JP2022021445A - Method and system for estimating state of secondary battery - Google Patents

Abstract

To estimate a deterioration state of a positive electrode for each deterioration factor without damaging a secondary battery.SOLUTION: A battery state estimation method for a secondary battery, which estimates a battery state, comprises: a capacity reduction amount specification step of specifying a capacity reduction amount ΔQ that is a battery capacity reduction amount from an initial capacity of a secondary battery; a first step of specifying a first capacity reduction amount Q1 derived from positive/negative electrode capacity deviation, based on a positive electrode potential and a temperature; a second step of specifying a second volume reduction amount Q2 derived from a side reaction of forming a film on a positive electrode active material, based on the positive electrode potential and the temperature; and a third step of calculating a third capacity reduction amount Q3 due to the structural change of the positive electrode active material by subtracting the first capacity reduction amount Q1 and the second capacity reduction amount Q2 from the capacity reduction amount ΔQ.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for estimating the state of a secondary battery and a system for estimating the state of the secondary battery.

As is well known, a secondary battery such as a lithium ion secondary battery is used as a power source for portable electronic devices and as a power source for electric vehicles and hybrid vehicles.
For example, in a lithium ion secondary battery mounted on a vehicle, in addition to deterioration factors such as temperature environment and elapsed time, the number of charge / discharge cycles also contributes as deterioration factors. Therefore, the degree of deterioration cannot be estimated only from the elapsed time, the mileage, and the like.

Therefore, Patent Document 1 discloses a method of estimating the deterioration of a lithium ion secondary battery by using the shift capacity corresponding to the positive / negative electrode composition, which is a factor of the decrease in the capacity of the lithium ion secondary battery. Specifically, the film formation current density in the side reaction at the negative electrode is obtained by using the Tafel equation that describes the relationship between the current density and the overvoltage. Then, the film forming current density is calculated for each predetermined cycle, and the positive / negative electrode composition-corresponding displacement capacity is calculated by integrating the film forming current density.

Japanese Unexamined Patent Publication No. 2017-190979

In the prior invention, only side reactions at the negative electrode are considered. However, in order to accurately determine the deterioration state of the lithium ion secondary battery, it is necessary to consider the amount of capacity decrease in the positive electrode, but it is difficult to determine because there are multiple factors for the capacity decrease in the positive electrode. Further, in order to determine the deteriorated state of the lithium ion secondary battery, the lithium ion secondary battery may be disassembled, but when reusing the lithium ion secondary battery, it is necessary to grasp the deteriorated state in a non-destructive manner. desirable.

The present invention has been made in view of such circumstances, and an object of the present invention is to estimate the deterioration state of the positive electrode for each deterioration factor without destroying the lithium ion secondary battery.

The battery state estimation method that solves the above problems is a battery state estimation method for a secondary battery that estimates the battery state, and specifies a capacity decrease amount that is a decrease amount of the battery capacity from the initial capacity of the secondary battery. A film is formed on the positive electrode active material based on the capacity reduction amount specifying step, the first step of specifying the first capacity reduction amount due to the positive and negative electrode capacity deviation based on the positive electrode potential and the temperature, and the positive electrode potential and the temperature. The structural change of the positive electrode active material is carried out in the second step of specifying the second volume reduction amount derived from the side reaction to be carried out, and by subtracting the first volume reduction amount and the second volume reduction amount from the volume reduction amount. The third step of calculating the amount of decrease in the third capacity according to the above is included.

The battery state estimation system that solves the above problems is a battery state estimation system for a secondary battery that estimates the battery state, and a first control device provided in a vehicle equipped with the secondary battery has a positive electrode potential and a positive electrode potential. The first step of specifying the first volume reduction amount due to the positive / negative electrode capacity shift based on the temperature, and the second volume reduction amount derived from the side reaction in which a film is formed on the positive electrode active material based on the positive electrode potential and the temperature. The second step of specifying the capacity reduction amount and the capacity reduction amount specifying step of specifying the capacity reduction amount, which is the amount of decrease in the battery capacity from the initial capacity of the secondary battery, and the capacity reduction The third step of calculating the third volume reduction amount due to the structural change of the positive electrode active material by subtracting the first volume reduction amount and the second volume reduction amount from the amount is executed.

According to the present inventor, the deterioration factors of the secondary battery are mainly the amount of decrease in the first capacity due to the displacement of the positive and negative electrodes, the amount of decrease in the second capacity due to the side reaction in which a film is formed on the positive electrode active material, and the positive electrode activity. Focusing on the third volume reduction due to the structural change of the secondary particles of the substance, the first volume reduction and the second volume reduction based on the positive electrode potential, the negative electrode potential, and the temperature, which are the usage histories of the secondary battery 11. It was estimated that the capacity was reduced. Then, the first volume decrease and the second volume decrease were subtracted from the volume decrease from the initial volume to estimate the third volume decrease due to the structural change of the secondary particles of the positive electrode active material. Therefore, the amount of decrease in the third capacity can be estimated without damaging the secondary battery.

Regarding the battery state estimation method, when the amount of decrease in the third capacity is less than the second threshold value, the secondary battery is determined as a secondary battery to be reused within a relatively wide SOC tolerance, and the above is described. Further, a determination step of determining the secondary battery as a secondary battery to be reused within a relatively narrow SOC tolerance when the amount of decrease in the third capacity is equal to or greater than the second threshold value is further performed. It may be included.

According to the above configuration, the use at the time of reuse according to the allowable range of SOC was determined based on the magnitude of the capacity decrease amount of the secondary battery. Therefore, it is possible to appropriately determine the intended use of the secondary battery when it is reused.

Regarding the battery state estimation method, the first step is a current density estimation step of estimating the film forming current density for each electrode, and a current value estimation for estimating a side reaction current value for each electrode based on the film forming current density. The current density estimation step includes a step of calculating the first capacitance reduction amount based on the difference between the side reaction current value of the negative electrode and the side reaction current value of the positive electrode and the time, and the current density estimation step is “i ₀ ”. Is the exchange current density, "α" is the transfer coefficient, "F" is the Faraday constant, "R" is the gas constant, "T" is the temperature, "E'" is the film formation potential, and "E" is the electrode potential. Then, the film forming current density is estimated based on the following equation (1), and the film forming current density is estimated.

前記電流値推定工程は、過電圧項を「η」としたとき、下記式（２）に基づいて前記副反応電流値を推定してもよい。

In the current value estimation step, when the overvoltage term is “η”, the side reaction current value may be estimated based on the following equation (2).

上記構成によれば、正負極容量ずれに由来する第１容量低下量を、ターフェルの式に基づき被膜形成電流密度を推定する工程と、被膜形成電流密度から副反応電流値を求める工程と、正極の副反応電流値及び負極の副反応電流値から第１容量低下量を算出する工程とによって求めた。このため、二次電池を解体することなく、第１容量低下量を推定することができる。

According to the above configuration, a step of estimating the film forming current density based on the Tafel equation, a step of obtaining a side reaction current value from the film forming current density, and a positive electrode for the amount of decrease in the first capacitance due to the positive / negative electrode capacitance shift. It was obtained by the step of calculating the first capacitance reduction amount from the side reaction current value of the above and the side reaction current value of the negative electrode. Therefore, the amount of decrease in the first capacity can be estimated without disassembling the secondary battery.

Regarding the battery state estimation method, in the second step, the second capacity reduction amount is specified based on the deterioration rate information indicating the relationship between the deterioration rate, which is the capacity reduction amount per hour, the positive potential and the temperature. The deterioration rate information is associated with a higher deterioration rate as the positive potential increases when the temperature is constant, and is associated with a higher deterioration rate as the temperature increases when the positive potential is constant. May be good.

According to the above embodiment, deterioration rate information defining the relationship between the deterioration rate of the positive electrode of the secondary battery 11 and the positive electrode potential and the temperature of the secondary battery 11 is prepared in advance, and based on the usage history of the secondary battery, By referring to the deterioration rate information, the amount of decrease in the second capacity due to storage deterioration of the positive electrode was determined. That is, as long as the usage history of the secondary battery is accumulated, the amount of decrease in the second capacity can be estimated without disassembling the secondary battery.

Regarding the battery state estimation method, the secondary battery is mounted on a vehicle, and a control device provided in the vehicle executes the first step of specifying the first capacity reduction amount due to the positive / negative electrode capacity deviation. Then, the second step of specifying the amount of the second volume decrease due to the side reaction in which a film is formed on the positive electrode active material may be executed.

According to the above configuration, the control device mounted on the vehicle acquires the voltage and temperature of the secondary battery, and estimates the first capacity reduction amount and the capacity reduction amount. Therefore, after the secondary battery is removed from the vehicle, the capacity reduction amount and the capacity reduction amount calculated in advance can be used, so that the deterioration state can be determined in a short time.

According to the present invention, the deterioration state of the positive electrode can be estimated for each deterioration factor without damaging the secondary battery.

The figure which shows the breakdown of the capacity decrease amount of the secondary battery of one Embodiment schematically. The figure which shows schematic the battery control circuit of the same embodiment. The figure which shows schematic the charge / discharge control circuit and deterioration determination apparatus of the same embodiment. The flowchart which shows the procedure of capacity reduction amount determination of the same embodiment. The graph which shows the relationship between the deterioration rate and the storage time derived from the storage deterioration of the positive electrode of the same embodiment for each positive electrode potential. The graph which shows the relationship between the deterioration rate derived from the preservation deterioration of the positive electrode of the same embodiment, and the positive electrode potential. The graph which shows the relationship between the deterioration rate and the storage time derived from the storage deterioration of the positive electrode of the same embodiment for each temperature. The graph which shows the relationship between the deterioration rate and the temperature derived from the storage deterioration of the positive electrode of the same embodiment. The schematic diagram of the map which shows the relationship between the deterioration rate derived from the preservation deterioration of the positive electrode of the same embodiment, and the positive electrode potential and temperature. The flowchart which shows the procedure of the deterioration state determination of the same embodiment. The figure which shows roughly the state estimation system of the modification example.

An embodiment of a state estimation method and a state estimation system for a secondary battery will be described with reference to FIGS. 1 to 10.
With reference to FIG. 1, an outline of a state estimation method for a lithium ion secondary battery (hereinafter referred to as a secondary battery) will be described. The main causes of the decrease in the capacity of the secondary battery are "(1) positive and negative electrode capacity deviation", "(2) storage deterioration of the positive electrode", and "(3) cycle deterioration of the positive electrode". In the present embodiment, the secondary battery will be described as including a positive electrode active material containing LiNiO ₂ and a negative electrode active material containing graphite as a main component.

"(1) Positive / negative electrode capacity deviation" is derived from the deviation between the positive electrode capacity and the negative electrode capacity. The capacity of the secondary battery is determined by the size of the region where the positive electrode capacity and the negative electrode capacity overlap in the operating range of the secondary battery. Even in the secondary battery in the initial state without deterioration, the positive electrode capacity and the negative electrode capacity are in a state of being deviated from each other. When a side reaction or the like progresses in both the positive electrode and the negative electrode, the positive electrode capacity and the negative electrode capacity decrease from the initial state. As a result, the deviation between the positive electrode capacity and the negative electrode capacity is widened, and the area where the positive electrode capacity and the negative electrode capacity overlap is further reduced. This expanded capacity shift is a capacity decrease due to the positive and negative electrode capacity shifts.

"(2) Storage deterioration of the positive electrode" is a phenomenon in which the positive electrode capacity itself decreases just by leaving it unattended. This decrease in capacity is due to a side reaction in which LiNiO ₂ , which is a positive electrode active material, forms a film containing NiO and the like. That is, the formation of the film prevents the storage and release of lithium ions into the positive electrode, and as a result, the capacity of the positive electrode is reduced.

"(3) Cycle deterioration of the positive electrode" is a phenomenon associated with a structural change of the secondary particles of the positive electrode active material, and the positive electrode capacity decreases as the secondary battery repeatedly charges and discharges. The secondary particles are secondary particles in which primary particles are gathered. Here, the "primary particle" refers to a particle considered to be a unit particle judging from its apparent geometrical morphology. Although it depends on the charging / discharging conditions, the positive electrode active material expands and contracts due to repeated charging / discharging, and the shell of the secondary particles collapses. When the shell of the secondary particles collapses, the conductive path of the electrons flowing through the particles of the positive electrode active material is cut, so that the capacity of the positive electrode decreases. Further, even if the positive electrode active material is not LiNiO ₂ , the positive electrode active material repeats expansion and contraction due to repeated charging and discharging, so that cycle deterioration occurs.

It is considered that the total capacity reduction amount ΔQ obtained by subtracting the estimated capacity Q'from the initial capacity Q of the secondary battery corresponds to the integrated amount of the capacity reduction amounts Q1 to Q3 for each of these factors. Of these, the first capacitance reduction amount Q1 (hereinafter, simply referred to as capacity reduction amount Q1) derived from the positive and negative electrode capacitance shift is a Tafel equation describing the relationship between the current density and the overvoltage according to the electrode reaction rate of the side reaction. It is possible to estimate from the side reaction current value of the positive electrode and the side reaction current value of the negative electrode based on. That is, when the overvoltages are the same, it can be said that the larger the current flows, the faster the reaction speed. Further, the second capacity decrease amount Q2 (hereinafter, simply referred to as capacity decrease amount Q2) due to storage deterioration of the positive electrode is estimated using a usage history including the temperature and battery voltage of the secondary battery and a map recorded in advance. It is possible.

On the other hand, the third capacity decrease amount Q3 (hereinafter, simply referred to as capacity decrease amount Q3) due to the cycle deterioration of the positive electrode is derived from the structural change of the secondary particles due to repeated charging and discharging of the positive electrode active material as described above, and is electrically generated. Since it occurs by a mechanism different from that of the chemical reaction, the amount of decrease in capacity cannot be estimated from Tafel's equation for obtaining the current density of the electrochemical reaction. Further, since it does not directly depend on the temperature and the battery voltage, it cannot be obtained from the battery temperature and the battery voltage like the capacity decrease amount Q2 due to the storage deterioration of the positive electrode. On the other hand, the capacity reduction amount Q3 can be determined by disassembling the secondary battery and extracting and analyzing the positive electrode active material, but when reusing the secondary battery, the capacity reduction amount should be estimated in a non-destructive manner. Is preferable.

Therefore, in the present embodiment, the total capacity reduction amount ΔQ, the capacity reduction amount Q1 due to the positive / negative electrode capacity deviation, and the capacity reduction amount Q2 due to the storage deterioration of the positive electrode are obtained, and the capacity reduction amount Q1 is obtained from the capacity reduction amount ΔQ. , Q2 is reduced to estimate the amount of capacity decrease Q3 due to the cycle deterioration of the positive electrode.

Then, the estimated capacity reduction amount Q3 is used to determine the use or condition when the secondary battery is reused. For example, when the capacity reduction amount Q3 is equal to or more than a predetermined value, the secondary battery is determined as a secondary battery to be reused within a relatively narrow SOC tolerance range, and the capacity reduction amount Q3 is less than the predetermined value. In the case, it is determined as a secondary battery to be reused within a relatively wide SOC tolerance. Alternatively, the allowable range of SOC of the secondary battery may be determined based on the capacity reduction amount Q3, or the temperature environment of the secondary battery, the lower limit voltage and the upper limit voltage, the charge / discharge control method, the usable period, etc. may be determined. You may.

Next, with reference to FIGS. 2 to 10, the state estimation method and the state estimation system of the secondary battery will be described in detail.
FIG. 2 is a diagram schematically showing a main part of a vehicle 10 equipped with a secondary battery 11. The vehicle 10 is a hybrid vehicle or an electric vehicle. The secondary battery 11 is an assembled battery in which a plurality of battery modules 11A are combined. The battery module 11A includes a positive electrode active material containing a lithium transition metal composite oxide such as LiNiO ₂ and a negative electrode active material containing a carbon material.

The vehicle 10 includes a battery control circuit 13 that connects the secondary battery 11 and the PCU 12. The PCU 12 has a built-in inverter and the like, and is connected to a motor generator 15 that functions as a generator and an electric motor. When the motor generator 15 functions as an electric motor, the motor generator 15 is driven by a current supplied from the secondary battery 11 via the PCU 12 to transmit a rotational force to the wheels. When the motor generator 15 functions as a generator, the motor generator 15 supplies a current to the secondary battery 11 via the PCU 12 to charge the secondary battery 11. Further, the secondary battery 11 may be one in which a current is supplied from an external charging device such as a charging stand via a charging / discharging control device (not shown).

Further, the battery control circuit 13 is provided with a voltage detection unit 16 and a current detection unit 17. Further, the vehicle 10 is provided with a control device 20 as a first control device for monitoring the state of the secondary battery 11. The control device 20 includes a calculation unit 21 such as a CPU, a memory 22 for temporarily storing calculation results, and a storage 23. The storage 23 records a state estimation program, history information of the secondary battery 11, and the like. The voltage detection unit 16 outputs the detected voltage value of the secondary battery 11 to the control device 20. The current detection unit 17 outputs the detected current value of the secondary battery 11 to the control device 20. The control device 20 stores the history information such as the voltage value and the current value acquired from the voltage detection unit 16 and the current detection unit 17 in the storage 23.

Further, the secondary battery 11 is provided with a temperature detection unit 18 for measuring the temperature T, which is the temperature inside the battery. The temperature detection unit 18 detects the temperature inside one or more battery modules 11A. The temperature detection unit 18 may detect the temperature on the outside of the battery module 11A and in the vicinity of the case of the battery module 11A.

The calculation unit 21 of the control device 20 acquires a voltage value, a current value, and a temperature at predetermined time intervals, and records the voltage value, the current value, and the temperature in the storage 23 as history information in association with the acquired time (or the elapsed time from the reference time). .. Further, the calculation unit 21 determines the capacity decrease amount Q1 due to the positive / negative electrode capacity deviation of the secondary battery 11 and the capacity decrease amount Q2 due to the cycle deterioration of the positive electrode based on the history information and the voltage value and the temperature. Is estimated according to the state estimation program, and those values are recorded in the storage 23.

FIG. 3 is a diagram schematically showing an inspection system 30 for determining a deterioration state of the secondary battery 11. The inspection system 30 measures the secondary battery 11 removed from the battery control circuit 13. The inspection system 30 includes a charge / discharge control circuit 31 and a deterioration determination device 35 as a second control device. The charge / discharge control circuit 31 includes a measurement charge / discharge device 32 connected to a power source (not shown), a voltage detection unit 33, and a current detection unit 34. The deterioration determination device 35 controls the charging / discharging device 32 for measurement. The measurement charge / discharge device 32 supplies a direct current to charge the secondary battery 11 based on the request from the deterioration determination device 35. Further, the charging / discharging device 32 for measurement discharges the secondary battery 11 based on the request from the deterioration determining device 35. An external load (not shown) may be connected to the charge / discharge control circuit 31. The control device 20 and the deterioration determination device 35 correspond to the state determination system.

The deterioration determination device 35 includes a calculation unit 36 such as a CPU, a memory 37 for temporarily storing the calculation result of the calculation unit 36, and a storage 38. The storage 38 records a deterioration determination program, history information of the secondary battery 11, deterioration determination information indicating the deterioration determination result, and the like. The history information is acquired from the control device 20. The method of acquiring the history information is not particularly limited. For example, when the control device 20 is also removed when the secondary battery 11 is removed from the vehicle 10, the removed control device 20 and the deterioration determination device 35 may be connected to acquire history information. Alternatively, the deterioration determination device 35 may be connected to an in-vehicle network or the like to acquire history information from the control device 20 mounted on the vehicle 10.

Next, with reference to FIGS. 4 and 5, the procedure of the state estimation method of the secondary battery 11 will be described together with its operation.
FIG. 4 shows a procedure of a capacity reduction amount estimation method executed by the control device 20 mounted on the vehicle 10. The control device 20 executes the state estimation program stored in the storage 23, and repeats the processes of steps S11 to S15 every predetermined time Δt. The estimation of the capacity reduction amount is not limited to the battery state of the secondary battery 11 such as a running state, a stopped state, a vehicle state such as a parked state, a charging state, a discharging state, and a state in which charging / discharging is not performed. It may be executed every time Δt of. Alternatively, it may be executed when at least one of the vehicle state and the battery state is a predetermined state.

First, the control device 20 acquires the temperature T from the temperature detection unit 18 (step S11). Further, the control device 20 acquires a voltage V, which is a voltage value, from the voltage detection unit 16 (step S12). Further, the control device 20 estimates the side reaction current value Ip of the positive electrode and the side reaction current value In of the negative electrode based on the acquired temperature T and voltage V (step S13).

A method of predicting the side reaction current value Ip of the positive electrode in step S13 will be described. First, the film-forming current density ip in the side reaction of the positive electrode that forms a film containing NiO is obtained according to the following equation (3) (current density estimation step). The larger the film formation current density ip, the higher the deterioration rate of the positive electrode due to this side reaction.

上記式（３）はターフェルの式に基づくものである。「ｉｏ」は、正極の副反応が平衡状態にある場合の交換電流密度であり、定数である。「α」は移動係数、「Ｆ」はファラデー定数、「Ｒ」は気体定数である。「Ｔ」は絶対温度であって、温度検出部１８から取得した温度Ｔである。また「Ｅｐ」は電圧Ｖから求められた正極電位であって、「Ｅｐ´」はＮｉＯ等を含む被膜が形成される被膜形成電位であり定数である。つまり、温度Ｔ及び正極電位Ｅｐに応じて、被膜形成電流密度ｉｐは変わる。

The above equation (3) is based on the Tafel equation. “Io” is an exchange current density when the side reaction of the positive electrode is in an equilibrium state, and is a constant. “Α” is a movement coefficient, “F” is a Faraday constant, and “R” is a gas constant. “T” is an absolute temperature, which is the temperature T obtained from the temperature detection unit 18. Further, "Ep" is a positive electrode potential obtained from the voltage V, and "Ep'" is a film forming potential at which a film containing NiO or the like is formed and is a constant. That is, the film forming current density ip changes depending on the temperature T and the positive electrode potential Ep.

Since the voltage V is the difference between the positive electrode potential Ep and the negative electrode potential En when the voltage value is detected, the positive electrode potential Ep and the negative electrode potential En are the temperature T and the voltage when the voltage value is measured. It can be obtained from V and each. Therefore, the voltage V, the temperature T, and the positive electrode potential Ep are specified using a map or graph obtained in advance. The same applies to the negative electrode potential En.

Next, using the film forming current density ip, the side reaction current value Ip of the positive electrode is obtained according to the equation (4) (current value estimation step).

「ηｐ」は過電圧項であって、正極の副反応の平衡電極電位と実際に反応が進行するときの正極電位Ｅｐとの差である。

“Ηp” is an overvoltage term, which is the difference between the equilibrium electrode potential of the side reaction of the positive electrode and the positive electrode potential Ep when the reaction actually proceeds.

Next, a method of estimating the side reaction current value In of the negative electrode will be described. The adverse reaction of the negative electrode is a reaction of forming SEI (Solid Electrolyte Interphase) formed on the surface of the negative electrode active material mainly by the decomposition reaction of the electrolyte. SEI is a film that can release and inhale lithium ions and suppresses the decomposition of electrolytes, but when it becomes thicker, it hinders the diffusion of lithium ions and causes a decrease in capacity. When estimating the side reaction current value In of the negative electrode, first, the film forming current density in of the negative electrode is obtained according to the following equation (5) (current density estimation step). The larger the film formation current density in, the greater the rate of deterioration of the side reaction due to the side reaction that produces SEI.

「ｉｏ」は、副反応が平衡状態にある場合の交換電流密度であり、定数である。「α」は移動係数、「Ｆ」はファラデー定数、「Ｒ」は気体定数である。「Ｔ」は絶対温度であって、温度検出部１８から取得した温度Ｔである。また「Ｅｎ」は負極電位であり、「Ｅｎ´」はＳＥＩ等が形成される被膜形成電位であって定数である。つまり、温度Ｔ及び負極電位Ｅｎに応じて、正極の交換電流密度ｉｏは変わる。

“Io” is the exchange current density when the side reaction is in equilibrium, and is a constant. “Α” is a movement coefficient, “F” is a Faraday constant, and “R” is a gas constant. “T” is an absolute temperature, which is the temperature T obtained from the temperature detection unit 18. Further, "En" is a negative electrode potential, and "En'" is a film forming potential on which SEI or the like is formed and is a constant. That is, the exchange current density io of the positive electrode changes depending on the temperature T and the negative electrode potential En.

Next, using the film forming current density in, the side reaction current value In of the negative electrode is obtained according to the equation (6) (current value estimation step).

「ηｎ」は過電圧項であって、負極の副反応の平衡電極電位と実際に反応が進行するときの負極電位Ｅｎとの差である。

“Ηn” is an overvoltage term, which is the difference between the equilibrium electrode potential of the side reaction of the negative electrode and the negative electrode potential En when the reaction actually proceeds.

When the side reaction current value Ip of the positive electrode and the side reaction current value In of the negative electrode are obtained in this way, the capacity decrease amount Q1 due to the capacity shift between the positive electrode and the negative electrode is estimated (step S14, first step). Specifically, the control device 20 calculates the capacity decrease amount Q1 due to the capacity shift per time Δt according to the following equation (7) using the side reaction current value Ip and the side reaction current value In.

次に、制御装置２０は、正極の保存劣化による容量低下量Ｑ２を推定する（ステップＳ１５、第２工程）。以下、保存劣化による容量低下量Ｑ２の推定方法について詳述する。

Next, the control device 20 estimates the amount of capacity decrease Q2 due to storage deterioration of the positive electrode (step S15, second step). Hereinafter, the method of estimating the capacity decrease amount Q2 due to storage deterioration will be described in detail.

First, the tendency of the positive electrode deterioration rate will be described with reference to FIGS. 5 to 8. 5 and 6 show the positive electrode voltage dependence of the positive electrode deterioration rate, and FIGS. 7 and 8 show the temperature dependence of the positive electrode deterioration rate. In FIG. 5, the horizontal axis is the square root (t ^1/2 ) of the battery storage time (t), and the vertical axis is the positive electrode specific volume (mAh / g). The deterioration rate line 100 has a positive electrode potential Ep of 3.886V, the deterioration rate line 101 has a positive electrode potential Ep of 3.984V, and the deterioration rate line 102 has a positive electrode potential Ep of 4.1V. Shows the deterioration rate at ° C. In each of the deterioration rate lines 100 to 102, the positive electrode specific capacity decreases as the storage time becomes longer. Further, among the deterioration rate lines 100 to 102, the deterioration rate line 102 having the highest positive electrode potential Ep has the largest absolute value of inclination and the highest deterioration rate. Further, the deterioration rate line 100 having the lowest positive electrode potential Ep has the smallest absolute value of slope and the lowest deterioration rate.

FIG. 6 replaces the graph shown in FIG. 5 with the relationship between the positive electrode potential Ep and the positive electrode deterioration rate. The positive electrode deterioration rate {(mAh / g) · t ^1/2 } is calculated by dividing the positive electrode specific volume by the square root (t ^1/2 ) of the storage time. As the positive electrode potential Ep increases, the deterioration rate increases exponentially.

7 and 8 are graphs showing the temperature dependence of the positive electrode deterioration rate. The horizontal axis of the graph of FIG. 7 is the square root (t ^1/2 ) of the storage time (t) of the battery, and the vertical axis is the positive electrode specific capacity (mAh / g) of the battery. The deterioration rate lines 110 to 112 have a positive electrode potential Ep of 4.1 V at the time of storage, the deterioration rate line 110 has a temperature of 60 ° C., the deterioration rate line 111 has a temperature of 75 ° C., and the deterioration rate line 112 has a temperature of 85 ° C. It was measured under the conditions. The deterioration rate lines 110 to 112 have a lower positive electrode specific capacity as the storage time becomes longer. The deterioration rate line 112 having the highest temperature has the largest absolute value of inclination and the highest deterioration rate. Further, the deterioration rate line 110 having the lowest temperature has the largest inclination and the lowest deterioration rate.

FIG. 8 replaces the graph shown in FIG. 7 with the relationship between the temperature and the deterioration rate. The vertical axis is the natural logarithm of the deterioration rate calculated by dividing the specific volume of the positive electrode by time. The horizontal axis is the reciprocal of the absolute temperature " ¹ / K" multiplied by "103". The higher the temperature, the higher the deterioration rate.

FIG. 9 schematically shows a map 120 as deterioration rate information created based on the graphs of FIGS. 5 to 8. The map 120 is for obtaining the deterioration rate (mAh / g · t ^1/2 ) from the temperature T and the positive electrode potential Ep. This map 120 is stored in the storage 23 of the control device 20 mounted on the vehicle 10. The vertical axis is the temperature, and the temperature increases in the upward direction in FIG. 9, and decreases in the downward direction. The horizontal axis is the positive electrode potential Ep, and the positive electrode potential Ep increases toward the right in FIG. When the temperature is constant, the higher the positive electrode potential, the higher the deterioration rate. Further, when the positive electrode potential is constant, the higher the temperature, the higher the deterioration rate. Further, the deterioration rate increases toward the upper left side of the map 120. That is, the higher the temperature and the higher the positive electrode potential, the higher the deterioration rate synergistically.

The control device 20 obtains the deterioration rate from the positive electrode potential Ep and the temperature T using the map 120 shown in FIG. Further, the control device 20 multiplies the deterioration rate by the time (Δt) to calculate the capacity decrease amount Q2 due to the storage deterioration of the positive electrode.

In this way, the control device 20 estimates the capacity reduction amount Q1 and Q2 every time Δt, and the integrated value (ΣQ1, ΣQ2) of the capacity reduction amount calculated up to the previous time (nth time) is added to this time (n + 1th time). The capacity reduction amounts Q1 and Q2 calculated in 1 are newly integrated.

By repeating steps S11 to S15 in this way, the capacity reduction amounts Q1 and Q2 recorded in the storage 23 of the control device 20 are updated. Alternatively, the capacity reduction amounts Q1 and Q2 calculated every predetermined time Δt may be stored in the storage 23 each time the calculation is performed.

Next, with reference to FIG. 10, a deterioration determination method performed after the method of estimating the capacity reduction amount will be described. In the present embodiment, the deterioration determination is performed by using the inspection system 30 after removing the secondary battery 11 from the vehicle 10.

First, the secondary battery 11 is connected to the charge / discharge control circuit 31, charged to 100% SOC, and then discharged to acquire the battery capacity Q'(step S21). The battery capacity Q'is the discharge capacity, and the method for measuring the capacity is not particularly limited, and may be estimated from information on the battery usage status or the like.

Next, the deterioration determination device 35 acquires the initial capacity Q (step S22). The initial capacity is stored in the storage 23 or the like of the deterioration determination device 35, or is a specified value peculiar to the secondary battery 11. Further, the deterioration determination device 35 subtracts the battery capacity Q'from the initial capacity Q to calculate the capacity reduction amount ΔQ of the entire battery (step S23, capacity reduction amount specifying step).

Further, the deterioration determination device 35 acquires the capacity reduction amount Q1 due to the positive and negative electrode capacity deviation calculated in step S14 and the capacity reduction amount Q2 due to storage deterioration of the positive electrode calculated in step S15 (step S25, third step).

The deterioration determination device 35 determines whether or not the battery capacity Q'exceeds the first threshold value Qth1 (step S26). The first threshold value Qth1 is set to the lower limit of the capacity of the reusable secondary battery 11. This lower limit is common regardless of the application. When the deterioration determination device 35 determines that the battery capacity Q'is equal to or less than the first threshold value Qth1 (step S26: NO), the deterioration determination device 35 determines that the secondary battery 11 cannot be reused (step S29).

On the other hand, when the deterioration determination device 35 determines that the battery capacity Q'is equal to or less than the first threshold value Qth1 (step S26: YES), the deterioration determination device 35 determines whether or not the capacity decrease amount Q3 due to the cycle deterioration of the positive electrode is less than the second threshold value Qth2. (Step S27, determination step). The second threshold value Qth2 is a threshold value for classifying the deteriorated state of the secondary battery 11 into a first deteriorated state and a second deteriorated state when it is determined that the secondary battery 11 can be reused.

When the deterioration determination device 35 determines that the capacity reduction amount Q3 is less than the second threshold value Qth2 (step S27: YES), the deterioration determination device 35 determines that the secondary battery 11 is in the first deterioration state (step S28). The first deteriorated state is a state in which deterioration has not progressed as much as the second deteriorated state. The secondary battery 11 in the first deteriorated state is used as the secondary battery 11 used in a usage state in which the allowable range of SOC is wide, that is, in a state where deep charging / discharging is performed. Specifically, the secondary battery 11 in the first deteriorated state is used for stationary purposes such as home-use stationary use and industrial stationary use, or is used in an electric vehicle (EV vehicle).

On the other hand, when the deterioration determination device 35 determines that the capacity decrease amount Q3 is equal to or greater than the second threshold value Qth2 (step S27: NO), the deterioration determination device 35 determines that the secondary battery 11 is in the second deterioration state (step S30). The second deteriorated state is a state in which the deterioration is more advanced than the first deteriorated state, and the allowable range of SOC of the secondary battery 11 is relatively narrowed. In the second deteriorated state, it cannot be used for stationary applications such as home-use stationary and industrial stationary, or for electric vehicles (EV vehicles), and for hybrid vehicles and backup batteries for automatic driving where shallow charging and discharging are performed. Allows the use of.

The effect of the above embodiment will be described.
(1) In the present inventor, the deterioration factors of the secondary battery 11 are mainly the capacity reduction amount Q1 due to the positive and negative electrode capacity deviation, the capacity reduction amount Q2 due to the storage deterioration of the positive electrode, and the capacity reduction amount Q3 due to cycle deterioration. I paid attention to that. Of these, it is difficult to quantify the amount of capacity decrease Q3 due to cycle deterioration unless the secondary battery is disassembled. Therefore, the capacity reduction amount Q1 and the capacity reduction amount Q2 were estimated based on the voltage V and the temperature T, which are the usage histories of the secondary battery 11. Then, the capacity reduction amount Q3 was estimated by subtracting the capacity reduction amount Q1 and the capacity reduction amount Q2 from the capacity reduction amount ΔQ based on the initial capacity Q. Therefore, the deterioration state of the positive electrode can be estimated for each deterioration factor without damaging the secondary battery 11.

(2) In the above embodiment, the use for reuse according to the allowable range of SOC is determined based on the size of the capacity reduction amount Q3 of the secondary battery 11. Therefore, it is possible to appropriately determine the intended use of the secondary battery 11 when it is reused.

(3) In the above embodiment, the step of estimating the film forming current density based on the Tafel equation and the step of obtaining the side reaction current value from the film forming current density for the capacity decrease amount Q1 derived from the positive and negative electrode capacitance deviation. It was obtained by the step of calculating the first capacitance reduction amount from the side reaction current value of the positive electrode and the side reaction current value of the negative electrode. Therefore, the capacity reduction amount Q1 can be estimated without disassembling the secondary battery 11.

(4) In the above embodiment, a map 120 that defines the relationship between the deterioration rate of the positive electrode of the secondary battery 11 and the positive electrode potential and the temperature of the secondary battery 11 is prepared in advance, and is based on the usage history of the secondary battery 11. , The capacity decrease amount Q2 due to the storage deterioration of the positive electrode was obtained by referring to the map 120. That is, as long as the usage history of the secondary battery 11 is accumulated, the capacity reduction amount Q2 can be estimated without disassembling the secondary battery 11.

(5) According to the above embodiment, the control device 20 mounted on the vehicle 10 acquires the usage history of the secondary battery 11 in use, and estimates the capacity reduction amount Q1 and the capacity reduction amount Q2. Therefore, after the secondary battery 11 is removed from the vehicle 10, the capacity reduction amount Q1 and the capacity reduction amount Q2 calculated in advance can be used, so that the deterioration state can be determined in a short time.

Each of the above embodiments can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
-In the above embodiment, the deterioration determination device 35 calculates the capacity reduction amount ΔQ. The deterioration determination device may be an external charging device such as a charging stand that charges the secondary battery 11. As shown in FIG. 11, the vehicle 130 includes an in-vehicle charge control device 131 for charging the secondary battery 11 by a current supplied from the external charging device 140, and a control device 20 (see FIG. 2). The in-vehicle charge control device 131 may also serve as the control device 20. The in-vehicle charge control device 131 and the external charge device 140 are connected by cable groups 132 and 133. In addition to the charging cable, the cable groups 132 and 133 have a communication line used for communication between the in-vehicle charge control device 131 and the external charging device 140. Then, data is transmitted and received between the in-vehicle charge control device 131 and the external charge device 140 through this communication line. In this embodiment, the external charging device 140 may discharge (or charge) the secondary battery 11 to measure the discharge capacity (or charge capacity). Then, the measured discharge capacity (or charge capacity) may be transmitted to the in-vehicle charge control device 131 through the communication line. The in-vehicle charge control device 131 transmits the received discharge capacity (or charge capacity) to the control device 20, and the control device 20 calculates the capacity reduction amount ΔQ from the initial capacity and the discharge capacity (or charge capacity). According to this, the deterioration state of the secondary battery 11 can be determined in the state where the secondary battery 11 is mounted on the vehicle 130. Then, when the control device 20 determines that the secondary battery 11 is in the first deteriorated state or the second deteriorated state, the control device 20 operates the notification device provided on the instrument panel or the like of the vehicle 130 to operate the secondary battery 11. You may be notified of the deterioration of. Further, in this embodiment, in addition to measuring the discharge capacity (or charge capacity), the external charging device 140 acquires the capacity reduction amounts Q1 and Q2 from the in-vehicle charge control device 131 via the communication line, and the capacity reduction amount. Q3 may be calculated. Then, the deterioration state of the secondary battery 11 may be determined.

-In the above embodiment, when determining the reuse of the secondary battery 11, the deterioration determination device 35 determines whether or not the battery capacity Q'exceeds the first threshold value Qth1 (step S26). However, if the capacity reduction amount Q3 and the capacity reduction amounts Q1 and Q2 have a certain degree of correlation, and if it can be determined at least whether or not the capacity reduction amount Q3 is less than the second threshold value Qth2 (step S27), step S26. May be omitted.

-In the deterioration determination of the secondary battery 11, it is determined whether or not the battery capacity Q'is equal to or less than the first threshold value Qth1 and whether or not the capacity decrease amount Q3 due to the cycle deterioration of the positive electrode is less than the second threshold value Qth2. I did it. In addition to this, it may be determined whether or not the parameters indicating the usage history such as the usage period of the secondary battery 11 and the number of charge / discharge cycles exceed the threshold value.

-In the above embodiment, the battery state estimation system includes a control device 20 which is a first control device and a deterioration determination device 35 which is a second control device. Instead of this, the control device 20 may be divided into a device for estimating the capacity reduction amount Q1 and a device for estimating the capacity reduction amount. The deterioration determination device 35 is divided into a device that executes a step of specifying the capacity reduction amount ΔQ and a device that executes a step of subtracting the capacity reduction amounts Q1 and Q2 from the capacity reduction amount ΔQ to calculate the capacity reduction amount Q3. May be good.

-In the above embodiment, the secondary battery 11 has been described as a lithium ion secondary battery mounted on the vehicles 10 and 130, but it may be mounted on a moving body other than the vehicle. Further, it may be used for stationary purposes such as stationary use for home use and stationary use for industrial use. The use of these secondary batteries 11 at the time of reuse is not particularly limited. Further, the secondary battery 11 may be a battery other than the lithium ion secondary battery. For example, the factors of the capacity decrease are mainly the first capacity decrease amount due to the positive / negative electrode capacity shift, the second capacity decrease amount due to the side reaction in which a film is formed on the positive electrode active material, and the structural change of the positive electrode active material. An alkaline secondary battery such as a nickel-metal hydride secondary battery may be used as long as it can be divided into the third capacity reduction amount derived from the above.

10, 130 ... Vehicle 11 ... Secondary battery 20 ... Control device as the first control device 35 ... Deterioration judgment device as the second control device 120 ... Map as deterioration speed information

Claims (6)

It is a method of estimating the state of a secondary battery that estimates the state of a battery.
The capacity reduction amount specifying step for specifying the capacity reduction amount, which is the battery capacity reduction amount from the initial capacity of the secondary battery, and the capacity reduction amount specifying step.
The first step of specifying the amount of decrease in the first capacity due to the displacement of the positive and negative electrodes based on the positive electrode potential and the temperature, and
A second step of specifying a second volume decrease due to a side reaction in which a film is formed on the positive electrode active material based on the positive electrode potential and the temperature.
The third step of calculating the third capacity reduction amount due to the structural change of the positive electrode active material by subtracting the first capacity reduction amount and the second capacity reduction amount from the capacity reduction amount.
Secondary battery state estimation method including. When the third capacity reduction amount is less than the second threshold value, the secondary battery is determined as a secondary battery to be reused within a relatively wide SOC tolerance range, and the third capacity reduction amount is the said. The first aspect of claim 1, further comprising a determination step of determining the secondary battery as a secondary battery to be reused within a relatively narrow SOC tolerance when the secondary threshold is equal to or higher than the second threshold. Secondary battery status estimation method. The first step is
A current density estimation process that estimates the film formation current density for each electrode,
A current value estimation step in which a side reaction current value is estimated for each electrode based on the film formation current density,
It includes a step of calculating the first capacity reduction amount based on the difference between the side reaction current value of the negative electrode and the side reaction current value of the positive electrode and the time.
In the current density estimation step, "i ₀ " is the exchange current density, "α" is the transfer coefficient, "F" is the Faraday constant, "R" is the gas constant, "T" is the temperature, and "E'" is the film formation. When the potential, "E", is used as the electrode potential, the film forming current density is estimated based on the following equation (1).

In the current value estimation step, when the overvoltage term is "η", the side reaction current value is estimated based on the following equation (2).

The method for estimating the state of a secondary battery according to claim 1 or 2. In the second step, the second capacity reduction amount is specified based on the deterioration rate information indicating the relationship between the deterioration rate, which is the capacity reduction amount per hour, the positive electrode potential, and the temperature.
The deterioration rate information is associated with a higher deterioration rate as the positive electrode potential increases when the temperature is constant, and a higher deterioration rate as the temperature increases when the positive electrode potential is constant. Item 6. The method for estimating the state of a secondary battery according to any one of Items 1 to 3. The secondary battery is mounted on the vehicle and
The control device provided in the vehicle
Obtain the voltage and temperature of the secondary battery,
The first step of specifying the amount of decrease in the first capacity due to the displacement of the positive and negative electrodes is executed.
The method for estimating the state of a secondary battery according to any one of claims 1 to 4, wherein the second step of specifying the amount of decrease in the second capacity due to a side reaction in which a film is formed on the positive electrode active material is executed. .. It is a secondary battery state estimation system that estimates the battery state.
The first control device provided in the vehicle equipped with the secondary battery is
The first step of specifying the amount of decrease in the first capacity due to the displacement of the positive and negative electrodes based on the positive electrode potential and the temperature, and
Based on the positive electrode potential and temperature, the second step of specifying the amount of the second volume decrease due to the side reaction of forming a film on the positive electrode active material is executed.
The second control device is
The capacity reduction amount specifying step for specifying the capacity reduction amount, which is the battery capacity reduction amount from the initial capacity of the secondary battery, and the capacity reduction amount specifying step.
A secondary battery including the third step of subtracting the first capacity reduction amount and the second capacity reduction amount from the capacity reduction amount to calculate the third capacity reduction amount due to the structural change of the positive electrode active material. State estimation system.

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