METHOD FOR ESTIMATING THE CHARGING RATE OF A BATTERY

Abstract

A method for estimating the charging rate of a battery, comprising: acquiring an SOC-OCV curve line for the battery with a charge / discharge hysteresis of Δ0.06V to 0.24V, calculating an average voltage of OCV for each SOC from the acquired result, and recording the relationship between the calculation result and the SOC; performing continuous charging or continuous discharging on the battery; performing back discharging, which is discharging 3% or more of a total capacity of the battery when the continuous charging was performed, and performing back charging, which is charging 3% or more of the total capacity of the battery when the continuous discharging was performed; and measuring the OCV of the battery and checking the value of the OCV against the recorded relationship between the SOC and the average voltage of the OCV to obtain an estimated value of the charging rate of the battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present disclosure relates to a method for estimating the charging rate (remaining capacity) of a battery. 2. Description of the related art

[0002] Published unexamined Japanese patent application No. 2017-227653 discloses a method for measuring a closed-circuit voltage (CCV) of a battery and estimating a charging speed of the battery from respective patterns according to a charging mode and a discharging mode. OVERVIEW OF THE INVENTION

[0003] However, according to conventional methods, the estimation accuracy for the charging rate (remaining capacity) of a battery deteriorates as the battery deteriorates.

[0004] 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 speed (remaining capacity) of the battery even when the battery deteriorates.

[0005] As a result of extensive research by the inventor, the inventor has found that the above-mentioned estimation accuracy is particularly degraded in batteries with large charge / discharge hysteresis (e.g., when Si is used as the negative electrode active material). A method disclosed in the present disclosure can also be applied to various secondary batteries such as solid-state batteries, semi-solid-state batteries, and batteries containing electrolytes.

[0006] The present application discloses a method for estimating a charging rate of a battery, the method comprising a step of detecting an SOC-OCV curve line for the battery with a charge / discharge hysteresis of Δ0.06V to 0.24V, calculating an average voltage of OCV for each SOC from a detected result, and recording a relationship between a calculation result and the SOC, a step of performing continuous charging or continuous discharging to the battery, a step of performing back-discharging which is discharging 3% or more of a total capacity of the battery when the continuous charging has been performed, and performing back-charging which is discharging 3% or more of the total capacity of the battery when the continuous discharging has been performed, and a step of measuring the OCV of the battery and checking the value of the OCV against the recorded relationship between the SOC and the average voltage of the OCV to obtain an estimated value of the charging speed of the battery.

[0007] Here, SOC and OCV are well known, and SOC means the state of charge of the battery and OCV means the open circuit voltage.

[0008] The back discharge and back charge can be adjusted between 4% and 6%.

[0009] After performing back-discharging and recharging, the charging and discharging of the battery may be suspended for a predetermined period of time, and then an estimated value of the battery state of charge may be determined.

[0010] According to the present disclosure, the accuracy of estimating the charging rate (remaining capacity) of a battery can be maintained even if the battery deteriorates. BRIEF DESCRIPTION OF THE CHARACTERS

[0011] Features, advantages and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying figures, in which like symbols denote like elements and in which: Fig. 1 is a block diagram showing the configuration of an estimation device 20; Fig. 2 is a diagram showing a charge / discharge hysteresis and an average voltage curve of a SOC-OCV characteristic of a battery; and Fig. 3 is a diagram showing the flow of a SOC estimation method S10 for the battery. DETAILED DESCRIPTION OF THE EMBODIMENTS 1. Battery control unit

[0012] A method for estimating the charging rate (remaining capacity) of a battery of the present disclosure is performed by an estimation device according to one embodiment. An estimation device 20 for a battery according to an example will be described with reference to the figures.

[0013] Fig. 1 is a block diagram showing a configuration of the estimation device 20 according to the present embodiment. As shown in Fig. 1, the estimation device 20 comprises a charging / discharging unit 21, a voltage measuring device 22 and a control device 23.

[0014] The charging / discharging unit 21 is a part that is electrically connected to the battery 10 and receives electric power from a power supply (not shown) or the like to charge and discharge the battery 10. The charging / discharging unit 21 has a switch and is configured to switch between charging and discharging by switching the switch. The charging / discharging unit 21 is also electrically connected to the control unit 23, and the switching of the switch (switching between charging and discharging) is executed by a command from the control unit 23.

[0015] The voltage measuring device 22 is a part electrically connected to the battery 10 to measure the OCV of the battery 10. Therefore, the voltage measuring device 22 is equipped with a voltmeter or the like. The voltage measuring device 22 is also electrically connected to the control unit 23 and is configured so that the control unit 23 can retrieve the voltage data obtained from the voltage measuring device 22.

[0016] The control unit 23 is a device for controlling the above-mentioned components, storing the necessary data, and calculating the charging rate to perform the method for estimating the charging rate of a battery described later. The control unit 23 can typically be configured by a computer.

[0017] The computer includes a central processing unit (CPU), which is a processor; a random access memory (RAM), which serves as a work area; a read-only memory (ROM), which serves as a storage unit; a receiving unit, which is an interface for receiving information into the computer, whether wired or wireless; and an output unit, which is an interface for sending information from the computer to the outside, whether wired or wireless. For example, a voltage measuring device 22 is connected to the receiving unit, and a charging / discharging unit 21 is connected to the output unit.

[0018] The computer stores a computer program for executing, as specific instructions, corresponding steps of a battery charging rate estimation method of the present disclosure. In the computer, the CPU, RAM, and ROM cooperate with each other as hardware resources and the computer program. Specifically, the CPU executes the computer program recorded in the ROM with the RAM acting as a work area, thereby giving instructions to the charge / discharge unit 21 via the output unit to control charging and discharging as described later, and performs calculation based on a signal representing the voltage obtained via the receiving unit. The information obtained or created by the CPU is stored in the RAM. 2. Battery

[0019] In the present disclosure, the battery 10 to be estimated for battery charging speed may include various secondary batteries, including solid-state batteries such as a solid-state battery and a semi-solid-state battery, as well as an electrolyte battery. These may include batteries with large charge / discharge hysteresis, particularly batteries with charge / discharge hysteresis in the range of Δ0.06V to Δ0.24V. Charge / discharge hysteresis refers to the difference (voltage difference) between the charge OCV and the discharge OCV at a certain SOC. Furthermore, batteries with a charge / discharge hysteresis in the range of Δ0.06V to Δ0.24V mean that the voltage difference at each SOC or all SOCs is within this range when the SOC is between 1% and 99%. Fig. Figure 2 shows the relationship between SOC and OCV according to an example. In this figure, the horizontal axis represents SOC (%) and the vertical axis represents OCV (V). For example, the charge / discharge hysteresis at a SOC of 50% is ΔV in Fig. 2. In other words, the relationship between SOC and OCV changes greatly between charging and discharging.

[0020] If the battery is a solid-state battery, the charge / discharge hysteresis is particularly large and is particularly noticeable when Si is used as the negative electrode active material. An example is a battery in which the positive electrode active material is LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, the negative electrode active material is Si and the electrolyte is Li3PS4.

[0021] However, secondary batteries using semi-solid batteries or electrolytes may also have a large charge / discharge hysteresis, and in such cases, the method disclosed in the present disclosure is useful. 3. Method for estimating the battery charging speed

[0022] In the present embodiment, the method for estimating the charging speed of a battery is carried out by the operation of the estimation device 20 described above. Fig. 3 shows a flow of a battery charging rate estimation method S10 according to one embodiment. However, the battery charging rate estimation method according to the present disclosure does not necessarily have to be executed by the estimation device 20 described above, but may also be executed by another device. The individual steps are described below. 3.1. Acquisition of the SOC-OCV curve (step S11)

[0023] In step S11 of detecting an SOC-OCV curve, the relationship between SOC and OCV during charging / discharging is detected. For example, detecting this curve means detecting a curve line "during charging" and a curve line "during discharging" in Fig. 2. In other words, the OCV during charging and the OCV during discharging are collected for each SOC at a predetermined interval.

[0024] It should be noted that the values ​​acquired in step S11 do not need to be acquired each time the SOC is estimated, and that an originally acquired and recorded value can be reused. 3.2. Calculation of the average voltage curve of OCV (step S12)

[0025] In step S12 of calculating an average voltage curve of the OCV, an average value of the OCV during charging and the OCV during discharging is calculated for each SOC for the OCVs detected in step S11. This results in a curve line based on the average voltage of OCV for each SOC (average voltage curve line), as indicated by "average value" in Fig. 2 is specified.

[0026] It should be noted that the average voltage curve of OCV obtained in step S12 does not need to be re-obtained each time the SOC is estimated, and it is possible to reuse an average voltage curve of OCV that was originally obtained and recorded. 3.3. Recording the relationship between SOC and average voltage (step S13)

[0027] In step S13 of recording an SOC-average voltage relationship, the relationship between the SOC and the average voltage of the OCV detected in step S12 is recorded. The above relationship is recorded, for example, in the ROM of the computer described above.

[0028] The form of the SOC-average voltage relationship to be recorded is not particularly limited and can be a formula obtained by formulating the average voltage curve line of OCV, or a map obtained by assigning a certain average voltage value to each SOC. 3.4. Determining whether one of the two types of loading and unloading is being performed (step S14)

[0029] In step S14, as a preparatory step for estimating the SOC, it is determined whether the estimation is performed based on charging or discharging. The decision may be made depending on the current situation. If charging is currently being performed, the controller 23 selects "during charging" and proceeds to step S21. If discharging is currently being performed, the controller 23 selects "during discharging" and proceeds to step S31. However, the present disclosure is not limited to this style, and the controller 23 may determine which of steps S21 and S31 to proceed to based on a predetermined condition.

[0030] A case where the process first proceeds to step S21 and then to step S31 will be described below. 3.5. Continuous charging (step S21)

[0031] In step S21 of continuous charging, the continuous charging of a battery in a predetermined ratio to the battery capacity (SOC 100%) is performed by the charging / discharging unit 21 in response to a command from the control unit 23. A picture is also shown in Fig. 2. It is possible to increase the SOC preferably in the range of 5% to 20% as the predetermined ratio. In other words, for example, continuous charging is performed so that the SOC increases by 10% or more. The value of the SOC increase caused by the continuous charging performed here does not need to be very precise and is only required to obtain a more reliable SOC increase equal to or greater than a certain SOC increase. 3.6. Back discharge (step S22)

[0032] In a back-discharging step S22, discharging is performed by the control unit 23 after the continuous charging in step 21 above is completed (for convenience, this is referred to as “back-discharging”). A figure is also shown in Fig. 2. The back discharge value is at least 2% or more of the battery capacity, preferably 3% or more, and more preferably 5%, as shown in the following test example (it does not have to be exactly 5%, but is in the range of 4% to 6%).

[0033] On the other hand, it is desirable that the amount (%) of back-discharging does not exceed the amount (%) of continuous charging in step S21. 3.7 Suspension (Step S23)

[0034] In the suspension step S23, after the back-discharge is completed in step S22, the controller 23 stops charging and discharging and remains suspended for a predetermined period of time. The predetermined period of time is not particularly limited, but can be set to 30 minutes or more. A long suspension is permissible, and there is no need to limit the upper limit. However, suspension for a certain period or longer will result in a reduction in the effect and is therefore a waste of time.

[0035] The inclusion of such a suspension stage S23 makes it possible to eliminate polarization in the battery more reliably. 3.8. OCV measurement (step S24)

[0036] In the OCV measuring step S24, the OCV (open circuit voltage) of the battery 10 at this time is measured by the voltage measuring device 22 through the control unit 23, and its value is detected by the control unit 23. 3.9 Continuous unloading (step S31)

[0037] In the continuous discharge step S31, the battery is continuously discharged in a predetermined ratio to the battery capacity (SOC 100%) in response to a command from the control unit 23 by the charging / discharging unit 21. A figure is also shown in Fig. 2. The SOC is preferably reduced in the range of 5% to 20% as a predetermined ratio. In other words, continuous discharging is performed, for example, to reduce the SOC by 10% or more. The SOC reduction ratio through the continuous discharging performed here does not need to be very precise, but is only required to more reliably achieve the same level as or more than a predetermined SOC reduction. 3.10. Reloading (Step S32)

[0038] In the recharging step S32, charging is performed by the control unit 23 after the continuous discharging in the above step 31 is completed (here, this is referred to as "recharging" for convenience). A picture is also shown in Fig. 2. Backcharging is defined as discharging at least 2% or more of the battery's capacity, preferably 3% or more, and preferably 5%, as shown in the following test example (it does not have to be strictly 5%, but it is in the range of 4% to 6%).

[0039] In addition, it is desirable that the amount (%) of recharge does not exceed the amount (%) of continuous discharge performed in step S31. 3.11. Suspension (Step S33)

[0040] In the suspension step S33, after the recharging is completed in step S32, the controller 23 stops charging and discharging and remains suspended for a predetermined period of time. The predetermined period of time is not particularly limited, but may be set to 30 minutes or more. A long suspension is permissible, and there is no need to limit the upper limit. However, suspension for a certain period or longer will result in a reduction in the effect and is therefore a waste of time.

[0041] The installation of such a suspension stage S33 makes it possible to eliminate polarization in the battery more reliably. 3.12. OCV measurement (step S34)

[0042] In the OCV measuring step S34, the OCV (open circuit voltage) of the battery 10 at this time is measured by the voltage measuring device 22 through the control unit 23, and its value is detected by the control unit 23. 3.13 SOC Estimation (Step S40)

[0043] In step S40 of the SOC estimation, the control unit 23 applies the OCV obtained in step S24 or step S34 to the relationship recorded in step S13 to calculate the value of the SOC (corresponding to an estimated value). For example, if the OCV obtained in step S24 or step S34 is Fig. 2 A (V), the SOC is estimated to be B (%) using the average value curve line. 4. Test example

[0044] The inventor prepared a battery according to an example and conducted a test to estimate the SOC (charging rate, remaining battery capacity) when the process proceeded to continuous charging in step S21 in step S14 and the SOC when the process proceeded to continuous discharging in step S31 in step S14. 4.1 Battery

[0045] A battery to be tested was prepared as follows. Positive electrode

[0046] Lithium nickelate coated with a solid electrolyte was used as the positive electrode active material. The positive electrode active material, solid electrolyte, conductive additive, binder, and dispersant were added to a dispersion liquid so that the weight ratio was 84.7:7.6:5.3:2.0:0.4 and kneaded to prepare a slurry. At this time, the solid content ratio was adjusted to 76%. This slurry was coated onto aluminum foil as the current collector foil using a blade with a coating gap of 350 μm. Negative electrode

[0047] Si, solid electrolyte, conductive additive, binder, and dispersant were added to the dispersion liquid in a weight ratio of 52.9:44.1:0.3:1.5:1.2 and kneaded to prepare a slurry. The solid content ratio at this time was set to 30%. This slurry was coated onto a Ni foil as a current collector foil using a blade with a coating gap of 450 µm. separator

[0048] Sulfide solid electrolyte and binder were added to a dispersion liquid so that the weight ratio was 99.1:0.9 and kneaded to prepare a slurry. The solid content ratio was adjusted to 38% at this time. This slurry was coated onto an aluminum foil with a blade with a coating gap of 75 µm. Preparing the battery

[0049] A separator was transferred to each of the positive and negative electrodes by passing the separator through rollers with a gap of 70 µm (roll pressing). The temperature at this time was 175°C and the pressure was 5 t / cm.

[0050] After transfer, the positive electrode with a diameter of 11.28 mm and the negative electrode with a diameter of 11.74 mm were punched out to produce round electrodes.

[0051] In addition, the separator was transferred to each electrode by uniaxial pressing. The temperature at this time was room temperature, the pressing pressure was 10 kN, and the pressing time was 10 seconds.

[0052] The positive and negative electrodes were then bonded together by uniaxial pressing. The bonding was performed in two separate pressing steps: a first pressing step and a second pressing step after the first pressing step. In the first pressing step, the temperature was set to 170°C, the pressing pressure to 1 kN, and the pressing time to 180 seconds. In the second pressing step, the temperature was set to 170°C, the pressing pressure to 50 kN, and the pressing time to 60 seconds.

[0053] The laminate of bonded positive and negative electrodes was sealed in a laminate film pouch to form a laminate cell. As clamping conditions, the laminate was first clamped at 20 MPa and held for 1 minute, and then held at a clamping force of 0.3 MPa. 4.2. Test 1

[0054] The average voltage relationship between SOC and OCV was determined in advance in steps S11 to S13, and then steps S21 to S24 were performed. Each step proceeds as follows. - Step S13: On the obtained curve line, the average voltage of OCV at 49% of SOC was 3.393 V, and the average voltage of OCV at 51% of SOC was 3.412 V. - Step S21: Continuous charging was performed from a state with an SOC of 0% to an SOC of 55%. - Step S22: Back discharge to 5% SOC has been performed. In other words, the theoretical SOC is 50%. - Step S23: The suspension time was set to 2 hours.

[0055] In the OCV measurement according to step S24, a value of 3.399 V was determined. This value is determined to be within the range of 3.393 V (SOC 49%) to 3.412 V (SOC 51%) of the curve line obtained in step S13, within ±1%. 4.3. Test 2

[0056] The average voltage relationship between SOC and OCV was determined in advance in steps S11 to S13, and steps S31 to S34 were performed. Each step is as follows. - Step S13: On the obtained curve line, the average voltage of OCV at SOC 49% was 3.393 V, and the average voltage of OCV at SOC 51% was 3.412 V. - Step S31: Continuous discharging was performed from a state with a SOC of 95% to a SOC of 45%. - Step S32: Recharge to 5% SOC is performed. In other words, the theoretical SOC is 50%. - Step S33: The suspension time was set to 2 hours.

[0057] In the OCV measurement according to step S34, a value of 3.393 V was determined. This value was found to be within a range of 3.393 V (SOC 49%) to 3.412 V (SOC 51%) on the curve line obtained in step S13 and within ±1%. 4.3 Test 3

[0058] The average voltage relationship between SOC and OCV was determined in advance in steps S11 to S13, and steps S21 to S24 were performed. Each step is as follows. -Step S13: On the obtained curve line, the average voltage of OCV at SOC 13% was 3.06 V. Step S21: Continuous charging was performed from a SOC state of 0% to a SOC state of 20%. -Step S22: Back-discharging to SOC 5% was performed. In other words, the theoretical SOC is 15%. -Step S23: The suspension time was set to 2 hours.

[0059] In the OCV measurement according to step S24, 3.066 V was determined, which corresponded to the value of 3.06 V (SOC 13%) based on the curve line determined in step S13, and the error could be limited to 2%. 4.4. Test 4

[0060] The average voltage relationship between SOC and OCV was determined in advance in steps S11 to S13, and steps S21 to S24 were performed. Each step is as follows. - Step S13: On the obtained curve line, the average voltage of OCV at SOC 44% was 3.35 V. Step S21: Continuous charging was performed from a SOC state of 0% to a SOC state of 50%. - Step S22: Back-discharging to 5% SOC was performed. In other words, the theoretical SOC was 45%. - Step S23: The suspension time was set to 2 hours.

[0061] When measuring the OCV in step S24, 3.350 V was determined. This corresponded to 3.35 V (SOC 14%) based on the curve obtained in step S13, and the error could be set to 1%. 5. Effect and the like

[0062] According to the present disclosure, the battery charging rate (remaining battery capacity) can be accurately estimated even when the battery is degraded. This effect is particularly noticeable for batteries with large charge / discharge hysteresis (e.g., when Si is used as the negative electrode active material, etc.).

[0063] The reason why such an effect is observed in the present disclosure is not necessarily clear, but for example, when Si is used as a negative electrode active material, the crystal phase state of Si is different during charging and discharging, so the charge / discharge hysteresis becomes large. In addition, back-discharging after continuous charging and back-discharging after continuous discharging are performed, causing the crystal phase during charging and the crystal phase during discharging to mix with each other, resulting in an average voltage between charging and discharging, which is considered to be one of the factors. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2017-227653

[0002]

Claims

[1] A method for estimating a charging rate of a battery, comprising: a step of acquiring a state of charge-open circuit voltage curve line for the battery having a charge / discharge hysteresis of Δ0.06V to 0.24V, calculating an average voltage of open circuit voltage for each state of charge from a acquired result, and recording a relationship between a calculation result and the state of charge; a step of performing continuous charging or continuous discharging of the battery; a step of performing back-discharging, which is discharging 3% or more of a total capacity of the battery when the continuous charging has been performed, and performing back-charging, which is charging 3% or more of the total capacity of the battery when the continuous discharging has been performed; and a step of measuring the open circuit voltage of the battery and checking a value of the open circuit voltage against the recorded relationship between the state of charge and the average voltage of the open circuit voltage to obtain an estimated value of the charging rate of the battery. [2] The method of claim 1, wherein the back-discharging and the back-charging are between 4% and 6%. [3] A method according to claim 1 or 2, wherein after performing the back-discharging and recharging, the charging and discharging of the battery are suspended for a predetermined period of time and then an estimate of the charging rate of the battery is determined.

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