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

Abstract

The invention relates to a lithium ion battery state-of-charge estimation method and device and a medium, and relates to the technical field of energy storage battery state monitoring, and the method comprises the steps: selecting a single frequency sampling point from an electrochemical impedance spectrum of a lithium ion battery, collecting the AC impedance of the lithium ion battery, obtaining the real part variable quantity of the AC impedance of the sampling point, and calculating the real part variable quantity of the sampling point; fitting the variable quantity of the sampling point with the corresponding charge state to obtain a first slope; and according to the linear relationship between the first slope and the charging current, calculating the state of charge of the lithium ion battery by measuring the real part of the charging current and the alternating current impedance in real time. Therefore, in the normal charging process of the lithium ion battery, the state-of-charge information of the battery can be accurately obtained, so that the working condition of the battery is optimized, and the safety of the battery and the whole system is improved.

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] At present, in order to cope with climate change and achieve low-carbon transformation of energy systems, countries around the world are actively promoting the construction of renewable energy, and battery energy storage systems are being promoted. Lithium-ion batteries have received extensive attention in the application of battery energy storage systems due to their high energy density, long cycle life, low self-discharge rate, and low environmental pollution, and are one of the main energy carriers.

[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 read the state of charge directly 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 spectrum can reflect the charge transfer and diffusion process inside the battery, and 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 state of charge, temperature, current, etc., which makes it difficult to achieve timeliness in the 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 method, device and medium for estimating the state of charge of a lithium-ion battery, which takes into account the influence of charging current and temperature on electrochemical impedance and can accurately estimate the state of charge of a lithium-ion battery during normal operation of the battery.

[0006] In a first aspect, the present disclosure provides a method for estimating a 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 the 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 at different charging currents is 0%-100% state of charge.

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

[0014] Optionally, the fitting method is a 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, for 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, fitting the change at the sampling point with a corresponding state of charge, and obtaining a first slope;

[0017] The calculation module is used to establish the 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 the 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 at different charging currents is 0%-100% state of charge.

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

[0023] Optionally, the fitting method is a 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 the lithium-ion battery, decouples its relationship with temperature, state of charge and charging current, and can accurately obtain the battery state of charge information during the normal charging process of the lithium-ion battery, thereby optimizing the 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 invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 The figure shows a battery state of charge estimation flow chart provided by an embodiment of the present disclosure;

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

[0030] Figure 3 The figure shows a schematic diagram of 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 The figure shows a schematic diagram of 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 provided by an embodiment of the present disclosure;

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

[0033] Figure 6 Shown is a schematic structural diagram of a lithium-ion battery state of charge estimation device provided in 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 in the embodiments can be combined with each other without 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 of the sampling point with the corresponding state of charge to obtain a first slope.

[0039] S3: 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.

[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, the present disclosure uses a 280Ah lithium-ion battery as an example for explanation, but it can also be applied to energy storage lithium-ion batteries of other capacities, and the present disclosure does not specifically limit this. In an optional embodiment provided by the present disclosure, S1 specifically comprises: using an electrochemical impedance spectroscopy calibration method to obtain an electrochemical impedance spectrum of a 280Ah lithium-ion battery sample 01, 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 real part change 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 spectrum of a lithium-ion battery provided in an embodiment of the present disclosure. Figure 3 The figure shows a schematic diagram of the connection between the electrochemical impedance measurement and the charging circuit of a sampling point provided by the embodiment of the present disclosure. Please refer to 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 alternating sinusoidal potential wave (or current) of different frequencies to the electrochemical system and measures the ratio of the alternating potential to the current signal (i.e., the impedance of the system) as the sinusoidal wave frequency changes. 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 text 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: the lithium-ion battery sample 01 is connected in parallel with the AC current source 02, a DC blocking capacitor 05 is provided between the AC current source 02 and the lithium-ion battery sample 01, 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, 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 by the voltage probe 04 and the current probe 03, and the components of the battery and voltage waveforms at the selected 100 Hz frequency are extracted by 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 a 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 once 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 schematic diagram. During the charging and discharging process of lithium-ion batteries, the single-point frequency 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 Figure 3 The circuit shown calculates the real part of the impedance corresponding to the sampling point.

[0051] Figure 4 FIG. 1 is a schematic diagram showing the relationship between the real part of the electrochemical impedance at a sampling point at 100 Hz and the state of charge at different charging currents provided by an embodiment of the present disclosure. Please refer to FIG. 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 selected sampling point corresponding to the frequency. 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 and the state of charge are linearly fitted, 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 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 at the frequency corresponding to the selected sampling point with respect to the state of charge. 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, and the real part of the impedance corresponding to the sampling point is calculated by 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, and it is obtained that 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 result can be used for other charging current scenarios.

[0056] Figure 5 The figure shows a schematic diagram of the relationship between the first slope and the charging current provided by the embodiment of the present disclosure. Figure 4 and Figure 5 , S3 is specifically: extracting the first slope of the real part of the electrochemical impedance of 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 linear regression equation obtained is:

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

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

[0059] The least square method is used again 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 charge state 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) between the change in the real part of the electrochemical impedance and the state of charge is established. 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 studies have shown that electrochemical impedance in the high-frequency region is less sensitive to temperature, thus weakening the effect of temperature on electrochemical impedance. In the high-frequency region, the impedance value is small, the phase angle is close to zero, and the charge transfer process is dominant; data in the high-frequency region plays a vital 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 spectrum 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 in the present disclosure, an electrochemical impedance spectroscopy is carried out on a lithium-ion battery sample 01 with a state of charge of 0%. The lithium-ion battery sample 01 is discharged to a cut-off voltage of 2.5V, corresponding to a state of charge of 0%, and is placed in a constant temperature box at 25°C for more than 1 hour. An electrochemical impedance spectroscopy calibration method is used to obtain the electrochemical impedance spectrum of the lithium-ion battery sample 01 at different charging currents, wherein the calibration range of the electrochemical impedance spectrum is 0.1Hz-200Hz.

[0066] Impedance is the resistance to the current in a circuit with resistance, inductance and capacitance. Impedance is usually represented by Z, which is a complex number. Its real part is called resistance and its imaginary part is called reactance. Therefore, the imaginary part of impedance is reactance, which represents the effect of the circuit element on the phase difference or phase shift of the alternating current. When the imaginary part of impedance is negative, it means that the circuit element leads the phase of the current ahead of the voltage, that is, 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 invention 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 individual lithium-ion batteries of different capacities, brands and individuals, 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 selection range is 0.25C-1.C, and C is the charge and discharge rate of the lithium-ion battery.

[0070] Specifically, the charging current is selected between 0.25 times 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. They are not listed here one by one. It is only necessary 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 within 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 is also called the battery's SOC, which stands for State of Charge. The state of charge, also known as the remaining capacity, represents the ratio of the remaining capacity of a lithium battery after a period of use or long-term storage to its fully charged capacity, usually expressed as a percentage. 0%-100% state of charge refers to the lithium-ion battery sample 01 from discharge to the cut-off voltage of 2.5V corresponding to 0% state of charge, and gradually charging to full corresponding to 100% state of charge.

[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 of 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 of 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 samples.

[0076] The present disclosure provides a method for estimating the state of charge of a lithium-ion battery, and the fitting method is linear regression. Linear regression is a statistical analysis method that uses regression analysis in mathematical statistics to determine the quantitative relationship between two or more variables that are interdependent, and has the advantages of being simple to understand and having high computational efficiency.

[0077] Figure 6 FIG. 1 is a schematic diagram of a lithium-ion battery state of charge estimation device provided by 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] The calculation module 102 is used to establish the 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;

[0079] Optionally, the sampling points are selected from a 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 the 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 sampling point is 2 minutes per time under different charging currents of the lithium-ion battery.

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

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

[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 lithium-ion battery state of charge estimation method as described above.

[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. Information can be computer-readable instructions, data structures, modules of programs, 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 disk read-only memory (CD-ROM), digital versatile disk (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 the present 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 "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0089] Those skilled in the art should understand that the embodiments of the present disclosure can be provided as methods and devices, and therefore, the present disclosure can be in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present disclosure can be in the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[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=1.25C is measured. It is known that the constants C=-23.8 and D=-10.4 in the linear regression equation (2), and the first slope A=-40.15 corresponding to the charging current of 1.25C can be calculated. Further, the first slope A is substituted into the linear regression equation (1), and the linear regression equation (1) of the real part change of the 100Hz electrochemical impedance and the state of charge is:

[0092] △Z r =-40.15*S

[0093] When the lithium-ion battery sample 01 is charged to 50% state of charge using the ampere-hour counting method, the measured 100Hz real part is 270.6μΩ, and the corresponding change △Zr is -19.7μΩ. The state of charge of the lithium-ion battery sample 01 calculated by the fitting formula obtained by formula (1) is 49.06%. That is, the state of charge of the lithium-ion battery can be estimated to be 49.06% by the lithium-ion battery state of charge estimation method provided by the present disclosure, and the error with the actual state of charge of the lithium-ion battery sample 01 of 50% is less than 1%, indicating 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 optimize the working conditions of the lithium-ion battery and improve 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. The method collects the current and voltage corresponding to the sampling points in the electrochemical impedance spectrum, calculates the real part of the impedance corresponding to the sampling points by Fourier transform, and establishes a linear regression equation (1) 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 above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be 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 will not be limited to the embodiments described herein, but will conform to the widest scope 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 selection range of the charging current is 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% charge state.

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, for 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, fitting the change at the sampling point with a corresponding state of charge, and obtaining a first slope; The calculation module is used to establish the 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 as claimed in claim 8, characterized in that: 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 as claimed in claim 8, characterized in that: 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 as claimed in claim 8, characterized in that: The selection range of the charging current is 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 as claimed in claim 8, characterized in that: The charging range of the lithium ion battery under different charging currents is 0%-100% charge state.

13. The device for estimating the state of charge of a lithium-ion battery as claimed in claim 8, characterized in that: 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 as claimed in claim 8, characterized in that: 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 described in any one of claims 1 to 7.

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