Pole piece preparation method, pole piece and battery cell

Abstract

The invention discloses a pole piece preparation method, a pole piece and a battery cell, and relates to the technical field of new energy batteries, the pole piece preparation method comprises the following steps: firstly, dividing a coating head into a plurality of intervals in a winding length direction by using a baffle plate, and preparing different positive pole slurry and negative pole slurry according to different intervals; and then the different kinds of slurry prepared in the first step are connected into the corresponding coating head compartment grooves respectively, and then coating and drying are conducted. By adjusting the coating mode, the flatness and uniformity of the pole piece of the battery cell are remarkably improved; specifically, the winding length direction is divided into a plurality of intervals, and the use amount of the conductive agent is adjusted according to the distance between each interval and a tab, so that the problem that the flatness and uniformity of the pole piece are reduced due to the increase of the volume of a battery cell and the increase of the thickness of an electrode is effectively solved, the current density distribution in the pole piece is optimized by the coating mode, and the uniformity of the pole piece is improved. And the polarization phenomenon is reduced, so that the overall performance of the battery cell is improved.

Description

Technical Field

[0001] This invention relates to the field of new energy battery technology, specifically to electrode preparation methods and electrode and battery cell. Background Technology

[0002] In the field of new energy batteries, especially in the manufacturing process of lithium-ion or sodium-ion batteries, the performance and stability of the battery cells are of paramount importance.

[0003] As the market continues to demand higher energy density and cycle life for batteries, the size of battery cells and the thickness of electrodes are also increasing, which poses a huge challenge to the manufacturing process of battery cells.

[0004] Traditional large-volume or thick-electrode cells often face the problem of reduced electrode flatness and uniformity during the manufacturing process.

[0005] Specifically, during disassembly and inspection, dark lines or black spots are easily found in the middle part of the battery cell, which is usually considered to be the result of poor electrolyte wetting. In addition, for fast-charging battery cells, lithium plating often occurs in the outer ring and non-tab areas. These areas are prone to performance bottlenecks due to low current density, which seriously affects the cycle life and safety of the battery cell. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing electrode sheets, as well as electrode sheets and battery cells, to solve the problems in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The electrode preparation method includes the following steps: Step 1: Use a baffle to divide the coating head into multiple sections along the winding length, and prepare different positive and negative electrode slurries according to different sections; Step 2: Inject the different slurries prepared in Step 1 into the corresponding coating head compartments, then coat and dry; Step 3: When the electrode is in the second to fourth section from the bottom of the coating oven, use physical methods to make indentations on the surface of the electrode. The indentations are not completely perpendicular to the coating belt direction. Step 4: The electrode sheets are cold-pressed, die-cut, and slit according to conventional processes to obtain the positive and negative electrode sheets to be wound.

[0008] Preferably, in step one, the amount of conductive agent in the corresponding positive and negative electrode slurries is adjusted according to the distance between each interval and the tab to achieve the purpose of adjusting the current density; the amount of conductive agent in the positive and negative electrode slurries in the intervals closer to the tab can be reduced; the amount of conductive agent in the positive and negative electrode slurries in the intervals closer to the middle of the electrode is greater than the amount of conductive agent in the positive and negative electrode slurries in the intervals closer to the tab; and the amount of conductive agent in the positive and negative electrode slurries in the intervals farther from the tab can be increased.

[0009] Preferably, the positive electrode slurry in the region near the tab is prepared by mixing and stirring lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a ratio of 98~99%: 0.5%~1%: 0.5%~1.5%. The positive electrode slurry in the area near the middle of the electrode is prepared by mixing lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and surfactant in a ratio of 95~97%: 1.5%~2.5%: 1.5%~2.5%: 0.1~0.5%. The positive electrode slurry in the region far from the tab is prepared by mixing lithium iron phosphate, carbon nanotubes, and polyvinylidene fluoride in a ratio of 96~97%:1.5%~2%:1.5%~2%.

[0010] Preferably, the negative electrode slurry in the region near the electrode tab is prepared by mixing and stirring graphite, conductive carbon black, and styrene-butadiene rubber in a ratio of 96~98%: 0.5%~2%: 1%~2%. The negative electrode slurry in the area near the middle of the electrode sheet is prepared by mixing graphite, conductive carbon black, styrene-butadiene rubber, and surfactant in a ratio of 94~96%: 0.5%~2.5%: 1%~2.5%: 0.1~1%. The negative electrode slurry in the region far from the tab is made by mixing graphite, carbon nanotubes, and styrene-butadiene rubber in a ratio of 96-97%: 0.5-2%: 1-2%.

[0011] Preferably, in step two, the thickness of the positive electrode coating is controlled between 0.400 and 0.450 mg / mm. 2 Within the specified range, the coating thickness of the negative electrode sheet is controlled between 0.150 and 0.175 mg / mm. 2 Within the range.

[0012] Preferably, in step three, the physical method involves an interval operation time, the interval operation time being controlled between 0.5 and 1 second, and the shape of the indentation is an intermittent series of short lines; the physical method includes, but is not limited to, using a laser to create the indentation or using compressed air to blow out the indentation.

[0013] Preferably, the indentation tilt angle is controlled between 5 and 15 degrees, and the distance between two adjacent indentations is controlled between 1 and 5 meters.

[0014] The electrode includes a positive electrode and a negative electrode, which are prepared by the above-described preparation method.

[0015] The battery cell uses the aforementioned positive and negative electrode sheets. The positive electrode sheets, negative electrode sheets, and separator are wound into a bare battery cell, which is then assembled and activated to obtain a finished battery cell.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention significantly improves the flatness and uniformity of the electrode sheets of the battery cell by adjusting the coating method. Specifically, by dividing the winding length direction into multiple intervals and adjusting the amount of conductive agent according to the distance between each interval and the electrode tab, the problem of decreased electrode flatness and uniformity caused by the increase in battery cell volume and electrode thickness is effectively solved. This coating method optimizes the current density distribution inside the electrode sheets, reduces polarization, and thus improves the overall performance of the battery cell.

[0017] 2. This invention further improves the performance and stability of the electrode by employing an indentation process. After the coating is dried to a certain degree, inclined indentations are made on the electrode surface. These indentations not only release the stress between different coating layers and prevent delamination during cold pressing, but also increase the surface roughness of the electrode and improve the wettability of the electrolyte on the electrode surface. This indentation process significantly improves the mechanical stability and electrochemical performance of the electrode, enabling the battery cell to exhibit better cycle stability and longer lifespan in high-temperature cycle tests. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the coating method of the present invention.

[0019] Figure 2 This is a comparison chart of the energy densities of Example 1 and Comparative Example 1.

[0020] Figure 3 This is a comparison chart of high-temperature cycling between Example 1 and Comparative Example 1. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] Example 1 In one embodiment, such as Figures 1-3 As shown, the electrode preparation method includes the following steps: Step 1: Use a baffle to divide the coating head into multiple sections along the winding length, and prepare different positive and negative electrode slurries according to different sections; Step 2: Inject the different slurries prepared in Step 1 into the corresponding coating head compartments, then coat and dry; Step 3: When the electrode is in the second to fourth section from the bottom of the coating oven, use physical methods to make indentations on the surface of the electrode. The indentations are not completely perpendicular to the coating belt direction. Step 4: The electrode sheets are cold-pressed, die-cut, and slit according to conventional processes to obtain the positive and negative electrode sheets to be wound.

[0023] In an optional embodiment, in step one, the amount of conductive agent used in the positive and negative electrode slurries near the tab can be reduced; the amount of conductive agent used in the positive and negative electrode slurries near the middle of the electrode is greater than that used in the positive and negative electrode slurries near the tab; and the amount of conductive agent used in the positive and negative electrode slurries far from the tab can be increased.

[0024] The purpose of adjusting the current density is achieved by adjusting the amount of conductive agent in the corresponding positive and negative electrode slurries according to the distance between each interval and the tab.

[0025] In an optional embodiment, the positive electrode slurry in the region near the tab is prepared by mixing and stirring lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a ratio of 98~99%: 0.5%~1%: 0.5%~1.5%. The positive electrode slurry in the area near the middle of the electrode is prepared by mixing lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and surfactant in a ratio of 95~97%: 1.5%~2.5%: 1.5%~2.5%: 0.1~0.5%. The positive electrode slurry in the region far from the tab is prepared by mixing lithium iron phosphate, carbon nanotubes, and polyvinylidene fluoride in a ratio of 96~97%:1.5%~2%:1.5%~2%.

[0026] The high current density near the electrode tab necessitates the construction of a low-resistance conductive network. Conductive carbon black can form a continuous chain structure, reducing sheet resistance. Polyvinylidene fluoride (PVDF) acts as a binder, providing adhesion between the electrode and the aluminum foil. Simultaneously, its polar groups (-CF2-) can form hydrogen bonds with the hydroxyl groups on the lithium iron phosphate surface, enhancing interfacial bonding. A high lithium iron phosphate content ensures optimal capacity utilization, making it suitable for high-energy battery designs.

[0027] Stress concentration in the central region (originating from coating drying shrinkage and winding tension) necessitates the use of surfactants (sodium carboxymethyl cellulose, CMC) to improve slurry dispersibility. CMC molecular chains can encapsulate lithium iron phosphate particles, reducing agglomeration and increasing electrode flexibility by 15%–20%. Increasing the ratio of conductive carbon black to polyvinylidene fluoride (PVDF) compensates for conductivity degradation in the central region; a simultaneous increase in the PVDF ratio maintains the electrode's mechanical strength. Adding trace amounts of CMC is not recommended; excessive amounts can cause a surge in slurry viscosity, affecting coating uniformity.

[0028] The lithium-ion transport path is long in areas far from the electrode tab, necessitating the introduction of carbon nanotubes to construct a three-dimensional conductive network. Carbon nanotubes can shorten the lithium-ion diffusion distance, reducing the polarization voltage at 5C rate. Controlled dispersion of carbon nanotubes ensures uniform distribution, preventing agglomeration that could lead to localized conductivity degradation. The optimized proportion of polyvinylidene fluoride (PVDF) balances electrode flexibility with electrolyte wettability.

[0029] In an optional embodiment, the negative electrode slurry in the region near the tab is prepared by mixing and stirring graphite, conductive carbon black, and styrene-butadiene rubber in a ratio of 96~98%:0.5%~2%:1%~2%. The negative electrode slurry in the area near the middle of the electrode sheet is prepared by mixing graphite, conductive carbon black, styrene-butadiene rubber, and surfactant in a ratio of 94~96%: 0.5%~2.5%: 1%~2.5%: 0.1~1%. The negative electrode slurry in the region far from the tab is made by mixing graphite, carbon nanotubes, and styrene-butadiene rubber in a ratio of 96-97%: 0.5-2%: 1-2%.

[0030] The high current density near the electrode tab necessitates a reinforced conductive network to reduce contact resistance. Conductive carbon black, with its high specific surface area, forms a continuous conductive path, reducing polarization. Styrene-butadiene rubber acts as a binder, providing adhesion between the electrode and the current collector while balancing the slurry's flowability. A high graphite content ensures optimal capacity utilization, making it suitable for high-rate charge / discharge applications.

[0031] Stress concentration occurs in the central region, necessitating the use of surfactants (such as sodium carboxymethyl cellulose, CMC) to improve slurry dispersibility, reduce graphite particle agglomeration, and enhance electrode flexibility. Surfactants can reduce the surface tension of the slurry, promoting uniform slurry spreading during coating and avoiding the "thick at the edges, thin in the middle" problem. Fine-tuning the ratio of conductive carbon black to SBR ensures conductivity while enhancing the electrode's peel strength.

[0032] The lithium-ion transport path is long in areas far from the electrode tab, necessitating the introduction of carbon nanotubes to construct a three-dimensional conductive network. Carbon nanotubes have higher conductivity than conductive carbon black, shortening the lithium-ion diffusion distance and improving rate performance. Controlling the proportion of carbon nanotubes to prevent agglomeration requires high-speed dispersion to achieve uniform distribution. Optimizing the graphite proportion balances capacity and conductivity, making it suitable for fast-charging batteries.

[0033] In an optional embodiment, in step two, the thickness of the positive electrode coating is controlled to be between 0.400 and 0.450 mg / mm. 2 Within the specified range, the coating thickness of the negative electrode sheet is controlled between 0.150 and 0.175 mg / mm. 2 Within the range.

[0034] The thickness range of the positive electrode coating can balance the active material loading and ion transport efficiency. Too thin (<0.400 mg / mm²) will lead to insufficient active material and capacity decay; too thick (>0.450 mg / mm²) may cause the lithium ion diffusion path to be too long and the polarization to be aggravated.

[0035] The thickness of the negative electrode coating can control the thickness of the SEI film formed on the negative electrode surface, avoiding excessive SEI film thickness and reduced first-time efficiency due to excessive coating (>0.175 mg / mm²), or lithium dendrite puncture due to excessive coating (<0.150 mg / mm²).

[0036] In an optional embodiment, in step three, the physical method includes an interval operation time, the interval operation time being controlled between 0.5 and 1 second, and the shape of the indentation is an intermittent short line connection; the physical method includes, but is not limited to, using a laser to create the indentation or using compressed air to blow out the indentation.

[0037] When creating indentations, whether using laser or compressed air methods, it's crucial to control the interval between operations. Specifically, after each indentation is created, a pause of 0.5 to 1 second is required before proceeding to the next operation. This interval helps prevent deformation or damage to the electrode sheet caused by continuous stress, while also ensuring a uniform distribution of indentations.

[0038] The indentation is designed with intermittent short lines connected together. This means the indentation is not a continuous straight line, but rather composed of short lines with intervals between them. This design helps release stress between different coating layers of the electrode and prevents delamination during cold pressing. Simultaneously, the intermittent short line connection also increases the surface roughness of the electrode, improving the wettability of the electrolyte on the electrode surface.

[0039] In an optional embodiment, the indentation tilt angle is controlled between 5 and 15 degrees, and the distance between two adjacent indentations is controlled between 1 and 5 meters.

[0040] The indentation is not completely perpendicular to the coating belt direction, but rather tilted at a certain angle (5-15 degrees). This design prevents wrinkling of the electrode sheet in the indentation direction, ensuring the flatness and uniformity of the electrode sheet. At the same time, the tilted indentation can also guide the flow direction of the electrolyte on the electrode surface to a certain extent, optimizing the electrolyte wetting effect.

[0041] Too small an interval (e.g., <1m) may cause stress superposition in the dense indentation area, leading to local deformation of the electrode; too large an interval (e.g., >5m) may weaken the effect of indentation on electrolyte wetting.

[0042] Example 2 In one embodiment, the electrode includes a positive electrode and a negative electrode, which are prepared by the above-described preparation method.

[0043] Example 3 In one embodiment, the battery cell uses the aforementioned positive and negative electrode sheets. The positive electrode sheets, negative electrode sheets, and separator are wound into a bare battery cell, which is then assembled and activated to obtain a finished battery cell.

[0044] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0045] Example 1 The battery cell is a 100Ah lithium iron phosphate aluminum-cased cell. A baffle is used to divide the coating head into multiple sections along the winding length (taking a three-section coating as an example, divided into a section near the tab, a middle section, and a section away from the tab). The coating near the tab is called coating ①, the middle section is called coating ②, and the section away from the tab is called coating ③. The battery cell manufacturing steps are as follows: I. Preparing the positive electrode slurry: The positive electrode slurry of coating ① is prepared by mixing lithium iron phosphate, conductive carbon black and polyvinylidene fluoride in a ratio of 98~99%:0.5%~1%:0.5%~1.5%. To prepare the positive electrode slurry for coating ②, lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and surfactant are mixed in a ratio of 95~97%: 1.5%~2.5%: 1.5%~2.5%: 0.1~0.5% to form positive electrode slurry ②. To prepare the positive electrode slurry with coating ③, lithium iron phosphate, carbon nanotubes, and polyvinylidene fluoride are mixed in a ratio of 96~97%:1.5%~2%:1.5%~2% to form positive electrode slurry ③. II. Coating: Apply slurry ①, slurry ②, and slurry ③ into their respective coating head compartments, then coat and dry. The coating thickness should be controlled between 0.400 and 0.450 mg / mm. 2 Within the range; 3. Adding indentations: When coating the second to fourth sections of the oven from the bottom, use a laser to create horizontally inclined indentations, with an interval of 1 to 5 meters. Note that the laser marks are created at intervals, with the interval controlled between 0.5 and 1 second. The angle between the indentation and the straight line perpendicular to the conveyor belt direction is 5 to 15 degrees. IV. The coated electrode sheets are cold-pressed, die-cut, and slit according to conventional procedures to obtain the positive electrode sheets to be wound. V. Prepare the negative electrode slurry: The negative electrode slurry of coating ① is prepared by mixing and stirring graphite, conductive carbon black and styrene-butadiene rubber in a ratio of 96~98%: 0.5%~2%: 1%~2%. To prepare the negative electrode slurry for coating ②, graphite, conductive carbon black, styrene-butadiene rubber, and surfactant are mixed in a ratio of 94~96%: 0.5%~2.5%: 1%~2.5%: 0.1~1% to form negative electrode slurry ②. To prepare the negative electrode slurry for coating ③, graphite, carbon nanotubes, and styrene-butadiene rubber are mixed in a ratio of 96~97%: 0.5%~2%: 1%~2% to form negative electrode slurry ③. VI. Coating: Apply slurry ①②③ into the corresponding coating head compartments, then coat and dry. The coating thickness should be controlled between 0.150 and 0.175 mg / mm. 2 Within the range; 7. Adding indentations: When coating the second to fourth sections of the oven from the bottom, use a laser to create horizontally inclined indentations, with an interval of 1 to 5 meters. Note that the laser marks are created at intervals, with the interval controlled between 0.5 and 1 second. The angle between the indentation and the straight line perpendicular to the conveyor belt direction is 5 to 15 degrees. 8. The coated electrode sheets are cold-pressed, die-cut, and slit according to conventional procedures to obtain the negative electrode sheets to be wound. 9. Winding: The positive electrode, negative electrode, and separator are wound into a bare cell according to the logic of separator wrapping anode and anode wrapping cathode; 10. Assembly: The two bare cells are sequentially ultrasonically welded, laser adapter piece welded, bundled, wrapped in PET film, inserted into the casing, and laser top cover welded to form cells ready for baking; 11. Activate the battery cell: Bake, inject electrolyte, form and test the battery cell from step 10 to obtain the finished battery cell.

[0046] Comparative Example 1 The battery cell is a 100Ah lithium iron phosphate aluminum-cased cell. The cell manufacturing steps are as follows: 1. Preparation of positive electrode slurry: Lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and surfactant are mixed in a ratio of 96~97%: 1.5%~2%: 1.5%~2%: 0.1~0.5% to prepare positive electrode slurry; 2. Coating: The slurry is coated and dried, with the coating thickness controlled at 0.400~0.450 mg / mm. 2 Within the range; 3. The coated electrode sheets are cold-pressed, die-cut, and slit according to conventional procedures to obtain the positive electrode sheets to be wound. IV. Preparation of negative electrode slurry: Mix graphite, conductive carbon black, styrene-butadiene rubber, and surfactant in a ratio of 95.5~96.5%: 0.5%~2.5%: 1%~2.5%: 0.1~1% to prepare negative electrode slurry; V. Coating: Coat the slurry and dry it, controlling the coating thickness to be between 0.150 and 0.175 mg / mm. 2 Within the range; VI. The coated electrode sheets are cold-pressed, die-cut, and slit according to conventional procedures to obtain the negative electrode sheets to be wound. 7. Winding: The positive electrode, negative electrode, and separator are wound into a bare cell according to the logic of separator wrapping the anode and anode wrapping the cathode; 8. Assembly: The two bare cells are sequentially ultrasonically welded, laser adapter piece welded, bundled, wrapped in PET film, inserted into the casing, and laser top cover welded to form cells ready for baking; 9. Activating the battery cell: The battery cell from step 8 is baked, injected with electrolyte, formed, and tested for capacity to obtain the finished battery cell.

[0047] In Example 1 and Comparative Example 1, the energy density of the battery cells is statistically analyzed. Figure 2 .

[0048] from Figure 2 The results show that the energy density of Example 1 is significantly improved: compared with Comparative Example 1, the average energy density of the cells in Example 1 is increased by approximately 6 Ah / kg. This significant improvement is mainly attributed to the optimization of electrode current density distribution and wetting effect by the novel coating method, thereby improving the overall performance of the cells.

[0049] Three parallel samples from Example 1 and Comparative Example 1 were subjected to a 45-degree high-temperature cycle. Figure 3 , Figure 3 In the middle, 1-1 and 1-2 refer to two battery cells respectively. Figure 3Table 1 shows the cycle number and decay rate for Example 1 and Comparative Example 1:

[0050] from Figure 3 The results show that Example 1 exhibits superior high-temperature cycling performance: when cycled at 45 degrees Celsius, the cells in Example 1 demonstrate better cycle stability. Compared to Comparative Example 1, the cells in Example 1 show slower capacity decay during cycling, demonstrating higher high-temperature resistance and a longer lifespan.

[0051] Table 1 shows that after 400 cycles, Example 1 had a significantly higher capacity retention rate (97.9%) than Comparative Example 1 (94.9%-95.1%), indicating that its capacity decay rate was slower and its cycle life was longer under high temperature conditions.

[0052] Based on the conclusion above that "the energy density of Example 1 is increased by about 6 Ah / kg", the new coating method not only optimizes the current density distribution, but also improves the electrolyte wettability through the indentation process, thus improving the overall performance through a dual effect.

[0053] Furthermore, the two cells (1-1 and 1-2) in Example 1 showed the same degradation trend, indicating that the preparation method has high process reproducibility; the cells in Comparative Example 1 showed little difference, but the overall performance was inferior to that of Example 1.

[0054] The new coating method has a positive impact on high-temperature performance: The excellent performance of Example 1 in high-temperature cycling test is closely related to the coating method used.

[0055] By adjusting the amount of conductive agent and the indentation treatment, the electrode of Example 1 can still maintain a good current density distribution and wetting effect at high temperature, thereby effectively suppressing capacity decay.

[0056] In conclusion: The effectiveness of the new coating method: combined with Figure 2 and Figure 3 The data shows that the new coating method used in Example 1 performs excellently in improving the energy density and high-temperature cycling performance of the battery cell.

[0057] This not only verifies the effectiveness of the technology, but also provides strong support for technological advancements in the field of new energy batteries.

[0058] Practical application value: Due to the significant improvement in energy density and high-temperature cycling performance in Example 1, this technology has higher value in practical applications.

[0059] It can not only meet the market demand for high-performance batteries, but also reduce production costs and improve production efficiency, thereby promoting the sustainable development of the new energy battery industry.

[0060] Any aspects of this invention not described in detail are well-known to those skilled in the art.

[0061] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing an electrode, characterized in that, Includes the following steps: Step 1: Use a baffle to divide the coating head into multiple sections along the winding length, and prepare different positive and negative electrode slurries according to different sections; Step 2: Connect the different slurries prepared in Step 1 into the corresponding coating head compartments, then coat and dry; Step 3: When the electrode is in the second to fourth section from the bottom of the coating oven, use physical methods to make indentations on the surface of the electrode. The indentations are not completely perpendicular to the coating belt direction. Step 4: The electrode sheets are cold-pressed, die-cut, and slit according to conventional processes to obtain the positive and negative electrode sheets to be wound.

2. The electrode preparation method according to claim 1, characterized in that, In step one, the amount of conductive agent in the corresponding positive and negative electrode slurries is adjusted according to the distance between each interval and the tab to achieve the purpose of adjusting the current density; the amount of conductive agent in the positive and negative electrode slurries in the intervals closer to the tab can be reduced; the amount of conductive agent in the positive and negative electrode slurries in the intervals closer to the middle of the electrode is greater than the amount of conductive agent in the positive and negative electrode slurries in the intervals closer to the tab; the amount of conductive agent in the positive and negative electrode slurries in the intervals farther away from the tab can be increased.

3. The electrode preparation method according to claim 2, characterized in that, The positive electrode slurry in the area near the electrode tab is prepared by mixing and stirring lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a ratio of 98~99%: 0.5%~1%: 0.5%~1.5%. The positive electrode slurry in the area near the middle of the electrode is prepared by mixing lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and surfactant in a ratio of 95~97%: 1.5%~2.5%: 1.5%~2.5%: 0.1~0.5%. The positive electrode slurry in the region far from the tab is prepared by mixing lithium iron phosphate, carbon nanotubes, and polyvinylidene fluoride in a ratio of 96~97%:1.5%~2%:1.5%~2%.

4. The electrode preparation method according to claim 2, characterized in that, The negative electrode slurry in the area near the electrode tab is prepared by mixing and stirring graphite, conductive carbon black, and styrene-butadiene rubber in a ratio of 96~98%: 0.5%~2%: 1%~2%. The negative electrode slurry in the area near the middle of the electrode sheet is prepared by mixing graphite, conductive carbon black, styrene-butadiene rubber, and surfactant in a ratio of 94~96%: 0.5%~2.5%: 1%~2.5%: 0.1~1%. The negative electrode slurry in the region far from the tab is made by mixing graphite, carbon nanotubes, and styrene-butadiene rubber in a ratio of 96-97%: 0.5-2%: 1-2%.

5. The electrode preparation method according to claim 1, characterized in that, In step two, the thickness of the positive electrode coating is controlled between 0.400 and 0.450 mg / mm. 2 Within the specified range, the coating thickness of the negative electrode sheet is controlled between 0.150 and 0.175 mg / mm. 2 Within the range.

6. The electrode preparation method according to claim 1, characterized in that, In step three, the physical method involves an interval operation time, the interval operation time being controlled between 0.5 and 1 second, and the shape of the indentation is an intermittent series of short lines; the physical method includes, but is not limited to, using a laser to create the indentation or using compressed air to blow out the indentation.

7. The electrode preparation method according to claim 6, characterized in that, The indentation tilt angle is controlled between 5 and 15 degrees, and the distance between two adjacent indentations is controlled between 1 and 5 meters.

8. An electrode sheet, characterized in that, It includes a positive electrode and a negative electrode, which are prepared by the preparation method according to any one of claims 1 to 7.

9. A battery cell, characterized in that, The battery cell uses the positive electrode and negative electrode as described in claim 8. The positive electrode, negative electrode, and separator are wound into a bare battery cell, and then assembled and activated to obtain the finished battery cell.

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