JP6360008B2 - Secondary battery system, vehicle including the same, and secondary battery control method - Google Patents

Description

  The present invention relates to a secondary battery system, a vehicle including the same, and a control method for the secondary battery, and more particularly to a technique for calculating a salt concentration distribution in an electrolyte solution of the 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 (salt concentration deviation) 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

  In many cases, the electrode body of the secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator sheet. When the temperature of the secondary battery or SOC (State Of Charge) changes, the volume change of each sheet (particularly the volume change of the active material layer of the positive electrode sheet and the negative electrode sheet) may occur. For example, when the sheet expands and the thickness of the sheet increases, the electrolytic solution easily flows inside the sheet, and the flow rate of the electrolytic solution can be increased. As a result, the salt concentration distribution inside the sheet changes.

  The flow rate of the electrolytic solution is calculated by solving an equation (liquid flow equation) that defines the flow of the electrolytic solution based on fluid dynamics. Furthermore, by substituting the flow rate calculated from the liquid flow equation into the equation (advection diffusion equation) that regulates the time change of the salt concentration due to salt diffusion while considering the flow rate of the electrolyte, The salt concentration is calculated. Thereby, the salt concentration distribution in the electrolytic solution can be calculated.

  As described above, since there is a correlation between the flow rate of the electrolytic solution and the thickness of the sheet, the flow rate of the electrolytic solution is determined according to the thickness of the sheet. The thickness of the sheet can be calculated in consideration of the balance of forces acting on the sheet by approximating the sheet to a spring.

  Generally, a secondary battery is classified into a square secondary battery, a cylindrical secondary battery, and a laminate type secondary battery according to its shape. Among these, it is desirable to calculate the flow rate of the electrolyte also for the cylindrical secondary battery in consideration of the above-described balance of forces. However, conventionally, in the cylindrical secondary battery, the relationship of force balance has not been considered when calculating the flow rate of the electrolyte. Therefore, there is room for improving the calculation accuracy of the salt concentration distribution.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the calculation accuracy of the salt concentration distribution in the electrolytic solution in a secondary battery system employing a cylindrical secondary battery. .

  A secondary battery system according to an aspect of the present invention includes a secondary battery and a secondary battery control device. The secondary battery includes an electrode body that is formed in a substantially cylindrical shape by winding a positive electrode sheet, a negative electrode sheet, and a separator sheet, 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 inside the electrode body, and calculates and calculates the salt concentration distribution in the electrolytic solution based on the calculated flow rate. The degree of deterioration of the secondary battery is estimated based on the distribution of the salt concentration. The liquid flow equation includes, as a parameter, a volume fraction indicating the ratio of the volume of the electrolyte contained in the electrode body to the volume of the electrode body. For each sheet of the positive electrode sheet and the negative electrode sheet, the control device balances the force established between the electrolyte pressure in each sheet, the elastic stress of each sheet, and the tension generated in the circumferential direction of each sheet. Using this relationship, the amount of change in the thickness in the radial direction of each sheet is calculated. Further, the control device calculates a volume fraction from the calculated amount of change in thickness.

  Preferably, the pressure is calculated based on the liquid flow equation by using the volume fraction calculated in the previous calculation. The elastic stress is defined by the amount of change in thickness in the radial direction of each sheet. The tension is defined by the amount of change in the circumferential length of each sheet.

  A vehicle according to another aspect of the present invention includes the above-described secondary battery system and a driving device that generates driving force using electric power from the secondary battery system.

  In the control method of a secondary battery according to still another aspect of the present invention, the secondary battery includes an electrode body formed in a substantially cylindrical shape by winding a positive electrode sheet, a negative electrode sheet, and a separator sheet, and an electrolytic solution Including. The control method uses a liquid flow equation that defines the flow rate of the electrolytic solution inside the electrode body, and calculates a flow rate of the electrolytic solution, and calculates a salt concentration distribution in the electrolytic solution based on the calculated flow rate. And estimating the degree of deterioration of the secondary battery based on the calculated salt concentration distribution. The liquid flow equation includes, as a parameter, a volume fraction indicating the ratio of the volume of the electrolyte contained in the electrode body to the volume of the electrode body. The step of calculating the flow velocity is established for each sheet of the positive electrode sheet and the negative electrode sheet between the pressure of the electrolytic solution in each sheet, the elastic stress of each sheet, and the tension generated in the circumferential direction of each sheet. The method includes a step of calculating a thickness change amount of each sheet in the radial direction using a force balance relationship, and a step of calculating a volume fraction from the calculated thickness change amount.

  According to the above configuration or method, by approximating each sheet to a spring in a substantially cylindrical secondary battery, the relationship between the pressure of the electrolyte, the elastic stress of each sheet, and the tension generated in each sheet is balanced. The flow velocity is calculated in consideration. Thereby, the calculation accuracy of the salt concentration distribution in the electrolytic solution can be improved as compared with the case where the force balance relationship is not considered.

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

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 side view of the cell contained in the battery shown in FIG. It is sectional drawing of the cell which follows the III-III line | wire shown in FIG. It is a figure for demonstrating the structure of the electrode body shown in FIG. It is a conceptual diagram for demonstrating the bias | inclination of the salt concentration in electrolyte solution. It is a figure for demonstrating the calculation method of salt concentration distribution. It is sectional drawing of the cell which follows the VII-VII line shown in FIG. It is a figure for demonstrating the relationship of the balance of force in each layer. It is a flowchart for demonstrating the calculation process of the increase amount of the internal resistance of the battery 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 is not limited to an electric vehicle, and can be applied 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 on which the secondary battery system according to the present embodiment is mounted. FIG. 1 mainly shows a system configuration related to charge / discharge control of an electric system in a vehicle.

  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 FIGS. 2 and 3) connected in series to each other. Typically, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery or a nickel hydride secondary 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. Voltage sensor 210 detects voltage VB of each cell in battery 100. Current sensor 220 detects current IB input / output to / from battery 100. The temperature sensor 230 detects the temperature (battery temperature) TB of the battery 100. Each sensor outputs a signal indicating the detection result to ECU 300. ECU 300 calculates the SOC (State Of Charge) of battery 100 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 signals from each sensor, ECU 300 reads out and executes a program stored in advance in ROM into RAM, thereby executing travel control of vehicle 1 and charge / discharge control of battery 100. 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 side view of cell 110 included in battery 100 shown in FIG. 3 is a cross-sectional view of the cell 110 taken along the line III-III shown in FIG.

  2 and 3, a battery case 120 includes a cylindrical case body 122 having an upper end (one end in the positive direction along the z-axis in the drawing) and a lid that closes the opening of the case body 122. 124. A positive electrode terminal 126 is provided on the upper surface of the battery case 120, and a negative electrode terminal 128 is provided on the lower surface of the battery case 120. Inside the battery case 120, an electrode body 130 is accommodated together with an electrolyte solution (not shown).

  FIG. 4 is a view for explaining the configuration of the electrode body 130 shown in FIG. 2 to 4, the electrode body 130 is formed by winding a positive electrode sheet 140 and a negative electrode sheet 150 into a substantially cylindrical shape via a separator sheet 160.

  The positive electrode sheet 140 includes a positive electrode current collector foil 142 and a positive electrode active material layer 144 formed on the surface of the positive electrode current collector foil 142. As the positive electrode current collector foil 142, a metal foil such as an aluminum foil can be used. Although not shown, the positive electrode active material layer 144 includes a positive electrode active material, a conductive material, and a binder. As the positive electrode active material, an oxide (lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, or the like) containing lithium and a transition metal element can be used.

  The negative electrode sheet 150 includes a negative electrode current collector foil 152 and a negative electrode active material layer 154 formed on the surface of the negative electrode current collector foil 152. As the negative electrode current collector foil 152, a metal foil such as a copper foil can be used. The negative electrode active material layer 154 includes a negative electrode active material, a conductive material, and a binder (all not shown). As the negative electrode active material, for example, a carbon-based material (graphite carbon, amorphous carbon, or the like) or an oxide containing lithium and a transition metal element can be used.

  As the separator sheet 160, for example, a porous sheet of a synthetic resin (polyolefin such as polyethylene) can be used.

  A core region Zc is formed in the vicinity of the center of the electrode body 130 in the direction along the central axis Az (hereinafter referred to as “width direction”). The core region Zc is a region where the positive electrode active material layer 144, the negative electrode active material layer 154, and the separator sheet 160 are densely stacked.

  The positive electrode sheet 140 and the negative electrode sheet 150 are overlapped with a slight shift in the width direction of the electrode body 130. From one side of the separator sheet 160 in the width direction, a region of the positive electrode sheet 140 where the positive electrode active material layer 144 is not formed protrudes. In the protruding region Zp on the positive electrode side, a positive electrode lead terminal 125 (see FIG. 3) electrically connected to the positive electrode terminal 126 is provided. Similarly, from the other side of the separator sheet 160 in the width direction, a region of the negative electrode sheet 150 where the negative electrode active material layer 154 is not formed protrudes. In the protruding region Zn on the negative electrode side, a negative electrode lead terminal 127 (see FIG. 3) electrically connected to the negative electrode terminal 128 is provided.

<Salt concentration distribution>
Since each of the positive electrode active material layer 144, the negative electrode active material layer 154, and the separator sheet 160 is a porous material, the inside thereof is immersed in an electrolytic solution. When a change in battery temperature TB or a change in SOC occurs, a change in volume of the electrolytic solution and a change in volume of the electrode body 130 occur, so that the flow of the electrolytic solution (hereinafter also referred to as “liquid flow”) occurs in each sheet. Can occur. As a result, the concentration distribution of the salt in the electrolytic solution (lithium salt in the present embodiment) changes from the initial state, which may cause a bias in the salt concentration.

  FIG. 5 is a conceptual diagram for explaining the uneven concentration of salt in the electrolytic solution. FIG. 5A shows an example of a salt concentration distribution in the stacking direction of each sheet (the radial direction of the wound body formed by winding each sheet: the direction along the straight line Lθ in FIG. 4). . The vertical axis represents the salt concentration. In FIG. 5A, the horizontal axis represents the position of the electrode body 130 in the stacking direction. With reference to FIG. 5A, when the battery 100 is charged (for example, during charging or immediately after charging). As shown by the curve CHG, the salt concentration near the negative electrode sheet 150 is higher than the salt concentration near the positive electrode sheet 140. On the other hand, when the battery 100 is discharged (for example, during or immediately after discharge), the salt concentration in the vicinity of the positive electrode sheet 140 is higher than the salt concentration in the vicinity of the negative electrode sheet 150 as shown by the curve DCH.

  FIG. 5B shows an example of the salt concentration distribution in the width direction of each sheet. In FIG. 5B, the horizontal axis represents the position of the electrode body 130 in the winding direction, and the vertical axis represents the salt concentration. Referring to FIG. 5B, when battery 100 is charged, the salt concentration at the center of core region Zc is higher than the salt concentrations at both ends, as shown by curve CHG. On the contrary, when the cell 110 is discharged, the salt concentration at the center of the core region Zc is lower than the salt concentrations at both ends, as shown by the curve DCH.

<Calculation of salt concentration distribution>
Such a salt concentration distribution is calculated by solving a liquid flow equation that defines the flow of the electrolytic solution based on fluid dynamics for each of the positive electrode sheet 140, the negative electrode sheet 150, and the separator sheet 160.

  FIG. 6 is a diagram for explaining a method for calculating a salt concentration distribution. Referring to FIG. 6, each of positive electrode active material layer 144, negative electrode active material layer 154, and separator sheet 160 is virtually divided into a plurality of minute regions S along the in-plane direction. For each of the plurality of minute regions 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 Formula (1) and Formula (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 permeability coefficient is represented by K _j , The volume fraction is represented by ε _{e, j} and the electrolyte pressure 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 sheet 140, the negative electrode sheet 150, and the separator sheet 160. That is, j = p indicates that the parameter relates to the positive electrode sheet 140. j = n indicates that the parameter relates to the negative electrode sheet 150. When j = s, it indicates that the parameter relates to the separator sheet 160. The component 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} is the ratio of the volume of the voids in the component j (in other words, the electrolyte that immerses the voids) to the entire volume of the component j (for example, when j = p, the positive electrode active material layer 144). Means.

In the electrode body 130, as the volume of the active material (positive electrode active material or negative electrode active material) changes depending on the battery temperature TB or SOC, the active material layer (positive electrode active material layer 144 or negative electrode active material layer 154) The volume can vary. As a result, the volume fraction ε _{e, j} of the electrolytic solution inside 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.

Although described later in detail, to calculate the volume fraction epsilon _{e, j,} the calculated volume fraction epsilon _{e, j} by substituting the above equation (1) and (2), calculates the flow velocity u _j can do.

Furthermore, 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 equation (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 . The thickness of each sheet represented by L _j. F is a Faraday constant.

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

<Mechanical model>
For example, when the salt concentration distribution is calculated at a predetermined calculation cycle, and the flow velocity u _j is calculated based on the calculated salt concentration distribution, the volume fraction ε _{e, j} is updated for each calculation. The volume fraction ε _{e, j} is calculated by calculating the amount of change in the thickness of the active material layer in the stacking direction (radial direction) using a dynamic model as described below. Hereinafter, the dynamic model applied to the cylindrical cell in the present embodiment will be described in detail.

  FIG. 7 is a cross-sectional view of the cell 110 along the line VII-VII shown in FIG. Referring to FIG. 7, the number of layers (number of sheets) of electrode body 130 formed by winding positive electrode sheet 140, negative electrode sheet 150, and separator sheet 160 is N (N is an integer of 3 or more). . Hereinafter, the outermost layer (for example, the negative electrode sheet 150) is referred to as a first layer. A layer in contact with the inside of the first layer (for example, separator sheet 160) is referred to as a second layer, and a layer in contact with the inside of the second layer (for example, positive electrode sheet 140) is referred to as a third layer. The innermost layer is the Nth layer.

The force acting on the electrode body 130 inside the cylindrical battery case 120 includes an electrolyte pressure P _n , an elastic stress F _n of each sheet, and a tension T _n generated by winding each sheet. Is mentioned. The subscript n (n is an integer of 1 or more and N or less) indicates a force relating to the nth layer. As described below in a steady state, for each layer of the first layer to the N layer, the relationship of force balance between the pressure P _n and the elastic stress F _n and the tension T _n holds.

  FIG. 8 is a diagram for explaining the relationship of force balance in each layer. With reference to FIG. 8, the balance of force in the left half region in the drawing (region on the left side of the straight line passing through point A-point B) in the cross section of electrode body 130 will be described in detail below. Since the electrode body 130 is formed by winding a plurality of sheets, the distance from the center O of each sheet of the first layer to the Nth layer is actually the position in the circumferential direction (FIG. 8). In this case, the distance from the center O and the angle θ are changed using polar coordinates. However, each sheet of the first layer to the Nth layer is approximated to a concentric circle here.

First, the relationship of force balance in the first layer will be described. Electrode body 130, tension T ₁ is applied to the tangential direction of the rightward in the drawing, and the tension T ₁ in the tangential direction of the rightward in the drawing at point B is acting at point A. The fact that the tension T ₁ acts in this way can be understood from the analogy of the tension acting on the pulley in classical mechanics.

On the other hand, the elastic stress F ₁ of the active material layer and the pressure P _{1 of the} electrolyte act on the point (r ₁ , θ). The sum of forces acting on each point from point A to point B along the circumference of the first layer is calculated by integrating elastic stress F ₁ and pressure P ₁ from angle θ = 0 to θ = π. Is done. In this embodiment, the components of the out of view the left direction of the elastic stress F _1, the sum of the components into out in view left direction of the pressure P _1, balanced with the tension T ₁ of the rightward in the drawing. Therefore, the following formula (5) is established.

Next, the relationship of force balance in the second layer will be described. The tensions to be considered in the balance of forces in the second layer are the force acting on the first layer and the second layer, that is, the tension T ₁ acting on the first layer and tightening the second layer from the outside, and the second layer. This is the tension T ₂ generated in itself. It is not necessary to consider the tension of the layer inside the second layer. Therefore, the tension that affects the balance of forces in the second layer is expressed as 2 (T ₁ + T ₂ ).

Similarly, the elastic stress and pressure to be considered in the balance of forces in the second layer are forces acting on the first layer and the second layer. However, the elastic stress F ₁ and the pressure P ₁ generated in the first layer cancel each other on the inner side in the radial direction and the outer side in the radial direction by the law of action / reaction. Therefore, only the elastic stress F ₂ and pressure P _{2 of} the second layer itself need be considered. From the above, the balance of forces in the second layer is expressed as the following formula (6).

  Similarly, the balance of forces of the i-th layer (i is an integer of 2 or more and N or less) can be expressed as the following formula (7).

When the volume of the active material layer changes with the change in battery temperature TB or SOC, the elastic stress F _{i of} each layer changes and the pressure P _{i of the} electrolytic solution can also change. Further, when a change in volume of the active material layer, it means that changing the length of each layer in the circumferential direction, the tension T _i generated in each layer can also vary. The variation of the elastic stress _{F i} in the i-th layer represents the [Delta] F _i, expressed as [Delta] P _i the variation of the pressure _{P i,} to represent the variation of tension _{T i} and [Delta] T _i, the equation (7), each change The following equation (8) is derived as an equation that holds between the quantities.

Hereinafter, the amount of change (total amount) in the thickness of the active material layer is represented by Δy _i . The amount of change (expansion amount) in the thickness of the active material layer accompanying the change in battery temperature TB or SOC is represented by Δy _0i . Variation of thickness of the active material layer due to the sheet is wound (the amount of contraction due to tightening in the tension T _i) represents the [Delta] y _si.

The following formula (9) is established between the above-described change amounts. In equation (9), the amount of change Δy _0i in the thickness of the active material layer accompanying the change in battery temperature TB or SOC is obtained by, for example, preparing a map between battery temperature TB, SOC, and amount of change Δy _oi in advance. It can be calculated from the battery temperature TB and SOC. Therefore, the unknowns included in Equation (9) are Δy _si and Δy _i .

Here, the variables included in the above equation (8) will be examined in more detail. The change amount ΔF _i of the elastic stress F _i of each sheet is proportional to the change amount (shrinkage amount) Δy _si of the thickness of each sheet. Therefore, the change amount [Delta] F _i of the elastic stress _{F i,} using the spring constant _{k i} is expressed by the following equation (10).

Moreover, the variation [Delta] T _m of the tension T _m is proportional to the amount of change in the circumferential direction of the length of each sheet. Therefore, variation ΔTm tension Tm, using the change amount [Delta] r _m of the Young's modulus _{E m} and the radius _{r m} of each sheet is expressed by the following equation (11). As the spring constant k _i and Young's modulus Em, value determined by simulation or experiment is given.

In the formula (11), the change amount [Delta] r _m of radius r _m is expressed as the sum of the amount of change in the thickness of each sheet from the N layer to the m-th layer (the total amount) [Delta] y _m (formula (12 )reference).

Therefore, the following formula (13) is derived by substituting the formulas (10) to (12) into the formula (8). In Expression (13), the amount of change ΔP _i in the electrolyte pressure can be calculated from the liquid flow equation (Expression (1)). Therefore, the unknowns included in Equation (13) are Δy _si and Δy _i .

From the above, by providing the equations (9) and (13) simultaneously, it is possible to calculate the unknown thickness variations Δy _si and Δy _i . Furthermore, if the change amount Δy _i of the thickness of each sheet is calculated, the change amount of the radius of the electrode body 130 can be calculated from the above equation (12).

<Calculation of volume fraction>
The volume fraction ε _{e, j} can be calculated from the amount of change in the radius of the electrode body 130 thus calculated. Hereinafter, an example of a method for calculating the volume fraction ε _{e, j} will be described.

The radius r of the entire electrode body 130 is equal to the radius r ₁ of the first layer of the electrode body 130. Therefore, the amount of change Δr of the radius r is expressed as the following formula (14).

The calculation of the volume fraction ε _{e, j} is repeated, for example, every predetermined calculation cycle. The volume of the electrode body 130 in the q-th calculation (q is a natural number) is expressed as V _all (q). Then, the volume change amount ΔV _all (q) of the electrode body 130 in the q-th calculation is expressed as the following formula (15).

Volume change ΔV _all (q) is the (q-1) th calculation result and the volume change amount ΔV _all (q-1) is, the radius _r 1 of the electrode body 130 (q-1), the radius _{r 1} Can be expressed as the following formula (16) using the change amount Δr ₁ (q).

Further, among the active material and voids constituting the active material layer, when the volume change amount of the active material is expressed as ΔV _s and the volume change amount of the void is expressed as ΔV _e , the volume change amount ΔV _s of the active material and the void volume Since the sum of the volume change amount ΔV _e is equal to the volume change amount ΔV _all of the active material layer, the following formula (17) is established. In the equation (17), the volume change amount ΔV _s of the active material can be calculated from the battery temperature TB and the SOC by preparing a map between the battery temperature TB, the SOC, and the volume change amount ΔV _s in advance. . On the other hand, the volume change amount ΔV _all of the active material layer can be sequentially calculated from the above equations (15) and (16) if an initial value is given. Therefore, the volume change amount ΔV _e (q) of the void is obtained from the equation (17).

The volume fraction ε _{e, j} is expressed by the following formula (18) using the void volume V _e (q) and the void volume change ΔV _e (q). By substituting the volume fraction ε _e calculated in this way into the liquid flow equation (formula (1)), the flow rate u _j of the electrolyte can be calculated.

<Calculation of increase in internal resistance>
FIG. 9 is a flowchart for explaining the calculation process of the internal resistance of battery 100 in the present embodiment. The control according to the flowchart shown in FIG. 9 is called and executed by the ECU 300 from the main routine when a predetermined condition is satisfied (for example, at the start of charge / discharge) or at a predetermined calculation cycle. Each step (hereinafter abbreviated as S) is basically realized by software processing by the ECU 300, but may be realized by hardware processing.

1 to 4, 8, and 9, in S <b> 10, ECU 300 determines parameters of electrode body 130 and an electrolytic solution. More specifically, ECU 300 reads transmission coefficient K _j , electrolyte density ρ, and viscosity μ from memory 310. As each parameter, a predetermined fixed value may be used, or a variable value corresponding to battery temperature TB or SOC may be used, for example.

In S20, ECU 300 calculates pressure P of the electrolytic solution based on Expression (1) and Expression (2). As the volume fraction ε _{e, j} at this time, the value calculated in the previous calculation can be used.

In S30, the ECU 300 determines the thickness of each layer of the electrode body 130 based on the formula (8) established between the thickness variations of each layer and the formula (13) defining the relationship of force balance. A change amount Δy _i is calculated.

In S40, the ECU 300 converts the change amount Δy _i of the thickness calculated in S30 into a change amount Δε _{e, j} of the volume fraction ε _{e, j} (see Expressions (14) to (18)).

In S50, the ECU 300 calculates the flow rate u _j of the electrolytic solution in the current calculation based on the equations (1) and (2).

In S60, the ECU 300 calculates the salt concentration c _{e, j} of each minute region S by substituting the flow velocity u _j calculated in S50 into the equation (4). Further, the ECU 300 calculates a salt concentration distribution from the salt concentration c _{e, j} .

  In S70, ECU 300 calculates an increase amount ΔR of internal resistance R of battery 100 based on the salt concentration distribution calculated in S60. 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. 10 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. 10, the horizontal axis represents the difference in salt concentration _ce, as an index value indicating the deviation of the _j, salts of a plurality of microscopic regions S concentration c _e, 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. 10, 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. 9, in S80, 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 S80), ECU 300 advances the process to S90, assuming that high-rate deterioration has progressed to some extent. In S90, ECU 300 restricts charging / discharging of battery 100 from the viewpoint of suppressing further high-rate deterioration of battery 100. Specifically, ECU 300 increases charging power upper limit value Win when internal resistance R increase amount ΔR is less than threshold value Rc compared to when internal resistance R increase amount ΔR is equal to or greater than threshold value Rc. And discharge electric power upper limit Wout is reduced. Thereafter, the process is returned to the main routine.

  On the other hand, if increase amount ΔR of internal resistance R is less than threshold value Rc (NO in S80), ECU 300 skips S90 and returns the process to the main routine, assuming that high-rate deterioration has not progressed much.

As described above, according to the present embodiment, the force balance is calculated by calculating the volume fraction ε _{e, j} in consideration of the balance of the forces acting on the electrode body 130 in the cylindrical cell. Compared with the case where the relationship is not considered (for example, when a fixed value is used as the volume fraction ε _{e, j} ), the calculation accuracy of the flow velocity u _j can be improved. 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.

[Modification 1]
In the above-described embodiment, the configuration in which the thickness of the active material layer in the positive electrode sheet 140 and the negative electrode sheet 150 changes while the thickness of the current collector foil does not change has been described as an example. However, in order to further improve the calculation accuracy of the flow rate u _j of the electrolytic solution, it is desirable to calculate the amount of change Δy _i in the thickness of the current collector foil as in the active material layer. However, since the current collector foil has properties different from those of the active material layer, it is necessary to correct the formulas (5) to (18) as the following (A) to (C).

  (A) Since the inside of the current collector foil is not immersed in the electrolyte solution, the pressure P of the electrolyte solution inside the current collector foil is set to zero.

(B) The expansion and contraction of the current collector foil are much smaller than the expansion and contraction of the active material layer. Therefore, in the above formulas (9) and (10), the amount of change Δy _{0 in} thickness accompanying the change in battery temperature TB or SOC is set to zero.

(C) Since the inside of the current collector foil is not immersed in the electrolytic solution, when calculating the volume change ΔV _all of the electrode body 130 based on the above formulas (14) to (18), the volume of the current collector foil Does not include changes.

[Modification 2]
As described in Expression (6) to Expression (8), the amount of change in the thickness of each layer of the electrode body 130 can be calculated using a relational expression of force balance. However, since a typical electronic control device for vehicle use lacks computing power, it may be difficult to formulate and solve all the layers. In such a case, it is desirable to treat some of the plurality of layers as one layer instead of establishing the above formula (8) for each of the plurality of layers. In this case, integrated values of several layers can be used as the sheet tension, spring constant, and Young's modulus. As a result, the amount of calculation can be reduced, so that the calculation accuracy of the volume fraction ε _{e, j} can be improved, and the calculation accuracy of the flow velocity u _j can be improved even with an electronic control device having a relatively low calculation capability. It becomes possible to make it.

  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 wheel, 60 acceleration sensor, 100 battery, 110 cell, 120 battery case, 122 case body, 124 lid body, 125 positive electrode lead terminal, 126 positive electrode terminal, 127 negative electrode lead terminal, 128 negative electrode terminal, 130 electrode body, 132 core part, 134, 136 part, 140 positive electrode sheet, 142 positive electrode current collector foil, 144 Positive electrode active material layer, 150 negative electrode sheet, 152 negative electrode current collector foil, 154 negative electrode active material layer, 160 separator sheet, 200 monitoring unit, 210 voltage sensor, 220 current sensor, 230 temperature sensor, 300 electronic control unit (ECU), 310 Me Mori.

Claims (4)

A secondary battery comprising an electrode body formed into a substantially cylindrical shape by winding a positive electrode sheet, a negative electrode sheet, and a separator sheet; and an electrolyte solution;
Calculate the flow rate of the electrolytic solution using a liquid flow equation that defines the flow of the electrolytic solution inside the electrode body, and calculate and calculate the salt concentration distribution in the electrolytic solution based on the calculated flow rate A controller for estimating a deterioration degree of the secondary battery based on the salt concentration distribution,
The liquid flow equation includes, as a parameter, a volume fraction indicating the ratio of the volume of the electrolyte contained in the electrode body to the volume of the electrode body,
The control device includes, for each sheet of the positive electrode sheet and the negative electrode sheet, a pressure of the electrolytic solution inside each sheet, an elastic stress of each sheet, and a tension generated in a circumferential direction of each sheet. A secondary battery that calculates the amount of change in thickness in the radial direction of each sheet using the balance of force balances between them, and calculates the volume fraction from the calculated amount of change in thickness system. The pressure is calculated based on the liquid flow equation by using the volume fraction calculated in the previous calculation,
The elastic stress is defined by the amount of change in thickness in the radial direction of each sheet,
The secondary battery system according to claim 1, wherein the tension is defined by a change amount of a length of each sheet in the circumferential direction. The secondary battery system according to claim 1 or 2,
A vehicle comprising: a driving device that generates driving force using electric power from the secondary battery system. A method for controlling a secondary battery comprising an electrode body formed into a substantially cylindrical shape by winding a positive electrode sheet, a negative electrode sheet, and a separator sheet, and an electrolyte solution,
Calculating the flow rate of the electrolytic solution using a liquid flow equation defining the flow rate of the electrolytic solution inside the electrode body;
Calculating a salt concentration distribution in the electrolyte based on the calculated flow rate;
Estimating the degree of deterioration of the secondary battery based on the calculated salt concentration distribution,
The liquid flow equation includes, as a parameter, a volume fraction indicating the ratio of the volume of the electrolyte contained in the electrode body to the volume of the electrode body,
The step of calculating the flow velocity is performed for each sheet of the positive electrode sheet and the negative electrode sheet.
Using the relationship of the balance of forces established between the pressure of the electrolytic solution inside each sheet, the elastic stress of each sheet, and the tension generated in the circumferential direction of each sheet, Calculating the amount of change in thickness in the radial direction;
Calculating the volume fraction from the calculated amount of change in thickness.

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