Nondestructive battery characteristics estimation method, nondestructive battery characteristics estimation program, and battery utilization method

Abstract

To solve the problem of a conventional characteristics estimation method that batteries of unknown origin are unusable.SOLUTION: A nondestructive battery characteristics estimation method according to the present invention causes a computer to automatically perform: a temporary parameter setting process S21 of setting a preset temporary value for each of the thickness of an electrode foil, the density of an active material layer coated to the electrode foil, the specific capacity of the active material layer, and the electrode capacity of the active material layer; a current state measurement process S22 of carrying out charging-discharging on a battery cell and estimating a degradation degree of the battery cell and a current electrode capacity that represents the current electrode capacity of the battery cell; a coating part structure calculation process S23 of calculating the cross sectional area of an electrode body accommodated in the battery cell and the coating part width of the electrode body on the basis of the dimensions measurable without destroying the battery cell; and an active material thickness calculation process S24 of calculating the thickness of the active material layer using the thickness of the electrode foil, the thickness of a separator, the density of the active material layer and the specific capacity of the active material layer, the current electrode capacity, the cross sectional area of the electrode body, and the coating part width of the electrode body.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a non-destructive battery characteristic estimation method, a non-destructive battery characteristic estimation program, and a battery usage method that estimate battery parameters necessary for battery control without destroying a battery whose manufacturing process or usage history is unknown, for example. [Background technology]

[0002] In recent years, secondary batteries that have been used for a specific purpose have come to be recycled for other purposes. However, when using secondary batteries, if the battery parameters for grasping the state of the secondary battery cannot be grasped, a problem occurs in which the battery control becomes unstable due to overcharging, overdischarging, etc. of the secondary battery. Thus, technologies for grasping the state of the secondary battery are disclosed in Patent Documents 1 to 3.

[0003] In the secondary battery state estimation device described in Patent Document 1, a model equation and parameters corresponding to the deactivation reaction between a precipitated reaction-related substance (e.g., a metal such as lithium) and an electrolyte are added to the battery model equation used in estimating the state of the secondary battery, thereby accurately estimating the amount of precipitated reaction-related substance in the secondary battery by dividing it into active components (e.g., active lithium) and inactive components (e.g., inactive lithium).

[0004] In the secondary battery state estimation device described in Patent Document 2, a battery state estimation unit estimates the internal state of the secondary battery for each calculation period according to a battery model formula, and estimates the charging rate and battery current based on the estimation result. Then, a parameter estimation unit acquires the battery current measured by the sensor and the SOC and battery current estimated by a battery state estimation unit 110. The parameter estimation unit estimates a capacity degradation parameter so as to minimize the rate of change of the error (estimation error) between the integrated value of the actual current and the integrated value of the estimated current relative to the charging rate. The estimation result of the capacity degradation parameter is reflected in the battery model by the battery state estimation unit.

[0005] The battery system described in Patent Document 3 includes a current sensor that detects the current of the secondary battery, and a controller that estimates a parameter. The controller calculates a first current integrated value by integrating the current detected by the current sensor during the period when the open circuit voltage of the secondary battery changes from the first open circuit voltage to the second open circuit voltage, and calculates a second current integrated value from the difference between the first charging rate corresponding to the first open circuit voltage and the second charging rate corresponding to the second open circuit voltage. At least one of the parameters is identified so that the difference between the first current integrated value and the second current integrated value is equal to or less than a predetermined value, and the smaller at least one of the average current value during the period when the open circuit voltage changes from the first open circuit voltage to the second open circuit voltage, the rate of change in the open circuit voltage characteristics at the first open circuit voltage and the second open circuit voltage, and the first current integrated value is, the smaller the weighting of the identified parameter is relative to the parameter to be estimated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-126411 A [Patent Document 2] JP 2010-60384 A [Patent Document 3] JP 2014-215181 A Summary of the Invention [Problem to be solved by the invention]

[0007] When recycling secondary batteries, it becomes necessary to use secondary batteries of unknown origin, in which the usage history of the secondary battery to be recycled is unknown, or information on the materials used in the secondary battery, manufacturing process, etc. is unknown. However, the techniques described in Patent Documents 1-3 are capable of estimating the state of a secondary battery of known origin to be controlled, but have a problem in that they are unable to estimate the state of a battery of unknown origin.

[0008] The present invention has been made in view of the above circumstances, and has an object to promote the use of secondary batteries whose origin is unknown. [Means for solving the problem]

[0009] One aspect of the non-destructive battery characteristic estimation method according to the present invention includes a temporary parameter setting process for setting predetermined temporary values ​​for each of the thickness of an electrode foil used in a battery cell, the thickness of a separator, the density of an active material layer coated on the electrode foil, the specific capacity of the active material layer, and the electrode capacity of the active material layer; a current state measurement process for estimating a degree of deterioration of the battery cell and a current electrode capacity that is the current electrode capacity of the battery cell by charging and discharging the battery cell while controlling the battery cell using the temporary values ​​set by the temporary parameter setting process; a coated portion structure calculation process for calculating a cross-sectional area of ​​an electrode body contained in the battery cell and a coated portion width of the electrode body based on dimensions that can be measured without destroying the battery cell; and an active material thickness calculation process for calculating a thickness of the active material layer using the electrode foil thickness, separator thickness, active material layer density, and specific capacity of the active material layer having the temporary values, the current electrode capacity, the cross-sectional area of ​​the electrode body, and the coated portion width of the electrode body.

[0010] One aspect of the non-destructive battery characteristic estimation program according to the present invention causes a computer to execute the following steps: a provisional parameter setting process for setting, to predetermined provisional values, each of a thickness of an electrode foil used in a battery cell, a thickness of a separator, a density of an active material layer coated on the electrode foil, a specific capacity of the active material layer, and an electrode capacity of the active material layer; a current state measurement process for estimating a degree of deterioration of the battery cell and a current electrode capacity that is a current electrode capacity of the battery cell by charging and discharging the battery cell while controlling the battery cell using the provisional values ​​set by the provisional parameter setting process; a coated portion structure calculation process for calculating a cross-sectional area of ​​an electrode body contained in the battery cell and a coated portion width of the electrode body based on dimensions that can be measured without destroying the battery cell; and an active material thickness calculation process for calculating a thickness of the active material layer using the electrode foil thickness, separator thickness, density of the active material layer, and specific capacity of the active material layer that have the provisional values, the current electrode capacity, the cross-sectional area of ​​the electrode body, and the coated portion width of the electrode body.

[0011] One aspect of the battery utilization method of the present invention includes a first determination process for receiving an input of product information including at least information on the battery type of a battery cell, determining a first provisional battery parameter set in advance based on the product information, and determining whether or not the battery type is a target battery type; a battery characteristic estimation process for measuring the dimensions of the battery cell determined to be the target battery type, and then assembling the battery cell in a state in which the battery cell can be charged and discharged, estimating a degree of deterioration of the battery cell and a current electrode capacity that is a current electrode capacity of the battery cell based on charge and discharge current values ​​and an output voltage value of the battery cell obtained by charging and discharging the assembled battery cell, and estimating a thickness of an active material layer of the battery cell based on the measurement results of the dimensions of the battery cell; and a battery characteristic estimation process for estimating a change in the battery resistance of the battery cell based on current and voltage values ​​obtained when the assembled battery cell is repeatedly charged and discharged multiple times. The method includes a characteristic degradation estimation process that estimates parameters that will be used for the characteristic degradation degree of the battery cell, a second judgment process that judges whether the battery cell can be used for an intended use based on the battery parameters obtained by the battery characteristic estimation process and the characteristic degradation estimation process, a battery parameter adaptation process that sets the parameters obtained by the battery characteristic estimation process and the characteristic degradation estimation process as battery parameters to be used for controlling the battery cell for the battery cell that has been judged to be usable for the intended use, and a battery usage process that updates the power limit of the battery cell in accordance with the degradation degree while performing a charging rate and degradation degree estimation process using the battery parameters set in the battery parameter adaptation process, and continues to use the battery cell until it is judged that the battery life of the battery cell has expired, and each process is performed automatically by a computer. Effect of the Invention

[0012] According to the non-destructive battery characteristic estimation method, non-destructive battery characteristic estimation program, and battery utilization method of the present invention, it is possible to reduce the time required to start utilizing a battery of unknown origin. [Brief description of the drawings]

[0013] [Figure 1] 10 is a flowchart illustrating the flow of a method of using a battery when the battery specifications are known. [Diagram 2] 4 is a flowchart illustrating a method of using a battery according to the first embodiment. [Diagram 3] 4 is a flowchart illustrating detailed processing of the battery characteristics estimation processing according to the first embodiment. [Figure 4] 2 is a graph illustrating an SOC-OCV curve used in the method for calculating a deterioration level of a secondary battery according to the first embodiment; [Diagram 5] 4 is a graph illustrating a dV / dQ plot obtained from actual measurement values ​​used in the method for calculating a deterioration level of a secondary battery according to the first embodiment; [Figure 6] 4 is a graph illustrating a dV / dQ plot obtained from theoretical values ​​used in the method for calculating a deterioration level of a secondary battery according to the first embodiment. [Figure 7] 4 is a graph illustrating a fitting process used in the method for calculating a deterioration level of a secondary battery according to the first embodiment; [Figure 8] 5 is a flowchart for explaining the operation of a deterioration level calculation program for a secondary battery according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In order to clarify the description, the following description and drawings are omitted and simplified as appropriate. In addition, each element shown in the drawings as a functional block performing various processes can be configured in hardware with a CPU (Central Processing Unit), memory, and other circuits, and in software, can be realized by a program loaded into memory. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware alone, software alone, or a combination thereof, and are not limited to any one of them. In addition, the same elements are given the same symbols in each drawing, and duplicated explanations are omitted as necessary.

[0015] Moreover, the above-mentioned program includes a set of instructions (or software code) for making the computer perform one or more functions described in the embodiment when the program is read into the computer. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or the tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray (registered trademark) disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may be transmitted on a transitory computer-readable medium or a communication medium. By way of example and not limitation, the transitory computer-readable medium or the communication medium includes electrical, optical, acoustic, or other forms of propagating signals.

[0016] In addition, the battery utilization method according to the first embodiment described below is performed by an automatic process in which multiple programs executed on separate computers are prepared for each process in the flow of battery utilization in cooperation with each other.

[0017] First embodiment In the following description, a method of using a battery that reuses a secondary battery will be described. Therefore, in the following description, the secondary battery will simply be referred to as a battery. Furthermore, in the method of using a battery according to the first embodiment, regardless of whether the battery is used as a battery pack made up of a combination of multiple batteries, the battery parameters and performance will be evaluated for each individual battery cell, so in the description, the term battery cell will be used.

[0018] First, before explaining the battery usage method according to the first embodiment, a battery usage method in which the non-destructive battery characteristic estimation method implemented in the battery usage method according to the first embodiment is not used will be explained as a comparative example.

[0019] Fig. 1 shows a flowchart explaining the flow of a method of using a battery when the battery specifications are known (a method of using a battery according to a comparative example). As shown in Fig. 1, in the method of using a battery according to the comparative example, detailed product information of the battery is input when starting to use the battery cell (step S101). Specifically, in step S101, the detailed product information includes the capacity of the new battery cell when it starts to be used, design information such as the thickness of the active material layers that make up the electrode plates, characteristic variations of the battery cell caused by manufacturing variations, and life characteristics of the battery cell.

[0020] Next, in the battery usage method according to the comparative example, the product information acquired in step S101 is used to acquire the characteristics of the battery cell and diagnose the battery cell (step S102). In this step S102, the battery cell is repeatedly charged and discharged to acquire information such as the full charge capacity of the battery cell, the terminal resistance value of the battery cell (hereinafter referred to as battery resistance), the input / output characteristics of the battery cell, and the degree of capacity deterioration compared to a new battery cell. When a battery cell is reused, its usage history up to that point is unknown, and by performing the process of step S102, information necessary for appropriately controlling the battery cell is obtained. The process of step S102 usually takes several months to about half a year.

[0021] Next, based on the information acquired in steps S101 and S102, it is determined whether the battery cell has the performance required for the intended use (step S103). If it is determined in step S103 that the battery cell does not have the performance required for the intended use, the battery cell is considered for recycling for another use.

[0022] On the other hand, if it is determined in step S103 that the battery cell has the performance required for the intended use, a battery parameter adaptation process is performed in which the information (e.g., battery parameters) acquired in steps S101 and S102 is set as battery control parameters in the system that uses the battery cell (step S104). Also, a power limit according to the performance of the battery cell is set in the system that uses the battery cell (step S105).

[0023] Thereafter, in the battery cell utilization method according to the comparative example, the charging rate (SOC: State Of Charge) and deterioration degree (SOH: State Of Health) of the battery cell are estimated (step S106) and the lifespan of the battery cell is predicted (step S107), and the battery cell is utilized until it is determined that the predicted lifespan has expired (YES branch of step S108).

[0024] As described above, in the battery usage method according to the comparative example, in order to use a battery cell, it is necessary to obtain information that can only be known by the battery manufacturer, such as the capacity of the battery cell when it is new, design information, characteristic variations, and life characteristics, and there is a problem that battery cells with unknown origins cannot be used. In addition, in the battery usage method according to the comparative example, it takes several months to understand the changes in battery characteristics caused by the use of the battery cell, so there is a problem that the period during which the battery cell cannot be used is extended. Furthermore, in the battery usage method according to the comparative example, in step S102, charging and discharging are repeated to obtain and diagnose the characteristics of the battery cell, so there is a problem that power not used for a specific purpose is required.

[0025] However, the battery usage method according to the first embodiment makes it possible to recycle even battery cells whose origins are unknown and whose information on the design and manufacture of the battery cell is difficult to obtain. Also, the battery usage method according to the first embodiment improves the accuracy of information for understanding the current characteristics of the battery cell while using the battery for a specific purpose, thereby shortening the unused period of the battery cell. The battery usage method according to the first embodiment will be specifically described below.

[0026] Fig. 2 shows a flowchart for explaining the battery usage method according to the first embodiment. In the battery usage method according to the first embodiment, first, product information including at least information on the battery type of the battery cell is input, and a first determination process is performed to determine first provisional battery parameters set in advance based on the product information and determine whether the battery type is a target one. In the example shown in Fig. 2, the first determination process is divided into steps S1 to S3.

[0027] In step S1, regardless of whether the identity of the battery cell is known or not, product information of the battery cell is input at the start of use (step S1). Specifically, in the battery usage method according to the first embodiment, information including at least the battery type of the battery cell to be used is input to the computer as product information in step S1. Here, secondary batteries are classified into lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries, etc., depending on the type of active material used. Therefore, in the battery usage method according to the first embodiment, information on the material from which the battery cell to be used is manufactured, such as a lead-acid battery, nickel-metal hydride battery, or lithium-ion battery, is provided to the computer as the battery type.

[0028] Next, in step S2, first provisional battery parameters (e.g., standard parameters) preset for each battery type of the battery cell to be used are provisionally determined as battery parameters (step S2). Here, the standard parameters in the battery utilization method according to the first embodiment are publicly available information, and are, for example, values ​​determined in advance by a business entity that reuses battery cells based on information published on a website or the like by a material manufacturer that is a supplier of the material for the battery cells. For example, the standard parameters include the thickness of the electrode foil, the thickness of the separator, the density of the active material layer coated on the electrode foil, the specific capacity of the active material layer, and the electrode capacity of the active material layer.

[0029] Next, in step S3, it is determined whether the battery cell to be used is a battery cell that is suitable for the intended use. Specifically, in step S3, for example, in a battery pack that uses a combination of multiple battery cells, it is necessary to combine battery cells of the same type, and it is determined whether the battery type is a target battery pack to be assembled. Also, in step S3, it may be determined to exclude battery cells that are obviously old, or battery cells whose shape is obviously unsuitable for the intended use.

[0030] Then, if it is determined in step S3 that the battery cell matches the intended use, a battery characteristic estimation process (step S6), a characteristic deterioration estimation process (step S7), and a second judgment process (step S8) are performed on the target battery cell.

[0031] In the battery characteristic estimation process in step S6, the dimensions of the battery cell determined to be the target battery type are measured, and then the battery cell is assembled in a state in which it can be charged and discharged. The deterioration level of the battery cell and the current electrode capacity of the battery cell are estimated based on the charge and discharge current value and the output voltage value of the battery cell obtained by charging and discharging the assembled battery cell, and the thickness of the active material layer of the battery cell is estimated based on the measurement results of the battery cell dimensions. The battery characteristic estimation process will be described in detail later. Note that in the example of FIG. 2, step S4 of measuring the dimensions of the battery cell is shown as a process prior to the battery characteristic estimation process, and step S5 of assembling the target battery cell so that it can be charged and discharged is shown.

[0032] In the characteristic deterioration estimation process in step S7, a parameter that is an indicator of the degree of characteristic deterioration of the battery cell is estimated based on the amount of change in battery resistance of the battery cell calculated from the current and voltage values ​​obtained when the battery cell assembled in step S5 is repeatedly charged and discharged multiple times.

[0033] In the second determination process in step S8, it is determined whether the battery cell can be used for the intended use based on the battery parameters obtained by the battery characteristic estimation process (step S6) and the characteristic deterioration estimation process (step S7). In the second determination process, if the battery cell is suitable for the intended use, a battery parameter adaptation process (step S9) and a battery use process (steps S10 to S13) are performed.

[0034] In the battery parameter adaptation process in step S9, the battery parameters obtained in the battery characteristic estimation process (step S6) and the characteristic deterioration estimation process (S7) are set as battery control parameters in the computer that controls the battery cell.

[0035] In the battery utilization process of steps S10 to S13, the battery control parameters set in the battery parameter adaptation process are used to estimate the charging rate (SOC: State Of Charge) and deterioration level (SOH: State Of Health), while updating the power limit of the battery cell according to the deterioration level, and the battery cell continues to be used until it is determined that the battery life of the battery cell has expired.

[0036] In the battery usage method according to the first embodiment, even battery cells whose characteristics are unknown can be used in a short period of time by using the battery according to the flow shown in Fig. 2. One of the processes for realizing this feature is the battery characteristics estimation process in step S6. Here, the battery characteristics estimation process will be described in detail.

[0037] FIG. 3 shows a flowchart for explaining the detailed processing of the battery characteristic estimation processing according to the first embodiment. As shown in FIG. 3, in the battery characteristic estimation processing, a provisional parameter setting processing is performed as step S21. In this provisional parameter setting processing, standard parameters in which provisional values ​​are set in advance for each of the thickness of the electrode foil used in the battery cell, the thickness of the separator, the density of the active material layer coated on the electrode foil, the specific capacity of the active material layer, and the electrode capacity of the active material layer are read into the computer as provisional parameters. The flowchart shown in FIG. 3 is an example of a lithium-ion storage battery. Therefore, in FIG. 3, as examples of standard parameters, the aluminum foil thickness Lal of the positive electrode foil, the copper foil thickness Lcu of the negative electrode foil, the separator thickness Ls, the positive electrode density ρp and the negative electrode density ρn as the density of the active material layer, the positive electrode specific capacity αp and the negative electrode specific capacity αn as the specific capacity of the active material, and the initial positive electrode capacity Qp_i and the initial negative electrode capacity Qn_i as the electrode capacity of the active material layer are shown. The standard parameters are the parameters read in step S2 of FIG. 2. Moreover, the initial positive electrode capacity Qp_i and the initial negative electrode capacity Qn_i are updated in the next step S22.

[0038] In the current state measurement process in step S22, the battery cell is charged and discharged while controlling the battery cell using the provisional values ​​set in the provisional parameter setting process in step S21, and the deterioration degree of the battery cell and the current electrode capacity (e.g., positive electrode capacity Qp and negative electrode capacity Qn) that is the current electrode capacity of the battery cell are estimated. In the current state measurement process according to the first embodiment, the battery cell is charged and discharged in order to obtain an SOC-OCV curve, which will be described later, but this charging and discharging only needs to be performed once, and does not need to be performed over a long period such as several months. Note that the charging and discharging in the current state measurement process may be performed multiple times. In addition, the initial positive electrode capacity Qp_i and the initial negative electrode capacity Qn_i are updated by the current electrode capacity estimated in the current state measurement process.

[0039] Here, the current state measurement process will be described in detail. In the following description, a lithium ion battery will be used as an example, but the following method can be applied to other types of batteries. In addition, the following description relates to a deterioration estimation process during the current state measurement process. In the current state measurement process, the positive electrode capacity Qp and the negative electrode capacity Qn are calculated by correcting the initial positive electrode capacity Qp_i and the initial negative electrode capacity Qn_i in consideration of the positive and negative electrode capacity ratio obtained as a result of the deterioration estimation process and the capacity of a new battery cell. In addition, the capacity of a new battery cell can be excluded from consideration if no information is available, and can be used as information to consider the estimated value if information on the capacity is available as an estimated value.

[0040] First, the charge and discharge characteristics of a battery cell will be described. FIG. 4 shows a graph for explaining a charging rate voltage curve (hereinafter, referred to as a SOC-OCV curve) used in the deterioration degree calculation method of a battery cell according to the first embodiment. As shown in FIG. 4, the open circuit voltage (OCV (Open Circuit Voltage)) of a battery cell changes according to the change in charging rate. This change occurs because the potential of the positive electrode and the potential of the negative electrode change due to the charge and discharge operation. In a battery cell, the difference between the potential of the positive electrode and the potential of the negative electrode becomes the open circuit voltage generated between the positive electrode terminal and the negative electrode terminal. The potential of the positive electrode and the potential of the negative electrode can be measured as the positive electrode OCP (Open Circuit Potential) and the negative electrode OCP, respectively. The positive electrode OCP and the negative electrode OCP can also be logically derived from the active material contained in the composite material applied to each electrode.

[0041] As shown in FIG. 4, the positive electrode OCP extends to a region where the charging rate (SOC (State Of Charge)) is 0% or less. This indicates that the charging rate of 0% is a state where the amount of lithium that the negative electrode can accept is exceeded, and that even when the charging rate becomes 0%, releasable lithium remains on the positive electrode side. In addition, in FIG. 4, the negative electrode OCP extends to a region where the charging rate is 100% or more. This indicates that the charging rate of 100% is a state where the amount of lithium that the positive electrode can accept is exceeded, and that even when the charging rate becomes 100%, releasable lithium remains on the negative electrode side. As will be described in detail later, when the battery cell deteriorates, the positive electrode OCP changes in shape to shift to the side where the charging rate becomes lower, and the negative electrode OCP changes in shape to extend to the side where the charging rate becomes higher.

[0042] Next, in the battery cell degradation calculation method according to the first embodiment, a dV / dQ plot showing the change in open circuit voltage accompanying the change in the charging rate is used in the process of calculating the degradation level of the battery cell. Fig. 5 shows a graph explaining the actual measurement differential plot (hereinafter referred to as the actual measurement dV / dQ plot) obtained from the actual measurement values ​​used in the battery cell degradation calculation method according to the first embodiment. As shown in Fig. 5, the actual measurement dV / dQ plot is a curve with a shape that emphasizes the change points in the SOC-OCV curve.

[0043] In addition, in the battery cell deterioration calculation method according to the first embodiment, a logical value charging rate voltage curve (hereinafter referred to as a logical value SOC-OCV curve) is generated from the difference between the positive electrode OCP and the negative electrode OCP logically derived from the active material contained in the composite material applied to each electrode, and a logical value differential plot (hereinafter referred to as a theoretical value dV / dQ plot) is generated from the logical SOC-OCV curve. FIG. 6 shows a graph illustrating a theoretical value dV / dQ plot obtained from the theoretical value used in the battery cell deterioration calculation method according to the first embodiment. The theoretical value dV / dQ plot shown in FIG. 6 is calculated using a theoretical value positive electrode OCP generated based on the content of lithium iron phosphate contained in the positive electrode composite material and a theoretical value negative electrode OCP generated based on the content of carbon contained in the negative electrode composite material.

[0044] As shown in FIG. 6, the logical value dV / dQ plot has a shape in which a peak occurs where the curvature change of the logically derived logical value SOC-OCV curve becomes large. When comparing the logical value dV / dQ plot shown in FIG. 6 with the measured value dV / dQ plot shown in FIG. 5, for example, the peak seen at a charging rate of 20% to 40% is shifted to the higher charging rate side in the measured value. Also, the peak seen at a charging rate of 60% to 80% in the theoretical value is no longer present in the measured value dV / dQ plot. Such differences are caused by changes in the SOC-OCV curve due to deterioration of the battery cell.

[0045] In the battery cell deterioration level calculation method according to the first embodiment, evaluation is performed by focusing on the change in OCP that occurs with battery deterioration, rather than directly evaluating the shift in the peak or the presence or absence of a peak. Therefore, the OCP change that occurs with battery deterioration and the fitting process used in the battery cell deterioration level calculation method according to the first embodiment will be described. Therefore, a graph for explaining the fitting process used in the battery cell deterioration level calculation method according to the first embodiment is shown in FIG.

[0046] In Figure 7, the positive and negative OCPs calculated from the actual measurements taken from the battery to be evaluated for degradation are shown, along with the theoretical positive OCP calculated based on the amount of lithium iron phosphate contained in the positive electrode composite material, and the theoretical negative OCP calculated based on the amount of carbon contained in the negative electrode composite material. This theoretical OCP can be assumed to be the OCP of a battery without degradation.

[0047] As shown in Figure 7, the positive OCP tends to shift toward a lower charging rate as the battery cell deteriorates. The negative OCP also tends to deform so that the curve is stretched toward a higher charging rate as the battery cell deteriorates. In a battery cell, the shape of the SOC-OCV curve changes due to deterioration due to such changes in OCP.

[0048] In the battery cell deterioration degree calculation method according to the first embodiment, the shift amount p1 of the positive electrode OCP is calculated as the deterioration degree parameter by utilizing the characteristics of the shape change of the OCP as shown in Fig. 7. More specifically, the shift amount p1 indicating the deterioration degree is calculated by the following procedure.

[0049] In the battery cell deterioration degree calculation method according to the first embodiment, the theoretical positive OCP is shifted using the fitting function G shown in equation (1), and a theoretical dV / dQ plot is generated from a theoretical SOC-OCV curve derived from an OCP curve in which the scaling of the theoretical negative OCP is changed. In other words, the fitting function G in equation (1) represents the theoretical dV / dQ plot.

number

[0050] In addition, in the battery cell deterioration level calculation method according to the first embodiment, the evaluation value J is calculated using the evaluation function shown in equation (2), and the validity of the shift amount p1 and the scaling rate p2 is evaluated based on this evaluation value J.

number

[0051] Here, the evaluation function used in the first embodiment is an overall evaluation term in which the first term of the formula (2) is an overall evaluation term that evaluates the difference between the theoretical value dV / dQ plot and the measured value dV / dQ plot over the entire charging rate. The second term of the formula (2) is a low charging rate region evaluation term that indicates the difference between the theoretical value dV / dQ plot and the measured value dV / dQ plot in the charging rate range of 0% to 30% (i.e., the low charging rate region) by setting the adjustment coefficient α to a value, for example, greater than 0 and less than 30. The third term of the formula (2) is a high charging rate region evaluation term that indicates the difference between the theoretical value dV / dQ plot and the measured value dV / dQ plot in the charging rate range of 70% to 100% (i.e., the high charging rate region) by setting the adjustment coefficient β to a value, for example, less than 100 and greater than 70. The adjustment coefficient α is preferably a value of about 20, more preferably about 15. The adjustment coefficient β is preferably a value of about 80, more preferably about 85.

[0052] Furthermore, in formula (2), the second term is multiplied by an adjustment coefficient k1, and the third term is multiplied by an adjustment coefficient k2. These adjustment coefficients k1 and k2 are coefficients for weighting the low charging rate region evaluation term (e.g., the second term) and the high charging rate region evaluation term (e.g., the third term) more heavily than the overall evaluation term (e.g., the first term), and are preferably values ​​of 100 or more, for example.

[0053] In addition, in formula (2), the value for evaluating the difference in the second term is set as a logarithmic value. This is a device for prioritizing the matching of the bases of the peaks of the differential plots over the peak apexes. Such a device is effective when emphasis is placed on fitting of the peak shape characteristics. In formula (2), the differential plots included in both the second and third terms may be set as logarithmic values, or the differential plots included in either one of them may be set as logarithmic values, or the differential plots included in both do not have to be set as logarithmic values. The differential plots included in which terms are to be applied with logarithmic values ​​can be determined based on the fitting conditions and the characteristics of the battery.

[0054] By adding the second and third terms to the evaluation function shown in equation (2), the constraints are strengthened in the low charge rate region of the negative OCP and the high charge rate region of the positive OCP, where shape change is small due to small lithium insertion stress caused by deterioration of the battery cell. As a result, the deterioration degree calculation method using the evaluation function shown in equation (2) can determine the deterioration degree of the battery cell based on the shift amount parameter that indicates the deterioration degree, without considering the difference in the shape of the OCP curve caused by the difference in the deterioration state of the battery.

[0055] In addition, in the method for calculating the deterioration level of a battery cell according to the first embodiment, the scaling factor p2 is changed. This scaling factor p2 is a parameter for estimating the positive and negative electrode capacity ratio, and by acquiring the scaling factor p2, it is possible to determine the change in the positive and negative electrode capacity ratio in addition to the deterioration level.

[0056] As described above, the method for calculating the deterioration level of a battery cell according to the first embodiment makes it possible to estimate the deterioration state even in a situation where data for each deterioration state of a battery from a new product or design information such as the capacity ratio of the positive and negative electrodes is unknown. This makes it possible to promote the reuse of batteries whose characteristics are unknown. For example, it takes an enormous amount of time to acquire deterioration data from a new product, but by using the method for calculating the deterioration level of a battery cell according to the first embodiment, it is possible to save the effort of acquiring the deterioration data.

[0057] In addition, in a battery cell, the positive and negative electrode capacity ratio may change according to deterioration, and if the battery deterioration mode does not match the pre-estimated value, there is a problem that an error occurs in the estimation result of the positive and negative electrode capacity ratio. However, by acquiring a scaling rate parameter indicating the amount of change in the positive and negative electrode capacity ratio in addition to the deterioration state, it is possible to estimate the positive and negative electrode capacity ratio of a used battery regardless of the deterioration mode. As a result, by using the method for calculating the deterioration degree of a battery cell according to the first embodiment, it is possible to further facilitate utilization.

[0058] Furthermore, in the method for calculating the deterioration level of a battery cell according to the first embodiment, the deterioration causes are expanded to include a decrease in the amount of lithium in the positive electrode, a decrease in the lithium acceptance capacity of the negative electrode, and a decrease in lithium by grasping the cause of deterioration from the shift amount p1 and the scaling rate p2, and it is not necessary to assume the deterioration mode in advance. This makes it possible to estimate the deterioration state of a battery cell for a wide range of deterioration modes.

[0059] Here, the battery cell deterioration level calculation method according to the first embodiment can be realized by executing a deterioration level calculation program that performs processing of the deterioration level calculation method in an arithmetic unit of a computer. Hereinafter, processing of the deterioration level calculation program when the battery cell deterioration level calculation method according to the first embodiment is executed by the deterioration level calculation program will be specifically described. Hereinafter, a flowchart for explaining the operation of the battery cell deterioration level calculation program according to the first embodiment will be shown in FIG.

[0060] As shown in FIG. 8, the battery cell deterioration degree calculation program according to the first embodiment first performs an actual value acquisition process to generate an actual value charging rate voltage curve (e.g., an actual value SOC-OCV curve) using the measurement results of the open circuit voltage of the battery cell when the charging rate is between 0% and 100% (step S31).

[0061] Next, the battery cell deterioration degree calculation program according to the first embodiment performs an actual measurement differential plot generation process to generate an actual measurement differential plot (e.g., an actual measurement dV / dQ plot) that plots the differential values ​​of the actual measurement SOC-OCV curve (step S32).

[0062] Next, the battery cell deterioration degree calculation program according to the first embodiment initializes the fitting function G shown in formula (1) by setting the shift amount p1 to 0 and the scaling rate p2 to 1 (step S33). Thereafter, the battery cell deterioration degree calculation program according to the first embodiment generates a theoretical charge rate voltage curve (e.g., theoretical SOC-OCV curve) calculated from the difference between a positive electrode open circuit potential theoretical value curve (e.g., theoretical positive electrode OCP) calculated from the content of at least one component (e.g., lithium iron phosphate) of the components of the positive electrode composite material of the battery cell and a negative electrode open circuit potential theoretical value curve (e.g., theoretical negative electrode OCP) calculated from the content of at least one component (e.g., carbon) of the components of the negative electrode composite material of the battery cell, and performs a theoretical value generation process to generate a theoretical dV / dQ plot using a fitting function G (e.g., formula (1)) that determines a theoretical differential plot (e.g., theoretical dV / dQ plot) that is a differential value of the theoretical SOC-OCV curve (step S34).

[0063] Here, in the above description, the shape of the theoretical positive electrode OCP can be logically derived from the type and content of the positive electrode active material. The positive electrode active material includes lithium cobalt oxide in addition to lithium iron phosphate. The shape of the theoretical negative electrode OCP can be logically derived from the type and content of the negative electrode active material. The negative electrode active material is often made mainly of carbon.

[0064] Next, the battery cell degradation degree calculation program according to the first embodiment performs an evaluation value calculation process (step S35) that calculates an evaluation value J using an evaluation function (for example, equation (2)) that calculates an evaluation value J indicating the magnitude of the difference between the theoretical value dV / dQ plot and the measured value dV / dQ plot. Here, the evaluation function has an overall evaluation term (first term in equation (2)) that indicates the overall difference between the theoretical value dV / dQ plot and the measured value dV / dQ plot, a high charging rate region evaluation term (for example, third term in equation (2)) that indicates the difference between the theoretical value dV / dQ plot and the measured value dV / dQ plot in a region where the charging rate is high, and a low charging rate region evaluation term (for example, second term in equation (2)) that indicates the difference between the theoretical value dV / dQ plot and the measured value dV / dQ plot in a region where the charging rate is low. In the evaluation function, the high charging rate region evaluation term and the low charging rate region evaluation term are weighted higher than the overall evaluation term.

[0065] Next, the deterioration degree calculation program for the battery cell according to the first embodiment repeats a theoretical value generation process (step S34) and an evaluation value calculation process (step S35) while varying a shift amount parameter p1 for shifting the theoretical positive open circuit potential curve (e.g., theoretical positive OCP) in the fitting function in the charge rate direction and a scaling rate parameter p2 for adjusting the length of the theoretical negative open circuit potential curve (e.g., theoretical negative OCP) in the charge rate direction in the fitting function, and performs an analysis process (steps S36 to S38) for outputting the shift amount parameter p1 that minimizes the evaluation value J as the deterioration degree of the battery cell. In the output process of step S38, the scaling rate parameter p2 that minimizes the evaluation value J is output as a parameter of the positive and negative electrode capacity ratio of the battery cell.

[0066] In the current state measurement process according to the first embodiment, the initial positive electrode capacity Qp_i and the initial negative electrode capacity Qp_n are corrected so that the battery capacity composed of the shift amount parameter p1 and the scaling rate parameter p2 becomes equal to the current battery capacity, and these corrected values ​​are set as the positive electrode capacity Qp and the negative electrode capacity Qn.

[0067] Next, in the method for using the battery according to the first embodiment, a coating structure calculation process is performed as step S23. In the coating structure calculation process, the cross-sectional area Sa of the electrode body housed in the battery cell and the coating width Lww of the electrode body are calculated based on dimensions that can be measured without destroying the battery cell. The cross-sectional area Sa of the electrode body is the cross-sectional area of ​​the electrode body when viewed from a direction perpendicular to the electrode lamination direction of the electrode body. The coating width Lww is, for example, the length of the longest side of the electrode body. In this case, the height Lwh of the electrode body is defined by the length of the longer side of the sides perpendicular to the side on which the coating width Lww is measured. The depth of the electrode body is defined by the length in the direction perpendicular to both the side on which the coating width Lww is measured and the side on which the height Lwh of the electrode body is measured.

[0068] Here, a first example of dimensions that can be measured without destroying a battery cell are the width, height, and depth of the battery cell case obtained by the visual inspection in step S4 in Fig. 2. In the coated portion structure calculation process that employs the first example, for example, the width, height, and depth of the electrode body within the case are estimated from the design tendency of similar battery cells, and the cross-sectional area Sa of the electrode body and the coated portion width Lww of the electrode body of the electrode body of the target battery cell are calculated based on the results of this estimation.

[0069] A second example of dimensions that can be measured without destroying a battery cell involves performing an X-ray inspection on the battery cell and calculating the cross-sectional area Sa of the electrode body and the width Lww of the coated portion of the electrode body based on the width, height, and depth of the electrode body photographed as a result of the X-ray inspection.

[0070] Next, in the method of using the battery according to the first embodiment, an active material thickness calculation process is performed as step S24. In the active material thickness calculation process, the thickness of the active material layer is calculated using the electrode foil thickness (e.g., aluminum foil thickness Lal and copper foil thickness Lcu) having a provisional value, the separator thickness Ls, the density of the active material layer (e.g., positive electrode density ρp and negative electrode density ρn), and the specific capacity of the active material layer (e.g., positive electrode specific capacity αp and negative electrode specific capacity αn), the current electrode capacity (e.g., positive electrode capacity Qp and negative electrode capacity Qn) calculated in step S22, and the cross-sectional area Sa of the electrode body and the coated portion width Lww of the electrode body calculated in step S23. A specific description of this active material thickness calculation process will be given below.

[0071] First, the electrode body has a structure in which a positive electrode foil, a negative electrode foil, and a separator are laminated so that the positive electrode foil and the negative electrode foil face each other with the separator interposed therebetween. Such a laminated structure may be a simple laminate of sheets, or may be a laminate in which the positive electrode foil, the negative electrode foil, and the separator are wound in a layered state. The capacity of the battery cell varies depending on the area in which the positive electrode active material coated on the positive electrode foil and the negative electrode active material coated on the negative electrode foil face each other. For this reason, in order to grasp the characteristics of the battery, it is necessary to grasp the coated area As. Here, in order to calculate the coated area As, first, the coated area length Lwh is calculated. This coated area length Lwh is expressed by equation (3).

number

number

[0072] Next, when the coated area As is known, the positive electrode capacity Qp and negative electrode capacity Qn of the battery cell can be expressed by equations (5) and (6).

number

number

[0073] Here, in formulas (5) and (6), the positive electrode capacity Qp and the negative electrode capacity Qn are known in step S22, but the positive electrode active material thickness Lp and the negative electrode active material thickness Ln remain unknown. Therefore, formula (7) is derived from formulas (5) and (6).

number

[0074] As described above, in the battery usage method according to the first embodiment, even if the battery cell has an unknown origin, unknown battery parameters can be extracted without destroying the battery cell. Then, by understanding the battery parameters, it becomes possible to safely control the battery cell. Note that in the battery usage method according to the first embodiment, the battery parameters used for control are estimated by calculation and contain many errors, so it is preferable to continue usage in a state of suppressing performance, such as suppressing the power limit, until the battery usage process of steps S10 to S13 progresses and the accuracy of the battery parameters improves.

[0075] In addition, in the battery usage method according to the first embodiment, the period during which the battery cell cannot be used to grasp the change in the battery characteristics caused by the use of the battery cell can be made much shorter than in the comparative example. Furthermore, in the battery usage method according to the first embodiment, since it is not necessary to acquire and diagnose the battery cell characteristics (step S102) in the comparative example to grasp the battery parameters, it is possible to reduce the power required during the period when the battery cell is not used for a specific purpose.

[0076] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present invention.

Claims

1. a provisional parameter setting process for setting provisional values ​​previously set for each of the thickness of an electrode foil used in a battery cell, the thickness of a separator, the density of an active material layer coated on the electrode foil, the specific capacity of the active material layer, and the electrode capacity of the active material layer; a current state measurement process for estimating a degree of deterioration of the battery cell and a current electrode capacity that is a current electrode capacity of the battery cell by performing charging and discharging of the battery cell while controlling the battery cell using the provisional values ​​set by the provisional parameter setting process; a coating structure calculation process for calculating a cross-sectional area of ​​the electrode body contained in the battery cell and a coating width of the electrode body based on dimensions that can be measured without destroying the battery cell; an active material thickness calculation process for calculating a thickness of the active material layer using the provisional values ​​of the thickness of the electrode foil, the thickness of the separator, the density of the active material layer, and the specific capacity of the active material layer, the current electrode capacity, the cross-sectional area of ​​the electrode body, and the width of the coated portion of the electrode body; A non-destructive battery characteristic estimation method in which the above is performed automatically by computer.

2. The non-destructive battery characteristic estimating method according to claim 1 , wherein the provisional value is a value set based on publicly available information.

3. The non-destructive battery characteristic estimation method according to claim 1, wherein the coating structure calculation process calculates the cross-sectional area of ​​the electrode body and the coated portion width of the electrode body based on the width, height and depth of the battery cell obtained by measuring the appearance of the battery cell.

4. The non-destructive battery characteristic estimation method according to claim 1, wherein the coating structure calculation process performs an X-ray inspection of the battery cell, and calculates the cross-sectional area of ​​the electrode body and the width of the coated portion of the electrode body based on the width, height and depth of the electrode body photographed as a result of the X-ray inspection.

5. The cross-sectional area is a cross-sectional area of ​​the electrode body when the electrode body is viewed from a direction perpendicular to the electrode stacking direction of the electrode body, The non-destructive battery characteristic estimating method according to claim 1 , wherein the coated portion width is the length of the longest side of the electrode assembly.

6. a provisional parameter setting process for setting a thickness of an electrode foil used in a battery cell, a thickness of a separator, a density of an active material layer coated on the electrode foil, a specific capacity of the active material layer, and an electrode capacity of the active material layer to provisional values ​​previously set; a current state measurement process for estimating a degree of deterioration of the battery cell and a current electrode capacity that is a current electrode capacity of the battery cell by performing charging and discharging of the battery cell while controlling the battery cell using the provisional values ​​set by the provisional parameter setting process; a coating structure calculation process for calculating a cross-sectional area of ​​an electrode body contained in the battery cell and a coating width of the electrode body based on dimensions that can be measured without destroying the battery cell; an active material thickness calculation process for calculating a thickness of the active material layer using the provisional values ​​of the thickness of the electrode foil, the thickness of the separator, the density of the active material layer, and the specific capacity of the active material layer, the current electrode capacity, the cross-sectional area of ​​the electrode body, and the width of the coated portion of the electrode body; A non-destructive battery characteristic estimation program that causes a computer to execute the above.

7. a first determination process for receiving product information including at least information on the battery type of the battery cell, determining first provisional battery parameters that are set in advance based on the product information, and determining whether the battery type is a target battery type; a battery characteristic estimation process for measuring the dimensions of the battery cell determined to be a target battery type, and then assembling the battery cell into a state in which the battery cell can be charged and discharged, estimating a degree of deterioration of the battery cell and a current electrode capacity that is a current electrode capacity of the battery cell based on a charge / discharge current value and an output voltage value of the battery cell obtained by charging and discharging the assembled battery cell, and estimating a thickness of an active material layer of the battery cell based on the measurement results of the dimensions of the battery cell; a characteristic degradation estimation process for estimating a parameter that is an index of a characteristic degradation degree of the battery cell based on an amount of change in battery resistance of the battery cell calculated from current and voltage values ​​obtained when the assembled battery cell is repeatedly charged and discharged a plurality of times; a second determination process for determining whether the battery cell can be used for a desired purpose based on battery parameters obtained by the battery characteristic estimation process and the characteristic deterioration estimation process; a battery parameter adaptation process for setting parameters obtained by the battery characteristic estimation process and the characteristic deterioration estimation process as battery parameters to be used for controlling the battery cell, for the battery cell determined to be usable for the intended use; a battery usage process for updating a power limit of the battery cell in accordance with the degree of deterioration while performing a process of estimating a charging rate and a degree of deterioration using the battery parameters set in the battery parameter adaptation process, and continuing to use the battery cell until it is determined that the battery life of the battery cell has expired; A method of using batteries in which each process is carried out automatically by a computer.

8. In the battery characteristic estimation process, a provisional parameter setting process for setting provisional values ​​previously set for each of the thickness of an electrode foil used in the battery cell, the thickness of a separator, the density of an active material layer coated on the electrode foil, the specific capacity of the active material layer, and the electrode capacity of the active material layer; a current state measurement process for estimating a deterioration degree of the battery cell and a current electrode capacity, which is a current electrode capacity of the battery cell, based on a charge / discharge current value obtained by charging / discharging the battery cell and an output voltage value of the battery cell while controlling the battery cell using the provisional values ​​set by the provisional parameter setting process; a coating structure calculation process for calculating a cross-sectional area of ​​the electrode body contained in the battery cell and a coating width of the electrode body based on dimensions that can be measured without destroying the battery cell; an active material thickness calculation process for calculating a thickness of the active material layer using the provisional values ​​of the thickness of the electrode foil, the thickness of the separator, the density of the active material layer, and the specific capacity of the active material layer, the current electrode capacity, the cross-sectional area of ​​the electrode body, and the width of the coated portion of the electrode body; The method for using a battery according to claim 7,

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