Battery lithium precipitation online detection method and device based on current excitation

Abstract

The invention discloses a battery lithium precipitation online detection method and device based on current excitation, and the method comprises the steps: taking short-time controllable small current excitation as a core, carrying out the charging test of a target battery based on an original charging protocol, setting an excitation current based on the internal resistance of the target battery, and carrying out the detection of the lithium precipitation of the battery. The method comprises the following steps: monitoring voltage and temperature changes and equivalent impedance caused by excitation current at different excitation times, and judging whether a lithium precipitation starting point and lithium precipitation are carried out or not by combining voltage abrupt change and the change trend of the equivalent impedance along with the state of charge / time / charging capacity, and determining whether lithium precipitation is carried out or not based on the corresponding voltage abrupt change and equivalent impedance at different excitation times. And screening the optimal excitation time by combining the curve smoothness and the lithium precipitation starting point change rate. According to the method, the charging protocol and steps of the target battery are not changed, the superposed current excitation is small, the time is short, the influence on the total charging time is small, the influence on the original charging process is small, the starting point synchronism and consistency of the corresponding lithium precipitation detection are high, and the method is clearly compared with other methods depending on charging pulse shelving.

Description

Technical Field

[0001] This invention belongs to the field of battery diagnostic technology and relates to an online diagnostic method for lithium plating in batteries. Specifically, it relates to a method for online lithium plating diagnosis of batteries by using current excitation signals to obtain the voltage difference change and impedance characteristics of the battery at different excitation times. Background Technology

[0002] Lithium-ion batteries are currently the most widely used energy storage and conversion devices with great application prospects in energy storage, power and other fields. Lithium plating in lithium-ion batteries is a key cause of capacity "plunge" and thermal runaway. Its non-destructive online diagnostic technology has become the core direction for upgrading battery management systems (BMS).

[0003] Current mainstream technologies have abandoned expensive implanted sensors, focusing instead on non-invasive analysis based on electrical signals. Among these, voltage relaxation methods, which identify lithium plating plateaus by capturing the voltage recovery inflection point after charging and allowing the circuit to settle, are the most mature applications. Differential voltage analysis (ICA / DVA) utilizes the derivative characteristics of voltage curves to amplify subtle thermodynamic changes caused by lithium plating. Voltage titration involves observing voltage drops after a short period of rest following charging. However, existing methods still face challenges such as significant interference from actual dynamic operating conditions, stringent requirements for settling time, and asynchrony with the onset of lithium plating under real charging conditions. Achieving highly sensitive real-time early warning for trace amounts of lithium plating without affecting the user experience remains a challenge. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a method and apparatus for online detection of lithium plating in batteries based on current excitation. By applying a short-term, controllable small current excitation signal during battery charging, the battery terminal voltage response characteristics are collected, and the excitation voltage difference, equivalent impedance parameters, and their variation patterns are extracted, thereby achieving real-time online diagnosis of the lithium plating state of the battery and detection of the lithium plating initiation point.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An online detection method for lithium plating in batteries based on current excitation includes the following steps:

[0007] Step 1, Charging test initialization:

[0008] The target battery is charged according to a preset charging protocol, and the reference charging characteristic curve of the battery under the charging protocol is obtained.

[0009] Step 2: Applying excitation signals and acquiring data:

[0010] During charging, an excitation current signal is superimposed on the target battery at preset intervals, and battery terminal voltage and temperature data before and after excitation are collected simultaneously. The preset interval is one or more of a time interval, a state-of-charge interval, or a charging capacity interval. The excitation current signal is a positive pulse current or a negative pulse current. The amplitude of the excitation current is determined based on the voltage acquisition accuracy and the battery internal resistance. The minimum duration of excitation is determined based on the sampling frequency. The specific steps are as follows:

[0011] Step 2.1, Setting the excitation interval:

[0012] The preset interval is determined based on the accuracy requirements of lithium plating diagnosis, and one or more of the following interval methods are adopted: time interval, state of charge interval, and charging capacity interval.

[0013] Step 2.2, Setting the excitation current signal:

[0014] Step 2.2.1: The excitation current signal is a positive pulse current or a negative pulse current;

[0015] Step 2.2.2, Excitation Current Amplitude The principles for determining:

[0016] (1) Lower limit constraint: The excitation current amplitude must satisfy the requirement that the voltage response can be effectively detected, that is:

[0017]

[0018] in, For the voltage acquisition accuracy of the voltage acquisition module, The internal resistance of the target battery;

[0019] (2) Upper limit constraint: The amplitude of the excitation current shall not exceed a preset ratio of the current charging current, and the preset ratio is preferably 1 / 5 to 1 / 20;

[0020] Step 2.3, Setting the duration of the stimulus:

[0021] The duration of the excitation current signal is 0.1s to 3s. The lower limit of the excitation duration satisfies the requirement that at least two effective voltage data points are acquired during the excitation period, i.e.:

[0022]

[0023] in, This refers to the sampling frequency of the voltage acquisition module;

[0024] Step 2.4, Voltage and Temperature Signal Acquisition:

[0025] Simultaneously acquire the terminal voltage and temperature signals of the target battery;

[0026] Step 3, Feature Parameter Extraction:

[0027] Based on the collected voltage data, the change in terminal voltage before and after excitation is calculated, and the equivalent impedance parameters are calculated in combination with the excitation current amplitude. The specific steps are as follows:

[0028] Step 3.1, Terminal voltage change Calculation:

[0029]

[0030] in: The terminal voltage value acquired before applying the excitation current; To incentivize at a certain moment during the period The voltage value;

[0031] Step 3.2, Equivalent Impedance Parameters Calculation:

[0032]

[0033] Step 3.3, Temperature Correction:

[0034] Temperature correction is performed on the equivalent impedance parameter based on the synchronously acquired temperature signal:

[0035]

[0036] in, These are the temperature-corrected equivalent impedance parameters. This is a temperature correction function. This is the actual temperature. For reference temperature;

[0037] Step 4, Lithium plating state determination:

[0038] Analyze the changing trends of equivalent impedance parameters or terminal voltage with respect to state of charge, time, or charging capacity; identify the second-stage characteristic evolution state of the characteristic curve; and determine the lithium plating initiation and state based on the descent starting point, descent amplitude, or descent slope. The specific steps are as follows:

[0039] Step 4.1, Trend Analysis:

[0040] Equivalent impedance parameter or terminal voltage difference Arrange the data by SOC, charging time, or charging capacity, and plot the trend curves.

[0041] Step 4.2, Method for determining the lithium plating start point:

[0042] The three-point accelerated descent method and / or slope threshold method are used to determine the lithium deposition starting point:

[0043] Three-point accelerated descent method:

[0044] Identify the location where the second downward trend appears in the curve of the change in equivalent impedance parameter or terminal voltage as a function of the charging process. If two consecutive data points show an accelerated decline in the second stage, then the first point of decline is determined as the starting point of lithium plating.

[0045] Slope threshold method:

[0046] Calculate the local slope of the trend curve:

[0047]

[0048] in, For the first Local slope of each data point For the first The equivalent impedance or voltage change value for each data point. The interval between adjacent data points is defined as follows: if multiple consecutive points in the second stage have negative slopes, and the absolute value of the slope reaches the absolute value of the average slope of that stage... More than times If the value is ≥2, then the position is determined to be the starting point of lithium plating;

[0049] Step 4.3, Lithium Plating State Determination:

[0050] Based on the lithium plating start point determination result, the following lithium plating status information is output: No lithium plating: No changes matching the lithium plating characteristics were detected during the entire charging process; Lithium plating occurred: Changes matching the lithium plating characteristics were detected, and the lithium plating start point position is output.

[0051] Step 5: Optimization of excitation parameters:

[0052] Based on the characteristic curves corresponding to different excitation durations, the optimal excitation time parameters are determined by comprehensively evaluating the curve smoothness index and the rate of change of lithium plating initiation index. The specific steps are as follows:

[0053] Step 5.1, Curve Smoothness Index:

[0054] The smoothness of the curve is calculated using the first-order difference standard deviation method, the signal-to-noise ratio (SNR) method, the moving average residual method, or the wavelet analysis method.

[0055] Step 5.2, Lithium plating starting point change rate index:

[0056]

[0057] in, The rate of change of the lithium plating initiation point. This represents the parameter change at the lithium plating initiation point. These are the parameter values ​​before the lithium plating initiation point.

[0058] An online lithium plating detection device for batteries based on current excitation, implementing the above method, comprises four parts: a charging module, a voltage and temperature monitoring module, a current excitation module, and a data processing module, wherein:

[0059] The charging module is responsible for performing the charging process of the target battery according to the preset charging protocol. It includes a charge-discharge tester and a host computer. The charge-discharge tester is responsible for providing the charging process of the target battery under the original charging protocol to be tested. The host computer is responsible for setting the charging steps of the target battery according to the original charging protocol.

[0060] The voltage and temperature monitoring module is responsible for collecting the terminal voltage and temperature signals of the target battery;

[0061] The current excitation module is responsible for applying excitation current signals to the target battery at preset intervals to highlight changes in the battery's internal state.

[0062] The data processing module is responsible for calculating the equivalent impedance parameter based on the change in terminal voltage before and after the excitation current signal is applied, and determining the lithium plating state of the target battery based on the change trend of the equivalent impedance parameter or the change in terminal voltage with the charging process.

[0063] The current excitation module is independent of the charging control module and superimposes an excitation current signal onto the target battery without interrupting the charging process.

[0064] The voltage acquisition accuracy of the voltage and temperature monitoring module is no less than 2mV;

[0065] The current excitation module is integrated with the voltage and temperature monitoring module into a single module.

[0066] Compared with the prior art, the present invention has the following advantages:

[0067] 1. This invention does not change the charging protocol and steps of the target battery, and the superimposed current excitation is small and short in duration, which has little impact on the total charging time and the original charging process. The corresponding lithium plating detection has strong synchronicity and consistency, which is in stark contrast to other methods that rely on charging pulse pauses.

[0068] 2. This invention relies only on information such as current, voltage, and temperature, without the need for additional sensing devices or disassembly. It is easy to operate, convenient to acquire data, low in cost, and non-destructive.

[0069] 3. The present invention diagnoses the lithium plating state of batteries based solely on differential processing of voltage data, and the signal acquisition relies on small current input / output excitation signals and voltage acquisition signals. Under the same acquisition frequency, the signal acquisition accuracy is higher and the diagnosis is more accurate.

[0070] 4. This invention proposes to use current excitation to explore the internal electrochemical state of the battery by measuring the voltage evolution at different time / capacity (SOC) stages during the charging process, combined with the analysis of the electrochemical mechanism related to lithium plating. Combined with voltage difference / impedance analysis, the evaluation method has higher accuracy and is applicable to various specifications of lithium-ion battery cells and modules. Attached Figure Description

[0071] Figure 1 This is a flowchart of an online detection method for lithium plating in batteries based on current excitation;

[0072] Figure 2 This is a schematic diagram of an online lithium plating detection device for batteries based on current excitation;

[0073] Figure 3 This is a design of the current excitation magnitude and frequency for online detection of lithium plating in batteries based on current excitation.

[0074] Figure 4 This is a schematic diagram showing the selection of voltage difference and equivalent impedance for online detection of lithium plating in batteries based on current excitation.

[0075] Figure 5 This paper describes the mechanism, analysis process, and results of online detection of lithium plating in batteries based on current excitation.

[0076] Figure 6 It represents the change in voltage drop with SOC under a certain current excitation. Detailed Implementation

[0077] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0078] This invention provides an online detection method for lithium plating in batteries based on current excitation. The method uses a short-time, controllable small current excitation as its core, performs charging tests on the target battery based on the original charging protocol, and sets the excitation current based on the internal resistance of the target battery. The system monitors the voltage, temperature, and equivalent impedance changes caused by the excitation current at different excitation times. It combines voltage spikes and equivalent impedance trends with state of charge (SOC) / time / charging capacity to determine the onset and presence of lithium plating. The system also analyzes voltage spikes and equivalent impedance at different excitation times. The optimal excitation time is selected by combining the curve smoothness with the rate of change of the lithium plating initiation point. For example... Figure 1 As shown, the specific steps are as follows:

[0079] Step 1, Charging test initialization:

[0080] The target battery is charged according to a preset charging protocol, and a baseline charging characteristic curve of the battery under this protocol is obtained. This provides the test object and target operating condition for subsequent online testing, wherein:

[0081] The target battery can be in the form of, but is not limited to, a battery module or battery pack formed by any one or more combinations of pouch batteries, cylindrical batteries, and prismatic batteries.

[0082] The negative electrode material of the target battery includes, but is not limited to, one or more of the following: silicon-based materials, silicon-graphite composite materials, graphite materials, lithium titanate materials, titanium niobium oxide materials, hard carbon materials, and soft carbon materials.

[0083] The cathode material of the target battery includes, but is not limited to, one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, nickel cobalt manganese ternary materials, nickel cobalt aluminum ternary materials, lithium-rich manganese-based materials, lithium manganese oxide, and other cathode materials containing transition metal oxides.

[0084] The preset charging protocols include, but are not limited to, constant current charging (CC), constant current-constant voltage charging (CC-CV), stepped constant current charging, pulse charging, multi-stage constant current-constant voltage charging, and any combination thereof.

[0085] Step 2: Applying excitation signals and acquiring data:

[0086] During the charging process in step 1, press Figure 3 An excitation current signal is applied to the target battery at preset intervals, and the terminal voltage and temperature signals of the target battery are acquired simultaneously. The specific steps are as follows:

[0087] Step 2.1, Setting the excitation interval:

[0088] The preset interval is determined based on the required accuracy of lithium plating diagnosis, and one or more of the following interval methods can be used:

[0089] Time interval: such as applying the stimulus every 30s, 60s, 120s, 180s, 300s, etc.;

[0090] State of charge interval: such as applying an excitation every 1%, 2%, 3%, 5%, 10% SOC, etc.;

[0091] Charging capacity interval: such as applying an excitation every 0.1Ah, 0.2Ah, 0.5Ah, 1Ah, etc.

[0092] The above interval methods can be combined arbitrarily or adjusted adaptively.

[0093] Step 2.2, Setting the excitation current signal:

[0094] The excitation current signal is either a positive pulse current or a negative pulse current.

[0095] Excitation current amplitude The principles for determining:

[0096] (1) Lower limit constraint: The excitation current amplitude must satisfy the requirement that the voltage response can be effectively detected, that is:

[0097]

[0098] in, For the voltage acquisition accuracy of the voltage acquisition module, This represents the internal resistance of the target battery. Example: If the voltage acquisition accuracy... =1mV, target battery internal resistance =50mΩ, then the excitation current amplitude >200mA.

[0099] (2) Upper limit constraint: The excitation current amplitude shall not exceed a preset ratio of the current charging current to reduce the impact on the original charging process. The preset ratio is preferably 1 / 5 to 1 / 20. In specific implementation, the excitation current amplitude can be set to 50mA, 100mA, 200mA, 510mA, 1.02A, etc., and can be flexibly selected according to the battery specifications and acquisition accuracy.

[0100] Step 2.3, Setting the duration of the stimulus:

[0101] The duration of the excitation current signal is 0.1s to 3s, with preferred values ​​including 0.1s, 0.2s, 0.5s, 1s, 1.5s, and 2s. The lower limit of the excitation duration satisfies the requirement that at least two effective voltage data points are acquired during the excitation period, i.e.:

[0102]

[0103] in, This refers to the sampling frequency of the voltage acquisition module. Example: If the sampling frequency... =20Hz (sampling interval 0.05s), then the minimum excitation duration ≥0.1s. Tests were conducted separately for subsequent optimal parameter selection.

[0104] Step 2.4, Voltage and Temperature Signal Acquisition:

[0105] The terminal voltage signal of the target battery is acquired synchronously, with a voltage acquisition accuracy of less than V / 10. , The target battery's internal resistance is used; the voltage acquisition accuracy is preferably not less than 2mV, more preferably not less than 1mV, and the sampling frequency is preferably not less than 10Hz, more preferably not less than 20Hz. The temperature signal of the target battery is acquired synchronously to correct for temperature drift of the equivalent impedance parameter. The temperature acquisition accuracy is preferably not less than 1℃, and the acquisition location includes one or more locations on the battery surface, battery tabs, and inside the battery (if available).

[0106] Step 2.5, Independence of the stimulus module:

[0107] In this step, the excitation current signal is applied by an excitation module independent of the charging control module, so that the excitation current is superimposed on the original charging current without interrupting or interfering with the execution of the original charging protocol. This design differs from the existing method of directly adjusting the charging current, avoiding the problem of current source response lag when the charging current is disconnected and then restarted, thus improving the real-time performance and accuracy of the detection.

[0108] Step 3, Feature Parameter Extraction:

[0109] Based on the voltage data collected in step 2, according to Figure 4 Calculate the change in terminal voltage before and after the excitation current signal is applied, and calculate the equivalent impedance parameters accordingly.

[0110] Step 3.1, Calculation of terminal voltage change:

[0111] Terminal voltage change The calculation method is as follows:

[0112]

[0113] in: The terminal voltage value (voltage of the last sampling point) was acquired before the excitation current was applied. To incentivize at a certain moment during the period The voltage value. In specific implementation, One or more of the following can be selected: the first voltage point acquired during the excitation period. The terminal voltage point collected during the excitation period The average voltage during the excitation period; the voltage value at any specified moment during the excitation period.

[0114] Step 3.2, Calculation of equivalent impedance parameters:

[0115] Equivalent impedance parameters The calculation method is as follows:

[0116]

[0117] in, This represents the change in terminal voltage. The excitation current amplitude. In a preferred embodiment, for different... By selecting a method, various equivalent impedance parameters, such as transient impedance at any given time, can be calculated for comprehensive analysis of the battery's internal state.

[0118] Step 3.3, Temperature Correction:

[0119] Temperature correction is performed on the equivalent impedance parameter based on the synchronously acquired temperature signal:

[0120]

[0121] in, This is a temperature correction function. This is the actual temperature. The reference temperature is 25°C. The temperature correction function can be determined using the Arrhenius model or a lookup table.

[0122] Step 4, Lithium plating state determination:

[0123] Analysis terminal voltage difference or equivalent impedance parameter By observing the changing trends during the charging process, the phased change patterns of the characteristic curves can be identified to determine the starting point and state of lithium plating.

[0124] Step 4.1, Trend Analysis:

[0125] Equivalent impedance parameter or terminal voltage difference according to Figure 5 The SOC, charging time, or charging capacity are arranged as shown. A trend curve is plotted, and the second stage begins when the first decline reaches a plateau. Figure 5 The trend of the scatter plot corresponding to the medium pressure difference is shown. Lithium plating characteristics: If lithium plating occurs, a sudden drop in equivalent impedance or voltage change occurs in the second stage. This is because when lithium plating occurs in the battery, the polarization of the negative electrode decreases (lithium plating is equivalent to providing deposition sites, reducing the original nucleation overpotential, slowing down or reversing the change in the negative electrode potential (abrupt / rapid change), which is reflected in the impedance as a decrease in the overall change value of the negative electrode potential, leading to an accelerated decrease in impedance, while the positive electrode basically maintains a constant change). This results in a larger change amplitude and a more negative slope compared to the steady period.

[0126] Step 4.2, Method for determining the lithium plating start point:

[0127] The lithium plating initiation point can be determined using one or more of the following methods:

[0128] Method 1: Three-point accelerated descent method:

[0129] Identify the point where the second downward trend appears in the curve of equivalent impedance parameter or terminal voltage change as a function of charging. If two consecutive data points show an accelerated decline in the second stage, the first decline point is identified as the starting point of lithium plating. (The decline in these two points compared to the previous point is greater than the average value in the second stage.)

[0130] Method 2: Slope Threshold Method

[0131] Calculate the local slope of the trend curve:

[0132]

[0133] in, For the first Local slope of each data point For the first The equivalent impedance or voltage change value for each data point. The interval between adjacent data points (SOC, time, or capacity). If multiple consecutive points in the second stage have negative slopes, and the absolute value of the slope reaches the absolute value of the average slope of that stage. More than twice ( ≥2, preferred If the value is 3, then the position is determined to be the starting point of lithium plating.

[0134] Step 4.3, Lithium Plating State Determination:

[0135] Based on the above lithium plating start determination results, the following lithium plating status information is output: No lithium plating: No changes matching the characteristics of lithium plating were detected during the entire charging process; Lithium plating occurred: Changes matching the characteristics of lithium plating were detected, and the lithium plating start position (SOC, time, or capacity) is output.

[0136] Step 5: Optimization of excitation parameters:

[0137] Based on the characteristic curves corresponding to different excitation durations, multiple indicators are comprehensively evaluated to determine the optimal excitation duration parameter.

[0138] Step 5.1, Curve Smoothness Index:

[0139] Curve smoothness is calculated using the first-order difference standard deviation method:

[0140] (1) Calculate the first-order difference sequence:

[0141]

[0142] (2) Calculate the standard deviation of the first difference. :

[0143]

[0144] in, For the first First difference of each data point The average of the first-order differences. Number of data points. Standard deviation. The smaller the value, the higher the curve smoothness, the smaller the fluctuation, and the more stable the detection results. Optionally, the following smoothness evaluation methods can also be used: signal-to-noise ratio (SNR) method, moving average residual method, and wavelet analysis method.

[0145] Step 5.2, Lithium plating starting point change rate index:

[0146] The rate of change of the lithium plating initiation point is defined as the ratio of the change in parameters at the lithium plating initiation point to the parameter value before the change:

[0147]

[0148] in, The rate of change of the lithium plating initiation point. This represents the parameter change at the lithium plating initiation point. These are the parameter values ​​before the lithium plating initiation point. The higher the value, the more pronounced the lithium plating characteristics, and the easier it is to identify accurately.

[0149] This invention applies current excitation at different times / SOC during the charging process and observes the changes in battery voltage difference and equivalent impedance. Combined with electrochemical mechanism analysis, it proposes to use short-time controllable small current excitation to mine lithium plating characteristic signals inside the battery to detect the lithium plating start-up and lithium plating state. The detection method has higher synchronization and consistency, and has little impact on the original charging process. It is applicable to lithium-ion battery cells and modules of various specifications.

[0150] Example:

[0151] 1. Experimental subjects and conditions:

[0152] Online testing and verification of fast charging lithium plating was conducted using 18650 cells with a capacity of 3400mAh.

[0153] 2. Charging protocol settings:

[0154] This embodiment uses 3C high current to charge the target battery for testing: the host computer sets the charging steps according to the protocol, and the charge and discharge tester provides the charging process of the target battery under the protocol.

[0155] 3. Excitation parameter settings and data acquisition:

[0156] 3.1 Excitation Current Parameters: Excitation Current Amplitude Determination: According to the method of the present invention, the excitation current must satisfy:

[0157] Lower limit:

[0158] Voltage acquisition accuracy (1mV) < Voltage response 1 / 10;

[0159] ;

[0160] Requirement: 1mV < (35mΩ × ) / 10, that is: > 10mV / 35mΩ ≈ 286mA;

[0161] Maximum:

[0162] The current is no more than 1 / 5 of the charging current = 10.2A / 5 = 2.04A.

[0163] This embodiment selects the excitation current amplitude. (Negative direction, i.e., discharge direction), which is 1 / 10 of the charging current, satisfying the above constraints. Voltage response verification: V = 35mΩ × 1.02A = 35.7mV, voltage acquisition accuracy of 1mV is 1 / 35.7 of this value, meeting the requirement of being less than 1 / 10.

[0164] 3.2 Excitation Time Parameters:

[0165] Excitation current application time: 1s; voltage monitoring module sampling frequency: 10Hz (sampling interval 100ms). Ten voltage data points can be collected within the 1s excitation time, exceeding the minimum requirement of 2 points.

[0166] 3.3 Excitation Interval Setting:

[0167] Excitation signals are applied at 2% SOC intervals, that is, an excitation is applied once at SOC = 2%, 4%, 6%, 8%, 12%, up to the upper limit of the charging voltage.

[0168] 3.4 Incentive Implementation Methods:

[0169] The current excitation module is independent of the charging module and is connected in parallel to both ends of the target battery. At the preset SOC point, the excitation module outputs a 1.02A discharge current for 1 second, which is superimposed on the original 10.2A charging current, causing the actual battery current to momentarily become 9.18A (10.2A - 1.02A). After the excitation ends, it returns to 10.2A. This method does not interrupt the charging output of the charge / discharge tester and avoids the response lag problem when the current is disconnected and then restarted.

[0170] 4. Data Acquisition and Feature Extraction:

[0171] 4.1 Calculation of terminal voltage difference:

[0172] Record the following when applying excitation at each SOC point:

[0173] : Voltage at the last sampling point before excitation;

[0174] : Voltage at the first sampling point after the excitation starts (at 100ms);

[0175] : Voltage at the end of excitation (1 second);

[0176] Calculation of terminal voltage difference:

[0177] Transient pressure difference: ;

[0178] Steady-state pressure difference: .

[0179] 4.2 Equivalent impedance calculation:

[0180] Transient equivalent impedance: ;

[0181] Steady-state equivalent impedance: ;

[0182] Note: Since the excitation current is in the discharge direction, the battery terminal voltage rises after the excitation is applied. It is a negative value.

[0183] 5. Lithium plating state determination:

[0184] Plot the voltage difference under excitation The curve showing the change in SOC is analyzed to determine its trend. Figure 6 The method of determining the starting point of lithium plating is as follows: According to the method of the present invention, if two consecutive points decrease in the second stage, the first point of decrease is taken as the starting point of lithium plating, that is, SOC 34% is the starting point of lithium plating.

[0185] Verification using the slope threshold method: Since the average slope of the second stage is 0, the slope of the later stage of the first stage is used as a reference to further confirm that lithium plating begins to occur in the SOC range of 34%-36%.

[0186] The test results show that:

[0187] 1. Under 3C fast charging conditions, lithium plating occurs at 34% SOC of this battery cell;

[0188] 2. The 1s excitation time has good curve smoothness and lithium plating initiation rate of change, and can be used as a reference excitation parameter for implementation;

[0189] 3. The method of the present invention can realize online real-time detection of lithium plating without interrupting the original charging protocol.

Claims

1. A current excitation-based online detection method for lithium precipitation of a battery, characterized in that The method comprises the following steps: Step 1, charging test initialization: Perform a charging process on the target battery according to a preset charging protocol, and obtain a reference charging characteristic curve of the battery under the charging protocol; Step 2, excitation signal application and data acquisition: During the charging process, superimpose an excitation current signal on the target battery at a preset interval, and synchronously collect the battery terminal voltage and temperature data before and after excitation; Step 3, characteristic parameter extraction: Based on the collected voltage data, calculate the terminal voltage variation before and after excitation, and calculate the equivalent impedance parameter in combination with the excitation current amplitude; Step 4, lithium precipitation state determination: Analyze the change trend of the equivalent impedance parameter or the terminal voltage variation with the state of charge, time or charging capacity, identify the second stage characteristic evolution state of the characteristic curve, and determine the lithium precipitation starting point and lithium precipitation state based on the descending starting point, descending amplitude or descending slope; Step 5, excitation parameter optimization: Based on the characteristic curves corresponding to different excitation durations, comprehensively evaluate the curve smoothness index and lithium precipitation starting point change rate index, and determine the optimal excitation time parameter.

2. The current excitation based online detection method of lithium precipitation in battery according to claim 1, characterized in that In step 1, the form of the target battery is any one or a combination of soft pack battery, cylindrical battery, square battery, battery module or battery pack; the negative electrode material of the target battery is one or more of silicon-based material, silicon-graphite composite material, graphite material, lithium titanate material, titanium-niobium oxide material, hard carbon material and soft carbon material; the positive electrode material of the target battery is one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium-rich manganese-based material and lithium manganate; and the preset charging protocol is constant current charging, constant current-constant voltage charging, step constant current charging, pulse charging, multi-stage constant current-constant voltage charging and any combination thereof.

3. The current excitation based online detection method of lithium deposition in battery according to claim 1, characterized in that The specific steps of step 2 are as follows: Step 2.1, setting of excitation interval: The preset interval is determined according to the lithium precipitation diagnosis accuracy requirement, and one or more of the following interval methods is used: time interval, state of charge interval, charging capacity interval; Step 2.2, setting of excitation current signal: Step 2.2.1, the excitation current signal is a positive pulse current or a negative pulse current; Step 2.2.2, determination of the excitation current amplitude of the principle: (1) Lower limit constraint: the excitation current amplitude needs to meet the condition that the voltage response can be effectively detected, i.e. wherein, is the voltage collection precision of the voltage collection module, is the internal resistance of the target battery; (2) Upper limit constraint: the excitation current amplitude does not exceed the preset proportion of the current charging current, and the preset proportion is 1 / 5~1 / 20; Step 2.3, setting of excitation duration: The duration of the excitation current signal is 0.1s~3s, and the lower limit of the excitation duration meets the condition that at least two effective voltage data points are collected during the excitation, i.e. wherein, is the sampling frequency of the voltage acquisition module; Step 2.4, voltage and temperature signal acquisition: Synchronously collect the terminal voltage signal and temperature signal of the target battery.

4. The current excitation-based online detection method for lithium precipitation of a battery according to claim 3, characterized in that In step 2.4, the voltage acquisition accuracy is less than V / 10, the sampling frequency is not less than 10Hz, and the collection position includes one or more of the battery surface, the battery tab and the battery interior.

5. The current excitation based online detection method of lithium deposition in battery according to claim 1, characterized in that The specific steps of step 3 are as follows: Step 3.1, change in terminal voltage Calculation: wherein: is the end voltage value acquired before the application of the excitation current; is the voltage value at a certain moment during the excitation; is the voltage value at a certain moment during the excitation; Step 3.2, equivalent impedance parameter Calculation: Step 3.3, temperature correction: Based on the synchronously collected temperature signal, the equivalent impedance parameter is temperature corrected: wherein, is a temperature corrected equivalent impedance parameter, is a temperature correction function, is an actual temperature, is a reference temperature.

6. The current excitation based online detection method of lithium deposition in battery as claimed in claim 1, wherein The specific steps of step 4 are as follows: Step 4.1, change trend analysis: equivalent impedance parameters or terminal voltage differential Arrange and draw trend curves according to SOC, charging time or charging capacity. Step 4.2, determination method of lithium precipitation starting point: Determine the lithium precipitation starting point by using three-point accelerated decline method and / or slope threshold method: Three-point accelerated decline method: Identify the position of the second downward trend in the equivalent impedance parameter or terminal voltage change curve with charging process, if there are two consecutive data points accelerated decline in the second stage, the first decline point is determined as the lithium precipitation starting point; Slope threshold method: Calculate the local slope of the change trend curve: wherein, is the local slope of the first data point, is the equivalent impedance or voltage change magnitude of the first data point, is the interval of adjacent data points, if the slope of the second stage is negative and the absolute value of the slope reaches times of the average absolute value of the slope of the stage ≥ 2, then the position is determined as the lithium precipitation starting point; Step 4.3, determination of lithium precipitation state: Based on the determination result of lithium precipitation starting point, output the following lithium precipitation state information: no lithium precipitation: no lithium precipitation characteristics are detected in the whole charging process; Lithium precipitation occurs: lithium precipitation characteristics are detected, and the lithium precipitation starting point position is output.

7. The current excitation based online detection method of lithium deposition in battery as claimed in claim 1, wherein The specific steps of step 5 are as follows: Step 5.1, curve smoothness index: Calculate the curve smoothness by using first-order difference standard deviation method, signal-to-noise ratio method, sliding average residual method or wavelet analysis method; Step 5.2, lithium precipitation starting point change rate index: wherein, is a change rate of the lithium precipitation onset point, is a parameter change amount at the lithium precipitation onset point, is a parameter value before the lithium precipitation onset point.

8. The current excitation-based online detection method for lithium precipitation of a battery according to claim 7, characterized in that In step 5.1, the method for calculating the curve smoothness by using first-order difference standard deviation method is: (1) Calculate the first-order difference sequence: (2) Calculate the standard deviation of the first-order difference : wherein, is the first order difference of the number of data points, is the average of the first order difference, is the number of data points.

9. A galvanostatically based on-line lithium plating detection device for a battery implementing the method of any one of claims 1-8, characterized by The device charging module, voltage and temperature monitoring module, current excitation module and data processing module, wherein: The charging module is responsible for performing the charging process on the target battery according to the preset charging protocol; The voltage and temperature monitoring module is responsible for collecting the terminal voltage signal and temperature signal of the target battery; The current excitation module is responsible for applying an excitation current signal to the target battery at a preset interval, highlighting the internal state change of the battery; The data processing module is responsible for calculating the equivalent impedance parameter according to the terminal voltage change before and after the excitation current signal is applied, and determining the lithium precipitation state of the target battery according to the change trend of the equivalent impedance parameter or the terminal voltage change with the charging process.

10. The current-excitation-based online lithium deposition detection device of claim 9, wherein The charging module includes a charge-discharge tester and an upper computer, the charge-discharge tester is responsible for providing the charging process of the target battery under the original charging protocol to be detected, and the upper computer is responsible for setting the charging steps of the target battery according to the original charging protocol; The current excitation module is independent of the charging control module, and the excitation current signal is superimposed on the target battery without interrupting the charging process; The voltage sampling accuracy of the voltage and temperature monitoring module is not less than 2mV; The current excitation module and the voltage and temperature monitoring module are integrated into an integrated module.

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