Negative electrode material, preparation method therefor, and use thereof

Abstract

The present application provides a negative electrode material, a preparation method therefor, and a use thereof. The negative electrode material comprises: a core, the core comprising a negative electrode active material; a carbon coating layer coating the core, the carbon coating layer comprising a first amorphous carbon layer and a polymer salt embedded in the first amorphous carbon layer; and a conductive material, the conductive material being located on the surface and / or inside of the carbon coating layer. The negative electrode material achieves balanced improvements in fast-charging performance, cycling performance, and high-temperature resistance, and can significantly improve the electrochemical performance of secondary batteries, including lithium-ion batteries and sodium-ion batteries. The present application further provides a preparation method for the negative electrode material and a use thereof.

Description

A negative electrode material, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411598754.1, filed on November 11, 2024, entitled “A negative electrode material and its preparation method and application”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to, but is not limited to, the field of secondary battery technology, specifically to a negative electrode material, its preparation method, and its application. Background Technology

[0003] With the continuous development of technology, the demand for rechargeable batteries (or simply batteries) in electronic products is growing rapidly, especially in fields such as electric vehicles and energy storage systems, which place higher demands on batteries' fast charging capabilities, cycle life, and high-temperature stability. Against this backdrop, battery manufacturing technology and the preparation technology of its key components (such as anode materials) have become important areas of research and development. As a crucial component of batteries, the performance of anode materials plays a vital role in the overall performance of the battery.

[0004] Since the introduction of lithium-ion batteries in the 1990s, graphite has been the mainstream anode material for lithium-ion batteries due to its low cost and stable performance. However, with the rapid development of the new energy industry, market demands for battery capacity and rate performance have been continuously increasing. Traditional graphite materials have gradually revealed their inherent shortcomings under high-rate conditions, such as poor kinetic performance, limited cycle capacity, and excessively rapid electrolyte consumption, which has restricted the widespread use of graphite materials. In addition to graphite, soft carbon and hard carbon have also been gradually applied to lithium-ion battery anode materials and are widely used in sodium-ion batteries. However, soft carbon and hard carbon also have similar problems, such as insufficient kinetic performance and poor cycle performance under high-rate conditions. Therefore, modifying these materials to improve the performance of secondary batteries and balancing and improving the overall rate performance, cycle performance, and high-temperature resistance of the battery remains one of the key research directions.

[0005] Therefore, there is an urgent need to develop a new anode material to improve the overall dynamic performance, cycle performance, and high-temperature resistance of batteries, in order to meet the ever-growing market demand. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] This application provides a negative electrode material that achieves a balanced improvement in fast charging performance, cycle performance, and high temperature resistance, and can significantly improve the electrochemical performance of secondary batteries, including lithium-ion batteries and sodium-ion batteries.

[0008] This application also provides a method for preparing a negative electrode material.

[0009] This application also provides a negative electrode sheet.

[0010] This application also provides a lithium-ion battery.

[0011] This application also provides an electrical device.

[0012] A first aspect of this application relates to a negative electrode material, comprising: a core, the core comprising a negative electrode active material; a carbon coating layer covering the core, the carbon coating layer comprising a first amorphous carbon layer and a polymer salt embedded in the first amorphous carbon layer; and a conductive material located on the surface and / or inside the carbon coating layer.

[0013] The negative electrode material according to the first aspect of this application has at least the following beneficial effects:

[0014] In the negative electrode material, the carbon coating layer includes a first amorphous carbon layer and a polymer salt embedded in the first amorphous carbon layer. The polymer salt readily attracts solvent molecules carrying charge carriers (e.g., lithium ions or sodium ions), reducing the resistance to charge carrier detachment from solvent molecules and effectively improving the desolvation resistance of the electrolyte on the electrode surface, thus enabling rapid charge carrier transport. Compared to ordinary polymers (in a non-salt-forming state), using polymer salts is more conducive to charge carrier exchange and transfer, thereby improving rate performance, which cannot be achieved with ordinary polymers. Furthermore, polymer salts do not participate in electrochemical reactions and do not consume charge carriers during cell charging and discharging, thus improving cycle performance. Compared to solutions that only coat amorphous carbon, the presence of polymer salts can reduce the degree of side reactions between the negative electrode active material and the electrolyte, improving high-temperature resistance and cycle performance. This is mainly because the amorphous carbon layer has a porous structure, which easily undergoes side reactions with the electrolyte at high temperatures; adding polymer salts reduces the probability of these side reactions.

[0015] In the first carbon coating layer, the first amorphous carbon layer effectively improves the conductivity of the polymer salt. By utilizing the intercalation structure formed between the first amorphous carbon layer and the polymer salt, the anchoring effect of the amorphous carbon layer on the polymer salt is fully utilized, enhancing the bonding force between the polymer salt and the negative electrode active material. This allows the polymer salt to be more firmly coated on the surface of the negative electrode active material, improving cycle performance. The amorphous carbon layer also protects the polymer salt, preventing it from dissolving into the solvent and damaging the original coating layer structure during the subsequent slurry preparation of the electrode sheet, thus improving the performance stability of subsequent processes.

[0016] The conductive layer can improve the overall conductivity of the negative electrode material, reduce the charge transfer impedance during the ion insertion / extraction process, promote electron exchange during ion insertion / extraction, increase the carrier transport rate at the electrode interface, and improve rate performance. When the surface of the first carbon coating layer is coated with a conductive material, this conductive material can construct a three-dimensional porous structure on the surface, forming an electrolyte storage space, increasing the electrolyte retention capacity of the electrode, and further promoting the efficient transport of carriers.

[0017] By designing the coating layer on the surface of the negative electrode material, higher rate performance was achieved, enabling rapid charge and discharge. Simultaneously, superior cycle performance and high-temperature resistance were also obtained. Results show that the constant-current charging capacity at a 3C charging rate reaches over 87.1% of the total capacity; under 45℃ high-temperature conditions, at a 1C charging and discharging rate, the capacity retention rate after 800 cycles is as high as 88.6%; after being placed at 60℃ high-temperature conditions for 30 days, at a 0.33C discharge rate, the capacity retention rate is as high as 87.2%, demonstrating excellent fast-charging performance, high-temperature resistance, and long-cycle performance.

[0018] According to some embodiments of this application, the first amorphous carbon layer in the carbon coating is selected from hard carbon or soft carbon.

[0019] According to some embodiments of this application, the carbon coating layer is obtained by sintering a blend of organic compound A and polymer salt, thereby carbonizing the organic compound A. The sintering employs a selective carbonization process, which, compared to conventional blending coating methods, can form a more stable embedded structure and fully utilize the anchoring effect of amorphous carbon on the polymer salt.

[0020] Specifically, the blend can be obtained by solution blending, which facilitates the uniform dispersion of organic compound A and polymer salt. To achieve selective carbonization, organic compound A with a carbonization temperature of T1 and polymer salt with a carbonization temperature of T2 can be selected (T1 < T2), and sintered at a temperature of T (T1 < T < T2) to obtain a carbon coating layer in which polymer salt is embedded in the first amorphous carbon layer.

[0021] According to some embodiments of this application, the carbonization temperature of the organic compound A is T1, the carbonization temperature of the polymer salt is T2, the softening temperature of the polymer salt is T0, and the sintering temperature is T. T, T0, T1, and T2 satisfy the following relationship: T1 < T < T2, and T0 < T. Furthermore, at temperature T, the organic compound A carbonizes to create pores, and the softened polymer salt can enter these pores, forming a more stable interlocking structure. Specifically, T can be made as close as possible to T1, while T2 can be as high as possible to reduce the impact of the carbonization process on the polymer salt.

[0022] According to some embodiments of this application, the temperature difference between T and T1 is 50 to 180°C, and the temperature difference between T2 and T1 is 50 to 300°C.

[0023] According to some embodiments of this application, T > 200°C, for example, it can be 200 to 500°C, specifically determined reasonably based on the carbonization temperature of organic compound A and polymer salt, and a suitable T value between the two is selected.

[0024] According to some embodiments of this application, T0 ≤ 200℃, specifically 90~200℃, and a suitable T0 value less than T is selected based on the sintering temperature T.

[0025] According to some embodiments of this application, the mass ratio of the first amorphous carbon layer to the polymer salt is 1 to 5:1, specifically 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any value between any two points. On the one hand, appropriately increasing the content of the first amorphous carbon layer is beneficial to improving rate performance; on the other hand, the presence of a certain amount of polymer salt can reduce side reactions between the negative electrode material and the electrolyte, improving cycle performance and high-temperature resistance. Therefore, by optimizing the ratio of the two, the overall electrical performance can be balanced and optimized.

[0026] According to some embodiments of this application, the mass ratio of the first amorphous carbon layer to the polymer salt is 1 to 3:1, and more specifically 1.5 to 2.5:1.

[0027] According to some embodiments of this application, the organic compound A is selected from one or more of ethylene tar, coal tar, coal tar pitch, rubber plasticizers (e.g., paraffin oil), styrene-butadiene rubber, urea-formaldehyde resin, monosaccharide compounds, polysaccharide compounds, carboxymethyl cellulose or its salts, polyacrylates, or polyacrylates. Since polymer salts are generally water-soluble, organic compound A can be selected from water-soluble organic compounds, such as monosaccharide compounds, polysaccharide compounds, carboxymethyl cellulose salts, polyacrylates, etc., or it can be selected from non-water-soluble organic compounds, in which case it can be a conventional aqueous dispersion of the organic compound, such as an emulsion, which facilitates mixing via solution methods.

[0028] According to some embodiments of this application, the polymer salt is selected from polymer lithium salt or polymer sodium salt. Lithium ions and sodium ions have similar structures and ionic radii. When applied to lithium-ion batteries or sodium-ion batteries, the lithium ions or sodium ions in the polymer salt can promote the exchange and transfer of lithium ions or sodium ions in the electrolyte within the polymer salt, further improving fast-charging performance.

[0029] According to some embodiments of this application, the polymer salt is selected from at least one of lithium polyacrylate, sodium polyacrylate, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, and lithium alginate. Non-limiting examples of the polymer salt include, for instance, when applied to lithium-ion batteries, it may be one or more of lithium polyacrylate, lithium carboxymethyl cellulose, and lithium alginate; when applied to sodium-ion batteries, it may be one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and sodium alginate.

[0030] According to some embodiments of this application, the polymer salt contains 0-5% carboxyl groups. For example, when the polymer salt is a carboxylate, the residual carboxyl content can be adjusted by controlling the carboxyl conversion rate. When all the carboxyl groups in the polymer are salted, the carboxyl content in the polymer salt is 0. Non-limiting examples of the carboxyl content in the polymer salt include: 0, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value between any two points.

[0031] According to some embodiments of this application, the polymer salt contains 1-5% carboxyl groups. Controlling the carboxyl group content to be too high is more conducive to ensuring high-temperature resistance.

[0032] According to some embodiments of this application, the polymer salt contains 1 to 3% carboxyl groups.

[0033] According to some embodiments of this application, the molecular weight of the polymer salt is 100W to 400W.

[0034] According to some embodiments of this application, the carbon coating layer has a mass percentage of 0.5% to 3% relative to the negative electrode material, specifically 0.5%, 1%, 2%, 3%, or any value between the two.

[0035] According to some embodiments of this application, the carbon coating layer has a mass percentage of 1% to 3% relative to the negative electrode material.

[0036] According to some embodiments of this application, the conductive material is coated on the surface of the first carbon coating layer.

[0037] According to some embodiments of this application, the conductive material is selected from at least one of graphene, carbon nanotubes, conductive carbon black, and carbon fiber. This application does not impose any limiting provisions on the type or size parameters of graphene, carbon nanotubes, conductive carbon black, or carbon fiber; any known type can be selected. This application does not particularly limit the sheet diameter of graphene; it can be selected based on experience. As an example, the sheet diameter of graphene can be selected as 0.5–10 μm, further examples are 1–10 μm, or 1–5 μm, or 1–3 μm, or 1–2 μm; the number of graphene layers can be selected as 1–50 layers, further examples are 1–30 layers. The carbon nanotubes can be common multi-walled carbon nanotubes or single-walled carbon nanotubes. The conductive carbon black can be selected as acetylene black, Super P, Ketjen black, etc.

[0038] According to some embodiments of this application, the conductive material contains hydroxyl groups. Introducing hydroxyl groups can increase the bonding force between the conductive material and the polymer salt. Especially when the polymer salt contains carboxyl groups, the condensation reaction between hydroxyl and carboxyl groups promotes the conductive material to be dispersed as close as possible to the polymer salt, thereby improving electronic conductivity. The hydroxyl functional group can be introduced using known processes such as oxidation, acid washing, and alkali washing, and the hydroxyl content can be easily controlled and adjusted by parameters such as reaction solution concentration, reaction temperature, and reaction time, without any limiting provisions.

[0039] According to some embodiments of this application, the mass content of hydroxyl groups in the conductive material is 1% to 5%, specifically 1%, 2%, 3%, 4%, 5%, or any value between any two points. Controlling the hydroxyl content to a certain level is more conducive to ensuring high-temperature resistance.

[0040] According to some embodiments of this application, the mass content of hydroxyl groups in the conductive material is 1% to 3%.

[0041] According to some embodiments of this application, the mass content of hydroxyl groups in the conductive material is 1% to 2%.

[0042] According to some embodiments of this application, the mass percentage of the conductive material relative to the negative electrode material is 0.05% to 2%, specifically 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, or any value between any two. The conductive material can improve electronic conductivity, thereby enhancing fast-charging performance and long-cycle performance. Controlling the content of the conductive material to avoid excessive levels can reduce side reactions between the electrolyte and the negative electrode, improving high-temperature performance and long-cycle performance.

[0043] According to some embodiments of this application, the mass percentage of the conductive material relative to the negative electrode material is 0.1% to 1%.

[0044] According to some embodiments of this application, the negative electrode material further includes a carbide of a dispersant. A certain amount of dispersant is added to improve the dispersibility of the conductive material. After the conductive material is dispersed inside and / or coated on the surface of the carbon coating layer, the added dispersant can be carbonized to improve conductivity; in this case, the negative electrode material also includes a carbide of the dispersant. Depending on the distribution of the conductive material, the carbide of the dispersant may coat the surface of the carbon coating layer and / or be located inside the carbon coating layer.

[0045] According to some embodiments of this application, the dispersant is selected from at least one of polyvinylidene fluoride or its derivatives, carboxymethyl cellulose or its derivatives (e.g., including oxidized carboxymethyl cellulose, carboxymethyl cellulose ester, oxidized carboxymethyl cellulose ester, etc.), salts of carboxymethyl cellulose or its derivatives (e.g., including corresponding sodium salts, lithium salts, etc.), polyvinylpyrrolidone or its derivatives, polyacrylic acid or its derivatives (e.g., including polyacrylates), polyacrylates, polystyrene-butadiene rubber, polyacrylamide, polyimide, polyamide-imide, and phenolic resins. Derivatives are included, but are not limited to, any known type derived from the corresponding polymer through a chemical reaction.

[0046] Specifically, the dispersant can be of a suitable type that is comparable to the carbonization temperature of organic compound A. The two types can be the same or different.

[0047] According to some embodiments of this application, the mass ratio of the dispersant to the conductive material is 1:1 to 10, specifically 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any value between any two points. Since the amount of dispersant is usually lower than, and at least not higher than, the amount of conductive material, the content of carbides formed after the dispersant carbonizes is significantly lower than the amount of dispersant added. The specific value can be easily calculated based on the type of dispersant and its carbon content.

[0048] According to some embodiments of this application, the mass ratio of the dispersant to the conductive material is 1:3 to 10.

[0049] According to some embodiments of this application, the mass ratio of the dispersant to the conductive material is 1:5 to 10.

[0050] According to some embodiments of this application, the negative electrode active material is selected from at least one of graphite, hard carbon, or soft carbon. Specifically, graphite can be one or more of artificial graphite, natural graphite, and mesophase carbon microspheres. Graphite is mainly used as the negative electrode active material for lithium-ion batteries, while hard carbon or soft carbon can be used in both lithium-ion and sodium-ion batteries.

[0051] According to some embodiments of this application, the particle size Dv50 of the negative electrode active material is 5 to 20 μm, specifically 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 17 μm, 20 μm or any value between any two points.

[0052] According to some embodiments of this application, the particle size Dv50 of the negative electrode active material is 7-16 μm.

[0053] According to some embodiments of this application, the negative electrode active material has a mass percentage of ≥90% relative to the negative electrode material.

[0054] According to some embodiments of this application, the negative electrode active material has a mass percentage of ≥91% relative to the negative electrode material.

[0055] According to some embodiments of this application, the negative electrode active material has a mass percentage of ≥95% relative to the negative electrode material.

[0056] According to some embodiments of this application, the surface of the core is coated with a second amorphous carbon layer, which is located between the core and the carbon coating layer. The second amorphous carbon layer can improve the bonding force between the carbon coating layer and the negative electrode active material, particularly promoting the tight bonding of the polymer salt in the carbon coating layer with the negative electrode material, enhancing the structural stability of the carbon coating layer, and improving the coating uniformity. Furthermore, the second amorphous carbon layer can effectively improve the overall conductivity of the negative electrode material, increase its liquid retention capacity and the desolvation rate of lithium and sodium ions on the surface of the negative electrode active material, and increase the number of active sites to enhance the ion intercalation rate.

[0057] According to some embodiments of this application, the second amorphous carbon layer is selected from hard carbon or soft carbon. Specifically, the second amorphous carbon layer is formed by carbonization of organic compound B, which can be selected from one or more of ethylene tar, coal tar, coal tar pitch, rubber plasticizer, styrene-butadiene rubber, urea-formaldehyde resin, monosaccharide compounds, or polysaccharide compounds.

[0058] According to some embodiments of this application, the mass percentage of the second amorphous carbon layer relative to the negative electrode material is 0.5% to 3%. Specifically, it can be 0.5%, 1%, 2%, 3%, or any value between any two points. Controlling the content of the second amorphous carbon layer to be not too high is more conducive to ensuring high-temperature resistance.

[0059] According to some embodiments of this application, the second amorphous carbon layer has a mass percentage of 1% to 3% relative to the negative electrode material.

[0060] Another embodiment of this application provides a method for preparing the above-mentioned negative electrode material, which includes the following steps:

[0061] S1. Prepare a mixture 1 containing organic matter A and polymer salt;

[0062] S2. Disperse the raw materials including the core in the mixture 1 to form mixture 2;

[0063] S3. After drying the mixture 2, sinter it under a protective atmosphere to carbonize the organic matter A in it, forming a carbon coating layer that covers the core.

[0064] S4. Prepare a mixture 3 containing conductive material. Disperse the product obtained in step S3 in the mixture 3 and dry it to obtain the negative electrode material.

[0065] Or it may include the following steps:

[0066] S1'. Prepare a mixture 4 containing the polymer salt, organic A, core and conductive material. After drying the mixture 4, sinter it under a protective atmosphere to carbonize the organic A in it, thereby obtaining the negative electrode material.

[0067] In the above method, the dispersant is used to improve the dispersibility of the conductive material, and carbonizing the dispersant helps to ensure conductivity.

[0068] After forming a carbon coating layer covering the core using a multi-step method (steps S1-S4), a conductive material is coated on the surface of the carbon coating layer. A structure containing conductive material inside the carbon coating layer is prepared by a one-step method (step S1'). The preparation process can be adjusted according to actual needs. Under the premise of meeting performance requirements, the one-step method can simplify the process flow and save preparation time and cost.

[0069] The above method involves coating the anode material with a mixed solution of organic compound A and polymer salt, followed by selective carbonization sintering (organic compound A is carbonized while the polymer salt remains uncarbonized). This process generates an in-situ intercalation structure of an amorphous carbon layer and polymer salt, which not only improves the conductivity of the anode material but also strengthens the bonding force between the anode surface and the polymer salt. This process effectively ensures the material's high-efficiency ion transport capability, improves the electrochemical reaction rate and overall battery performance, especially under high-rate and high-temperature conditions, guaranteeing stability and lifespan under long-cycle operating conditions.

[0070] It should be noted that in step S3, by adjusting the ratio of organic matter A and polymer salt, for example, the mass ratio of the amorphous carbon layer formed by the carbonization of organic matter A to the polymer salt is 1 to 5:1, a powdered product can be obtained directly after carbonization, or the powder material can be obtained by simple grinding, without the need for long-term crushing processes such as ball milling.

[0071] It should be understood that in order to achieve selective carbonization, the sintering temperature should be appropriately higher than the carbonization temperature of organic compound A, and appropriately lower than the carbonization temperature of polymer salt, for example, referring to the relevant implementation methods for anode materials mentioned above.

[0072] According to some embodiments of this application, the solid-liquid mass ratio of the mixtures 2-4 is independently selected from 1:1 to 5, wherein the solid-liquid mass ratio is the mass ratio of the solid phase to the liquid phase in the corresponding mixture.

[0073] According to some embodiments of this application, a dispersant is further added to the mixture 3, and step S4 further includes: carbonizing the dispersant after drying to obtain the negative electrode material; or, a dispersant is further added to the mixture 4, and in step S1', the organic compound A and the dispersant are carbonized through sintering to obtain the negative electrode material. The type and amount of dispersant are selected with reference to the relevant embodiments of the negative electrode material described above.

[0074] It should be understood that when a dispersant is added, the carbonization temperature of the dispersant should be lower than that of the polymer salt, and the sintering temperature in the above method should be appropriately higher than the carbonization temperature of the dispersant so that the polymer salt is not carbonized when the dispersant is carbonized. Specifically, the carbonization temperature of the dispersant can be determined by referring to the carbonization temperature T1 of organic compound A mentioned above, and by combining the types of dispersants listed above, it is easy to select a suitable type of dispersant that meets the requirements.

[0075] According to some embodiments of this application, the negative electrode material further includes a second amorphous carbon layer, and the preparation method of the negative electrode material further includes: before step S1, coating the surface of the core with the second amorphous carbon layer. Therefore, it can be understood that the core in step S2 or step S1' is a core coated with the second amorphous carbon layer. Specifically, the method for forming the second amorphous carbon layer can employ known solid-phase, liquid-phase, or gas-phase methods. For example, in a solid-phase method, an organic substance B such as asphalt is coated onto the surface of the negative electrode active material and carbonized in a carbonization furnace; in a liquid-phase method, the negative electrode active material and organic substance B are slurried, dried, and then carbonized; in a gas-phase method, an organic carbon source (e.g., methane, ethylene, acetylene) is used for carbon deposition, and the deposition equipment can be a rotary kiln.

[0076] According to some embodiments of this application, the dispersed phase of the mixture 1, mixture 3, and mixture 4 is selected from one or more of water, NMP, ethanol, and ethylene glycol.

[0077] According to some embodiments of this application, the protective atmosphere is an inert atmosphere, specifically nitrogen, argon, etc.

[0078] Another embodiment of this application provides a negative electrode sheet, wherein the raw materials for preparing the negative electrode sheet include the aforementioned negative electrode material.

[0079] This negative electrode sheet, based on the coating structure design of the negative electrode material, particularly the intercalation structure of the first amorphous carbon layer and polymer salt, and the introduction of conductive materials, effectively improves the overall conductivity and carrier transport rate of the negative electrode sheet. The introduction of polymer salt reduces the desolvation resistance of the negative electrode sheet during charge and discharge, enabling rapid carrier transfer and significantly improving rate performance. Furthermore, the presence of polymer salt reduces side reactions between the negative electrode material and the electrolyte, extending the lifespan of the negative electrode sheet and giving it excellent cycle stability and high-temperature resistance.

[0080] It should be understood that negative electrode sheets typically also include negative electrode current collectors, negative electrode conductive agents, and negative electrode binders. The specific selection of these components or the preparation technology of the negative electrode sheet are conventional technologies and can be easily selected according to actual needs.

[0081] Another embodiment of this application provides a secondary battery including the negative electrode sheet described above.

[0082] This anode material significantly improves charge / discharge rate performance in rechargeable batteries, especially excelling in fast-charging scenarios. The presence of polymer salt reduces electrolyte consumption, allowing the battery to maintain a high capacity retention rate even after long-term cycling, thus extending the overall battery life. Through the combined action of the first amorphous carbon layer and the conductive material, the charge transfer impedance during ion insertion / extraction is reduced, improving battery stability and tolerance to high-temperature environments. Therefore, the design based on this anode material enables the rechargeable battery to possess excellent long-cycle performance, fast-charging performance, and high-temperature stability, better meeting the requirements of high-performance applications.

[0083] It should be understood that secondary batteries typically also include a positive electrode, a separator, and an electrolyte. The relevant technologies are conventional and can be easily selected according to actual needs.

[0084] According to some embodiments of this application, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0085] Another embodiment of this application provides an electrical device including the aforementioned secondary battery.

[0086] The negative electrode material design ensures the battery's high-efficiency fast charging capability, meeting the demand for high-rate fast charging, and improves cycle performance and high-temperature resistance by reducing side reactions, thus extending the service life of the electrical device.

[0087] Electrical devices specifically include electric vehicles (such as electric cars, electric motorcycles, and electric bicycles), energy storage systems (such as home energy storage systems and photovoltaic energy storage systems), or mobile devices (such as smartphones, tablets, and laptops).

[0088] In this article, the term "multiple" means two or more than two kinds.

[0089] "Approximately" indicates an error range of ±2%.

[0090] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0091] The accompanying drawings are used to provide a further understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0092] Figure 1 is a schematic diagram of the structure of the negative electrode material of this application.

[0093] Reference numerals: 010, core; 020, second amorphous carbon layer; 030, carbon coating layer; 031, first amorphous carbon layer; 032, polymer salt; 040, conductive material. Detailed Implementation

[0094] The following are specific embodiments of this application, and the technical solutions of this application will be further described in conjunction with the embodiments, but this application is not limited to these embodiments.

[0095] In the examples and comparative examples, the molecular weights of lithium polyacrylate and lithium carboxymethyl cellulose were 100W to 400W, and their softening points were 90 to 200°C.

[0096] The hydroxyl groups in graphene can be introduced through conventional acidification modification methods, and the hydroxyl content can be easily adjusted by acid concentration, acidification temperature, and acidification time.

[0097] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0098] Example 1

[0099] Referring to Figure 1, a negative electrode material includes a core 010 and a second amorphous carbon layer 020, a carbon coating layer 030, and a conductive material 040 sequentially coated on the surface of the core 010. The carbon coating layer 030 includes a first amorphous carbon layer 031 and a polymer salt 032 embedded in the first amorphous carbon layer 031.

[0100] Among them, core 010 is artificial graphite with a particle size Dv50 of 13μm. Conductive material 040 is graphene with a sheet diameter of 1-2μm and 1-20 layers.

[0101] The preparation method of the negative electrode composite material is as follows:

[0102] S1. Prepare a mixture 1 containing organic matter A and polymer salt;

[0103] S2. Disperse the nuclei in mixture 1 to form mixture 2;

[0104] S3. After drying the mixture 2, sinter it under a protective atmosphere to carbonize the organic matter A in it, forming a carbon coating layer that covers the core.

[0105] S4. Prepare a mixture 3 containing conductive material and dispersant. Disperse the product obtained in step S3 in the mixture 3. After drying, carbonize the dispersant to obtain the negative electrode material.

[0106] For reference, see Tables 1 and 2 for the types and amounts of organic compound A, conductive materials, and dispersants.

[0107] The sintering temperature in step S3 and the carbonization temperature in step S4 are both 230°C, and the protective atmosphere is nitrogen. In step S3, since the proportion of organic matter A is higher than that of polymer salt, a powdered product can be obtained after sintering, without the need for crushing.

[0108] Both mixture 1 and mixture 3 contain water as the dispersed phase. The amount of water added to mixture 1 is 2000g, and the mass ratio of the solid phase to the liquid phase in mixture 3 is 1:1 to 5.

[0109] In this embodiment, the negative electrode material is prepared using a multi-step method. Referring to the previous text, a one-step method can also be used to prepare the composite material, although the distribution of the conductive material and the carbide of the dispersant differs between the two methods. It should be understood that, for the one-step method, the polymer salt 032 is embedded in the first amorphous carbon layer 031, which includes both the polymer salt 032 being embedded inside the first amorphous carbon layer 031 and the polymer salt 032 being embedded on the surface of the first amorphous carbon layer 031; both states can coexist.

[0110] In step S1, both organic compound A and polymer salt are water-soluble, and mixture 1 is an aqueous solution of the two, which can achieve uniform dispersion. Referring to the previous text, organic compound A can be a non-water-soluble organic compound. In this case, a conventional dispersion of the corresponding substance (such as an emulsion) can be selected. Thus, mixture 1 is an aqueous dispersion of organic compound A dispersed in a polymer salt solution.

[0111] After solution blending, organic compound A and polymer salt can be uniformly dispersed, resulting in an intercalation structure of organic compound A carbides (i.e., the first amorphous carbon layer) and polymer salt after sintering, namely carbon coating layer 030. It is understood that the carbon coating layer structure shown in Figure 1 is only schematic and is mainly used to illustrate the intercalation morphology, and does not represent the actual microstructure of carbon coating layer 030.

[0112] Examples 2 to 9, and Comparative Examples 1 to 5

[0113] The differences from Example 1 are shown in Tables 1 and 2.

[0114] Specifically, in Example 8, the preparation method of the negative electrode composite material is as follows:

[0115] S0. Using the solid-phase method, the raw material is asphalt with a carbon content of 60%. 1000g of core (artificial graphite) and 33.33g of asphalt are mixed evenly and placed in a carbonization furnace. Nitrogen gas is introduced into the protective atmosphere, the sintering temperature is 1200℃, and the sintering time is 12h to obtain a core coated with a second amorphous carbon layer.

[0116] S1. Prepare a mixture 1 containing organic matter A and polymer salt;

[0117] S2. Disperse the cores coated with the second amorphous carbon layer in the mixture 1 to form mixture 2;

[0118] S3. After drying the mixture 2, sinter it under a protective atmosphere to carbonize the organic matter A and form a carbon coating layer covering the core.

[0119] S4. Prepare a mixture 3 containing conductive material and dispersant. Disperse the product obtained in step S3 in the mixture 3. After drying, carbonize the dispersant to obtain the negative electrode material.

[0120] In Example 8, the remaining details of the preparation method are the same as in Example 1.

[0121] Comparative Example 6

[0122] A negative electrode material was prepared, wherein a polymer salt is coated on the surface of a first carbonized layer. The specific steps are as follows:

[0123] S1. Artificial graphite and organic matter A are dispersed in water, dried, and carbonized at temperature T to obtain powder 1;

[0124] S2. Disperse powder 1 and polymer salt in water and dry to obtain powder 2;

[0125] S3. After uniformly dispersing powder 2, conductive material, and dispersant in water, dry the mixture and sinter it at temperature T to obtain the negative electrode material.

[0126] The relevant material types, proportions, and process parameters are shown in Tables 1 and 2.

[0127] Table 1

[0128] Table 2

[0129] Test case

[0130] Used to demonstrate the performance of negative electrode materials in lithium-ion batteries.

[0131] 1. Preparation of lithium-ion half-cells

[0132] Under a dry argon atmosphere, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (by weight ratio approximately 1:1:1) were mixed. LiPF6 was added to the resulting solvent and mixed thoroughly to obtain an electrolyte with a LiPF6 concentration of approximately 1.15 mol / L. The negative electrode material, conductive carbon black, and binders CMC and SBR obtained in the examples and comparative examples were added to deionized water at a weight ratio of approximately 94.5:1.5:1.5:1.5, and stirred to form a slurry. A coating of approximately 100 μm thickness was formed using a doctor blade and dried in a vacuum drying oven at approximately 85°C for approximately 12 hours. The dried material was then cut into discs with a diameter of approximately 1 cm using a punch press. In a glove box, a lithium metal sheet was used as the counter electrode, and a Ceglard composite membrane was selected as the separator. The aforementioned electrolyte was added to assemble a coin cell.

[0133] 2. Fabrication of lithium-ion full batteries

[0134] 2.1. Preparation of negative electrode sheet

[0135] The negative electrode material, negative electrode conductive agent (conductive carbon black), binder SBR, and thickener CMC obtained in the examples and comparative examples were mixed in a weight ratio of approximately 96:1:1.6:1.4. An appropriate amount of water was added, and the mixture was kneaded at a solid content of approximately 60wt%–75wt%. An appropriate amount of water was added to adjust the viscosity of the slurry to approximately 3000–8000 Pa·s, thus preparing a negative electrode slurry. The prepared negative electrode slurry was coated onto a copper foil current collector, with a wet film thickness of approximately 100 μm. After drying, it was cold-pressed to obtain a negative electrode sheet. The types and ratios of the negative electrode conductive agent, binder, and thickener, as well as the proportion of the negative electrode active material, can be added according to actual conditions. The preparation technique of the negative electrode sheet follows conventional methods and is not subject to limiting provisions.

[0136] 2.2 Preparation of full cells

[0137] The prepared negative electrode, positive electrode, electrolyte, and separator are assembled into a lithium-ion full battery using conventional methods.

[0138] The positive electrode is a conventional lithium-ion battery positive electrode, and the positive electrode active material is LiFePO4; the separator is a porous polyethylene polymer film. In addition, polypropylene separators or composite separators can also be selected.

[0139] The negative electrode, separator, and positive electrode are stacked in sequence, wound into a bare cell, placed in a battery case, and injected with electrolyte (the same electrolyte used in the aforementioned half-cell). After processes such as encapsulation, settling, and formation, a lithium-ion battery is obtained.

[0140] 3. Test Items

[0141] 3.1 Negative Electrode Testing

[0142] Take the negative electrode sheet prepared in Section 2.1 and cut it to a width of 20 mm and a length of L1. Place the aforementioned electrolyte in a beaker, and then place the cut negative electrode sheet in the electrolyte, with the negative electrode sheet partially immersed in the electrolyte for an immersion length of L2 (L2 < L1). Record the time t for the electrolyte to diffuse to the top of the electrode sheet. Then, the electrolyte absorption rate of the electrode sheet is (L1-L2) / t.

[0143] 3.2 Capacity Test

[0144] The prepared half-cell was tested using a LAND series battery testing system with a charge / discharge rate of 0.05C and a voltage of 5mV to 2V. The discharge capacity was recorded, and the specific capacity of the negative electrode material was calculated.

[0145] 3.3 Charging Rate Test

[0146] At 25℃, discharge at 0.33C to 2.0V, let stand for 5 minutes, charge at 3C to 3.75V, and then charge at constant voltage to 0.05C and let stand for 5 minutes. The ratio of the constant current charging capacity to the total capacity (the sum of the capacities of the constant current and constant voltage charging stages) is the charging rate.

[0147] 3.4 High-Temperature (45℃) Cyclic Performance Test

[0148] The test temperature was 45℃. The battery was charged at a constant current of 1C to 3.75V, then charged at a constant voltage of 0.05C. After resting for 5 minutes, it was discharged at 1C to 2.0V. The discharge capacity obtained in this step was used as the initial capacity. A 1C charge / discharge cycle test was performed, and the ratio of the discharge capacity to the initial capacity for each cycle was recorded to obtain the capacity decay curve. The capacity retention rate after 800 cycles at 45℃ was recorded to evaluate the battery's high-temperature cycle performance.

[0149] 3.5 High Temperature (60℃) Storage Performance Test:

[0150] At 25℃, the cell is charged at a constant current of 0.33C to 3.75V, then at a constant voltage of 0.05C. After resting for 5 minutes, it is discharged at 0.33C to 2.0V. The discharge capacity obtained in this step is taken as the baseline capacity C1. The cell is placed in a high-temperature chamber at 60℃ for 30 days, then removed and charged at 25℃ at a constant current of 0.33C to 3.75V, then at a constant voltage of 0.05C. After resting for 5 minutes, it is discharged at 0.33C to 2.0V. The capacity obtained in this step is taken as the recovery capacity C3 after high-temperature storage. The capacity retention rate after high-temperature storage is calculated as C3 / C1*100%.

[0151] Sections 3.3 to 3.5 focus on testing the prepared full cells.

[0152] The test results are shown in Table 3.

[0153] Table 3

[0154] The results above show that Examples 1, 2, and 7, through the rational design of the carbon coating layer and conductive materials, have better overall performance in terms of rate capability, high temperature resistance, and cycle performance, and have achieved a significant improvement in electrical performance.

[0155] Examples 2, 3, and 4, compared with Comparative Examples 1 and 2, illustrate that as the proportion of organic compound A increases, the proportion of amorphous carbon layer obtained after carbonization increases, which helps enhance the electrolyte retention performance of the electrode and increases the active sites for lithium intercalation in the negative electrode, thereby improving the overall rate performance of the negative electrode. However, the increase in the amorphous carbon layer reduces the specific capacity of the negative electrode, leading to a decrease in energy density. Furthermore, with the increase in the amorphous carbon layer, the degree of side reactions between graphite and electrolyte also increases at high temperatures. This is because the specific surface area of ​​the amorphous carbon layer and the conductive material is relatively large, making them prone to side reactions with the electrolyte. As the content increases, the degree of side reactions also increases, leading to deterioration of high-temperature performance. Therefore, rationally designing the ratio of amorphous carbon layer to polymer salt in the carbon coating layer (adjusted by the ratio of organic compound A and polymer salt) and its content helps to achieve a better balance between fast charging and high-temperature performance, thereby further optimizing electrical performance.

[0156] Examples 2, 5, and 6, compared with Comparative Examples 3 and 4, illustrate that conductive materials can effectively improve the electrolyte absorption and retention capacity of the negative electrode, replenish electrolyte consumption during cycling, shorten the diffusion path of lithium ions in the negative electrode, and reduce diffusion resistance. Conductive materials can also improve the overall electronic conductivity of the negative electrode, thereby improving fast-charging performance and long-cycle performance. When the content of conductive material is too high (>2% of the mass of the negative electrode material), the degree of side reactions with the electrolyte increases, leading to a decrease in high-temperature performance and initial efficiency, affecting long-cycle performance. In contrast, appropriately reducing the content of conductive material can more effectively balance these performance characteristics and achieve a better overall effect.

[0157] A comparison of Examples 2 and 8 illustrates that the second amorphous carbon layer can further enhance the liquid absorption and retention properties of the graphite anode, increase lithium intercalation active sites, and thus improve the fast-charging performance of the graphite anode. The second amorphous carbon layer can also strengthen the bonding strength between the carbon coating layer and the graphite surface, improving the overall structural stability of the anode material and thus enhancing long-cycle performance. However, the added amorphous carbon layer may undergo side reactions with the electrolyte, potentially affecting high-temperature performance. Therefore, through the rational design of the second amorphous carbon layer, a better balance between fast-charging performance and high-temperature resistance can be achieved.

[0158] A comparison of Examples 2 and 9 illustrates that when the polymer salt and the conductive material have matching functional groups on their surfaces, the conductive material tends to coat the distribution sites of the polymer salt, which is beneficial for improving the electronic conductivity of the negative electrode material and enhancing rate performance and cycle performance. The high-temperature storage performance slightly declines, possibly because the introduction of functional groups increases side reactions with the electrolyte at high temperatures.

[0159] Comparing Examples 2 and 5 and 6, it is evident that the polymer salt in the carbon coating layer can effectively improve the desolvation efficiency of lithium ions on the graphite anode surface in the electrolyte, thereby significantly enhancing fast-charging performance. In Comparative Example 5, the high carbonization temperature caused the entire second coating layer to transform into amorphous carbon, increasing lithium ion consumption during cycling and leading to deteriorated cycle performance. High-temperature performance also deteriorated due to the increased amorphous carbon. Furthermore, the carbonization generates inorganic compounds (such as Li₂CO₃ and Na₂CO₃), which cannot effectively release lithium or sodium ions in the electrolyte solvent, thus losing their ion exchange function and failing to effectively improve fast-charging performance. Comparative Example 6 shows that when the polymer salt completely coats the surface of the amorphous carbon layer, the overall electronic conductivity of the material deteriorates, negatively impacting fast-charging and cycle performance, but not significantly affecting high-temperature resistance. Therefore, although the presence of polymer salt significantly improves fast-charging performance, its distribution and structure on the graphite surface need to be rationally designed. When the polymer salt forms an intercalation structure with the amorphous carbon layer, the overall electrical performance is significantly better.

[0160] In summary, lithium-ion batteries manufactured using the negative electrode material of this application significantly improve rate performance while enhancing battery stability and tolerance in high-temperature environments. Based on the battery's excellent long-cycle performance, fast-charging performance, and high-temperature stability, it can better meet the performance, range, and service life requirements of electrical devices such as new energy vehicles.

[0161] The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application.

Claims

1. A negative electrode material, comprising: The core includes a negative electrode active material; A carbon coating layer covering the core, the carbon coating layer comprising a first amorphous carbon layer and a polymer salt embedded in the first amorphous carbon layer; A conductive material, wherein the conductive material is located on the surface and / or inside the carbon coating layer.

2. The negative electrode material of claim 1, wherein, The mass ratio of the first amorphous carbon layer to the polymer salt is 1 to 5:1; and / or, the polymer salt is selected from polymer lithium salt or polymer sodium salt; and / or, the polymer salt contains 0 to 5% by mass of carboxyl groups; and / or, the carbon coating layer has a mass percentage of 0.5% to 3% relative to the negative electrode material.

3. The negative electrode material according to claim 1 or 2, wherein The conductive material is selected from at least one of graphene, carbon nanotubes, conductive carbon black, and carbon fiber; and / or, the conductive material contains hydroxyl groups, wherein the mass content of the hydroxyl groups is 1% to 5%; and / or, the mass percentage of the conductive material relative to the negative electrode material is 0.05% to 2%.

4. The negative electrode material according to any one of claims 1-3, wherein, The negative electrode active material is selected from at least one of graphite, hard carbon, or soft carbon; and / or, the particle size Dv50 of the negative electrode active material is 5 to 20 μm.

5. The negative electrode material according to any one of claims 1 to 4, wherein, The surface of the core is coated with a second amorphous carbon layer, which is located between the core and the carbon coating layer; optionally, the mass percentage of the second amorphous carbon layer relative to the negative electrode material is 0.5% to 3%.

6. A method for preparing a negative electrode material as described in any one of claims 1-5, comprising the following steps: S1. Prepare a mixture 1 containing organic matter A and the polymer salt; S2. Disperse the raw materials including the core into the mixture 1 to form mixture 2; S3. After drying the mixture 2, sinter it under a protective atmosphere to carbonize the organic matter A in it, forming a carbon coating layer that covers the core. S4. Prepare a mixture 3 containing conductive material. Disperse the product obtained in step S3 in the mixture 3 and dry it to obtain the negative electrode material. Or it may include the following steps: S1'. Prepare a mixture 4 containing the polymer salt, organic A, core and conductive material. After drying the mixture 4, sinter it under a protective atmosphere to carbonize the organic A and obtain the negative electrode material.

7. The production method according to claim 6, wherein A dispersant is also added to the mixture 3. Step S4 further includes: carbonizing the dispersant after drying to obtain the negative electrode material; or, a dispersant is also added to the mixture 4. In step S1', organic A and the dispersant are carbonized by sintering to obtain the negative electrode material. Optionally, the solid-liquid mass ratio of the mixtures 2-4 is independently selected from 1:1 to 5; Optionally, when the negative electrode material further includes a second amorphous carbon layer, the method for preparing the negative electrode material further includes: before step S1, coating the surface of the core with the second amorphous carbon layer; Optionally, the organic compound A is selected from one or more of ethylene tar, coal tar, coal pitch, rubber plasticizer, styrene-butadiene rubber, urea-formaldehyde resin, monosaccharide compounds, polysaccharide compounds, carboxymethyl cellulose or its salts, polyacrylates or polyacrylates; Optionally, the dispersant is selected from at least one of polyvinylidene fluoride or its derivatives, carboxymethyl cellulose or its derivatives, salts of carboxymethyl cellulose or its derivatives, polyvinylpyrrolidone or its derivatives, polyacrylic acid or its derivatives, polyacrylate, polystyrene-butadiene rubber, polyacrylamide, polyimide, polyamide-imide, and phenolic resin. Optionally, the mass ratio of the dispersant to the conductive material is 1:1 to 10; Optionally, the carbonization temperature of the organic compound A is T1, the carbonization temperature of the polymer salt is T2, the softening temperature of the polymer salt is T0, and the sintering temperature is T. T, T0, T1, and T2 satisfy the following relationship: T1 < T < T2, and T0 < T.

8. A negative electrode sheet, wherein the raw materials for preparing the negative electrode sheet include the negative electrode material as described in any one of claims 1-5.

9. A secondary battery, comprising the negative electrode sheet as described in claim 8; optionally, the secondary battery is a lithium-ion battery or a sodium-ion battery.

10. An electrical device comprising the secondary battery as described in claim 9.

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