Graphite material and preparation method thereof, electrode and lithium ion battery

Abstract

The invention discloses a graphite material and a preparation method thereof, an electrode and a lithium ion battery, and relates to the field of lithium ion batteries. Aerosol is adopted to assist vapor deposition, so that the loading uniformity of the nano-metal catalyst is improved, the particle size of the nano-metal is inhibited from growing, and the cost of raw materials is relatively low; nanopores are formed in the graphite basal plane through micro-etching, so that lithium embedding channels on the graphite surface are increased, the diffusion path of Li < + > in a graphite bulk phase is reduced, and the rapid charging performance of graphite is improved; a nano transition metal catalyst is deposited on the surface of graphite, so that efficient fixed-point etching is realized, and the pore-forming proportion of a graphite basal plane is increased; due to the existence of the nano-catalyst, the depth-diameter ratio of pores after gas phase etching is increased, and a lithium embedding channel of a single pore is increased; the lithium intercalation channels on the graphite surface are increased through micro-etching, the Li < + > diffusion path is reduced, and the fast charging and high power performance of the graphite material is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a graphite material and a preparation method thereof, an electrode and a lithium ion battery. Background Art

[0002] Advanced batteries are a key supporting technology for my country's "dual carbon" goals and the development of its Electric China strategy. Lithium-ion batteries are widely used in electric vehicles, portable electronic devices, and energy storage. Graphite anode materials are constrained by slow lithium insertion kinetics and low operating potential. Electric vehicles, in particular, are experiencing rapid development thanks to the advancements in lithium-ion batteries. However, unlike the rapid recharging capabilities of fuel-powered vehicles, a significant disadvantage of electric vehicles is their long charging times. Furthermore, low-altitude aircraft have gradually entered the commercialization phase in recent years, offering broad potential for future development. These industrial and societal demands place higher demands on the fast-charging capabilities of lithium-ion batteries.

[0003] Graphite is the most widely used negative electrode active material in lithium-ion batteries. It has the advantages of low lithium insertion potential, high conductivity, high cycle stability, abundant raw materials and low cost. It will remain the mainstream negative electrode material for a long time in the future. However, the two-dimensional layered structure of graphite determines the + Lithium ions must be embedded from the end faces of the material, resulting in a long lithium ion diffusion path. Furthermore, the small interlayer spacing of graphite (0.335nm) also results in high lithium ion diffusion resistance. Furthermore, since the lithium insertion potential of graphite is similar to that of metallic lithium, there is a severe polarization phenomenon during high-rate charging, which causes the lithium insertion potential of the graphite negative electrode to be lower than 0 V, leading to surface lithium deposition. This not only causes capacity loss and cycle attenuation, but can even lead to serious safety issues such as internal short circuits and thermal runaway.

[0004] It is generally believed that ion transport is the rate-limiting step for lithium insertion in graphite materials. This process mainly includes Li + Diffusion process in electrolyte and electrode materials. Interface and interfacial phase are common in LIBs. When the graphite negative electrode is charged and discharged at high rates, Li + The diffusion rate inside the particles does not match the rate of lithium insertion and removal on the particle surface, and various polarizations will inevitably occur, including ohmic drop, concentration overpotential, and charge transfer overpotential. Based on the above understanding, the optimization strategy of graphite negative electrode basically starts from particle structure design and interface modification. For the structural design of graphite particles, on the one hand, by refining the particle size and secondary granulation, the Li + The bulk diffusion path and the expansion of lithium insertion channels can reduce the ion transmission resistance and improve the fast charging performance. On the other hand, acid and base etchants such as potassium hydroxide and phosphoric acid can be used to construct nano-scale gaps on the graphite surface to increase the lithium insertion channels on the graphite surface and reduce Li +Diffusion path in the graphite bulk phase. Interface modification includes constructing a functional carbon coating layer on the graphite surface and introducing element doping to improve Li + The migration rate at the interface increases, thereby improving the fast charging performance of graphite.

[0005] Chinese patent application CN114784273A (published on July 22, 2022) discloses a method for preparing multi-channel fast-charging graphite. This method uses a mixed etchant of bisulfate and sulfuric acid to etch the graphite surface, creating pores that serve as lithium insertion channels and shortening the lithium ion migration path. However, acid etching can easily lead to intercalation between graphite layers, causing them to peel off during cycling, impacting cycling stability.

[0006] Chinese patent application CN114094079A (published on February 25, 2022) discloses a method for preparing a fast-charging graphite anode material. This method uses a strong alkaline solution, such as potassium hydroxide, as an etchant to wet-etch graphite, creating nanopores on the graphite surface. This creates channels for lithium insertion and improves the material's rate capability and low-temperature performance. However, alkaline etching is highly corrosive to the equipment, has low controllability, and poor etching uniformity. The etchant preferentially reacts with carbon on the graphite end faces to form pores, providing limited lithium insertion channels.

[0007] Existing technical solutions typically use chemical etchants such as potassium hydroxide and phosphoric acid to micro-etch the graphite surface to form nanopores and construct multi-channel graphite. However, etchants like potassium hydroxide are highly corrosive to equipment and require stringent reaction conditions, making the degree of etching difficult to control. Furthermore, due to the high number of defects on the graphite end faces, their reactivity with the etchant is high, while the reactivity of the graphite basal plane is relatively weak, resulting in limited additional lithium insertion channels. Summary of the Invention

[0008] Purpose of the invention: The first aspect of the present invention is to provide a graphite material with a high aspect ratio; the second aspect of the present invention is to provide a method for preparing a graphite material based on aerosol-loaded nano-transition metal salt precursors to form etched channels under the oxidation action of a gaseous oxidant; the third aspect of the present invention is to provide an electrode comprising the aforementioned graphite material and having fast charging and high power performance; the fourth aspect of the present invention is to improve a lithium-ion battery comprising the aforementioned electrode.

[0009] Technical solution:

[0010] In the first aspect of the present invention, the present application provides a graphite material, comprising porous graphite, wherein the D50 of the porous graphite is 5-20 μm, the specific surface area is 5-30 m 2 / g;

[0011] The porous graphite includes a graphite carrier and etched channels distributed on the surface of the graphite carrier. The diameter of the etched channels is 5-200 nm, and the aspect ratio is 1:(1-400).

[0012] The diameter-to-depth ratio is the ratio of the diameter of the etched channel to its depth. The detection methods of the etched channel include but are not limited to scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray tomography, confocal laser scanning microscopy, and white light interferometry. The preferred detection means in this application are atomic force microscopy and transmission electron microscopy.

[0013] Furthermore, the porous graphite contains etching channels, and the etching channels are formed by etching the nano transition metal catalyst distributed on the surface of the graphite carrier under the action of gaseous oxidation.

[0014] Furthermore, the graphite carrier includes any one or more combinations of artificial graphite, flake graphite, microcrystalline graphite, and mesophase carbon microspheres.

[0015] Furthermore, the specific surface area of ​​the porous graphite is 8-15 m 2 / g.

[0016] Furthermore, the graphite material further comprises a carbon coating layer coated on the surface of the porous graphite; the graphite material comprising the carbon coating layer has a specific surface area of ​​1-5 m 2 / g.

[0017] Optionally, the specific surface area of ​​the graphite material is 1.0-3.0 m 2 / g, wherein the specific surface area of ​​the porous graphite is 3.5-35 m 2 / g.

[0018] Preferably, the specific surface area of ​​the graphite material is 1.0-2.0 m 2 / g, wherein the specific surface area of ​​the porous graphite is 4.5-10 m 2 / g.

[0019] Furthermore, the residual carbon content of the hard carbon-coated porous graphite is 0.5-3 wt %; as a further optimization of the present invention, the residual carbon content of the hard carbon-coated porous graphite is 1-2 wt %.

[0020] Under the low coating design, the specific surface area of ​​graphite is relatively high, and the coverage rate of surface defects is limited, which leads to intensified side reactions and poor cycle stability; high coating design increases the residual carbon content, thickens the amorphous carbon layer, and increases the side reactions between the carbon layer and the electrolyte, which also leads to reduced initial efficiency and cycle stability of the graphite material; in addition, the excessive thickness of the carbon layer increases the resistance of the graphite, causing the battery to heat up more under high current conditions.

[0021] On the basis that the porous graphite has an etched channel with a diameter of 5-200 nm and a depth of 0.2-2 μm, the specific surface area of ​​the graphite material can be 1.0-3.0 m 2 / g, wherein the specific surface area of ​​the porous graphite is 3.5-35 m 2 / g; further preferably, the specific surface area of ​​the graphite material is 1.0-2.0 m 2 / g, wherein the specific surface area of ​​the porous graphite is 4.5-10 m 2 / g, further improving the fast charging, high power performance and cycle performance of graphite materials.

[0022] In the second aspect of the present invention, the present application provides a method for preparing a graphite material, comprising the following steps:

[0023] Step 1, preparation of a precursor solution: dissolving at least one transition metal salt in a dispersant to obtain a precursor solution;

[0024] Step 2, catalyst deposition: dispersing the precursor solution on the surface of the graphite support to form a nano-transition metal catalyst that catalyzes the oxidation reaction of the graphite support to form an etching channel;

[0025] Step 3, preparation of porous graphite: the graphite carrier loaded with nano-transition metal catalyst reacts with an oxidizing gas for etching graphite to form etching channels, and the porous graphite is obtained after acid washing.

[0026] The carrier inert gas includes, but is not limited to, one of argon, nitrogen, helium, neon, krypton, and xenon.

[0027] Furthermore, the cation of the transition metal salt described in step 1 is any one of the cations of nickel, cobalt, copper, manganese, iron, and titanium; and the anion of the transition metal salt is any one of the nitrate ion, sulfate ion, chloride ion, iodide ion, and bromide ion.

[0028] This application uses metal salts or halides with moderate decomposition reaction rates. If the transition metal complex decomposes slowly, it is not conducive to the rapid deposition of the metal catalyst. Too long a deposition time may also cause the deposited crystals to grow, resulting in a decrease in the uniformity of the catalyst.

[0029] Furthermore, the concentration of the precursor solution in step 1 is 1-100 mmol / L; the dispersant includes one or more of water, methanol, ethanol, and acetone.

[0030] Furthermore, the particle size of the nano transition metal catalyst in step 2 is 5-200 nm; and the deposition amount of the nano transition metal catalyst is 0.01-0.1 wt% of the graphite.

[0031] Further preferably, the particle size of the nano transition metal catalyst in step 2 is 10-50 nm; the deposition amount of the nano transition metal catalyst is 0.01-0.05 wt % of the graphite; and the transition metal in the nano transition metal catalyst is nickel or cobalt.

[0032] Furthermore, the deposition temperature in step 2 is 200-600° C. and the deposition time is 10-60 min.

[0033] Furthermore, the concentration of the precursor solution is 5-40 mmol / L, the atomization volume in the atomization operation is 80-150 mL / min, and the deposition time is 20-30 min.

[0034] The dispersant in the atomized droplets of the precursor solution is rapidly vaporized, and the nano-metal salt is precipitated and loaded on the graphite surface, while decomposing into metal oxides, thereby achieving low-temperature and uniform deposition of the metal catalyst. If the concentration of the precursor solution is too high or the physical and chemical amount is too large, the particle size of the precipitated nano-metal salt will be too large or the particles will agglomerate and fuse.

[0035] By adopting aerosol-assisted vapor deposition and optimizing the concentration and deposition time of the precursor solution, the uniformity of catalyst deposition and etching uniformity are improved, while the graphite structure is better protected, the fast charging and high power performance of the graphite material are improved, and a high cycle performance is maintained.

[0036] Furthermore, in the preparation of the nano transition metal catalyst in step 2, the precursor solution is deposited on the surface of the graphite carrier in the form of an aerosol. The precursor solution is first atomized and then mixed with a carrier inert gas to form an aerosol, which is deposited on the surface of the graphite carrier.

[0037] Furthermore, the flow rate of the oxidizing gas in step three is 100-200 mL / min; the oxidizing gas in step three includes one or more of water vapor, carbon dioxide, oxygen, and sulfur trioxide.

[0038] If the oxidizing gas flow rate is too high, it may cause excessive oxidation and deactivation of the catalyst, excessive etching of graphite, and structural collapse; if the oxidizing gas flow rate is too low, it will result in a low degree of etching, insufficient aspect ratio of the etched channel, and few new lithium insertion channels on the surface of the obtained graphite material, and the rate performance of the electrode using graphite material will be limited.

[0039] Furthermore, the etching temperature in step 3 is 500-1000° C., and the etching time is 1-24 hours.

[0040] Furthermore, the pickling adopts a pickling solution, and the pickling solution includes one of hydrochloric acid, dilute nitric acid, and dilute sulfuric acid.

[0041] Furthermore, the pickling solution is a hydrochloric acid or nitric acid solution with a concentration of 0.8-1.2M, and the pickling time is 2-4h; or the pickling solution is a sulfuric acid solution with a concentration of 0.4-0.6M, and the pickling time is 2-4h.

[0042] Furthermore, the method for preparing the graphite material further includes a fourth step of carbon coating;

[0043] The carbon coating step is to fill the nanopores and surface of the porous graphite with a liquid coating agent through a liquid phase coating process, and then obtain a hard carbon coating layer after high-temperature carbonization to obtain a multi-channel fast-filling graphite material;

[0044] The liquid coating agent includes one or more of liquid phenolic resin, asphalt, and coal tar; and the carbonization temperature is 800-1200°C.

[0045] The present application provides a method for preparing a graphite material. First, a small amount of nano-transition metal or transition metal compound particles is deposited on the graphite surface by aerosol-assisted vapor deposition (AACVD) as a nanocatalyst. An oxidizing gas is used as an etchant to etch the solid-solid interface of the catalyst-loaded graphite surface at specific locations under controlled reaction conditions to form nano-lithium intercalation channels, thereby preparing porous graphite. The porous graphite is then acid-washed to remove the catalyst, followed by liquid-phase coating and high-temperature sintering. A hard carbon coating is then constructed on the graphite surface and within the nanopores to obtain a multi-channel fast-filling graphite material.

[0046] As to the third aspect of the present invention, the present application provides an electrode, comprising the graphite material described in the present application or the graphite material obtained by the preparation method described in the present application.

[0047] As to the fourth aspect of the present invention, the present application provides a lithium ion battery comprising the electrode described in the present application.

[0048] Beneficial effects: 1) The application adopts aerosol-assisted vapor deposition, which not only reduces the cost of raw materials, but also improves the uniformity of nano-metal catalyst loading and inhibits the growth of nano-metal particles; the graphite base is micro-etched to form nano-pores on the graphite base, which increases the lithium insertion channel on the graphite surface and reduces Li + The diffusion path of the graphite bulk phase improves the fast charging performance of graphite; by depositing nanocatalysts on the graphite surface, not only the gas phase etching efficiency is improved, but also fixed-point etching is achieved, thereby increasing the pore formation ratio of the graphite basal surface; the presence of nanocatalysts helps to increase the aspect ratio of the pores after gas phase etching and increase the lithium insertion channel of a single pore; by micro-etching, the lithium insertion channel on the graphite surface is increased, reducing the Li + The diffusion path significantly increases the fast charging and high power performance of graphite materials.

[0049] 2) Furthermore, aerosol-assisted vapor deposition is used, and the concentration of the precursor solution, the deposition time, and the flow rate of the oxidizing gas are optimized. These characteristics cooperate with each other to better improve the uniformity of catalyst deposition and etching uniformity, while better protecting the graphite structure, improving the fast charging and high power performance of the graphite material, and maintaining high cycle performance.

[0050] 3) Furthermore, the acid concentration in the pickling step is optimized, which further improves the fast charging, high power performance and cycle performance of the graphite material; pickling can remove the catalyst particles covering the entrance of the graphite pores, ensure the smooth flow of ion / electron transmission channels, and improve the cycle life and Coulomb efficiency; if the pickling concentration is too low, the catalyst will not be completely dissolved; if the pickling concentration is too high, the acid molecules will be embedded in the graphite interlayer, destroying the stability of the graphite interlayer structure, causing layered exfoliation of the graphite during the cycle.

[0051] 4) Furthermore, the particle size of the graphite carrier is optimized and matched with the etched channels in the porous graphite. The porous graphite achieves the unity of low aspect ratio pore size, high specific surface area, efficient mass transfer and stable conductive network through the coordinated design of low aspect ratio pores, specific surface area and particle size. The moderate particle size range avoids the agglomeration problem caused by too fine particles, while ensuring the mechanical stability of the material in the electrode. The small particle size increases the contact area between the electrode and the electrolyte, accelerating the charge transfer rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of gas phase catalytic etching of a multi-channel fast-filling graphite material obtained by the preparation method of Example 2 of the present invention;

[0053] Figure 2 This is a comparison of electron microscope images of the graphite raw material before and after etching and pickling in Example 2 of the present invention;

[0054] Figure 3 This is a schematic diagram comparing the reaction process of water vapor etching catalyzed by nano-metal particles and water vapor etching without catalyst. DETAILED DESCRIPTION

[0055] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] Example 1

[0057] A method for preparing a multi-channel fast-filling graphite material includes the following preparation steps:

[0058] Step 1: Preparation of precursor solution: Dissolve the transition metal salt in a dispersant to obtain a precursor solution.

[0059] The cations of the transition metal salt are any one or more combinations of cations of nickel, cobalt, copper, manganese, iron, and titanium; and the anions of the transition metal salt are any one or more combinations of nitrate ions, sulfate ions, chloride ions, iodide ions, and bromide ions.

[0060] The concentration of the precursor solution is 1-100 mmol / L; the dispersant includes any one or more combinations of water, methanol, ethanol, and acetone.

[0061] Step 2: Catalyst deposition: The precursor solution is dispersed on the surface of the graphite carrier to form a nano-transition metal catalyst that catalyzes the oxidation reaction of the graphite carrier to form an etching channel.

[0062] The particle size of the nano transition metal catalyst is 5-200 nm; and the deposition amount of the nano transition metal catalyst is 0.01-0.1 wt% of the graphite.

[0063] The deposition temperature is 200-600° C., and the deposition time is 10-60 min.

[0064] Among them, in the preparation of nano transition metal catalysts, the precursor solution is deposited on the surface of the graphite carrier in the form of an aerosol. The precursor solution is first atomized and then mixed with the carrier inert gas to form an aerosol, which is deposited on the surface of the graphite carrier.

[0065] Step 3: Preparation of porous graphite: The graphite carrier loaded with nano-transition metal catalyst reacts with an oxidizing gas for etching graphite to form etching channels, and porous graphite is obtained after acid washing.

[0066] Oxidizing gas flow rate 100-200 mL / min;

[0067] The oxidizing gas includes one or more of water vapor, carbon dioxide, oxygen, and sulfur trioxide.

[0068] The etching temperature is 500-1000℃, and the etching time is 1-24h.

[0069] The pickling solution used in pickling includes one of hydrochloric acid, dilute nitric acid and dilute sulfuric acid.

[0070] Optionally, in addition to the above process, the preparation process of this embodiment may further include step four: a carbon coating step;

[0071] The carbon coating step is to fill the nanopores and surface of the porous graphite with a liquid coating agent through a liquid phase coating process, and then obtain a hard carbon coating layer after high-temperature carbonization to obtain a multi-channel fast-filling graphite material;

[0072] The liquid coating agent includes one or more of liquid phenolic resin, asphalt and coal tar; and the carbonization temperature is 800-1200°C.

[0073] The multi-channel fast-filling graphite material includes porous graphite obtained by the above preparation method, wherein the D50 of the porous graphite is 5-20 μm and the specific surface area is 5-30 m 2 / g;

[0074] The porous graphite includes a graphite carrier and etched channels distributed on the surface of the graphite carrier. The diameter of the etched channels is 5-200 nm, and the diameter-to-depth ratio is 1:(1-400).

[0075] The diameter-to-depth ratio is the ratio of the diameter of the etched channel to its depth. The detection methods of the etched channel include but are not limited to scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray tomography, confocal laser scanning microscopy, and white light interferometry. The preferred detection means in this application are atomic force microscopy and transmission electron microscopy.

[0076] Optionally, the multi-channel fast-filling graphite material may further include a carbon coating layer coated on the surface of the porous graphite; the graphite material including the carbon coating layer has a specific surface area of ​​1-5 m 2 / g.

[0077] Example 2

[0078] A method for preparing a multi-channel fast-filling graphite material includes the following preparation steps:

[0079] (1) Preparation of precursor solution: Add nickel nitrate to ethanol to prepare a 10 mmol / L precursor solution.

[0080] (2) Catalyst deposition: The precursor solution was ultrasonically atomized with a controlled atomization rate of 100 mL / min, and nitrogen was used as a carrier to carry the aerogel on graphite (5 kg; specific surface area 1.55 m 2 / g) surface was vapor deposited at a temperature of 350 °C and a deposition time of 30 min.

[0081] (3) Preparation of porous graphite: After cutting off the aerogel gas source, the furnace temperature was raised to 600 °C, and preheated steam was introduced at a flow rate of 200 ml / min, and the etching was continued for 2 h. After etching, the graphite was acid-washed with 1M hydrochloric acid solution for 4 h to remove the nano-nickel, and then dried to obtain porous graphite. The etching process of the graphite carrier formed etching channels such as Figure 1 , Figure 1 In the figure, 1 represents a graphite support; 2 represents nanocatalyst particles; and 3 represents an etching channel.

[0082] Graphite before and after etching Figure 2 As shown, Figure 2In the figure, a, graphite support before etching; b, graphite support after etching.

[0083] Schematic diagram comparing the reaction process of water vapor etching catalyzed by nano-metal particles and water vapor etching without catalyst, as shown in Figure 3 shown.

[0084] (4) Carbon coating step: 70 g of liquid phenolic resin and 4 kg of porous graphite were placed in a high-speed fusion machine for high-speed mixing and coating. The mixture was then heated to 1000 °C under a nitrogen atmosphere for high-temperature carbonization for 2 h to obtain multi-channel fast-filling graphite.

[0085] Example 3

[0086] A method for preparing a multi-channel fast-filling graphite material includes the following preparation steps:

[0087] (1) Preparation of precursor solution: Add nickel nitrate to methanol to prepare a 20 mmol / L precursor solution.

[0088] (2) Catalyst deposition: The precursor solution was ultrasonically atomized with a controlled atomization rate of 100 mL / min, and nitrogen was used as a carrier to carry the aerogel on graphite (5 kg; specific surface area 1.55 m 2 / g) surface was vapor deposited at a temperature of 350 °C and a deposition time of 20 min.

[0089] (3) Preparation of porous graphite: After cutting off the aerogel gas source, the furnace temperature was raised to 500°C, and preheated water vapor was introduced at a flow rate of 100 ml / min. The etching was continued for 6 h. After etching, the graphite was acid-washed with 1 M hydrochloric acid solution for 4 h to remove the nano-nickel and then dried.

[0090] (4) Carbon coating step: 180 g of coal tar and 4 kg of micro-etched graphite were placed in a high-speed fusion machine for high-speed mixing and coating. The mixture was then placed in a nitrogen atmosphere and heated to 1100°C for high-temperature carbonization for 2 h to obtain multi-channel fast-filling graphite.

[0091] Example 4

[0092] A method for preparing a multi-channel fast-filling graphite material includes the following preparation steps:

[0093] (1) Preparation of precursor solution: Add cobalt sulfate to methanol to prepare a 20 mmol / L precursor solution.

[0094] (2) Catalyst deposition: The precursor solution was ultrasonically atomized with a controlled atomization rate of 100 mL / min, and nitrogen was used as a carrier to carry the aerogel on graphite (5 kg; specific surface area 1.55 m 2 / g) surface was vapor deposited at a temperature of 350 °C and a deposition time of 20 min.

[0095] (3) Preparation of porous graphite: After cutting off the aerogel gas source, the furnace temperature was raised to 550°C, and preheated CO2 was introduced at a flow rate of 200 mL / min. The etching was continued for 2 h. The etched graphite was acid-washed with 1 M hydrochloric acid solution for 4 h to remove the metallic cobalt, and then dried.

[0096] (4) Carbon coating step: 140 g of liquid phenolic resin and 4 kg of micro-etched graphite were placed in a high-speed fusion machine for high-speed mixing and coating. The mixture was then placed in a nitrogen atmosphere and heated to 1000°C for high-temperature carbonization for 2 hours to obtain multi-channel fast-filling graphite;

[0097] Example 5

[0098] A method for preparing a multi-channel fast-filling graphite material is different from Example 2 in that the water vapor etching time in step (2) is 4 hours, and the rest of the experimental process remains the same.

[0099] Example 6

[0100] A method for preparing a multi-channel fast-filling graphite material is different from Example 2 in that the aerosol deposition time in step (1) is 60 min, the catalyst deposition amount is increased, the amount of liquid phenolic resin in step (3) is increased to 180 g, and the rest of the experimental process remains the same.

[0101] Example 7

[0102] A method for preparing a multi-channel fast-filling graphite material, which differs from Example 2 in that the aerosol deposition time in step (1) is 60 min; and the deposition temperature is 200°C.

[0103] Example 8

[0104] A method for preparing a multi-channel fast-filling graphite material, which differs from Example 2 in that the concentration of the precursor solution in step (1) is 50 mmol / L, and the atomization volume in the atomization operation is 200 mL / min.

[0105] Example 9

[0106] A method for preparing a multi-channel fast-filling graphite material, which differs from Example 2 in that the concentration of the precursor solution in step (1) is 50 mmol / L, the atomization volume in the atomization operation is 200 mL / min, the aerosol deposition time is 60 min; and the deposition temperature is 200°C.

[0107] Example 10

[0108] A method for preparing a multi-channel fast-filling graphite material, which differs from Example 2 in that the hydrochloric acid concentration in step (2) is 1.2 M and the pickling time is 4 h.

[0109] Comparative Example 1

[0110] A method for preparing a multi-channel fast-filling graphite material includes the following preparation steps:

[0111] (1) Preparation of porous graphite: 5 kg of artificial graphite was placed in a rotary furnace. Nitrogen was continuously passed through the furnace to evacuate the air inside. The furnace temperature was raised to 600 °C. Preheated water vapor was introduced at a flow rate of 200 ml / min and etching was continued for 2 h.

[0112] (2) Carbon coating step: 70g of liquid phenolic resin and 4kg of etched graphite were placed in a high-speed fusion machine for high-speed mixing and coating. The mixture was then placed in a nitrogen atmosphere and heated to 1000℃ for high-temperature carbonization for 2h to obtain multi-channel fast-filling graphite.

[0113] Comparative Example 2

[0114] A method for preparing a multi-channel fast-filling graphite material includes the following preparation steps:

[0115] (1) Preparation of precursor solution: Add nickel nitrate to ethanol to prepare a 10 mmol / L precursor solution.

[0116] (2) Catalyst deposition: The precursor solution was ultrasonically atomized with a controlled atomization volume of 100 mL / min. The aerogel was carried by nitrogen as a carrier on a graphite (5 kg; specific surface area 1.55 m 2 / g) surface was vapor-deposited at a temperature of 350°C and a deposition time of 30 min;

[0117] (3) Preparation of porous graphite: After cutting off the aerogel gas source, the furnace temperature was raised to 600°C, and preheated water vapor was introduced at a flow rate of 200 mL / min. The etching was continued for 2 h. The etched graphite was pickled with 1 M hydrochloric acid and water to remove metallic manganese, and then dried to obtain fast-filling graphite.

[0118] Comparative Example 3

[0119] A method for preparing a multi-channel fast-filling graphite material, which differs from Example 2 in that the porous graphite is prepared by alkaline etching, and the preparation process is as follows:

[0120] 5 kg of artificial graphite and 10 g of KOH were evenly dispersed in water, and then the mixture was obtained by spray drying and transferred to a rotary kiln. Argon gas was continuously passed through the kiln to evacuate the air in the kiln. The furnace temperature was raised to 700 °C, and etching was continued for 1 h. The porous graphite was then washed and dried to obtain the result.

[0121] Comparative Example 4

[0122] A method for preparing a multi-channel fast-filling graphite material is different from Example 2 in that the preparation process of the porous graphite is different. The preparation process is as follows:

[0123] Weigh 100.0g Ni(NO3)2.6H2O and dissolve it in a mixed solution of 2.0L deionized water and 1.0L ethanol.

[0124] After all the particles are dissolved, weigh about 2.00 kg of graphite (with a specific surface area of ​​1.55 m 2 / g) were mixed with the aforementioned solution, stirred for 4 hours, and dried at 120°C. The powder was then gently ground and placed in a tube furnace at 500°C for 4 hours with an argon flow rate of 20 mL / min. After calcination at 500°C, the powder was heated to 800°C and held for 24 hours while preheated water vapor was introduced at a flow rate of 200 mL / min for etching for 2 hours. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The reacted graphite was removed for liquid-phase coating and sintering.

[0125] Test example

[0126] The graphite negative electrode materials described in Examples 2-10 and Comparative Examples 1-4 were homogenized and coated and assembled into button half-cells for electrochemical performance testing. The experimental data are shown in Tables 1 and 2. The scheme is as follows:

[0127] Graphite material, conductive agent SP, conductive agent VGCF, and aqueous binder LA136 were mixed uniformly in a mass ratio of 85:5:5:5. Deionized water was used as a dispersant to prepare a slurry, which was coated on a copper foil surface and then dried in a vacuum oven. Graphite electrode sheets were cut and then produced. The counter electrode in the half-cell assembly was a lithium metal sheet, and the separator was a Celgard 2400 microporous PP membrane. The electrochemical window for cycling testing was set at 0.005-1.5 V. The discharge cycle was first at 0.5 C to 0.005 V, then at 0.02 C to 0.005 V. The charge cycle was 0.5 C to 1.5 V.

[0128] Table 1. Catalysts, specific surface areas of graphite before and after etching, and residual carbon content after carbon coating in the preparation methods of the examples and comparative examples

[0129] Material Particle size of nanocatalyst particles in catalytic deposition (nm) The proportion of catalyst deposition relative to graphite substrate (%) <![CDATA[Specific surface area after graphite etching (porous graphite / (m 2 / g)]]> <![CDATA[Specific surface area of the coated material (multi-channel fast-charging graphite material) / (m 2 / g)]]> Residual carbon content / (%) Example 2 10 0.05 7.91 1.85 1 Example 3 20 0.10 9.22 1.43 1.5 Example 4 50 0.10 5.13 1.19 2 Example 5 10 0.05 16.98 2.11 1 Example 6 30 0.10 10.8 1.27 3 Example 7 10 0.10 3.89 1.40 1 Example 8 50 0.50 30.15 2.77 1 Example 9 200 1.00 25.07 2.28 1 Example 10 10 0.05 7.73 1.69 1 Comparative Example 1 / / 1.98 1.24 1 Comparative Example 2 10 0.05 8.37 / / Comparative Example 3 / / 71.2 4.52 1 Comparative Example 4 200 1.5 4.47 1.09 1

[0130] Table 2. Electrical test results of graphite coin cells obtained using the methods of Examples 2-10 and Comparative Examples 1-4:

[0131] Material First lithium removal capacity (mAh / g) First efficiency (%) 100-week capacity retention rate (%) 2C delithiation capacity (mAh / g) 5C delithiation capacity (mAh / g) Example 2 354.2 94.8 91.5 330.5 209.6 Example 3 352.3 93.8 87.1 321.8 187.5 Example 4 353.4 94.0 90.4 323.1 192.7 Example 5 352.0 92.9 85.2 338.1 233.2 Example 6 351.7 93.5 83.3 327.7 221.9 Example 7 350.8 94.3 86.8 297.3 156.0 Example 8 348.4 91.7 78.4 302.6 175.4 Example 9 345.9 92.6 81.2 271.1 161.0 Example 10 352.8 93.9 90.2 317.5 201.3 Comparative Example 1 352.7 94.1 85.7 269.0 103.6 Comparative Example 2 351.1 93.2 65.6 295.3 167.7 Comparative Example 3 346.8 92.8 77.5 308.3 180.2 Comparative Example 4 349.2 92.5 80.1 280.9 133.5

[0132] like Figure 3 As shown, scanning electron microscopy shows that after catalytic etching, the overall surface of the graphite negative electrode material becomes rough and porous, providing additional channels for lithium ion embedding, which is beneficial to improving the fast charging capability of graphite.

[0133] The electrochemical test results show that Example 5 improves the surface etching degree by extending the vapor phase etching time, significantly increases the specific surface area of ​​the graphite material, constructs more lithium insertion channels on the graphite base, and further improves the high-rate performance of the graphite. However, due to the increased etching degree, the specific surface area of ​​the graphite is relatively high under the low coating design, and the surface defect coverage rate is limited, resulting in intensified side reactions and poor cycle stability.

[0134] Example 6 increases the amount of nanocatalyst deposited to increase the active etching sites and the nanopores on the graphite surface after etching, thereby improving the high-rate performance of graphite. At the same time, by increasing the amount of liquid-phase coating agent used, the specific surface area is effectively controlled, and the defects and pores on the graphite surface are coated and filled. However, due to the increase in residual carbon content due to high coating amount, the amorphous carbon layer becomes thicker, and the side reactions between the carbon layer and the electrolyte increase, which also leads to a decrease in the first efficiency and cycle stability of the graphite material. In addition, an excessively thick carbon layer increases the resistance of the graphite, causing the battery to heat up more under high current conditions. Experiments 7, 8, and 9 increased the amount of nanocatalyst deposition by increasing the deposition time, solution concentration, or atomization volume, respectively. However, this also caused the catalyst particles to continue to grow and even fuse with each other, resulting in the destruction of the graphite matrix structure after etching and a larger pore depth ratio. The graphite is prone to layered exfoliation during the cycle. The poor performance of Example 7 may be due to the fact that the catalyst deposition temperature used is too low and the deposition time is too long, which may lead to incomplete decomposition of nickel nitrate, generating less active nickel oxides or undecomposed residues. At the same time, due to the poor migration ability of metal particles at low temperatures, they are severely agglomerated to form large-sized particles, which easily lead to low efficiency of subsequent water vapor etching, uneven distribution of etching channels, over-etching or under-etching in some areas, affecting the integrity and mechanical strength of the graphite structure.

[0135] In Comparative Example 1, no nanocatalyst was deposited, the direct etching effect of water vapor was poor, the specific surface area of ​​graphite increased little, the expansion of effective lithium insertion channels was limited, and the rate performance of the graphite material was poor.

[0136] In Comparative Example 2, the multi-channel fast-charging graphite was prepared without liquid phase coating treatment, and the surface defects of the graphite and the side reactions of the electrolyte were aggravated, resulting in accelerated capacity decay of the graphite material.

[0137] Comparative Example 3 uses a conventional potassium hydroxide alkaline etching process to etch the surface of graphite. Potassium hydroxide has strong etching ability, but the controllability and uniformity of the etching degree at high temperature are poor. The resulting graphite has a large specific surface area. Although the lithium insertion channels are abundant, some pores cannot be completely filled after being coated with the liquid phase, resulting in a large side reaction between the graphite and the electrolyte and poor cycle stability. In addition, due to the large number of defects on the graphite end faces and the high aspect ratio of the etched channels, the lithium insertion channels added to the graphite basal surface are insufficient, resulting in poor graphite stability and a decrease in the overall electrical energy of the electrode.

[0138] In Comparative Example 4, the catalyst is deposited on the graphite surface by the liquid phase method. The crystal precipitation and growth in the liquid phase are difficult to control, resulting in a larger catalyst particle size and a larger pore size after etching, thereby destroying the graphite matrix structure and affecting the long-cycle performance of the graphite.

[0139] By analyzing the data obtained from the electrochemical test, it can be found that the expansion of lithium insertion channels by controlled micro-etching on the graphite surface helps to shorten the Li + The diffusion path and interface diffusion resistance are significantly improved, thereby significantly improving the high rate performance of graphite materials and the capacity under low temperature conditions. By uniformly filling the nanopores on the graphite surface through liquid phase coating, surface defects can be reduced and side reactions can be inhibited, thereby improving the cycle stability of graphite materials.

[0140] The above embodiments are all preferred embodiments of the present invention and are only used to specifically illustrate the solutions of the present invention and should not be regarded as limiting the present invention. For those skilled in the art, various improvements and optimizations can be made without departing from the technical principles of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the invention should be included in the scope of protection of the present invention.

Claims

1. A graphite material, characterized in that: The porous graphite has a D50 of 5-20 μm and a specific surface area of ​​5-30 m 2 / g; The porous graphite includes a graphite carrier and etched channels distributed on the surface of the graphite carrier. The diameter of the etched channels is 5-200 nm, and the aspect ratio is 1:(1-400).

2. A graphite material according to claim 1, characterized in that, The porous graphite contains etching channels, which are formed by etching nano transition metal catalysts distributed on the surface of the graphite carrier under the action of gaseous oxidation.

3. A graphite material according to claim 1 or 2, characterized in that: The graphite carrier includes any one or more combinations of artificial graphite, flake graphite, microcrystalline graphite, and mesophase carbon microspheres.

4. A graphite material according to claim 3, characterized in that, The specific surface area of ​​the porous graphite is 8-15m 2 / g.

5. The graphite material according to claim 4, characterized in that: The graphite material further comprises a carbon coating layer coated on the surface of the porous graphite; the graphite material comprising the carbon coating layer has a specific surface area of ​​1-5 m 2 / g.

6. The graphite material according to claim 5, characterized in that: The specific surface area of ​​the graphite material is 1.0-2.0 m 2 / g, wherein the specific surface area of ​​the porous graphite is 4.5-10 m 2 / g.

7. A method for preparing a graphite material, characterized in that: The following steps are involved: Step 1, preparation of a precursor solution: dissolving at least one transition metal salt in a dispersant to obtain a precursor solution; Step 2, catalyst deposition: dispersing the precursor solution on the surface of the graphite support to form a nano transition metal catalyst that catalyzes the oxidation reaction of the graphite support; Step 3, preparation of porous graphite: the graphite carrier loaded with nano-transition metal catalyst reacts with an oxidizing gas for etching graphite to form etching channels, and porous graphite is obtained after acid washing.

8. A method for preparing a graphite material according to claim 7, characterized in that: The cation of the transition metal salt described in step 1 is any one of the cations of nickel, cobalt, copper, manganese, iron, and titanium; the anion of the transition metal salt is any one of the nitrate ion, sulfate ion, chloride ion, iodide ion, and bromide ion.

9. A method for preparing a graphite material according to claim 7 or 8, characterized in that: The concentration of the precursor solution in step 1 is 1-100 mmol / L; the dispersant includes any one or more combinations of water, methanol, ethanol, and acetone.

10. A method for preparing a graphite material according to claim 7, characterized in that: The particle size of the nano transition metal catalyst in step 2 is 5-200 nm; the deposition amount of the nano transition metal catalyst is 0.01-0.1 wt% of the graphite.

11. A method for preparing a graphite material according to claim 7 or 8, characterized in that: The deposition temperature in step 2 is 200-600° C. and the deposition time is 10-60 min.

12. A method for preparing a graphite material according to claim 11, characterized in that: The concentration of the precursor solution is 5-40 mmol / L, the atomization volume in the atomization operation is 80-150 mL / min, and the deposition time is 20-30 min.

13. A method for preparing a graphite material according to any one of claims 7 to 8, 10 or 12, characterized in that: The precursor solution is deposited on the surface of the graphite carrier in the form of an aerosol. The precursor solution is first atomized and then mixed with a carrier inert gas to form an aerosol, which is then deposited on the surface of the graphite carrier.

14. A method for preparing a graphite material according to claim 13, characterized in that: The oxidizing gas flow rate in step 3 is 100-200 mL / min; The oxidizing gas in step three includes one or more of water vapor, carbon dioxide, oxygen, and sulfur trioxide.

15. A method for preparing a graphite material according to any one of claims 7 to 8, 10, 12 or 14, characterized in that: The etching temperature in step 3 is 500-1000° C., and the etching time is 1-24 hours.

16. The method for preparing a graphite material according to claim 7, characterized in that: The pickling solution used in the pickling includes one of hydrochloric acid, dilute nitric acid and dilute sulfuric acid.

17. The method for preparing a graphite material according to claim 16, characterized in that: The pickling solution is a hydrochloric acid or nitric acid solution with a concentration of 0.8-1.2M, and the pickling time is 2-4 hours; or the pickling solution is a sulfuric acid solution with a concentration of 0.4-0.6M, and the pickling time is 2-4 hours.

18. A method for preparing a graphite material according to any one of claims 7-8, 10, 12, 14, 16-17, characterized in that: Also includes step four carbon coating step; The carbon coating step is to fill the nanopores and surface of the porous graphite with a liquid coating agent through a liquid phase coating process, and then obtain a hard carbon coating layer after high-temperature carbonization to obtain a multi-channel fast-filling graphite material; The liquid coating agent includes one or more of liquid phenolic resin, asphalt, and coal tar; and the carbonization temperature is 800-1200°C.

19. An electrode, characterized in that: The graphite material comprises the graphite material according to any one of claims 1 to 6, or the graphite material obtained by the preparation method according to any one of claims 7 to 18.

20. A lithium ion battery comprising the electrode according to claim 19.

Images