Composite negative electrode material, preparation method thereof and battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a composite negative electrode material, a preparation method thereof and a battery. The composite negative electrode material comprises a carbon material framework, a silicon-based material, a solid electrolyte and nitrogen-doped amorphous carbon; wherein the silicon-based material and the solid electrolyte are embedded on the surface of the carbon material framework, and at least part of the nitrogen-doped amorphous carbon is combined between the interface of the carbon material framework and the silicon-based material and the solid electrolyte. The carbon material framework-nitrogen-doped amorphous carbon-solid electrolyte in the composite negative electrode material forms a three-dimensional ion-electron dual-conduction network, has extremely high ion conductivity and electronic conductivity, significantly improves the kinetic performance, has extremely high interface stability and guarantees the connectivity of the conduction network. The composite negative electrode material has high energy density and high kinetic performance.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to composite anode materials and their preparation methods, and batteries. Background Technology

[0002] With the development of battery technology, in addition to traditional carbon materials, silicon-based materials are often introduced into battery anode materials to form silicon-carbon composites, which can improve the energy density of the anode material and increase the battery capacity. However, the kinetic performance of these anode materials still needs improvement. To address this, some technical solutions involve adding solid electrolytes to the anode material to improve the lithium-ion conductivity; others involve adding smaller carbon materials to improve the electronic conductivity.

[0003] However, on the one hand, existing technologies often simply mix these materials together physically, resulting in low bonding strength and high interfacial impedance, which affects the stability and conductivity of the ion conduction network and the electron conduction network. On the other hand, silicon-based materials are prone to volume expansion during charge-discharge cycles. Under the impact of these volume changes, problems such as easy interruption of the ion conduction network and easy breakage of the conductive network are further caused. As a result, the performance improvement of adding solid electrolytes and smaller carbon materials to anode materials, especially silicon-carbon anode materials, is limited. Although the battery has a high capacity, the improvement in dynamic performance is limited, and the cycle performance and rate performance are not high. Summary of the Invention

[0004] The purpose of this application is to provide composite anode materials, their preparation methods, and batteries, aiming to solve the problem of poor dynamic performance of anode materials in the prior art.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a composite anode material, comprising a carbon material framework, a silicon-based material, a solid electrolyte, and nitrogen-doped amorphous carbon; In this process, at least a portion of the silicon-based material and the solid electrolyte are embedded on the surface of the carbon material framework, and at least a portion of the nitrogen-doped amorphous carbon is bonded between the carbon material framework and the silicon-based material and the solid electrolyte.

[0006] The composite anode material of this application has several beneficial effects. First, silicon-based materials are high-capacity lithium storage active centers, which can work synergistically with the carbon material framework to improve the energy density of the material.

[0007] Secondly, the carbon material framework can not only be used for lithium-ion insertion and extraction, and has a certain lithium storage capacity; it can also serve as the main support, providing a continuous macroscopic electron transport network; it can support silicon-based materials and solid electrolytes, and play a preliminary confinement role on silicon-based materials, suppressing their volume expansion.

[0008] Thirdly, solid electrolytes can not only form fast ion transport channels, significantly improving the migration rate of lithium ions; but they also often have a high modulus, which can serve as rigid support nodes, further synergizing with the carbon material framework to exert a stronger confinement effect, suppressing the volume expansion of silicon-based materials, and reducing damage to electron transport networks and ion transport networks.

[0009] Fourthly, firstly, nitrogen-doped amorphous carbon is bonded in a manner similar to being laid at the interface between the carbon material skeleton and the silicon-based material and solid electrolyte. It can act as a flexible buffer component, playing a role in dispersing stress. It can synergistically exhibit the performance characteristics of combining rigidity and flexibility with the solid electrolyte, further buffering the stress impact of the volume expansion of the silicon-based material. Secondly, nitrogen-doped amorphous carbon not only acts as a flexible conductive link, but also, due to its N-type doping, can provide additional free electrons, thus significantly improving the electronic conductivity in synergy with the carbon material skeleton. Thirdly, because it is rich in lone pair electrons, it can form strong coordination bonds with elements in the silicon-based material and metal ions in the solid electrolyte, playing a bridging and anchoring role. It has a high interfacial bonding strength with the silicon-based material and solid electrolyte, thereby improving the bonding stability between the silicon-based material and the solid electrolyte, and also improving the bonding stability between the silicon-based material, the solid electrolyte and the carbon material skeleton surface. It provides an interfacial bonding force far exceeding that of conventional physical adsorption, greatly reducing the electronic and ionic conduction impedance at the interface. Therefore, it can further enhance the effects of the first to third aspects mentioned above, and greatly improve the kinetic performance of the composite anode material.

[0010] In summary, the carbon framework, nitrogen-doped amorphous carbon, and solid electrolyte in the composite anode material constitute a three-dimensional ion-electron dual-conduction network, exhibiting extremely high ion and electronic conductivity, significantly improving kinetic performance, and possessing extremely high interfacial stability, ensuring the connectivity of the conduction network. The silicon-based material is embedded within this dual-conduction network, providing high lithium storage capacity and suppressing and buffering volume expansion during charge and discharge, further reducing the impact on the dual-conduction network and ensuring its connectivity. Therefore, this composite anode material possesses both high energy density and high kinetic performance.

[0011] Secondly, this application provides a method for preparing a composite negative electrode material, comprising the following steps: It provides a dispersion and a carbon material framework, the dispersion including a solvent, and also including silicon-based materials, solid electrolytes and nitrogen-containing carbon sources dispersed in the solvent; The dispersion was mixed with a carbon material framework to obtain a mixed slurry; After evaporating the solvent in the mixed slurry, carbonization is performed to generate nitrogen-doped amorphous carbon from the nitrogen-containing carbon source, thus obtaining a composite anode material.

[0012] The preparation method is controllable, and the resulting composite anode material has a stable structure and properties, with both high energy density and high kinetic performance.

[0013] Thirdly, this application provides a battery in which the negative electrode contains the composite negative electrode material described above, or contains the composite negative electrode material prepared by the preparation method described above.

[0014] The battery of this application contains the composite negative electrode material of this application, which has high energy density and kinetic performance, and the volume expansion is suppressed. Therefore, the battery of this application has both high energy density and high rate performance, and the volume expansion rate of the negative electrode is also low. The battery has high structural stability and good cycle performance. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the preparation method of Example 1 of this application; Figure 2 This is the XRD pattern of the hard carbon in Example 1 of this application; Figure 3 This is a 15kx magnified SEM image of the composite negative electrode material of Example 1 of this application; Figure 4 This is a 5kx magnified SEM image of the composite negative electrode material of Example 1 of this application; Figure 5 This is a schematic diagram of the Young's modulus test results for the negative electrode in Comparative Example 1; Figure 6 This is a schematic diagram of the Young's modulus test results of the negative electrode in Embodiment 1 of this application; Figure 7 This is a comparison chart of the cycle performance of the batteries in Example 1 and Comparative Example 2. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0019] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions mean any combination of these items, including any combination of single or multiple items.

[0020] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0021] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0022] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, a first feature may also be referred to as a second feature, and similarly, a second feature may also be referred to as a first feature. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0023] The first aspect of this application provides a composite anode material, comprising a carbon material framework, a silicon-based material, a solid electrolyte, and nitrogen-doped amorphous carbon; In this structure, silicon-based materials and solid electrolytes are embedded on the surface of a carbon material framework, and at least some nitrogen-doped amorphous carbon is bonded between the carbon material framework and the silicon-based materials and solid electrolytes.

[0024] The composite anode material of this application has several beneficial effects. First, silicon-based materials are high-capacity lithium storage active centers, which can work synergistically with the carbon material framework to improve the energy density of the material.

[0025] Secondly, the carbon material framework can not only be used for lithium-ion insertion and extraction, and has a certain lithium storage capacity; it can also serve as the main support, providing a continuous macroscopic electron transport network; it can support silicon-based materials and solid electrolytes, and play a preliminary confinement role on silicon-based materials, suppressing their volume expansion.

[0026] Thirdly, solid electrolytes can not only form fast ion transport channels, significantly improving the migration rate of lithium ions; but they also often have a high modulus, which can serve as rigid support nodes, further synergizing with the carbon material framework to exert a stronger confinement effect, suppressing the volume expansion of silicon-based materials, and reducing damage to electron transport networks and ion transport networks.

[0027] Fourthly, firstly, nitrogen-doped amorphous carbon is bonded in a manner similar to being laid at the interface between the carbon material skeleton and the silicon-based material and solid electrolyte. It can act as a flexible buffer component, playing a role in dispersing stress. It can synergistically exhibit the performance characteristics of combining rigidity and flexibility with the solid electrolyte, further buffering the stress impact of the volume expansion of the silicon-based material. Secondly, nitrogen-doped amorphous carbon not only acts as a flexible conductive link, but also, due to its N-type doping, can provide additional free electrons, thus significantly improving the electronic conductivity in synergy with the carbon material skeleton. Thirdly, because it is rich in lone pair electrons, it can form strong coordination bonds with elements in the silicon-based material and metal ions in the solid electrolyte, playing a bridging and anchoring role. It has a high interfacial bonding strength with the silicon-based material and solid electrolyte, thereby improving the bonding stability between the silicon-based material and the solid electrolyte, and also improving the bonding stability between the silicon-based material, the solid electrolyte and the carbon material skeleton surface. It provides an interfacial bonding force far exceeding that of conventional physical adsorption, greatly reducing the electronic and ionic conduction impedance at the interface. Therefore, it can further enhance the effects of the first to third aspects mentioned above, and greatly improve the kinetic performance of the composite anode material.

[0028] In summary, the carbon framework, nitrogen-doped amorphous carbon, and solid electrolyte in the composite anode material constitute a three-dimensional ion-electron dual-conduction network, exhibiting extremely high ion and electronic conductivity, significantly improving kinetic performance, and possessing extremely high interfacial stability, ensuring the connectivity of the conduction network. The silicon-based material is embedded within this dual-conduction network, providing high lithium storage capacity and suppressing and buffering volume expansion during charge and discharge, further reducing the impact on the dual-conduction network and ensuring its connectivity. Therefore, this composite anode material possesses both high energy density and high kinetic performance.

[0029] Regarding carbon material frameworks: The main functions of the carbon material framework are lithium storage, conductivity, and supporting other components in the composite anode material. It can also synergistically improve electronic conductivity with nitrogen-doped amorphous carbon, and work with the solid electrolyte and nitrogen-doped amorphous carbon to confine and buffer the silicon-based material. In some embodiments, the carbon material framework includes at least one of hard carbon, soft carbon, and graphite, with hard carbon being the preferred choice. These carbon materials possess excellent lithium storage, conductivity, and load-bearing properties, and can further synergize with the aforementioned nitrogen-doped amorphous carbon and solid electrolyte to achieve corresponding performance, significantly improving the kinetic performance of the composite anode material.

[0030] In some embodiments, the Dv50 particle size of the carbon material framework is 0.05 μm to 10 μm, and may include, but is not limited to, any value or any two values ​​among 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 5 μm, and 10 μm. This particle size range balances high specific surface area and packing density, and further facilitates the carrying and synergistic effect of other components in the composite anode material, thereby further improving the kinetic performance of the composite anode material.

[0031] In some embodiments, the carbon material skeleton in the composite anode material has a mass percentage of 40% to 80%, which may include, but is not limited to, any value or any two values ​​between 40%, 50%, 60%, 70%, and 80%. These content ranges are beneficial for constructing a continuous and stable electron conduction network, and provide corresponding lithium storage capacity and space to accommodate other components, so as to better construct a three-dimensional ion-electron dual conduction network and maintain its stability, thereby significantly improving kinetic performance.

[0032] Regarding solid electrolytes: The primary function of solid-state electrolytes is to provide lithium-ion conduction pathways, forming a three-dimensional ion conduction network within the composite anode material. Furthermore, solid-state electrolytes generally have a high modulus, and as rigid support nodes, they can further synergize with the carbon material framework to confine the silicon-based material. In some embodiments, the solid-state electrolyte includes oxide solid-state electrolytes, which, in exemplary cases, may include, but are not limited to, at least one of lithium aluminum titanium phosphate (LATP), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium lanthanum zirconium oxide (LLZO), and lithium lanthanum titanium oxide (LLTO). These oxide solid-state electrolytes possess excellent ionic conductivity and chemical stability, along with high modulus and strength. They form rigid support nodes on the surface of the carbon material framework, maintaining the stability and smooth flow of the ion conduction network while synergizing with the carbon material framework to confine the material, suppressing the volume expansion of the silicon-based material. Furthermore, in conjunction with nitrogen-doped amorphous carbon, they exhibit a balance of rigidity and flexibility, reducing the impact on the dual conduction network and enabling the composite anode material to maintain high kinetic performance.

[0033] In some embodiments, the average particle size of the solid electrolyte is 200 nm to 800 nm, and may include, but is not limited to, any value or any two values ​​between 200 nm, 300 nm, 400 nm, 600 nm, and 800 nm. Solid electrolytes with these particle sizes can be better embedded on the surface of the carbon material framework, forming a large number of ion conduction nodes and improving lithium-ion conductivity; they can also better synergize with the carbon material framework to exert a confinement effect on the silicon-based material, suppressing the volume expansion of the silicon-based material, reducing the impact on the dual conduction network, and enabling the composite anode material to maintain high kinetic performance.

[0034] In some embodiments, the solid electrolyte comprises 2% to 15% by mass in the composite anode material, including but not limited to any value or any two of 2%, 5%, 8%, 10%, 12%, and 15%. These contents of solid electrolyte enable the composite anode material to exhibit high ionic conductivity and significantly suppress the volume expansion of the silicon-based material.

[0035] Regarding nitrogen-doped amorphous carbon: Nitrogen-doped amorphous carbon can play multiple roles in composite anode materials. First, compared to the electrically neutral or weakly P-type conductivity of amorphous carbon, nitrogen doping can modify it into N-type doping. The extra lone pair electrons can provide additional free charge carriers, so nitrogen-doped amorphous carbon itself has extremely high conductivity. It can act as a flexible conductive link, improve the conductive network of the carbon material framework, and significantly improve the electronic conductivity in synergy with the carbon material framework.

[0036] Secondly, nitrogen-doped amorphous carbon, as an N-type doped material, has nitrogen rich in lone pair electrons, which can form strong coordination bonds with elements in silicon-based materials and metal ions in solid electrolytes, playing a bridging and anchoring role. Therefore, it has a high interfacial bonding strength with silicon-based materials and solid electrolytes, thereby improving the bonding stability between silicon-based materials and solid electrolytes. It can also improve the bonding stability between silicon-based materials, solid electrolytes and carbon material framework surfaces, providing interfacial bonding forces far exceeding those of conventional physical adsorption, and greatly reducing the electronic and ionic conduction impedance of the interface.

[0037] Third, at least some nitrogen-doped amorphous carbon is bonded between the carbon material framework and the silicon-based material and solid electrolyte. This bonding method is similar to laying nitrogen-doped amorphous carbon on the surface of the carbon material framework. It can act as a flexible buffer component, play a role in dispersing stress, and work together with the carbon material framework and solid electrolyte to suppress the volume expansion of the silicon-based material. Furthermore, it works together with the solid electrolyte to exhibit the performance characteristics of combining rigidity and flexibility, and further buffer the stress impact of the volume expansion of the silicon-based material.

[0038] In some embodiments, nitrogen-doped amorphous carbon contains at least one of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen. These nitrogen-containing groups enable nitrogen-doped amorphous carbon to further enhance the aforementioned effects of improving the conductivity of nitrogen-doped amorphous carbon and synergistically improving the electronic conductivity of the carbon material framework. It also further enhances the aforementioned effects of forming strong coordination bonds with silicon-based materials and solid electrolytes, playing a bridging and anchoring role, and further enhancing the interfacial bonding stability and reducing interfacial impedance.

[0039] In some embodiments, the mass percentage of nitrogen in the nitrogen-doped amorphous carbon is 1% to 6%, and may include, but is not limited to, any value or a range between any two of 1%, 2%, 4%, and 6%. These mass percentages of nitrogen further contribute to improving the conductivity of the nitrogen-doped amorphous carbon and enhancing its interfacial bridging and anchoring effects.

[0040] In some embodiments, the mass percentage of nitrogen-doped amorphous carbon in the composite anode material is 3% to 10%, and may include, but is not limited to, any value or any two of 3%, 5%, 7%, and 10%. This mass percentage of nitrogen-doped amorphous carbon further facilitates synergistic conductivity with the carbon material framework, further improving the continuity and stability of the conductive network and significantly increasing the electronic conductivity of the composite anode material. Simultaneously, it further enhances the aforementioned bridging and anchoring effects and flexible buffering effects, further improving the electronic and ionic conductivity of the composite anode material.

[0041] The aforementioned carbon material framework, solid electrolyte, and nitrogen-doped amorphous carbon work together to form a three-dimensional ion-electron dual conduction network. This network is stable and can significantly improve the kinetic performance of the composite anode material.

[0042] Regarding silicon-based materials: In some embodiments, the silicon-based material includes at least one of elemental silicon and silicon oxide. These silicon-based materials have high lithium storage capacity and can significantly improve the energy density of composite anode materials. Furthermore, silicon oxide, depending on its degree of oxidation, can also help reduce volume expansion.

[0043] In some embodiments, the average particle size of the silicon-based material is less than 200 nm. In exemplary cases, it may include, but is not limited to, any value or a range between any two of 70 nm, 100 nm, 150 nm, and 180 nm. Silicon-based materials with these particle sizes can be better embedded on the surface of the carbon material framework, achieving high lithium storage capacity while being better confined by the carbon material framework and solid electrolyte, and buffered by nitrogen-doped amorphous carbon.

[0044] In some embodiments, the mass percentage of silicon-based material in the composite anode material is 10% to 40%, and may include, but is not limited to, any value or a range between any two of 10%, 20%, 30%, and 40%. These contents of silicon-based material are beneficial for the composite anode material to have a high energy density, while also reducing the impact on the dual conduction network, resulting in higher electronic and ionic conductivity in the composite anode material.

[0045] Regarding the entire composite anode material: Silicon-based materials and solid-state electrolytes are embedded on the surface of a carbon material framework, with at least a portion of nitrogen-doped amorphous carbon bonded between them and the carbon framework. This "embedding" can be partial, meaning the bottom of the silicon-based material and solid-state electrolyte particles is embedded in the surface of the carbon framework, but some protrudes from it; or it can be complete, meaning the entire particle is embedded within the carbon framework. Since the modulus of silicon-based materials and solid-state electrolytes is generally higher than that of the carbon framework (meaning they are harder), these embedded structures can be formed. Combined with the above description, these components can work synergistically, especially as the carbon framework, solid-state electrolyte, and nitrogen-doped amorphous carbon together form a three-dimensional ion-electron dual-conduction network. This stable network reduces the impact of silicon-based material volume expansion on the conduction network. The silicon-based material then serves as the lithium storage active center, improving the energy density of the composite anode material. Besides the above bonding methods, nitrogen-doped amorphous carbon can also be bonded to the surface of the carbon framework, coated with silicon-based materials, or coated with solid-state electrolytes.

[0046] In some embodiments, at least a portion of the silicon-based material and the solid electrolyte are coated with nitrogen-doped amorphous carbon. This coating can be partial or full. This coating-type bonding allows the nitrogen-doped amorphous carbon to effectively absorb and dissipate the stress generated by the volume expansion of the silicon-based material, further enhancing the buffering effect of the nitrogen-doped amorphous carbon on the volume expansion of the silicon-based material. It also allows for the formation of more coordination bonds between the silicon-based material and the solid electrolyte and the nitrogen-doped amorphous carbon, further strengthening the bonding strength between the nitrogen-doped amorphous carbon and the silicon-based material and the solid electrolyte, improving the bonding stability between the silicon-based material and the solid electrolyte, and also improving the bonding stability between the silicon-based material, the solid electrolyte, and the carbon material framework surface, further reducing interfacial impedance and improving the kinetic performance of the composite anode material.

[0047] In some embodiments, lithium silicate is bonded between the silicon-based material and the solid-state electrolyte. In air, the surface of silicon is easily oxidized to form a very thin silicon oxide layer, and an oxide layer also exists on the surface of the silicon oxide. Residual alkalis, such as lithium hydroxide or lithium carbonate, are often present on the surface of the oxide solid-state electrolyte. These silicon oxides readily react chemically with the residual alkalis to generate lithium silicate. This method of bonding lithium silicate between the silicon-based material and the solid-state electrolyte not only facilitates a tighter bond between the two, further enhancing the confinement effect of the solid-state electrolyte on the silicon-based material; moreover, lithium silicate is also a good lithium-ion conductor, and converting residual alkali into lithium silicate further enriches the lithium-ion conduction network, which is beneficial for improving the kinetic performance of the composite anode material.

[0048] In some embodiments, the carbon material framework includes hard carbon, and the solid electrolyte includes at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium tantalum oxide, and lithium lanthanum zirconium oxide. The total mass percentage of the carbon material framework, solid electrolyte, and nitrogen-doped amorphous carbon in the composite anode material is 60%–90%. The solid electrolyte in this composite anode material includes an oxide solid electrolyte, which has high ionic conductivity and high modulus, and can synergistically exert a rigid confinement effect with the hard carbon framework. The nitrogen-doped amorphous carbon and the solid electrolyte synergistically exert a buffering effect that combines rigidity and flexibility, jointly suppressing and buffering the volume expansion of the silicon-based material. Moreover, the nitrogen-doped amorphous carbon itself also has high electronic conductivity, which can better play a bridging and anchoring role, improve the bonding stability between the silicon-based material and the solid electrolyte, and also improve the bonding stability between the solid electrolyte, the silicon-based material, and the pore walls in the carbon framework. Therefore, the carbon material framework, solid electrolyte, and nitrogen-doped amorphous carbon can form a three-dimensional ion-electron dual conduction network with high stability, and its mass percentage in the composite anode material is beneficial to improving the kinetic performance of the composite anode material.

[0049] The second aspect of this application provides a method for preparing a composite negative electrode material, including the following steps S10 to S30: Step S10: Provide a dispersion and a carbon material framework. The dispersion includes a solvent, and also includes a silicon-based material, a solid electrolyte, and a nitrogen-containing carbon source dispersed in the solvent.

[0050] This step can provide the raw materials for the preparation method of this application. The types of silicon-based materials, solid electrolytes, and carbon material frameworks, as well as their relevant physicochemical parameters, can be found in the descriptions of the composite anode materials in the embodiments of this application above.

[0051] In some embodiments, the silicon-based material may include at least one of elemental silicon and silicon oxide; in some embodiments, the average particle size of the silicon-based material is less than 200 nm. In some embodiments, the solid electrolyte includes at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium oxide, and lithium lanthanum titanium oxide; in some embodiments, the particle size distribution of the solid electrolyte is 200 nm to 800 nm.

[0052] In some embodiments, the carbon material framework includes at least one of hard carbon, soft carbon, and graphite. In some embodiments, the Dv50 particle size of the carbon material framework is 0.05 μm to 10 μm. In some embodiments, the specific surface area of ​​hard carbon is 10 m². 2 / g~500 m 2 / g, with a pore size of 0.3 nm to 5 nm and a porosity of 10% to 40%. In some embodiments, the specific surface area of ​​the soft carbon is 1 m². 2 / g~100 m 2 / g, with a pore size of 1 nm to 10 nm and a porosity of 5% to 30%. In some embodiments, the specific surface area of ​​graphite is 1 m² / g. 2 / g~20 m 2 / g, pore size 0.5 nm~5 nm, porosity 1%~10%.

[0053] In some embodiments, the nitrogen-containing carbon source includes at least one of polyvinylpyrrolidone, polyacrylonitrile, polydopamine, polyaniline, and chitosan. These nitrogen-containing carbon sources are all organic compounds containing nitrogen, which can be converted into nitrogen-doped amorphous carbon during subsequent carbonization processes. This carbon plays a role in providing flexible buffering, conductive bonding, and enhancing binding strength, thereby improving the kinetic performance of the resulting composite anode material.

[0054] In some embodiments, the mass ratio of nitrogen-doped amorphous carbon to carbon material framework generated from silicon-based materials, solid electrolyte, and nitrogen-containing carbon source is (10–40):(2–15):(3–10):(40–80). These mass ratios allow for synergistic effects among the components, resulting in a composite anode material with both high energy density and high kinetic performance. The specific amount of nitrogen-containing carbon source in the raw materials can be determined as follows: the nitrogen-containing carbon source is separately subjected to subsequent carbonization treatment in a protective atmosphere to obtain nitrogen-doped amorphous carbon. The mass ratio of nitrogen-doped amorphous carbon to nitrogen-containing carbon source is calculated, and the measured value is in the tens of percent. When weighing the raw materials, the required mass of nitrogen-doped amorphous carbon is divided by this mass ratio to obtain the required mass of nitrogen-containing carbon source.

[0055] The dispersion preparation method in this step can uniformly disperse silicon-based materials, solid electrolytes, and nitrogen-containing carbon sources in a solvent to form a homogeneous and stable dispersion system. In the example, the solvent may include, but is not limited to, at least one of ethanol, deionized water, N-methylpyrrolidone (NMP), and isopropanol, and the dispersion method may include, but is not limited to, high-energy sand milling.

[0056] Step S10 first provides a dispersion of these three components. Since the nitrogen-containing carbon source contains nitrogen-containing functional groups, such as amide groups, amine groups, five-membered nitrogen-containing rings, and six-membered nitrogen-containing aromatic rings, it can first undergo strong coordination with the surfaces of the silicon-based material and the solid electrolyte, which is beneficial for the nitrogen-containing carbon source to bind to the surfaces of the silicon-based material and the solid electrolyte. In the example, the nitrogen-containing carbon source can coat both surfaces and even form a uniform coating layer, further facilitating the formation of nitrogen-doped amorphous carbon and its synergistic effects with the silicon-based material and the solid electrolyte during subsequent carbonization processes.

[0057] Step S20: Mix the dispersion with the carbon material skeleton to obtain a mixed slurry.

[0058] In this step, because the silicon-based materials and solid electrolytes in the dispersion generally have a higher modulus (i.e., are harder) than the carbon material framework, they will embed onto the surface of the carbon material framework during mixing. Furthermore, since the silicon-based materials, solid electrolytes, and nitrogen-containing carbon source are already dispersed in the dispersion, this method of liquid-phase dispersion followed by mixing with the carbon material framework facilitates uniform bonding of each component with the carbon material framework. This promotes synergistic effects among the components in the composite anode material, improving the material's kinetic performance.

[0059] In the example, the mixing process can be carried out by methods such as sand milling, which can last for 0.5 h to 1.5 h. Sand milling can apply a strong shearing force, which is beneficial for embedding the relatively hard silicon-based material and solid electrolyte on the surface of the relatively soft carbon material framework, and the bonding is strong. In addition, sand milling helps to reduce the particle size of each component, which is more conducive to exerting a synergistic effect.

[0060] After mixing, the nitrogen-containing carbon source will also bind to the surface of each particle, acting like glue. After subsequent carbonization, it will solidify like glue, making the components composite into a whole, thus obtaining a composite anode material.

[0061] Step S30: After evaporating the solvent in the mixed slurry, carbonization treatment is carried out to generate nitrogen-doped amorphous carbon from the nitrogen-containing carbon source, thus obtaining the composite anode material.

[0062] In step S30, the solvent is first evaporated, allowing the components to come into close contact and initially form. The nitrogen-containing carbon source can better bind to the carbon material framework, silicon-based material, and solid electrolyte. Then, the carbonization process is carried out, and the nitrogen-containing carbon source is carbonized in situ into nitrogen-doped amorphous carbon, which binds to the carbon material framework, silicon-based material, and solid electrolyte. This, in turn, works with the carbon material framework and solid electrolyte to build a stable, continuous, and interfacially stable three-dimensional ion-electron dual conduction network. Combined with the high energy density of the silicon-based material, the resulting composite anode material has both high energy density and high kinetic performance.

[0063] After carbonization, in some embodiments, at least a portion of the silicon-based material and the solid electrolyte are coated with nitrogen-doped amorphous carbon, further enhancing their synergistic effect.

[0064] In some embodiments, the solid electrolyte is an oxide solid electrolyte with residual alkali on its surface, and the silicon-based material also has a silicon oxide layer on its surface. At high temperatures, the two will generate components such as lithium silicate, which can not only further improve the bonding strength between the two, but also further improve the ionic conductivity of the composite anode material.

[0065] In the example, step S30 can utilize a rotary evaporator to remove the solvent, followed by further grinding and sieving to obtain the precursor to be carbonized. In some embodiments, the carbonization temperature is 600 ℃ to 800 ℃, and the carbonization process can be carried out in a protective atmosphere, such as under nitrogen protection. The temperature can be increased to 600 ℃ to 800 ℃ at a heating rate of 5 ℃ / min, and then held for 2 h to 4 h to allow the nitrogen-containing carbon source to fully pyrolyze and carbonize into nitrogen-doped amorphous carbon, thereby obtaining the composite anode material.

[0066] A third aspect of this application provides a battery, wherein the negative electrode of the battery contains the composite negative electrode material described in the embodiments of this application, or contains the composite negative electrode material prepared by the preparation method described in the embodiments of this application.

[0067] The battery in this application embodiment contains the composite negative electrode material of this application. This material has high energy density and kinetic performance, and volume expansion is suppressed. Therefore, the battery of this application has both high energy density and high rate performance, and the volume expansion rate of the negative electrode is also low. The battery has high structural stability and good cycle performance.

[0068] In the embodiments, in addition to the composite negative electrode material as the negative electrode active material, the negative electrode may also contain other types of negative electrode active materials, including binders and conductive agents. In the embodiments, the binder can be a commonly used electrode binder, such as polyacrylic acid and its salts, styrene-butadiene rubber, etc. In the embodiments, the conductive agent can be a commonly used conductive agent, such as at least one of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes.

[0069] In the embodiments, the negative electrode preparation process can be as follows: mixing composite negative electrode material, conductive agent and binder to obtain negative electrode slurry, coating the negative electrode slurry on current collector, and preparing negative electrode sheet through drying, rolling and die cutting and other steps.

[0070] The battery in this application embodiment can be a liquid battery, which contains an electrolyte and a separator. The battery in this application embodiment can also be a solid-state battery, which contains a solid electrolyte membrane.

[0071] In some embodiments, the battery includes a solid electrolyte membrane bonded to the surface of the negative electrode, and the preparation method includes the following steps G10 to G20: Step G10: The slurry including the composite negative electrode material is subjected to a first film-forming treatment on at least one side of the current collector to obtain the negative electrode.

[0072] This step is for preparing the negative electrode sheet; for details, please refer to the above description of negative electrode sheet preparation.

[0073] Step G20: Coat the surface of the negative electrode with a slurry containing solid electrolyte membrane raw materials, and perform a second film formation process to obtain a solid electrolyte membrane bonded to the surface of the negative electrode.

[0074] This step employs an in-situ casting integrated molding process. Since the negative electrode film often contains pores, and the slurry containing the solid electrolyte membrane raw material is fluid, coating it on the surface of the negative electrode facilitates the slurry's full penetration into the pores of the negative electrode and into the interior of the negative electrode film. After the second film-forming treatment, the solid electrolyte membrane can form an integrated structure with the negative electrode, creating numerous interlocking structures at the microscopic level, resulting in a seamless structure macroscopically. Furthermore, because the negative electrode contains composite negative electrode materials, the nitrogen-doped amorphous carbon within it is often rich in nitrogen-containing groups such as pyridine nitrogen and pyrrole nitrogen. Due to its N-type doping morphology and these polar groups, it can greatly enhance its interaction with the solid electrolyte in the slurry, forming strong coordination bonds, etc., thus significantly reducing the ionic impedance at the solid-solid interface between the negative electrode and the solid electrolyte membrane. Therefore, compared to the traditional method of separately preparing and assembling the negative electrode and solid electrolyte membrane, this method achieves a macroscopic integration, realizing a leap from "two-dimensional planar contact" to three-dimensional contact. Microscopically, the enhanced bonding between the two significantly reduces the interfacial impedance between the negative electrode and the solid electrolyte membrane, increases ionic conductivity, further improves kinetic performance, enhances the rate performance of the battery, and also improves the battery's cycle performance. This method also saves the steps of separately preparing the solid electrolyte membrane and stacking the membranes, improving the battery assembly efficiency.

[0075] In the example, the slurry containing the solid electrolyte membrane raw material may include solvents, binders, solid electrolytes, etc., and may include polyethylene oxide (PEO), LLZTO nanoparticles and lithium salts (such as lithium bis(trifluoromethanesulfonyl)imide, LiTFSI).

[0076] In the example, step G20 can utilize a specially designed mold. The negative electrode sheet is placed within the groove of a specially designed casting mold, which has adjustable depth limiting borders. Then, a slurry including solid electrolyte membrane raw materials is uniformly poured onto the surface of the negative electrode sheet, using the slurry's fluidity to fill the negative electrode pores. Next, it is dried (or polymerized in situ) under a vacuum or inert atmosphere. After the solvent evaporates, the solid electrolyte membrane and the negative electrode form a seamless, integrated structure. Finally, it is directly assembled; the integrated electrode sheet obtained after demolding does not require a separator and can be directly assembled with the positive electrode to obtain a solid-state battery.

[0077] The following description is based on specific embodiments.

[0078] Example 1 This embodiment provides a composite anode material, its preparation method, and a battery. Please refer to [reference needed]. Figure 1 The preparation method includes the following steps S1 to S5: S1: Provide raw materials.

[0079] The silicon-based material is nano-silicon, with a Dv50 particle size of approximately 50 nm. The solid electrolyte is LLZTO, with the chemical formula Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 The Dv50 particle size is approximately 300 nm. The nitrogen-containing carbon source is polyvinylpyrrolidone (PVP, nitrogen content 12.6%). The carbon material framework is hard carbon, with a Dv50 particle size of approximately 5 μm, a pore size distribution of 0.5 nm to 2 nm, a porosity of 18%, and a specific surface area of ​​94 m². 2 / g, with a graphitization degree of 18%. The mass ratio of nitrogen-doped amorphous carbon and carbon material framework that can be generated from the above silicon-based material, solid electrolyte, and nitrogen-containing carbon source is 20:5:5:70.

[0080] S2: Prepare the dispersion.

[0081] 20 g of silicon nanoparticles, 5 g of LLZTO nanoparticles, and 5 g of PVP were completely dissolved / dispersed in 200 mL of anhydrous ethanol and dispersed using a high-energy sand mill for 2 hours to obtain a dispersion. In this step, the amide groups of PVP interact strongly with the surfaces of the two nanoparticles, achieving uniform encapsulation.

[0082] S3: Crosslinked with the backbone.

[0083] Add 70 g of hard carbon to the dispersion and continue stirring and mixing with a high-energy sand mill for 1 hour to obtain a mixed slurry. The high shear force of the high-energy sand mill is beneficial for the embedding of silicon-based materials and solid electrolyte particles on the surface of the carbon material skeleton, which is the so-called cold welding effect; at the same time, the nitrogen-containing carbon source is bonded to the surface of each component like glue before carbonization, and after subsequent carbonization, it will solidify like glue, so that the components are combined into a whole, resulting in a composite anode material.

[0084] S4: Drying and carbonization.

[0085] The solvent in the mixed slurry was removed using a rotary evaporator, and the precursor was obtained by grinding and sieving. Under nitrogen protection, the temperature was increased to 800 °C at a heating rate of 5 °C / min, and carbonized at this temperature for 3 hours to convert the nitrogen-containing carbon source into nitrogen-doped amorphous carbon, thus obtaining the composite anode material.

[0086] S5: Battery fabrication.

[0087] The composite negative electrode material, conductive agent and binder are mixed in a ratio of 90:5:5 to form a negative electrode slurry, which is then coated on copper foil, dried, rolled and sliced ​​to form a negative electrode sheet.

[0088] The negative electrode sheet, lithium sheet, separator, and electrolyte are assembled into a CR2032 coin cell lithium-ion battery. The separator is a polypropylene separator, and the electrolyte contains 1 mol / L lithium hexafluorophosphate (LiPF6), as well as ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1.

[0089] Example 2 This embodiment provides a composite negative electrode material and its preparation method, as well as a battery. The only difference from Embodiment 1 is that the type of nitrogen-containing carbon source is changed from PVP to polyacrylonitrile (PAN), with a nitrogen content of 26.4%. All other steps are the same.

[0090] Example 3 This embodiment provides a composite anode material, its preparation method, and a battery. The only difference from Embodiment 1 is that the nitrogen-containing carbon source material is changed from PVP to polydopamine (PDA), with a nitrogen content of 9%. All other steps are the same.

[0091] Example 4 This embodiment provides a composite negative electrode material and its preparation method, as well as a battery. The only difference from Embodiment 1 is that the type of nitrogen-containing carbon source is changed from PVP to polyaniline, with a nitrogen content of 15.4%. All other steps are the same.

[0092] Example 5 This embodiment provides a composite anode material and its preparation method, as well as a battery. The only difference from Embodiment 1 is that the mass ratio of silicon-based material, solid electrolyte, nitrogen-doped amorphous carbon generated from nitrogen-containing carbon source, and carbon material framework is changed from 20:5:5:70 to 20:5:10:65, increasing the proportion of nitrogen-containing carbon source and decreasing the proportion of carbon material framework. All other steps are the same.

[0093] Example 6 This embodiment provides a composite anode material and its preparation method, as well as a battery. The only difference from Embodiment 1 is that the mass ratio of silicon-based material, solid electrolyte, nitrogen-doped amorphous carbon generated from nitrogen-containing carbon source, and carbon material framework is changed from 20:5:5:70 to 20:5:20:55, increasing the proportion of nitrogen-containing carbon source and decreasing the proportion of carbon material framework. All other steps are the same.

[0094] Example 7 This embodiment provides a composite negative electrode material and its preparation method, as well as a battery. The only difference from Embodiment 1 is that the type of solid electrolyte is changed from LLZTO to lithium aluminum titanium phosphate (LATP). All other steps are the same.

[0095] Example 8 This embodiment provides a composite anode material and its preparation method, as well as a battery. The only difference from Embodiment 1 is that the mass ratio of silicon-based material, solid electrolyte, nitrogen-doped amorphous carbon generated from a nitrogen-containing carbon source, and carbon material framework is changed from 20:5:5:70 to 20:10:5:65, increasing the proportion of solid electrolyte and decreasing the proportion of carbon material framework. All other steps are the same.

[0096] Example 9 This embodiment provides a composite anode material, its preparation method, and a battery. The only difference from Embodiment 1 is that the carbon material framework is changed from hard carbon to soft carbon, the Dv50 particle size remains unchanged at approximately 5 μm, and other parameters, such as pore size distribution of 1 nm to 8 nm, porosity of 22%, and specific surface area of ​​46 m², are also different. 2 / g, with a graphitization degree of 57%. All other steps are the same.

[0097] Example 10 This embodiment provides a composite anode material, its preparation method, and a battery. The only difference from Embodiment 1 is that the carbon material framework is changed from hard carbon to graphite, the Dv50 particle size remains unchanged at approximately 5 μm, and other parameters, such as pore size distribution of 0.5 nm to 3 nm, porosity of 3%, and specific surface area of ​​10 m², are also different. 2 / g. All other steps are the same.

[0098] Example 11 This embodiment provides a composite anode material and its preparation method, as well as a battery. The only difference from Embodiment 1 is that the mass ratio of silicon-based material, solid electrolyte, nitrogen-doped amorphous carbon generated from a nitrogen-containing carbon source, and carbon material framework is changed from 20:5:5:70 to 40:5:5:50, increasing the proportion of silicon-based material and decreasing the proportion of carbon material framework. All other steps are the same.

[0099] Example 12 This embodiment provides a composite negative electrode material, its preparation method, and a battery. The only difference from Embodiment 1 is that step S5, after the negative electrode sheet is made, is changed to the preparation of a solid-state battery. Specifically, the negative electrode sheet is first laid flat on a substrate of a specially made polytetrafluoroethylene (PTFE) casting mold. Then, in-situ casting is performed: the three components, namely 65 wt% PEO, 25 wt% LiTFSI, and 10 wt% LLZTO nanoparticles, are dissolved in acetonitrile to prepare a polymer electrolyte slurry, which is then uniformly cast onto the surface of the negative electrode sheet, utilizing the fluidity of the liquid phase to allow it to fully penetrate the pores of the negative electrode. Finally, integrated molding is performed: the material is dried in a vacuum drying oven at 50 ℃ for 24 hours. After the solvent has completely evaporated, the material is demolded to form an integrated structure of the solid electrolyte membrane and the negative electrode sheet. Finally, it is assembled with the positive electrode sheet to form a solid-state battery. All other steps are the same.

[0100] Example 13 This embodiment provides a composite negative electrode material and its preparation method, and a battery. The only difference from Embodiment 12 is that the solid electrolyte membrane is not cast in situ on the negative electrode sheet to form an integrated structure. Instead, the solid electrolyte membrane raw material in Embodiment 12 is formed into a film separately, and finally stacked with the negative electrode sheet and the positive electrode sheet (same as Embodiment 12) to form a solid battery.

[0101] Comparative Example 1 This comparative example provides a negative electrode material and its preparation method, as well as a battery. The only difference from Example 1 is that: there is no solid electrolyte in the raw materials, and the mass ratio of silicon-based material, solid electrolyte, nitrogen-doped amorphous carbon generated from nitrogen-containing carbon source, and carbon material framework is changed from 20:5:5:70 to 20:0:5:75. All other steps are the same.

[0102] Comparative Example 2 This comparative example provides a negative electrode material, its preparation method, and a battery. The only difference from Example 1 is that the raw materials do not contain a nitrogen-containing carbon source, but are replaced with a nitrogen-free phenolic resin. All other steps are the same.

[0103] Comparative Example 3 This comparative example provides a negative electrode material, its preparation method, and a battery. The only difference from Example 1 is that the raw materials do not contain a nitrogen-containing carbon source, but are replaced with nitrogen-free glucose. All other steps are the same.

[0104] Comparative Example 4 This comparative example provides a negative electrode material, its preparation method, and a battery. The only difference from Example 1 is that the raw materials do not contain a nitrogen-containing carbon source, but are replaced with nitrogen-free starch. All other steps are the same.

[0105] Comparative Example 5 This comparative example provides a negative electrode material and its preparation method, as well as a battery. The only difference from Example 1 is that the raw materials do not contain a nitrogen-containing carbon source, and the mass ratio of silicon-based material, solid electrolyte, nitrogen-containing carbon source to nitrogen-doped amorphous carbon and carbon material framework is changed from 20:5:5:70 to 20:5:0:75. All other steps are the same.

[0106] The differences between the cases are shown in Table 1. The mass ratio of the four components in Table 1 refers to the mass ratio of silicon-based materials, solid electrolytes, nitrogen-doped amorphous carbon that can be generated from carbon sources, and carbon material framework.

[0107]

[0108] Relevant performance tests and results analysis I. Testing of Composite Anode Materials and Their Raw Materials 1. X-ray diffraction analysis X-ray diffraction analysis was performed on the carbon material frameworks of Examples 1, 9, and 10. The test results for the hard carbon in Example 1 are as follows: Figure 2 As shown. The differences in the XRD patterns of hard carbon, soft carbon, and graphite are mainly reflected in the peak shape and intensity of the (002) diffraction peak. Hard carbon exhibits a broad and weak (002) peak at 22°–25°, indicating a disordered structure; soft carbon shows a more obvious (002) peak near 24°–26°; graphite has a sharp and strong (002) peak at 26.4°, indicating that it has the highest degree of graphitization and crystallinity.

[0109] 2. SEM Testing The composite anode materials prepared in each case were analyzed by scanning electron microscopy. The SEM image of Example 1 at 15kx magnification is shown below. Figure 3 As shown, the SEM image magnified 5 k times is as follows: Figure 4 As shown. From Figure 3 , Figure 4As can be seen, this composite anode material exhibits a multi-level structure ranging from micrometers to nanometers. Larger micrometer-sized hard carbon particles serve as the physical support framework, with numerous nano-silicon particles and LLZTO solid electrolyte particles tightly adhered to their surfaces and pores. The nitrogen-containing carbon source (PVP) in the precursor is transformed in situ into a nitrogen-doped amorphous carbon (NC) layer after high-temperature carbonization. This nitrogen-doped carbon layer not only coats the surface of the aforementioned nanoparticles but also acts as a flexible conductive link, playing a bridging and anchoring role, forming a conductive bonding network that firmly cross-links the nano-silicon, LLZTO, and hard carbon framework. This structural design effectively suppresses severe agglomeration and volume expansion of the nano-silicon particles, reducing their shedding; simultaneously, the nitrogen-doped carbon network, hard carbon framework, and LLZTO together construct a highly efficient electron-ion dual conduction network in the material, exhibiting high stability. Therefore, the composite anode material possesses both high energy density and kinetic performance. The anode sheet also exhibits high structural stability, cycle performance, and rate performance.

[0110] 3. Electronic conductivity test The negative electrode powder prepared for each case was tested using a powder resistivity tester via a four-probe method. A fixed amount of powder was loaded into an insulating test mold, and a constant pressure of 10 MPa was applied. The volume resistance of the powder was measured under the pressure holding condition, and the electronic conductivity was calculated by combining the compaction thickness of the powder at this time. The results are recorded in Table 2.

[0111] II. Electrode / Button Cell Performance Testing 1. Ion conduction performance test The Rct values ​​of the negative electrode sheets prepared for each case were tested using EIS. Specifically, an electrochemical workstation was used. The negative electrode sheet was assembled into a coin cell with a lithium metal counter electrode, a separator, and a liquid electrolyte. After the open-circuit voltage stabilized, an AC voltage amplitude of 5 mV was set, and the frequency scan range was 100 kHz to 0.01 Hz for AC impedance testing. The Rct value was obtained by fitting an equivalent circuit. The charge transfer impedance indicates the rate of ion conduction; a higher charge transfer impedance indicates poorer interfacial ion conduction and lower ion conductivity. The results are recorded in Table 2.

[0112] 2. Expansion rate of negative electrode sheet The thickness H1 of the negative electrode active film layer (excluding the current collector) in the battery prepared in each case was tested. Under the same charge and discharge conditions, 100 charge and discharge cycles were performed to test the thickness H2 of the negative electrode active film layer. The electrode expansion rate was obtained by calculating (H2 - H1) ÷ H1 × 100%.

[0113] 3. Electrode Young's Modulus Test The Young's modulus of the negative electrode sheets in the batteries prepared in each case was characterized using atomic force microscopy (AFM) nanoindentation testing. The test results for Example 1 are as follows: Figure 6 As shown, the test results for Comparative Example 1 are as follows: Figure 5 As shown. Figure 5 As can be seen, in Comparative Example 1, without the addition of LLZTO, the Young's modulus of the electrode was lower. Figure 6 As can be seen, the Young's modulus of the electrode containing LLZTO in Example 1 is increased, indicating that the addition of LLZTO can enhance the mechanical stability of the electrode, mainly by suppressing the volume expansion of silicon-based materials. This is because LLZTO, as an inorganic ceramic-based solid electrolyte, possesses mechanical strength and stiffness far exceeding that of silicon and hard carbon. During lithium insertion / extraction cycles, silicon undergoes a dramatic volume expansion exceeding 300%, while LLZTO exhibits excellent volume stability with almost zero strain during this process. Therefore, introducing such high-hardness, zero-strain particles into the composite anode material system can effectively suppress the volume expansion of silicon-based materials through its rigid framework, effectively buffering and suppressing the overall volume expansion of the silicon-based electrode, thereby improving the structural stability of the anode electrode and the entire battery.

[0114] 4. Initial capacity and cycle performance testing at 0.5C The unactivated batteries obtained from each case study were tested using a battery testing system with a test voltage range of 0.01 V to 1.5 V. Before the formal cycle test, the batteries were activated for two cycles with a small current of 0.05C to form a stable and uniform SEI film. Subsequently, constant current charge-discharge cycle tests were performed at a rate of 0.5C, and the battery's discharge specific capacity and cycle performance were recorded.

[0115] The initial capacity at 0.5x was obtained in the first two laps, and the results are recorded in Table 2. The cycling performance was then obtained, with a comparison graph showing the cycling performance of Example 1 and Comparative Example 2 as shown below. Figure 7 As shown. Figure 7 As can be seen, the cycling performance of Comparative Example 2 is significantly worse than that of Example 1.

[0116] 5. Ratio Performance Test Rate performance testing was used to evaluate the battery's charge and discharge capabilities at different current densities. The battery's performance under rapid charge and discharge conditions was tested by gradually increasing the current density. Specific test conditions included current densities of 0.1C, 0.2C, 0.5C, 1C, 3C, and 5C, with five charge-discharge cycles performed at each rate. By analyzing the specific capacity changes at different rates, rate performance and structural stability could be evaluated. The results are recorded in Table 2. Furthermore, Examples 12 and 13 were both solid-state batteries. Solid-state batteries generally have lower rate performance than electrolyte batteries; therefore, the batteries in these two cases were discharged at a 2C rate.

[0117]

[0118] III. Case Comparison Explanation Examples 1 to 4 all use silicon-based materials, solid electrolytes, nitrogen-containing carbon sources, and carbon material skeletons to prepare composite anode materials. Although the nitrogen-containing carbon source was adjusted, the final electronic conductivity and ionic conductivity were ideal, and the battery capacity and rate performance were similar and good, with low electrode volume expansion rate.

[0119] Examples 5 and 6 further increased the amount of nitrogen-containing carbon source, reducing the amount of carbon material framework. However, the electronic conductivity increased significantly, indicating that nitrogen-doped amorphous carbon has high conductivity and can act as a flexible conductive link. Working synergistically with the carbon material framework, it can significantly improve the conductivity of the three-dimensional conductive network. However, due to the reduced carbon material framework, the battery capacity decreases. Furthermore, in Example 6, due to the excessive addition of nitrogen-containing carbon source, although the electronic conductivity was high, foaming occurred during carbonization. This reduced the inhibitory and buffering effect of the composite anode material on the volume expansion of the silicon-based material, and also affected the interfacial bonding strength, leading to a decrease in other properties. When used in the electrode, the volume expansion was slightly higher after 100 cycles.

[0120] Example 7 changed the solid electrolyte from LLZTO to LATP, which reduced costs, but LATP contains Ti. 4+ In the low-potential environment of the negative electrode, slight reduction and other side reactions are prone to occur, leading to an increase in interfacial impedance. Furthermore, the mechanical strength and shear modulus of the garnet-structured LLZTO in Example 1 are significantly higher than those of LATP. Therefore, LLZTO can form a more rigid physical framework within the composite negative electrode material, providing better rigid confinement of silicon expansion than LATP, and maintaining a more intact structure. Therefore, the performance of Example 7 is lower than that of Example 1.

[0121] Example 8 increased the amount of solid electrolyte, which reduced the amount of carbon material skeleton, resulting in a slight decrease in electronic conductivity and affecting performance such as rate capability; however, the ionic conductivity was improved, and the inhibition effect on the volume expansion of silicon-based materials was also slightly enhanced.

[0122] In Example 9, the carbon material framework was changed to soft carbon. Soft carbon has a slightly higher electronic conductivity than hard carbon, consistent with the electrode test results. However, the active lithium storage performance of soft carbon is not as good as that of hard carbon, so its specific capacity is lower than that of Example 1. Moreover, the synergistic suppression effect of soft carbon, solid electrolyte, and nitrogen-doped amorphous carbon on the volume expansion of silicon-based materials is also poor, significantly less effective than the combined rigid-flexible effect of hard carbon, solid electrolyte, and nitrogen-doped amorphous carbon. Therefore, the electrode volume expansion is higher than that of Example 1.

[0123] In Example 10, the carbon material framework was replaced with graphite. Graphite has a higher electronic conductivity than hard carbon, consistent with the electrode test results. However, graphite's active lithium storage performance is inferior to that of hard carbon, resulting in a lower specific capacity than in Example 1. Furthermore, the synergistic suppression effect of graphite, solid electrolyte, and nitrogen-doped amorphous carbon on the volume expansion of silicon-based materials is poor, significantly less effective than the combined rigid-flexible effect of hard carbon, solid electrolyte, and nitrogen-doped amorphous carbon. In addition, graphite itself exhibits a higher volume expansion rate during charge and discharge than hard carbon. Overall, the electrode volume expansion is higher than in Example 1.

[0124] In Example 11, the silicon-based material content was greatly increased, resulting in a significant improvement in energy density. However, the excessive silicon-based material also reduced the amount of hard carbon used, leading to a significant decrease in electronic conductivity, difficulty in suppressing volume expansion, and potential damage to the ion conduction network, thus affecting ion conductivity.

[0125] Examples 12 and 13 are both solid-state batteries. Regarding electronic conductivity, since the raw materials of the solid electrolyte membrane in Example 12 have already permeated into the negative electrode and solidified, and the four-probe method would then contact the insulating polymer, and given that solid-state batteries are primarily compared based on the solid-solid interface impedance between the solid electrolyte membrane and the electrode, electronic conductivity was not tested in these two cases. In Example 12, the negative electrode and solid electrolyte membrane form an integrated structure. Compared to the separate film formation and stacking method in Example 13, the interface impedance between the negative electrode and the solid electrolyte membrane in Example 12 is significantly lower, by several times. In solid-state batteries, 2C is already a relatively high rate capability, and Example 12 still maintains high rate performance, while Example 13, due to its excessively high interface impedance, exhibits poor rate performance and a very low discharge capacity at 0.5C.

[0126] In Comparative Example 1, there was no solid electrolyte, and the hard carbon content was slightly increased, resulting in a slight increase in the electronic conductivity of the electrode. However, the ionic conductivity was significantly lower than that of Example 1. Furthermore, due to the lack of synergistic confinement between the solid electrolyte and hard carbon, only nitrogen-doped amorphous carbon and hard carbon were present, making it difficult to suppress the volume expansion of the silicon-based material, leading to significant electrode thickness expansion after cycling. A slightly increased hard carbon content could also increase capacity, but the rate performance was not as good as that of Example 1.

[0127] In Comparative Examples 2 to 4, the nitrogen-containing carbon sources were all replaced with nitrogen-free carbon sources. Therefore, the resulting materials were all amorphous carbon without nitrogen elements. Their electronic conductivity was significantly lower than that of Example 1. Furthermore, due to the lack of the flexible buffering, bridging, and anchoring effects of nitrogen-doped amorphous carbon, the stress impact from the volume expansion of the silicon-based material was difficult to buffer, leading to poor stability of both the ion and electron conduction networks, and ultimately lower overall performance. Figure 7It can be seen that the cycling performance of Comparative Example 2 is also significantly worse than that of Example 1, further demonstrating the synergistic effect of nitrogen-doped amorphous carbon generated from nitrogen-containing carbon sources on the original system.

[0128] In Comparative Example 5, no carbon source was added. The compatibility between the silicon-based material, the solid electrolyte, and the carbon material framework was poor, the interfacial impedance was extremely high, and the bonding was not strong. It was even more difficult for them to work together to suppress the volume expansion of the silicon-based material. Therefore, the performance was the worst among all the cases.

[0129] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite negative electrode material, characterized in that: This includes carbon material frameworks, silicon-based materials, solid electrolytes, and nitrogen-doped amorphous carbon; The silicon-based material and the solid electrolyte are embedded on the surface of the carbon material skeleton, and at least a portion of the nitrogen-doped amorphous carbon is bonded between the carbon material skeleton and the silicon-based material and the solid electrolyte.

2. The composite negative electrode material according to claim 1, characterized in that, The nitrogen-doped amorphous carbon satisfies at least one of the following (1) to (3): (1) The nitrogen-doped amorphous carbon contains at least one of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen; (2) The mass percentage of nitrogen in the nitrogen-doped amorphous carbon is 1% to 6%; (3) The mass percentage of nitrogen-doped amorphous carbon in the composite negative electrode material is 3% to 10%.

3. The composite negative electrode material according to claim 1 or 2, characterized in that, The solid electrolyte satisfies at least one of the following (1) to (4): (1) The solid electrolyte includes at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium oxide, and lithium lanthanum titanium oxide; (2) The average particle size of the solid electrolyte is 200 nm to 800 nm; (3) The solid electrolyte in the composite negative electrode material has a mass percentage content of 2% to 15%; (4) The solid electrolyte is dispersed in the carbon material skeleton.

4. The composite negative electrode material according to claim 1 or 2, characterized in that, The silicon-based material satisfies at least one of the following (1) to (4): (1) The silicon-based material includes at least one of elemental silicon and silicon oxide; (2) The average particle size of the silicon-based material is less than 200 nm; (3) The silicon-based material has a mass percentage content of 10% to 40% in the composite anode material; (4) The silicon-based material is dispersed in the carbon material skeleton.

5. The composite negative electrode material according to claim 1 or 2, characterized in that, The carbon material framework satisfies at least one of the following (1) to (3): (1) The carbon material framework includes at least one of hard carbon, soft carbon, and graphite; (2) The Dv50 particle size of the carbon material skeleton is 0.05 μm to 10 μm; (3) The carbon material skeleton in the composite negative electrode material has a mass percentage of 40% to 80%.

6. The composite negative electrode material according to claim 1 or 2, characterized in that: At least a portion of the silicon-based material and the solid electrolyte are coated with the nitrogen-doped amorphous carbon; and / or, Lithium silicate is bonded between the silicon-based material and the solid electrolyte; and / or, The carbon material framework includes hard carbon, and the solid electrolyte includes at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium tantalum oxide, and lithium lanthanum zirconium oxide. The total mass of the carbon material framework, the solid electrolyte, and the nitrogen-doped amorphous carbon in the composite anode material is 60% to 90%.

7. A method for preparing a composite negative electrode material, characterized in that, Includes the following steps: A dispersion and a carbon material framework are provided, wherein the dispersion includes a solvent and further includes a silicon-based material, a solid electrolyte, and a nitrogen-containing carbon source dispersed in the solvent; The dispersion was mixed with a carbon material framework to obtain a mixed slurry; The solvent in the mixed slurry is evaporated and then carbonized to generate nitrogen-doped amorphous carbon from the nitrogen-containing carbon source, thus obtaining a composite anode material.

8. The preparation method according to claim 7, characterized in that: The nitrogen-containing carbon source includes at least one of polyvinylpyrrolidone, polyacrylonitrile, polydopamine, polyaniline, and chitosan; and / or, The mass ratio of the nitrogen-doped amorphous carbon and the carbon material framework generated from the silicon-based material, the solid electrolyte, and the nitrogen-containing carbon source is (10–40):(2–15):(3–10):(40–80); and / or, The mixing process includes a sanding process; and / or, The carbonization process is carried out at a temperature of 600 ℃ to 800 ℃.

9. A battery, characterized in that, The negative electrode of the battery contains a composite negative electrode material as described in any one of claims 1 to 6, or a composite negative electrode material prepared by the preparation method described in claim 7 or 8.

10. The battery according to claim 9, characterized in that, The preparation method includes the following steps: A solid electrolyte membrane bonded to the surface of the negative electrode. A slurry comprising the composite negative electrode material is subjected to a first film-forming treatment on at least one side of the current collector to obtain a negative electrode; A slurry containing solid electrolyte membrane raw materials is coated onto the surface of the negative electrode, and a second film-forming treatment is performed to obtain a solid electrolyte membrane bonded to the surface of the negative electrode.

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