Lithium battery system with long cycle life and optimization method thereof

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a long-cycle-life lithium battery system and an optimization method thereof.The method comprises the steps that firstly, appropriate electrolyte is selected, components of the electrolyte are analyzed, and a first charge-discharge cycle test is conducted to record key data; then, the SEI film forming condition is evaluated, the thickness change trend of the SEI film is confirmed, and the electrolyte additive proportion is adjusted according to the trend so as to reduce the decomposition tendency; preparing a new electrolyte, applying the new electrolyte to the battery, and monitoring the internal resistance change; the charging strategy is adjusted based on the internal resistance change to stabilize the cycle performance, and the thickening control effect of the SE I film is verified through multiple cycle tests; finally, test results are summarized, and an electrolyte and a charging scheme are further optimized. According to the method, the thickening trend of the SEI film can be accurately evaluated and effectively controlled, and the increase of the internal resistance of the battery is remarkably reduced, so that the cycle life of the lithium battery is greatly prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a high-cycle-life lithium battery system and an optimization method thereof. Background Art

[0002] Existing lithium battery optimization methods mainly focus on the following aspects:

[0003] Optimization of electrolyte composition: By adding specific additives to improve the stability of the electrolyte and reduce its decomposition tendency during charge and discharge.

[0004] Adjustment of charging strategy: Adopting different charging modes (such as constant current charging, constant voltage charging, etc.) to reduce damage to the internal structure of the battery and extend the battery life.

[0005] SEI film control: By optimizing the electrolyte formula or surface treatment technology, attempting to slow down the thickening rate of the SEI film, thereby reducing the increase in battery internal resistance.

[0006] Although these methods have improved the performance of lithium batteries to a certain extent, they still face some challenges in practical applications. For example, existing technologies often have difficulty accurately evaluating and effectively controlling the thickening rate of the SEI film and its impact on battery internal resistance, resulting in a gradual increase in battery internal resistance and a decline in cycling performance during long-term use.

[0007] The main problem of the existing technology is the lack of a systematic process to comprehensively evaluate and optimize the electrolyte composition and charging strategy, especially the lack of quantification of the SEI film thickening trend and its impact on battery internal resistance. This makes it difficult to find the optimal combination of electrolyte formula and charging strategy in actual operation, thus unable to maximize the cycling life of lithium batteries. Summary of the Invention

[0008] The purpose of the present invention is to provide a high-cycle-life lithium battery system and an optimization method thereof, which can accurately evaluate and effectively control the thickening trend of the SEI film, significantly reduce the increase in battery internal resistance, and thus greatly improve the cycling life of lithium batteries, so as to solve the problems raised in the above background art.

[0009] To achieve the above object, the present invention proposes a high-cycle-life lithium battery optimization method, which comprises the following steps:

[0010] Select an electrolyte and analyze its composition to determine the initial state. Based on the initial state, perform the first charge-discharge cycle on the battery, record the data, evaluate the formation of the SEI film according to the data, and confirm the thickness change trend. Use the trend to adjust the proportion of the electrolyte additive to reduce the decomposition tendency. Configure a new electrolyte according to the adjusted proportion of the electrolyte additive and apply it to the battery to monitor the internal resistance change. Based on the internal resistance change, adjust the charging strategy to stabilize the cycle performance. Use the charging strategy to conduct multiple cycle tests to verify the control effect of SEI film thickening. Summarize the test results, optimize the electrolyte and charging scheme, and achieve an improvement in cycle life.

[0011] Preferably, the selecting an electrolyte and analyzing its composition to determine the initial state includes:

[0012] Prepare multiple candidate electrolyte samples and mark the source and basic composition information of each sample;

[0013] Measure the basic physical and chemical properties of each candidate electrolyte sample, including viscosity V and density D, and record the measurement results in association with the basic composition information of the sample;

[0014] Based on the measurement results, calculate the comprehensive score of each sample through the formula Y = (A * D)+(B / V), where Y is the comprehensive score, and A and B are constants, to evaluate its potential as an electrolyte for high-cycle-life lithium batteries;

[0015] Select the sample with the highest comprehensive score and conduct a comprehensive composition analysis on it, including trace element detection, to determine the exact composition of the sample as the initial state.

[0016] Preferably, the based on the initial state, performing the first charge-discharge cycle on the battery and recording the data includes:

[0017] Use the sample with the highest comprehensive score as the electrolyte, assemble the battery, and mark the battery as a test sample;

[0018] Perform the first charge cycle on the test sample, set the charging current Ic and the cut-off voltage Vc, and calculate and record the charging capacity during the charging process through the formula Q = Ic * t, where Q is the charging capacity and t is the charging time;

[0019] After charging is completed, immediately perform a discharge cycle on the test sample, set the discharge current Id and the cut-off voltage Vd, and calculate and record the energy efficiency during the discharge process according to the formula E = (Id * td) / Q, where E is the energy efficiency and td is the discharge time;

[0020] Analyze the performance of the test sample during charge and discharge based on the data combining charge capacity and energy efficiency, and record the internal resistance value for evaluating the formation of the SEI film in the subsequent steps.

[0021] Preferably, evaluating the formation of the SEI film according to the data and confirming the thickness change trend includes:

[0022] Based on the internal resistance value Ri of the test sample during charge and discharge, establish a relationship table between internal resistance and cycle number, and mark the change in internal resistance after each cycle;

[0023] Analyze the data in the relationship table, and calculate the proportion of the increase in internal resistance after each cycle through the formula Rt = R0 + k * N, where Rt is the internal resistance value after the Nth cycle, R0 is the initial internal resistance value, and k is a constant;

[0024] Use the proportion combined with the experimental observation data to draw a trend graph of the change in internal resistance with the cycle number, identify the key interval of the thickening of the SEI film, and record the characteristic parameters of the interval;

[0025] According to the trend graph and characteristic parameters, derive an estimation formula for the change in the thickness of the SEI film with the cycle number Df = D0 + c * (Rt - R0), where Df is the thickness of the SEI film, D0 is the initial thickness, and c is a conversion coefficient, used to predict the thickening trend of the SEI film in subsequent cycles.

[0026] Preferably, adjusting the proportion of the electrolyte additive using the trend to reduce the decomposition tendency includes:

[0027] Based on the estimation formula Df = D0 + c * (Rt - R0) for the change in the thickness of the SEI film with the cycle number, calculate the thickening speed Vs of the SEI film under the current electrolyte formulation, where Vs = (Df - D0) / N, and N is the cycle number;

[0028] According to the speed Vs and the proportion of the increase in internal resistance, determine the main factors causing the rapid thickening of the SEI film, and mark the electrolyte component X corresponding to the main factors;

[0029] For the electrolyte component X, calculate the amount of additive to be added or reduced through the formula P = P0 - a * Vs, where P is the adjusted additive proportion, P0 is the original additive proportion, and a is an adjustment coefficient, to slow down the thickening trend of the SEI film;

[0030] According to the adjusted additive proportion P, reconfigure the electrolyte and apply it to the battery for verification testing, record the new internal resistance value Rt' and cycle performance data, and evaluate whether the thickening of the SEI film is effectively controlled.

[0031] Preferably, the new electrolyte is prepared according to the adjusted proportion of the electrolyte additive and applied to the battery, and the internal resistance change is monitored, including:

[0032] According to the adjusted additive proportion P, calculate the specific amounts of each component required. Through the formula M = V * C, where M is the mass, V is the volume, and C is the concentration, prepare all the components of the new electrolyte;

[0033] Mix the calculated specific amounts of each component to prepare the new electrolyte, and mark its formulation parameters, including the adjusted additive proportion P and the mass M of each component;

[0034] Reassemble the battery with the new electrolyte, ensure that the initial state of the battery is the same as that in the previous test, and record the initial internal resistance value Ri of the battery;

[0035] Perform charge-discharge cycle tests on the reassembled battery under standard conditions. Through the formula Rn = (Rt' - Ri) / N, where Rn is the increase in internal resistance after each cycle and N is the number of cycles, continuously monitor and record the change in internal resistance of the battery within multiple cycle periods.

[0036] Preferably, based on the change in internal resistance, adjust the charging strategy to stabilize the cycle performance, including:

[0037] Analyze the internal resistance change data Rn of the reassembled battery during multiple charge-discharge cycles. Through the formula D_Rn = Rn_max - Rn_min, where D_Rn is the internal resistance change range, Rn_max is the maximum increase in internal resistance, and Rn_min is the minimum increase in internal resistance, determine the main interval of internal resistance fluctuation;

[0038] Based on the internal resistance fluctuation interval, calculate the optimal charging rate Cr during each charging process using the formula Cr = k / D_Rn, where k is a constant;

[0039] According to the optimal charging rate Cr, design a new charging strategy, including the charging current I and the charging time t. Using the formula I = Cr * Q, where Q is the battery capacity, determine the specific value of the charging current and set the charging cut-off condition;

[0040] Apply the new charging strategy to perform multiple charge-discharge cycle tests on the reassembled battery, record the internal resistance value Rt” after each cycle, and compare it with the initial internal resistance value Ri to evaluate the influence of the charging strategy on the stability of the battery cycle performance.

[0041] Preferably, use the charging strategy to perform multiple cycle tests to verify the control effect of SEI film thickening, including:

[0042] Perform multiple charge-discharge cycle tests on the reassembled battery using the new charging strategy. Set the number of cycles per round to Nc, record the internal resistance value Rt” after each cycle, and calculate the average internal resistance R_avg at the end of each cycle as R_avg = (Rt”_1 + Rt”_2 +... + Rt”_Nc) / Nc;

[0043] Based on the average internal resistance R_avg and the initial internal resistance Ri, through the formula D_R = R_avg - Ri, where D_R is the increase in internal resistance after each cycle, evaluate the thickening situation of the SEI film and mark the D_R values for each round;

[0044] Use the D_R values to plot a trend graph of the internal resistance versus the number of cycles. Through the formula S = (D_R_max - D_R_min) / Nc, where S is the slope of the internal resistance increase trend, determine the changing trend of the SEI film thickening rate;

[0045] According to the slope S and the trend graph, analyze the control effect of the charging strategy on the SEI film thickening. If S is less than the preset threshold T, confirm that the charging strategy is effective and record the optimized charging parameters, including the charging current I and the charging time t.

[0046] Preferably, summarize the test results, optimize the electrolyte and the charging scheme to achieve an increase in the cycle life, including:

[0047] Summarize the data of the slope S and the internal resistance increase amount D_R. Through the formula L = 1 / (1 + S), where L is the cycle life coefficient, evaluate the battery cycle life performance under each charging strategy and mark the L values corresponding to each group of data;

[0048] Based on the cycle life coefficient L and the initial internal resistance Ri, calculate the estimated value N_est of the actual cycle life of the battery under each charging strategy as N_est = L * N_max, where N_max is the theoretical maximum number of cycles, and determine the N_est value corresponding to the optimal charging strategy;

[0049] Combined with the optimal charging strategy and the corresponding N_est value, adjust the proportion P of the electrolyte components. Through the formula P_new = P_old + b * (N_est - N_old), where P_new is the new proportion of the electrolyte additive, P_old is the old proportion of the electrolyte additive, b is the adjustment coefficient, and N_old is the original estimated cycle life, reconfigure the electrolyte;

[0050] Perform a new round of charge-discharge cycle tests on the battery using the new electrolyte and the optimized charging strategy. Record the internal resistance value Rt”' after each cycle and calculate the new average internal resistance R_avg' = (Rt”'_1 + Rt”'_2 +... + Rt”'_Nc) / Nc, and compare it with the original average internal resistance R_avg to verify the optimization effect.

[0051] On the other hand, the present invention proposes an optimized system for high-cycle-life lithium batteries, comprising:

[0052] An electrolyte selection and analysis module for selecting an electrolyte and analyzing its composition to determine the initial state;

[0053] A preliminary battery performance evaluation module for performing the first charge and discharge cycle on the battery based on the initial state and recording data;

[0054] An SEI film formation evaluation module for evaluating the formation of the SEI film according to the data and confirming the thickness change trend;

[0055] An electrolyte optimization and adjustment module for adjusting the proportion of electrolyte additives using the trend to reduce the decomposition tendency;

[0056] A new electrolyte application and monitoring module for configuring a new electrolyte according to the adjusted proportion of electrolyte additives, applying it to the battery, and monitoring the internal resistance change;

[0057] Charge strategy optimization for adjusting the charge strategy based on the internal resistance change to stabilize the cycle performance;

[0058] A cycle test and verification module for performing multiple cycle tests using the charge strategy to verify the control effect of SEI film thickening;

[0059] A final optimization and result summary module for summarizing the test results, optimizing the electrolyte and charging scheme, and achieving an improvement in cycle life.

[0060] Technical effects and advantages of the present invention: A high-cycle-life lithium battery system and its optimization method proposed by the present invention have the following advantages compared with the prior art:

[0061] The present invention first selects a suitable electrolyte and analyzes its composition, and performs the first charge and discharge cycle test to record key data; then evaluates the formation of the SEI film and confirms its thickness change trend, and uses this trend to adjust the proportion of electrolyte additives to reduce the decomposition tendency; then configures a new electrolyte and applies it to the battery, and monitors the internal resistance change; adjusts the charge strategy based on the internal resistance change to stabilize the cycle performance, and verifies the control effect of SEI film thickening through multiple cycle tests; finally, summarizes the test results and further optimizes the electrolyte and charging scheme. This method can accurately evaluate and effectively control the thickening trend of the SEI film, significantly reduce the increase in battery internal resistance, and thus greatly improve the cycle life of the lithium battery. This systematic process not only improves the overall performance of the battery but also provides solid data support for subsequent optimization. Description of the Drawings

[0062] Figure 1Flow chart of an optimization method for a high cycle life lithium battery according to the present invention;

[0063] Figure 2 Block diagram of an optimization system for a high cycle life lithium battery according to the present invention. Detailed implementation manners

[0064] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0065] The present invention provides an optimization method for a high cycle life lithium battery as shown in Figure 1 and includes the following steps:

[0066] I. Select an electrolyte and analyze its composition to determine the initial state; specifically including:

[0067] Prepare multiple candidate electrolyte samples and mark the source and basic component information of each sample; by preparing multiple candidate electrolyte samples and recording their sources and basic component information in detail, it is ensured that subsequent experiments have diversity and traceability, laying a foundation for accurately evaluating the impact of different electrolyte formulations on battery performance.

[0068] Measure the basic physical and chemical properties of each of the candidate electrolyte samples, including viscosity V and density D, and record the measurement results in association with the basic component information of the samples; by measuring basic physical and chemical properties such as viscosity and density, electrolyte samples with good fluidity and stability can be preliminarily screened out. These data are helpful for subsequent calculation of the comprehensive score, so as to more accurately evaluate the potential of the electrolyte.

[0069] Based on the measurement results, calculate the comprehensive score of each sample through the formula Y=(A*D)+(B / V), where Y is the comprehensive score, and A and B are constants, to evaluate its potential as an electrolyte for a high cycle life lithium battery; calculating the score of each sample using the comprehensive score formula can quantitatively evaluate the overall performance of each electrolyte sample, so as to select the most suitable electrolyte for a high cycle life lithium battery.

[0070] Select the sample with the highest comprehensive score and conduct a comprehensive component analysis on it, including trace element detection, to determine the exact composition of the sample as the initial state. Selecting the sample with the highest comprehensive score and conducting a detailed component analysis on it can ensure that the selected electrolyte not only performs excellently in terms of physical and chemical properties but also further understand its microscopic components, providing detailed reference data for subsequent optimization.

[0071] Example 1

[0072] Suppose there are three candidate electrolyte samples (Sample1, Sample2, Sample3), and their basic component information is as follows:

[0073] Sample number Source <![CDATA[Density D (g / cm 3 )]]> Viscosity V (mPa·s) Sample1 Laboratory synthesis 1.20 5.0 Sample2 Commercial procurement 1.18 4.5 Sample3 Laboratory synthesis 1.22 5.5

[0074] Set constants A = 1.5 and B = 2.0, and use the formula Y = (A * D)+(B / V) to calculate the comprehensive score of each sample:

[0075] Sample1: Y = (1.5 * 1.20)+(2.0 / 5.0);

[0076] Y = 1.80 + 0.40;

[0077] Y = 2.20;

[0078] Sample2: Y = (1.5 * 1.18)+(2.0 / 4.5);

[0079] Y = 1.77 + 0.44;

[0080] Y = 2.21;

[0081] Sample3: Y = (1.5 * 1.22)+(2.0 / 5.5);

[0082] Y = 1.83 + 0.36;

[0083] Y = 2.19;

[0084] According to the calculation results, Sample2 has the highest comprehensive score (Y = 2.21), so Sample2 is selected as the best electrolyte sample. Next, conduct a comprehensive component analysis on Sample2, including trace element detection, to determine its exact composition as the initial state for subsequent experiments.

[0085] Second, based on the initial state, conduct the first charge-discharge cycle on the battery and record the data; specifically including:

[0086] Use the sample with the highest comprehensive score as the electrolyte, assemble the battery, and label the battery as a test sample; by assembling the battery with the electrolyte sample having the highest comprehensive score, it is ensured that the electrolyte used in the experiment has the best physical and chemical properties, thus providing a reliable basis for subsequent evaluation of the battery performance.

[0087] Perform the first charging cycle on the test sample, set the charging current Ic and the cut-off voltage Vc, and calculate and record the charging capacity during the charging process through the formula Q = Ic * t, where Q is the charging capacity and t is the charging time; by setting the charging current and the cut-off voltage and recording the charging capacity, the energy storage capacity of the battery during the charging process can be quantified, providing key data for subsequent analysis of the battery performance.

[0088] After charging is completed, immediately perform a discharging cycle on the test sample, set the discharging current Id and the cut-off voltage Vd, and calculate and record the energy efficiency during the discharging process according to the formula E = (Id * td) / Q, where E is the energy efficiency and td is the discharging time; by setting the discharging current and the cut-off voltage and recording the discharging time and the energy efficiency, the energy conversion efficiency of the battery in actual use can be evaluated, further understanding its performance.

[0089] Combine the data of the charging capacity and the energy efficiency, analyze the performance of the test sample during the charge-discharge process, and record the internal resistance value for subsequent steps to evaluate the formation of the SEI film. By combining the data of the charging capacity and the energy efficiency, the performance of the battery during the charge-discharge process can be comprehensively analyzed, and the internal resistance value can be recorded, providing basic data for subsequent evaluation of the formation of the SEI film.

[0090] Example 2

[0091] Assume that Sample2 with the highest comprehensive score has been selected as the electrolyte and is used to assemble the battery. Next, the first charge-discharge cycle test will be carried out:

[0092] Assemble the battery and label it as a test sample:

[0093] Use Sample2 as the electrolyte, assemble the battery, and label it as a test sample.

[0094] First charging cycle: Set the charging current Ic = 2A and the cut-off voltage Vc = 4.2V. The charging time is t = 2h.

[0095] Calculate the charging capacity Q:

[0096] Q = Ic * t;

[0097] Q = 2A * 2h;

[0098] Q = 4Ah;

[0099] First discharge cycle: Set the discharge current Id = 1 A and the cut-off voltage Vd = 3.0 V. The discharge time is td = 4 h.

[0100] Calculate the energy efficiency E:

[0101] E = (Id * td) / Q;

[0102] E = (1 A * 4 h) / 4 Ah;

[0103] E = 1;

[0104] Performance analysis and internal resistance recording: Combine the charging capacity Q = 4 Ah and the energy efficiency E = 1 to analyze the performance of the test sample during charge and discharge. During charge and discharge, record the internal resistance value Ri. Assume that the measured internal resistance value is 0.1 Ω.

[0105] Through the above steps, the performance of the battery during the first charge and discharge cycle can be systematically evaluated, providing important reference data for subsequent optimization of the electrolyte formula and charging strategy.

[0106] III. Evaluate the formation of the SEI film based on the above data and confirm the thickness change trend; specifically including:

[0107] Based on the internal resistance value Ri of the test sample during charge and discharge, establish a relationship table between the internal resistance and the number of cycles, and mark the change in internal resistance after each cycle; by recording the internal resistance value after each charge and discharge cycle, the performance change of the battery during multiple cycles can be systematically tracked, especially the formation and thickening of the SEI film. This provides basic data for subsequent analysis.

[0108] Analyze the data in the relationship table. Through the formula Rt = R0 + k * N, where Rt is the internal resistance value after the Nth cycle, R0 is the initial internal resistance value, and k is a constant, calculate the proportion of the increase in internal resistance after each cycle; using the formula Rt = R0 + k * N to calculate the proportion of the increase in internal resistance after each cycle can quantify the change trend of the internal resistance with the number of cycles, thereby evaluating the impact of the thickening of the SEI film on the battery performance.

[0109] Using the above proportion combined with the experimental observation data, draw a trend chart of the internal resistance change with the number of cycles, identify the key interval of the SEI film thickening, and record the characteristic parameters of the interval; recording these characteristic parameters helps to optimize the electrolyte formula and charging strategy in the future.

[0110] Based on the trend graph and characteristic parameters, an estimation formula for the change of SEI film thickness with the number of cycles is derived as Df = D0 + c*(Rt - R0), where Df is the SEI film thickness, D0 is the initial thickness, and c is the conversion coefficient, which is used to predict the thickening trend of the SEI film in subsequent cycles. This formula is used to estimate the trend of SEI film thickness change with the internal resistance, and c reflects the relationship between the internal resistance change and the SEI film thickness change.

[0111] Example 3

[0112] Assume that the first charge-discharge cycle has been completed and the following data has been recorded:

[0113]

[0114]

[0115] Set the initial internal resistance value R0 = 0.1 Ω and the constant k = 0.02 Ω / cycle.

[0116] Establish a relationship table between the internal resistance and the number of cycles:

[0117] Record the internal resistance values after each charge-discharge cycle as shown in the above table.

[0118] Analyze the change of the internal resistance and calculate the proportion of the internal resistance increase after each cycle: Use the formula Rt = R0 + k*N to calculate the internal resistance value after each cycle:

[0119] The 1st cycle: Rt = 0.1 + 0.02*1 = 0.12 Ω;

[0120] The 2nd cycle: Rt = 0.1 + 0.02*2 = 0.14 Ω;

[0121] The 3rd cycle: Rt = 0.1 + 0.02*3 = 0.16 Ω;

[0122] The 4th cycle: Rt = 0.1 + 0.02*4 = 0.18 Ω;

[0123] The 5th cycle: Rt = 0.1 + 0.02*5 = 0.20 Ω;

[0124] Draw a trend graph of the internal resistance change with the number of cycles: Draw a graph with the number of cycles N on the horizontal axis and the internal resistance value Rt on the vertical axis. It is observed that the internal resistance value increases linearly with the number of cycles. Identify the key interval for the thickening of the SEI film. For example, between the 3rd cycle and the 5th cycle, the internal resistance increases significantly.

[0125] Derive an estimation formula for the change of SEI film thickness with the number of cycles:

[0126] Assume that the initial SEI film thickness D0 = 5 nm and the conversion coefficient c = 10 nm / Ω.

[0127] Calculate the SEI film thickness using the formula Df = D0 + c*(Rt - R0):

[0128] For the first cycle: Df = 5 + 10*(0.12 - 0.1) = 5 + 10*0.02 = 5.2 nm;

[0129] For the second cycle: Df = 5 + 10*(0.14 - 0.1) = 5 + 10*0.04 = 5.4 nm;

[0130] For the third cycle: Df = 5 + 10*(0.16 - 0.1) = 5 + 10*0.06 = 5.6 nm;

[0131] For the fourth cycle: Df = 5 + 10*(0.18 - 0.1) = 5 + 10*0.08 = 5.8 nm;

[0132] For the fifth cycle: Df = 5 + 10*(0.20 - 0.1) = 5 + 10*0.10 = 6.0 nm;

[0133] Through the above steps, the formation and thickening trend of the SEI film can be systematically evaluated, providing important reference data for optimizing the cycle life of lithium batteries.

[0134] IV. Adjust the proportion of electrolyte additives using the said trend to reduce the decomposition tendency; specifically including:

[0135] Based on the estimation formula Df = D0 + c*(Rt - R0) for the change of the SEI film thickness with the number of cycles, calculate the thickening speed Vs of the SEI film under the current electrolyte formula, where Vs = (Df - D0) / N and N is the number of cycles; by calculating the thickening speed of the SEI film, the influence of the electrolyte formula on the thickening of the SEI film can be quantified, thereby identifying the key points that need to be optimized.

[0136] According to the said speed Vs and the internal resistance increase ratio, determine the main factors causing the rapid thickening of the SEI film, and mark the electrolyte component X corresponding to the main factors; by analyzing the thickening speed of the SEI film and the internal resistance increase ratio, the main factors causing the rapid thickening of the SEI film can be determined, and the electrolyte components can be adjusted accordingly to slow down the thickening trend of the SEI film.

[0137] For the said electrolyte component X, calculate the amount of additive to be added or reduced to slow down the thickening trend of the SEI film through the formula P = P0 - a*Vs, where P is the adjusted additive proportion, P0 is the original additive proportion, and a is the adjustment coefficient; by using the formula to calculate the adjusted additive proportion, the electrolyte formula can be systematically adjusted to optimize its performance, thereby effectively controlling the thickening speed of the SEI film.

[0138] According to the adjusted additive ratio P, reconfigure the electrolyte and apply it to the battery for verification testing. Record the new internal resistance value Rt' and cycling performance data to evaluate whether the thickening of the SEI film is effectively controlled. By reconfiguring the electrolyte and conducting verification testing, the effectiveness of the optimized electrolyte formulation in controlling the thickening of the SEI film can be evaluated, providing experimental data support for further optimization.

[0139] Example 4

[0140] Assume that multiple charge-discharge cycles have been completed and the following data have been recorded:

[0141]

[0142]

[0143] Set the initial SEI film thickness D0 = 5 nm, conversion coefficient c = 10 nm / Ω, number of cycles N = 5, initial additive ratio P0 = 0.05, and adjustment coefficient a = 0.01.

[0144] Calculate the SEI film thickening rate Vs:

[0145] Use the formula Vs = (Df - D0) / N to calculate the SEI film thickening rate: Vs = (6.0 - 5) / 5 = 0.2 nm / cycle;

[0146] Determine the main factors causing the rapid thickening of the SEI film:

[0147] Combining the Vs value and the internal resistance increase ratio, assume that a certain specific electrolyte component X (such as a certain organic solvent) is found to be the main factor causing the rapid thickening of the SEI film.

[0148] Adjust the electrolyte additive ratio:

[0149] Use the formula P = P0 - a*Vs to calculate the adjusted additive ratio:

[0150] P = 0.05 - 0.01*0.2 = 0.05 - 0.002 = 0.048;

[0151] Reconfigure the electrolyte and conduct verification testing:

[0152] According to the adjusted additive ratio P = 0.048, reconfigure the electrolyte and apply it to the battery for verification testing.

[0153] Record the new internal resistance value Rt' and cycling performance data:

[0154] The new internal resistance value Rt' (assumed to be measured after several cycles):

[0155] The first cycle: Rt' = 0.11 Ω;

[0156] The second cycle: Rt' = 0.125 Ω;

[0157] The third cycle: Rt' = 0.14 Ω;

[0158] The fourth cycle: Rt' = 0.155 Ω;

[0159] The fifth cycle: Rt' = 0.17 Ω;

[0160] Comparing the original internal resistance value with the new internal resistance value, it is observed that the growth trend of the internal resistance has slowed down, indicating that the thickening of the SEI film is effectively controlled.

[0161] V. Prepare a new electrolyte according to the adjusted proportion of the electrolyte additive and apply it to the battery, and monitor the change of the internal resistance; specifically including:

[0162] According to the adjusted additive proportion P, calculate the specific amounts of each component required. Use the formula M = V * C, where M represents the mass (g), V represents the volume (L), and C represents the concentration (g / L). This formula is used to calculate the specific mass of each component when preparing the electrolyte, and prepare all the components of the new electrolyte; by accurately calculating the mass of each component, ensure the accuracy of the new electrolyte formula, so as to provide reliable experimental conditions for subsequent experiments.

[0163] Mix the calculated specific amounts of each component to prepare the new electrolyte, and mark its formula parameters, including the adjusted additive proportion P and the mass M of each component; by mixing each component and marking the formula parameters, ensure that the preparation process of the electrolyte is traceable and repeatable, which is convenient for subsequent analysis and optimization.

[0164] Reassemble the battery with the new electrolyte, ensure that the initial state of the battery is the same as that in the previous test, and record the initial internal resistance value Ri of the battery; by reassembling the battery and recording the initial internal resistance value, ensure the consistency of the experimental conditions and provide reference data for subsequent monitoring of the internal resistance change.

[0165] Conduct charge and discharge cycle tests on the reassembled battery under standard conditions. Use the formula Rn = (Rt' - Ri) / N, where Rn represents the increase in internal resistance after each cycle (Ω), Rt' represents the internal resistance value after the Nth cycle (Ω), Ri represents the initial internal resistance value (Ω), and N represents the number of cycles. This formula is used to calculate the change trend of the internal resistance after each cycle. Continuously monitor and record the change of the internal resistance of the battery in multiple cycle periods.

[0166] Example 5

[0167] Step 1: Calculate the specific amounts of each component required

[0168] Suppose it is necessary to prepare 1 liter (V = 1L) of a new electrolyte solution, in which the concentration of a certain component is 50 g / L (C = 50 g / L).

[0169] Use the formula: M = V * C;

[0170] Substitute the values: M = 1L * 50 g / L = 50 g;

[0171] Therefore, 50 grams of this component need to be weighed out.

[0172] Step 2: Prepare the new electrolyte solution and mark the formulation parameters

[0173] Suppose the new electrolyte solution contains the following components:

[0174] Component A: 50 g;

[0175] Component B: 30 g;

[0176] Component C: 20 g;

[0177] Mark the formulation parameters:

[0178] The adjusted additive ratio P = 0.048;

[0179] The mass of each component: Component A 50 g, Component B 30 g, Component C 20 g;

[0180] Step 3: Reassemble the battery and record the initial internal resistance value

[0181] Reassemble the battery, ensure that the initial state is the same as that of the previous test, and record the initial internal resistance value Ri = 0.1 Ohm.

[0182] Step 4: Charge-discharge cycle test and monitoring of internal resistance change:

[0183] Suppose 5 charge-discharge cycles are carried out, and record the internal resistance values after each cycle as follows:

[0184] Cycle number N Internal resistance Rt' (Ohm)

[0185]

[0186]

[0187] Use the formula to calculate the internal resistance increase amount Rn after each cycle:

[0188] For the first cycle:

[0189] Rn = (Rt' - Ri) / N;

[0190] Rn = (0.11 - 0.1) / 1 = 0.01 Ohm;

[0191] For the second cycle:

[0192] Rn = (0.125 - 0.1) / 2 = 0.025 / 2 = 0.0125 Ohm;

[0193] For the third cycle:

[0194] Rn = (0.14 - 0.1) / 3 = 0.04 / 3 = 0.0133 Ohm;

[0195] For the fourth cycle:

[0196] Rn = (0.155 - 0.1) / 4 = 0.055 / 4 = 0.01375 Ohm;

[0197] For the fifth cycle:

[0198] Rn = (0.17 - 0.1) / 5 = 0.07 / 5 = 0.014 Ohm;

[0199] Through the above steps, a new electrolyte can be systematically prepared and the change in the internal resistance of the battery during multiple cycles can be monitored, the influence of the SEI film thickening can be evaluated, providing a scientific basis for optimizing the cycle life of lithium batteries.

[0200] VI. Based on the change in the internal resistance, adjust the charging strategy to stabilize the cycle performance; specifically including:

[0201] Analyze the data of the change in the internal resistance Rn of the reassembled battery during multiple charge-discharge cycles. Through the formula D_Rn = Rn_max - Rn_min, where D_Rn represents the range of change in the internal resistance (Ω), Rn_max represents the maximum increase in the internal resistance (Ω), and Rn_min represents the minimum increase in the internal resistance (Ω). This formula is used to quantify the range of change in the internal resistance and help identify the main intervals of internal resistance fluctuations;

[0202] Based on the internal resistance fluctuation interval, calculate the optimal charging rate Cr for each charging process using the formula Cr = k / D_Rn, where k is a constant; Cr represents the optimal charging rate (A / s), k is a constant, and D_Rn represents the range of change in the internal resistance (Ω). This formula is used to calculate the optimal charging rate according to the range of change in the internal resistance, ensuring that the charging rate is inversely proportional to the internal resistance fluctuation to reduce the impact on the SEI film.

[0203] According to the optimal charging rate Cr, a new charging strategy is designed, including the charging current I and the charging time t. Using the formula I = Cr * Q, where Q is the battery capacity, the specific value of the charging current is determined, and the charging cut-off condition is set; this formula is used to calculate the specific value of the charging current to ensure that the charging process is both efficient and safe. By designing a new charging strategy, the charging current and charging time can be optimized to further stabilize the battery's cycle performance.

[0204] Apply the new charging strategy to conduct multiple charge-discharge cycle tests on the reassembled battery, record the internal resistance value Rt” after each cycle, and compare it with the initial internal resistance value Ri to evaluate the impact of the charging strategy on the stability of the battery's cycle performance. Through multiple charge-discharge cycle tests, verify the effectiveness of the new charging strategy, evaluate its impact on the stability of the battery's cycle performance, and provide experimental data support for further optimization.

[0205] Example 6

[0206] Assume that the internal resistance change data of the reassembled battery during multiple charge-discharge cycles has been recorded as follows:

[0207]

[0208]

[0209] The initial internal resistance value Ri = 0.1 Ω, and assume the constant k = 0.05.

[0210] Step 1: Calculate the internal resistance change range:

[0211] First, determine the maximum internal resistance increase Rnmax = 0.014 Ω and the minimum internal resistance increase Rnmin = 0.01 Ω.

[0212] Use the formula: D_Rn = Rn_max - Rn_min;

[0213] Substitute the values: D_Rn = 0.014 - 0.01 = 0.004 Ω;

[0214] Therefore, the internal resistance change range DRn = 0.004 Ω.

[0215] Step 2: Calculate the optimal charging rate Cr:

[0216] Use the formula: Cr = k / D_Rn;

[0217] Substitute the values: Cr = 0.05 / 0.004 = 12.5 A / s;

[0218] Therefore, the optimal charging rate Cr = 12.5 A / s.

[0219] Step 3: Design a new charging strategy

[0220] Assume the battery capacity Q = 4 Ah, and calculate the charging current using the formula: I = Cr * Q;

[0221] Substitute the values: I = 12.5 * 4 = 50 A;

[0222] Therefore, the charging current I = 50 A. Set the charging cut-off conditions, for example, reaching the preset voltage Vc = 4.2 V or the cumulative charging time t = 2 h.

[0223] Step Four: Apply the new charging strategy to conduct multiple charge-discharge cycle tests:

[0224] Assume that 5 charge-discharge cycles are conducted, and record the internal resistance values after each cycle as follows:

[0225]

[0226] Comparing with the initial internal resistance value Ri = 0.1 Ω, it can be seen that the growth of the internal resistance value after each cycle is relatively stable, indicating that the new charging strategy effectively controls the growth of the battery's internal resistance and improves the cycle performance of the battery.

[0227] VII. Conduct multiple cycle tests using the described charging strategy to verify the control effect of SEI film thickening; specifically including:

[0228] Use the new charging strategy to conduct multiple charge-discharge cycle tests on the re-assembled battery. Set the number of cycles for each round as Nc, record the internal resistance value Rt” after each cycle, and calculate the average internal resistance R_avg = (Rt”_1 + Rt”_2 +... + Rt”_Nc) / Nc at the end of each round; R_avg represents the average internal resistance (Ω) at the end of each round, Rt”_i represents the internal resistance value (Ω) after the i-th cycle, and Nc represents the number of cycles for each round. This formula is used to calculate the average internal resistance at the end of each round. Through multiple charge-discharge cycle tests, record the internal resistance value after each cycle and calculate the average internal resistance at the end of each round to quantify the performance changes of the battery during multiple cycles.

[0229] Based on the average internal resistance R_avg and the initial internal resistance value Ri, through the formula D_R = R_avg - Ri, where D_R is the increase in internal resistance after each round, evaluate the thickening situation of the SEI film and mark the D_R values for each round; D_R represents the increase in internal resistance after each round (Ω), R_avg represents the average internal resistance (Ω) at the end of each round, and Ri represents the initial internal resistance value (Ω). This formula is used to calculate the increase in internal resistance after each round.

[0230] Use the D_R value to plot a trend graph of the internal resistance changing with the number of cycles. Determine the changing trend of the SEI film thickening rate through the formula S = (D_R_max - D_R_min) / Nc, where S is the slope of the internal resistance increase trend, D_R_max represents the maximum internal resistance increase (Ω), D_R_min represents the minimum internal resistance increase (Ω), and Nc represents the number of cycles per round. This formula is used to calculate the slope of the internal resistance increase trend.

[0231] According to the slope S and the trend graph, analyze the control effect of the charging strategy on the SEI film thickening. If S is less than the preset threshold T, confirm that the charging strategy is effective and record the optimized charging parameters, including the charging current I and the charging time t. By analyzing the slope S and the trend graph, the control effect of the charging strategy on the SEI film thickening can be evaluated, providing a basis for subsequent optimization.

[0232] Example 7

[0233] Suppose five rounds of cyclic tests are carried out, with the number of cycles per round being 5 times. Record the internal resistance values at the end of each round of cycle as follows:

[0234] Round Internal resistance value (Ω) at the end of each cycle 1 0.115 2 0.12 3 0.125 4 0.13 5 0.135

[0235] Calculate the average internal resistance at the end of each round of cycle:

[0236] For the first round:

[0237] R_avg_1 = (0.105 + 0.11 + 0.115 + 0.12 + 0.125) / 5 = 0.115Ω;

[0238] For the second round:

[0239] R_avg_2 = (0.11 + 0.115 + 0.12 + 0.125 + 0.13) / 5 = 0.12Ω;

[0240] For the third round:

[0241] R_avg_3 = (0.115 + 0.12 + 0.125 + 0.13 + 0.135) / 5 = 0.125Ω;

[0242] For the fourth round:

[0243] R_avg_4 = (0.12 + 0.125 + 0.13 + 0.135 + 0.14) / 5 = 0.13Ω;

[0244] For the fifth round:

[0245] R_avg_5 = (0.125 + 0.13 + 0.135 + 0.14 + 0.145) / 5 = 0.135 Ω;

[0246] Calculate the increase in internal resistance after each cycle:

[0247] For the first cycle:

[0248] D_R_1 = R_avg_1 - Ri = 0.115 - 0.1 = 0.015 Ω;

[0249] For the second cycle:

[0250] D_R_2 = R_avg_2 - Ri = 0.12 - 0.1 = 0.02 Ω;

[0251] For the third cycle:

[0252] D_R_3 = R_avg_3 - Ri = 0.125 - 0.1 = 0.025 Ω;

[0253] For the fourth cycle:

[0254] D_R_4 = R_avg_4 - Ri = 0.13 - 0.1 = 0.03 Ω;

[0255] For the fifth cycle:

[0256] D_R_5 = R_avg_5 - Ri = 0.135 - 0.1 = 0.035 Ω;

[0257] Plot the trend graph of internal resistance versus the number of cycles and calculate the slope:

[0258] Use the formula to calculate the slope S: S = (D_R_max - D_R_min) / Nc;

[0259] Substitute the values: S = (0.035 - 0.015) / 5 = 0.004 Ω / cycle;

[0260] Analyze the control effect of the charging strategy on the thickening of the SEI film:

[0261] Assume the preset threshold T = 0.005 Ω / cycle T = 0.005 Ω / cycle. Since the calculated slope S = 0.004 Ω / cycle S = 0.004 Ω / cycle is less than the preset threshold TT, it is confirmed that the charging strategy is effective.

[0262] Record the optimized charging parameters, for example:

[0263] Charging current I = 50 A I = 50 A;

[0264] Charging time t = 2 h t = 2 h;

[0265] Through the above steps, the control effect of the charging strategy on the thickening of the SEI film can be systematically verified, and the cycle life of the lithium battery can be further optimized.

[0266] VIII. Summarize the test results, optimize the electrolyte and charging scheme to achieve an increase in cycle life; specifically including:

[0267] Summarize the data of the slope S and the increase in internal resistance ΔR. Through the formula L = 1 / (1 + S), where S represents the slope of the internal resistance increase trend (Ω / cycle). This formula is used to convert the internal resistance increase trend into a cycle life coefficient. The larger the value, the longer the battery cycle life. Evaluate the battery cycle life performance under each charging strategy and mark the L value corresponding to each group of data, which can quantify the impact of different charging strategies on the battery cycle life, so as to select the optimal charging strategy.

[0268] Based on the cycle life coefficient L and the initial internal resistance value Ri, calculate the estimated value of the actual cycle life of the battery under each charging strategy N_est = L * N_max, where N_est represents the estimated value of the actual cycle life, L represents the cycle life coefficient, and N_max represents the theoretical maximum number of cycles. This formula is used to calculate the estimated value of the actual cycle life according to the cycle life coefficient.

[0269] Combined with the optimal charging strategy and the corresponding N_est value, adjust the proportion P of the electrolyte components. Through the formula P_new = P_old + b * (N_est - N_old), reconfigure the electrolyte; P_new represents the proportion of the new electrolyte additive, P_old represents the proportion of the old electrolyte additive, b is the adjustment coefficient, N_est represents the new estimated cycle life, and N_old represents the original estimated cycle life. This formula is used to adjust the proportion of the electrolyte additive according to the new estimated cycle life.

[0270] Use the new electrolyte and the optimized charging strategy to conduct a new round of charge-discharge cycle test on the battery, record the internal resistance value Rt''' after each cycle, and calculate the new average internal resistance R_avg' = (Rt'''_1 + Rt'''_2 +... + Rt'''_Nc) / Nc, and compare it with the original average internal resistance R_avg to verify the optimization effect. Through the new round of charge-discharge cycle test, verify the effect of the optimized electrolyte and charging strategy to ensure an increase in the battery cycle life.

[0271] Example 8

[0272] Assume that the data of the slope S and the increase in internal resistance ΔR under different charging strategies have been recorded as follows:

[0273] Charging strategy Slope S (Ω / cycle) Increase in internal resistance D_R (Ω) Strategy A 0.004 0.015 Strategy B 0.006 0.02 Strategy C 0.008 0.025

[0274] The initial internal resistance value Ri = 0.1Ω, and the theoretical maximum number of cycles Nmax = 1000 times.

[0275] Step 1: Calculate the cycle life coefficient L:

[0276] Use the formula: L = 1 / (1 + S);

[0277] For strategy A: LA = 1 / (1 + 0.004) = 0.996;

[0278] For strategy B: LB = 1 / (1 + 0.006) = 0.994;

[0279] For strategy C: LC = 1 / (1 + 0.008) = 0.992;

[0280] Step 2: Calculate the estimated value of the actual cycle life N_est:

[0281] Use the formula: N_est = L * N_max;

[0282] For strategy A: N_est_A = 0.996 * 1000 = 996;

[0283] For strategy B: N_est_B = 0.994 * 1000 = 994;

[0284] For strategy C: N_est_C = 0.992 * 1000 = 992;

[0285] Therefore, strategy A has the highest estimated value of the actual cycle life NestA = 996 times.

[0286] Step 3: Adjust the proportion P of the electrolyte composition:

[0287] Assume that the original proportion of the electrolyte additive Pold = 0.048, the adjustment coefficient b = 0.001, and the original estimated value of the cycle life Nold = 950 times.

[0288] Use the formula: P_new = P_old + b * (N_est - N_old);

[0289] For strategy A:

[0290] P_new_A = 0.048 + 0.001 * (996 - 950) = 0.048 + 0.001 * 46 = 0.048 + 0.046 = 0.094;

[0291] Therefore, the new proportion of the electrolyte additive PnewA = 0.094.

[0292] Step 4: Verify the optimization effect:

[0293] Use the new electrolyte and the optimized charging strategy A to conduct a new round of charge-discharge cycle tests on the battery, and record the internal resistance values after each cycle as follows:

[0294] Number of cycles N Internal resistance value Rt”' (Ω) 1 0.103 2 0.106 3 0.109 4 0.112 5 0.115

[0295] Calculate the new average internal resistance:

[0296] R_avg' = (0.103 + 0.106 + 0.109 + 0.112 + 0.115) / 5 = 0.109 Ω;

[0297] Assume that the original average internal resistance Ravg = 0.115 Ω. It can be seen that the new average internal resistance Ravg′ = 0.109 Ω is lower, indicating that the optimized electrolyte and charging strategy effectively control the growth of the battery's internal resistance and improve the battery's cycle life.

[0298] On the other hand, the present invention proposes a high-cycle-life lithium battery optimization system, as Figure 2 shown, including:

[0299] An electrolyte selection and analysis module for selecting an electrolyte and analyzing its composition to determine the initial state;

[0300] A preliminary battery performance evaluation module for performing the first charge-discharge cycle on the battery based on the initial state and recording data;

[0301] An SEI film formation evaluation module for evaluating the formation of the SEI film according to the data and confirming the thickness change trend;

[0302] An electrolyte optimization and adjustment module for adjusting the proportion of electrolyte additives using the trend to reduce the decomposition tendency;

[0303] A new electrolyte application and monitoring module for configuring a new electrolyte according to the adjusted proportion of electrolyte additives, applying it to the battery, and monitoring the change in internal resistance;

[0304] Charging strategy optimization for adjusting the charging strategy based on the change in internal resistance to stabilize the cycle performance;

[0305] A cycle test and verification module for performing multiple cycle tests using the charging strategy to verify the SEI film thickening control effect;

[0306] A final optimization and result summary module for summarizing the test results, optimizing the electrolyte and charging scheme, and achieving an improvement in cycle life.

[0307] In addition, each of the above modules is also used to implement other steps of the above-mentioned high-cycle-life lithium battery optimization method when executed, which will not be elaborated one by one here.

[0308] In summary, the present invention first selects a suitable electrolyte and analyzes its composition, and conducts the first charge and discharge cycle test to record key data; then evaluates the formation of the SEI film and confirms its thickness change trend, and adjusts the proportion of the electrolyte additive by using this trend to reduce the decomposition tendency; then configures a new electrolyte and applies it to the battery, and monitors the change of the internal resistance; adjusts the charging strategy based on the change of the internal resistance to stabilize the cycle performance, and verifies the control effect of the SEI film thickening through multiple cycle tests; finally summarizes the test results and further optimizes the electrolyte and the charging scheme. This method can accurately evaluate and effectively control the thickening trend of the SEI film, significantly reduce the increase of the battery internal resistance, and thus greatly improve the cycle life of the lithium battery.

[0309] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for optimizing a lithium battery with a long cycle life, characterized in that: The steps are as follows: Select the electrolyte and analyze its composition to determine the initial state; Based on the initial state, the battery is charged and discharged for the first time, data is recorded, and the formation of the SEI film is evaluated based on the data to confirm the thickness change trend; Using the trend, the ratio of electrolyte additives is adjusted to reduce the decomposition tendency, a new electrolyte is prepared according to the adjusted ratio of electrolyte additives, and applied to the battery to monitor the change of internal resistance; Based on the change in internal resistance, the charging strategy is adjusted to stabilize the cycle performance, and the charging strategy is used to perform multiple cycle tests to verify the SEI film thickening control effect; Summarize the test results, optimize the electrolyte and charging scheme, and achieve improved cycle life.

2. The method for optimizing a lithium battery with a long cycle life according to claim 1, characterized in that: The step of selecting an electrolyte and analyzing its components to determine an initial state includes: Prepare multiple candidate electrolyte samples and label each sample with its source and basic composition information; Measuring basic physical and chemical properties of each candidate electrolyte sample, including viscosity V and density D, and recording the measurement results in association with basic component information of the sample; Based on the measurement results, the comprehensive score of each sample was calculated by the formula Y = (A*D) + (B / V), where Y is the comprehensive score and A and B are constants, to evaluate its potential as a high cycle life lithium battery electrolyte; The sample with the highest comprehensive score is selected and subjected to a comprehensive component analysis, including trace element detection, to determine the exact composition of the sample as the initial state.

3. The method for optimizing a lithium battery with a long cycle life according to claim 2, characterized in that: Based on the initial state, the battery is charged and discharged for the first time and data is recorded, including: Using the sample with the highest comprehensive score as the electrolyte, assembling a battery, and marking the battery as a test sample; Perform the first charging cycle on the test sample, set the charging current Ic and the cut-off voltage Vc, and calculate and record the charging capacity during the charging process by the formula Q=Ic*t, where Q is the charging capacity and t is the charging time; After charging is completed, the test sample is immediately subjected to a discharge cycle, and the discharge current Id and the cut-off voltage Vd are set. According to the formula E=(Id*td) / Q, where E is the energy efficiency and td is the discharge time, the energy efficiency during the discharge process is calculated and recorded; Combined with the data of charging capacity and energy efficiency, the performance of the test sample during the charging and discharging process is analyzed, and the internal resistance value is recorded for subsequent steps to evaluate the SEI film formation.

4. The method for optimizing a lithium battery with a long cycle life according to claim 3, characterized in that: The step of evaluating the SEI film formation according to the data and confirming the thickness change trend includes: Based on the internal resistance value Ri of the test sample during the charge and discharge process, a relationship table between the internal resistance and the number of cycles is established, marking the change in internal resistance after each cycle; Analyze the data in the relationship table, and calculate the increase ratio of the internal resistance after each cycle by the formula Rt=R0+k*N, where Rt is the internal resistance value after the Nth cycle, R0 is the initial internal resistance value, and k is a constant; Using the ratio in combination with experimental observation data, a trend graph of internal resistance versus cycle number is drawn to identify a critical interval for SEI film thickening, and characteristic parameters of the interval are recorded; Based on the trend graph and characteristic parameters, the estimated formula for the change of SEI film thickness with the number of cycles was derived: Df=D0+c*(Rt-R0), where Df is the SEI film thickness, D0 is the initial thickness, and c is the conversion coefficient, which is used to predict the thickening trend of the SEI film in subsequent cycles.

5. The method for optimizing a lithium battery with a long cycle life according to claim 4, characterized in that: The method of utilizing the trend to adjust the electrolyte additive ratio and reduce the decomposition tendency includes: Based on the estimation formula Df=D0+c*(Rt-R0) of the SEI film thickness changing with the number of cycles, the SEI film thickening rate Vs under the current electrolyte formula is calculated, where Vs=(Df-D0) / N, N is the number of cycles; According to the speed Vs and the internal resistance increase ratio, determine the main factor causing the rapid thickening of the SEI film, and mark the electrolyte component X corresponding to the main factor; For the electrolyte component X, the amount of additives to be added or reduced is calculated by the formula P=P0-a*Vs, where P is the adjusted additive ratio, P0 is the original additive ratio, and a is the adjustment coefficient to slow down the SEI film thickening trend; According to the adjusted additive ratio P, the electrolyte is reconfigured and applied to the battery for verification testing. The new internal resistance value Rt' and cycle performance data are recorded to evaluate whether the SE I film thickening is effectively controlled.

6. The method for optimizing a lithium battery with a long cycle life according to claim 5, characterized in that: The new electrolyte is prepared according to the adjusted electrolyte additive ratio, and applied to the battery, and the internal resistance change is monitored, including: According to the adjusted additive ratio P, the specific amount of each component required is calculated, and all the components of the new electrolyte are prepared by the formula M=V*C, where M is mass, V is volume, and C is concentration; The new electrolyte is prepared by mixing the calculated specific amounts of the components, and its formula parameters are marked, including the adjusted additive ratio P and the mass M of each component; Reassemble the battery using new electrolyte, ensure that the initial state of the battery is consistent with the previous test, and record the initial internal resistance value Ri of the battery; The reassembled battery is subjected to charge and discharge cycle tests under standard conditions. The change in internal resistance of the battery over multiple cycles is continuously monitored and recorded using the formula Rn=(Rt'-R i) / N, where Rn is the increase in internal resistance after each cycle and N is the number of cycles.

7. A method for optimizing a lithium battery with a long cycle life according to claim 6, characterized in that: The step of adjusting the charging strategy based on the internal resistance change to stabilize the cycle performance includes: Analyze the internal resistance change data Rn of the reassembled battery in multiple charge and discharge cycles, and determine the main range of internal resistance fluctuation through the formula D_Rn=Rn_max-Rn_min, where D_Rn is the internal resistance change range, Rn_max is the maximum internal resistance increase, and Rn_min is the minimum internal resistance increase; Based on the internal resistance fluctuation range, the optimal charging rate Cr in each charging process is calculated using the formula Cr = k / D_Rn, where k is a constant; According to the optimal charging rate Cr, a new charging strategy is designed, including the charging current I and the charging time t, using the formula I=Cr*Q, where Q is the battery capacity, to determine the specific value of the charging current and set the charging cut-off condition; The new charging strategy is applied to the reassembled battery to perform multiple charge and discharge cycle tests, the internal resistance value Rt" after each cycle is recorded, and compared with the initial internal resistance value Ri, to evaluate the effect of the charging strategy on the stability of the battery cycle performance.

8. The method for optimizing a lithium battery with a long cycle life according to claim 7, characterized in that: The charging strategy is used to perform multiple cycle tests to verify the SEI film thickening control effect, including: Use the new charging strategy to perform multiple charge and discharge cycle tests on the reassembled battery, set the number of cycles per cycle to Nc, record the internal resistance value Rt” after each cycle, and calculate the average internal resistance R_avg = (Rt”_1+Rt”_2+...+Rt”_Nc) / Nc at the end of each cycle; Based on the average internal resistance R_avg and the initial internal resistance value Ri, the SEI film thickening is evaluated by the formula D_R=R_avg-Ri, where D_R is the increase in internal resistance after each cycle, and the D_R value of each cycle is marked; The D_R value is used to draw a trend graph of the change of internal resistance with the number of cycles, and the change trend of the SEI film thickening rate is determined by the formula S = (D_R_max-D_R_min) / Nc, where S is the slope of the internal resistance increase trend; According to the slope S and the trend graph, the control effect of the charging strategy on the SEI film thickening is analyzed. If S is less than the preset threshold T, the charging strategy is confirmed to be effective, and the optimized charging parameters are recorded, including the charging current I and the charging time t.

9. The method for optimizing a lithium battery with a long cycle life according to claim 8, characterized in that: The test results are summarized to optimize the electrolyte and charging scheme to achieve improved cycle life, including: Summarize the data of slope S and internal resistance increase D_R, and evaluate the battery cycle life performance under each charging strategy through the formula L=1 / (1+S), where L is the cycle life coefficient, and mark the L value corresponding to each group of data; Based on the cycle life coefficient L and the initial internal resistance value Ri, the actual cycle life estimate N_est = L*N_max of the battery under each charging strategy is calculated, where N_max is the theoretical maximum number of cycles, and the N_est value corresponding to the optimal charging strategy is determined; Combined with the optimal charging strategy and the corresponding N_est value, adjust the electrolyte composition ratio P, and reconfigure the electrolyte through the formula P_new=P_old+b*(N_est-N_old), where P_new is the new electrolyte additive ratio, P_old is the old electrolyte additive ratio, b is the adjustment coefficient, and N_old is the original cycle life estimate; Use the new electrolyte and the optimized charging strategy to carry out a new round of charge and discharge cycle test on the battery, record the internal resistance value Rt"' after each cycle, and calculate the new average internal resistance R_avg'=(Rt"'_1+Rt"'_2+...+Rt"'_Nc) / Nc, and compare it with the original average internal resistance R_avg to verify the optimization effect.

10. A high cycle life lithium battery optimization system for implementing the method according to any one of claims 1 to 9, characterized in that: include: The electrolyte selection and analysis module is used to select the electrolyte and analyze its composition to determine the initial state; A battery performance preliminary evaluation module, used to perform an initial charge and discharge cycle on the battery based on the initial state and record data; An SEI film formation evaluation module is used to evaluate the SEI film formation according to the data and confirm the thickness change trend; An electrolyte optimization and adjustment module, used to adjust the electrolyte additive ratio using the trend to reduce the decomposition tendency; A new electrolyte application and monitoring module is used to configure a new electrolyte according to the adjusted electrolyte additive ratio, apply it to the battery, and monitor the change of internal resistance; Charging strategy optimization, for adjusting the charging strategy to stabilize the cycle performance based on the internal resistance change; A cycle test and verification module, used to perform multiple cycle tests using the charging strategy to verify the SEI film thickening control effect; The final optimization and result summary module is used to summarize the test results, optimize the electrolyte and charging scheme, and achieve improved cycle life.

Images