Estimation method for battery charging rate

Abstract

To provide a method for maintaining estimation accuracy of a charging rate (residual capacity) of a battery even if the battery is deteriorated.SOLUTION: A method for estimating charging rate of a battery includes the steps of: obtaining an SOC-OCV curve of a battery with charge / discharge hysteresis of Δ0.06 V to 0.24 V, calculating an average voltage of OCV for each SOC from the obtained result, and recording a relation between the calculation result and the SOC; continuously charging or continuously discharging the battery; performing return discharging for discharging power 3% or more with respect to the total capacity of the battery when continuously charging, and return charging for charging power 3% or more with respect to the total capacity of the battery when continuously discharging; measuring OCV of the battery and obtaining an estimated value of a charging rate of the battery in collation with the relation between SOC with the OCV value recorded and an average voltage of the 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 the respective patterns 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 consideration 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 0.24 V, calculating the average voltage of the OCV for each SOC from the obtained curve, and recording the relationship between the calculation result and the SOC; continuously charging or discharging the battery; performing a back-discharge in which the battery is discharged by 3% or more of its total capacity when continuously charged, or a back-charge in which the battery is charged by 3% or more of its total capacity when continuously discharged; and measuring the OCV of the battery and obtaining an estimate of the charging rate of the battery based on the relationship between the recorded SOC and the average voltage of the OCV. 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] The return discharge and return charge can be 4% to 6%.

[0009] After the return discharge and return charge, the charging and discharging of the battery may be suspended for a predetermined period of time before an estimated value of the battery's state of charge is obtained. [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 The battery 10 for which the state of charge of a battery is estimated in this disclosure can be various secondary batteries, such as 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 and the average voltage of the OCV obtained in step S12 is recorded. This record is stored in the ROM of the computer, for example. 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%). An example of this rate is shown in Figure 2. A preferable rate is an increase in SOC in the range of 5% to 20%. In other words, continuous charging is performed so that the SOC increases by 10% or more, for example. The increase in SOC due to continuous charging here does not need to be highly accurate; it is sufficient to ensure that an SOC increase of the same level as or greater than the predetermined SOC increase is obtained.

[0027] 3.6. Return discharge (process S22) In the return discharge step S22, the control unit 23 discharges the battery after the continuous charging is completed in the above step 21 (for convenience, this will be referred to as "return discharge"). An image of this process is also shown in Figure 2. The return discharge is performed by discharging at least 2% of the battery capacity, preferably 3% or more, and more preferably 5% (it does not have to be strictly 5%, but is in the range of 4% to 6%) as shown in the test example below. On the other hand, it is preferable that the magnitude (%) of the return discharge does not exceed the magnitude (%) of the continuous charge carried out in step S21.

[0028] 3.7. Pause (process S23) In the pause step S23, after the return discharge is completed in step S22, the control unit 23 stops charging and discharging and leaves (pauses) the battery for a predetermined time. The predetermined time is not particularly limited, but can be 30 minutes or more. The battery may be paused for a long time, and there is no particular upper limit. However, if the battery is paused for a long time, the effect is reduced and time is wasted. By including this resting step S23, polarization in the battery can be more reliably eliminated.

[0029] 3.8.OCV measurement (process S24) In the OCV measurement step S24, 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.

[0030] 3.9. 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%). An example of this rate is shown in Figure 2. 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 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.

[0031] 3.10. Return charging (step S32) In the return charge step S32, the control unit 23 charges the battery after the continuous discharge has been completed in the above step 31 (for convenience, this will be referred to as "return charge"). An image of this process is also shown in Figure 2. The return charge discharges at least 2% of the battery capacity, preferably 3% or more, and more preferably 5% (it does not have to be strictly 5%, but is in the range of 4% to 6%) as shown in the test example below. On the other hand, it is preferable that the magnitude (%) of the return charge does not exceed the magnitude (%) of the continuous discharge carried out in step S31.

[0032] 3.11. Pause (process S33) In the pause step S33, after the return charge is completed in step S32, the control unit 23 stops charging and discharging and leaves (pauses) for a predetermined time. The predetermined time is not particularly limited, but can be 30 minutes or more. A long pause is also possible, and there is no particular upper limit, but pausing for longer than a certain length of time will have little effect on the effect and will be a waste of time. By including such a resting step S33, polarization in the battery can be more reliably eliminated.

[0033] 3.12.OCV measurement (process S34) In the OCV measurement step S34, 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.

[0034] 3.13.SOC estimation (process S40) In the SOC estimation step S40, the control unit 23 applies the OCV obtained in step S24 or step S34 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 S24 or step S34 is A(V) in Figure 2, the SOC is estimated to be B(%) using the average value curve.

[0035] 4. Test Example The inventor actually fabricated one example of a battery and conducted tests to estimate the SOC (filling rate, remaining battery capacity) when process S14 was changed to continuous charging process S21 and when process S31 was changed to continuous discharging process.

[0036] 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.

[0037] [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.

[0038] [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.

[0039] [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.

[0040] Test 1 The relationship between the SOC and the average voltage of the OCV was obtained in advance through steps S11 to S13, and then steps S21 to S24 were carried out. Each step is as follows. Step S13: In the obtained curve, the average voltage of the OCV was 3.393V when the SOC was 49%, and 3.412V when the SOC was 51%. · Process S21: Continuous charging was performed from 0% SOC to 55% SOC. Step S22: A 5% return discharge was performed at SOC, i.e., the theoretical SOC was 50%. · Process S23: The rest time was set to 2 hours.

[0041] When the OCV was measured following step S24, 3.399V was obtained, which was within the range of 3.393V (SOC 49%) to 3.412V (SOC 51%) according to the curve obtained in step S13, and was found to be within ±1%.

[0042] Test 2 The relationship between the SOC and the average voltage of the OCV was obtained in advance through steps S11 to S13, and then steps S31 to S34 were carried out. Each step is as follows. Step S13: In the obtained curve, the average voltage of the OCV was 3.393V when the SOC was 49%, and 3.412V when the SOC was 51%. Step S31: Continuous discharge was performed from an SOC of 95% to an SOC of 45%. Step S32: 5% SOC back charge was performed, i.e., the theoretical SOC was 50%. · Process S33: The rest time was set to 2 hours.

[0043] When the OCV was measured following step S34, 3.393 V was obtained, which was within the range of 3.393 V (SOC 49%) to 3.412 V (SOC 51%) according to the curve obtained in step S13, and was found to be within ±1%.

[0044] Test 3 The relationship between the SOC and the average voltage of the OCV was obtained in advance through steps S11 to S13, and then steps S21 to S24 were carried out. Each step is as follows. Step S13: In the obtained curve, the average voltage of OCV was 3.06V when SOC was 13%. · Process S21: Continuous charging was performed from 0% SOC to 20% SOC. Step S22: A 5% return discharge was performed at SOC, i.e., the theoretical SOC was 15%. · Process S23: The rest time was set to 2 hours.

[0045] When the OCV was measured following step S24, 3.066 V was obtained, which was similar to the 3.06 V (SOC 13%) obtained from the curve obtained in step S13, with an error of within 2%.

[0046] Test 4 The relationship between the SOC and the average voltage of the OCV was obtained in advance through steps S11 to S13, and then steps S21 to S24 were carried out. Each step is as follows. Step S13: In the obtained curve, the average voltage of OCV was 3.35V when the SOC was 44%. · Process S21: Continuous charging was performed from 0% SOC to 50% SOC. Step S22: A 5% return discharge was performed at SOC, i.e., the theoretical SOC was 45%. · Process S23: The rest time was set to 2 hours.

[0047] When the OCV was measured following step S24, 3.350 V was obtained, which was the same as 3.35 V (SOC 14%) according to the curve obtained in step S13, with an error of within 1%.

[0048] 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, for example, when Si is used as the negative electrode active material, the crystalline phase state of Si differs between charge and discharge, resulting in large charge-discharge hysteresis. In response to this, one possible reason is that by performing return-discharge after continuous charge and return-charge after continuous discharge, the crystalline phase during charge and the crystalline phase during discharge mix, resulting in an average voltage between charge and discharge. [Explanation of symbols]

[0049] 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; continuously charging or discharging the battery; a step of performing a back-discharge of discharging the battery by 3% or more of the total capacity when the battery is continuously charged, and a back-charge of charging the battery by 3% or more of the total capacity when the battery is continuously discharged; 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 charging rate of a battery according to claim 1, wherein the return discharge and the return charge are between 4% and 6%.

3. 3. The method for estimating the state of charge of a battery according to claim 1, wherein, after the return-discharging and the return-charging, charging and discharging of the battery is suspended for a predetermined period of time, and then the estimated state of charge of the battery is obtained.

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