Multidimensional and multiscale carbon-coated lithium-ion battery positive electrode material and preparation method thereof

Abstract

The present invention provides a multidimensional and multiscale carbon-coated lithium-ion battery cathode material and a preparation method thereof. The preparation method uses lithium nickel cobalt manganese oxide or lithium iron phosphate as raw materials, graphite as an auxiliary material, resin as a grinding medium, and coated carbon raw materials, and aluminum nitrate or nickel nitrate as a catalyst and dopant. The resin and graphite are first mixed, then exfoliated using a three-roll differential speed mill. The mixture is washed various times, and after adding the catalyst and dopant, the raw materials are added and mixed using a three-roll differential speed mill. The mixture is then freeze-dried and heat-treated to obtain the battery cathode material. The product of the present invention has good conductivity and stability, improves battery capacity, cycle performance, rate capability, and other performance, and can meet the demand for new materials in fields such as energy storage batteries and power batteries.

Description

Technical Field

[0001] The present invention relates to a multi-dimensional and multi-scale carbon-coated lithium ion battery positive electrode material and a preparation method thereof, belonging to the technical field of lithium ion battery positive electrode materials. Background Art

[0002] Currently, the positive electrode materials of lithium-ion batteries include: lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, ternary oxides and inorganic substances.

[0003] Layered lithium nickel cobalt manganese oxide (LiNi x Co y Mn z O2, x+y+z=1, Li-NCM) positive electrode material combines the advantages of LiCoO2, LiNiO2, and LiMnO2. With the advantages of high specific capacity, good cycle performance, good thermal stability, stable structure and low cost, it has become the most promising ternary positive electrode material at present. However, the main disadvantage of Li-NCM material is its low electrical conductivity and tap density. During the preparation process, due to the similar radius of nickel ions and lithium ions, some nickel ions will occupy lithium sites and lithium-nickel mixing will occur, resulting in a decrease in the reversible discharge specific capacity of Li-NCM material and poor cycle performance. This greatly restricts the application of Li-NCM material in high-power lithium-ion batteries.

[0004] When lithium iron phosphate (LiFePO4) is used as the positive electrode material, the electronic conductivity (rate is only 10 -9 -10 -10 S / cm) and ion diffusion efficiency are extremely low, resulting in large resistance polarization in the reaction and poor rate performance. These shortcomings greatly limit the widespread application of lithium iron phosphate in practice.

[0005] In view of this, it is indeed necessary to propose a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material and a preparation method thereof to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a multidimensional and multiscale carbon-coated lithium-ion battery positive electrode material and a preparation method thereof, which has good conductivity and stability, improves the battery's capacity, cycle performance, rate capability and other properties, and can meet the demand for new materials in the fields of energy storage batteries, power batteries, etc.

[0007] To achieve the above objectives, the present invention provides a method for preparing a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material, which mainly comprises the following steps:

[0008] Step 1, adding 1-5 wt% of graphite auxiliary material to 95-99 wt% of resin, and stirring and mixing in a 40-70° C. water bath for 5-30 minutes to obtain a mixture A;

[0009] Step 2: The mixture A obtained in step 1 is peeled by a three-roll differential speed grinding machine, and after repeated peeling, the mixture is collected from the discharge roller to obtain a mixture B;

[0010] Step 3: remove part of the resin by dissolving it with alcohol, add 50-200 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat step 3 and continue washing with alcohol, and finally centrifuge to obtain substance C;

[0011] Step 4: Using the impurity liquid removed after the final alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation is measured, 0.01-0.5 wt% of the nitric acid compound raw material is dissolved therein, and the mixture is then mixed with the substance C and stirred for 1-10 minutes to obtain a mixture D;

[0012] Step 5, adding mixture D to the lithium compound and stirring and mixing for 5-10 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 3-12 wt% of the mass fraction of mixture E;

[0013] Step 6: The mixture E is further fully peeled and mixed by a three-roll differential speed mill, and after repeated peeling multiple times, the mixture is collected from the discharge roller to obtain a mixture F;

[0014] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at a temperature of -50°C to -30°C to obtain a mixture G;

[0015] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment at a temperature of 2-10°C / min from room temperature. -1 The temperature is raised to 500-850°C at a rate of 100-200°C, kept at this temperature for 1-5 hours, and then naturally cooled to room temperature to obtain a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material.

[0016] As a further improvement of the present invention, in step 2, the three-roll differential grinder includes a discharge roller N1, a center roller N2 and a feed roller N3, wherein the speed ratio of the feed roller N3, the center roller N2 and the discharge roller N1 is 1:3:9, and during the cyclic peeling process, the gap between the center roller N2 and the feed roller N3 is always larger than the gap between the discharge roller N1 and the center roller N2, and the number of cyclic peeling times is 15-17 times.

[0017] As a further improvement of the present invention, during the 1st to 4th cyclic peeling, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 40 and 200 μm.

[0018] As a further improvement of the present invention, during the 5th to 8th peeling cycle, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 10 and 40 μm.

[0019] As a further improvement of the present invention, during the 9th to 12th peeling cycles, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 2.5 μm and 10 μm.

[0020] As a further improvement of the present invention, after the 13th cyclic peeling, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 0.5-2.5 μm.

[0021] As a further improvement of the present invention, in step 4, the nitric acid compound raw material is aluminum nitrate or nickel nitrate.

[0022] As a further improvement of the present invention, in step 5, the lithium compound is lithium nickel cobalt manganese oxide or lithium iron phosphate.

[0023] As a further improvement of the present invention, in step 6, the number of cyclic peeling is 2-3 times. After the cyclic peeling is completed, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 0.5-5 μm.

[0024] To achieve the above objectives, the present invention also provides a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material, which is prepared using the above-mentioned method for preparing the multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material.

[0025] The beneficial effects of the present invention are as follows: the present invention adopts a three-roll mill grinding and exfoliation technology to overcome the interlayer van der Waals force through the shear force generated by the differential speed of the three rollers and the force formed by the high-viscosity resin and the phosphorus flake graphite / expanded graphite, thereby achieving the goal of exfoliating layered materials with a thickness of microns to prepare a large number of graphene-like nanosheets, and after the exfoliation, the crystal interlayer spacing of the nanosheets becomes larger. The graphene-like nanosheets prepared by this method are more efficient and lower cost than graphene prepared by adding traditional technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of obtaining a graphene-like nanosheet material by exfoliating graphite as a raw material in a resin through a three-roll grinder.

[0027] Figure 2This is the TEM image of the graphene-like nanosheets, carbon nanotubes and amorphous carbon composite modified material obtained after three-roll grinding and peeling, alcohol cleaning, freeze drying and heat treatment. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] It should be noted here that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions of the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0030] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0031] like Figure 1 and Figure 2 As shown, the present invention discloses a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material, and a preparation method of the multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material, which mainly includes the following steps:

[0032] Step 1, adding 1-5 wt% of graphite auxiliary material to 95-99 wt% of resin, and stirring and mixing in a 40-70° C. water bath for 5-30 minutes to obtain a mixture A;

[0033] Step 2: The mixture A obtained in step 1 is peeled by a three-roll differential speed grinding machine, and after repeated peeling, the mixture is collected from the discharge roller to obtain a mixture B;

[0034] Step 3: remove part of the resin by dissolving it with alcohol, add 50-200 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat step 3 and continue washing with alcohol, and finally centrifuge to obtain substance C;

[0035] Step 4: Using the impurity liquid removed after the final alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation is measured, 0.01-0.5 wt% of the nitric acid compound raw material is dissolved therein, and the mixture is then mixed with the substance C and stirred for 1-10 minutes to obtain a mixture D;

[0036] Step 5, adding mixture D to the lithium compound and stirring and mixing for 5-10 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 3-12 wt% of the mass fraction of mixture E;

[0037] Step 6: The mixture E is further fully peeled and mixed by a three-roll differential speed mill, and after repeated peeling multiple times, the mixture is collected from the discharge roller to obtain a mixture F;

[0038] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at a temperature of -50°C to -30°C to obtain a mixture G;

[0039] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment at a temperature of 2-10°C / min from room temperature. -1 The temperature is raised to 500-850°C at a rate of 100-200°C, kept at this temperature for 1-5 hours, and then naturally cooled to room temperature to obtain a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material.

[0040] Steps 1 to 8 are described in detail below.

[0041] In step 2, the three-roll differential grinding machine includes a discharge roller N1, a center roller N2 and a feed roller N3, wherein the speed ratio of the feed roller N3, the center roller N2 and the discharge roller N1 is 1:3:9, and in the cyclic peeling process, the gap between the center roller N2 and the feed roller N3 is always larger than the gap between the discharge roller N1 and the center roller N2, and the number of cyclic peeling is 15-17 times; it should be noted that the roller spacing is different in different cyclic peeling times. When the cyclic peeling is performed for the 1st to 4th time, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are larger than the gap between the discharge roller N1 and the center roller N2. The gaps are all between 40-200 μm; during the 5th to 8th cycle peeling, the gap between the center roller N2 and the feed roller N3, and the gap between the discharge roller N1 and the center roller N2 are all between 10-40 μm; during the 9th to 12th cycle peeling, the gap between the center roller N2 and the feed roller N3, and the gap between the discharge roller N1 and the center roller N2 are all between 2.5-10 μm; after the 13th cycle peeling, the gap between the center roller N2 and the feed roller N3, and the gap between the discharge roller N1 and the center roller N2 are all between 0.5-2.5 μm.

[0042] In step 6, the number of cyclic peeling is 2-3 times. After the cyclic peeling is completed, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 0.5-5 μm.

[0043] In the present invention, the battery positive electrode material uses lithium nickel cobalt manganese oxide as raw material, graphite as auxiliary material, resin as grinding medium and coated carbon raw material, and aluminum nitrate as catalyst and dopant. Among them, the lithium nickel cobalt manganese oxide raw material is a commercial product with a tap density of 1.8-2.6g / cm 3 , the particle size (D50) is 2-16 μm, the resin is one of polyvinyl alcohol, polyvinylidene fluoride resin, epoxy resin, phenolic resin, and polyethylene resin, the graphite is one or both of flake graphite and expanded graphite, the flake graphite raw material has a length and width of 50-500 μm and a thickness of 5-50 μm, and the expanded graphite raw material has a length and width of 300-2000 μm and a thickness of 50-500 μm. In addition, a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material prepared from lithium nickel cobalt manganese oxide as a raw material, wherein the lithium nickel cobalt manganese oxide accounts for 93-97.5wt% of the total mass, the graphene-like material accounts for 2-4wt% of the total mass, the amorphous carbon accounts for 0.4-2wt% of the total mass, and the carbon nanotubes account for 0.1-1wt% of the total mass. Of course, in other embodiments of the present invention, the battery positive electrode material can also use lithium iron phosphate as raw material, nickel nitrate as catalyst and dopant, and the bulk density of the lithium iron phosphate raw material is 0.5-0.9g / cm 3 , the median diameter is 0.5-5 μm, which can be set as needed and is not limited here. In addition, a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material prepared from lithium iron phosphate as a raw material, wherein lithium iron phosphate accounts for 93-97.4wt% of the total mass, graphene-like materials account for 2-4wt% of the total mass, amorphous carbon accounts for 0.4-2wt% of the total mass, and carbon nanotubes account for 0.1-1wt% of the total mass.

[0044] The following is a detailed description with reference to the Examples and Comparative Examples. Examples 1-3 use lithium nickel cobalt manganese oxide as a raw material and aluminum nitrate as a catalyst and dopant. Comparative Examples 1-6 are comparative examples of Examples 1-3.

[0045] In Example 1, lithium nickel cobalt manganese oxide is used as raw material, flake graphite is used as auxiliary material, phenolic resin is used as grinding medium and coated carbon raw material, aluminum nitrate is used as catalyst and dopant, and the tap density of the lithium nickel cobalt manganese oxide is 2.0 g / 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, and the specific steps include:

[0046] Step 1, adding 3.5 wt% of flake graphite to 96.5 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0047] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, the mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0048] Step 3: Remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 4, and finally centrifuge to obtain substance C;

[0049] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.05 wt% of aluminum nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0050] Step 5, adding mixture D to lithium nickel cobalt manganese oxide and stirring for 5 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 6 wt% of the mass fraction of mixture E;

[0051] Step 6: The mixture E is further fully stripped and mixed by a three-roll differential speed mill, and the stripping cycle is repeated three times, with the gap between N3 and N2 set to 4 μm, and the gap between N2 and N1 set to 2 μm, and the mixture F is collected from the discharge roller;

[0052] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -45°C to obtain a mixture G;

[0053] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750°C at a rate of 100°C, kept warm for 4 hours, and then naturally cooled to room temperature to obtain graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material.

[0054] Weigh 0.07 g of the graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material prepared in this example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 h, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like carbon nanotube amorphous carbon coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 204.8mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 94%, the initial ohmic internal resistance is 1.65Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 3.08Ω.

[0055] Example 2, using lithium nickel cobalt manganese oxide as raw material, expanded graphite as auxiliary material, epoxy resin as grinding medium and coated carbon raw material, aluminum nitrate as catalyst and dopant, the tap density of the lithium nickel cobalt manganese oxide is 2.2g / cm 3 The particle size (D50) is 6 μm, the length and width of the expanded graphite raw material is 1000 μm, and the thickness is 100 μm, which specifically includes the following steps:

[0056] Step 1, adding 3.5 wt% of expanded graphite to 96.5 wt% of epoxy resin, and mixing them in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0057] Step 2: The mixture A obtained in step 1 is peeled off by a three-roll differential speed grinder. After 15 cycles of peeling, a mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 200 μm, and the gap between N2 and N1 is 80 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 40 μm, and the gap between N2 and N1 is 20 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 10 μm, and the gap between N2 and N1 is 5 μm; during the 13th to 15th cycles of peeling, the gap between N3 and N2 is 3 μm, and the gap between N2 and N1 is 1 μm;

[0058] Step 3: remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 3 times, and finally centrifuge to obtain substance C;

[0059] Step 4: Using the impurity liquid removed after the final alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the volume of the substance C obtained by centrifugation was measured, 0.1 wt% of aluminum nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0060] Step 5, adding mixture D to lithium nickel cobalt manganese oxide and stirring for 5 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 5 wt% of the mass fraction of mixture E;

[0061] Step 6: The mixture E is further fully exfoliated and mixed by a three-roll differential speed mill, and the exfoliation and mixing are repeated twice, with the gap between N3 and N2 set to 4 μm, and the gap between N2 and N1 set to 2 μm, and the mixture F is collected from the discharge roller;

[0062] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -40°C to obtain a mixture G;

[0063] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 2°C / min -1 The temperature was raised to 600°C at a rate of 1000 ℃, kept warm for 5 hours, and then naturally cooled to room temperature to obtain graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material.

[0064] Weigh 0.07 g of the graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material prepared in this example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 h, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like carbon nanotube amorphous carbon coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 188.5mAh g -1The capacity retention rate after 200 cycles under 1C conditions is 90%, the initial ohmic internal resistance is 3.22Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 6.16Ω.

[0065] Example 3, using lithium nickel cobalt manganese oxide as raw material, flake graphite as auxiliary material, water-soluble acrylic resin as grinding medium and coated carbon raw material, aluminum nitrate as catalyst and dopant, the tap density of the lithium nickel cobalt manganese oxide is 2.4g / cm 3 The particle size (D50) is 10 μm, the length and width of the flake graphite raw material are 150 μm, and the thickness is 12 μm, which specifically includes the following steps:

[0066] Step 1, adding 3.5 wt% of flake graphite to 96.5 wt% of water-soluble acrylic resin, and stirring and mixing them in a 50° C. water bath for 15 minutes to obtain a mixture A;

[0067] Step 2: The mixture A obtained in step 1 is peeled off by a three-roll differential speed grinder. After 15 cycles of peeling, a mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 200 μm, and the gap between N2 and N1 is 80 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 40 μm, and the gap between N2 and N1 is 20 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 10 μm, and the gap between N2 and N1 is 5 μm; during the 13th to 15th cycles of peeling, the gap between N3 and N2 is 3 μm, and the gap between N2 and N1 is 1 μm;

[0068] Step 3: Dissolve and remove part of the water-soluble acrylic resin with deionized water / tap water / distilled water, add 100 vol% water to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washings to 3 times, and finally centrifuge to obtain substance C;

[0069] Step 4: Using the impurity liquid removed after the last water-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the volume of the substance C obtained by centrifugation was measured, 0.1 wt% of aluminum nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0070] Step 5, adding mixture D to lithium nickel cobalt manganese oxide and stirring for 5 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 5 wt% of the mass fraction of mixture E;

[0071] Step 6: The mixture E is further fully exfoliated and mixed by a three-roll differential speed mill, and the exfoliation and mixing are repeated twice, with the gap between N3 and N2 set to 4 μm, and the gap between N2 and N1 set to 2 μm, and the mixture F is collected from the discharge roller;

[0072] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -40°C to obtain a mixture G;

[0073] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 2°C / min -1 The temperature was raised to 600°C at a rate of 1000 ℃, kept warm for 5 hours, and then naturally cooled to room temperature to obtain graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material.

[0074] Weigh 0.07 g of the graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material prepared in this example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 h, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like carbon nanotube amorphous carbon coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 178.3mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 88%, the initial ohmic internal resistance is 3.91Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 8.12Ω.

[0075] Comparative Example 1: This preparation method is different from Example 1 in that there is no three-roll mill stripping, no phenolic resin, and no aluminum nitrate. As a result, there is no carbon nanotube and amorphous carbon coating. Instead, the battery is assembled directly using lithium nickel cobalt manganese oxide raw material. The lithium nickel cobalt manganese oxide raw material is a commercially available product with a tap density of 2.0 g / cm 3 , the particle size (D50) is 4μm.

[0076] Weigh 0.07g of the lithium nickel cobalt manganese oxide raw material, 0.015g of acetylene black (conductive agent), and 0.015g of PVDF (HSV900, binder) of this comparative example, grind them thoroughly, add 0.4mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10h, cut them into discs with a diameter of 12mm and assemble them in a glove box with an argon atmosphere. Use metal lithium sheet as the counter electrode, 1M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble a CR2032 type button lithium battery. At 25°C, under 1C conditions, the voltage window is 2.0-4.3V. The battery material assembled with the lithium nickel cobalt manganese oxide raw material positive electrode material is subjected to constant current charge and discharge test. The discharge capacity after 200 cycles under 1C conditions is 101.5mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 75%, the initial ohmic internal resistance is 18.89Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 40.58Ω.

[0077] Comparative Example 2: This preparation method differs from Example 1 in that no flake graphite is exfoliated on a three-roll mill, but phenolic resin is present and aluminum nitrate is absent. After heat treatment, an amorphous carbon coating is present, but no carbon nanotubes or graphene-like nanosheets are present. Instead, only amorphous carbon-coated lithium nickel cobalt manganese oxide is formed. The specific preparation steps are as follows:

[0078] The preparation method of the amorphous carbon-coated nickel cobalt manganese oxide battery positive electrode material in this comparative example uses nickel cobalt manganese oxide as a raw material and phenolic resin as a coating carbon raw material. The nickel cobalt manganese oxide raw material is a commercially available product with a tap density of 2.0 g / cm 3 , the particle size (D50) is 4 μm; the specific steps are as follows:

[0079] Step 1, adding phenolic resin to lithium nickel cobalt manganese oxide and stirring and mixing for 5 minutes to obtain a mixture A, wherein the amount of the phenolic resin added accounts for 6 wt% of the mass fraction of the mixture A;

[0080] Step 2: Mixture A was further fully mixed by a three-roll differential speed mill, and the mixing cycle was repeated three times, with the gap between N3 and N2 set to 4 μm, and the gap between N2 and N1 set to 2 μm, and mixture B was collected from the discharge roller;

[0081] Step 3, placing the mixture B in a freeze dryer and freeze-drying it under vacuum at -45°C to obtain a mixture C;

[0082] Step 4: Place the freeze-dried mixture C in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1The temperature was raised to 750 °C at a rate of 100 °C, kept at that temperature for 4 h, and then naturally cooled to room temperature to obtain an amorphous carbon-coated nickel cobalt manganese oxide battery positive electrode material.

[0083] Weigh 0.07 g of the amorphous carbon-coated nickel cobalt manganese oxide battery positive electrode material prepared in this comparative example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 hours, cut them into discs with a diameter of 12 mm and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with amorphous carbon-coated nickel cobalt manganese oxide cathode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 130.5mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 82%, the initial ohmic internal resistance is 15.07Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 33.80Ω.

[0084] Comparative Example 3: This preparation method differs from Example 1 in that the flake graphite is exfoliated on a three-roll mill, but the phenolic resin is completely washed off at the end. Furthermore, no aluminum nitrate is present, and no heat treatment is required. Therefore, no carbon nanotubes or amorphous carbon coating is present. Instead, only graphene-like nanosheet composite lithium nickel cobalt manganese oxide is formed. The specific preparation steps are as follows:

[0085] The preparation method of the graphene-like composite nickel cobalt manganese oxide battery positive electrode material in this comparative example uses nickel cobalt manganese oxide as a raw material, flake graphite as an auxiliary material, and phenolic resin as a grinding medium. The nickel cobalt manganese oxide raw material is a commercially available product with a tap density of 2.0 g / 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 specific steps are as follows:

[0086] Step 1, adding 3.5 wt% of flake graphite to 96.5 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0087] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, a mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0088] Step 3: Remove the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 15 times, and finally centrifuge to obtain substance C;

[0089] Step 4: adding substance C to lithium nickel cobalt manganese oxide and stirring for 5 minutes to obtain a mixture D, wherein the amount of substance C added accounts for 6 wt% of the mass fraction of the mixture D;

[0090] Step 5: Mixture D is further fully exfoliated and mixed by a three-roll differential speed mill, and the exfoliation cycle is repeated three times, with the gap between N3 and N2 set to 4 μm and the gap between N2 and N1 set to 2 μm. Mixture E is collected from the discharge roller;

[0091] Step 6: Place the mixture E in a freeze dryer and freeze-dry it under vacuum at -45°C to obtain a mixture F;

[0092] Step 7: Place the freeze-dried mixture F in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750 °C at a rate of 100 °C, kept at that temperature for 4 h, and then naturally cooled to room temperature to obtain a graphene-like composite nickel cobalt manganese oxide lithium cathode material for batteries.

[0093] Weigh 0.07g of the graphene-like composite nickel cobalt manganese oxide positive electrode material prepared in this comparative example, 0.015g of acetylene black (conductive agent), and 0.015g of PVDF (HSV900, binder). After thorough grinding, add 0.4mL of NMP to disperse and mix, and then evenly coat on aluminum foil. After vacuum drying at 120°C for 10h, cut into discs with a diameter of 12mm and assemble in an argon atmosphere glove box. Use metal lithium sheet as the counter electrode, 1M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, under 1C conditions, the voltage window is 2.0-4.3V. The battery assembled with the graphene-like composite nickel cobalt manganese oxide positive electrode material is subjected to constant current charge and discharge test. The discharge capacity after 200 cycles under 1C conditions is 148.0mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 85%, the initial ohmic internal resistance is 11.35Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 24.48Ω.

[0094] Comparative Example 4: This preparation method differs from Example 1 in that no flake graphite is exfoliated on a three-roll mill, phenolic resin and aluminum nitrate are present, and heat treatment is required, resulting in the presence of carbon nanotubes and amorphous carbon coating, thereby forming carbon nanotube-amorphous carbon-coated aluminum-doped lithium nickel cobalt manganese oxide. The specific preparation steps are as follows:

[0095] The preparation method of the carbon nanotube amorphous carbon coated aluminum doped nickel cobalt manganese oxide battery positive electrode material in this comparative example uses nickel cobalt manganese oxide as raw material, phenolic resin as grinding medium and coated carbon raw material, aluminum nitrate as catalyst and dopant, which is a commercially available product with a tap density of 2.0 g / cm 3 , the particle size (D50) is 4 μm; the specific steps are as follows:

[0096] Step 1: Add phenolic resin to lithium nickel cobalt manganese oxide and stir and mix for 8 minutes to obtain mixture A, wherein the amount of phenolic resin added accounts for 6wt% of the mass fraction of mixture A. Then, 0.05wt% of aluminum nitrate raw material is dissolved in alcohol and added to mixture A to obtain mixture B.

[0097] Step 2: Mixture B was further fully mixed by a three-roll differential speed mill, and the mixing was circulated for 3 times, with the gap between N3 and N2 set to 4 μm, and the gap between N2 and N1 set to 2 μm, and mixture C was collected from the discharge roller;

[0098] Step 3, placing the mixture C in a freeze dryer and freeze-drying it under vacuum at -45°C to obtain a mixture D;

[0099] Step 4: Place the freeze-dried mixture D in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750°C at a rate of 1000 ℃, kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt lithium manganese oxide.

[0100] Weigh 0.07 g of the carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide positive electrode material prepared in this comparative example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 hours, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with carbon nanotube amorphous carbon coated aluminum-doped nickel cobalt manganese oxide cathode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 168.4mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 88%, the initial ohmic internal resistance is 6.19Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 11.86Ω.

[0101] Comparative Example 5: This preparation method differs from Example 1 in that the drying method used is oven drying rather than freeze drying, and the graphene-like carbon nanotube amorphous carbon-coated aluminum-doped lithium nickel cobalt manganese oxide formed by oven drying. The specific preparation steps are as follows:

[0102] The preparation method of the graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material in this comparative example uses nickel cobalt manganese oxide as a raw material, flake graphite as an auxiliary material, phenolic resin as a grinding medium and a coated carbon raw material, and aluminum nitrate as a catalyst and a dopant. The lithium nickel cobalt manganese oxide raw material is a commercially available product with a tap density of 2.0 g / 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 specific steps are as follows:

[0103] Step 1, adding 3.5 wt% of flake graphite to 96.5 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0104] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, a mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0105] Step 3: Remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 4, and finally centrifuge to obtain substance C;

[0106] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.05 wt% of aluminum nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0107] Step 5, adding mixture D to lithium nickel cobalt manganese oxide and stirring for 5 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 6 wt% of the mass fraction of mixture E;

[0108] Step 6: The mixture E is further fully stripped and mixed by a three-roll differential speed mill, and the stripping cycle is repeated three times, with the gap between N3 and N2 set to 4 μm, and the gap between N2 and N1 set to 2 μm, and the mixture F is collected from the discharge roller;

[0109] Step 7: Place the mixture F in an oven and dry it at 50° C. to obtain a mixture G;

[0110] Step 8: Place the dried mixture G in a tube furnace and heat-treat it under argon gas, starting from room temperature at 5°C / min. -1 The temperature was raised to 750°C at a rate of 1000 ℃, kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide.

[0111] Weigh 0.07 g of the graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide positive electrode material prepared in this comparative example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 hours, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like carbon nanotube amorphous carbon coated with aluminum-doped nickel cobalt manganese oxide positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 182.8mAh g -1 , the capacity retention rate after 200 cycles under 1C conditions is 90%, the initial ohmic internal resistance is 3.46Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 6.82Ω.

[0112] Comparative Example 6: This preparation method differs from Example 1 in that the phenolic resin is washed four times, while this comparative example washes once. This is to achieve a different carbon coating thickness during subsequent heat treatment. The specific preparation steps are as follows:

[0113] The preparation method of the graphene-like nanosheet carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material in this comparative example uses nickel cobalt manganese oxide as a raw material, flake graphite as an auxiliary material, phenolic resin as a grinding medium and a coated carbon raw material, and aluminum nitrate as a catalyst and a dopant. The lithium nickel cobalt manganese oxide raw material is a commercially available product with a tap density of 2.0 g / cm 3 , the particle size (D50) is 4 μm; the length and width of the flake graphite raw material is 150 μm, and the thickness is 12 μm. The specific steps are as follows:

[0114] Step 1, adding 3.5 wt% of flake graphite to 96.5 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0115] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, the mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0116] Step 3: remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube for centrifugation and remove impurities, repeat this step to control the number of alcohol washing times to 1, and finally centrifuge to obtain substance C;

[0117] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.05 wt% of aluminum nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0118] Step 5, adding mixture D to lithium nickel cobalt manganese oxide and stirring for 5 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 6 wt% of the mass fraction of mixture E;

[0119] Step 6: The mixture E is further fully stripped and mixed by a three-roll differential speed mill, and the stripping cycle is repeated three times, with the gap between N3 and N2 set to 4 μm, and the gap between N2 and N1 set to 2 μm, and the mixture F is collected from the discharge roller;

[0120] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -45°C to obtain a mixture G;

[0121] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750°C at a rate of 100°C, kept warm for 4 hours, and then naturally cooled to room temperature to obtain graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide battery positive electrode material.

[0122] Weigh 0.07 g of the graphene-like carbon nanotube amorphous carbon-coated aluminum-doped nickel cobalt manganese oxide positive electrode material prepared in this comparative example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 hours, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like carbon nanotube amorphous carbon coated with aluminum-doped nickel cobalt manganese oxide positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 155.2mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 86%, the initial ohmic internal resistance is 7.78Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 13.75Ω.

[0123] Table 1 below shows a performance comparison of Examples 1-3 and Comparative Examples 1-6.

[0124] Table 1 Performance comparison of Examples 1-3 and Comparative Examples 1-6

[0125]

[0126]

[0127] Examples 4-6 use lithium iron phosphate as a raw material and nickel nitrate as a catalyst and a dopant. Comparative Examples 7-12 are comparative examples of Examples 4-6.

[0128] Example 4, using lithium iron phosphate as raw material, flake graphite as auxiliary material, phenolic resin as grinding medium and coated carbon raw material, nickel nitrate as catalyst and dopant, the bulk density of the lithium iron phosphate is 0.8g / cm 3 , the median diameter is 2 μm, the length and width of the flake graphite raw material is 150 μm, and the thickness is 12 μm, which specifically includes the following steps:

[0129] Step 1, adding 4 wt% of flake graphite to 96 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0130] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, the mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0131] Step 3: Remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 4, and finally centrifuge to obtain substance C;

[0132] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.05 wt% of nickel nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0133] Step 5, adding mixture D to lithium iron phosphate and stirring for 8 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 6 wt% of the mass fraction of mixture E;

[0134] Step 6: The mixture E was further fully stripped and mixed by a three-roll differential speed mill, and the stripping cycle was repeated three times, with the gap between N3 and N2 set to 1.5 μm, and the gap between N2 and N1 set to 0.5 μm, and the mixture F was collected from the discharge roller;

[0135] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -45°C to obtain a mixture G;

[0136] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750°C at a rate of 100°C, kept warm for 4 hours, and then naturally cooled to room temperature to obtain a graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery positive electrode material.

[0137] Weigh 0.07 g of the graphene-like nanosheet carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate positive electrode material prepared in this example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 h, cut them into discs with a diameter of 12 mm and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like nanosheets, carbon nanotubes, amorphous carbon coated with nickel-doped lithium iron phosphate positive electrode materials was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 154.4mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 93%, the initial ohmic internal resistance is 4.25Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 6.60Ω.

[0138] Example 5, using lithium iron phosphate as raw material, expanded graphite as auxiliary material, epoxy resin as grinding medium and coated carbon raw material, nickel nitrate as catalyst and dopant, the bulk density of the lithium iron phosphate is 0.6g / cm 3 , the median 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 specific steps include:

[0139] Step 1, adding 2 wt% of expanded graphite to 98 wt% of epoxy resin, and mixing them in a 40° C. water bath by stirring for 10 minutes to obtain a mixture A;

[0140] Step 2: The mixture A obtained in step 1 is peeled off by a three-roll differential speed grinder. After 15 cycles of peeling, a mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 200 μm, and the gap between N2 and N1 is 80 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 40 μm, and the gap between N2 and N1 is 20 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 10 μm, and the gap between N2 and N1 is 5 μm; during the 13th to 15th cycles of peeling, the gap between N3 and N2 is 3 μm, and the gap between N2 and N1 is 1 μm;

[0141] Step 3: remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 3 times, and finally centrifuge to obtain substance C;

[0142] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.2 wt% of nickel nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 10 minutes to obtain a mixture D;

[0143] Step 5, adding mixture D to lithium iron phosphate and stirring for 5 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 8 wt% of the mass fraction of mixture E;

[0144] Step 6: The mixture E was further fully exfoliated and mixed by a three-roll differential speed mill, and the exfoliation and mixing were repeated twice, with the gap between N3 and N2 set to 1.5 μm, and the gap between N2 and N1 set to 0.5 μm, and the mixture F was collected from the discharge roller;

[0145] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -40°C to obtain a mixture G;

[0146] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 3°C / min -1 The temperature was raised to 650°C at a rate of 100°C, kept warm for 5 hours, and then naturally cooled to room temperature to obtain a graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery positive electrode material.

[0147] Weigh 0.07 g of the graphene-like nanosheet carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate positive electrode material prepared in this example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 h, cut them into discs with a diameter of 12 mm and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like nanosheets, carbon nanotubes, amorphous carbon coated with nickel-doped lithium iron phosphate positive electrode materials was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 138.2mAh g -1The capacity retention rate after 200 cycles under 1C conditions is 88%, the initial ohmic internal resistance is 6.63Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 11.24Ω.

[0148] Example 6, using lithium iron phosphate as raw material, flake graphite as auxiliary material, polyethylene resin as grinding medium and coated carbon raw material, nickel nitrate as catalyst and dopant, the bulk density of the lithium iron phosphate is 0.5g / cm 3 , the median diameter is 4.5 μm, the length and width of the flake graphite raw material is 200 μm, and the thickness is 20 μm, which specifically includes the following steps:

[0149] Step 1, adding 5 wt% of flake graphite to 95 wt% of polyethylene resin, and stirring the mixture in a 50° C. water bath for 15 minutes to obtain a mixture A;

[0150] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 15 cycles of peeling, a mixture B is collected from the discharge roller; the speed ratio of the three rollers of the three-roll differential speed grinder is feed roller N3: center roller N2: discharge roller N1 is 1:3:9, and during the 1st to 4th cycle peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycle peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycle peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 15th cycle peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0151] Step 3: Remove part of the resin by dissolving with alcohol, add 50 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube for centrifugation and remove impurities, repeat this step to control the number of alcohol washing times to 6, and finally centrifuge to obtain substance C;

[0152] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.05 wt% of nickel nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0153] Step 5, adding mixture D to lithium iron phosphate and stirring for 9 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 10 wt% of the mass fraction of mixture E;

[0154] Step 6: The mixture E was further fully stripped and mixed by a three-roll differential speed mill, and the stripping cycle was repeated three times, with the gap between N3 and N2 set to 1.5 μm, and the gap between N2 and N1 set to 0.5 μm, and the mixture F was collected from the discharge roller;

[0155] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -40°C to obtain a mixture G;

[0156] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 8°C min -1 The temperature was raised to 700°C at a rate of 1000 ℃, kept warm for 2 hours, and then naturally cooled to room temperature to obtain a graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery positive electrode material.

[0157] Weigh 0.07 g of the graphene-like nanosheet carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery positive electrode material prepared in this example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 h, cut them into discs with a diameter of 12 mm, and assemble them in an argon atmosphere glove box. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like nanosheets, carbon nanotubes, amorphous carbon coated with nickel-doped lithium iron phosphate positive electrode materials was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 132.7mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 85%, the initial ohmic internal resistance is 8.72Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 15.14Ω.

[0158] Comparative Example 7: This preparation method is different from Example 1 in that there is no three-roll mill peeling, no phenolic resin, and no nickel nitrate. As a result, there is no carbon nanotube and amorphous carbon coating. Instead, the battery is directly assembled using lithium iron phosphate raw materials. The bulk density of the lithium iron phosphate raw materials is 0.8 g / cm 3 , the median diameter is 2um.

[0159] Weigh 0.07g of the lithium iron phosphate raw material, 0.015g of acetylene black (conductive agent), and 0.015g of PVDF (HSV900, binder) of this comparative example, grind them thoroughly, add 0.4mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10h, cut them into discs with a diameter of 12mm and assemble them in a glove box with an argon atmosphere. Use metal lithium sheet as the counter electrode, 1M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble a CR2032 type button lithium battery. At 25°C, under 1C conditions, the voltage window is 2.0-4.3V. The battery material assembled with the lithium iron phosphate raw material positive electrode material is subjected to constant current charge and discharge test. The discharge capacity after 200 cycles under 1C conditions is 82mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 70%, the initial ohmic internal resistance is 20.89Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 50.78Ω.

[0160] Comparative Example 8: This preparation method differs from Example 1 in that no flake graphite is exfoliated on a three-roll mill, but phenolic resin is present and nickel nitrate is absent. After heat treatment, an amorphous carbon coating is present, but no carbon nanotubes or graphene-like nanosheets are present. Instead, only amorphous carbon-coated lithium iron phosphate is formed. The specific preparation steps are as follows:

[0161] The preparation method of the amorphous carbon-coated lithium iron phosphate battery positive electrode material in this comparative example uses lithium iron phosphate as raw material and phenolic resin as the coated carbon raw material. The lithium iron phosphate raw material has a bulk density of 0.8g / cm 3 , the median diameter is 2um; the specific steps are as follows:

[0162] Step 1, adding phenolic resin to lithium iron phosphate and stirring and mixing for 8 minutes to obtain a mixture A, wherein the amount of the phenolic resin added accounts for 6 wt% of the mass fraction of the mixture A;

[0163] Step 2: Mixture A was further fully mixed by a three-roll differential speed mill, and the mixture was circulated and mixed three times, with the gap between N3 and N2 set to 1.5 μm, and the gap between N2 and N1 set to 0.5 μm, and mixture B was collected from the discharge roller;

[0164] Step 3, placing the mixture B in a freeze dryer and freeze-drying it under vacuum at -45°C to obtain a mixture C;

[0165] Step 4: Place the freeze-dried mixture C in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1The temperature was raised to 750 °C at a rate of 100 °C, kept at that temperature for 4 h, and then naturally cooled to room temperature to obtain an amorphous carbon-coated lithium iron phosphate battery positive electrode material.

[0166] Weigh 0.07g of the amorphous carbon-coated lithium iron phosphate battery positive electrode material prepared in this comparative example, 0.015g of acetylene black (conductive agent), and 0.015g of PVDF (HSV900, binder), grind them thoroughly, add 0.4mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10h, cut them into discs with a diameter of 12mm and assemble them in a glove box with an argon atmosphere. Use metal lithium sheet as the counter electrode, 1M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, under 1C conditions, the voltage window is 2.0-4.3V. The battery assembled with the amorphous carbon-coated lithium iron phosphate positive electrode material is subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions is 98.2mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 78%, the initial ohmic internal resistance is 17.42Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 38.56Ω.

[0167] Comparative Example 9: This preparation method differs from Example 1 in that the flake graphite is exfoliated on a three-roll mill, but the phenolic resin is completely washed off at the end. Furthermore, no nickel nitrate is present, and no heat treatment is required. Therefore, no carbon nanotubes or amorphous carbon coating is present, resulting in only graphene-like nanosheet composite lithium iron phosphate. The specific preparation steps are as follows:

[0168] The preparation method of the graphene-like composite lithium iron phosphate battery positive electrode material of this comparative example uses lithium iron phosphate as raw material, flake graphite as auxiliary material, and phenolic resin as grinding medium. The lithium iron phosphate raw material has a bulk density of 0.8g / cm 3 , the median diameter is 2um; the flake graphite raw material has a length and width of 150μm and a thickness of 12μm; the specific steps are as follows:

[0169] Step 1, adding 4 wt% of flake graphite to 96 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0170] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, a mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0171] Step 3: Remove the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 15 times, and finally centrifuge to obtain substance C;

[0172] Step 4: adding substance C to lithium iron phosphate and stirring for 8 minutes to obtain a mixture D, wherein the amount of substance C added accounts for 6 wt% of the mass fraction of the mixture D;

[0173] Step 5: Mixture D was further fully exfoliated and mixed by a three-roll differential speed mill, and the exfoliation cycle was repeated three times, with the gap between N3 and N2 set to 1.5 μm and the gap between N2 and N1 set to 0.5 μm. Mixture E was collected from the discharge roller;

[0174] Step 6: Place the mixture E in a freeze dryer and freeze-dry it under vacuum at -45°C to obtain a mixture F;

[0175] Step 7: Place the freeze-dried mixture F in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750°C at a rate of 100°C, kept warm for 4 hours, and then naturally cooled to room temperature to obtain a graphene-like composite lithium iron phosphate battery positive electrode material.

[0176] Weigh 0.07g of the graphene-like composite lithium iron phosphate positive electrode material prepared in this comparative example, 0.015g of acetylene black (conductive agent), and 0.015g of PVDF (HSV900, binder), grind them thoroughly, add 0.4mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10h, cut them into discs with a diameter of 12mm and assemble them in a glove box with an argon atmosphere. Use metal lithium sheet as the counter electrode, 1M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble a CR2032 type button lithium battery. At 25°C, under 1C conditions, the voltage window is 2.0-4.3V. The battery assembled with the graphene-like composite lithium iron phosphate positive electrode material is subjected to constant current charge and discharge test. The discharge capacity after 200 cycles under 1C conditions is 112.5mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 82%, the initial internal resistance is 15.33Ω, and the internal resistance after 200 cycles under 1C conditions is 30.62Ω.

[0177] Comparative Example 10: This preparation method differs from Example 1 in that no flake graphite is exfoliated on a three-roll mill, phenolic resin and nickel nitrate are present, and heat treatment is required, resulting in the presence of carbon nanotubes and amorphous carbon coating, thereby forming carbon nanotubes and amorphous carbon-coated nickel-doped lithium iron phosphate. The specific preparation steps are as follows:

[0178] The preparation method of the carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery positive electrode material in this comparative example uses lithium iron phosphate as a raw material, phenolic resin as a grinding medium and a coated carbon raw material, nickel nitrate as a catalyst and a dopant, and a lithium iron phosphate raw material with a bulk density of 0.8 g / cm3 and a median diameter of 2 μm. The specific steps are as follows:

[0179] Step 1: Add phenolic resin to lithium iron phosphate and stir and mix for 8 minutes to obtain mixture A, wherein the amount of phenolic resin added accounts for 6wt% of the mass fraction of mixture A. Then, 0.05wt% of nickel nitrate raw material is dissolved in alcohol and added to mixture A to obtain mixture B.

[0180] Step 2: Mixture B was further fully mixed by a three-roll differential speed mill, and the mixing was circulated for 3 times, with the gap between N3 and N2 set to 1.5 μm, and the gap between N2 and N1 set to 0.5 μm, and mixture C was collected from the discharge roller;

[0181] Step 3, placing the mixture C in a freeze dryer and freeze-drying it under vacuum at -45°C to obtain a mixture D;

[0182] Step 4: Place the freeze-dried mixture D in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750°C at a rate of 1000 ℃, kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate.

[0183] Weigh 0.07 g of the carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate positive electrode material prepared in this comparative example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 hours, cut them into discs with a diameter of 12 mm and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 118.7mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 83%, the initial ohmic internal resistance is 12.57Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 22.15Ω.

[0184] Comparative Example 11: This preparation method differs from Example 1 in that the drying method used is oven drying rather than freeze drying, and the graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate formed by oven drying is as follows:

[0185] The preparation method of the graphene-like carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate battery positive electrode material in this comparative example uses lithium iron phosphate as raw material, flake graphite as auxiliary material, phenolic resin as grinding medium and coated carbon raw material, nickel nitrate as catalyst and dopant, lithium iron phosphate raw material, and bulk density of 0.8g / cm 3 , the median diameter is 2um; the flake graphite raw material has a length and width of 150μm and a thickness of 12μm; the specific steps are as follows:

[0186] Step 1, adding 4 wt% of flake graphite to 96 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0187] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, the mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0188] Step 3: remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat this step to control the number of alcohol washing times to 3 times, and finally centrifuge to obtain substance C;

[0189] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.05 wt% of nickel nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0190] Step 5, adding mixture D to lithium iron phosphate and stirring for 8 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 6 wt% of the mass fraction of mixture E;

[0191] Step 6: The mixture E was further fully stripped and mixed by a three-roll differential speed mill, and the stripping cycle was repeated three times, with the gap between N3 and N2 set to 1.5 μm, and the gap between N2 and N1 set to 0.5 μm, and the mixture F was collected from the discharge roller;

[0192] Step 7: Place the mixture F in an oven and dry it at 50° C. to obtain a mixture G;

[0193] Step 8: Place the dried mixture G in a tube furnace and heat-treat it under argon gas, starting from room temperature at 5°C / min. -1 The temperature was raised to 750°C at a rate of 1000 ℃, kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate.

[0194] Weigh 0.07 g of the graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate positive electrode material prepared in this comparative example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 hours, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 141.0mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 86%, the initial ohmic internal resistance is 6.16Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 10.28Ω.

[0195] Comparative Example 12: This preparation method differs from Example 1 in that the phenolic resin is washed four times, while this comparative example washes once. This is to achieve a different carbon coating thickness during subsequent heat treatment. The specific preparation steps are as follows:

[0196] The preparation method of the graphene-like nanosheet carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate battery positive electrode material in this comparative example uses lithium iron phosphate as raw material, flake graphite as auxiliary material, phenolic resin as grinding medium and coated carbon raw material, nickel nitrate as catalyst and dopant, lithium iron phosphate raw material, and bulk density of 0.8g / cm 3 , the median diameter is 2um; the flake graphite raw material has a length and width of 150μm and a thickness of 12μm; the specific steps are as follows:

[0197] Step 1, adding 4 wt% of flake graphite to 96 wt% of phenolic resin, and mixing the mixture in a 50° C. water bath by stirring for 15 minutes to obtain a mixture A;

[0198] Step 2, the mixture A obtained in step 1 is peeled by a three-roll differential speed grinder, and after 16 cycles of peeling, the mixture B is collected from the discharge roller; during the 1st to 4th cycles of peeling, the gap between N3 and N2 is 100 μm, and the gap between N2 and N1 is 50 μm; during the 5th to 8th cycles of peeling, the gap between N3 and N2 is 25 μm, and the gap between N2 and N1 is 12 μm; during the 9th to 12th cycles of peeling, the gap between N3 and N2 is 6 μm, and the gap between N2 and N1 is 3 μm; during the 13th to 16th cycles of peeling, the gap between N3 and N2 is 1.5 μm, and the gap between N2 and N1 is 0.5 μm;

[0199] Step 3: remove part of the resin by dissolving it with alcohol, add 100 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube for centrifugation and remove impurities, repeat this step to control the number of alcohol washing times to 1, and finally centrifuge to obtain substance C;

[0200] Step 4: Using the impurity liquid removed after the last alcohol-washed resin centrifugation in Step 3 as a solvent, an equal volume of the impurity liquid to the substance C obtained by centrifugation was measured, 0.05 wt% of nickel nitrate raw material was dissolved in the impurity liquid, and then mixed with the substance C and stirred for 5 minutes to obtain a mixture D;

[0201] Step 5, adding mixture D to lithium iron phosphate and stirring for 8 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 6 wt% of the mass fraction of mixture E;

[0202] Step 6: The mixture E was further fully stripped and mixed by a three-roll differential speed mill, and the stripping cycle was repeated three times, with the gap between N3 and N2 set to 1.5 μm, and the gap between N2 and N1 set to 0.5 μm, and the mixture F was collected from the discharge roller;

[0203] Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at -45°C to obtain a mixture G;

[0204] Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment, starting from room temperature at 5°C / min -1 The temperature was raised to 750°C at a rate of 100°C, kept warm for 4 hours, and then naturally cooled to room temperature to obtain a graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate battery positive electrode material.

[0205] Weigh 0.07 g of the graphene-like carbon nanotube amorphous carbon-coated nickel-doped lithium iron phosphate positive electrode material prepared in this comparative example, 0.015 g of acetylene black (conductive agent), and 0.015 g of PVDF (HSV900, binder), grind them thoroughly, add 0.4 mL of NMP to disperse and mix, and then evenly coat them on aluminum foil. After vacuum drying at 120°C for 10 hours, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use metallic lithium sheet as the counter electrode, 1 M LiPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and Celegard2400 as the diaphragm to assemble into a CR2032 type button lithium battery. At 25°C, the voltage window was 2.0-4.3V under 1C conditions. The battery assembled with graphene-like carbon nanotube amorphous carbon coated nickel-doped lithium iron phosphate positive electrode material was subjected to constant current charge and discharge tests. The discharge capacity after 200 cycles under 1C conditions was 125.2mAh g -1 The capacity retention rate after 200 cycles under 1C conditions is 84%, the initial ohmic internal resistance is 10.14Ω, and the ohmic internal resistance after 200 cycles under 1C conditions is 19.68Ω.

[0206] As shown in Table 2 below, the performance comparison of Examples 4-6 and Comparative Examples 7-12 is shown.

[0207] Table 2 Performance comparison of Examples 4-6 and Comparative Examples 7-12

[0208]

[0209]

[0210] In summary, the present invention adopts a three-roll mill grinding and exfoliation technology to overcome the interlayer van der Waals force by utilizing the shear force generated by the differential speed of the three rollers and the force formed by the high-viscosity resin and the flake graphite / expanded graphite, thereby exfoliating the layered material with a thickness of micrometers to prepare a large number of graphene-like nanosheets. After exfoliation, the interlayer spacing of the crystals becomes larger. The graphene-like nanosheets prepared by this method are more efficient and lower cost than graphene prepared by adding traditional techniques.

[0211] After graphite is exfoliated by three rollers at differential speeds, it forms graphene-like nanosheets, which are then mixed with lithium nickel-cobalt-manganese oxide or lithium iron phosphate on the same device. After two or three cycles of exfoliation, the gap between each roller is adjusted to 1-5 μm. This not only grinds and disperses the lithium nickel-cobalt-manganese oxide, forcing it to be refined, but also further strengthens the contact and coating between the graphene-like nanosheets and the lithium nickel-cobalt-manganese oxide or lithium iron phosphate. Due to the viscosity of the resin, conventional drying techniques tend to cause the mixture F to form a paste-like agglomerate. The present invention utilizes freeze-drying technology to produce a powder with excellent dispersion.

[0212] The present invention uses aluminum nitrate or nickel nitrate as a catalyst and dopant, and the aluminum nitrate or nickel nitrate solution is evenly mixed with the resin. During the subsequent heat treatment process at 500-850°C, the aluminum nitrate catalyzes the resin to generate carbon nanotubes in situ. This method has better dispersibility than externally added carbon nanotubes and saves costs. Its special tubular structure and intertwined network structure can accelerate the transmission rate of Li+ ions. At the same time, during the subsequent heat treatment process, aluminum ions of the aluminum nitrate will be doped into lithium nickel cobalt manganese oxide or lithium iron phosphate, which can reduce the degree of lithium-nickel mixing caused by nickel ions occupying lithium sites, thereby improving the electrochemical performance of the positive electrode material.

[0213] The present invention prepares aluminum-doped lithium nickel cobalt manganese oxide or nickel-doped lithium iron phosphate, which is formed by exfoliating micron-sized graphite in a resin through three-roll grinding, forming graphene-like nanosheets, catalyzing part of the resin to form carbon nanotubes through heat treatment, and pyrolyzing part of the resin to form amorphous carbon coating. The three modification technologies of Al or Ni doping, composite conductive agent (two-dimensional graphene-like nanosheets, one-dimensional carbon nanotubes), and amorphous carbon coating are integrated to prepare a low-cost, high-performance lithium-ion battery positive electrode material. The two-dimensional graphene-like nanosheets obtained by three-roll differential grinding and peeling not only have a larger crystal interlayer spacing, which can allow more foreign reactants to be embedded in the reaction, but also have a significantly increased specific surface area compared to the original graphite, which can greatly improve its conductivity; the interpenetration of one-dimensional carbon nanotubes and the coating of zero-dimensional amorphous carbon on lithium nickel cobalt manganese oxide or lithium iron phosphate, the three carbon forms form a three-dimensional network structure that is conducive to further improving its electronic conduction and ion transport, and reducing its polarization and impedance during charging and discharging. At the same time, the graphene-like nanosheets, carbon nanotubes, and amorphous carbon form a "protective barrier" for lithium nickel cobalt manganese oxide or lithium iron phosphate, inhibiting the side reaction of the electrolyte on lithium nickel cobalt manganese oxide or lithium iron phosphate, thereby greatly increasing the structural stability and electrical conductivity of lithium nickel cobalt manganese oxide or lithium iron phosphate, and greatly improving the electrochemical performance of lithium nickel cobalt manganese oxide or lithium iron phosphate to meet the needs of new energy vehicles, electric vehicles, large-scale energy storage, starting power supplies and other fields.

[0214] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material, characterized by: The following steps are involved: Step 1, adding 1-5 wt% of graphite auxiliary material to 95-99 wt% of resin, and stirring and mixing in a 40-70° C. water bath for 5-30 minutes to obtain a mixture A; Step 2: The mixture A obtained in step 1 is peeled by a three-roll differential speed grinding machine, and after repeated peeling, the mixture is collected from the discharge roller to obtain a mixture B; Step 3: remove part of the resin by dissolving it with alcohol, add 50-200 vol% alcohol to the mixture B obtained by stripping, stir and ultrasonically assist for 10 minutes, place it in a centrifuge tube, centrifuge and remove impurities, repeat step 3 and continue washing with alcohol, and finally centrifuge to obtain substance C; Step 4: Using the impurity liquid removed after the final alcohol-washed resin centrifugation in Step 3 as a solvent, measuring an equal volume of the impurity liquid to the substance C obtained by centrifugation, dissolving 0.01-0.5 wt % of a nitric acid compound raw material therein, and then mixing and stirring with the substance C for 1-10 minutes to obtain a mixture D; wherein the nitric acid compound raw material is aluminum nitrate or nickel nitrate; Step 5: Adding mixture D to the lithium compound positive electrode material and stirring and mixing for 5-10 minutes to obtain mixture E, wherein the amount of mixture D added accounts for 3-12 wt% of the mass fraction of mixture E; Step 6: The mixture E is further fully peeled and mixed by a three-roll differential speed mill, and after repeated peeling multiple times, the mixture is collected from the discharge roller to obtain a mixture F; Step 7, placing the mixture F in a freeze dryer, and freeze-drying it under vacuum at a temperature of -50°C to -30°C to obtain a mixture G; Step 8: Place the freeze-dried mixture G in a tube furnace under argon for heat treatment at a temperature of 2-10°C / min from room temperature. -1 The temperature is raised to 500-850°C at a rate of 100-200°C, kept at this temperature for 1-5 hours, and then naturally cooled to room temperature to obtain a multi-dimensional and multi-scale carbon-coated lithium-ion battery cathode material; The multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material is a graphene-like nanosheet, a carbon nanotube and an amorphous carbon-coated lithium-ion battery positive electrode material.

2. The method for preparing a multidimensional and multiscale carbon-coated lithium-ion battery positive electrode material according to claim 1, wherein: In step 2, the three-roll differential grinder includes a discharge roller N1, a center roller N2 and a feed roller N3, wherein the speed ratio of the feed roller N3, the center roller N2 and the discharge roller N1 is 1:3:9, and during the cyclic peeling process, the gap between the center roller N2 and the feed roller N3 is always larger than the gap between the discharge roller N1 and the center roller N2, and the number of cyclic peeling times is 15-17 times.

3. The method for preparing the multidimensional and multiscale carbon-coated lithium-ion battery positive electrode material according to claim 2, characterized in that: During the 1st to 4th peeling cycles, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 40 μm and 200 μm.

4. The method for preparing a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material according to claim 2, characterized in that: During the 5th to 8th peeling cycle, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 10 μm and 40 μm.

5. The method for preparing the multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material according to claim 2, characterized in that: During the 9th to 12th peeling cycle, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 2.5 μm and 10 μm.

6. The method for preparing the multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material according to claim 2, characterized in that: After the 13th peeling cycle, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 0.5 μm and 2.5 μm.

7. The method for preparing a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material according to claim 1, characterized in that: In step 5, the lithium compound is lithium nickel cobalt manganese oxide or lithium iron phosphate.

8. The method for preparing a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material according to claim 2, characterized in that: In step 6, the number of cyclic peeling is 2-3 times. After the cyclic peeling is completed, the gap between the center roller N2 and the feed roller N3 and the gap between the discharge roller N1 and the center roller N2 are both between 0.5-5 μm.

9. A multidimensional and multiscale carbon-coated lithium-ion battery cathode material, characterized by: The method for preparing a multi-dimensional and multi-scale carbon-coated lithium-ion battery positive electrode material is used as described in any one of claims 1 to 8.

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