, the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) are calculated. The calculation method of the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) is the same as the calculation method in the control process of step S2 in the first embodiment. In step S45, the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) and the voltage amplitude ratio threshold (1.1) are compared, and the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is the voltage amplitude ratio threshold (1.1). It is determined whether or not it is as follows. When the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is higher than the voltage amplitude ratio threshold value (1.1), in step S46, the controller 10 charges the secondary battery 2. Next, in step S47, charging of the secondary battery is stopped. Then, the controller 10 re-executes the control processing of step S44 and step S45.

On the other hand, when the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is equal to or less than the voltage amplitude ratio threshold value (1.1), in step S48, the controller 10 sets the current SOC to the lower limit value (lower limit) of the SOC usage range. Determined to SOC).

When it is determined in the control process of the comparison determination in step S41 that the estimated SOC is equal to or higher than the lower limit value (SOC _{_0-5} %) of the lower limit SOC determination range, that is, the estimated SOC is within the lower limit SOC determination range. If this is the case, in step S49, the controller 10 calculates the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ). The calculation method of the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) is the same as the calculation method in the control process of step S2 in the first embodiment.

In step S50, the controller 10 compares the calculated voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) with the voltage amplitude ratio threshold value (1.1), and calculates the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ). Is less than the voltage amplitude ratio threshold (1.1). When the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is less than the voltage amplitude ratio threshold value (1.1), the controller 10 discharges the secondary battery 2 in step S51. Then, the controller 10 executes the control processing of steps S52 to S57. The control process of steps S52 to S57 is the same as the control process of steps S35 to S40.

If it is determined in the comparison determination in step S50 that the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is equal to or greater than the voltage amplitude ratio threshold value (1.1), the controller 10 uses the secondary battery 2 in step S58. Charge. Then, the controller 10 executes the control processing of steps S59 to S64. The control process of steps S59 to S64 is the same as the control process of steps S43 to S48.

Then, the controller 10 stores the SOC usage range determined by the control processing of steps S40, S48, S57, and S64 in the memory in association with the calculated voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ). The controller 10 controls the charging / discharging of the secondary battery 2 so that the SOC is included in the SOC usage range stored in the memory during normal use of the secondary battery 2.

FIG. 12 is a graph for explaining the relationship between the SOC size estimated by the control process in step S32 and the charge / discharge of the secondary battery 2. As shown in FIG. 12, the lower limit SOC determination range is set to a predetermined SOC (± 5%) width centering on the lower limit value of the SOC usage range previously determined. When the estimated SOC is larger than the upper limit value (SOC _{_0} + 5%) of the lower limit SOC determination range, the secondary battery 2 is discharged, so that the SOC approaches the lower limit SOC determination range from the high SOC side (arrow H in FIG. 12). See). On the other hand, when the estimated SOC is smaller than the lower limit value (SOC _{_0-5} %) of the lower limit SOC determination range, the secondary battery 2 is charged, so that the SOC approaches the lower limit SOC determination range from the low SOC side (FIG. 12). See arrow L). Then, in the present embodiment, after the SOC is within the lower limit SOC determination range, the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) is calculated, and the current SOC usage range is calculated based on the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ). Is determined. As a result, the number of repetitions of the control loops of steps S36 to S39 and the control loops of steps S53 to S56 can be reduced.

As described above, in the present embodiment, the value (voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} )) indicating the difference in responsiveness between the discharge voltage response and the charge voltage response is associated with the determined SOC usage range. The charging and / or discharge of the secondary battery 2 is controlled so that the SOC is within the predetermined SOC range including the lower limit value of the SOC usage range determined last time, and the SOC is the lower limit SOC determination range. After becoming inside, a value (voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} )) indicating the difference in responsiveness between the discharge voltage response and the charge voltage response is calculated. Then, based on the value (voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} )) indicating the difference in responsiveness between the discharge voltage response and the charge voltage response, which is calculated after the SOC falls within the lower limit SOC determination range, the current SOC Determine the range of use. As a result, when determining the SOC usage range, charging / discharging can be controlled while avoiding the SOC range in which the contribution of the metal active material of the negative electrode is high as much as possible. As a result, it is possible to suppress a decrease in the capacity of the lithium ion secondary battery due to deterioration of the metal active material of the negative electrode.

In the present embodiment, the lower limit SOC determination range is set so as to have a predetermined SOC width (for example, ± 5%) centered on the lower limit value of the SOC usage range determined last time, but the SOC width is set to an arbitrary value. can. If the width of the SOC is too large, the number of control loops in steps S36 to S39 and the number of control loops in steps S53 to S56 may increase. Further, if the width of the SOC is too small, the calculated voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ) may repeatedly become larger or smaller than the voltage amplitude ratio threshold value and may not converge to the voltage amplitude ratio threshold value. Therefore, the width of the SOC is preferably about twice the estimation error of the SOC.

In the present embodiment, the controller 10 calculates the voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ) from the discharge voltage amplitude (ΔV _{_d} ) and the charge voltage amplitude (ΔV _{_c} ). The SOC usage range of the secondary battery 2 may be determined based on the voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ). In steps S36, S44, S49, S53, S60, the controller 10 calculates the voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ) instead of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ). .. In steps S37, S45, S50, S54, S61, the controller 10 compares the calculated voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ) with the voltage amplitude difference threshold. The voltage amplitude difference threshold is a preset threshold similar to the voltage amplitude ratio threshold. Then, in steps S37, S45, S54, and S61, the controller 10 uses the SOC when the calculated voltage amplitude difference (ΔV _{_d} − ΔV _{_c} or ΔV _{_c} − ΔV _{_d} ) reaches the voltage amplitude difference threshold. Determine the lower limit SOC of the range.

Although the embodiments of the present invention have been described above, these embodiments have been described for facilitating the understanding of the present invention, and have not been described for the purpose of limiting the present invention. Therefore, each element disclosed in the above-described embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.

<Creation of prototype (example)>
Graphite carbon (Gr) and silicon oxide (SiO) are mixed at a mass ratio of 95: 5 as the negative electrode active material, and styrene butadiene rubber (SBR) is used as the binder (binding agent) to make a slurry on the copper foil. By applying, a negative electrode layer was created. A positive electrode layer was prepared by using lithium nickelate (NCA) as a positive electrode active material, carbon black as a conductive auxiliary agent, and PVDF as a binder (binding agent) to form a slurry and applying it on an aluminum foil. A polyethylene (PE) film was used as the separator. As the electrolytic solution, a solution in which lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethylmethyl carbonate (EMC) was used. A test cell (prototype) was created by sandwiching a stack of a negative electrode layer, a separator, and a positive electrode layer with an aluminum laminate, injecting an electrolytic solution into the laminate, and sealing the periphery of the laminate.

<Evaluation of Examples>
(1) The prototype was charged and discharged as follows in order to adjust the SOC. First, the battery was discharged until the battery voltage reached 2.5 V at the discharge current value (0.2 C). After discharging, the battery was charged with a charging current value (0.2C) up to a target voltage corresponding to SOC 10%. After reaching the target voltage corresponding to SOC 10%, the process shifts to constant voltage charging, and charging is terminated when the charging current value drops to 0.01C.
(2) (1) For the prototype after SOC adjustment, the voltage change was measured in the following manner. First, after 1 minute or more had passed after the end of charging, an alternating current was input to the prototype for 5 seconds, and the voltage change was recorded. The frequency of this alternating current was 2 Hz, the current amplitude was 4 mA, and the waveform was a triangular wave. The voltage change at this time was recorded as a change allowance with respect to the voltage before the input of the alternating current. Then, the peak value _{V_d} (n) of the voltage on the discharge side and the peak value _{V_c} (n) on the charge side were calculated. Here, n is a positive integer representing the number of cycles, and in this embodiment, the value of n is 10. Next, the discharge voltage amplitude ( _{ΔV_d} ) and the charge voltage amplitude ( _{ΔV_c} ) were calculated by calculating the average values of the calculated 10 points _{V_d} (n) and _{V_c} (n). Finally, the discharge voltage amplitude ( _{ΔV_d} ) was divided by the charge voltage amplitude ( _{ΔV_c} ) to calculate the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ).
(3) The prototype after the voltage measurement in (2) was charged with a charging current value (0.2C) up to a target voltage corresponding to SOC 30%. After reaching the target voltage corresponding to SOC 30%, constant voltage charging was performed until the current value dropped to 0.01 C (SOC adjustment).
(4) Charging / discharging was controlled by applying an alternating current in the same manner as in (2), the voltage change at that time was recorded, and the voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} ) was calculated.
(5) After (4), the SOC of (3) is adjusted with the voltage corresponding to 50% of SOC as the target voltage, and the voltage change measurement (voltage amplitude ratio ( _{ΔV_d} / _{ΔV_c} )) of (4) is included. ) Was performed.

<Evaluation result of the example>
After adjusting the SOC to 10%, plotting the voltage change measured in (2) gave the measurement result as shown in the graph of FIG. 13 (a). In FIG. 13 (a), graph а represents a change in alternating current, and graph b represents a voltage response to alternating current. When the calculated voltage amplitudes ( _{ΔV_d} , _{ΔV_c} ) are plotted for each SOC (10%, 30%, 50%) by the evaluation method of (1) to (5), FIGS. 13 (b) to 13 (b) to FIG. The measurement result as shown in the graph of 13 (d) was obtained. In FIGS. 13 (b) to 13 (d), the horizontal axis is common to SOC, and the vertical axis is the ratio of voltage amplitude ( _{ΔV_d} , _{ΔV_c} ) and voltage amplitude ( _{ΔV_d} , _{ΔV_c} ) ( It represents _{ΔV_d} / _{ΔV_c} ) and the difference ( _{ΔV_d} − _{ΔV_c} ) of the voltage amplitudes ( _{ΔV_d} , _{ΔV_c} ), respectively. Further, in FIG. 13 (b), the graph а represents the change in the discharge voltage amplitude ( _{ΔV_d} ), and the graph b represents the change in the charge voltage amplitude ( _{ΔV_c} ).

As shown in FIGS. 13 (c) and 13 (d), the ratio (ΔV_ _d / ΔV_ _c ) and difference (ΔV_ _d − ΔV_ ₎ of the voltage amplitudes (ΔV_d, ΔV_c) in the range of SOC of 30% or less _. It can be confirmed that _c ) is larger than the value in the range where the SOC is larger than 30%. That is, in the embodiment, it was confirmed that in the SOC range in which SiO greatly contributes to charge / discharge, the difference in the amplitude of the voltage response during charging and discharging becomes larger than in the SOC range in which Gr contributes.

1 ... Judgment device 2 ... Secondary battery 10 ... Controller 11 ... Voltage sensor 12 ... Current sensor 13 ... DCDC converter 21 ... Positive electrode layer 22 ... Negative electrode layer 23 ... Separator 24 ... Positive electrode tab 25 ... Negative electrode tab 26 ... Upper exterior member 27 ... Lower exterior member

Claims (5)

In a method of controlling a lithium ion secondary battery having a negative electrode containing graphite and a metal active material.
By controlling the charge and discharge of the lithium ion secondary battery,
When charging / discharging is stopped, the voltage response to the AC current input or the current response to the AC voltage input is calculated.
The difference in responsiveness between the discharge voltage response, which is the voltage response on the discharge side, and the charge voltage response, which is the voltage response on the charge side, or the discharge current response, which is the current response on the discharge side, and the current response on the charge side. A control method for determining the usage range (SOC usage range) of the charge state (SOC) of the lithium ion secondary battery based on the difference in responsiveness from the charge current response. In the control method according to claim 1,
The value of the voltage amplitude ratio (ΔV _{_d} / ΔV _{_c} ), which is the ratio of the amplitude of the discharge voltage response (ΔV _{_d} ) to the amplitude of the charge voltage response (ΔV _{_c} ), or the amplitude of the discharge current response (ΔI _{_d).} ) And the value of the current amplitude ratio (ΔI _d / ΔI _c), which is the ratio of the amplitude (ΔI _{_d} ) of the charge current response, within the SOC usage range in which the value of the current amplitude ratio (ΔI _{_d} / ΔI _{_c} ) is less than a predetermined threshold. A control method for controlling charging and / or discharging. In the control method according to claim 1 or 2,
A memory indicating a difference in responsiveness between the discharge voltage response and the charge voltage response or a difference in responsiveness between the discharge current response and the charge current response is associated with the determined SOC usage range. Remember to
The charging and / or discharging of the lithium ion secondary battery is controlled so that the SOC is within the predetermined SOC range including the lower limit value of the SOC usage range determined last time.
After the SOC is within the predetermined SOC range, a value indicating the difference in responsiveness between the discharge voltage response and the charge voltage response or the difference in responsiveness between the discharge current response and the charge current response is calculated. ,
A value indicating the difference in responsiveness between the discharge voltage response and the charge voltage response or the difference in responsiveness between the discharge current response and the charge current response, which is calculated after the SOC falls within the predetermined SOC range. A control method for determining the SOC usage range this time based on. In the control method according to any one of claims 1 to 3,
A control method in which the metal active material contains Si. In the control method according to any one of claims 1 to 4,
A control method for determining the SOC usage range in a state where the lithium ion secondary battery is connected to an electric power grid.

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