Method and device for evaluating infiltration effect of pole piece

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a method and device for evaluating the infiltration effect of a pole piece, and the method comprises the steps: S1, obtaining a pole piece sample; s2, testing the initial thickness of the pole piece sample; s3, testing the thickness of the infiltrated pole piece sample; step S4, calculating the expansion rate corresponding to each thickness value obtained in the step S3; s5, calculating the standard deviation of each expansion rate obtained in the step S4; s6, the pole piece infiltration effect is judged based on the expansion rate, and the method for evaluating the pole piece infiltration effect has the advantages of being simple in process, short in period and low in cost and is suitable for daily monitoring and short-term verification tests of a production line.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a method and device for evaluating the wetting effect of electrode sheets. Background Art

[0002] The wetting effect of the electrode sheet and the electrolyte injection effect of the battery are two concepts that are closely related but different in the battery manufacturing process. Although the wetting effect of the electrode sheet can reflect the electrolyte injection effect of the battery to a certain extent, the two are not equivalent. Among them, the wetting effect of the electrode sheet refers to the penetration and diffusion of the electrolyte on the surface of the electrode sheet, as well as the interaction ability between the electrolyte and the active material of the electrode sheet, mainly including evaluations of aspects such as the wetting speed, wetting depth, wetting area, and the interfacial stability between the electrolyte and the electrode sheet after wetting. A good wetting effect can ensure that the electrolyte fully and evenly penetrates into the electrode sheet, makes full contact with the active material, and improves the energy density, cycle life, and rate performance of the battery. Poor wetting will cause the electrolyte to fail to effectively penetrate into the electrode sheet, limit the transmission of lithium ions, and reduce the performance of the battery. The electrolyte injection effect of the battery refers to the process and result of injecting the electrolyte into the battery, which includes the injection amount, injection method, injection speed of the electrolyte, and the distribution of the electrolyte on the surface of the electrode sheet after injection. The electrolyte injection effect of the battery directly affects the uniformity and stability of the electrolyte, and thus affects the overall performance of the battery. A good injection effect can ensure that the electrolyte is fully and evenly distributed on the surface of the electrode sheet, providing favorable conditions for subsequent electrochemical reactions. Therefore, in the actual production process, the electrolyte injection effect of the battery has a direct impact on the wetting effect. If the injection effect is poor, it may lead to poor wetting of the electrode sheet. Lithium ions will be hindered during the charge and discharge process, the migration path will become longer, affecting the rate performance and forming an interface during formation, resulting in black spots and lithium deposition, increasing the internal resistance, capacity decline, and long-term cycle performance degradation.

[0003] However, when most existing patents evaluate the electrolyte injection effect of the battery, they often focus more on the wetting effect of the electrode sheet itself, that is, conducting an electrolyte wetting effect test on the electrode sheet that has not been assembled into a battery. What they focus on is the liquid absorption ability formed by the performance of the electrode sheet itself, without considering the influence of the injection parameters on the wetting effect of the entire battery. In fact, this evaluation method of the wetting effect of the electrode sheet is completely divorced from the actual production process of the battery, ignores the influence of the injection process on the wetting effect, and most patents for evaluating the wetting effect of the electrode sheet are not applicable to the battery that has already completed the injection. At the same time, there is currently a lack of a specific evaluation method for the quality of the injection process parameters in the industry.

[0004] In summary, in today's industry where cost reduction and efficiency improvement are constantly emphasized, providing a method that can take into account the impact of liquid injection parameters on the liquid injection effect of batteries, is simple to operate, and can evaluate at low cost and quickly is of great significance for guiding the production process of production lines and identifying in advance the product quality risks caused by poor infiltration. Summary of the Invention

[0005] The object of the present invention is to provide a method and device for evaluating the infiltration effect of electrode sheets based on the swelling rate in view of the above existing technical problems.

[0006] In view of this, on the one hand, the present invention provides a method for evaluating the infiltration effect of electrode sheets, including the steps of:

[0007] S0. Prepare several un-injected batteries of the same batch;

[0008] S1. Extract a battery from step S0, disassemble it to obtain a first electrode sheet to be tested, and take n-fold electrode sheets from the first electrode sheet to be tested as the first electrode sheet sample, where n≥1 and n is a positive integer;

[0009] S2. Take P test points on each folded electrode sheet of the first electrode sheet sample, and measure the initial thickness Z np0 of the electrode sheet; where P≥1 and P is a positive integer, and Z np0 represents the initial thickness of the electrode sheet at the Pth test point on the nth folded electrode sheet;

[0010] S3. Extract k un-injected batteries from step S0, and sequentially perform liquid injection and aging on them; where the aging times of the k un-injected batteries are different, k≥1 and k is a positive integer;

[0011] After the aging of the k batteries is completed, disassemble them to obtain the second electrode sheets to be tested of each battery, and take n-fold electrode sheets from the second electrode sheets to be tested of each battery as the second electrode sheet samples; take P test points on each folded electrode sheet of the second electrode sheet samples, and measure the thickness Z npk of the electrode sheet after aging, where Z npk represents the thickness of the electrode sheet after aging at the Pth test point on the nth folded electrode sheet of the kth battery;

[0012] S4. Calculate the swelling rates S Znpk of the electrode sheets after aging of the k batteries at different test points respectively: where:

[0013] S Znpk is the swelling rate of the electrode sheet after aging at the Pth test point on the nth fold of the kth battery, where is the average value of the initial thicknesses of the electrode sheets at all test points on all folded electrode sheets of the first electrode sheet sample;

[0014] S5. Calculate the standard deviation of the swelling rate of the aged electrode sheets in each of the k batteries at different test points respectively;

[0015] S6. Determine the wetting effect of the electrode sheet based on the standard deviation of the swelling rate in S5 of the k batteries.

[0016] Furthermore, the step S5 includes: the standard deviation A of the swelling rate of the aged electrode sheet of each battery at different test points zk is calculated according to the following formula:

[0017]

[0018] Furthermore, the step S6 includes:

[0019] Based on A calculated in step S5 zk determine the wetting effect of the electrode sheet. When the A of the electrode sheet sample to be tested zk meets the following determination conditions:

[0020] |A z(k-1) - A zk | < △A Z wherein, A zk represents the standard deviation of the swelling rate of the kth battery, and A z(k-1) represents the standard deviation of the swelling rate of the (k - 1)th battery;

[0021] it is considered that the electrode sheet samples of this batch have been completely wetted, and the optimal aging time of this batch of samples is the aging time corresponding to the (k - 1)th battery.

[0022] Furthermore, the first electrode sheet to be tested and the second electrode sheet to be tested have the same polarity, and the first electrode sheet to be tested and the second electrode sheet to be tested are respectively and independently a positive electrode sheet or a negative electrode sheet;

[0023] When the first electrode sheet to be tested is a negative electrode sheet, the value of △A Z is 0.0005 - 0.001;

[0024] When the first electrode sheet to be tested is a positive electrode sheet, the value of △A Z is 0.0003 - 0.0007.

[0025] Furthermore, for the continuous electrode sheet obtained by disassembly, there are a plurality of creases arranged at intervals along its length direction. These creases divide the continuous electrode sheet into several parts, and the electrode sheet between two adjacent creases forms a folded electrode sheet.

[0026] Furthermore, in the step S1, n folded electrode sheets are cut from the first electrode sheet to be tested at intervals;

[0027] In step S2, n-fold electrodes are cut at intervals from the second electrode to be tested of each battery as the second electrode samples.

[0028] Further, the aging times of the k batteries independently include 12 h - 50 h.

[0029] Further, the aging times of the k batteries are set to increase in a gradient manner.

[0030] Further, in step S1, the disassembly of the first electrode to be tested is carried out in an environment with a temperature of 23 ± 3°C and a dew point of DP ≤ -45°C; in step S2, the disassembly of the second electrode to be tested is carried out in an environment with a temperature of 23 ± 3°C and a dew point of DP ≤ -45°C.

[0031] Further, in step S2, P = 9, and the selection process of the 9 test points on each folded electrode is as follows:

[0032] First, draw equally divided lines on each folded electrode of the first electrode sample or the second electrode sample according to the size of each folded electrode, and equally divide the electrode sample to be tested into four equal parts in the length direction and the width direction through the equally divided lines. Then, obtain the intersections of 9 different equally divided lines, and use the intersections of different equally divided lines as the 9 test points on each folded electrode. The numbers of each test point are sequentially recorded as a, b,..., i.

[0033] On the other hand, the present invention also provides a device for evaluating the wetting effect of an electrode, including:

[0034] The first battery disassembly unit: used to extract a battery from a non-injected battery and disassemble the extracted battery to obtain the first electrode to be tested, and take n-fold electrodes from the first electrode to be tested as the first electrode samples, where n ≥ 1 and n is a positive integer;

[0035] The first thickness detection unit: after taking P test points from each folded electrode of the first electrode sample, the first thickness detection unit is used to measure the initial thickness Z of the electrode np0 ; where P ≥ 1 and P is a positive integer, and Z np0 represents the initial thickness of the electrode at the Pth test point on the nth folded electrode;

[0036] The liquid injection unit: used to extract k non-injected batteries from non-injected batteries, and sequentially inject liquid and age them, where the aging times of the k non-injected batteries are different, k ≥ 1, and k is a positive integer;

[0037] The second battery disassembly unit: after the aging of the k batteries is completed, use the second battery disassembly unit to disassemble and obtain the second electrode to be tested of each battery, and take n-fold electrodes from the second electrode to be tested of each battery as the second electrode samples;

[0038] Second thickness detection unit: Take P test points on each folded pole piece of the second pole piece sample, and use the second thickness detection unit to measure the thickness Z of the pole piece after aging. npk , where Z npk represents the thickness of the pole piece after aging at the Pth test point on the nth folded pole piece of the kth battery;

[0039] Data processing unit: The first thickness detection unit and the second thickness detection unit are respectively connected to the data processing unit in signal.

[0040] The data processing unit is used to calculate the swelling rate S of the pole pieces of k batteries after aging at different test points respectively Znpk : Where:

[0041] S Znpk is the swelling rate of the pole piece after aging at the Pth test point on the nth fold of the kth battery, where is the average value of the initial thicknesses of the pole pieces at all test points on all folded pole pieces of the first pole piece sample;

[0042] The data processing unit is also used to calculate the standard deviation of the swelling rates of the pole pieces of each of the k batteries after aging at different test points based on the swelling rates S of the pole pieces of the above k batteries after aging at different test points Znpk ; The data processing unit determines the wetting effect of the pole piece based on the standard deviation of the swelling rate.

[0043] The beneficial effects of the present invention are:

[0044] The method for evaluating the wetting effect of the pole piece according to the present invention has the advantages of simple process, short cycle and low cost, and is suitable for daily monitoring and short-term verification tests of production lines. Description of the Drawings

[0045] Figure 1 is a schematic diagram of the way to determine 9 test points in the pole piece to be measured according to the present invention;

[0046] Figure 2 is a schematic diagram of the pole piece sampling method in the present invention;

[0047] Figure 3 is the negative electrode interface diagram after full charge and full discharge corresponding to the aging time of 12h in the verification example of the present invention;

[0048] Figure 4 is the negative electrode interface diagram after full charge and full discharge corresponding to the aging time of 24h in the verification example of the present invention;

[0049] Figure 5These are the negative electrode interface diagrams after full charge and formation corresponding to the aging times of 36 h and 48 h in the verification examples of the present invention. The left side shows the interface diagram corresponding to 36 h, and the right side shows the interface diagram corresponding to 48 h;

[0050] Figure 6 This is the statistical chart of the negative electrode interface after full charge and formation corresponding to different aging times in the verification examples of the present invention. Detailed implementation manners

[0051] Next, the technical solutions in the embodiments of the present application will be clearly described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope protected by the present application.

[0052] For the sake of convenience of description, technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the authorization specification. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation.

[0053] It should be noted that in the present application, the terms "include", "comprise", or any other variant thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device including a series of elements not only includes those elements but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article, or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article, or device including that element. In addition, it should be pointed out that the methods and devices in the embodiments of the present application are not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in a reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. Additionally, the features described with reference to certain examples may be combined in other examples.

[0054] A method for evaluating the wetting effect of a pole piece, comprising:

[0055] S0. Prepare a number of un-injected batteries of the same batch;

[0056] S1. Extract a battery from step S0, disassemble it to obtain a first test pole piece, and take n folded pole pieces from the first test pole piece as the first pole piece sample, where n≥1 and n is a positive integer;

[0057] S2. Take P test points on each folded pole piece of the first pole piece sample, and measure the initial thickness Z of the pole piece. np0 ; where P≥1 and P is a positive integer, and Z np0 represents the initial thickness of the pole piece at the Pth test point on the nth folded pole piece;

[0058] S3. Extract k un-injected batteries from step S0, and perform liquid injection and aging on them in sequence; among them, the aging times of the k un-injected batteries are different, k≥1, and k is a positive integer;

[0059] After the aging of the k batteries is completed, disassemble to obtain the second pole pieces to be measured of each battery, and take the n-folded pole pieces from the second pole pieces to be measured of each battery as the second pole piece samples; take P test points on each folded pole piece of the second pole piece samples, and measure the thickness Z of the pole piece after aging. npk , where Z npk represents the thickness of the pole piece after aging at the Pth test point on the nth folded pole piece of the kth battery;

[0060] S4. Calculate the expansion rates S of the pole pieces after aging of the k batteries at different test points respectively. Znpk : Among them:

[0061] S Znpk is the expansion rate of the pole piece after aging at the Pth test point on the nth fold of the kth battery, where is the average value of the initial thicknesses of the pole pieces at all test points on all folded pole pieces of the first pole piece sample;

[0062] It can be understood that the first pole piece sample has n folded pole pieces, and there are P test points on each folded pole piece, then is the average value of the initial thicknesses of the pole pieces at the n*P test points of the first pole piece sample.

[0063] S5. Calculate the standard deviations of the expansion rates of the pole pieces after aging of each of the k batteries at different test points respectively;

[0064] S6. Based on the standard deviations of the expansion rates in S5 of the k batteries, determine the wetting effect of the pole pieces.

[0065] Further, the step S5 includes: the standard deviation A of the expansion rates of the pole pieces after aging of each battery at different test points zk is calculated according to the following formula:

[0066]

[0067] Further, the step S6 includes:

[0068] According to A calculated in step S5 zkJudge the soaking effect of the electrode sheet. When the A of the electrode sheet sample to be measured zk meets the following judgment conditions:

[0069] |A z(k-1) - A zk | < △A Z where A zk represents the standard deviation of the swelling rate of the kth battery, and A z(k-1) represents the standard deviation of the swelling rate of the (k - 1)th battery;

[0070] It is considered that the electrode sheet samples of this batch have been completely soaked, and the optimal aging time for the samples of this batch is the aging time corresponding to the (k - 1)th battery.

[0071] It should be noted that the value of △A in this application Z can be selected according to actual needs.

[0072] As some examples of the present invention, the polarities of the first electrode sheet to be measured and the second electrode sheet to be measured are the same, and the first electrode sheet to be measured and the second electrode sheet to be measured are independently a positive electrode sheet or a negative electrode sheet;

[0073] When the first electrode sheet to be measured is a negative electrode sheet, the value of △A Z is 0.0005 - 0.001;

[0074] When the first electrode sheet to be measured is a positive electrode sheet, the value of △A Z is 0.0003 - 0.0007.

[0075] For the method for evaluating the soaking effect of the electrode sheet based on the swelling rate of the present invention, it can not only evaluate the soaking effect of the electrode sheet sample, but also confirm how much aging time the electrode sheet can reach complete soaking according to the result obtained in step S6, guide the actual production process, and apply an appropriate high-temperature aging treatment time to the electrode sheet.

[0076] It should be noted that, as Figure 2 shown, for the continuous electrode sheet obtained by disassembling, there are a plurality of spaced-apart, widthwise extending broken lines (crease marks) along its length direction. Taking these broken lines (crease marks) naturally formed by winding as a distinction, the electrode sheet area divided by two adjacent broken lines (crease marks) is 1 fold. Specifically, as Figure 2 the red lines in show the positions and directions of some broken lines (crease marks). These broken lines (crease marks) divide the continuous electrode sheet into several parts, and the electrode sheet between two adjacent broken lines (crease marks) constitutes the one-fold electrode sheet described in the present invention.

[0077] As some examples of the present invention, for a battery with a total number of folds of 121, when n is 3, the 1st, 61st, and 121st folds can be taken as the electrode sample; when n is 4, the 1st, 41st, 81st, and 121st folds can be taken as the electrode sample.

[0078] As some examples of the present invention, in the step S1, n-fold electrode pieces are cut at intervals from the first electrode piece to be tested;

[0079] In the step S2, n-fold electrode pieces are cut at intervals from the second electrode piece to be tested of each battery as the second electrode sample

[0080] In this sampling method, by including the folds near the beginning and the end of the core, it can be ensured that the electrode samples cover different positions of the entire core, more comprehensively reflecting the impregnation situation of the entire core. On this basis, in addition to the beginning and the end of the core, the total number of folds of the core is roughly evenly divided into (n - 1) parts for uniform interval sampling, which can ensure that the electrode samples are evenly distributed on the core. This helps to reduce the deviation caused by overly concentrated sampling positions, improve the accuracy of the evaluation of the impregnation effect. At the same time, this sampling method is applicable to cores with different total numbers of folds. Whether the total number of folds of the core is more or less, the sampling requirements can be met by adjusting the value of m and the sampling positions. This multi-point sampling method can better reflect the impregnation situation of the entire battery and reduce the influence of accidental errors on the evaluation results. At the same time, in the present invention, sampling is carried out according to a fixed sampling rule, which can standardize the sampling process and facilitate subsequent data analysis and processing.

[0081] As some examples of the present invention, the aging times of the k batteries independently include 12h - 50h.

[0082] As some examples of the present invention, the aging times of the k batteries are set to increase in a gradient. It can be understood that the increasing gradient can be selected according to actual needs. For example, the absolute value of the difference in the formation times of any two adjacent batteries can be selected as 2h, or it can also be 4h, etc. It can be understood that when the absolute value of the difference in the formation times of any two adjacent batteries is smaller, the natural test results are more accurate.

[0083] As a preferred example of the present invention, in the step S1, the disassembly of the first electrode piece to be tested is carried out in an environment with a temperature of 23 ± 3°C and a dew point of DP ≤ -45°C; in the step S2, the disassembly of the second electrode piece to be tested is carried out in an environment with a temperature of 23 ± 3°C and a dew point of DP ≤ -45°C.

[0084] As a preferred example of the present invention, in the steps S1 and S2, the thickness testing instrument used can be a micrometer.

[0085] Preferably, in the step S2, P is 9, and the selection process of the 9 test points on each folded pole piece is as follows:

[0086] First, draw equidistant lines on the basis of the size of each folded pole piece of the first pole piece sample or the second pole piece sample, and equally divide the pole piece sample to be measured into four equal parts in the length direction and the width direction through the equidistant lines. Then, obtain the intersections of 9 different equidistant lines, and use the intersections of different equidistant lines as the 9 test points on each folded pole piece. The numbers of each test point are sequentially recorded as a, b, …, i.

[0087] Example 1:

[0088] This example illustrates a method for evaluating the infiltration effect of a pole piece, including:

[0089] S0. Prepare 5 un-injected 54Ah batteries of the same batch;

[0090] Among them, the positive electrode ratio (mass ratio) of the battery: LiFePO4:SP:CNT:PVDF = 96:1:1:2;

[0091] Negative electrode mass ratio: graphite:CMC:SBR:SP = 95:2:2:1;

[0092] S1. Extract 1 un-injected battery from step S0, and disassemble it to obtain a positive electrode pole piece and a negative electrode pole piece in an environment of 25°C and a dew point: DP of -45°C. Taking the negative electrode pole piece as an example, take 1 folded pole piece from the negative electrode pole piece as the first pole piece sample;

[0093] S2. Take 9 test points on each folded pole piece of the first pole piece sample, and measure the initial thickness Z of the pole piece np0 ; The initial thicknesses of the pole pieces at the 9 test points are as follows (unit: mm):

[0094] Z 110 = 0.1106, Z 120 = 0.1123, Z 130 = 0.1115, Z 140 = 0.1106, Z 150 = 0.1105, Z 160 = 0.1043,

[0095] Z 170 = 0.1109, Z 180 = 0.1109, Z 190 = 0.1105;

[0096] S3. Extract 4 un-injected batteries from step S0, and sequentially perform liquid injection and high-temperature aging (43 ± 3°C) on them; among them, the aging times of the 4 un-injected batteries are 12h, 24h, 36h, and 48h respectively;

[0097] Among them, the mass components of the electrolyte are as follows:

[0098] LiFP6:LiFSI:EC:EMC:VC:DTD:FEC:TMSP:EOEOEA = 30:5:48:112:4:2:2:1:1;

[0099] After the aging of the above 4 batteries is completed, in an environment of 25°C and a dew point: DP of -45°C, disassemble to obtain the negative electrode sheets of each battery as the second test electrode sheets, and take 1 folded electrode sheet from the second test electrode sheets of each battery as the second electrode sheet sample; take 9 test points on each folded electrode sheet of the second electrode sheet sample, and measure the thickness Z of the electrode sheet after aging npk , where the thickness of the electrode sheet after aging at the 9 test points is as follows;

[0100] For the first battery with an aging time of 12h: Z 111 = 0.1176, Z 121 = 0.1198, Z 131 = 0.1173, Z 141 = 0.1161, Z 151 = 0.1162, Z 161 = 0.1141, Z 171 = 0.1176, Z 181 = 0.1131, Z 191 = 0.1197;

[0101] For the second battery with an aging time of 24h: Z 112 = 0.1153, Z 122 = 0.1204, Z 132 = 0.1188, Z 142 = 0.1184, Z 152 = 0.119, Z 162 = 0.1194, Z 172 = 0.1171, Z 182 = 0.1184, Z 192 = 0.1192;

[0102] For the third battery with an aging time of 36h: Z 113 = 0.1218, Z 123 = 0.1198, Z 133 = 0.1218, Z 143 = 0.1196, Z 153 = 0.1187, Z 163 = 0.1186, Z 173 = 0.1189, Z 183= 0.1193, Z 193 = 0.1207;

[0103] For the fourth cell with an aging time of 48 h: Z 114 = 0.1224, Z 124 = 0.1205, Z 134 = 0.1204, Z 144 = 0.1200, Z 154 = 0.1192, Z 164 = 0.1189, Z 174 = 0.1216, Z 184 = 0.1204, Z 194 = 0.1189;

[0104] S4, calculate the swelling rate S of the electrodes of the 4 cells after aging at different test points Znpk , and the specific results are as follows;

[0105] For the first cell with an aging time of 12 h: S Z111 = 0.0668, S Z121 = 0.0868, S Z131 = 0.0641, S Z141 = 0.0532, S Z151 = 0.0541, S Z161 = 0.0351, S Z171 = 0.0668, S Z181 = 0.0260, S Z191 = 0.0859;

[0106] For the second cell with an aging time of 24 h: S Z112 = 0.0460, S Z122 = 0.0922, S Z132 = 0.0777, S Z142 = 0.0741, S Z152 = 0.0795, S Z162 = 0.0832, S Z172 = 0.0623, S Z182 = 0.0741, S Z192 = 0.0813;

[0107] For the third cell with an aging time of 36 h: S Z113 = 0.1049, S Z123 = 0.0868, S Z133 = 0.1049, S Z143 = 0.0850, S Z153 = 0.0768, SZ163 = 0.0759, S Z173 = 0.0786, S Z183 = 0.0822, S Z193 = 0.0950;

[0108] For the fourth cell with an aging time of 48 h: S Z114 = 0.1104, S Z124 = 0.0931, S Z134 = 0.0922, S Z144 = 0.0886, S Z154 = 0.0813, S Z164 = 0.0786, S Z174 = 0.1031, S Z184 = 0.0922, S Z194 = 0.0786

[0109] S5, calculate the standard deviation A of the swelling rate of the aged electrode sheets of each of the 4 cells at different test points respectively zk , as follows:

[0110] The standard deviation of the swelling rate of the first cell with an aging time of 12 h, Az1 = 0.0193;

[0111] The standard deviation of the swelling rate of the second cell with an aging time of 24 h, Az2 = 0.0126;

[0112] The standard deviation of the swelling rate of the third cell with an aging time of 36 h, Az3 = 0.0107;

[0113] The standard deviation of the swelling rate of the fourth cell with an aging time of 48 h, Az4 = 0.0102;

[0114] S6, for every two adjacent standard deviations of the swelling rate, evaluate the wetting effect according to whether the discrimination formula |A zk - A z(k+1) | < △A Z In this example, △A Z takes the value of 0.001, as follows:

[0115] |A z1 - A z2 | = 0.0067, does not satisfy |A zk - A z(k+1) | < △A Z , it is considered that the aging for 12 h does not meet the wetting requirement;

[0116] |A z2 - A z3 | = 0.0019, does not satisfy |A zk - Az(k+1) |<△A Z It is considered that the aging for 24 h does not meet the infiltration requirement;

[0117] |A z3 -A z4 | = 0.0005, which meets the requirement of |A zk -A z(k+1) |<△A Z It is considered that the aging for 36 h meets the infiltration requirement;

[0118] Therefore, it is finally considered that 36 h is the optimal infiltration duration.

[0119] Example 2

[0120] This example provides a device for evaluating the infiltration effect of a pole piece, including:

[0121] The first battery disassembly unit: used to extract a battery from an un-injected battery, disassemble the extracted battery to obtain the first pole piece to be tested, and take n folded pole pieces from the first pole piece to be tested as the first pole piece sample, where n≥1 and n is a positive integer;

[0122] The first thickness detection unit: after taking P test points from each folded pole piece of the first pole piece sample, the first thickness detection unit is used to measure the initial thickness Z of the pole piece np0 ; where P≥1 and P is a positive integer, and Z np0 represents the initial thickness of the pole piece at the Pth test point on the nth folded pole piece;

[0123] The injection unit: used to extract k un-injected batteries from the un-injected battery, and inject and age them in sequence. Among them, the aging times of the k un-injected batteries are different, where k≥1 and k is a positive integer;

[0124] The second battery disassembly unit: after the aging of the k batteries is completed, use the second battery disassembly unit to disassemble and obtain the second pole piece to be tested for each battery, and take n folded pole pieces from the second pole piece to be tested for each battery as the second pole piece sample;

[0125] The second thickness detection unit: take P test points on each folded pole piece of the second pole piece sample, and use the second thickness detection unit to measure the thickness Z of the pole piece after aging npk where Z npk represents the thickness of the pole piece after aging at the Pth test point on the nth folded pole piece of the kth battery;

[0126] The data processing unit: The first thickness detection unit and the second thickness detection unit are respectively connected to the data processing unit in a signal connection;

[0127] The data processing unit is used to calculate the expansion rate S of the pole pieces after aging of the k batteries at different test pointsZnpk : Wherein:

[0128] S Znpk is the swelling rate of the electrode sheet after aging at the P-th test point on the n-th fold of the k-th battery, where is the average value of the initial thickness of the electrode sheet at all test points on all folded electrode sheets of the first electrode sheet sample;

[0129] The data processing unit is further configured to calculate the standard deviation of the swelling rate of the electrode sheets after aging of each of the k batteries at different test points based on the swelling rate S of the electrode sheets after aging of the above-mentioned k batteries Znpk at different test points; the data processing unit determines the wetting effect of the electrode sheet based on the standard deviation of the swelling rate.

[0130] In some embodiments, the first battery disassembly unit and the second thickness detection unit may be completely the same or different. For example, the first battery disassembly unit and the second thickness detection unit independently include manually disassembling the battery by hand or disassembling it using a battery disassembly fixture in the prior art.

[0131] In some embodiments, the first thickness detection unit and the second thickness detection unit may be completely the same or different. For example, the first thickness detection unit and the second thickness detection unit independently include manually measuring the thickness by hand or using a fixture for measuring the thickness of the electrode sheet in the prior art. Among them, manually measuring the thickness by hand may include a vernier caliper, a micrometer, etc.; the fixture for measuring the thickness of the electrode sheet in the prior art includes a laser thickness gauge, etc.

[0132] In some embodiments, the data processing unit may be a processor or the like.

[0133] In some embodiments, the data processing unit is further configured to calculate the standard deviation of the swelling rate of the electrode sheets after aging of each of the k batteries at different test points based on the swelling rate S of the electrode sheets after aging of the above-mentioned k batteries Znpk at different test points, which specifically includes:

[0134] The standard deviation A of the swelling rate of the electrode sheets after aging of each battery at different test points zk is calculated according to the following formula:

[0135]

[0136] In some embodiments, the data processing unit determines the wetting effect of the electrode sheet based on the standard deviation of the swelling rate, which specifically includes:

[0137] When the A of the electrode sheet sample to be tested zk meets the following determination conditions:

[0138] |A z(k-1) -A zk |<△A Z When, where A zk represents the standard deviation of the swelling rate of the k-th battery, and A z(k-1) represents the standard deviation of the swelling rate of the (k - 1)-th battery;

[0139] It is considered that the sample of the current batch of electrode sheets has been completely infiltrated, and the optimal aging time for this batch of samples is the aging time corresponding to the (k - 1)-th battery.

[0140] Specifically, the value of △A can be input into the data processing unit, and an algorithm can be set. When the data processing unit calculates that |A Z -A z(k-1) -A zk |<△A Z the output shows that the optimal aging time for this batch of samples is the aging time corresponding to the (k - 1)-th battery.

[0141] In some embodiments, the first electrode sheet to be tested and the second electrode sheet to be tested have the same polarity, and the first electrode sheet to be tested and the second electrode sheet to be tested are independently a positive electrode sheet or a negative electrode sheet respectively;

[0142] When the first electrode sheet to be tested is a negative electrode sheet, the value of △A Z is 0.0005 to 0.001;

[0143] When the first electrode sheet to be tested is a positive electrode sheet, the value of △A Z is 0.0003 to 0.0007.

[0144] Verification example:

[0145] During the charging process of the battery, due to poor infiltration, there are differences in the infiltration states of different regions of the negative electrode sheet. During the formation process, when the SEI film is formed, such differences in the infiltration state will, in the light case, lead to inconsistent stress distributions between regions, thus causing the surface stress of the negative electrode sheet to be distorted, resulting in wrinkles or irregular protrusions or depressions; in the severe case, it will directly affect the film-forming quality of the SEI film, causing lithium plating or the appearance of black spots.

[0146] Select another 4 batteries of the same batch, and perform liquid injection and room-temperature aging on them in sequence; among them, the aging times of the 4 non-liquid-injected batteries are 12h, 24h, 36h, and 48h respectively (i.e., these 4 batteries are processed exactly the same as the battery in step S3).

[0147] After the above 4 batteries are aged, they are then subjected to formation and grading in sequence;

[0148] The steps of the formation are as follows:

[0149] The whole process is carried out under a negative pressure value of -75 KPA;

[0150] The first step: Constant current charging at 0.05C, cut-off time 60 min, cut-off voltage 3.1V, cut-off capacity 2.8 Ah;

[0151] The second step: Constant current charging at 0.1C, cut-off time 60 min, cut-off voltage 3.3V, cut-off capacity 5.5 Ah;

[0152] The third step: Constant current charging at 0.2C, cut-off time 31 min, cut-off voltage 3.5V, cut-off capacity 6.5 Ah;

[0153] The fourth step: Constant current discharging at 0.2C, cut-off time 1 min, cut-off voltage 2.5V, cut-off capacity 1.0 Ah;

[0154] The steps of capacitance grading are as follows:

[0155] The first step: Constant current and constant voltage charging at 0.5C, 3.65V, cut-off time 300 min, cut-off voltage 2.7V, cut-off capacity 60 Ah;

[0156] The second step: Constant current discharging at 1C, cut-off time 120 min, cut-off voltage 2.5V, cut-off capacity 60 Ah;

[0157] The third step: Constant current discharging at 0.5C, cut-off time 120 min, cut-off voltage 2.5V, cut-off capacity 10 Ah;

[0158] The fourth step: Constant current discharging at 0.2C, cut-off time 30 min, cut-off voltage 2.5V, cut-off capacity 5.5 Ah;

[0159] The fifth step: Constant current discharging at 0.1C, cut-off time 30 min, cut-off voltage 2.5V, cut-off capacity 2.9 Ah;

[0160] The sixth step: Constant current charging at 0.5C, cut-off time 24 min, cut-off voltage 3.65V, cut-off capacity 12 Ah;

[0161] The sixth step: Constant current charging at 0.1C, cut-off time 17.8 min, cut-off voltage 3.2V, cut-off capacity 2 Ah;

[0162] After capacitance grading is completed, the 4 batteries are disassembled to obtain their negative electrode plates in an environment of 25℃ and dew point: DP is -45℃, as specifically Figures 3 - 6 shown:

[0163] As can be seen from the figure, for the interface after 12 hours of aging, there are many wrinkles accompanied by black spots and a small amount of lithium plating; for the interface after 24 hours of aging, there are more wrinkles; for the interfaces after 36 hours and 48 hours of aging, the interfaces are golden yellow, flat and normal. Thus, 36 hours is the optimal aging time. That is, the method provided by the present invention can evaluate the wetting effect of the electrode sheet accurately and quickly.

[0164] In summary, it can be known that: the method for evaluating the wetting effect of the electrode sheet provided by the present invention is based on measuring the thickness of the electrode sheet to calculate the swelling rate, so as to evaluate the wetting degree of the electrode sheet under different aging times. Through the swelling rate at each point of the electrode sheet, it can not only evaluate the wetting effect of the electrode sheet, judge whether the wetting degree meets the production requirements, effectively monitor the actual effect of wetting in the production line, and identify in advance the product quality risks caused by poor wetting; but also according to the results obtained in step S6, confirm how much aging time the electrode sheet takes to reach complete wetting, determine the optimal aging time, guide the actual production process, apply an appropriate high-temperature aging treatment time to the electrode sheet, and achieve the balance point of product quality, production efficiency and production cost, which has very important practical significance.

[0165] The method for evaluating the wetting effect of the electrode sheet described in the present invention has the advantages of simple process, short cycle and low cost, and is suitable for the daily monitoring of the production line and short-term verification tests.

[0166] Through actual tests, it is found that although there are certain errors in the method for evaluating the wetting effect of the electrode sheet described in the present invention, and the relevant parameters obtained cannot completely replace laboratory testing, it still has very important practical significance. It focuses on the relative change trend rather than a single value, can obtain a large amount of data quickly and at low cost, evaluate the liquid injection and wetting effect of the electrode sheet through data comparison, is suitable for the rapid response of the production line, and can guide the production of the production line.

[0167] The embodiments of the present application have been described above in conjunction with the accompanying drawings. Without conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all belong to the protection scope of the present application.

Claims

1. A method for evaluating the infiltration effect of a pole piece, characterized in that, Including the steps: S0. Prepare a number of un-injected batteries of the same batch. S1. Extract a battery from step S0, disassemble it to obtain a first test electrode, and take n-fold electrodes from the first test electrode as the first electrode sample, where n≥1 and n is a positive integer. S2, take P test points on each folded pole piece of the first pole piece sample, and measure the initial thickness Z of the pole piece np0 ; where P ≥ 1 and P is a positive integer, Z np0 represents the initial thickness of the pole piece at the P-th test point on the n-th folded pole piece; S3. Extract k un-injected batteries from step S0, and sequentially perform injection and aging on them. Among them, the aging times of the k un-injected batteries are different, k≥1 and k is a positive integer. After the aging of k batteries is completed, disassemble to obtain the second electrode to be tested of each battery, and take n folded electrodes from the second electrode to be tested of each battery as the second electrode sample; take P test points on each folded electrode of the second electrode sample, and measure the thickness Z of the electrode after aging npk , where Z npk represents the thickness of the electrode after aging at the Pth test point on the nth folded electrode of the kth battery; S4. Calculate the swelling rate S of the electrodes of k batteries after aging at different test points respectively Znpk where: S Znpk is the swelling rate after aging of the electrode at the P-th test point on the n-th fold of the k-th battery, where is the average value of the initial thickness of the electrode at all test points on all folded electrodes of the first electrode sample; S5. Calculate the standard deviation of the swelling rate of the aged electrodes of each of the k batteries at different test points respectively. S6. Based on the standard deviation of the swelling rate in S5 of the k batteries, determine the wetting effect of the electrodes.

2. The method for evaluating the impregnation effect of the electrode sheet according to claim 1, characterized in that The step S5 includes: the standard deviation A of the swelling rate of the aged electrode sheet of each battery at different test points zk Calculated according to the following formula:

3. The method for evaluating the impregnation effect of the electrode sheet according to claim 2, wherein, The step S6 includes: A obtained according to step S5 zk Determine the impregnation effect of the electrode sheet. When A of the electrode sheet sample to be measured zk Meets the following determination conditions: |A z(k-1) -A zk |<△A Z When, where A zk represents the standard deviation of the expansion rate of the k-th battery, and A z(k-1) represents the standard deviation of the expansion rate of the (k - 1)-th battery; It is considered that the electrode samples of this batch are fully wetted, and the optimal aging time of this batch of samples is the aging time corresponding to the (k - 1)-th battery.

4. The method for evaluating the impregnation effect of the electrode sheet according to claim 3, characterized in that, The polarities of the first test electrode and the second test electrode are the same, and the first test electrode and the second test electrode are independently the positive electrode or the negative electrode respectively. When the first electrode to be measured is a negative electrode, the value of △A Z is 0.0005 to 0.001; When the first electrode to be measured is a positive electrode, the value of △A Z is 0.0003 to 0.0007.

5. The method for evaluating the impregnation effect of the electrode sheet according to claim 1, wherein For the continuous electrode obtained by disassembly, there are multiple creases arranged at intervals along its length direction. These creases divide the continuous electrode into several parts, and the electrode between two adjacent creases constitutes a folded electrode.

6. The method for evaluating the impregnation effect of the electrode sheet according to claim 5, wherein, In the step S1, n-fold electrodes are cut from the first test electrode at intervals. In step S2, n-fold electrodes are cut from the second test electrode of each battery at intervals as the second electrode sample.

7. The method for evaluating the impregnation effect of the electrode sheet according to claim 6, wherein The aging times of the k batteries respectively independently include 12h - 50h.

8. The method for evaluating the wetting effect of the electrode sheet according to claim 6, wherein The aging times of the k batteries are set to increase in a gradient.

9. The method for evaluating the impregnation effect of the electrode sheet according to claim 1, wherein In the step S1, the disassembly of the first test electrode is carried out in an environment with a temperature of 23±3°C and a dew point of DP≤ - 45°C; in step S2, the disassembly of the second test electrode is carried out in an environment with a temperature of 23±3°C and a dew point of DP≤ - 45°C.

10. An apparatus for evaluating the wetting effect of a pole piece, characterized in that, Including: The first battery disassembly unit: used to extract a battery from the un-injected battery, disassemble the extracted battery to obtain a first test electrode, and take n-fold electrodes from the first test electrode as the first electrode sample, where n≥1 and n is a positive integer. First thickness detection unit: After taking P test points from each folded pole piece of the first pole piece sample, the first thickness detection unit is used to measure the initial thickness Z of the pole piece np0 ; where P ≥ 1 and P is a positive integer, and Z np0 represents the initial thickness of the pole piece at the Pth test point on the nth folded pole piece; The injection unit: used to extract k un-injected batteries from the un-injected battery, and sequentially perform injection and aging on them. Among them, the aging times of the k un-injected batteries are different, k≥1 and k is a positive integer. The second battery disassembly unit: after the aging of the k batteries is completed, use the second battery disassembly unit to disassemble and obtain the second test electrode of each battery, and take n-fold electrodes from the second test electrode of each battery as the second electrode sample. Second thickness detection unit: Take P test points on each folded pole piece of the second pole piece sample, and use the second thickness detection unit to measure the thickness Z of the pole piece after aging npk , where Z npk represents the thickness of the pole piece after aging at the Pth test point on the nth folded pole piece of the kth battery; The data processing unit: the first thickness detection unit and the second thickness detection unit are respectively connected to the data processing unit in a signal connection. The data processing unit is used to calculate the swelling rate S of the electrode sheets after aging of k batteries at different test points respectively Znpk wherein: S Znpk is the swelling rate after aging of the electrode at the P-th test point on the n-th fold of the k-th battery, where is the average value of the initial thickness of the electrode at all test points on all folded electrodes of the first electrode sample; The data processing unit is further configured to calculate the standard deviation of the swelling rate of the aged electrode sheets of each of the k batteries at different test points based on the swelling rate S of the aged electrode sheets of the k batteries at different test points. Znpk The data processing unit determines the wetting effect of the electrode sheets based on the standard deviation of the swelling rate.

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