Lithium ion battery state of charge estimation method, device, medium

Abstract

The present disclosure relates to a lithium ion battery state of charge estimation method, device and medium, and relates to the technical field of energy storage battery state monitoring, comprising: selecting a single frequency sampling point from the electrochemical impedance spectrum of a lithium ion battery to collect the alternating current impedance of the lithium ion battery, obtaining the change amount of the real part of the sampling point alternating current impedance, fitting the change amount of the sampling point with the corresponding state of charge to obtain a first slope; according to the linear relationship between the first slope and the charging current, the state of charge of the lithium ion battery is calculated by real-time measurement of the charging current and the real part of the alternating current impedance. In this way, the battery state of charge information can be accurately obtained during the normal charging process of the lithium ion battery, thereby optimizing the working conditions of the battery, improving the safety of the battery and the overall system.

Description

Technical Field

[0001] The present disclosure relates to the technical field of energy storage battery status monitoring, and in particular to a method, device, and medium for estimating the state of charge of a lithium-ion battery. Background Art

[0002] To combat climate change and achieve a low-carbon transition to energy systems, countries around the world are actively promoting the development of renewable energy, and battery energy storage systems are gaining popularity. Lithium-ion batteries, due to their high energy density, long cycle life, low self-discharge rate, and minimal environmental impact, have garnered widespread attention in battery energy storage systems and are a key energy carrier.

[0003] Monitoring the state of charge of energy storage batteries is an important factor in ensuring their normal operation. However, there is a nonlinear relationship between lithium-ion voltage and state of charge, and it is affected by battery current, making it difficult to directly read the state of charge from the battery voltage. The coulomb counting method is prone to error accumulation, resulting in inaccurate state of charge estimation.

[0004] As an important characteristic parameter of the battery, the electrochemical impedance spectroscopy can reflect the charge transfer and diffusion processes inside the battery. It has attracted widespread attention in the application of characterizing the battery status. In particular, the information on the state of charge can effectively prevent the battery from overcharging and triggering thermal runaway, ensuring the safe and stable operation of the energy storage system. However, the acquisition time of the electrochemical impedance spectrum is long and is affected by many factors, such as the state of charge, temperature, current, etc., making it difficult to achieve timely characterization of the battery status in actual application scenarios. Therefore, how to accurately estimate the battery state of charge when the battery is operating normally has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] In order to solve the above technical problems, the present disclosure provides a lithium-ion battery state of charge estimation method, device, and medium, which take into account the influence of charging current and temperature on electrochemical impedance, and can accurately estimate the lithium battery state of charge during normal operation of the battery.

[0006] In a first aspect, the present disclosure provides a method for estimating the state of charge of a lithium-ion battery, comprising:

[0007] Selecting a single frequency sampling point from the electrochemical impedance spectrum of the lithium-ion battery, obtaining a change in the real part of the AC impedance at the sampling point, and fitting the change at the sampling point with a corresponding state of charge to obtain a first slope;

[0008] According to the linear relationship between the first slope and the charging current, a relationship between the state of charge of the lithium-ion battery and the charging current and the AC impedance is established, and the state of charge of the lithium-ion battery is calculated by measuring the charging current and the real part of the AC impedance in real time.

[0009] Optionally, the sampling points are selected from a high frequency region of the electrochemical impedance spectrum.

[0010] Optionally, the high frequency region refers to a region where the electrochemical impedance spectroscopy is carried out on a lithium-ion battery with a state of charge of 0%, a frequency range of 0.1 Hz-200 Hz, an ambient temperature of 25° C., and an imaginary part of the impedance is negative.

[0011] Optionally, the charging current is selected in a range of 0.25C-1.25C, where C is the charge and discharge rate of the lithium-ion battery.

[0012] Optionally, the charging range of the lithium-ion battery under different charging currents is 0%-100% state of charge.

[0013] Optionally, when the lithium-ion battery is under different charging currents, the sampling frequency of the sampling points is 2 minutes per time.

[0014] Optionally, the fitting method is the least squares method.

[0015] In a second aspect, based on the same inventive concept, the present disclosure provides a device for estimating the state of charge of a lithium-ion battery, the device comprising:

[0016] a fitting module, configured to select a single frequency sampling point from the electrochemical impedance spectrum of the lithium-ion battery, obtain a change in the real part of the AC impedance at the sampling point, and fit the change at the sampling point with a corresponding state of charge to obtain a first slope;

[0017] The calculation module is used to establish a relationship between the state of charge of the lithium-ion battery and the charging current and the AC impedance according to the linear relationship between the first slope and the charging current, and calculate the state of charge of the lithium-ion battery by measuring the charging current and the real part of the AC impedance in real time.

[0018] Optionally, the sampling points are selected from a high frequency region of the electrochemical impedance spectrum.

[0019] Optionally, the high frequency region refers to a region where the electrochemical impedance spectroscopy is carried out on a lithium-ion battery with a state of charge of 0%, a frequency range of 0.1 Hz-200 Hz, an ambient temperature of 25° C., and an imaginary part of the impedance is negative.

[0020] Optionally, the charging current is selected in a range of 0.25C-1.25C, where C is the charge and discharge rate of the lithium-ion battery.

[0021] Optionally, the charging range of the lithium-ion battery under different charging currents is 0%-100% state of charge.

[0022] Optionally, when the lithium-ion battery is under different charging currents, the sampling frequency of the sampling points is 2 minutes per time.

[0023] Optionally, the fitting method is the least squares method.

[0024] In a third aspect, based on the same inventive concept, the present disclosure provides a computer-readable storage medium having a computer program stored thereon, the program being used to execute the lithium-ion battery state of charge estimation method as described in the first aspect.

[0025] Compared with the prior art, the technical solution provided by the embodiments of the present disclosure has the following advantages: the present disclosure is based on the single-point frequency electrochemical impedance of lithium-ion batteries, decoupling its relationship with temperature, state of charge and charging current, and can accurately obtain battery state of charge information during the normal charging process of lithium-ion batteries, thereby optimizing battery operating conditions and improving the safety of the battery and the overall system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0027] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 FIG2 is a flow chart of a battery state of charge estimation method according to an embodiment of the present disclosure;

[0029] Figure 2 Shown is a schematic diagram of an electrochemical impedance spectroscopy of a lithium-ion battery provided by an embodiment of the present disclosure;

[0030] Figure 3 FIG2 is a schematic diagram showing the connection between the electrochemical impedance measurement of a sampling point and the charging circuit provided by an embodiment of the present disclosure;

[0031] Figure 4 Schematic diagram showing the relationship between the change in the real part of the electrochemical impedance at a sampling point at 100 Hz and the state of charge at different charging currents according to an embodiment of the present disclosure;

[0032] Figure 5 FIG2 is a schematic diagram showing the relationship between a first slope and a charging current provided by an embodiment of the present disclosure;

[0033] Figure 6 FIG2 is a schematic structural diagram of a lithium-ion battery state of charge estimation device provided by an embodiment of the present disclosure. DETAILED DESCRIPTION

[0034] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features therein can be combined with each other in the absence of conflict.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0036] Figure 1 The figure shows a battery state of charge estimation flow chart provided by the embodiment of the present disclosure. Please refer to Figure 1 The present disclosure provides a method for estimating the state of charge of a lithium-ion battery, comprising:

[0037] S1: Select a single frequency sampling point from the electrochemical impedance spectrum of a lithium-ion battery.

[0038] S2: Obtain the real part change of the AC impedance at the sampling point, and fit the change at the sampling point with the corresponding state of charge to obtain a first slope.

[0039] S3: Establishing a relationship between the state of charge of the lithium-ion battery and the charging current and the AC impedance based on the linear relationship between the first slope and the charging current.

[0040] S4: Calculate the state of charge of the lithium-ion battery by measuring the charging current and the real part of the AC impedance in real time.

[0041] Specifically, this disclosure uses a 280Ah lithium-ion battery as an example, but is also applicable to energy storage lithium-ion batteries of other capacities, and this disclosure is not specifically limited to this. In an optional embodiment provided by this disclosure, S1 specifically comprises: obtaining an electrochemical impedance spectrum of a 280Ah lithium-ion battery sample 01 using an electrochemical impedance spectroscopy calibration method, selecting a single frequency sampling point based on the electrochemical impedance spectrum to collect the AC impedance of the lithium-ion battery, and further analyzing the relationship between the change in the real part of the AC impedance at the sampling point and the corresponding state of charge.

[0042] Figure 2 FIG. 1 is a schematic diagram of an electrochemical impedance spectroscopy of a lithium-ion battery provided by an embodiment of the present disclosure. Figure 3 The figure shows a schematic diagram of the connection between the electrochemical impedance measurement and charging circuit of a sampling point provided by the embodiment of the present disclosure. Figures 1 to 3In the field of electrochemistry, electrochemical impedance spectroscopy (EIS) is a commonly used tool for studying electrochemical systems. It applies a small-amplitude AC sinusoidal potential wave (or current) of varying frequencies to the electrochemical system and measures how the ratio of the AC potential to the current signal (i.e., the impedance of the system) changes with the frequency of the sinusoidal wave. The results of EIS are usually expressed in the form of an impedance spectrum. Please refer to Figure 2 The electrochemical impedance spectrum includes the real part of impedance and the imaginary part of impedance, among which the real part of impedance includes high frequency, medium frequency and low frequency. It should be noted that the "sampling point" in the article is selected in the high frequency region of the electrochemical impedance spectrum, and the sampling point collects the single point frequency in the electrochemical impedance spectrum.

[0043] Please refer to Figure 3 In an optional embodiment provided by the present disclosure, S2 is specifically as follows: a lithium-ion battery sample 01 is connected in parallel with an AC current source 02, a DC blocking capacitor 05 is provided between the AC current source 02 and the lithium-ion battery sample 01, and the capacitance value of the DC blocking capacitor 05 is 4700 μF. A voltage probe 04 is connected to the positive and negative ends of the lithium-ion battery sample 01, and a current probe 03 is connected between the lithium-ion battery sample 01 and the AC power supply. The frequency of the AC current source 02 is set to 100 Hz. The current and voltage waveforms passing through the lithium-ion battery sample 01 are collected using the voltage probe 04 and the current probe 03. The components of the battery and voltage waveforms at the selected 100 Hz frequency are extracted using discrete Fourier transform:

[0044]

[0045] where v n and i n are the sampling signals of battery voltage or current in the time domain, N is the total number of sampling points, T is the sampling period, and k is selected so that

[0046] The calculation formula for battery impedance is:

[0047]

[0048] Take its real part as the real part of impedance.

[0049] Please continue to refer to Figure 3 The other end of the lithium-ion battery sample 01 is connected to the charger 06, and the constant current charging method is adopted. The charging current selection range is 0.25C-1.25C. During the charging process, the electrochemical impedance corresponding to the single point frequency of the selected sampling point is collected and calculated every two minutes, and the real part of the impedance is calculated.

[0050] It should be noted that Figure 2The electrochemical impedance spectrum shown is a static diagram. During the charge and discharge process of lithium-ion batteries, the frequency of a single point changes dynamically and in real time according to the differences in current, temperature and other factors. Therefore, the frequency of the sampling point needs to be selected in real time and measured by Figure 3 The circuit shown calculates the real part of the impedance corresponding to the sampling point.

[0051] Figure 4 The figure shows the relationship between the change of the real part of the electrochemical impedance at a sampling point at 100Hz and the state of charge at different charging currents according to the embodiment of the present disclosure. Figure 4 In an optional embodiment provided in the present disclosure, when the charging current of the lithium-ion battery sample 01 is 0.5C and the frequency of the AC current source 02 is 100Hz, please combine Figure 3 , the AC current source 02 emits the current corresponding to the selected sampling point (single-point frequency), and the two ends of the lithium-ion battery generate voltage fluctuations of the corresponding frequency. Then, the current and voltage graphs flowing through the lithium-ion battery sample 01 are collected through the voltage probe 04 and the current probe 03. The collected voltage and current are the voltage and current components of the frequency corresponding to the selected sampling point. The voltage and current waveform components of the sampling point are extracted using Fourier transform, and the real part of the impedance corresponding to the sampling point is calculated. It can be observed that under a charging current of 0.5C, the change in the real part of the electrochemical impedance at 100Hz shows an obvious linear relationship with the state of charge. The change in the real part of the electrochemical impedance at the selected sampling point is linearly fitted with the state of charge, and the fitting equation is obtained as follows:

[0052] △Z r =A*S (1)

[0053] Among them, △Z r Represents the change in the real part of the electrochemical impedance, S represents the state of charge, and A is the fitting coefficient. The fitting coefficient A is the first slope. The least squares method is used to calculate the linear regression equation coefficient of the real part of the electrochemical impedance with respect to the state of charge at the frequency corresponding to the selected sampling point. At a charging current of 0.5C, the first slope A 0.5C =-22.

[0054] Similarly, in an optional embodiment provided by the present disclosure, after selecting a single frequency sampling point in the high-frequency region of the electrochemical impedance spectrum, charging currents of 0.75C and 1C are applied to the sampling point respectively, and the voltage and current components corresponding to the sampling point frequency are collected by the voltage probe 04 and the current probe 03. The real part of the impedance corresponding to the sampling point is calculated using Fourier transform, and the change in the real part of the electrochemical impedance at the sampling point is linearly fitted with the state of charge to obtain A 0.75C =-28.96, A 1C =-34.1.

[0055] It should be noted that at 0% state of charge, the difference in AC impedance caused by different charging currents is small, so only one charging current scenario needs to be tested, and the results can be used for other charging current scenarios.

[0056] Figure 5 The figure shows the relationship between the first slope and the charging current provided by the embodiment of the present disclosure. Figure 4 and Figure 5 Specifically, S3 is as follows: extracting the first slope of the real part of the electrochemical impedance at the sampling point with respect to the state of charge, and finding that the first slope has an obvious linear relationship with the charging current. In order to establish the relationship between the state of charge and the AC impedance under the corresponding charging current of the lithium-ion battery sample 01, the first slope is fitted with the corresponding charging current, and the resulting linear regression equation is:

[0057] A=C*I+D(2)

[0058] Wherein, A is the first slope, I is the charging current, and C and D are both constants.

[0059] The least square method is again used to calculate the linear regression equation (2). In an optional embodiment provided by the present disclosure, the constants C in the linear regression equation (2) are -23.8 and D is -10.4.

[0060] S4 specifically includes: measuring the charging current and AC impedance of the lithium-ion battery sample 01 in real time, and combining the linear regression equation (1) and the linear regression equation (2) proposed in the present disclosure to estimate the state of charge of the lithium-ion battery sample 01.

[0061] In this way, a single frequency sampling point is collected in the electrochemical impedance spectrum corresponding to the charging current, and the current and voltage waveforms are obtained according to the single-point frequency corresponding to the sampling point. The real part of the impedance corresponding to the sampling point is calculated using Fourier transform, and a linear regression equation (1) is established between the change in the real part of the electrochemical impedance and the state of charge. Based on the relationship between the first slope in the linear regression equation (1) and the charging current, a linear regression equation (2) is fitted to obtain the state of charge of the lithium-ion battery. By measuring the charging current and AC impedance in real time, the state of charge of the lithium-ion battery can be estimated more accurately.

[0062] The present disclosure provides a method for estimating the state of charge of a lithium-ion battery, wherein sampling points are selected from a high-frequency region of an electrochemical impedance spectrum.

[0063] Existing research has shown that electrochemical impedance in the high-frequency region is less sensitive to temperature, thus mitigating the effects of temperature on electrochemical impedance. In this region, impedance values ​​are low, the phase angle approaches zero, and charge transfer dominates; data from this region plays a crucial role in studying battery performance.

[0064] The present disclosure provides a method for estimating the state of charge of a lithium-ion battery. The high-frequency region refers to the region where the electrochemical impedance spectroscopy is carried out on a lithium-ion battery with a state of charge of 0%, the frequency range is 0.1 Hz-200 Hz, the ambient temperature is 25°C, and the imaginary part of the impedance is negative.

[0065] In an optional embodiment provided by the present disclosure, an electrochemical impedance spectroscopy is performed on a lithium-ion battery sample 01 with a state of charge of 0%. The lithium-ion battery sample 01 is discharged to a cutoff voltage of 2.5V, corresponding to a state of charge of 0%, and is allowed to stand in a constant temperature box at 25°C for more than 1 hour. The electrochemical impedance spectroscopy calibration method is used to obtain the electrochemical impedance spectra of the lithium-ion battery sample 01 at different charging currents, wherein the calibration range of the electrochemical impedance spectroscopy is 0.1Hz-200Hz.

[0066] Impedance is the resistance to current flow in a circuit composed of resistors, inductors, and capacitors. Impedance, often represented by Z, is a complex number whose real part is called resistance and whose imaginary part is called reactance. Therefore, the imaginary part of impedance, or reactance, represents the phase difference or phase shift of the circuit element on the AC current. When the imaginary part of impedance is negative, it indicates that the circuit element's phase of the current leads the voltage, meaning that the current signal leads the voltage signal.

[0067] Please refer to Figure 2 The electrochemical impedance spectrum includes a real impedance part and an imaginary impedance part. The real impedance part includes a high-frequency region, a medium-frequency region, and a low-frequency region. The imaginary impedance part corresponding to the medium-frequency region and the low-frequency region is positive, and the imaginary impedance part corresponding to the high-frequency region is negative. The present disclosure performs sampling in the high-frequency region where the imaginary impedance part is negative to reduce the influence of temperature on the electrochemical impedance of the sampling point.

[0068] Taking into account the differences between different capacities, brands and individual lithium-ion batteries, it is necessary to measure the real part of the electrochemical impedance corresponding to the frequency of the initially selected sampling point for the actual individual lithium-ion battery at 0% state of charge and ambient temperature of 25°C.

[0069] The present disclosure provides a method for estimating the state of charge of a lithium-ion battery, wherein the charging current is selected in the range of 0.25C–1.C, where C is the charge and discharge rate of the lithium-ion battery.

[0070] Specifically, the charging current is selected between 0.25 and 1.25 times the charge and discharge rate of the lithium-ion battery. Optionally, the charging current in the embodiment of the present disclosure is selected from 0.5C, 0.75C, and 1C. In addition, the charging current of the lithium-ion battery can also be selected from 0.25C, 0.3C, 0.35C, 0.4C, 0.45C, 0.55C, 0.6C, 0.65C... and so on. The charging current is not listed here one by one. It is sufficient that the charging current is within the range of 0.25C-1.25C. If the charging current is less than 0.25C, the charging current is too small, and the battery impedance does not change much under a certain number of cycles. If the charging current is greater than 1.25C, the charging current is too large, and the charge transfer impedance will increase, which will increase the sampling error and affect the fitting results.

[0071] In this way, setting the charging current in the range of 0.25C-1.25C is conducive to the reasonable selection of sampling points and improves the fitting accuracy.

[0072] The present disclosure provides a method for estimating the state of charge of a lithium-ion battery. The charging range of the lithium-ion battery under different charging currents is 0%-100% state of charge.

[0073] In lithium batteries, the state of charge (SOC), also known as the battery's SOC (State of Charge), represents the ratio of a lithium battery's remaining capacity after a period of use or long-term disuse to its fully charged capacity, often expressed as a percentage. The 0%-100% SOC refers to the process of lithium-ion battery sample 01 being discharged to a cutoff voltage of 2.5V (0% SOC) and then gradually charged to a full charge (100% SOC).

[0074] The present disclosure provides a method for estimating the state of charge of a lithium-ion battery. The sampling frequency of the lithium-ion battery sample 01 under different charging currents is 2 minutes per time.

[0075] If the sampling frequency is less than 2 min / time, the sampling interval is small, the change in the real part of the electrochemical impedance at the sampling point is small, and the first slope obtained by fitting is large, resulting in a smaller state of charge estimation result for the lithium-ion battery sample 01; if the sampling frequency is greater than 2 min / time, the sampling interval is large, the change in the real part of the electrochemical impedance at the sampling point is large, and the first slope obtained by fitting is small, resulting in a larger state of charge estimation result for the lithium-ion battery sample 01. Both of these will cause inaccurate estimation results. Therefore, setting the sampling frequency of the sampling point to 2 min / time can improve the fitting accuracy, thereby improving the accuracy of the state of charge estimation results of the battery sample.

[0076] This disclosure provides a method for estimating the state of charge of a lithium-ion battery, using a linear regression fitting method. Linear regression is a statistical analysis method that uses regression analysis in mathematical statistics to determine the quantitative relationship between two or more interdependent variables. It has the advantages of being simple to understand and highly computationally efficient.

[0077] Figure 6 FIG. 1 is a schematic diagram of a lithium-ion battery state of charge estimation device according to an embodiment of the present disclosure. Figure 6 As shown, the lithium-ion battery state of charge estimation device 100 is applied to the battery end, including: a fitting module 101, which is used to select a single frequency sampling point from the electrochemical impedance spectrum of the lithium-ion battery, obtain the real part change of the AC impedance at the sampling point, and fit the change of the sampling point with the corresponding state of charge to obtain a first slope;

[0078] a calculation module 102 for establishing a relationship between the state of charge of the lithium-ion battery and the charging current and the AC impedance based on the linear relationship between the first slope and the charging current, and calculating the state of charge of the lithium-ion battery by measuring the charging current and the real part of the AC impedance in real time;

[0079] Optionally, the sampling points are selected from the high frequency region of the electrochemical impedance spectrum.

[0080] Optionally, the high frequency region refers to a region where the electrochemical impedance spectroscopy is carried out on a lithium-ion battery with a state of charge of 0%, a frequency range of 0.1 Hz-200 Hz, an ambient temperature of 25° C., and the imaginary part of the impedance is negative.

[0081] Optionally, the charging current is selected in a range of 0.25C-1.25C, where C is the charge and discharge rate of the lithium-ion battery.

[0082] Optionally, the charging range of the lithium-ion battery at different charging currents is 0%-100% state of charge.

[0083] Optionally, the sampling frequency of the lithium-ion battery under different charging currents is 2 minutes per time.

[0084] Optionally, the fitting method is the least squares method.

[0085] Thus, the present disclosure provides a lithium-ion battery state of charge estimation device, which, by adopting the lithium-ion battery state of charge estimation method as described above, can dynamically and relatively accurately estimate the state of charge of the lithium-ion battery based on the relationship between the charging current and the AC impedance corresponding to the lithium-ion battery state of charge.

[0086] In a third aspect, based on the same inventive concept, the present disclosure provides a computer-readable storage medium having a computer program stored thereon, the program being used to execute the aforementioned method for estimating the state of charge of a lithium-ion battery.

[0087] Computer-readable storage media include permanent and non-permanent, removable and non-removable media that can be used to store information by any method or technology. The information can be computer-readable instructions, data structures, program modules or other data. Examples of computer-readable storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined in this disclosure, computer-readable storage media does not include temporary computer-readable media (transitory media), such as modulated data signals and carrier waves.

[0088] It should be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0089] Those skilled in the art will appreciate that the embodiments of the present disclosure may be provided as methods or apparatuses. Thus, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present disclosure may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0090] Method validation

[0091] In an optional embodiment provided by the present disclosure, the charging current I of the lithium-ion battery sample 01 is obtained by online measurement, and the charging current I is measured to be 1.25C. Given the constants C = -23.8 and D = -10.4 in the linear regression equation (2), the first slope A corresponding to the charging current of 1.25C can be calculated to be -40.15. Further, the first slope A is substituted into the linear regression equation (1), and the linear regression equation (1) of the change in the real part of the electrochemical impedance at 100Hz and the state of charge is:

[0092] △Z r =-40.15*S

[0093] Using the ampere-hour counting method, it was determined that when lithium-ion battery sample 01 was charged to 50% state of charge, the measured 100Hz real part was 270.6μΩ, and the corresponding change ΔZr was -19.7μΩ. The state of charge of lithium-ion battery sample 01 calculated using the fitting formula obtained from formula (1) was 49.06%. In other words, the lithium-ion battery state of charge estimation method provided by the present disclosure can estimate the state of charge of the lithium-ion battery to be 49.06%, which is less than 1% from the actual state of charge of 50% of lithium-ion battery sample 01. This shows that the lithium-ion battery state of charge estimation method provided by the present disclosure can more accurately estimate the state of charge information of the lithium-ion battery during normal charging, which is beneficial to optimizing the operating conditions of the lithium-ion battery and improving the safety of the battery and the overall system.

[0094] In summary, the present disclosure provides a method, device, and medium for estimating the state of charge of a lithium-ion battery. By collecting the current and voltage corresponding to the sampling points in the electrochemical impedance spectrum, the real part of the impedance corresponding to the sampling points is calculated using Fourier transform, and a linear regression equation (1) is established between the change in the real part of the electrochemical impedance and the state of charge. Based on the relationship between the first slope and the charging current in the linear regression equation (1), a linear regression equation (2) is obtained by fitting. By measuring the charging current and the AC impedance in real time, the state of charge of the lithium-ion battery can be estimated more accurately.

[0095] The foregoing description is intended only to provide specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the embodiments described herein, but rather to be construed in the broadest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for estimating the state of charge of a lithium-ion battery, characterized in that: include: Selecting a single frequency sampling point from the electrochemical impedance spectrum of the lithium-ion battery, obtaining a change in the real part of the AC impedance at the sampling point, and fitting the change at the sampling point with a corresponding state of charge to obtain a first slope; According to the linear relationship between the first slope and the charging current, a relationship between the state of charge of the lithium-ion battery and the charging current and the AC impedance is established, and the state of charge of the lithium-ion battery is calculated by measuring the charging current and the real part of the AC impedance in real time.

2. The method for estimating the state of charge of a lithium-ion battery according to claim 1, wherein: The sampling points are selected from the high frequency region of the electrochemical impedance spectrum.

3. The method for estimating the state of charge of a lithium-ion battery according to claim 2, wherein: The high-frequency region refers to the region where the electrochemical impedance spectroscopy is carried out on a lithium-ion battery with a state of charge of 0%, a frequency range of 0.1 Hz-200 Hz, an ambient temperature of 25°C, and the imaginary part of the impedance is negative.

4. The method for estimating the state of charge of a lithium-ion battery according to claim 1, wherein: The charging current is selected in the range of 0.25C - 1.25C, where C is the charge and discharge rate of the lithium-ion battery.

5. The method for estimating the state of charge of a lithium-ion battery according to claim 1, wherein: The charging range of the lithium-ion battery under different charging currents is 0% - 100% state of charge.

6. The method for estimating the state of charge of a lithium-ion battery according to claim 1, wherein: The sampling frequency of the sampling points is 2 minutes per time under different charging currents of the lithium-ion battery.

7. The method for estimating the state of charge of a lithium-ion battery according to claim 1, wherein: The fitting method is the least squares method.

8. A device for estimating the state of charge of a lithium-ion battery, characterized in that: The device comprises: a fitting module, configured to select a single frequency sampling point from the electrochemical impedance spectrum of the lithium-ion battery, obtain a change in the real part of the AC impedance at the sampling point, and fit the change at the sampling point with a corresponding state of charge to obtain a first slope; The calculation module is used to establish a relationship between the state of charge of the lithium-ion battery and the charging current and the AC impedance according to the linear relationship between the first slope and the charging current, and calculate the state of charge of the lithium-ion battery by measuring the charging current and the real part of the AC impedance in real time.

9. The device for estimating the state of charge of a lithium-ion battery according to claim 8, wherein: The sampling points are selected from the high frequency region of the electrochemical impedance spectrum.

10. The device for estimating the state of charge of a lithium-ion battery according to claim 9, wherein: The high-frequency region refers to the region where the electrochemical impedance spectroscopy is carried out on a lithium-ion battery with a state of charge of 0%, a frequency range of 0.1 Hz-200 Hz, an ambient temperature of 25°C, and the imaginary part of the impedance is negative.

11. The device for estimating the state of charge of a lithium-ion battery according to claim 8, wherein: The charging current is selected in the range of 0.25C - 1.25C, where C is the charge and discharge rate of the lithium-ion battery.

12. The device for estimating the state of charge of a lithium-ion battery according to claim 8, wherein: The charging range of the lithium-ion battery under different charging currents is 0% - 100% state of charge.

13. The device for estimating the state of charge of a lithium-ion battery according to claim 8, wherein: The sampling frequency of the sampling points is 2 minutes per time under different charging currents of the lithium-ion battery.

14. The device for estimating the state of charge of a lithium-ion battery according to claim 8, wherein: The fitting method is the least squares method.

15. A computer-readable storage medium having a computer program stored thereon, characterized in that: The program is used to execute the method for estimating the state of charge of a lithium-ion battery as claimed in any one of claims 1 to 7.

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