JP7028072B2 - Battery system - Google Patents

Description

The present disclosure relates to a battery system comprising a lithium ion battery in which a material (for example, a spinel compound) in which a phase transition can occur during charging / discharging is used as a positive electrode active material.

Japanese Unexamined Patent Publication No. 2013-72659 (Patent Document 1) discloses a battery system including a lithium ion battery. This battery system calculates the Li concentration on the surface of the positive electrode active material by using the diffusion equation of the lithium (Li) concentration in the positive electrode active material as a battery model, and calculates the positive electrode potential from the Li concentration on the surface of the positive electrode active material. calculate.

Japanese Unexamined Patent Publication No. 2013-72659 Japanese Unexamined Patent Publication No. 2016-91802

In a lithium ion battery, it is known that when the potential of the negative electrode falls below a predetermined precipitation limit line, lithium may precipitate on the surface of the negative electrode and deteriorate. In order to suppress this lithium precipitation, for example, the positive electrode potential is calculated using the battery model shown in Patent Document 1, and the lithium ion so that the negative electrode potential calculated using the positive electrode potential does not fall below the precipitation limit line. It is desirable to limit the input (charging) of the battery.

However, when a material that can undergo a phase transition during charging / discharging (for example, a spinel compound) is used as the positive electrode active material, the behavior of the positive electrode potential changes according to the charging / discharging history due to the influence of the phase transition of the positive electrode active material. Can change. Therefore, if the battery model of Patent Document 1 that does not consider the phase transition of the positive electrode active material is used as the battery model used for calculating the positive electrode potential, the positive electrode potential cannot be calculated accurately. As a result, it is not possible to accurately determine whether or not the negative electrode potential has reached the precipitation limit line, and there is a concern that the input restriction (Li precipitation suppression) of the lithium ion battery cannot be appropriately performed.

The present disclosure has been made to solve the above-mentioned problems, and an object thereof is to limit the input of a lithium ion battery (Li precipitation) in a lithium ion battery having a positive electrode active material in which a phase transition can occur during charging / discharging. Suppression) is to be performed appropriately.

The battery system according to the present disclosure includes a lithium ion battery having a positive electrode active material in which a phase transition can occur during charging / discharging, and a control device for controlling charging / discharging of the lithium ion battery. The control device calculates the positive electrode potential of the lithium ion battery using the diffusion equation of lithium in the positive electrode active material considering the phase ratio of each phase of the positive electrode active material, and determines the voltage between terminals of the lithium ion battery and the positive electrode potential. It is used to calculate the negative electrode potential of the lithium ion battery and limit the charging of the lithium ion battery so that the negative electrode potential does not fall below the lithium precipitation limit line.

In the above system, the positive electrode potential of the lithium ion battery is calculated using a diffusion equation considering the phase ratio of each phase of the positive electrode active material. This makes it possible to accurately calculate the positive electrode potential in consideration of the phase transition of the positive electrode active material. The negative electrode potential is calculated from the positive electrode potential calculated accurately in this way, and the charging of the lithium ion battery is restricted so that the negative electrode potential does not fall below the lithium precipitation limit line. As a result, it is possible to appropriately limit the input of the lithium ion battery (suppress Li precipitation).

According to the present disclosure, in a lithium ion battery having a positive electrode active material in which a phase transition can occur during charging / discharging, input restriction (li precipitation suppression) of the lithium ion battery can be appropriately performed.

It is a block diagram which shows the whole composition of the vehicle which carried out the battery system. It is a figure which shows the structure of a cell. It is a flowchart which shows an example of the processing procedure which is executed when the ECU limits the input of a cell. It is a conceptual diagram of a battery model. It is a figure for demonstrating the calculation method of Li concentration distribution. It is a figure which shows the state of the phase transition which occurs in a positive electrode active material schematically. It is a flowchart which shows an example of the processing procedure which is executed when the ECU calculates a positive electrode potential. It is a figure which shows an example of the relationship between the surface Li concentration of the positive electrode active material particle, and the positive electrode open circuit potential. It is a flowchart which shows an example of the processing procedure which is executed when the ECU calculates a positive electrode potential.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

Hereinafter, a configuration in which the battery system according to the embodiment of the present disclosure is mounted on a vehicle will be described as an example. However, the use of the battery system is not limited to the vehicle, and may be, for example, stationary.

<Battery system configuration>
FIG. 1 is a block diagram schematically showing an overall configuration of a vehicle 100 equipped with a battery system according to the present embodiment. The vehicle 100 is a vehicle (hybrid vehicle, electric vehicle, or fuel cell vehicle) that can travel using electric power, and includes a motor generator (MG) 1, a power transmission gear 2, a drive wheel 3, and electric power. It includes a control unit (PCU: Power Control Unit) 4, a system main relay (SMR: System Main Relay) 5, and a battery system 200.

The battery system 200 includes an assembled battery 10, a voltage sensor 21, a current sensor 22, a temperature sensor 23, and an electronic control unit (ECU) 30.

MG1 is, for example, a three-phase AC rotary electric machine. The output torque of MG 1 is transmitted to the drive wheels 3 via the power transmission gear 2. The MG 1 can also generate electricity by the rotational force of the drive wheels 3 during the regenerative braking of the vehicle 100. Although FIG. 1 shows a configuration in which only one MG is provided, the number of MGs is not limited to one and may be two or more.

PCU4 includes an inverter and a converter (not shown). When the assembled battery 10 is discharged, the converter boosts the voltage supplied from the assembled battery 10 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive the MG1. On the other hand, when charging the assembled battery 10, the inverter converts the AC power generated by the MG 1 into DC power and supplies it to the converter. The converter steps down the voltage supplied from the inverter and supplies it to the assembled battery 10.

The SMR 5 is electrically connected to a power line connecting the assembled battery 10 and the PCU 4. When the SMR 5 is closed in response to a control signal from the ECU 30, electric power can be exchanged between the assembled battery 10 and the PCU 4.

The assembled battery 10 is configured to include a plurality of (for example, several) battery blocks (not shown), and each battery block is configured to include a plurality of (for example, several to several tens) single batteries 11. .. Each of the plurality of cell cells 11 is a lithium ion battery.

The voltage sensor 21 detects the voltage between terminals (battery voltage Vb) of each cell 11. The current sensor 22 detects the current (battery current Ib) input / output to / from the assembled battery 10. The temperature sensor 23 detects the temperature of each cell 11 (battery temperature Tb). Each sensor outputs the detection result to the ECU 30. The voltage sensor 21 may detect the voltage of the battery block. The voltage Vb of the cell 11 can be calculated by dividing the voltage of the voltage block by the number of cells. Further, the temperature sensor 23 may detect the temperature of the battery block.

The ECU 30 includes a CPU (Central Processing Unit) 31, a memory 32, and an input / output buffer (not shown). The ECU 30 controls the PCU 4 and the SMR 5 based on the signal received from each sensor and the map and the program stored in the memory 32.

FIG. 2 is a diagram showing the configuration of the cell 11. Since the configuration of each cell 11 is common, only one cell 11 is typically shown in FIG. The cell 11 is, for example, a square sealed cell, and includes a case 12, a safety valve 13 provided in the case 12, an electrode body 14 housed in the case 12, and an electrolytic solution (not shown). In FIG. 2, a part of the case 12 is seen through to show the electrode body 14.

The case 12 includes a case body 121 and a lid 122, both of which are made of metal, and is sealed by welding the lid 122 all around the opening provided in the case body 121. When the pressure inside the case 12 exceeds a predetermined value, the safety valve 13 discharges a part of the gas (hydrogen gas or the like) inside the case 12 to the outside. The electrode body 14 includes a positive electrode 141, a negative electrode 142, and a separator 143. The positive electrode 141 is inserted in the bag-shaped separator 143, and the positive electrode 141 inserted in the separator 143 and the negative electrode 142 are alternately laminated. The positive electrode 141 and the negative electrode 142 are electrically connected to a positive electrode terminal and a negative electrode terminal (not shown), respectively.

In the present embodiment, a spinel-based compound is used as a material for the active material of the positive electrode 141. Spinnel compounds used as materials for the positive electrode active material of lithium-ion batteries include, for example, lithium manganate (LiMn ₂ O ₄ ) and lithium manganate silicate (LiNi _0.5 Mn _1.5 O ₄ ). .. Hereinafter, an example in which lithium manganate manganate (LiNi _0.5 Mn _1.5 O ₄ ) is mainly used as the material of the active material of the positive electrode 141 will be described. Various conventionally known materials can be used for the negative electrode 142, the separator 143, and the electrolytic solution.

<Battery input restriction (Li precipitation suppression)>
It is known that in a lithium ion battery, when the potential of the negative electrode 142 falls below the precipitation limit line, lithium (Li) may precipitate on the surface of the negative electrode 142 and deteriorate. The precipitation limit line is the potential of the negative electrode 142 at which lithium begins to precipitate on the surface of the negative electrode 142.

In order to suppress this lithium precipitation, the ECU 30 according to the present embodiment includes the detection results (battery voltage Vb, battery current Ib and battery temperature Tb) of the voltage sensor 21, the current sensor 22 and the temperature sensor 23, and a battery model described later. The _positive potential potential V _p is _{calculated using} Performs processing to limit. The “positive electrode potential V _p ” is the potential of the positive electrode 141 of the cell 11 when the cell 11 is energized. The “negative electrode potential V _n ” is the potential of the negative electrode 142 of the cell 11 when the cell 11 is energized.

In the cell 11 according to the present embodiment, as described above, a spinel-based compound is used as a material for the positive electrode active material. When a spinel-based compound is used as a material for a positive electrode active material, it is known that a phase transition can occur in the positive electrode active material during charging and discharging of the cell 11. For example, when lithium manganate manganate (LiNi _0.5 Mn _1.5 O ₄ ) is used, the Li1 phase (LiNi _0.5 Mn _1.5 O ₄ ) and the Li1 / 2 phase (Li _0.5 Ni) are used. Bidirectional phase transition between _0.5 Mn _1.5 O ₄ ) and bidirectional between Li 1/2 phase and Li 0 phase (Ni _0.5 Mn _1.5 O ₄ ). Phase transitions can occur. In the cell 11 in which the spinel compound is used as the material of the positive electrode active material, the behavior of the positive electrode potential _Vp may change according to the charge / discharge history due to the influence of the phase transition of the positive electrode active material.

Therefore, if a conventional battery model that does not consider the phase transition of the positive electrode active material is used as the battery model used for calculating the positive electrode potential V _p , the positive electrode potential V _p cannot be calculated accurately. As a result, it is not possible to accurately determine whether or not the negative electrode potential V _n has reached the precipitation limit line, and there is a concern that the battery input restriction (Li precipitation suppression) cannot be appropriately performed.

Therefore, the ECU 30 according to the present embodiment calculates the positive electrode potential _Vp using a battery model formula (described later) in consideration of the phase ratio of each phase of the positive electrode active material. As a result, the positive electrode potential V _p can be calculated accurately, and as a result, it can be accurately determined whether or not the negative electrode potential V _n has reached the precipitation limit line. Li precipitation suppression) can be appropriately performed.

FIG. 3 is a flowchart showing an example of a processing procedure executed when the ECU 30 limits the input of the cell 11. This flowchart is repeatedly executed every time a predetermined condition is satisfied or at a predetermined calculation cycle.

The ECU 30 acquires the detection results (battery voltage Vb, battery current Ib, and battery temperature Tb) of the voltage sensor 21, the current sensor 22, and the temperature sensor 23 (step S10).

Next, the ECU 30 calculates the positive electrode potential _Vp using the information acquired in step S10 and the battery model formula in consideration of the phase ratio of each phase of the positive electrode active material (step S20). This process will be described in detail later.

Next, the ECU 30 calculates a value (= V _p −Vb) obtained by subtracting the battery voltage Vb acquired in step S10 from the positive electrode potential V _p calculated in step S20 as the negative electrode potential V _n (step S30). The value obtained by adding the salt concentration overvoltage to the value obtained by subtracting the battery voltage Vb from the positive electrode potential V _p (= V1-Vb + salt concentration overvoltage) may be calculated as the negative electrode potential V _n . The salt concentration overvoltage is a voltage generated when a concentration difference occurs in the electrolytic solution between the positive and negative electrodes. The salt concentration overvoltage can be calculated by a known calculation method using an existing battery model.

Next, the ECU 30 determines whether or not the negative electrode potential V _n is below the limiting start potential (step S40). The limiting start potential is the negative electrode potential at which the input limitation of the cell 11 is started. If the input limitation of the cell 11 is started after the negative electrode potential V _n falls below the precipitation limit line, Li precipitation may not be completely suppressed. Therefore, the limitation start potential is set to a predetermined control margin from the precipitation limit line ( For example, it is desirable to set the value as high as several mV).

When the negative electrode potential V _n is lower than the limit start potential (YES in step S40), the ECU 30 limits the input of the cell 11 (step S50). Specifically, the ECU 30 reduces the charging current of the cell 11. As a result, Li precipitation on the surface of the negative electrode 142 is suppressed.

On the other hand, when the negative electrode potential V _n is not lower than the limit start potential (NO in step S40), the ECU 30 does not limit the input of the cell 11 (step S60). Specifically, the ECU 30 does not reduce the charging current of the cell 11. As a result, it is possible to prevent the charging of the cell 11 from being excessively restricted.

<Battery model>
Next, the battery model used for calculating the positive electrode potential _Vp (step S20 in FIG. 3) will be described in detail.

FIG. 4 is a conceptual diagram of the battery model in the present embodiment. In this battery model, the positive electrode 141 of the lithium-ion battery (cell 11) is modeled as containing an aggregate of spherical positive electrode active materials 151, and the negative electrode 142 is modeled as containing an aggregate of spherical negative electrode active materials 152. There is. When the lithium ion battery is discharged, lithium ions (indicated by Li ⁺ ) and electrons (indicated by e- ⁾ are released at the interface between the negative electrode active material 152 and the electrolytic solution, while the positive electrode active material 151 and the electrolytic solution are released. Lithium ions and electrons are absorbed at the interface. When the lithium ion battery is charged, a reaction opposite to the above reaction occurs with respect to the emission / absorption of lithium ions and electrons.

In general, the computing power of the vehicle-mounted ECU is lower than the computing power of the research and development computing device. Therefore, in the vehicle-mounted battery system 200, it is required to reduce the computing load of the ECU 30. Therefore, in this embodiment, the battery model is simplified as follows. That is, where the positive electrode 141 contains a large number of positive electrode active materials, in the battery model of the present embodiment, a large number of positive electrode active materials are represented by a single positive electrode active material (positive electrode active material model) 151. Similarly, since the negative electrode 142 contains a large number of negative electrode active materials, in the battery model of the present embodiment, a large number of negative electrode active materials are represented by a single negative electrode active material (negative electrode active material model) 152. Using the active material model simplified in this way, the Li concentration distribution inside the positive electrode active material 151 is calculated. Similarly, the Li concentration distribution inside the negative electrode active material 152 can be calculated.

FIG. 5 is a diagram for explaining a method for calculating the Li concentration distribution inside the positive electrode active material model 151. In this battery model, it is assumed that the Li concentration distribution in the circumferential direction of the polar coordinates is uniform inside the spherical positive electrode active material model 151, and only the Li concentration distribution in the radial direction is considered. In other words, the positive electrode active material model 151 is a one-dimensional model in which the moving direction of lithium is limited to the radial direction. In the following description, those with the subscript " _s " mean the values in the positive electrode active material.

The Li concentration c _s (r) inside the positive electrode active material model 151 is the radial coordinate r of the positive electrode active material model 151 (r: the distance from the center of each point, r ₀ : the radius of the positive electrode active material model 151). It can be expressed as a function above. The Li concentration c _s (r ₀ ) when the coordinate r is the radius r ₀ of the positive electrode active material model 151 is the surface Li concentration of the positive electrode active material particles.

In the positive electrode active material model 151 shown in FIG. 5, the Li concentration cs ( _r ) is calculated according to the diffusion equation described later for each region N-divided (N: 2 or more natural numbers) in the radial direction. As a result, the Li concentration distribution in the radial direction as shown by the solid line in FIG. 5 is calculated.

<Calculation of positive electrode potential _Vp considering the phase transition of the positive electrode active material>
It is known that the positive electrode potential V _p is determined by the positive electrode open circuit potential _{Up and the overvoltage η p due} to the resistance component at the time of Li transfer (during charging / discharging) on the surface of the positive electrode active material. The positive electrode open circuit potential _Up is the potential of the positive electrode 141 of the cell 11 when the cell 11 is in the non-energized state (no load state).

The positive electrode open circuit potential _Up has a characteristic that changes depending on the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles. Therefore, in order to accurately calculate the positive electrode open circuit potential Up, it is _desirable to accurately calculate the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles.

Conventionally, the Li concentration distribution in the positive electrode active material has been calculated by using the Li diffusion equation represented by the formula (M2a) in Japanese Patent Application Laid-Open No. 2013-72659 as a battery model formula.

However, the conventional battery model formula does not consider the phase transition of the positive electrode active material. Therefore, as in the present embodiment, in the cell 11 using lithium manganate manganate (spinel-based compound), which can cause phase transfer in the positive electrode active material during charging and discharging, as the material of the positive electrode active material, a conventional battery is used. If the model formula is used, the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles cannot be calculated accurately, and as a result, the positive electrode open circuit potential _Up cannot be calculated accurately. I am concerned.

FIG. 6 is a diagram schematically showing a state of phase transition generated in the positive electrode active material 151 by the discharge of the cell 11.

When the cell 11 is discharged, lithium ions are inserted (absorbed) into the positive electrode active material 151. Lithium ions inserted in the positive electrode active material 151 diffuse in the positive electrode active material 151. At this time, a bias in the Li concentration c _s occurs, and a structural change (phase transition) occurs preferentially from the portion where the Li concentration c _s is high. As a result, Li1 phase, Li1 / 2 phase, and Li0 phase may coexist in the positive electrode active material 151. Since the Li diffusion rate is different for each phase (Li1 phase, Li1 / 2 phase, Li0 phase), the phase ratio of each phase affects the movement of lithium ions in the positive electrode active material 151.

Therefore, in the present embodiment, a conditional expression for phase transition is added according to the Li concentration _{cs in the positive electrode active material 151, and the Li diffusion coefficient D s used} in the Li diffusion equation is set for each phase of the positive electrode active material. By changing according to the phase ratio, the positive electrode open circuit potential _Up is calculated accurately.

Specifically, the distribution of the Li concentration c _s (r) inside the positive electrode active material model 151 (including the surface Li concentration c _s (r ₀ )) is measured using the Li diffusion equation shown in the following equation (1). To calculate.

However, the Li diffusion coefficient D _s in the formula (1) is changed according to the phase ratio ε _{s, j} of each phase of the positive electrode active material 151 as shown in the following formula (2).

In the formula (2), “ε _{s, j} ” is the phase ratio of the j phase (j = 1, 2, 3) of the positive electrode active material 151. That is, ε _{s, 1} is the phase ratio of the first phase (for example, Li1 phase), ε _{s, 2} is the phase ratio of the second phase (for example, Li1 / 2 phase), and ε _{s, 3} is the third phase (for example, Li0 phase). ) Phase ratio. The sum of the phase ratio ε _{s, 1} , the phase ratio ε _{s, 2} and the phase ratio ε _{s, 3} is “1”.

Further, "D _{s, j"} is a Li diffusion coefficient in the j phase, and is a value corresponding to the Li diffusion rate in the j phase. The Li diffusion coefficient D _{s, j} in the j phase can be determined, for example, with the battery temperature Tb as a parameter.

The phase ratio ε _{s, j} shall be calculated by the Abrami type phase transition formula as shown in the following formula (3).

In the formula (3), "R _jk " is the phase transition rate from the j phase to the k phase. "K _jk " is a phase transition rate coefficient from the j phase to the k phase. “ _{Cs, j} ” is the Li concentration in the j phase. “ _{Cs, jk, threshold} ” is the Li concentration at the time of the phase transition from the j phase to the k phase.

Further, since the amount of substance (Li amount) is preserved even if a phase transition occurs, the relational expression of the following equation (4) holds.

These equations (1) to (4) are Li diffusion equations in the positive electrode active material in consideration of the phase ratios ε _{s and j} of each phase of the positive electrode active material in the present embodiment. By using these formulas (1) to (4), the distribution of the Li concentration c _s (r) in the positive electrode active material (including the surface Li concentration c _s (r ₀ )) is changed to the phase transition of the positive electrode active material. Can be calculated accurately in consideration of.

FIG. 7 is a flowchart showing an example of a processing procedure executed by the ECU 30 in the processing for calculating the positive electrode potential _Vp (step S20 in FIG. 3).

The ECU 30 uses the battery model equations (1) to (4) described above in consideration of the phase ratios ε _{s and j} of each phase of the positive electrode active material, and distributes the Li concentration c _s (r) in the positive electrode active material. The surface Li concentration c _s (r ₀ ) is included) is calculated (step S21). At this time, the ECU 30 sequentially changes the radius r to r ₀ , r ₀ − Δr, r ₀ − 2Δr, ..., 0, while the Li concentration c _s (r) (r = r ₀ ) at each radius r. The surface Li concentration c _s (r ₀ ) is included) is calculated using the above-mentioned battery model equations (1) to (4). As a result, the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles is accurately calculated in consideration of the phase transition of the positive electrode active material.

Next, the ECU 30 calculates the positive electrode open circuit potential Up from the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles calculated in step _S21 (step S23). The positive electrode open circuit potential _Up is the potential of the positive electrode 141 of the cell 11 when the cell 11 is in the non-energized state (no load state).

FIG. 8 is a diagram showing an example of the relationship between the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles and the positive electrode open circuit potential _Up . As shown in FIG. 8, the positive electrode open circuit potential _Up has a characteristic that changes depending on the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles. In the memory 32 of the ECU 30, as shown in FIG. 8, the correspondence relationship between the surface Li concentration _cs ( _{r 0} ) of the positive electrode active material particles and the positive electrode open circuit potential Up is obtained and stored in advance by an experiment or the like. There is. The ECU 30 calculates the positive electrode open circuit potential Up corresponding to the surface Li concentration c _s (r ₀ ) calculated in step _S21 with reference to the correspondence stored in the memory 32.

Returning to FIG. 7, the ECU 30 calculates the positive electrode potential V _p by substituting the positive electrode _open circuit potential Up calculated in step S23 into the following equation (5) (step S25).

Positive electrode potential V _{p = Positive electrode open circuit potential Up + Overvoltage η p ...} (5)
In the formula (5), the overvoltage η _p is an overvoltage generated during charging / discharging due to the resistance component at the time of Li transfer on the surface of the positive electrode active material, as described above. The overvoltage η _p can be calculated by a known calculation method derived from the Butler-Volmer relational expression.

After that, the ECU 30 proceeds to the process in step S30 of FIG. That is, the ECU 30 calculates the value obtained by subtracting the battery voltage Vb from the positive electrode potential Vp calculated in step _S25A as the negative electrode potential _Vn . As a result, the negative electrode potential V _n can be calculated accurately in consideration of the phase ratios ε _{s and j} of each phase of the positive electrode active material, and as a result, whether or not the negative electrode potential V _n is lower than the limiting start potential. (Determination of step S40 in FIG. 3) can be accurately performed.

As described above, the ECU 30 according to the present embodiment calculates the positive electrode potential V _p using the Li diffusion equation in consideration of the phase ratios ε _{s and j} of each phase of the positive electrode active material. As a result, the positive electrode potential V _p can be calculated accurately in consideration of the phase transition of the positive electrode active material, so that it is determined whether or not the negative electrode potential V _n has reached the precipitation limit line (step 40 of FIG. 3). Judgment) can be performed accurately. As a result, even in the cell (lithium ion battery) 11 using lithium manganate manganate (spinel-based compound), which may cause phase transfer in the positive electrode active material during charging and discharging, as the positive electrode material, the input restriction of the cell 11 ( Li precipitation suppression) can be appropriately performed.

<Modification example>
In the above-described embodiment, the Li diffusion coefficient D _s used in the Li diffusion equation is changed according to the phase ratios ε _{s and j} of each phase of the positive electrode active material, whereby the positive electrode open circuit potential _Up is accurately set. Calculated.

On the other hand, in this modification, the positive electrode open circuit potential _Up is accurate by solving the Li diffusion equation for each phase (it is considered that Li diffuses in each phase according to the difference in Li concentration of each phase). Calculate well.

Specifically, in this modification, the distribution of the Li concentration c _s (r) in the positive electrode active material (including the surface Li concentration c _s (r ₀ )) is diffused in the same manner as in the above-described embodiment. Although it is calculated using an equation, it is treated as if a Li diffusion equation exists for each phase as shown in the following equations (1a) to (1c).

In the formulas (1a) to (1c), " _{cs, j} (r)" is the Li concentration in the radius r of the j phase (j = 1, 2, 3) in the positive electrode active material 151. That is, " _{cs, 1} (r)" in the formula (1a) is the Li concentration in the radius r of the first phase (for example, Li1 phase). “ _{Cs, 2} (r)” in the formula (1b) is the Li concentration in the radius r of the second phase (for example, Li1 / 2 phase). “Cs _{, 3} (r)” in the formula (1c) is the Li concentration in the radius r of the third phase (for example, Li0 phase).

Further, also in this modification, the phase ratio ε _{s, j} of each phase is calculated by the Abrami type phase transition formula shown in the above formula (3), as in the above-described embodiment.

Further, in this modification as well, as in the above-described embodiment, the amount of substance (Li amount) is preserved even if the phase transition occurs, so that the relational expression of the above-mentioned equation (4) holds.

These equations (1a) to (1c), (3), and (4) are the Li diffusion equations in the positive electrode active material in consideration of the phase ratios ε _{s and j} of each phase of the positive electrode active material in this modification. be. By using these formulas (1a) to (1c), (3), and (4), the distribution of the Li concentration c _s (r) in the positive electrode active material (surface Li concentration c _s (r ₀ )) is also included. ) Can be calculated accurately in consideration of the phase transition of the positive electrode active material.

FIG. 9 is a flowchart showing an example of a processing procedure executed by the ECU 30 in the process of calculating the positive electrode potential _Vp (step S20 in FIG. 3) according to this modification.

The ECU 30 uses the battery model equations (1a) to (1c), (3), and (4) described above in consideration of the phase transition of the positive electrode active material, and distributes the Li concentration c _s (r) in the positive electrode active material. (Including the surface Li concentration c _s (r ₀ )) is calculated (step S21A).

Specifically, the ECU 30 sequentially changes the radius r to r ₀ , r ₀ − Δr, r ₀ − 2Δr, ..., 0 for each Li concentration c _{s, j} (r) of each phase of the positive electrode active material. However, the Li concentration c _{s, j} (r) of each phase at each radius r (including the surface Li concentration c _{s, j} (r ₀ ) of each phase when r = r ₀ ) is sequentially calculated. Further, the ECU 30 calculates the phase ratio ε _{s, j} of each phase of the positive electrode active material. Then, the ECU 30 uses the battery model formula (4) to determine the surface inside the positive electrode active material from the calculated surface Li concentration c _{s, j} (r ₀ ) of each phase and the phase ratio ε _{s, j} of each phase. The Li concentration c _s (r ₀ ) is calculated. As a result, the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles is accurately calculated in consideration of the phase transition of the positive electrode active material.

Next, the ECU 30 stores the positive electrode open circuit potential Up corresponding to the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles calculated in step _S21A in the above-mentioned memory 32 in the correspondence relationship shown in FIG. (Step S23A).

Next, the ECU 30 calculates the positive electrode potential V _p by substituting the positive electrode open circuit potential Up calculated in step _S23A into the above equation (5) (step S25A).

After that, the ECU 30 proceeds to the process in step S30 of FIG. That is, the ECU 30 calculates the value obtained by subtracting the battery voltage Vb from the positive electrode potential Vp calculated in step _S25A as the negative electrode potential _Vn . As a result, the negative electrode potential V _n can be calculated accurately in consideration of the phase transition of the positive electrode active material, and as a result, it is determined whether or not the negative electrode potential V _n is below the limiting start potential (step in FIG. 3). The determination of S40) can be performed accurately.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present disclosure is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

2 power transmission gear, 3 drive wheels, 10 sets of batteries, 11 single batteries, 12 cases, 13 safety valves, 14 electrodes, 21 voltage sensors, 22 current sensors, 23 temperature sensors, 30 ECUs, 32 memories, 100 vehicles, 121 cases. Body, 122 lid, 141 positive electrode, 142 negative electrode, 143 separator, 151 positive electrode active material, 152 negative electrode active material, 200 battery system.

Claims (1)

A lithium-ion battery having a positive electrode active material that can undergo a phase transition during charging and discharging,
A control device for controlling the charge and discharge of the lithium ion battery is provided.
The control device is
The positive electrode potential of the lithium ion battery was calculated using the diffusion equation of lithium in the positive electrode active material in consideration of the phase ratio of each phase of the positive electrode active material.
The negative electrode potential of the lithium ion battery is calculated using the voltage between the terminals of the lithium ion battery and the positive electrode potential.
A battery system that limits the charging of the lithium ion battery so that the negative electrode potential does not fall below the lithium precipitation limit line.

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