A method of analyzing the extent of cell wet-out

Abstract

The application provides a method for analyzing the infiltration degree of an electric core. The method can quantitatively analyze the distribution of electrolyte in a pole piece, and thus can be used for targeted electrolyte distribution control and performance improvement, and further effectively optimizes the cycle performance and other electrochemical performances of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a method for analyzing the infiltration degree of an electric core. BACKGROUND

[0002] At present, lithium ion batteries have been widely developed in 3C electronic devices, electric vehicles and energy storage fields, and the market has a sharp increase in demand for higher energy density and better performance lithium ion batteries. In the development of high energy density lithium ion batteries, how to improve the capacity utilization of electrodes and solve the problem of difficult infiltration caused by high compaction density are key technical challenges, and effective improvement of the infiltration of electrolyte is considered as the key to solving this problem. In the manufacture of lithium ion batteries, uneven infiltration will lead to uneven distribution of current density, and the formed solid electrolyte interface film (SEI) is unstable; meanwhile, incomplete infiltration directly affects the performance of the battery, leading to lithium precipitation and causing a series of safety problems. In summary, the electrolyte of lithium ion batteries is the core part of the development of lithium ion batteries, and the evaluation of the infiltration of the electrolyte on the electrode is the key to the development of high-performance lithium ion batteries.

[0003] At present, the infiltration detection technology is very limited, such as the calculation of dry area, the EDS test of P element content, and the observation of full charge interface. The calculation of dry area and the observation of full charge interface are visual methods, and the calculation of dry area can only macroscopically detect the infiltration; the observation of full charge interface can be used to determine whether the infiltration is sufficient by observing whether there are dark spots on the full charge interface after formation, but the method has great limitations because the full charge interface after formation is related to many factors such as film formation and wave edge of the electrode sheet. The EDS test of P element content uses EDS to measure the difference in P element content in different areas of the electrode sheet to obtain the difference in infiltration, which can be used to characterize the infiltration. The method is a semi-quantitative detection method because it is not accurate in microcosm, and the test precision is low, and only a few selected areas can be scanned, and the P element content of the surface layer is often tested.

[0004] Therefore, the above-mentioned existing methods generally have the disadvantages of poor repeatability and inability to accurately evaluate the true infiltration of the electrolyte, and it is necessary to develop an analysis method for more accurately evaluating the infiltration performance of the electrolyte, realizing quantitative detection of the electrolyte distribution, and then performing targeted control and performance improvement. SUMMARY

[0005] To solve the problems and deficiencies in the prior art, the present application provides a method for analyzing the impregnation degree of an electric core, which can quantitatively analyze the distribution of electrolyte in the electrode sheet, thereby enabling targeted electrolyte distribution control and performance improvement, and effectively optimizing the cycle performance and other electrochemical performances of the battery.

[0006] The present application provides a method for analyzing the impregnation degree of an electric core, comprising the following steps: S1. disassembling the electric core in an empty state after formation to obtain an electrode sheet; the electrode sheet contains electrolyte, and the electrolyte contains characteristic elements; the electrode sheet includes at least one of a positive electrode sheet and a negative electrode sheet; S2. dividing the electrode sheet into n regions in the length direction, and dividing each region into m regions in the width direction of the electrode sheet at the central position in the length direction to obtain K first sample regions, K = n x m; the length of the first sample region is L1, the width is W1, and the thickness is H1; at the same time, the electrode sheet is divided into positive and negative sides with the current collector as the dividing line, and the positive and negative sides are divided into x regions in the width direction, and each region is divided into y regions in the thickness direction to obtain Y second sample regions, Y = 2 x x y; the length of the second sample region is L2, the width is W2, and the thickness is H2; S3. testing the content of the characteristic elements in the K first sample regions and the Y second sample regions of the electrode sheet; the characteristic elements include at least one of P, S, B, F, N, Si, Al, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Ge, In, Ir, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Sb, Sn, Sr, Ta, Ti, V, W, Y, Zn, Zr; S4. when the ratio of the content of the characteristic elements in any two regions of the first sample region of the electrode sheet is greater than 2, and the content of the characteristic elements in the region with lower content of the characteristic elements is taken as the divisor; and / or when the ratio of the content of the characteristic elements in any two regions of the second sample region of the electrode sheet is greater than 2, and the content of the characteristic elements in the region with lower content of the characteristic elements is taken as the divisor; it is judged that the impregnation degree of the electrode sheet is insufficient.

[0007] In some cases, during the operation of the electric core, the electrolyte may stay in some positions inside the electric core and cannot fully impregnate between the positive and negative electrodes and the edge of the electric core, resulting in the situation that the electrolyte cannot be fully impregnated in some areas, which is electrolyte impregnation deficiency. When the electrolyte impregnation is insufficient, the following problems will occur: (1) lithium precipitation occurs inside the electric core or at the edge. In the case of insufficient electrolyte impregnation, the positive and negative electrodes of lithium ions are likely to meet inside the electric core, generating heat and gas, thereby expelling the electrolyte and forming lithium precipitation. Once lithium precipitation is serious, it will not only affect the performance and service life of the electric core, but also cause safety hazards. (2) The service life of the electric core is shortened. The electrolyte is one of the important components in the electric core, and if the electrolyte impregnation is insufficient, it will seriously affect the service life of the electric core.

[0008] Therefore, how to accurately evaluate the impregnation of the electrolyte in the battery cell to the electrode sheet has a key role in further effectively improving the performance and life of the battery cell.

[0009] The electrolyte is composed of a solvent, an additive, and a lithium salt. Generally, the solvent has a relatively small relative molecular mass (for example, EC: 88.06, DMC: 90.08, generally less than 100) and a high content, and is easier to impregnate. The lithium salt and the additive have a relatively high relative molecular mass and a low content, and are difficult to impregnate, especially the additive, some functional additives have a very small proportion (0.5-2%) in the electrolyte, and have a very significant influence on the performance of the battery cell. Therefore, we pay more attention to the distribution of the additive or some difficult-to-impregnate lithium salt in the electrode sheet. From the element composition of the electrolyte composition, C, H, and O elements are commonly contained in each component. In addition to C, H, and O, there are other elements that can distinguish the electrolyte components, which are called characteristic elements. For example, the lithium salt is usually LiPF6, and P and F are characteristic elements of the component. The additive usually has PS, LIFSI, LiODFB, etc. PS contains the characteristic element S, LIFSI contains the characteristic elements S, F, and N, and LiODFB contains the characteristic elements F and B. Therefore, for the additive or some lithium salt, we can analyze the distribution of the characteristic elements contained in the additive or some lithium salt in the battery cell (mainly the positive and negative electrode sheets, and of course the separator) to analyze the distribution of the electrolyte in the battery cell, and then improve the insufficient impregnation of the electrolyte, and further optimize the cycle performance and safety performance of the battery cell. Moreover, because the components that are more difficult to impregnate in the electrolyte composition are the additive and some lithium salt, and these components have a greater influence on the performance of the battery, analyzing the distribution of the characteristic elements contained in the additive and these lithium salts in the battery cell can more accurately indicate the distribution of the additive and these lithium salts in the battery cell, that is, it is more accurate for analyzing the impregnation degree of the electrolyte in the battery cell, and thus it can be more clear to optimize the impregnation performance of the electrolyte and improve the electrochemical performance of the battery.

[0010] Therefore, the present application mainly divides the electrode sheet into multiple regions in multiple dimensions, analyzes the content of the characteristic elements in these regions, and thus can basically cover the content of the characteristic elements in all regions of the electrode sheet, and thus can have a more accurate quantitative analysis of the impregnation degree of the electrolyte on the electrode sheet. Furthermore, by comparing and analyzing the content of the characteristic elements in these regions, the impregnation degree of which regions of the electrode sheet is insufficient can be analyzed, and targeted measures can be taken to improve the impregnation degree of these regions, thereby improving the overall impregnation degree of the electrode sheet and achieving the purpose of optimizing the performance of the battery.

[0011] It should be noted that the method for analyzing the degree of impregnation of the battery cell provided by the present application is a quantitative analysis of the content of the characteristic elements in multiple regions of the pole piece. Therefore, compared with the method of the prior art, it is a more accurate and effective method for representing the degree of impregnation of the battery cell. Therefore, it has important practical significance for guiding the further optimization of the impregnation performance of the battery cell to further optimize the performance of the battery.

[0012] Preferably, in S2, in the K first sample regions to be tested, when the pole piece is a positive pole piece, L1≥50 mm, W1≥19.6 mm, H1≥106 μm; when the pole piece is a negative pole piece, L1≥50 mm, W1≥19.6 mm, H1≥130 μm; in the Y second sample regions to be tested, when the pole piece is a positive pole piece, L2≥1492 mm, W2≥19.1 mm, H2≥17.6 μm; when the pole piece is a negative pole piece, L2≥1563 mm, W2≥19.6 mm, H2≥21.6 μm. When the regions are divided in the length and thickness directions of the pole piece, the size of each sample region to be tested is controlled to be within a certain range. In this way, when the powder scraped from the pole piece is tested to determine the content of the characteristic elements, there is enough sample amount for related testing, which avoids inaccurate test results due to too little sample amount, and affects the accurate analysis of the degree of impregnation of the pole piece and the battery cell.

[0013] Preferably, in S2, when the pole piece is a positive pole piece, L1=50 mm, W1=19.6 mm, H1=106 μm; when the pole piece is a negative pole piece, L1=50 mm, W1=19.6 mm, H1=130 μm; when the pole piece is a positive pole piece, L2=1492 mm, W2=19.1 mm, H2=17.6 μm; when the pole piece is a negative pole piece, L2=1563 mm, W2=19.6 mm, H2=21.6 μm. When the regions are divided in the length and thickness directions respectively, the size of the sample region to be tested is the above-mentioned values. When the powder scraped from the pole piece is tested to determine the content of the characteristic elements, there is enough sample amount for related testing, which avoids inaccurate test results due to too little sample amount, and affects the accurate analysis of the degree of impregnation of the pole piece and the battery cell. It also ensures that the pole piece can be divided into regions sufficiently to ensure that all regions of the pole piece are covered, which improves the accuracy of the analysis results of the degree of impregnation of the electrolyte, and more accurately improves the impregnation performance of the regions of the pole piece with insufficient impregnation, thereby optimizing the performance of the battery.

[0014] Preferably, in S2, K≥9; Y≥18. When the pole piece is divided into regions in the length and thickness directions, the number of divided regions is ensured to be large, which can more accurately represent the electrolyte impregnation of each region of the pole piece, thereby more accurately representing the degree of impregnation of the pole piece and the battery cell as a whole, and providing a more accurate improvement direction for further improving the degree of impregnation of the pole piece and the battery cell.

[0015] Preferably, in S2, K=9; Y=18.

[0016] Preferably, in S2, the characteristic elements include at least one of P, S, and B.

[0017] Preferably, in S2, the content of the characteristic elements in the tab is tested by an inductively coupled plasma spectrometer. The inductively coupled plasma spectrometer test is referred to as ICP test, and the content of the characteristic elements in the tab is tested by the ICP test method, which has high accuracy, especially for ppm content level, and can also achieve relatively accurate test, so as to more accurately characterize the infiltration in the battery cell.

[0018] Preferably, the electrolyte includes the following components: lithium salt, organic solvent, film-forming additive, and functional additive; the mass ratio of lithium salt: organic solvent: film-forming additive: functional additive is 12-18: 74-85: 2-5: 1-4; the lithium salt includes lithium hexafluorophosphate; the organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; the film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate; and the functional additive includes at least one of lithium bisfluorosulfonylimide, lithium difluorophosphate bixofluoride, lithium difluorophosphate, lithium bisoxalate borate, 1,3-propanesulfonic acid lactone, and ethylene sulfate. The method for analyzing the infiltration degree of the battery cell provided by the application is suitable for various electrolyte components, especially for the electrolyte with the above-mentioned ratio and material composition, and the method provided by the application has greater adaptability for analyzing the infiltration degree of the battery cell, can more accurately analyze the content of the characteristic elements in the additive and lithium salt, that is, can more accurately analyze the infiltration degree of the electrolyte in the battery cell, and can more accurately optimize the infiltration performance of the battery cell.

[0019] Preferably, the positive electrode sheet comprises a positive electrode material, a first conductive agent, a first binder; the mass ratio of the positive electrode material, the first conductive agent, and the first binder is 95-99:1-3.5:0.5-1.5; the positive electrode material comprises at least one of a lithium iron phosphate positive electrode material, a ternary lithium nickel cobalt manganese oxide positive electrode material, and a lithium manganese iron phosphate positive electrode material; the first conductive agent comprises at least one of conductive carbon black and a carbon nanotube; the first binder comprises at least one of polyvinylidene fluoride; the negative electrode sheet comprises a negative electrode material, a second conductive agent, and a second binder; the mass ratio of the negative electrode material, the second conductive agent, and the second binder is 95-99:0.3-2:1-3.5; the negative electrode material comprises at least one of natural graphite, artificial graphite, and a silicon-carbon negative electrode; the second conductive agent comprises conductive carbon black; and the second binder comprises at least one of carboxymethyl cellulose and butadiene-styrene rubber. For the above-mentioned composition of the positive and negative electrode sheets commonly used in the market, the analysis method provided by the present application has greater adaptability, and thus has important guiding significance for analyzing the current lithium battery and for further improving the wettability of the battery cell to improve the performance of the battery cell.

[0020] Preferably, the above-mentioned battery cell comprises a cylindrical battery cell. In the cylindrical battery cell, when the electrolyte is injected into the battery cell, the electrolyte flows and penetrates from the center hole of the roll core to the bottom of the shell, and then flows from both ends of the positive and negative electrodes to the middle position. The electrolyte is composed of lithium salt, solvent and additive. Different components have different molecular weights and diameters, and there are also differences in distribution equilibrium. According to the column chromatography model: the roll core can be regarded as a stationary phase, and the electrolyte is a mobile phase. When the two phases move relative to each other, because of the differences in the distribution equilibrium of each component in the electrolyte, the concentration of each component in the stationary phase is different. In addition, the pores in the electrode sheet or the separator have a certain filtering effect on the electrolyte. The above factors cause the distribution or wettability of the electrolyte to be different at different places in the cylindrical battery cell, resulting in a decrease in the performance of the cylindrical battery cell. Therefore, the analysis of the wettability of the electrolyte in the cylindrical battery cell has greater significance in the field of lithium batteries. The method provided by the present application can accurately analyze the wettability of the electrolyte in the cylindrical battery cell, and thus has more important guiding significance for further optimizing the overall wettability of the cylindrical battery cell and improving the performance of the cylindrical battery cell. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 For the A / B / C battery cell 1C / 3C cycle performance at room temperature in Example 1.

[0022] Figure 2 For the sampling schematic diagram of the electrode sheet divided into regions in the length direction in Example 1 (first divided into regions in the length direction and then in the width direction).

[0023] Figure 3The sampling diagram for dividing the electrode in the thickness direction in Example 1 (first in the width direction and then in the thickness direction).

[0024] Figure 4 The 1C / 5C room temperature cycle performance of the improved A / B cell and the original C cell (control group) in Example 1. DETAILED DESCRIPTION

[0025] In order to enable personnel in the technical field to better understand the technical solutions of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments.

[0026] Example 1

[0027] According to the process of homogenization-coating-rolling-cutting-winding-assembly-formation, three batches of cylindrical cells A / B / C were prepared in the laboratory. The positive electrode sheet formula is: ternary lithium nickel cobalt manganese oxide: 97%, SP: 1.2%, CNT: 0.8%, PVDF: 1%; the negative electrode sheet formula is: graphite: 97%, SP: 0.8%, CMC: 1%, SBR: 1.2%. The size of the positive and negative electrode sheets in the cell is shown in Table 1.

[0028] Table 1 Size information of positive and negative electrode sheets of the cell

[0029]

[0030] The electrolyte formula in this embodiment is: EC (ethylene carbonate): 15.60%, DMC (dimethyl carbonate): 55.35%, EMC (methyl ethyl carbonate): 7.45%, LiPF6: 16%, LiFSI: 0.8%, FEC: 3.0%, LiODFB: 0.8%, PS: 1%. The formula of the cell is the same, and there are differences in the process technology, which leads to differences in the degree of electrolyte infiltration in the cell, resulting in large differences in cycle performance. The cycle performance of the C cell is better, and the 1C / 3C (charge rate is 1C, discharge rate is 3C) cycle performance 100 week capacity retention rate is 99.61%, the 100 week capacity retention rates of A and B cells are 92.64% and 96.34% respectively, and there are different degrees of attenuation, such as Figure 1 .

[0031] The elemental distribution of the positive and negative electrodes of cells A, B, and C was quantitatively characterized using ICP testing to identify the root cause (electrolyte wetting condition) and improve electrical performance. By disassembling the A / B / C cells into their empty states, visually apparent poor wetting was observed in the negative electrode. Therefore, this embodiment focuses on analyzing the elemental distribution of the negative electrode, and based on the electrolyte formulation of this embodiment, primarily examines the distribution (degree of wetting) of the three characteristic elements P, S, and B within the cell.

[0032] The wetting degree (condition) of cells A, B, and C is analyzed according to the following steps:

[0033] S1. Disassemble the cell into an empty state to obtain positive and negative electrodes; since it can be observed that the negative electrode has obvious poor electrolyte wetting at the visual level, the experimental process mainly analyzes the distribution of the three characteristic elements P, S and B in the negative electrode.

[0034] S2. Divide the negative electrode into 3 (n) equal regions along its length (e.g., Figure 2 The head, middle, and tail regions of the electrode are divided into three equal parts (m) along the width of the negative electrode at the center of each region's length, resulting in K first sample regions to be tested, where K = 3 × 3 (n × m) = 9. (Reference) Figure 2 Regions ① to ⑨; the length of the first sample region to be tested is L1, the width is W1, and the thickness is H1; L1 = 50 mm, W1 = 19.6 mm, H1 = 130 μm;

[0035] Simultaneously, using the current collector as a dividing line, the negative electrode sheet is divided into positive and negative sides. Each of the positive and negative sides is then divided into three equal regions along its width, and each region is further divided into three equal regions along its thickness, resulting in Y second sample regions to be tested. Y = 2 × 3 × 3(2 × x × y) = 9. (Reference) Figure 3 The front and back sides are divided into upper, middle, and lower regions respectively; the second sample region to be tested has a length of L2, a width of W2, and a thickness of H2; L2 = 1563 mm, W2 = 19.6 mm, and H2 = 21.6 μm;

[0036] S3. Test the content of P, S, B in 9 (K) first sample areas and 18 (Y) second sample areas of the negative plate of A / B / C battery, i.e. scrape powder from these areas and then test the content of P, S, B in these areas by ICP test method; the test results of P, S, B in 9 (K) first sample areas of the negative plate are shown in Table 2, and the test results of P, S, B in 18 (Y) second sample areas of the negative plate are shown in Table 3; Table 2 Test results of P, S, B (elements) in 9 (K) first sample areas of the negative plate of A / B / C battery (sampling in the direction of length first and then width)

[0037]

[0038] Table 3 Test results of P, S, B (elements) in 18 (Y) second sample areas of the negative plate of A / B / C battery (sampling in the direction of width first and then thickness)

[0039]

[0040]

[0041] By analyzing the data in Table 2 and Table 3, it can be seen from Table 2 (sampling in the direction of length first and then width) that the P and S elements in the negative plate of A and B batteries have little difference with the P and S elements in C battery, and the B element has large difference. By carefully comparing the P, S, and B content data of each first sample area in the negative plate of A and B batteries in Table 2, it can be found that in the P element distribution matrix and the S element distribution matrix, the P element content ratio and the S element content ratio of any two areas are less than 2 (with the element content of the area with lower element content as the divisor), which indicates that the P and S elements have good infiltration in the negative plate of A and B batteries. It can be further found that in the B element distribution matrix, the B element content ratio (with the element content of the area with lower element content as the divisor) of any two areas can be calculated to have more ratios greater than 2, and the maximum ratio even reaches 4.62, which indicates that the B element has insufficient infiltration in the negative plate of A and B batteries. And through relevant calculation, the average B element of A, B, and C batteries is 124.7, 121, and 144 respectively. In particular, the B element content in the middle area of the negative plate in B battery is about 50% of that in C battery, and that in A battery is lower, about 42%.

[0042] Similar to Table 2, from Table 3 (sampling from wide to thick direction), the P and S elements of A and B cells are slightly lower than C cell, but the difference is not large, and after careful comparison of the P, S and B content data of each second to be tested sample area in the negative plate of A and B cells in Table 3, it can be found that in the positive-1-up, positive-1-middle, positive-1-down, negative-1-up, negative-1-middle, negative-1-down, positive-2-up, positive-2-middle, positive-2-down, negative-2-up, negative-2-middle, negative-2-down, positive-3-up, positive-3-middle, positive-3-down, negative-3-up, negative-3-middle, negative-3-down areas, the P element content ratio and S element content ratio of any two areas are less than 2 (with the element content of the area with lower element content as the divisor), which indicates that the P and S elements in the negative plate of A and B cells have good infiltration degree; and it can be further found that in the above-mentioned areas, the B element content ratio (with the element content of the area with lower element content as the divisor) of any two areas can be calculated to have more values greater than 2, and the maximum value even reaches 4.62, which indicates that the B element in the negative plate of A and B cells has insufficient infiltration degree. And through relevant calculation, the average B element content of A cell is 94, the average B element content of B cell is 121, and the average B element content of C cell is 212. The B element corresponds to LiODFB additive, which is mainly used to improve the cycle performance and electrochemical stability. Therefore, it can be concluded that the uneven distribution of LiODFB additive is the root cause of the poor cycle performance.

[0043] S4. According to S3, the distribution of P, S and B in the negative electrode sheet is analyzed from different dimensions. In the 9 (K) first sample areas and 18 (Y) second sample areas, the ratio of B element content of any two areas is greater than 2 (using the element content of the area with lower element content as the divisor). Therefore, it is determined that the negative electrode sheet is insufficiently infiltrated with B element. Therefore, according to the above analysis results, the influence of the injection process parameter on the infiltration is verified and the infiltration is improved. The original process parameters: vacuum degree-87kpa, positive pressure 0.3Mpa, cycle number 6 times, 24h standing at room temperature after injection; improvement scheme 1: vacuum degree-87kpa, positive pressure 0.3Mpa, cycle number 10 times, 24h standing at room temperature after injection; improvement scheme 2: vacuum degree-87kpa, positive pressure 0.3Mpa, cycle number 6 times, 24h standing at 45℃ high temperature after injection. The element distribution of the improved scheme 1-2 after formation is quantitatively characterized. The element distribution of the positive electrode sheet has little difference in the length and thickness directions of the electrode sheet, while the element distribution of the negative electrode sheet has great difference. The detection results of P, S and B content in the 9 (K) first sample areas of the negative electrode sheet of the improved A / B cell (sampling in the length direction first and then in the width direction), and the detection results of P, S and B content in the 18 (Y) second sample areas of the negative electrode sheet of the A / B cell are shown in Tables 4 and 5, respectively.

[0044] Table 4 Detection results of P, S and B content in the 9 (K) first sample areas of the negative electrode sheet of the improved A / B cell (sampling in the length direction first and then in the width direction)

[0045]

[0046] Table 5 Detection results of P, S and B content in the 18 (Y) second sample areas of the negative electrode sheet of the A / B cell (sampling in the width direction first and then in the thickness direction)

[0047]

[0048]

[0049] By analyzing the data in Tables 4 and 5, it can be seen that the P, S and B elements in the improvement schemes 1 and 2 are higher than the C battery cell by a certain margin. As for the B element affecting the cycle performance of the battery cell, in the improvement schemes 1 and 2, no matter in each first sample area (respectively in the P, S and B element distribution matrix, sampling in the length direction first and then in the width direction), or in each second sample area (respectively in the positive-1-up, positive-1-middle, positive-1-down, negative-1-up, negative-1-middle, negative-1-down, positive-2-up, positive-2-middle, positive-2-down, negative-2-up, negative-2-middle, negative-2-down, positive-3-up, positive-3-middle, positive-3-down, negative-3-up, negative-3-middle, negative-3-down areas, sampling in the width direction first and then in the thickness direction), the P, S and B element content ratio (using the element content of the area with lower element content as the divisor) of any two areas is not greater than 2, that is, the infiltration performance of the B element in the negative plate is successfully improved, and the infiltration degree of the B element in the negative plate is further improved. At the same time, it can also be seen from Tables 4 and 5 that the average B element of the improvement scheme 1 is 225, and the average B element of the improvement scheme 2 is 229, both of which are higher than the average B element of the C battery cell 212. Therefore, as shown in Figure 4 the test of the improved A and B battery cells (corresponding to the improvement schemes 1 and 2 respectively) in the 1C / 5C (referring to the charge rate being 1C and the discharge rate being 5C) normal temperature cycle performance (250 cycles), the capacity retention rate of the improvement scheme 1 is 89.91%, and the capacity retention rate is increased by 1.97%; the capacity retention rate of the improvement scheme 2 is 92.42%, and the capacity retention rate is increased by 4.48%. Compared with the capacity retention rate (87.94%) of the 250-week control group (the original C battery cell), it even has a higher capacity retention rate. Therefore, by using the method for analyzing the infiltration degree of the battery cell provided by the present application, the infiltration degree of each important component in the electrolyte can be analyzed from the microscopic angle (for example, the microscopic angle of the characteristic element distribution), so that the root cause affecting the cycle performance and other electrochemical performances of the battery cell can be accurately found out, and then the corresponding improvement can be quickly and effectively made according to the root cause, so as to achieve the purpose of quickly and effectively optimizing the cycle performance of the battery.

[0050] In addition, the application of the present application is not limited to the P, S and B elements contained in the electrolyte. For example, the Si element distribution in the widely used silicon-based negative electrode at the present stage can also be characterized by this method. The capacity of the Si negative electrode is high, and the expansion coefficient is high, and whether the dispersion of the Si element is uniform seriously affects the electrical performance of the negative electrode. In addition, some impurity metal elements can also be tested, such as Al, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Ge, In, Ir, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Sb, Sn, Sr, Ta, Ti, V, W, Y, Zn, Zr, etc.

[0051] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application is described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, and these modifications or replacements are within the protection scope of the present application.

Claims

1. A method of analyzing the extent of cell impregnation, characterized by, The method comprises the following steps: S1. disassembling the cell after chemical conversion to obtain a pole piece; the pole piece contains electrolyte, and the electrolyte contains characteristic elements; the pole piece includes at least one of a positive pole piece and a negative pole piece; S2. dividing the pole piece into n regions in the length direction, and dividing each region into m regions in the width direction at the central position in the length direction to obtain K first sample regions, K=n*m; the length of the first sample region is L1, the width is W1, and the thickness is H1; Meanwhile, the pole piece is divided into positive and negative sides with the current collector as the dividing line, and the positive and negative sides are divided into x regions in the width direction, and each region is divided into y regions in the thickness direction to obtain Y second sample regions, Y=2*x*y; the length of the second sample region is L2, the width is W2, and the thickness is H2; S3. testing the content of the characteristic elements in the K first sample regions and the Y second sample regions; the characteristic elements include at least one of P, S, B, F, N, Si, Al, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Ge, In, Ir, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Sb, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr; S4. When the ratio of the content of the characteristic elements in any two regions of the first sample region of the pole piece is greater than 2, and the content of the characteristic elements in the region with lower content of the characteristic elements is taken as the divisor; and / or, when the ratio of the content of the characteristic elements in any two regions of the second sample region of the pole piece is greater than 2, and the content of the characteristic elements in the region with lower content of the characteristic elements is taken as the divisor; it is judged that the pole piece is insufficiently infiltrated; In the S2, in the K first sample regions, when the pole piece is a positive pole piece, L1≥50mm, W1≥19.6mm, and H1≥106μm; when the pole piece is a negative pole piece, L1≥50mm, W1≥19.6mm, and H1≥130μm; In the Y second sample regions, when the pole piece is the positive pole piece, L2≥1492mm, W2≥19.1mm, and H2≥17.6μm; when the pole piece is the negative pole piece, L2≥1563mm, W2≥19.6mm, and H2≥21.6μm; In the S2, K≥9; Y≥18.

2. The method of claim 1, wherein: In the K first sample regions in the S2, when the pole piece is a positive pole piece, L1=50mm, W1=19.6mm, and H1=106μm; when the pole piece is a negative pole piece, L1=50mm, W1=19.6mm, and H1=130μm; In the Y second sample areas, when the pole piece is the positive pole piece, L2=1492mm, W2=19.1mm, H2=17.6μm; when the pole piece is the negative pole piece, L2=1563mm, W2=19.6mm, H2=21.6μm.

3. The method of claim 2, wherein the method is performed by: In the S2, K=9; Y=18. ​ 4. The method of claim 1, wherein: In the S3, the characteristic element includes at least one of P, S and B.

5. The method of claim 1, wherein: In the S3, the content of the characteristic element in the pole piece is tested by an inductively coupled plasma spectrometer.

6. The method for analyzing the degree of cell wetting as described in claim 1, characterized in that, The electrolyte includes the following components: a lithium salt, an organic solvent, a film-forming additive, a functional additive; the mass ratio of the lithium salt, the organic solvent, the film-forming additive and the functional additive is 12-18:74-85:2-5:1-4; The lithium salt includes lithium hexafluorophosphate. The organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate. The film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate. The functional additive includes at least one of lithium difluorosulfonylimide, lithium difluorobisoxalate phosphate, lithium difluorophosphate, lithium bisoxalate borate, 1,3-propanesulfonic acid lactone and ethylene sulfate.

7. The method for analyzing the degree of cell wetting as described in claim 1, characterized in that, The positive pole piece includes a positive electrode material, a first conductive agent and a first binder; the mass ratio of the positive electrode material, the first conductive agent and the first binder is 95-99:1-3.5:0.5-1.5; The positive electrode material includes at least one of lithium iron phosphate positive electrode material, ternary lithium nickel cobalt manganese oxide positive electrode material and lithium manganese iron phosphate positive electrode material; The first conductive agent includes at least one of conductive carbon black and carbon nanotube; and the first binder includes at least one of polyvinylidene fluoride. The negative pole piece includes a negative electrode material, a second conductive agent and a second binder; the mass ratio of the negative electrode material, the second conductive agent and the second binder is 95-99:0.3-2:1-3.5; The negative electrode material includes at least one of natural graphite, artificial graphite and silicon-carbon negative electrode; The second conductive agent includes conductive carbon black; and the second binder includes at least one of carboxymethyl cellulose and butadiene styrene rubber.

8. The method of claim 1, wherein: The battery cell includes a cylindrical battery cell. ​

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