CN119153672B

CN119153672B - A full carbon coated positive electrode material and its preparation method and use

Info

Publication number: CN119153672B
Application number: CN202411649316.3A
Authority: CN
Inventors: 陈勃涛; 王继增; 李庆龙; 赵晶晶; 李文强; 朱武
Original assignee: Tianjin Guoan Mengguli New Material Technology Co ltd
Current assignee: Tianjin Guoan Mengguli New Material Technology Co ltd
Priority date: 2024-11-19
Filing date: 2024-11-19
Publication date: 2025-02-28
Anticipated expiration: 2044-11-19
Also published as: CN119153672A

Abstract

The present invention belongs to the field of battery technology. The present invention provides a full carbon coated positive electrode material and a preparation method and use thereof. The preparation method comprises mixing a positive electrode material, water and a water-soluble polymer under a vacuum negative pressure environment to obtain a gel-like mixture, and then drying and carbonizing to obtain a full carbon coated positive electrode material. The present invention uses a water-soluble polymer as a carbon coating precursor, and completes the full coating of the positive electrode material from the inside to the outside by the water-soluble polymer through a vacuum negative pressure method, so that after carbonization, the electronic conductive network can be fully constructed from the inside to the outside. Compared with the surface carbon coating of traditional small molecule glucose and/or the mixed coating of conductive carbon materials, the water-soluble polymer after high temperature carbonization in the present invention can achieve seamless coating of the positive electrode material, can significantly enhance the conductive performance of the material interface, and solve the problems of poor cycle performance and oxygen precipitation caused by loose coating or microcracks of carbon materials in lithium-rich manganese-based positive electrode materials.

Description

All-carbon coated positive electrode material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of batteries, and relates to an all-carbon coated positive electrode material, and a preparation method and application thereof.

Background

Along with the enhancement of global energy crisis and environmental protection consciousness, new energy automobiles are rapidly developed as one of important means for energy conservation and emission reduction. The popularization of new energy automobiles promotes the innovation of power battery technology, wherein the performance of a positive electrode material serving as a core component of a battery directly influences the energy density, the safety and the service life of the battery.

In recent years, with the rapid expansion of new energy automobile markets and the rapid replacement of traditional fuel vehicles, the automobile markets have increasingly demanded high energy density and high safety long-life battery cathode materials. In this context, lithium-rich manganese-based positive electrode materials have been attracting attention due to their high energy density, environmental friendliness, low cost, and the like.

The lithium-rich manganese-based positive electrode material is a typical layered transition metal oxide that can provide additional capacity by utilizing the redox reaction of lattice oxyanions at high voltages, thereby significantly increasing the energy density of the battery. However, lithium-rich manganese-based cathode materials face the following key problems in commercial applications:

First, under high voltage, the lattice oxygen anions on the surface of the positive electrode material provide high capacity under high voltage, and at the same time, the oxidation-reduction reaction releases oxygen, so that serious gassing problem is caused, and serious threat is caused to the safety of the battery. Thirdly, in the charge and discharge process, the lithium-rich manganese-based positive electrode material can generate volume change, so that serious microcracks are generated on the surface of the material, the microcracks can aggravate the infiltration and corrosion of electrolyte, and the occurrence of interface side reaction is accelerated, thereby reducing the cycle stability of the material.

Currently, there are some effective means in the art to improve the interfacial conductivity of lithium-rich manganese-based cathode materials, such as surface carbon coating (e.g., conventional glucose hydrothermal carbon coating, high Wen Huofa coating, etc.) and/or blend coating of highly conductive carbon materials (e.g., graphene, carbon nanotubes, etc.). The carbon coating modified lithium-rich manganese-based positive electrode material, especially the surface carbon coating can obviously improve conductivity and inhibit oxygen precipitation on the surface of the positive electrode material by reducing contact between the interface of the positive electrode material and electrolyte, thereby becoming one of research hot spot directions of the lithium-rich manganese-based positive electrode material with high cycle stability and high multiplying power. Compared with the carbon-coated lithium-rich polycrystalline cathode material, the lithium-rich polycrystalline cathode material without the carbon material has poor conductivity and poor interface stability, so that the lithium-rich polycrystalline material shows high oxygen release and poor cycle performance, and the practical application of the lithium-rich polycrystalline cathode material is seriously hindered.

However, the conventional means of surface carbon coating, such as hydrothermal carbon coating, requires long-time reaction under high pressure and high temperature conditions, which not only increases the production cost, but also is difficult to realize large-scale industrial production, and because the used carbon source, such as glucose, has smaller molecular weight, the surface coating can only be performed through severe hydrothermal conditions, the factors of reaction temperature, pressure, time and the like need to be precisely controlled, which clearly increases the difficulty of process control, thus being unsuitable for large-scale industrial low-cost production, while the high Wen Huofa coating can avoid the pressure limitation of the hydrothermal reaction, but requires higher temperature, and easily causes uneven surface conductive carbon coating, poor conductive consistency, uneven conductivity, and the mixed coating of graphene, carbon nano tubes and the like can not realize seamless connection of a carbon material and a positive electrode material, compared with the surface carbon coating, has limited conductivity for improving the material, can not effectively inhibit the separation of lattice oxygen at the interface of the positive electrode material, can not inhibit microcracks generated in the material circulation process, and can not prevent the contact and side reaction of the positive electrode material and electrolyte from occurring.

Therefore, there is still a need to develop a new technical solution to solve or improve the problems associated with the development of lithium-rich manganese-based cathode materials, or other cathode materials with microcracks, poor conductivity or unsophisticated carbon coating, in actual service work in a simple and easy manner at low cost, so as to comprehensively improve the electrochemical performance and stability of the cathode materials and promote the development of commercialized processes.

Disclosure of Invention

In view of the problems existing in the prior art, the invention aims to provide an all-carbon coated positive electrode material, a preparation method and application thereof, wherein the preparation method comprises the steps of under vacuum negative pressure environment, and mixing the positive electrode material, water and a water-soluble polymer to obtain a gel mixture, and drying and carbonizing to obtain the full-carbon coated positive electrode material. The invention adopts water-soluble polymer as carbon coating precursor, and completes the full coating of the water-soluble polymer on the anode material from inside to outside by vacuum negative pressure method, thus completing the full construction of the electronic conductive network from inside to outside after carbonization, compared with the traditional surface carbon coating of small molecular glucose and/or the mixed coating of conductive carbon material, the water-soluble polymer carbonized at high temperature can realize seamless coating of the positive electrode material, can obviously enhance the conductivity of a material interface, and solves the problems of poor cycle performance, oxygen precipitation and the like of the lithium-rich manganese-based positive electrode material caused by the untight coating and/or microcracks of the carbon material.

In order to achieve the purpose, the invention adopts the following technical scheme:

In a first aspect, the present invention provides a method for preparing an all-carbon coated cathode material, the method comprising:

And (3) mixing the positive electrode material, water and a water-soluble polymer in a vacuum negative pressure environment to obtain a gelatinous mixture, and sequentially drying and carbonizing the gelatinous mixture to obtain the full-carbon coated positive electrode material.

The invention adopts water-soluble polymer as carbon coating precursor, and completes the full coating of the water-soluble polymer on the positive electrode material from inside to outside by a vacuum negative pressure method, in the process, due to the certain viscosity of the water-soluble polymer, the water-soluble polymer can be adsorbed on the surface of the positive electrode material and can be filled into the positive electrode material by vacuum negative pressure, and gradually cause gelation reaction, thus obtaining gelatinous mixture, and then the gelatinous mixture is dried and carbonized for heat treatment, thus completing the full construction of an electronic conductive network from inside to outside, solving the problems of poor cycle performance, poor conductivity, oxygen precipitation and the like of the positive electrode material caused by the existence or occurrence of untight contact or microcracks of the traditional carbon material and the positive electrode material, and being particularly suitable for improving and improving the electrochemical performance and stability of the lithium-rich manganese-based positive electrode material.

The following technical scheme is a preferred technical scheme of the invention, but is not a limitation of the technical scheme provided by the invention, and the technical purpose and beneficial effects of the invention can be better achieved and realized through the following technical scheme.

As a preferable technical scheme of the invention, the vacuum degree of the vacuum negative pressure environment is-0.01 to-0.13 MPa, such as -0.01MPa、-0.02MPa、-0.025MPa、-0.03MPa、-0.035MPa、-0.04MPa、-0.045MPa、-0.05MPa、-0.055MPa、-0.06MPa、-0.065MPa、-0.07MPa、-0.075MPa、-0.08MPa、-0.085MPa、-0.09MPa、-0.095MPa、-0.1MPa、-0.11MPa、-0.12MPa or-0.13 MPa, etc.

Preferably, the method of achieving the vacuum negative pressure environment comprises suction filtration.

Preferably, the vacuum degree of the vacuum negative pressure environment increases with an increase in D50 particle diameter of the positive electrode material.

Preferably, the degree of vacuum (MPa) of the vacuum negative pressure environment is used as a dependent variable, the D50 particle diameter (μm) of the positive electrode material is used as an independent variable, and the following functional relationship y= -0.0051x-0.0029 is satisfied, and x and y satisfy the calculation relationship of pure numerical values in μm and MPa, respectively.

That is, in the present invention, as the particle diameter of the positive electrode material particles increases, the degree of vacuum of the optimum vacuum negative pressure required tends to increase linearly within a certain range and the relationship.

Preferably, the D50 particle size of the positive electrode material is 2.5 to 10.5 μm, for example, 2.5 μm, 3.5 μm, 4.5 μm, 5.5 μm, 6.5 μm, 7.5 μm, 8.5 μm, 9.5 μm or 10.5 μm, etc.

According to the preferred technical scheme, the positive electrode material comprises a lithium ion battery positive electrode active material and/or a sodium ion battery positive electrode active material, wherein the lithium ion battery positive electrode active material comprises at least one of lithium cobaltate, lithium nickel manganese oxide, ternary positive electrode material, quaternary positive electrode material, lithium iron phosphate, lithium iron manganese phosphate or lithium-rich manganese-based positive electrode material.

The preparation method disclosed by the invention does not need to be specific to a specific lithium-rich manganese-based positive electrode material, and has universality, namely the positive electrode material can be selected to be other series of positive electrode materials with microcracks and poor conductivity, so that the effect of coating all carbon on any positive electrode material from inside to outside is realized, and the electrochemical performance of the material is improved.

Preferably, the lithium-rich manganese-based positive electrode material comprises a polycrystalline or single crystal, including particles of small, medium, and large different sizes.

The invention is not particularly limited to the method for preparing the positive electrode material, and reasonable selection and adjustment should be performed according to the needs and design.

Illustratively, the method for preparing the lithium-rich manganese-based positive electrode material includes mixing a hydroxide precursor of the lithium-rich manganese-based positive electrode material with a lithium source, and sintering to obtain the lithium-rich manganese-based positive electrode material.

Preferably, the lithium source comprises lithium carbonate.

Preferably, the amount of the lithium source and the hydroxide precursor of the lithium-rich manganese-based positive electrode material is controlled to be 1 (1.5-1.6) according to the ratio of the molar amount of the lithium element to the total molar amount of the transition metal element, for example, 1:1.5, 1:1.51, 1:1.52, 1:1.53, 1:1.54, 1:1.55, 1:1.56, 1:1.57, 1:1.58, 1:1.59, or 1:1.6, etc.

Preferably, the sintering is performed under an oxygen-containing atmosphere comprising air.

Preferably, the sintering temperature is 800-1100 ℃, such as 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃ or the like, and the sintering time is 12-14 h, such as 12h, 12.5h, 13h, 13.5h, 14h or the like.

Preferably, the chemical formula of the hydroxide precursor of the lithium-rich manganese-based positive electrode material includes Mn _xCo_yNi_1-x-y(OH)₂ or Mn _xCo_yNi_1-x-yCO₃, wherein 0< x.ltoreq.1, for example, x may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc., 0.ltoreq.y <1, for example, y may be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc., x+y.ltoreq.1, for example x+y may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc.

Preferably, the D50 particle size of the hydroxide precursor of the lithium-rich manganese-based positive electrode material is 2.5-10.5 μm, for example, 2.5 μm, 3.5 μm, 4.5 μm, 5.5 μm, 6.5 μm, 7.5 μm, 8.5 μm, 9.5 μm or 10.5 μm, etc., and the specific surface area BET value is 10-40 m ²/g, for example, 10m ²/g、15m²/g、20m²/g、25m²/g、30m²/g、35m²/g or 40m ²/g, etc.

Preferably, the method for preparing the hydroxide precursor of the lithium-rich manganese-based positive electrode material comprises the steps of preparing a mixed metal salt solution of transition metal, mixing the mixed metal salt solution with a precipitator and a complexing agent, carrying out precipitation reaction, and then carrying out aging, solid-liquid separation, drying and sieving to obtain the hydroxide precursor of the lithium-rich manganese-based positive electrode material.

Preferably, the total metal ion concentration of the transition metal in the mixed metal salt solution of the transition metal is 120-140 g/L, for example 120g/L, 125g/L, 130g/L, 135g/L or 140g/L, etc.

Preferably, the precipitant comprises an alkaline solution, and the concentration of the alkaline solution is 8-12 mol/L, for example 8mol/L, 8.5mol/L, 9mol/L, 9.5mol/L, 10mol/L, 10.5mol/L, 11mol/L, 11.5mol/L or 12mol/L, etc.

Preferably, the complexing agent comprises ammonia at a concentration of 8wt% to 25wt%, such as 8wt%, 10wt%, 13wt%, 15wt%, 18wt%, 20wt%, 23wt% or 25wt%, etc.

Preferably, the precipitation reaction is carried out under an inert atmosphere.

Preferably, the precipitation reaction comprises a nucleation reaction followed by a growth reaction.

Preferably, the temperature of the precipitation reaction is 40-70 ℃, for example 40 ℃,45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃ or the like.

Preferably, the pH of the nucleation reaction is 10 to 12, for example 10, 10.2, 10.4, 10.6, 10.8, 11, 11.2, 11.4, 11.6, 11.8 or 12, etc.

Preferably, the time of the nucleation reaction is 1-2 hours, for example 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2 hours, etc.

Preferably, the pH of the growth reaction is 9.5 to 12, for example 9.5, 9.8, 10, 10.3, 10.5, 10.8, 11, 11.3, 11.5, 11.8 or 12, etc.

Preferably, the time of the growth reaction is 30-40 h, for example 30h, 32h, 34h, 36h, 38h or 40h, etc.

Preferably, the drying temperature is 100-120 ℃, such as 100 ℃, 105 ℃, 110 ℃, 115 ℃,120 ℃, or the like, and the drying time is 8-16 hours, such as 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, or the like.

As a preferred embodiment of the present invention, the water-soluble polymer includes at least one of polyethylene glycol, polyacrylamide or polyacrylic acid, and preferably polyethylene glycol.

The water-soluble micromolecules such as glucose and the like cannot be adsorbed on the surface of the material by the negative pressure method, and can only be coated by a severe hydrothermal condition, while the carbon source is a water-soluble macromolecule which can be adsorbed on the surface of the material by vacuum negative pressure and permeated into the positive electrode material for gelation, can be gently and rapidly carried out at room temperature, and is suitable for large-scale industrialized amplification.

As a preferred embodiment of the present invention, the polyethylene glycol includes at least one of PEG600 to PEG10000, for example PEG600, PEG800, PEG1000, PEG1500, PEG2000, PEG4000, PEG6000, PEG8000, or PEG 10000.

As a preferable technical scheme of the invention, the solid-to-liquid ratio of the positive electrode material to the water is (0.2-2.5) mg/1 mL, for example, 0.2 mg/1 mL, 0.5 mg/1 mL, 0.8 mg/1 mL, 1 mg/1 mL, 1.3 mg/1 mL, 1.5 mg/1 mL, 1.8 mg/1 mL, 2 mg/1 mL, 2.2 mg/1 mL, or 2.5 mg/1 mL.

As a preferable technical scheme of the invention, the mass ratio of the positive electrode material to the water-soluble polymer is (100-1000): 1, for example, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1 or 1000:1, etc.

According to a preferred technical scheme of the invention, the mixing method comprises stirring, wherein the stirring speed is 300-800 rpm, such as 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 650rpm, 700rpm, 750rpm or 800rpm, the stirring temperature is 15-35 ℃, such as 15 ℃, 20 ℃, 25 ℃, 30 ℃ or 35 ℃, and the stirring time is 20-40 min, such as 20min, 25min, 30min, 35min or 40 min.

According to the preferred technical scheme, the temperature of the drying is 150-200 ℃, such as 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃ or 200 ℃ and the like, and the time is 8-16 h, such as 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or 16h and the like.

According to the preferred technical scheme, the carbonization is performed under an inert protective atmosphere, and the carbonization temperature is 300-500 ℃, such as 300 ℃, 330 ℃, 350 ℃, 380 ℃, 400 ℃, 420 ℃, 450 ℃, 480 ℃ or 500 ℃ and the like, and the time is 2-3 h, such as 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h and the like.

According to the invention, the water-soluble polymer is carbonized at high temperature preferably under the inert protective gas, so that the seamless carbon coating of the anode material from inside to outside is realized, the conductivity of the anode material can be effectively improved, the circulation stability of the anode material can be improved, the interface of the anode material is prevented from being contacted with electrolyte, further, the surface side reaction is inhibited, particularly, the interfacial oxygen precipitation of the lithium-rich manganese-based anode material can be effectively inhibited, and the circulation reversibility of lattice oxygen can be promoted.

In a second aspect, an all-carbon coated cathode material is obtained according to the preparation method of the first aspect.

In a third aspect, a battery comprises the all-carbon coated positive electrode material according to the second aspect.

For reasons of space limitations and to avoid redundancy, the present invention does not list all of the points in the above range, but is not limited to only the listed values, as other non-listed values in the above range are equally applicable.

Compared with the prior art, the invention has at least the following beneficial effects:

According to the preparation method, the water-soluble polymer is adopted to perform seamless coating on the positive electrode material through vacuum negative pressure, so that the water-soluble polymer can be poured into microcracks of the positive electrode material, then the seamless carbon coating on the lithium-rich manganese-based positive electrode material from inside to outside is realized through heating carbonization, and the problems of poor cycling stability, interface side reaction, interface oxygen precipitation and the like of the lithium-rich manganese-based polycrystalline positive electrode material can be solved. The method is quite different from the prior art of carbon coating such as a glucose hydrothermal method, the glucose hydrothermal method has harsh reaction conditions, a reaction kettle is needed, the reaction conditions are dangerous, and the coating duration is long. Compared with the mixed coating of graphene, carbon nano tube and the like, the mixed coating of graphene and carbon nano tube only can realize uneven mixed coating, but the conductivity of the material cannot be improved to the greatest extent, the conductivity of the contact area of the composite material can only be improved, microcracks generated in the circulation process of the positive electrode material cannot be restrained, and although the conductivity of the material can be improved to a certain extent, the circulation stability of the positive electrode material cannot be ensured. Compared with the traditional carbon coating material, the method has the advantages that on one hand, the method can realize the mild and rapid full-carbon coating of the anode material from inside to outside under the aqueous condition, and the coated carbon source is cheap and easy to obtain, and on the other hand, the obtained anode material is optimized in conductivity, can inhibit microcracks generated in the circulation process, and further can improve the circulation stability and the multiplying power discharge capacity of the material.

Drawings

FIG. 1 is a schematic flow chart of a method for preparing an all-carbon coated cathode material of example 1;

FIG. 2 is an FE-SEM test chart of the lithium-rich manganese-based material polycrystalline precursor Mn _0.65Ni_0.35(OH)₂ of example 1;

FIG. 3 is an FE-SEM image of an all-carbon coated positive electrode material obtained in example 1;

FIG. 4 is an XRD pattern of the all-carbon coated cathode material obtained in example 1;

FIG. 5 is a graph showing the cycle performance of the all-carbon coated cathode material of example 1 compared with the cathode material obtained in comparative example 1-1;

FIG. 6 is a Nyquist plot test chart of the all-carbon coated cathode material of example 1 and the cathode material obtained in comparative example 1-1;

fig. 7 is a linear fit of the vacuum levels of the positive electrode materials of different particle sizes in example 1 and example 4 for the most suitable vacuum negative pressures.

Detailed Description

The technical scheme of the invention is further described by the following specific embodiments.

It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

Example 1

The embodiment provides a preparation method of an all-carbon coated cathode material, as shown in fig. 1, the preparation method includes:

(1) Preparing a precursor of the lithium-rich manganese-based polycrystalline cathode material:

According to the chemical formula of Mn _0.65Ni_0.35(OH)₂ of the lithium-rich manganese-based material polycrystalline precursor, preparing a mixed metal salt solution of transition metal according to the mole ratio of Mn to Ni, controlling the total metal ion concentration to be 130g/L, and simultaneously preparing 10mol/L of precipitant alkali solution and 16wt% of complexing agent ammonia water. Firstly preparing starting base solution in a reaction kettle, and introducing nitrogen below the liquid surface to ensure an anaerobic environment. The method comprises the steps of preparing mixed metal salt solution, complexing agent ammonia water and precipitant alkali solution, respectively, uniformly and continuously pumping the mixed metal salt solution, the complexing agent ammonia water and the precipitant alkali solution into a reaction kettle to perform precipitation reaction, specifically, controlling the temperature of a reaction system in a primary reaction kettle and a secondary reaction kettle to be 55 ℃, controlling the off-line pH of nucleation to be 11.4, performing nucleation reaction for 1.5 hours, closing a pump of the alkali solution after the nucleation is finished, enabling the pH of the system to suddenly drop to be 10, performing growth reaction for 35 hours until the D50 of a reaction product reaches the required granularity, stopping the precipitation reaction, aging for 4.5 hours, performing suction filtration, washing the aging product with hot alkali and hot water to be neutral and drying the reaction product at 110 ℃ for 12 hours, and sieving the reaction product by using a sieve to obtain the precursor of the lithium-enriched manganese-based polycrystalline cathode material. The particle size D50 of the precursor is 6 μm and the BET is 26m ²/g;

Preparing a lithium-rich manganese-based polycrystalline positive electrode material:

Mixing lithium source lithium carbonate with the obtained precursor Mn _0.65Ni_0.35(OH)₂ of the lithium-rich manganese-based polycrystalline cathode material according to the ratio of the molar quantity of lithium element to the total molar quantity of transition metal of 1:1.55), dividing the mixture into air, and sintering the mixture at constant temperature of 950 ℃ for 13 hours to obtain the lithium-rich manganese-based polycrystalline cathode material with the granularity D50 of 6 mu m;

(2) Gel-like mixture is prepared by vacuum negative pressure method:

350mL of distilled water is measured and added into a clean suction filtration bottle, a rotor is added into the suction filtration bottle, and the suction filtration bottle is placed on a magnetic stirrer. Weighing 300g of the obtained lithium-rich manganese-based polycrystalline cathode material, transferring the obtained lithium-rich manganese-based polycrystalline cathode material into a suction filter flask, weighing 1.6g of water-soluble polymer polyethylene glycol as a carbon source, adding the carbon source into the suction filter flask, starting stirring and suction filtering equipment, maintaining a vacuum negative pressure state in the suction filter flask, maintaining the vacuum degree at-0.03 MPa, stirring at normal temperature for 30min at the rotating speed of 650rpm, filtering the material in the suction filter flask after the reaction is finished to obtain a gelatinous mixture, and then filtering the obtained sample

Preparing an all-carbon coated positive electrode material by high-temperature carbonization:

and (3) putting the obtained gelatinous mixture into an oven at 180 ℃ for drying for 12 hours, then putting the dried sample into a tube furnace, introducing nitrogen, and carbonizing at 400 ℃ for 2.5 hours to obtain the all-carbon coated anode material.

Example 2

The present embodiment provides a method for preparing an all-carbon coated cathode material, in which different water-soluble polymers and/or different amounts of water-soluble polymers are used in step (2), and specific adjustments are shown in table 1, and other conditions are identical to those of embodiment 1 except for the above.

Example 3

The embodiment provides a preparation method of an all-carbon coated positive electrode material, wherein in the step (2) of the preparation method, different vacuum negative pressures are adopted, the specific adjustment is shown in table 1, and other conditions are identical to those of the embodiment 1 except for the above.

Example 4

The embodiment provides a preparation method of an all-carbon coated cathode material, wherein in the preparation method step (1), the cathode materials with different granularity D50 are obtained by adjusting preparation parameters, and in the step (2), the vacuum degree of different vacuum negative pressures is adopted, and the specific adjustment is shown in the table 1, and other conditions are identical to those of the embodiment 1 except the above.

Example 5

The embodiment provides a preparation method of an all-carbon coated positive electrode material, which adopts new positive electrode materials such as NCM811, NCA, LMFP and the like to replace the lithium-rich manganese-based positive electrode material obtained in the step (1), and makes corresponding adjustment on the dosage of polyethylene glycol and the vacuum degree of a vacuum negative pressure environment in the step (2), wherein the specific adjustment is shown in a table 1, and other conditions are identical to those of the embodiment 1 except the specific adjustment.

Comparative example 1

The comparative example provides a preparation method of a positive electrode material, wherein in the step (2) of the preparation method, water-soluble small molecules such as glucose and the like are adopted to replace the water-soluble high molecules, or no carbon source is added, and the specific adjustment is shown in table 1, and other conditions are identical to those of the example 1 except the above.

Comparative example 2

This comparative example provides a method for producing a positive electrode material in which the vacuum negative pressure state is not applied in step (2), and the specific adjustment is as shown in table 1, except for the above, the conditions are exactly the same as in example 1.

Comparative example 3

The present comparative example provides a method for preparing a positive electrode material, which uses new positive electrode materials NCM811, NCA, LMFP, etc. instead of the lithium-rich manganese-based positive electrode material obtained in step (1), uses a water-soluble small molecule such as glucose, etc. instead of the water-soluble polymer in step (2), or does not add any carbon source, and/or does not apply a vacuum negative pressure state in step (2), specifically adjusted as shown in table 1, except for the above, other conditions are exactly the same as in example 1.

Characterization and testing:

I. Fig. 2 is an FE-SEM test chart of the lithium-rich manganese-based material polycrystalline precursor Mn _0.65Ni_0.35(OH)₂ obtained in example 1, and it can be seen from the figure that the obtained precursor has a polycrystalline morphology, the primary particle crystallinity is good, and the particle size is about 6 μm.

Fig. 3 is an FE-SEM image of the all-carbon coated cathode material obtained in example 1, and it can be seen from the image that the morphology of primary particles of the all-carbon coated cathode material formed by vacuum negative pressure method and carbonization remained good, and the particle size was about 6 μm.

Fig. 4 is an XRD pattern of the all-carbon coated cathode material obtained in example 1, and it can be seen from the figure that the structure of the lithium-rich manganese-based cathode material is not affected after all-carbon coating.

And II, preparing the positive electrode materials obtained in the examples and the comparative examples into positive electrode plates, namely uniformly dispersing the positive electrode materials, carbon black, a binder PVDF and N-methylpyrrolidone by ultrasonic waves to prepare slurry, coating the slurry on an aluminum foil by using a scraper, drying the slurry in a vacuum drying oven for 12 hours, rolling the positive electrode plates, and cutting the positive electrode plates.

And (3) further assembling the obtained positive plate into a battery, namely completing the assembly of the negative electrode shell, the positive electrode shell, the diaphragm, the obtained positive plate, the negative electrode lithium plate and the obtained battery in a glove box, wherein the electrolyte is lithium hexafluorophosphate. And standing the assembled battery for a period of time, installing the assembled battery on a battery test system (the voltage range is 2.3-4.55V), performing constant current charge and discharge and other tests, and testing the impedance of the battery by using an electrochemical workstation.

Fig. 5 is a graph comparing the cycle performance of the all-carbon coated cathode material of example 1 with that of the cathode material obtained in comparative example 1-1, and it can be seen from the graph that the all-carbon coated cathode material obtained in example 1 has higher cycle retention rate, almost no attenuation of capacity and better cycle stability at 2.3-4.55 v.

The comparison of the cycle performance data of the remaining examples and comparative examples is shown in table 1, and it can be seen from the table that, compared with comparative examples 1-1 to 1-3, the cycle retention rate of the lithium-rich manganese-based positive electrode material is improved by performing all-carbon coating with polyethylene glycol, polyacrylic acid and polyacrylamide as carbon sources in examples 1 and 2, which indicates that the cycle stability of the lithium-rich manganese-based positive electrode material can be significantly improved after high-temperature carbonization of the water-soluble polymer carbon coated precursor. In addition, it can be concluded from the results in Table 1 that polyethylene glycol polymers have the greatest improvement in cycling stability to materials and the best performance compared to other polymeric carbon sources, probably due to the abundance of alcoholic hydroxyl groups in polyethylene glycol. The results of the comparative example using the small molecular carbon source are basically consistent with those of the comparative example using no carbon source, because the small molecular carbon source has water solubility and cannot be effectively adsorbed in micropores of the positive electrode material, and can not flow out directly or be coated on the surface of the positive electrode material, and the results of the small molecular carbon source using a vacuum negative pressure method and the results of the small molecular carbon source not using the carbon source are basically consistent, so that no obvious effect is achieved.

Fig. 6 is a Nyquist plot of the positive electrode material coated with all carbon of example 1 and the positive electrode material obtained in comparative example 1-1, including a high frequency region on the left side and a low frequency region on the right side. The right intercept of the semicircle represents Rct, which is the charge transfer impedance of the sample, and it can be seen from the graph that the Rct of the positive electrode material is reduced after the full carbon coating in the embodiment 1, which indicates that the full carbon coating positive electrode material can effectively enhance the conductivity of the material and reduce the charge transfer resistance.

Examples 3 and 4 of table 1 show the effect of all-carbon coating of positive electrode materials of different particle sizes under vacuum degrees of different vacuum negative pressures, and comparative example 2-1 shows the effect of carbon coating using water-soluble polymer under low vacuum (0 MPa) and normal pressure of non-negative pressure, and it can be seen from the table that the excessive or the too-small vacuum negative pressure is not good for the cycle stability of the positive electrode materials. The possible reason is that when the vacuum negative pressure is too small, even in the low vacuum or normal pressure range, the water-soluble polymer cannot completely penetrate and achieve the full coating of the positive electrode material from inside to outside, and when the vacuum negative pressure is too large, the structural damage of the positive electrode material may be caused. Therefore, the circulation stability of the positive electrode material can be effectively improved only when the vacuum negative pressure is in a proper range.

Fig. 7 is a linear fitting graph of the vacuum degree of the positive electrode materials with different particle sizes corresponding to the most suitable vacuum negative pressure in the embodiment 1 and the embodiment 4, and it can be seen from the graph that the required vacuum negative pressure shows a linear increasing trend within a certain range along with the increase of the particle size, and through linear fitting analysis, the vacuum degree (MPa) of the vacuum negative pressure environment is taken as a dependent variable, the D50 particle size (mum) of the positive electrode material is taken as the independent variable, and the following functional relation y= -0.0051x-0.0029 is satisfied.

From the above, it can be seen that the invention adopts the water-soluble polymer as the carbon coating precursor, and completes the full coating of the water-soluble polymer on the positive electrode material from inside to outside by the vacuum negative pressure method, in this process, due to the certain viscosity of the water-soluble polymer, the water-soluble polymer is adsorbed to the positive electrode material to avoid being able to be poured into the positive electrode material by the vacuum negative pressure, and gradually causes gelation reaction, thereby obtaining a gelatinous mixture, and then the gelatinous mixture is dried and carbonized for heat treatment, thus completing the full construction of the electronic conductive network from inside to outside, so as to solve the problems of poor circulation performance, poor conductivity, oxygen precipitation and the like of the positive electrode material caused by the untight coating of the carbon material and the existence or occurrence of microcracks, and the invention is particularly suitable for improving and enhancing the electrochemical performance and stability of the lithium-rich manganese-based positive electrode material.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention.

In addition, the specific features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various possible combinations are not described further.

Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.

Claims

1. The preparation method of the all-carbon coated positive electrode material is characterized by comprising the following steps of:

mixing a positive electrode material, water and a water-soluble polymer in a vacuum negative pressure environment with the vacuum degree of-0.01 to-0.13 MPa, wherein the mass ratio of the positive electrode material to the water-soluble polymer is (100-1000): 1, so as to obtain a gel-like mixture, and sequentially drying and carbonizing the obtained gel-like mixture to obtain the all-carbon coated positive electrode material.

2. The method according to claim 1, wherein the degree of vacuum in the vacuum negative pressure environment is used as a dependent variable, the D50 particle diameter of the positive electrode material is used as an independent variable, and the following functional relationship y= -0.0051x-0.0029 is satisfied, and x and y satisfy the calculation relationship of pure numerical values in μm and MPa, respectively.

3. The method according to claim 2, wherein the positive electrode material has a D50 particle size of 2.5 to 10.5 μm.

4. The method according to claim 1, wherein the positive electrode material comprises a positive electrode active material of a lithium ion battery and/or a positive electrode active material of a sodium ion battery, and the positive electrode active material of the lithium ion battery comprises at least one of lithium cobaltate, lithium nickel manganese oxide, ternary positive electrode material, quaternary positive electrode material, lithium iron phosphate, lithium iron manganese phosphate or lithium-rich manganese-based positive electrode material.

5. The method of claim 1, wherein the water-soluble polymer comprises at least one of polyethylene glycol, polyacrylamide, or polyacrylic acid.

6. The method according to claim 1, wherein the mixing method comprises stirring, the stirring speed is 300-800 rpm, the stirring temperature is 15-35 ℃, and the stirring time is 20-40 min;

the temperature of the drying is 150-200 ℃ and the time is 8-16 h;

The carbonization is carried out in an inert protective atmosphere, the temperature of the carbonization is 300-500 ℃, and the time is 2-3 hours.

7. An all-carbon coated positive electrode material, characterized by being obtained according to the preparation method of any one of claims 1 to 6.

8. A battery comprising the all-carbon coated positive electrode material according to claim 7.