Control program, control method, and control device for secondary batteries
The control program and method dynamically set voltage limits based on electrode degradation to prevent side reactions, ensuring safety and prolonged performance of secondary batteries.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOYOTA BATTERY CO LTD
- Filing Date
- 2024-12-25
- Publication Date
- 2026-07-07
Smart Images
Figure 2026113305000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a control program, a control method, and a control device for controlling a secondary battery such as a lithium ion battery, for example.
Background Art
[0002] In a secondary battery such as a lithium ion battery, battery control is performed to ensure the safety of the battery and to extract performance over a long period of time. Therefore, an example of a control method for a secondary battery is disclosed in Patent Document 1.
[0003] The control device described in Patent Document 1 has a controller that controls charging and discharging of a secondary battery. The controller acquires the positive electrode potential and the negative electrode potential of the secondary battery, and controls the charging and discharging of the secondary battery so that each of the positive electrode potential and the negative electrode potential changes within a range of an upper limit value and a lower limit value corresponding to each of the positive electrode potential and the negative electrode potential. When acquiring the positive electrode potential and the negative electrode potential, a deterioration parameter is used to correct the local charging rate of the positive electrode and the negative electrode of the secondary battery, and based on the corrected local charging rate and open circuit potential characteristic data, the open circuit potential of the positive electrode and the negative electrode is corrected. The deterioration parameter includes a maintenance rate of the single electrode capacity in the positive electrode, a maintenance rate of the single electrode capacity in the negative electrode, and a variation amount of the battery capacity of the secondary battery due to a change in the correspondence relationship between the average charging rate inside the active material of the positive electrode and the average charging rate inside the active material of the negative electrode from an initial state. The open circuit potential characteristic data is data that defines the relationship between the local charging rate on the surface of the active material of the positive electrode and the open circuit potential of the positive electrode, and the relationship between the local charging rate on the surface of the active material of the negative electrode and the open circuit potential of the negative electrode.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
[0005] To ensure the safety of secondary batteries while maintaining their performance over a long period, it is necessary to suppress their degradation. This degradation can be suppressed, for example, by using the charging and discharging of the secondary battery within a range that does not cause side reactions at the electrodes, as described in Patent Document 1. However, Patent Document 1 only corrects the local charge levels of the positive and negative electrodes using degradation parameters and does not restrict the battery's operating conditions (e.g., upper and lower voltage limits of the output voltage), which has the problem of not being able to effectively suppress degradation.
[0006] This invention has been made in view of the above circumstances, and aims to ensure the safety of secondary batteries while maximizing their performance over a long period of time. [Means for solving the problem]
[0007] One aspect of the control program for a secondary battery according to the present invention includes: a measurement process for acquiring the output voltage, charge / discharge current, and battery temperature of a secondary battery to be controlled; an adaptation process for inputting the output voltage, charge / discharge current, and battery temperature to adapt a state estimation model for estimating the charge level of the secondary battery to the actual state of the secondary battery; a positive electrode estimation process for estimating the capacity degradation and charge level of the positive electrode using the state estimation model; a negative electrode estimation process for estimating the capacity degradation and charge level of the negative electrode using the state estimation model; and a fitting process for adapting the positive electrode open circuit potential curve and the negative electrode open circuit potential curve to the current state using the positive electrode corresponding point on the positive electrode and the positive electrode corresponding point on the positive electrode corresponding to the charge level estimated using the state estimation model. The computer is instructed to perform the following operations: an upper limit voltage setting process, which sets the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the charge level at which electrical characteristics are obtained in which the degradation rate of both the positive and negative electrodes are reduced, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after fitting, to be the upper limit voltage during charging and discharging of the secondary battery; and a lower limit voltage setting process, which sets the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the lower charge level among the charge levels at which electrical characteristics are obtained in which the degradation rate of both the positive and negative electrodes are reduced, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after fitting, to be the lower limit voltage during charging and discharging of the secondary battery.
[0008] One aspect of the secondary battery control method according to the present invention includes: a measurement process for acquiring the output voltage, charge / discharge current, and battery temperature of a secondary battery to be controlled; an adaptation process for adapting a state estimation model for estimating the charge level of the secondary battery to the actual state of the secondary battery by inputting the output voltage, the charge / discharge current, and the battery temperature; a positive electrode estimation process for estimating the capacity degradation and charge level of the positive electrode using the state estimation model; a negative electrode estimation process for estimating the capacity degradation and charge level of the negative electrode using the state estimation model; and a fitting process for adapting the positive electrode open circuit potential curve and the negative electrode open circuit potential curve to the current state using the positive electrode corresponding point on the positive electrode and the positive electrode corresponding point on the positive electrode corresponding to the charge level estimated using the state estimation model. The following processes are performed automatically by a computer: an upper limit voltage setting process, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after fitting, where the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the charge level at which electrical characteristics are obtained in which the degradation rate of both the positive electrode and the negative electrode are reduced is set to the upper limit voltage during charging and discharging of the secondary battery; and a lower limit voltage setting process, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after fitting, where the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the lower charge level among the charge levels at which electrical characteristics are obtained in which the degradation rate of both the positive electrode and the negative electrode are reduced is set to the lower limit voltage during charging and discharging of the secondary battery.
[0009] One embodiment of the control device for a secondary battery according to the present invention is a control device for controlling the charging and discharging of a secondary battery, the control device having a memory for storing data and a program, and a calculation unit that performs a process to set an upper limit voltage and a lower limit voltage during charging and discharging of the secondary battery by executing the program, the calculation unit performing a measurement process to acquire the output voltage, charge / discharge current and battery temperature of the secondary battery to be controlled, an adaptation process that takes the output voltage, the charge / discharge current and the battery temperature as inputs and adapts a state estimation model for estimating the charge rate of the secondary battery to the actual state of the secondary battery, a positive electrode estimation process that estimates the capacity degradation and charge rate of the positive electrode using the state estimation model, a negative electrode estimation process that estimates the capacity degradation and charge rate of the negative electrode using the state estimation model, and a positive electrode corresponding point on the positive electrode and the positive electrode corresponding to the charge rate estimated using the state estimation model The system is configured to perform the following steps: a fitting process that uses the corresponding positive electrode point to adapt the positive electrode open circuit potential curve and the negative electrode open circuit potential curve to the current state; an upper limit voltage setting process that sets the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the charge level at which electrical characteristics are obtained in which the degradation rate of both the positive electrode and the negative electrode are reduced, to the upper limit voltage during charging and discharging of the secondary battery; and a lower limit voltage setting process that sets the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the lower charge level among the charge levels at which electrical characteristics are obtained in which the degradation rate of both the positive electrode and the negative electrode are reduced, to the lower limit voltage during charging and discharging of the secondary battery. [Effects of the Invention]
[0010] According to the control program, control method, and control device for secondary batteries of the present invention, it is possible to ensure the safety of the secondary battery while extracting its performance over a long period of time. [Brief explanation of the drawing]
[0011] [Figure 1]This graph illustrates the SOC-OCP curve, which outlines the control method for a secondary battery according to Embodiment 1. [Figure 2] This is a flowchart illustrating the flow of the degradation suppression process implemented in the secondary battery control method according to Embodiment 1. [Figure 3] This is a flowchart illustrating the flow of the upper limit voltage setting process performed in the secondary battery control method according to Embodiment 1. [Figure 4] This is a flowchart illustrating the flow of the lower limit voltage setting process performed in the secondary battery control method according to Embodiment 1. [Figure 5] This diagram illustrates the first to fourth voltages calculated in the upper limit voltage setting process and the lower limit voltage setting process according to Embodiment 1. [Modes for carrying out the invention]
[0012] For clarity of explanation, the following descriptions and drawings have been omitted and simplified as appropriate. Furthermore, each element shown in the drawings as a functional block performing various processes can be composed of a CPU (Central Processing Unit), memory, and other circuits in hardware terms, and implemented in software terms by programs loaded into memory. Therefore, it will be understood by those skilled in the art that these functional blocks can be implemented in various ways using hardware alone, software alone, or a combination thereof, and are not limited to any one of these. In each drawing, the same elements are denoted by the same reference numeral, and redundant explanations have been omitted where necessary.
[0013] Furthermore, the program described above includes, when loaded into a computer, a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored in a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disc (DVD), Blu-ray® disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically, or otherwise propagating signals.
[0014] Embodiment 1 The secondary battery control device according to Embodiment 1 maintains the performance of the secondary battery safely and over a long period of time by performing degradation suppression treatment. Therefore, Figure 1 shows a graph illustrating the relationship between the charge level and the open-circuit potential curves of the positive and negative electrodes (SOC-OCP curve), which outlines the secondary battery control method according to Embodiment 1. Figure 1 is a diagram illustrating the problems caused by secondary battery degradation. In the degradation suppression treatment, the upper and lower voltage limits during charging and discharging of the secondary battery are updated to follow the degradation state of the secondary battery. Therefore, in Figure 1, the SOC-OCV curve is shown superimposed on the SOC-OCP curve. The SOC-OCV curve is a reference value and shows the relationship between the charge level and the open-circuit voltage of the output voltage of the secondary battery.
[0015] As shown in Figure 1, the open-circuit voltage (OCV) of a secondary battery changes in accordance with the change in charge level. This change occurs because the potentials of the positive electrode and the negative electrode change due to the charging and discharging operation. In a secondary battery, the difference between the potentials of the positive electrode and the negative electrode becomes the open-circuit voltage between the positive and negative electrode terminals. These potentials of the positive and negative electrodes can be measured as the positive OCP (Open Circuit Potential) and negative OCP, respectively. Furthermore, the positive OCP and negative OCP can also be logically derived from the active material contained in the composite material coated on each electrode.
[0016] Furthermore, as shown in Figure 1, the positive electrode OCP extends to the region where the State of Charge (SOC) is 0% or less. This indicates that a 0% charge rate is a state where the amount of lithium the negative electrode can accept exceeds the limit, and even when the charge rate reaches 0%, there is still lithium available to release on the positive electrode side. Also, in Figure 1, the negative electrode OCP extends to the region where the charge rate is 100% or more. This indicates that a 100% charge rate is a state where the amount of lithium the positive electrode can accept exceeds the limit, and even when the charge rate reaches 100%, there is still lithium available to release on the negative electrode side.
[0017] As a secondary battery degrades, the positive electrode OCP shifts to the left towards a lower charge level or the positive electrode capacity itself decreases, while the negative electrode OCP shifts to the right or the negative electrode capacity itself decreases. Due to these changes in the positive and negative electrode OCPs, the range in which the charge level is 0% to 100% narrows. At this time, if the upper and lower voltage limits set for the output voltage of the secondary battery are not changed during the charging and discharging operation, the battery will be used in a range of open-circuit potential where the degradation rate of the secondary battery is accelerated, leading to a problem of accelerated degradation of the secondary battery. Figure 1 shows the difference in the upper voltage limit with and without degradation suppression treatment, but degradation suppression treatment is also applied to the lower voltage limit. In the degradation suppression treatment according to Embodiment 1, upper and lower voltage limits are set that avoid using the region where the degradation rate is accelerated from the perspective of the positive electrode OCP and negative electrode OCP.
[0018] Note that the deterioration of the positive electrode and the negative electrode means that, for example, overcharging or overdischarging of the secondary battery causes side reactions such as lithium precipitation and positive electrode active material disintegration in each electrode of the secondary battery, leading to an increase in battery resistance and a decrease in performance such as a decrease in capacity.
[0019] Fig. 2 shows a flowchart for explaining the flow of the deterioration suppression process implemented in the control method of the secondary battery according to Embodiment 1. The deterioration suppression process shown in Fig. 2 is realized, for example, by executing a control program that realizes the deterioration suppression process in a control device that controls the charge and discharge of the secondary battery. The control device has, for example, a memory that stores data and programs, and an arithmetic unit that executes a deterioration suppression process for setting the upper limit voltage and the lower limit voltage during charge and discharge of the secondary battery by executing the control program. That is, the control method of the secondary battery according to Embodiment 1 is realized by performing automatic processing by a computer by executing a control program for performing a deterioration suppression process on the computer.
[0020] As shown in Fig. 2, in the deterioration suppression process according to Embodiment 1, first, a measurement process for acquiring the output voltage, charge and discharge current, and battery temperature of the secondary battery to be controlled is performed (step S1). Subsequently, an adaptation process is performed in which the output voltage, charge and discharge current, and battery temperature are input and a state estimation model for estimating the state of charge (SOC) of the secondary battery is adapted to the actual state of the secondary battery (step S2). By the processes of steps S1 and S2, the state estimation model held in the control device is updated to a model capable of calculating the actual internal state of the secondary battery.
[0021] After that, in the degradation suppression process according to Embodiment 1, a positive electrode estimation process (step S3) for estimating the capacity degradation and charge rate of the positive electrode using a state estimation model, and a negative electrode estimation process (step S4) for estimating the capacity degradation and charge rate of the negative electrode using a state estimation model are performed. Further, in the degradation suppression process, a fitting process (step S5) is performed to adapt the positive electrode open circuit potential curve (positive electrode OCP curve) and the negative electrode open circuit potential curve (negative electrode OCP curve) to the current state using the positive electrode corresponding point on the positive electrode corresponding to the charge rate estimated using the state estimation model and the positive electrode corresponding point on the positive electrode. The processes of steps S3 to S5 correct the capacity shift associated with the degradation of the secondary battery and the decrease in the single electrode capacity (positive electrode capacity and negative electrode capacity).
[0022] Subsequently, in the degradation suppression process according to Embodiment 1, an upper limit voltage setting process (step S6) and a lower limit voltage setting process (step S7) are performed. In the upper limit voltage setting process (step S6), the difference potential between the positive electrode OCP curve and the negative electrode OCP curve at the point corresponding to the charge rate at which electrical characteristics with low degradation rates for both the positive electrode and the negative electrode are obtained in the positive electrode open circuit potential curve (positive electrode OCP curve) and the negative electrode open circuit potential curve (negative electrode OCP curve) after the fitting process (step S5) is set as the upper limit voltage during charging and discharging of the secondary battery. In the lower limit voltage setting process (step S7), the difference potential between the positive electrode OCP curve and the negative electrode OCP curve at the point corresponding to the charge rate on the low charge rate side among the charge rates at which electrical characteristics with low degradation rates for both the positive electrode and the negative electrode are obtained in the positive electrode OCP curve and the negative electrode OCP curve after the fitting process (step S5) is set as the lower limit voltage during charging and discharging of the secondary battery. Hereinafter, the upper limit voltage setting process and the lower limit voltage setting process will be described in more detail.
[0023] Figure 3 shows a flowchart illustrating the flow of the upper limit voltage setting process performed in the secondary battery control method according to Embodiment 1. Figure 5 shows a diagram illustrating the first to fourth voltages calculated in the upper limit voltage setting process and the lower limit voltage setting process according to Embodiment 1. In the following, the upper limit voltage setting process will be explained with reference to Figure 3, with reference to Figure 5 as appropriate. Figure 5 illustrates the OCV curve, positive electrode OCP curve, and negative electrode OCP curve of a secondary battery at a certain point in time as an example, showing a state in which the first voltage V1, which will be described later, is smaller than the second voltage V2, and the third voltage V3 is smaller than the fourth voltage V4.
[0024] As shown in Figure 3, in the upper limit voltage setting process, first, the charge level at which no side reactions occur at the negative and positive electrodes in the high charge level region (i.e., the region where overcharging occurs) is calculated. In this region, lithium deposition is at least possible as a side reaction at the negative electrode. Also, positive electrode active material decay is at least possible as a side reaction at the positive electrode. Therefore, in the upper limit voltage setting process, a negative electrode maximum charge level calculation process is performed to calculate the negative electrode maximum charge level (SOC[1]) at which at least lithium deposition does not occur as a side reaction at the negative electrode (step S10). Also, in the upper limit voltage setting process, a positive electrode minimum charge level calculation process is performed to calculate the positive electrode minimum charge level (SOC[2]) at which at least positive electrode active material decay does not occur as a side reaction at the positive electrode (step S11).
[0025] Next, in the upper limit voltage setting process, a high-charge-side potential difference calculation process is performed, in which the potential difference between the positive OCP curve and the negative OCP curve at the maximum negative charge level SOC[1] is calculated as the first voltage V1, and the potential difference between the positive OCP curve and the negative OCP curve at the minimum positive charge level SOC[2] is calculated as the second voltage V2 (step S12). Then, in the upper limit voltage setting process, if the first voltage V1 is less than or equal to the second voltage V2 (YES branch of step S13), the upper limit voltage is updated with the first voltage V1 (step S14), and if the first voltage V1 is greater than the second voltage V2 (NO branch of step S13), the upper limit voltage is updated with the second voltage V2 (step S15).
[0026] Here, referring to Figure 5, the first voltage V1 and the second voltage V2 calculated in the high charge-side potential difference calculation process (step S12) will be explained. As shown in Figure 5, the region in which the degradation rate of the negative electrode accelerates corresponds to the region in which the charge level is higher than the inflection point of the negative electrode OCP curve. For example, in the negative electrode, when lithium deposition begins, the resistance of the negative electrode increases sharply, causing an inflection point in the negative electrode OCP curve. Therefore, in the negative electrode maximum charge level calculation process in step S10, the charge level corresponding to the inflection point of the negative electrode OCP curve is defined as the negative electrode maximum charge level SOC[1]. Then, in the high charge-side potential difference calculation process in step S12, the difference potential between the positive electrode OCP curve and the negative electrode OCP curve at the negative electrode maximum charge level SOC[1] is defined as the first voltage V1.
[0027] Furthermore, as shown in Figure 5, the region where the degradation rate of the positive electrode accelerates corresponds to the region where the charge level is higher than the inflection point of the positive electrode OCP curve. For example, in the positive electrode, when the decay of the positive electrode active material begins, the resistance of the positive electrode increases sharply, causing an inflection point to occur in the positive electrode OCP curve. Therefore, in the positive electrode minimum charge level calculation process in step S11, the charge level corresponding to the inflection point of the positive electrode OCP curve is set as the positive electrode minimum charge level SOC[2]. Then, in the high charge level side potential difference calculation process in step S12, the difference potential between the positive electrode OCP curve and the negative electrode OCP curve at the positive electrode minimum charge level SOC[2] is set as the second voltage V2. In the example shown in Figure 5, since the first voltage V1 is smaller than the second voltage V2, the first voltage V1 is set as the upper limit voltage.
[0028] Next, Figure 4 shows a flowchart illustrating the flow of the lower limit voltage setting process performed in the secondary battery control method according to Embodiment 1. The lower limit voltage setting process will be explained below with reference to Figure 4, and with reference to Figure 5 as appropriate.
[0029] As shown in Figure 4, in the lower limit voltage setting process, first, the charge level at which no side reactions occur at the positive and negative electrodes in the low charge level region (i.e., the region where over-discharge occurs) is calculated. In this region, at least lithium oversupply is considered as a side reaction at the positive electrode. Also, at least copper leaching is considered as a side reaction at the negative electrode. Therefore, in the lower limit voltage setting process, a positive electrode maximum charge level calculation process is performed to calculate the positive electrode maximum charge level (SOC) [3] at which at least lithium oversupply does not occur as a side reaction at the positive electrode (step S20). Also, in the lower limit voltage setting process, a negative electrode minimum charge level calculation process is performed to calculate the positive electrode minimum charge level (SOC) [4] at which at least copper leaching does not occur as a side reaction at the negative electrode (step S21).
[0030] Next, in the lower limit voltage setting process, a low charge level side potential difference calculation process is performed, in which the potential difference between the positive OCP curve and the negative OCP curve at the positive electrode maximum charge level SOC[3] is calculated as the third voltage V3, and the potential difference between the positive OCP curve and the negative OCP curve at the negative electrode minimum charge level SOC[4] is calculated as the fourth voltage V4 (step S22). Then, in the lower limit voltage setting process, if the third voltage V3 is smaller than the fourth voltage V4 (YES branch of step S23), the upper limit voltage is updated with the fourth voltage V4 (step S24), and if the third voltage V3 is less than or equal to the fourth voltage V4 (NO branch of step S23), the upper limit voltage is updated with the third voltage V3 (step S25) (lower limit voltage update process).
[0031] Here, referring to Figure 5, the third voltage V3 and the fourth voltage V4 calculated in the low charge level side potential difference calculation process (step S22) will be explained. As shown in Figure 5, the region in which the degradation rate of the positive electrode accelerates corresponds to the region in which the charge level is lower than the inflection point of the positive electrode OCP curve. For example, in the positive electrode, when lithium oversupply begins, the resistance of the positive electrode drops sharply, causing an inflection point in the positive electrode OCP curve. Therefore, in the positive electrode maximum charge level calculation process in step S20, the charge level corresponding to the inflection point of the positive electrode OCP curve is defined as the positive electrode maximum charge level SOC[3]. Then, in the low charge level side potential difference calculation process in step S22, the difference potential between the positive electrode OCP curve and the negative electrode OCP curve at the positive electrode maximum charge level SOC[3] is defined as the third voltage V3.
[0032] Furthermore, as shown in Figure 5, the region where the degradation rate of the negative electrode accelerates corresponds to the region where the charge level is lower than the inflection point of the negative electrode OCP curve. For example, when copper dissolution begins in the negative electrode, the resistance of the negative electrode drops sharply, causing an inflection point in the negative electrode OCP curve. Therefore, in the negative electrode minimum charge level calculation process in step S21, the charge level corresponding to the inflection point of the negative electrode OCP curve is set as the negative electrode minimum charge level SOC[4]. Then, in the high charge level side potential difference calculation process in step S22, the differential potential between the positive electrode OCP curve and the negative electrode OCP curve at the negative electrode minimum charge level SOC[4] is set as the fourth voltage V4. In the example shown in Figure 5, since the third voltage V3 is greater than the fourth voltage V4, the fourth voltage V4 is set as the upper limit voltage.
[0033] As described above, the control method including degradation suppression processing according to Embodiment 1 updates the state estimation model and uses the state estimation model to limit the output voltage of the secondary battery during charging and discharging to upper and lower voltage limits that avoid the region in which the degradation rate of the secondary battery accelerates. As a result, by applying the control method according to Embodiment 1, it becomes possible to continuously suppress the degradation of the secondary battery. Furthermore, when the control method according to Embodiment 1 is applied, the usable range of the secondary battery can be expanded to the maximum extent possible with respect to the degradation state of the battery. In other words, by applying the control method according to Embodiment 1, it becomes possible to maximize the performance of the secondary battery while ensuring its safety and suppressing degradation.
[0034] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention.
Claims
1. Measurement process to acquire the output voltage, charge / discharge current, and battery temperature of the secondary battery to be controlled, A fitting process is performed to adapt a state estimation model, which estimates the charge level of the secondary battery by inputting the output voltage, the charge / discharge current, and the battery temperature, to the actual state of the secondary battery. A positive electrode estimation process that estimates the capacity degradation and charge level of the positive electrode using the aforementioned state estimation model, A negative electrode estimation process that estimates the capacity degradation and charge level of the negative electrode using the aforementioned state estimation model, A fitting process is performed to adapt the positive electrode open-circuit potential curve and the negative electrode open-circuit potential curve to the current state using the positive electrode corresponding points on the positive electrode that correspond to the charge rate estimated using the state estimation model, An upper limit voltage setting process is performed to set the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the charge level at which electrical characteristics are obtained in which the degradation rate of both the positive electrode and the negative electrode are reduced, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after the fitting process, to set the upper limit voltage during charging and discharging of the secondary battery. A lower limit voltage setting process is performed to set the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the lower charge rate among the charge rates that yield electrical characteristics where the degradation rate of both the positive electrode and the negative electrode is low, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after the fitting process, to set the lower limit voltage during charging and discharging of the secondary battery. A control program for secondary batteries that causes a computer to execute.
2. The aforementioned upper limit voltage setting process is, A process for calculating the maximum charge level of the negative electrode in which no side reactions occur, and A positive electrode minimum charge rate calculation process that calculates the positive electrode minimum charge rate at which no side reactions occur for the positive electrode, A high-charge-rate-side potential difference calculation process is performed, which calculates the potential difference between the positive electrode open-circuit potential curve and the negative electrode open-circuit potential curve at the maximum charge rate of the negative electrode as a first voltage, and calculates the potential difference between the positive electrode open-circuit potential curve and the negative electrode open-circuit potential curve at the minimum charge rate of the positive electrode as a second voltage. A control program for a secondary battery according to claim 1, which performs an upper limit voltage update process, wherein if the first voltage is less than or equal to the second voltage, it updates the upper limit voltage with the first voltage, and if the first voltage is greater than the second voltage, it updates the upper limit voltage with the second voltage.
3. The lower limit voltage setting process is as follows: A positive electrode maximum charge rate calculation process that calculates the positive electrode maximum charge rate at which no side reactions occur for the positive electrode, A negative electrode minimum charge level process is performed to calculate the minimum charge level at which no side reactions occur with respect to the negative electrode. A low-charge-side potential difference calculation process is performed, which calculates the potential difference between the positive electrode open-circuit potential curve and the negative electrode open-circuit potential curve at the positive electrode's maximum charge level as a third voltage, and calculates the potential difference between the positive electrode open-circuit potential curve and the negative electrode open-circuit potential curve at the negative electrode's minimum charge level as a fourth voltage. A control program for a secondary battery according to claim 1, which performs a lower limit voltage update process, which updates the upper limit voltage with the fourth voltage if the third voltage is less than or equal to the fourth voltage, and updates the upper limit voltage with the third voltage if the third voltage is greater than the fourth voltage.
4. Measurement process to acquire the output voltage, charge / discharge current, and battery temperature of the secondary battery to be controlled, A fitting process is performed to adapt a state estimation model, which estimates the charge level of the secondary battery by inputting the output voltage, the charge / discharge current, and the battery temperature, to the actual state of the secondary battery. A positive electrode estimation process that estimates the capacity degradation and charge level of the positive electrode using the aforementioned state estimation model, A negative electrode estimation process that estimates the capacity degradation and charge level of the negative electrode using the aforementioned state estimation model, A fitting process is performed to adapt the positive electrode open-circuit potential curve and the negative electrode open-circuit potential curve to the current state using the positive electrode corresponding points on the positive electrode that correspond to the charge rate estimated using the state estimation model, An upper limit voltage setting process is performed to set the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the charge level at which electrical characteristics are obtained in which the degradation rate of both the positive electrode and the negative electrode are reduced, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after the fitting process, to set the upper limit voltage during charging and discharging of the secondary battery. A lower limit voltage setting process is performed to set the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the lower charge rate among the charge rates that yield electrical characteristics where the degradation rate of both the positive electrode and the negative electrode is low, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after the fitting process, to set the lower limit voltage during charging and discharging of the secondary battery. A method for controlling secondary batteries that performs this process automatically using a computer.
5. A control device for controlling the charging and discharging of a secondary battery, The control device is Memory for storing data and programs, The system includes a calculation unit that executes a program to set the upper and lower voltage limits for charging and discharging the secondary battery, The aforementioned arithmetic unit, Measurement process to acquire the output voltage, charge / discharge current, and battery temperature of the secondary battery to be controlled, A fitting process is performed to adapt a state estimation model, which estimates the charge level of the secondary battery by inputting the output voltage, the charge / discharge current, and the battery temperature, to the actual state of the secondary battery. A positive electrode estimation process that estimates the capacity degradation and charge level of the positive electrode using the aforementioned state estimation model, A negative electrode estimation process that estimates the capacity degradation and charge level of the negative electrode using the aforementioned state estimation model, A fitting process is performed to adapt the positive electrode open-circuit potential curve and the negative electrode open-circuit potential curve to the current state using the positive electrode corresponding points on the positive electrode that correspond to the charge rate estimated using the state estimation model, An upper limit voltage setting process is performed to set the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the charge level at which electrical characteristics are obtained in which the degradation rate of both the positive electrode and the negative electrode are reduced, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after the fitting process, to the upper limit voltage during charging and discharging of the secondary battery. A lower limit voltage setting process is performed to set the difference potential between the positive electrode open circuit potential curve and the negative electrode open circuit potential curve at a point corresponding to the lower charge rate among the charge rates that yield electrical characteristics where the degradation rate of both the positive electrode and the negative electrode is low, in the positive electrode open circuit potential curve and the negative electrode open circuit potential curve after the fitting process, to the lower limit voltage during charging and discharging of the secondary battery. A control device for a secondary battery configured to perform the following actions.