An electrode material and its preparation method in lithium-ion batteries

Abstract

This invention discloses an electrode material, its preparation method, and a lithium-ion battery. The electrode material comprises bismuth sulfide, a carbon layer coated on the surface of the bismuth sulfide, a nitrogen layer coated on the surface of the carbon layer, and a nitrogen-carbon layer coated on the surface of the nitrogen layer. This invention forms the electrode material by sequentially coating the surface of bismuth sulfide with a carbon layer, a nitrogen layer, and a nitrogen-carbon layer. The carbon layer, acting as a skeletal support, effectively alleviates the significant stress on the bismuth sulfide during charging and discharging, reduces the volume change of the bismuth sulfide, and thus improves the cycle stability of the bismuth sulfide. The nitrogen layer effectively reduces the side reactions between the bismuth sulfide and the electrolyte, thereby reducing the battery's self-discharge rate and increasing its energy density, resulting in a more stable and longer battery life. The nitrogen-carbon layer enhances the charge transfer rate during charging and discharging and helps improve the conductivity and structural stability of the bismuth sulfide during repeated lithiation / delithiation processes.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to an electrode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid development of society, the application of new energy as a key technology has gradually expanded, including aerospace, military, medical, and electric vehicles. However, new energy sources suffer from uneven spatial and temporal distribution, and energy storage provides a relatively ideal solution for "peak shaving and valley filling." Therefore, finding energy storage devices with high energy density is a major trend for future development. Among various electrochemical energy storage devices, lithium-ion batteries have been widely studied due to their advantages such as high energy density, long cycle life, and low pollution. Currently, graphite-type carbon anode materials are widely used in commercial lithium-ion batteries. However, the theoretical specific capacity of graphite (372 mAh·g) is limited. -1 The specific capacity of anode materials is relatively low, making it impossible to achieve the high energy density required by some modern electronic devices. The exploration and development of anode materials with high specific capacity and high safety has become a research hotspot in the field of lithium-ion batteries.

[0003] Metal sulfides, as active materials for rechargeable lithium-ion batteries, have attracted extensive research due to their higher specific capacity and operational safety compared to traditional graphite anodes. Examples include iron sulfide, tin sulfide, and bismuth sulfide. Bismuth sulfide, in particular, is considered an excellent candidate for lithium-ion batteries because it is a nested, indirect bandgap semiconductor with a bandgap of 1.3 eV. This layered structure provides a safe lithium intercalation potential (0.5-0.8 V vs. Li) and a specific capacity of 625 mAh / g. However, some problems remain when studying the storage applications of bismuth sulfide anodes in lithium-ion batteries, including excessive volume changes during cycling, low electronic conductivity, and the precipitation and dissolution of polysulfide intermediates in the electrolyte during charge and discharge, leading to low utilization of the anode material and rapid capacity decay.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide an electrode material, a method for preparing the same, and a lithium-ion battery, aiming to solve the problems of excessive volume change and low electronic conductivity of existing electrode materials during cycling.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides an electrode material comprising bismuth sulfide, a carbon layer coated on the surface of the bismuth sulfide, a nitrogen layer coated on the surface of the carbon layer, and a nitrogen-carbon layer coated on the surface of the nitrogen layer.

[0008] Preferably, the bismuth sulfide has a spherical morphology and a diameter of 1-2 μm.

[0009] Preferably, the thickness of the carbon layer is 5-10 nm.

[0010] Preferably, the thickness of the nitrogen layer is 5-10 nm.

[0011] Preferably, the thickness of the nitrogen-carbon layer is 10-20 nm.

[0012] Preferably, in the nitrogen-carbon layer, the mass ratio of nitrogen to carbon is 0.2.

[0013] A second aspect of the present invention provides a method for preparing an electrode material, the method comprising the following steps:

[0014] Preparation of bismuth sulfide;

[0015] The bismuth sulfide and carbon source are dissolved in a first solvent, and then subjected to hydrothermal treatment and a first annealing treatment in sequence, so that carbon is coated on the surface of the bismuth sulfide, denoted as C@Bi2S3;

[0016] The C@Bi2S3 and a nitrogen source are dissolved in a second solvent, and a first deposition process and a second annealing process are performed sequentially to coat the surface of the C@Bi2S3 with nitrogen, which is denoted as CN@Bi2S3.

[0017] The CN@Bi2S3 was dissolved in a third solvent, and the pH was adjusted to 7.5-9.5. Then, a nitrogen-carbon source was added, and a second deposition treatment and a third annealing treatment were performed in sequence to coat the CN@Bi2S3 surface with nitrogen and carbon, thus obtaining the electrode material, denoted as CN-NC@Bi2S3.

[0018] Preferably, the carbon source is selected from one or more of glucose, sodium acetate, and methanol;

[0019] The nitrogen source is selected from one or more of urea, boron nitride, and cyanide;

[0020] The nitrogen and carbon source is selected from one or more of melamine, ethylenediamine, and dopamine hydrochloride;

[0021] The first solvent, the second solvent, and the third solvent are each independently selected from deionized water or ethanol.

[0022] Preferably, the hydrothermal treatment temperature is 120-150℃ and the hydrothermal treatment time is 10-12h;

[0023] The temperature of the first annealing treatment is 400-500℃, and the time of the first annealing treatment is 1-5h;

[0024] The temperature of the second annealing treatment is 400-500℃, and the time of the second annealing treatment is 1-5h;

[0025] The temperature of the third annealing treatment is 400-500℃, and the time of the third annealing treatment is 1-5h;

[0026] The methods for the first deposition treatment and the second deposition treatment are each independently selected from one of spin coating, dipping, and spraying.

[0027] In a third aspect, the present invention provides a lithium-ion battery comprising a negative electrode material, wherein the negative electrode material comprises the electrode material described above or an electrode material prepared by the preparation method described above.

[0028] Beneficial Effects: This invention provides an electrode material, its preparation method, and a lithium-ion battery. The invention involves sequentially coating a carbon layer, a nitrogen layer, and a carbon-nitrogen layer onto the surface of bismuth sulfide to form the electrode material. The carbon layer, acting as a skeletal support, effectively alleviates the significant stress on bismuth sulfide during charging and discharging, reducing volume changes and thus improving cycle stability. The nitrogen layer effectively reduces side reactions between bismuth sulfide and the electrolyte, thereby lowering the battery's self-discharge rate and increasing energy density, resulting in a more stable and longer battery life. The carbon-nitrogen layer enhances the charge transfer rate during charging and discharging and helps improve the conductivity and structural stability of bismuth sulfide during repeated lithiation / delithiation processes. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a lithium-ion battery assembly structure prepared according to a preferred application example of the present invention.

[0030] Figure 2 These are XRD comparison images of the negative electrode materials prepared in Example 1 and Comparative Example 1 of this invention as negative electrodes for lithium-ion batteries.

[0031] Figure 3 This is an XPS image of the negative electrode material prepared in Example 1 of this invention.

[0032] Figure 4 This is a SEM image of the negative electrode material prepared in Example 1 of this invention.

[0033] Figure 5 This is a charge-discharge curve of the negative electrode material prepared in Example 1 of the present invention as the negative electrode of a lithium-ion battery.

[0034] Figure 6 This is a charge-discharge curve of the negative electrode material prepared in Comparative Example 1 of this invention as the negative electrode of a lithium-ion battery.

[0035] Figure 7This is a cycle performance test diagram of the negative electrode material prepared in Example 1 and Comparative Example 1 of the present invention as a negative electrode for a lithium-ion battery.

[0036] Figure 8 This is a rate performance test chart of the negative electrode material prepared in Example 1 and Comparative Example 1 of the present invention as a negative electrode for a lithium-ion battery. Detailed Implementation

[0037] This invention provides an electrode material, its preparation method, and a lithium-ion battery. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] This invention provides an electrode material comprising bismuth sulfide, a carbon layer coated on the surface of the bismuth sulfide, a nitrogen layer coated on the surface of the carbon layer, and a nitrogen-carbon layer coated on the surface of the nitrogen layer.

[0039] In this embodiment of the invention, a carbon layer, a nitrogen layer, and a nitrogen-carbon layer are sequentially coated on the surface of bismuth sulfide to form an electrode material. The carbon layer, as a skeletal support, can effectively alleviate the enormous stress on bismuth sulfide during charging and discharging, reduce the volume change of bismuth sulfide, and thus improve the cycle stability of bismuth sulfide. The nitrogen layer can effectively reduce the side reactions between bismuth sulfide and the electrolyte, thereby reducing the self-discharge rate of the battery and increasing the energy density, making the battery more stable and longer-lasting. The nitrogen-carbon layer can improve the charge transfer rate during charging and discharging and help bismuth sulfide improve conductivity and structural stability during repeated lithiation / delithiation processes.

[0040] In some embodiments, the bismuth sulfide has a spherical morphology and a diameter of 1-2 μm.

[0041] This intercalation structure of spherical bismuth sulfide stores Li through a fast transport path. +Bismuth sulfide nanospheres do not undergo electrochemical reactions with the electrodes. Furthermore, spherical bismuth sulfide possesses a high specific surface area and good particle distribution. This higher specific surface area promotes the conduction of more electrons and lithium ions on and within the electrode surface, thereby improving the overall conductivity and electrochemical performance of the battery. Specifically, when the size of the bismuth sulfide nanospheres is between 1-2 μm, it offers several advantages: 1. Increased specific surface area: The 1-2 μm size range provides a suitable balance, maintaining a large specific surface area to enhance electrode activity and increase lithium ion insertion and extraction rates, while reducing side reactions and excessive SEI film formation caused by excessively large surfaces. 2. Stable structure: Micron-sized particles provide a more stable structure, avoiding large volume changes during charge and discharge, thus reducing material pulverization and failure. 3. Good conductivity and ion diffusion: The 1-2 μm size ensures a balance between conductivity and ion diffusion, avoiding both the high interfacial resistance problem at nanoscale and the excessively long diffusion paths caused by excessively large particle sizes.

[0042] In some embodiments, the thickness of the carbon layer is 5-10 nm.

[0043] The present invention controls the thickness of the carbon layer within this range, which has the following three advantages: 1. Improved electronic conductivity: Carbon layer is a good conductive material, and a suitable thickness can significantly improve the electronic conductivity of the electrode and reduce internal resistance. 2. Prevention of volume expansion and structural collapse: A moderately thick carbon layer can provide a buffering effect during lithium-ion insertion and extraction, reducing the volume change of the negative electrode material and preventing the collapse of the electrode structure. 3. Effects of excessive thickness or thinness: If the carbon layer thickness exceeds 10 nanometers, it may increase the overall thickness of the electrode, leading to an increase in the electron and ion transport distance and a reduction in rate performance; if the carbon layer thickness is less than 5 nanometers, it is difficult to form an effective protective layer and cannot effectively prevent the occurrence of side reactions.

[0044] In some embodiments, the thickness of the nitrogen layer is 5-10 nm.

[0045] This invention controls the thickness of the nitrogen layer within this range, offering the following three advantages: 1. Increased electronic conductivity: Nitrogen doping improves the electronic conductivity of materials because nitrogen atoms can introduce additional electrons and increase conductivity. A suitable thickness (5-10 nm) ensures sufficient electron transport without affecting the overall conductivity of the material. 2. Stable SEI film: A moderate nitrogen layer thickness reduces direct contact between the electrolyte and the negative electrode material, thus contributing to the formation of a stable solid electrolyte interface (SEI) film and reducing electrolyte decomposition and side reactions. 3. Effects of excessive thickness or thinness: If the nitrogen layer thickness exceeds 10 nm, it increases the diffusion paths of electrons and ions, reducing the rate performance of the battery; if the thickness is less than 5 nm, the coating effect is not significant, making it difficult to form a stable interface protective layer.

[0046] In some embodiments, the thickness of the nitrogen-carbon layer is 10-20 nm.

[0047] This invention controls the thickness of the nitrogen-rich carbon layer within this range, offering three advantages: 1. Improved conductivity and ionic conductivity: The nitrogen-rich carbon layer combines the advantages of nitrogen doping and carbon materials, simultaneously improving electronic and ionic conductivity, thereby enhancing the overall battery performance. 2. Stabilized SEI film: The nitrogen-rich carbon layer promotes the formation of a uniform SEI film, reducing electrolyte decomposition and side reactions, and extending the battery's cycle life. 3. Effects of excessive thickness or thinness: If the thickness of the nitrogen-rich carbon layer exceeds 10 nanometers, it may lead to an increase in the overall electrode thickness, thus affecting the electron and ion transport rates; if the thickness is less than 5 nanometers, it cannot provide sufficient conductivity and SEI film stability, affecting battery performance.

[0048] In summary, appropriate coating thickness and nanosphere size can optimize the performance of lithium-ion battery anodes, while excessively thick or thin coatings can create an imbalance between conductivity, ion transport rate, and structural stability, affecting the overall performance of the battery.

[0049] In some embodiments, the mass ratio of nitrogen to carbon in the nitrogen-carbon layer is 0.2.

[0050] This invention controls the nitrogen to carbon mass ratio at 0.2, which has the following advantages: 1. Optimized electronic conductivity: In the nitrogen-carbon layer, nitrogen doping can effectively introduce additional free electrons, improving the conductivity of the material. When the nitrogen doping ratio is 0.2, an equilibrium point can be reached, significantly improving the overall conductivity without significantly damaging the conductivity of the carbon layer. This enhanced conductivity is mainly due to the enrichment of π electrons and the introduction of defects caused by nitrogen doping, which can improve the charge transfer capability of carbon-based materials. 2. Promoted lithium-ion diffusion: Nitrogen doping can generate certain defects and active sites in the carbon network, which facilitate the adsorption and diffusion of lithium ions. Therefore, when N:C = 0.2, this moderate doping can maximize the structural stability of the carbon material while introducing more active sites, improving the rate performance and reversible capacity of the electrode material. 3. Improved SEI film stability: The nitrogen-doped layer can provide a uniform electron distribution and chemical environment, which helps to form a uniform solid electrolyte interface (SEI) film on the electrode surface. An appropriate doping ratio (e.g., 0.2) can optimize interface stability, reduce side reactions, and improve cycle stability.

[0051] In summary, a nitrogen-to-carbon ratio of 0.2 achieves a good balance in electronic conductivity, lithium-ion diffusion, and SEI film stability, thus improving the electrochemical performance of bismuth sulfide nanosphere anode materials. Excessively high or low nitrogen doping ratios can lead to imbalances in conductivity, structural stability, and electrochemical reactions, thereby affecting the overall battery performance.

[0052] When the N:C ratio exceeds or falls below 0.2, the following effects occur: 1. Effects exceeding 0.2 (higher nitrogen content): Reduced conductivity: Excessive nitrogen doping may disrupt the original structure of the carbon layer, leading to a decrease in the delocalization of π electrons in the carbon network, thereby reducing electronic conductivity. This increases the battery's internal resistance and reduces the rate performance of the electrode; Negative effects of excessive defects: High nitrogen content introduces excessive structural defects. While these defects can serve as active sites, they also accelerate the degradation of the electrode material, leading to faster capacity decay. 2. Effects below 0.2 (lower nitrogen content): Insignificant doping effect: When the nitrogen content is too low (e.g., N:C < 0.1), it cannot effectively improve the electronic structure and conductivity of the carbon layer. A lack of sufficient active sites may slow down the kinetics of lithium-ion insertion and extraction, reducing the battery's specific capacity and cycle performance; SEI film instability: Insufficient nitrogen doping reduces the stability of the SEI film, potentially leading to uneven contact between the electrolyte and the electrode surface, resulting in uneven electrochemical reactions and affecting the battery's cycle life.

[0053] This invention provides a method for preparing an electrode material, the method comprising the following steps:

[0054] Preparation of bismuth sulfide;

[0055] The bismuth sulfide and carbon source are dissolved in a first solvent, and then subjected to hydrothermal treatment and a first annealing treatment in sequence, so that carbon is coated on the surface of the bismuth sulfide, denoted as C@Bi2S3;

[0056] The C@Bi2S3 and a nitrogen source are dissolved in a second solvent, and a first deposition process and a second annealing process are performed sequentially to coat the surface of the C@Bi2S3 with nitrogen, which is denoted as CN@Bi2S3.

[0057] The CN@Bi2S3 was dissolved in a third solvent, and the pH was adjusted to 7.5-9.5. Then, a nitrogen-carbon source was added, and a second deposition treatment and a third annealing treatment were performed in sequence to coat the CN@Bi2S3 surface with nitrogen and carbon, thus obtaining the electrode material, denoted as CN-NC@Bi2S3.

[0058] In some embodiments, the pH adjusting substance used to adjust the pH value is at least one of triaminemethane, tris(hydroxymethyl)aminomethane, and phosphate buffer.

[0059] The preparation method provided in this invention is simple, low-cost, and has good application prospects.

[0060] In some embodiments, the step of preparing bismuth sulfide specifically includes:

[0061] Bismuth salt and sulfur source were dissolved in deionized water at a molar ratio of 2:3, and then stirred in a magnetic stirrer for 2 hours to obtain a mixed solution.

[0062] The mixed solution was placed in a homogeneous reactor with a PTFE liner and reacted at 120°C for 12 hours; after cooling to room temperature, it was washed and filtered to obtain a black precipitate.

[0063] The black precipitate was dried in an oven at 60°C for 4 hours to obtain bismuth sulfide.

[0064] In some embodiments, the bismuth salt is selected from at least one of bismuth acetate, bismuth nitrate, bismuth sulfate, and bismuth chloride, and the sulfur source is selected from at least one of glutathione, thioether, and thiol.

[0065] In some embodiments, the carbon source is selected from one or more of glucose, sodium acetate, and methanol;

[0066] The nitrogen source is selected from one or more of urea, boron nitride, and cyanide;

[0067] The nitrogen and carbon source is selected from one or more of melamine, ethylenediamine, and dopamine hydrochloride;

[0068] The first solvent, the second solvent, and the third solvent are each independently selected from deionized water or ethanol.

[0069] In some embodiments, the hydrothermal treatment temperature is 120-150°C, and the hydrothermal treatment time is 10-12 hours;

[0070] The temperature of the first annealing treatment is 400-500℃, and the time of the first annealing treatment is 1-5h;

[0071] The temperature of the second annealing treatment is 400-500℃, and the time of the second annealing treatment is 1-5h;

[0072] The temperature of the third annealing treatment is 400-500℃, and the time of the third annealing treatment is 1-5h;

[0073] The methods for the first deposition treatment and the second deposition treatment are each independently selected from one of spin coating, dipping, and spraying.

[0074] The first, second, and third annealing treatments of this invention are all performed in an inert gas environment. Under the action of high-temperature annealing, the three-layer interface (carbon layer, nitrogen layer, and nitrocarbon layer) is in close contact with the surface gaps of the Bi2S3 nanospheres, thereby improving the conductivity and stability of the Bi2S3 nanospheres.

[0075] This invention provides a method for preparing an electrode material, comprising the following steps:

[0076] Bismuth salt and sulfur source were dissolved in deionized water at a molar ratio of 2:3, and then stirred in a magnetic stirrer for 2 hours to obtain a mixed solution.

[0077] The mixed solution was placed in a homogeneous reactor with a PTFE liner and reacted at 120°C for 12 hours. After cooling to room temperature, it was washed and filtered to obtain a black precipitate.

[0078] The above-mentioned black precipitate was dried in an oven at a temperature of 60°C for 4 hours to obtain Bi2S3 nanospheres.

[0079] Bismuth sulfide nanospheres were dispersed in deionized water, and after adding glucose and stirring for 5 hours, a suspension was obtained.

[0080] The above suspension was placed in a homogeneous reactor with a PTFE liner and reacted at 150°C for 12 hours. After cooling to room temperature, it was washed and filtered to obtain a black precipitate.

[0081] The above-mentioned black precipitate was dried in an oven at a temperature of 60°C for 4 hours. After drying, it was heat-treated to obtain C@Bi2S3 nanospheres.

[0082] C@Bi2S3 nanospheres and a nitrogen source were dissolved in a suitable solvent and stirred for 4 hours to obtain a suspension. The suitable solvent was ethanol or deionized water.

[0083] The above suspension was subjected to sedimentation, followed by washing and filtration to obtain a black precipitate.

[0084] The above-mentioned black precipitate was dried in an oven at a temperature of 60°C for 4 hours. After drying, it was heat-treated to obtain CN@Bi2S3 nanospheres.

[0085] CN@Bi2S3 nanospheres were dispersed in deionized water and stirred for 5 hours. A pH-adjusting substance was continuously added to adjust the pH of the solution to about 8.5. A nitrogen-carbon source was added, and the mixture was stirred for 12 hours before being filtered to obtain a black precipitate.

[0086] The above-mentioned black precipitate was dried in an oven at a temperature of 60°C for 4 hours. After drying, CN-NC@Bi2S3 nanospheres were obtained by heat treatment.

[0087] This invention also provides a lithium-ion battery, which includes a negative electrode material, comprising the electrode material described above or an electrode material prepared by the preparation method described above.

[0088] The negative electrode material provided in the embodiments of the present invention is applied to lithium-ion batteries, giving them good cycle stability and rate performance.

[0089] In some embodiments, the lithium-ion battery includes a positive electrode, a negative electrode, a gasket, a spring, a separator, and an electrolyte, wherein the negative electrode is prepared from the aforementioned electrode material.

[0090] In some embodiments, the negative electrode further includes a conductive agent (carbon black) and a binder (2% CMC), wherein the mass ratio of the negative electrode material, the conductive agent, and the binder is 7:2:1 or 8:1:1.

[0091] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are intended only to illustrate the present invention and not to limit it. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0092] Example 1

[0093] The preparation of a lithium-ion battery negative electrode includes the following steps:

[0094] The electrode material is prepared as follows:

[0095] Step 1: Dissolve Bi(NO3)3·5H2O and glutathione (GSH) in deionized water at a molar ratio of 2:3. Then, stir in a magnetic stirrer for 2 hours to obtain a mixed solution. Transfer the mixed solution to a homogeneous reactor with a PTFE liner and react at 120°C for 12 hours. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60°C for 4 hours to obtain Bi2S3 nanospheres.

[0096] Step 2: Disperse the Bi2S3 nanospheres obtained in Step 1 in deionized water, add 0.2g of glucose and stir for 5h to obtain a suspension. Transfer the suspension to a homogeneous reactor with a PTFE liner and react at 150℃ for 12h. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then anneal at 500℃ for 1h under Ar atmosphere to obtain C@Bi2S3 nanospheres.

[0097] Step 3: Dissolve the C@Bi2S3 nanospheres obtained in Step 2 and 0.2g of boron nitride in deionized water. After stirring for 4h, a suspension is obtained. After washing and filtration by deposition, a black precipitate is obtained. The black precipitate is transferred to an oven and dried at 60℃ for 4h. Then, it is annealed at 500℃ for 1h under Ar atmosphere to obtain CN@Bi2S3 nanospheres.

[0098] Step 4: Disperse the CN@Bi2S3 nanospheres (0.306g) obtained in Step 3 in 750mL of deionized water and stir for 5h. Then, continuously add 0.15g of triaminemethane until the pH value is adjusted to 8.5. Then, add 0.034g of dopamine hydrochloride and stir overnight. After washing and filtration, a black precipitate is obtained. Filter with deionized water and alcohol to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then, anneal at 500℃ for 1h under Ar atmosphere to obtain CN-NC@Bi2S3 nanospheres.

[0099] The negative electrode is prepared as follows:

[0100] The CN-NC@Bi2S3 nanospheres prepared above were used as the negative electrode active material for lithium-ion batteries, carbon black as the conductive agent, sodium carboxymethyl cellulose as the binder, and deionized water as the solvent. The negative electrode active material, conductive agent, and binder were mixed uniformly at a mass ratio of 7:2:1 and stirred for 12 hours to form a homogeneous slurry. This slurry was then coated onto copper foil using a 16 μm doctor blade, dried in a vacuum drying oven at 80°C for 12 hours, and finally cut into 12 mm diameter discs.

[0101] Example 2

[0102] The preparation of a lithium-ion battery negative electrode includes the following steps:

[0103] The electrode material is prepared as follows:

[0104] Step 1: Dissolve Bi(NO3)3·5H2O and glutathione (GSH) in deionized water at a molar ratio of 2:3. Then, stir in a magnetic stirrer for 2 hours to obtain a mixed solution. Transfer the mixed solution to a homogeneous reactor with a PTFE liner and react at 120°C for 12 hours. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60°C for 4 hours to obtain Bi2S3 nanospheres.

[0105] Step 2: Disperse the Bi2S3 nanospheres obtained in Step 1 in deionized water, add 0.2g of glucose and stir for 5h to obtain a suspension. Transfer the suspension to a homogeneous reactor with a PTFE liner and react at 150℃ for 12h. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then anneal at 500℃ for 1h under Ar atmosphere to obtain C@Bi2S3 nanospheres.

[0106] Step 3: Dissolve the C@Bi2S3 nanospheres obtained in Step 2 and 0.2g of boron nitride in deionized water. After stirring for 4h, a suspension is obtained. After washing and filtration by deposition, a black precipitate is obtained. The black precipitate is transferred to an oven and dried at 60℃ for 4h. Then, it is annealed at 500℃ for 1h under Ar atmosphere to obtain CN@Bi2S3 nanospheres.

[0107] Step 4: Disperse the CN@Bi2S3 nanospheres (0.153g) obtained in Step 3 in 750mL of deionized water and stir for 5h. Then, continuously add 0.15g of triaminemethane until the pH value is adjusted to 8.5. Then, add 0.017g of dopamine hydrochloride and stir overnight. After washing and filtration, a black precipitate is obtained. Filter with deionized water and alcohol to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then, anneal at 500℃ for 1h under Ar atmosphere to obtain CN-NC@Bi2S3 nanospheres.

[0108] The negative electrode is prepared as follows:

[0109] The CN-NC@Bi2S3 nanospheres prepared above were used as the negative electrode active material for lithium-ion batteries, carbon black as the conductive agent, sodium carboxymethyl cellulose as the binder, and deionized water as the solvent. The negative electrode active material, conductive agent, and binder were mixed uniformly at a mass ratio of 7:2:1 and stirred for 12 hours to form a homogeneous slurry. This slurry was then coated onto copper foil using a 16 μm doctor blade, dried in a vacuum drying oven at 80°C for 12 hours, and finally cut into 12 mm diameter discs.

[0110] Example 3

[0111] The preparation of a lithium-ion battery negative electrode includes the following steps:

[0112] The electrode material is prepared as follows:

[0113] Step 1: Dissolve Bi(NO3)3·5H2O and glutathione (GSH) in deionized water at a molar ratio of 2:3. Then, stir in a magnetic stirrer for 2 hours to obtain a mixed solution. Transfer the mixed solution to a homogeneous reactor with a PTFE liner and react at 120°C for 12 hours. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60°C for 4 hours to obtain Bi2S3 nanospheres.

[0114] Step 2: Disperse the Bi2S3 nanospheres obtained in Step 1 in deionized water, add 0.2g of glucose and stir for 5h to obtain a suspension. Transfer the suspension to a homogeneous reactor with a PTFE liner and react at 150℃ for 12h. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then anneal at 500℃ for 1h under Ar atmosphere to obtain C@Bi2S3 nanospheres.

[0115] Step 3: Dissolve the C@Bi2S3 nanospheres obtained in Step 2 and 0.2g of boron nitride in deionized water. After stirring for 4h, a suspension is obtained. After washing and filtration by deposition, a black precipitate is obtained. The black precipitate is transferred to an oven and dried at 60℃ for 4h. Then, it is annealed at 500℃ for 1h under Ar atmosphere to obtain CN@Bi2S3 nanospheres.

[0116] Step 4: Disperse the CN@Bi2S3 nanospheres (0.306g) obtained in Step 3 in 750mL of deionized water and stir for 5h. Then, continuously add 0.15g of triaminemethane until the pH value is adjusted to 9.5. Add 0.034g of dopamine hydrochloride and stir overnight. After washing and filtration, a black precipitate is obtained. Filter with deionized water and alcohol to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then, anneal at 500℃ for 1h under Ar atmosphere to obtain CN-NC@Bi2S3 nanospheres.

[0117] The negative electrode is prepared as follows:

[0118] The CN-NC@Bi2S3 nanospheres prepared above were used as the negative electrode active material for lithium-ion batteries, carbon black as the conductive agent, sodium carboxymethyl cellulose as the binder, and deionized water as the solvent. The negative electrode active material, conductive agent, and binder were mixed uniformly at a mass ratio of 7:2:1 and stirred for 12 hours to form a homogeneous slurry. This slurry was then coated onto copper foil using a 16 μm doctor blade, dried in a vacuum drying oven at 80°C for 12 hours, and finally cut into 12 mm diameter discs.

[0119] Example 4

[0120] The preparation of a lithium-ion battery negative electrode includes the following steps:

[0121] The electrode material is prepared as follows:

[0122] Step 1: Dissolve Bi(NO3)3·5H2O and glutathione (GSH) in deionized water at a molar ratio of 2:3. Then, stir in a magnetic stirrer for 2 hours to obtain a mixed solution. Transfer the mixed solution to a homogeneous reactor with a PTFE liner and react at 120°C for 12 hours. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60°C for 4 hours to obtain Bi2S3 nanospheres.

[0123] Step 2: Disperse the Bi2S3 nanospheres obtained in Step 1 in deionized water, add 0.2g of glucose and stir for 5h to obtain a suspension. Transfer the suspension to a homogeneous reactor with a PTFE liner and react at 150℃ for 12h. After cooling to room temperature, wash and filter to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then anneal at 500℃ for 1h under Ar atmosphere to obtain C@Bi2S3 nanospheres.

[0124] Step 3: Dissolve the C@Bi2S3 nanospheres obtained in Step 2 and 0.2g of boron nitride in deionized water. After stirring for 4h, a suspension is obtained. After washing and filtration by deposition, a black precipitate is obtained. The black precipitate is transferred to an oven and dried at 60℃ for 4h. Then, it is annealed at 500℃ for 1h under Ar atmosphere to obtain CN@Bi2S3 nanospheres.

[0125] Step 4: Disperse the CN@Bi2S3 nanospheres (0.306g) obtained in Step 3 in 750mL of deionized water and stir for 5h. Then, continuously add 0.15g of triaminemethane until the pH value is adjusted to about 8.5. Then, add 0.034g of dopamine hydrochloride and stir overnight. After washing and filtration, a black precipitate is obtained. Filter with deionized water and alcohol to obtain a black precipitate. Transfer the black precipitate to an oven and dry at 60℃ for 4h. Then, anneal at 500℃ for 1h under Ar atmosphere to obtain CN-NC@Bi2S3 nanospheres.

[0126] The negative electrode is prepared as follows:

[0127] The CN-NC@Bi2S3 nanospheres prepared above were used as the negative electrode active material for lithium-ion batteries, carbon black as the conductive agent, sodium carboxymethyl cellulose as the binder, and deionized water as the solvent. The negative electrode active material, conductive agent, and binder were mixed uniformly at a mass ratio of 7:2:1 and stirred for 12 hours to form a homogeneous slurry. This slurry was then coated onto copper foil using a 16 μm doctor blade, dried in a vacuum drying oven at 80°C for 12 hours, and finally cut into 12 mm diameter discs.

[0128] Comparative Example 1

[0129] The preparation of a lithium-ion battery negative electrode includes the following steps:

[0130] The electrode material is prepared as follows:

[0131] Step 1: Dissolve 0.2425g of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) in 30mL of deionized water and stir rapidly for 1h to obtain solution A;

[0132] Step 2: Add 0.3073g of glutathione (GSH) to solution A, stir for 1 hour to obtain turbid solution B;

[0133] Step 3: Transfer the turbid liquid B to a homogeneous reactor with a 50 mL polytetrafluoroethylene liner and react at 120 °C for 12 h. After cooling to room temperature, filter with deionized water and alcohol to obtain a black precipitate. Place the black precipitate in an oven and keep it at 60 °C for 12 h to obtain Bi2S3 nanospheres.

[0134] The negative electrode is prepared as follows:

[0135] The Bi2S3 nanospheres prepared above were used as the negative electrode active material for lithium-ion batteries, carbon black as the conductive agent, sodium carboxymethyl cellulose as the binder, and deionized water as the solvent. The negative electrode active material, conductive agent, and binder were mixed uniformly at a mass ratio of 7:2:1 and stirred for 12 hours to form a homogeneous slurry. This slurry was then coated onto copper foil using a 16 μm doctor blade, dried in a vacuum drying oven at 80°C for 12 hours, and finally cut into 12 mm diameter discs.

[0136] Comparative Example 2

[0137] The preparation of a lithium-ion battery negative electrode includes the following steps:

[0138] The electrode material is prepared as follows:

[0139] Step 1: Dissolve 10 mmol of melamine in 30 mL of ethanol and stir for 30 min. Then add 3 mL of formaldehyde solution and stir for 1 h to obtain mixture A. Add 1 mmol of citric acid to solution A and stir for 1 h. Then transfer the mixture to a high-pressure reactor and place the high-pressure reactor in a blower dryer. React at 200 °C for 10 h. Wash the obtained product with water and ethanol and then place it in a vacuum drying oven and dry at 60 °C for 8 h to obtain powder sample B.

[0140] Step 2: Place the powder sample B obtained in Step 1 in a tube furnace and anneal it under an Ar atmosphere at a temperature of 750℃ and a heating rate of 5℃·min. -1 The annealing time is 2 hours, and the final NC material is obtained.

[0141] The negative electrode is prepared as follows:

[0142] The Bi2S3 nanospheres prepared above were used as the negative electrode active material for lithium-ion batteries, carbon black as the conductive agent, sodium carboxymethyl cellulose as the binder, and deionized water as the solvent. The negative electrode active material, conductive agent, and binder were mixed uniformly at a mass ratio of 7:2:1 and stirred for 12 hours to form a homogeneous slurry. This slurry was then coated onto copper foil using a 16 μm doctor blade, dried in a vacuum drying oven at 80°C for 12 hours, and finally cut into 12 mm diameter discs.

[0143] Application examples

[0144] In the lithium-ion battery, the negative electrode prepared in Examples 1-4 and Comparative Examples 1 and 2 is used as the working electrode, lithium metal foil as the counter electrode, a Whatman GF / A glass fiber filter as the separator, and the electrolyte is 1.0 mol L⁻¹. -1 LiPF6, the solution is ethylene carbonate-dimethyl carbonate (1:1 vol%), the assembly process is as follows: Figure 1 As shown. All batteries were assembled in a glove box. Electrochemical performance tests were performed after standing in a 25°C incubator for 6 hours.

[0145] Electrochemical performance testing methods

[0146] Using the LAND CT2001A battery tester system, the voltage was measured between 0.01 and 3.0V against Li / Li. + Constant current charge-discharge processes were performed at different voltage ranges and current densities. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were also recorded at ambient temperature (~25°C) using a CS2350H electrochemical workstation.

[0147] Performance testing experiment

[0148] X-ray diffraction tests were performed on the negative electrode materials of Example 1 and Comparative Example 1. The test results are as follows: Figure 2 As shown.

[0149] The diffraction peaks of Example 1 and Comparative Example 1 matched well with the standard comparison card (PDF#17-0320), indicating good crystallinity.

[0150] The negative electrode material prepared in Example 1 was subjected to scanning electron microscopy (SEM) testing, and the test results are as follows: Figure 3 As shown.

[0151] High-resolution XPS spectra of Bi 4f and S 2p of the sample are as follows: Figure 3 As shown in a, Bi 4f 7 / 2 and 4f 5 / 2 The peaks are located at approximately 159 eV and 164 eV, respectively. There are also two weak peaks at 158.61 and 159.88 eV, belonging to S... 2- matter S2p 3 / 2 and S2p 1 / 2 The presence of these elements indicates that sulfur atoms are bonded to bismuth. Figure 3 Figure b shows the presence of CC (283.30 eV), CN (284.87 eV), and C=O (287.20 eV)11,29. CC and CN may originate from the decomposition of dopamine hydrochloride. The high-resolution XPS spectrum of N 1s is shown below. Figure 3 As shown in Figure c, the N 1s peak consists of two main peaks. The peak at 395.6 eV belongs to pyridine nitrogen, while the peak at 397.5 eV belongs to graphitic nitrogen. The peaks at 402.8 eV and 404.3 eV belong to pyrrole nitrogen and N-oxide, respectively. The presence of these four nitrogen types indicates that nitrogen atoms were successfully doped into the amorphous carbon layer during carbonization. The results show that the main nitrogen types are highly reactive pyridine nitrogen and N-oxide with high electronic conductivity. The abundant nitrogen in the amorphous carbon layer provides more lithium reaction sites and enhances the adsorption capacity of polysulfides due to increased polarity, playing an important role in improving electrode kinetics and maintaining structural integrity.

[0152] The negative electrode material prepared in Example 1 was subjected to scanning electron microscopy (SEM) testing, and the test results are as follows: Figure 4 As shown.

[0153] The morphology of the negative electrode material is nanospheres, and the thickness of the CN-CN layer is about 20 nm.

[0154] The constant current charge-discharge performance of the negative electrode materials prepared in Example 1 and Comparative Example 1 was tested, and the test results are as follows: Figure 5 , Figure 6 , Figure 7 As shown.

[0155] from Figure 5It can be seen that the anode material prepared in Example 1 achieved a first-cycle discharge specific capacity of 753 mAh g. -1 The charge-discharge curves from the 100th to the 200th cycle almost overlap, indicating that the negative electrode material has good cycle stability; when cycled to the 200th cycle, the coulombic efficiency is 99.46%, which indicates that the energy loss is small.

[0156] from Figure 6 It can be seen that the first-cycle discharge specific capacity of the negative electrode material prepared in Comparative Example 1 is 830.8 mAh g. -1 As charging and discharging proceed, the discharge specific capacity continues to decrease, resulting in poor stability. The coulombic efficiency after the 100th cycle is 97.03%, and the energy loss is higher than that of the negative electrode material prepared in Example 1.

[0157] like Figure 7 As shown, the reversible specific capacity of the anode material prepared in Comparative Example 1 eventually stabilized at 343.9 mAh g⁻¹. -1 The reversible specific capacity of the negative electrode material prepared in Example 1 eventually stabilized at 636.1 mAh g. -1 Compared with the negative electrode material of Comparative Example 1, the negative electrode material prepared in Example 1 showed a significant improvement in cycle stability and a marked improvement in final electrochemical performance.

[0158] Rate performance tests were conducted on the negative electrode materials prepared in Example 1 and Comparative Example 1, such as... Figure 8 As shown, Comparative Example 1 exhibits poor rate performance. Its structure is damaged after charging and discharging at high current densities, and its performance cannot be recovered even after returning to low current density discharge. This indicates that due to its limited conductivity and drastic volume changes during the lithiation / degradation reaction, it cannot withstand rapid discharge / charge rates. In contrast, Example 1 exhibits capacities of 643.9 mAh g at current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, and 1 A / g. -1 536.1mAh g -1 454.7mAh g -1 and 345.3mAh g -1 When the current density recovers to 0.1 A / g, the reversible capacity of the negative electrode material gradually recovers to 576.3 mAh g-1. This indicates that even during rapid lithiation / degradation, the negative electrode material remains tightly fixed on the electrode, exhibiting good rate performance. After high-rate charging and discharging, when the charge and discharge rate is changed back to low-rate, the battery performance remains basically unchanged and can recover to the performance at the first charge and discharge rate.

[0159] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. An electrode material, characterized in that, The electrode material includes bismuth sulfide, a carbon layer coated on the surface of the bismuth sulfide, a nitrogen layer coated on the surface of the carbon layer, and a nitrogen-carbon layer coated on the surface of the nitrogen layer.

2. The electrode material according to claim 1, characterized in that, The bismuth sulfide has a spherical morphology and a diameter of 1-2 μm.

3. The electrode material according to claim 1, characterized in that, The thickness of the carbon layer is 5-10 nm.

4. The electrode material according to claim 1, characterized in that, The thickness of the nitrogen layer is 5-10 nm.

5. The electrode material according to claim 1, characterized in that, The thickness of the nitrogen-carbon layer is 10-20 nm.

6. The electrode material according to claim 1, characterized in that, In the nitrogen-carbon layer, the mass ratio of nitrogen to carbon is 0.

2.

7. A method for preparing an electrode material, characterized in that, The preparation method includes the following steps: Preparation of bismuth sulfide; The bismuth sulfide and carbon source are dissolved in a first solvent, and then subjected to hydrothermal treatment and a first annealing treatment in sequence, so that carbon is coated on the surface of the bismuth sulfide, denoted as C@Bi2S3; The C@Bi2S3 and a nitrogen source are dissolved in a second solvent, and a first deposition process and a second annealing process are performed sequentially to coat the surface of the C@Bi2S3 with nitrogen, which is denoted as CN@Bi2S3. The CN@Bi2S3 was dissolved in a third solvent, and the pH was adjusted to 7.5-9.

5. Then, a nitrogen-carbon source was added, and a second deposition treatment and a third annealing treatment were performed in sequence to coat the CN@Bi2S3 surface with nitrogen and carbon, thus obtaining the electrode material, denoted as CN-NC@Bi2S3.

8. The method for preparing the electrode material according to claim 7, characterized in that, The carbon source is selected from one or more of glucose, sodium acetate, and methanol; The nitrogen source is selected from one or more of urea, boron nitride, and cyanide; The nitrogen and carbon source is selected from one or more of melamine, ethylenediamine, and dopamine hydrochloride; The first solvent, the second solvent, and the third solvent are each independently selected from deionized water or ethanol.

9. The method for preparing the electrode material according to claim 7, characterized in that, The hydrothermal treatment temperature is 120-150℃, and the hydrothermal treatment time is 10-12h; The temperature of the first annealing treatment is 400-500℃, and the time of the first annealing treatment is 1-5h; The temperature of the second annealing treatment is 400-500℃, and the time of the second annealing treatment is 1-5h; The temperature of the third annealing treatment is 400-500℃, and the time of the third annealing treatment is 1-5h; The methods for the first deposition treatment and the second deposition treatment are each independently selected from one of spin coating, dipping, and spraying.

10. A lithium-ion battery, the lithium-ion battery comprising a negative electrode material, characterized in that, The negative electrode material includes the electrode material according to any one of claims 1-6 or the electrode material prepared by the preparation method according to any one of claims 7-9.

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