Estimation method of battery capacity and SOC estimation method of battery

Abstract

To provide a method of accurately estimating battery capacity, and a method of accurately estimating battery SOC based on estimated battery capacity acquired by the estimation method of battery capacity.SOLUTION: The method of estimating battery capacity includes causing a computer to execute the following steps: (a) charging is performed under a prescribed provisional SOC of 80% or more and a prescribed temperature, over a prescribed time at prescribed charging speed to acquire specific internal resistance; and (b) estimated battery capacity is acquired from specific internal resistance on the basis of a first prescribed relation. The method of estimating battery SOC includes causing a computer to execute after the step (b) the following steps: (i) estimated amount of change of the SOC due to degraded battery is acquired on the basis of a second prescribed relation from the estimated battery capacity; or (ii) estimated SOC that has changed due to the degraded battery is acquired on the basis of a third prescribed relation from the estimated battery capacity.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for estimating battery capacity and a method for estimating the state of charge (SOC) of a battery.

Background Art

[0002] Techniques for estimating the state of charge (SOC) based on the open circuit voltage (OCV) of a battery are known.

[0003] For example, Patent Document 1 discloses a SOC estimation device and a SOC estimation method that can estimate an SOC-OCV characteristic closer to the true value according to the charging and discharging implementation status with respect to the variation of the SOC-OCV characteristic due to the charging and discharging history, estimate the value of SOC using the estimated SOC-OCV characteristic, and reduce the estimation error of SOC.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In addition to this, various methods for estimating SOC are known, but there is still a need for a method for accurately estimating SOC.

[0006] In addition to being able to accurately estimate the SOC of the battery, it is desirable to be able to accurately estimate the battery capacity.

[0007] An object of the present disclosure is to provide a method for accurately estimating battery capacity and a method for accurately estimating the SOC of a battery based on the estimated battery capacity obtained by such a method for estimating battery capacity.

Means for Solving the Problems

[0008] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> 1. A method for estimating battery capacity, comprising causing a computer to perform the steps of: (a) determining the specific internal resistance at a predetermined charge rate for a predetermined time at a predetermined interim SOC of 80% or greater and at a predetermined temperature; and (b) calculating an estimated battery capacity from the specified internal resistance based on a first relationship between the specified internal resistance and the battery capacity that is specified in advance; <Aspect 2> The method for estimating a SOC of a battery according to aspect 1, further comprising causing a computer to execute the following steps after step (b): (i) determining an estimated change in SOC due to battery degradation from the estimated battery capacity based on a second relationship between the estimated battery capacity and a change in SOC due to battery degradation, or (ii) calculating an estimated SOC after a change due to battery degradation from the estimated battery capacity based on a third relationship specified in advance between the estimated battery capacity and the SOC after a change due to battery degradation; <Aspect 3> the first relationship has a linear expression; and The coefficient of determination of the linear equation is 0.8 or more. 3. The method according to embodiment 1 or 2. <Aspect 4> The predetermined time is 20 seconds or more, and The predetermined charging rate is 3C or higher. 3. The method according to embodiment 1 or 2. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a method for accurately estimating battery capacity, and a method for accurately estimating the SOC of a battery based on the estimated battery capacity obtained by such a method for estimating battery capacity. [Brief explanation of the drawings]

[0010]

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DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist of the disclosure.

[0012] 《Method for Estimating Battery Capacity》 The method of the present disclosure for estimating the battery capacity includes causing a computer to execute the following steps: (a) obtaining a specific internal resistance by charging at a predetermined charging rate for a predetermined time at a predetermined provisional SOC of 80% or more and a predetermined temperature, and (b) obtaining an estimated battery capacity from the specific internal resistance based on a previously specified first relationship between the specific internal resistance and the battery capacity.

[0013] As shown in Figures 5 and 6, according to the study of the present inventors, the coefficient of determination of the linear equation showing the relationship between the internal resistance (specific internal resistance) and battery capacity of a battery measured by charging under predetermined conditions where the provisional SOC is 80% or higher was 0.8 or higher. In other words, the specific internal resistance and battery capacity in this case showed a high correlation. As a result, the present inventors discovered that the battery capacity can be accurately estimated from the specific internal resistance. In other words, the method of the present disclosure allows accurate estimation of battery capacity, although the measurement conditions are limited.

[0014] In contrast, as shown in Figures 5 and 6, the coefficient of determination of the linear equation showing the relationship between the specific internal resistance and battery capacity of the battery measured by charging under predetermined conditions where the provisional SOC was less than 80% was less than 0.8. In other words, the correlation between the specific internal resistance and battery capacity in this case was low.

[0015] In FIG. 5, the values of the specific internal resistance and battery capacity are shown as relative values, with the maximum measured value being 1.0.

[0016] Figure 7 shows the relationship between battery voltage (V) and the voltage derivative of capacity (dQ / dV) when two batteries with different battery capacities due to degradation were charged for five seconds using CC charging at 1C. As shown in Figure 7, when the batteries were charged at a battery voltage corresponding to a provisional SOC of 80% or higher, the difference in the voltage derivative of capacity (dQ / dV) could be accurately distinguished between the two batteries with different battery capacities due to degradation (see the right side of the line indicating "SOC 80%" in Figure 7).

[0017] That is, as shown in Figure 7, when charging at a battery voltage corresponding to a provisional SOC of 80% or more, the dQ / dV curves of the battery whose capacity had decreased due to degradation (the "low battery capacity" battery) and the dQ / dV curves of the battery whose capacity had not decreased due to degradation and remained large (the "large battery capacity" battery) could be separated. Here, the voltage derivative of capacity (dQ / dV) refers to the battery capacity at each voltage. Therefore, as shown in Figure 7, when charging at a battery voltage corresponding to a provisional SOC of 80% or more, there was a clear difference in the battery capacity between the battery whose capacity had decreased due to degradation (the "low battery capacity" battery) and the battery whose capacity had not decreased due to degradation and remained large (the "large battery capacity" battery). In other words, Figure 7 suggests that there is also a correlation between battery voltage and battery capacity.

[0018] In contrast, as also shown in Figure 7, when charging was performed at a battery voltage corresponding to a provisional SOC of less than 80%, it was not possible to distinguish between the battery capacity of a battery whose capacity had decreased due to degradation (a battery with a "small battery capacity") and a battery whose capacity had not decreased due to degradation and remained large (a battery with a "large battery capacity") (see the left side of the line indicating "SOC 80%" in Figure 7).

[0019] In FIG. 7, the dQ / dV values are shown as relative values with the maximum measured value taken as 1.0, and the battery voltage values are shown as relative values with the SOC of 80% taken as 1.0.

[0020] In the context of this disclosure, "provisional SOC" means an SOC that is measured or estimated prior to step (a).

[0021] The predetermined interim SOC may be 80% or more, 85% or more, 90% or more, or 95% or more, and may be less than 100%, 95% or less, 90% or less, 85% or less, or 80% or less.

[0022] Regarding the present disclosure, the "specific internal resistance" means the internal resistance of a battery measured by charging at a predetermined charging rate over a predetermined time at a predetermined provisional SOC of 80% or more and a predetermined temperature.

[0023] Regarding the method of the present disclosure, the first relationship has a linear equation, and the coefficient of determination R of the linear equation 2 may be 0.8 or more. Note that the coefficient of determination R 2 is the value obtained by squaring the correlation coefficient R, and the closer it is to 1.0, the higher the correlation between the specific internal resistance and the battery capacity, and the higher the degree of fit of the regression equation. Here, as the first relationship having a linear equation, for example, it may be a map showing the relationship between the specific internal resistance and the battery capacity.

[0024] As shown in FIGS. 5 and 6, according to the study by the present inventors, when the provisional SOC is 80% or more, the coefficient of determination R 2 was greater than 0.8. On the other hand, when the provisional SOC was less than 80%, the coefficient of determination R 2 was less than 0.8. Specifically, when the provisional SOC was 75%, the coefficient of determination R 2 was 0.6 or less, and when the provisional SOC was 70% and 65%, the coefficient of determination R 2 was 0.5 or less. That is, when the provisional SOC is 80% or more, the correlation between the specific internal resistance and the battery capacity becomes high, and thus the estimated battery capacity can be accurately obtained.

[0025] The predetermined time may be 20 seconds or more, 25 seconds or more, or 30 seconds or more, and may be 30 seconds or less, 25 seconds or less, or 20 seconds or less.

[0026] The predetermined charging rate may be 3C or more, 4C or more, or 5C or more, and may be 5C or less, 4C or less, or 3C or less.

[0027] 《Method for Estimating SOC of Battery》 The method of the present disclosure for estimating the SOC of a battery includes further causing a computer to execute the following steps after step (b): (i) obtaining an estimated change amount of the SOC associated with battery degradation from the estimated battery capacity based on a predefined second relationship between the estimated battery capacity and the change amount of the SOC associated with battery degradation, or (ii) obtaining an estimated SOC after the change associated with battery degradation from the estimated battery capacity based on a predefined third relationship between the estimated battery capacity and the SOC after the change associated with battery degradation.

[0028] As described above, a technique for estimating the SOC based on the OCV of a battery is known. In this regard, the present inventors have found that due to the degradation of the battery associated with the degradation of the positive and negative electrodes caused by charge and discharge, that is, for example, due to a decrease in the battery capacity, a difference occurs between the SOC estimated in relation to the OCV of the battery and the actual SOC, that is, the SOC may change due to the degradation of the battery.

[0029] In this regard, the present inventors have found that based on a predefined relationship between the estimated battery capacity and the change amount of the SOC associated with battery degradation or the SOC after the change, it is possible to obtain an estimated change amount of the SOC associated with battery degradation or an estimated SOC after the change from the estimated battery capacity.

[0030] The method of the present disclosure for estimating the SOC of a battery is particularly effective in batteries in which the SOC changes mainly due to the degradation of the positive and negative electrodes, such as solid-state batteries. In the context of the present disclosure, "solid-state battery" means a battery that uses at least a solid electrolyte as an electrolyte. Therefore, a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. Further, the solid-state battery of the present disclosure may be an all-solid-state battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0031] The method of the present disclosure for estimating battery capacity and SOC may be executed by a system for estimating battery capacity and SOC. This system includes an ECU. A typical configuration of the ECU includes at least a ROM (Read Only Memory) that stores a program for performing such control, a CPU (Central Processing Unit) capable of executing the program, a RAM (Random Access Memory) that temporarily stores data, and input / output ports.

[0032] Various signals from voltage sensors, current sensors, temperature sensors, etc. are input to the ECU via the input ports. Also, drive signals to loads (power consumers and / or power suppliers) are output from the ECU via the output ports.

[0033] The ECU is provided with provisional SOC determination means, specific internal resistance acquisition means, estimated battery capacity acquisition means, and SOC change amount acquisition means or changed SOC acquisition means.

[0034] The provisional SOC determination means is configured to determine whether the provisional SOC is 80% or more. The method for determining whether the provisional SOC is 80% or more is not particularly limited, and for example, a conventionally known method commonly used in a general battery system as a method for determining whether a measured value is equal to or greater than a threshold value can be adopted.

[0035] The specific internal resistance acquisition means is configured to acquire (estimate) the specific internal resistance. The method for acquiring the specific internal resistance is not particularly limited, and a conventionally known method commonly used in a general battery system can be adopted. For example, based on various data detected by a voltage sensor and a current sensor, by dividing the voltage change during charge and discharge by the change in current at that time, a method for estimating the specific internal resistance (for example, a method of linearly approximating a parameter of the current change amount and a parameter based on the voltage change amount and the impedance change amount, and calculating the slope of the approximated straight line as the impedance of the battery) is exemplified.

[0036] By means of a specific internal resistance acquisition means, the specific internal resistance can be obtained when charging is performed at a predetermined charging rate for a predetermined time at a predetermined provisional SOC and temperature that are 80% or more.

[0037] The estimated battery capacity acquisition means is configured to acquire an estimated battery capacity. The estimated battery capacity can be obtained from the specific internal resistance based on a previously specified first relationship between the specific internal resistance and the battery capacity. Here, the first relationship may be, for example, a map showing the relationship between the specific internal resistance and the battery capacity.

[0038] FIG. 2 is an example of a map showing the relationship between the specific internal resistance and the battery capacity. This map may be created in advance by plotting the specific internal resistance acquired by the specific internal resistance acquisition means and the battery capacity. This map can be created for each temperature at which charging is performed.

[0039] The battery capacity may be obtained by arbitrary battery capacity acquisition means. The method for obtaining the battery capacity is not particularly limited, and a conventionally known method routinely used in a general battery system may be adopted. For example, based on various data detected by a voltage sensor, a current sensor, a temperature sensor, etc., according to a battery model formula, a method for obtaining the battery capacity of a secondary battery (for example, storing the open circuit voltage characteristics of the positive and negative electrodes of the secondary battery obtained in advance, and referring to this stored data and the data detected by the voltage sensor, the current sensor, and the temperature sensor to extract the active material amount, capacity density, and resistance value of the positive and negative electrodes, and using the extracted parameters to obtain the battery capacity of the secondary battery) is exemplified.

[0040] The estimated battery capacity acquisition means can derive the estimated battery capacity by causing the ECU to execute a process of substituting the specific internal resistance acquired by the specific internal resistance acquisition means into the linear equation constituting the created map.

[0041] The SOC change amount acquisition means is configured to acquire the change amount of the SOC associated with the deterioration of the battery. The change amount of the SOC associated with the deterioration of the battery can be obtained from the estimated battery capacity based on a pre-specified second relationship between the estimated battery capacity and the change amount of the SOC associated with the deterioration of the battery. Here, the second relationship may be, for example, a map showing the relationship between the estimated battery capacity and the change amount of the SOC associated with the deterioration of the battery.

[0042] FIG. 3 is an example of a map showing the relationship between the estimated battery capacity and the change amount of the SOC associated with the deterioration of the battery. This map may be created in advance by plotting the estimated battery capacity and the change amount of the SOC associated with the deterioration of the battery. The change amount of the SOC associated with the deterioration of the battery in this map can be obtained, for example, by performing a general endurance test on the battery, creating SOC-OCV curves before and after the endurance test as shown in FIG. 4, and taking the difference in SOC before and after the endurance test for the same OCV. Further, during the above-mentioned endurance test, the battery capacity is also measured, and a map can be created by plotting the relationship between the measured battery capacity and the calculated change amount of the SOC. This map can be created for each SOC. In FIG. 4, the OCV value is shown as a relative value with the value before the endurance test (initial) when the SOC is 0 being 1.0.

[0043] The SOC change amount acquisition means can derive the change amount of the SOC associated with the deterioration of the battery by causing the ECU to execute a process of substituting the estimated battery capacity acquired by the estimated battery capacity acquisition means into the linear equation constituting the created map.

[0044] The post-change SOC acquisition means is configured to acquire the post-change SOC associated with the deterioration of the battery. The post-change SOC associated with the deterioration of the battery can be obtained from the estimated battery capacity based on a pre-specified third relationship between the estimated battery capacity and the post-change SOC associated with the deterioration of the battery. Here, the third relationship may be, for example, a map showing the relationship between the estimated battery capacity and the post-change SOC associated with the deterioration of the battery.

[0045] In this method, the map showing the relationship with the estimated battery capacity may be prepared in advance. The SOC after the change due to battery degradation in this map may be, for example, the SOC after a general durability test on the battery. Furthermore, the battery capacity may also be measured during the durability test, and the map can be prepared by plotting the relationship between the measured battery capacity and the SOC after the change due to battery degradation. This map can be prepared for each SOC.

[0046] The post-change SOC acquisition means can derive a corrected SOC by having the ECU execute a process of substituting the estimated battery capacity acquired by the estimated battery capacity acquisition means into a linear equation that constitutes the created map.

[0047] The disclosed method for estimating battery capacity and battery SOC will be described below with reference to the flowchart illustrated in FIG.

[0048] In S101, the ECU starts charging the battery.

[0049] In S102, the ECU determines whether the provisional SOC is equal to or greater than 80% using the provisional SOC determination means. If the provisional SOC is equal to or greater than 80%, the ECU executes the process of S103. If the provisional SOC is less than 80%, the ECU executes the process of S101 again.

[0050] In S103, the ECU acquires the specific internal resistance when the battery is charged under predetermined conditions using the specific internal resistance acquisition means. The specific internal resistance can be calculated based on the voltage and current of the battery during charging. The ECU can acquire the battery voltage based on the output of the voltage sensor. The ECU can also acquire the battery current based on the output of the current sensor.

[0051] In S104, the ECU obtains an estimated battery capacity from the specific internal resistance acquired in S103 based on, for example, a map showing the relationship between the specific internal resistance and the battery capacity by means of an estimated battery capacity acquisition means. Here, the map showing the relationship between the specific internal resistance and the battery capacity can be created in advance and stored in the ROM. In this case, the ECU can obtain the estimated battery capacity by executing a process of substituting the specific internal resistance acquired in S103 into the linear equation constituting the above map read from the ROM.

[0052] Note that since the internal resistance of the battery may change according to the temperature of the battery, if information indicating the relationship between the internal resistance and the temperature of the battery is obtained in advance, the internal resistance corresponding to this temperature can be obtained by acquiring the temperature of the battery. The temperature of the battery can be acquired using a temperature sensor. The information indicating the relationship between the internal resistance and the temperature of the battery can be stored in the ROM. The information indicating the relationship between the internal resistance and the temperature of the battery can be represented as a map or a function.

[0053] In S105, the ECU can obtain the change amount of SOC due to battery degradation from the estimated battery capacity obtained in S104 based on, for example, a map showing the relationship between the battery capacity and the change amount of SOC due to battery degradation by means of a SOC change amount acquisition means. Here, the map showing the relationship between the battery capacity and the change amount of SOC due to battery degradation can be created in advance and stored in the ROM. In this case, the ECU can obtain the estimated change amount of SOC due to battery degradation by executing a process of substituting the estimated battery capacity acquired in S104 into the linear equation constituting the above map read from the ROM.

[0054] In S106, the ECU can obtain the estimated SOC after battery degradation from the estimated battery capacity obtained in S104 based on a map showing the relationship between the battery capacity and the SOC after changes due to battery degradation by means of the post-change SOC acquisition means. Here, the map showing the relationship between the battery capacity and the SOC after changes due to battery degradation can be created in advance and stored in the ROM. In this case, the ECU can obtain the estimated SOC after changes due to battery degradation by executing a process of substituting the estimated battery capacity obtained in S104 into the linear equation constituting the above map read from the ROM.

[0055] The SOC of the battery can be estimated by S105 or S106.

[0056] According to the SOC estimated by the method of the present disclosure, for example, the output of the battery can be controlled with high precision based on a map created for each temperature showing the relationship between the SOC estimated by the method of the present disclosure and the output value of the battery. For example, when the change in SOC due to battery degradation is not considered, the output value based on the above map may be different from the actual value. In contrast, according to the SOC estimated by the method of the present disclosure, the actual value can be output.

Claims

1. A method for estimating battery capacity, comprising causing a computer to execute the following steps: (a) At a predetermined provisional SOC of 80% or more and a predetermined temperature, charging at a predetermined charging rate for a predetermined time to obtain a specific internal resistance, and (b) Based on a previously specified first relationship between the specific internal resistance and the battery capacity, obtaining an estimated battery capacity from the specific internal resistance.

2. A method for estimating the SOC of a battery, comprising further causing a computer to execute the following step after the step (b) in the method according to Claim 1: (i) Based on a previously specified second relationship between the estimated battery capacity and the change amount of SOC associated with battery degradation, obtaining an estimated change amount of SOC associated with battery degradation from the estimated battery capacity, or (ii) Based on a previously specified third relationship between the estimated battery capacity and the SOC after change associated with battery degradation, obtaining an estimated SOC after change associated with battery degradation from the estimated battery capacity.

3. The first relationship has a linear equation, and The coefficient of determination of the linear equation is 0.8 or more, The method according to Claim 1 or 2.

4. The predetermined time is 20 seconds or more, and The predetermined charging rate is 3C or more, The method according to Claim 1 or 2.

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