A dry-process battery electrode sheet, a method of manufacturing the same, and a battery including the same

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a dry-process battery pole piece, a preparation method thereof and a battery comprising the pole piece. The method comprises the following steps: S1. preparing a composite current collector; S2. preparing an electrode film: comprising the following steps, S21. preparing a positive electrode film, S22. preparing a negative electrode film; S3: preparing a pole piece blank: sequentially stacking the positive electrode film, the composite current collector and the negative electrode film, performing gradient pressure rolling at 120-180 DEG C, the pressure linearly increases from 5-10 MPa at the edge to 15-20 MPa at the center, the rolling speed is 1-3 m / min, and the pole piece blank is formed; and S4: preparing a dry-process battery pole piece. The composite current collector adopts a three-layer substrate structure of'metal substrate layer-mesoporous carbon-MOF composite transition layer-conductive polymer transition layer', gradient pores are formed through laser drilling, and an Al2O3 nano coating is deposited to enhance the interface bonding.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a dry-process battery pole piece, a preparation method thereof and a battery comprising the pole piece. BACKGROUND

[0002] Lithium ion batteries are widely used in the fields of new energy vehicles and energy storage systems due to their high energy density and long cycle life. The structure and performance of the electrode pole piece, as a core component of the battery, directly determine the overall performance of the battery. The dry-process preparation process has become an important development direction for the preparation of pole pieces due to its characteristics of no need for organic solvents, short process, and good environmental protection.

[0003] The existing dry-process battery pole piece technology has many deficiencies: the interface bonding force between the current collector and the electrode film is weak, and peeling easily occurs; the wettability of the electrolyte to the dry-process pole piece is insufficient, affecting ion transmission; the high-nickel positive electrode material is prone to interface side reactions, and has poor cycle stability; the silicon-based negative electrode has poor conductivity and serious volume expansion; and the uneven distribution of the conductive network leads to high internal resistance of the pole piece.

[0004] Therefore, a dry-process battery pole piece, a preparation method thereof and a battery comprising the pole piece are designed to solve the above problems in the background art. SUMMARY

[0005] In view of the above deficiencies in the prior art, the application provides a dry-process battery pole piece, a preparation method thereof and a battery comprising the pole piece to solve the problems in the background art.

[0006] To solve the above technical problems, the application adopts the following technical solutions:

[0007] A preparation method of a dry-process battery pole piece, comprising the following steps,

[0008] S1. Preparing a composite current collector: sequentially depositing a mesoporous carbon-MOF composite transition layer and a conductive polymer transition layer on the surface of a metal substrate layer to form a composite current collector substrate, manufacturing gradient pores penetrating the entire composite current collector substrate, depositing an Al2O3 coating on the inner wall of the gradient pores, and obtaining a composite current collector;

[0009] S2. Preparing an electrode film: comprising the following steps,

[0010] S21. Preparing a positive electrode film: mixing a core-shell structure positive electrode active material, carbon fibers, carbon nanotubes and a composite binder in a high-speed mixer at a ratio of 1500-2000 rpm for 3-5 hours; performing directional arrangement of the mixed materials under the assistance of a 0.1-0.5T magnetic field, and performing fiberization treatment at 150-200℃ for 2-5 hours to press into a positive electrode film with a thickness of 50-300μm;

[0011] S22. Negative electrode film preparation: MXene modified negative electrode active material, carbon fiber, carbon nanotube and composite binder are mixed in a high-speed mixer at 1500-2000 rpm for 3-5 hours; the mixed material is subjected to directional arrangement under the assistance of a 0.1-0.5T magnetic field, and is subjected to fiberization treatment at 150-200℃ for 2-5 hours, and is pressed into a negative electrode film with a thickness of 50-300μm;

[0012] S3: Preparation of electrode tab blank: the positive electrode film, the composite current collector and the negative electrode film are stacked in sequence, and are subjected to gradient pressure rolling at 120-180℃, the pressure is linearly increased from 5-10MPa at the edge to 15-20MPa at the center, and the rolling speed is 1-3m / min, to form an electrode tab blank;

[0013] S4: Preparation of dry battery electrode tab: the electrode tab blank is subjected to plasma treatment for 30-120s under the action of a mixed gas of argon and oxygen with a volume ratio of 3:1 at a power of 50-150W; after the treatment, the electrode tab blank is activated in a Li2SO4 solution with a concentration of 0.1mol / L at a constant voltage of 0.5V for 30min, to obtain a dry battery electrode tab.

[0014] Further, the metal substrate layer in step S1 is an aluminum foil or a copper foil, and the aluminum foil with a thickness of 5-20μm is selected when the positive electrode tab is prepared, and the copper foil with a thickness of 5-20μm is selected when the negative electrode tab is prepared.

[0015] Further, the preparation method of the mesoporous carbon-MOF composite transition layer in step S1 comprises: dispersing mesoporous carbon precursor and MOF powder in ethanol at a mass ratio of 7:3, and then calcining at 300-500℃ for 2-4 hours under a nitrogen atmosphere to form a mesoporous carbon-MOF composite transition layer, the thickness of the mesoporous carbon-MOF composite transition layer is 2-5μm, and the mesopore size is 2-5nm.

[0016] Further, the conductive polymer transition layer in step S1 is a composite layer of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate and graphene, and the mass of graphene accounts for 5%-10% of the total mass of the conductive polymer transition layer, and the thickness of the conductive polymer transition layer is 1-5μm.

[0017] Further, the gradient pores passing through the whole composite current collector substrate are processed, which comprises: using a laser drilling device, taking the metal substrate layer side as the starting end and the conductive polymer transition layer side as the ending end, controlling the laser power to be linearly reduced from 50-60W to 20-30W, and at the same time maintaining the drilling rate of 100-200 holes / s, so that the pore diameter is linearly increased from 5-20μm at the metal substrate layer side to 50-200μm at the conductive polymer transition layer side.

[0018] Further, the Al2O3 coating layer deposited on the inner wall of the gradient pores comprises: taking trimethylaluminum and water as precursors, depositing 5-15 cycles at a temperature of 100-150 DEG C by atomic layer deposition technology to form an Al2O3 nano coating layer with a thickness of 1-3 nm.

[0019] Further, the preparation method of the core-shell structure positive electrode active material in step S2 comprises the following steps: dispersing high-nickel ternary material powder in a lithium iron phosphate precursor solution, and calcining after hydrothermal reaction at 180-220 DEG C for 6-12 hours to obtain a core-shell structure positive electrode active material with high-nickel ternary material as the core and lithium iron phosphate material as the shell.

[0020] In step S2, the carbon fibers and carbon nanotubes are arranged in a direction under the assistance of a magnetic field of 0.1-0.5T to form an ordered interwoven directional conductive network, the directional conductive network is formed by interweaving carbon fibers with a length-diameter ratio of 50-100 and carbon nanotubes with a diameter of 10-20 nm at a mass ratio of 3:1, the length of the carbon fibers is 5-20 microns, and the length of the carbon nanotubes is 10-50 microns.

[0021] The preparation method of the MXene modified negative electrode active material in step S2 comprises the following steps: mixing silicon-carbon composite material and graphite at a mass ratio of 1:3-1:5, adding MXene nanosheets with a mass percentage of 1-3% and modifying by ball milling to obtain the MXene modified negative electrode active material.

[0022] Further, the composite binder is composed of polytetrafluoroethylene and multi-arm polyethylene glycol at a mass ratio of 3:1, and the total mass of the composite binder accounts for 2%-4% of the total mass of the mixed materials.

[0023] The application also provides a dry-process battery pole piece prepared by the above preparation method, which comprises the following steps:

[0024] The composite current collector comprises a composite current collector substrate sequentially comprising a metal base layer, a mesoporous carbon-MOF composite transition layer and a conductive polymer transition layer, and the composite current collector substrate is provided with gradient pores penetrating through the composite current collector substrate, the pore size of the gradient pores linearly increases from the metal base layer to the conductive polymer transition layer, and the inner wall of the gradient pores is provided with an Al2O3 nano coating layer with a thickness of 1-3 nm.

[0025] The electrode film comprises a positive electrode film and a negative electrode film, and the positive electrode film and the negative electrode film are connected in a barb-shaped embedded manner through the gradient pores, the inside is provided with a directional conductive network, and the active material of the positive electrode film is a core-shell structure with high-nickel ternary material as the core and lithium iron phosphate material as the shell.

[0026] The active material of the negative electrode film is a silicon-carbon-graphite composite powder modified by MXene, and the surface of the active material is coated with a nano zirconium oxide modification layer with a thickness of 3-5 nm.

[0027] The application further provides a battery comprising the dry-process battery pole piece, the separator film and the electrolyte.

[0028] The separator film is a polypropylene film coated with an Al2O3 ceramic layer with a thickness of 1-3 μm.

[0029] The electrolyte is composed of a solvent system and a solute, wherein the solvent system is a mixture of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a volume ratio of 1:1:1, and the solute is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate is 1 mol / L.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] 1. The application constructs a high-performance dry-process battery pole piece preparation system through multi-dimensional structure design and process innovation. The core scheme includes the collaborative design of the composite current collector and the electrode film: the composite current collector adopts a three-layer substrate structure of "metal substrate layer-mesoporous carbon-MOF composite transition layer-conductive polymer transition layer", gradient pores are formed through laser drilling, and an Al2O3 nano coating is deposited to enhance the interface bonding; the electrode film is optimized according to the positive and negative electrode characteristics, the positive electrode adopts a core-shell active material with high-nickel ternary material as the core and lithium iron phosphate as the shell, and the negative electrode adopts a silicon-carbon-graphite composite powder modified by MXene, both of which are directionally arranged to form a conductive network interwoven with carbon fibers and carbon nanotubes, and the pole piece is prepared through gradient pressing and plasma-electrochemical dual activation processes.

[0032] 2. The gradient pores and Al2O3 coating of the composite current collector increase the peeling strength to more than 55 N / m, which is 150% higher than that of the traditional process; the core-shell structure positive electrode material suppresses the high-nickel side reaction, and the MXene modified negative electrode alleviates the volume expansion, and the capacity retention rate after 500 cycles is more than 90%; the directional conductive network and the mesoporous transition layer synergistically act, and the volume conductivity is increased to more than 95 S / cm; the gradient pressing and the dual activation process shorten the electrolyte immersion time from 10 minutes to 3 minutes, and significantly optimize the ion transmission efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a preparation method flow chart of the dry-process battery pole piece of the application;

[0034] Figure 2 It is a second flow chart of the preparation method of the dry-process battery pole piece of the application;

[0035] Figure 3 It is a first composition schematic diagram of the dry-process battery pole piece of the application;

[0036] Figure 4 It is a second composition schematic diagram of the dry-process battery pole piece of the application;

[0037] Figure 5 Figure 3 is a schematic diagram of a third composition of a dry-process battery electrode sheet according to the present application;

[0038] The reference signs in the drawings of the specification include:

[0039] 101, metal substrate layer; 102, mesoporous carbon-MOF composite transition layer; 103, conductive polymer transition layer; 104, negative electrode film; 105, positive electrode film; 106, gradient pores; 107, Al2O3 nano coating. DETAILED DESCRIPTION

[0040] In order for those skilled in the art to better understand the present application, the technical solutions of the present application are further described below in conjunction with the drawings and examples.

[0041] Among them, the drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation on the present patent; in order to better illustrate the embodiments of the present application, some components of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0042] A preparation method of a dry-process battery electrode sheet, comprising the following steps,

[0043] S1. Preparation of composite current collector: sequentially depositing mesoporous carbon-MOF composite transition layer 102 and conductive polymer transition layer 103 on the surface of metal substrate layer 101 to form a composite current collector substrate, manufacturing gradient pores 106 throughout the whole of the composite current collector substrate, depositing Al2O3 coating 107 on the inner wall of the gradient pores, and obtaining a composite current collector;

[0044] S2. Preparation of electrode film: comprising the following steps,

[0045] S21. Preparation of positive electrode film: mixing core-shell structure positive electrode active material, carbon fiber, carbon nanotube and composite binder in a high-speed mixer at 1500-2000 rpm for 3-5 hours; performing directional arrangement of the mixed materials under the assistance of a 0.1-0.5 T magnetic field, and performing fiberization treatment at 150-200℃ for 2-5 hours, and pressing into a positive electrode film with a thickness of 50-300 μm;

[0046] S22. Preparation of negative electrode film: mixing MXene modified negative electrode active material, carbon fiber, carbon nanotube and composite binder in a high-speed mixer at 1500-2000 rpm for 3-5 hours; performing directional arrangement of the mixed materials under the assistance of a 0.1-0.5 T magnetic field, and performing fiberization treatment at 150-200℃ for 2-5 hours, and pressing into a negative electrode film with a thickness of 50-300 μm;

[0047] S3: Preparing the electrode blank: stacking the positive electrode film, the composite current collector, and the negative electrode film in sequence, and performing gradient pressure rolling at 120-180°C, with the pressure linearly increasing from 5-10 MPa at the edge to 15-20 MPa at the center, and the rolling speed being 1-3 m / min, to form the electrode blank;

[0048] S4: Preparing the dry battery electrode: treating the electrode blank with a mixed gas of argon and oxygen in a volume ratio of 3:1 using plasma at a power of 50-150 W for 30-120 s; and after the treatment, activating the electrode blank in a Li2SO4 solution with a concentration of 0.1 mol / L at a constant voltage of 0.5 V for 30 min to obtain the dry battery electrode.

[0049] Specifically, the interface is enhanced through a three-level design of "composite current collector substrate + gradient porosity + nano coating". The composite current collector has a multilayer structure of "metal substrate layer-mesoporous carbon-MOF transition layer-conductive polymer transition layer", the mesoporous carbon-MOF transition layer improves the ion adsorption capacity through a high specific surface area (100-300 m² / g), and the conductive polymer transition layer (poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate composite with graphene) optimizes the electron conduction; the gradient porosity (pore size 5-20 μm→50-200 μm) throughout the substrate forms a mechanical interlocking structure, and the chemical bonding effect of the 1-3 nm thick Al2O3 nano coating on the inner wall of the pores further improves the peeling strength to more than 55 N / m, while inhibiting the side reaction between the metal current collector and the electrolyte.

[0050] Further, the metal substrate layer in step S1 is an aluminum foil or a copper foil, and a 5-20 μm thick aluminum foil is selected when preparing the positive electrode, and a 5-20 μm thick copper foil is selected when preparing the negative electrode.

[0051] Further, the preparation method of the mesoporous carbon-MOF composite transition layer in step S1 comprises: dispersing the mesoporous carbon precursor and the MOF powder in ethanol at a mass ratio of 7:3, coating, and calcining at 300-500°C for 2-4 hours in a nitrogen atmosphere to form the mesoporous carbon-MOF composite transition layer, the thickness of the mesoporous carbon-MOF composite transition layer being 2-5 μm, and the mesopore size being 2-5 nm.

[0052] Further, the conductive polymer transition layer in step S1 is a composite layer of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate and graphene, wherein the mass of graphene accounts for 5%-10% of the total mass of the conductive polymer transition layer, and the thickness of the conductive polymer transition layer is 1-5 μm.

[0053] Further, the gradient porosity formed throughout the composite current collector substrate includes: using a laser drilling device, taking the metal substrate layer side as the starting end and the conductive polymer transition layer side as the ending end, controlling the laser power to linearly decrease from 50-60W to 20-30W while maintaining a drilling rate of 100-200 holes / s, and linearly increasing the pore diameter from 5-20μm at the metal substrate layer side to 50-200μm at the conductive polymer transition layer side.

[0054] Further, the Al2O3 coating deposited on the inner wall of the gradient porosity includes: using trimethylaluminum and water as precursors, depositing 5-15 cycles at a temperature of 100-150℃ by atomic layer deposition technology to form an Al2O3 nano-coating with a thickness of 1-3nm.

[0055] Further, the preparation method of the core-shell structure positive electrode active material in step S2 includes: dispersing high-nickel ternary material powder in a lithium iron phosphate precursor solution, and calcining after hydrothermal reaction at 180-220℃ for 6-12 hours to obtain a core-shell structure positive electrode active material with high-nickel ternary material as the core and lithium iron phosphate material as the shell; using the "structure regulation + surface functionalization" strategy, the positive electrode has high-nickel ternary material as the core and lithium iron phosphate as the shell, which isolates the high-nickel core from the electrolyte through the physical barrier effect, inhibits the dissolution of transition metals, and the capacity retention rate after 500 cycles is improved to 92%; the negative electrode is modified by ball milling 1-3% MXene nanosheets, which constructs a three-dimensional conductive network by using its two-dimensional sheet structure, and at the same time buffers the 300% volume expansion of silicon-carbon materials, and the volume conductivity is improved to more than 95S / cm. In the present application, high-nickel ternary material is used as the inner core of the core-shell structure (such as NCM811, lithium nickel cobalt manganese 811, where the number "811" represents the molar ratio of nickel (Ni), cobalt (Co), and manganese (Mn) in the positive electrode material is 8:1:1), which has a high capacity advantage and a synergistic effect with the lithium iron phosphate (LFP) shell.

[0056] In step S2, the carbon fibers and carbon nanotubes are arranged in a direction under the assistance of a magnetic field of 0.1-0.5T to form an ordered interwoven directional conductive network, the directional conductive network is formed by interweaving carbon fibers with a length-diameter ratio of 50-100 and carbon nanotubes with a diameter of 10-20nm at a mass ratio of 3:1, the length of the carbon fibers is 5-20μm, and the length of the carbon nanotubes is 10-50μm; the carbon fibers with a length-diameter ratio of 50-100 (length 5-20μm) serve as a framework to provide mechanical support and construct a main conductive path. The length-diameter ratio range balances the mechanical strength and conductive continuity, avoiding uneven dispersion due to excessive length or network rupture due to excessive shortness. The carbon nanotubes: carbon nanotubes with a diameter of 10-20nm and a length of 10-50μm are filled in the gap between the carbon fibers to enhance the interface conductive efficiency through nanoscale contact. The diameter of the carbon nanotubes is selected to be consistent with the optimal range (10-20nm) for optimizing carrier transmission in existing research.

[0057] Mass ratio 3:1: Carbon fibers serve as the main framework, and carbon nanotubes serve as secondary conductive bridges. The ratio is experimentally verified to achieve the target of volume conductivity ≥95S / cm. Through 0.1-0.5T magnetic field orientation, the carbon fibers are arranged in parallel along the film surface, and the carbon nanotubes are connected in three-dimensional space to form a regular conductive network, significantly reducing the ion transmission resistance.

[0058] The preparation method of the MXene modified negative electrode active material in step S2 comprises the following steps: mixing a silicon-carbon composite material and graphite at a mass ratio of 1:3-1:5, adding MXene nanosheets with a mass percentage of 1-3% through ball milling modification to obtain a MXene modified negative electrode active material.

[0059] Further, the composite binder is composed of polytetrafluoroethylene and multi-arm polyethylene glycol at a mass ratio of 3:1, and the total mass of the composite binder accounts for 2%-4% of the total mass of the mixed materials.

[0060] The whole process adopts a dry process (without organic solvents), and the performance is realized through "fiberization treatment + plasma-electrochemical dual activation". Fiberization treatment (150-200℃) enhances the stability of the binder network, plasma treatment introduces hydrophilic electric groups, and 0.1mol / L lithium sulfate solution constant voltage activation (0.5V, 30min) promotes the formation of a stable SEI film, finally realizing the dual optimization of the uniformity of the electrode sheet density and the electrochemical stability.

[0061] The application also provides a dry battery electrode sheet prepared by the above preparation method, which comprises:

[0062] The composite current collector comprises, from inside to outside, a metal base layer, a mesoporous carbon-MOF composite transition layer and a conductive polymer transition layer, and a gradient pore is arranged through the composite current collector base, the pore size of the gradient pore linearly increases from the metal base layer to the conductive polymer transition layer, and the inner wall of the gradient pore is provided with an Al2O3 nano coating with a thickness of 1-3 nm.

[0063] The electrode film comprises a positive electrode film 105 and a negative electrode film 104, and is connected in a reverse-spike embedded manner through the gradient pore, and is provided with a directional conductive network inside; and the active material of the positive electrode film is a core-shell structure with a high-nickel ternary material as a core and a lithium iron phosphate material as a shell.

[0064] The active material of the negative electrode film is a MXene modified silicon-carbon-graphite composite powder, and the surface of the active material is coated with a 3-5 nm thick nano zirconium oxide modification layer.

[0065] The application further provides a battery comprising the dry-process battery electrode piece, the isolation film and the electrolyte.

[0066] The isolation film is a polypropylene film coated with an Al2O3 ceramic layer with a thickness of 1-3 microns.

[0067] The electrolyte is composed of a solvent system and a solute, wherein the solvent system is a mixture of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a volume ratio of 1:1:1, and the solute is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate is 1 mol / L.

[0068] Example 1

[0069] Step S1: preparation of a composite current collector

[0070] An aluminum foil with a thickness of 8 microns is selected (positive electrode); mesoporous carbon precursor and ZIF-67 are dispersed in ethanol at a mass ratio of 7:3, calcined at 350 DEG C for 2.5 hours in a nitrogen atmosphere after coating, to form a 2-micron-thick mesoporous carbon-MOF composite transition layer (mesoporous 2 nm, specific surface area 150 m² / g); a poly 3,4-ethylenedioxythiophene-polystyrene sulfonate solution doped with 5% graphene is coated to form a 1-micron-thick conductive polymer transition layer.

[0071] Laser drilling: the power is reduced from 50 W to 20 W, the drilling rate is 100 holes per second, and the pore size is 5 microns to 50 microns; atomic layer deposition for 5 cycles to form an Al2O3 coating with a thickness of 1 nm.

[0072] Step S2: preparation of a positive electrode film

[0073] NCM811 is dispersed in a lithium iron phosphate precursor, and after hydrothermal reaction at 180 DEG C for 6 hours, calcination (core-shell mass ratio 3:1, shell thickness 5 nm), and coating of 3 nm zirconium oxide.

[0074] Active material 93%, carbon fiber 5% (aspect ratio 50, length 5 pm), carbon nanotube 1% (diameter 10 nm, length 10 pm) and composite binder 2% (polytetrafluoroethylene: multi-armed polyethylene glycol = 3:1) were mixed in a high-speed mixer at 1500 rpm for 3 hours; 0.1 T magnetic field was oriented and arranged, and the fiberization treatment was carried out at 150°C for 2 hours, and then the positive electrode film with a thickness of 50 pm was pressed.

[0075] Steps S3-S4:

[0076] 120°C gradient rolling (edge 5 MPa→center 15 MPa, roller speed 1 m / min); plasma treatment (50 W power, 30 s, Ar / O2=3:1); 0.1 mol / L Li2SO4 solution 0.5 V activation for 30 min.

[0077] Performance test:

[0078] Peeling strength 55 N / m, volume conductivity 95 S / cm, electrolyte infiltration time 4 min, 500 cycle retention rate 90%, 1C discharge capacity 155 mAh / g, electrode sheet resistance 45 mΩ·cm, ion transport rate 3.2×10⁻ 4 cm / s, low temperature (-20°C) discharge capacity retention rate 80%.

[0079] Example 2

[0080] Step S1: Preparation of composite current collector

[0081] 12 pm thick aluminum foil was selected; mesoporous carbon precursor and ZIF-67 were dispersed at a ratio of 7:3, calcined at 400°C for 3 hours in a nitrogen atmosphere after coating, forming a 3 pm thick mesoporous carbon-MOF composite transition layer (mesopore 3 nm, specific surface area 200 m² / g); coating a solution of 8% graphene-doped poly 3,4-ethylenedioxythiophene-polystyrene sulfonate to form a 3 pm thick conductive polymer transition layer.

[0082] Laser drilling: power from 55 W to 25 W, drilling rate 150 holes / s, pore diameter 10 pm→150 pm; atomic layer deposition for 10 cycles to form a 2 nm thick Al2O3 coating.

[0083] Step S2: Preparation of positive electrode film

[0084] NCM811 was dispersed in lithium iron phosphate precursor, and after hydrothermal reaction at 200°C for 9 hours, calcination (core-shell mass ratio 3:1, shell thickness 8 nm), coated with 4 nm zirconium oxide.

[0085] Active material 92%, carbon fiber 5% (aspect ratio 80, length 12 pm), carbon nanotube 3% (diameter 15 nm, length 30 pm) and composite binder 3% were mixed in a high-speed mixer at 1800 rpm for 4 hours; 0.3T magnetic field was arranged in a direction, and the fiberization treatment was carried out at 180°C for 3.5 hours, and then the positive electrode film with a thickness of 180 pm was pressed.

[0086] Steps S3-S4:

[0087] 150°C gradient rolling (edge 8 MPa→center 18 MPa, roller speed 2 m / min); plasma treatment (100 W power, 60 s, Ar / O2=3:1); 0.1 mol / L Li2SO4 solution 0.5 V activation for 30 min. Performance test:

[0088] Peeling strength 58 N / m, volume conductivity 98 S / cm, electrolyte infiltration time 3 min, 500 cycle retention rate 92%, 1C discharge capacity 158 mAh / g, electrode sheet resistance 42 mΩ·cm, ion transport rate 3.5×10⁻ 4 cm / s, low temperature (-20°C) discharge capacity retention rate 82%.

[0089] Example 3

[0090] Step S1: Preparation of composite current collector

[0091] 20 pm thick aluminum foil was selected; mesoporous carbon precursor and ZIF-67 were dispersed at a ratio of 7:3, calcined at 500°C for 4 hours in a nitrogen atmosphere after coating, forming a 5 pm thick mesoporous carbon-MOF composite transition layer (mesopore 5 nm, specific surface area 300 m² / g); coating a solution of poly 3,4-ethylenedioxythiophene-polystyrene sulfonate doped with 10% graphene to form a 5 pm thick conductive polymer transition layer.

[0092] Laser drilling: power from 60 W to 30 W, drilling rate 200 holes / s, pore diameter 20 pm→200 pm; atomic layer deposition for 15 cycles to form a 3 nm thick Al2O3 coating.

[0093] Step S2: Preparation of positive electrode film

[0094] NCM811 was dispersed in lithium iron phosphate precursor, and after hydrothermal reaction at 220°C for 12 hours, calcination (core-shell mass ratio 3:1, shell thickness 10 nm), and coating 5 nm zirconium oxide.

[0095] Active material 91%, carbon fiber 5% (aspect ratio 100, length 20 μm), carbon nanotube 4% (diameter 20 nm, length 50 μm) and composite binder 4% were mixed in a high-speed mixer at 2000 rpm for 5 hours; 0.5T magnetic field was arranged in the direction, and the fiberization treatment was carried out at 200°C for 5 hours, and then the positive electrode film with a thickness of 300 μm was pressed.

[0096] Steps S3-S4:

[0097] 180°C gradient rolling (edge 10 MPa→center 20 MPa, roller speed 3 m / min); plasma treatment (150 W power, 120 s, Ar / O2=3:1); 0.1 mol / L Li2SO4 solution 0.5 V activation for 30 min.

[0098] Performance test:

[0099] Peeling strength 56 N / m, volume conductivity 96 S / cm, electrolyte infiltration time 5 min, 500 cycle retention rate 91%, 1C discharge capacity 157 mAh / g, electrode sheet resistance 44 mΩ·cm, ion transport rate 3.3×10⁻ 4 cm / s, low temperature (-20°C) discharge capacity retention rate 81%.

[0100] Comparative Example 1

[0101] Key difference: composite current collector without gradient porosity and inner wall Al2O3 coating, and the rest of the parameters are consistent with Example 2.

[0102] Performance test:

[0103] Peeling strength 32 N / m, volume conductivity 97 S / cm, electrolyte infiltration time 8 min, 500 cycle retention rate 91%, 1C discharge capacity 157 mAh / g, electrode sheet resistance 43 mΩ·cm, ion transport rate 3.4×10⁻ 4 cm / s, low temperature (-20°C) discharge capacity retention rate 81%.

[0104] Comparative Example 2

[0105] Key difference: positive active material is pure NCM811 (without lithium iron phosphate shell), and the rest of the parameters are consistent with Example 2.

[0106] Performance test:

[0107] Peeling strength 57 N / m, volume conductivity 98 S / cm, electrolyte infiltration time 3 min, 500 cycle retention rate 75%, 1C discharge capacity 156 mAh / g, electrode sheet resistance 42 mΩ·cm, ion transport rate 3.5×10⁻ 4 cm / s, low temperature (-20°C) discharge capacity retention rate 82%.

[0108] Comparative Example 3

[0109] Key difference: the conductive network is not magnetically oriented (randomly dispersed), and the rest of the parameters are consistent with Example 2.

[0110] Performance test:

[0111] Peeling strength 58 N / m, bulk conductivity 62 S / cm, electrolyte infiltration time 3 min, 500 cycle retention rate 92%, 1C discharge capacity 158 mAh / g, electrode sheet resistance 85 mΩ·cm, ion transport rate 3.5 x 10⁻ 4 cm / s, low temperature (-20°C) discharge capacity retention rate 82%.

[0112] Comparative Example 4

[0113] Key difference: the composite current collector has no mesoporous carbon-MOF transition layer, and the rest of the parameters are consistent with Example 2

[0114] Performance test:

[0115] Peeling strength 57 N / m, bulk conductivity 97 S / cm, electrolyte infiltration time 3 min, 500 cycle retention rate 92%, 1C discharge capacity 158 mAh / g, electrode sheet resistance 43 mΩ·cm, ion transport rate 1.8 x 10⁻ 4 cm / s, low temperature (-20°C) discharge capacity retention rate 65%.

[0116] Summary of performance test results

[0117]

[0118] Analysis: The peeling strengths of the three examples are 55 N / m, 58 N / m, and 56 N / m, respectively, all meeting the requirement of "≥ 55 N / m", verifying the enhancing effect of the composite current collector structure "metal base layer-mesoporous carbon-MOF transition layer-conductive polymer transition layer + gradient porosity + Al2O3 coating" on the interfacial bonding force.

[0119] Bulk conductivity: 95 S / cm, 98 S / cm, and 96 S / cm, respectively, all meeting the standard of "≥ 95 S / cm", proving that the carbon fiber-carbon nanotube conductive network (aspect ratio 50-100, diameter 10-20 nm, mass ratio 3:1) formed by magnetic field assisted orientation can stably improve the electron transport efficiency.

[0120] Cycle stability: 500 cycle capacity retention rate is 90%-92%, meeting the requirement of "≥ 90%", reflecting the inhibition effect of the positive electrode core-shell structure (high-nickel ternary as core, lithium iron phosphate as shell) on the side reaction.

[0121] Comparative Example 1 (without gradient pores and Al2O3 coating): the peeling strength is reduced from 58 N / m of Example 2 to 32 N / m, and the electrolyte infiltration time is extended from 3 min to 8 min, proving that the mechanical interlocking of the gradient pores and the chemical bonding of the Al2O3 coating are the core factors for improving the interfacial bonding force and electrolyte infiltration;

[0122] Comparative Example 2 (without positive electrode core-shell structure): the capacity retention rate is reduced to 75% after 500 cycles, verifying that the physical isolation of the lithium iron phosphate shell layer to the high-nickel ternary material in the core-shell structure can effectively inhibit the dissolution of transition metals and side reactions;

[0123] Comparative Example 3 (without magnetic field assisted orientation): the volume conductivity is suddenly reduced to 62 S / cm, and the electrode sheet resistance is increased to 85 mΩ·cm, indicating that the magnetic field orientation is a key process for ensuring the regularity of the conductive network and reducing the electron transport resistance;

[0124] Comparative Example 4 (without mesoporous carbon-MOF composite transition layer): the ion transport rate is reduced to 1.8×10⁻ 4 cm / s, and the low-temperature discharge capacity retention rate is reduced to 65%, reflecting the optimization effect of the mesoporous structure (2-5 nm) of the mesoporous carbon-MOF transition layer on ion adsorption and transport.

[0125] The above are only embodiments of the present application, and the circuits and electronic components and modules involved are prior art, which can be fully implemented by those skilled in the art without further description. The content protected by the present application does not involve the improvement of software and methods. The specific structure and characteristics of the scheme are not described in detail here, and the ordinary technical personnel in the art know all the ordinary technical knowledge in the field of the application before the application date or the priority date, can know all the prior art in the field, and have the ability to apply conventional experimental means before the date, and the ordinary technical personnel in the art can improve and implement the scheme under the inspiration of the present application, some typical known structures or known methods should not be an obstacle for the ordinary technical personnel in the art to implement the present application. It should be pointed out that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should be considered as the protection scope of the present application, which will not affect the effect and practicality of the patent.

Claims

1. A method for preparing a dry-process battery electrode, characterized in that: Includes the following steps, S1. Preparation of composite current collector: A mesoporous carbon-MOF composite transition layer and a conductive polymer transition layer are sequentially deposited on the surface of a metal substrate to form a composite current collector substrate. Gradient pores that penetrate the entire composite current collector substrate are created on the composite current collector substrate. An Al2O3 coating is deposited on the inner wall of the gradient pores to obtain the composite current collector. The method for preparing the mesoporous carbon-MOF composite transition layer includes: dispersing mesoporous carbon precursor and MOF powder in ethanol at a mass ratio of 7:3, coating and then calcining at 300-500℃ for 2-4 hours under a nitrogen atmosphere to form a mesoporous carbon-MOF composite transition layer with a thickness of 2-5μm and a mesopore size of 2-5nm. S2. Preparation of electrode film: including the following steps S21. Preparation of positive electrode film: The core-shell structure positive electrode active material, carbon fiber, carbon nanotube and composite binder are dry mixed in a high-speed mixer at 1500-2000 rpm for 3-5 hours; the mixed material is oriented under the assistance of a magnetic field of 0.1-0.5T, and fiberized at 150-200℃ for 2-5 hours, and pressed into a positive electrode film with a thickness of 50-300μm; The preparation method of the core-shell structured positive electrode active material includes: dispersing high-nickel ternary material powder in a lithium iron phosphate precursor solution, and calcining it after hydrothermal reaction at 180-220℃ for 6-12 hours to obtain a core-shell structured positive electrode active material with high-nickel ternary material as the core and lithium iron phosphate material as the shell. S22. Preparation of negative electrode film: MXene-modified negative electrode active material, carbon fiber, carbon nanotube and composite binder are mixed in the same proportion in a high-speed mixer at 1500-2000 rpm for 3-5 hours; the mixed materials are oriented under the assistance of a magnetic field of 0.1-0.5T, and fiberized at 150-200℃ for 2-5 hours, and pressed into a negative electrode film with a thickness of 50-300μm; S3: Preparation of electrode blank: The positive electrode film, composite current collector and negative electrode film are stacked in sequence and subjected to gradient pressure rolling at 120-180℃. The pressure increases linearly from 5-10MPa at the edge to 15-20MPa at the center. The rolling speed is 1-3m / min to form the electrode blank. S4: Preparation of dry-process battery electrode: The electrode blank is subjected to plasma treatment with a mixture of argon and oxygen in a volume ratio of 3:1 at a power of 50-150W for 30-120s; after treatment, it is placed in a Li2SO4 solution with a concentration of 0.1mol / L and activated at a constant voltage of 0.5V for 30min to obtain the dry-process battery electrode.

2. The method for preparing a dry-process battery electrode as described in claim 1, characterized in that: The metal substrate layer mentioned in step S1 is aluminum foil or copper foil. When preparing the positive electrode sheet, aluminum foil with a thickness of 5-20 μm is selected, and when preparing the negative electrode sheet, copper foil with a thickness of 5-20 μm is selected.

3. The method for preparing a dry-process battery electrode as described in claim 1, characterized in that: The conductive polymer transition layer in step S1 is a composite layer of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate and graphene, wherein the mass of graphene accounts for 5%-10% of the total mass of the conductive polymer transition layer, and the thickness of the conductive polymer transition layer is 1-5 μm.

4. The method for preparing a dry-process battery electrode as described in claim 1, characterized in that: The process of creating gradient pores that penetrate the entire composite current collector substrate includes: using a laser drilling device, starting from the metal substrate layer and ending at the conductive polymer transition layer, controlling the laser power to linearly decrease from 50-60W to 20-30W while maintaining a drilling rate of 100-200 holes / second, so that the pore diameter of the formed pores linearly increases from 5-20μm on the metal substrate layer side to 50-200μm on the conductive polymer transition layer side.

5. The method for preparing a dry-process battery electrode as described in claim 1, characterized in that: The deposition of an Al2O3 coating on the inner wall of the gradient pores includes: using trimethylaluminum and water as precursors, depositing 5-15 cycles at a temperature of 100-150°C using atomic layer deposition technology to form an Al2O3 nano-coating with a thickness of 1-3 nm.

6. The method for preparing a dry-process battery electrode as described in claim 1, characterized in that: In step S2, carbon fibers and carbon nanotubes are oriented and arranged under the assistance of a 0.1-0.5T magnetic field to form an ordered interwoven oriented conductive network. The oriented conductive network is formed by interweaving carbon fibers with an aspect ratio of 50-100 and carbon nanotubes with a diameter of 10-20nm at a mass ratio of 3:

1. The length of the carbon fibers is 5-20μm and the length of the carbon nanotubes is 10-50μm. The preparation method of the MXene-modified anode active material in step S2 includes: mixing silicon-carbon composite material and graphite at a mass ratio of 1:3-1:5, adding MXene nanosheets at a mass percentage of 1-3%, and modifying by ball milling to obtain the MXene-modified anode active material.

7. The method for preparing a dry-process battery electrode as described in claim 1, characterized in that: The composite binder is composed of polytetrafluoroethylene and multi-arm polyethylene glycol in a 3:1 mass ratio, and its total mass accounts for 2%-4% of the total mass of the mixed materials.

8. A dry-process battery electrode, prepared by the method according to any one of claims 1-7, characterized in that: include: The composite current collector comprises, from the inside out, a metal substrate, a mesoporous carbon-MOF composite transition layer, and a conductive polymer transition layer. The composite current collector substrate is provided with gradient pores, the pore size of which increases linearly from the metal substrate to the conductive polymer transition layer. The inner wall of the gradient pores is provided with an Al2O3 nano-coating with a thickness of 1-3 nm. The electrode film, including the positive electrode film and the negative electrode film, is connected by barbed interlocking through gradient pores. It has an internal directional conductive network. The active material of the positive electrode film is a core-shell structure with a high-nickel ternary material as the core and lithium iron phosphate material as the shell. The active material of the negative electrode film is MXene-modified silicon-carbon-graphite composite powder, and the surface of the active material is coated with a 3-5nm thick nano-zirconia modification layer.

9. A battery, characterized in that: Includes the dry-process battery electrode, separator, and electrolyte as described in claim 8; The isolation membrane is a polypropylene membrane coated with a 1-3 μm thick Al2O3 ceramic layer; The electrolyte consists of a solvent system and a solute. The solvent system is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:

1. The solute is lithium hexafluorophosphate with a concentration of 1 mol / L.

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