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

Abstract

The application relates to a graphite negative electrode composite material, a preparation method thereof and a lithium ion battery. The graphite negative electrode composite material comprises a graphite core layer and a coating layer on the surface of the graphite core layer, and the coating layer comprises a phosphorus-doped graphite-phase carbon nitride material. The graphite negative electrode composite material has higher capacity, higher first coulomb efficiency and better rate performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a graphite anode composite material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and no memory effect, are widely used in 3C digital electronics, power tools, electric bicycles, and electric vehicles. However, with the continuous development of society, people have higher requirements and expectations for lithium-ion batteries, guiding the development of power batteries towards higher energy density and higher performance. In addition, in the field of 3C digital electronics, people also have new requirements for the battery life of electronic devices. Therefore, in order to meet the future development needs of the battery field for high energy density, long battery life, and higher rate performance, it is urgent to develop anode materials with higher specific capacity, higher initial coulombic efficiency, better rate performance, and better long-cycle stability.

[0003] Graphite anode materials possess advantages such as high energy density, good cycle performance, mature preparation technology, and low manufacturing cost, making them the mainstream commercial anode material for lithium-ion batteries. While the specific capacity and fast-charging performance of graphite anode materials can be improved through methods such as spheroidization, oxidation modification, fluorination modification, surface chemical treatment, and surface coating, traditional methods rarely exceed their theoretical capacity of 372 mAh / g, and it is also difficult to simultaneously improve both capacity and rate performance. For example:

[0004] There are methods to coat the surface of graphite with a layer of hard carbon or soft carbon. Although surface coating can reduce interfacial resistance and improve fast charging performance, soft carbon or hard carbon has the disadvantage of significantly reducing capacity, making it difficult to improve both capacity and fast charging performance at the same time.

[0005] There are methods to modify the surface of graphite by doping it with elements such as N, P, S, and B. Although doping can improve the fast charging performance of the material, it will affect the rate performance and battery safety performance. Moreover, this method is costly and not easy to mass-produce.

[0006] Therefore, obtaining graphite anode materials with higher specific capacity and better rate performance is one of the key issues in improving the performance of lithium-ion batteries. Summary of the Invention

[0007] Based on this, the present invention provides a graphite anode composite material with higher specific capacity and better rate performance, a method for preparing the same, and a lithium-ion battery containing the same.

[0008] In a first aspect, the present invention provides a graphite anode composite material, comprising a graphite core layer and a coating layer located on the surface of the graphite core layer, the coating layer comprising a phosphorus-doped graphite-phase carbon nitride material.

[0009] In one embodiment, the mass percentage of phosphorus atoms in the coating layer is 0.1% to 5%;

[0010] In one embodiment, the mass ratio of nitrogen atoms to phosphorus atoms in the coating layer is 10 to 575;

[0011] In one embodiment, the mass percentage of P=N bonds in the coating layer is 40% to 60%.

[0012] In one embodiment, the thickness of the coating layer is 20 nm to 250 nm;

[0013] In one embodiment, the content of phosphorus and nitrogen atoms in the lattice of the graphite core layer is ≤50ppm;

[0014] In one embodiment, the content of phosphorus atoms present in elemental form in the coating layer is ≤0.1wt%.

[0015] In one embodiment, the specific surface area of ​​the graphite anode composite material is 0.5–2 m². 2 / g;

[0016] In one embodiment, the tap density of the graphite anode composite material is 0.9–1.2 g / cm³. 3 ;

[0017] In one embodiment, the graphite anode composite material has a compaction density of 1.7–2.2 g / cm³ under a pressure of 5T. 2 .

[0018] A second aspect of the present invention provides a method for preparing a graphite anode composite material, comprising the following steps:

[0019] The phosphorus-containing compound and the carbon and nitrogen-containing compound are heated separately until they are vaporized to produce gaseous elemental phosphorus or phosphides and gaseous graphitic carbon nitride.

[0020] The gaseous elemental phosphorus or phosphide reacts with the gaseous graphitic carbon nitride to generate gaseous phosphorus-doped graphitic carbon nitride.

[0021] The phosphorus-doped graphite phase carbon nitride in the gas phase is deposited on the graphite surface to form a coating layer.

[0022] In one embodiment, the temperature at which the phosphorus-containing compound is heated is 400°C to 600°C;

[0023] In one embodiment, the temperature at which the carbon and nitrogen-containing compound is heated is 400°C to 600°C;

[0024] In one embodiment, the phosphorus-containing compound includes at least one of sodium hypophosphite, red phosphorus, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate;

[0025] In one embodiment, the carbon and nitrogen-containing compound includes at least one of melamine and urea;

[0026] In one embodiment, the mass ratio of the carbon- and nitrogen-containing compound to the phosphorus-containing compound is 1 to 5:1.

[0027] In one embodiment, during the reaction of the gaseous elemental phosphorus or phosphide with the gaseous graphitic carbon nitride, the gaseous elemental phosphorus or phosphide is transported by gas flow to contact the gaseous graphitic carbon nitride.

[0028] In one embodiment, the conveying distance is 10cm to 15cm.

[0029] In one embodiment, the temperature at which the gaseous elemental phosphorus or phosphide reacts with the gaseous graphitic carbon nitride to generate gaseous phosphorus-doped graphitic carbon nitride is 400°C to 600°C.

[0030] In one embodiment, the step of depositing the gaseous phosphorus-doped graphitic carbon nitride phase onto a graphite surface includes:

[0031] The phosphorus-doped graphitic carbon nitride in the gas phase is conveyed by the gas flow to a rotary device containing the graphite. The flow rate of the gas flow is 1.5 L / min to 8.5 L / min, and the rotation speed of the rotary device is 10 to 20 r / min.

[0032] A third aspect of the present invention provides a lithium-ion battery, characterized in that it comprises the graphite anode composite material described in the first aspect or the graphite anode composite material prepared by the preparation method described in the second aspect.

[0033] The aforementioned graphite anode composite material, by setting a coating layer of phosphorus-doped graphitic carbon nitride on the surface of the graphite core layer, helps to increase the specific capacity of the battery to over 380 mAh / g, while also improving the rate performance of the composite material. In addition, this graphite anode composite material also has the advantages of high long-cycle stability and high initial coulombic efficiency.

[0034] The above-mentioned method for preparing graphite anode composite material involves heating, gas-phase reaction, and deposition steps to form a coating layer of graphite phase carbon nitride material, including phosphorus doped, on the surface of graphite. The resulting graphite anode composite material has high specific capacity, high initial coulombic efficiency, and good rate performance, while also having low production cost and being easy to scale up. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a graphite anode composite material according to an example of the present invention;

[0036] Figure 2 This is a schematic diagram of the apparatus used in the preparation method of the graphite anode composite material, which is an example of the present invention. Detailed Implementation

[0037] The graphite anode composite material of the present invention, its preparation method, and its application are further described in detail below with reference to specific embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0039] In this article, "at least one" means any one, two or more of the listed items.

[0040] In this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0041] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0042] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0043] Unless otherwise specified, the percentage content involved in this invention refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures.

[0044] Unless otherwise specified, all percentage concentrations mentioned in this invention refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0045] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument.

[0046] like Figure 1 As shown, one example of the present invention provides a graphite anode composite material, including a graphite core layer 101 and a coating layer 102 located on the surface of the graphite core layer 101. The coating layer 102 includes a phosphorus-doped graphitic carbon nitride material. It is understood that the coating layer 102 may completely cover the entire surface of the graphite core layer 101, or it may partially cover the surface of the graphite core layer 101.

[0047] This graphite anode composite material possesses advantages such as high specific capacity, high initial coulombic efficiency, and good rate performance. Its possible underlying principle is as follows:

[0048] (1) Phosphorus-doped graphitic carbon nitride material (P-C3N4) contains a large number of pyrrole N “hole” defects in the crystal lattice, and the double bond nitrogen atoms of the P=N group at the edge of the vacancy enable it to reversibly adsorb lithium ions, which means that it has many lithium storage active sites. In addition, the layers of phosphorus-doped graphitic carbon nitride material are bonded by van der Waals forces, and the interlayer gap is relatively large, which is conducive to lithium ion insertion and storage, thereby greatly improving the overall specific capacity of the material, which can increase the specific capacity to more than 380 mAh / g. Since the core is a graphite core layer and the outer shell is a very thin phosphorus-doped graphitic carbon nitride material layer, the structure does not lose the tap density and compaction density of the material, thus exhibiting high energy density characteristics.

[0049] (2) Since graphitic carbon nitride itself has low conductivity, after phosphorus doping, P=N groups are formed, which can significantly increase the conductivity and carrier mobility of graphitic carbon nitride, thereby effectively improving the mobility of lithium ions, and ultimately resulting in improved rate performance of the material.

[0050] In addition, this graphite anode composite material also has the advantage of good cycle stability. The possible principle is that the layers in the structure of phosphorus-doped graphite phase carbon nitride material can be relatively smooth. Therefore, the coating layer is elastic and can expand and contract with the graphite particles, maintaining the integrity of the coating layer during the lithium insertion and extraction process. At the same time, it can avoid direct contact between the electrolyte and the graphite, thereby preventing solvent molecules from embedding into the graphite interlayer spacing and causing graphite material to delaminate. Therefore, it can improve the long-term cycle stability of the composite material.

[0051] In one example, the graphite core layer is made of either natural or artificial graphite.

[0052] In one example, the material of the graphite core layer has a D50 of 5 μm to 20 μm.

[0053] In one example, the tap density of the graphite core material is 0.95–1.25 g / cm³. 3 .

[0054] In one example, the material of the graphite core layer had a compaction density of 2–2.5 g / cm³ under a pressure of 5T. 3 .

[0055] In one example, the phosphorus and nitrogen atom content in the graphite core lattice is ≤50 ppm. This ensures the material's initial coulombic efficiency and cycling stability. Since phosphorus and nitrogen atoms have larger atomic radii than carbon atoms, their doping into the graphite core disrupts the graphite crystal structure, leading to a larger specific surface area and affecting the material's initial coulombic efficiency and cycling performance. Therefore, the lower the phosphorus and nitrogen atom content in the graphite core lattice, the better. Preferably, the phosphorus and nitrogen atom content in the graphite core lattice is 0.

[0056] In one example, the mass percentage of phosphorus atoms in the coating layer 102 is 0.1% to 5%. Specifically, the mass percentage of phosphorus atoms in the coating layer 102 includes, but is not limited to: 0.1%, 0.2%, 0.3%, 0.35%, 0.37%, 0.38%, 0.4%, 0.5%, 0.55%, 0.58%, 0.65%, 0.7%, 0.78%, 0.8%, 0.9%, 0.95%, 1%, 1.14%, 1.2%, 1.6%, 1.8%, 1.84%, 1.9%, 2%, 3%, 4%, and 5%.

[0057] In one example, the mass ratio of nitrogen atoms to phosphorus atoms in the coating layer 102 is 10 to 575. Specifically, the mass ratio of nitrogen atoms to phosphorus atoms in the coating layer 200 includes, but is not limited to: 10, 20, 25, 30, 30.9, 32, 35, 40, 50, 50.1, 52, 55, 60.2, 65, 70, 73.1, 75, 80, 90, 95, 98.8, 100, 130, 140, 145, 150, 151.2, 154, 160, 180, 200, 400, and 575.

[0058] In one example, the mass percentage of nitrogen atoms in the coating layer 102 is 40% to 80%. Specifically, the mass percentage of nitrogen atoms in the coating layer 102 includes, but is not limited to: 40%, 50%, 55%, 56%, 56.98%, 57.18%, 57.23%, 57.25%, 57.27%, 57.32%, 57.49%, 58%, 60%, 65%, 70%, 75%, and 80%.

[0059] In one example, the mass percentage of carbon atoms in the coating layer 102 is 30% to 60%. Specifically, the mass percentage of carbon atoms in the coating layer 102 includes, but is not limited to: 30%, 35%, 38%, 40%, 41.18%, 41.68%, 41.78%, 41.99%, 42.1%, 42.13%, 42.38%, 43%, 45%, 50%, 55%, and 60%.

[0060] In one example, the coating layer 102 contains P=N bonds. Further, the mass percentage of P=N bonds in the coating layer 102 is 40% to 60%. Specifically, the mass percentage of P=N bonds in the coating layer 200 includes, but is not limited to: 40%, 43%, 44%, 47%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, and 60%.

[0061] In one example, the content of phosphorus atoms in elemental form in the coating layer 200 is ≤0.1wt%. This further ensures the material's initial coulombic efficiency and cycle stability.

[0062] In one example, the thickness of the coating layer 102 is 20nm to 250nm. Specifically, the thickness of the coating layer 102 includes, but is not limited to: 20nm, 50nm, 70nm, 76nm, 80nm, 100nm, 110nm, 121nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, and 250nm.

[0063] In one example, the phosphorus-doped graphitic carbon nitride material in the coating layer 102 is a two-dimensional layered structure.

[0064] In one example, the specific surface area of ​​the graphite anode composite material is 0.5–2 m². 2 / g.

[0065] In one example, the tap density of the graphite anode composite material was 0.9–1.2 g / cm³. 3 .

[0066] In one example, the graphite anode composite material had a compaction density of 1.7–2.2 g / cm³ under a pressure of 5T. 2 .

[0067] In one example, the specific capacity of the graphite anode composite material is ≥380 mAh / g. Understandably, specific capacity is typically obtained by testing the graphite anode composite material as a carbon anode material assembled into a coin cell.

[0068] In one example, the initial coulombic efficiency of the graphite anode composite material is ≥90%. Understandably, the initial coulombic efficiency is typically obtained by testing the graphite anode composite material as a carbon anode material assembled into a coin half-cell.

[0069] In one example, the graphite anode composite material exhibits a 1C rate charge retention rate ≥ 65%. Understandably, the rate charge retention rate is typically obtained by testing the graphite anode composite material as a carbon anode material assembled into a coin cell.

[0070] One example of the present invention provides a method for preparing a graphite anode composite material, comprising the following steps:

[0071] S1: Heat the phosphorus-containing compound and the carbon and nitrogen-containing compound separately until they are vaporized to produce gaseous elemental phosphorus or phosphides and gaseous graphitic carbon nitride.

[0072] S2: React the gaseous elemental phosphorus or phosphide with the gaseous graphitic carbon nitride to generate gaseous phosphorus-doped graphitic carbon nitride.

[0073] S3: Deposit the phosphorus-doped graphite phase carbon nitride in the gas phase onto the graphite surface to form a coating layer.

[0074] The above-mentioned method for preparing graphite anode composite materials involves a simple heat treatment of phosphorus-containing compounds and carbon and nitrogen-containing compounds to volatilize gaseous elemental phosphorus or phosphides and gaseous graphitic carbon nitride (g-C3N4), which react to form phosphorus-doped graphitic carbon nitride material (P-C3N4). This material is then uniformly deposited on the graphite surface upon cooling to form a coating layer. Compared with traditional methods, this method offers significant advantages in terms of low cost and scalability. Understandably, the coating layer can completely cover the entire surface of the graphite or only partially cover its surface.

[0075] Furthermore, forming a gaseous phosphorus-doped graphitic carbon nitride material (P-C3N4) before deposition coating allows for more uniform phosphorus doping and simplifies the process. Simultaneously, compared to solid-phase doping reactions, the reaction between gaseous elemental phosphorus or phosphides and gaseous graphitic carbon nitride results in more thorough and uniform contact between the two compounds. Almost all elemental phosphorus participates in the reaction, leaving only very little or no elemental phosphorus in the coating layer. This also generates more P=N, resulting in a more uniform distribution.

[0076] Specifically, in step S1:

[0077] In one example, the phosphorus-containing compound is heated to a temperature of 400°C to 600°C. Temperatures that are too low will not produce gaseous elemental phosphorus or phosphides, while temperatures that are too high may cause other compounds to vaporize simultaneously, forming C3N4 compounds of other elements, which can affect the material's properties. Specifically, the heating temperatures of the phosphorus-containing compound include, but are not limited to: 400°C, 450°C, 480°C, 500°C, 520°C, 550°C, and 600°C.

[0078] In one example, the carbon and nitrogen-containing compound is heated to a temperature of 400°C to 600°C. Specifically, the heating temperature of the carbon and nitrogen-containing compound includes, but is not limited to, 400°C, 450°C, 480°C, 500°C, 520°C, 550°C, and 600°C.

[0079] In one example, the phosphorus-containing compound includes at least one selected from sodium hypophosphite, red phosphorus, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Without limitation, the gaseous phosphide is gaseous phosphine.

[0080] In one example, the carbon and nitrogen-containing compound includes at least one of melamine and urea.

[0081] In one example, the mass ratio of the carbon and nitrogen-containing compound to the phosphorus-containing compound is 1 to 5:1. A mass ratio that is too large results in insufficient phosphorus doping, leading to fewer P=N double bonds and a lower specific capacity. Conversely, a mass ratio that is too small results in excessive phosphorus, leading to too many P=N bonds and affecting the material's yield, coulombic efficiency, and cycle life. Specifically, the mass ratio of the carbon and nitrogen-containing compound to the phosphorus-containing compound includes, but is not limited to, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, and 5:1.

[0082] Specifically, in step S2:

[0083] In one example, the conditions for the reaction to generate gaseous phosphorus-doped graphitic carbon nitride include a temperature of 400°C to 600°C. Specifically, the temperatures for the reaction to generate gaseous phosphorus-doped graphitic carbon nitride include, but are not limited to, 400°C, 450°C, 480°C, 500°C, 520°C, 550°C, and 600°C.

[0084] In one example, the step of reacting gaseous elemental phosphorus or phosphide with gaseous graphitic carbon nitride to generate gaseous phosphorus-doped graphitic carbon nitride includes:

[0085] The gaseous elemental phosphorus or phosphide is transported by the gas flow to contact and react with the gaseous graphitic carbon nitride. For example, the phosphorus-containing compound can be positioned upstream of the carbon- and nitrogen-containing compound along the gas flow direction.

[0086] In one example, the gas flow is an inert gas. Specifically, the inert gas includes, but is not limited to, at least one of nitrogen, argon, helium, neon, krypton, and xenon.

[0087] In one example, the flow rate of the gas stream is 1.5 L / min to 8.5 L / min. A flow rate < 1.5 L / min results in insufficient coating thickness on the graphite surface, affecting the material's capacity; a flow rate > 8.5 L / min leads to incomplete reaction between the gaseous P-oxide and gaseous C3N4, resulting in too few P=N bonds, which also affects the specific capacity and first-efficiency. Specifically, the flow rate of the gas stream includes, but is not limited to: 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, 3.5 L / min, 4 L / min, 4.5 L / min, 5 L / min, 5.5 L / min, 6 L / min, 6.5 L / min, 7 L / min, 7.5 L / min, 8 L / min, and 8.5 L / min.

[0088] In one example, the gaseous elemental phosphorus or phosphide is transported by gas flow to contact the gaseous graphitic carbon nitride at a distance of 10cm to 15cm. This ensures complete reaction between the gaseous elemental phosphorus or phosphide and the graphitic carbon nitride. Specifically, the transport distance includes, but is not limited to, 10cm, 11cm, 12cm, 13cm, 14cm, and 15cm.

[0089] Understandably, in this step, the gaseous elemental phosphorus or phosphide reacts with the gaseous graphitic carbon nitride to generate gaseous phosphorus-doped graphitic carbon nitride (coating material) before proceeding to the next step, such as deposition in contact with graphite material in a rotary kiln.

[0090] Specifically, in step S3:

[0091] In one example, the gaseous phosphorus-doped graphitic carbon nitride is transported by a gas stream to the surface of the graphite for deposition. Further, the gas stream is an inert gas. Specifically, the inert gas includes, but is not limited to, at least one of nitrogen, argon, helium, neon, krypton, and xenon. It is understood that the graphite does not require heating treatment, so that the gaseous phosphorus-doped graphitic carbon nitride deposits upon cooling after being transported to the surface of the graphite by the gas stream.

[0092] In one example, the airflow velocity is 1.5 L / min to 8.5 L / min. Specifically, the airflow velocity includes, but is not limited to: 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, 3.5 L / min, 4 L / min, 4.5 L / min, 5 L / min, 5.5 L / min, 6 L / min, 6.5 L / min, 7 L / min, 7.5 L / min, 8 L / min, and 8.5 L / min.

[0093] In one example, the graphite is stirred and / or tumbled during the deposition process.

[0094] In one example, the step of depositing the gaseous phosphorus-doped graphitic carbon nitride phase onto a graphite surface includes:

[0095] The phosphorus-doped graphitic carbon nitride in the gas phase is conveyed by the gas flow to a rotary device containing the graphite. The flow rate of the gas flow is 1.5 L / min to 8.5 L / min, and the rotation speed of the rotary device is 10 to 20 r / min.

[0096] Specifically, the airflow velocity includes, but is not limited to: 1.5L / min, 2L / min, 2.5L / min, 3L / min, 3.5L / min, 4L / min, 4.5L / min, 5L / min, 5.5L / min, 6L / min, 6.5L / min, 7L / min, 7.5L / min, 8L / min, and 8.5L / min. The rotational speed of the rotary device is 10r / min, 13r / min, 15r / min, 17r / min, and 20r / min.

[0097] Understandably, the deposition time can be adjusted according to the thickness of the coating layer. In one example, the deposition time is 10 min to 50 min. Specifically, the deposition time includes, but is not limited to: 10 min, 15 min, 20 min, 25 min, 30 min, 45 min, 40 min, 45 min, and 50 min.

[0098] Further, see Figure 2 In one example of the present invention, the preparation method of the graphite anode composite material is carried out in a preparation apparatus. The preparation apparatus is provided with a heating furnace 201 and a rotary kiln 202 sequentially along the gas flow direction. The heating furnace 201 is used to load phosphorus-containing compounds and compounds containing carbon and nitrogen. Optionally, the phosphorus-containing compound is loaded upstream of the carbon and nitrogen-containing compounds along the gas flow direction. The rotary kiln 202 is used to load graphite and to keep the graphite in a stirring and / or tumbling state. Simultaneously, the rotary kiln 202 is not heat-treated, so that the gaseous phosphorus-doped graphite-phase carbon nitride directly deposits on the surface of the graphite particles upon "cooling," obtaining the graphite anode composite material; that is, this process does not require further heat treatment.

[0099] Furthermore, it is understandable that the graphite anode composite material prepared by the above preparation method has the characteristics and advantages of the aforementioned graphite anode composite material, which will not be repeated here.

[0100] An example of the present invention provides a lithium-ion battery comprising the graphite anode composite material as described above or the graphite anode composite material prepared by the preparation method described above.

[0101] The following are specific examples.

[0102] Example 1:

[0103] In this embodiment, sodium hypophosphite is used as a phosphorus-containing precursor, and melamine is used as a nitrogen- and carbon-containing precursor. The graphite material is spherical natural graphite with a D50 of 17 μm and a tap density of 1.05 g / cm³. 3 The compaction density under 5T pressure is 2.07 g / cm³. 3 .

[0104] The preparation process is as follows: 5 kg of sodium hypophosphite and 5 kg of melamine are weighed and placed in a nitrogen atmosphere furnace, with the sodium hypophosphite positioned 10 cm upstream of the melamine. The nitrogen flow rate is 5 L / min. The furnace temperature is raised to 500℃ and maintained at this temperature. The sodium hypophosphite and melamine continuously generate gaseous phosphine and carbon nitride, which react to produce gaseous phosphorus-doped carbon nitride (P-C3N4). This gaseous P-C3N4 is then introduced into a rotary kiln containing natural graphite at a rotation speed of 15 r / min. Upon cooling, the gaseous P-C3N4 deposits on the surface of the natural graphite, forming a coating layer. The entire deposition process takes 30 minutes, resulting in a deposition thickness of 200 nm, thus obtaining the graphite anode composite material.

[0105] Example 2:

[0106] This embodiment uses red phosphorus as a phosphorus-containing precursor and urea as a nitrogen- and carbon-containing precursor. The graphite material is secondary particle artificial graphite with a D50 of 17 μm and a tap density of 0.95 g / cm³. 3 The compaction density under 5T conditions is 2.03 g / cm³. 3 .

[0107] The preparation process is as follows: Weigh 5 kg of red phosphorus and 5 kg of urea, and then place them in a nitrogen atmosphere furnace, with the red phosphorus positioned 10 cm upstream of the urea. The nitrogen flow rate is 5 L / min. The furnace temperature is raised to 450℃ and maintained at this temperature. The red phosphorus and urea continuously generate gaseous phosphorus and carbon nitride, and react to produce gaseous phosphorus-doped carbon nitride (P-C3N4). This gaseous P-C3N4 is then introduced into a rotary kiln containing artificial graphite, rotating at 15 r / min. Upon cooling, the gaseous P-C3N4 deposits on the surface of the artificial graphite, forming a coating layer. The entire deposition process takes 30 minutes, resulting in a deposition thickness of 200 nm, thus obtaining the graphite anode composite material.

[0108] Example 3

[0109] This example uses ammonium phosphate as a phosphorus-containing precursor and urea as a nitrogen- and carbon-containing precursor. The graphite material is single-particle artificial graphite with a D50 of 8 μm and a tap density of 1.04 g / cm³. 3 The compaction density under 5T conditions is 1.88 g / cm³. 3 .

[0110] The preparation process is as follows: Weigh 5 kg of ammonium phosphate and 5 kg of urea, and then place them in a nitrogen atmosphere furnace. The ammonium phosphate is placed 10 cm upstream of the urea. The nitrogen flow rate is 5 L / min. The furnace temperature is raised to 500℃ and maintained at that temperature. Ammonium phosphate and urea continuously generate gaseous phosphine and carbon nitride, and react to produce gaseous phosphorus-doped carbon nitride P-C3N4. This gaseous carbon nitride is then introduced into a rotary kiln containing artificial graphite at a rotation speed of 15 r / min. Upon cooling, the gaseous phosphorus-doped carbon nitride P-C3N4 deposits on the surface of the artificial graphite, forming a coating layer. The entire deposition time is 20 min, and the deposition thickness is 150 nm, thus obtaining the graphite anode composite material.

[0111] Example 4

[0112] The raw materials and preparation process are the same as in Example 1, except that the coating deposition time is 10 min and the deposition thickness is 76 nm, resulting in a graphite anode composite material.

[0113] Example 5

[0114] The raw materials and preparation process are the same as in Example 1, except that the coating deposition time is 20 min and the deposition thickness is 121 nm, resulting in a graphite anode composite material.

[0115] Example 6

[0116] The raw materials and preparation process are the same as in Example 1, except that the coating deposition time is 40 min and the deposition thickness is 210 nm, resulting in a graphite anode composite material.

[0117] Example 7

[0118] The raw materials and preparation process are the same as in Example 1, except that the coating deposition time is 50 min and the deposition thickness is 250 nm, resulting in a graphite composite material.

[0119] Comparative Example 1

[0120] The raw materials and preparation process are the same as in Example 1, except that sodium hypophosphite is not added.

[0121] Test example:

[0122] I. Testing Method:

[0123] (1) Electrochemical testing:

[0124] The graphite anode composite materials obtained in the various embodiments and comparative examples of the present invention were used as the anode active materials. They were mixed according to a mass ratio of anode active material: conductive carbon black: CMC: SBR = 95.3:1.5:1.4:1.8, and after being mixed with deionized water as a solvent, the mixture was coated onto copper foil. The coating surface density was 6.5 ± 0.1 mg / cm³. 2 After vacuum drying at 90℃, a negative electrode sheet is obtained, and the negative electrode sheet is then rolled to a compaction density of 1.65±0.02 g / cm³. 3 The negative electrode, lithium sheet, electrolyte (1 mol / L LiPF6, EC:EMC = 1:1) and Celgard 2400 separator were assembled into a 2016 coin cell. The resulting cell was subjected to rate and cycle tests at 25±2℃.

[0125] The 1C rate test conditions are as follows: ① Discharge to 0.01V with 0.1C and maintain constant voltage for 5 hours; charge to 1.5V with 0.1C; ② Discharge to 0.01V with 0.2C and maintain constant voltage at 0.01C; charge to 1.5V with 0.2C; ③ Discharge to 0.01V with 0.01C and maintain constant voltage at 0.01C; charge to 1.5V with 2C and 0.2C; ④ Discharge to 0.01V with 0.2C and maintain constant voltage at 0.01C; charge to 1.5V with 0.2C; ⑤ Discharge to 0.01V with 1C and maintain constant voltage at 0.01C; charge to 1.5V with 0.2C; ⑥ Discharge to 0.01V with 2C.

[0126] The cycle test conditions were: 0.2C charge / discharge rate, voltage range 0.01V to 1.5V. The first-week charge specific capacity, first-week efficiency, and 50-week coin cycle stability were tested respectively, and the 1C (CC / 0.2C CC+CV) charge and 50-week capacity retention rate were calculated.

[0127] (2) Specific surface area determination of graphite anode composite material:

[0128] The measurement was performed using a McBee 3020 instrument and the gas adsorption BET method.

[0129] (3) Measurement of compaction density of graphite anode composite material under 5T conditions:

[0130] The equipment uses an automatic powder compaction density meter (UTM7305). The testing method involves placing a certain mass of powder sample inside a metal sleeve and maintaining it under a certain pressure for a certain time. The ratio of the sample's mass to its compacted volume can be calculated using the following formula:

[0131] ρ = 10M / (S*H)

[0132] Where ρ: compaction density, g / m³ 3 ;

[0133] M: Powder mass, g;

[0134] S: Cross-sectional area of ​​the top column, which is 1.293 cm² in this instrument. 2 ;

[0135] H: Powder thickness measured by a thickness gauge, in mm;

[0136] (4) Measurement of tap density of graphite anode composite material:

[0137] The American CANTA automatic tap density meter was used, referring to GB / T 21354 General Method for Determination of Tap Density of Powder Products.

[0138] (5) XPS test:

[0139] X-ray photoelectron spectroscopy (XPS) can analyze materials from the surface down to a depth of approximately 5 nm to 10 nm (typically around 5 nm), allowing for quantitative analysis of elemental concentrations in about half of the surface layer. Furthermore, narrow-scan analysis can reveal the bonding states of elements.

[0140] X-ray photoelectron spectroscopy (XPS) can be performed, for example, using the ULVAC-PHI Quantera II X-ray photoelectron spectroscopy analyzer. X-ray source: Al monochromatic 100 μm, 25 W, 15 kV; surface unetched; photoelectron extraction angle: 45°; bonding energy correction: the C1s peak is set to 284.6 eV; XPS is measured on graphite anode composite materials. Based on the obtained XPS spectrum, peak P2P3 / 2, appearing in the binding energy range of 128 eV to 144 eV, is decomposed and curve-fitted to determine the peak area of ​​P=N.

[0141] The test results are shown in Table 1 below:

[0142] Table 1

[0143]

[0144]

[0145] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0146] The embodiments described above are merely illustrative of several implementations of the present invention, designed to facilitate a detailed understanding of the technical solutions of the present invention, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided by the present invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this invention patent should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A graphite anode composite material, characterized in that, The composite material includes a graphite core layer and a coating layer on the surface of the graphite core layer. The coating layer comprises phosphorus-doped graphitic carbon nitride material. The thickness of the coating layer is 20 nm to 250 nm. The graphite anode composite material has a compaction density of 1.7 to 2.2 g / cm³ under a pressure of 5T. 2 .

2. The graphite anode composite material according to claim 1, characterized in that, The graphite anode composite material satisfies at least one of the following characteristics (1) to (5): (1) The mass percentage of phosphorus atoms in the coating layer is 0.1% to 5%; (2) The mass ratio of nitrogen atoms to phosphorus atoms in the coating layer is 10~575; (3) The mass percentage of P=N bonds in the coating layer is 40%~60%; (4) The content of phosphorus atoms and nitrogen atoms in the lattice of the graphite core layer is ≤50ppm; (5) The content of phosphorus atoms in the coating layer in elemental form is ≤0.1wt%.

3. The graphite anode composite material according to claim 1 or 2, characterized in that, The graphite anode composite material satisfies at least one of the following characteristics (1) to (2): (1) The specific surface area of ​​the graphite anode composite material is 0.5~2m². 2 / g; (2) The tap density of the graphite anode composite material is 0.9~1.2 g / cm³. 3 .

4. A method for preparing a graphite anode composite material, characterized in that, Includes the following steps: Heating phosphorus-containing compounds or red phosphorus and carbon and nitrogen-containing compounds separately until they are vaporized to produce gaseous elemental phosphorus or phosphides and gaseous graphitic carbon nitride. The gaseous elemental phosphorus or phosphide reacts with the gaseous graphitic carbon nitride to generate gaseous phosphorus-doped graphitic carbon nitride. The phosphorus-doped graphite phase carbon nitride in the gas phase is deposited on the graphite surface to form a coating layer.

5. The method for preparing the graphite anode composite material according to claim 4, characterized in that, Includes at least one of the following features (1) to (5): (1) The temperature at which the phosphorus-containing compound is heated is 400℃~600℃; (2) The temperature at which the carbon and nitrogen-containing compound is heated is 400℃~600℃; (3) The phosphorus-containing compound includes at least one of sodium hypophosphite, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; (4) The carbon and nitrogen-containing compounds include at least one of melamine and urea; (5) The mass ratio of the carbon and nitrogen-containing compound to the phosphorus-containing compound is 1 to 5:

1.

6. The method for preparing the graphite anode composite material according to claim 4, characterized in that, During the reaction between the gaseous elemental phosphorus or phosphide and the gaseous graphitic carbon nitride, the gaseous elemental phosphorus or phosphide is transported by gas flow to contact the gaseous graphitic carbon nitride.

7. The method for preparing the graphite anode composite material according to claim 6, characterized in that, The conveying distance is 10cm~15cm.

8. The method for preparing the graphite anode composite material according to claim 4, characterized in that, The temperature at which the gaseous elemental phosphorus or phosphide reacts with the gaseous graphitic carbon nitride to generate gaseous phosphorus-doped graphitic carbon nitride is 400℃~600℃.

9. The method for preparing the graphite anode composite material according to any one of claims 4 to 8, characterized in that, The step of depositing phosphorus-doped graphitic carbon nitride in the gaseous phase onto a graphite surface includes: The phosphorus-doped graphite phase carbon nitride in the gas phase is transported by gas flow to a rotary device containing the graphite. The flow rate of the gas flow is 1.5 L / min to 8.5 L / min, and the rotation speed of the rotary device is 10 to 20 r / min.

10. A lithium-ion battery, characterized in that, This includes the graphite anode composite material as described in any one of claims 1 to 3, or the graphite anode composite material prepared by the preparation method described in any one of claims 4 to 9.

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