A method of predicting lithium battery capacity retention

Abstract

The application belongs to the technical field of evaluating lithium ion battery performance, and particularly relates to a method for predicting lithium battery capacity retention rate. The method comprises the following steps: (1) fitting functions of lithium loss capacity in the negative electrode sheet of the lithium battery and cycle number and functions of electrolyte lithium loss capacity and cycle number; (2) fitting a function of total lithium loss capacity and cycle number; and (3) fitting a function of discharge capacity of the lithium battery in the cycle process and cycle number through the total capacity of lithium in the positive electrode sheet, the total loss capacity, the first circle calibration capacity and the second circle calibration capacity, and further obtaining a function of the lithium battery capacity retention rate and cycle number. The method predicts the lithium battery capacity retention rate based on active lithium loss, can detect the cycle life and health state of the lithium battery, shortens the battery development cycle and saves experimental cost, and meanwhile, the method for predicting the lithium battery capacity retention rate has high accuracy, and the predicted value has high consistency with the experimental value.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery performance evaluation technology, specifically relating to a method for predicting lithium battery capacity retention rate. Background Technology

[0002] Lithium-ion batteries have achieved significant breakthroughs since their commercialization in 1991 due to their advantages such as light weight, high energy density, and long cycle life. However, there are still many limitations to the application of lithium-ion batteries in electric vehicles, such as slow charging rates, rapid cycle life degradation, and thermal runaway. The goal in the lithium-ion battery field has always been to charge the battery to 80% SOC within 15 minutes. However, achieving fast charging, improving battery life, and enhancing safety requires ensuring high cycle stability and good capacity retention of the positive and negative electrode materials. Generally speaking, the cycle stability and capacity retention of lithium-ion batteries are closely related to the structural changes of the positive and negative electrode materials before and after lithium insertion / extraction. The more stable the structure during the lithium insertion / extraction process, the better the cycle stability and the higher the capacity retention of the lithium battery.

[0003] Currently, there are relatively many methods in the industry for evaluating the capacity retention rate of lithium-ion batteries. Generally, long-cycle testing is used to assess the cycle performance of positive / negative electrode materials and the capacity retention rate of lithium-ion batteries. This method is the most intuitive and accurate, but it is time-consuming and inefficient. Chinese patent document CN110658473A discloses a method for evaluating the storage performance of lithium-ion battery positive electrode materials, assessing capacity retention through the first discharge capacity ratio and further deriving the stability of the positive and negative electrode materials. Chinese patent document CN113884930A discloses a method for predicting the cycle life and health status of power batteries, using the equivalent coulombic average value of the first n cycles to predict the capacity retention rate after m cycles. These two methods are relatively quick and simple, but their accuracy is low, especially the method of assessing capacity retention rate through the first discharge capacity ratio, which yields results with a large deviation from reality. Meanwhile, many existing technologies use data-driven and artificial intelligence-based methods to predict the remaining life and capacity retention rate of lithium-ion batteries, such as machine learning, neural networks, and Kalman filtering. These methods rely on the amount and source of data, cannot reflect the degradation mechanism of lithium batteries, and suffer from low efficiency and large bias. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects in the prior art, such as large deviation between test results and actual results and low efficiency when predicting the capacity retention rate of lithium batteries, and thus provide a method for predicting the capacity retention rate of lithium batteries.

[0005] To this end, the present invention provides the following technical solution.

[0006] This invention provides a method for predicting the capacity retention rate of lithium batteries, comprising the following steps:

[0007] (1) Cyclic testing was performed on the lithium battery under test, and the lithium loss capacity M in the negative electrode of the lithium battery was obtained by fitting. loss M is a function of the number of cycles x loss =m(x), M loss This refers to the lithium capacity loss caused by the negative electrode after x cycles;

[0008] The lithium loss capacity N in the electrolyte of the lithium battery was obtained by fitting. loss N is a function of the number of cycles x loss =n(x), N loss This refers to the lithium capacity loss caused by the electrolyte after x cycles;

[0009] (2) The total lithium loss capacity Q is obtained by fitting the lithium loss capacity in the negative electrode and the lithium loss capacity in the electrolyte. loss Q is a function of the number of cycles x. loss = q1(x), where Q loss It is the total lithium capacity loss caused by the negative electrode and electrolyte after x cycles, denoted as the total loss capacity.

[0010] (3) The total capacity Q of lithium in the positive electrode total Total loss capacity Q loss The discharge capacity Q of the lithium battery during cycling is obtained by fitting the first cycle calibration capacity Q1 and the second cycle calibration capacity Q2. rete Q is a function of the number of cycles x. rete =q2(x), thus obtaining the function of lithium battery capacity retention rate δ and cycle number x;

[0011] in,

[0012] Q1 is the first-cycle capacity of the lithium battery calibrated at 0.33C. rete It is the actual discharge capacity of the lithium battery per revolution.

[0013] In step (3), the total lithium capacity Q in the positive electrode sheet total =aQ calc ;

[0014] Where 'a' is the delithiation coefficient, which can be obtained empirically or by discharging with a small current of 0.01-0.1C, comparing the discharge capacity with the theoretical capacity Q. calc The ratio;

[0015] Q calcThe theoretical capacity of the cathode material is obtained through first-principles calculations. Specifically, density functional theory (DFT) and generalized gradient approximation (GGA-PBE) are used for structural optimization, and the calculation methods can be those commonly used in this field.

[0016] In step (2), the total loss capacity Q loss The function relating the number of cycles x is:

[0017] Q loss =M loss +N loss .

[0018] In step (3), when Q loss ≤Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q1 + (x - 1) × (Q2 - Q1);

[0019] When Q loss >Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q total -Q loss .

[0020] In step (1), the lithium loss capacity M in the negative electrode of the lithium battery loss The function relating the number of cycles x is:

[0021] M loss =be cx ;

[0022] Where b and c are both constants.

[0023] In step (1), the lithium loss capacity N in the electrolyte of the battery loss The function relating the number of cycles x is:

[0024] N loss =mx 3 +nx 2 +kx+p;

[0025] Where m, n, k, and p are all constants.

[0026] Furthermore, after the lithium battery under test has completed the cycle test, the residual lithium content in the negative electrode is tested by inductively coupled plasma method, laser-induced breakdown spectroscopy or X-ray energy dispersive spectroscopy, and converted into the lithium loss capacity in the negative electrode.

[0027] Furthermore, after the lithium battery under test has completed the cycle test, the residual lithium content in the electrolyte is tested by inductively coupled plasma method, laser-induced breakdown spectroscopy or X-ray energy dispersive spectroscopy, and converted into the lithium loss capacity in the electrolyte.

[0028] The temperature range for the cyclic test is -10 to 60°C.

[0029] Furthermore, in the fitting function M loss and N loss When x is not less than 200, the number of cycles is not less than 200.

[0030] The lithium battery systems applicable to this invention include lithium iron phosphate, ternary, and cobalt-free systems, among many others, demonstrating high versatility.

[0031] Capacity rise phenomenon: During battery cycling, the discharge capacity in the later cycle is greater than that in the previous cycle, i.e., Q1 < Q2 < Q3 < Q4 < ... < Q n >Q n+1 >Q n+2 >Q n+3 >..., the capacity retention rate is ≥100%.

[0032] Furthermore, the discharge capacity of a battery exhibiting a capacity upswing phenomenon, when Q... loss ≤Q total - At Q1, the discharge capacity Q of the lithium battery rete =Q1 + (x - 1) × (Q2 - Q1);

[0033] When Q loss >Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q total -Q loss .

[0034] Furthermore, the discharge capacity of a battery that does not exhibit a capacity increase phenomenon, Q rete =Q total -Q loss .

[0035] The technical solution of this invention has the following advantages:

[0036] 1. The method for predicting the capacity retention rate of a lithium battery provided by the present invention includes: (1) performing a cycle test on the lithium battery under test, and obtaining the lithium loss capacity M in the negative electrode of the lithium battery by fitting. loss M is a function of the number of cycles x loss =m(x), M loss This represents the lithium capacity loss caused by the negative electrode after x cycles; the lithium capacity loss N in the electrolyte of the lithium battery is obtained by fitting. lossN is a function of the number of cycles x loss =n(x), N loss (1) The lithium loss capacity caused by the electrolyte after x cycles; (2) The total lithium loss capacity Q is obtained by fitting the lithium loss capacity in the negative electrode and the lithium loss capacity in the electrolyte. loss Q is a function of the number of cycles x. loss = q1(x), where Q loss The total lithium loss caused by the negative electrode and electrolyte after x cycles is denoted as the total loss capacity; (3) the total lithium capacity Q passing through the positive electrode. total Total loss capacity Q loss The discharge capacity Q of the lithium battery during cycling is obtained by fitting the first cycle calibration capacity Q1 and the second cycle calibration capacity Q2. rete Q is a function of the number of cycles x. rete =q2(x), thus obtaining the lithium battery capacity retention rate δ as a function of the number of cycles x. This method predicts the lithium battery capacity retention rate based on active lithium loss, which can not only detect the cycle life and health status of the lithium battery, shorten the battery development cycle, and save experimental costs; at the same time, the method for predicting the lithium battery capacity retention rate of this invention has high accuracy and a high degree of agreement between the predicted value and the experimental value.

[0037] The method for predicting lithium battery capacity retention provided by this invention can also determine whether the battery has a capacity upturn phenomenon, and predict the battery capacity upturn phenomenon.

[0038] 2. The method for predicting the capacity retention rate of lithium batteries provided by this invention is based on the active lithium loss capacity of the negative electrode and electrolyte to predict the capacity retention rate of the whole battery, accurately reflecting the capacity decay mechanism of the battery. This method is simple and efficient, and is applicable to many battery systems such as lithium iron phosphate, ternary, and cobalt-free systems. The method provided by this invention is less affected by temperature and rate conditions, has a wide range of applications, and has high universality.

[0039] The method provided by this invention can predict the capacity retention rate of batteries with capacity upturn, as well as the capacity retention rate of batteries without capacity upturn, and has a wide range of applications. Attached Figure Description

[0040] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the assembly process of a single battery according to Embodiment 1 of the present invention;

[0042] Figure 2 This is a fitted curve of lithium loss capacity versus cycle number in the negative electrode material of Embodiment 1 of the present invention;

[0043] Figure 3 This is a fitted curve of lithium loss capacity in the electrolyte versus the number of cycles in Example 1 of the present invention;

[0044] Figure 4 These are the predicted and measured values ​​of the capacity retention rate of the lithium battery under different cycle numbers in Embodiment 1 of the present invention. Detailed Implementation

[0045] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0046] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0047] Example 1

[0048] This embodiment provides a method for predicting the capacity retention rate of lithium batteries, including the following steps:

[0049] (I) Using NCM613 (specific composition: LiNi) 0.6 Co 0.1 Mn 0.3 Taking a single-cell battery with O2 as the positive electrode material and graphite as the negative electrode material as an example, the preparation method of the single-cell battery is as follows:

[0050] (1) Pretreatment of positive and negative electrode sheets: Cut the positive and negative electrode sheets, wipe the tabs, clean them, and apply adhesive;

[0051] (2) Assembly of a single battery cell: such as Figure 1 As shown, the electrodes are stacked in the order of negative electrode sheet - separator - positive electrode sheet - separator - negative electrode sheet, and then sequentially welded with tabs and sealed with electrolyte to obtain the assembled battery. The electrolyte injection coefficient is higher than the normal coefficient. In this embodiment, the separator is a polypropylene separator (PP separator), and the electrolyte is A60. Specifically, this embodiment is a single battery, which requires more electrolyte than soft-pack and square-shell cells. Therefore, the electrolyte injection volume is 4.0 ml.

[0052] (3) The assembled single cell is left to stand at 40°C for 3-24 hours to ensure that the electrolyte completely wets the positive and negative electrode materials, and then pre-charged to form a single cell. In this embodiment, the standing time is 3 hours.

[0053] The first-cycle discharge capacity of a single battery cell was calibrated at 25°C and 0.33C constant current and constant voltage (CCCV), denoted as Q1. The measured first-cycle discharge capacity Q1 of the single battery cell in this embodiment was 147mAh. Furthermore, the second-cycle discharge capacity of the single battery cell was calibrated, denoted as Q2. The measured second-cycle discharge capacity Q2 of the single battery cell in this embodiment was 147.1042mAh.

[0054] (II) Testing of active lithium loss capacity

[0055] (1) Thirty-six highly consistent single-cell batteries were selected for cycle testing. Three batteries were used for charge-discharge testing in each cycle to obtain the discharge capacity of the lithium battery under different cycle numbers, i.e., 12 sets of cycle numbers. Three parallel samples were set for each cycle number. The test conditions for cycle testing were 25℃ and 0.8C constant current charge-discharge test, with cycles of 50 cycles, 100 cycles, 200 cycles, 300 cycles, 400 cycles, 500 cycles, 600 cycles, 700 cycles, 800 cycles, 900 cycles, 1000 cycles, and 1100 cycles respectively. After the cycle test, the negative electrode was post-processed. Specifically, a 0.1C small current discharge was performed to remove all the active lithium in the negative electrode. The battery was then disassembled, and the negative electrode and electrolyte were retained for subsequent testing. Furthermore, the discharge capacity of a single battery cell was recorded at various cycle numbers, and the average value was taken among parallel samples to obtain the discharge capacity Q of the lithium battery at different cycle numbers. x , denoted as Q 1 Q 2 ...Q 12 Furthermore, the measured capacity retention rate δ' of the battery under different cycle numbers is obtained, and the measured capacity retention rate δ' is Q. x The ratio to Q1.

[0056] (2) Test of lithium loss capacity in the negative electrode sheet: The negative electrode sheet was cleaned with dimethyl carbonate (DMC), oxidized, and the overhang region (the overhang region refers to the area of ​​the negative electrode sheet that extends beyond the positive electrode sheet in both length and width) was removed. The negative electrode sheet was then soaked in an appropriate amount of deionized water to remove the current collector. Finally, inductively coupled plasma (ICP) testing was performed to measure the residual lithium content in the negative electrode sheet. This residual lithium is the lithium lost from the negative electrode sheet. Based on the measured lithium content, it was converted into the capacity of the negative electrode sheet. The conversion formula is as follows: [Formula for the capacity loss of each negative electrode sheet].

[0057]

[0058] Where m is the mass of the negative electrode material region after removing the overhang and current collector; F is the Faraday constant; wt% is the lithium mass percentage obtained from ICP testing; M Li It is the relative molecular mass of Li.

[0059] The test results for the 36 batteries are denoted as M. 1-1 loss M 1-2 loss M 1-3 loss M 2-1 loss M 2-2 loss M 2-3 loss M 3-1 loss M 3-2 loss M 3-3 loss ...M 12-1 loss M 12-2 loss M 12-3 loss Specific values ​​are shown in Table 1, for M under each group of cycle counts. loss Calculate the average value, denoted as M1. loss M2 loss M3 loss ······M 12 loss Specific values ​​are shown in Table 1. The function M of the loss capacity of active lithium on the negative electrode and the number of cycles x was obtained by fitting. loss =m(x), specifically M loss =27.502e 0.0007x The test results and fitted curves for lithium loss capacity and cycle count in the negative electrode are shown in [reference needed]. Figure 2 .

[0060] Table 1. Active lithium loss capacity M of the negative electrode sheet loss

[0061]

[0062]

[0063] Testing the lithium loss capacity in the electrolyte: After long-term cycling, the battery consumes a certain amount of electrolyte, reducing the electrolyte volume to insufficient levels for testing. Therefore, the electrolyte after the charge-discharge test needs to be diluted, and then inductively coupled plasma (ICP) is used to test the residual lithium content. Simultaneously, the lithium content of the pure electrolyte also needs to be tested. The increase in lithium content in the electrolyte after removing the lithium content of the blank electrolyte is converted into the corresponding capacity. The calculation formula is as follows: This increase in lithium content in the electrolyte represents the lithium loss capacity in the electrolyte.

[0064]

[0065] Where n is the mass of the electrolyte; F is the Faraday constant; wt% is the lithium content obtained by ICP testing, which has been adjusted to remove the lithium content in the blank electrolyte, and is expressed as a mass percentage; M Li It is the relative molecular mass of Li.

[0066] The test results for the 36 batteries are denoted as N. 1-1 loss N 1-2 loss N 1-3 loss N 2-1 loss N 2-2 loss N 2-3 loss N 3-1 loss N 3-2 loss N 3-3 loss ·····N 12-1 loss N 12-2 loss N 12-3 loss Specific values ​​are shown in Table 2, for N under each group of cycle counts. loss Calculate the average value, denoted as N1. loss N2 loss N3 loss ·····N 12 lossSpecific values ​​are shown in Table 2. The function N of lithium loss capacity in the electrolyte and the number of cycles x was obtained through fitting. loss =n(x), specifically N loss =3×10 9 x 3 -4×10 6 x 2 +0.0047x+0.8054. The test results and fitted curves for lithium loss capacity and cycle count in the electrolyte are shown below. Figure 3 .

[0067] Table 2 Electrolyte capacity loss N loss

[0068] Number of cycles Parallel sample 1 (mAh) Parallel sample 2 (mAh) Parallel sample 3 (mAh) Average value (mAh) 50 0.98 0.63 1.11 0.91 100 1.19 1.31 1.39 1.30 200 1.86 1.72 1.70 1.76 300 1.89 1.91 1.94 1.92 400 2.12 2.41 1.79 2.11 500 2.52 2.44 2.48 2.48 600 2.68 2.89 2.76 2.78 700 3.09 3.13 3.13 3.12 800 3.14 3.22 3.12 3.16 900 3.91 3.88 3.86 3.89 1000 4.44 4.56 4.51 4.51 1100 4.70 4.63 4.62 4.65

[0069] (2) The total active lithium loss capacity Q is obtained by fitting the lithium loss capacity in the negative electrode and the lithium loss capacity in the electrolyte. loss Q is a function of the number of cycles x. loss =q1(x)=M loss +N loss =m(x)+n(x)=, 27.502e 0.0007x +3×10 9 x 3 -4×10 6 x 2 +0.0047x+0.8054. Where Q loss The active lithium loss capacity caused by the negative electrode and electrolyte after x cycles is denoted as the total active lithium loss capacity.

[0070] (3) The total lithium capacity Q in the positive electrode total =aQ calc ;

[0071] Where 'a' is the delithiation coefficient, which can be obtained empirically or by comparing the discharge capacity with the theoretical capacity Q obtained from discharging at a small current of 0.01-0.1C. calc The ratio. Based on experience, the delithiation coefficient α of the cathode material is generally between 0.25 and 1. For example, the delithiation coefficient of layered structure materials is generally between 0.4 and 0.7, that of olivine structure is between 0.65 and 1, and that of spinel structure is around 0.75. In this embodiment, the cathode electrode NCM613 is a layered structure, and based on experience, α is taken as 0.5; Q calc This is the theoretical capacity of the cathode material, calculated using first-principles calculations. Specifically, density functional theory (DFT) and generalized gradient approximation (GGA-PBE) are used for structural optimization. In this embodiment, the theoretical capacity Q is... calcThe total capacity Q of the lithium in the positive electrode is 362mAh. total It has a capacity of 181mAh.

[0072] The actual capacity Q of a lithium battery during cycling. rete The function q2(x) is related to the number of cycles x:

[0073] When Q loss ≤Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q1 + (x - 1) × (Q2 - Q1);

[0074] When Q loss >Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q total -Q loss ;

[0075] The predicted capacity retention rate δ of a lithium battery is a function of the number of cycles x: Formula 1.

[0076] Furthermore, for some batteries, during the early cycling stages, the discharge capacity of the later cycle may be greater than that of the earlier cycle, i.e., Q1 < Q2 < Q3 < Q4 < ... < Q n >Q n+1 >Q n+2 >Q n+3 >..., commonly known as the capacity upturn phenomenon, occurs when these batteries exhibit a capacity upturn, satisfying Q... loss ≤Q total -Q1, when the battery capacity increase phenomenon disappears, Q is satisfied. loss >Q total -Q1; A battery exhibiting capacity increase, with a discharge capacity Q. rete It is calculated using the following formula:

[0077] When Q loss ≤Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q1 + (x - 1) × (Q2 - Q1);

[0078] When Q loss >Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q total -Q loss .

[0079] For other types of batteries, during the cycling process, the discharge capacity of each subsequent cycle is consistently lower than that of the previous cycle. These batteries do not exhibit a capacity increase phenomenon, and throughout the entire cycle, the discharge capacity of the lithium battery satisfies Q. loss >Q total -Q1, therefore, the discharge capacity Q of a battery that does not exhibit capacity rise phenomenon. rete =Q total -Q loss .

[0080] Specifically, in this embodiment, the battery exhibits a capacity increase phenomenon; therefore, the battery discharge capacity Q... rete Satisfy the following formula,

[0081] When Q loss ≤Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q1+(x-1)×(Q2-Q1)=147+(x-1)×(147.1042-147)=147+0.1042(x-1);

[0082] When Q loss >Q total - At time Q1, the discharge capacity Q of the lithium battery rete =Q total -Q loss =181-27.502e 0.0007x -3×10 9 x 3 +4×10 6 x 2 -0.0047x -0.8054;

[0083] The predicted capacity retention rate δ of a lithium battery is a function of the number of cycles x: Formula 1.

[0084] Equation 1 can be used to predict the capacity retention rate of the lithium battery in this embodiment at different cycle numbers, thus predicting the cycle life and health status of the lithium battery. The measured capacity retention rate δ' and the predicted capacity retention rate δ' of the lithium battery at different cycle numbers are shown below. Figure 4 ,pass Figure 4 It can be seen that the lithium battery capacity retention rate predicted by the method provided by this invention is close to the measured value, and the accuracy is high.

[0085] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for predicting the capacity retention rate of a lithium battery, characterized in that, Includes the following steps, S1, Perform cycle testing on the lithium battery under test, and obtain the lithium loss capacity M in the negative electrode of the lithium battery by fitting. loss With the number of cycles x function M loss =m( x M loss It was through x The lithium capacity loss caused by the negative electrode after a cycle; The lithium loss capacity N in the electrolyte of the lithium battery was obtained by fitting. loss With the number of cycles x function N loss =n( x ), N loss It was through x The lithium capacity loss caused by the electrolyte after a cycle; S2, by fitting the lithium loss capacity in the negative electrode and the lithium loss capacity in the electrolyte, the total lithium loss capacity Q is obtained. loss With the number of cycles x The function, Q loss =q1( x ), where Q loss It was through x The total lithium capacity lost due to the negative electrode and electrolyte after one cycle is denoted as the total loss capacity. S3, through the total lithium capacity Q in the positive electrode plate total Total loss capacity Q loss The discharge capacity Q of the lithium battery during cycling is obtained by fitting the first cycle calibration capacity Q1 and the second cycle calibration capacity Q2. rete With the number of cycles x The function, Q rete =q2( x This allows us to obtain the lithium battery capacity retention rate δ and the number of cycles. x The function; in, , Q1 is the first-cycle rated capacity of the lithium battery at 0.33C. rete It is the discharge capacity of a lithium battery during cycling.

2. The method according to claim 1, characterized in that, In step S3, the total lithium capacity Q in the positive electrode sheet total =aQ calc ; Where 'a' is the delithiation coefficient, which is an empirical value or obtained by discharging with a small current of 0.01-0.1C, and is a ratio of the discharge capacity to the theoretical capacity Q. calc The ratio; Q calc It is the theoretical capacity of the cathode material calculated using first-principles calculations.

3. The method according to claim 2, characterized in that, Total loss capacity Q loss With the number of cycles x The function is, Q loss =M loss +N loss 。 4. The method according to any one of claims 1-3, characterized in that, In step S3, when Q loss ≤Q total -Q1, the discharge capacity Q of the lithium battery during cycling. rete = Q1+( x -1)×(Q2-Q1); When Q loss >Q total - At time Q1, the discharge capacity Q of the lithium battery rete = Q total -Q loss .

5. The method according to any one of claims 1-3, characterized in that, In step S1, the lithium loss capacity M in the negative electrode of the lithium battery loss With the number of cycles x The function is, M loss = be cx ; Where b and c are both constants.

6. The method according to any one of claims 1-3, characterized in that, In step S1, the lithium loss capacity N in the electrolyte of the lithium battery is... loss With the number of cycles x The function is, N loss =m x 3 +n x 2 +k x +p; Where m, n, k, and p are all constants.

7. The method according to claim 5, characterized in that, After the lithium battery under test has completed the cycle test, the residual lithium content in the negative electrode is tested by inductively coupled plasma method, laser-induced breakdown spectroscopy or X-ray energy dispersive spectroscopy, and the residual lithium content is converted into the lithium loss capacity in the negative electrode.

8. The method according to claim 6, characterized in that, After the lithium battery under test has completed the cycle test, the residual lithium content in the electrolyte is tested by inductively coupled plasma method, laser-induced breakdown spectroscopy or X-ray energy dispersive spectroscopy, and the residual lithium content is converted into the lithium loss capacity in the electrolyte.

9. The method according to any one of claims 1-3 or 7-8, characterized in that, The temperature range for the cyclic test is -10 to 60°C.

10. The method according to any one of claims 1-3 or 7-8, characterized in that, In the fitting function M loss and N loss At that time, the number of cycles x Not less than 200.

Images