Method and device for lithium precipitation detection of power battery

Abstract

The present disclosure relates to a method for lithium precipitation detection of a battery cell of a power battery, comprising: obtaining a plurality of alternating current impedances measured at a plurality of states of charge (SOC) by the battery cell, the plurality of alternating current impedances being measured in a non-driving state of a vehicle; based on the plurality of alternating current impedances, fitting the alternating current impedances as a function of SOC; the goodness of fit of the function is calculated, the lithium precipitation fraction of the battery cell is calculated based on the goodness of fit, and the lithium precipitation fraction is used for indicating the lithium precipitation degree of the battery cell.

Description

Technical Field

[0001] The present disclosure relates to the field of electric vehicles, and more specifically to a method and device for detecting lithium plating in power batteries. Background Art

[0002] In recent years, the new energy vehicle industry has rapidly grown. Electric vehicles (EVs) have gained popularity among consumers due to their energy-saving, high-efficiency, low-carbon, and environmentally friendly features. With the widespread use of EVs, onboard power battery technology has gained increasing attention. Currently, EV power batteries are primarily lithium-ion (Li-ion) batteries, such as lithium iron phosphate batteries and ternary lithium batteries. These batteries offer advantages such as high energy density, a wide operating temperature range, and a long storage life.

[0003] For lithium-ion batteries, during the charge and discharge process, lithium ions in the battery will pass through the separator and travel back and forth between the positive and negative electrodes. During the charging process, lithium ions are deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte; during the discharge process, lithium ions are deintercalated from the negative electrode and re-combined with the compounds at the positive electrode. However, in scenarios such as charging or fast charging in low-temperature environments, lithium-ion batteries may experience lithium plating. That is, the lithium ions deintercalated from the positive electrode cannot be intercalated into the negative electrode, causing these lithium ions to precipitate at the negative electrode and form a layer of metallic lithium. Lithium plating will cause the lithium ions in the lithium-ion battery to decrease, resulting in reduced power battery energy and shortened service life. It will also produce lithium dendrites at the negative electrode, puncturing the separator and causing a battery short circuit, which in turn poses a serious safety hazard. Therefore, lithium plating testing of power batteries is crucial to the user experience and safety of electric vehicles.

[0004] Because lithium-ion batteries typically have sealed exterior packaging, it's difficult to detect whether lithium deposition has occurred. Therefore, a non-destructive method for detecting lithium deposition is needed. However, existing methods for lithium deposition detection often require thorough battery charging and discharging in a laboratory setting, and the calculation methods are complex, making them less applicable. Summary of the Invention

[0005] In view of this, the present disclosure proposes an improved lithium plating detection method, which uses impedance data measured when the vehicle is not driving to calculate a score indicating the degree of lithium plating in the battery cell in a relatively simple manner. This method has the advantages of simple calculation and wide applicability.

[0006] According to one aspect of the present disclosure, a method for detecting lithium plating in a power battery cell is provided, comprising: obtaining multiple AC impedances measured at multiple states of charge of the battery cell, the multiple AC impedances being measured when the vehicle is not driving; fitting the AC impedance as a function of the SOC based on the multiple AC impedances; and calculating the goodness of fit of the function, and calculating a lithium plating fraction of the battery cell based on the goodness of fit, the lithium plating fraction being used to indicate the degree of lithium plating occurring in the battery cell.

[0007] According to an embodiment of the present disclosure, the non-driving state includes: the vehicle is being charged, the vehicle is discharging to the energy storage system, or the vehicle is parked with the engine turned off.

[0008] According to an embodiment of the present disclosure, when multiple AC impedances are measured while the vehicle is charging or discharging to an energy storage system and is not in motion, the multiple AC impedances are measured by: pausing charging / discharging at multiple different SOCs during the vehicle's charging or discharging process and applying multiple AC pulses with different frequencies to the battery cells; and calculating the AC impedance at the corresponding frequency based on the battery cell's response to the multiple AC pulses at each of the multiple SOCs. Furthermore, the multiple AC pulses with different frequencies are provided by an external device used to charge or discharge the vehicle.

[0009] According to an embodiment of the present disclosure, when multiple AC impedances are measured while the vehicle is in a non-driving state with the engine off and parked, the multiple AC impedances are measured by: applying multiple AC pulses with different frequencies to the battery cells at multiple different SOCs when the vehicle is parked and the multiple SOCs correspond to the SOCs of the vehicle when the engine is off and parked at different times; and calculating the AC impedance at the corresponding frequency based on the response of the battery cells to the multiple AC pulses at each of the multiple SOCs. Furthermore, fitting the AC impedance as a function of the SOC based on the multiple AC impedances includes: selecting a first subset of the measured AC impedances corresponding to a specific range of the additional parameter based on an additional parameter; and fitting the AC impedance as a function of the SOC based on the first subset of the measured multiple AC impedance values, wherein the additional parameter includes: the ambient temperature at the time of measurement, the battery cell temperature at the time of measurement, and the measurement time.

[0010] According to an embodiment of the present disclosure, the goodness of fit of a function is calculated, and the lithium plating fraction of the battery cell is calculated based on the goodness of fit, including: for a function fitted based on the AC impedance value measured under each AC pulse in a plurality of AC pulses, calculating the goodness of fit of the function corresponding to each AC pulse; and calculating the lithium plating fraction of the battery cell based on the goodness of fit of the function corresponding to each AC pulse.

[0011] According to an embodiment of the present disclosure, the plurality of SOCs are evenly distributed within a range spanning at least 50% of the SOCs, and / or the number of the plurality of SOCs is greater than or equal to 5.

[0012] According to another aspect of the present disclosure, a device for detecting lithium plating of a power battery cell is provided, the device comprising: a processor and a memory, wherein computer program instructions are stored in the memory, wherein when the computer program instructions are executed by the processor, the device executes the above-mentioned method for detecting lithium plating of a power battery cell.

[0013] According to another aspect of the present disclosure, a computer-readable storage medium is provided, on which computer program instructions are stored, and a computer program product is provided, including the computer program instructions. When the computer program instructions are executed by a processor, the processor executes the above-mentioned method for lithium plating detection of battery cells for power batteries.

[0014] According to another aspect of the present disclosure, a system for lithium plating detection of battery cells of a power battery is provided, comprising: an energy exchange facility for providing charging and / or discharging services to a vehicle; and a lithium plating detection module, the lithium plating detection module being communicatively connected to the energy exchange facility; wherein the energy exchange facility is configured to: suspend charging / discharging at different states of charge during charging or discharging of the vehicle, and apply multiple AC pulses with different frequencies to the battery cells; and provide multiple AC impedances measured at multiple SOCs to the lithium plating detection module, wherein the multiple AC impedances are calculated at each of the multiple SOCs according to the response of the battery cells to the multiple AC pulses; the lithium plating detection module is configured to: fit the AC impedance as a function of the SOC based on the multiple AC impedances; and calculate the goodness of fit of the function, and calculate the lithium plating score of the battery cell based on the goodness of fit, the lithium plating score being used to indicate the degree of lithium plating occurring in the battery cell.

[0015] Based on the above, according to the method and device for lithium plating detection of power batteries provided by the present disclosure, it is possible to utilize the non-use time period of the vehicle, such as when the vehicle is charging or discharging, or even during the regular parking period of the vehicle, to measure the impedance of the power battery cell and perform data fitting. At the same time, the present disclosure recognizes that there is a correlation between the goodness of fit of the AC impedance of the cell and whether lithium plating occurs in the cell, and on this basis proposes to calculate the lithium plating score of the cell based on the goodness of fit to indicate the degree of lithium plating in the cell. In this way, it is possible to perform non-destructive lithium plating detection on the cell in a simple and accurate manner without affecting the user's use of the vehicle.

[0016] On the other hand, the present disclosure also provides a system for detecting lithium plating in power battery cells. The system can not only provide charging / discharging services for the vehicle, but also detect whether lithium plating occurs in the vehicle's current power battery cells while charging / discharging the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and / or other aspects and advantages of the present disclosure will become more apparent and more readily understood from the following detailed description of embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0018] Figure 1 is a flow chart showing a method for detecting lithium plating of a power battery cell according to an embodiment of the present disclosure;

[0019] Figure 2 is an example scenario showing lithium plating detection in a charging / discharging scenario according to an embodiment of the present disclosure;

[0020] Figure 3 FIG2 is another example scenario showing lithium plating detection in a parking and engine-off scenario according to an embodiment of the present disclosure;

[0021] Figure 4 is a block diagram showing a system for detecting lithium plating of a power battery cell according to an embodiment of the present disclosure; and

[0022] Figure 5 1 is a block diagram showing a device for detecting lithium plating of a power battery cell according to an embodiment of the present disclosure.

[0023] It should be understood that these drawings are used to provide a further understanding of the embodiments of the present disclosure and constitute part of the specification. Together with the embodiments of the present disclosure, they are used to explain the technical solutions of the present disclosure and do not constitute a limitation of the present disclosure. In addition, in the drawings, the same reference numerals generally represent the same components or steps. DETAILED DESCRIPTION

[0024] In order to better illustrate the technical solution of the present disclosure, the present disclosure is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that based on the embodiments described in the present disclosure, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present disclosure, and the embodiments described herein are only part of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure. These embodiments are merely illustrative and exemplary, and therefore should not be interpreted as limiting the scope of the present disclosure.

[0025] For purposes of illustration and not limitation, the present disclosure will primarily use an electric vehicle's power battery as an example to illustrate the technical solutions of the present disclosure. The term "electric vehicle" broadly refers to any vehicle that is at least partially powered by an onboard power battery, including, for example, pure electric vehicles and hybrid electric vehicles.

[0026] First, the overall technical concept of the present disclosure and the terms involved are explained.

[0027] The power battery is a core component of electric vehicles, responsible for storing and releasing electrical energy to power the vehicle for driving and other applications. The power battery serves as the vehicle's power source. A power battery is typically a battery pack consisting of multiple cells connected in series and / or parallel. The state of charge (SOC) of a power battery can be expressed as the ratio of the battery's currently available remaining capacity to its full capacity after a full charge. Therefore, in some scenarios, SOC can simply be considered the vehicle's "remaining charge." Generally speaking, there is a certain correlation between the impedance of a power battery cell and SOC. Therefore, a function model that approximates the SOC and cell impedance (cell impedance relative to SOC) can be approximated through data fitting. The goodness of fit can be used to evaluate the difference between the fitted function model and the actual data, thereby measuring the function model's ability to interpret the actual data and its predictive accuracy.

[0028] However, as mentioned above, lithium-ion batteries are prone to lithium plating in scenarios such as low-temperature charging and fast charging, resulting in the precipitation of metallic lithium at the negative electrode of a single battery cell, and the number of lithium ions in the power battery is correspondingly reduced. The present disclosure recognizes that the true impedance of the battery cell will be affected by the lithium plating phenomenon and change its correlation with the SOC, thereby causing the goodness of fit between the impedance of the battery cell and the SOC to decrease. In other words, the true impedance of the battery cell where lithium plating occurs will significantly deviate from the corresponding fitting value, and in certain SOC intervals, the difference between the true impedance and the corresponding fitting value will be greater. Therefore, by utilizing this effect of the lithium plating phenomenon on the impedance of the battery cell, the present disclosure proposes to perform data fitting on the AC impedance of the battery cell and calculate the lithium plating score of the battery cell based on the goodness of fit to indicate the degree of lithium plating in the battery cell, thereby providing a method for calculating simple and easy lithium plating detection without the need to thoroughly charge and discharge the power battery.

[0029] Figure 1 The flowchart of the method for detecting lithium plating of a power battery cell according to an embodiment of the present disclosure is shown. Figure 1 As shown, the exemplary method 100 of the present disclosure may include the following steps:

[0030] In step S101 , a plurality of AC impedances measured at a plurality of SOCs of a battery cell are obtained, where the plurality of AC impedances are measured when the vehicle is not in a driving state.

[0031] Specifically, the vehicle's non-driving state can include when the vehicle is charging, discharging to an energy storage system (such as V2G), or the vehicle is parked and ignited. In the non-driving state, the vehicle does not charge or discharge the power battery cells due to driving behavior. Therefore, when measuring the AC impedance of the battery cells in this non-driving state, the corresponding SOC remains essentially unchanged, ensuring the accuracy of the measured AC impedance.

[0032] In addition, according to an embodiment of the present disclosure, it is possible to select the SOC at a specific time interval (for example, every 10 minutes during the charge / discharge process) to measure the AC impedance of the battery cell, or to select the SOC at a specific level (for example, 30%, 40% ... 80%) to measure the AC impedance of the battery cell, and depending on the specific needs of the data fitting, it is preferred to measure the AC impedance of the battery cell at 5 or more discrete SOCs, and each measured SOC is as evenly distributed as possible across a larger range (for example, at least greater than 50% of the SOC range) to obtain better data fitting results. In addition, the specific number of SOCs used to measure the AC impedance of the battery cell can be determined by weighing factors such as the amount of data computation, storage cost, and performance requirements.

[0033] In addition, the measurement of the AC impedance of the battery cell can be performed by a corresponding module in the vehicle, for example, it can be completed by the impedance measurement module of the battery management system (BMS) of the vehicle, or by other devices outside the vehicle (for example, energy exchange facilities) or corresponding modules therein. The multiple AC impedances measured in the non-driving state of the vehicle and the corresponding SOC will be recorded in a storage medium and obtained by the entity to perform lithium deposition detection for subsequent processing of lithium deposition detection. For example, the measured multiple AC impedances can be provided to a data analysis system located in the cloud or a similar external server for the data analysis system to perform data fitting and calculate the lithium deposition score based on multiple AC impedances for subsequent processing.

[0034] In step S102 , based on a plurality of AC impedances measured at a plurality of SOCs, the AC impedance is fitted as a function of the SOC.

[0035] Generally, the AC impedance of a battery cell can be expressed in complex form, that is, multiple AC impedances measured at multiple SOCs can include impedance values ​​with real and imaginary parts corresponding to different SOC values. Since the real part of the complex number can better reflect the practical significance of the physical quantity, it is necessary to fit the relationship between the real part of the AC impedance and the SOC. Specifically, first, an appropriate fitting function is selected as a mathematical model to describe the relationship between the AC impedance and the SOC. For example, according to an embodiment of the present disclosure, the AC impedance as a function of the SOC can be expressed as the following formula:

[0036]

[0037] Among them, y impedance-real is the real part of the AC impedance of the cell, x soc is the SOC value, and α, β0, β1, β2 are the model parameters of the fitting function. The above fitting function and model parameters are only preferred embodiments of the present disclosure. It can be understood that other linear functions, nonlinear functions or exponential functions can also be used as mathematical models to describe the relationship between AC impedance and SOC. After determining the mathematical model, fitting algorithms such as least squares method and maximum likelihood estimation method are used. Based on the existing multiple AC impedances measured at multiple SOCs, the values ​​of the model parameters α, β0, β1, β2 in the above fitting function can be solved, thereby obtaining the AC impedance as a function of SOC, that is, y impedance-r =f(x soc ).

[0038] In step S103 , the goodness of fit of the AC impedance as a function of the SOC is calculated, and the lithium plating fraction of the battery cell is calculated based on the goodness of fit.

[0039] As mentioned above, data fitting is to determine an optimal function model that can describe the relationship between data through a limited number of known data (such as measured values). This model is intended to make any unknown data conform to the function model as much as possible. Goodness of fit in this article can broadly refer to a measure used to represent the difference between the fitted value and the true value, so goodness of fit is usually used to measure the validity and reliability of the fitting model. For example, commonly used goodness of fit can include measures such as residual sum of squares, root mean square error or mean square error. According to an embodiment of the present disclosure, the goodness of fit of AC impedance as a function of SOC can adopt the residual sum of squares algorithm, which is expressed as the following formula:

[0040]

[0041] Among them, R 2 is the goodness of fit of the function, the denominator SST (Total Sum of Squares) is the total sum of squares, which represents the true value y i(In this embodiment, it is the real part of the AC impedance of the battery cell) and the mean of the true value The sum of squares of the differences between the two, the numerator SSR (Regression Sum of Squares) is the regression sum of squares, which represents the fitted value The mean of the true value The sum of the squares of the differences between , and in this example, the true value y i is the real part of the AC impedance of the cell measured at n SOCs, and the fitted value is the predicted value calculated by substituting the SOC value as the independent variable into the function obtained by the above fitting. Therefore, in this embodiment, the value of the goodness of fit is between 0 and 1, and the closer the value is to 1, the closer the fitted value of the function is to the actual measured AC impedance. Conversely, the closer the value is to 0, the more the fitted value of the function deviates from the actual measured AC impedance. For example, the true value y measured at 30%, 40%, 50%, 60%, and 80% respectively i They are: 0.0014, 0.0015, 0.0016, 0.0018, 0.0019 respectively; the fitting values ​​calculated at these SOCs by the fitting function based on these true values They are: 0.0016, 0.0015, 0.0016, 0.0017, 0.0019, based on these true values ​​y i Their corresponding fitted values It can be calculated that the goodness of fit of the fitting function is approximately 0.737.

[0042] As described above, the present disclosure has recognized that the real impedance of the battery cell will be affected by the lithium plating phenomenon. Specifically, for the battery cell where lithium plating occurs, the real impedance of the battery cell will seriously deviate from its corresponding fitting value in some SOC intervals (for example, in the low SOC interval), and the higher the degree of lithium plating, the greater the difference between the real impedance of the battery cell and the fitting value of the impedance. Accordingly, this difference will be reflected as a decrease in the goodness of fit of the fitted function. On the contrary, for the battery cell where lithium plating does not occur, the relationship between its AC impedance and SOC can be better reflected by the fitting function, that is, compared to the case where lithium plating does not occur, the goodness of fit of the function fitted for the AC impedance of the battery cell where lithium plating occurs is lower, and the more serious the degree of lithium plating occurs in the battery cell, the lower the goodness of fit. Therefore, based on this correlation, the goodness of fit of the AC impedance as a function of SOC can be used to calculate the lithium plating score for indicating the degree of lithium plating in the battery cell. For example, according to an embodiment of the present disclosure, the goodness of fit value in the above example can be percentage-based (×100%) as the lithium plating score of the battery cell, or the goodness of fit value falling into the corresponding interval can be mapped to a fixed score or a qualitative rating (excellent, good, poor).

[0043] Thus, the lithium plating score of the battery cell calculated based on the goodness of fit can quantify the degree of lithium plating in the battery cell. For example, in this embodiment, the higher the lithium plating score, the lower the degree of lithium plating in the battery cell (or the lower the possibility of lithium plating), and vice versa. The degree of lithium plating in the battery cell is higher. On this basis, the lithium plating score can be further compared with a specific threshold to give a qualitative judgment on whether lithium plating has occurred in a specific battery cell.

[0044] In addition, the above method is described for a single cell of a power battery, that is, the lithium plating detection method of the embodiment of the present disclosure is for lithium plating detection at the cell level. This is because the lithium plating detection of the power battery should follow the "barrel principle", that is, lithium plating in any cell of the power battery will cause the service life and safety of the entire power battery to be damaged. Therefore, whether lithium plating occurs in the power battery should depend on the degree of lithium plating in each cell. It can be understood that lithium plating detection at the power battery level can be achieved by executing the lithium plating detection method of the present disclosure on each cell in the power battery.

[0045] Combination of the above Figure 1 The overall process of a lithium deposition detection method for power battery cells is described through various exemplary embodiments. The above method can utilize impedance data measured when the vehicle is not driving to relatively simply calculate a score indicating the degree of lithium deposition in the cell. This method does not require thorough battery charging and discharging or a complete charge-discharge characteristic curve, but only requires impedance measurements at multiple discrete SOCs to obtain relatively accurate lithium deposition detection results. This provides a widely applicable and computationally simple lithium deposition detection method.

[0046] Figure 2 An example scenario for lithium plating detection according to an embodiment of the present disclosure is shown. Specifically, in this scenario, the vehicle 201 is being charged by an energy exchange facility 202 (such as a charging pile, a discharging pile, or a multifunctional pile with integrated charging and discharging functions) or is discharging to an energy storage system (e.g., V2G). In this case, in order to increase the data used to fit the AC impedance as a function of SOC, intermittent impedance measurements can be performed during the charging / discharging process to obtain AC impedance at different frequencies, so as to help better fit the data of the AC impedance and thus more accurately detect whether lithium plating occurs in the battery cell. According to an embodiment of the present disclosure, multiple AC pulses with different frequencies can be provided by the energy exchange facility 202 for providing charging or discharging for the vehicle.

[0047] Specifically, during the charging / discharging process of the vehicle, charging / discharging is suspended at different SOCs (e.g., 30%, 40% ... 80%), and multiple AC pulses with different frequencies are applied to the cells of the power battery. For example, in the charging scenario, when the energy exchange facility 202 charges the power battery 2001 of the vehicle 201 to a SOC level of 30%, charging of the vehicle is suspended, and three sinusoidal AC pulses with an amplitude of 15mV and frequencies of 0.01Hz, 0.1Hz, and 1Hz are applied to the cell of the power battery (e.g., cell 1). Each AC pulse can last for several seconds, so that the impedance measurement module 2002 of the vehicle 201 can obtain the voltage change and current change of the two sections of the cell, that is, the response of the cell to the multiple AC pulses, and calculate the AC impedance corresponding to the 30% SOC level at the corresponding frequency. After applying multiple AC pulses, restart charging the power battery and pause charging when the battery reaches a SOC level of 40%. Apply the same multiple AC pulses to the battery cell and calculate the AC impedance at the corresponding frequency corresponding to the 40% SOC level. Repeat the above process multiple times until the AC impedance measured at a sufficient number of SOCs is obtained, and each SOC includes the AC impedance at the above three frequencies.

[0048] According to an embodiment of the present disclosure, these AC impedances can be transmitted from the vehicle 201 to the energy exchange facility 202, and further transmitted by the energy exchange facility 202 to the cloud 203 (for example, the data analysis system located in the cloud as described above), or directly from the vehicle 201 to the cloud 203, so that the method described above according to the present disclosure can be performed at the cloud 203, that is, based on the obtained multiple AC impedances, the AC impedance is fitted as a function of the SOC, and the goodness of fit of the function is calculated, and the lithium plating fraction of the battery cell is calculated based on the goodness of fit. In this embodiment, the AC impedances at the above three frequencies are included at each SOC, so the AC impedances corresponding to the same frequency can be used for data fitting, and the corresponding three functions can be fitted respectively. For example, from 30% SOC to 80% SOC, an AC pulse with the above three frequencies is applied every 10% SOC, and a total of 3×6=18 AC impedances can be measured at 6 SOC levels. On this basis, the data fitting method described above can be used to fit the AC impedance corresponding to the frequency of 0.01 Hz at 6 SOC levels as a function of SOC y 0.01Hz =f(x soc ), similarly, the AC impedance corresponding to the other two frequencies (0.1Hz and 1Hz) can be fitted as a function of SOC y 0.1Hx =f(x soc ) and y 1Hz =f(xsoc ).

[0049] Then, for the function fitted based on the AC impedance value measured under each AC pulse, the goodness of fit of the function corresponding to each AC pulse is calculated. For example, the function y corresponding to the AC pulse with a frequency of 0.01 Hz can be calculated using the goodness of fit calculation method described above. 0.01 Goodness of fit Function y corresponding to an AC pulse with a frequency of 0.1 Hz 0.1 Goodness of fit And the goodness of fit of the function y1 corresponding to the 1Hz AC pulse And based on the goodness of fit of the function corresponding to each AC pulse Together, the lithium plating score of the power battery is calculated. For example, a weight can be assigned to the goodness of fit of the function corresponding to each AC pulse, and the lithium plating score of the battery cell can be calculated by weighting each goodness of fit, or the goodness of fit of the function corresponding to each AC pulse can be combined into a fusion algorithm to comprehensively consider the AC impedance at different frequencies. The calculated lithium plating score can directly indicate the degree of lithium plating occurring in a specific battery cell in a quantitative manner, or it can be compared with a predetermined threshold to give a rating of a specific battery cell or power battery or the risk of lithium plating occurring (for example, low, medium, or high). For example, Figure 2 As shown, the lithium plating score calculated by the cloud 203 can be provided to the user terminal 204 and presented to the user in a visual manner, or can also be provided to the energy exchange facility 202 and presented to the user by the energy exchange facility 202, or used to execute other actions or strategies.

[0050] It can be seen that the lithium plating detection method disclosed in the present invention can be applied to the charging / discharging scenario of the vehicle. By intermittently providing AC pulses during the charging / discharging process of the vehicle to obtain AC impedance at different frequencies, the data fitting effect of the AC impedance can be further improved with almost no impact on the user experience, thereby improving the accuracy of lithium plating detection.

[0051] Figure 3 Another example scenario for lithium deposition detection according to an embodiment of the present disclosure is shown. Specifically, in this scenario, the vehicle 201 is in a state of being stopped and the engine is turned off. Figure 2 Similar to the embodiment of FIG, multiple AC pulses with different frequencies can be applied to the battery cells when the vehicle is turned off and parked. According to an embodiment of the present disclosure, multiple AC pulses with different frequencies can be provided by an impedance measurement module 2002 within the vehicle (for example, which can be integrated into the vehicle's BMS).

[0052] Specifically, for example, a user arrives at work at 9:00 AM on Monday and stops vehicle 201. The current SOC is 83%. At the current SOC, three sinusoidal AC pulses with an amplitude of 15mV and frequencies of 0.01Hz, 0.1Hz, and 1Hz are applied to the power battery cell (e.g., cell 1). Each AC pulse lasts for several seconds, allowing the impedance measurement module 2002 of vehicle 201 to obtain the voltage and current changes in the two sections of the cell, that is, the cell's response to the multiple AC pulses, and calculate the AC impedance at the corresponding frequency corresponding to the 83% SOC level. Thereafter, the user returns home at 8:00 PM on Monday and stops vehicle 201 again. The current SOC is 74%. The same multiple AC pulses are applied at the current SOC, and the AC impedance at the corresponding frequency corresponding to the 74% SOC level is calculated. Afterwards, the user arrives in the suburbs at 11 a.m. on Tuesday and stops the vehicle 201. The current SOC is 54%. The same multiple AC pulses are applied at the current SOC, and the AC impedance at the corresponding frequency corresponding to the SOC level of 54% is calculated. Afterwards, the user may charge the vehicle briefly on Wednesday and return home at 11 a.m. and stop the vehicle 201. The current SOC is 66%. The same multiple AC pulses are applied at the current SOC, and the AC impedance at the corresponding frequency corresponding to the SOC level of 66% is calculated. It can be seen that, for example, in a period of time within a week, the vehicle may be in a stopped state multiple times at different times and dates, and the SOC at each stop may be different, so it is different from Figure 2 Similar to the embodiment of FIG. 1 , in this embodiment, the AC impedance measured at a sufficient number of SOCs can also be obtained, and the AC impedance at the above three frequencies is included at each SOC.

[0053] In addition, considering that the vehicle may be stalled and parked in completely different locations and weather conditions, the ambient temperature and cell temperature when measuring the AC impedance are quite different, and the temperature will change the impedance characteristics of the cell, thereby affecting the trend of the change of the AC impedance with SOC. Therefore, if the AC impedance measured at different temperatures is fitted, the accuracy of the fitting will be affected. In addition, the power battery will have energy decay as the use time increases. Similarly, the impedance characteristics exhibited by the cells in different decay stages will also vary depending on the battery use time. Therefore, fitting the impedance data with a long time interval will also affect the accuracy of the fitting. In order to avoid a decrease in the accuracy of the fitting, it is necessary to screen the AC impedance used for data fitting. According to an embodiment of the present disclosure, based on an additional parameter, a first subset corresponding to a specific range of the additional parameter is selected from the multiple measured AC impedances, and based on the first subset of the multiple measured AC impedance values, the AC impedance is fitted as a function of SOC, wherein the additional parameter may include: the ambient temperature at the time of measurement, the cell temperature at the time of measurement, and the measurement time (such as the date of measurement or a more specific time). For example, data corresponding to an ambient temperature (or battery cell temperature) of 20 to 25 degrees Celsius can be selected from all the measured AC impedances. Additionally or alternatively, data corresponding to a specific period (for example, within a week) can be selected as the AC impedance for data fitting, thereby avoiding the use of AC impedance data with large differences in battery cell conditions for fitting.

[0054] In addition, if Figure 3 As shown, the AC impedance for data fitting can be directly transmitted from the vehicle 201 to the cloud 203, so that the method described above according to the present disclosure can be executed at the cloud 203, which is combined with the above Figure 1 and Figure 2 In addition, the lithium plating score calculated by the cloud 203 can be provided to the user terminal 204 and presented to the user in a visual manner, or can be directly provided to the vehicle 201 and presented to the user through a display device in the vehicle 201 (e.g., an onboard screen), or used to execute other actions or strategies.

[0055] It can be seen that the lithium plating detection method disclosed in the present invention can also be applied to the scenario where the vehicle is parked and turned off in daily life. By utilizing the idle period when the user is not using the vehicle, AC pulses are provided at different SOCs to obtain AC impedance at different frequencies, which can further improve the data fitting effect of the AC impedance and thereby improve the accuracy of lithium plating detection, and has almost no impact on the user experience.

[0056] Combination of the above Figure 2 and Figure 3 Two typical application scenarios of the lithium plating detection method according to the embodiments of the present disclosure are described respectively.

[0057] In addition, in the above embodiments, the frequency, amplitude and pulse type of the AC pulse are only examples, and other AC pulses can be selected depending on the specific application. Figure 2 and Figure 3 Only the elements and signal flows that are highly relevant to the content of the described embodiment are schematically shown. For example, only the application of AC pulses to cell 1 in the power battery 2001 is shown. It can be understood that AC pulses can also be applied to any number of cells in the power battery 2001 and corresponding lithium plating detection can be performed. In addition, in the above embodiment, the processing of performing data fitting and calculating the lithium plating score is performed at the cloud 203. According to other embodiments of the present disclosure, at least part of these processes can also be performed at the vehicle 201 or the energy exchange facility 202, or completed by different entities in the system, and the various entities in the system can communicate with each other.

[0058] Figure 4 A block diagram of a system for detecting lithium plating in a power battery cell according to an embodiment of the present disclosure is shown.

[0059] like Figure 4 As shown, the present disclosure provides a lithium plating detection system 300, which includes: an energy exchange facility 301 for providing charging and / or discharging services to a vehicle 201, and a lithium plating detection module 302 for detecting whether lithium plating occurs in a power battery cell. For example, the energy exchange facility 202 described above can be used as an example of the energy exchange facility 301 of the lithium plating detection system 300, and the cloud 203 or the data analysis system located in the cloud described above can be used as an example of the lithium plating detection module 302 of the lithium plating detection system 300. The lithium plating detection module 302 can be integrated into the energy exchange facility 301 and run as an internal module thereof, or the lithium plating detection module 302 and the energy exchange facility 301 can be integrated into the same device. In this case, the lithium plating detection module and the energy exchange facility can communicate via an internal bus. Alternatively, the lithium plating detection module 302 can be geographically separated from the energy exchange facility 301. In this case, the lithium plating detection module and the energy exchange facility can communicate via a wired or wireless manner.

[0060] Specifically, the energy exchange facility 301 is configured to suspend charging / discharging at different states of charge (SOC) during charging or discharging of the vehicle, and as described above, apply multiple AC pulses with different frequencies to the battery cell, and provide multiple AC impedances measured at multiple SOCs to the lithium plating detection module, wherein the multiple AC impedances are calculated at each of the multiple SOCs based on the response of the battery cell to the multiple AC pulses. For example, it can be completed by the impedance measurement module of the BMS inside the vehicle, or by the energy exchange facility itself, without limitation. In addition, the lithium plating detection module 302 is configured to fit the AC impedance as a function of SOC based on the received multiple AC impedances, and calculate the goodness of fit of the function, and calculate the lithium plating score of the battery cell based on the goodness of fit, and the lithium plating score is used to indicate the degree of lithium plating in the battery cell. The specific lithium plating detection method is consistent with the description above and will not be repeated here.

[0061] It can be seen that the lithium plating detection system according to the embodiment of the present disclosure can not only provide charging / discharging services for the vehicle, but also detect whether lithium plating occurs in the battery cells of the vehicle's current power battery while charging / discharging the vehicle, thereby realizing a multifunctional energy conversion station. For example, this multifunctional energy conversion station can be used in electric vehicle charging stations or maintenance centers and other places that can provide multiple services for vehicles.

[0062] Figure 5 1 is a block diagram showing a device for detecting lithium plating of a power battery cell according to an embodiment of the present disclosure.

[0063] like Figure 5 As shown, an apparatus 500 for detecting lithium plating in power battery cells includes a processor 501 and a memory 502. The apparatus 500 may be a computer integrated into a vehicle or a remote server. It should be understood that the illustrated structure is exemplary and non-restrictive, and that the apparatus 500 may include other components in addition to these units. However, as these components are not relevant to the embodiments of the present disclosure, their illustration and description are omitted herein.

[0064] In addition, since the specific details of the operations performed by the device 500 for lithium plating detection of power battery cells according to the embodiment of the present disclosure are roughly the same as the details described above, some descriptions of the same details are omitted herein for the purpose of brevity.

[0065] The processor 501 may be a central processing unit (CPU), a microcontroller unit (MCU), a data signal processor (DSP), or other forms of processing units with data processing capabilities and / or instruction execution capabilities, and may utilize computer program instructions stored in the memory 502 to perform desired functions, wherein when the computer program instructions are executed by the processor 501, the device 500 performs the following operations for lithium plating detection of the battery cell of the power battery: obtaining multiple AC impedances measured at multiple SOCs of the battery cell; fitting the AC impedance as a function of the SOC based on the multiple AC impedances; and calculating the goodness of fit of the fitted function, and calculating the lithium plating score of the battery cell based on the goodness of fit. Wherein, the multiple AC impedances are measured in the non-driving state of the vehicle, and the non-driving state includes: the vehicle is charging, the vehicle is discharging to the energy storage system, or the vehicle is in a stalled state, and preferably, the multiple SOCs are evenly distributed over a range of at least 50% of the SOC, and / or the number of the multiple SOCs is greater than or equal to 5.

[0066] In addition, when the computer program instructions are executed by the processor 501, the apparatus 500 is caused to further perform the following operations:

[0067] During the vehicle's charging / discharging process, charging / discharging is suspended at multiple different SOCs, and multiple AC pulses with different frequencies are applied to the battery cells. Alternatively, when the vehicle is parked, multiple AC pulses with different frequencies are applied to the battery cells at multiple different SOCs, the multiple SOCs corresponding to the SOCs at different times when the vehicle is parked and the AC impedance at the corresponding frequency is calculated based on the battery cell's response to the multiple AC pulses. A goodness of fit of the function corresponding to each AC pulse is calculated for a function fitted based on the AC impedance values ​​measured at each AC pulse, and a lithium deposition fraction of the battery cell is calculated based on the goodness of fit of the function corresponding to each AC pulse. Furthermore, when the multiple AC impedances are measured while the vehicle is parked and the vehicle is not in the driving state, a first subset corresponding to a specific range of the additional parameter is selected from the measured multiple AC impedances based on the additional parameter, and the AC impedance is fitted as a function of the SOC based on the first subset. The additional parameter includes: ambient temperature at the time of measurement, battery cell temperature at the time of measurement, and measurement time.

[0068] The memory 502 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. One or more computer program instructions may be stored on the computer-readable storage medium, so that the processor 501 can execute the program instructions to implement the above-described functions and / or other desired functions of the embodiments described above, and / or to perform the above-described methods according to the embodiments of the present disclosure. Various applications and various data may also be stored in the computer-readable storage medium.

[0069] The present disclosure further provides a computer-readable storage medium having computer program instructions stored thereon, wherein when the computer program instructions are executed by a processor, the steps performed by the processor described above are implemented, consistent with the corresponding contents of the various embodiments described above. In addition, it should be understood that each component or module in the above-mentioned device can be implemented by hardware, can also be implemented by software, or can also be implemented by a combination of hardware and software.

[0070] The above description, in conjunction with the accompanying drawings, fully describes the method and apparatus for detecting lithium plating in power battery cells according to the embodiments of the present disclosure. Through the various aspects and embodiments of the present disclosure, non-destructive lithium plating detection can be performed on battery cells in a simple and accurate manner without affecting the user's use of the vehicle.

[0071] Furthermore, the basic principles of the present disclosure have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the embodiments of the present disclosure are merely illustrative and not restrictive, and it should not be assumed that these advantages, strengths, and effects are required of each embodiment of the present disclosure. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not limit the present disclosure to necessarily being implemented using these specific details.

[0072] The block diagrams of the devices, equipment, devices, and systems involved in the embodiments of the present disclosure are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, equipment, devices, and systems can be connected, arranged, or configured in any manner. Words such as "including," "comprising," "having," and the like are open-ended words that mean "including but not limited to," and can be used interchangeably therewith. The words "or" and "and" used herein refer to the words "and / or" and can be used interchangeably therewith unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and can be used interchangeably therewith.

[0073] Additionally, as used herein, "or" used in a list of items beginning with "at least one" indicates a separate list, so that, for example, a list of "at least one of A, B, or C" means A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). Furthermore, the word "exemplary" does not mean that the example described is preferred or better than other examples.

[0074] It should also be noted that in the apparatus and method of the present disclosure, each component or each step can be decomposed and / or recombined, and such decomposition and / or recombination should be regarded as equivalent solutions of the present disclosure.

[0075] It will be understood by those skilled in the art that all or any part of the methods and devices disclosed herein can be implemented in hardware, firmware, software, or a combination thereof, in any computing device (including a processor, storage medium, etc.) or a network of computing devices. The hardware can be a general-purpose processor, a digital signal processor (DSP), an ASIC, a field programmable gate array signal (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof, designed to perform the functions described herein. The general-purpose processor can be a microprocessor, but as an alternative, the processor can be any commercially available processor, controller, microcontroller, or state machine. The processor can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. The software can be present in any form of computer-readable tangible storage medium. By way of example and not limitation, such computer-readable tangible storage media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other tangible medium that can be used to carry or store desired program code in the form of instructions or data structures and can be accessed by a computer. As used herein, disk includes compact disk (CD), laser disk, optical disk, digital versatile disk (DVD), floppy disk, and Blu-ray disk.

[0076] Various changes, substitutions, and modifications of the technology described herein may be made without departing from the teachings of the appended claims. Moreover, the scope of the claims of this disclosure is not limited to the specific aspects of the processes, machines, manufactures, compositions of things, means, methods, and actions described above. Currently existing or later developed processes, machines, manufactures, compositions of things, means, methods, or actions that perform substantially the same function or achieve substantially the same results as the corresponding aspects described herein may be utilized. Accordingly, the appended claims include within their scope such processes, machines, manufactures, compositions of things, means, methods, or actions.

[0077] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0078] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present disclosure to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A method for detecting lithium plating in a power battery cell, comprising: Obtaining a plurality of AC impedances measured at a plurality of states of charge (SOCs) of the battery cell, wherein the plurality of AC impedances are measured when the vehicle is not in motion; fitting the AC impedance as a function of SOC based on the plurality of AC impedances; as well as The goodness of fit of the function is calculated, and a lithium plating fraction of the battery cell is calculated based on the goodness of fit, where the lithium plating fraction is used to indicate the degree of lithium plating occurring in the battery cell.

2. The method according to claim 1, wherein The non-driving state includes: The vehicle is being charged, the vehicle is discharging to an energy storage system, or the vehicle is in a shutdown state.

3. The method according to claim 2, wherein: The non-driving state is when the vehicle is charging or discharging to the energy storage system, and the multiple AC impedances are measured by the following steps: During charging or discharging of the vehicle, pausing charging / discharging at different SOCs and applying a plurality of AC pulses with different frequencies to the battery cell; as well as At each of the plurality of SOCs, an AC impedance at a corresponding frequency is calculated based on responses of the battery cell to the plurality of AC pulses.

4. The method according to claim 3, wherein: The plurality of AC pulses having different frequencies are provided by an external device for charging or discharging the vehicle.

5. The method according to claim 2, wherein: When the multiple AC impedances are measured when the vehicle is in the non-driving state with the engine turned off and parked, the multiple AC impedances are measured by the following steps: When the vehicle is shut down and parked, applying a plurality of AC pulses with different frequencies to the battery cell at a plurality of different SOCs, the plurality of SOCs corresponding to the SOCs when the vehicle is shut down and parked at different times; as well as At each of the plurality of SOCs, an AC impedance at a corresponding frequency is calculated based on responses of the battery cell to the plurality of AC pulses.

6. The method according to claim 5, wherein: The step of fitting the AC impedance as a function of the SOC based on the multiple AC impedances includes: Based on the additional parameter, selecting a first subset corresponding to a specific range of the additional parameter from the plurality of measured AC impedances; and fitting the AC impedance as a function of SOC based on the first subset of the measured plurality of AC impedance values, The additional parameters include: the ambient temperature during measurement, the battery cell temperature during measurement, and the measurement time.

7. The method according to any one of claims 3 to 6, wherein The calculating the goodness of fit of the function, and calculating the lithium plating fraction of the battery cell based on the goodness of fit, includes: calculating a goodness of fit of a function corresponding to each AC pulse for a function fitted based on the AC impedance value measured at each of the plurality of AC pulses; and The lithium plating fraction of the battery cell is calculated based on the goodness of fit of the function corresponding to each AC pulse.

8. The method according to claim 1, wherein The plurality of SOCs are evenly distributed over a range spanning at least 50% of the SOCs, and / or the number of the plurality of SOCs is greater than or equal to 5.

9. A device for detecting lithium plating in a power battery cell, the device comprising: processor; and a memory having computer program instructions stored therein, Wherein, when the computer program instructions are executed by the processor, the device is enabled to perform the method for lithium plating detection of a power battery cell according to any one of claims 1 to 8.

10. A computer-readable storage medium having computer program instructions stored thereon, wherein when the computer program instructions are executed by a processor, the processor executes the method for lithium plating detection of a power battery cell according to any one of claims 1 to 8.

11. A computer program product, comprising computer program instructions, which, when executed by a processor, enable the processor to perform the method for lithium plating detection in a power battery cell according to any one of claims 1 to 8.

12. A system for detecting lithium plating in a power battery cell, comprising: Energy exchange facilities for providing charging and / or discharging services to vehicles; as well as A lithium deposition detection module is communicatively connected to the energy exchange facility; wherein, The energy exchange facility is configured to: During charging or discharging of the vehicle, pausing charging / discharging at different states of charge (SOC) and applying a plurality of AC pulses having different frequencies to the battery cell; and Providing a plurality of AC impedances measured at the plurality of SOCs to the lithium plating detection module, wherein the plurality of AC impedances are calculated at each of the plurality of SOCs based on the response of the battery cell to the plurality of AC pulses; The lithium deposition detection module is configured as follows: Fitting the AC impedance as a function of SOC based on the plurality of AC impedances; and The goodness of fit of the function is calculated, and a lithium plating fraction of the battery cell is calculated based on the goodness of fit, where the lithium plating fraction is used to indicate the degree of lithium plating occurring in the battery cell.

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