Measurement device, measurement method, and storage medium

Abstract

The present application provides a determination device, a determination method and a storage medium for determining the amount of SEI generated by a negative electrode of a lithium ion battery. A determination device for determining the amount of SEI generated by a negative electrode of a lithium ion battery comprises: a charge and discharge control unit for performing charge and discharge control of the lithium ion battery; a voltage measurement unit for measuring the discharge voltage of the lithium ion battery; a current measurement unit for measuring the discharge current of the lithium ion battery; a discharge time measurement unit for measuring the discharge time of the lithium ion battery; a storage unit for storing the measurement results of the voltage measurement unit, the current measurement unit and the discharge time measurement unit; and a calculation unit for calculating the amount of SEI generated by the negative electrode of the lithium ion battery.

Description

[0001] Citation of relevant applications

[0002] This application claims priority based on Japanese Patent Application No. 2022-038080, filed on March 11, 2022, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a measuring device, a measuring method, and a storage medium. Background Technology

[0004] Lithium-ion batteries, characterized by their large capacity, small size, and lightweight design, are widely used in mobile devices such as smartphones and laptops. Furthermore, in recent years, they have also been commercially available as batteries for hybrid and electric vehicles, further expanding their applications. Therefore, there is a need to further improve the performance of lithium-ion batteries, and the Solid Electrolyte Interphase (SEI) coating formed at the electrode-electrolyte interface is considered one of the key factors in achieving this performance.

[0005] A lithium-ion battery consists of a positive electrode containing lithium and a negative electrode that absorbs lithium. Charging (or discharging) occurs as lithium moves from the positive electrode to the negative electrode (or vice versa) via an electrolyte. A coating called an electrolyte interphase (SEI) is formed on the surface of the negative electrode by decomposing the electrolyte. This SEI coating facilitates the insertion and removal of lithium ions from the electrode and helps to suppress further electrolyte decomposition, thus improving performance. However, there are issues where an excessively thin SEI coating leads to electrolyte decomposition, while an excessively thick coating results in increased resistance. Such an SEI coating negatively impacts the battery's lifespan and efficiency. Therefore, measuring the amount of SEI coating formed on the negative electrode is important for evaluating the degradation of lithium-ion batteries.

[0006] Previously, the determination of the amount of SEI coating formed on the negative electrode involved disassembling the lithium-ion battery and performing inductively coupled plasma (ICP) luminescence analysis to measure the amount of Li in the negative electrode SEI coating, or using dV / dQ analysis to obtain the Ah-OCP curves (discharge power-open circuit potential curves) of the positive and negative electrodes and determining the amount of SEI formed on the negative electrode based on the positional changes of the potential ends of the positive and negative electrodes.

[0007] Japanese Patent Application Publication No. 2020-109367 discloses a method related to estimating the internal state of a secondary battery. The method is characterized in that a parameter estimation unit reads various initial values ​​from a parameter storage unit, such as the estimated capacity of the positive and negative electrodes, the estimated battery charge of the secondary battery, the estimated initial charge of the positive and negative electrodes, and the initial value of the battery temperature, and updates the positive electrode capacity degradation coefficient, the negative electrode capacity degradation coefficient, the negative electrode charge degradation coefficient, the first internal resistance degradation coefficient, and / or the second internal resistance degradation coefficient.

[0008] Japanese Patent Application Publication No. 2015-230817 discloses a technology that detects the reduction of lithium caused by capacity degradation of the positive and negative electrodes and side reactions, and determines the SOC operating range that can suppress the degradation of a single cell based on the detection results.

[0009] Japanese Patent Application Publication No. 2018-084549 discloses a state estimation device for a secondary battery that can accurately estimate the charge rate of a battery by taking into account the amount of degradation products in the positive or negative electrode. Summary of the Invention

[0010] However, an increase in the amount of SEI (Sediment Ignition) formed on the negative electrode is a known major cause of lithium-ion battery degradation. When attempting to calculate the amount of SEI formed on the negative electrode using dV / dQ analysis based on the positional changes of the potential terminals of the positive and negative electrodes, the result is a value obtained by combining the amount of SEI formed on the negative electrode with the negative electrode shrinkage rate, which cannot accurately determine the amount of SEI formed. To date, no method has been found that incorporates the negative electrode shrinkage rate into the measurement of the amount of SEI formed on the negative electrode.

[0011] The present invention provides a measuring apparatus, a measuring method, and a storage medium for measuring the amount of SEI generated on the negative electrode of a lithium-ion battery.

[0012] The measuring apparatus, measuring method, and storage medium for measuring the SEI generation amount of the negative electrode of a lithium-ion battery of the present invention adopt the following structure.

[0013] (1): A measuring device according to one aspect of the present invention is used to measure the amount of SEI generated at the negative electrode of a lithium-ion battery. The measuring device comprises: a charge / discharge control unit for controlling the charge and discharge of the lithium-ion battery; a voltage measuring unit for measuring the discharge voltage of the lithium-ion battery; a current measuring unit for measuring the discharge current of the lithium-ion battery; a discharge time measuring unit for measuring the discharge time of the lithium-ion battery; a storage unit for storing the measurement results of the voltage measuring unit, the current measuring unit, and the discharge time measuring unit; and a calculation unit for calculating the amount of SEI generated at the negative electrode of the lithium-ion battery. The calculation unit performs the following processing: based on the results of the voltage measuring unit, the current measuring unit, and the discharge time measuring unit read from the storage unit, it obtains an initial positive electrode Ah-OCP curve and an initial negative electrode Ah curve by fitting a dV / dQ curve and a charge / discharge curve. -OCP curve; calculate the shrinkage rate (%) of the positive and negative electrodes relative to the initial value; calculate the positive and negative electrode Ah-OCP curves with only shrinkage rate applied, obtained by multiplying the shrinkage rate (%) by the fixed point (potential) derived under durability conditions based on the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve; calculate the offset Z of the fixed point of the positive electrode Ah-OCP curve with only shrinkage rate applied and the fixed point of the degraded positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; calculate the offset A of the fixed point of the negative electrode Ah-OCP curve with only shrinkage rate applied and the fixed point of the degraded negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; and calculate as the negative electrode SEI generation amount = AZ.

[0014] (2): One aspect of the present invention provides a method for determining the SEI generation amount of the negative electrode in a lithium-ion battery. Based on the results of a charge-discharge test of the lithium-ion battery, an initial positive electrode Ah-OCP curve and an initial negative electrode Ah-OCP curve are obtained by fitting the dV / dQ curve and the charge-discharge curve. The shrinkage rate (%) of the positive and negative electrodes relative to their initial values ​​is calculated. Based on the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve, the shrinkage rate (%) is multiplied by the fixed point (potential) derived under durability conditions. The obtained positive electrode Ah-OCP curve and negative electrode Ah-OCP curve, which only apply the shrinkage rate, are used to calculate the offset Z of Ah between the fixed point of the positive electrode Ah-OCP curve with only the shrinkage rate and the fixed point of the degraded positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; the offset A of Ah between the fixed point of the negative electrode Ah-OCP curve with only the shrinkage rate and the fixed point of the degraded negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve is calculated; and the negative electrode SEI generation amount = AZ is calculated.

[0015] (3): In one aspect of the present invention, the storage medium is a non-transitory storage medium that can be read by a computer and stores a program for measuring the amount of SEI generated on the negative electrode of a lithium-ion battery, wherein the program causes the computer to perform the following processing: obtaining an initial positive electrode Ah-OCP curve and an initial negative electrode Ah-OCP curve by fitting the dV / dQ curve and the charge-discharge curve based on the results of the charge-discharge test of the lithium-ion battery; calculating the shrinkage rate (%) of the positive electrode and the negative electrode relative to the initial value; and calculating the solid content derived under durability conditions based on the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve. The positive and negative electrode Ah-OCP curves, obtained by multiplying the shrinkage rate (%) by a fixed point (potential) as a reference, are calculated using only the shrinkage rate. The offset Z of Ah from the fixed point of the positive electrode Ah-OCP curve using only the shrinkage rate and the fixed point of the degraded positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve is calculated. The offset A of Ah from the fixed point of the negative electrode Ah-OCP curve using only the shrinkage rate and the fixed point of the degraded negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve is calculated. And this is calculated as the negative electrode SEI generation amount = AZ.

[0016] According to the schemes described in (1) to (3) above, by taking into account the negative electrode shrinkage rate, the amount of SEI generated on the negative electrode can be measured with good accuracy. As a result, the performance of lithium-ion batteries can be evaluated more accurately, and energy efficiency can be improved while environmental impact can be reduced.

[0017] This method can extract the potential shift between the positive and negative electrodes associated with SEI formation, a major cause of degradation in lithium-ion batteries, from electrochemical measurements without disassembly and analysis. Therefore, it is useful in providing information about the entire battery without disassembly and analysis, and in accurately extracting the potential shift caused by SEI formation. Attached Figure Description

[0018] Figure 1 This is a block diagram showing the main structural components of a measuring device based on an embodiment of the present invention.

[0019] Figure 2 This is a flowchart illustrating a measurement method based on one embodiment of the present invention.

[0020] Figure 3 The Ah-OCP curves of the positive and negative electrodes are obtained by dV / dQ analysis and charge-discharge curve fitting in a measurement method based on an embodiment of the present invention.

[0021] Figure 4 In a measurement method based on an embodiment of the present invention, according to Figure 3 The Ah-OCP curves of the positive and negative electrodes are calculated by multiplying the shrinkage rate by the fixed point (potential) derived under durability conditions, and only the shrinkage rate is applied to the Ah-OCP curves of the positive and negative electrodes.

[0022] Figure 5 These are the Ah-OCP curves of the positive and negative electrodes after degradation, obtained using a measurement method based on an embodiment of the present invention. Detailed Implementation

[0023] Hereinafter, with reference to the accompanying drawings, embodiments of the measuring apparatus, measuring method, and storage medium for measuring the amount of SEI generated at the negative electrode of the lithium-ion battery of the present invention will be described.

[0024] <Structure of the measuring device>

[0025] Figure 1 This is a block diagram illustrating the main structural components of a measuring device based on an embodiment of the present invention. Figure 1 As shown, the measuring device 1 of this embodiment includes a charge / discharge control unit 10, a current measuring unit 20, a voltage measuring unit 30, a discharge time measuring unit 40, a storage unit 50, and a calculation unit 60. This measuring device 1 uses power supplied from the charger CHG to charge the lithium-ion battery BAT and performs charge / discharge tests.

[0026] The charger CHG supplies the measuring device 1 with the power required to charge the lithium-ion battery BAT.

[0027] The charge / discharge control unit 10 controls the charge and discharge of the lithium-ion battery BAT.

[0028] The storage unit 50 stores the measurement results of the current measuring unit 20, the voltage measuring unit 30, and the discharge time measuring unit 40. In addition, the storage unit 50 also stores the calculation results of the calculation unit 60.

[0029] The calculation unit 60 uses time-series data stored in the storage unit 50 to calculate the amount of negative electrode SEI generated in the lithium-ion battery BAT. More specifically, based on the time-series data stored in the storage unit 50, initial positive electrode Ah-OCP curves and initial negative electrode Ah-OCP curves are obtained by fitting dV / dQ curves and charge-discharge curves. The shrinkage rate (%) of each of the positive and negative electrodes relative to the initial value is calculated. Based on the initial positive electrode Ah-OCP curves and the initial negative electrode Ah-OCP curves, the positive electrode Ah-OCP value obtained by multiplying the shrinkage rate (%) by a fixed point (potential) derived under durability conditions is calculated, which is the value of the positive electrode Ah-OCP value applied only to the shrinkage rate. The offset Z of Ah from the fixed point of the positive electrode Ah-OCP curve (using only the shrinkage rate) and the fixed point of the degraded positive electrode Ah-OCP curve (calculated by fitting the dV / dQ curve and charge / discharge curve) is calculated from the OCP curve and the negative electrode Ah-OCP curve. The offset A of Ah from the fixed point of the negative electrode Ah-OCP curve (using only the shrinkage rate) and the fixed point of the degraded negative electrode Ah-OCP curve (calculated by fitting the dV / dQ curve and charge / discharge curve) is calculated as the negative electrode SEI generation amount = AZ.

[0030] The charge / discharge control unit 10, storage unit 50, and arithmetic unit 60 of the measuring device 1 described above are implemented by executing programs (software) through a hardware processor such as a CPU (Central Processing Unit). Some or all of these components can be implemented using hardware (including the circuitry) such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), and GPU (Graphics Processing Unit), or through the coordinated use of software and hardware. The program can be pre-saved in a storage device such as an HDD (Hard Disk Drive) or flash memory (a storage device with a non-transitory storage medium), or it can be saved in a removable storage medium such as a DVD or CD-ROM (a non-transitory storage medium), and installed by mounting the storage medium onto a drive device.

[0031] The measuring device 1 described above can be mounted on a mobile body that operates using an electric motor. In such a mobile body, a lithium-ion battery (BAT) for supplying power to drive the electric motor is also mounted. Furthermore, the measuring device 1 mounted on the mobile body can, for example, calculate the amount of negative electrode SEI generated by the lithium-ion battery (BAT) through self-monitoring, evaluate the performance and degradation of the lithium-ion battery, and issue warnings for repair or replacement. It should be noted that the lithium-ion battery (BAT) can also be a battery package, such as a cassette type, that can be detachably mounted to and from the mobile body.

[0032] Here, the aforementioned mobile vehicle, for example, can be a BEV (Battery Electric Vehicle) that is driven by an electric motor powered by electricity supplied from a lithium-ion battery (BAT). Alternatively, the aforementioned mobile vehicle can also be a PHV (Plug-in Hybrid Vehicle) or PHEV (Plug-in Hybrid Electric Vehicle) that enables a hybrid vehicle to have an external charging function. It should be noted that the mobile vehicle is not limited to four-wheeled vehicles, but can also be a straddle-type two-wheeled vehicle, a three-wheeled vehicle (including a vehicle with two front wheels and one rear wheel in addition to the front wheel and two rear wheels), a assisted bicycle, or an electric boat, etc.

[0033] <Actions of the arithmetic unit>

[0034] Figure 2This is a flowchart illustrating an example of the operation of the calculation unit 60 of a measuring device based on an embodiment of the present invention. Figures 3 to 5 The Ah-OCP curve is calculated by the arithmetic unit 60.

[0035] (S11) Based on the results of the charge-discharge test of the lithium-ion battery, the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve were obtained by fitting the dV / dQ curve and the charge-discharge curve. Figure 3 ).

[0036] (S12) Next, calculate the shrinkage rate (%) of the positive electrode and the negative electrode relative to the initial value.

[0037] (S13) Next, the computer calculates, based on the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve, a positive electrode Ah-OCP curve and a negative electrode Ah-OCP curve that only apply the shrinkage rate, obtained by multiplying the fixed point (potential) derived under durability conditions by the shrinkage rate (%). Figure 4 The Ah-OCP curve is unaffected by the electrode shrinkage rate only at the fixed point.

[0038] (S14) The computer calculates the offset Z of Ah from the fixed point of the positive electrode Ah-OCP curve using only the shrinkage rate and the fixed point of the deteriorated positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve. Figure 5 ).

[0039] (S15) The computer calculates the offset A of Ah from the fixed point of the negative electrode Ah-OCP curve using only the shrinkage rate and the fixed point of the deteriorated negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve. Figure 5 ).

[0040] (S16) The computer calculates the amount of negative SEI generated as AZ.

[0041] The implementation methods described above can be performed as follows.

[0042] A measuring device for measuring the SEI generation amount at the negative electrode of a lithium-ion battery, comprising:

[0043] Storage medium, which stores commands that can be read by a computer; and

[0044] The processor, which is connected to the storage medium,

[0045] The processor enables the computer to perform the following processes by executing commands that can be read into the computer:

[0046] Based on the results of charge-discharge tests of lithium-ion batteries, initial positive electrode Ah-OCP curves and initial negative electrode Ah-OCP curves were obtained by fitting dV / dQ curves and charge-discharge curves. The shrinkage rate (%) of each of the positive and negative electrodes relative to their initial values ​​was calculated. Based on the initial positive electrode Ah-OCP curves and the initial negative electrode Ah-OCP curves, the positive electrode Ah-OCP curve, obtained by multiplying the shrinkage rate (%) by the fixed point (potential) derived under durability conditions, was calculated, thus applying only the shrinkage rate. The curve and the negative electrode Ah-OCP curve; calculate the offset Z of Ah between the fixed point of the positive electrode Ah-OCP curve with only the shrinkage rate applied and the fixed point of the degraded positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; calculate the offset A of Ah between the fixed point of the negative electrode Ah-OCP curve with only the shrinkage rate applied and the fixed point of the degraded negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; calculate as the negative electrode SEI generation amount = AZ.

[0047] The above description illustrates specific embodiments of the present invention, but the present invention is not limited to such embodiments in any way, and various modifications and substitutions can be made without departing from the spirit of the present invention.

Claims

1. A measuring device for measuring the amount of SEI generated at the negative electrode of a lithium-ion battery, wherein, The measuring device includes: The charge and discharge control unit controls the charging and discharging of the lithium-ion battery. The voltage measuring unit measures the discharge voltage of the lithium-ion battery; The current measuring unit measures the discharge current of the lithium-ion battery; The discharge time measuring unit measures the discharge time of the lithium-ion battery. The storage unit stores the measurement results of the voltage measuring unit, the current measuring unit, and the discharge time measuring unit; and The computing unit calculates the amount of SEI generated at the negative electrode of the lithium-ion battery. The arithmetic unit enables the computer to perform the following processes: Based on the results of the voltage measuring unit, the current measuring unit, and the discharge time measuring unit read from the storage unit, the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve are obtained by fitting the dV / dQ curve and the charge-discharge curve. Calculate the shrinkage rate (%) of the positive electrode and the negative electrode relative to their initial values. Based on the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve, the shrinkage rate (%) is multiplied by the fixed point derived under durability conditions to obtain the positive electrode Ah-OCP curve and the negative electrode Ah-OCP curve, which only apply the shrinkage rate. The fixed point is the potential. The offset Z of Ah from the fixed point of the positive electrode Ah-OCP curve with only the shrinkage rate applied is calculated, which is the offset of Ah from the fixed point of the deteriorated positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve. Calculate the offset A of Ah from the fixed point of the negative electrode Ah-OCP curve using only the shrinkage rate and the fixed point of the degraded negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; and The amount of SEI generated at the negative electrode is calculated as A - Z.

2. A method for determining the amount of SEI generated at the negative electrode of a lithium-ion battery, wherein, Based on the results of the charge and discharge tests of lithium-ion batteries, the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve were obtained by fitting the dV / dQ curve and the charge and discharge curve. Calculate the shrinkage rate (%) of the positive electrode and the negative electrode relative to their initial values. Based on the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve, the shrinkage rate (%) is multiplied by the fixed point derived under durability conditions to obtain the positive electrode Ah-OCP curve and the negative electrode Ah-OCP curve, which only apply the shrinkage rate. The fixed point is the potential. The offset Z of Ah from the fixed point of the positive electrode Ah-OCP curve with only the shrinkage rate applied is calculated, which is the offset of Ah from the fixed point of the deteriorated positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve. Calculate the offset A of Ah from the fixed point of the negative electrode Ah-OCP curve using only the shrinkage rate and the fixed point of the degraded negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; and The amount of SEI generated at the negative electrode is calculated as A - Z.

3. A storage medium that stores a non-transitory program for measuring the amount of SEI generated at the negative electrode of a lithium-ion battery, and is readable by a computer, wherein... The program causes the computer to perform the following processing: Based on the results of the charge and discharge tests of lithium-ion batteries, the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve were obtained by fitting the dV / dQ curve and the charge and discharge curve. Calculate the shrinkage rate (%) of the positive electrode and the negative electrode relative to their initial values. Based on the initial positive electrode Ah-OCP curve and the initial negative electrode Ah-OCP curve, the shrinkage rate (%) is multiplied by the fixed point derived under durability conditions to obtain the positive electrode Ah-OCP curve and the negative electrode Ah-OCP curve, which only apply the shrinkage rate. The fixed point is the potential. The offset Z of Ah from the fixed point of the positive electrode Ah-OCP curve with only the shrinkage rate applied is calculated, which is the offset of Ah from the fixed point of the deteriorated positive electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve. Calculate the offset A of Ah from the fixed point of the negative electrode Ah-OCP curve using only the shrinkage rate and the fixed point of the degraded negative electrode Ah-OCP curve calculated by fitting the dV / dQ curve and the charge-discharge curve; and The amount of SEI generated at the negative electrode is calculated as A - Z.

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