Anode materials and their preparation methods, electrochemical devices and electronic devices

Abstract

The application provides a negative electrode material and a preparation method thereof, an electrochemical device and an electronic device. The negative electrode material comprises graphite and a coating on at least part of the surface of the graphite. The coating contains carbon elements, oxygen elements, nitrogen elements and metal elements. The metal elements include at least one of Zn, Co, Li, Zr or Al. The negative electrode material provided by the application can enable the electrochemical device to have excellent low-temperature performance and high energy density.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage, and in particular to a negative electrode material and its preparation method, an electrochemical device using the negative electrode material, and an electronic device using the electrochemical device. Background Technology

[0002] Lithium-ion batteries, as a new type of high-energy green battery, are widely used in laptops, mobile phones, and new energy electric vehicles. However, the performance degradation and reduced battery life of lithium-ion batteries at low temperatures limit their application. Therefore, improving the capacity utilization and battery life of lithium-ion batteries at low temperatures is crucial.

[0003] The performance of lithium-ion batteries at low temperatures is affected by the lithium-ion transport rate. While it's possible to improve the fast-charging and low-temperature performance of lithium-ion batteries by coating graphite with amorphous carbon, such as pitch or resin, this requires higher carbonization temperatures and results in a loss of energy density, making it difficult to simultaneously improve both low-temperature performance and energy density. Summary of the Invention

[0004] This application provides a negative electrode material, a method for preparing the same, an electrochemical device, and an electronic device.

[0005] The first aspect of this application provides a negative electrode material, including graphite and a coating located on at least a portion of the surface of the graphite, the coating containing carbon, oxygen, nitrogen and a metal element, the metal element including at least one selected from Zn, Co, Li, Zr or Al.

[0006] In this application, a negative electrode material is obtained by coating the graphite surface with a metal-containing compound and bio-based polyamide to form a partially carbonized carbon network containing metal dopants. The graphite surface is coated with a material containing carbon, nitrogen, oxygen and metal elements. Bio-based polyamides contain oxygen-containing five-membered rings and amide bonds. Oxygen-containing five-membered rings, amide bonds, and metal elements also exist on the surface of graphite. The oxygen-containing five-membered rings cross-link with graphite to form a curved carbon network structure (the oxygen-containing five-membered rings cross-link between the graphite layers, and the oxygen-containing five-membered rings and graphite layers are not on the same plane, changing the curvature of the carbon network structure). This carbon network structure enhances the attraction to lithium ions, thereby facilitating the rapid desolvation of lithium ions and improving the low-temperature performance of the anode material. The metal elements in the aforementioned anode material are doped into the curved carbon network structure, improving the electronic conductivity of the anode material. Simultaneously, the amide bonds present in the coating material are beneficial for increasing the adsorption capacity of lithium ions and further enhancing the capacity of the electrochemical device at room temperature, thus increasing the energy density of the electrochemical device. Therefore, the electrochemical device exhibits both excellent low-temperature performance and high energy density.

[0007] Based on the first aspect, in some possible implementations, the mass percentage of the metal element is 0.05% to 0.2% based on the mass of the negative electrode material. This is beneficial for reducing the impedance of the electrochemical device and for improving the conductivity of the negative electrode material, thereby further enabling the electrochemical device to have excellent low-temperature performance and energy density.

[0008] Based on the first aspect, in some possible implementations, the coating contains at least one of the following structural segments:

[0009]

[0010] The aforementioned structural fragments contain oxygen-containing five-membered rings, amide bonds, nitrogen-containing benzene rings, or nitrogen-containing five-membered rings. These five-membered ring structures can crosslink between graphite layers, altering the curvature of the graphite carbon network structure. This carbon network structure enhances the attraction to lithium ions, improves desolvation capability, and improves the low-temperature performance of the electrochemical device. The amide bonds can increase the adsorption capacity of lithium ions, thereby increasing the energy density of the electrochemical device. The nitrogen-containing benzene rings in the coating can improve the electronic conductivity and structural stability of the carbon network structure, which is beneficial for improving the low-temperature performance of the electrochemical device.

[0011] Based on the first aspect, in some possible implementations, in an inert atmosphere, the weight loss rate of the negative electrode material from 35°C to 800°C is 0.15% to 0.3%. The weight loss rate of the negative electrode material is within a specific range, which corresponds to maintaining the mass of the coating material within a certain range, thereby ensuring that the negative electrode material contains a certain amount of coating material, which is beneficial for improving the low-temperature performance and energy density of the electrochemical device.

[0012] Based on the first aspect, in some possible implementations, the mass percentage of nitrogen element is 0.1% to 2% based on the mass of the negative electrode material. This is beneficial for improving the electronic conductivity of the negative electrode material; it can also contain a certain amount of amide bonds on the surface of the negative electrode material to further improve the energy density and low-temperature performance of the electrochemical device.

[0013] Based on the first aspect, in some possible implementations, the mass percentage of oxygen is 0.1% to 3% based on the mass of the negative electrode material. This can improve the stability of the negative electrode material, thereby improving the cycle performance and energy density of the electrochemical device.

[0014] Based on the first aspect, in some possible implementations, the mass percentage of carbon element is 95% to 99% based on the mass of the negative electrode material; this is beneficial for improving the conductivity and cycle performance of the negative electrode material, and for enabling the electrochemical device to have a higher energy density.

[0015] Based on the first aspect, in some possible implementations, graphite includes at least one of artificial graphite or natural graphite. Artificial and natural graphite can improve the lithium-ion transport performance of the negative electrode material, thereby enabling the electrochemical device to achieve better charging performance, and even better low-temperature charging performance, while maintaining a high energy density.

[0016] Based on the first aspect, in some possible implementations, the graphitization degree of the negative electrode material is 94% to 98%. This allows the negative electrode material to have high capacity and excellent kinetic performance, which is beneficial to improving the energy density of the electrochemical device; and the graphitization degree of the negative electrode material within the above range can fully utilize the performance of graphite.

[0017] Based on the first aspect, in some possible implementations, the particle size Dv50 of the negative electrode material is 8 μm to 15 μm; this is beneficial for reducing side reactions between the negative electrode material and the electrolyte, so that the electrochemical device can have good low-temperature performance as well as good energy density.

[0018] Based on the first aspect, in some possible implementations, the tap density of the negative electrode material is 0.9 g / cm³. 3 Up to 1.1 g / cm 3 The tap density within this range is beneficial for increasing the energy density of the negative electrode material, and when using this negative electrode material to prepare slurry, it also helps to reduce the amount of binder used and has good processing performance.

[0019] Based on the first aspect, in some possible implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g to 3m 2 / g, which helps to reduce side reactions between the negative electrode material and the electrolyte, giving the electrochemical device good low-temperature performance and energy density.

[0020] The second aspect of this application also provides a method for preparing a negative electrode material, wherein biomass polyamide is dissolved in a solvent and a metal-containing compound is added, and the mixture is stirred to obtain a coated slurry. The residual carbon mass ratio of the biomass polyamide and the metal-containing compound at the same carbonization temperature is 1:(1-5), and the metal element in the metal-containing compound includes at least one of Zn, Co, Li, Zr or Al.

[0021] Add coating slurry to graphite and mix thoroughly to obtain an intermediate;

[0022] In an inert atmosphere, the intermediate is placed at a carbonization temperature of 400℃ to 800℃ for 2 hours to 5 hours to obtain the anode material.

[0023] In the above preparation method, the coating slurry is coated on graphite. After the above carbonization process, the coating slurry is uniformly coated on the surface of graphite. Part of the coating slurry is carbonized and forms a carbon network containing metal dopants, while part of the coating slurry remains on the surface of graphite. This results in the coating containing oxygen-containing five-membered rings and amide bonds, thereby enabling the electrochemical device to have both good low-temperature performance and high energy density.

[0024] Based on the second aspect, in some possible implementations, biomass polyamides contain at least one of the following structural segments:

[0025]

[0026] The degree of polymerization (n) of the aforementioned structural fragments is 500–2000. The oxygen-containing five-membered ring structure contained in these fragments can crosslink with graphite, altering the curvature of the graphite carbon network structure, enhancing its attraction to lithium ions, facilitating lithium ion desolvation, improving the low-temperature performance of the anode material, and also promoting the doping of metal elements into the oxygen-containing five-membered ring structure, thereby improving the electronic conductivity of the anode material and ultimately enhancing the low-temperature performance and energy density of the electrochemical device.

[0027] Based on the second aspect, in some possible embodiments, the metal-containing compound is selected from at least one of the following compounds: C8H 10 N4Zn, C 24 H 12 O 13 Zn4, C4H6N2C o, Li3 P O4, LiF, C 48 H 24 O 32 Zr6, C 24 H 16 O 32 Zr6 or C 18 H 10 Al3O 17 During the carbonization process, some metal compounds remain on the surface of graphite. These residues, along with the metal elements doped into the carbon network structure, not only improve the electronic conductivity of the anode material, but the ligands in the metal compounds also promote the desolvation of lithium ions, thereby improving the low-temperature performance of the electrochemical device.

[0028] A third aspect of this application provides an electrochemical device including a negative electrode material containing an oxygen-containing five-membered ring, an amide bond, and a metal element, which enables the electrochemical device to have both excellent low-temperature performance and high energy density.

[0029] The fourth aspect of this application provides an electronic device including an electrochemical device. The electrochemical device has excellent low-temperature performance and energy density, which is beneficial to improving the service life of the electronic device and its versatility in low-temperature environments. Attached Figure Description

[0030] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0031] Figure 1 In the image, (a) is a scanning electron microscope image of the negative electrode material in Example 1 of this application; (b) is a magnified view of (a).

[0032] Figure 2 The above are charge-discharge curves of the coin cell co-intercalation capacity test of the negative electrode material in Example 1 and Comparative Example 1 of this application.

[0033] Figure 3 This is a full-cell 0-degree cycle capacity retention curve of the negative electrode material in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0034] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. 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 in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0035] During charging of an electrochemical device, solvated lithium ions diffuse through the electrolyte liquid phase. Once the diffused lithium ions reach the solid electrolyte interphase (SEI) membrane on the negative electrode surface, they peel off the outer solvation sheath, a process commonly known as desolvation. The desolvated lithium ions then diffuse through the SEI membrane to the negative electrode surface and embed themselves into the negative electrode material's crystal lattice. During battery discharge, a similar microscopic process occurs on the positive electrode side. This slow desolvation process can lead to severe electrochemical polarization during low-temperature charging and discharging, causing the battery to quickly reach its cutoff voltage, thus limiting the normal operation of lithium-ion batteries under low-temperature conditions.

[0036] This application provides a negative electrode material, a method for preparing the same, an electrochemical device, and an electronic device.

[0037] One embodiment of this application provides an electrochemical device, which includes a housing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the housing.

[0038] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, the electrochemical device is a pouch battery. In other embodiments, the electrochemical device can also be a steel-cased battery, an aluminum-cased battery, etc.

[0039] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The electrode assembly can be a stacked structure, formed by alternating layers of the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding layers of the positive electrode, separator, and negative electrode.

[0040] Negative electrode sheet

[0041] The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector. The negative current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative active layer contains a negative electrode material.

[0042] The negative electrode material includes graphite and a coating located on at least a portion of the surface of the graphite. The coating contains carbon, oxygen, nitrogen, and a metal element, including at least one of Zn, Co, Li, Zr, or Al.

[0043] The negative electrode material provided in this application is obtained by coating the graphite surface with metal-containing compounds and bio-based polyamide to form a partially carbonized carbon network containing metal dopants. In the process of forming the carbon network, the graphite surface forms a coating containing carbon, nitrogen, oxygen and metal elements. Bio-based polyamides contain oxygen-containing five-membered rings and amide bonds. On the surface of graphite, oxygen-containing five-membered rings, amide bonds, and metal elements exist. The oxygen-containing five-membered rings crosslink with graphite to form a curved carbon network structure (the oxygen-containing five-membered rings can crosslink between graphite layers; the oxygen-containing five-membered rings and graphite layers are not on the same plane, changing the curvature of the carbon network structure). This carbon network structure enhances the attraction to lithium ions, thereby facilitating the rapid desolvation of lithium ions and improving the low-temperature performance of the anode material. The metal elements in the aforementioned anode material are doped into the curved carbon network structure, improving the electronic conductivity of the anode material. Simultaneously, the amide bonds present in the coating enhance the lithium-ion adsorption capacity and further improve the capacity of the electrochemical device at room temperature, increasing the energy density of the anode material. Therefore, the anode material exhibits both excellent low-temperature performance and high energy density.

[0044] In some embodiments, the mass percentage of the metal element is 0.05% to 0.2% based on the mass of the negative electrode material. The content of the metal element affects the low-temperature performance and energy density of the electrochemical device. A metal element content within the aforementioned range is beneficial for reducing the impedance of the electrochemical device and improving the conductivity of the negative electrode material, thereby further enabling the electrochemical device to possess excellent low-temperature performance and energy density. If the mass percentage of the metal element in the negative electrode material is large, the metal element content is high, and the metal element easily forms alloys with lithium ions, increasing the impedance of the electrochemical device and thus affecting its low-temperature performance and energy density. Conversely, if the mass percentage of the metal element in the negative electrode material is small, the metal element content is low, and the effect of the metal element on improving the low-temperature performance and energy density of the electrochemical device is limited. In some embodiments, the mass percentage of the metal element, based on the mass of the negative electrode material, can be 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or any value within the range of any two of the above values.

[0045] In some embodiments, the covering contains at least one of the following structural segments:

[0046] The aforementioned structural fragments contain oxygen-containing five-membered rings, amide bonds, nitrogen-containing benzene rings, or nitrogen-containing five-membered rings. The five-membered ring structure can be cross-linked between graphite layers, which can change the curvature of the carbon network structure of graphite. This carbon network structure enhances the attraction to lithium ions, thereby improving the desolvation ability and improving the low-temperature performance of the electrochemical device. The amide bond can increase the adsorption capacity of lithium ions and increase the energy density of the electrochemical device. The nitrogen-containing benzene ring can improve the electronic conductivity and structural stability of the carbon network structure, which is beneficial to improving the low-temperature performance of the electrochemical device.

[0047] In some embodiments, under an inert atmosphere, the weight loss rate of the negative electrode material when heated from 35°C to 800°C is 0.15% to 0.3%. Under an inert atmosphere and at the aforementioned reaction temperature, the graphite in the negative electrode material does not react and is not lost; instead, the corresponding coating decomposes within the aforementioned temperature range, and some substances in the coating react. Within the aforementioned temperature range, the weight loss rate of the negative electrode material is within a specific range, which corresponds to maintaining the mass of the coating in the negative electrode material within a certain range, thereby ensuring that the negative electrode material contains a certain amount of coating, which is beneficial for improving the low-temperature performance and energy density of the electrochemical device. In some embodiments, the weight loss rate of the negative electrode material when heated from 35°C to 800°C can be 0.15%, 0.18%, 0.2%, 0.23%, 0.25%, 0.27%, 0.3%, or any value within the range of any two of the aforementioned values.

[0048] In some embodiments, graphite includes at least one of artificial graphite and natural graphite. Artificial and natural graphite can improve the lithium-ion transport performance of the negative electrode material, thereby enabling the electrochemical device to achieve better charging performance, and even better low-temperature charging performance, while maintaining a high energy density.

[0049] In some embodiments, the mass percentage of nitrogen in the negative electrode material is between 0.1% and 2%. A nitrogen mass percentage within this range can, on the one hand, improve electronic conductivity through the nitrogen-doped carbon network structure, and on the other hand, maintain a certain amount of amide bonds on the surface of the negative electrode material, thereby further improving the energy density and low-temperature performance of the electrochemical device. In some embodiments, the mass percentage of nitrogen in the negative electrode material can be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0050] In some embodiments, the carbon content is 95% to 99% based on the mass of the anode material. A carbon content within a specific range is beneficial for improving the conductivity and cycle performance of the anode material, and for enabling the electrochemical device to have a higher energy density. In some embodiments, the carbon content can be 95%, 96%, 97%, 98%, 99%, or any value within a range of any two of the above values, based on the mass of the anode material.

[0051] In some embodiments, the mass percentage of oxygen, based on the mass of the negative electrode material, is 0.1% to 3%, which can improve the stability of the negative electrode material, thereby improving the cycle performance and energy density of the electrochemical device. In some embodiments, the mass percentage of oxygen, based on the mass of the negative electrode material, can be 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 2.7%, 3%, or any value within the range of any two of the above values.

[0052] In some embodiments, the graphitization degree of the negative electrode material is 94% to 98%. A graphitization degree within this range allows the negative electrode material to possess higher capacity and better kinetic performance, which is beneficial for improving the energy density of the electrochemical device. Furthermore, a graphitization degree within this range allows for the full utilization of graphite's properties. In some embodiments, the graphitization degree of the negative electrode material can be 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or any value within the range of any two of the above values.

[0053] In some embodiments, the particle size Dv50 of the negative electrode material is 8 μm to 15 μm. A particle size Dv50 within this range is beneficial for reducing side reactions between the negative electrode material and the electrolyte, thereby contributing to good low-temperature performance and energy density in the electrochemical device. Wherein, D... V 50, also known as the "median particle size," represents the particle size that, in the volume-based particle size distribution of the negative electrode material, reaches 50% of the total volume, measured from the smallest particle size. In other words, particles smaller than this size account for 50% of the total volume of the negative electrode material particles. In some embodiments, the particle size Dv50 of the negative electrode material can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value within the range of any two of the above values.

[0054] In some embodiments, the tap density of the negative electrode material is 0.9 g / cm³. 3 Up to 1.1 g / cm 3 This tap density range is beneficial for increasing the energy density of the negative electrode material, and when using this negative electrode material to prepare the slurry, it also helps to reduce the amount of binder used and has good processing performance. In some embodiments, the tap density of the negative electrode material can be 0.9 g / cm³. 3 0.95g / cm 3 0.98g / cm 3 1g / cm 3 1.05g / cm 3 1.1g / cm 3 Or any value within the range formed by any two of the above values.

[0055] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g to 3m 2 / g, with a specific surface area of ​​the negative electrode material within the above range, is beneficial for reducing side reactions between the negative electrode material and the electrolyte, resulting in good low-temperature performance and energy density of the electrochemical device. In some embodiments, the specific surface area of ​​the negative electrode material can be 0.5m². 2 / g, 0.8m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g or any value within the range of any two of the above values.

[0056] This application also provides a method for preparing a negative electrode material, including:

[0057] (1) Dissolve biomass polyamide in a solvent and add a metal-containing compound, and stir to obtain a coated slurry. The mass ratio of residual carbon of biomass polyamide and metal-containing compound at the same carbonization temperature is 1:(1-5). The metal element in the metal-containing compound includes at least one of Zn, Co, Li, Zr or Al.

[0058] In the above preparation steps, the biomass polyamide contains oxygen-containing five-membered rings and amide bond groups, thereby providing a source for the formation of the coating, and the metal-containing compound provides a source of metal elements in the coating.

[0059] Under an inert gas (such as nitrogen or argon), the residual carbon mass ratio of biomass polyamide and metal-containing compounds is controlled at the same carbonization temperature. This allows for the control and adjustment of the elemental content ratio in the resulting coating after carbonization. The carbonization temperature refers to the temperature at which the coating slurry reacts with graphite in an inert atmosphere. The residual carbon mass ratio of biomass polyamide and metal-containing compounds at the same carbonization temperature can be 1:1, 1:2, 1:3, 1:4, 1:5, or any value within the range of any two of these values.

[0060] The solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, toluene, dichloromethane, dichloroethane, tetrahydrofuran, dimethyl sulfoxide, or water.

[0061] (2) Add coating slurry to graphite and mix evenly to obtain intermediate.

[0062] During the above-mentioned addition process, graphite powder is first added to the V-type high-efficiency mixer, and the coating slurry is slowly added while stirring, so that the coating slurry and graphite are fully and evenly mixed.

[0063] (3) In an inert atmosphere, the intermediate is placed at a carbonization temperature of 400℃ to 800℃ for 2h to 5h to obtain the negative electrode material.

[0064] In the final anode material, the coating accounts for 0.5-2% of the graphite mass.

[0065] In an inert atmosphere, graphite and coating slurry in the intermediate are carbonized, and the coating slurry is coated onto the graphite to obtain the anode material.

[0066] In some embodiments, the inert atmosphere includes at least one of nitrogen or argon.

[0067] The carbonization temperature can be 400℃, 500℃, 600℃, 700℃, 800℃, or any value within the range of any two of the above values. Compared to graphite-coated pitch (carbonization temperature around 1100℃), the carbonization temperature used in this application is lower than that of the carbonized graphite-coated carbide, which also helps to reduce the energy density loss in the negative electrode material. During the carbonization process, the temperature is increased at a rate of 5℃ / min.

[0068] The carbonization time can be 2h, 3h, 3.5h, 4h, 5h, or any value within the range of any two of the above values. Within a specific time, the coating slurry is fully coated on the graphite to obtain the negative electrode material.

[0069] In the above preparation method, the coating slurry is coated on graphite. After the above carbonization process, the coating slurry is uniformly coated on the surface of graphite. Part of the coating slurry is carbonized and forms a carbon network containing metal dopants, while part of the coating slurry remains on the surface of graphite. This results in the coating containing oxygen-containing five-membered rings and amide bonds, thereby enabling the electrochemical device to have both good low-temperature performance and high energy density.

[0070] In some embodiments, biomass polyamides contain at least one of the following structural segments:

[0071]

[0072] The degree of polymerization (n) of the aforementioned structural fragments is 500–2000. The oxygen-containing five-membered ring structure contained in these fragments can crosslink with graphite, altering the curvature of the graphite carbon network structure, enhancing its attraction to lithium ions, facilitating lithium ion desolvation, improving the low-temperature performance of the anode material, and also promoting the doping of metal elements into the oxygen-containing five-membered ring structure, thereby improving the electronic conductivity of the anode material and ultimately enhancing the low-temperature performance and energy density of the electrochemical device.

[0073] In some embodiments, the metal-containing compound is selected from at least one of the following compounds: C8H 10 N4Zn (abbreviated as ZIF-8), C 24 H 12 O 13 Zn4 (MOF-5), C4H6N2Co (ZIF-67), Li3PO4, LiF, C 48 H 24 O 32 Zr6 (abbreviated as UIO-66), C 24 H 16 O 32 Zr6 (MOF-808 for short) or C 18 H 10 Al3O 17(MIL-100(Al) for short). After carbonization, the aforementioned metal-containing compounds form metal elements doped into the carbon network structure, which can improve the electronic conductivity of the anode material. During the carbonization process, some of these metal-containing compounds remain on the surface of graphite. These residues, along with the metal elements doped into the carbon network structure, not only improve the electronic conductivity of the anode material but also promote lithium-ion desolvation capability, thus improving the low-temperature performance of the electrochemical device. For example, ZIF-8, in addition to providing a metal Zn source, has ligands rich in nitrogen-containing five-membered heterocyclic groups. The anode material prepared from it also contains some residual ligands, which can further enhance the lithium-ion desolvation capability and improve the energy density and low-temperature performance of the electrochemical device. MOF-5, in addition to providing a metal Zn source, also contains a carboxylic acid benzene ring structure, which can increase the electron cloud density of the carbon network structure, thereby further enhancing the lithium-ion desolvation capability and improving the energy density and low-temperature performance of the electrochemical device. Similarly, ZIF-67 exhibits the same effects as ZIF-8. Its nitrogen-containing five-membered heterocyclic group not only enhances lithium-ion desolvation capability, but the nitrogen doping in its five-membered ring further improves the electronic conductivity of the carbon network structure, thereby increasing the electronic conductivity of the anode material. Li3PO4 is an excellent film-forming additive. During the carbonization and coating process on the graphite surface, some Li3PO4 may form on the graphite surface. When the anode material is applied to an electrochemical device, it can improve the composition of the anode material during the first lithium insertion, which is beneficial for improving the lithium-ion desolvation capability and thus improving the low-temperature performance of the electrochemical device. Similarly, LiF and Li3PO4 have the same effects. MOF-808, UIO-66, and MIL-100(Al) all have stable metal centers, and their corresponding crystal structures are regular and contain nanoscale pores, which facilitates the sieving of lithium-ion solvation and allows lithium ions to pass through easily, thereby improving the lithium-ion desolvation capability. Therefore, the metal-containing compound provided in this application can not only provide a source of metal elements and improve the conductivity of the negative electrode material, but also enhance the lithium-ion desolvation capability, thereby improving the low-temperature performance of the electrochemical device.

[0074] The negative electrode active layer also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the negative electrode active layer and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0075] The negative electrode active layer may further include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0076] Separating membrane

[0077] The material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0078] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0079] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0080] electrolyte

[0081] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives. The organic solvent in the electrolyte of this application can be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte of this application; it can be any electrolyte known in the prior art. The additives in the electrolyte of this application can be any additives known in the prior art that can be used as electrolyte additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate. In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiP O2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTF SI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiF SI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiB OB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0082] Positive electrode sheet

[0083] The positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive active layer contains a positive active material, which includes compounds that reversibly insert and extract lithium ions (i.e., lithiation intercalation compounds). In some embodiments, the positive active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive active material may include, but is not limited to, lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate.

[0084] The positive electrode active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0085] The positive electrode active layer may also include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0086] The aforementioned electrochemical device is applied to electronic devices to power loads within them. Furthermore, the negative electrode material in this electrochemical device exhibits excellent low-temperature performance and energy density, which is beneficial for improving the lifespan of the electronic device and its application in low-temperature environments. These electronic devices may include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0087] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0088] Example 1

[0089] <Preparation of Anode Materials>

[0090] 1. Take 75g of FDCA-derived bio-based polyamide (solid content 13.98%, viscosity 210,000 cp, degree of polymerization 1000-1200, containing structural fragments including...) The FDCA-derived bio-based polyamide was uniformly dissolved in 1 L of N,N-dimethylacetamide, followed by the addition of 75 g of ZIF-8 powder. The mixture was stirred at room temperature for 12 h to obtain a coating agent slurry. The residual carbon mass ratio of FDCA-derived bio-based polyamide and ZIF-8 powder at 600 °C was 1:1.

[0091] 2. Add 10 kg of artificial graphite powder to a V-type high-efficiency mixer, and slowly add the coating agent slurry while stirring to mix it evenly with the graphite powder to obtain a mixed powder.

[0092] 3. The above mixed powder is transferred into a rotary kiln for heat treatment. The temperature is increased to 600 degrees Celsius at 5 degrees Celsius / min under an inert atmosphere and held for 3 hours to obtain the negative electrode material.

[0093] <Preparation of Negative Electrode Sheets>

[0094] The above-mentioned negative electrode material, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) were mixed at a weight ratio of 95:2:3. Deionized water was added, and the mixture was stirred until homogeneous to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was uniformly coated onto one surface of a 10 μm thick copper foil current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided coating of negative electrode material layer and a coating thickness of 80 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material layer. The sheet was dried under vacuum at 120°C for 1 hour, and then cold-pressed, cut, and slit to obtain a negative electrode sheet with a size of 78 mm × 875 mm.

[0095] <Preparation of the positive electrode>

[0096] Lithium cobalt oxide (LiCoO2), acetylene black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (NMP) was then added and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector. The foil was then dried at 120°C for 1 hour to obtain a positive electrode sheet with a single-sided coating of 60 μm thick positive electrode material. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. This sheet was dried under vacuum at 120°C for 1 hour, and then cold-pressed, cut, and slit to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0097] <Preparation of Electrolyte>

[0098] In an argon-atmospheric glove box with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1, and then lithium salt lithium hexafluorophosphate (LiPF6) was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, with the balance being non-aqueous organic solvent.

[0099] <Preparation of the separating membrane>

[0100] A 7μm thick polypropylene / polyethylene composite film was used as the separator.

[0101] <Preparation of Lithium-ion Batteries>

[0102] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The electrode assembly is then wound up. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. Following vacuum sealing, settling, formation (with an upper limit voltage of 4.5V, a formation temperature of 70℃, and a settling time of 2 hours), degassing, and edge trimming, a lithium-ion battery is obtained.

[0103] Example 2

[0104] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 400 degrees, the rest is the same as in Example 1.

[0105] Example 3

[0106] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 800 degrees, the rest is the same as in Example 1.

[0107] Example 4

[0108] Except for step 1 in the preparation of the negative electrode material, in which 75g of FDCA-derived bio-based polyamide is uniformly dissolved in 1L of N,N-dimethylacetamide and then 75g of ZIF-67 powder is added, the rest is the same as in Example 1.

[0109] Example 5

[0110] Except for step 1 in the preparation of the negative electrode material, in which 75g of FDCA-derived bio-based polyamide is uniformly dissolved in 1L of water and then 50g of lithium phosphate powder is added, the rest is the same as in Example 1.

[0111] Example 6

[0112] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 400 degrees, the rest is the same as step 5.

[0113] Example 7

[0114] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 800 degrees, the rest is the same as in Example 5.

[0115] Example 8

[0116] Except for step 1 in the preparation of the negative electrode material, in which 75g of FDCA-derived bio-based polyamide is uniformly dissolved in 1L of N,N-dimethylformamide and then 100g of UIO-66 powder is added, the rest is the same as in Example 1.

[0117] Example 9

[0118] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 400 degrees, the rest is the same as in Example 8.

[0119] Example 10

[0120] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 800 degrees, the rest is the same as in Example 8.

[0121] Example 11

[0122] Except for step 1 in the preparation of the negative electrode material, in which 75g of FDCA-derived bio-based polyamide is uniformly dissolved in 1L of N,N-dimethylformamide and then 100g of MIL-100(Al) powder is added, the rest is the same as in Example 1.

[0123] Example 12

[0124] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 400 degrees, the rest is the same as in Example 11.

[0125] Example 13

[0126] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 800 degrees, the rest is the same as in Example 11.

[0127] Example 14

[0128] Except for step 1 in the preparation of the negative electrode material, in which 75g of FDCA-derived bio-based polyamide is uniformly dissolved in 1L of N,N-dimethylacetamide, followed by the addition of 75g of ZIF-8 powder and 50g of lithium phosphate powder, the rest is the same as in Example 1.

[0129] Example 15

[0130] Except for step 1 in the preparation of the negative electrode material, where 75g of FDCA-derived bio-based polyamide is uniformly dissolved in 1L of N,N-dimethylacetamide, followed by the addition of 150g of ZIF-8 powder, and the mixture is stirred at room temperature for 12 hours to obtain the coating agent slurry, the rest is the same as in Example 1.

[0131] Comparative Example 1

[0132] Only the graphite raw material from step 2 of the anode material preparation is used as the anode material, and no other processing is performed.

[0133] Comparative Example 2

[0134] Except for step 1 in the preparation of the negative electrode material, in which 75g of FDCA-derived bio-based polyamide is uniformly dissolved in 1L of N,N-dimethylacetamide and stirred at room temperature for 12h to obtain the coating agent slurry, the rest is the same as in Example 1.

[0135] Comparative Example 3

[0136] Except for step 3 in the preparation of the negative electrode material, where the heat treatment temperature is replaced with 1000 degrees, the rest is the same as in Example 1.

[0137] The negative electrode materials prepared in each embodiment and comparative example, as well as the assembled lithium-ion batteries, were tested.

[0138] Test method:

[0139] Negative electrode material to be tested: A fully discharged lithium-ion battery was disassembled, and the negative electrode was soaked in ethylene carbonate (DMC) for 20 minutes. Then, it was rinsed with DMC and acetone respectively to remove the electrolyte and the surface solid electrolyte interphase (SEI) film. After that, it was placed in an oven and baked at 80°C for 12 hours to obtain the processed negative electrode sheet. The negative electrode material layer on the negative electrode sheet was scraped off with a scraper, and the scraped negative electrode material powder was heat-treated in a tube furnace at 350°C for 4 hours under argon protection to obtain the negative electrode material.

[0140] (1) Element content test:

[0141] The mass percentage content of C, N, and O elements in the negative electrode material was tested using a German Elementar elemental analyzer.

[0142] The mass percentage content of metal elements in the anode material was tested using microwave digestion and PE ICP-OE S Optima 7000DV.

[0143] (2) Weight loss rate test of negative electrode material:

[0144] Thermogravimetric analysis of the material was performed using a NETZ S CH STA 449F 3 Jupiter, referring to the standards JY_T0589.1-2020 / JY_T 0589.4-2020 / JY_T 0589.5-2020 "General Rules for Thermal Analysis Methods". 99.99% nitrogen was used, the heating rate was 10℃ / min, and the cutoff temperature was 800℃.

[0145] (3) Graphitization degree test of negative electrode material:

[0146] The anode material was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D 8 ADVANCE) with Cu Kα as the target. The voltage and current were 40 kV / 40 mA, the scanning angle range was 5° to 80°, the scanning step size was 0.00836°, and the step time was 0.3 s. Simultaneously, 15% silicon powder was added. Based on the principle of the internal standard method, the peak position of the silicon standard was used to calibrate the instrument and reduce testing errors, thereby accurately calculating the characteristic peak positions of the graphite anode material and obtaining the degree of graphitization of the graphite anode material.

[0147] (4) Specific surface area SSA test of negative electrode material:

[0148] According to the national standard "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), the specific surface area of ​​the negative electrode material was tested by nitrogen adsorption using a specific surface area analyzer (model TristarⅡ3020M).

[0149] (5) Particle size Dv50 test:

[0150] The particle size of the negative electrode material was measured using a Malvern particle size analyzer (MasterSizer 2000). 0.02 g of negative electrode material particles were added to a 50 mL clean beaker, along with 20 mL of ethanol as a dispersant. The mixture was ultrasonicated for 30 min in a 120 W ultrasonic cleaner to completely disperse the negative electrode material particles in the ethanol, obtaining a sample dispersion. The particle size Dv50 of the negative electrode material particles was then measured using the Malvern particle size analyzer.

[0151] (6) Tap density (TD) test:

[0152] According to the national standard GB / T 24533-2019, the tap density TD of the negative electrode material was tested using a density analyzer (model GeoPyc 1365).

[0153] (7) Scanning electron microscope tests:

[0154] According to the national standard GB / T 38887-2020, the negative electrode material was tested using a ZEI S-SEM (Sigma-02-33) scanning electron microscope.

[0155] (8) Button cell co-embedded capacity test:

[0156] Referring to the national standard GB / T 24533-2019, "Graphite Anode Materials for Lithium-ion Batteries," the anode material was prepared into a negative electrode sheet through mixing, coating, rolling, punching, and drying (the specific process is consistent with the negative electrode sheet preparation method in Example 1). Lithium sheets were used as the positive electrode sheet, and coin cells were assembled for testing. However, the electrolyte used was 1M LiPF6 dissolved in a three-component solvent (EC:PC:EMC = 1:1:1). The coin cells were kept at 25℃ for 12 hours, discharged at 0.05C to 5.0mV, discharged at 50μA to 5.0mV, and discharged at 20μA to 5.0mV. The capacity of the coin cells at these times was recorded as the co-intercalation capacity. The cells were then charged at 0.1C to 2.0V, and the capacity of the coin cells at this time was recorded as the co-intercalation / deintercalation capacity.

[0157] (9) Test method for liquid phase transport impedance (Rion) of lithium-ion batteries:

[0158] The lithium-ion battery was tested at 0°C using a Bio-Logic VMP3 B electrochemical workstation manufactured by Biologic (France), with a frequency range of 5 mHz to 1000 kHz and an amplitude of 5 mV. After data acquisition, impedance complex plane plots were used to analyze the data and obtain the lithium-ion liquid phase transport impedance (Rion).

[0159] (10) Lithium-ion battery energy density ratio test:

[0160] Five lithium-ion batteries from each of the comparative examples and embodiments were used, and the average value was taken. First, a first charge and discharge cycle was performed in an environment of 25°C. Constant current and constant voltage charging was performed at a charging current of 0.5C until the upper limit voltage reached 4.48V. Then, constant current discharge was performed at a discharge current of 0.2C, with a discharge cutoff voltage of 3V. The energy density of each embodiment and comparative example was calculated: Energy density (Wh / L) = Discharge capacity (Wh) / Lithium-ion battery volume (L). The percentage increase in energy density of each embodiment relative to Comparative Example 1 was calculated (i.e., the percentage of energy density relative to Comparative Example 1).

[0161] (11) Lithium-ion battery capacity retention test at -20 degrees Celsius:

[0162] The lithium-ion battery was placed in a 25°C environment for 6 hours, then charged at a constant current (CC) rate of 1C until it reached 4.48V. Afterward, it was switched to constant voltage (CV) charging, and charging was stopped when the current dropped below 0.05C. The battery was then allowed to rest for 5 minutes. Next, it was discharged at a constant current of 0.2C to 3V, and the 25°C discharge capacity was recorded. Then, it was fully charged to 4.48V using the same CC+CV charging mode at a 1C rate. The lithium-ion battery was then placed in a -20°C environment for 6 hours, and discharged at a constant current of 0.2C to 3V, and the -20°C discharge capacity was recorded. The calculation formula was: -20°C capacity retention rate = [-20°C discharge capacity / 25°C discharge capacity] × 100%. Five lithium-ion batteries were used for each comparative example and embodiment, and the average value was taken as the final result.

[0163] (12) Capacity retention rate of lithium-ion batteries at 0 degrees Celsius:

[0164] In an environment of 0°C, the first charge and discharge cycle was performed. Constant current and constant voltage charging was carried out at a charging current of 0.5C until the upper limit voltage reached 4.48V. Then, constant current discharge was performed at a discharge current of 0.5C, with a discharge cutoff voltage of 3V. The discharge capacity A of the lithium-ion battery was measured. Then, in an environment of 0°C, the above steps were repeated for 800 charge and discharge cycles. The discharge capacity B of the lithium-ion battery on the 800th cycle was measured. The 0-degree cycle capacity retention rate of the lithium-ion battery is calculated as B / A × 100%. Five lithium-ion batteries from each comparative example and embodiment were taken, and the average value was taken as the final result.

[0165] Figure 1 The image in (a) and (b) is a scanning electron microscope image of the negative electrode material in Example 1. It can be seen from (a) and (b) that a network structure is formed on the surface of the graphite, and the network structure is cross-linked with the graphite.

[0166] In this application, during coin cell battery testing, a component that readily co-intercalates with graphite (lithium ions and part of the electrolyte solvent co-intercalate into the graphite layer), such as propylene carbonate (PC), is added to the electrolyte of the coin cell. The coating effect of the graphite coating in the negative electrode material can be compared using an electrolyte containing PC. Comparing the negative electrode material of Example 1 and the graphite in Comparative Example 1, in the coin cell lithium co-intercalation test, the lower the co-intercalation capacity and the higher the reversible capacity in the PC-containing electrolyte, indicating a more significant desolvation capability of the negative electrode material and a better coating effect. This further verifies the coating effect of the negative electrode material. Figure 2 In comparison with Comparative Example 1, the co-lithiation curve of Example 1 shows that the coating on the surface of the negative electrode material has a better coating effect, which improves the desolvation ability of the negative electrode material and can improve the low-temperature performance of the electrochemical device.

[0167] Figure 3 The graphs show the full-cell capacity retention rates at 0 degrees Celsius for the negative electrode materials in Example 1 and Comparative Example 1. Figure 3 As can be seen from the example, after the graphite surface was coated, the low-temperature cycle capacity retention rate of the corresponding assembled full cell was improved.

[0168] The preparation conditions for each embodiment and comparative example are described in Table 1.

[0169] Table 1

[0170]

[0171]

[0172] Note: " / " in Table 1 indicates that the corresponding substance or parameter does not exist.

[0173] Table 2

[0174]

[0175]

[0176] Referring to Tables 1 and 2, compared to the comparative example, after pyrolysis at different temperatures, the negative electrode materials in the examples were coated with a coating, which significantly improved the energy density and low-temperature performance of the electrochemical device. In Examples 1 to 15, the content of the same metal in the negative electrode material varied at different heat treatment temperatures, and its residual rate also varied. The higher the temperature, the lower the content of the metal element, and the lower the weight loss rate of the negative electrode material.

[0177] Compared to Comparative Examples 1 and 2, Examples 1 and 3 significantly improved the energy density and low-temperature performance of the electrochemical device. The addition of ZIF-8 in Examples 1 and 3, while providing single-atom zinc doping, also resulted in a nitrogen-containing five-membered ring-rich ligand, 2-methylimidazolium, which further improved the energy density ratio and low-temperature performance, achieving a balance between improving both. In Example 1, the co-intercalation capacity was significantly reduced at a heat treatment temperature of 600°C, and the liquid phase transfer impedance at 0°C was also significantly lowered, indicating a significant improvement in the low-temperature performance of the electrochemical device. At this temperature, the FDCA-derived polyamide partially decomposes, and its oxygen-containing five-membered rings and amide bonds can crosslink with the graphite surface to form a curved carbon network, thereby enhancing the attraction to lithium ions and inducing rapid desolvation of lithium ions. Similarly, after treatment at 600°C, Example 4 showed desolvation effect and low-temperature cycling performance that were essentially equivalent to Example 1.

[0178] In Examples 5 to 7, when lithium phosphate (Li3PO4) is used as a metal compound additive, it can also reduce the co-intercalation capacity and improve the energy density and low-temperature performance of the electrochemical device. This is because lithium phosphate can improve the SEI film composition of the anode material during the first lithium intercalation, which is beneficial to improving the lithium-ion desolvation capability. At the same time, the presence of lithium ions in lithium phosphate can effectively improve the first coulombic efficiency of the full cell, thereby increasing the energy density of the electrochemical device. This allows the electrochemical device to maintain a high energy density while also improving low-temperature performance.

[0179] In Examples 8 to 13, when different types of MOF are used as metal-containing compound additives, they can maintain a certain crystal structure after heat treatment because they have stable metal centers. This plays a role in sieving solvents for the conduction of lithium ions on the surface of the negative electrode material, and can also improve the lithium ion desolvation ability, which is beneficial to improving the low-temperature performance of electrochemical devices.

[0180] In Example 14, the surface of the negative electrode material contained two metallic elements, and the electrochemical device still exhibited good energy density and low-temperature performance. In Example 15, by varying the mass of the added metal-containing compound, the electrochemical device still exhibited good energy density and low-temperature performance compared to the comparative example at different residual carbon ratios.

[0181] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises graphite and a coating on at least part of the surface of the graphite, the coating containing carbon elements, oxygen elements, nitrogen elements and metal elements, the metal elements including at least one of Zn, Zr or Al.

2. The negative electrode material of claim 1, wherein, The mass percentage of the metal elements in the negative electrode material is 0.05% to 0.2% based on the mass of the negative electrode material.

3. The negative electrode material of claim 1, wherein, The coating contains at least one of the following structural fragments: 、 、 、 、 、 。 4. The negative electrode material of claim 1, wherein, The weight loss rate of the negative electrode material is 0.15% to 0.3% when the temperature is raised from 35ºC to 800ºC in an inert atmosphere.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that, The negative electrode material further satisfies at least one of the following conditions: (1) the mass percentage of the nitrogen elements is 0.1% to 2% based on the mass of the negative electrode material; (2) the mass percentage of the oxygen elements is 0.1% to 3% based on the mass of the negative electrode material; (3) the mass percentage of the carbon elements is 95% to 99% based on the mass of the negative electrode material.

6. The negative electrode material according to any one of claims 1 to 4, characterized in that, The negative electrode material further satisfies at least one of the following conditions: (1) the graphite comprises at least one of artificial graphite or natural graphite; (2) the graphitization degree of the negative electrode material is 94% to 98%; (3) the particle size Dv50 of the negative electrode material is 8μm to 15μm; (4) the tap density of the negative electrode material is 0.9 g / cm 3 to 1.1 g / cm 3 ; (5) the specific surface area of the negative electrode material is 0.5 m 2 / g to 3 m 2 / g.

7. A method of producing the negative electrode material according to any one of claims 1 to 6, characterized by, The method comprises: dissolving biomass polyamide in a solvent and adding a metal-containing compound, stirring to obtain a coating slurry, the mass ratio of the biomass polyamide and the metal-containing compound at the same carbonization temperature being 1:(1-5), the metal elements in the metal-containing compound including at least one of Zn, Zr or Al; adding the coating slurry to graphite, mixing to obtain an intermediate; carbonizing the intermediate in an inert atmosphere at a carbonization temperature of 400ºC to 800ºC for 2h to 5h to obtain the negative electrode material.

8. The production method according to claim 7, characterized by, The biomass polyamide contains at least one of the following structural fragments: 、 、 、 ； The degree of polymerization n of the structural fragment is 500-2000.

9. The production method according to claim 8, characterized by, The metal-containing compound is selected from at least one of the following compounds: C8H 10 N4Zn, C 24 H 12 O 13 Zn4, C4H6N2Co, Li3PO4, LiF, C 48 H 24 O 32 Zr6, C 24 H 16 O 32 Zr6or C 18 H 10 Al3O 17 .

10. An electrochemical device, characterized by, The method comprises the negative electrode material of any one of claims 1 to 6.

11. An electronic device, comprising: The method comprises the electrochemical device of claim 10.

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