JP6898585B2 - Secondary battery state estimation method and state estimation system - Google Patents

Description

The present invention relates to a secondary battery state estimation method and a state estimation system.

In recent years, there is an urgent need to reduce the amount of carbon dioxide in order to deal with global warming. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs) (hereinafter referred to as "vehicles"), and charging and discharging are indispensable for their widespread use. Secondary batteries, which are possible batteries, are being actively developed.

As a secondary battery, a lithium ion secondary battery having the highest theoretical energy among all batteries is attracting attention, and is currently being rapidly developed. A lithium ion secondary battery generally has a configuration in which a positive electrode and a negative electrode having an active material layer in which an active material or the like is applied to a current collector together with a binder are connected via an electrolyte layer and housed in a battery exterior. Have.

The vehicle power supply system uses the electric energy stored in the lithium-ion secondary battery to drive the motor, and also stores the electric energy in the lithium-ion secondary battery by the regenerative power generation of the motor. As described above, even after the stored electric energy is used by discharging the lithium ion secondary battery, the electric energy can be stored and taken out again by charging.

However, it is known that the internal resistance of a secondary battery gradually increases as it is repeatedly charged and discharged, and the rechargeable battery capacity decreases. Furthermore, if excessive charging and discharging are repeated, not only the secondary battery deteriorates but also it may be damaged. Therefore, the power supply system of the vehicle is in the state of charge (SOC: System of Charge) of the secondary battery in use. ) Is required to be grasped as accurately as possible.

In relation to this, Patent Document 1 below describes an equivalent circuit modeled by measuring the current value of a secondary battery obtained by sampling at predetermined cycles and the resistance value and capacitance value by the AC impedance method. Based on the above, a technique for estimating the SOC of a secondary battery is disclosed.

However, in the technique of Patent Document 1, the overvoltage of the secondary battery is estimated on the assumption that the resistance value and the capacitance value of the equivalent circuit are constant. Therefore, for example, when the overvoltages of the positive electrode active material and the negative electrode active material of the secondary battery are large and the overvoltage strongly depends on the SOC, there is a problem that an error occurs in the estimation of the overvoltage and the SOC cannot be estimated accurately.

Japanese Patent No. 4984527 International Publication No. 2014/128904 Pamphlet

The present invention has been made in view of the above problems. Therefore, an object of the present invention is a state of a secondary battery in which the SOC can be estimated accurately even when the overvoltage of the positive electrode active material and the negative electrode active material of the secondary battery is large and the overvoltage strongly depends on the SOC. It is to provide an estimation method and a state estimation system.

The above object of the present invention is achieved by the following.

The method of estimating the charge state of the secondary battery calculates the difference between the average rate of change at the time of relaxation after stopping the discharge of the terminal voltage of the secondary battery and the average rate of change at the time of discharging the terminal voltage. .. Subsequently, the equivalent circuit of the secondary battery is selected based on the difference. Then, the equivalent circuit is used to estimate the open circuit voltage of the secondary battery, and the charge state of the secondary battery is estimated based on the open circuit voltage.

Further, the secondary battery state estimation system includes a difference calculation unit, an equivalent circuit selection unit, an open circuit voltage estimation unit, and a charge state estimation unit. The difference calculation unit calculates the difference between the average rate of change at the time of relaxation after stopping the discharge of the terminal voltage of the secondary battery and the average rate of change at the time of discharging the terminal voltage. The equivalent circuit selection unit selects the equivalent circuit of the secondary battery based on the difference. The open circuit voltage estimation unit estimates the open circuit voltage of the secondary battery using the equivalent circuit. The charge state estimation unit estimates the charge state of the secondary battery based on the open circuit voltage.

Since it can be determined whether or not the lithium diffusion overvoltage is increasing from the difference in the average rate of change between when the terminal voltage of the secondary battery is relaxed and when it is discharged, the lithium diffusion overvoltage is considered when the lithium diffusion overvoltage is increasing. You can select the equivalent circuit. Therefore, the SOC of the secondary battery can be estimated accurately in a short time.

It is a schematic hardware block diagram which shows the structure of the state estimation system of the secondary battery which concerns on one Embodiment. It is sectional drawing which shows the schematic structure of the secondary battery shown in FIG. It is a functional block diagram which shows the function of the control part shown in FIG. It is a circuit diagram which illustrates the equivalent circuit considering the lithium diffusion overvoltage. In one embodiment, it is a flowchart illustrating a procedure for estimating SOC of a secondary battery. It is a schematic diagram explaining the change with respect to time of the terminal voltage of the secondary battery at the time of discharge and the time of relaxation. _{It is a graph exemplifying the relationship between the difference V sub} and the terminal voltage of a secondary battery for the current cell and the lithium rich / silicon alloy cell. It is a graph which illustrates the increase of the overvoltage at the end of discharge for a lithium-rich / silicon alloy cell.

Hereinafter, embodiments of the secondary battery state estimation system will be described with reference to the attached drawings. In the figure, the same reference numerals are used for the same members. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

(Embodiment)
FIG. 1 is a schematic hardware block diagram showing a configuration of a secondary battery state estimation system according to an embodiment, and FIG. 2 is a cross-sectional view showing a schematic configuration of the secondary battery shown in FIG. Further, FIG. 3 is a functional block diagram showing the function of the control unit shown in FIG. 1, and FIG. 4 is a circuit diagram illustrating an equivalent circuit in consideration of the lithium diffusion overvoltage.

<Secondary battery state estimation system 100>
As shown in FIG. 1, the secondary battery state estimation system (hereinafter, also simply referred to as “system”) 100 includes a secondary battery 200, a current measuring unit 300, a voltage measuring unit 400, a load 500, and a control unit 600. .. The system 100 is mounted on a vehicle, for example.

The system 100 estimates the SOC of the secondary battery 200 using the battery model (equivalent circuit) of the secondary battery 200. Hereinafter, the configuration of the system 100 will be described in detail.

<Secondary battery 200>
As shown in FIG. 2, the secondary battery (hereinafter, also simply referred to as “battery”) 200 has a structure in which the power generation element 21 is sealed inside the battery exterior 29.

[Power generation element]
The power generation element 21 has a substantially rectangular shape, is charged through a charging reaction, and is discharged through a discharging reaction. The power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are laminated. The positive electrode has a structure in which the positive electrode active material layers 15 are arranged on both sides of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layers 13 are arranged on both sides of the negative electrode current collector 11.

The pair of positive electrode active material layers 15 and the negative electrode active material layer 13 are arranged so as to face each other with the separator 17 interposed therebetween. Further, the negative electrode (negative electrode current collector 11 and negative electrode active material layer 13), separator 17, and positive electrode (positive electrode current collector 12 and positive electrode active material layer 15) are laminated in this order, and the adjacent negative electrode and separator 17 are laminated in this order. , And a positive electrode constitute one cell cell 19. Each cell 19 is electrically connected in parallel.

The positive electrode current collector 12 and the negative electrode current collector 11 are attached with a positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are electrically connected to each electrode (positive electrode and negative electrode), respectively, and the battery exterior 29. It has a structure that is led out to the outside of the battery exterior body 29 so as to be sandwiched between the ends of the battery. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 are attached to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via positive electrode leads and negative electrode leads (not shown), respectively, as needed. You may. For mounting, for example, ultrasonic welding or resistance welding may be used.

[Current collector]
The materials constituting the negative electrode current collector 11 and the positive electrode current collector 12 are not particularly limited, but a metal is preferably used. Specific examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Further, the foil may be a metal surface coated with aluminum. Of these, aluminum, stainless steel, and copper are preferable from the viewpoint of electron conductivity and battery operating potential.

The sizes of the negative electrode current collector 11 and the positive electrode current collector 12 are determined according to the intended use of the battery 200. For example, if it is used for a large battery that requires high energy density, a current collector having a large area is used. The thickness of the negative electrode current collector 11 and the positive electrode current collector 12 is also not particularly limited, and is usually about 1 to 100 μm.

[Positive electrode active material layer]
The positive electrode active material layer 15 contains a positive electrode active material capable of accumulating and releasing a substance (ion) that travels between the positive electrode active material layer 15 and the negative electrode active material layer 13 in an electrode reaction.

For example, when the battery 200 is a lithium ion secondary battery, a lithium-transition metal composite oxide is preferable, and the positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , _{LiFeO 2,} LiNi _0.5 Mn _{0. .5 O 2, LiNi 1/3 Mn 1/3} Co 1/3 O 2, oxides having a layered rock-salt structure, such as _{Li 2 MnO 3, LiMn 2 O} 4, LiNi 0.5 Mn 1.5 O 4 Oxides having a spinel-type structure such as, LiFePO ₄ , and oxides having an olivine-type structure such as _{LiCoPO 4 can be used.}

In addition, transition metal oxides and sulfides such as _{V 2} O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , and MoO _{3 , PbO 2} , AgO, NiOOH, and the like can be used. Further, depending on the case, two or more kinds of positive electrode active materials may be used in combination.

Further, in the present embodiment, _{a lithium-rich (lithium excess type) metal composite oxide in which the positions of Li (Li x} M _1-x ) O ₂ and M (transition metal) are substituted with Co, Ni and Mn is used as a positive electrode. It can be used for the active material layer 15. It is known that the positive electrode active material containing these lithium-rich materials has a higher overvoltage than the conventional materials that are not lithium-rich.

The conductive auxiliary agent contained in the positive electrode active material layer 15 has a function of improving the conductivity of the positive electrode active material, and for example, carbon powder such as graphite and various carbon fibers such as vapor-grown carbon fiber (VGCF). Consists of.

The binder contained in the positive electrode active material layer 15 has a function as a binder between the positive electrode current collector 12 and the positive electrode active material layer 15. For example, the binder includes polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), and styrene butadiene rubber. (SBR), polyacrylonitrile (PAN), polymethylacrylate (PMA), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or a mixture thereof can be used.

[Negative electrode active material layer]
The negative electrode active material layer 13 contains a negative electrode active material, a conductive auxiliary agent, a binder and the like. The negative electrode active material layer 13 contains a negative electrode active material capable of accumulating and releasing a substance (ion) that travels between the positive electrode active material layer 15 and the negative electrode active material layer 13 in an electrode reaction. As the negative electrode active material, for example, as the carbon material, a graphite-based carbon material (graphite) such as natural graphite, artificial graphite, or expanded graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, hard carbon, or the like can be used. it can. More preferably, graphite such as natural graphite, artificial graphite, and expanded graphite can be used. As the natural graphite, for example, scaly graphite, lump graphite and the like can be used. As the artificial graphite, massive graphite, vapor-grown graphite, scaly graphite, and fibrous graphite can be used. Among these, particularly preferable materials are scaly graphite and lump graphite. When scaly graphite or lump graphite is used, the packing density is high, which is particularly advantageous. Further, depending on the case, two or more kinds of negative electrode active materials may be used in combination.

Further, in the present embodiment, a silicon-based material such as a silicon alloy can be used for the negative electrode active material layer 13. Silicon alloys are known to have higher overvoltages than carbon materials. Further, as the negative electrode active material, metal oxide (MeO), SiO, Sn and the like can also be used. The Me represents a metal, and is selected from, for example, Mn, Co, Ni, Cu, Fe, Sn, and the like. The metal oxides, SiO and Sn are materials having a high capacity but a large overvoltage.

The conductive auxiliary agent contained in the negative electrode active material layer 13 has a function of improving the conductivity of the negative electrode active material, and for example, carbon powder such as graphite and various carbon fibers such as vapor-grown carbon fiber (VGCF). Consists of.

The binder contained in the negative electrode active material layer 13 has a function as a binder between the negative electrode current collector 11 and the negative electrode active material layer 13, and is composed of, for example, polyvinylidene fluoride (PVdF). Further, in addition to the solvent-based binder such as polyvinylidene fluoride, an aqueous binder (for example, styrene-butadiene rubber) in which polymer fine particles and a rubber material are dispersed in water may be used.

[Separator]
The separator 17 is provided between the positive electrode active material layer 15 and the negative electrode active material layer 13, and electrically separates the positive electrode active material layer 15 and the negative electrode active material layer 13. The separator 17 holds an electrolytic solution between the positive electrode active material layer 15 and the negative electrode active material layer 13 to ensure the conductivity of ions. For example, as the separator 17, a porous film made of polyolefin such as polypropylene (PP) or polyethylene (PE), a porous film made of ceramic, or the like is used. Further, aramid having heat resistance may be used.

The electrolytic solution is a non-aqueous (system) electrolytic solution. Ions move between the positive electrode active material layer 15 and the negative electrode active material layer 13 via the electrolytic solution to charge and discharge the electricity stored in the power generation element 21. For example, the electrolytic solution is a form in which a supporting salt such as a lithium salt is dissolved in an organic solvent. The organic solvent may be any solvent as long as it can sufficiently dissolve the supporting salt. For example, (1) cyclic carbonates such as propylene carbonate and ethylene carbonate, and (2) chains such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate. State carbonates, (3) ethers such as tetrahydrofuran, 2-methyl tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyetane, (4) lactones such as γ-butyrolactone, At least one or two selected from (5) nitriles such as acetonitrile, (6) esters such as methyl propionate, (7) amides such as dimethylformamide, (8) methyl acetate and methyl formate. Examples thereof include a plasticizer such as an aprotonic solvent in which the above is mixed. These organic solvents may be used alone or in combination of two or more. As the supporting salt, conventionally known ones are used. For example, Li (C ₂ F ₅ SO ₂ ) ₂ N (LiBETI), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F _5). SO ₂ ) ₂ N or the like is used.

[Current collector plate]
The materials constituting the current collector plates 25 and 27 are not particularly limited, and known highly conductive materials conventionally used as current collector plates for lithium ion secondary batteries can be used. As the constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. The same material may be used or different materials may be used for the positive electrode current collector plate 25 and the negative electrode current collector plate 27.

[Battery exterior]
The battery exterior 29 is composed of, for example, a laminated sheet having a metal plate inside, and covers and seals the power generation element 21 from both sides to accommodate the power generation element 21.

<Current measuring unit 300>
The current measuring unit 300 measures the current flowing through the battery 200 (hereinafter, referred to as “battery current Ib”). When the battery 200 is discharged, the battery current (discharge current) Ib <0, and when the battery 200 is charged, the battery current (charge current) Ib> 0. The measurement result of the battery current Ib is transmitted to the control unit 600 (see the dashed arrow).

<Voltage measuring unit 400>
The voltage measuring unit 400 measures the terminal voltage of the battery 200 (hereinafter, referred to as “terminal voltage Vb”). In particular, in the present embodiment, the voltage measuring unit 400 measures the terminal voltage Vb when the battery 200 is discharged and the terminal voltage Vb when the battery 200 is relaxed after the discharge is stopped. The measurement result of the terminal voltage Vb is transmitted to the control unit 600 (see the broken line arrow).

<Load 500>
The load 500 has, for example, a traveling motor mounted on the vehicle. The load 500 is driven by the output power from the battery 200. Further, the load 500 charges the battery 200 by the regenerative power of the traveling motor. Alternatively, a power generation / power supply mechanism may be arranged separately from the load 500, and the battery 200 may be configured to be charged by the charging current from the power generation / power supply mechanism.

<Control unit 600>
The control unit 600 controls the load 500, estimates the SOC of the battery 200, and outputs the SOC. The control unit 600 generates a control signal Sc for controlling the drive of the load 500 based on the battery current Ib measured by the current measurement unit 300 and the terminal voltage Vb measured by the voltage measurement unit 400.

The control unit 600 has a calculation unit 610 and a storage unit 620. The arithmetic unit 610 includes a CPU (not shown), and the storage unit 620 includes a memory including a RAM and a ROM (not shown). Various functions are realized by the CPU executing the program stored in the RAM. The control unit 600 may be configured by, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

As shown in FIG. 3, in the present embodiment, the control unit 600 includes each functional unit of the difference calculation unit 630, the equivalent circuit selection unit 640, the open circuit voltage estimation unit 650, and the charge state estimation unit 660.

The difference calculation unit 630 calculates the average rate of change of the terminal voltage Vb with respect to time between the time when the battery 200 is discharged and the time when the battery 200 is relaxed after the discharge is stopped, based on the measurement result of the voltage measurement unit 400. Calculate the difference in the average rate of change. The specific calculation method of the average rate of change will be described later.

The equivalent circuit selection unit 640 selects the equivalent circuit of the battery 200 based on the difference in the average rate of change. The equivalent circuit selection unit 640 is one of a plurality of equivalent circuits including the current type equivalent circuit in which the resistance value and the capacitance value are constant and the equivalent circuit in consideration of the lithium diffusion overvoltage as the equivalent circuit of the battery 200. Select. Since the current type equivalent circuit is a conventionally known equivalent circuit, detailed description thereof will be omitted here.

As shown in FIG. 4, the equivalent circuit considering the lithium diffusion overvoltage includes the electrolyte resistance Rs, the resistance Rp and the capacitance Cp on the positive electrode side, the resistance Rn and the capacitance Cn on the negative electrode side, and the open circuit voltage (OCV) of the battery 200. : Open Circuit Voltage) Represents a power source.

The value of the resistance Rp and the value of the resistance Rn can be set according to the material of the positive electrode active material and the negative electrode active material, respectively. In the present embodiment, the resistance Rp and the resistance Rn corresponding to the positive electrode active material including the lithium-rich material and the negative electrode active material including the silicon alloy are stored in advance in the storage unit 620.

The open circuit voltage estimation unit 650 estimates the OCV of the battery 200. The open circuit voltage estimation unit 650 calculates the overvoltage ΔV of the battery 200 using the equivalent circuit selected by the equivalent circuit selection unit 640, and estimates the OCV of the battery 200 using the overvoltage ΔV and the terminal voltage Vb. The overvoltage ΔV is calculated by the following mathematical formula (1).

Since ΔVp and ΔVn can be approximately calculated using a known algorithm, detailed description thereof will be omitted here.

The charge state estimation unit 660 estimates the SOC of the battery 200 at the time of discharge based on the OCV. For example, in a lithium ion secondary battery, it is known that there is a strong correlation between OCV and SOC. The storage unit 620 holds map data or a relational expression representing the relationship between the OCV and the SOC, and the charge state estimation unit 660 outputs the SOC corresponding to the OCV estimated by the open circuit voltage estimation unit 650.

Hereinafter, a method of estimating the SOC of the battery 200 will be described with reference to FIGS. 5 to 8. FIG. 5 is a flowchart illustrating the procedure of the process of estimating the SOC of the battery 200 in the present embodiment. The processing of the flowchart shown in FIG. 5 is realized by the CPU executing a program stored in the RAM for estimating the SOC of the battery 200.

Further, FIG. 6 is a schematic diagram illustrating a change in the terminal voltage of the secondary battery with time during discharge and relaxation, and FIG. 7 is a difference V _sub and a secondary battery for the current cell and the lithium-rich / silicon alloy cell. It is a graph which illustrates the relationship with a terminal voltage.

Further, FIG. 8 is a graph illustrating an increase in overvoltage at the end of discharge for a lithium-rich / silicon alloy cell.

As shown in FIG. 5, first, the terminal voltage Vb of the battery 200 is measured (step S101). 6, the control unit 600 starts the discharging of the battery 200 at time _{t 1.} The control unit 600 controls the load 500 so that the discharge current Ib from the battery 200 becomes constant. The terminal voltage Vb of the battery 200 changes from V _{0 to V 1} along the discharge curve Kd with the passage of time t. The voltage measuring unit 400 measures the terminal voltage Vb while the battery 200 is discharging.

Subsequently, the control unit 600 stops the discharging of the battery 200 at time _{t 2.} The terminal voltage Vb of the battery 200 changes along the transition curve Kr with the passage of time t. The voltage measuring unit 400 measures the terminal voltage Vb while the battery 200 is relaxed. The terminal voltage Vb data measured during discharge and relaxation is transmitted to the control unit 600 and stored in the storage unit 620. The time required to measure the terminal voltage Vb during discharge and relaxation is about several tens of seconds.

Next, the difference in the average rate of change is calculated (step S102). The difference calculation unit 630 calculates the difference between the average rate of change of the terminal voltage Vb with respect to time when the battery 200 is relaxed and the average rate of change of the terminal voltage Vb with respect to time when the battery 200 is discharged.

Specifically, the average rate of change ΔV _out / Δt ₁ when the terminal voltage Vb changes by the amount of change ΔV _{out during the first time Δt 1} when the battery 200 is discharged is calculated. Further, the average rate of change ΔV _relax / Δt ₂ when the terminal voltage Vb changes by the amount of change ΔV _{relax during the second time Δt 2} when the battery 200 is discharged is calculated. V _sub can be expressed as the following mathematical formula (2).

In the above mathematical formula (1), ΔV _out / Δt ₁ corresponds to the sum of the product (Ib · Rs) of the discharge current Ib and the electrolyte resistance Rs and the reaction overvoltage Vr. The reaction overvoltage Vr is defined as the overvoltage due to the resistance component that appears up to _{Δt 1 when discharging a predetermined charge.} Further, ΔV _relax / Δt ₂ corresponds to the lithium diffusion overvoltage Vd. Lithium diffusion overvoltage Vd is defined as the overvoltage due to the resistance component that appears up to _{Δt 2 when there is no load.} Therefore, V _sub can be expressed as the following mathematical formula (3).

Since the relaxation time of the secondary battery is usually longer than the discharge time, it is set to _{Δt 2} > Δt _1. In this embodiment, for example, Δt ₁ = 3 (s) and Δt ₂ = 10 (s) are set.

Next, the equivalent circuit of the battery 200 is selected (step S103). The equivalent circuit selection unit 640 selects the equivalent circuit of the battery 200 based on _{the difference V sub.}

As shown in FIG. 7, for example, _{in the current cell in which the layered LiMO 2} , the spinnel type LiM ₂ O ₄ , and the olivine type LiMPO ₄ are used as the positive electrode active material and graphite is used as the negative electrode active material, the V _sub is the terminal voltage. It does not depend on Vb and shows a constant value of approximately 0.001 to 0.002 (V).

Also, Li rich / Si cell, i.e. the cell using a negative electrode active material containing a positive electrode active material and the silicon alloy of lithium-rich _systems, the range of _{V sub} is less than 4 (mV) (constant _{region), V sub} terminals It shows a value approximately 0.004 (V) constant with respect to the voltage Vb. On the other hand, in _{the range (increasing range) where V sub} is 4 (mV) or more, V _sub increases as the terminal voltage Vb decreases. As described above, the present inventor _{has found that V sub} depends on the terminal voltage Vb in the Li rich / Si cell.

When V _sub is in a certain range, the lithium diffusion overvoltage Vd is larger than the sum of Ib · Rs and the reaction overvoltage Vr, and _{the magnitude of V sub} is substantially constant. Since the change in the lithium diffusion overvoltage Vd is small in a certain range, the error is small even if the SOC of the battery 200 is estimated using the current equivalent circuit. Therefore, the equivalent circuit selection unit 640 selects the current type equivalent circuit.

On the other hand, when V _sub is in the increasing region, the lithium diffusion overvoltage Vd is larger than the sum of Ib · Rs and the reaction overvoltage Vr, and the lithium diffusion overvoltage Vd is larger than the sum of Ib · Rs and the reaction overvoltage Vr. It has increased significantly. Therefore, if the current equivalent circuit is applied to the estimation of the overvoltage ΔV of the battery 200, an error may occur and the SOC of the battery 200 may not be estimated accurately. Therefore, the equivalent circuit selection unit 640 selects an equivalent circuit in consideration of the lithium diffusion overvoltage when the _{V sub is in the increasing region.}

As described above, the equivalent circuit selection unit 640 selects _{the current type equivalent circuit when the difference V sub} is equal to or less than the first predetermined voltage _{, while the equivalent circuit selection unit 640 selects the current type equivalent circuit when the difference V sub} is larger than the first predetermined voltage. Select an equivalent circuit that takes the lithium diffusion overvoltage into consideration. In the example shown in FIG. 7, the first predetermined voltage is, for example, 4 (mV).

Next, the OCV of the battery 200 is estimated (step S104). The open circuit voltage estimation unit 650 estimates the OCV of the battery 200 using the selected equivalent circuit. The OCV can be calculated from the following mathematical formula (4) based on the terminal voltage Vb and the overvoltage ΔV of the battery 200.

Next, the SOC of the battery 200 is estimated (step S105). The charge state estimation unit 660 uses the OCV calculated in step S104 to estimate the SOC of the battery 200 at the time of discharge based on the map data or the relational expression representing the relationship between the OCV and the SOC.

Next, _{it is determined whether or not V sub} is larger than the second predetermined voltage (step S106). As described above, when the terminal voltage Vb of the battery 200 is measured, the discharge current Ib from the battery 200 is controlled to be constant. However, in the lithium ion secondary battery, the lithium diffusion overvoltage Vd may suddenly increase at the end of discharge, and the terminal voltage Vb of the battery 200 may reach the lower limit voltage. The lower limit voltage is, for example, 2.5 (V). The battery 200 may have an electric charge remaining even after the terminal voltage Vb reaches the lower limit voltage.

For example, as shown in FIG. 8, the battery 200 has a capacity of about 15% when the terminal voltage Vb reaches the lower limit of 2.5 (V). Therefore, in the present embodiment, before the next processing is executed, the discharge current Ib from the battery 200 is throttled (limited) according to the magnitude of _{the difference V sub, and the discharge is restarted.} The control unit 600 functions as a discharge current limiting unit, and can control the load 500 so as to limit the discharge current Ib from the battery 200 when the _{V sub is larger than a second predetermined voltage, for example, 8 (mV).} Step S107). On the other hand, when the V _sub is equal to or lower than the second predetermined voltage, the discharge current Ib from the battery 200 is maintained as it is. Then, the control unit 600 ends the control process (end).

As described above, in the processing of the flowchart shown in FIG. 5, the equivalent circuit of the battery 200 is selected based on _{the difference Vsub} of the average rate of change between the relaxation of the terminal voltage Vb and the discharge, and the OCV is estimated from the equivalent circuit. Then, the SOC is estimated from the OCV.

The timing at which the processing of the above flowchart is executed can be appropriately set according to the environment and conditions in which the system 100 is used. For example, the control unit 600 may be configured to constantly repeat the above process while the vehicle is in operation. Alternatively, the control unit 600 may be configured to execute the above process at the timing when an event such as the driver of the vehicle stepping on the accelerator or applying the brake is generated.

The secondary battery state estimation method and the secondary battery state estimation system of the present embodiment described above have the following effects.

(A) Since it can be determined whether or not the lithium diffusion overvoltage Vd is increasing from _{the difference Vsub} of the average rate of change between when the terminal voltage Vb of the battery 200 is relaxed and when it is discharged, the lithium diffusion overvoltage Vd is increasing. In some cases, an equivalent circuit can be selected in consideration of the lithium diffusion overvoltage. Therefore, the SOC of the battery 200 can be estimated accurately in a short time of about several tens of seconds.

(B) Since the terminal voltage Vb when the battery 200 is discharged and the terminal voltage Vb when the battery 200 is relaxed after the discharge is stopped are measured, it is based on the output voltage from the actual cell (actual cell). SOC can be estimated.

_{(C) By setting the second} time Δt 2 at the time of relaxation larger than _{the first time Δt 1} at the time of discharge, the lithium diffusion overvoltage Vd that appears in a time range slower than the reaction overvoltage Vr can be reduced to the terminal at the time of relaxation. It can be reflected in the average rate of change of the voltage Vb.

(D) When the difference V _sub is larger than the first predetermined voltage, the equivalent circuit considering the lithium diffusion overvoltage is used, so that the SOC of the battery 200 can be estimated accurately in a short time of about several tens of seconds.

(E) When the difference V _sub is larger than the second predetermined voltage, the discharge current Ib of the battery 200 is limited, so that the electric charge accumulated in the battery 200 before the terminal voltage Vb reaches the lower limit voltage is efficiently used without waste. Can be used up.

(F) Since the battery 200 has a positive electrode active material 150 containing an excess of lithium and a negative electrode active material 130 containing a silicon alloy, a high-capacity secondary battery can be realized.

As described above, in the embodiment, the method for estimating the state of the secondary battery and the state estimation system for the secondary battery of the present invention have been described. However, it goes without saying that the present invention can be appropriately added, modified, and omitted by those skilled in the art within the scope of the technical idea.

100 Rechargeable battery state estimation system,
200 rechargeable battery,
300 current measuring unit,
400 Voltage measuring unit,
500 load,
600 control unit,
610 arithmetic unit,
620 Memory,
630 Difference calculation unit 640 Equivalent circuit selection unit,
650 Open circuit voltage estimation unit,
660 Charge state estimation unit.

Claims (12)

It is a method of estimating the charge status of the secondary battery.
The step (a) of calculating the difference between the average rate of change at the time of relaxation after stopping the discharge of the terminal voltage of the secondary battery and the average rate of change at the time of discharging the terminal voltage.
In step (b) of selecting the equivalent circuit of the secondary battery based on the difference,
In step (c) of estimating the open circuit voltage of the secondary battery using the equivalent circuit,
In step (d) of estimating the charge state of the secondary battery based on the open circuit voltage,
The method. Before step (a)
The present invention further comprises a step of measuring the terminal voltage of the secondary battery while discharging the secondary battery, then stopping the discharge of the secondary battery, and measuring the terminal voltage while relaxing the secondary battery. Item 1. The method according to Item 1. The average rate of change of the terminal voltage during the discharge is
It is a value obtained by dividing the amount of change in the terminal voltage in the first time during the discharge by the first time.
The average rate of change of the terminal voltage during the relaxation is
It is a value obtained by dividing the amount of change in the terminal voltage in the second time during the relaxation by the second time.
The method according to claim 1 or 2, wherein the second time is set to a value longer than the first time. The secondary battery has a positive electrode active material containing an excess of lithium and a negative electrode active material containing a silicon alloy.
In step (b),
The method according to any one of claims 1 to 3, wherein when the difference is larger than the first predetermined voltage, an equivalent circuit considering the lithium diffusion overvoltage is selected. When the difference is larger than the second predetermined voltage,
The method according to any one of claims 1 to 4, further comprising a step of limiting the discharge current of the secondary battery and starting the discharge after the step (d). The method according to any one of claims 1 to 3, and 5 , wherein the secondary battery has a positive electrode active material containing an excess of lithium and a negative electrode active material containing a silicon alloy. A difference calculation unit that calculates the difference between the average rate of change at the time of relaxation after stopping the discharge of the terminal voltage of the secondary battery and the average rate of change at the time of discharging the terminal voltage.
An equivalent circuit selection unit that selects the equivalent circuit of the secondary battery based on the difference,
An open circuit voltage estimation unit that estimates the open circuit voltage of the secondary battery using the equivalent circuit,
A charge state estimation unit that estimates the charge state of the secondary battery based on the open circuit voltage,
A secondary battery state estimation system that has. The seventh aspect of claim 7, further comprising a voltage measuring unit for measuring the terminal voltage of the secondary battery at the time of discharging and the terminal voltage at the time of relaxation after the discharge of the secondary battery is stopped. Secondary battery state estimation system. The average rate of change of the terminal voltage during the discharge is
It is a value obtained by dividing the amount of change in the terminal voltage in the first time during the discharge by the first time.
The average rate of change of the terminal voltage during the relaxation is
It is a value obtained by dividing the amount of change in the terminal voltage in the second time during the relaxation by the second time.
The secondary battery state estimation system according to claim 7 or 8, wherein the second time is set to a value longer than the first time. The secondary battery has a lithium ion secondary battery including a positive electrode active material containing an excess of lithium and a negative electrode active material containing a silicon alloy.
The equivalent circuit selection unit
The state estimation system for a secondary battery according to any one of claims 7 to 9, wherein when the difference is larger than the first predetermined voltage, an equivalent circuit considering the lithium diffusion overvoltage is selected. The state estimation of the secondary battery according to any one of claims 7 to 10, further comprising a discharge current limiting unit that limits the discharge current of the secondary battery when the difference is larger than the second predetermined voltage. system. The secondary battery includes a positive electrode active material containing excess lithium, Ru lithium ion secondary battery der and a negative electrode active material containing silicon alloy, according to any one of claims 7-9, and 11 Secondary battery state estimation system.

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