JP2017010882A - Secondary battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy in calculation of salt concentration distribution in a secondary battery system that calculates salt concentration distribution based on the flow rate of electrolyte solution in an electrode body.SOLUTION: An ECU 300 virtually divides an anode plate 140 (anode active material layer 144) into a plurality of areas R. Lithium concentration in each of the areas R is regarded to be uniform. The ECU 300 calculates volume Vfrom the lithium concentration for each of the areas R. By integrating the volumes Vof the areas R, the entire volume ΔVof the anode plate 140 is calculated. The volume expansion rate βof the anode plate 140 is calculated from an amount ΔVof change in the entire volume of the anode plate 140.SELECTED DRAWING: Figure 11

Description

  The present invention relates to a secondary battery system, and more particularly to a technique for calculating a salt concentration distribution in an electrolyte solution of a secondary battery.

  It is known that the internal resistance increases when charging and discharging with a large current are repeated in a secondary battery. The amount of increase in internal resistance depends on the salt concentration distribution (bias) in the electrolyte. The amount of increase in internal resistance increases as the salt concentration bias increases.

  Since the increase in internal resistance causes a decrease in battery performance, a configuration for calculating the salt concentration distribution in the electrolyte has been proposed in order to grasp the amount of increase in internal resistance. For example, Japanese Patent Laying-Open No. 2010-60406 (Patent Document 1) discloses a configuration for calculating a concentration distribution of a lithium salt in an active material model for each of a negative electrode and a positive electrode in a lithium ion secondary battery (for example, Patent Document 1). Paragraph [0119]).

JP 2010-60406 A

  When the SOC (State Of Charge) of the battery changes, the volume of the electrode body can change. With the volume change (expansion or contraction) of the electrode body, the electrolytic solution can flow inside the positive electrode, the negative electrode, and the separator, each of which is a porous material. The salt concentration distribution in the electrolytic solution can be calculated by solving an equation (liquid flow equation) that defines the flow of the electrolytic solution based on fluid dynamics for each of the positive electrode, the negative electrode, and the separator.

  The liquid flow equation for the negative electrode includes the volume expansion coefficient of the negative electrode as a parameter. The volume expansion coefficient of the negative electrode can be calculated from the SOC based on, for example, a map showing the relationship between the SOC of the battery and the volume expansion coefficient of the negative electrode. The same applies to the positive electrode and the separator.

  In a general battery model, the volume expansion coefficient of the negative electrode is uniquely determined when the SOC of the battery is determined. On the other hand, when the graphite is used as the negative electrode material in the lithium ion secondary battery, for example, when the lithium concentration distribution in the negative electrode active material layer is different even if the SOC of the battery is the same, We focused on the point that the volume expansion coefficient of the negative electrode may be different. In other words, the present inventors have focused on the point that hysteresis due to the lithium concentration distribution in the negative electrode active material layer may exist in the volume expansion coefficient of the negative electrode.

  If the influence of hysteresis is not taken into account, the volume expansion coefficient of the negative electrode may not be calculated with high accuracy. As a result, the calculation accuracy of the flow velocity calculated using the volume expansion coefficient of the negative electrode may be limited. As a result, there is room for improvement in the calculation accuracy of the salt concentration distribution.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to calculate a salt concentration distribution by taking into account the influence of hysteresis in a secondary battery system that calculates a salt concentration distribution in an electrolytic solution. It is to improve accuracy.

  A secondary battery system according to an aspect of the present invention includes a lithium ion secondary battery and a control device. The lithium ion secondary battery includes an electrode body in which a positive electrode and a negative electrode having a graphite material are stacked with a separator interposed therebetween, and an electrolytic solution. The control device calculates the flow rate of the electrolytic solution using a liquid flow equation that defines the flow of the electrolytic solution for each of the positive electrode, the negative electrode, and the separator, and based on the calculated flow rate, the salt concentration distribution in the electrolytic solution And the degree of deterioration of the lithium ion secondary battery is estimated based on the calculated salt concentration distribution. The liquid flow equation includes the volume expansion coefficient of the negative electrode as a parameter. The control device virtually divides the negative electrode into a plurality of regions. In each of the plurality of regions, it can be considered that the lithium concentration inside is uniform. For each of the plurality of regions, the control device calculates the volume from the lithium concentration, adds the volumes of each of the plurality of regions, calculates the total volume of the negative electrode, and calculates the negative electrode volume from the amount of change in the total volume of the negative electrode. It is comprised so that a volume expansion coefficient may be calculated.

  According to the above configuration, the negative electrode is virtually divided into a plurality of regions. Then, the volume of each region is calculated based on the lithium concentration distribution in the negative electrode (negative electrode active material layer). Furthermore, the total volume of the negative electrode is calculated by integrating the volume of each region. Then, the volume expansion coefficient is calculated from the change amount of the entire volume. By adopting such a calculation method, a configuration that does not consider the lithium concentration distribution in the negative electrode (for example, a configuration that simply calculates a volume expansion coefficient using a map from the SOC (State Of Charge) of a lithium ion secondary battery) and In comparison, the calculation accuracy of the volume expansion coefficient can be improved. As a result, since the calculation accuracy of the flow velocity in the negative electrode is improved, it is possible to improve the calculation accuracy of the salt concentration distribution.

  ADVANTAGE OF THE INVENTION According to this invention, the calculation accuracy of salt concentration distribution can be improved in the secondary battery system which calculates salt concentration distribution in electrolyte solution.

It is a block diagram which shows roughly the structure of the vehicle by which the secondary battery system which concerns on this Embodiment is mounted. It is a figure which shows the structure of a battery in detail. It is an expanded view of a laminated body. It is an external view of a laminated body. It is a conceptual diagram for demonstrating an example of salt concentration distribution in the lamination direction of an electrode body. It is a conceptual diagram for demonstrating an example of salt concentration distribution in the in-plane direction of an electrode body. It is a figure for demonstrating a battery model. It is a figure which shows the change of the volume expansion coefficient of a negative electrode plate in comparison at the time of charge of a battery, and discharge. It is a figure which shows the relationship between the capacity | capacitance of a negative electrode plate, and an electric potential. It is a figure for demonstrating the change of the volume expansion coefficient accompanying a stage change. It is a figure for demonstrating the calculation method of the volume expansion coefficient of a negative electrode plate. It is a flowchart for demonstrating the calculation process of the battery deterioration degree in this Embodiment. It is a figure which shows an example of the correspondence of the bias | inclination of salt concentration, and the increase amount of internal resistance.

  Hereinafter, embodiments of the present invention 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 the secondary battery system according to the present invention is mounted on an electric vehicle will be described as an embodiment of the present invention. However, the secondary battery system according to the present invention can be applied not only to an electric vehicle but also to any electric vehicle equipped with a secondary battery such as a hybrid vehicle and a fuel cell vehicle. Moreover, the use of the secondary battery system according to the present invention is not limited to vehicles.

[Embodiment]
<Vehicle configuration>
FIG. 1 is a block diagram schematically showing a configuration of a vehicle 1 on which a secondary battery system 10 according to the present embodiment is mounted. FIG. 1 shows a system configuration related to charge / discharge control of the electric system in the vehicle 1.

  Referring to FIG. 1, a vehicle 1 includes a secondary battery system 10, a system main relay (SMR) 20, a power control unit (PCU) 30, a motor generator (MG: Motor). Generator) 40 and drive wheels 50. The secondary battery system 10 includes a battery 100, a monitoring unit 200, and an electronic control unit (ECU: Electronic Control Unit) 300.

  Battery 100 includes a plurality of cells 110 (see FIG. 2) connected in series to each other. Typically, a non-aqueous electrolyte secondary battery such as a lithium ion battery or a nickel metal hydride battery is applied to each cell. In this embodiment, a configuration to which a lithium ion secondary battery is applied will be described as an example.

  Monitoring unit 200 includes a voltage sensor 210, a current sensor 220, and a temperature sensor 230. The voltage sensor 210 detects the voltage (battery voltage) VB of each cell in the battery 100. The current sensor 220 detects a current (input / output current) IB input / output to / from the secondary battery system 10. The temperature sensor 230 detects the temperature (battery temperature) TB of each cell. Each sensor outputs a signal indicating the detection result to ECU 300. ECU 300 calculates the SOC (State Of Charge) of each cell based on the signal from each sensor.

  The SMR 20 is electrically connected between the battery 100 and the PCU 30. The SMR 20 is turned on / off in response to a control signal from the ECU 300. Thereby, conduction | electrical_connection and interruption | blocking between the battery 100 and PCU30 are switched.

  PCU 30 includes, for example, a converter and an inverter (both not shown). The PCU 30 is configured to be capable of bi-directional power conversion between the battery 100 and the MG 40 in accordance with a switching command from the ECU 300. The converter is configured to perform bidirectional DC voltage conversion between the battery 100 and the inverter. The inverter is configured to perform bidirectional power conversion between DC power and AC power input / output to / from the MG 40.

  More specifically, the inverter converts DC power supplied from the battery 100 via the converter into AC power and supplies the AC power to the MG 40. Thereby, the MG 40 generates the driving force of the driving wheel 50. On the other hand, at the time of regenerative braking of vehicle 1, the inverter converts AC power (regenerative power) generated by MG 40 into DC power and supplies it to the converter. Thereby, the battery 100 is charged.

  ECU 300 includes a CPU (Central Processing Unit) (not shown), a memory 310 such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and an input / output interface (not shown). . Based on the signals from the sensors, the ECU 300 reads out a program stored in advance in a ROM or the like to the RAM and executes it, thereby executing control related to vehicle running and charging / discharging. Note that at least a part of the ECU 300 may be configured by hardware such as an electronic circuit.

<Battery configuration>
FIG. 2 is a diagram showing the configuration of the battery 100 in more detail. Referring to FIGS. 1 and 2, battery 100 includes a plurality of cells 110, a pair of end plates 112, a restraining band 114, and a plurality of bus bars 116. The number of cells is not particularly limited. The x axis, the y axis, and the z axis are orthogonal to each other. The upper vertical direction is the positive direction of the z-axis.

  Each of the plurality of cells 110 has a battery case 111 having a flat rectangular shape, for example. The plurality of cells 110 are stacked in the y direction so that the side surfaces having the largest area face each other with a distance therebetween. In FIG. 2, one end in the stacking direction is partially shown in the stack configured by stacking a plurality of cells 110. A pair of end plates 112 (only one is shown in FIG. 2) are disposed so as to face one end and the other end in the stacking direction (y direction), respectively. The pair of end plates 112 are restrained by a restraining band 114 with all the cells 110 sandwiched therebetween.

  Each cell 110 has a positive terminal and a negative terminal. A positive electrode terminal of a certain cell is disposed so as to face a negative electrode terminal of an adjacent cell. A positive electrode terminal of a certain cell and a negative electrode terminal of an adjacent cell are fastened by a bus bar 116 using bolts and nuts (both not shown). Thereby, the plurality of cells 110 are connected to each other in series. An electrode body 120 (see FIGS. 3 and 4) is accommodated in each of the battery cases 111 of the plurality of cells 110.

  FIG. 3 is a development view of the electrode body 120. FIG. 4 is an external view of the electrode body 120. Referring to FIGS. 3 and 4, electrode body 120 includes a positive electrode plate 130, a negative electrode plate 140, and a separator 150.

  As shown in FIG. 3, the positive electrode plate 130, the negative electrode plate 140, and the separator 150 are laminated | stacked and the laminated body is formed. Further, as shown by an arrow AR in FIG. 4, a wound body is formed by winding the laminated body around the x axis. The x direction is the in-plane direction of each layer, and the y direction is the stacking direction of each layer. In addition, it is not essential to form the electrode body 120 as a wound body.

  The positive electrode plate 130 includes a current collector foil 132 and a positive electrode active material layer 134 formed on the surface of the current collector foil 132. The positive electrode active material layer 134 includes a positive electrode active material, a conductive material, and a binder (none of which are shown). Similarly, the negative electrode plate 140 includes a current collector foil 142 and a negative electrode active material layer 144 formed on the surface of the current collector foil 142. The negative electrode active material layer 144 includes a negative electrode active material, a conductive material, and a binder (all not shown). In the present embodiment, an example in which graphitic carbon (graphite) is used as the material of the negative electrode plate 140 will be described. The separator 150 is provided between the positive electrode plate 130 and the negative electrode plate 140. A region where the positive electrode active material layer 134 and the negative electrode active material layer 144 face each other through the separator 150 is indicated by A.

<Salt concentration distribution>
Since each of the positive electrode active material layer 134, the negative electrode active material layer 144, and the separator 150 is a porous material, the inside thereof is impregnated with an electrolytic solution. When the temperature change or SOC change of the cell 110 occurs, the volume change of the electrolytic solution and the volume change of the electrode body 120 may occur. Due to such a volume change, an electrolyte flow (hereinafter also referred to as “liquid flow”) may occur in each of the positive electrode active material layer 134, the negative electrode active material layer 144, and the separator 150. When the liquid flow occurs, the concentration distribution of the salt (lithium salt in the present embodiment) in the electrolytic solution changes from the initial state, and there is a possibility that the salt concentration is biased.

FIG. 5 is a conceptual diagram for explaining an example of a salt concentration distribution in the stacking direction (y direction) of the electrode body 120. In FIG. 5, the horizontal axis represents the position y of the electrode body 120 in the stacking direction. It represents the position of the positive electrode plate 130 in _{y p,} represents the position of the negative electrode plate 140 at _{y n,} representing the position of the separator 150 at _{y s.} The vertical axis represents the salt concentration.

  Referring to FIG. 5, when cell 110 is charged, the salt concentration near negative electrode plate 140 is higher than the salt concentration near positive electrode plate 130, as shown by curve CHG. On the contrary, when the cell 110 is discharged, the salt concentration near the positive electrode plate 130 becomes higher than the salt concentration near the negative electrode plate 140 as shown by the curve DCH.

  FIG. 6 is a conceptual diagram for explaining an example of the salt concentration distribution in the in-plane direction (x direction) of the electrode body 120. In FIG. 6, the horizontal axis represents the position x in the in-plane direction of the electrode body 120, and the vertical axis represents the salt concentration.

  Referring to FIG. 6, when cell 110 is charged (for example, during charging or immediately after charging), the salt concentration near the center of region A is the salt concentration at both ends of region A as shown by curve CHG. Higher than. On the other hand, when the cell 110 is discharged (for example, during or immediately after discharge), the salt concentration near the center of the region A is lower than the salt concentrations at both ends of the region A as shown by the curve DCH. .

  Such a salt concentration distribution is calculated by constructing a battery model of the cell 110 and solving a liquid flow equation describing the flow of the electrolytic solution based on fluid dynamics. More specifically, the flow rate of the electrolytic solution is calculated using the liquid flow equation for each of the positive electrode plate 130, the negative electrode plate 140, and the separator 150. Further, the salt concentration distribution is calculated based on the calculated flow velocity.

<Battery model>
FIG. 7 is a diagram for explaining a battery model. Referring to FIG. 7, each of positive electrode plate 130, negative electrode plate 140, and separator 150 is virtually divided into a plurality of minute regions S along the in-plane direction. For each minute region S, the flow velocity is calculated based on the following formulas (1) and (2).

Equation (1) is an equation describing the liquid flow at time t, and is known as the Navier-Stokes equation. Equation (2) is a continuous equation regarding the law of conservation of mass of the electrolyte. In the equations (1) and (2), the flow rate of the electrolytic solution is represented by u _j , the density of the electrolytic solution is represented by ρ, the viscosity of the electrolytic solution is represented by μ, the transmission coefficient is represented by K _j , and the volume of the electrolytic solution The fraction is represented by ε _{e, j} and the pressure (internal pressure) of the electrolyte is represented by p. The unknowns are the flow velocity u _j and the pressure p.

The subscript j attached to each parameter of the flow velocity u _j , the transmission coefficient K _j , and the volume fraction ε _{e, j} is used to distinguish the positive electrode plate 130, the negative electrode plate 140, and the separator 150. That is, j = p indicates that the parameter relates to the positive electrode plate 130. j = n indicates that the parameter relates to the negative electrode plate 140. When j = s, it indicates that the parameter relates to the separator 150. The subscript j is also used for parameters (salt concentration c _{e, j,} etc.) described later, but the meaning is equivalent. The volume fraction ε _{e, j} means the ratio of the volume of the electrolytic solution in the component j to the entire volume of the component j (for example, in the case of the negative electrode plate 140, the negative electrode active material layer 144).

The volume of the electrode body 120 can change according to a change in the battery temperature TB or a change in the SOC. The negative electrode plate 140 will be described. When the electrode body 120 expands, an electrolyte flows from the center C of the negative electrode plate 140 (more specifically, the negative electrode active material layer 144) toward both ends (an arrow with a flow rate u _j attached). ). On the other hand, when the electrode body 120 contracts, the electrolyte flows from both ends of the negative electrode active material layer 144 toward the center C. The same applies to the positive electrode active material layer 134 and the separator 150.

The volume change of the electrode body 120 will be described in more detail. In the electrode body 120, the volume of the active material layer changes as the volume of the positive electrode active material and the negative electrode active material (hereinafter sometimes collectively referred to as “active material”) changes according to the battery temperature TB or SOC. Can do. Then, the volume fraction ε _{e, j of} the electrolytic solution impregnated in the active material layer changes. The change amount Δε _{e, j} of the volume fraction ε _{e, j} is expressed by the following equation (3) using the volume expansion rate β _j of the component j.

Will be described later in detail a method of calculating the volume expansion ratio beta _j, but if the calculated volume expansion ratio beta _j, it is possible to calculate the volume fraction epsilon _{e, j} by using equation (3). Furthermore, the flow velocity u _j can be calculated by substituting the calculated volume fraction ε _{e, j} into the above formulas (1) and (2).

If the flow velocity u _j is calculated, the salt concentration c _{e, j} in the electrolytic solution can be calculated based on the following formula (4). Equation (4) is known as the advection diffusion equation. In Equation (4), the first term on the left side defines the change in salt concentration at a predetermined time. The second term on the left side defines the change in salt concentration depending on the flow rate u _{j of the} electrolyte. The first term on the right side defines the diffusion state of the salt in the electrolyte. It represents the effective diffusion coefficient of the electrolyte solution _D ^e, in ^{j eff.} The second term on the right side defines the amount of salt produced in the electrolyte. The transport number of the salt in the electrolytic solution is represented by t ₊ ⁰ . F is a Faraday constant.

By calculating the salt concentration c _{e, j} for each of the plurality of minute regions S based on the equation (4), the salt concentration distribution (the bias of the salt concentration c _{e, j} ) can be obtained.

Here, as can be seen from the above formulas (1) and (3), the liquid flow equation relating to the negative electrode plate 140 includes the volume expansion coefficient β _n of the negative electrode plate 140 as a parameter. The volume expansion coefficient β _n of the negative electrode plate 140 can be calculated from the SOC of the cell 110, for example, but in the present embodiment, the present inventors have identified the negative electrode plate 140 (more specific even if the SOC is the same). Specifically, attention was paid to the fact that when the lithium concentration distribution in the negative electrode active material layer 144) is different, the volume expansion coefficient β _n of the negative electrode plate 140 may be different.

8, a change in expansion coefficient beta _n of the negative electrode plate 140 is a diagram showing a comparison in time of charging the battery 100 and at the time of discharge. 8 and FIG. 9 described later, the horizontal axis represents the SOC of the cell 110, and the vertical axis represents the volume expansion coefficient β _n of the negative electrode plate 140. Curve C shows the relationship between the SOC of cell 110 and the volume expansion coefficient β _{n of} negative electrode plate 140 when battery 100 is charged. Curve D shows the relationship between the SOC of cell 110 and the volume expansion coefficient β _{n of} negative electrode plate 140 when battery 100 is discharged.

As shown in FIG. 8, when graphite is used as a negative electrode material in a lithium ion secondary battery as in the present embodiment, the volume expansion coefficient β _n of the negative electrode plate 140 is different between charging and discharging of the cell 110. The way of change can be different. This is because the lithium concentration distribution in the negative electrode active material layer 144 is different when the cell 110 is charged and discharged even if the SOC is the same. Thus, the volume expansion ratio beta _n, there may be a hysteresis due to the lithium concentration distribution.

Without considering the influence of hysteresis, it may not be able to calculate the volume expansion coefficient beta _n of the negative electrode plate 140 with high accuracy. Then, the limit may occur in calculation accuracy of the velocity u _n which is calculated by using the volumetric expansion coefficient beta _n of the negative electrode plate 140. As a result, there is room for improvement in the calculation accuracy of the salt concentration distribution.

Therefore, according to the present embodiment, a configuration in which the volume of the negative electrode plate 140 is calculated in consideration of the lithium concentration distribution in the negative electrode active material layer 144 is employed. More specifically, the negative electrode plate 140 is virtually divided into a plurality of regions R. Then, the volume of each region R is calculated according to the lithium concentration distribution. Furthermore, by by integrating the volume of each region R calculated obtaining a negative electrode plate 140 total volume, the volume expansion coefficient beta _n of the negative electrode plate 140 is calculated.

First, at the time of charging the battery 100 and the time of discharge differ lithium concentration in the negative electrode active material layer 144, so that the way of change of the volume expansion factor beta _n as is briefly described for different reasons.

  FIG. 9 is a diagram showing the relationship between the capacitance of the negative electrode plate 140 and the potential. In FIG. 9, the horizontal axis represents the negative electrode capacity (capacity per unit weight of the negative electrode plate 140) (unit: mAh / g). The vertical axis represents the potential of the negative electrode plate 140 with respect to lithium metal.

  Referring to FIG. 9, when graphite is used as a negative electrode material, lithium is occluded between layers of a layered structure of graphite. It is known that graphite has a stage structure that regularly occludes lithium for each specific layer. Stage structures can be classified into four types. In stage 1, lithium is occluded in each layer. On the other hand, in stage 4, there are three layers in which lithium is not occluded between two layers in which lithium is occluded. Thus, the stage n (n = 1, 2, 3, 4) refers to a state in which (n−1) layers in which lithium is not stored exist between layers in which lithium is stored.

  When the negative electrode capacity is divided into the three ranges T12, T23, and T34, in the range T12, the graphite mainly takes the state where the stage 1 and the stage 2 coexist. In the range T23, the graphite mainly takes a state where the stage 2 and the stage 3 coexist. In the range T34, the graphite mainly takes a state where the stage 3 and the stage 4 coexist. This is because graphite is an active material that causes a two-phase coexistence reaction.

Figure 10 is a diagram for explaining the change of volume expansion ratio beta _n with the stage change. In FIG. 10, the horizontal axis represents the capacity per unit weight of the negative electrode plate 140. The vertical axis represents the volume expansion coefficient β _n of the negative electrode plate 140.

FIG. 10 shows an example in which graphite reaches from stage 4 to stage 2 through stage 3 when battery 100 is charged. Between each stage, the volume fluctuation rate β _n of the negative electrode plate 140 may change nonlinearly. Therefore, when the stage is switched with charging / discharging, there is a possibility that the change in the volume expansion coefficient β _n becomes abrupt.

As described with reference to FIG. 9, the stage structure of graphite depends on the negative electrode capacity of the negative electrode plate 140. However, if there is a bias in the lithium concentration in the active material, the stage structure (more specifically, the ratio of the coexistence state of the stage structure) may be different even if the negative electrode capacities are equal. Therefore, the volume expansion coefficient β _n of the negative electrode plate 140 varies depending on how the lithium concentration in the active material is biased. Generally, when the SOC increases due to charging of the battery 100 and reaches the value S1, and when the SOC decreases due to discharging of the battery 100 and reaches the same value S1, the lithium concentration distribution in the active material is Different. Therefore, depending on whether the battery 100 is in a charged state or a discharged state, the volume expansion coefficient β _n varies even if the SOC is the same.

Next, a method for calculating the volume expansion coefficient β _n of the negative electrode plate 140 from the lithium concentration distribution in the active material layer (negative electrode active material layer 144) of the negative electrode plate 140 will be described in more detail.

Figure 11 is a diagram for explaining a method of calculating the expansion coefficient beta _n of the negative electrode plate 140. FIG. 11A shows a calculation method in the comparative example, and FIG. 11B shows a calculation method in the present embodiment.

  Referring to FIG. 11A, in the negative electrode active material layer 144, insertion and extraction of lithium are mainly performed on the surface opposite to the current collector foil 142. That is, the right side in the figure is the surface of the negative electrode plate 140, and the left side in the figure is the inside of the negative electrode plate 140. The lithium concentration on the surface side of the negative electrode plate 140 is higher than the lithium concentration inside the negative electrode plate 140. As described above, in the negative electrode active material layer 144, unevenness in lithium concentration can occur.

However, in the comparative example, such unevenness in lithium concentration is not taken into consideration. In the comparative example, the map or arithmetic expression indicating the relationship between the SOC and the negative electrode plate 140 overall expansion coefficient beta _n of the battery 100 is prepared in advance. Then, the volume expansion coefficient β _n of the negative electrode plate 140 is calculated from the SOC of the battery 100.

  On the other hand, in this embodiment, as shown in FIG. 11B, the negative electrode plate 140 is virtually divided into (i × j) regions R. The size of each region R is preferably set to be sufficiently small by performing a simulation or the like in advance. This makes it possible to assume that the internal lithium concentration is uniform in each of the plurality of regions R.

For each region R, the negative electrode capacity C_i _{, j} corresponding to the internal lithium concentration is calculated. Since this calculation method is known, detailed description will not be repeated, but the negative electrode capacity _{C_i, j} can be calculated based on a battery chemical reaction model. For example, by using the model described in FIG. 9 and FIG. 10, the negative electrode capacity _{C_i} of each region R depends on the SOC of the battery 100 and whether the battery 100 is in a charged state or a discharged state _{. j} can be calculated.

Furthermore, the negative electrode capacity _{C _i, j} and the volume _{V _i,} by previously preparing in advance a map or arithmetic expression indicating the relationship between the _j, the negative electrode capacity _{C _i,} the volume from the _{j V _i,} calculates the _j. Thereby, the volume _{V_i, j} of each of (i × j) regions R is calculated. Then, the volume V _all of the negative electrode plate 140 can be calculated by integrating the volumes _{V_i, j} of each region R (see the following formula (5)).

The volume V _all is calculated, for example, every time a predetermined condition is satisfied or every predetermined calculation cycle. When the volume V _all calculated in the n-th (n: integer) calculation is expressed as V _all (n), the volume change ΔV (between the (n−1) -th calculation and the n-th calculation. n) is expressed as the following formula (6).

Since the reference volume of the negative electrode plate 140 is known, the volume expansion coefficient β _n of the negative electrode plate 140 can be calculated by calculating the volume change ΔV of the negative electrode plate 140.

Thus, according to the present embodiment, negative electrode plate 140 is virtually divided into a plurality of regions R. In each of the plurality of regions R, the lithium concentration inside can be regarded as uniform. Then, based on the lithium concentration distribution in the active material layer 144, negative electrode capacity _{C _i} of each region _{R, j} is calculated, the negative electrode capacity _{C _i,} the volume from the _{j V _i, j} is calculated. Furthermore, the total volume of the negative electrode plate 140 is calculated by integrating the volumes _{V_i, j} of the regions R. And volume expansion coefficient (beta) _n is computed from the variation | change_quantity of the whole volume. By adopting such a calculation method, it is possible to improve the calculation accuracy of the volume expansion coefficient β _n as compared with the configuration not considering the lithium concentration distribution in the negative electrode active material layer 144 (the configuration of the comparative example). As a result, since the improved calculation accuracy of the flow velocity u _n of the negative electrode plate 140, it is possible to improve the calculation accuracy of the salt concentration distribution.

  FIG. 12 is a flowchart for explaining battery deterioration degree calculation processing in the present embodiment. Control according to the flowchart shown in FIG. 12 is called and executed from the main routine by ECU 300 when a predetermined condition is satisfied (for example, at the start of charging / discharging) or at a predetermined calculation cycle. Each step (hereinafter, step is abbreviated as S) is basically realized by software processing by the ECU 300, but may be realized by hardware processing. Below, the calculation process regarding the negative electrode plate 140 is demonstrated.

1 to 4, 7, and 12, in S <b> 10, ECU 300 determines each parameter of electrode body 120 and electrolytic solution. More specifically, ECU 300 reads transmission coefficient K _n , electrolyte solution density ρ, and viscosity μ from memory 310.

As each parameter, a predetermined fixed value may be used, or for example, a variable value corresponding to the battery temperature TB or SOC may be used. For example, the density ρ of the electrolytic solution changes according to the battery temperature TB. Therefore, if a map showing the correspondence between the density ρ and the battery temperature TB is prepared in advance, the density ρ corresponding to the battery temperature TB can be calculated. The same applies to the viscosity of the transmission coefficient K _n and an electrolyte mu.

In S20, ECU 300 is negative electrode capacity _{C _i} of each region R where the negative electrode plate 140 is divided _virtually, the volume from the _{j V _i,} calculates the _j. For example by previously preparing the arithmetic expression or a map in advance, can be converted negative electrode capacity C _{_i, j} is the volume V _{_i,} to _j.

In S30, the ECU 300 calculates the total volume V _all of the negative electrode plate 140 by integrating the volume _{V_i, j} of each region R calculated in S20 for all regions (see the above formula (5)). .

In S40, the ECU 300 calculates the difference value between the nth calculation cycle (current calculation cycle) and the (n-1) th calculation cycle (previous calculation cycle), thereby calculating the total volume of the negative electrode plate 140. The change amount ΔV _all (n) is calculated (see the above formula (6)).

In S50, the ECU 300 calculates the volume expansion coefficient β _n of the negative electrode plate 140 from the volume change amount ΔV _all (n) of the negative electrode plate 140.

In S60, the ECU 300 converts the volume expansion rate β _n into the volume fraction ε _{e, n} of the negative electrode plate 140 based on the above equation (3).

In S70, ECU 300 may read various parameters and volume expansion ratio beta _n the above equation calculated in S60 at S10 (1), by applying to (2), to calculate the flow velocity _{u n} of the electrolytic solution.

In S80, ECU 300 substitutes the flow velocity _{u n} calculated at S70 on the equation (4), is calculated salt concentration _{c e,} the _n. Further, the ECU 300 calculates a salt concentration distribution based on the salt concentration c _{e, n} of each micro region S.

  In S90, ECU 300 calculates increase amount ΔR of internal resistance R of battery 100 based on the salt concentration distribution. Since the increase amount ΔR of the internal resistance R is an index value indicating the degree of deterioration of the battery 100 (the progress rate of high-rate deterioration), this process corresponds to the process of estimating the degree of deterioration of the battery 100. The increase amount ΔR of the internal resistance R can be calculated as follows, for example.

FIG. 13 is a diagram illustrating an example of a correspondence relationship between the deviation of the salt concentration c _{e, j} and the increase amount ΔR of the internal resistance R. 13, the horizontal axis represents the difference in salt concentration c _e, as an index value indicating the deviation of the _j, salt concentration c _e among multiple small areas _S, the maximum value and the minimum value of _j. The vertical axis represents the increase amount ΔR of the internal resistance R.

Referring to FIG. 13, the amount of increase ΔR of internal resistance R increases as the difference in salt concentration c _{e, j} increases. By storing such a correspondence relationship in advance in the memory 310 of the ECU 300 as a map (or an arithmetic expression), the increase amount ΔR of the internal resistance R can be calculated according to the difference in the salt concentration c _{e, j.} . As a result, it is possible to detect an increase in the internal resistance R due to deterioration due to charging / discharging with a large current (high-rate deterioration).

  Returning to FIG. 12, in S100, the ECU 300 determines whether or not the increase amount ΔR of the internal resistance R is equal to or greater than a predetermined threshold value Rc. If increase amount ΔR of internal resistance R is equal to or greater than threshold value Rc (YES in S100), ECU 300 advances the process to S120, assuming that high-rate deterioration has progressed to some extent. In S120, ECU 300 restricts charging / discharging of battery 100 from the viewpoint of suppressing further high-rate deterioration of battery 100. Specifically, ECU 300 decreases charge power upper limit value Win and discharge power upper limit value Wout as compared with the increase in internal resistance R. Thereafter, the process is returned to the main routine.

  On the other hand, if the increase amount ΔR of the internal resistance R is the threshold value Rc (NO in S100), the ECU 300 skips S110 and returns the process to the main routine, assuming that the high-rate deterioration has not progressed much.

As described above, according to this embodiment, by calculating the flow velocity u _n in consideration of the hysteresis effect of the expansion coefficient beta _n of the negative electrode plate 140, it is possible to improve the calculation accuracy of the flow velocity u _n . As a result, the calculation accuracy of the salt concentration distribution can be improved. Thereby, since the calculation accuracy of the increase amount ΔR of the internal resistance R is improved, it is possible to appropriately protect the battery 100 from high rate deterioration.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention 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.

  1 vehicle, 10 secondary battery system, 20 system main relay (SMR), 30 power control unit (PCU), 40 motor generator (MG), 50 drive wheels, 60 acceleration sensor, 100 battery, 110 cell, 111 battery case, 112 end plate, 114 restraint band, 116 bus bar, 130 positive electrode plate, 132, 142 current collector foil, 134 positive electrode active material layer, 140 negative electrode plate, 144 negative electrode active material layer, 150 separator, 160, 170 interface, 200 monitoring unit, 210 voltage sensor, 220 current sensor, 230 temperature sensor, 300 electronic control unit (ECU), 310 memory.

Claims (1)

An electrode body in which a positive electrode and a negative electrode having a graphite material are laminated via a separator, and a lithium ion secondary battery including an electrolytic solution;
For each of the positive electrode, the negative electrode, and the separator, the flow rate of the electrolytic solution is calculated using a liquid flow equation that defines the flow of the electrolytic solution, and the salt in the electrolytic solution is calculated based on the calculated flow rate. A control device that calculates a concentration distribution and estimates the degree of deterioration of the lithium ion secondary battery based on the calculated salt concentration distribution;
The liquid flow equation includes a volume expansion coefficient of the negative electrode as a parameter,
The control device virtually divides the negative electrode into a plurality of regions,
In each of the plurality of regions, the lithium concentration inside can be regarded as uniform,
The controller is
For each of the plurality of regions, calculate the volume from the lithium concentration,
By integrating the volume of each of the plurality of regions, the total volume of the negative electrode is calculated,
A secondary battery system configured to calculate a volume expansion coefficient of the negative electrode from an amount of change in the total volume of the negative electrode.

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