CN115763722A

CN115763722A - Multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material and preparation method thereof

Info

Publication number: CN115763722A
Application number: CN202211269609.XA
Authority: CN
Inventors: 黄军同; 冯善志; 罗智聪; 陈智; 万文俊; 李文鹏; 冯志军; 王继宏
Original assignee: Nanchang Hangkong University
Current assignee: Nanchang Hangkong University
Priority date: 2022-10-18
Filing date: 2022-10-18
Publication date: 2023-03-07

Abstract

The invention provides a multidimensional multi-scale carbon-coated lithium ion battery anode material and a preparation method thereof. The product of the invention has good conductivity and stability, improves the capacity, the cycle performance, the multiplying power and other performances of the battery, and can meet the requirements of the fields of energy storage batteries, power batteries and the like on new materials.

Description

Multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material and preparation method thereof

Technical Field

The invention relates to a multi-dimensional and multi-scale carbon-coated lithium ion battery anode material and a preparation method thereof, belonging to the technical field of lithium ion battery anode materials.

Background

The current positive electrode materials of lithium ion batteries include: lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobaltate, lithium manganese oxide, ternary oxide, inorganic matter and the like.

Layered lithium nickel cobalt manganese (LiNi) _x Co _y Mn _z O ₂ X + y + z =1, li-NCM) positive electrode material incorporating LiCoO ₂ 、LiNiO ₂ 、LiMnO ₂ The three materials have the advantages of high specific capacity, good cycle performance, good thermal stability, stable structure, low cost and the like, and become the most promising ternary cathode material at present, however, the main disadvantages of the Li-NCM material are that the conductivity and the tap density are low, and in the preparation process, because the radiuses of nickel ions and lithium ions are close, part of nickel ions occupy the lithium position and the phenomenon of mixed discharging of lithium and nickel occurs, so that the reversible discharge specific capacity of the Li-NCM material is reduced, the cycle performance is poor, and the application of the Li-NCM material to a high-power lithium ion battery is greatly restricted.

And lithium iron phosphate (LiFePO) ₄ ) When used as a positive electrode material, the material has an electron conductivity (rate of only 10) ^-9 -10 ^-10 S/cm) and ion diffusion efficiency are extremely low, resulting in increased resistance polarization during reaction, which makes the rate capability thereof poor, and these disadvantages greatly limit the wide application of lithium iron phosphate in practice.

In view of the above, it is necessary to provide a multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material and a preparation method thereof to solve the above problems.

Disclosure of Invention

The invention aims to provide a multi-dimensional and multi-scale carbon-coated lithium ion battery anode material and a preparation method thereof, which have good conductivity and stability, improve the capacity, the cycle performance, the multiplying power and other properties of a battery, and can meet the requirements of the fields of energy storage batteries, power batteries and the like on new materials.

In order to achieve the purpose, the invention provides a preparation method of a multi-dimensional and multi-scale carbon-coated lithium ion battery anode material, which mainly comprises the following steps:

step 1, adding 1-5wt% of graphite auxiliary material into 95-99wt% of resin, and stirring and mixing the graphite auxiliary material in a water bath at 40-70 ℃ for 5-30min to obtain a mixture A;

step 2, peeling the mixture A obtained in the step 1 through a three-roller differential grinding machine, circularly peeling for multiple times, and collecting a mixture B from a discharging roller;

step 3, removing part of resin through alcohol dissolution, adding 50-200vol% alcohol into the mixture B obtained through stripping, placing the mixture into a centrifuge tube for centrifugation and removing impurity liquid through stirring and ultrasonic assistance for 10min, repeating the step 3, continuously washing the mixture with alcohol, and finally centrifuging the mixture to obtain a substance C;

step 4, taking the impurity solution removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity solution with the volume equal to that of the substance C obtained by centrifugation, dissolving 0.01-0.5wt% of nitric compound raw material in the impurity solution, and mixing and stirring the nitric compound raw material and the substance C for 1-10min to obtain a mixture D;

step 5, adding the mixture D into a lithium compound, stirring and mixing for 5-10min to obtain a mixture E, wherein the addition amount of the mixture D accounts for 3-12wt% of the mass fraction of the mixture E;

step 6, further fully stripping and mixing the mixture E through a three-roller differential grinding machine, and collecting the mixture F from a discharge roller after repeated circulation stripping;

step 7, placing the mixture F in a freeze dryer, and carrying out freeze drying under the environment of vacuum and 50-30 ℃ below zero to obtain a mixture G;

step 8,Placing the mixture G after freeze drying in a tube furnace, performing heat treatment under argon gas at 2-10 deg.C/min from room temperature ^-1 The temperature is raised to 500-850 ℃, the temperature is kept for 1-5h, and then the temperature is naturally lowered to the room temperature, so as to obtain the multidimensional multi-scale carbon-coated lithium ion battery anode material.

As a further improvement of the present invention, in step 2, the three-roll differential grinding machine comprises a discharge roll N1, a central roll N2 and a feed roll N3, wherein the rotation speed ratio of the feed roll N3, the central roll N2 and the discharge roll N1 is 1:3: and 9, in the circulating stripping process, the gap between the central roller N2 and the feeding roller N3 is always larger than the gap between the discharging roller N1 and the central roller N2, and the circulating stripping frequency is 15-17 times.

As a further improvement of the invention, when the circulation stripping is carried out for 1 to 4 times, the clearance between the central roller N2 and the feeding roller N3 and the clearance between the discharging roller N1 and the central roller N2 are both between 40 and 200 μm.

As a further improvement of the invention, when the circulation stripping is carried out for 5-8 times, the clearance between the central roller N2 and the feeding roller N3 and the clearance between the discharging roller N1 and the central roller N2 are both between 10-40 μm.

As a further improvement of the invention, when the circulation stripping is carried out for 9-12 times, the clearance between the central roller N2 and the feeding roller N3 and the clearance between the discharging roller N1 and the central roller N2 are both between 2.5-10 μm.

As a further improvement of the present invention, after 13 th of the cyclic peeling, the gap between the center roll N2 and the feed roll N3 and the gap between the discharge roll N1 and the center roll N2 are each between 0.5 and 2.5 μm.

As a further improvement of the present invention, in step 4, the raw material of the nitric compound is aluminum nitrate or nickel nitrate.

As a further improvement of the present invention, in step 5, the lithium compound is lithium nickel cobalt manganese oxide or lithium iron phosphate.

As a further improvement of the invention, in the step 6, the number of times of cyclic stripping is 2-3, and after the cyclic stripping is finished, the gap between the central roller N2 and the feeding roller N3 and the gap between the discharging roller N1 and the central roller N2 are both between 0.5-5 μm.

In order to achieve the purpose, the invention also provides a multi-dimensional and multi-scale carbon-coated lithium ion battery anode material which is prepared by applying the preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery anode material.

The beneficial effects of the invention are: according to the invention, the grinding and stripping technology of the three-roll grinder is adopted, and the inter-layer van der Waals force is overcome through the shearing force generated by the three-roll differential speed and the acting force formed by the high-viscosity resin and the flake graphite/expanded graphite, so that a large amount of graphene-like nanosheets are prepared by stripping the layered materials with the micron-sized thickness, and the crystal layer spacing of the graphene-like nanosheets is enlarged after stripping.

Drawings

FIG. 1 shows that graphite is used as a raw material and passes through three rollers in resin and (5) peeling by using a grinder to obtain the schematic diagram of the graphene-like nanosheet material.

FIG. 2 is a TEM image of the graphene-like nanosheet, carbon nanotube and amorphous carbon composite modified material obtained after three-roll grinding and stripping, alcohol cleaning, freeze drying and heat treatment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.

It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme of the present invention are shown in the drawings, and other details not closely related to the present invention are omitted.

In addition, it is also to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

As shown in fig. 1 and fig. 2, the invention discloses a multidimensional and multi-scale carbon-coated lithium ion battery anode material and a preparation method of the multidimensional and multi-scale carbon-coated lithium ion battery anode material, wherein the method mainly comprises the following steps:

step 3, removing part of resin through alcohol dissolution, adding 50-200vol% alcohol into the mixture B obtained through stripping, stirring and ultrasonically assisting for 10min, placing the mixture into a centrifugal tube for centrifugation, removing impurity liquid, repeating the step 3, continuously cleaning the mixture with alcohol, and finally centrifuging to obtain a substance C;

step 4, taking the impurity liquid removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity liquid with the same volume as the centrifuged substance C, dissolving 0.01-0.5wt% of nitric compound raw material in the impurity liquid, and mixing and stirring the mixture with the substance C for 1-10min to obtain a mixture D;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and heating the mixture G at 2-10 ℃ for min from room temperature ^-1 The temperature is raised to 500-850 ℃, the temperature is kept for 1-5h, and then the temperature is naturally lowered to the room temperature, so as to obtain the multidimensional multi-scale carbon-coated lithium ion battery anode material.

The following will describe step 1 to step 8 in detail.

In step 2, the three-roll differential grinding machine comprises a discharge roll N1, a central roll N2 and a feed roll N3, wherein the rotation speed ratio of the feed roll N3 to the central roll N2 to the discharge roll N1 is 1:3:9, in the circulating stripping process, the gap between the central roller N2 and the feeding roller N3 is always larger than the gap between the discharging roller N1 and the central roller N2, and the circulating stripping frequency is 15-17 times; it should be noted that, in the times of different cyclic peeling, the roller spacing is different, and when the cyclic peeling is performed for the 1 st to 4 th times, the gap between the central roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the central roller N2 are both between 40 to 200 μm; when the circulation stripping is carried out for 5-8 times, the gap between the central roller N2 and the feeding roller N3 and the gap between the discharging roller N1 and the central roller N2 are both between 10 and 40 mu m; when the circulation stripping is carried out for 9-12 times, the clearance between the central roller N2 and the feeding roller N3 and the clearance between the discharging roller N1 and the central roller N2 are both between 2.5 and 10 mu m; after 13 th time of the cyclic peeling, the gap between the center roll N2 and the feed roll N3 and the gap between the discharge roll N1 and the center roll N2 were each between 0.5 and 2.5 μm.

In step 6, the number of times of cyclic stripping is 2-3, and after the cyclic stripping is completed, the gap between the central roller N2 and the feeding roller N3 and the gap between the discharging roller N1 and the central roller N2 are both between 0.5-5 μm.

In the invention, the battery anode material adopts nickel cobalt lithium manganate as a raw material, graphite as an auxiliary material, resin as a grinding medium and a carbon-coated raw material, and aluminum nitrate as a catalyst and a dopant. Wherein the nickel cobalt lithium manganate raw material is a commercial product, and the tap density is 1.8-2.6g/cm ³ The particle size (D50) is 2-16 μm, and the resin is one of polyvinyl alcohol, polyvinylidene fluoride resin, epoxy resin, phenolic resin and polyethylene resinThe graphite is one or two of crystalline flake graphite and expanded graphite, the length and width of the crystalline flake graphite is 50-500 μm, the thickness is 5-50 μm, the length and width of the expanded graphite is 300-2000 μm, and the thickness is 50-500 μm. And the multi-dimensional multi-scale carbon-coated lithium ion battery cathode material is prepared by taking nickel cobalt lithium manganate as a raw material, wherein the nickel cobalt lithium manganate accounts for 93-97.5wt% of the total mass, the graphene-like substance accounts for 2-4wt% of the total mass, the amorphous carbon accounts for 0.4-2wt% of the total mass, and the carbon nano tube accounts for 0.1-1wt% of the total mass. Of course, in other embodiments of the present invention, the battery positive electrode material may also use lithium iron phosphate as a raw material, nickel nitrate as a catalyst and a dopant, and the loose packing density of the lithium iron phosphate raw material is 0.5-0.9g/cm ³ The median diameter is 0.5-5um, and can be specifically set according to needs without any limitation. And the multi-dimensional multi-scale carbon-coated lithium ion battery anode material is prepared by taking lithium iron phosphate as a raw material, wherein the lithium iron phosphate accounts for 93-97.4wt% of the total mass, the graphene-like accounts for 2-4wt% of the total mass, the amorphous carbon accounts for 0.4-2wt% of the total mass, and the carbon nano tube accounts for 0.1-1wt% of the total mass.

The following will specifically describe with reference to examples and comparative examples, wherein examples 1-3 use lithium nickel cobalt manganese oxide as raw material, aluminum nitrate as catalyst and dopant, and comparative examples 1-6 are comparative examples of examples 1-3.

Example 1, nickel cobalt lithium manganate with a tap density of 2.0g/cm was used as a raw material, flake graphite as an auxiliary material, phenol resin as a grinding medium and a carbon-coated raw material, and aluminum nitrate as a catalyst and a dopant ³ The method is characterized in that the particle size (D50) is 4 μm, the length and width of the flake graphite raw material are 150 μm, and the thickness is 12 μm, and the method specifically comprises the following steps:

step 1, adding 3.5wt% of crystalline flake graphite into 96.5wt% of phenolic resin, and stirring and mixing the crystalline flake graphite in a water bath at 50 ℃ for 15min to obtain a mixture A;

step 2, peeling the mixture A obtained in the step 1 through a three-roller differential grinding machine, circularly peeling for 16 times, and collecting a mixture B from a discharging roller; when the circulation stripping is carried out for 1-4 times, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; when the circulation stripping is carried out for 5-8 times, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; when the circulation stripping is carried out for 9-12 times, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; when the circulation stripping is carried out for 13-16 times, the clearance between N3 and N2 is 1.5 μm, and the clearance between N2 and N1 is 0.5 μm;

step 3, removing part of resin through alcohol dissolution, adding alcohol with the volume fraction of 100vol% into the mixture B obtained through stripping, placing the mixture B into a centrifugal tube for centrifugation and impurity removal through stirring and ultrasonic assistance for 10min, repeating the step to control the number of times of alcohol washing to be 4 times, and finally centrifuging to obtain a substance C;

step 4, taking the impurity liquid removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity liquid with the same volume as the centrifuged substance C, dissolving 0.05wt% of aluminum nitrate raw material in the impurity liquid, and mixing and stirring the mixture with the substance C for 5min to obtain a mixture D;

step 5, adding the mixture D into the nickel cobalt lithium manganate, stirring and mixing for 5min to obtain a mixture E, wherein the adding amount of the mixture D accounts for 6wt% of the mass fraction of the mixture E;

step 6, further fully stripping and mixing the mixture E through a three-roller differential grinding machine, circularly stripping for 3 times, setting the gap between N3 and N2 to be 4 microns and the gap between N2 and N1 to be 2 microns, and collecting a mixture F from a discharging roller;

step 7, placing the mixture F in a freeze dryer, and carrying out freeze drying in a vacuum environment at-45 ℃ to obtain a mixture G;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ for min from room temperature ^-1 The temperature is raised to 750 ℃, the temperature is kept for 4 hours, and then the temperature is naturally lowered to room temperature, so as to obtain the graphene-like carbon nano tube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery anode material.

Weighing 0.07g of the graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery anode material prepared in the embodiment, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder),fully grinding, adding 0.4mL of NMP, dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ in vacuum for 10h, cutting into round pieces with the diameter of 12mm, assembling in a glove box under argon atmosphere, taking a metal lithium piece as a counter electrode, and adding 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel-cobalt manganese oxide lithium battery anode material at 25 ℃ and under the condition of 1C with the voltage window of 2.0-4.3V, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 204.8mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 94%, the initial ohmic internal resistance is 1.65 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 3.08 omega.

Example 2 lithium nickel cobalt manganese oxide with a tap density of 2.2g/cm, expanded graphite as an auxiliary material, epoxy resin as a grinding medium and a carbon-coated raw material, and aluminum nitrate as a catalyst and a dopant was used as a raw material ³ The particle size (D50) is 6 μm, the length and width of the expanded graphite raw material are 1000 μm, and the thickness is 100 μm, and the method specifically comprises the following steps:

step 1, adding 3.5wt% of expanded graphite into 96.5wt% of epoxy resin, and stirring and mixing the expanded graphite in a water bath at 50 ℃ for 15min to obtain a mixture A;

step 2, peeling the mixture A obtained in the step 1 through a three-roller differential grinding machine, circularly peeling for 15 times, and collecting a mixture B from a discharging roller; when the circulation stripping is carried out for 1-4 times, the gap between N3 and N2 is 200 μm, and the gap between N2 and N1 is 80 μm; when the circulation stripping is carried out for 5-8 times, the gap between N3 and N2 is 40 μm, and the gap between N2 and N1 is 20 μm; when the circulation stripping is carried out for 9-12 times, the gap between N3 and N2 is 10 μm, and the gap between N2 and N1 is 5 μm; circularly stripping for 13-15 times, wherein the gap between N3 and N2 is 3 μm, and the gap between N2 and N1 is 1 μm;

step 3, removing part of resin through alcohol dissolution, adding alcohol with the volume fraction of 100vol% into the mixture B obtained through stripping, placing the mixture B into a centrifugal tube for centrifugation and impurity removal through stirring and ultrasonic assistance for 10min, repeating the step to control the number of times of alcohol cleaning to be 3 times, and finally centrifuging to obtain a substance C;

step 4, taking the impurity liquid removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity liquid with the same volume as the centrifuged substance C, dissolving 0.1wt% of aluminum nitrate raw material in the impurity liquid, and mixing and stirring the mixture with the substance C for 5min to obtain a mixture D;

step 5, adding the mixture D into the nickel cobalt lithium manganate, stirring and mixing for 5min to obtain a mixture E, wherein the adding amount of the mixture D accounts for 5wt% of the mass fraction of the mixture E;

step 6, further fully stripping and mixing the mixture E through a three-roller differential grinding machine, circularly stripping and mixing for 2 times, setting the gap between N3 and N2 to be 4 microns and the gap between N2 and N1 to be 2 microns, and collecting a mixture F from a discharging roller;

step 7, placing the mixture F in a freeze dryer, and carrying out freeze drying in a vacuum environment at-40 ℃ to obtain a mixture G;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and heating the mixture G at 2 ℃ min from room temperature ^-1 The temperature is raised to 600 ℃, the temperature is kept for 5 hours, and then the temperature is naturally lowered to the room temperature, so as to obtain the graphene-like carbon nano tube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery anode material.

Weighing 0.07g of graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ for 10 hours in vacuum, cutting into a wafer with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC 1:1 by volume) is used as electrolyte, celegard2400 is used as a diaphragm, and the CR2032 type button lithium battery is assembled. At 25 ℃, under the condition of 1C, the voltage window is 2.0-4.3V for the graphene-like carbon nano tube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery positive electrodeThe battery assembled by the electrode material is subjected to constant-current charge and discharge test, and the specific discharge capacity after 200 cycles under the condition of 1C is 188.5mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 90%, the initial ohmic internal resistance is 3.22 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 6.16 omega.

Example 3 lithium nickel cobalt manganese oxide with a tap density of 2.4g/cm was used as a starting material, flake graphite as an auxiliary material, water-soluble acrylic resin as a grinding medium and a carbon-coated starting material, and aluminum nitrate as a catalyst and a dopant ³ The particle size (D50) is 10 μm, the length and width of the flake graphite raw material is 150 μm, and the thickness is 12 μm, and the method specifically comprises the following steps:

step 1, adding 3.5wt% of flake graphite into 96.5wt% of water-soluble acrylic resin, and stirring and mixing the flake graphite in a water bath at 50 ℃ for 15min to obtain a mixture A;

step 2, peeling the mixture A obtained in the step 1 through a three-roller differential grinding machine, circularly peeling for 15 times, and collecting a mixture B from a discharging roller; when the circulation stripping is carried out for 1-4 times, the clearance between N3 and N2 is 200 μm, and the clearance between N2 and N1 is 80 μm; when the circulation stripping is carried out for 5-8 times, the gap between N3 and N2 is 40 μm, and the gap between N2 and N1 is 20 μm; when the circulation stripping is carried out for 9-12 times, the gap between N3 and N2 is 10 μm, and the gap between N2 and N1 is 5 μm; circularly stripping for 13-15 times, wherein the gap between N3 and N2 is 3 μm, and the gap between N2 and N1 is 1 μm;

3, dissolving and removing part of water-soluble acrylic resin by deionized water/tap water/distilled water, adding water with the volume fraction of 100vol% into the mixture B obtained by stripping, stirring and ultrasonically assisting for 10min, putting into a centrifugal tube for centrifuging and removing impurity liquid, repeating the step, controlling the alcohol cleaning frequency to be 3 times, and finally centrifuging to obtain a substance C;

step 4, taking the impurity liquid removed after the last water washing resin in the step 3 is centrifuged as a solvent, measuring the impurity liquid with the same volume as the centrifuged substance C, dissolving 0.1wt% of aluminum nitrate raw material in the impurity liquid, and mixing and stirring the mixture with the substance C for 5min to obtain a mixture D;

Weighing 0.07g of graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ for 10 hours in vacuum, cutting into a wafer with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Under the condition of 25 ℃, a constant-current charge-discharge test is carried out on a battery assembled by the aluminum-doped nickel-cobalt lithium manganate battery anode material coated with the graphene-like carbon nano tube amorphous carbon under the condition of 1C and the voltage window is 2.0-4.3V, and the discharge specific capacity after 200 cycles under the condition of 1C is 178.3mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 88 percent, the initial ohmic internal resistance is 3.91 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 8.12 omega.

Comparative example 1, which is different from example 1 in that there is no three-roll mill peeling, no phenol resin, and no aluminum nitrateAs a result, the carbon nano tube and the amorphous carbon do not exist for coating, but the nickel cobalt lithium manganate raw material is directly used for battery assembly, is a commercial product and has the tap density of 2.0g/cm ³ The particle size (D50) was 4 μm.

Weighing 0.07g of nickel cobalt lithium manganate raw material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying in vacuum at 120 ℃ for 10 hours, cutting into round pieces with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium piece as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Under the condition of 25 ℃, a constant-current charge-discharge test is carried out on a battery material assembled by a nickel cobalt lithium manganate raw material cathode material under the condition of 1C voltage window of 2.0-4.3V, and the discharge specific capacity after 200 cycles under the condition of 1C is 101.5mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 75 percent, the initial ohmic internal resistance is 18.89 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 40.58 omega.

Comparative example 2, the preparation method is different from example 1 in that no scale graphite is stripped by a three-roll grinder, but phenolic resin is present, no aluminum nitrate is present, and after heat treatment, amorphous carbon coating is present, but no carbon nano tube is present, and no graphene-like nano sheet is present, so that only amorphous carbon-coated nickel cobalt lithium manganate is formed. The preparation method comprises the following specific steps:

the preparation method of the amorphous carbon-coated nickel cobalt lithium manganate battery cathode material adopts nickel cobalt lithium manganate as a raw material, phenolic resin as a coated carbon raw material, wherein the nickel cobalt lithium manganate raw material is a commercially available product, and has a tap density of 2.0g/cm ³ The particle size (D50) is 4 μm; the method comprises the following specific steps:

step 1, adding phenolic resin into nickel cobalt lithium manganate, stirring and mixing for 5min to obtain a mixture A, wherein the adding amount of the phenolic resin accounts for 6wt% of the mass fraction of the mixture A;

step 2, further and fully mixing the mixture A through a three-roller differential grinding machine, circularly mixing for 3 times, setting the gap between N3 and N2 to be 4 microns and the gap between N2 and N1 to be 2 microns, and collecting a mixture B from a discharging roller;

step 3, placing the mixture B in a freeze dryer, and carrying out freeze drying in a vacuum environment at-45 ℃ to obtain a mixture C;

step 4, placing the mixture C after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ per minute from room temperature ^-1 The temperature rise rate is up to 750 ℃, the temperature is kept for 4 hours, and then the temperature is naturally reduced to the room temperature, so that the amorphous carbon coated nickel cobalt manganese lithium battery anode material is obtained.

Weighing 0.07g of amorphous carbon-coated nickel-cobalt-manganese-acid lithium battery positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ in vacuum for 10 hours, cutting into a wafer with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium wafer as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Under the condition of 25 ℃, a constant-current charge-discharge test is carried out on a battery assembled by the amorphous carbon coated lithium nickel cobalt manganese oxide positive electrode material under the condition of 1C and the voltage window is 2.0-4.3V, and the discharge specific capacity after 200 cycles under the condition of 1C is 130.5mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 82%, the initial ohmic internal resistance is 15.07 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 33.80 omega.

Compared with the preparation method of example 1, the preparation method of the composite nickel cobalt lithium manganate has the difference that the crystalline flake graphite is stripped by a three-roll grinder, but the phenolic resin is completely cleaned, no aluminum nitrate is added, and no heat treatment is needed, so that the carbon nano tube and amorphous carbon coating do not exist, and only the graphene-like nanosheet composite nickel cobalt lithium manganate is formed. The preparation method comprises the following specific steps:

the preparation method of the graphene-like composite nickel cobalt lithium manganate battery positive electrode material of the comparative example adopts nickel cobalt lithium manganate as a raw material and scale stonesThe ink is used as an auxiliary material, the phenolic resin is used as a grinding medium, the nickel cobalt lithium manganate raw material is a commercial product, and the tap density is 2.0g/cm ³ The particle size (D50) is 4 μm; the length and width of the flake graphite raw material is 150 mu m, and the thickness is 12 mu m; the method comprises the following specific steps:

step 2, peeling the mixture A obtained in the step 1 through a three-roller differential grinding machine, circularly peeling for 16 times, and collecting a mixture B from a discharging roller; when the circulation stripping is carried out for 1-4 times, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; when the circulation stripping is carried out for 5-8 times, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; when the circulation stripping is carried out for 9-12 times, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; when the circulation stripping is carried out 13-16 times, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

step 3, dissolving and removing resin by alcohol, adding alcohol with the volume fraction of 100vol% into the mixture B obtained by stripping, stirring and ultrasonically assisting for 10min, placing into a centrifugal tube for centrifuging and removing impurity liquid, repeating the step, controlling the alcohol cleaning frequency to be 15 times, and finally centrifuging to obtain a substance C;

step 4, adding the substance C into the nickel cobalt lithium manganate, stirring and mixing for 5min to obtain a mixture D, wherein the adding amount of the substance C accounts for 6wt% of the mass fraction of the mixture D;

step 5, further fully stripping and mixing the mixture D through a three-roller differential grinding machine, circularly stripping for 3 times, setting the gap between N3 and N2 to be 4 microns and the gap between N2 and N1 to be 2 microns, and collecting the mixture E from a discharging roller;

step 6, placing the mixture E in a freeze dryer, and carrying out freeze drying in a vacuum environment at-45 ℃ to obtain a mixture F;

step 7, placing the mixture F after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ for min from room temperature ^-1 The temperature rise rate is up to 750 ℃, the temperature is kept for 4 hours, and then the temperature is naturally reduced to the room temperature, so that the graphene-like composite nickel cobalt manganese oxide lithium battery anode material is obtained.

Weighing 0.07g of graphene-like composite nickel cobalt lithium manganate positive electrode material prepared by the comparative example, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying in vacuum at 120 ℃ for 10 hours, cutting into wafers with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium wafer as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the graphene-like composite nickel cobalt lithium manganate positive electrode material at 25 ℃ and under the condition of 1C with the voltage window of 2.0-4.3V, wherein the discharge specific capacity after 200 cycles under the condition of 1C is 148.0mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 85%, the initial ohmic internal resistance is 11.35 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 24.48 omega.

Comparative example 4, the preparation method is different from example 1 in that no scale graphite is peeled off by a three-roll mill, phenolic resin is contained, aluminum nitrate is contained, and heat treatment is required, so that carbon nanotubes and amorphous carbon coating exist, and thus carbon nanotube amorphous carbon coated aluminum doped nickel cobalt lithium manganate is formed. The preparation method comprises the following specific steps:

the preparation method of the carbon nano tube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery positive electrode material adopts nickel cobalt lithium manganate as a raw material, phenolic resin as a grinding medium and a carbon coating raw material, aluminum nitrate as a catalyst and a doping agent, is a commercially available product, and has the tap density of 2.0g/cm ³ The particle size (D50) is 4 μm; the method comprises the following specific steps:

step 1, adding phenolic resin into nickel cobalt lithium manganate, stirring and mixing for 8min to obtain a mixture A, wherein the adding amount of the phenolic resin accounts for 6wt% of the mass fraction of the mixture A, and dissolving 0.05wt% of aluminum nitrate raw material into alcohol to be added into the mixture A to obtain a mixture B.

Step 2, further and fully mixing the mixture B through a three-roller differential grinding machine, circularly mixing for 3 times, setting the gap between N3 and N2 to be 4 microns and the gap between N2 and N1 to be 2 microns, and collecting the mixture C from a discharging roller;

step 3, placing the mixture C in a freeze-drying machine, and carrying out freeze-drying in a vacuum environment at-45 ℃ to obtain a mixture D;

step 4, placing the mixture D after freeze drying in a tube furnace for heat treatment under argon, and heating the mixture D from room temperature at 5 ℃ for min ^-1 The temperature rising rate is up to 750 ℃, the temperature is kept for 4 hours, and then the temperature is naturally reduced to the room temperature, so that the carbon nano tube amorphous carbon coated aluminum doped nickel cobalt lithium manganate is obtained.

Weighing 0.07g of carbon nanotube amorphous carbon coated aluminum doped nickel cobalt lithium manganate positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersion and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ in vacuum for 10 hours, cutting into a circular sheet with the diameter of 12mm, assembling in a glove box in an argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the carbon nano tube amorphous carbon coated aluminum doped nickel cobalt lithium manganate cathode material at 25 ℃ and under the condition of 1C at a voltage window of 2.0-4.3V, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 168.4mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 88 percent, the initial ohmic internal resistance is 6.19 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 11.86 omega.

Comparative example 5, the preparation method is different from example 1 in that the drying method is drying rather than freeze drying, and the graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt lithium manganate is formed by the drying method. The preparation method comprises the following specific steps:

the preparation method of the graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery positive electrode material of the comparative example adopts nickel cobalt manganeseLithium manganate as raw material, crystalline flake graphite as auxiliary material, phenolic resin as grinding medium and carbon-coated raw material, aluminium nitrate as catalyst and doping agent, and said nickel-cobalt lithium manganate as commercial product with tap density of 2.0g/cm ³ The particle size (D50) is 4 μm; the length and width of the flake graphite raw material are 150 μm, and the thickness is 12 μm; the method comprises the following specific steps:

step 3, removing part of resin through alcohol dissolution, adding alcohol with the volume fraction of 100vol% into the mixture B obtained through stripping, placing the mixture B into a centrifugal tube for centrifugation and removing impurity liquid through stirring and ultrasonic assistance for 10min, repeating the step, controlling the number of times of alcohol cleaning to be 4, and finally centrifuging to obtain a substance C;

step 4, taking the impurity solution removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity solution with the volume equal to that of the substance C obtained by centrifugation, dissolving 0.05wt% of aluminum nitrate raw material in the impurity solution, and mixing and stirring the dissolved raw material with the substance C for 5min to obtain a mixture D;

step 7, placing the mixture F in an oven, and drying at 50 ℃ to obtain a mixture G;

step 8, placing the dried mixture G in a tube furnace for heat treatment under argon, and performing heat treatment at the room temperature of 5 ℃ for min ^-1 And (3) raising the temperature to 750 ℃, preserving the heat for 4 hours, and then naturally cooling to room temperature to obtain the graphene-like carbon nanotube amorphous carbon coated aluminum-doped nickel-cobalt lithium manganate.

Weighing 0.07g of graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt lithium manganate positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ in vacuum for 10 hours, cutting into wafers with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium wafer as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt lithium manganate cathode material at 25 ℃ and under the condition of 1C at a voltage window of 2.0-4.3V, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 182.8mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 90%, the initial ohmic internal resistance is 3.46 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 6.82 omega.

Comparative example 6, the preparation method is different from example 1 in the number of times of washing the phenolic resin, example 1 is washed 4 times, and the comparative example is washed 1 time, aiming at the difference of the carbon coating thickness in the subsequent heat treatment. The preparation method comprises the following specific steps:

the preparation method of the positive electrode material of the graphene-like nanosheet carbon nanotube amorphous carbon coated aluminum-doped nickel-cobalt lithium manganate battery adopts nickel-cobalt lithium manganate as a raw material, flake graphite as an auxiliary material, phenolic resin as a grinding medium and a carbon-coated raw material, and aluminum nitrate as a catalyst and a doping agent, wherein the nickel-cobalt lithium manganate raw material,is a commercial product and has a tap density of 2.0g/cm ³ The particle size (D50) is 4 μm; the length and width of the flake graphite raw material is 150 micrometers, the thickness is 12 micrometers, and the method comprises the following specific steps:

step 3, removing part of resin through alcohol dissolution, adding alcohol with the volume fraction of 100vol% into the mixture B obtained through stripping, placing the mixture B into a centrifugal tube for centrifugation and removing impurity liquid through stirring and ultrasonic assistance for 10min, repeating the step, controlling the number of times of alcohol cleaning to be 1, and finally centrifuging to obtain a substance C;

step 6, further fully stripping and mixing the mixture E through a three-roller differential grinding machine, circularly stripping for 3 times, setting the gap between N3 and N2 to be 4 micrometers and the gap between N2 and N1 to be 2 micrometers, and collecting a mixture F from a discharging roller;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ for min from room temperature ^-1 The temperature rise rate is up to 750 ℃, the temperature is kept for 4 hours, and then the temperature is naturally reduced to the room temperature, so that the graphene-like carbon nano tube amorphous carbon coated aluminum doped nickel cobalt manganese oxide lithium battery anode material is obtained.

Weighing 0.07g of graphene-like carbon nanotube amorphous carbon coated aluminum doped nickel cobalt lithium manganate positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ in vacuum for 10 hours, cutting into wafers with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium wafer as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC 1:1 by volume) is used as electrolyte, celegard2400 is used as a diaphragm, and the CR2032 type button lithium battery is assembled. Performing constant-current charge and discharge test on a battery assembled by the graphene-like carbon nanotube amorphous carbon coated aluminum-doped nickel cobalt lithium manganate cathode material at 25 ℃ and under the condition of 1C at a voltage window of 2.0-4.3V, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 155.2mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 86 percent, the initial ohmic internal resistance is 7.78 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 13.75 omega.

The following table 1 shows the performance of examples 1-3 compared to comparative examples 1-6.

TABLE 1 comparison of the Properties of examples 1-3 with comparative examples 1-6

Examples 4 to 6 use lithium iron phosphate as a raw material, nickel nitrate as a catalyst and a dopant, and comparative examples 7 to 12 are comparative examples of examples 4 to 6.

Example 4, lithium iron phosphate was used as a raw material, flake graphite was used as an auxiliary material, phenol resin was used as a grinding medium and a carbon-coated raw material, nickel nitrate was used as a catalyst and a dopant, and the apparent density of the lithium iron phosphate was 0.8g/cm ³ The medium diameter is 2 μm, the length and width of the flake graphite raw material are 150 μm, and the thickness is 12 μm, and the method specifically comprises the following steps:

step 1, adding 4wt% of crystalline flake graphite into 96wt% of phenolic resin, and stirring and mixing the crystalline flake graphite in a water bath at 50 ℃ for 15min to obtain a mixture A;

step 4, taking the impurity solution removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity solution with the same volume as the centrifuged substance C, dissolving 0.05wt% of nickel nitrate raw material in the impurity solution, and mixing and stirring the mixture with the substance C for 5min to obtain a mixture D;

step 5, adding the mixture D into lithium iron phosphate, stirring and mixing for 8min to obtain a mixture E, wherein the adding amount of the mixture D accounts for 6wt% of the mass fraction of the mixture E;

step 6, further fully stripping and mixing the mixture E through a three-roller differential grinding machine, circularly stripping for 3 times, setting the gap between N3 and N2 to be 1.5 mu m and the gap between N2 and N1 to be 0.5 mu m, and collecting a mixture F from a discharging roller;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and heating the mixture G at 5 ℃ min from room temperature ^-1 And (3) keeping the temperature for 4 hours when the temperature rise rate reaches 750 ℃, and then naturally cooling to room temperature to obtain the graphene-like carbon nanotube amorphous carbon coated nickel doped lithium iron phosphate battery positive electrode material.

Weighing 0.07g of graphene-like nanosheet carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate cathode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ for 10 hours in vacuum, cutting into a wafer with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Under the condition of 25 ℃, a constant-current charge-discharge test is carried out on a battery assembled by the nickel-doped lithium iron phosphate cathode material coated with the amorphous carbon nano-tube similar to the graphene nano-sheet under the condition of 1C and the voltage window is 2.0-4.3V, and the specific discharge capacity after 200 cycles under the condition of 1C is 154.4mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition was 93%, the initial ohmic internal resistance was 4.25 Ω, and the ohmic internal resistance after 200 cycles under the 1C condition was 6.60 Ω.

Example 5, lithium iron phosphate was used as a raw material, expanded graphite was used as an auxiliary material, epoxy resin was used as a grinding medium and a carbon-coated raw material, nickel nitrate was used as a catalyst and a dopant, and the apparent density of the lithium iron phosphate was 0.6g/cm ³ The medium diameter is 4 μm, the length and width of the flake graphite raw material is 1000 μm, and the thickness is 100 μm, and the method specifically comprises the following steps:

step 1, adding 2wt% of expanded graphite into 98wt% of epoxy resin, and stirring and mixing the expanded graphite in a water bath at 40 ℃ for 10min to obtain a mixture A;

step 4, taking the impurity solution removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity solution with the same volume as the centrifuged substance C, dissolving 0.2wt% of nickel nitrate raw material in the impurity solution, and mixing and stirring the mixture with the substance C for 10min to obtain a mixture D;

step 5, adding the mixture D into lithium iron phosphate, stirring and mixing for 5min to obtain a mixture E, wherein the adding amount of the mixture D accounts for 8wt% of the mass fraction of the mixture E;

step 6, further fully stripping and mixing the mixture E through a three-roller differential grinding machine, circularly stripping and mixing for 2 times, setting the gap between N3 and N2 to be 1.5 mu m and the gap between N2 and N1 to be 0.5 mu m, and collecting a mixture F from a discharging roller;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and heating at 3 ℃ for min from room temperature ^-1 The temperature rising rate is 650 ℃, the temperature is kept for 5 hours, and then the temperature is naturally reduced to the room temperature, so that the graphene-like carbon nano tube amorphous carbon bag is obtainedAnd (3) a nickel-coated doped lithium iron phosphate battery positive electrode material.

Weighing 0.07g of graphene-like nanosheet carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate cathode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ for 10 hours in vacuum, cutting into a wafer with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the graphene-like nanosheet carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate cathode material at 25 ℃ and under the condition of 1C at a voltage window of 2.0-4.3V, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 138.2mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 88 percent, the initial ohmic internal resistance is 6.63 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 11.24 omega.

Example 6, lithium iron phosphate was used as a raw material, flake graphite was used as an auxiliary material, polyethylene resin was used as a grinding medium and a carbon-coated raw material, nickel nitrate was used as a catalyst and a dopant, and the apparent density of the lithium iron phosphate was 0.5g/cm ³ The medium diameter is 4.5 μm, the length and width of the flake graphite raw material is 200 μm, and the thickness is 20 μm, and the method specifically comprises the following steps:

step 1, adding 5wt% of flake graphite into 95wt% of polyethylene resin, and stirring and mixing the flake graphite in a water bath at 50 ℃ for 15min to obtain a mixture A;

step 2, peeling the mixture A obtained in the step 1 through a three-roller differential grinding machine, circularly peeling for 15 times, and collecting a mixture B from a discharging roller; the three-roller speed ratio of the three-roller differential grinding machine is that a feed roller N3, a central roller N2, a discharge roller N1 is 1; when the circulation stripping is carried out for 5-8 times, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; when the circulation stripping is carried out for 9-12 times, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; circularly stripping for 13-15 times, wherein the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

step 3, removing part of resin through alcohol dissolution, adding alcohol with the volume fraction of 50vol% into the mixture B obtained through stripping, placing the mixture B into a centrifugal tube for centrifugation and impurity removal through stirring and ultrasonic assistance for 10min, repeating the step to control the number of alcohol washing times to be 6, and finally performing centrifugation to obtain a substance C;

step 5, adding the mixture D into lithium iron phosphate, stirring and mixing for 9min to obtain a mixture E, wherein the adding amount of the mixture D accounts for 10wt% of the mass fraction of the mixture E;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and heating at 8 ℃ for min from room temperature ^-1 And (3) keeping the temperature for 2 hours when the temperature rising rate reaches 700 ℃, and then naturally cooling to room temperature to obtain the graphene-like carbon nanotube amorphous carbon coated nickel doped lithium iron phosphate battery positive electrode material.

Weighing 0.07g of graphene-like nanosheet carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate battery positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying in vacuum at 120 ℃ for 10 hours, and cutting into 12 mm-diameter lithium iron phosphate batteriesWafers, assembled in a glove box under argon atmosphere, with a metallic lithium plate as the counter electrode, 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the graphene-like nanosheet carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate cathode material at 25 ℃ and under the condition of 1C at a voltage window of 2.0-4.3V, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 132.7mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 85%, the initial ohmic internal resistance is 8.72 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 15.14 omega.

Comparative example 7, the preparation method is different from example 1 in that neither three-roll mill stripping nor phenol resin nor nickel nitrate is provided, and as a result, carbon nanotube and amorphous carbon coating is not provided, but battery assembly is directly performed using a lithium iron phosphate raw material having a apparent density of 0.8g/cm ³ And the median diameter is 2um.

Weighing 0.07g of lithium iron phosphate raw material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, then uniformly coating on an aluminum foil, cutting into circular sheets with the diameter of 12mm after vacuum drying at 120 ℃ for 10 hours, assembling in a glove box in argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery material assembled by the lithium iron phosphate raw material anode material under the condition of 1C and the voltage window of 2.0-4.3V at 25 ℃, wherein the discharge specific capacity after 200 cycles under the condition of 1C is 82mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 70%, the initial ohmic internal resistance is 20.89 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 50.78 omega.

Comparative example 8, the preparation method is different from example 1 in that no scale graphite is peeled off by a three-roll grinder, but there is phenolic resin and no nickel nitrate, there is amorphous carbon coating after heat treatment, but there are no carbon nanotubes, and there are no graphene-like nanoplatelets, so that only amorphous carbon-coated lithium iron phosphate is formed. The preparation method comprises the following specific steps:

the preparation method of the amorphous carbon-coated lithium iron phosphate battery positive electrode material adopts lithium iron phosphate as a raw material and phenolic resin as a coated carbon raw material, and the apparent density of the lithium iron phosphate raw material is 0.8g/cm ³ The median diameter is 2um; the method comprises the following specific steps:

step 1, adding phenolic resin into lithium iron phosphate, stirring and mixing for 8min to obtain a mixture A, wherein the adding amount of the phenolic resin accounts for 6wt% of the mass fraction of the mixture A;

step 2, further and fully mixing the mixture A through a three-roller differential grinding machine, and circularly mixing for 3 times, setting the gap between N3 and N2 to be 1.5 mu m and the gap between N2 and N1 to be 0.5 mu m, and collecting a mixture B from a discharging roller;

step 4, placing the mixture C after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ per minute from room temperature ^-1 The temperature rising rate is up to 750 ℃, the temperature is kept for 4 hours, and then the temperature is naturally reduced to the room temperature, so that the amorphous carbon coated lithium iron phosphate battery anode material is obtained.

Weighing 0.07g of amorphous carbon-coated lithium iron phosphate battery positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying in vacuum at 120 ℃ for 10 hours, cutting into a wafer with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC 1:1 by volume) is used as electrolyte, celegard2400 is used as a diaphragm, and the CR2032 type button lithium battery is assembled. Performing constant current charge and discharge test on a battery assembled by the amorphous carbon coated lithium iron phosphate anode material at the temperature of 25 ℃ and the voltage window of 2.0-4.3V under the condition of 1C, and performing 200-time circulation after discharge under the condition of 1CThe specific capacity is 98.2mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 78 percent, the initial ohmic internal resistance is 17.42 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 38.56 omega.

In comparison with example 1, the difference of the preparation method of comparative example 9 is that the crystalline flake graphite is stripped by a three-roll grinder, but the phenolic resin is completely cleaned, nickel nitrate is not needed, and heat treatment is not needed, so that carbon nanotubes and amorphous carbon coating do not exist, and only graphene-like nanosheet composite lithium iron phosphate is formed. The preparation method comprises the following specific steps:

the preparation method of the graphene-like composite lithium iron phosphate battery positive electrode material adopts lithium iron phosphate as a raw material, crystalline flake graphite as an auxiliary material and phenolic resin as a grinding medium, and the apparent density of the lithium iron phosphate raw material is 0.8g/cm ³ The median diameter is 2um; the length and width of the flake graphite raw material is 150 mu m, and the thickness is 12 mu m; the method comprises the following specific steps:

step 3, removing resin through alcohol dissolution, adding alcohol with the volume fraction of 100vol% into the mixture B obtained through stripping, placing the mixture into a centrifugal tube for centrifugation and removing impurity liquid through stirring and ultrasonic assistance for 10min, repeating the step, controlling the number of times of alcohol cleaning to be 15 times, and finally centrifuging to obtain a substance C;

step 4, adding the substance C into the lithium iron phosphate, stirring and mixing for 8min to obtain a mixture D, wherein the adding amount of the substance C accounts for 6wt% of the mass fraction of the mixture D;

step 5, further fully stripping and mixing the mixture D through a three-roller differential grinding machine, circularly stripping for 3 times, setting the gap between N3 and N2 to be 1.5 mu m and the gap between N2 and N1 to be 0.5 mu m, and collecting the mixture E from a discharging roller;

step 7, placing the mixture F after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ for min from room temperature ^-1 And (3) raising the temperature to 750 ℃, preserving the heat for 4 hours, and then naturally cooling to room temperature to obtain the graphene-like composite lithium iron phosphate battery positive electrode material.

Weighing 0.07g of graphene-like composite lithium iron phosphate positive electrode material prepared in the comparative example, 0.015g of acetylene black (conductive agent), and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, performing vacuum drying at 120 ℃ for 10 hours, cutting into a wafer with the diameter of 12mm, assembling in a glove box in an argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the graphene-like composite lithium iron phosphate positive electrode material at 25 ℃ and under the condition of 1C with the voltage window of 2.0-4.3V, wherein the discharge specific capacity after 200 cycles under the condition of 1C is 112.5mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 82%, the initial internal resistance is ohm 15.33 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 30.62 omega.

Comparative example 10, the preparation method is different from example 1 in that there is no flake graphite peeled off by a three-roll mill, there is phenolic resin, there is nickel nitrate, and heat treatment is required, so there are carbon nanotubes and amorphous carbon coating, thus forming carbon nanotube amorphous carbon coated nickel doped lithium iron phosphate. The preparation method comprises the following specific steps:

according to the preparation method of the carbon nanotube amorphous carbon coated nickel doped lithium iron phosphate battery positive electrode material in the comparative example, lithium iron phosphate is adopted as a raw material, phenolic resin is adopted as a grinding medium and a coated carbon raw material, nickel nitrate is adopted as a catalyst and a doping agent, the bulk density of the lithium iron phosphate raw material is 0.8g/cm & lt 3 & gt, and the median diameter is 2 microns; the method comprises the following specific steps:

step 1, adding phenolic resin into lithium iron phosphate, stirring and mixing for 8min to obtain a mixture A, wherein the adding amount of the phenolic resin accounts for 6wt% of the mass fraction of the mixture A, and dissolving 0.05wt% of nickel nitrate raw material into alcohol to be added into the mixture A to obtain a mixture B.

Step 2, further and fully mixing the mixture B through a three-roller differential grinding machine, circularly mixing for 3 times, setting the gap between N3 and N2 to be 1.5 mu m and the gap between N2 and N1 to be 0.5 mu m, and collecting a mixture C from a discharging roller;

step 4, placing the mixture D after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ for min from room temperature ^-1 The temperature is raised to 750 ℃, the temperature is kept for 4 hours, and then the temperature is naturally reduced to the room temperature, so that the nickel-doped lithium iron phosphate coated with the carbon nano tube amorphous carbon is obtained.

Weighing 0.07g of carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate positive electrode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ in vacuum for 10 hours, cutting into a wafer with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium sheet as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant current charge and discharge test on a battery assembled by the carbon nano tube amorphous carbon coated nickel-doped lithium iron phosphate cathode material at 25 ℃ and under the condition of 1C and with the voltage window of 2.0-4.3V, and performing 200 cycles under the condition of 1CThe specific discharge capacity is 118.7mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 83%, the initial ohmic internal resistance is 12.57 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 22.15 omega.

Comparative example 11, the preparation method differs from example 1 in that the drying method is oven drying rather than freeze drying, and the drying method is used to form graphene-like carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate. The preparation method comprises the following specific steps:

the preparation method of the positive electrode material of the graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery in the comparative example adopts lithium iron phosphate as a raw material, crystalline flake graphite as an auxiliary material, phenolic resin as a grinding medium and a coated carbon raw material, nickel nitrate as a catalyst and a doping agent, and the apparent density of the lithium iron phosphate raw material is 0.8g/cm ³ The median diameter is 2um; the length and width of the flake graphite raw material is 150 mu m, and the thickness is 12 mu m; the method comprises the following specific steps:

step 2, stripping the mixture A obtained in the step 1 through a three-roller differential grinding machine, circularly stripping for 16 times, and collecting a mixture B from a discharge roller; when the circulation stripping is carried out for 1-4 times, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; when the circulation stripping is carried out for 5-8 times, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; when the circulation stripping is carried out for 9-12 times, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; when the circulation stripping is carried out 13-16 times, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

step 8, placing the dried mixture G in a tube furnace for heat treatment under argon, and performing heat treatment at the room temperature of 5 ℃ for min ^-1 The temperature is raised to 750 ℃ at the speed, the temperature is kept for 4 hours, and then the temperature is naturally reduced to room temperature, so that the nickel-doped lithium iron phosphate coated by the graphene-like carbon nano tube amorphous carbon is obtained.

Weighing 0.07g of graphene-like carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate cathode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ for 10 hours in vacuum, cutting into wafers with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium wafer as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the nickel-doped lithium iron phosphate cathode material coated with the graphene-like carbon nanotube amorphous carbon under the condition of 1C at the voltage window of 2.0-4.3V at 25 ℃, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 141.0mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition was 86%, the initial ohmic internal resistance was 6.16 Ω, and the ohmic internal resistance after 200 cycles under the 1C condition was 10.28 Ω.

Comparative example 12, the preparation method is different from example 1 in the number of times of washing the phenolic resin, example 1 is washed 4 times, and the comparative example is washed 1 time, aiming at the difference of the carbon coating thickness in the subsequent heat treatment. The preparation method comprises the following specific steps:

the preparation method of the positive electrode material of the graphene-like nanosheet carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery in the comparative example adopts lithium iron phosphate as a raw material, crystalline flake graphite as an auxiliary material, phenolic resin as a grinding medium and a coated carbon raw material, nickel nitrate as a catalyst and a doping agent, and the apparent density of the lithium iron phosphate raw material is 0.8g/cm ³ The median diameter is 2um; the length and width of the flake graphite raw material is 150 mu m, and the thickness is 12 mu m; the method comprises the following specific steps:

step 3, removing part of resin through alcohol dissolution, adding alcohol with the volume fraction of 100vol% into the mixture B obtained through stripping, placing the mixture B into a centrifugal tube for centrifugation and impurity removal through stirring and ultrasonic assistance for 10min, repeating the step to control the number of alcohol washing times to be 1, and finally performing centrifugation to obtain a substance C;

step 4, taking the impurity solution removed after the last alcohol cleaning resin in the step 3 is centrifuged as a solvent, measuring the impurity solution with the volume equal to that of the substance C obtained by centrifugation, dissolving 0.05wt% of nickel nitrate raw material in the impurity solution, and mixing and stirring the dissolved material with the substance C for 5min to obtain a mixture D;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and performing heat treatment at 5 ℃ for min from room temperature ^-1 And (3) keeping the temperature for 4 hours when the temperature rise rate reaches 750 ℃, and then naturally cooling to room temperature to obtain the graphene-like carbon nanotube amorphous carbon coated nickel doped lithium iron phosphate battery positive electrode material.

Weighing 0.07g of graphene-like carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate cathode material, 0.015g of acetylene black (conductive agent) and 0.015g of PVDF (HSV 900, binder), fully grinding, adding 0.4mL of NMP for dispersing and mixing, uniformly coating on an aluminum foil, drying at 120 ℃ for 10 hours in vacuum, cutting into wafers with the diameter of 12mm, assembling in a glove box in argon atmosphere, taking a metal lithium wafer as a counter electrode, and 1M LiPF ₆ The solution (EC: DEC solvent 1:1 by volume) was used as electrolyte, and Celegard2400 was used as separator to assemble CR2032 type button lithium battery. Performing constant-current charge and discharge test on a battery assembled by the nickel-doped lithium iron phosphate cathode material coated with the graphene-like carbon nanotube amorphous carbon under the condition of 1C at the voltage window of 2.0-4.3V at 25 ℃, wherein the specific discharge capacity after 200 cycles under the condition of 1C is 125.2mAh g ^-1 The capacity retention rate after 200 cycles under the 1C condition is 84%, the initial ohmic internal resistance is 10.14 omega, and the ohmic internal resistance after 200 cycles under the 1C condition is 19.68 omega.

The following table 2 shows the performance of examples 4-6 compared to comparative examples 7-12.

TABLE 2 comparison of the Properties of examples 4-6 with comparative examples 7-12

In conclusion, the three-roll grinding and stripping technology adopted by the invention overcomes the inter-layer van der Waals force through the shearing force generated by the three-roll differential speed and the acting force formed by the high-viscosity resin and the phosphorus flake graphite/expanded graphite, so that a large amount of graphene-like nanosheets are prepared by stripping the layered materials with the micron-sized thickness, and the crystal layer spacing of the graphene-like nanosheets is enlarged after stripping.

Graphite is ground and stripped through a three-roller differential speed to form graphene-like nanosheets, and the graphene-like nanosheets are further continuously mixed with lithium nickel cobalt manganese oxide or lithium iron phosphate on the equipment, and are subjected to circulating stripping for 2-3 times, gaps between every two roller shafts are adjusted to be 1-5 microns, so that the lithium nickel cobalt manganese oxide can be ground, dispersed and forcedly refined, and the contact and coating of the graphene-like nanosheets and the lithium nickel cobalt manganese oxide or lithium iron phosphate can be further strengthened. Because the resin has certain viscosity, the mixture F is easy to form pasty agglomerates by the traditional drying technology, and the powder with good dispersion effect can be obtained by adopting the freeze drying technology for treatment.

The aluminum nitrate or the nickel nitrate is used as a catalyst and a doping agent, the aluminum nitrate or the nickel nitrate solution is uniformly mixed with the resin, and the aluminum nitrate catalyzes the resin to generate the carbon nano tube in situ in the subsequent heat treatment process at 500-850 ℃.

According to the invention, the low-cost and high-performance lithium ion battery anode material is prepared by integrating three modification technologies of Al or Ni doping, composite conductive agent (two-dimensional graphene nano sheet and one-dimensional carbon nano tube) and amorphous carbon coating. The two-dimensional graphene nanosheets obtained by three-roller differential grinding and stripping have enlarged crystal layer spacing, can allow more foreign reactants to perform embedding reaction, and has greatly improved specific surface area and conductivity compared with the original graphite; the interpenetration of the one-dimensional carbon nano tube and the zero-dimensional amorphous carbon coated lithium nickel cobalt manganese oxide or lithium iron phosphate form a three-dimensional network structure, which is favorable for further improving the electron conduction and ion transmission of the three-dimensional carbon nano tube, and reduces the polarization and impedance of the three-dimensional carbon nano tube in the charging and discharging process, meanwhile, the graphene-like nano sheet, the carbon nano tube and the amorphous carbon form a 'protective barrier' for the lithium nickel cobalt manganese oxide or the lithium iron phosphate, and the side reaction of electrolyte to the lithium nickel cobalt manganese oxide or the lithium iron phosphate is inhibited, so that the structural stability and the electric conductivity of the lithium nickel cobalt manganese oxide or the lithium iron phosphate are greatly increased, the electrochemical performance of the lithium nickel cobalt manganese oxide or the lithium iron phosphate is greatly improved, and the requirements in the fields of new energy automobiles, electric vehicles, large-scale energy storage, starting power supplies and the like are met.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention.

Claims

1. A preparation method of a multi-dimensional and multi-scale carbon-coated lithium ion battery anode material is characterized by comprising the following steps: the method mainly comprises the following steps:

step 7, placing the mixture F in a freeze dryer, and carrying out freeze drying in a vacuum environment at the temperature of minus 50-minus 30 ℃ to obtain a mixture G;

step 8, placing the mixture G after freeze drying in a tube furnace for heat treatment under argon, and heating the mixture G at the temperature of 2-10 ℃ for min from room temperature ^-1 The temperature is raised to 500-850 ℃, the temperature is preserved for 1-5h, and then the temperature is naturally lowered to the room temperature, so as to obtain the multidimensional multi-scale carbon-coated lithium ion battery anode material.

2. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery positive electrode material according to claim 1, characterized by comprising the following steps: in step 2, the three-roller differential grinding machine comprises a discharge roller N1, a central roller N2 and a feed roller N3, wherein the rotation speed ratio of the feed roller N3 to the central roller N2 to the discharge roller N1 is 1:3: and 9, in the circulating stripping process, the gap between the central roller N2 and the feeding roller N3 is always larger than the gap between the discharging roller N1 and the central roller N2, and the circulating stripping frequency is 15-17 times.

3. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material according to claim 2, characterized by comprising the following steps: and when the circulation stripping is carried out for 1-4 times, the clearance between the central roller N2 and the feeding roller N3 and the clearance between the discharging roller N1 and the central roller N2 are both between 40 and 200 mu m.

4. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material according to claim 2, characterized by comprising the following steps: and when the circulation stripping is carried out for 5-8 times, the gap between the central roller N2 and the feeding roller N3 and the gap between the discharging roller N1 and the central roller N2 are both between 10 and 40 mu m.

5. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material according to claim 2, characterized by comprising the following steps: and when the circulation stripping is carried out for 9-12 times, the clearance between the central roller N2 and the feeding roller N3 and the clearance between the discharging roller N1 and the central roller N2 are both between 2.5 and 10 mu m.

6. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material according to claim 2, characterized by comprising the following steps: after 13 th time of the cyclic peeling, the gap between the center roll N2 and the feed roll N3 and the gap between the discharge roll N1 and the center roll N2 were each between 0.5 and 2.5 μm.

7. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material according to claim 1, characterized by comprising the following steps: in step 4, the raw material of the nitric compound is aluminum nitrate or nickel nitrate.

8. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery positive electrode material according to claim 1, characterized by comprising the following steps: in step 5, the lithium compound is lithium nickel cobalt manganese oxide or lithium iron phosphate.

9. The preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery positive electrode material according to claim 2, characterized by comprising the following steps: in the step 6, the number of times of the cyclic stripping is 2-3, and after the cyclic stripping is finished, the gap between the central roller N2 and the feeding roller N3 and the gap between the discharging roller N1 and the central roller N2 are both between 0.5 and 5 microns.

10. A multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material is characterized in that: the multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material is prepared by the preparation method of the multi-dimensional and multi-scale carbon-coated lithium ion battery cathode material according to any one of claims 1 to 9.