JP2019212392A - Battery system - Google Patents

Abstract

To provide a lithium ion battery including a positive electrode active material that may cause phase transition during charging/discharging, in which input restriction (Li deposition suppression) of the lithium ion battery is properly performed.SOLUTION: A battery system includes a lithium ion battery including a positive electrode active material that may cause phase transition during charging/discharging, and an ECU (control unit) for controlling the charging/discharging of the lithium ion battery. The ECU calculates a positive electrode potential using a lithium diffusion equation considering the phase ratio of each phase of the positive electrode active material, calculates, as a negative electrode potential, a value obtained by subtracting the positive electrode potential from an inter-terminal voltage of the battery, and restricts the charging of the lithium ion battery such that the negative electrode potential does not fall below a lithium deposition limit line.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to a battery system including a lithium ion battery in which a material (for example, a spinel compound) capable of generating a phase transition during charge / discharge is used as a positive electrode active material.

  Japanese Patent Laying-Open 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.

JP 2013-72659 A JP, 2006-91802, A

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

  However, when a material (for example, a spinel compound) that can generate a phase transition during charge / discharge is used as the positive electrode active material, the behavior of the positive electrode potential depends on the charge / discharge history due to the effect 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 accurately calculated. As a result, it cannot be accurately determined whether or not the negative electrode potential has reached the deposition limit line, and there is a concern that input limitation (Li deposition suppression) of the lithium ion battery cannot be performed appropriately.

  The present disclosure has been made in order to solve the above-described problems. The object of the present disclosure is to limit the input of a lithium ion battery (Li precipitation) in a lithium ion battery having a positive electrode active material capable of causing a phase transition during charge and discharge. (Suppression) is performed appropriately.

  A battery system according to the present disclosure includes a lithium ion battery having a positive electrode active material capable of causing phase transition during charging and discharging, and a control device that controls charging and 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 calculates the inter-terminal voltage and the positive electrode potential of the lithium ion battery. Use 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 deposition limit line.

  In the above system, the positive electrode potential of the lithium ion battery is calculated using a diffusion equation that considers the phase ratio of each phase of the positive electrode active material. Thereby, the positive electrode potential can be accurately calculated in consideration of the phase transition of the positive electrode active material. Thus, the negative electrode potential is calculated from the positive electrode potential calculated with high accuracy, and charging of the lithium ion battery is limited so that the negative electrode potential does not fall below the lithium deposition limit line. As a result, it is possible to appropriately limit the input of the lithium ion battery (suppression of Li precipitation).

  According to the present disclosure, in a lithium ion battery having a positive electrode active material that can undergo phase transition during charge and discharge, input restriction (Li precipitation suppression) of the lithium ion battery can be appropriately performed.

It is a block diagram which shows roughly the whole structure of the vehicle carrying a battery system. It is a figure which shows the structure of a cell. It is a flowchart which shows an example of the process sequence performed when ECU restrict | 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 typically the mode of the phase transfer generate | occur | produced in a positive electrode active material. It is a flowchart which shows an example of the process sequence performed when ECU calculates a positive electrode electric potential. It is a figure which shows an example of the relationship between the surface Li density | concentration of a positive electrode active material particle, and a positive electrode open circuit electric potential. It is a flowchart which shows an example of the process sequence performed when ECU calculates a positive electrode electric potential.

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

  Hereinafter, a configuration in which a battery system according to an 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 a vehicle, and may be a stationary one, for example.

<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 run using electric power, and includes a motor generator (MG: Motor Generator) 1, a power transmission gear 2, drive wheels 3, and electric power. A control unit (PCU) 4, a system main relay (SMR) 5, and a battery system 200 are provided.

  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: Electronic Control Unit) 30.

  MG1 is, for example, a three-phase AC rotating electric machine. The output torque of the MG 1 is transmitted to the drive wheel 3 via the power transmission gear 2. The MG 1 can also generate power by the rotational force of the drive wheels 3 during 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.

  Although not shown, the PCU 4 includes an inverter and a converter. When the battery pack 10 is discharged, the converter boosts the voltage supplied from the battery pack 10 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power and drives MG1. On the other hand, when the battery pack 10 is charged, the inverter converts 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 that connects the assembled battery 10 and the PCU 4. When SMR 5 is closed in response to a control signal from ECU 30, power can be exchanged between assembled battery 10 and PCU 4.

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

  The voltage sensor 21 detects the inter-terminal voltage (battery voltage Vb) of each unit cell 11. The current sensor 22 detects a current (battery current Ib) input / output to / from the assembled battery 10. The temperature sensor 23 detects the temperature (battery temperature Tb) of each unit cell 11. Each sensor outputs the detection result to the ECU 30. The voltage sensor 21 may detect the voltage of the battery block. By dividing the voltage of the voltage block by the number of cells, the voltage Vb of the cells 11 can be calculated. 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). ECU 30 controls PCU 4 and SMR 5 based on a signal received from each sensor and a map and a program stored in memory 32.

  FIG. 2 is a diagram illustrating a configuration of the single battery 11. Since the configuration of each unit cell 11 is common, only one unit cell 11 is representatively shown in FIG. The unit 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 accommodated in the case 12, and an electrolytic solution (not shown). In FIG. 2, the electrode body 14 is shown through a part of the case 12.

  The case 12 includes a case main body 121 and a lid body 122 both made of metal, and the lid body 122 is hermetically sealed by welding the entire circumference of the lid body 122 on an opening provided in the case main 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 into a bag-shaped separator 143, and the positive electrode 141 and the negative electrode 142 inserted into the separator 143 are alternately stacked. 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 this embodiment, a spinel compound is used as a material for the active material of the positive electrode 141. Examples of spinel compounds used as a positive electrode active material for lithium ion batteries include lithium manganate (LiMn ₂ O ₄ ) and lithium nickel manganate (LiNi _0.5 Mn _1.5 O ₄ ). . Hereinafter, an example in which lithium nickel 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 (suppression of Li deposition)>
In a lithium ion battery, it is known that lithium (Li) may be deposited and deteriorated on the surface of the negative electrode 142 when the potential of the negative electrode 142 falls below the deposition limit line. The deposition limit line is the potential of the negative electrode 142 where lithium begins to precipitate on the surface of the negative electrode 142.

In order to suppress this lithium deposition, ECU 30 according to the present embodiment detects the detection results (battery voltage Vb, battery current Ib, and battery temperature Tb) of voltage sensor 21, current sensor 22, and temperature sensor 23, and a battery model to be described later. calculating the positive electrode potential V _p with the input battery voltage Vb and the positive electrode potential V _p to calculate the negative electrode potential V _n and a, the negative electrode potential V _n is so as not to fall below the deposition limit line cell 11 (charging) The process of restricting is performed. “Positive electrode potential V _p ” is the potential of the positive electrode 141 of the unit cell 11 when the unit cell 11 is in an energized state. The “negative electrode potential V _n ” is the potential of the negative electrode 142 of the unit cell 11 when the unit cell 11 is in an energized state.

In unit cell 11 according to the present embodiment, as described above, a spinel compound is used as the material of the positive electrode active material. When a spinel compound is used as a material for the positive electrode active material, it is known that a phase transition can occur in the positive electrode active material during charging / discharging of the unit cell 11. For example, when lithium nickel manganate (LiNi _0.5 Mn _1.5 O ₄ ) is used, a Li1 phase (LiNi _0.5 Mn _1.5 O ₄ ) and a Li1 / 2 phase (Li _0.5 Ni _0.5 Mn _1.5 O ₄ ) and bi-directional phase transition between Li 1/2 phase and Li 0 phase (Ni _0.5 Mn _1.5 O ₄ ). Phase transitions can occur. In cells 11 spinel compound is used as the material of the positive electrode active material, the influence of the phase transition of the positive electrode active material, the behavior of the positive electrode potential V _p may vary depending on the charge and discharge history.

Therefore, as a battery model used to calculate the positive electrode potential V _p, the use of conventional battery model without considering the phase transition of the positive electrode active material can not be calculated with the positive potential V _p accuracy. As a result, the anode potential V _n can not be determined with high accuracy whether or not reached precipitation limit line, there is concern that can not be performed input limit of the battery a (Li deposition suppression) properly.

Therefore, ECU 30 of this embodiment calculates the positive electrode potential V _p using the battery model equation in consideration of the phase fraction of each phase of the positive electrode active material (described below). Thus, the positive electrode potential V _p can be calculated accurately, as a result, since whether the anode potential V _n has reached the deposition limit line can be determined accurately, the input of the cell 11 limit ( Li precipitation suppression) can be performed appropriately.

  FIG. 3 is a flowchart illustrating an example of a processing procedure executed when the ECU 30 performs input restriction on the single battery 11. This flowchart is repeatedly executed every time a predetermined condition is satisfied or every predetermined calculation cycle.

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

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

Then, ECU 30 determines whether or not the anode potential _{V n} is below a limit starting potential (step S40). The restriction start potential is a negative electrode potential at which input restriction of the unit cell 11 is started. When the negative electrode potential V _n begins to input limit of the cell 11 from below the deposition limit line, because it may not be suppressed Li deposition, a predetermined control margin than deposit limit line restriction start voltage ( For example, it is desirable to set the value higher by about several mV.

When the negative electrode potential _{V n} is below a limit starting potential (YES in step S40), ECU 30 performs input limit of the cell 11 (step S50). Specifically, the ECU 30 reduces the charging current of the cell 11. Thereby, 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 below the limit onset potential (NO in step S40), ECU 30 does not perform the input limit of the cell 11 (step S60). Specifically, the ECU 30 does not reduce the charging current of the unit cell 11. Thereby, it is suppressed that charge of the cell 11 is restrict | limited excessively.

<Battery model>
Next, the battery model used to calculate the positive electrode potential V _p (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 (unit cell 11) includes an assembly of spherical positive electrode active materials 151, and the negative electrode 142 is modeled as an assembly of spherical negative electrode active materials 152. Yes. At the time of discharging of the lithium ion battery, while 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, the positive electrode active material 151 and the electrolytic solution Lithium ions and electrons are absorbed at the interface. When a lithium ion battery is charged, a reaction opposite to the above reaction occurs with respect to the release / absorption of lithium ions and electrons.

  In general, the computing capacity of an in-vehicle ECU is lower than the computing capacity of a research and development computing device. Therefore, in the in-vehicle battery system 200, it is required to reduce the computation load of the ECU 30. Therefore, in the present embodiment, the battery model is simplified as follows. That is, the positive electrode 141 includes a large number of positive electrode active materials. In the battery model in this 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, the negative electrode 142 includes a large number of negative electrode active materials. In the battery model in this embodiment, a large number of negative electrode active materials are represented by a single negative electrode active material (negative electrode active material model) 152. The Li concentration distribution inside the positive electrode active material 151 is calculated using the simplified active material model. Similarly, the Li concentration distribution inside the negative electrode active material 152 can also 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 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, the suffix “ _s ” means a value in the positive electrode active material.

The Li concentration c _s (r) inside the positive electrode active material model 151 is a coordinate r in the radial direction of the positive electrode active material model 151 (r: distance from the center of each point, r ₀ : 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 c _s (r) is calculated according to a diffusion equation described later for each region that is divided into N (N: natural number of 2 or more) in the radial direction. Thereby, the Li concentration distribution in the radial direction as shown by the solid line in FIG. 5 is calculated.

<Calculation of the positive electrode potential V _p 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 U _p and the overvoltage η _p due to the resistance component at the time of Li transfer (charge / discharge) on the surface of the positive electrode active material. SeikyokuHiraki circuit potential U _p 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).

SeikyokuHiraki circuit potential _{U p} has a characteristic that changes depending on the surface Li concentration _c s of the positive electrode active material particle _{(r 0).} Therefore, in order to accurately calculate the SeikyokuHiraki circuit potential U _p, it is desirable to calculate the surface Li concentration c _s of the positive electrode active material particles _{(r 0)} accurately.

  Conventionally, the Li concentration distribution in the positive electrode active material has been calculated using the Li diffusion equation represented by the formula (M2a) in JP2013-72659A as the 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, the single battery 11 using lithium manganate (spinel-based compound) that can cause phase transfer in the positive electrode active material during charge and discharge as the material of the positive electrode active material is a conventional battery. with model equation can not be calculated surface Li concentration c _s of the positive electrode active material particles _{(r 0)} accurately, as a result, may become impossible to accurately calculate the SeikyokuHiraki circuit potential U _p Concerned.

  FIG. 6 is a diagram schematically showing the state of phase transfer generated in the positive electrode active material 151 due to the discharge of the unit cell 11.

When the single battery 11 is discharged, lithium ions are inserted (absorbed) into the positive electrode active material 151. The lithium ions inserted into the positive electrode active material 151 diffuse in the positive electrode active material 151. At this time, cause deviation of the Li concentration c _s, preferentially structural change from partial Li concentration c _s is high (phase transition) occurs. As a result, in the positive electrode active material 151, a Li1 phase, a Li1 / 2 phase, and a Li0 phase can be mixed. 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 c _s 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 varying depending on the phase ratio is calculated accurately SeikyokuHiraki circuit potential U _p.

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

However, the Li diffusion coefficient D _s in the equation (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 equation (2).

In Expression (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 (eg, Li1 phase), ε _{s, 2} is the phase ratio of the second phase (eg, Li1 / 2 phase), and ε _{s, 3} is the third phase (eg, 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”.

“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 using, for example, the battery temperature Tb as a parameter.

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

In Expression (3), “R _jk ” is a phase transition speed 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 phase transition from the j phase to the k phase.

  Moreover, since the substance amount (Li amount) is preserved even when the phase transition occurs, the following relational expression (4) holds.

These equations (1) to (4) are Li diffusion equations in the positive electrode active material in consideration of the phase ratio ε _{s, 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 (surface Li concentration _c s (including _{r 0)),} the phase transition of the positive electrode active material Can be calculated with high accuracy.

Figure 7 is a flowchart illustrating an example of a processing procedure executed in the processing of ECU30 calculates the positive electrode potential _{V p} (step S20 in FIG. 3).

The ECU 30 uses the battery model equations (1) to (4) described above in consideration of the phase ratio ε _{s, j} of each phase of the positive electrode active material to distribute the Li concentration c _s (r) in the positive electrode active material ( The surface Li concentration c _s (including r ₀ ) 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 changing the Li concentration c _s (r) at each radius r (when r = r ₀ ). The surface Li concentration c _s (including r ₀ ) is calculated using the battery model equations (1) to (4) described above. Thereby, 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.

Then, ECU 30 from the surface Li concentration _c s of the positive electrode active material particles calculated in the step S21 _{(r 0),} calculates the SeikyokuHiraki circuit potential _{U p} (step S23). SeikyokuHiraki circuit potential U _p 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).

Figure 8 is a diagram showing an example of the relationship between the surface Li concentration c _s of the positive electrode active material particle and _{(r 0)} and SeikyokuHiraki circuit potential U _p. As shown in FIG. 8, SeikyokuHiraki circuit potential U _p has a characteristic that changes depending on the surface Li concentration c _s of the positive electrode active material particle _{(r 0).} The ECU30 memory 32, as shown in FIG. 8, the correspondence relationship between the surface Li concentration c _{s (r 0)} and SeikyokuHiraki circuit potential U _p of the positive electrode active material particles are stored is obtained in advance by experiment or the like Yes. ECU30 refers to the correspondence relation stored in the memory 32, calculates the SeikyokuHiraki circuit potential _{U p} corresponding to the surface Li concentration _c s calculated in step S21 _{(r 0).}

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

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

Thereafter, the ECU 30 advances the process to step S30 in FIG. That, ECU 30 calculates a value obtained by subtracting the battery voltage Vb from the positive potential _{V p} calculated in step S25A as the negative electrode potential _{V n.} Thus, considering the phase ratio epsilon _{s, j} of each phase of the positive electrode active material can be calculated anode potential V _n accurately, as a result, whether the negative electrode potential V _n is below the limit onset potential (Step S40 in FIG. 3) can be accurately determined.

As described above, the ECU 30 according to the present embodiment calculates the positive electrode potential V _p using the Li diffusion equation considering the phase ratio ε _{s, j} of each phase of the positive electrode active material. Accordingly, since the positive electrode potential V _p can be accurately calculated in consideration of the phase transition of the positive electrode active material, it is determined whether or not the negative electrode potential V _n has reached the precipitation limit line (step 40 in FIG. 3). Determination) can be performed with high accuracy. As a result, even in a single battery (lithium ion battery) 11 using lithium nickel manganate (spinel compound) that can cause phase transfer in the positive electrode active material during charge and discharge as a positive electrode material, the input restriction of the single battery 11 ( Li precipitation suppression) can be performed appropriately.

<Modification>
In the above embodiment, by changing in accordance with Li diffusion coefficient D _s to a phase ratio epsilon _{s, j} of each phase of the positive electrode active material used in Li diffusion equation, accurately SeikyokuHiraki circuit potential U _p Calculated.

In contrast, in this modification, (think Li is diffused within each phase in response to each phase of Li density difference) of Li solving the diffusion equation for each phase by, accuracy SeikyokuHiraki circuit potential U _p Calculate well.

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

In the formulas (1a) to (1c), “c _{s, j} (r)” is the Li concentration at 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 at the radius r of the first phase (for example, Li1 phase). “Cs ₂ (r)” in the formula (1b) is the Li concentration at the radius r of the second phase (for example, Li1 / 2 phase). “C _{s, 3} (r)” in the formula (1c) is the Li concentration at the radius r of the third phase (for example, Li0 phase).

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

  Also in this modified example, the amount of substance (Li amount) is preserved even when a phase transition occurs, as in the above-described embodiment, and thus the relational expression of the above-described expression (4) holds.

These equations (1a) to (1c), (3), and (4) are Li diffusion equations in the positive electrode active material in consideration of the phase ratio ε _{s, j} of each phase of the positive electrode active material in this modification. is there. Also by using these formulas (1a) to (1c), (3), (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 included. ) Can be accurately calculated in consideration of the phase transition of the positive electrode active material.

Figure 9 is a flowchart illustrating an example of a processing procedure executed in the process of ECU30 according to the present modification calculates the positive electrode potential V _p (step S20 in FIG. 3).

The ECU 30 uses the above battery model equations (1a) to (1c), (3), and (4) in consideration of the phase transition of the positive electrode active material, to distribute 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. Accordingly, 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 included) 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 equation (4) to calculate the surface in 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. Thereby, 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 U _p corresponding to the surface Li concentration c _s (r ₀ ) of the positive electrode active material particles calculated in step S21A, as shown in FIG. To calculate (step S23A).

Then, ECU 30 by substituting the SeikyokuHiraki circuit potential _{U p} calculated in step S23A in the above equation (5) to calculate the positive electrode potential _{V p} (step S25A).

Thereafter, the ECU 30 advances the process to step S30 in FIG. That, ECU 30 calculates a value obtained by subtracting the battery voltage Vb from the positive potential _{V p} calculated in step S25A as the negative electrode potential _{V n.} Accordingly, the negative electrode potential V _n can be accurately calculated 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 limit start potential (step of FIG. 3). S40) can be performed with high accuracy.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  2 power transmission gear, 3 driving wheel, 10 assembled battery, 11 cell, 12 case, 13 safety valve, 14 electrode body, 21 voltage sensor, 22 current sensor, 23 temperature sensor, 30 ECU, 32 memory, 100 vehicle, 121 case Main body, 122 Lid body, 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 capable of causing phase transition during charge and discharge;
A controller for controlling charging and discharging of the lithium ion battery,
The control device includes:
Calculate 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,
Calculate the negative electrode potential of the lithium ion battery using the voltage between the terminals of the lithium ion battery and the positive electrode potential,
A battery system that limits charging of the lithium ion battery so that the negative electrode potential does not fall below a lithium deposition limit line.

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