Phosphorus-doped graphite materials, their preparation methods and applications, and negative electrode sheets

Abstract

This application belongs to the field of graphite modification technology, specifically relating to phosphorus-doped graphite materials, their preparation methods and applications, and negative electrode sheets. The preparation method provided in this application includes the following steps: mixing a phosphorus source and graphite to prepare a mixture; under a protective gas atmosphere, heating the mixture to 300℃~900℃ at a heating rate of 1℃ / min~10℃ / min for a first calcination, and then cooling to 100℃~500℃ at a cooling rate of 1℃ / min~10℃ / min for a second calcination, thereby preparing the phosphorus-doped graphite material. The preparation method provided in this application is simple, low-cost, and easily scalable for industrial production. Furthermore, the phosphorus-doped graphite material provided in this application, when used as a negative electrode material for lithium-ion batteries, can significantly improve the battery's capacity and cycle performance.

Description

Technical Field

[0001] This application relates to the field of graphite modification technology, specifically to a phosphorus-doped graphite material, its preparation method and application, and a negative electrode sheet. Background Technology

[0002] Graphite is an important carbon material. Its unique properties, such as high temperature resistance, good electrical and thermal conductivity, lubricity, plasticity, and chemical stability, make it widely used in semiconductor materials, composite materials, battery electrode materials, hydrogen storage materials, field emission materials, and ultra-sensitive sensors. With the continuous improvement of graphite material preparation technology, doping has been found to be an effective way to modify the electronic structure and chemical properties of graphite. During doping, heteroatoms are incorporated into the graphite lattice, which not only effectively introduces band gaps but also increases the defect and local reactivity of graphite, thereby generating many new functions. Therefore, heteroatom doping has been considered one of the effective ways to improve the capacity, rate performance, and first-efficiency of graphite materials.

[0003] Among heteroatoms, phosphorus has an extremely high theoretical specific capacity (~2500 mA hg). −1 A suitable lithiation potential (approximately 0.7 V vs. Li) + Phosphorus has attracted much attention from researchers due to its advantages such as low cost and high efficiency. However, the radii of phosphorus atoms differ significantly from those of carbon atoms, making it difficult to incorporate phosphorus into the graphite lattice. Furthermore, phosphorus's poor electrical conductivity and volume expansion during cycling hinder its widespread application. Summary of the Invention

[0004] Based on this, this application provides a phosphorus-doped graphite material, its preparation method and application, and an anode sheet. The preparation method provided in this application enables phosphorus to be effectively incorporated into graphite. Furthermore, when the phosphorus-doped graphite material prepared in this application is used as an anode active material, it can effectively improve the lithium storage performance and cycle stability of the battery.

[0005] A first aspect of this application provides a method for preparing a phosphorus-doped graphite material, comprising the following steps:

[0006] A mixture is prepared by mixing a phosphorus source and graphite.

[0007] Under a protective gas atmosphere, the mixture is heated to 300°C to 900°C at a heating rate of 1°C / min to 10°C / min for a first calcination.

[0008] Then, the temperature is lowered to 100℃~500℃ at a cooling rate of 1℃ / min~10℃ / min for a second calcination to prepare the phosphorus-doped graphite material.

[0009] In one embodiment, the mass ratio of the phosphorus source to graphite is (5~30):1.

[0010] In one embodiment, the phosphorus source includes one or more of sodium hypophosphite, red phosphorus, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0011] In one embodiment, the first calcination time is 0.5h to 10h.

[0012] In one embodiment, the second calcination time is 12h to 48h.

[0013] In one embodiment, the graphite includes one or more of synthetic graphite and natural graphite.

[0014] A second aspect of this application provides a phosphorus-doped graphite material, which is prepared by the phosphorus-doped graphite material preparation method described in any embodiment of the first aspect of this application.

[0015] In one embodiment, the phosphorus atomic percentage in the phosphorus-doped graphite material is 0.5 at% to 5 at%.

[0016] A third aspect of this application provides the application of the phosphorus-doped graphite material described in any embodiment of the second aspect of this application in a negative electrode active material.

[0017] A fourth aspect of this application provides a negative electrode sheet comprising a phosphorus-doped graphite material, a conductive agent, and a binder, wherein the phosphorus-doped graphite material is the phosphorus-doped graphite material described in any embodiment of the second aspect of this application.

[0018] In one embodiment, the conductive agent includes one or more of carbon fiber, conductive carbon black, carbon nanotubes, and graphene.

[0019] In one embodiment, the adhesive includes one or more of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose, and styrene-butadiene rubber.

[0020] In one embodiment, the compaction density of the negative electrode is 1.40 g / cm³. 3 ~1.70 g / cm 3 .

[0021] In one embodiment, the mass ratio of the phosphorus-doped graphite material, the conductive agent, and the binder is (92~98):(0.5~2):(1.5~7.5).

[0022] In the preparation method provided in this application, phosphorus in the phosphorus source is sublimated through a first high-temperature calcination, allowing it to diffuse into the pores of the graphite material along with a protective gas. A second low-temperature calcination further cools the phosphorus, enabling in-situ phosphorus doping with the graphite material, successfully incorporating it into the carbon matrix framework through chemical bonds, thus successfully preparing phosphorus-doped graphite material. Furthermore, the preparation method provided in this application is simple, low-cost, and easily scalable for industrial production. Moreover, the phosphorus-doped graphite material provided in this application, when used as a negative electrode material for lithium-ion batteries, can significantly improve battery capacity and cycle performance. Attached Figure Description

[0023] Figure 1 This is a SEM image of the phosphorus-doped artificial graphite material prepared in Example 1 of this application. Detailed Implementation

[0024] The following detailed description, in conjunction with specific embodiments, provides a more complete and clear account of the phosphorus-doped graphite material, its preparation method, its application, and the negative electrode sheet of this application. This application 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 this application.

[0025] 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 application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0026] In this article, "one or more" refers to any one, two or more of the listed items.

[0027] In this application, terms such as "first aspect," "second aspect," "third aspect," "fourth aspect," and "fifth 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," "fourth," and "fifth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0028] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0029] In this application, numerical ranges are referred to as continuous unless otherwise specified, 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 a feature or characteristic, 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 incorporated.

[0030] Unless otherwise specified, the percentage content mentioned in this application refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures.

[0031] Unless otherwise specified, all percentage concentrations mentioned in this application 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.

[0032] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0033] A first aspect of this application provides a method for preparing a phosphorus-doped graphite material, comprising the following steps:

[0034] A mixture is prepared by mixing a phosphorus source and graphite.

[0035] Under a protective gas atmosphere, the mixture is heated to 300°C to 900°C at a heating rate of 1°C / min to 10°C / min for a first calcination.

[0036] Then, the temperature is lowered to 100℃~500℃ at a cooling rate of 1℃ / min~10℃ / min for a second calcination to prepare the phosphorus-doped graphite material.

[0037] In the preparation method provided in this application, phosphorus in the phosphorus source is sublimated through a first high-temperature calcination, allowing it to diffuse into the pores of the graphite material along with a protective gas. A second low-temperature calcination further cools the phosphorus, enabling in-situ phosphorus doping with the graphite material, successfully incorporating it into the carbon matrix framework through chemical bonds, thus successfully preparing phosphorus-doped graphite material. Furthermore, the preparation method provided in this application is simple, low-cost, and easily scalable for industrial production. Moreover, the phosphorus-doped graphite material provided in this application, when used as a negative electrode material for lithium-ion batteries, can significantly improve battery capacity and cycle performance.

[0038] Understandably, in this application, the heating rate during the first calcination process can be selected from any value between 1℃ / min and 10℃ / min. Specifically, the heating rate during the first calcination process includes, but is not limited to, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, or 10℃ / min. The temperature of the first calcination can be selected from any value between 300℃ and 900℃. Specifically, the temperature of the first calcination includes, but is not limited to, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃.

[0039] Understandably, in this application, the cooling rate during the second calcination process can be selected from any value between 1℃ / min and 10℃ / min. Specifically, the cooling rate during the second calcination process includes, but is not limited to, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, or 10℃ / min. The temperature of the second calcination can be selected from any value between 100℃ and 500℃. Specifically, the temperature of the second calcination includes, but is not limited to, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, or 500℃.

[0040] Understandably, the temperature for the first calcination in this application can be selected from any value between 300℃ and 900℃. The temperature for the second calcination can be selected from any value between 100℃ and 500℃. Preferably, the temperature of the first calcination is 200℃ to 400℃ higher than the temperature of the second calcination. Ensuring that the temperature difference between the first and second calcination temperatures allows phosphorus to sublimate at the first calcination temperature, enabling it to successfully diffuse into the voids of the graphite material; further combined with the second low-temperature calcination, phosphorus is in-situ doped with the graphite material, thereby successfully preparing phosphorus-doped graphite material.

[0041] In one example, the mass ratio of the phosphorus source to graphite is (5~30):1. It is understood that the mass ratio of the phosphorus source to graphite can be selected from any value between (5~30):1. Specifically, the mass ratio of the phosphorus source to graphite includes, but is not limited to, 5:1, 6:1, 7:1, 8:1, 10:1, 12:1, 15:1, 17:1, 18:1, 20:1, 22:1, 25:1, 27:1, 28:1, 29:1, or 30:1.

[0042] In one example, the phosphorus source includes one or more of sodium hypophosphite, red phosphorus, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Ammonium dihydrogen phosphate represents a substance with the chemical formula NH4H2PO4; diammonium hydrogen phosphate represents a substance with the chemical formula (NH4)2HPO4.

[0043] In one example, the first calcination time is 0.5 h to 10 h. Understandably, the first calcination time can be selected from any value between 0.5 h and 10 h. Specifically, the first calcination time includes, but is not limited to, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, or 10 h.

[0044] In one example, the second calcination time is 12h to 48h. Understandably, the second calcination time can be selected from any value between 12h and 48h. Specifically, the second calcination time includes, but is not limited to, 12h, 15h, 16h, 18h, 20h, 22h, 24h, 28h, 30h, 32h, 35h, 38h, 40h, 42h, 45h, 46h, or 48h.

[0045] Understandably, this application does not limit the type and source of graphite. In one example, the graphite includes one or more of artificial graphite and natural graphite. Natural graphite is a mineral with a special structure, composed of carbon. Natural graphite is a naturally occurring carbon-rich organic compound, a mineral raw material that naturally transforms under long-term action in a high-temperature, high-pressure geological environment. It is usually in flake or scaly form and is widely used in industry. The preparation method provided in this application can dope natural graphite with phosphorus to further broaden the application range of natural graphite.

[0046] Compared to natural graphite, artificial graphite has the advantages of controllable structure and high purity. Artificial graphite is typically produced from carbonaceous raw materials with low impurity content through processes such as batching, mixing, molding, carbonization, and graphitization. The preparation method provided in this application is also applicable to artificial graphite. The "artificial graphite" mentioned in this application can be single-particle artificial graphite or secondary-particle artificial graphite. It is understood that this application does not limit the type of artificial graphite; conventional artificial graphite can be phosphorus-doped using the preparation method provided in this application. For example, the preparation process of single-particle artificial graphite includes the following steps:

[0047] a1. Petroleum coke, needle coke or pitch coke are crushed, spheroidized and shaped and fine powder is removed to prepare intermediate material;

[0048] a2. The intermediate material is heat-treated at 500℃~650℃ for 6h~20h, and then graphitized at 2000℃~3200℃ for 20h~60h to prepare graphite particles.

[0049] a3. The graphite particles are sequentially wet-granulated at a rotation speed of 250 r / min to 1400 r / min for 8 min to 70 min, and then carbonized at a temperature of 1100℃ to 1250℃ to prepare single-particle artificial graphite. It can be understood that if the raw material in step a1 only includes petroleum coke, then step a3 will prepare petroleum coke single-particle artificial graphite. If the raw material in step a1 only includes needle coke, then step a3 will prepare needle coke single-particle artificial graphite. If the raw material in step a1 only includes pitch coke, then step a3 will prepare pitch coke single-particle artificial graphite.

[0050] For example, the preparation process of secondary particles includes the following steps:

[0051] b1. Pulverize petroleum coke, needle coke or pitch coke to prepare small particulate substrate;

[0052] b2. Using asphalt as a binder, mix it with the small-particle substrate from step b1 to prepare a binder; the mass percentage of asphalt in the binder is 1wt%~20wt%.

[0053] b3. The binder prepared in step b2 is granulated at 600℃~700℃, graphitized at 2000℃~2800℃ for 30min~180min, wet-granulated at 250 r / min~1400 r / min, and carbonized at 1100℃~1250℃ to prepare secondary granulated artificial graphite. Understandably, if the raw material in step b1 only includes petroleum coke, then step b3 will produce petroleum coke secondary granulated artificial graphite. If the raw material in step b1 only includes needle coke, then step b3 will produce needle coke secondary granulated artificial graphite. If the raw material in step b1 only includes pitch coke, then step b3 will produce pitch coke secondary granulated artificial graphite.

[0054] The phosphorus-doped artificial graphite prepared by the method of this application has phosphorus successfully incorporated into the carbon matrix framework in the form of chemical bonds, and the interaction is enhanced, which can improve the conductivity of artificial graphite, improve its lithium storage performance in lithium-ion batteries, and enhance its performance as an electrode material.

[0055] In one more specific example, the method for preparing the phosphorus-doped graphite material includes the following steps:

[0056] A mixture is prepared by mixing phosphorus source and graphite at a mass ratio of (5~30):1;

[0057] Under a protective gas atmosphere, the mixture is heated to 300°C to 900°C at a heating rate of 1°C / min to 10°C / min for a first calcination, which lasts for 0.5 to 10 hours.

[0058] The phosphorus-doped graphite material is prepared by cooling the material to 100℃~500℃ at a cooling rate of 1℃ / min~10℃ / min for a second calcination time of 12h~48h.

[0059] A second aspect of this application provides a phosphorus-doped graphite material, prepared by the method for preparing phosphorus-doped graphite materials described in any example of the first aspect of this application.

[0060] In one example, the atomic percentage of phosphorus in the phosphorus-doped graphite material is 0.5 at% to 5 at%. It is understood that, in this application, the atomic percentage of phosphorus in the phosphorus-doped graphite material can be selected from any value between 0.5 at% and 5 at%. Specifically, the atomic percentage of phosphorus in the phosphorus-doped graphite material includes, but is not limited to, 0.5 at%, 1 at%, 1.3 at%, 1.5 at%, 1.7 at%, 2 at%, 2.2 at%, 2.5 at%, 2.7 at%, 2.8 at%, 3 at%, 3.2 at%, 3.5 at%, 3.8 at%, 4 at%, 4.2 at%, 4.5 at%, 4.7 at%, 4.8 at%, or 5 at%.

[0061] In the phosphorus-doped graphite material prepared in this application, the atomic percentage of phosphorus is between 0.5 at% and 5 at%, which gives it the following advantages: (1) Improved conductivity: The doping of phosphorus can significantly improve the conductivity of graphite materials, which have lower resistivity and better electronic conductivity, making them more efficient and effective in electronic devices and conductive materials. (2) Improved lithium storage performance: The introduction of phosphorus can improve the lithium-ion storage capacity and cycle stability of graphite materials, thereby enhancing the energy density and lifespan of batteries. (3) Enhanced chemical stability: The chemical stability of phosphorus-doped graphite materials is enhanced, and they are more resistant to external environments such as oxidation, acid, and alkali. This makes phosphorus-doped graphite potentially valuable in fields involving chemical reactions and requiring high corrosion resistance. (4) Regulation of physical properties: Phosphorus doping can introduce additional electronic states and energy levels, and regulate the optical, magnetic, and thermal physical properties of graphite materials. This also provides new opportunities for the application of phosphorus-doped graphite in optoelectronic devices, magnetic materials, and thermal conductive materials.

[0062] A third aspect of this application provides the application of the phosphorus-doped graphite material described in any example of the second aspect of this application in a negative electrode active material. The introduction of phosphorus can improve the lithium-ion storage capacity and cycle stability of the graphite material, thereby enhancing the energy density and lifespan of the battery.

[0063] A fourth aspect of this application provides a negative electrode sheet comprising a phosphorus-doped graphite material, a conductive agent, and a binder, wherein the phosphorus-doped graphite material is the phosphorus-doped graphite material described in any example of the second aspect of this application.

[0064] In one example, the mass ratio of the phosphorus-doped graphite material, the conductive agent, and the binder is (92~98):(0.5~2):(1.5~7.5). Understandably, the mass ratio of the phosphorus-doped graphite material, the conductive agent, and the binder can be any value between (92~98):(0.5~2):(1.5~7.5). Specifically, the mass ratio of phosphorus-doped graphite material, conductive agent, and binder includes, but is not limited to, 92:0.5:7.5, 92:1:7, 92:2:6, 93:0.5:6.5, 93:1:6, 93:2:5, 94:0.5:5.5, 94:1:5, 94:2:4, 95:0.5:4.5, 95:1:4, 95:2:3, 96:0.5:3.5, 96:1:3, 96:2:2, 97:0.5:2.5, or 98:0.5:1.5.

[0065] In one example, the conductive agent includes one or more of carbon fibers, conductive carbon black, carbon nanotubes, and graphene.

[0066] In one example, the adhesive includes one or more of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose, and styrene-butadiene rubber.

[0067] In one example, the compaction density of the negative electrode is 1.4 g / cm³. 3 ~1.7 g / cm 3 Understandably, the compaction density of the negative electrode can be selected from 1.4 g / cm³. 3 ~1.7 g / cm 3 Any value between [amount] and [value]. Specifically, the compaction density of the negative electrode sheet includes, but is not limited to, 1.4 g / cm³. 3 1.5 g / cm 3 1.6 g / cm 3 Or 1.7 g / cm 3 .

[0068] In one example, the double-sided coating density of the negative electrode is 100 g / m². 2 ~300 g / m 2 .

[0069] In one example, the thickness of the negative electrode is 80 μm to 150 μm.

[0070] This application also provides a method for preparing a negative electrode sheet, comprising the following steps: mixing nitrogen-doped artificial graphite, a conductive agent, and a binder in a solvent according to a mass ratio to prepare a negative electrode slurry;

[0071] The negative electrode slurry is coated onto the surface of the negative electrode current collector, dried, and then rolled to prepare the negative electrode sheet; the compacted density of the negative electrode sheet is 1.4 g / cm³. 3 ~1.7g / cm 3 The surface density of the double-sided coating is 100 g / m². 2 ~300 g / m 2 Thickness ranges from 80μm to 150μm.

[0072] A fifth aspect of this application provides a lithium-ion battery, including a positive electrode and a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode is the negative electrode described in any example of the fourth aspect of this application.

[0073] A sixth aspect of this application also provides an electrical device including the lithium-ion battery described in the fifth aspect of this application. The electrical device may include any device or apparatus powered by a lithium-ion battery, such as mobile devices (mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0074] The following are specific embodiments. Unless otherwise specified, all raw materials used in the embodiments are commercially available. The following specific embodiments are intended to provide a further detailed description of the present invention to help those skilled in the art and researchers further understand the invention. The technical conditions, etc., do not constitute any limitation on the present invention. Any modifications made within the scope of the claims of this invention are within the protection scope of the claims of this invention.

[0075] The artificial graphite used in this application embodiment is petroleum coke secondary particle artificial graphite, which is prepared by the preparation method described in this application. Its main performance indicators are shown in Table 1:

[0076] Table 1

[0077]

[0078] Example 1

[0079] Example 1 of this application provides a phosphorus-doped artificial graphite material and its preparation method, the specific steps of which are as follows:

[0080] (1) Weigh red phosphorus and artificial graphite in a mass ratio of 10:1, put them into a mortar and grind them evenly, then ball mill them to prepare a mixture;

[0081] (2) The mixture was transferred to a quartz boat and placed in a tube furnace. Under argon protection, the temperature was increased to 650℃ at a rate of 5℃ / min and held for 5 hours for the first calcination. Then, the temperature was decreased to 300℃ at a rate of 2℃ / min and held for 24 hours for the second calcination. After natural cooling, phosphorus-doped modified artificial graphite was obtained. The SEM image of the prepared phosphorus-doped modified artificial graphite is shown below. Figure 1 As shown.

[0082] Example 2

[0083] Example 2 of this application provides a phosphorus-doped artificial graphite material and its preparation method, the specific steps of which are as follows:

[0084] (1) Weigh red phosphorus and artificial graphite in a mass ratio of 30:1, grind and mix them evenly in a mortar, and then ball mill them to prepare a mixture;

[0085] (2) The mixture was transferred to a quartz boat and placed in a tube furnace. Under the protection of argon, the temperature was raised to 650°C at a rate of 5°C / min and held for 5 hours for the first calcination. Then, the temperature was lowered to 300°C at a rate of 2°C / min and held for 24 hours for the second calcination. After natural cooling, phosphorus-doped modified artificial graphite was obtained.

[0086] Example 3

[0087] Example 3 of this application provides a phosphorus-doped artificial graphite material and its preparation method, the specific steps of which are as follows:

[0088] (1) Weigh red phosphorus and artificial graphite in a mass ratio of 5:1, grind and mix them evenly in a mortar, and then ball mill them to prepare a mixture;

[0089] (2) The mixture was transferred to a quartz boat and placed in a tube furnace. Under the protection of argon, the temperature was raised to 650°C at a rate of 5°C / min and held for 5 hours for the first calcination. Then, the temperature was lowered to 300°C at a rate of 2°C / min and held for 24 hours for the second calcination. After natural cooling, phosphorus-doped modified artificial graphite was obtained.

[0090] Example 4

[0091] Example 4 is basically the same as Example 1, the main difference being that the temperature for the first calcination in Example 4 is 850°C, and the temperature for the second calcination is 450°C.

[0092] Example 5

[0093] Example 5 is basically the same as Example 1, the main difference being that the first calcination temperature in Example 5 is 400°C, and the second calcination temperature is 100°C.

[0094] Comparative Example 1

[0095] The artificial graphite in Comparative Example 1 was not treated with phosphorus. The artificial graphite used in Comparative Example 1 was artificial graphite.

[0096] Comparative Example 2

[0097] Comparative Example 2 is basically the same as Example 1, except that Comparative Example 2 does not include the second calcination step.

[0098] Comparative Example 3

[0099] Comparative Example 3 is basically the same as Example 1, except that the first calcination step is not included in Comparative Example 3.

[0100] Comparative Example 4

[0101] Comparative Example 4 is basically the same as Example 1, except that the mass ratio of red phosphorus to artificial graphite in Comparative Example 4 is 3:1.

[0102] The specific surface area and phosphorus doping content of the phosphorus-doped modified artificial graphite of Examples 1-5 and the petroleum coke-modified artificial graphite of Comparative Examples 1-4 were tested. The specific surface area was obtained by the Brunauer-Emmett-Teller (BET) method. The phosphorus doping content was obtained by X-ray photoelectron spectroscopy (XPS). The corresponding specific surface area and X-ray photoelectron spectroscopy analyses are shown in Table 2.

[0103] Table 2

[0104]

[0105] Table 2 shows the P2p peak fitting results, revealing the presence of PC bonds in the phosphorus-doped modified artificial graphite of Examples 1-5, with PC bond peak areas ranging from 0.4% to 9.17%. This indicates that in the preparation method provided in this application, during the first high-temperature calcination, red phosphorus first sublimates into white phosphorus, with some white phosphorus molecules being expelled with argon gas and others diffusing into the pores of the graphite material. Upon cooling, the white phosphorus is converted back into red phosphorus. This method achieves in-situ phosphorus doping during high-temperature carbonization, successfully incorporating it into the carbon matrix framework in the form of chemical bonds to enhance interfacial interactions.

[0106] In Comparative Example 1, untreated artificial graphite was used, and its PC bond peak area was 0. In Comparative Example 2, the second calcination step was omitted, so the sublimated white phosphorus could not be doped into the carbon matrix, resulting in a PC bond peak area of ​​approximately 0. In Comparative Example 3, the first calcination step was omitted, so the red phosphorus could not diffuse into the pores of the graphite matrix, resulting in a PC bond peak area of ​​approximately 0 in the prepared graphite material. In Comparative Example 4, the mass ratio of red phosphorus to artificial graphite was 3:1, which was too low, preventing the red phosphorus from performing in-situ phosphorus doping on the graphite material.

[0107] Example 6

[0108] (1) The phosphorus-doped artificial graphite material, carbon black and styrene-butadiene rubber prepared in Example 1 were dissolved in water at a mass ratio of 96.2:0.8:3 to prepare a negative electrode slurry with a solid content of 53±2%;

[0109] (2) The negative electrode slurry prepared in step (1) is coated onto copper foil, dried, and rolled to prepare the negative electrode sheet, so that the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 The surface density of a single-sided coating is 90 g / m². 2 The thickness of the negative electrode sheet after rolling is 126μm.

[0110] (3) Preparation of the positive electrode sheet: Lithium iron phosphate, carbon nanotubes, SP, and PVDF were added to a stirred tank in a mass ratio of 97:0.5:0.5:2. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of an aluminum foil, and after drying, a positive electrode active layer was formed on both sides of the positive electrode current collector to obtain a positive electrode sheet. The compaction density of the positive electrode sheet was 2.45 g / cm³. 3 The surface density of the double-sided coating is 356 g / m². 2 .

[0111] (4) The diaphragm is made of polyethylene and the electrolyte is a lithium iron phosphate system-specific electrolyte.

[0112] (5) After stacking the positive electrode, separator and negative electrode in sequence, they are wound to form a core, then packaged with aluminum-plastic film, and after baking to remove moisture, electrolyte is injected into it. After hot pressing and other processes, a lithium-ion battery is obtained.

[0113] Examples 7-8

[0114] Examples 7-8 are basically the same as Example 6, the main difference being that the phosphorus-doped graphite materials used in Examples 2 and 3 are used in Examples 7 and 8, respectively.

[0115] Examples 9-10

[0116] Examples 9-10 are basically the same as Example 6, the main difference being that Examples 9 and 10 use the phosphorus-doped graphite materials from Examples 4 and 5, respectively.

[0117] Comparative Examples 5 to 8

[0118] Comparative Examples 5 to 8 are basically the same as Example 1, except that Comparative Examples 5 to 8 use artificial graphite or phosphorus-doped graphite materials from Comparative Examples 1 to 4, respectively.

[0119] Testing process

[0120] The lithium-ion batteries prepared in the examples and comparative examples were subjected to capacity and first-efficiency tests. The specific test conditions were as follows: test temperature 25℃; voltage range: 2.5 V~3.65 V; charge / discharge rate: 0.33C. The specific conditions for the cycle performance tests of the lithium-ion batteries prepared in the examples and comparative examples were as follows: test temperature 25℃; voltage range: 2.5 V~3.65 V; charge / discharge rate: CC 1C-DC 1C. The corresponding test results are shown in Table 3.

[0121] Table 3

[0122]

[0123] As shown in Table 3, when the phosphorus-doped artificial graphite prepared in Examples 1 to 5 of this application is used as the negative electrode active material, it can effectively improve the capacity performance of the lithium-ion batteries in Examples 6 to 10, making its capacity ≥1.98Ah, and reduce the volume change during the cycling process of the lithium-ion battery, thereby improving the cycle stability and making its capacity retention rate ≥92.5%.

[0124] Comparative Examples 5 to 8 were made from the graphite materials of Comparative Examples 1 to 4 of this application. Since the phosphorus doping content in the graphite materials of Comparative Examples 1 to 4 was about 0, when they were used as negative electrode active materials, the capacity and cycle stability of the lithium-ion batteries of Comparative Examples 5 to 8 were lower than those of Examples 6 to 10.

[0125] 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.

[0126] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, 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 this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application 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 patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a phosphorus-doped graphite material, characterized in that, Includes the following steps: A mixture is prepared by mixing a phosphorus source and graphite; the phosphorus source is red phosphorus. Under a protective gas atmosphere, the mixture is heated to 600°C–900°C at a heating rate of 1°C / min–10°C / min for a first calcination. Then, the temperature is lowered to 300℃ to 500℃ at a cooling rate of 1℃ / min to 10℃ / min for a second calcination to prepare the phosphorus-doped graphite material.

2. The method for preparing phosphorus-doped graphite material according to claim 1, characterized in that, The mass ratio of the phosphorus source to graphite is (5-30):

1.

3. The method for preparing phosphorus-doped graphite material according to claim 1, characterized in that, The preparation method has one or more of the following characteristics: (1) The first calcination time is 0.5h to 10h; (2) The second calcination time is 12h to 48h.

4. The method for preparing phosphorus-doped graphite material according to any one of claims 1 to 3, characterized in that, The graphite includes one or more of artificial graphite and natural graphite.

5. A phosphorus-doped graphite material, characterized in that, The phosphorus-doped graphite material was prepared by the preparation method according to any one of claims 1 to 4.

6. The phosphorus-doped graphite material according to claim 5, characterized in that, The phosphorus atomic percentage in the phosphorus-doped graphite material is 0.5 at% to 5 at%.

7. The application of the phosphorus-doped graphite material according to claim 5 or 6 in negative electrode active materials.

8. A negative electrode sheet, characterized in that, It includes phosphorus-doped graphite material, a conductive agent, and a binder, wherein the phosphorus-doped graphite material is the phosphorus-doped graphite material as described in claim 5 or 6.

9. The negative electrode sheet according to claim 8, characterized in that, The negative electrode has one or more of the following characteristics: (1) The conductive agent includes one or more of carbon fiber, conductive carbon black, carbon nanotubes and graphene; (2) The adhesive includes one or more of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose and styrene-butadiene rubber; (3) The compaction density of the negative electrode sheet is 1.4 g / cm³. 3 ~1.7g / cm 3 ; (4) The mass ratio of the phosphorus-doped graphite material, the conductive agent and the binder is (92-98):(0.5-2):(1.5-7.5).

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