Method for estimating battery state of charge

Abstract

To provide a method capable of maintaining estimation accuracy of a state of charge (residual capacity) of a battery even when the battery has been somewhat deteriorated.SOLUTION: A method for estimating a state of charge (SOC) of a battery comprises the steps of: acquiring an SOC-OCV curve for a battery with a charge / discharge hysteresis of Δ0.06 V to 0.24 V, calculating an average voltage of OCV for each SOC from the acquired curve, and recording a relation between the calculated curve and the SOC; consecutively charging or consecutively discharging the battery, and then repeatedly applying charge pulse and discharge pulse loads 30 to 100 times; and measuring the OCV of the battery, and obtaining an estimated value of the SOC of the battery by comparing the OCV value with the recorded relation between the SOC and the average voltage of OCV.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for estimating the charge rate (remaining capacity) of a battery. [Background technology]

[0002] Patent Document 1 discloses a method of measuring the closed circuit voltage (CCV) of a battery and estimating the state of charge from each pattern depending on the charge mode and discharge mode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-227653 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with conventional methods, the accuracy of estimating the battery's charge rate (remaining capacity) decreases when the battery deteriorates.

[0005] The present disclosure has been made in view of the above circumstances, and aims to provide a method that can maintain the accuracy of estimating the charging rate (remaining capacity) of a battery even if the battery deteriorates. [Means for solving the problem]

[0006] As a result of extensive research, the inventors have found that the above estimation accuracy is particularly reduced in batteries with large charge / discharge hysteresis (for example, when Si is used as the negative electrode active material). Furthermore, the method of the present disclosure can be applied to various secondary batteries, such as solid-state batteries such as all-solid-state batteries and semi-solid-state batteries, and batteries containing an electrolyte solution.

[0007] The present application discloses a method for estimating the charging rate of a battery, the method comprising the steps of: obtaining an SOC-OCV curve for a battery having a charge / discharge hysteresis of Δ0.06 V to Δ0.24 V; calculating an average OCV voltage for each SOC from the obtained curve; and recording the relationship between the calculated curve and the SOC; continuously charging or discharging the battery, and then repeatedly applying a charge pulse and a discharge pulse load in a range of 30 to 100 times; and measuring the OCV of the battery and estimating the charging rate of the battery based on the relationship between the recorded SOC and the average OCV voltage. Here, SOC and OCV are well known, and SOC means the state of charge of a battery, and OCV means the open circuit voltage.

[0008] In the method for estimating the state of charge of a battery, the charging pulse may be applied first during continuous charging, and the discharging pulse may be applied first during continuous discharging.

[0009] In the above-described method for estimating the state of charge of a battery, the estimated value of the state of charge of the battery may be obtained after the repetition of the charging pulse load and the discharging pulse load has finished and charging and discharging of the battery has been suspended for a predetermined period of time. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to maintain the accuracy of estimating the battery's charging rate (remaining capacity) even if the battery has deteriorated. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing the configuration of the estimation device 20. [Figure 2] FIG. 2 is a graph showing the charge / discharge hysteresis and average voltage curves of the SOC-OCV characteristics of a battery. [Figure 3] FIG. 3 is a diagram showing the flow of the battery SOC estimation method S10. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1. Battery control device The method for estimating the charging rate (remaining capacity) of a battery according to the present disclosure is executed by an estimation device as one embodiment. An estimation device 20 for a battery according to one example will be described below with reference to the drawings.

[0013] 1 is a block diagram showing the configuration of an estimation device 20 according to this embodiment. As shown in FIG. 1, the estimation device 20 includes a charge / discharge unit 21, a voltage measurement unit 22, and a control unit .

[0014] The charging / discharging unit 21 is electrically connected to the battery 10, receives power from a power supply device (not shown) or the like, and charges / discharges the battery 10. The charging / discharging unit 21 has a switch, and is configured to switch between charging and discharging by switching the switch. Furthermore, the charge / discharge unit 21 is electrically connected to the control unit 23, and the switching (switching between charging and discharging) is performed in response to a command from the control unit 23.

[0015] The voltage measurement unit 22 is electrically connected to the battery 10 and measures the OCV of the battery 10. Therefore, the voltage measurement unit 22 is configured with a voltmeter or the like. The voltage measurement unit 22 is also electrically connected to the control unit 23, and is configured so that the control unit 23 can acquire the voltage data obtained by the voltage measurement unit 22.

[0016] The control unit 23 is a device that controls the above-mentioned components, stores necessary data, and calculates the charging rate in order to execute the method for estimating the charging rate of a battery, which will be described later. The control unit 23 can typically be configured as a computer.

[0017] The computer includes a CPU (Central Processing Unit) which is a processor, RAM (Random Access Memory) which functions as a working area, ROM (Read-Only Memory) which is a storage unit, a receiving unit which is an interface that receives information into the computer whether wired or wireless, and an output unit which is an interface that sends information from the computer to the outside whether wired or wireless. For example, a voltage measurement unit 22 is connected to the receiving unit, and a charge / discharge unit 21 is connected to the output unit.

[0018] The computer stores a computer program for executing each step of the method for estimating the state of charge of a battery according to the present disclosure as specific instructions. The computer's hardware resources, a CPU, RAM, and ROM, work together with the computer program. Specifically, the CPU executes the computer program stored in the ROM in the RAM, which functions as a work area, to issue instructions to the charging / discharging unit 21 via the output unit to control charging / discharging as described below, and also performs calculations based on signals representing voltages acquired via the receiving unit. Information acquired or generated by the CPU is stored in the RAM.

[0019] 2.Battery In the present disclosure, the battery 10 for which the state of charge of a battery is estimated can be any of a variety of secondary batteries, including solid-state batteries such as all-solid-state batteries and semi-solid-state batteries, and batteries containing electrolytes. Among these, batteries with large charge / discharge hysteresis, specifically those with a charge / discharge hysteresis in the range of Δ0.06 V to Δ0.24 V, can be cited. Here, charge / discharge hysteresis refers to the difference (voltage difference) between the OCV upon charging and the OCV upon discharging at a certain SOC. Furthermore, a battery with a charge / discharge hysteresis in the range of Δ0.06 V to Δ0.24 V means that the voltage difference falls within this range at any or all SOCs between 1% and 99%. Figure 2 shows the SOC-OCV relationship for one example. In this figure, the horizontal axis represents SOC (%) and the vertical axis represents OCV (V). For example, the charge / discharge hysteresis when the SOC is 50% is ΔV in Figure 2. In other words, the relationship between SOC and OCV changes significantly between charging and discharging.

[0020] When the battery is an all-solid-state battery, the charge / discharge hysteresis is particularly large, and this is particularly noticeable when Si is used as the negative electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3 Examples include those composed of O2, anode active material Si, and electrolyte Li3PS4. However, even semi-solid batteries and secondary batteries using electrolytes can have large charge / discharge hysteresis, and in such cases the method of the present disclosure is useful.

[0021] 3. Battery charge rate estimation method The method for estimating the state of charge of a battery in this embodiment is executed by operating the above-described estimation device 20. Figure 3 shows a flow of the method S10 for estimating the state of charge of a battery according to one embodiment. However, the method for estimating the state of charge of a battery according to the present disclosure does not necessarily have to be executed by the above-described estimation device 20, and may be executed by another device. Each step is explained below.

[0022] 3.1. Obtaining the SOC-OCV curve (Step S11) In the process S11 of acquiring the SOC-OCV curve, the relationship between the SOC and OCV during charging and discharging is acquired. For example, this curve is obtained by obtaining the "charging" curve and the "discharging" curve in Figure 2. In other words, the OCV during charging and the OCV during discharging are obtained for each SOC at a predetermined interval. The value obtained in this step S11 does not need to be obtained each time the SOC is estimated, and the value obtained and recorded initially can be reused.

[0023] 3.2. OCV average voltage curve calculation (step S12) In step S12 of calculating the OCV average voltage curve, the average value of the OCV during charging and discharging is calculated for each SOC for the OCV obtained in step S11. This results in a curve (average voltage curve) of the average OCV voltage for each SOC, as shown by "average value" in Figure 2. The average voltage curve of the OCV obtained in step S12 does not need to be obtained each time the SOC is estimated, and the one that was initially obtained and recorded can be reused.

[0024] 3.3. SOC-average voltage relationship recording (step S13) In step S13 of recording the SOC-average voltage relationship, the relationship between the SOC obtained in step S12 and the average voltage of the OCV is recorded. This record is stored, for example, in the ROM of the computer. The form of the SOC-average voltage relationship to be recorded is not particularly limited, and may be an equation that formulates the average voltage curve of the OCV, or a map that assigns a specific average voltage value to each SOC.

[0025] 3.4. Determining whether charging or discharging is in progress (step S14) In step S14, when estimating the SOC, it is determined whether to estimate the SOC based on charging or discharging. This determination may be made depending on the situation at the time, and if charging is currently being performed, the control unit 23 selects "during charging" and proceeds to step S21, and if discharging is currently being performed, the control unit 23 selects "during discharging" and proceeds to step S31. However, this is not limited to this, and the control unit 23 may determine whether to proceed to step S21 or step S31 based on predetermined conditions. Below, the case where the process proceeds to step S21 will be explained first, and then the case where the process proceeds to step S31 will be explained.

[0026] 3.5. Continuous charging (step S21) In the continuous charging step S21, the charge / discharge unit 21, in response to a command from the control unit 23, continuously charges the battery at a predetermined rate relative to the battery capacity (SOC 100%). A preferable rate is an increase in SOC in the range of 5% to 20%. That is, continuous charging is performed so that the SOC increases by, for example, 10% or more. However, the rate of increase in SOC due to continuous charging performed here does not need to be highly accurate; it is sufficient to more reliably achieve an SOC increase that is equal to or greater than the predetermined SOC increase.

[0027] 3.6. Charging Pulse Load (Process S22) In the charge pulse load process S22, after continuous charging in process S21, the charge / discharge unit 21 applies a load equivalent to charging to the battery 10 in the form of pulse waves in response to a command from the control unit 23. The pulse width, pulse current, and number of pulses of the applied pulse wave are not particularly limited, but for example, the pulse width is about 10 seconds, the pulse current is at a 2C rate, and the number of pulses is one.

[0028] 3.7. Discharge pulse load (step S23) In the discharge pulse load step S23, after the charge pulse load in step S22, the charge / discharge unit 21 applies a load equivalent to discharging to the battery 10 in the form of pulse waves in response to a command from the control unit 23. The pulse width, pulse current, and number of pulses of the applied pulse wave are not particularly limited, but for example, the pulse width is about 10 seconds, the pulse current is at a 2C rate, and the number of pulses is one.

[0029] 3.8. Judgment of the prescribed number of times (step S24) In step S24 of determining the specified number of times, the control unit 23 determines whether the number of times steps 22 and 23 have been repeated has reached the specified number of times. If the number of times has not reached the specified number of times, the result is No, the number of times of repetition is incremented by one, and the process returns to step S22. On the other hand, if the number of times has reached the specified number of times, the result is Yes, and the process proceeds to step S25. The specified number of repetitions can be 30 to 100 times, more preferably 50 to 80 times, and even more preferably 80 times.

[0030] 3.9. Pause (process S25) In the resting step S25, after the repetition of step S22 (charge pulse load) and step S23 (discharge pulse load) is completed, the control unit 23 stops charging and discharging and leaves (rests) for a predetermined time. The predetermined time is not particularly limited, but can be 30 minutes or more. A long rest period is also acceptable, and there is no particular upper limit, but resting for more than a certain period of time will have little effect on the effect and will be a waste of time. By including this resting step S25, polarization in the battery can be more reliably eliminated.

[0031] 3.10.OCV measurement (process S26) In the OCV measurement step S26, the control unit 23 measures the OCV (open circuit voltage) of the battery 10 at that time from the voltage measurement unit 22, and the control unit 23 acquires the value.

[0032] 3.11. Continuous Discharge (Process S31) In the continuous discharge step S31, the charge / discharge unit 21, in response to a command from the control unit 23, continuously discharges the battery at a predetermined rate relative to the battery capacity (SOC 100%). A preferable rate is a reduction in SOC in the range of 5% to 20%. That is, for example, continuous discharge is performed so that the SOC decreases by 10% or more. The rate of SOC decrease due to continuous discharge performed here does not need to be highly accurate; it is sufficient to more reliably achieve an SOC decrease that is equal to or greater than the predetermined SOC decrease.

[0033] 3.12. Discharge pulse load (step S32) In the discharge pulse load process S32, after the continuous discharge in process S31, the charge / discharge unit 21 applies a load equivalent to discharging to the battery 10 in the form of pulse waves in response to a command from the control unit 23. The pulse width, pulse current, and number of pulses of the applied pulse wave are not particularly limited, but for example, the pulse width is about 10 seconds, the pulse current is at a 2C rate, and the number of pulses is one.

[0034] 3.13. Charging pulse load (step S33) In the charge pulse load step S33, after the discharge pulse load in step S32, the charge / discharge unit 21 applies a load equivalent to charging to the battery 10 in the form of pulse waves in response to a command from the control unit 23. The pulse width, pulse current, and number of pulses of the applied pulse wave are not particularly limited, but for example, the pulse width is about 10 seconds, the pulse current is at a 2C rate, and the number of pulses is one.

[0035] 3.14. Determine the specified number of times (step S34) In step S34 for determining the predetermined number of times, the control unit 23 determines whether the number of times steps 32 and 33 have been repeated reaches the predetermined number. If the number of times has not reached the predetermined number of times, the result is No, the number of times of repetition is incremented by one, and the process returns to step S32. On the other hand, if the number of times has reached the predetermined number of times, the result is Yes, and the process proceeds to step S35. The specified number of repetitions can be 30 to 100 times, more preferably 50 to 80 times, and even more preferably 80 times.

[0036] 3.15. Pause (process S35) In the resting step S35, after the repetition of step S32 (discharge pulse load) and step S33 (charge pulse load) is completed, the control unit 23 stops charging and discharging and leaves (rests) for a predetermined time. The predetermined time is not particularly limited, but can be 30 minutes or more. A long rest period is also acceptable, and there is no particular upper limit, but resting for a longer period than this will reduce the effect and waste time. By including this resting step S25, polarization in the battery can be more reliably eliminated.

[0037] 3.16.OCV measurement (process S36) In the OCV measurement step S36, the control unit 23 measures the OCV (open circuit voltage) of the battery 10 at that time from the voltage measurement unit 22, and the control unit 23 acquires the value.

[0038] 3.17.SOC estimation (process S40) In the SOC estimation step S40, the control unit 23 applies the OCV obtained in step S26 or step S36 to the relationship recorded in step S13 to calculate the SOC value (corresponding to an estimated value). For example, if the OCV obtained in step S26 or step S36 is A(V) in Figure 2, the SOC is estimated to be B(%) using the average value curve.

[0039] 4. Test Example The inventors actually fabricated one example of a battery and conducted a test to estimate the SOC (charging rate, remaining battery capacity) when the battery was continuously charged in step S21 in step S14.

[0040] 4.1.Batteries The battery to be tested was fabricated as follows. [Positive electrode] Lithium nickel oxide coated with a solid electrolyte was used as the positive electrode active material. The solid electrolyte, conductive additive, binder, and dispersant were added to a dispersion in a weight ratio of 84.7:7.6:5.3:2.0:0.4, and the mixture was kneaded to prepare a slurry. The solid content was adjusted to 76%. This slurry was applied to aluminum foil as a current collector foil using a blade with a coating gap of 350 μm.

[0041] [Negative electrode] The silicon, solid electrolyte, conductive additive, binder, and dispersant were added to a dispersion liquid in a weight ratio of 52.9:44.1:0.3:1.5:1.2, and the mixture was kneaded to prepare a slurry. The solid content was adjusted to 30%. This slurry was applied to Ni foil as a current collector foil using a blade with a coating gap of 450 μm.

[0042] [Separator] The sulfide solid electrolyte and binder were added to the dispersion liquid at a weight ratio of 99.1:0.9 and kneaded to prepare a slurry. The solid content was adjusted to 38%. This slurry was then applied to an aluminum foil using a blade with a coating gap of 75 μm.

[0043] [Battery construction] The separator was transferred onto each of the positive and negative electrodes by passing it through rolls with a gap of 70 μm once (roll press) at a temperature of 175° C. and a pressure of 5 t / cm. After the transfer, the positive electrode and the negative electrode were punched out to prepare circular electrodes with a diameter of 11.28 mm and 11.74 mm, respectively. Furthermore, a separator was transferred onto each electrode using a uniaxial press at room temperature, with a pressure of 10 kN and a pressing time of 10 seconds. The positive and negative electrodes were then bonded using a uniaxial press. The bonding was performed in two steps: a first press and a second press after the first press. The first press was performed at a temperature of 170°C, with a pressure of 1 kN and a press time of 180 seconds, while the second press was performed at a temperature of 170°C, with a pressure of 50 kN and a press time of 60 seconds. The laminated body of the joined positive and negative electrodes was sealed in a bag made of laminate foil to form a laminate cell. The restraint conditions were first restrained at 20 MPa and held for 1 minute, and then maintained at a restraint force of 0.3 MPa.

[0044] 4.2. Test conditions In this example, the relationship between the SOC and the average voltage of the OCV is obtained in advance through steps S11 to S13, and then steps S21 to S26 are carried out. Each step is as follows. Step S13: In the obtained curve, the average voltage of OCV was 3.380V when SOC was 48% and 3.421V when SOC was 52%. · Process S21: For testing purposes, continuous charging was performed from 0% SOC so that the SOC after charging would be 50%. Step S22: Pulse charging was performed with a pulse width of 10 seconds and a pulse current of 2C rate (7.2mA). Step S23: A pulse discharge was performed with a pulse width of 10 seconds and a pulse current of 2C rate (7.2mA). Process S24: Six cases were performed with the specified number of repetitions being 0, 10, 30, 50, 80, and 100. · Process S25: The rest time was set to 2 hours.

[0045] 4.3.Results As a result, the following results were obtained at each specified number of repetitions of the OCV measurement in step S26. Number of repetitions: 0: 3.474V 10 cycles: 3.441V 30 cycles: 3.412V 50 cycles: 3.410V 80 cycles: 3.399V 100 cycles: 3.393V

[0046] Comparing the results with the curve obtained in step S13, which is the average OCV voltage of 3.380V when the SOC is 48% and 3.421V when the SOC is 52%, the OCV voltage is between 3.380V and 3.421V for the specified number of repetitions of 30, 50, 80, and 100, which is within ±2%, allowing the charge rate (remaining capacity) to be estimated with high accuracy. On the other hand, when the specified number of repetitions is 0 or 10, the voltage is outside this range, indicating a decrease in accuracy.

[0047] 5. Effects etc. According to the present disclosure, it is possible to accurately estimate the battery's charging rate (remaining battery capacity) even if the battery has deteriorated. This effect is particularly noticeable in batteries with large charge / discharge hysteresis (for example, when Si is used as the negative electrode active material). The reason why such an effect is observed in the present disclosure is not entirely clear; however, one possible reason is that, for example, when Si is used as the negative electrode active material, the crystalline phase state of Si differs during charging and discharging, resulting in large charge-discharge hysteresis. In response to this, repeated application of charge-discharge pulses causes the crystalline phase during charging and the crystalline phase during discharging to mix, resulting in an average charge-discharge voltage. [Explanation of symbols]

[0048] 10... battery, 20... estimation device, 21... charge / discharge unit, 22... voltage measurement unit, 23... control unit

Claims

1. 1. A method for estimating a state of charge of a battery, comprising: a step of obtaining an SOC-OCV curve for the battery having a charge / discharge hysteresis of Δ0.06V to 0.24V, calculating an average voltage of the OCV for each SOC from the obtained results, and recording the relationship between the calculation results and the SOC; a step of repeatedly applying a charge pulse and a discharge pulse load in a range of 30 to 100 times after continuously charging or continuously discharging the battery; measuring the OCV of the battery and deriving an estimate of the battery's state of charge based on the OCV value in relation to the recorded average voltage of the SOC and the OCV; A method for estimating the battery charge rate.

2. 2. The method for estimating a state of charge of a battery according to claim 1, wherein the charging pulse is applied first during the continuous charging, and the discharging pulse is applied first during the continuous discharging.

3. 3. The method for estimating the charging rate of a battery according to claim 1, wherein, after the repetition of the charging pulse load and the discharging pulse load has ended, charging and discharging of the battery is paused for a predetermined period of time before the estimated charging rate of the battery is obtained.

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