Pole piece, preparation method thereof and secondary battery

Abstract

The invention provides a pole piece, the pole piece comprises a functional current collector and an active material layer arranged on the surface of the functional current collector, the functional current collector comprises a polymer base material and a conductive layer arranged on the surface of the polymer base material, the conductive layer comprises a metal layer, the conductive layer is provided with a micropore array, the micropore array comprises a micropore structure, and the metal layer is arranged in the micropore structure. The micropore structure satisfies that the pore channel extends along the thickness direction of the functional current collector, the radial cross section is hexagonal, the aperture is 5-50 [mu] m, and the pore density is 103-105 pores / cm < 2 >. By constructing the special micropore array on the surface of the functional current collector, on one hand, the surface density of the formed electrode active material layer is improved, and on the other hand, the pole piece still has good conductivity and mechanical property under the condition that the high-surface-density electrode active material layer is arranged; and the energy density, the structural stability and the working stability of the pole piece are synergistically optimized.

Description

Technical Field

[0001] The present invention belongs to the field of secondary battery materials, and in particular, relates to a pole piece and a preparation method thereof, and a secondary battery. Background Art

[0002] As the new energy vehicle industry continues to demand high-energy-density, low-cost, and highly safe lithium-ion batteries, current collectors, as core battery components, urgently need to overcome the lightweight bottleneck of traditional metal foils. Composite current collectors utilize a "metal layer-polymer substrate-metal layer" sandwich structure. By replacing part of the metal with a polymer substrate, they significantly reduce current collector weight and the risk of internal short circuits.

[0003] However, due to the characteristics of the composite current collector having an ultra-thin metal layer, the electrical conductivity of the composite current collector is worse than that of the traditional foil current collector. If the composite current collector is used as a carrier of a high-area-density electrode active material layer, the high-area-density electrode active material layer will cause the electron transmission path to be extended. Due to the relatively poor conductivity of the composite current collector, the interface resistance between the composite current collector and the electrode active material layer is significantly increased, affecting the rate performance and capacity of the battery. Moreover, as the surface density of the electrode active material layer increases, its internal stress increases significantly, weakening its interface composite with the composite current collector, causing the pole piece to easily delaminate during the cycle. In order to increase the surface density of the electrode active material layer, the current process increases the rolling pressure in the process of coating the electrode active material slurry or adds a high-viscosity binder to the electrode active material slurry. However, high-pressure rolling can easily cause the elongation of the polymer substrate of the composite current collector to drop significantly, and the density of microcracks in the metal layer of the composite current collector increases sharply, which manifests as embrittlement of the pole piece and significant deterioration of the tensile strength of the pole piece. However, excessive binder will block the conductive path on the electrode active material layer and induce the volume expansion of the electrode during the battery cycle, which will significantly reduce the peel strength of the electrode.

[0004] In summary, the current common composite current collectors are difficult to achieve the conductivity and mechanical strength properties that match the high surface density active coating, making it impossible to take into account the surface density, conductivity, and mechanical properties of the active coating of the electrode using the composite current collector, which restricts the improvement of the energy density of the secondary battery. Summary of the Invention

[0005] The object of the present invention is to provide a pole piece and a preparation method thereof, and a secondary battery, which can have a good electrode active material loading capacity and achieve good electrical conductivity and mechanical properties while maintaining the lightweight advantage of a composite current collector.

[0006] According to one aspect of the present invention, a pole piece is provided, which includes a functional current collector and an active material layer arranged on the surface of the functional current collector, the functional current collector includes a polymer substrate and a conductive layer arranged on the surface of the polymer substrate, the conductive layer includes a metal layer, the conductive layer is provided with a micropore array, the micropore array includes a micropore structure, and the micropore structure meets the following requirements: the pores extend along the thickness direction of the functional current collector, the radial cross section is hexagonal, the pore diameter is 5μm to 50μm, and the pore density is 10 3 Holes / cm 2 ~10 5 Holes / cm 2 . In the pole piece provided by the present invention, the electrode active material is filled in the microporous structure of the functional current collector, which effectively increases the interfacial contact area between the electrode active material and the functional current collector, and utilizes the electrode active material and the microporous structure to construct a mechanical interlocking structure to strengthen the interfacial composite between the electrode active material layer and the functional current collector. At the composite interface between the functional current collector and the negative electrode active material layer, the microporous structure with a hexagonal radial cross-section can fully release the residual stress through a multi-directional stress dispersion mechanism, promote the close bonding between the functional current collector and the negative electrode active material layer, and enable the negative electrode sheet to achieve a higher peeling strength. At the same time, the hexagonal edges of the microporous structure can better disperse the load when the negative electrode sheet is subjected to external force, which not only enables the functional current collector and the negative electrode sheet to have excellent pressure-bearing capacity, and can maintain structural integrity during multiple rolling presses, but also can improve the tensile strength of the functional current collector and the negative electrode sheet, and have high tensile strength. In addition, the microporous structure can act as a directional infiltration channel for the electrolyte, and its hexagonal pore structure can avoid the problem of edge power supply inside the microporous structure, and reduce the interfacial impedance between the functional current collector and the negative electrode active material layer. A plurality of microporous structures are arranged in an array on the surface of the functional current collector to form a microporous array. Based on the shape of the microporous structure, the size and distribution of the microporous structure are further controlled, so that the microporous array can synergistically play the structural advantages of the plurality of microporous structures, promote the uniform filling of the electrode active material slurry on the surface of the functional current collector, and form a uniform anchor point between the electrode active material layer and the functional current collector. At the same time, it can also synergistically optimize the stress transmission network and the conductive network between the functional current collector and the electrode active material layer, so that the electrode piece has excellent conductive properties and mechanical properties, and can match the conductive properties and mechanical properties required to match the high-surface-density electrode active material layer. In summary, in the electrode piece provided by the present invention, by constructing a special microporous array on the surface of the functional current collector, on the one hand, the loading capacity of the functional current collector for the electrode active material is improved, and the surface density of the electrode active material layer formed thereby is increased. On the other hand, the functional current collector has conductive properties and mechanical strength properties that match the high-surface-density electrode active material layer, so that the electrode piece still has good conductive properties and mechanical properties when a high-surface-density electrode active material layer is set, and the energy density, structural stability and working stability of the electrode piece are synergistically optimized.

[0007] Preferably, the total surface density of the electrode active material layer is ≥20 mg / cm 2 The electrode active material layer is composed of n sub-electrode active material layers, where n is a positive integer greater than 1, and the surface density of the n sub-electrode active material layers increases gradiently in a direction away from the functional current collector.

[0008] Preferably, the number n of sub-electrode active material layers is 3 layers.

[0009] Preferably, the surface density gradient of adjacent sub-active material layers is 2 mg / cm 2 ~4 mg / cm 2 .

[0010] Along the direction away from the polymer substrate, the three sub-electrode active material layers stacked in sequence are marked as the first sub-active material layer, the second sub-active material layer, and the third sub-active material layer; when the electrode is a positive electrode, preferably, the surface density of the first sub-active material layer is 5 mg / cm 2 ~7 mg / cm 2 The surface density of the second active material layer is 7 mg / cm 2 ~9 mg / cm 2 The surface density of the third active material layer is 9 mg / cm 2 ~12mg / cm 2 When the electrode is a negative electrode, preferably, the surface density of the first sub-active material layer is 4 mg / cm 2 ~6mg / cm 2 The surface density of the second active material layer is 6 mg / cm 2 ~8mg / cm 2 The surface density of the third active material layer is 8 mg / cm 2 ~10mg / cm 2 .

[0011] Preferably, the microporous structure meets the following requirements: pore size is 20 μm to 30 μm, pore density is 4×10 4 Holes / cm 2 ~10 5 Holes / cm 2 By precisely controlling the size and density of the microporous structure, the overall performance of the electrode can be optimized simultaneously.

[0012] Preferably, the pore spacing of the microporous structure is 10 μm to 100 μm.

[0013] Preferably, the pore spacing of the microporous structure is 40 μm to 60 μm.

[0014] Preferably, the pore depth of the microporous structure does not exceed the thickness of the conductive layer.

[0015] Preferably, the thickness of the conductive layer is 500 nm to 2000 nm.

[0016] Preferably, the conductive layer further comprises a protective layer. In the conductive layer, the protective layer is stacked and covers the interface of the metal layer away from the polymer substrate.

[0017] Preferably, the edge grain size of the microporous structure is ≤300nm. Controlling the edge grain size of the microporous structure within this range can further improve the mechanical properties of the electrode, specifically by improving the peel strength and tensile strength of the electrode.

[0018] Preferably, the edge roughness Ra of the microporous structure satisfies Ra≥0.5 μm.

[0019] Preferably, the preparation of the functional current collector includes the following operations: using a laser energy density of ~ The ultraviolet laser etching process is used to construct a microporous structure on the surface of the functional current collector precursor, which includes a polymer substrate and a conductive layer. By precisely controlling the energy density of the ultraviolet laser, damage to the polymer substrate and slag defects can be simultaneously suppressed, ensuring the edge grain refinement of the microporous structure (≤300nm) and the insulation strength of the polymer base film. If the ultraviolet laser energy density is > The plasma shock wave generated by the metal vaporization of the metal layer can easily cause the polymer base film to break down, and the heat accumulation causes the edge grains of the microporous structure to coarsen (> 500nm), which reduces the conductivity of the conductive layer. If the laser energy density of the ultraviolet laser is less than , the laser ablation may not be thorough, resulting in residual slag on the pore wall of the microporous structure, which will weaken the strength of the functional current collector anchoring with the electrode active coating using the microporous structure. In addition, it will also lead to a decrease in processing efficiency.

[0020] Preferably, the metal material constituting the metal layer includes at least one of aluminum, aluminum alloy, silver, silver alloy, copper, copper alloy, gold, gold alloy, nickel, nickel alloy, iron, iron alloy, titanium, titanium alloy, manganese, and manganese alloy.

[0021] Preferably, the thickness of the metal layer is 500 nm to 1500 nm.

[0022] Preferably, the thickness of the metal layer is 800 nm to 1200 nm.

[0023] Preferably, the metal layer is produced by magnetron sputtering.

[0024] Preferably, the conductive layer further comprises a protective layer, and in the conductive layer, the protective layer is stacked and covers the interface of the metal layer away from the polymer substrate.

[0025] Preferably, the material constituting the protective layer includes at least one of metal oxides, carbides, nitrides, alloys, and carbon materials. Preferably, the metal oxides include aluminum oxide, nickel oxide, chromium oxide, etc., and at least one of carbides. Preferably, the carbides include Preferably, the nitride comprises TiN. Preferably, the alloy comprises a Cr-Mo-Ni alloy. Preferably, the carbon material comprises at least one of graphite, carbon black, and carbon nanotubes.

[0026] Preferably, the thickness of the protective layer is 10 nm to 50 nm.

[0027] Preferably, the thickness of the protective layer is 20 nm to 50 nm.

[0028] Preferably, the protective layer is prepared by magnetron sputtering.

[0029] Preferably, the polymer material constituting the polymer substrate includes at least one of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyimide (PI) and the like.

[0030] Preferably, the thickness of the polymer substrate is 1 μm to 15 μm.

[0031] Preferably, the thickness of the polymer substrate is 3 μm to 10 μm.

[0032] Preferably, a primer layer is provided between the polymer substrate and the conductive layer. Methods for preparing the primer layer include, but are not limited to, physical vapor deposition (such as heated vacuum evaporation, magnetron sputtering, etc.), chemical vapor deposition, electroplating, and chemical plating.

[0033] Preferably, the material constituting the primer layer includes at least one of silicon oxide, aluminum oxide, nickel, chromium, nickel-chromium alloy, titanium oxide, silicon aluminum alloy, polyacrylamide, and polyurethane.

[0034] Preferably, the thickness of the primer layer is 1 nm to 50 nm.

[0035] Preferably, the thickness of the primer layer is 20 nm to 40 nm.

[0036] Preferably, the primer layer is prepared by magnetron sputtering.

[0037] According to a second aspect of the present invention, a method for preparing the above-mentioned electrode sheet is provided, comprising the following four stages of rolling treatment performed in sequence: S1. pre-pressing, coating the surface of the functional current collector with an electrode active material slurry, and rolling the sheet obtained thereby to form a first active coating on the surface of the functional current collector; S2. primary transition pressing, coating the surface of the first active coating with an electrode active material slurry, and rolling the sheet obtained thereby to form a second active coating on the surface of the first active coating; S3. secondary transition pressing, coating the surface of the second active coating with an electrode active material slurry, and rolling the sheet obtained thereby to form a third active coating on the surface of the second active coating ; S4. Final pressing, rolling the sheet obtained; the rolling temperature of the rolling treatment is 50℃~130℃, and the viscosity of the electrode active slurry used for coating is 2000mPa~10000mPa; in S1, the rolling roller line pressure is 60N / mm~100N / mm, the rolling temperature is 50℃~80℃, and the solid content of the electrode active material slurry is 40%~65%; the rolling treatment of each stage of S1, S2, S3, and S4 meets that the rolling roller line pressure increases step by step by 50N / mm~120N / mm; the rolling treatment of each stage of S1, S2, and S3 meets that the viscosity of the electrode active material slurry increases step by step by 1000mPa~5000mPa.

[0038] During the pre-pressing process, the microporous structure on the surface of the functional current collector can provide hexagonal infiltration channels for the electrode active material slurry. Under the guidance of the capillary permeation effect, the electrode active material slurry is evenly filled in the microporous structure along the hexagonal channels. At the same time, because the hexagonal microporous structure can fully release stress, it effectively avoids the local accumulation of stress in the functional current collector caused by rolling, improves the spreading performance of the electrode active material slurry on the surface of the functional current collector, and is conducive to the formation of an electrode active coating with high flatness and high surface density. In order to ensure that the advantages of the microporous structure can be fully utilized, a segmented rolling process is designed in the process of forming the electrode active material layer, and the rolling pressure and active material slurry viscosity of each stage of the rolling process are optimized by gradient increment. On the one hand, it avoids the damage of the microporous structure due to rolling, and ensures that it can always maintain the hexagonal pore structure before and after the rolling process. On the other hand, as the loading amount of the electrode active material gradually increases, the electrode active material can be effectively compacted to finally form an electrode active material layer with a high surface density. In the rolling process of each stage mentioned above: in the pre-pressing process, the basic compaction of the bottom electrode active material is achieved, the electrode active material enters the microporous structure, and the attachment basis of the electrode active material layer on the surface of the functional current collector is established; in the first transition pressing process, the densification of the electrode active material layer and the optimization of the conductive network are promoted; in the second transition pressing process, the thermal compensation of the electrode active material layer is achieved by further increasing the rolling temperature and rolling pressure; finally, the surface thermal sealing of the electrode active material layer is completed by final pressing to achieve the overall densification of the electrode active coating.

[0039] When the electrode sheet is a negative electrode sheet, preferably, the viscosity of the electrode active slurry used for coating in S1 is 2000mPa~4000mPa, the viscosity of the electrode active slurry used for coating in S2 is 4000mPa~6000mPa, and the viscosity of the electrode active slurry used for coating in S3 is 6000mPa~8000mPa.

[0040] When the electrode is a positive electrode, preferably, the viscosity of the electrode active slurry used for coating in S1 is 3000mPa~5000mPa, the viscosity of the electrode active slurry used for coating in S2 is 6000mPa~8000mPa, and the viscosity of the electrode active slurry used for coating in S3 is 8000mPa~10000mPa.

[0041] When the electrode sheet is a negative electrode sheet, preferably: in S1, the rolling roller line pressure is 60N / mm~80N / mm, and the rolling temperature is 50℃~60℃; in S2, the rolling roller line pressure is 100N / mm~130N / mm, and the rolling temperature is 60℃~80℃; in S3, the rolling roller line pressure is 180N / mm~220N / mm, and the rolling temperature is 80℃~100℃; in S4, the rolling roller line pressure is 250N / mm~280N / mm, and the rolling temperature is 100℃~120℃.

[0042] When the electrode sheet is a positive electrode sheet, preferably: in S1, the rolling roller line pressure is 80N / mm~100N / mm, and the rolling temperature is 60℃~80℃; in S2, the rolling roller line pressure is 120N / mm~150N / mm, and the rolling temperature is 80℃~100℃; in S3, the rolling roller line pressure is 200N / mm~250N / mm, and the rolling temperature is 100℃~120℃; in S4, the rolling roller line pressure is 300N / mm~350N / mm, and the rolling temperature is 120℃~130℃.

[0043] When the electrode is a negative electrode, preferably, the thickness of the first active coating is 10 μm to 60 μm, the thickness of the second active coating is 20 μm to 60 μm, and the thickness of the third active coating is 10 μm to 60 μm.

[0044] When the electrode is a positive electrode, preferably, the thickness of the first active coating is 10 μm to 80 μm, the thickness of the second active coating is 20 μm to 80 μm, and the thickness of the third active coating is 10 μm to 80 μm.

[0045] According to a third aspect of the present invention, a secondary battery is provided, comprising the electrode sheet as described above. DETAILED DESCRIPTION

[0046] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0047] Example 1 1. Preparation of functional current collector (1) Pretreatment of polymer substrate In this example, a PP base film with a thickness of 4.5 μm was used as a polymer substrate for preparing a functional current collector. The polymer substrate was immersed in acetone, ethanol, and deionized water solution in sequence and ultrasonically cleaned for 10 min each to remove oil stains on the surface of the PP film.

[0048] (2) Preparation of base layer The pretreated PP film was placed in a magnetron sputtering machine, and a 30 nm thick primer layer was deposited on both sides of the PP film. The specific process conditions were as follows: a nickel-chromium target (Ni:Cr=7:3, purity ≥99.99%) was used as the target material, the power density was 2 kW, the argon flow rate was 50 mL / min, the coating vacuum was 0.05 Pa, the coating time was 6 s, and the temperature of the main roller during the coating process was -5°C. The first PP composite film consisting of a primer layer, a PP film, and a primer layer stacked in sequence was prepared.

[0049] (3) Preparation of metal layer The first PP composite film was placed in a magnetron sputtering machine, and a metal layer with a thickness of 1μm±0.1μm was deposited on both sides of the first PP composite film. The specific process conditions were: a copper target (purity ≥99.99%) was used as the target material, the power density was 10kW, the argon flow rate was 100mL / min, the coating vacuum was 0.05Pa, the coating time was 20s, and the temperature of the main roller during the coating process was -20℃. A second PP composite film consisting of a metal layer, a primer layer, a PP film, a primer layer, and a metal layer stacked in sequence was prepared.

[0050] (4) Preparation of protective layer The second PP composite film was placed in a magnetron sputtering machine, and a layer of 30 nm thick was deposited on each side of the second PP composite film. The metal layer is used as a protective layer. The specific process conditions are: aluminum target (purity ≥ 99.99%) as the target material, power density of 3kW, coating vacuum of 0.05Pa, Ar flow rate of 150mL / min, The flow rate was 50 mL / min and the coating time was 20 s to prepare a functional current collector precursor consisting of a metal layer, a primer layer, a PP film, a primer layer, and a metal layer. On either side of the PP film, a conductive layer was formed by stacking a primer layer and a metal layer.

[0051] (5) Construction of microwell array The functional current collector precursor was used as the substrate, and an ultraviolet laser (wavelength 355 nm, spot diameter 20 μm) was used to set the laser energy density to , the pulse frequency is 80kHz, and a microporous structure with a hexagonal radial cross section is constructed on the surface of the functional current collector precursor (conductive layer). The pores of the microporous structure extend along the thickness direction of the functional current collector, and the pore depth of the microporous structure is not the thickness of the conductive layer. Moreover, the pore size of the microporous structure is 20μm and the pore density is hole / Thus, the functional current collector of this embodiment is obtained.

[0052] 2. Preparation of negative electrode sheet Calculated by mass, the materials used to prepare the negative electrode active slurry in this embodiment include 1.5 parts of CMC powder, 1 part of graphene, 0.5 parts of carbon nanoparticles, 95 parts of SiO@C powder, 0.4 parts of TPU emulsion (solid content 40%), and 1.6 parts of SBR emulsion (solid content 48%).

[0053] (1) Preparation of negative electrode active material slurry Step 1: CMC powder and deionized water were mixed in a mass ratio of 4:96 and stirred for 2 hours until the CMC powder was completely dissolved, thereby forming a transparent adhesive solution, which was marked as CMC adhesive solution.

[0054] Step 2: Graphene and carbon nanotubes were mixed in a mass ratio of 2:1, deionized water was added to the resulting mixture for pre-wetting, and then ultrasonic treatment (frequency 40 kHz) was performed for 30 minutes to peel off the agglomerates, thereby obtaining a conductive agent dispersion slurry.

[0055] Step 3: In this embodiment, SiO@C powder is used as the negative electrode active material. The SiO@C powder is added to the above-mentioned CMC glue solution. The resulting slurry is continuously stirred at a stirring speed of 100 rpm. TPU emulsion is simultaneously added dropwise to the slurry for 3 hours.

[0056] Step 4: Add the conductive agent dispersion slurry mentioned above to the mixed slurry prepared in step 3. The conductive agent dispersion slurry is added in three times, with an interval of 15 minutes between each addition. During this period, planetary stirring (revolution 20 rpm, rotation 800 rpm) is used to avoid shear damage to the silicon structure.

[0057] Step 5: Finally, add SBR emulsion to the mixed slurry prepared in step 4. During the addition, provide low-speed stirring (50 rpm) to the slurry to avoid the breakage of long-chain molecules. The stirring time is 10 minutes.

[0058] During the preparation of the negative electrode active material slurry in this embodiment, the solid content is adjusted by increasing or decreasing the deionized water content according to the real-time viscosity test results, thereby controlling the viscosity of the negative electrode active material slurry.

[0059] (2) Coating roller pressing S1. Preload The functional current collector prepared in this embodiment was subjected to plasma surface activation treatment (power 500 W), and a low-viscosity negative electrode active material slurry (viscosity of 3000 mPa•s) was coated on the surface of the functional current collector by doctor blade coating. The coating speed was 3 m / min, and the wet film thickness of the coating was 40 μm. Subsequently, the sheet coated with the low-viscosity negative electrode active material slurry was placed on an unwinder and pulled to the entrance of the roller press through a constant tension control system. The dust removal device was started simultaneously to remove surface dust. A gas-liquid booster pump roller press was used, and the initial roller gap was set to 1.5 times the thickness of the sheet through the wedge gap adjustment mechanism. A tungsten carbide spray roller line was used, and the roller line pressure was set to 60 N / mm and the roller surface temperature was 60°C. The sheet was pre-pressed to complete preliminary compaction, thereby forming the first active coating on the surface of the functional current collector.

[0060] S2. Primary transition pressure The surface of the first active coating layer is coated with a medium-viscosity negative electrode active material slurry (viscosity of 5000 mPa•s) by blade coating, with a coating speed of 2.5 m / min and a wet film thickness of 50 μm. Subsequently, the sheet coated with the medium-viscosity negative electrode active material slurry is placed on a hydraulic servo pressure roller press, and the roller gap is dynamically adjusted by the AGC automatic thickness control system. A tension swing roller with a staggered arrangement of Teflon rubber rings is used to increase the roller line pressure to 100 N / mm and the roller surface temperature to 60°C, completing a transition pressure on the sheet to form a second active coating layer on the surface of the first active coating layer.

[0061] S3. Secondary transition pressure A high-viscosity negative electrode active material slurry (viscosity of 7000 mPa•s) is coated on the surface of the second active coating by blade coating, with a coating speed of 2 m / min and a wet film thickness of 60 μm. Subsequently, the coil coated with the high-viscosity negative electrode active material slurry is switched to an electromagnetic induction heating roller press. The main roller has a built-in flat induction coil, the roller line pressure is increased to 180 N / mm, and the roller surface temperature is raised to 80°C. The wrinkles of the coil are eliminated through the PINCH stretching mechanism (differential speed ratio 1.05-1.2), and the sheet is subjected to secondary transition pressing, thereby forming a third active coating on the surface of the second active coating.

[0062] S4. Final pressure Finally, a fully hydraulic AGC high-rigidity roller press (rigidity ≥ 5GN / m) was used to perform final pressing on the sheet, increasing the roller line pressure to 250N / mm and the roller surface temperature to 100°C to complete the final pressing and achieve densification of the negative electrode active coating.

[0063] (3) Drying and cutting: The negative electrode semi-finished product is dried in stages. Pre-drying is performed at 80°C for 10 minutes (to remove the solvent). Final drying is then performed at 120°C for 10 minutes (to solidify the binder and achieve a residual solvent content of <0.5%). After drying, the electrode sheets are cut according to the required electrode size, and the resulting negative electrode sheet surface density is measured.

[0064] Example 2 This example prepared a functional current collector and negative electrode sheet using the same method as in Example 1. This example differs from Example 1 in that, during the preparation of the functional current collector, the microporous structure constructed in the conductive layer has a hexagonal radial cross-section and a pore size of 30 μm. Aside from these differences, the remaining procedures and materials for preparing the functional current collector, and further preparing the negative electrode sheet using the functional current collector, remain strictly consistent with those in Example 1.

[0065] Example 3 This embodiment prepares the functional current collector and negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, and the pore density of the microporous structure is 6×10 4 Holes / cm 2 Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0066] Example 4 This embodiment prepares the functional current collector and negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, the pore size of the microporous structure is 15 μm, and the pore density is 9×10 4 Holes / cm 2 , thus making the functional current collector prepared in this embodiment have substantially the same total radial cross-sectional area of ​​the microporous structure as the functional current collector prepared in Example 1. Aside from the aforementioned differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, were strictly consistent with those in Example 1.

[0067] Example 5 This embodiment refers to the preparation of functional current collector and negative electrode sheet in accordance with the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, the pore size of the microporous structure is 40 μm, and the pore density is , thus making the functional current collector prepared in this embodiment have substantially the same total radial cross-sectional area of ​​the microporous structure as the functional current collector prepared in Example 1. Aside from the aforementioned differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, were strictly consistent with those in Example 1.

[0068] Example 6 This embodiment prepares the functional current collector and negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, the pore size of the microporous structure is 5 μm, and the pore density is 10 5 Holes / cm 2 Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0069] Example 7 This embodiment refers to the preparation of functional current collector and negative electrode sheet in accordance with the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, the pore size of the microporous structure is 50 μm, and the pore density is 10 3 Holes / cm 2 Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0070] Example 8 This embodiment prepares the functional current collector and the negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the laser energy power of the ultraviolet laser process used to construct the microporous structure in the conductive layer is adjusted to Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0071] Example 9 This embodiment prepares the functional current collector and the negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the laser energy power of the ultraviolet laser process used to construct the microporous structure in the conductive layer is adjusted to Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0072] Example 10 This embodiment prepares the functional current collector and the negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the laser energy power of the ultraviolet laser process used to construct the microporous structure in the conductive layer is adjusted to Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0073] Example 11 This embodiment prepares the functional current collector and the negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the laser energy power of the ultraviolet laser process used to construct the microporous structure in the conductive layer is adjusted to Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0074] Example 12 This embodiment prepares the functional current collector and the negative electrode sheet with reference to the embodiment 1. The difference from the embodiment 1 is that in the process of preparing the functional current collector, the laser energy power of the ultraviolet laser process used to construct the microporous structure in the conductive layer is adjusted to Except for the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0075] Comparative Example 1 This comparative example prepared a functional current collector and a negative electrode sheet using the same method as Example 1. This comparative example differs from Example 1 in that the step of constructing a micropore array is omitted during the preparation of the functional current collector. Consequently, the functional current collector prepared in this comparative example lacks a micropore array comprising a microporous structure. Aside from these differences, the remaining steps and materials for preparing the functional current collector, and further preparing the negative electrode sheet using the functional current collector, remain strictly consistent with those in Example 1.

[0076] Comparative Example 2 This comparative example prepared a functional current collector and negative electrode sheet with reference to Example 1. This comparative example differs from Example 1 in that, during the preparation of the functional current collector, the microporous structure constructed in the conductive layer had a circular radial cross-section. Aside from these differences, the remaining procedures and materials for preparing the functional current collector, and further preparing the negative electrode sheet using the functional current collector, remained strictly consistent with those in Example 1.

[0077] Comparative Example 3 This comparative example refers to Example 1 to prepare the functional current collector and the negative electrode sheet. The difference from Example 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, the pore size of the microporous structure is 4 μm, and the pore density is , thus making the functional current collector prepared in this comparative example have substantially the same total radial cross-sectional area of ​​the microporous structure as the functional current collector prepared in Example 1. Aside from the aforementioned differences, the other operations and related materials for preparing the functional current collector in this comparative example, i.e., further preparing the negative electrode sheet using the functional current collector, were strictly consistent with those in Example 1.

[0078] Comparative Example 4 This comparative example refers to Example 1 to prepare the functional current collector and the negative electrode sheet. The difference from Example 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, the pore size of the microporous structure is 75 μm, and the pore density is hole / , thus making the functional current collector prepared in this comparative example have substantially the same total radial cross-sectional area of ​​the microporous structure as the functional current collector prepared in Example 1. Aside from the aforementioned differences, the other operations and related materials for preparing the functional current collector in this comparative example, i.e., further preparing the negative electrode sheet using the functional current collector, were strictly consistent with those in Example 1.

[0079] Comparative Example 5 This comparative example refers to Example 1 to prepare the functional current collector and the negative electrode sheet. The difference from Example 1 is that in the process of preparing the functional current collector, the radial cross section of the microporous structure constructed in the conductive layer is hexagonal, the pore size of the microporous structure is 158 μm, and the pore density is 8×10 2 Holes / cm 2 , thus making the functional current collector prepared in this comparative example have substantially the same total radial cross-sectional area of ​​the microporous structure as the functional current collector prepared in Example 1. Aside from the aforementioned differences, the other operations and related materials for preparing the functional current collector in this comparative example, i.e., further preparing the negative electrode sheet using the functional current collector, were strictly consistent with those in Example 1.

[0080] Test Example 1 1. Test subjects The negative electrode sheets prepared in Examples 1 to 12 and Comparative Examples 1 to 5 were used as test objects.

[0081] 2. Test items and test standards (1) Tensile strength test The tensile strength test of the test object was carried out in accordance with the standards GB / T1040.3-2006 and GB / T10003-2008.

[0082] (2) Peel force test First, use a flat paper cutter to cut the rolled test object into long strips with a length of 170 mm and a width of 30 mm. Wipe the scaleless steel ruler clean until there is no stain or dust on the surface. Then, apply 60 mm wide transparent tape horizontally to the bottom of the dried scaleless steel ruler, making the transparent tape and the cross-section of the scaleless steel ruler flush. Next, apply 25 mm wide double-sided tape to the transparent tape, making the length and width of the double-sided tape the same, and centered. Finally, affix the test sample to the double-sided tape, making the test sample flush with the end face of the stainless steel plate. Use a pressure wheel (2 kg) with a diameter of 84 mm and a height of 45 mm to roll back and forth on the surface of the test sample twice. The free end of the test sample was fixed to the upper mold of the tensile tester, and the bottom end of the stainless steel plate was fixed to the lower mold of the tensile tester. The tensile tester was started and a 180° peel test was performed at a peeling speed of 50 mm / min to obtain the maximum peel strength.

[0083] (3) Surface density detection Cut the test object into a regular shape (area 100cm 2 The test sample is then balanced in a dry environment (25°C, humidity ≤ 30%) to constant weight (mass change ≤ 0.1%), and the mass of the test sample in mg is measured using a high-precision microbalance. Each test object is repeated 10 times in parallel, with each repeat being a test sample. The average mass of the 10 test samples in mg is calculated as the areal density of the test object.

[0084] 3. Test results The test results are shown in Table 1.

[0085] Table 1. Test result statistics of test case 1

[0086] The functional current collector used to prepare the negative electrode sheet in Comparative Example 1 does not have a microporous structure. The negative electrode active material slurry is difficult to penetrate into the functional current collector, and the negative electrode active material cannot be loaded into the functional current collector. As a result, the negative electrode active material layer density of the negative electrode sheet of Comparative Example 1 is significantly lower than that of other test objects. In addition, the peel strength and tensile strength measured for the negative electrode sheet of Comparative Example 1 are significantly lower. Due to the lack of a microporous structure, the functional current collector of Comparative Example 1 is prone to stress concentration under roller pressing, which increases the resistance of the negative electrode active material slurry to spread on the surface of the functional current collector, making it difficult to form an active coating with high flatness and good uniformity. The stress concentration at the composite interface between the negative electrode active material layer and the functional current collector formed in this way makes it difficult for the two to be tightly bonded, resulting in significantly low peel strength and tensile strength of the negative electrode sheet. At the same time, the lack of a microporous structure causes the surface of the functional current collector of Comparative Example 1 to lack electrolyte infiltration channels. Coupled with the poor composite of the functional current collector and the negative electrode active material layer, the conductive properties of the negative electrode sheet prepared in Comparative Example 1 will be compromised. The relatively low peel strength and tensile strength indicate that the functional current collector of Comparative Example 1 is not suitable for loading a negative electrode active material layer with a high surface density. Even if the surface density of the negative electrode active material layer loaded by the above-mentioned functional current collector can be further increased, the negative electrode sheet thus prepared cannot give full play to the advantages of the high surface density negative electrode active material layer. Instead, it will cause the conductivity and mechanical properties of the negative electrode to deteriorate more seriously.

[0087] The functional current collectors used in the test objects provided in Examples 1 to 12 and Comparative Examples 2 to 5 are all provided with a microporous structure distributed in the conductive layer. The microporous structure can serve as a storage space for the negative electrode active material, thereby improving the functional current collector's loading capacity for the negative electrode active material and increasing the surface density of the negative electrode active material layer. Among these test objects, the comprehensive performance of the test objects provided in Examples 1 to 12 is significantly better. In Examples 1 to 12, the functional current collectors used are all provided with a microporous structure with a hexagonal radial cross section in the conductive layer included therein. These microporous structures are arranged in an array, and their size and distribution meet the requirements of a pore diameter of 5 μm to 50 μm and a pore density of 10 3 Holes / cm 2 ~10 5 Holes / cm 2. At the composite interface between the functional current collector and the negative electrode active material layer, the microporous structure with a hexagonal radial cross-section can fully release the residual stress through a multi-directional stress dispersion mechanism, promote the close bonding between the functional current collector and the negative electrode active material layer, and enable the negative electrode sheet to achieve a higher peel strength. At the same time, the hexagonal edges of the microporous structure can better disperse the load when the negative electrode sheet is subjected to external force. Not only can the functional current collector and the negative electrode sheet have excellent pressure-bearing capacity, they can also maintain structural integrity during multiple rolling presses, and the tensile strength of the negative electrode sheet can be improved, and the negative electrode sheet has high tensile strength. In addition, the hexagonal channels provided by the microporous structure can be used as directional infiltration channels for the electrolyte. The hexagonal channels can avoid the problem of edge power supply inside the microporous structure and reduce the interface impedance between the functional current collector and the negative electrode active material layer. A plurality of microporous structures are arranged in an array on the surface of the functional current collector to form a microporous array. Based on the shape of the microporous structure, the size and distribution of the microporous structure are further controlled, so that the microporous array can synergistically exert the structural advantages of the multiple microporous structures, promote the uniform filling of the negative electrode active material slurry on the surface of the functional current collector, and form a uniform anchor point between the negative electrode active material layer and the functional current collector. At the same time, it can also synergistically optimize the stress transmission network and the conductive network between the functional current collector and the negative electrode active material layer, so that the negative electrode sheet has excellent conductive properties and mechanical properties, which can match the conductive properties and mechanical properties required to adapt to the high surface area negative electrode active material layer.

[0088] The functional current collector used in Comparative Example 2 also has a microporous structure in its conductive layer. However, the peel strength and tensile strength measured for the negative electrode sheet of Comparative Example 2 are significantly inferior to those of the negative electrode sheets provided in Examples 1 to 12. This is because the radial cross-section of the microporous structure provided on the functional current collector in Comparative Example 2 is circular. Such a microporous structure has limited ability to regulate the interfacial stress between the functional current collector and the negative electrode active material layer. The interfacial stress between the functional current collector and the negative electrode active material layer is not fully released, thereby weakening the interfacial composite between the two and reducing the peel strength of the negative electrode sheet. At the same time, the tensile and compressive strength of the microporous structure with circular edges are not as good as those of the microporous structure with hexagonal edges, resulting in a low tensile strength measured for the negative electrode sheet of Comparative Example 2.

[0089] The functional current collectors used in Examples 1 to 7 and Comparative Examples 3 to 5 are all provided with a microporous structure with a hexagonal radial cross-section. The difference between these functional current collectors lies in the size and distribution of the microporous structure. It can be clearly seen from the test results of this test example that the comprehensive performance of the test objects provided by Examples 1 to 7 is better. As mentioned above, in Examples 1 to 7, by controlling the pore size and pore density of the microporous structure of the functional current collector, the size and distribution of these microporous structures can be made more reasonable, so that the microporous array formed by these microporous structures can synergistically exert the structural advantages of multiple microporous structures, so that the negative electrode sheet based on these functional current collectors can achieve a significant improvement in comprehensive performance. The microporous structure provided on the functional current collector of Comparative Example 3 has a relatively small pore size and a relatively large pore density, which leads to stress concentration on the surface of the functional current collector. The relatively small microporous structure greatly increases the resistance to the infiltration of the negative active material slurry, and the filling amount of the negative active material slurry in the microporous structure is reduced, and there is even a situation where the microporous structure cannot be effectively filled. The pore size of the microporous structure on the functional current collector of Comparative Example 4 is relatively large, and the pore size of the microporous structure on the functional current collector of Comparative Example 5 is relatively large and the pore density is relatively small. The relatively large microporous structure increases the probability of uneven filling of the microporous structure by the negative active material slurry, and the relatively small pore density of the microporous structure leads to uneven distribution of interface anchor points between the functional current collector and the negative active material layer, and the interface bonding force between the functional current collector and the negative active material layer is significantly reduced, which is manifested in obvious deterioration of the peel strength and tensile strength.

[0090] Further comparison with Examples 1 to 7 shows that among the negative electrode sheets prepared in these examples, the negative electrode sheets of Examples 1 to 3 have better comprehensive performance. In particular, the functional current collectors prepared in the three groups of Example 1, Example 4, and Example 5 have basically the same total radial cross-sectional area of ​​the microporous structure. However, the peel strength and tensile strength measured for the negative electrode sheet of Example 1 are both the highest values, indicating that by further optimizing the size and distribution of the microporous structure, the active material filling uniformity and the interface stress distribution can be improved, thereby achieving a synergistic improvement in the comprehensive performance of the negative electrode sheet.

[0091] Referring to the construction methods of the above embodiments, it can be seen that the difference between Examples 1, 8, 9, 10, 11, and 12 is that a microporous structure is constructed on the surface of the functional current collector precursor using ultraviolet lasers of different laser energy powers. As the laser energy density of the ultraviolet laser increases, the edge grain size of the microporous structure also increases. In the above embodiments, the edge grain size of the microporous structure constructed on the functional current collector is as follows: in Example 1, the edge grain size of the microporous structure is 270nm±10nm; in Example 8, the edge grain size of the microporous structure is 200nm±10nm; in Example 9, the edge grain size of the microporous structure is 250nm±10nm; in Example 10, the edge grain size of the microporous structure is 290nm±10nm; in Example 11, the edge grain size of the microporous structure is 480nm±10nm; in Example 12, the edge grain size of the microporous structure is 530nm±10nm. Based on the above-mentioned edge grain size data of the microporous structure, combined with the electrode performance test results corresponding to the above-mentioned embodiment in Table 1, it can be seen that: when the edge grain size of the microporous structure does not exceed 300nm, the mechanical properties of the corresponding negative electrode sheet are excellent. In addition, controlling the edge grain size of the microporous structure within this range effectively reduces the grain boundary scattering effect, significantly improves the carrier mobility of the conductive layer, and thereby improves the conductivity of the conductive layer, thereby reducing the interfacial impedance between the functional current collector and the negative electrode active material layer, and significantly improving the conductivity of the negative electrode sheet. As the edge grain size of the microporous structure increases, the mechanical properties of the negative electrode sheet gradually decreases. When the edge grain size of the microporous structure is between 500nm and above, the decline in the mechanical properties of the negative electrode sheet is significantly greater. Therefore, controlling the edge grain size of the microporous structure within a range of no more than 500nm can better exert the microporous structure's optimization effect on the performance of the negative electrode sheet. More preferably, controlling the edge grain size of the microporous structure within a range of no more than 300nm can synergistically improve the conductive and mechanical properties of the negative electrode sheet. By controlling the laser energy density of the ultraviolet laser used to construct the microporous structure to no more than The edge grain size of the microporous structure can be maintained within the range of no more than 500nm. However, the laser density of the ultraviolet laser should not be too low. If the laser energy density of the ultraviolet laser is less than , the laser ablation may not be thorough, resulting in residual slag on the pore walls of the microporous structure, which will weaken the strength of the functional current collector anchoring with the negative electrode active coating using the microporous structure. In addition, it will also lead to a decrease in processing efficiency.

[0092] Example 13 This example prepared the functional current collector and negative electrode sheet with reference to Example 1. The only difference from Example 1 is that during the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure during the first transition pressing step was adjusted to 120 N / mm. Aside from these differences, the other operations and materials involved in preparing the functional current collector, and further preparing the negative electrode sheet using the functional current collector, remained strictly consistent with those in Example 1.

[0093] Example 14 This example prepared the functional current collector and negative electrode sheet with reference to Example 1. The only difference from Example 1 is that during the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure during the primary transition press was adjusted to 120 N / mm, and the roller line pressure during the secondary transition press was adjusted to 160 N / mm. Aside from these differences, the other operations and materials involved in preparing the functional current collector, and thus the negative electrode sheet, using the functional current collector, remained strictly consistent with those in Example 1.

[0094] Example 15 This example prepared the functional current collector and negative electrode sheet with reference to Example 1. The only difference from Example 1 is that during the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure during the primary transition pressing step was adjusted to 120 N / mm, and the roller line pressure during the secondary transition pressing step was adjusted to 210 N / mm. Aside from these differences, the other operations and materials involved in preparing the functional current collector, and thus the negative electrode sheet using the functional current collector, remained strictly consistent with those in Example 1.

[0095] Example 16 This example prepared the functional current collector and negative electrode sheet with reference to Example 1. The only difference from Example 1 is that during the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure during the primary transition pressing step was adjusted to 120 N / mm, and the roller line pressure during the secondary transition pressing step was adjusted to 230 N / mm. Aside from these differences, the other operations and materials involved in preparing the functional current collector, and thus the negative electrode sheet, using the functional current collector, remained strictly consistent with those in Example 1.

[0096] Example 17 This example prepared the functional current collector and negative electrode sheet with reference to Example 1. The only difference from Example 1 is that during the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure during the primary transition pressing step was adjusted to 120 N / mm, and the roller line pressure during the secondary transition pressing step was adjusted to 140 N / mm. Aside from these differences, the other operations and materials involved in preparing the functional current collector, and thus the negative electrode sheet, using the functional current collector, remained strictly consistent with those in Example 1.

[0097] Example 18 This example prepared the functional current collector and negative electrode sheet with reference to Example 1. The only difference from Example 1 is that during the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure in the pre-pressing step was adjusted to 55 N / mm, and the roller line pressure in the primary transition pressing step was adjusted to 120 N / mm. Aside from these differences, the other operations and materials involved in preparing the functional current collector and further preparing the negative electrode sheet using the functional current collector remained strictly consistent with those in Example 1.

[0098] Example 19 This example prepares the functional current collector and negative electrode sheet with reference to Example 1. The difference from Example 1 is that in the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure in the pre-pressing step is adjusted to 110 N / mm, the roller line pressure in the primary transition pressing step is adjusted to 160 N / mm, the roller line pressure in the secondary transition pressing step is adjusted to 210 N / mm, and the roller line pressure in the final pressing step is adjusted to 260 N / mm. Aside from these differences, the other operations and related materials for preparing the functional current collector in this example, i.e., the further preparation of the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0099] Example 20 This example prepared the functional current collector and negative electrode sheet with reference to Example 1. The difference from Example 1 is that in the coating roller pressing process for preparing the negative electrode sheet, the roller line pressure in the pre-pressing step was adjusted to 100 N / mm, the roller line pressure in the primary transition pressing step was adjusted to 150 N / mm, and the roller line pressure in the secondary transition pressing step was adjusted to 200 N / mm. Apart from these differences, the other operations and related materials for preparing the functional current collector in this example, i.e., the further preparation of the negative electrode sheet using the functional current collector, were strictly consistent with those in Example 1.

[0100] Example 21 This example prepared the functional current collector and negative electrode sheet with reference to Example 13. The difference from Example 13 is that in the coating roller pressing process for preparing the negative electrode sheet, the viscosity of the negative electrode active material slurry used in the pre-pressing step, the primary transition pressing step, and the secondary transition pressing step was the same: 5000 mPa·s. Apart from these differences, the other operations and related materials for preparing the functional current collector in this example, i.e., the further preparation of the negative electrode sheet using the functional current collector, remained strictly consistent with those in Example 13.

[0101] Example 22 This example prepared the functional current collector and negative electrode sheet with reference to Example 13. The difference from Example 13 is that in the coating and roller-pressing process for preparing the negative electrode sheet, the viscosity of the negative electrode active material slurry used in the pre-pressing step was adjusted to 7000 mPa·s, and the viscosity of the negative electrode active material slurry used in the secondary step was adjusted to 3000 mPa·s. Apart from these differences, the other operations and related materials for preparing the functional current collector in this example, i.e., the further preparation of the negative electrode sheet using the functional current collector, were strictly consistent with those in Example 13.

[0102] Example 23 This example prepared the functional current collector and negative electrode sheet with reference to Example 13. The difference from Example 13 is that during the coating and rolling process for preparing the negative electrode sheet, the viscosity of the negative electrode active material slurry used in the first step was adjusted to 3500 mPa·s. Apart from these differences, the other operations and materials involved in preparing the functional current collector and further preparing the negative electrode sheet using the functional current collector in this example were strictly consistent with those in Example 13.

[0103] Example 24 This example prepared the functional current collector and negative electrode sheet with reference to Example 13. The difference from Example 13 is that during the coating and rolling process for preparing the negative electrode sheet, the viscosity of the negative electrode active material slurry used in the first step was adjusted to 6500 mPa·s. Apart from these differences, the other operations and materials involved in preparing the functional current collector and further preparing the negative electrode sheet using the functional current collector in this example were strictly consistent with those in Example 13.

[0104] Example 25 This example prepares the functional current collector and negative electrode sheet with reference to Example 1. The difference from Example 1 is that in this example, during the preparation of the negative electrode active material slurry, the amount of TPU emulsion is adjusted to 0.6 parts and the amount of SBR emulsion is adjusted to 1.4 parts; and in step 3 of preparing the negative electrode active material slurry, the CMC emulsion and the TPU emulsion are first blended, and then SiO@C powder is added to the resulting mixture. Apart from the above differences, the other operations and related materials for preparing the functional current collector in this example, i.e., further preparing the negative electrode sheet using the functional current collector, are strictly consistent with those in Example 1.

[0105] Example 26 This embodiment prepares the functional current collector and the negative electrode sheet with reference to Example 1. The difference from Example 1 is that in the selection of raw materials for preparing the negative electrode active material slurry, this embodiment uses graphene of equal mass to replace the carbon nanotubes used in Example 1 for preparing the negative electrode active material slurry, that is, the conductive agent used in this embodiment to prepare the negative electrode active material slurry is all graphene, and its mass is equal to the total mass of the graphene and carbon nanotubes used in Example 1. First, the CMC emulsion and the TPU emulsion are blended, and then SiO@C powder is added to the resulting mixture. In addition to the above differences, the other operations and related materials for preparing the functional current collector in this embodiment, that is, the application of the functional current collector to further prepare the negative electrode sheet, are strictly consistent with those in Example 1.

[0106] Test Example 2 1. Test subjects The negative electrode sheets prepared in Examples 13 to 26 were used as test objects.

[0107] 2. Test items and test standards (1) Pole tensile strength test The same as test example 1.

[0108] (2) Electrode peeling force test The same as test example 1.

[0109] (3) Surface density detection The same as test example 1.

[0110] 3. Test results The test results of this test example are shown in Table 4. For clear comparison, Table 4 also includes the test result data of the object provided in Example 1 in Test Example 1.

[0111] In the preparation of negative electrode sheets, as described in Example 1 and Examples 13-20, the roller pressure at each stage of the coating and rolling process was controlled to achieve differentiated performance in terms of surface density, peel strength, and tensile strength. For ease of comparison, Table 2 lists the roller pressure at each stage of the coating and rolling process for the negative electrode sheets prepared in Example 1 and Examples 13-20. Combined with the test results shown in Table 4, it can be seen that among the test subjects provided in the above examples, the negative electrode sheet provided in Example 13 achieved the best overall performance. The coating and rolling process in Example 13 included four stages of rolling: pre-pressing (S1), primary transition pressing (S2), secondary transition pressing (S3), and final pressing (S4). In S1, the roller pressure was 60 N / mm. The roller pressure in each of S1, S2, S3, and S4 increased in increments of 50 N / mm to 120 N / mm.

[0112] Taking Example 13 as a control, the roller line pressure settings of Example 1 and Examples 14 to 20 in the coating roller pressing process were compared and sorted out, and the specific situations are as follows: (1) Example 1, the gradient of the roller pressure between S1 and S2 is relatively small; (2) Example 14, the gradient of the roller pressure between S2 and S3 is relatively small; (3) Example 15, the gradient of the roller pressure between S3 and S4 is relatively small; (4) Example 16, the gradient of the roller pressure between S2 and S3 is relatively large, and the gradient of the roller pressure between S3 and S4 is relatively small; (5) Example 17, the gradient of the roller pressure between S2 and S3 is relatively small, and the gradient of the roller pressure between S3 and S4 is relatively large; (6) Example 18, the roller pressure of S1 is relatively small; (7) Example 19, the roller pressure of S1 is relatively large; (8) Example 20, the roller pressure of S1 is relatively large.

[0113] During the pre-pressing process of preparing the negative electrode sheet, the negative electrode active material slurry infiltrates and fills the microporous structure. Through pre-pressing, the basic compaction of the underlying electrode active material is achieved, and the adhesion foundation of the electrode active material layer on the surface of the functional current collector is established. By comparing Examples 13, 18, 19, and 20, it is shown that during the pre-pressing process, if the rolling pressure is too high, the microporous structure of the functional current collector may be damaged, and the structural advantages of the microporous structure cannot be fully exerted. In the rolling process after pre-pressing, if the rolling pressure is insufficient, the negative electrode active material may not be fully rolled, resulting in a decrease in the surface density and flatness of the negative electrode active material layer. At the same time, the adhesion of the negative electrode active material layer to the surface of the functional current collector decreases, and the peel strength of the negative electrode sheet also decreases. Furthermore, by sorting out the experimental variables of Examples 1, 13, 14, 15, 16, and 17 and comparing the corresponding experimental result data, it is shown that when the pressures used for the initial pressing and the final pressing are not much different, the product quality of the negative electrode sheet can be comprehensively improved by reasonably designing the rolling pressure gradient between the rolling processes at each stage.

[0114] Table 2. Roller line pressures at each stage of roller pressing in Example 1 and Examples 13 to 20

[0115] Referring to Example 13, in the process of preparing the negative electrode sheets in Examples 21-24, the viscosity of the negative electrode active material slurry used in the roller pressing process at each stage of the coating and rolling process was controlled to achieve differentiated performance in terms of surface density, peel strength, and tensile strength of the negative electrode sheets. For ease of comparison, Table 3 lists the viscosity of the negative electrode active material slurry used in the roller pressing process at each stage of the coating and rolling process for preparing the negative electrode sheets in Examples 13 and Examples 21-24. Combined with the test results shown in Table 4, it can be seen that among the test objects provided in the above examples, the negative electrode sheet provided by Example 13 has the best overall performance. In Example 13, in the coating roller pressing process for preparing the negative electrode sheet, the viscosity of the negative electrode active material slurry used in the pre-pressing (S1), the primary transition pressing (S2), and the secondary transition pressing (S3) respectively increases step by step with a gradient of 1000mPa to 5000mPa. As a result, in the roller pressing treatment at the above different stages, the pressure bearing and pressure buffering capabilities of the negative electrode active material slurry can be well adapted to the roller pressing pressure at different roller pressing stages, which can not only avoid the damage to the microporous structure of the functional current collector due to the gradually increasing roller pressing pressure, but also gradually increase the negative electrode active material loading amount of the functional current collector.

[0116] Taking Example 13 as a control, the roller line pressure settings of the roller pressing treatment in the coating roller pressing process of Examples 21 to 24 were compared and sorted out, and the specific situations are as follows: (1) In Example 21, the roller pressing treatments in stages S1, S2, and S3 use electrode active material slurries with the same viscosity; (2) In Example 22, the viscosity of the electrode active material slurries used in the roller pressing treatments in stages S1, S2, and S3 decreases step by step; (3) In Example 23, the viscosity gradient formed by the electrode active material slurries used in S1 and S2 is relatively small; (4) In Example 24, the viscosity gradient formed by the electrode active material slurries used in S2 and S3 is relatively small.

[0117] Table 3. Viscosity of negative electrode active material slurry during roller pressing at each stage of Example 13 and Example 21-24

[0118] Referring to Example 13, Examples 25 and 26 changed the formula composition of the negative electrode active material slurry during the preparation of the negative electrode sheets. From the test results shown in Table 4, it can be seen that the negative electrode sheets prepared in Examples 25 and 26 can also take into account the formation of a high surface density negative electrode active material layer and achieve high peel strength and high tensile strength.

[0119] Table 4. Test result statistics of test case 2

[0120] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents, but these modifications or replacements are all within the scope of protection of the present invention.

Claims

1. A pole piece, characterized in that: The pole piece includes a functional current collector and an electrode active material layer arranged on the surface of the functional current collector, the functional current collector includes a polymer substrate and a conductive layer arranged on the surface of the polymer substrate, the conductive layer includes a metal layer, the conductive layer is provided with a micropore array, and the micropore array includes a micropore structure. The microporous structure satisfies the following requirements: the pores extend along the thickness direction of the functional current collector, the radial cross section is hexagonal, the pore diameter is 5 μm to 50 μm, and the pore density is 10 3 Holes / cm 2 ~10 5 Holes / cm 2 .

2. The pole piece according to claim 1, characterized in that: Electrode active material layer: The total surface density of the electrode active material layer is ≥ 20 mg / cm 2 The electrode active material layer is composed of n sub-electrode active material layers, where n is a positive integer greater than 1, and the surface density of the n sub-electrode active material layers increases gradually in a direction away from the functional current collector.

3. The pole piece according to claim 2, characterized in that: The number n of the sub-electrode active material layers is 3.

4. The pole piece according to claim 1, characterized in that: The functional current collector satisfies at least one of the conditions a, b, c, and d: a. The microporous structure meets the following requirements: pore size of 20 μm to 30 μm, pore density of 4 × 10 4 Holes / cm 2 ~10 5 Holes / cm 2 ; b. The pore depth of the microporous structure does not exceed the thickness of the conductive layer; c. The conductive layer further comprises a protective layer, wherein the protective layer is laminated and covers the interface of the metal layer away from the polymer substrate in the conductive layer; d. The edge grain size of the microporous structure is ≤300 nm.

5. The pole piece according to any one of claims 1 to 4, characterized in that: The preparation of the functional current collector includes the following operations: using a laser energy density of The microporous structure is constructed on the surface of the functional current collector precursor by using an ultraviolet laser etching process, and the functional current collector precursor includes the polymer substrate and the conductive layer.

6. The method for preparing a pole piece according to any one of claims 1 to 5, characterized in that: The rolling process consists of four stages, which are carried out in sequence as follows: S1. Pre-pressing, coating the surface of the functional current collector with an electrode active material slurry, and rolling the resulting sheet to form a first active coating on the surface of the functional current collector; S2. a transition pressure, coating the surface of the first active coating with an electrode active material slurry, and rolling the sheet thus obtained to form a second active coating on the surface of the first active coating; S3 secondary transition pressure, coating the surface of the second active coating electrode active material slurry, the sheet thus obtained is rolled to form a third active coating on the surface of the second active coating; S4 final pressure, the resulting sheet is rolled; The rolling temperature of the rolling treatment is 50°C to 130°C, and the viscosity of the electrode active slurry used for coating is 2000mPa to 10000mPa; in S1, the rolling roller line pressure is 60N / mm to 100N / mm, the rolling temperature is 50°C to 80°C, and the solid content of the electrode active material slurry is 40% to 65%; the rolling treatments in each stage of S1, S2, S3, and S4 meet the requirement that the rolling roller line pressure increases step by step by 50 N / mm to 120 N / mm; the rolling treatments in each stage of S1, S2, and S3 meet the requirement that the viscosity of the electrode active material slurry increases step by step by 1000mPa to 5000mPa.

7. The preparation method according to claim 6, characterized in that: When the electrode sheet is a negative electrode sheet, the viscosity of the electrode active slurry used for coating in S1 is 2000mPa-4000mPa, the viscosity of the electrode active slurry used for coating in S2 is 4000mPa-6000mPa, and the viscosity of the electrode active slurry used for coating in S3 is 6000mPa-8000mPa; When the electrode sheet is a positive electrode sheet, the viscosity of the electrode active slurry used for coating in S1 is 3000mPa~5000mPa, the viscosity of the electrode active slurry used for coating in S2 is 6000mPa~8000mPa, and the viscosity of the electrode active slurry used for coating in S3 is 8000mPa~10000mPa.

8. The preparation method according to claim 6, characterized in that: When the electrode sheet is a negative electrode sheet: in S1, the roller line pressure is 60N / mm-80N / mm, and the rolling temperature is 50°C-60°C; in S2, the roller line pressure is 100N / mm-130N / mm, and the rolling temperature is 60°C-80°C; in S3, the roller line pressure is 180N / mm-220N / mm, and the rolling temperature is 80°C-100°C; in S4, the roller line pressure is 250N / mm-280N / mm, and the rolling temperature is 100°C-120°C; When the electrode sheet is a positive electrode sheet: in S1, the roller line pressure is 80 N / mm~100 N / mm, and the rolling temperature is 60℃~80℃; in S2, the roller line pressure is 120 N / mm~150 N / mm, and the rolling temperature is 80℃~100℃; in S3, the roller line pressure is 200 N / mm~250 N / mm, and the rolling temperature is 100℃~120℃; in S4, the roller line pressure is 300 N / mm~350 N / mm, and the rolling temperature is 120℃~130℃.

9. The preparation method according to claim 6, characterized in that: When the electrode is a negative electrode, the thickness of the first active coating is 10 μm to 60 μm, the thickness of the second active coating is 20 μm to 60 μm, and the thickness of the third active coating is 10 μm to 60 μm; When the electrode is a positive electrode, the thickness of the first active coating is 10 μm to 80 μm, the thickness of the second active coating is 20 μm to 80 μm, and the thickness of the third active coating is 10 μm to 80 μm.

10. A secondary battery, characterized in that: The secondary battery comprises the electrode according to any one of claims 1 to 5.

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