Negative electrode material test method
By controlling the difference in elongation of the current collector and the coating direction, the areal density fluctuation is reduced, which solves the problem of inaccuracy in the test results of the negative electrode material and achieves higher test accuracy and consistency.
Patent Information
- Application Number
- CN202510116641.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-23
- Publication Date
- 2026-07-24
AI Technical Summary
In existing coin cell tests using negative electrode materials, the weight difference leads to inaccurate test results for specific capacity, cycle performance, and rate performance, resulting in poor repeatability and reproducibility.
The current collector has a first-direction elongation greater than the second-direction elongation. The negative electrode material slurry is coated along the first direction and rolled along the second direction. Electrode samples are selected, and the included angle is controlled to be 80° to 100° to reduce the influence of current collector surface density fluctuation.
It significantly improves the accuracy, repeatability, and reproducibility of electrochemical parameters, and enhances the precision of specific capacity test results.
Smart Images
Figure CN122449236A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of negative electrode material testing technology, and more specifically, to negative electrode material testing methods. Background Technology
[0002] Currently, in the research and development of anode materials, it is usually necessary to prepare coin cells to conduct various performance tests on the anode materials, which helps researchers understand the electrochemical performance of the anode materials and provides valuable reference for the development of new battery materials.
[0003] Among the testing parameters for coin cell batteries, specific capacity is one of the most important. Specific capacity directly reflects the amount of electricity that a unit mass of the negative electrode material can store, and it is a crucial indicator for evaluating battery energy density. High specific capacity means that the battery can store more energy with the same weight or volume, thereby improving the device's range. By conducting coin cell testing, the specific capacity of the negative electrode material can be evaluated, thus revealing its energy density performance in practical applications.
[0004] Currently, testing of coin cells for anode materials requires setting up multiple sets of parallel samples for comparison. If the weight difference of coin cells is large, the measured specific capacity, cycle performance, rate performance, etc. will be affected, leading to inaccurate results. The repeatability and reproducibility of the test results of the electrochemical parameters (especially specific capacity) of anode materials are poor. Summary of the Invention
[0005] This application proposes a negative electrode material testing method, which can improve the accuracy, repeatability and reproducibility of electrochemical parameters obtained from coin cell testing, and can improve the accuracy of specific capacity test results.
[0006] In a first aspect, this application provides a method for testing negative electrode materials, comprising the following steps:
[0007] A current collector is provided, the current collector having a first direction and a second direction, the elongation of the first direction of the current collector being greater than the elongation of the second direction, and the angle between the first direction and the second direction being 80° to 100°;
[0008] A slurry containing a negative electrode material is coated along a direction parallel to the first direction onto at least one surface of the current collector and dried to obtain an electrode sheet. The surface of the electrode sheet is provided with an active material layer containing the negative electrode material.
[0009] The electrode sheet is rolled along the second direction, and multiple electrode sheet samples are selected on the electrode sheet;
[0010] The electrode samples were assembled into coin cells and electrochemical parameters were tested to obtain the electrochemical parameters of the electrode samples, including specific capacity.
[0011] In some embodiments, the centers of the selected plurality of electrode samples extend along the same straight line; the angle between the straight line and the extension of the first direction is 80° to 100°.
[0012] In some embodiments, the length of the current collector is 250mm to 400mm and the width is 100mm to 180mm, and the length direction of the current collector is the first direction.
[0013] In some embodiments, a coater is used to apply the slurry along a length direction parallel to the current collector onto at least one surface of the current collector, wherein the coating width of the coater is smaller than the width of the current collector. In some embodiments, the coating width of the coater is 60 mm to 120 mm.
[0014] In some embodiments, when multiple electrode samples are selected, the gap between any two adjacent electrode samples is 2mm to 4mm, and the distance of the electrode sample from the edge of the current collector along the second direction is greater than 6mm.
[0015] In some embodiments, the current collector is a copper foil.
[0016] In some embodiments, the elongation of the current collector in the first direction is P1, where 1.5 ≤ P1 ≤ 3.
[0017] In some embodiments, the elongation of the current collector in the second direction is P2%, where 0.5 ≤ P2 < 1.5.
[0018] In some embodiments, the step of rolling the electrode sheet along the second direction and selecting multiple electrode samples on the electrode sheet includes:
[0019] The electrode sheet is cut along the second direction to form multiple square strips of electrode sheet, and each of the multiple square strips of electrode sheet is subjected to roll forming, with the roll forming pressure controlled at 5T to 6T, to obtain a pre-treated electrode sheet;
[0020] At least four electrode samples are selected along the second direction in the coating area of the pretreated electrode.
[0021] At least two current collector samples are selected in the uncoated area of the pretreated electrode along the second direction.
[0022] In some embodiments, the step of selecting the current collector includes: cutting the current collector along the width direction of the current collector material to obtain the current collector, wherein the width direction of the current collector material is a first direction.
[0023] In some embodiments, the negative electrode material includes at least one of graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials.
[0024] In some embodiments, the method further includes: calculating the specific capacity of the negative electrode material based on the specific capacity of the electrode sample, the mass of the electrode sample, the mass of the current collector sample, and the mass ratio of the negative electrode material in the active material layer, wherein the repeatability range of the specific capacity value of the negative electrode material is <2 mAh / g.
[0025] The technical solution of this application has at least the following beneficial effects:
[0026] The negative electrode material testing method provided in this application involves coating a slurry containing the negative electrode material onto a current collector along a first direction, which improves the uniformity of the active material layer formed on the surface of the current collector, resulting in a more uniform areal density of the active material layer. Next, the electrode is rolled along a second direction. Since the elongation of the current collector in the first direction is greater than that in the second direction, the areal density fluctuation of the current collector in the rolled electrode is smaller. Then, multiple electrode samples are selected on the electrode, and the angle between the second and first directions is controlled to be 80°–100°, that is, the second direction is perpendicular or nearly perpendicular to the first direction, which can better reduce the impact of current collector areal density fluctuations on the quality of the electrode samples.
[0027] Extensive testing revealed that the areal density of the current collector fluctuates significantly in the first direction. For example, the coefficient of variation of the areal density of copper foil can reach approximately 0.3% to 0.5%. The electrode samples obtained using the process described in this application achieve a coefficient of variation of approximately 0.1% for the copper foil, or even lower. Therefore, this application employs rolling the electrode along the second direction and then selecting electrode samples to further reduce the impact of the current collector's areal density fluctuation on the electrochemical parameter testing of the negative electrode material. Electrode samples obtained through this method show minimal fluctuations in specific capacity during coin cell voltage testing, significantly improving the accuracy, repeatability, and reproducibility of the electrochemical parameters obtained from coin cell testing, and enhancing the precision of specific capacity test results. Attached Figure Description
[0028] Figure 1 This is a schematic diagram of the cutting method and coating direction of the current collector material in the prior art;
[0029] Figure 2 A schematic diagram illustrating the cutting method and coating direction of the current collector material provided in the embodiments of this application;
[0030] Figure 3 A schematic diagram illustrating the coating and selection of the current collector provided in the embodiments of this application;
[0031] Figure 4 A schematic diagram illustrating the selection method of dried electrode sheets provided by existing technology. Detailed Implementation
[0032] The following are preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the protection scope of the present invention.
[0033] In a first aspect, this application provides a method for testing negative electrode materials, comprising the following steps:
[0034] Step S10: Provide a current collector, the current collector having a first direction and a second direction, the elongation of the first direction of the current collector being greater than the elongation of the second direction, and the angle between the first direction and the second direction being 80° to 100°;
[0035] Step S20: A slurry containing a negative electrode material is coated along a direction parallel to the first direction onto at least one surface of the current collector, and dried to obtain an electrode sheet. The surface of the electrode sheet is provided with an active material layer containing the negative electrode material.
[0036] Step S30: Roll the electrode sheet along the second direction and select multiple electrode sheet samples on the electrode sheet;
[0037] Step S40: Assemble the electrode sample into a coin cell and test its electrochemical parameters to obtain the electrochemical parameters of the electrode sample, including specific capacity.
[0038] The negative electrode material testing method provided in this application involves coating a slurry containing the negative electrode material onto a current collector along a first direction, which improves the uniformity of the active material layer formed on the surface of the current collector, resulting in a more uniform areal density of the active material layer. Next, the electrode is rolled along a second direction. Since the elongation of the current collector in the first direction is greater than that in the second direction, the areal density fluctuation of the current collector in the rolled electrode is smaller. Then, multiple electrode samples are selected on the electrode, and the angle between the second and first directions is controlled to be 80°–100°, that is, the second direction is perpendicular or nearly perpendicular to the first direction, which can better reduce the impact of current collector areal density fluctuations on the quality of the electrode samples.
[0039] Extensive testing revealed that the areal density of the current collector fluctuates significantly in the first direction. For example, the coefficient of variation of the areal density of copper foil can reach approximately 0.3% to 0.5%. The electrode samples obtained using the process described in this application achieve a coefficient of variation of approximately 0.1% for the copper foil, or even lower. Therefore, this application employs rolling the electrode along the second direction and then selecting electrode samples, which reduces the impact of the current collector's areal density fluctuation on the electrochemical parameter testing of the negative electrode material. Electrode samples obtained through this method show minimal fluctuations in specific capacity during coin cell voltage testing, significantly improving the accuracy, repeatability, and reproducibility of the electrochemical parameters obtained from coin cell testing, and enhancing the precision of specific capacity test results.
[0040] It should be noted that in this application, "parallel or perpendicular to the first direction" can be completely parallel or approximately parallel to the first direction, or perpendicular or approximately perpendicular to the first direction during the test. The floating angle is ±10°, which can be -10°, -5°, 0°, 5°, 10° or any value between them, and is not limited here.
[0041] The testing method of this application will be described in detail below with reference to the embodiments:
[0042] Step S10: Provide a current collector having a first direction and a second direction, wherein the elongation of the first direction of the current collector is greater than the elongation of the second direction, and the angle between the first direction and the second direction is 80° to 100°.
[0043] In some implementations, the current collector material can be obtained commercially and is mainly in the form of a wound structure. The current collector material includes single-sided electrolytic copper foil, double-sided electrolytic copper foil, etc.
[0044] In some embodiments, the current collector is an electrolytic copper foil. As the negative electrode current collector of the battery, the copper foil plays an important role in collecting and transporting electrons. High-performance electrolytic copper foil can improve the charge-discharge performance, cycle life and safety of lithium-ion batteries.
[0045] The current collector material used in the coin cell testing of negative electrode materials is typically electrolytic copper foil rolls. The production process of electrolytic copper foil mainly includes four core steps: solution preparation, electrolysis, surface treatment, and product slitting. The electrolysis process involves placing the cathode roller and anode in the electrolyte. After current is applied, copper ions in the electrolyte deposit on the cathode roller, forming copper foil. As electrolysis progresses, the copper foil gradually thickens, and once the required thickness is reached, it is peeled off from the cathode roller. During electrolysis, the uneven distribution of current density along the width of the copper foil leads to variations in its thickness and areal density. Especially in the electrolytic production of wide copper foil, it is difficult to ensure a uniform distribution of current density, resulting in significant fluctuations in the areal density of the copper foil along its width.
[0046] In some embodiments, the elongation rate of the current collector in the first direction is P1%, where 1.5 ≤ P1 ≤ 3. Specifically, the elongation rate of the current collector in the first direction can be 1.5%, 1.8%, 1.9%, 2.0%, 2.2%, 2.3%, 2.5%, 2.8%, 3%, or any value between them, and is not limited here. It should be noted that in this application, the elongation rate P = (L1 - L0) / L0 × 100% = (length of copper foil after rolling - length of copper foil before rolling) / length of copper foil before rolling * 100%.
[0047] In some embodiments, the elongation rate of the current collector in the second direction is P2%, where 0.5 ≤ P2 < 1.5. Specifically, the elongation rate of the current collector in the second direction can be 1.49%, 1.4%, 1.3%, 1.2%, 1.0%, 0.9%, 0.8%, 0.6%, 0.5%, or any value between them, and is not limited herein.
[0048] In this application, since the elongation of the current collector in the first direction is greater than that in the second direction, by adjusting the direction of the rolling, the quality fluctuation of the copper foil after rolling is further reduced, which can improve the accuracy of the test results.
[0049] In this application, the step of selecting the current collector in S10 includes: cutting the current collector along the width direction of the current collector material to obtain the current collector material, wherein the width direction of the current collector material is a first direction.
[0050] Figure 1 This is a schematic diagram of the cutting method and coating direction of the current collector material in the prior art. Figure 2 This is a schematic diagram illustrating the cutting method and coating direction of the current collector material provided in an embodiment of this application. (See attached diagram.) Figure 1 As shown, in the prior art, the current collector material has a width direction and a length direction, and the coating direction is generally consistent with the length direction. For example... Figure 2As shown in this application, the width direction of the current collector raw material is the first direction, and the length direction is the second direction. In this application, the current collector raw material is cut into long strips along the first direction for later use. The length direction of the cut current collector is the first direction, and the width direction of the cut current collector is the second direction. The slurry containing the negative electrode material is coated on at least one surface of the current collector along a direction parallel to the first direction. That is, the coating direction is parallel or nearly parallel to the first direction.
[0051] In some embodiments, the width of the current collector material is 250mm to 400mm, that is, the length of the current collector obtained by cutting is 250mm to 400mm. Specifically, it can be 250mm, 280mm, 300mm, 320mm, 350mm, 360mm, 380mm, 400mm or any value between them, and is not limited here.
[0052] In some embodiments, the width of the current collector is 100mm to 180mm, specifically 100mm, 120mm, 130mm, 140mm, 150mm, 160mm, 170mm, 180mm or any value between them, and is not limited here.
[0053] In some embodiments, the thickness of the current collector is 4μm to 12μm, specifically 4μm, 6μm, 8μm, 10μm, or 12μm, etc., and is not limited here.
[0054] Step S20: A slurry containing a negative electrode material is coated on at least one surface of the current collector along a direction parallel to the first direction, and dried to obtain an electrode sheet. The surface of the electrode sheet is provided with an active material layer containing the negative electrode material.
[0055] In some embodiments, the particle size D50 of the negative electrode material is 0.1 μm to 30 μm, specifically it can be 0.1 μm, 1 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 19 μm, 20 μm, 30 μm or any value between them, and is not limited here.
[0056] In some embodiments, the negative electrode material includes at least one of graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials.
[0057] In some embodiments, the silicon-based material can be a pure silicon material, a pure silicon-oxygen anode material, a composite of silicon anode material and carbon material, or a composite of silicon-oxygen anode material and carbon material, etc., and is not limited here.
[0058] In some embodiments, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
[0059] In some embodiments, the binder may be at least one of styrene-butadiene rubber (SBR), waterborne acrylic resin, and carboxymethyl cellulose (CMC), and the thickener may be carboxymethyl cellulose (CMC). However, this application is not limited to these materials.
[0060] In some embodiments, the above-mentioned slurry can be prepared according to conventional methods in the art. For example, the negative electrode material and optional conductive agent and binder are usually dispersed in a solvent, which can be deionized water, to form a uniform slurry. The slurry is then coated on the current collector and, after drying, cold pressing and other processes, the negative electrode sheet is obtained.
[0061] In some embodiments, the negative electrode material, conductive agent (conductive carbon black), binder (polyvinylidene fluoride, abbreviated as PVDF), and N-methylpyrrolidone (abbreviated as NMP) are weighed using a balance at a mass ratio of (88-95):(1-2):(4-10):(5-30), and placed in a high-speed disperser for high-speed dispersion. After dispersion, a slurry with uniform dispersion and qualified flowability is obtained.
[0062] In some embodiments, the negative electrode material, conductive agent (conductive carbon black), binder (carboxymethyl cellulose), and pure water are weighed using a balance at a mass ratio of (95-98):(1-3):(0.8-2.0):(30-50), and then placed in a high-speed disperser for high-speed dispersion. After dispersion, a slurry with uniform dispersion and qualified flowability is obtained.
[0063] Understandably, during the slurry preparation process, the ratio of negative electrode material, binder and conductive agent can be adjusted to make the negative electrode material uniformly dispersed in the slurry and optimize the flow properties of the slurry so that the slurry can be uniformly coated.
[0064] In some embodiments, the slurry fineness is <30 μm. The slurry fineness can be measured by dropping the negative electrode slurry into the groove of a scraper fineness gauge, ensuring the sample is evenly distributed within the groove. Using a scraper perpendicular to the plate, the negative electrode slurry is pulled across the entire length of the groove at an appropriate speed. The depth to which particles are uniformly exposed in the groove is observed along a 30° angle to the incident light, and this thickness is recorded as the slurry fineness.
[0065] In some embodiments, the viscosity of the slurry is in the range of 2000 mPa·s to 10000 mPa·s, specifically 2000 mPa·s, 4000 mPa·s, 5000 mPa·s, 7000 mPa·s, 8000 mPa·s, 9000 mPa·s, 10000 mPa·s or any value between them, and is not limited herein.
[0066] Figure 3 A schematic diagram illustrating the coating and selection of the current collector provided in the embodiments of this application, as shown below. Figure 3 As shown, this application controls the slurry to be coated along a direction parallel to the first direction, which improves the uniformity of the active material layer formed on the surface of the current collector, making the areal density of the active material layer more uniform. The coating direction is parallel or approximately parallel to the first direction.
[0067] In some embodiments, the current collector is placed flat on a plate and vacuum-absorbed to ensure uniform adsorption. The well-dispersed slurry is then evenly placed in the center of a coater, which applies the slurry along a first direction to at least one surface of the current collector. The coating width of the coater is less than the width of the current collector. The uncoated portion of the current collector can be used for subsequent selection of current collector samples.
[0068] In some embodiments, the coating width of the applicator is 60mm to 120mm, specifically 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 115mm, 120mm or any value between them, and is not limited here.
[0069] In some implementations, the exposed portions of the electrode sheet, 3 cm each from the head and tail, are first cut off with a blade, and then the electrode sheet is transferred to a forced-air drying oven for baking.
[0070] In some embodiments, the solvent in the slurry is removed by vacuum drying at a temperature of 60°C to 120°C for 1 to 6 hours. When the vacuum oven is opened to release pressure, an inert gas is used for depressurization. The inert gas is selected from at least one of He, Ne, and Ar.
[0071] Step S30, as Figure 3 As shown, the electrode sheet is rolled along the second direction, and multiple electrode sheet samples are selected on the electrode sheet.
[0072] In some embodiments, the angle between the second direction and the first direction is 80° to 100°, specifically 80°, 85°, 88°, 90°, 92°, 95°, 98°, 100° or any value between them, and is not limited herein. This application controls the angle between the second direction of the rolling process and the first direction, wherein the rolling direction is perpendicular to or nearly perpendicular to the first direction.
[0073] In some implementations, step S30 specifically includes:
[0074] like Figure 3 As shown, the dried electrode sheet is cut along the second direction to form multiple square strips of electrode sheet, and the multiple square strips of electrode sheet are subjected to roll pressing treatment, with the roll pressing pressure controlled at 5T to 6T, to obtain pretreated electrode sheet;
[0075] At least four electrode samples are selected along the second direction in the coating area of the pretreated electrode.
[0076] At least two current collector samples are selected in the uncoated area of the pretreated electrode along the second direction.
[0077] In some embodiments, the dried electrode is first cut into square strips along the second direction, with the width H of the square strips being 2cm to 6cm. The two ends of the square strips are uncoated areas 10, i.e., blank areas for current collectors, used to select current collector samples 11, and coated areas 20 of the square strips are used to select electrode samples 12.
[0078] like Figure 3 As shown, when selecting multiple electrode samples, the gap L1 between any two adjacent electrode samples is 2mm to 4mm. Specifically, it can be 2mm, 2.5mm, 3mm, 3.5mm, 4mm, or any value in between, and is not limited here. Controlling the spacing between electrode samples within the above range can reduce correlation interference between electrode samples and ensure the independence of each electrode sample.
[0079] In some embodiments, the distance L2 between the electrode sample 12 and the edge of the current collector along the second direction is greater than 6 mm. Specifically, it can be 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm or any value between them, and is not limited here.
[0080] In some implementations, to match the shape of the button cell, the electrode sheets can be punched using a punching machine to obtain circular electrode sheets.
[0081] In some implementations, before selecting samples, one square electrode strip needs to be rolled and its thickness measured. The strip is then punched, weighed, and its areal density calculated. The theoretical thickness at the compacted density is then calculated using the areal density: Electrode roll thickness = Rolled electrode areal density / Compacted density + Current collector roll thickness. After rolling the remaining square electrode strips to the required thickness, a punching machine is used to punch 2-6 electrode samples and 2-4 current collector samples along the second direction.
[0082] In some embodiments, the diameter of the electrode sample and the current collector sample is the same, which can be 8 to 16 mm. In other embodiments, it can also be 8 mm, 10 mm, 14 mm, 16 mm, etc., and is not limited here.
[0083] Figure 4 A schematic diagram illustrating the selection method of the dried electrode sheet provided by the prior art, as shown below. Figure 4As shown, in the prior art, the electrode rolling and sample selection are generally carried out along the first direction of the current collector (i.e., the width direction). The selected electrode sample is greatly affected by the fluctuation of the surface density of the current collector, and the measured performance parameters (such as specific capacity) are greatly affected.
[0084] In some embodiments, the centers of the selected multiple electrode samples extend along the same straight line; the angle between the straight line and the extension of the first direction is 80° to 100°. This selection of multiple electrode samples is equivalent to a set of parallel samples, resulting in very small quality fluctuations, very similar electrochemical performance data, low overall data volatility, and a very small difference in measured specific capacity, significantly improving the consistency of coining capacitance within the same batch of samples.
[0085] During the coin cell test, the specific capacity of the negative electrode material is calculated as shown in equations (1) to (2):
[0086] The mass of the negative electrode material = (mass of the electrode sample - mass of the current collector sample m0) × the mass ratio of the negative electrode material in the active material layer; Equation (1) Specific capacity of negative electrode material = capacity ÷ mass of negative electrode material; Equation (2)
[0087] It should be noted that many factors affect the accuracy of the specific capacity test in the current coin cell testing process for negative electrode materials. For example, the mass of the current collector in the same set of parallel samples fluctuates greatly, which means that the areal density of the current collector itself fluctuates greatly. Second, the mass m0 of the current collector sample in equation (1) is not accurately weighed and cannot accurately represent the mass of the current collector in the electrode sample to be tested. Third, the mass m0 of the current collector sample in equation (1) is the mass of the current collector before rolling and does not consider the elongation of the current collector after rolling. These three main reasons lead to the inaccuracy of the mass of the negative electrode material calculated using equation (1), which in turn causes a large fluctuation in the specific capacity of the negative electrode material in the coin cell test of equation (2), affecting the accuracy of the performance evaluation of the negative electrode material.
[0088] This application involves coating the copper foil with a slurry along a first direction. During coating, the effective coating area is smaller than the width of the copper foil in the second direction after cutting. This results in uncoated copper foil along both sides of the second direction, facilitating subsequent electrode rolling and punching to obtain copper foil test pieces whose centers are aligned with the center of the electrode sample to be tested. Since the areal density fluctuation of the copper foil sample obtained by punching along the second direction is minimal, the quality of the copper foil sample in the uncoated areas on both sides of the electrode can accurately represent the copper foil quality of the electrode sample to be tested, significantly improving the accuracy of coin cell specific capacity testing.
[0089] According to experimental tests, after cutting the copper foil to the same size as the test piece, a rolling pressure of 4T to 5T is applied using a roller press. The length change of the copper foil sample before and after rolling is measured, and the elongation of the copper foil is calculated accordingly. The elongation of the copper foil is calculated as follows: Copper foil elongation δ = Copper foil length before rolling - Copper foil length after rolling / Copper foil length before rolling * 100%. Experimental investigation revealed that the elongation of the 9μm copper foil in the width direction after rolling is approximately 1.5%-3%, while the elongation in the second direction is approximately 0.5%-1.5%. Therefore, this application adopts rolling processing of the square strip of the electrode sheet from the second direction, that is, the cutting direction is consistent with the rolling direction. The copper foil of the electrode sheet obtained after rolling has a smaller elongation, which can reduce the fluctuation of the quality of different electrode sheet samples caused by the change of copper foil thickness. This can improve the accuracy of the quality m0 of the punched current collector sample (e.g., copper foil sample) and improve the accuracy of the performance evaluation of the negative electrode material.
[0090] In the test scheme of this application, firstly, the slurry is coated along the first direction to obtain an electrode sheet that is conducive to subsequent rolling and punching in the second direction. Secondly, rolling and selecting the sample of the square strip of the electrode sheet in the second direction can reduce the deformation of the copper foil and minimize the impact of the current collector surface density fluctuation in the width direction on the test results, thereby improving the accuracy of the mass m0 of the current collector sample (e.g., copper foil sample) and improving the accuracy of the performance evaluation of the negative electrode material. Finally, since the mass of the current collector sample is very close to the mass of the current collector in the electrode sample, the average weight m0 of the current collector sample is weighed and substituted into equations (1) to (2) to calculate a more accurate mass of the active material layer. This can improve the accuracy, repeatability, and reproducibility of the coin cell test of the negative electrode material without reducing the test efficiency.
[0091] In some embodiments, the obtained electrode samples are weighed using a balance with a weight of 1 / 100,000. For each sample, four electrode samples with the closest weight are selected from eight electrode samples, marked, and placed in a vacuum oven for vacuum baking for more than 8 hours. The dried electrode samples are used for subsequent assembly of button cells.
[0092] Step S40: Assemble the electrode sample into a coin cell and test its electrochemical parameters to obtain the electrochemical parameters of the electrode sample, including specific capacity.
[0093] The electrode sample was used as the positive electrode, and the lithium sheet was used as the negative electrode.
[0094] In some embodiments, the composition of the electrolyte in the coin cell is not specifically limited and can be formulated according to actual needs. The electrolyte includes lithium salts, organic solvents, and optional additives.
[0095] In some embodiments, the lithium salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluorooxalate phosphate, LiN(SO2RF)2, LiN(SO2F)(SO2RF), bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalateborate), lithium difluorooxalateborate, and lithium difluorooxalateborate.
[0096] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of unchanged main claims. First, the quality fluctuation of copper foil obtained by different punching methods is explored:
[0097] First, a section of copper foil with a width of 130 mm and a thickness of 9 μm is randomly cut from a roll of copper foil along the width direction. A 14 mm punching machine is used to punch six copper foil samples with a diameter of φ=14 mm along the width direction of the copper foil. The same method is repeated to punch 10 sections of copper foil. The mass of the multiple copper foil samples along the width direction of the copper foil is obtained by weighing.
[0098] Next, a section of copper foil is randomly cut from the same roll of copper foil along the width direction. A 14mm punching machine is used to punch six copper foil samples with a diameter of φ=14mm along the direction perpendicular to the width of the copper foil (i.e., the length direction). The same method is repeated to punch 10 sections of copper foil. The weights of the multiple copper foil samples perpendicular to the width of the copper foil are obtained.
[0099] Finally, statistical analysis was performed based on the quality data of multiple copper foil samples. The range is the difference between the maximum and minimum quality values in a set of copper foil samples. The relative standard deviation (RSD) is calculated as S / X * 100%, where S is the standard deviation and X is the mean.
[0100] Table 1. Quality fluctuation of copper foil samples parallel to the width of the copper foil.
[0101]
[0102] Table 2. Quality fluctuation of copper foil samples perpendicular to the width of the copper foil.
[0103]
[0104]
[0105] To minimize the impact of copper foil areal density fluctuations along the width direction on the specific capacity test of coin cells, and to improve the stability of the coated electrode, this application's method uses punching along the same copper foil direction perpendicular to the width direction to obtain multiple copper foil samples with very small mass fluctuations. The average mass difference of the φ=14mm copper foil sample is 0.02mg, which is significantly reduced compared to the average mass difference of 0.15mg for the φ=14mm copper foil sample obtained by punching along the width direction. After subsequent coating and rolling processes, since the width direction of the copper foil is equal to the first direction and the length direction is equal to the second direction, the areal density fluctuation of the copper foil in the second direction is smaller than that in the first direction. The current collector masses of the parallel electrode samples obtained by weighing are more similar, reducing the impact on the specific capacity test results of the negative electrode material.
[0106] Since the areal density fluctuation of copper foil in the second direction is smaller than that in the first direction, the portion with larger areal density fluctuation has a larger elongation after rolling. Therefore, the elongation of the current collector in the second direction in this application is smaller than that in the first direction. By selecting the electrode sample after rolling the electrode along the second direction, the mass of the current collector sample (copper foil sample) after rolling can be close to that of the copper foil in the electrode sample. Therefore, copper foil with minimal mass fluctuation can be obtained, thereby improving the accuracy and reproducibility of the specific capacity calculation of the negative electrode material.
[0107] Second, the applicant explored the electrochemical performance testing of electrode samples obtained by different coating and punching methods:
[0108] Example 1
[0109] Step 1: Battery slurry preparation and dispersion: Weigh the graphite anode material, conductive agent SP, and binder PVDF in a ratio of 92:2:6 using a balance of 0.01%, add an appropriate amount of solvent N-methylpyrrolidone (abbreviated as NMP), put it into a high-speed disperser, disperse at 1000 r / min for 2 min, and then disperse at a high speed of 2000 r / min for 8 min. After dispersion, a uniformly dispersed anode slurry with qualified flowability is obtained.
[0110] Step 2, Slurry Coating: After the negative electrode slurry is well dispersed, a section of copper foil is randomly cut from the copper foil roll along the width direction. The length of the copper foil is 300mm and the width is 130mm. The copper foil has a first direction (i.e., the length direction) and a second direction (i.e., the width direction). The elongation of the copper foil in the second direction is less than that in the first direction. The copper foil is placed flat on the coating machine and vacuumed to adsorb evenly. A 200μm I-beam coater is placed in the middle of the copper foil. The negative electrode slurry is evenly placed in the middle of the coater and coated along the first direction. The first direction is completely parallel to the length direction of the copper foil. After coating, the coater is wiped clean. The electrode is transferred to the experimental table using a flat plate. 3cm of the electrode head and tail are cut off with a blade. Then the electrode is transferred to a 100℃ forced-air drying oven and baked for 2 hours.
[0111] Step 3, Electrode Rolling and Punching: After coating and drying, a negative electrode sheet is obtained. The relatively uniform part in the middle of the negative electrode sheet is cut into several 4cm wide square strips along the second direction. First, roll one square strip along the second direction and measure the thickness. After punching, weigh and calculate the electrode sheet surface density. Calculate the theoretical thickness under the corresponding compaction density. Theoretical electrode sheet thickness = electrode sheet surface density after rolling / compaction density + foil thickness after rolling.
[0112] After rolling the remaining small electrode sheets to the required theoretical thickness along the second direction, punch four small round electrode sheets (φ=14mm) and two copper foils (φ=14mm) using a punching machine. The angle between the line connecting the centers of the electrode and copper foil samples and the width direction of the copper foil should be 90°. The gap between the punched electrode samples should be 3mm, and the distance from the electrode sample to the uncoated edge should be 7mm. At this point, the mass of the uncoated copper foil sample at the electrode edge is very close to the mass of the copper foil in the electrode sample. Since the copper foil is rolled, the average mass of the copper foil is weighed and substituted into Formula 1 to calculate a more accurate mass of the negative electrode material. Punching the second row of electrode sheets in the same way yields a total of eight small round electrode sheets and four small round copper foils.
[0113] Step 4: Weighing and Drying the Electrodes: After punching the holes, all electrodes are weighed using a 1 / 100,000 balance. For each sample, four electrode samples with the closest weight are selected from eight samples and marked. These electrode samples will be used for subsequent coin cell assembly. Simultaneously, the weight of each electrode sample and the corresponding copper foil sample are substituted into Formula 1 to calculate the weight of the negative electrode material on each electrode sample. After all electrodes are weighed, they are placed in a vacuum oven and dried under vacuum for at least 8 hours.
[0114] Step 5: Battery Assembly and On-Cabinet Testing: Transfer the dried electrode sheets to a glove box with a water and oxygen content of <0.1ppm. Prepare the necessary materials and consumables for assembly in advance: CR2016 battery case, 16mm diameter lithium sheet, 16mm diameter nickel foam, 16mm diameter gasket, 19mm diameter separator, and electrolyte. The battery assembly sequence is: negative electrode case - nickel foam - lithium sheet - 30μL electrolyte - separator - 30μL electrolyte - electrode sheet to be tested - gasket - positive electrode case. Assemble into a CR2016 coin cell. Assemble 4 CR2016 coin cells for each sample.
[0115] After assembly, the button cells are sealed using a CR2016 sealing machine. After wiping away any excess electrolyte from the battery surface, the batteries are placed on the Blue Electric test cabinet fixture. The active material mass and nominal specific capacity of each battery are entered, and the following charge / discharge regime is invoked to start the test. The test yields electrochemical performance data for the graphite anode material, including its initial charge specific capacity, initial discharge specific capacity, and initial efficiency.
[0116] The charge and discharge regime for the button cell battery provided in this embodiment is as follows: resting: 10h; rate discharge: 0.1C, 0.09C, 0.08C, 0.07C, 0.06C, 0.05C, 0.04C, 0.03C, 0.02C, 0.01C to 0.005V; resting: 10min; rate charge: 0.1C to 2.0V.
[0117] After the test is completed, the specific capacity of the first charge and the specific capacity of the first discharge are obtained. The initial coulombic efficiency = specific capacity of the first discharge / specific capacity of the first charge.
[0118] Example 2
[0119] The only difference from Example 1 is that in step S2, the angle between the first direction and the extension line of the copper foil's length direction is 10°.
[0120] Example 3
[0121] The only difference from Example 1 is that in step S2, the angle between the first direction and the extension line of the copper foil's length direction is -10°.
[0122] Example 4
[0123] The only difference from Example 1 is that in step S3, the angle between the line connecting the centers of the electrode sample and the copper foil sample and the first direction is 80°.
[0124] Example 5
[0125] The only difference from Example 1 is that in step S3, the angle between the line connecting the centers of the electrode sample and the copper foil sample and the first direction is 70°.
[0126] Example 6
[0127] The only difference from Example 1 is that in step S3, the gap between the electrode samples obtained by punching is 2mm, and the distance between the electrode samples and the uncoated edge is 8mm.
[0128] Example 7
[0129] The only difference from Example 1 is that in step S3, the gap between the electrode samples obtained by punching is 4mm, and the distance between the electrode samples and the uncoated edge is 6mm.
[0130] Example 8
[0131] The only difference from Example 1 is the battery slurry preparation and dispersion: the silicon-carbon anode material, conductive agent SP, and binder LA133 adhesive are weighed according to the ratio of 92:2:6 using a balance of 0.01%, and placed in a high-speed disperser. First, disperse at 1000 r / min for 2 min, and then disperse at a high speed of 2000 r / min for 8 min. After dispersion, a uniformly dispersed anode slurry with qualified flowability is obtained.
[0132] Comparative Example 1
[0133] The difference from Example 1 is that:
[0134] In step 2, a copper foil roll with a width of 130mm is used. The elongation of the copper foil roll in the width direction is greater than that in the length direction. During coating, a 300mm*130mm section of copper foil is cut, that is, the elongation of the copper foil in the length direction is less than that in the width direction. The angle between the coating direction and the width direction of the copper foil roll is 90°.
[0135] In step 3, the line connecting the centers of the small electrode discs and the small copper foil discs at the punching positions forms a 0° angle with the line connecting the width (horizontal) of the copper foil.
[0136] Comparative Example 2
[0137] The difference from Example 1 is that:
[0138] In step 3, the rolling direction of the electrode sheet is parallel to the length direction of the copper foil.
[0139] The performance of the anode materials prepared in the examples and comparative examples was tested, and the results of the performance tests are shown in Table 3:
[0140] Table 3. Performance test results of each embodiment and comparative example.
[0141]
[0142]
[0143]
[0144] As can be seen from the experimental results obtained from Examples 1-8 and Comparative Examples 1-2 in Table 3, the range of charge specific capacity of the four coin cells prepared in the examples is <3 mAh / g, and the range of repeatability and reproducibility of the charge specific capacity of the coin cells is <2 mAh / g; the range of charge specific capacity of the four coin cells prepared using Examples 1, 6, and 7 is <2 mAh / g, and the range of repeatability and reproducibility of the charge specific capacity of the coin cells is <1 mAh / g. This greatly improves the consistency of the test results of the coin cells, and the repeatability and reproducibility of the same sample are significantly improved compared with the comparative examples.
[0145] Comparative Example 1: Because the slurry coating did not adopt a first direction that is parallel or nearly parallel to the copper foil, the measured specific capacity of the negative electrode material fluctuated greatly, and the repeatability and reproducibility were poor. This was mainly because the copper foil quality substituted into formula (1) was inaccurate and could not represent the copper foil quality of the electrode sample. Therefore, the consistency, repeatability and reproducibility of the button cell assembled and tested using this scheme were poor.
[0146] In Comparative Example 2, because the rolling direction is based on the width direction, the elongation of the copper foil in the width direction is greater than that in the length direction, resulting in greater quality fluctuations of the copper foil and poor consistency, repeatability, and reproducibility of the assembled and tested button cells.
[0147] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.
Claims
1. A method for testing negative electrode materials, characterized in that, Includes the following steps: A current collector is provided, the current collector having a first direction and a second direction, the elongation of the first direction of the current collector being greater than the elongation of the second direction, and the angle between the first direction and the second direction being 80° to 100°; A slurry containing a negative electrode material is coated along a direction parallel to the first direction onto at least one surface of the current collector and dried to obtain an electrode sheet. The surface of the electrode sheet is provided with an active material layer containing the negative electrode material. The electrode sheet is rolled along the second direction, and multiple electrode sheet samples are selected on the electrode sheet; The electrode samples were assembled into coin cells and electrochemical parameters were tested to obtain the electrochemical parameters of the electrode samples, including specific capacity.
2. The method for testing negative electrode materials according to claim 1, characterized in that, The centers of the selected multiple electrode samples extend along the same straight line; the angle between the straight line and the extension of the first direction is 80° to 100°.
3. The method for testing negative electrode materials according to claim 1, characterized in that, The length of the current collector is 250mm to 400mm and the width is 100mm to 180mm, and the length direction of the current collector is the first direction.
4. The method for testing negative electrode materials according to claim 3, characterized in that, The slurry is applied to at least one surface of the current collector along a length direction parallel to the current collector using a coater, wherein the coating width of the coater is less than the width of the current collector; and / or, the coating width of the coater is 60 mm to 120 mm.
5. The method for testing negative electrode materials according to claim 1, characterized in that, When selecting multiple electrode samples, the gap between any two adjacent electrode samples is 2mm to 4mm, and the distance between the electrode sample and the edge of the current collector along the second direction is greater than 6mm.
6. The method for testing negative electrode materials according to claim 1, characterized in that, The current collector satisfies the following characteristics: (1) The elongation of the current collector in the first direction is P1%, 1.5≤P1≤3; (2) The elongation of the current collector in the second direction is P2%, 0.5≤P2<1.5; (3) The current collector is a copper foil.
7. The method for testing negative electrode materials according to any one of claims 1 to 6, characterized in that, The step of rolling the electrode sheet along the second direction and selecting multiple electrode sample sheets on the electrode sheet includes: The electrode sheet is cut along the second direction to form multiple square strips of electrode sheet, and each of the multiple square strips of electrode sheet is subjected to roll forming, with the roll forming pressure controlled at 5T to 6T, to obtain a pre-treated electrode sheet; At least four electrode samples are selected along the second direction in the coating area of the pretreated electrode. At least two current collector samples are selected in the uncoated area of the pretreated electrode along the second direction.
8. The method for testing negative electrode materials according to any one of claims 1 to 6, characterized in that, The selection step of the current collector includes: cutting the current collector along the width direction of the current collector material to obtain the current collector, wherein the width direction of the current collector material is the first direction.
9. The method for testing negative electrode materials according to any one of claims 1 to 6, characterized in that, The negative electrode material includes at least one of graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials.
10. The method for testing negative electrode materials according to claim 1, characterized in that, The method further includes: calculating the specific capacity of the negative electrode material based on the specific capacity of the electrode sample, the mass of the electrode sample, the mass of the current collector sample, and the mass ratio of the negative electrode material in the active material layer, wherein the repeatability range of the specific capacity value of the negative electrode material is <2 mAh / g.