Design evaluation method of lithium ion battery

Abstract

The invention discloses a design evaluation method of a lithium ion battery, and belongs to the technical field of lithium ion batteries. Comprising the steps of determining pole piece design parameters; calculating a material characteristic coefficient according to the material system; calculating a tab position factor according to the tab position coordinates; testing the resistance of the diaphragm; calculating an evaluation coefficient; and performing multi-stage evaluation judgment and outputting optimization suggestions. According to the method, the geometric dimension of the pole piece, the resistance of the diaphragm, the material characteristics, the tab design and the tab position are comprehensively considered, the battery design scheme is comprehensively and quantitatively evaluated, whether the design scheme meets the energy efficiency requirement or not can be quickly judged, the development period is effectively shortened, and the development cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a design and evaluation method for lithium-ion batteries. Background Technology

[0002] The strong demand for energy storage batteries in recent years has driven rapid iteration and upgrading. From 280Ah to 314Ah, the energy of a single battery cell has exceeded 1000Wh. Looking at the development trend, single-cell batteries with energy capacities above 1800Wh will gradually become mainstream. Between 2023 and 2025, several major lithium battery manufacturers successively released various models of energy storage cells, including 587Ah, 650Ah, and 648Ah. Batteries are being iterated almost annually, and energy storage cells are becoming increasingly larger, with energy densities exceeding 430Wh / L.

[0003] Large-capacity energy storage cells can only be designed with high areal density and high compaction density, but at the same time, the requirements for electrical performance, especially energy efficiency, are also higher, needing to ensure high energy efficiency while maintaining energy density. This poses a challenge to battery design and development: how to quickly evaluate whether the design scheme is reasonable and whether it meets key performance indicators, such as impedance and energy efficiency.

[0004] The impedance of a lithium-ion battery directly affects its charge-discharge capability, energy efficiency, and lifespan. Reducing battery impedance is key to improving overall battery performance. Lithium-ion battery impedance mainly includes ohmic impedance, diffusion impedance, and charge transfer impedance. Material selection, formulation design, and structural design all significantly influence these three impedances.

[0005] Existing methods for evaluating designs in the early stages of battery development have the following limitations: (1) Single evaluation parameters: Existing methods mainly consider the effects of electrode surface density and compaction density alone, or only consider whether the tab design meets the flow requirements, without comprehensively considering the electrode formulation design, electrode size, tab size and tab position, etc. (2) Lack of correlation with material properties: Existing evaluation methods do not consider the influence of differences in specific capacity and compaction density of different active materials on resistivity; (3) Ignore the influence of the tab position: The positional distribution of the tab along the length of the electrode has a significant impact on the current uniformity and temperature distribution, but existing methods lack a quantitative assessment of the tab position factor; (4) Lack of hierarchical guidance in evaluation results: Existing methods mostly use a single threshold for judgment, which cannot provide targeted optimization suggestions for design problems of different degrees. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a design evaluation method for lithium-ion batteries. By establishing a multi-parameter evaluation coefficient that comprehensively considers electrode formulation, electrode size, tab design, and tab position, and by introducing material characteristic coefficients and tab position factors, a comprehensive quantitative evaluation of battery design schemes is achieved. At the same time, a multi-level evaluation system is established to output corresponding optimization suggestions for different evaluation levels.

[0007] The technical solution of the present invention is as follows: A design evaluation method for lithium-ion batteries, comprising the following steps: S1: Determine the design parameters of the positive and negative electrodes according to the battery design objectives. The design parameters include electrode length, electrode width, tab width, tab thickness, number of tabs, and position coordinates of each tab along the length of the electrode. S2: Determine the material characteristic coefficients based on the material systems of the positive and negative electrodes; S3: Calculate the electrode position factor based on the electrode position coordinates; S4: Prepare positive and negative electrode samples, and use a four-probe resistance meter to test the film resistance of the positive electrode and the film resistance of the negative electrode. S5: Calculate the positive electrode design evaluation coefficient and the negative electrode design evaluation coefficient; S6: Multi-level evaluation and judgment based on evaluation coefficients; S7: Output optimization suggestions based on the results of multi-level evaluation.

[0008] In step S2: The material property coefficient K m Calculated using the following formula: K m =(Q0 / Q)×(ρ c / ρ0) 0.5 ; Where Q is the actual specific capacity of the active substance, and Q0 is the theoretical specific capacity of the active substance; ρ c ρ0 represents the actual compacted density of the electrode, while ρ0 represents the design baseline compacted density of the electrode. For lithium iron phosphate cathodes, Q0 = 170 mAh / g, ρ0 = 2.5 g / cm³. 3 ; For the artificial graphite anode, Q0 = 372 mAh / g, ρ0 = 1.55 g / cm³. 3 .

[0009] In step S3, the calculation of the electrode position factor P is as follows: P=1+α×σ x ; Where, σ x Let x be the position coordinates of each pole piece. iα is the position sensitivity coefficient relative to the normalized standard deviation of the electrode length L.

[0010] σ x The calculation is as follows: ; Where L is the electrode length, x i Let σ represent the position coordinates of each electrode tab along the length of the electrode plate, n be the number of electrodes, and x̄ be the average value of the normalized position coordinates of each electrode tab. When the electrodes are uniformly distributed, σ x As the value approaches 0, P approaches 1.

[0011] In step S5, the positive electrode design evaluation coefficient η is calculated according to the following formula. + and negative electrode design evaluation coefficient η - : η=[(L×D) 1.12 ×R 2 ×K m ] / [2W×S×n×P×10 4 ]; Where L is the electrode length, D is the electrode width, W is the tab width, S is the tab thickness, n is the number of tabs, and R is the diaphragm resistance.

[0012] In step S6, the multi-level evaluation determination based on the evaluation coefficients includes: For the positive electrode: Positive electrode design evaluation coefficient η + ≤4 is grade A: Excellent; 4 < positive electrode design evaluation coefficient η + ≤6 is classified as Grade B: Qualified, positive electrode design evaluation coefficient η + >6 is classified as Grade C: Optimization is needed.

[0013] Step S6, the multi-level evaluation determination based on the evaluation coefficients, also includes: For the negative electrode: Negative electrode design evaluation coefficient η - ≤0.01 is classified as Grade A: Excellent; 0.01 < negative electrode design evaluation coefficient η - ≤0.02 is classified as Grade B: Qualified, negative electrode design evaluation coefficient η - >0.02 is classified as Grade C: Optimization is required.

[0014] In step S7, When the positive electrode evaluation result is Grade C, optimization suggestions will be output in the following priority order: When the resistance R of the positive electrode film + When the resistance is >300mΩ, adjust the positive electrode formulation to reduce the film resistance; When W < 35mm, increase the tab width to 35~45mm; When n < 100, increase the number of electrodes to 100-120; When P > 1.05, optimize the uniformity of electrode position distribution.

[0015] In step S7, When the negative electrode evaluation result is Grade C, optimization suggestions are given in the following priority order: When the resistance R of the negative electrode film - When the resistance is >15mΩ, it is recommended to adjust the negative electrode formulation to reduce the film resistance; When W < 35mm, it is recommended to increase the tab width to 35~45mm; When n < 100, it is recommended to increase the number of electrodes to 100-120; When P > 1.05, optimize the uniformity of electrode position distribution.

[0016] It also includes a temperature correction step: S8: When the battery operating temperature T≠25℃, the evaluation coefficient η T Perform temperature correction: η T =η×[1+β×(T-25)]; Where β is the temperature coefficient.

[0017] In this invention, the "positive electrode design evaluation coefficient η" + "" refers to a dimensionless evaluation index that comprehensively reflects the influence of positive electrode area, film resistance, material properties, and tab design parameters on the positive electrode current conduction performance; "negative electrode design evaluation coefficient η" - The definition of "corresponds to this".

[0018] In this invention, the "pole position factor P" refers to the formula P=1+α×σ. x The calculated dimensionless coefficient is used to quantify the impact of tab distribution uniformity on battery performance. When the tabs are uniformly distributed along the length of the electrode, the normalized standard deviation σ is... x When the electrode distribution is uneven, σ approaches 0, and P approaches 1; when the electrode distribution is uneven, σ... x As the value increases, P>1. The closer the P value is to 1, the more uniform the electrode distribution, which is more beneficial to battery performance.

[0019] In this invention, "uniform distribution of electrode tabs" means that the electrode tab position factor P ≤ 1.05 (corresponding to σ). x ≤0.25).

[0020] The lithium-ion battery design evaluation method provided by this invention has the following beneficial effects: This invention establishes a system that simultaneously considers electrode geometry (L, D), diaphragm resistance (R), tab design (W, S, n), and material properties (K). mThe multi-parameter comprehensive evaluation system of the electrode position (P) and the electrode location overcomes the limitations of the single-parameter evaluation in the existing technology.

[0021] This invention uses K m The coefficient incorporates the actual specific capacity and compaction density of the active material into the evaluation system, enabling the evaluation results to reflect the impact of material performance on battery design.

[0022] This invention proposes a tab position factor P, which quantifies the uniformity of tab distribution and incorporates it into the evaluation formula, filling a gap in the prior art.

[0023] This invention categorizes evaluation results into three levels: A, B, and C, and provides specific optimization suggestions for level C designs, thereby improving the practicality and guidance of the evaluation method.

[0024] This invention provides a temperature correction formula, making the evaluation method applicable to battery design evaluation under different operating temperature conditions.

[0025] This invention has determined key parameters such as the formula exponent (1.12), position sensitivity coefficient (α), and temperature coefficient (β) through a large amount of experimental data, and provides clear technical basis.

[0026] This invention requires only the fabrication of a small number of electrode samples to test the film resistance, enabling a comprehensive evaluation of the battery design scheme. This effectively reduces the number of times the entire battery is fabricated and tested, lowers development costs, and shortens the development cycle. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] This invention provides a design evaluation method for lithium-ion batteries, comprising the following steps: S1: Determine the design parameters of the positive and negative electrodes based on the battery design objectives, including electrode length L, electrode width D, tab width W, tab thickness S, number of tabs n, and position coordinates x of each tab. i .

[0029] S2: Determine the material property coefficient K based on the material system. m : K m =(Q0 / Q)×(ρ c / ρ0) 0.5 ; Where Q is the actual specific capacity of the active substance, and Q0 is the theoretical specific capacity of the active substance; ρ cρ0 represents the actual compacted density of the electrode, while ρ0 represents the design baseline compacted density of the electrode. For lithium iron phosphate cathodes, Q0 = 170 mAh / g, ρ0 = 2.5 g / cm³. 3 ; For the artificial graphite anode, Q0 = 372 mAh / g, ρ0 = 1.55 g / cm³. 3 .

[0030] This coefficient reflects the degree of deviation between the actual and theoretical properties of the active material. When the specific capacity Q of the active material is close to the theoretical value Q0, and the compaction density ρ... c When K approaches the baseline value ρ0 m ≈1; When the material properties deviate significantly from the theoretical value, K m The corresponding increase in size places higher demands on the design.

[0031] S3: Calculate the electrode position factor P: P=1+α×σ x ; Where σ x σ represents the normalized standard deviation of the electrode positions, reflecting the uniformity of the electrode distribution. When the electrodes are uniformly distributed, σ x When the electrode distribution is uneven, σ approaches 0, and P approaches 1; when the electrode distribution is uneven, σ... x Increasing the value of P (>1) places higher demands on the design. α is the position sensitivity coefficient, calibrated experimentally.

[0032] in, ; Where L is the electrode length, x i Let be the position coordinates of each tab along the length of the electrode plate, n be the number of tabs, and x̄ be the average value of the normalized position coordinates of each tab.

[0033] S4: Prepare electrode samples and test the film resistance R.

[0034] S5: Calculate the overall evaluation coefficient: η=[(L×D) 1.12 ×R 2 ×K m ] / [2W×S×n×P×10 4 ]; Where n is the number of tabs; L is the length of the electrode (m); D is the width of the electrode (mm); W is the width of the tab (mm); S is the thickness of the tab (μm); and R is the film resistance (mΩ). When substituting the above units into the formula, a coefficient of 10 is used. 4 Ensure that the evaluation coefficient η is within a range that is easy to interpret. The evaluation formula provided by this invention is an engineering approximation model, and there is a certain fitting error between the calculated actual evaluation coefficient η and the measured energy efficiency. Based on validation tests using 30 sets of samples, the model prediction accuracy is within ±15%, r 2 =0.956. The η values ​​given in each embodiment are correction values ​​based on measured data, taking into account the influence of factors such as material batch differences and process fluctuations.

[0035] The coefficients of the formula are determined based on the following: R 2 The contribution of the film resistance to the total battery impedance is proportional to the square of the current path length. Based on Ohm's law and the current distribution characteristics within the electrode surface, using the square term of resistance more accurately reflects the impact of resistance on overall performance. Through testing 30 groups of different film resistance samples, R was confirmed... 2 Correlation with energy efficiency (r) 2 =0.956) is better than R(r 2 =0.847).

[0036] Denominator coefficient 2: Considering that the battery adopts a double-sided coating process, both the front and back sides participate in current conduction at the same time, a coefficient of 2 is introduced into the denominator.

[0037] Coefficient 10 4 Used for dimensional balance and numerical adjustment to ensure that the evaluation coefficient η is within a range that is easy to interpret.

[0038] S6: Multi-level evaluation and judgment: The evaluation results are divided into three levels: A (excellent), B (qualified), and C (needs optimization).

[0039] For the positive electrode: Positive electrode design evaluation coefficient η + ≤4 is grade A: Excellent; 4 < positive electrode design evaluation coefficient η + ≤6 is classified as Grade B: Qualified, positive electrode design evaluation coefficient η + >6 is classified as Grade C: Optimization is needed.

[0040] For the negative electrode: Negative electrode design evaluation coefficient η - ≤0.01 is classified as Grade A: Excellent; 0.01 < negative electrode design evaluation coefficient η - ≤0.02 is classified as Grade B: Qualified, negative electrode design evaluation coefficient η - >0.02 is classified as Grade C: Optimization is required.

[0041] S7: When the evaluation is grade C, output targeted optimization suggestions based on the contribution of each parameter.

[0042] When the positive electrode evaluation result is Grade C, optimization suggestions will be output in the following priority order: When R +When the resistance is >300mΩ, adjust the positive electrode formulation to reduce the film resistance; When W < 35mm, increase the tab width to 35~45mm; When n < 100, increase the number of electrodes to 100-120; When P > 1.05, optimize the uniformity of electrode position distribution; When the negative electrode evaluation result is Grade C, optimization suggestions are given in the following priority order: When R - When the resistance is >15mΩ, it is recommended to adjust the negative electrode formulation to reduce the film resistance; When W < 35mm, it is recommended to increase the tab width to 35~45mm; When n < 100, it is recommended to increase the number of electrodes to 100-120; When P > 1.05, optimize the uniformity of electrode position distribution.

[0043] S8: When the battery operating temperature T≠25℃, the evaluation coefficient η T Perform temperature correction: η T =η×[1+β×(T-25)]; Where β is the temperature coefficient.

[0044] The lithium-ion battery of the present invention includes a positive electrode, a negative electrode, a separator, and tabs; The positive electrode sheet comprises lithium iron phosphate as the positive electrode active material, SP as the conductive agent, and PVDF as the binder, with a mass ratio of (96.7~96.8):(1.2~1.5):(1.8~2.0); the coating surface density of the positive electrode sheet is 380~390 g / m³. 2 The compacted density is 2.53~2.55 g / cm³. 3 The diaphragm resistance is 260~280mΩ; The negative electrode sheet comprises graphite as the negative electrode active material, SP as the conductive agent, CMC as the thickener, and SBR as the binder, in a mass ratio of 96.2:1:1.2:1.6; the surface density of the negative electrode sheet coating is 188 g / m³. 2 The compacted density is 1.56 g / cm³. 3 The diaphragm resistance is 8mΩ; The tabs are 35-40mm wide, number 100-110, and 13μm thick, and are evenly distributed along the length of the electrode sheet. The uniformity coefficient of the tab position is P≤1.05. The lithium-ion battery adopts a winding process and has a double-row tab structure.

[0045] Positive electrode preparation method: Lithium iron phosphate (LFP), conductive agent SP, and binder PVDF are added to N-methylpyrrolidone (NMP) solvent in a set ratio for homogenization. The prepared slurry is coated onto aluminum foil current collector according to the designed areal density. After drying, it is rolled according to the designed compaction density to obtain the positive electrode.

[0046] Negative electrode preparation method: Artificial graphite (Gr), conductive agent SP, thickener CMC, and binder SBR are mixed in a set ratio and homogenized with deionized water as solvent. The prepared slurry is coated onto copper foil current collector according to the designed surface density. After drying, it is rolled according to the designed compaction density to obtain the negative electrode.

[0047] Material property coefficient K m calibration For lithium iron phosphate (LFP) cathode material systems: Theoretical specific capacity Q0 = 170 mAh / g, reference compaction density ρ0 = 2.5 g / cm³ 3 .

[0048] For artificial graphite anode material systems: Theoretical specific capacity Q0 = 372 mAh / g, reference compaction density ρ0 = 1.55 g / cm³ 3 . Calibration of the electrode position factor P Basis for determining multi-level evaluation standards By preparing battery samples with different η values, their energy efficiency was tested, and the correspondence between η and energy efficiency was established. Determination of the position sensitivity coefficient α By fitting simulation results with experimental data, the model prediction accuracy was compared under different values ​​of α (0.1, 0.15, 0.2, 0.25, 0.3). The results show that when α=0.2, the deviation between the model's predicted energy efficiency and the measured value is the smallest (error <2%), and the temperature rise prediction error is <1.5℃. Calibration of temperature coefficient β A constant temperature chamber was used to control the ambient temperature, and tests were conducted at five temperature points: 0℃, 10℃, 25℃, 35℃, and 45℃. After stabilizing at each temperature point for 2 hours, the electrode film resistance and the energy efficiency of the finished battery were measured. Each experiment was repeated 3 times, and the average value was taken.

[0049] Positive electrode temperature coefficient β + The determination Using 25℃ as the reference temperature, the change in resistance of the positive electrode film at different temperatures was tested, and the temperature coefficient was calculated. Based on the above experimental data, the positive electrode temperature coefficient β + The formula for calculating β is: + = (R T - R 25 ) / (R 25 ×ΔT). Based on data from various temperature points, the positive electrode temperature coefficient β + The value range is 0.008~0.012 / ℃, and the recommended value is 0.010 / ℃.

[0050] Negative electrode temperature coefficient β - The determination The same method was used to test the change in resistance of the negative electrode film with temperature. Based on the data from various temperature points, the negative electrode temperature coefficient β - The value range is 0.005~0.008 / ℃, with a recommended value of 0.006 / ℃. The temperature sensitivity of the negative electrode is lower than that of the positive electrode, mainly because the electronic conductivity of the graphite negative electrode is higher and less affected by temperature.

[0051] Temperature correction formula verification Using the temperature correction formula η T =η×[1+β×(T-25)] is used to correct the evaluation coefficient at different temperatures, and the results are compared with the measured energy efficiency for verification. The verification results show that the temperature correction formula can accurately reflect the impact of temperature on battery performance, with a prediction accuracy within ±0.5%, which meets the requirements of engineering applications.

[0052] Based on the above experimental study, the temperature coefficient values ​​are determined as follows: (1) Positive electrode temperature coefficient: β + = 0.008~0.012 / ℃, recommended value 0.010 / ℃; (2) Negative electrode temperature coefficient: β - = 0.005~0.008 / ℃, recommended value 0.006 / ℃.

[0053] The temperature correction formula applies to the operating temperature range of 0~45℃. If the temperature exceeds this range, it is recommended to recalibrate the temperature characteristics.

[0054] Example 1 Grade A design, increased electrode width and optimized formula. Positive electrode: LFP:SP:PVDF=96.7:1.5:1.8, coating surface density 388g / m² 2 The compacted density is 2.53 g / cm³. 3 The measured capacity Q = 160mAh / g, R + =260mΩ, K m + =1.069.

[0055] Negative electrode: Gr:SP:CMC:SBR=96.2:1:1.2:1.6, coating surface density 188g / m² 2 Compacted density 1.56 g / cm³ 3 The measured capacity Q = 355mAh / g, R - =8mΩ, K m - =1.052.

[0056] Design parameters: Positive electrode L=32000mm, D=190mm; tab width W=40mm, number n=100, thickness S=13μm, uniformly distributed, σ x =0.05, P=1.01.

[0057] Evaluation calculation: η + =3.89≤4, judged as Grade A.

[0058] Finished battery energy efficiency: 95.21%.

[0059] Example 2 Class B design, increasing electrode width Positive electrode: LFP:SP:PVDF=96.8:1.2:2.0, coating surface density 388g / m² 2 Compacted density 2.55 g / cm³ 3 The measured capacity Q = 158mAh / g, R + =280mΩ, K m + =1.086.

[0060] Negative electrode: Same as in Example 1.

[0061] Design parameters: Positive electrode L=32000mm, D=190mm; tab width W=40mm, number n=100, thickness S=13μm, uniformly distributed, P=1.01.

[0062] Evaluation calculation: η + =5.18, 4<η + ≤6, classified as Grade B.

[0063] Finished battery energy efficiency: 94.66%.

[0064] Example 3 Grade B design, increasing the number of electrodes. Positive electrode: LFP:SP:PVDF=96.8:1.2:2.0, coating surface density 388g / m² 2 Compacted density 2.55 g / cm³ 3 R + =280mΩ, K m + =1.086.

[0065] Negative electrode: Same as in Example 1.

[0066] Design parameters: Positive electrode L=32000mm, D=190mm; tab width W=35mm, number n=110, thickness S=13μm, uniformly distributed, P=1.01.

[0067] Evaluation calculation: η + =5.39, 4<η + ≤6, classified as Grade B.

[0068] Finished battery energy efficiency: 94.31%.

[0069] Example 4 Class B boundary design Positive electrode: LFP:SP:PVDF=96.8:1.2:2.0, coating surface density 388g / m² 2 Compacted density 2.55 g / cm³ 3 R + =280mΩ, K m + =1.086.

[0070] Negative electrode: Same as in Example 1.

[0071] Design parameters: Positive electrode L=32000mm, D=190mm; tab width W=38mm, number n=105, thickness S=13μm, uniformly distributed, P=1.01.

[0072] Evaluation calculation: η + =5.95, 4<η + ≤6, classified as Grade B (close to the boundary).

[0073] Finished battery energy efficiency: 94.05%.

[0074] Example 5 Negative electrode Class B design: Optimization of negative electrode film resistance Positive electrode: Same as in Example 1.

[0075] Negative electrode: Gr:SP:CMC:SBR=96.2:1:1.2:1.6, coating areal density 188g / m² 2 Compacted density 1.56 g / cm³ 3 The measured capacity Q = 355mAh / g, R - =8mΩ, K m - =1.052.

[0076] Design parameters: negative electrode L=32000mm, D=190mm, tab width W=40mm, quantity n=100, thickness S=13μm, uniform distribution, P=1.01.

[0077] Evaluation calculation: η - =0.0121, 0.01<η - If the value is ≤0.02, it is classified as Grade B.

[0078] Finished battery energy efficiency: charge / discharge efficiency 94.55%.

[0079] Example 6 Negative electrode Class A design: Comprehensive optimization Positive electrode: Same as in Example 1.

[0080] Negative electrode: Gr:SP:CMC:SBR=96.5:0.8:1.2:1.5, coating surface density 185g / m² 2 Compacted density 1.55 g / cm³ 3 The measured capacity Q = 360mAh / g, R - =6mΩ, K m - =1.034.

[0081] Design parameters: negative electrode L=32000mm, D=190mm, tab width W=45mm, quantity n=110, thickness S=13μm, uniform distribution, P=1.01.

[0082] Evaluation calculation: η - =0.0058, η - If the value is ≤0.01, it is classified as Grade A.

[0083] Finished battery energy efficiency: charge / discharge efficiency 95.62%.

[0084] Comparative Example 1 Class C design, η + Exceeding the standard Positive electrode: LFP:SP:PVDF=96.8:1.2:2.0, coating surface density 388g / m²2 Compacted density 2.55 g / cm³ 3 R + =280mΩ, K m + =1.086.

[0085] Negative electrode: Same as in Example 1.

[0086] Design parameters: Positive electrode L=32000mm, D=190mm; tab width W=35mm, number n=95, thickness S=13μm, uniformly distributed, P=1.01.

[0087] Evaluation calculation: η + =6.25>6, therefore it is classified as Grade C.

[0088] Optimization suggestion output: It is recommended to increase the tab width to 40mm or increase the number of tabs to 110.

[0089] Finished battery energy efficiency: 93.80%.

[0090] Comparative Example 2 Class C design, uneven electrode placement Positive electrode: LFP:SP:PVDF=96.8:1.2:2.0, coating surface density 388g / m² 2 Compacted density 2.55 g / cm³ 3 R + =280mΩ, Km + =1.086.

[0091] Negative electrode: Same as in Example 1.

[0092] Design parameters: Positive electrode L=32000mm, D=190mm; tab width W=40mm, number n=100, thickness S=13μm, unevenly distributed (concentrated at both ends of the electrode), σ x =0.35, P=1.07.

[0093] Evaluation calculation: η + =4.89, 4<η + ≤6, classified as Grade B.

[0094] However, the uneven distribution of the tabs led to excessively high local temperature rise (the maximum temperature rise was 16.2°C, which is significantly higher than the uniformly distributed 9.1°C in Example 2).

[0095] The actual energy efficiency was only 93.25%, lower than the expected level for Grade B.

[0096] This comparative example shows that even when the evaluation coefficient η is in the B-level range, uneven distribution of the tab position will still lead to a decrease in actual performance, verifying the important influence of the tab position factor P on battery performance.

[0097] Comparative Example 3 Negative electrode C-level design: diaphragm resistance too high Positive electrode: Same as in Example 1.

[0098] Negative electrode: Gr:SP:CMC:SBR=96.0:1.2:1.3:1.5, coating surface density 195g / m² 2 Compacted density 1.62 g / cm³ 3 (Over-compaction), measured capacity Q=340mAh / g, R - =18mΩ, K m - =1.115.

[0099] Design parameters: negative electrode L=32000mm, D=190mm, tab width W=40mm, quantity n=100, thickness S=13μm, uniform distribution, P=1.01.

[0100] Evaluation calculation: η - =0.0552, η - >0.02, classified as Grade C.

[0101] Optimization suggestion: R - =18mΩ>15mΩ, so it is recommended to first adjust the negative electrode formula to reduce the film resistance.

[0102] Finished battery energy efficiency: charge / discharge efficiency 92.15%.

[0103] Comparative Example 4 Negative electrode Class C design: Insufficient number of tabs Positive electrode: Same as in Example 1.

[0104] Negative electrode: Gr:SP:CMC:SBR=96.2:1:1.2:1.6, coating areal density 188g / m² 2 Compacted density 1.56 g / cm³ 3 The measured capacity Q = 355mAh / g, R - =8mΩ, K m - =1.052.

[0105] Design parameters: negative electrode L=32000mm, D=190mm, tab width W=35mm, quantity n=80 (insufficient quantity), thickness S=13μm, uniformly distributed, P=1.01.

[0106] Evaluation calculation: η - =0.0218, η - >0.02, classified as Grade C.

[0107] Optimization suggestion: R - =8mΩ≤15mΩ, W=35mm≥35mm, but n=80<100, it is recommended to increase the number of tabs to 100~120.

[0108] Finished battery energy efficiency: charge / discharge efficiency 93.42%.

[0109] Comparative Example 5 Negative electrode Class C design: Uneven electrode tab placement Positive electrode: Same as in Example 1.

[0110] Negative electrode: Gr:SP:CMC:SBR=96.2:1:1.2:1.6, coating areal density 188g / m² 2 Compacted density 1.56 g / cm³ 3 The measured capacity Q = 355mAh / g, R - =8mΩ, K m - =1.052.

[0111] Design parameters: Negative electrode L=32000mm, D=190mm, tab width W=40mm, number n=100, thickness S=13μm, tabs concentrated at both ends of the electrode, σ x =0.45, P=1.09.

[0112] Evaluation calculation: η - =0.0224, η - >0.02, classified as Grade C.

[0113] Optimization suggestion: R - =8mΩ≤15mΩ, W=40mm≥35mm, n=100≥100, but P=1.09>1.05 needs optimization. It is recommended to optimize the uniformity of the electrode position distribution so that the electrodes are evenly distributed along the length of the electrode sheet.

[0114] Finished battery energy efficiency: charge / discharge efficiency 93.08%.

[0115] The summary is as follows: Based on Example 2, the effects of the evaluation coefficient correction at different temperatures were tested as follows: The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Contents not described in detail in this specification belong to prior art known to those skilled in the art.

Claims

1. A design evaluation method for lithium-ion batteries, characterized in that, Includes the following steps: S1: Determine the design parameters of the positive and negative electrodes according to the battery design objectives. The design parameters include electrode length, electrode width, tab width, tab thickness, number of tabs, and position coordinates of each tab along the length of the electrode. S2: Determine the material characteristic coefficients based on the material systems of the positive and negative electrodes; S3: Calculate the electrode position factor based on the electrode position coordinates; S4: Prepare positive and negative electrode samples, and use a four-probe resistance meter to test the film resistance of the positive electrode and the film resistance of the negative electrode. S5: Calculate the positive electrode design evaluation coefficient and the negative electrode design evaluation coefficient; S6: Multi-level evaluation and judgment based on evaluation coefficients; S7: Output optimization suggestions based on the results of multi-level evaluation.

2. The design evaluation method for a lithium-ion battery according to claim 1, characterized in that, In step S2: The material property coefficient K m Calculated using the following formula: K m =(Q0 / Q)×(ρ c / p0) 0.5 ; Where Q is the actual specific capacity of the active substance, and Q0 is the theoretical specific capacity of the active substance; ρ c ρ is the actual compaction density of the electrode, and ρ0 is the design benchmark compaction density of the electrode.

3. The design evaluation method for a lithium-ion battery according to claim 2, characterized in that, In step S3, the calculation of the electrode position factor P is as follows: P=1+α×σ x ; Where, σ x Let x be the position coordinates of each pole piece. i α is the position sensitivity coefficient relative to the normalized standard deviation of the electrode length L.

4. The design evaluation method for a lithium-ion battery according to claim 3, characterized in that, σ x The calculation is as follows: ； Where L is the electrode length, x i Let σ represent the position coordinates of each electrode tab along the length of the electrode plate, n be the number of electrodes, and x̄ be the average value of the normalized position coordinates of each electrode tab. When the electrodes are uniformly distributed, σ x As the value approaches 0, P approaches 1.

5. The design evaluation method for a lithium-ion battery according to claim 4, characterized in that, In step S5, the positive electrode design evaluation coefficient η is calculated according to the following formula. + and negative electrode design evaluation coefficient η - : η=[(L×D) 1.12 ×R 2 ×K m ] / [2W×S×n×P×10 4 ]; Where L is the electrode length, D is the electrode width, W is the tab width, S is the tab thickness, n is the number of tabs, and R is the diaphragm resistance.

6. The design evaluation method for a lithium-ion battery according to claim 5, characterized in that, In step S6, the multi-level evaluation determination based on the evaluation coefficients includes: For the positive electrode: Positive electrode design evaluation coefficient η + ≤4 is grade A: Excellent; 4 < positive electrode design evaluation coefficient η + ≤6 is classified as Grade B: Qualified, positive electrode design evaluation coefficient η + >6 is classified as Grade C: Optimization is required.

7. The design evaluation method for a lithium-ion battery according to claim 5, characterized in that, Step S6, the multi-level evaluation determination based on the evaluation coefficients, also includes: For the negative electrode: Negative electrode design evaluation coefficient η - ≤0.01 is classified as Grade A: Excellent; 0.01 < negative electrode design evaluation coefficient η - ≤0.02 is classified as Grade B: Qualified, negative electrode design evaluation coefficient η - >0.02 is classified as Grade C: Optimization is required.

8. The design evaluation method for a lithium-ion battery according to claim 6, characterized in that, In step S7, When the positive electrode evaluation result is Grade C, optimization suggestions will be output in the following priority order: When R + When the resistance is >300mΩ, adjust the positive electrode formulation to reduce the film resistance; When W < 35mm, increase the tab width to 35~45mm; When n < 100, increase the number of electrodes to 100-120; When P > 1.05, optimize the uniformity of electrode position distribution.

9. The design evaluation method for a lithium-ion battery according to claim 7, characterized in that, In step S7, When the negative electrode evaluation result is Grade C, optimization suggestions are given in the following priority order: When R - When the resistance is >15mΩ, it is recommended to adjust the negative electrode formulation to reduce the film resistance; When W < 35mm, it is recommended to increase the tab width to 35~45mm; When n < 100, it is recommended to increase the number of electrodes to 100-120; When P > 1.05, optimize the uniformity of electrode position distribution.

10. The design evaluation method for a lithium-ion battery according to claim 1, characterized in that, It also includes a temperature correction step: S8: When the battery operating temperature T≠25℃, the evaluation coefficient η T Perform temperature correction: or T =η×[1+β×(T-25)]; Where β is the temperature coefficient.

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