A method for producing a wound positive electrode battery material

Abstract

This invention relates to the field of battery manufacturing technology and discloses a method for preparing a wound positive electrode battery material, comprising the following steps: preparing positive and negative electrode slurries; constructing a wedge-shaped transition region with a thickness gradient by intermittent coating at the beginning and end of the coating; after drying and hot rolling, introducing a radial compression factor and a geometric correction coefficient, and dynamically calculating the theoretical length required for each turn of the positive electrode coating section; cutting the material at a specific thickness of the wedge-shaped transition region as an anchor point, and then stacking and winding it with the negative electrode sheet and separator. This invention disperses edge stress through the wedge structure, preventing separator puncture; utilizes dynamic calculation to compensate for the volume shrinkage of porous materials under tension, eliminating interlayer cumulative deviations, ensuring that the effective area of ​​the positive electrode is always within the negative electrode coating range, and effectively preventing edge lithium deposition. Furthermore, the use of a modified flexible binder solves the problem of brittle fracture of thick electrodes, improving battery safety performance and yield.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a method for preparing a wound positive electrode battery material. Background Technology

[0002] With the increasing demand for high-energy-density, long-cycle-life batteries in electric vehicles and energy storage systems, increasing the thickness of the electrode coating has become an important means to improve battery capacity density. However, in the manufacturing process of wound batteries, a thicker electrode coating brings severe stress management challenges to electrode processing and winding processes.

[0003] In existing winding processes, there is often a thickness difference between the coated and uncoated areas on the current collector surface. When electrodes are stacked and wound, this abrupt change in thickness creates significant stress concentration points at the electrode edges. Under the combined action of winding tension and subsequent electrode expansion, the sharp coating edges, lacking an effective stress buffer structure, are prone to excessive normal compression of the separator, leading to localized damage or even puncture, which can trigger micro-short circuits within the battery, posing a safety hazard.

[0004] Furthermore, to ensure the electrochemical performance and safety of the battery, the process design requires that the negative electrode completely cover the positive electrode in terms of geometric dimensions. This is to prevent lithium plating during charging, as lithium ions at the edges of the positive electrode cannot be inserted into the negative electrode. Traditional electrode cutting processes typically calculate the theoretical length of each turn of the electrode based on the ideal Archimedean spiral model. This calculation model often assumes that the thickness of the electrode and the separator are constant.

[0005] However, actual electrode materials have porous structures, and the separator also has a certain degree of elasticity. Under the winding tension of several hundred grams, the electrode assembly undergoes non-negligible compressive deformation in the radial direction, resulting in an actual winding radius smaller than the theoretically calculated radius. Existing length calculation methods, by neglecting this radial compression effect, generate accumulated phase deviations as the number of winding turns increases. This causes the actual position of the positive electrode after winding to exceed the coverage area of ​​the negative electrode, severely affecting the cycle stability and lifespan of the battery. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a wound positive electrode battery material, which solves the problems of separator puncture caused by stress concentration at the edge of the electrode in wound batteries, and lithium plating caused by misalignment of the positive and negative electrode coating due to neglecting the radial compression effect of the material.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a wound positive electrode battery material includes the following steps:

[0009] Positive and negative electrode slurries were prepared separately.

[0010] An intermittent coating process is used to coat the positive electrode slurry onto the current collector surface, constructing a wedge-shaped transition region with a thickness gradient at the head and tail of the coating, while retaining blank sections;

[0011] The coated electrode sheets are dried and hot rolled to obtain the finished positive electrode sheet;

[0012] Based on the physical thickness of the positive electrode, negative electrode and separator, combined with the spiral geometric growth and radial compression effect during the winding process, the theoretical length required for each turn of the positive electrode coating section is dynamically calculated, and the position in the wedge transition area where the thickness is between zero and the thickness of the main coating is used as the positioning anchor point for cutting.

[0013] The slit positive electrode sheet, negative electrode sheet and separator are stacked and wound together;

[0014] In the dynamic calculation and cutting steps, the length of each positive electrode coating section is not equal and increases with the number of winding turns to ensure that the effective coating area of ​​the positive electrode is always within the coverage area of ​​the negative electrode coating area after winding.

[0015] By employing the above technical solution, this invention utilizes the rheological properties of the slurry to construct a physical wedge structure at the beginning and end of the coating, transforming the vertical edge contour into a gentle thickness gradient. This geometrically gradient structure effectively disperses the normal compressive stress of the electrode edge on the separator during winding, preventing separator puncture due to excessive coating thickness. Simultaneously, this invention introduces a compensation factor for radial compression effects into the calculation model for the cutting length. During actual winding, the porous electrode material and separator undergo volume shrinkage under tension, resulting in a thinner interlayer stack thickness. This invention corrects this physical error through dynamic calculation, accurately outputting the actual physical arc length required for each turn, eliminating the relative position misalignment of the positive and negative electrodes caused by the accumulation of turns, ensuring that the positive electrode is always completely covered by the negative electrode in the circumferential direction, thereby avoiding edge lithium plating.

[0016] Preferably, in the step of constructing a wedge-shaped transition zone with a thickness gradient at the head and tail of the coating, the length of the wedge-shaped transition zone is controlled between 0.5 and 1.0 mm.

[0017] The blank section is the uncoated area between two adjacent coating sections, and the length of the blank section is controlled between 2.4-2.6 mm; the wet film thickness in the wedge-shaped transition zone increases linearly from zero to the main coating thickness of the positive electrode coating section.

[0018] By adopting the above technical solution, a wedge length of 0.5-1.0 mm is the optimal range for balancing the space utilization of active materials and the stress release effect. If the length is too short, the edge stress dispersion will be insufficient; if the length is too long, the volumetric energy density of the battery will be reduced. Combined with precise blank segment control, the positioning accuracy of the electrode sheet is achieved during the high-speed cutting process.

[0019] Preferably, the specific implementation of dynamic calculation and slicing is as follows: introduce a geometric correction factor and a radial compression factor to calculate the comprehensive perimeter increment that covers the interlayer thickness stacking and material elastic compression;

[0020] Based on the length of the effective coating area of ​​the first positive electrode, the coating length of each subsequent ring is calculated recursively using the comprehensive perimeter increment, so that the coating length of the (n+1)th ring is greater than the coating length of the nth ring.

[0021] The positioning anchor points are selected at positions where the thickness of the wedge-shaped transition zone reaches 45% to 55% of the compacted thickness of the main coating. The positioning anchor points are identified by a vision inspection system, and laser cutting or mechanical cutting is controlled based on the calculated dynamic coordinates.

[0022] By adopting the above technical solution, using the area near the midpoint of the wedge-shaped region as the anchor point, the grayscale recognition interference from the reflective area of ​​the metal current collector and the full-thickness coating area can be avoided, providing stable visual features. The recursive calculation logic ensures that the length of each turn of the electrode sheet precisely matches the actual geometric circumference under the current winding level.

[0023] Preferably, the geometric correction factor is related to the shape of the battery: when preparing a cylindrical battery, the geometric correction factor is taken as the value of pi;

[0024] When preparing square wound batteries, the geometric correction factor ranges from 2.8 to 3.1, depending on the width and thickness of the winding needles.

[0025] The radial compressibility factor ranges from 0.96 to 0.98 and is used to compensate for the thickness loss of the electrode and diaphragm pore structure under winding tension.

[0026] By adopting the above technical solution, the radial compressibility factor K is set between 0.96 and 0.98, reflecting the actual volume shrinkage rate of the porous electrode under a tension of 300 to 500 grams. The introduction of this factor negatively corrects the theoretical calculation value based on the Archimedes spiral formula, preventing the problem of excessively long positive electrode sheets due to idealization of the calculation model, which would then extend beyond the negative electrode coverage area on the outer winding.

[0027] Preferably, the positive electrode slurry includes a modified flexible binder, which is a copolymer formed by copolymerization of 100 parts by weight of polyvinylidene fluoride, 5.0-10.0 parts by weight of butyl acrylate and maleic anhydride in 1.0-2.0 parts by weight.

[0028] By adopting the above technical solution, this invention addresses the problem of brittle fracture in thick electrodes by synthesizing a binder with an internal plasticizing effect through chemical modification. Its mechanism of action is as follows: the polyvinylidene fluoride backbone provides electrochemical stability under high voltage conditions; the grafted butyl acrylate side chains reduce the crystallinity and glass transition temperature of the copolymer molecular chains, endowing the binder with flexibility under bending deformation; the grafted maleic anhydride groups form chemical bonds with the hydroxyl groups on the surface of the active material or the surface of the current collector metal through a ring-opening reaction, improving the interfacial bonding strength and ensuring that the thick coating does not shed powder or crack during winding and rolling.

[0029] Preferably, the modified flexible adhesive is prepared by the following steps:

[0030] The polyvinylidene fluoride powder was dissolved in N-methylpyrrolidone solvent and stirred at a temperature of 55℃-65℃ until completely dissolved.

[0031] Add butyl acrylate monomer and maleic anhydride functional monomer, and stir to disperse;

[0032] Expel all air and introduce inert gas for protection, raise the temperature to 75℃-85℃, add benzoyl peroxide as an initiator, and react in a sealed environment at a constant temperature for 12-16 hours.

[0033] The reaction solution was poured into a mixture of deionized water and ethanol as a precipitant, and after washing, filtering, and vacuum drying, the modified flexible adhesive was obtained.

[0034] By adopting the above technical solution, the synthesis route of the modified binder was clarified. In the solution polymerization system, the monomer ratio and reaction temperature were strictly controlled, achieving random or block copolymerization of each functional monomer on the main chain, thus ensuring batch stability of product viscosity and grafting rate.

[0035] Preferably, in the drying and hot rolling steps, the compaction thickness of the positive electrode single-sided coating and the total thickness of the negative electrode sheet are controlled so that the ratio of the thickness of the positive electrode single-sided active material to the thickness of the negative electrode single-sided active material is maintained between 0.8:1.0 and 0.85:1.0; and the separator adopts a double-layer structure with the total thickness of the double-layer structure controlled between 0.018 mm and 0.024 mm.

[0036] By adopting the above technical solution, the geometric boundary for capacity matching between the positive and negative electrodes is defined, ensuring that the negative electrode has sufficient lithium intercalation redundancy capacity and space.

[0037] Preferably, the preparation process of the positive electrode slurry includes: dissolving the modified flexible binder to form a glue solution, adding a conductive agent for high-speed dispersion, controlling the linear velocity at 15 m / s to 20 m / s, and the dispersion time at 3 to 5 hours;

[0038] Then, positive electrode active material is added, the total solid content of the slurry is adjusted to 68% to 72%, and the slurry viscosity is controlled between 5000 mPa second and 8000 mPa second.

[0039] The positive electrode active material is selected from lithium nickel cobalt manganese oxide and lithium iron phosphate.

[0040] The conductive agent is made by mixing SuperP with carbon nanotubes.

[0041] By adopting the above technical solution, the stepwise dispersion process ensures that the conductive agent is fully wetted in the modified binder solution and a uniform conductive network is constructed. The high viscosity and high solid content slurry system helps to maintain the uniformity of particle distribution in the thick coating during the drying process and prevents the active material from settling.

[0042] Preferably, the process parameters for constructing the wedge-shaped transition zone include: using a slot extrusion coating machine equipped with a back suction control system;

[0043] Adjust the material cut-off back suction pressure to -3.0 kPa to -6.0 kPa;

[0044] The valve closing stroke time is controlled to be 5 to 10 milliseconds, and a natural tail is formed by the balance between the fluid inertia of the slurry and the back suction force.

[0045] By employing the above technical solution, and precisely adjusting the negative pressure value of the back-suction module and the valve operating frequency, the fluid shearing behavior at the moment of slurry disconnection is actively controlled. Appropriate negative pressure and delay allow the slurry to form a tail of a specific length under the influence of surface tension and inertia, thereby constructing the desired geometric wedge shape without the need for additional mechanical shaping equipment.

[0046] Preferably, in the drying and hot rolling steps, the temperature of the hot rolling is 80°C to 100°C and the pressure is 40 tons to 60 tons.

[0047] During the overlapping and winding step, the winding tension is controlled between 300 g / f and 500 g / f.

[0048] When preparing prismatic batteries, after winding, the process also includes a step of hot-pressing the core to flatten it, with a hot-pressing temperature of 75°C to 85°C and a pressure of 0.4 MPa to 0.6 MPa.

[0049] By adopting the above technical solutions, the hot rolling process improves the compaction density of the electrode; and the subsequent winding tension and hot pressing flattening treatment, combined with the aforementioned radial compression factor calculation, ensure the regularity of the cell shape while minimizing the residual stress inside the electrode and preventing the electrode from rebounding and deforming.

[0050] In summary, the present invention has at least one of the following beneficial technical effects:

[0051] 1. By constructing a wedge-shaped transition region with gradually varying thickness at the beginning and end of the positive electrode coating, the abrupt change in vertical thickness at the electrode edge is transformed into a gentle gradient structure. This disperses the normal compressive stress on the separator caused by the edge during winding and tightening and electrode expansion, solving the problem of separator puncture caused by excessive coating thickness in high-energy-density batteries and improving the physical safety performance of the cell.

[0052] 2. A dynamic slitting model incorporating a radial compressibility factor was established. The volume shrinkage characteristics of porous electrode materials and separators under winding tension were corrected and calculated. By precisely controlling the physical length of each positive electrode coating section, the cumulative deviation caused by neglecting the compression effect in the traditional geometric calculation model was eliminated. This ensured that the effective active area of ​​the positive electrode was always within the coverage of the negative electrode throughout the entire life cycle, preventing edge lithium deposition.

[0053] 3. A modified flexible binder grafted with butyl acrylate and maleic anhydride was adopted. By introducing flexible side chains, the crystallinity and modulus of polyvinylidene fluoride were reduced, and the chemical bonding of anhydride groups was used to enhance the interfacial adhesion. This overcame the brittle fracture and powder shedding problems that easily occur in thick electrode coatings during small curvature winding and hot rolling, and ensured the structural integrity of the electrode sheet during high-speed processing. Attached Figure Description

[0054] Figure 1 This is a line graph illustrating the winding alignment process capability analysis of the present invention.

[0055] Figure 2 This is a trend diagram of the interlayer coating allowance of the electrode in this invention. Detailed Implementation

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Preparation Examples 1-3:

[0058] Preparation Example 1:

[0059] This preparation example provides a method for preparing a modified flexible adhesive m-PVDF-A, including the following steps:

[0060] 100g of polyvinylidene fluoride (PVDF) powder was added to a three-necked flask containing 800mL of N-methylpyrrolidone (NMP) and mechanically stirred in a 60℃ water bath until the PVDF powder was completely dissolved to obtain a homogeneous solution.

[0061] Add 8.0g of butyl acrylate (BA) monomer and 1.5g of maleic anhydride (MAH) functional monomer to the above solution, and continue stirring for 30 minutes to ensure uniform dispersion of the monomers;

[0062] High-purity nitrogen gas was continuously introduced into the reaction system for 30 minutes to purge the air. Then the system temperature was raised to 80°C, and 0.5g of benzoyl peroxide BPO initiator was added. The reaction was stirred for 14 hours under constant temperature and sealed conditions.

[0063] After the reaction was completed, the reaction solution was slowly poured into a precipitant mixture of 2000 mL of deionized water and ethanol in a volume ratio of 1:1. After standing and separating into layers, the mixture was filtered to obtain a white precipitate. The precipitate was washed three times with anhydrous ethanol and then dried in a vacuum drying oven at 80°C for 24 hours. After grinding and sieving, the modified flexible binder m-PVDF-A was obtained.

[0064] The results showed that the grafting rate of butyl acrylate in the obtained m-PVDF-A was 6.8%, the grafting rate of maleic anhydride was 1.2%, and the intrinsic viscosity was 2.1 dl / g.

[0065] Preparation Example 2:

[0066] This preparation example provides a method for preparing a highly flexible modified adhesive m-PVDF-B, including the following steps:

[0067] 100g of polyvinylidene fluoride (PVDF) powder was added to a three-necked flask containing 800mL of N-methylpyrrolidone (NMP) and mechanically stirred in a 60℃ water bath until the PVDF powder was completely dissolved to obtain a homogeneous solution.

[0068] Add 10.0g of butyl acrylate (BA) monomer and 1.5g of maleic anhydride (MAH) functional monomer to the above solution, and continue stirring for 30 minutes to ensure uniform dispersion of the monomers. This formulation uses the upper limit of the butyl acrylate content in the raw material range, aiming to minimize the glass transition temperature of the copolymer within the allowable range to improve flexibility.

[0069] High-purity nitrogen gas was continuously introduced into the reaction system for 30 minutes to purge the air. Then the system temperature was raised to 80°C, and 0.5g of benzoyl peroxide BPO initiator was added. The reaction was stirred for 16 hours under constant temperature and sealed conditions.

[0070] After the reaction was completed, the reaction solution was slowly poured into a precipitant mixture of 2000 mL of deionized water and ethanol in a volume ratio of 1:1. After standing and separating into layers, the mixture was filtered to obtain a white precipitate. The precipitate was washed three times with anhydrous ethanol and then dried in a vacuum drying oven at 80°C for 24 hours. After grinding and sieving, the highly flexible modified binder m-PVDF-B was obtained.

[0071] The obtained m-PVDF-B was found to have a butyl acrylate grafting rate of 8.6%, a maleic anhydride grafting rate of 1.2%, and an intrinsic viscosity of 2.0 dl / g.

[0072] Preparation Example 3:

[0073] This preparation example provides a method for preparing a high-strength modified adhesive m-PVDF-C, including the following steps:

[0074] 100g of polyvinylidene fluoride (PVDF) powder was added to a three-necked flask containing 800mL of N-methylpyrrolidone (NMP) and mechanically stirred in a 60℃ water bath until the PVDF powder was completely dissolved to obtain a homogeneous solution.

[0075] Add 5.0g of butyl acrylate (BA) monomer and 1.0g of maleic anhydride (MAH) functional monomer to the above solution, and continue stirring for 30 minutes to ensure uniform dispersion of the monomers. This formulation uses the lower limit of the raw material range of modified monomer dosage, aiming to retain the high crystallinity and mechanical strength of the matrix material.

[0076] High-purity nitrogen gas was continuously introduced into the reaction system for 30 minutes to purge the air. Then the system temperature was raised to 80°C, and 0.5g of benzoyl peroxide BPO initiator was added. The reaction was stirred for 12 hours under constant temperature and sealed conditions.

[0077] After the reaction was completed, the reaction solution was slowly poured into a 1:1 mixture of deionized water and ethanol. After standing and separating into layers, the mixture was filtered to obtain a white precipitate. The precipitate was washed three times with anhydrous ethanol and then dried in a vacuum drying oven at 80°C for 24 hours. After grinding and sieving, the high-strength modified binder m-PVDF-C was obtained.

[0078] The grafting rate of butyl acrylate in the obtained m-PVDF-C was determined to be 4.2%, the grafting rate of maleic anhydride was 0.8%, and the intrinsic viscosity was 2.2 dl / g.

[0079] Examples 1-4:

[0080] Example 1:

[0081] This embodiment provides a method for preparing a wound positive electrode battery material, including the following steps:

[0082] Adhesive preparation: The modified flexible adhesive m-PVDF-A synthesized in Preparation Example 1 was selected.

[0083] Cathode slurry preparation: The following components were weighed by mass percentage: 96.0% NCM811 (positive active material), 2.0% conductive agent (SuperP and carbon nanotubes mixed at a mass ratio of 7:3), and 2.0% binder. The binder was a mixture of m-PVDF-A and conventional PVDF (grade HSV900) at a mass ratio of 5:5. The binder was dissolved in NMP solvent to prepare a gel. The conductive agent was first added and dispersed at a high speed of 18 m / s for 4 hours. Then, the active material was added, and the total solids content of the slurry was adjusted to 70%, with the slurry viscosity controlled at 6000 mPa·s.

[0084] Negative electrode slurry preparation: Artificial graphite, conductive carbon black, thickener CMC and binder SBR are mixed in conventional proportions and deionized water is used as solvent to prepare a negative electrode slurry with a viscosity of 3000 mPa·s.

[0085] Precision intermittent coating and wedge-shaped zone construction: A slot extrusion coater equipped with a piezoelectric ceramic valve and a backflow control system was used for positive electrode coating on a 13μm thick carbon-coated aluminum foil substrate. The coating speed was set to 50m / min. By adjusting the backflow pressure to -4.5kPa and the valve closing stroke time to 8ms, a natural tail was formed in the slurry at the moment of disconnection, thus constructing a wedge-shaped transition zone with a length of 0.8mm at both ends of the coating. Within this zone, the wet film thickness gradually increases from zero to the target thickness. The length of the pure aluminum foil blank section between two adjacent coating sections was controlled to be 2.5mm.

[0086] Electrode rolling: The dried positive electrode sheet is hot rolled at 90℃, controlling the compacted thickness T1 of the single-sided coating of the positive electrode to be 70μm. The total thickness T2 of the negative electrode sheet after coating and rolling is 160μm. The total thickness T3 of the double-layer separator used is 24μm.

[0087] Dynamic Slitting: A winding geometry correction coefficient is set to correspond to the characteristics of a cylindrical battery, and a radial compression factor is introduced. The effective calculation anchor point is the position where the thickness of the wedge transition region reaches half the thickness of the main coating. Based on the Archimedes' principle, the required length of the positive electrode coating area for each turn is dynamically calculated based on the cumulative thickness increment of the positive electrode, negative electrode, and separator, ensuring that the coating length of the (n+1)th turn is greater than that of the nth turn. A CCD vision system is used to identify the anchor point position, and laser slitting is performed based on the calculated dynamic coordinates to ensure that the complete wedge structure is retained on both sides of each positive electrode sheet.

[0088] Battery assembly: The negative electrode, separator, and positive electrode are stacked sequentially and wound under a tension of 400g to form a 21700 cylindrical cell. Due to the aforementioned wedge structure and dynamic length compensation, the positive electrode edge makes smooth contact with the separator, and the effective area of ​​the positive electrode is always within the negative electrode's coverage area. After casing, welding, electrolyte injection, and formation, the finished battery is obtained.

[0089] Example 2:

[0090] This embodiment provides a method for preparing a wound positive electrode battery material, including the following steps:

[0091] Adhesive preparation: The modified flexible adhesive m-PVDF-B synthesized in Preparation Example 2 was selected.

[0092] Preparation of positive electrode slurry: The positive electrode active material NCM811 was weighed out at 95.5% by mass, the conductive agent at 2.5%, and the binder at 2.0%. The binder was a mixture of m-PVDF-B and conventional PVDF at a mass ratio of 3:7. The binder was dissolved in NMP, and after high-speed dispersion, addition of the active material, and vacuum degassing, a positive electrode slurry with a solid content of 71% and a viscosity of 5500 mPa·s was obtained.

[0093] Negative electrode slurry preparation: Artificial graphite was used as the active material, combined with conductive agent, CMC and SBR, and deionized water was used as solvent to prepare the negative electrode slurry. The process parameters were the same as in Example 1.

[0094] Precision intermittent coating and wedge-shaped region construction: A slot extrusion coater was used for positive electrode coating. To address the high space utilization requirements of square batteries, the length of the wedge-shaped transition zone at the beginning and end of the coating was precisely controlled to 0.5 mm by finely adjusting the back pressure of the piezoelectric valve to -3.5 kPa and shortening the valve action time, thus reducing the occupation of ineffective active material areas. Simultaneously, the blank section length between adjacent coating sections was controlled to 2.5 mm.

[0095] Electrode rolling: The positive electrode sheet is compacted in a hot roller press, controlling the compaction thickness T1 of the single-sided coating of the positive electrode to be 65μm. The total thickness T2 of the negative electrode sheet is 150μm. The total thickness T3 of the double-layer separator is 20μm.

[0096] Dynamic cutting: For the flat winding structure of square batteries, the geometric correction coefficient (set to 3.0) is adjusted to adapt to the width and thickness characteristics of the winding needles. The position where the thickness of the wedge transition zone reaches 50% is used as the positioning anchor point. Based on the principle of thickness superposition and the incremental logic after correction for square winding, the theoretical length of the positive electrode coating section is calculated round by round, and the laser die-cutting position is controlled accordingly to ensure that the length of the cut electrode sheet meets the geometric requirements of layer-by-layer wrapping.

[0097] Battery assembly: The positive and negative electrode sheets are stacked with the separator and wound onto a winding needle to form a flat core. After winding, the core undergoes a hot-pressing flattening treatment at 80°C and 0.5MPa to eliminate winding stress and ensure a tight fit between the wedge-shaped area and the separator. Subsequently, through casing, top cover welding, electrolyte injection, and formation processes, a square power battery is produced.

[0098] Example 3:

[0099] This embodiment provides a method for preparing a wound positive electrode battery material, including the following steps:

[0100] Binder preparation: The high-strength modified binder m-PVDF-C synthesized in Preparation Example 3 was selected. Although this formulation has a low degree of modification, it retains a high degree of crystallinity, aiming to verify the performance of the high-adhesion formulation in high-density electrodes.

[0101] Cathode slurry preparation: To achieve a high energy density design and increase the proportion of active material, 96.5% of the positive electrode active material NCM811, 2.0% of the conductive agent, and 1.5% of the binder were weighed. The binder was a mixture of m-PVDF-C and conventional PVDF at a mass ratio of 5:5. The components were dispersed in NMP to prepare a high-solids-content (72%) and high-viscosity (7500 mPa·s) positive electrode slurry to ensure the sedimentation stability of the thick coating.

[0102] Negative electrode slurry preparation: Negative electrode slurry is prepared in a conventional manner, and the formula is adjusted to make the compaction density of the negative electrode suitable for the high energy density positive electrode, and the viscosity is controlled at 3500 mPa·s.

[0103] Precision intermittent coating and wedge formation: To address the issue of edge breakage during thick coating roll-up, the coating process is designed to create a long, gently sloping wedge-shaped zone. The material breakage back suction pressure is adjusted to -5.5 kPa, and the back suction delay time is appropriately extended, thereby forming a wedge-shaped transition zone with a length of 1.0 mm at both ends of the coating. This length is at the upper limit of the process window, aiming to maximize the use of geometric gradients to disperse stress. The blank section length is set to 2.5 mm.

[0104] Electrode rolling: High-density rolling is performed, with the compaction thickness T1 of the positive electrode single-sided coating set at 80μm (reaching the design upper limit) and the total thickness T2 of the negative electrode at 170μm. The ratio of the thickness of the active material on the single side of the positive and negative electrodes is strictly controlled to ensure capacity utilization and the safety boundary of lithium plating.

[0105] Dynamic slitting: Due to the thickness of the electrode sheet, the winding radius tends to increase more significantly with the number of turns. Using the position where the thickness of the wedge-shaped transition zone reaches 50% as the calculation anchor point, the theoretical length of each slitting segment is calculated using dynamic incremental logic. This calculation fully considers the interlayer radius jump caused by the thick electrode, ensuring that the cut electrode sheet maintains a constant negative electrode coating allowance after winding.

[0106] Battery Assembly: The above-mentioned electrodes are assembled into high-capacity batteries. Thanks to the excellent interfacial bonding of m-PVDF-C and the synergistic effect of the 1.0mm long wedge region, even with a thick coating of 80μm, no cracks or material loss occurred at the edges of the wound electrodes, and the separator was subjected to uniform stress without the risk of puncture.

[0107] Example 4:

[0108] This embodiment provides a method for preparing a wound positive electrode battery material, including the following steps:

[0109] Binder preparation: No modified binder is synthesized; commercially available conventional battery-grade polyvinylidene fluoride is directly selected as the sole binder component.

[0110] Preparation of positive electrode slurry: 96.0% of the positive electrode active material NCM811, 2.0% of the conductive agent, and 2.0% of the conventional binder HSV900 were weighed according to the following mass percentages. The binder powder was directly dissolved in NMP solvent, followed by the sequential addition of the conductive agent and active material. A positive electrode slurry with a solid content of 70% and a viscosity of 6200 mPa·s was prepared by a high-speed dispersion process. Compared with Example 1, except for the type of binder, the other proportions and process parameters remained the same.

[0111] Negative electrode slurry preparation: The negative electrode slurry was prepared using the same formulation and process as in Example 1.

[0112] Precision intermittent coating and wedge-shaped zone construction: A coating device equipped with a piezoelectric ceramic valve and a back-suction control system was used. Although no flexible modified binder was used, a wedge-shaped transition zone with a physical morphology of 0.8 mm was still constructed at the beginning and end of the coating by adjusting the valve back-suction parameters (back-suction pressure -4.5 kPa, action time 8 ms). This step utilizes geometric gradient to compensate for the high rigidity of conventional binders, thereby reducing edge stress concentration. The blank section length was maintained at 2.5 mm.

[0113] Electrode rolling: The process parameters are the same as in Example 1. The positive electrode is hot rolled to a single-sided coating thickness T1 of 70 μm, and the total thickness T2 of the negative electrode is 160 μm. Since conventional binders are relatively hard, special attention should be paid to whether the edges rebound or become brittle after rolling.

[0114] Dynamic Slicing: The dynamic coordinate calculation logic of this invention is applied. Anchor points are set at 50% thickness of the wedge region, without relying on any special material markings. Based on the superposition effect of the physical thicknesses of the positive and negative electrodes and the separator, the theoretical growth required for each turn of the positive electrode sheet is calculated. After locating the anchor points using a vision system, laser cutting is controlled to ensure that each electrode sheet has a precisely calculated length, guaranteeing that the wrapping position of the negative electrode over the positive electrode does not shift after winding.

[0115] Battery assembly: 21700 cylindrical batteries are fabricated by sequentially stacking and winding the layers. During the winding process, the geometric slope of the wedge-shaped area protects the separator from being punctured by the hard edges formed by conventional adhesives, and dynamic length compensation ensures that the perimeter change caused by the increase in thickness is accurately offset, ultimately completing the assembly, electrolyte injection, and formation of the battery cells.

[0116] Comparative Examples 1-4:

[0117] Comparative Example 1:

[0118] The difference compared to Example 1 is as follows:

[0119] The coating process lacks back suction control, resulting in a nearly vertical right-angled edge (without a wedge-shaped transition zone).

[0120] The dynamic incremental compensation formula is not used in the slitting calculation; instead, a simple equal-interval slitting method is adopted (i.e., the electrode length Ln of each turn is constant). All other raw materials and procedures are the same.

[0121] Comparative Example 2:

[0122] The difference compared to Example 1 is as follows:

[0123] No back-suction control was implemented in the coating process, resulting in approximately vertical right-angled edges (without a wedge-shaped transition zone). The slitting calculation still uses the dynamic incremental compensation formula of this invention. All other raw materials and steps remain the same.

[0124] Comparative Example 3:

[0125] The difference compared to Example 1 is as follows:

[0126] In the dynamic slitting calculation logic, the radial compression factor K was not introduced (i.e., K=1.0 was set). Although the Archimedes' spiral formula was used for calculation, the physical fact that the porous structure of the electrode and diaphragm will be compressed under a winding tension of 400g was ignored, and the perimeter was directly extrapolated using the theoretical static thickness of the material. The coating process retains a wedge-shaped transition zone of 0.8mm. All other raw materials and steps are the same.

[0127] Comparative Example 4:

[0128] The difference compared to Example 1 is as follows:

[0129] In the dynamic slitting step, the effective calculation anchor point is changed to the starting point of the wedge transition zone (i.e., at 0% thickness), instead of the 50% thickness point of the present invention. All other materials and steps remain the same.

[0130] Test Examples 1-5:

[0131] Test Example 1: Mechanical Properties of Adhesive and Flexibility of Electrode

[0132] Experimental instructions and procedures:

[0133] The positive electrode sheets prepared in Examples 1 to 4 and subjected to the rolling process were taken as the test samples, and the simple binder casting samples in each example were also taken. The electrode sheets were cut into strips with a specification of 20mm × 150mm along the coating direction, and 10 parallel samples were prepared for each set of examples.

[0134] A high-precision tensile testing machine was used to perform a 180° peel strength test. A special test tape (3M 600) was evenly applied to the electrode coating surface, and a 2kg standard pressure roller was used to roll it back and forth three times to eliminate air bubbles. The current collector end of the electrode was fixed to the lower clamp, and the free end of the tape was fixed to the upper clamp. The tensile speed was set to 50mm / min, and the average force value during the peeling process was recorded and converted into peel strength.

[0135] Perform a shaft bending test. Wrap the electrode sample around stainless steel cylindrical shafts with diameters of 2mm, 3mm, 4mm, 5mm, 6mm, 8mm, and 10mm, with the coated side facing outwards. Hold the bent position for 5 seconds at room temperature and visually inspect the coating surface at the bend for cracks or detachment from the current collector. Record the minimum shaft diameter that the coating can withstand without cracking.

[0136] To evaluate the modulus properties of the material itself, dynamic thermomechanical analysis was performed on pure binder casting samples to determine their storage modulus and glass transition temperature at 25°C.

[0137] Experimental data:

[0138] Table 1. Summary of test data on the mechanical properties of the electrodes and the properties of the binders in each embodiment.

[0139]

[0140] Conclusion Analysis:

[0141] According to the data in Table 1, the electrode sheets prepared using modified binders in Examples 1 to 3 are superior to those of Example 4, which uses conventional PVDF, in terms of peel strength and flexibility.

[0142] The data differences reflect the material modification mechanism of this scheme. In Example 4, the conventional PVDF exhibits a high storage modulus and a high glass transition temperature, demonstrating greater rigidity. In the minimum bending diameter test, Example 4 could only withstand a bend of 8.0 mm, indicating its difficulty in adapting to deformations with small radii of curvature. If a wedge-shaped region of 0.5-1.0 mm in length is forcibly constructed during the coating process, the high modulus of the conventional material will cause microcracks to form at the edges during drying shrinkage or winding bending. This is why, although Example 4 employs a wedge-shaped process, yield still needs to be monitored.

[0143] In contrast, Examples 1 to 3 introduced the polar monomer maleic anhydride and the flexible monomer butyl acrylate. The improved peel strength is attributed to the chemical bonding or strong physical adsorption of the MAH groups with the current collector and active material surface, enhancing interfacial adhesion. The improved flexibility is directly related to the introduction of the BA segment; DMA data shows that the Tg point of the modified material shifts downward, and the energy storage modulus decreases. Example 2 has the highest BA content, with the modulus reduced to 312.8 MPa and the bending diameter reaching 2.0 mm, confirming the adaptability of the highly flexible formulation to thick or small-core batteries. Example 1, as a balanced formulation, maintains sufficient cohesion (moderate peel strength) while improving the bending capacity to the 3.0 mm level, sufficient to support the wedge-shaped transition zone structure of the claims without brittle fracture during winding, thus verifying the technical feasibility of reducing the material modulus to match the geometric wedge design.

[0144] Test Example 2: Process Capability Analysis of Winding Alignment

[0145] Experimental instructions and procedures:

[0146] Using the process parameters of Example 1, the coating and slitting of the positive electrode sheet were performed continuously to prepare 500 positive electrode sheets. As a comparison, 500 positive electrode sheets were prepared using the parameter conditions of Comparative Example 3 and Comparative Example 4, respectively.

[0147] The three sets of electrode sheets were fed into a fully automatic winding machine for winding 21700 cylindrical cells. The winding needle speed was fixed at 1500 rpm, the winding tension was 400 g, and the diaphragm tension and correction parameters were kept constant.

[0148] Twenty samples were randomly selected from each group of completed battery cells using an equally spaced sampling method. The samples were then subjected to X-ray scanning using a high-resolution industrial micro-focus X-ray inspection device.

[0149] In the X-ray image, locate the outermost coil of the battery cell (i.e., the final winding section) and measure the physical distance between the edge of the positive electrode coating and the edge of the negative electrode coating in the circumferential tangential direction. The measurement standard specifies that a negative electrode exceeding a positive electrode coating is a positive value, and a positive electrode exceeding a negative electrode coating is a negative value.

[0150] The specification center value for this process is set to 2.00 mm, and the specification tolerance range is ±1.00 mm (i.e., lower limit LSL = 1.00 mm, upper limit USL = 3.00 mm). Record the measured values ​​of each sample, and calculate the mean, standard deviation, and process capability index.

[0151] Experimental data:

[0152] Table 2. Sampled measured data of winding alignment in Example 1 and Comparative Example

[0153]

[0154] Conclusion Analysis Combined with Appendix Figure 1 As shown:

[0155] According to the data in Table 2, Example 1 demonstrates superior control over winding alignment, with a CPK value as high as 10.37, far exceeding the standard of 1.33 required for general industrial process control. The measured data are closely distributed around the target value of 2.00 mm, with a standard deviation of only 0.032 mm, indicating that the electrode length compensation for each turn is extremely accurate.

[0156] This verifies the effectiveness of the half-height anchoring and dynamic incremental compensation mechanism in this scheme. The radius of the Archimedes spiral structure increases non-linearly with the number of turns. Example 1 introduces a correction term M×(T) that includes pi and a compression factor. total This eliminates the phase lag between the positive and negative electrodes. Simultaneously, by using the 50% thickness of the wedge region as the calculation anchor point, the center of mass distribution is locked to the cutting coordinates, ensuring that even slight fluctuations in the coating tail shape do not affect the positioning accuracy of the effective coating area.

[0157] In contrast, Comparative Example 3, using a linear superposition formula, failed to compensate for the circumference difference caused by the helical increment, resulting in a lag in the relative position of the outer positive electrode sheet. The average winding alignment was only 1.053 mm, and there were multiple NG points below the lower limit (<1.0 mm), which would directly lead to the risk of edge lithium plating in actual batteries. Although Comparative Example 4 introduced a formula correction, with an average value close to 2.0 mm, it used 0% thickness (i.e., the tailing start point) as the anchor point. The tailing length fluctuation caused by the rheology of the slurry during the coating process (such as a jump from 0.5 mm to 0.8 mm) was directly transmitted to the cutting size, resulting in a large data dispersion (standard deviation 0.482 mm, CPK only 0.68), which could not meet the quality stability requirements of large-scale automated production.

[0158] Test Example 3: Diaphragm Integrity and Insulation Performance Test

[0159] Experimental instructions and procedures:

[0160] During the preparation processes of Examples 1, 4, Comparative Example 1, and Comparative Example 2, 100 bare battery cells were randomly selected from each example after being wound and hot-pressed (80°C, 0.8 MPa, holding pressure for 60 seconds). At this time, the battery cells had not yet been encased and injected with electrolyte, and were in a dry assembly state.

[0161] Insulation withstand voltage tests were performed using a comprehensive safety tester. The positive and negative probes of the tester were clamped to the positive and negative tabs of the battery cell, respectively. The test voltage was set to DC 250V, the holding time to 2.0 seconds, and the upper limit of leakage current to 2.0mA. If the leakage current exceeded the upper limit during the test, the instrument judged it as NG; if it was below the upper limit, it was judged as OK. The number of short circuits and the distribution of leakage current through the sample were recorded for each group of samples.

[0162] The samples were destructively disassembled after testing. The winding needle was rotated in the opposite direction to unwind the core, and the diaphragm area at the corresponding positions of the beginning and end edges of the positive electrode sheet was inspected under a strong light. The proportion of diaphragms with light-transmitting spots (plastic deformation), dead folds, or physical perforations was carefully counted.

[0163] Experimental data:

[0164] Table 3. Statistics on insulation withstand voltage test and diaphragm condition of each group of cells

[0165]

[0166] Conclusion Analysis:

[0167] According to the data in Table 3, Examples 1 and 4 outperformed Comparative Examples 1 and 2 in terms of insulation performance, confirming that the wedge-shaped transition zone structure is a key factor in preventing physical puncture of the diaphragm.

[0168] Comparative Examples 1 and 2 employed a right-angle edge coating process, resulting in a step-like abrupt change in coating thickness at the edges. Under the high pressure of the hot-pressing process, the rigid positive electrode edge generated extremely high stress concentration on the diaphragm surface, leading to a diaphragm damage rate exceeding 90%. The Hi-Pot test short-circuit rates were 14.0% and 17.0%, respectively, and the average leakage current was also at a high level, indicating that the dielectric strength of the diaphragm had been compromised.

[0169] Example 1 introduces a 0.8mm long wedge-shaped transition region, transforming the contact surface geometry from a right angle to a gentle slope. According to the principles of contact mechanics, this geometric gradient increases the radius of curvature at the contact point between the positive electrode edge and the diaphragm, converting concentrated stress into gradient stress distributed along the slope, thus effectively protecting the diaphragm. Data shows that Example 1 achieved zero short circuits, with an average leakage current of only 12.4μA, indicating an intact diaphragm structure.

[0170] Furthermore, a comparison of Examples 1 and 4 reveals that although both employ a wedge-shaped structure, Example 1, using a modified binder, outperforms Example 4, which uses conventional PVDF, in terms of leakage current control and membrane indentation rate. This verifies the modulus buffering effect of m-PVDF: because the modified binder reduces the Young's modulus at the coating edge, it allows for a slight elastic yield under pressure, further absorbing localized stress caused by mechanical tolerances. This compensates for the shortcomings of simple geometric control in terms of material hardness, achieving optimal insulation protection.

[0171] Test Example 4: Electrode Interlayer Alignment Stability Test

[0172] Experimental instructions and procedures:

[0173] Five 21700-type wound batteries each prepared in Example 1, Comparative Example 3, and Comparative Example 4 were selected. To eliminate interference caused by electrode expansion after formation and to verify the geometric accuracy of the manufacturing dimensions, dry cells that were wound and hot-pressed but not yet injected with electrolyte were selected as test objects.

[0174] The battery cell is destructively dissected in the drying room. The steel shell is cut longitudinally using a special jig to remove the core. The inner ring of the core is fixed, and the electrode and separator are unrolled in reverse at a constant speed until they are completely flat.

[0175] Define the head of the winding core (near the winding needle) as the first turn. Select the 5th turn (inner area), the 15th turn (middle area), and the 25th turn (outer area) as feature measurement points.

[0176] At the three characteristic locations mentioned above, an image measuring instrument was used to measure the length by which the edge of the negative electrode coating area extends beyond the edge of the positive electrode coating area. During measurement, the value was positive when the negative electrode completely covers the positive electrode; if the positive electrode extends beyond the negative electrode, it was recorded as a negative value. Three measurements were taken at each location for each battery, and the average value was recorded.

[0177] Experimental data:

[0178] Table 4. Measured distribution of positive and negative electrode coating margins at different numbers of turns

[0179]

[0180] Conclusion Analysis Combined with Appendix Figure 2 As shown:

[0181] According to the data in Table 4, the coating allowance values ​​of the inner, middle and outer rings in Example 1 remained highly consistent, with an average value of around 2.00 mm. The interlayer drift was only 0.02 mm, indicating that the relative positions of the positive and negative electrodes did not change with the increase of the winding radius.

[0182] This result confirms the geometric accuracy of the dynamic incremental compensation mechanism proposed in this scheme. The wound battery is arranged in an Archimedean spiral; as the number of turns n increases, the radius increases linearly, resulting in the required circumference increment ΔL per turn being non-constant. Example 1 uses the formula Ln+1=Ln+M×(T) total The introduction of a comprehensive increment M, which includes a geometric correction factor and a compression factor, precisely offsets the nonlinear changes in perimeter caused by thickness stacking, thereby eliminating phase hysteresis.

[0183] Conversely, the data from Comparative Example 3 reveals the decisive role of the radial compression factor in winding dynamics. The data shows that the inner wrap allowance is 2.10 mm (within the normal range), but the allowance value shows a monotonically decreasing trend with the number of turns, dropping sharply to 0.42 mm by the 25th turn.

[0184] This is because Comparative Example 3 neglected the elastic compression of the material in its calculations (setting K=1.0), resulting in a theoretical winding radius in the calculation model that is larger than the actual physical radius. The length of each turn of the positive electrode calculated by the formula is slightly longer than the geometric circumference required for actual winding. This slight excess length has a cumulative effect during the winding process of more than 20 turns, causing the positive electrode to lead the negative electrode in the circumferential direction (i.e., positive electrode elongation), gradually consuming the reserved coating allowance. If a compression factor is not introduced for negative correction, the outer ring is very prone to severe lithium plating due to insufficient allowance, which is completely consistent with the disassembly results in Test Example 5.

[0185] Comparative Example 4 reveals the importance of anchor point decoupling. Although its interlayer drift is small, the numerical dispersion between samples is large. This is because Comparative Example 4 uses the coating start point as the cutting calculation anchor point, while in the actual coating process, the length of the wedge-shaped tail fluctuates within a certain range due to the rheological properties of the slurry. This process fluctuation is directly transmitted to the positioning system, causing random shifts in the coating allowance benchmark for different batteries. Example 1 uses the 50% thickness point as the anchor point, utilizing the central invariance of this point in the mass distribution, effectively avoiding the impact of tail shape fluctuations on dimensional accuracy and ensuring the consistency of the manufacturing process.

[0186] Test Example 5: Electrochemical Cycle Life and Macroscopic Lithium Plating Observation

[0187] Experimental instructions and procedures:

[0188] Twenty 21700 cylindrical batteries each from Examples 1, 4, Comparative Example 1, and Comparative Example 3 that had been prepared and undergone formation were selected.

[0189] Standard charge-discharge cycle tests were conducted in an ambient chamber at 25±2℃. The charging mode was 1C constant current charging to 4.2V, followed by constant voltage charging to a cutoff current of 0.05C; the discharging mode was 1C constant current discharging to 2.75V. 500 charge-discharge cycles were performed continuously.

[0190] Record the discharge capacity for each cycle and calculate the capacity retention rate of the 500th cycle relative to the 1st cycle.

[0191] After the cycle is complete, bring all batteries to full charge. Disassemble the batteries in a dry glove box with a dew point below -40°C. Carefully peel off the steel casing from the positive electrode, and remove the negative electrode and lay it flat.

[0192] Visually inspect the surface of the negative electrode under strong light, especially the area corresponding to the edge of the positive electrode coating. Count the number of batteries with gray or silvery-white lithium metal deposition spots and record the main locations where lithium plating occurs.

[0193] Experimental data:

[0194] Table 5. Capacity retention and lithium disassembly statistics after 500 cycles

[0195]

[0196] Conclusion Analysis:

[0197] According to the data in Table 5, Example 1 exhibited the best electrochemical stability, with an average capacity retention of over 92% after 500 cycles, and no lithium plating was observed after disassembly. Although Example 4 also used a wedge-shaped process, the conventional binder was relatively hard, leading to microcracks at the electrode edges or poor interfacial contact during long-term cyclic expansion and contraction. This resulted in a slightly lower capacity retention than Example 1 and the appearance of a small amount of lithium plating. This indicates that the modified binder m-PVDF contributes to improving long-term cycling stability, but geometric control plays a dominant role.

[0198] Comparative Example 3 directly verifies the crucial role of dynamic incremental compensation in preventing lithium plating. Although this group used wedge-shaped coating (protecting the separator and avoiding the severe ablation seen in Comparative Example 1), the use of a linear calculation formula neglected the helical geometric effect. Disassembly results showed a clear spatial distribution of lithium plating: the inner ring was normal, while the outer ring (>20 rings) had a lithium plating rate as high as 70%-75%. As the number of rings increased, the positive electrode length calculated by the linear formula was insufficient, causing the outer positive electrode to gradually approach or even exceed the edge of the negative electrode. During charging, lithium ions exceeding the negative electrode range could not be embedded in the graphite layer and were directly reduced to metallic lithium on the negative electrode surface, leading to rapid capacity decay and safety hazards.

[0199] Comparative Example 1 illustrates the dual defects of right-angled edges and calculation errors. Right-angled edges cause the membrane to deform under pressure, leading to localized pore blockage and hindering lithium-ion transport; simultaneously, the linear formula results in alignment deviations. The combined effect of these two factors results in a lithium plating rate exceeding 90% and the lowest capacity retention rate, demonstrating that the geometric wedge structure and dynamic slitting logic of this invention are indispensable and synergistic.

Claims

1. A method for preparing a wound positive electrode battery material, characterized in that, Includes the following steps: Positive and negative electrode slurries were prepared separately. The positive electrode slurry is coated onto the surface of the current collector using an intermittent coating process, and a wedge-shaped transition region with a thickness gradient is constructed at the head and tail of the coating, while blank sections are retained. The coated current collector is dried and hot-rolled to obtain the finished positive electrode sheet. Based on the physical thickness of the positive electrode, negative electrode and separator, combined with the helical geometric growth and radial compression effect during the winding process, the theoretical length required for each turn of the positive electrode coating section is dynamically calculated, and the position in the wedge-shaped transition area where the thickness is between zero and the thickness of the main coating is used as the positioning anchor point for cutting. The slit positive electrode sheet, negative electrode sheet and separator are stacked and wound together; In the dynamic calculation and slitting steps, the length of each positive electrode coating section is not equal and increases with the number of winding turns, ensuring that the effective coating area of ​​the positive electrode is always within the coverage area of ​​the negative electrode coating area after winding.

2. The method for preparing a wound positive electrode battery material according to claim 1, characterized in that, In the step of constructing a wedge-shaped transition zone with a thickness gradient at the head and tail of the coating, the length of the wedge-shaped transition zone is controlled between 0.5 and 1.0 mm. The blank segment is the uncoated area between two adjacent coated segments, and the length of the blank segment is controlled between 2.4-2.6 mm; The wet film thickness in the wedge-shaped transition region increases linearly from zero to the main coating thickness of the positive electrode coating section.

3. The method for preparing a wound positive electrode battery material according to claim 1, characterized in that, The specific implementation method of the dynamic calculation and segmentation is as follows: By introducing geometric correction factors and radial compressibility factors, the comprehensive perimeter increment, which covers interlayer thickness stacking and material elastic compression, is calculated. Using the length of the first ring of the effective coating area of ​​the positive electrode as a reference, the coating length of each subsequent ring is recursively calculated using the comprehensive perimeter increment, so that the coating length of the (n+1)th ring is greater than the coating length of the nth ring. The positioning anchor point is selected at a position where the thickness of the wedge-shaped transition zone reaches 45% to 55% of the compacted thickness of the main coating. The positioning anchor points are identified by a visual inspection system, and laser cutting or mechanical slitting is controlled based on the calculated dynamic coordinates.

4. The method for preparing a wound positive electrode battery material according to claim 1, characterized in that, In the drying and hot rolling steps, the compaction thickness of the positive electrode single-sided coating and the total thickness of the negative electrode sheet are controlled so that the ratio of the thickness of the positive electrode single-sided active material to the thickness of the negative electrode single-sided active material is maintained between (0.8-0.85):1.

0. Furthermore, the diaphragm adopts a double-layer structure, and the total thickness of the double-layer structure is controlled between 0.018-0.024 mm.

5. The method for preparing a wound positive electrode battery material according to claim 1, characterized in that, The positive electrode slurry contains a modified flexible binder, which is a copolymer formed by copolymerization of 100 parts by weight of polyvinylidene fluoride, 5.0-10.0 parts by weight of butyl acrylate and maleic anhydride in 1.0-2.0 parts by weight.

6. The method for preparing a wound positive electrode battery material according to claim 5, characterized in that, The modified flexible adhesive is prepared by the following steps: The polyvinylidene fluoride powder was dissolved in N-methylpyrrolidone solvent and stirred at a temperature of 55℃-65℃ until completely dissolved. Add butyl acrylate monomer and maleic anhydride functional monomer, and stir to disperse; Expel all air and introduce inert gas for protection, raise the temperature to 75℃-85℃, add benzoyl peroxide as an initiator, and react in a sealed environment at a constant temperature for 12-16 hours. The reaction solution was poured into a mixture of deionized water and ethanol as a precipitant, and after washing, filtering, and vacuum drying, the modified flexible adhesive was obtained.

7. The method for preparing a wound positive electrode battery material according to claim 1, characterized in that, The preparation process of the positive electrode slurry includes: The modified flexible adhesive is dissolved to form an adhesive solution. A conductive agent is added first and then dispersed at high speed, with the linear velocity controlled at 15-20 m / s and the dispersion time being 3-5 h. Then, positive electrode active material is added, the total solid content of the slurry is adjusted to 68%-72%, and the viscosity of the slurry is controlled between 5000-8000 mPa·s; The positive electrode active material is selected from lithium nickel cobalt manganese oxide and lithium iron phosphate. The conductive agent is made by mixing SuperP with carbon nanotubes.

8. The method for preparing a wound positive electrode battery material according to claim 2, characterized in that, The process parameters for constructing the wedge-shaped transition region include: A slot extrusion coating machine equipped with a back suction control system is used; Adjust the material cut-off back suction pressure to -3.0--6.0 kPa; The valve closing stroke time is controlled to be 5-10ms, and a natural tail is formed by the balance between the fluid inertia of the slurry and the back suction force.

9. The method for preparing a wound positive electrode battery material according to claim 1, characterized in that, In the drying and hot rolling steps, the temperature of the hot rolling is 80℃-100℃ and the pressure is 40-60t; In the step of lamination and winding, the winding tension is controlled between 300-500 gf; When preparing square batteries, after winding, the process also includes a step of hot-pressing and flattening the core. The hot-pressing temperature is 75℃-85℃ and the pressure is 0.4-0.6MPa.

10. The method for preparing a wound positive electrode battery material according to claim 3, characterized in that, The geometric correction factor is related to the shape of the battery: When preparing a cylindrical battery, the geometric correction coefficient is taken as the value of pi; When preparing a square wound battery, the geometric correction factor ranges from 2.8 to 3.1, depending on the width and thickness of the winding needles. The radial compressibility factor ranges from 0.96 to 0.98.

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