Carbon-coated bismuth nano composite negative electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion battery negative electrodes, and discloses a carbon-coated bismuth nano composite negative electrode material and a preparation method thereof, the carbon-coated bismuth nano composite negative electrode material comprises a porous carbon skeleton, a bismuth nano core and an ultrathin carbon shell; the particle size of the bismuth nano core is 5-50nm, and the bismuth nano core is uniformly dispersed in holes of the porous carbon skeleton; the thickness of the ultrathin carbon shell is 5-50nm, and the ultrathin carbon shell is combined with the surface of the bismuth nano core through a Bi-O-C covalent bond; the pore diameter of the porous carbon skeleton is 10-200nm, and the porous carbon skeleton is prepared from the following raw materials in parts by weight: 90-110 parts of phenolic resin, 15-20 parts of an active agent, 8-10 parts of a template agent and 5-7 parts of modified nano titanium dioxide; and the modified nano titanium dioxide is a hollow carbon-coated titanium dioxide nanosphere composite material, so that electron conduction is promoted, the rate capability is improved, the structural stability and interface integrity of the material in a complex electrochemical environment are ensured, and the cycling stability and reliability of the battery are further improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode technology, specifically relating to a carbon-coated bismuth nanocomposite anode material and its preparation method. Background Technology

[0002] As a core component of new energy storage and power batteries, the improvement of lithium-ion batteries in terms of energy density, fast charging performance, and cycle life highly depends on the innovation of anode materials. Currently, mainstream anode materials have significant performance bottlenecks: traditional graphite anodes have a volumetric capacity of only 840 mAh·cm⁻³, and are prone to lithium dendrite precipitation during high-rate fast charging, causing safety hazards; although silicon-based anodes have excellent theoretical capacity, their lithium intercalation volume expansion rate exceeds 300%, and the electrode structure is prone to pulverization and collapse during cycling, making it difficult to meet the requirements for long life.

[0003] The practical application of bismuth-based anodes faces two major technical challenges: First, bismuth undergoes a volume expansion rate of 260-300% during lithium intercalation. This drastic volume change can lead to particle breakage in the electrode material, resulting in a severe capacity decay exceeding 20% ​​after 10 cycles. Existing modification techniques, such as simple mechanical composites with carbon materials, suffer from insufficient rigidity in the carbon framework, making it difficult to resist the stress generated by repeated expansion and contraction, often leading to carbon layer cracking and pore collapse. Second, bismuth-based materials have low intrinsic conductivity and poor electron transport dynamics, resulting in significant capacity loss during high-rate charge and discharge. Existing conductive modification methods, such as traditional carbon coating processes, suffer from uneven carbon layer thickness and weak interfacial bonding with bismuth particles, failing to construct a continuous and efficient electron transport network and reducing cycle stability.

[0004] Furthermore, in the preparation of porous carbon frameworks for existing bismuth-based anodes, the porosity and pore size distribution of the carbon framework are difficult to match the expansion requirements of bismuth nanoparticles. Simultaneously, during cycling, interfacial separation easily occurs due to stress, leading to the disruption of electron and ion transport pathways. These problems collectively restrict the industrial application of bismuth-based anodes in high-energy-density, long-life lithium-ion batteries. Therefore, developing a modification technology that can simultaneously address volume expansion buffering, electron conduction enhancement, and interfacial bonding strengthening has become a key breakthrough direction for the practical application of bismuth-based anodes. Summary of the Invention

[0005] To address the shortcomings mentioned in the background art, the present invention aims to provide a carbon-coated bismuth nanocomposite anode material and its preparation method. By adding modified nano-titanium dioxide, the deformation and structural collapse of the carbon skeleton caused by the volume expansion of bismuth are effectively suppressed, maintaining the integrity of the overall material structure, promoting electron conduction, improving rate performance, significantly enhancing the interfacial bonding force between the components, ensuring the structural stability and interfacial integrity of the material under complex electrochemical environments, and further improving the cycle stability and reliability of the battery.

[0006] The objective of this invention can be achieved through the following technical solutions: A carbon-coated bismuth nanocomposite anode material is composed of a porous carbon framework, bismuth nanocores, and an ultrathin carbon shell. The bismuth nanocores have a particle size of 5-50 nm and are uniformly dispersed within the pores of the porous carbon framework. The ultrathin carbon shell has a thickness of 5-50 nm and is bonded to the surface of the bismuth nanocores via Bi-OC covalent bonds. The porous carbon framework has a pore size of 10-200 nm and comprises the following raw materials in parts by weight: 90-110 parts of phenolic resin, 15-20 parts of activator, 8-10 parts of template agent, and 5-7 parts of modified nano-titanium dioxide. The modified nano-titanium dioxide is hollow carbon-supported titanium dioxide nanospheres.

[0007] More preferably, the surfactant is CTAB.

[0008] More preferably, the template agent is silicon dioxide.

[0009] More preferably, the method for preparing the modified nano-titanium dioxide includes the following steps: A1. Mix ammonia, anhydrous ethanol and deionized water evenly, add tetraethyl orthosilicate, stir for 20-30 min, add resorcinol, sonicate for 10-15 min, magnetically stir for 15-20 min, then add formaldehyde and stir at 40-50℃ for 6-8 h, cool to 20-30℃ and stir for 12-15 h, wash with anhydrous ethanol and deionized water, and dry to obtain silica-coated resorcinol-formaldehyde resin powder; A2. The silica-coated resorcinol-formaldehyde resin powder is heated to 300-400℃ at 3-5℃ / min, and then heated to 700-800℃ at 5-8℃ / min. It is then soaked in 5-6wt% ammonium bifluoride solution for 2-4 hours, followed by sonication at 200-300W for 6-8 minutes. After centrifugation, it is washed with deionized water until pH=7, and dried at 60-70℃ for 6-8 hours to obtain hollow mesoporous carbon spheres. A3. Hollow mesoporous carbon spheres were ultrasonically dispersed in isopropanol, and then diethylenetriamine was added to the dispersion. The mixture was stirred for 20-30 min, titanium isopropoxide was added, and the mixture was stirred for 20-30 min. The mixture was then transferred to a polytetrafluoroethylene reactor and reacted at a constant temperature of 200-300℃ for 24-48 h. After centrifugation, anhydrous ethanol was added, and the mixture was calcined at 600-700℃ for 2-3 h in a mixed atmosphere of argon and hydrogen to obtain hollow carbon-supported titanium dioxide nanospheres.

[0010] More preferably, in A1, ammonia, anhydrous ethanol, and deionized water are mixed in a volume ratio of 3:4:4, and tetraethyl orthosilicate, resorcinol, and formaldehyde are mixed in a mass ratio of 10:3:4.

[0011] More preferably, the preparation method of the carbon-coated bismuth nanocomposite anode material includes the following steps: S1. Mix ammonia, anhydrous ethanol and deionized water, stir magnetically for 5-10 min, add resorcinol, stir magnetically at 60-70℃ for 20-30 min, add formaldehyde solution dropwise, stir at 50-60℃ for 10-15 min, wash the precipitate with deionized water 3-5 times to obtain resorcinol-formaldehyde nanosphere dispersion. Add hollow carbon-supported titanium dioxide nanospheres to deionized water, sonicate for 30-40 min, then pour into the resorcinol-formaldehyde nanosphere dispersion, sonicate for 20-30 min, and stir magnetically for 30-40 min to obtain hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion. S2. Add deionized water, anhydrous ethanol, CTAB and ammonia to a beaker, stir magnetically for 10-15 min, pour in the hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion from step S1, stir at 30-40℃ for 1-2 h, add TEOS dropwise, stir at 30-40℃ for 2-3 h, wash alternately with deionized water and anhydrous ethanol 3-5 times, and vacuum dry to obtain carbon-silicon double-coated titanium dioxide composite microspheres. S3. Place the dried composite microspheres into a porcelain crucible, purge with nitrogen for 30-40 min, raise the temperature to 300-400℃ at 1℃ / min, hold for 2-3 h, continue to raise the temperature to 900-1000℃ at 1℃ / min, hold for 1-2 h, and cool naturally to room temperature to obtain titanium carbide-silicon carbide-coated composite microspheres. Add hydrofluoric acid, stir for 24-28 h, wash with deionized water and anhydrous ethanol 5-7 times, and vacuum dry to obtain a porous carbon framework. S4. Take blocky bismuth metal, crush it with a crusher, and control the particle size D by screening. 50 The bismuth particles are 0.1~1000μm in size. They are placed in a tube furnace and calcined at 700~800℃ for 2~3h under an Ar atmosphere. The calcined bismuth particles and the porous carbon skeleton from step S3 are added to a mortar and ground for 10~15min according to the bismuth mass ratio of 20%~70%. They are then vacuum dried for 12~15h. S5. Place the dried mixture into the rotary kiln crucible and introduce a reducing gas mixture of CO and methane. The temperature is increased to 1500-1700℃ at a rate of 5-8℃ / min, and the pressure inside the furnace is 0.01-0.02MPa. After the process is completed, a reducing gas is continuously introduced, and the furnace temperature is reduced to 700-800℃. The material is then ultrasonically cleaned 2-4 times with anhydrous ethanol and vacuum dried at 80-90℃ for 6-8 hours to obtain carbon-coated bismuth nanocomposite anode material.

[0012] More preferably, in step S3, the heat transfer efficiency of the rotary kiln, in which CO and methane are mixed at a volume ratio of 1:1, is increased by 3 times compared to the static furnace, resulting in a carbon layer thickness deviation of <±5nm in the product.

[0013] The beneficial effects of this invention are: This invention incorporates modified nano-titanium dioxide, which provides stable support within the material system, maintaining the structural stability of the carbon-coated bismuth nanocomposite anode material and preventing battery performance degradation due to structural collapse. In the carbon-coated bismuth nanocomposite anode material, the highly conductive intermediate layer of modified nano-titanium dioxide forms excellent electronic contact with the carbon framework and bismuth nanoparticles, constructing a continuous electron transport path and promoting rapid electron migration throughout the material. This effectively improves the material's conductivity and electrochemical performance. The stress buffering effect of the SO-Ti dynamic covalent bonds of the modified nano-titanium dioxide, along with the formation of Ti-OC and Bi-O-Ti covalent bonds between its surface-active groups and the carbon framework and bismuth nanonuclei, strengthens interfacial bonding, preventing bismuth particle aggregation and carbon layer detachment during cycling. This significantly enhances the interfacial bonding between components, ensuring the structural stability and interfacial integrity of the material under complex electrochemical environments, further improving the battery's cycle stability and reliability.

[0014] In summary, this invention addresses key issues such as severe volume expansion, low conductivity, and defects in traditional processes in bismuth-based anodes through structural innovation and process optimization. It significantly improves the cycle stability, rate performance, and industrial feasibility of the material, providing an effective solution for the application of high-energy-density, long-life lithium-ion battery anode materials. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1: A method for preparing modified nano-titanium dioxide, comprising the following steps: A1. Mix 30 mL of ammonia water, 40 mL of anhydrous ethanol and 40 mL of deionized water evenly, add 10 g of tetraethyl orthosilicate, stir for 25 min, add 3 g of resorcinol, sonicate for 10 min, magnetically stir for 15 min, then add 4 g of formaldehyde and stir at 45 °C for 7 h, cool to 25 °C and stir for 13 h, wash with anhydrous ethanol and deionized water, dry to obtain silica-coated resorcinol-formaldehyde resin powder. A2. 20g of silica-coated resorcinol-formaldehyde resin powder was heated to 300-400℃ at 3-5℃ / min, and then heated to 750℃ at 6℃ / min. It was soaked in 300mL of 5wt% ammonium fluoride solution for 3h, then sonicated at 250W for 7min. After centrifugation, it was washed with deionized water until pH=7 and dried at 65℃ for 7h to obtain hollow mesoporous carbon spheres. A3. Disperse 5g of hollow mesoporous carbon spheres ultrasonically into 200mL of isopropanol, then add 0.25g of diethylenetriamine to the dispersion and stir for 25min. Add 5g of titanium isopropoxide and stir for 25min. Transfer to a polytetrafluoroethylene reactor and react at 250℃ for 30h. Centrifuge and add anhydrous ethanol. Calcinate at 650℃ for 2.3h in a mixed atmosphere of argon and hydrogen to obtain hollow carbon-supported titanium dioxide nanospheres.

[0017] Example 2: Preparation method of carbon-coated bismuth nanocomposite anode material, comprising the following raw materials in parts by weight: A carbon-coated bismuth nanocomposite anode material is composed of a porous carbon framework, bismuth nanonuclei, and an ultrathin carbon shell. The bismuth nanonuclei have a particle size of 50 nm and are uniformly dispersed in the pores of the porous carbon framework. The ultrathin carbon shell has a thickness of 5 nm and is bonded to the surface of the bismuth nanonuclei through Bi-OC covalent bonds. The porous carbon framework has a pore size of 200 nm and comprises the following raw materials in parts by weight: 110 parts phenolic resin, 15 parts CTAB, 10 parts silicon dioxide, and 5 parts modified nano-titanium dioxide. The modified nano-titanium dioxide is the hollow carbon-supported titanium dioxide nanospheres prepared in Example 1.

[0018] The above preparation method includes the following steps: S1. Mix ammonia, anhydrous ethanol and deionized water, stir magnetically for 10 min, add resorcinol, stir magnetically at 60℃ for 30 min, add formaldehyde solution dropwise, stir at 50℃ for 15 min, wash the precipitate three times with deionized water to obtain resorcinol-formaldehyde nanosphere dispersion, add hollow carbon-supported titanium dioxide nanospheres to deionized water, sonicate for 40 min, then pour into the resorcinol-formaldehyde nanosphere dispersion, sonicate for 20 min, stir magnetically for 40 min to obtain hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion; S2. Add deionized water, anhydrous ethanol, CTAB and ammonia to a beaker, stir magnetically for 10 min, pour in the hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion from step S1, stir at 40℃ for 1 h, add TEOS dropwise, stir at 40℃ for 2 h, wash alternately with deionized water and anhydrous ethanol 5 times, and vacuum dry to obtain carbon-silicon double-coated titanium dioxide composite microspheres. S3. Place the dried composite microspheres into a porcelain crucible, purge with nitrogen for 30 min, raise the temperature to 400℃ at 1℃ / min, hold for 2 h, continue to raise the temperature to 1000℃ at 1℃ / min, hold for 1 h, and cool naturally to room temperature to obtain titanium carbide silicon carbide coated composite microspheres. Add hydrofluoric acid, stir for 28 h, wash with deionized water and anhydrous ethanol 5 times, and vacuum dry to obtain a porous carbon framework. S4. Take blocky bismuth metal, crush it with a crusher, and control the particle size D by screening. 50The bismuth particles are 1000 μm in size. They are placed in a tube furnace and calcined at 700 °C for 3 h in an Ar atmosphere. The calcined bismuth particles and the porous carbon skeleton from step S3 are added to a mortar and ground for 15 min, and then vacuum dried for 12 h. S5. Place the dried mixture into the rotary kiln crucible and introduce a reducing gas mixture of CO and methane. The temperature was increased to 1500℃ at 8℃ / min, the furnace pressure was 0.02MPa, and after the process was completed, a reducing gas was continuously introduced, and the furnace temperature was reduced to 700℃. The material was ultrasonically cleaned 4 times with anhydrous ethanol and vacuum dried at 80℃ for 8 hours to obtain carbon-coated bismuth nanocomposite anode material.

[0019] Example 3: Preparation method of carbon-coated bismuth nanocomposite anode material, comprising the following raw materials in parts by weight: A carbon-coated bismuth nanocomposite anode material is composed of a porous carbon framework, bismuth nanonuclei, and an ultrathin carbon shell. The bismuth nanonuclei have a particle size of 30 nm and are uniformly dispersed in the pores of the porous carbon framework. The ultrathin carbon shell has a thickness of 20 nm and is bonded to the surface of the bismuth nanonuclei through Bi-OC covalent bonds. The porous carbon framework has a pore size of 80 nm and comprises the following raw materials in parts by weight: 100 parts phenolic resin, 18 parts CTAB, 9 parts silicon dioxide, and 6 parts modified nano-titanium dioxide. The modified nano-titanium dioxide is the hollow carbon-supported titanium dioxide nanospheres prepared in Example 1.

[0020] The above preparation method includes the following steps: S1. Mix ammonia, anhydrous ethanol and deionized water, stir magnetically for 8 min, add resorcinol, stir magnetically at 65℃ for 25 min, add formaldehyde solution dropwise, stir at 55℃ for 8 min, wash the precipitate with deionized water 3-4 times to obtain resorcinol-formaldehyde nanosphere dispersion, add hollow carbon-supported titanium dioxide nanospheres to deionized water, sonicate for 35 min, then pour into resorcinol-formaldehyde nanosphere dispersion, sonicate for 25 min, stir magnetically for 35 min to obtain hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion; S2. Add deionized water, anhydrous ethanol, CTAB and ammonia to a beaker, stir magnetically for 13 min, pour in the hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion from step S1, stir at 35°C for 1.5 h, add TEOS dropwise, stir at 35°C for 2.5 h, wash alternately with deionized water and anhydrous ethanol 4 times, and vacuum dry to obtain carbon-silicon double-coated titanium dioxide composite microspheres. S3. Place the dried composite microspheres into a porcelain crucible, purge with nitrogen for 35 min, raise the temperature to 350℃ at 1℃ / min, hold for 2.5 h, continue to raise the temperature to 950℃ at 1℃ / min, hold for 1.5 h, and cool naturally to room temperature to obtain titanium carbide silicon carbide coated composite microspheres. Add hydrofluoric acid, stir for 25 h, wash with deionized water and anhydrous ethanol 6 times, and vacuum dry to obtain a porous carbon framework. S4. Take blocky bismuth metal, crush it with a crusher, and control the particle size D by screening. 50 The bismuth particles were placed in a tube furnace and calcined at 750°C for 2.5 h under an Ar atmosphere. The calcined bismuth particles and the porous carbon skeleton from step S3 were added to a mortar and ground for 13 min, and then vacuum dried for 14 h. S5. Place the dried mixture into the rotary kiln crucible and introduce a reducing gas mixture of CO and methane. The temperature was increased to 1600℃ at a rate of 6℃ / min, and the pressure inside the furnace was 0.015MPa. After the process was completed, a reducing gas was continuously introduced, and the furnace temperature was reduced to 750℃. The material was ultrasonically cleaned three times with anhydrous ethanol and vacuum dried at 85℃ for 7 hours to obtain carbon-coated bismuth nanocomposite anode material.

[0021] Example 4: Preparation method of carbon-coated bismuth nanocomposite anode material, comprising the following raw materials in parts by weight: A carbon-coated bismuth nanocomposite anode material is composed of a porous carbon framework, bismuth nanocores, and an ultrathin carbon shell. The bismuth nanocores have a particle size of 5 nm and are uniformly dispersed in the pores of the porous carbon framework. The ultrathin carbon shell has a thickness of 50 nm and is bonded to the surface of the bismuth nanocores through Bi-OC covalent bonds. The porous carbon framework has a pore size of 10 nm and comprises the following raw materials in parts by weight: 90 parts phenolic resin, 20 parts CTAB, 8 parts silicon dioxide, and 7 parts modified nano-titanium dioxide. The modified nano-titanium dioxide is the hollow carbon-supported titanium dioxide nanospheres prepared in Example 1.

[0022] The above preparation method includes the following steps: S1. Mix ammonia, anhydrous ethanol and deionized water, stir magnetically for 5 min, add resorcinol, stir magnetically at 70℃ for 20 min, add formaldehyde solution dropwise, stir at 60℃ for 10 min, wash the precipitate 5 times with deionized water to obtain resorcinol-formaldehyde nanosphere dispersion, add hollow carbon-supported titanium dioxide nanospheres to deionized water, sonicate for 30 min, then pour into resorcinol-formaldehyde nanosphere dispersion, sonicate for 30 min, stir magnetically for 30 min to obtain hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion; S2. Add deionized water, anhydrous ethanol, CTAB and ammonia to a beaker, stir magnetically for 15 min, pour in the hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion from step S1, stir at 30~40℃ for 1 h, add TEOS dropwise, stir at 40℃ for 2 h, wash alternately with deionized water and anhydrous ethanol 5 times, and vacuum dry to obtain carbon-silicon double-coated titanium dioxide composite microspheres. S3. Place the dried composite microspheres into a porcelain crucible, purge with nitrogen for 30 min, raise the temperature to 400℃ at 1℃ / min, hold for 2 h, continue to raise the temperature to 1000℃ at 1℃ / min, hold for 1 h, and cool naturally to room temperature to obtain titanium carbide silicon carbide coated composite microspheres. Add hydrofluoric acid, stir for 28 h, wash with deionized water and anhydrous ethanol 5 times, and vacuum dry to obtain a porous carbon framework. S4. Take blocky bismuth metal, crush it with a crusher, and control the particle size D by screening. 50 The bismuth particles are 1000 μm in size. They are placed in a tube furnace and calcined at 700 °C for 3 h in an Ar atmosphere. The calcined bismuth particles and the porous carbon skeleton from step S3 are added to a mortar and ground for 15 min, and then vacuum dried for 12 h. S5. Place the dried mixture into the rotary kiln crucible and introduce a reducing gas mixture of CO and methane. The temperature was increased to 1500℃ at 8℃ / min, the furnace pressure was 0.02MPa, and after the process was completed, a reducing gas was continuously introduced, and the furnace temperature was reduced to 700℃. The material was ultrasonically cleaned 4 times with anhydrous ethanol and vacuum dried at 80℃ for 8 hours to obtain carbon-coated bismuth nanocomposite anode material.

[0023] Comparative Example 1: A carbon-coated bismuth nanocomposite anode material, with the same composition and preparation as in Example 4, except that modified nano-titanium dioxide was not added. The preparation method of the carbon-coated bismuth nanocomposite anode material includes the following steps: S1. Mix ammonia, anhydrous ethanol and deionized water, stir magnetically for 10 min, add resorcinol, stir magnetically at 65℃ for 25 min, add formaldehyde solution dropwise, stir at 55℃ for 10 min, wash the precipitate 4 times with deionized water to obtain resorcinol-formaldehyde nanosphere dispersion. S2. Add deionized water, anhydrous ethanol, CTAB and ammonia to a beaker, stir magnetically for 10 min, pour in the dispersion from step S1, stir at 35°C for 1.5 h, add TEOS dropwise, stir at 35°C for 2.5 h, wash with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry to obtain carbon-silicon double-coated composite microspheres. S3. Place the dried composite microspheres into a porcelain crucible, purge with nitrogen for 35 min, raise the temperature to 350℃ at 1℃ / min and hold for 2.5 h, then raise the temperature to 950℃ at 1℃ / min and hold for 1.5 h, and cool naturally to room temperature to obtain titanium carbide silicon carbide coated composite microspheres. Add hydrofluoric acid and stir for 25 h, wash with deionized water and anhydrous ethanol 6 times, and vacuum dry to obtain a porous carbon framework. S4. Take a block of bismuth metal and crush it, controlling D. 50 The bismuth content is 600 μm. It is calcined at 750 °C for 2.5 h under Ar atmosphere, mixed with the porous carbon framework of step S3 at a mass ratio of 50%, ground in a mortar for 15 min, and vacuum dried at 65 °C for 14 h. S5. Place the mixture into a rotary furnace, introduce a CO and methane mixed gas with a volume ratio of 1:1, heat to 1600℃ at 6℃ / min, maintain the furnace pressure at 0.015MPa, after which continue to introduce reducing gas until the furnace temperature drops to 750℃, cool to room temperature in Ar atmosphere, ultrasonically clean 3 times with anhydrous ethanol, and vacuum dry at 85℃ for 7h to obtain carbon-coated bismuth nanocomposite anode material.

[0024] Performance testing Inside an argon-filled glove box, copper foil electrodes coated with carbon-coated bismuth nanocomposite negative electrode material, PE composite separators pre-wetted with electrolyte, and adapted lithium iron phosphate aluminum foil electrodes are stacked in sequence. 1 mol / L LiPF6 is dissolved in ethylene carbonate electrolyte. After assembly with gaskets and springs, the batteries are pressed and sealed using a button battery packaging machine. After static activation, the battery assembly is completed. In the tests of Examples 2-4 and Comparative Example 1, the fast charging rate was tested according to GB / T36276-2018. The sample was placed in a constant temperature environment at 25±2℃ and charged at a constant current rate of 0.1C to the charging cutoff voltage. After charging, the sample was left to stand for a period of time, and then discharged at a constant current rate of 0.1C to the discharging cutoff voltage. The discharge capacity was recorded. The cycle life was tested according to GB / T31484-2015. The sample was placed in an environmental test chamber with the temperature controlled at 25±2℃ and charged at a constant current rate of 1C to the charging cutoff voltage of the battery. Then, it was discharged at a constant current rate of 1C to the discharging cutoff voltage of the battery, thus completing one charge-discharge cycle. After a certain number of cycles, the battery capacity was tested, and the number of cycles was recorded, which is the cycle life of the battery.

[0025] Table 1. Detection of carbon-coated bismuth nanocomposite anode materials

[0026] As shown in Table 1, the fast-charging rates of Examples 2-4 are significantly higher than those of Comparative Example 1. The hollow carbon-coated structure of the modified nano-titanium dioxide constructs a highly efficient electron transport network. Its highly conductive intermediate layer, together with the porous carbon framework and bismuth nanonuclei, forms a continuous conductive pathway, reducing electron transport resistance. Simultaneously, the gradient pore size of the porous carbon framework and the rigid support of the modified nano-titanium dioxide work synergistically to maintain unobstructed ion channels, ensuring rapid lithium-ion diffusion at a high rate of 20C. The cycle life of Examples 2-4 is far greater than that of Comparative Example 1, solving the bottleneck of capacity decay >20% after 10 cycles in the background technology. The stress buffering effect of the SO-Ti dynamic covalent bonds of the modified nano-titanium dioxide strengthens the interfacial bonding force, preventing bismuth particle agglomeration and carbon layer shedding during cycling. Among them, Example 3 shows the best effect. Its performance advantages fully verify that the modified nano-titanium dioxide maintains the integrity of the overall material structure, improves rate performance, significantly enhances the interfacial bonding force between components, ensures the structural stability and interfacial integrity of the material under complex electrochemical environments, and further improves the cycle stability and reliability of the battery.

[0027] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0028] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A carbon-coated bismuth nanocomposite anode material, characterized in that, It is composed of a porous carbon framework, bismuth nanonuclei, and an ultrathin carbon shell; the bismuth nanonuclei have a particle size of 5-50 nm and are uniformly dispersed in the pores of the porous carbon framework; the ultrathin carbon shell has a thickness of 5-50 nm and is bonded to the surface of the bismuth nanonuclei through Bi-OC covalent bonds; the porous carbon framework has a pore size of 10-200 nm and includes the following raw materials in parts by weight: 90-110 parts of phenolic resin, 15-20 parts of activator, 8-10 parts of template agent, and 5-7 parts of modified nano-titanium dioxide; The modified nano-titanium dioxide is a hollow carbon-supported titanium dioxide nanosphere.

2. The carbon-coated bismuth nanocomposite anode material according to claim 1, characterized in that, The active agent is CTAB.

3. The carbon-coated bismuth nanocomposite anode material according to claim 1, characterized in that, The template agent is silicon dioxide.

4. The carbon-coated bismuth nanocomposite anode material according to claim 1, characterized in that, The method for preparing the modified nano-titanium dioxide includes the following steps: A1. Mix ammonia, anhydrous ethanol and deionized water evenly, add tetraethyl orthosilicate, stir for 20-30 min, add resorcinol, sonicate for 10-15 min, magnetically stir for 15-20 min, then add formaldehyde and stir at 40-50℃ for 6-8 h, cool to 20-30℃ and stir for 12-15 h, wash with anhydrous ethanol and deionized water, and dry to obtain silica-coated resorcinol-formaldehyde resin powder; A2. The silica-coated resorcinol-formaldehyde resin powder is heated to 300-400℃ at 3-5℃ / min, and then heated to 700-800℃ at 5-8℃ / min. It is then soaked in 5-6wt% ammonium bifluoride solution for 2-4 hours, followed by sonication at 200-300W for 6-8 minutes. After centrifugation, it is washed with deionized water until pH=7, and dried at 60-70℃ for 6-8 hours to obtain hollow mesoporous carbon spheres. A3. Hollow mesoporous carbon spheres were ultrasonically dispersed in isopropanol, and then diethylenetriamine was added to the dispersion. The mixture was stirred for 20-30 min, titanium isopropoxide was added, and the mixture was stirred for 20-30 min. The mixture was then transferred to a polytetrafluoroethylene reactor and reacted at a constant temperature of 200-300℃ for 24-48 h. After centrifugation, anhydrous ethanol was added, and the mixture was calcined at 600-700℃ for 2-3 h in a mixed atmosphere of argon and hydrogen to obtain hollow carbon-supported titanium dioxide nanospheres.

5. The carbon-coated bismuth nanocomposite anode material according to claim 4, characterized in that... In A1, ammonia, anhydrous ethanol, and deionized water are mixed in a volume ratio of 3:4:4, while tetraethyl orthosilicate, resorcinol, and formaldehyde are mixed in a mass ratio of 10:3:

4.

6. A method for preparing the carbon-coated bismuth nanocomposite anode material as described in claims 1-4, characterized in that, Includes the following steps: S1. Mix ammonia, anhydrous ethanol and deionized water, stir magnetically for 5-10 min, add resorcinol, stir magnetically at 60-70℃ for 20-30 min, add formaldehyde solution dropwise, stir at 50-60℃ for 10-15 min, wash the precipitate with deionized water 3-5 times to obtain resorcinol-formaldehyde nanosphere dispersion. Add hollow carbon-supported titanium dioxide nanospheres to deionized water, sonicate for 30-40 min, then pour into the resorcinol-formaldehyde nanosphere dispersion, sonicate for 20-30 min, and stir magnetically for 30-40 min to obtain hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion. S2. Add deionized water, anhydrous ethanol, CTAB and ammonia to a beaker, stir magnetically for 10-15 min, pour in the hollow carbon-supported resorcinol-formaldehyde-titanium dioxide mixed dispersion from step S1, stir at 30-40℃ for 1-2 h, add TEOS dropwise, stir at 30-40℃ for 2-3 h, wash alternately with deionized water and anhydrous ethanol 3-5 times, and vacuum dry to obtain carbon-silicon double-coated titanium dioxide composite microspheres. S3. Place the dried composite microspheres into a porcelain crucible, purge with nitrogen for 30-40 min, raise the temperature to 300-400℃ at 1℃ / min, hold for 2-3 h, continue to raise the temperature to 900-1000℃ at 1℃ / min, hold for 1-2 h, and cool naturally to room temperature to obtain titanium carbide-silicon carbide-coated composite microspheres. Add hydrofluoric acid, stir for 24-28 h, wash with deionized water and anhydrous ethanol 5-7 times, and vacuum dry to obtain a porous carbon framework. S4. Take blocky bismuth metal, crush it with a crusher, and control the particle size D by screening. 50 The bismuth particles are 0.1~1000μm in size. They are placed in a tube furnace and calcined at 700~800℃ for 2~3h under an Ar atmosphere. The calcined bismuth particles and the porous carbon skeleton from step S3 are added to a mortar and ground for 10~15min according to the bismuth mass ratio of 20%~70%. They are then vacuum dried for 12~15h. S5. Place the dried mixture into the rotary kiln crucible and introduce a reducing gas mixture of CO and methane. The temperature is increased to 1500-1700℃ at a rate of 5-8℃ / min, and the pressure inside the furnace is 0.01-0.02MPa. After the process is completed, a reducing gas is continuously introduced, and the furnace temperature is reduced to 700-800℃. The material is then ultrasonically cleaned 2-4 times with anhydrous ethanol and vacuum dried at 80-90℃ for 6-8 hours to obtain carbon-coated bismuth nanocomposite anode material.

7. The method for preparing the carbon-coated bismuth nanocomposite anode material according to claim 6, characterized in that, In step S5, the heat transfer efficiency of the rotary kiln, which mixes CO and methane at a volume ratio of 1:1, is increased by 3 times compared to the static furnace, resulting in a carbon layer thickness deviation of <±5nm in the product.

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