A tin disulfide-doped silicon-carbon negative electrode material, a preparation method and application thereof

Abstract

The application discloses a tin disulfide doped silicon-carbon negative electrode material and a preparation method and application thereof. The silicon-carbon negative electrode material comprises tubular carbon material and tin disulfide, the tin disulfide is located on the surface of the tubular carbon material, and each of the tubular carbon material contains at least one nanosilicon. The silicon-carbon negative electrode material in the application contains tin disulfide, and the specific capacity and rate performance of the silicon-carbon negative electrode material can be improved; the silicon and carbon material can inhibit the volume expansion of the tin disulfide, and the silicon, carbon material and tin disulfide show good compatibility. Therefore, the tin disulfide doped silicon-carbon negative electrode material has excellent specific capacity and rate performance, and when the material is applied to a battery, the battery has good specific capacity, rate performance and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a tin disulfide-doped silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] Silicon-based materials have the potential to replace graphite as the next-generation anode material for lithium-ion batteries due to their high theoretical specific capacity (4200 mAh / g), suitable discharge voltage, and abundant reserves. However, silicon-based materials undergo significant volume expansion during cyclic charge-discharge cycles, leading to cracking and pulverization of the anode structure. Therefore, to compensate for the shortcomings of silicon-based materials, combining nano-silicon with various carbon materials to form silicon-carbon composites is a feasible approach, as carbon materials can improve the conductivity of the composite and provide a buffer for the volume expansion of silicon. However, due to the relatively low theoretical specific capacity of carbon materials, their contribution to the overall specific capacity of silicon-carbon composites is small. Consequently, conventional silicon-carbon composites have relatively low specific capacities. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a tin disulfide-doped silicon-carbon anode material with high specific capacity.

[0004] This invention also proposes a method for preparing tin disulfide-doped silicon-carbon anode material.

[0005] The present invention also proposes a negative electrode.

[0006] The present invention also proposes a secondary battery.

[0007] In a first aspect, the present invention provides a tin disulfide-doped silicon-carbon anode material comprising a tubular carbon material and tin disulfide, wherein the tin disulfide is located on the surface of the tubular carbon material, and each of the tubular carbon materials contains at least one nano-silicon.

[0008] The tin disulfide-doped silicon-carbon anode material according to embodiments of the present invention has at least the following beneficial effects:

[0009] Tin disulfide has a layered structure similar to graphite, but its theoretical specific capacity (1231 mAh / g) is higher than that of graphite. Furthermore, due to its wider interlayer spacing, it facilitates rapid lithium-ion and electron transfer, thus exhibiting excellent rate performance. In this invention, the silicon-carbon anode material contains tin disulfide, which improves its specific capacity and rate performance. Meanwhile, nano-silicon and carbon materials suppress the volume expansion of tin disulfide, and the nano-silicon and carbon materials exhibit good compatibility with tin disulfide. Therefore, the silicon-carbon anode material of this invention possesses excellent specific capacity and rate performance. When applied to batteries, it results in batteries with good specific capacity, rate performance, and cycle stability.

[0010] In some embodiments of the present invention, the tin disulfide is in the form of nanosheets.

[0011] In some preferred embodiments of the present invention, the surface of the carbon material is provided with a plurality of tin disulfide nanosheets, some or all of which have one end connected to the surface of the carbon material and the other end away from the carbon material.

[0012] In the above embodiments, a plurality of tin disulfide nanosheets are disposed on the surface of the carbon material. Tin disulfide can improve the overall specific capacity of the silicon-carbon anode material. When the silicon-carbon anode material is applied to a battery, the tin disulfide nanosheets disposed on the surface of the carbon material can promote the rapid transfer of lithium ions and electrons, thereby improving the overall rate performance of the silicon-carbon anode material. When silicon nanoparticles undergo volume changes during lithiation and delithiation, the in-situ growth of tin disulfide nanosheets on the surface of the carbon material can assist in the radial stress dispersion, thereby maintaining the structural stability of the silicon-carbon anode material.

[0013] In some embodiments of the present invention, the tin disulfide nanosheets are grown in situ on the surface of the carbon material.

[0014] In some embodiments of the present invention, the wall thickness of the tubular carbon material is 20-80 nm.

[0015] In some embodiments of the present invention, the average particle size of the nano-silicon is 60-100 nm.

[0016] In some embodiments of the present invention, the silicon-carbon anode material is a fibrous material, and the fiber diameter of the silicon-carbon anode material is 250-400 nm.

[0017] In some preferred embodiments of the present invention, the tubular carbon material is a carbon nanofiber material.

[0018] Typically, during the initial discharge of a lithium-ion battery, thermodynamic instability exists between the electrode material and the organic electrolyte. The electrolyte undergoes a reduction reaction on the negative electrode surface, and the reduction products deposit on the surface, forming a passivation film called the solid electrolyte layer (SEI). The SEI is an ionic conductor and an electronic insulator, allowing lithium ions to pass through while hindering electron passage. It is also insoluble in the electrolyte solvent, preventing solvent molecules from co-intercalating and avoiding direct contact between the electrode and the electrolyte, thus effectively inhibiting further decomposition of the electrolyte.

[0019] Through the above embodiments, in this invention, the tubular carbon nanofiber material encapsulates multiple nano-silicon particles in its inner cavity. When the silicon-carbon anode material is applied to a battery, a solid electrolyte layer is formed on the surface of the carbon nanofiber material, rather than on the surface of a single nano-silicon particle. This limits the number of solid electrolyte layers while avoiding the loss of raw materials. Moreover, the carbon nanofiber material has a one-dimensional ultrafast conductive path, which is beneficial to improving the overall electrochemical performance of the silicon-carbon anode material.

[0020] In some preferred embodiments of the present invention, multiple nano-silicon particles within a tubular carbon material are movable relative to each other, and there is a gap between the inner wall of the tubular carbon material and the nano-silicon particles.

[0021] In some more preferred embodiments of the present invention, the gap between the inner wall of the tubular carbon material and the nano-silicon is 80-200 nm; the gap between the nano-silicon particles is 1-300 nm.

[0022] In a second aspect, the present invention provides a method for preparing a tin disulfide-doped silicon-carbon anode material, comprising the following steps:

[0023] S1, nano-silicon is taken and coated with a sacrificial layer material to obtain sacrificial layer coated nano-silicon, which is intermediate I; wherein, the sacrificial layer material includes metal carbonate;

[0024] S2, Intermediate I is mixed with a carbon source material, and then electrospun and carbonized to obtain a composite material in which a carbon material layer coats Intermediate I, which is Intermediate II; wherein, the carbon source material includes a polymer carbon source;

[0025] S3, after removing the sacrificial layer, a composite material with carbon material layer coated with nano-silicon is obtained, which is intermediate III;

[0026] S4, intermediate III is mixed with sulfur source material and tin tetrachloride, and reacted to obtain the silicon-carbon anode material.

[0027] In some embodiments of the present invention, in step S1, the metal carbonate includes at least one of barium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, or lead carbonate.

[0028] In some embodiments of the present invention, in step S1, the metal carbonate is barium carbonate.

[0029] Barium carbonate has a decomposition temperature as high as 1450℃, while the decomposition temperatures of other carbonates are generally below 800℃. The preparation of silicon-carbon anode materials requires high-temperature carbonization (generally below 1000℃). When the carbonization temperature is higher than the decomposition temperature, the carbonate will decompose into the corresponding metal oxides and carbon dioxide. For example, zinc carbonate begins to decompose at 90℃ and can be completely decomposed within 1 hour at 350℃. The continuous generation and accumulation of carbon dioxide within the coating structure will cause an increase in pressure, thereby damaging the coating layer.

[0030] This invention uses barium carbonate as a template to create the void space around silicon particles. Barium carbonate has a higher decomposition temperature than other carbonates and can maintain its own stability during high-temperature carbonization, thereby keeping the carbon nanofiber structure stable. Compared with organic templates (such as surfactants), after the removal of barium carbonate, no structural carbon material remains between the silicon particle surface and the carbon material layer wall. Therefore, when the silicon particles undergo volume changes during lithiation and delithiation, no additional stress is generated on the carbon material layer wall, which is beneficial to maintaining the overall structural stability of the silicon-carbon anode material.

[0031] In some embodiments of the present invention, step S1 specifically includes the following steps: mixing sodium carbonate aqueous solution with nano-silicon, then mixing with barium chloride aqueous solution to obtain a mixture, and separating it to obtain intermediate I;

[0032] Alternatively, barium chloride aqueous solution is mixed with nano-silicon, and then mixed with sodium carbonate aqueous solution to obtain a mixture, which is then separated to obtain intermediate I.

[0033] In the process of coating silicon materials with the sacrificial layer, especially in the preparation of carbonates, this invention does not limit the order of solution mixing. For example, silicon can be added to barium chloride solution first, and then sodium carbonate solution can be added to obtain barium carbonate-coated silicon nanoparticles, or silicon can be added to sodium carbonate solution first, and then barium chloride solution can be added to obtain barium carbonate-coated silicon nanoparticles, etc. The preparation steps of this invention are flexible and have stronger industrial application capabilities.

[0034] In some preferred embodiments of the present invention, in step S1, the molar ratio between sodium carbonate, barium chloride, and nano-silicon is controlled at (0.8-1.2):(0.8-1.2):(0.1-0.5).

[0035] In some more preferred embodiments of the present invention, in step S1, the concentration of sodium carbonate in the sodium carbonate aqueous solution is 0.1-1.0 mol / L; and the concentration of barium chloride in the barium chloride aqueous solution is 0.1-1.0 mol / L.

[0036] In some more preferred embodiments of the present invention, in step S1, the molar ratio of sodium carbonate to nano-silicon is (0.8-1.2):(0.1-0.5); in the step of mixing barium chloride aqueous solution with nano-silicon, the molar ratio of barium chloride to nano-silicon is (0.8-1.2):(0.1-0.5).

[0037] In some more preferred embodiments of the present invention, in step S1, the molar ratio of sodium carbonate to barium chloride is (0.8-1.2):(0.8-1.2).

[0038] In some preferred embodiments of the present invention, in step S1, nano-silicon is dispersed in an aqueous sodium carbonate solution to obtain dispersion I, and then dispersion I is added dropwise to an aqueous barium chloride solution to obtain a mixture;

[0039] Alternatively, nano-silicon can be dispersed in an aqueous barium chloride solution to obtain dispersion II, and then dispersion II can be added dropwise to an aqueous sodium carbonate solution to obtain a mixture;

[0040] In some more preferred embodiments of the present invention, in step S1, after the mixture is filtered, a crude product of intermediate I is obtained, which is then washed with water and dried to obtain intermediate I.

[0041] In some more preferred embodiments of the present invention, in step S1, dispersion I is added dropwise to a barium chloride aqueous solution, and dispersion II is added dropwise to a sodium carbonate aqueous solution, and the dropwise addition method is preferably to add while stirring.

[0042] In some embodiments of the present invention, in step S2, the polymer carbon source includes at least one of polyacrylonitrile (PAN) or polyvinylpyrrolidone (PVP).

[0043] In some embodiments of the present invention, step S2 specifically includes the following steps:

[0044] S2-1, intermediate I, polymer carbon source and organic solvent containing N,N-dimethylformamide are mixed to obtain mixture A, which is stirred at temperature T1 to obtain spinning precursor;

[0045] S2-2, the spinning precursor is electrospun to obtain nanofibers, and the nanofibers are carbonized to obtain intermediate II.

[0046] In some preferred embodiments of the present invention, in step S2-1, the content of intermediate I in mixture A is 20-100 g / L.

[0047] In some preferred embodiments of the present invention, in step S2-1, the mass ratio of the polymer carbon source to intermediate I is (1-20):1.

[0048] In some preferred embodiments of the present invention, in step S2-1, the organic solvent includes N,N-dimethylformamide and solvent I, wherein the volume ratio of N,N-dimethylformamide to solvent I is (1-5):1. Preferably, solvent I includes at least one of ethanol, acetone, tetrahydrofuran, isopropanol, or methylpyrrolidone.

[0049] In some preferred embodiments of the present invention, in step S2-1, the mixture A is stirred at a temperature of 50-80°C for 12-24 hours to obtain a spinning precursor. Preferably, the stirring method is magnetic stirring.

[0050] In some preferred embodiments of the present invention, in step S2-2, the spinning precursor is loaded into a syringe for electrospinning, wherein the voltage range is 15-25kV, the jet flow rate is 0.2-1.0mL / min, and nanofibers are collected at a distance of 12-18cm from the syringe needle. Preferably, aluminum foil is used to collect the nanofibers at a distance of 15cm from the needle.

[0051] In some more preferred embodiments of the present invention, in step S2-2, the nanofibers are dried and then carbonized.

[0052] In some preferred embodiments of the present invention, in step S2-2, the nanofibers are carbonized under an inert atmosphere. Preferably, the inert atmosphere includes at least one of nitrogen or argon.

[0053] In some more preferred embodiments of the present invention, in step S2-2, the carbonization temperature is 500-800℃, the carbonization time is 2-5h, and the heating rate is 1-10℃ / min.

[0054] In some more preferred embodiments of the present invention, the carbonization step of the nanofibers in step S2-2 specifically includes the following operations: the nanofibers are heated to 500-800°C in a tube furnace at a rate of 1-10°C / min and carbonized for 2-5 hours to obtain intermediate II.

[0055] In some embodiments of the present invention, in step S3, an acidic substance is used to remove the sacrificial layer.

[0056] This invention uses inorganic metal carbonates (such as barium carbonate) as templates. After acid washing, no substances remain on the surface of the nano-silicon particles. Therefore, it can ensure that there is sufficient volume space around the silicon particles to accommodate the volume change of silicon, which is beneficial to the long-term stability of silicon-carbon anode materials under working conditions.

[0057] In some embodiments of the present invention, in step S3, intermediate II is washed with hydrochloric acid to remove the sacrificial layer, yielding intermediate III. Preferably, the concentration of hydrogen chloride in the hydrochloric acid is 1-5 mol / L.

[0058] In some embodiments of the present invention, step S3 specifically includes the following steps: washing the precursor C with hydrochloric acid 3-5 times, and then washing it with deionized water 3-5 times to remove the sacrificial layer.

[0059] In some embodiments of the present invention, in step S4, the sulfur source material includes at least one of l-cysteine, thioacetamide (TAA), or thiourea.

[0060] In some embodiments of the present invention, in step S4, a mixture B containing intermediate III, sulfur source material and tin tetrachloride is taken and heated to react, thereby obtaining the silicon-carbon anode material.

[0061] In some preferred embodiments of the present invention, in step S4, the heating temperature is 150-300°C and the heating time is 12-24 hours.

[0062] In some preferred embodiments of the present invention, in step S4, mixture B is taken, heated to react, separated, washed, and vacuum dried to obtain the silicon-carbon anode material.

[0063] In some more preferred embodiments of the present invention, in step S4, the vacuum drying temperature is 60-100°C and the time is 8-24 hours.

[0064] In some embodiments of the present invention, step S4 specifically includes the following operations: intermediate III, sulfur source material, tin tetrachloride pentahydrate (SnCl4·5H2O), and deionized water are mixed in a mass ratio of (600-1200):(2-5):1:(200-500) to obtain mixture B. Mixture B is placed in a reactor and reacted at 150-300°C for 12-24 hours. The solid is separated, washed, and dried at 60-100°C for 8-24 hours to obtain the silicon-carbon anode material.

[0065] In some preferred embodiments of the present invention, in step S4, the separated solid is washed with ethanol and then washed with water.

[0066] In a third aspect, the present invention provides a negative electrode comprising the aforementioned tin disulfide-doped silicon-carbon negative electrode material.

[0067] In a fourth aspect, the present invention provides a secondary battery comprising the aforementioned negative electrode.

[0068] In some embodiments of the present invention, the secondary battery includes at least one of a lithium-ion battery or a sodium-ion battery.

[0069] The beneficial effects of this invention include:

[0070] (1) In this invention, barium carbonate is used as a template to create the void space around the silicon particles. Barium carbonate has a higher decomposition temperature than other carbonates and can maintain its own stability during high-temperature carbonization, thereby keeping the structure of the carbon nanofiber material stable. Compared with the more common silicon dioxide template, the removal of barium carbonate in this invention only requires hydrochloric acid instead of the highly corrosive hydrofluoric acid, which is environmentally friendly and pollution-free. Compared with organic templates, such as surfactants, the removal of barium carbonate will not leave any structural carbon substances between the surface of the silicon particles and the wall of the carbon nanofiber material. Therefore, when the volume of the silicon particles changes during the lithiation and delithiation process, no additional stress will be generated on the wall of the carbon nanofiber material, which is beneficial to maintaining the overall structural stability of the silicon-carbon anode material.

[0071] (2) The silicon-carbon anode material described in this invention contains tin disulfide, which can improve the overall specific capacity of the silicon-carbon anode material. Furthermore, due to the characteristic that the tin disulfide nanosheets are located on the surface of the carbon material, it can also promote the rapid transfer of lithium ions and electrons, thereby improving the overall rate performance of the silicon-carbon anode material. When the silicon nanoparticles undergo volume changes during the lithiation and delithiation process, the in-situ growth of tin disulfide nanosheets on the surface of the carbon material can assist in the radial stress dispersion, thereby ensuring the structural stability of the silicon-carbon anode material.

[0072] (3) Carbon nanofiber material (tubular carbon material) encapsulates multiple nano-silicon particles. When the silicon-carbon anode material is applied to lithium-ion batteries, the solid electrolyte layer inside the battery can be generated on the surface of the carbon nanofiber material, rather than on the surface of a single nano-silicon particle. This limits the number of solid electrolyte layers and avoids the loss of raw materials. Moreover, carbon nanofiber material has a one-dimensional ultrafast conductive path, which is beneficial to the improvement of the overall electrochemical performance of silicon-carbon anode material.

[0073] (4) The method for preparing tin disulfide-doped silicon-carbon anode material proposed in this invention uses inexpensive raw materials, has a simple preparation process, is environmentally friendly and pollution-free, and is suitable for large-scale industrial production and application. Attached Figure Description

[0074] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0075] Figure 1 This is a schematic diagram of the structure of the tin disulfide-doped silicon-carbon anode material in Example 1 of the present invention;

[0076] Figure 2 This is a graph showing the rate performance test results of the button cell in Embodiment 1 of the present invention;

[0077] Figure 3 The graph shows the cycle stability test results of the button battery in Embodiment 1 of the present invention. Detailed Implementation

[0078] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0079] Unless otherwise specified, the experimental methods described in the following examples are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used are all commercially available from the conventional market unless otherwise specified.

[0080] The nano-silicon used was purchased from Shanghai Naio Nanotechnology Co., Ltd., item number: NO-E-003-2.

[0081] Example 1

[0082] This embodiment discloses a tin disulfide-doped silicon-carbon anode material, the structural schematic of which is shown below. Figure 1 As shown, its preparation process includes:

[0083] (I) Sodium carbonate and barium chloride were dissolved in deionized water at a molar ratio of 1:1 to prepare sodium carbonate solution and barium chloride solution with a concentration of 0.1 mol / L, respectively. Then, the nano-silicon was uniformly dispersed in the barium chloride solution at a molar ratio of 0.1:1 to obtain a suspension. The suspension was added dropwise to the sodium carbonate solution while stirring. After filtration, washing with deionized water and drying, precursor A of barium carbonate coated nano-silicon was obtained.

[0084] (II) Polyacrylonitrile and precursor A are added to an organic liquid (the organic liquid is a mixture of N,N-dimethylformamide and ethanol in a volume ratio of 2:1) at a mass ratio of 5:1 to obtain a mixture. The content of precursor A in the mixture is 20 g / L. The mixture is magnetically stirred at 50°C for 24 h to obtain spinning precursor B.

[0085] (III) Precursor B was loaded into a 5 mL syringe and electrospun. The voltage was controlled at 15 kV and the jet flow rate was 0.2 mL / min. The nanofibers were collected using aluminum foil at a distance of 15 cm from the needle. After drying, the nanofibers were transferred to a tube furnace and carbonized in an inert gas atmosphere (nitrogen or argon) at a temperature of 2 °C / min to 500 °C for 2 h to obtain composite precursor C consisting of carbon nanofibers coating precursor A.

[0086] (IV) The precursor C was washed with hydrochloric acid solution and deionized water (washed 3 times with 1 mol / L hydrochloric acid solution and then 3 times with deionized water) to remove the barium carbonate template coated on the surface of the nano-silicon. After drying, the precursor D of carbon nanofiber coated with nano-silicon with a structure similar to egg yolk shell was obtained (where the nano-silicon has certain gaps around it).

[0087] (V) The precursor D, l-cysteine ​​(sulfur source reagent), tin tetrachloride pentahydrate and deionized water were stirred and mixed evenly in a mass ratio of 600:3:1:400. The resulting suspension was then transferred to a polytetrafluoroethylene-lined reactor and reacted at 150°C for 18 hours. After the reaction, the black powder was collected by centrifugation, washed three times with ethanol, then washed three times with deionized water, and then dried in a vacuum drying oven at 80°C for 12 hours to obtain silicon-carbon anode material.

[0088] This embodiment also provides a negative electrode, comprising the tin disulfide-doped silicon-carbon negative electrode material prepared in this embodiment. The preparation process of the negative electrode includes: mixing the silicon-carbon negative electrode material with conductive carbon black (SP) and binder (PVDF, molecular weight 500,000) in a mass ratio of 8:1:1 to form a slurry, coating it onto a copper foil to obtain a coating layer, drying it in a vacuum drying oven at 80°C for 12 hours, and finally cutting it into 10mm diameter circular pieces and weighing them for later use. The copper foil thickness in the negative electrode is 10μm, and the coating layer thickness is approximately 80μm. The solvent used to prepare the slurry is N-methylpyrrolidone (NMP), with 1g of electrode active material (silicon-carbon negative electrode material + conductive carbon black + binder) added to 5mL of NMP solvent.

[0089] This embodiment also provides a lithium-ion battery, including the negative electrode described in this embodiment; furthermore, in this embodiment:

[0090] Positive electrode: Lithium foil, 50μm thick;

[0091] Electrolyte: It is prepared by mixing LiPF6 and a mixed solvent. The concentration of LiPF6 in the electrolyte is 1 mol / L. The mixed solvent is prepared by mixing ethylene carbonate, diethyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1.

[0092] Separator: Polypropylene membrane; the polypropylene membrane was purchased from Elite Battery Technology Co., Ltd., model Celgard2400; other separators obtained from conventional markets or other commercial channels may also be used.

[0093] The battery manufacturing process includes assembling the positive electrode, negative electrode, electrolyte, and separator into a CR2025 button cell in an argon-filled glove box.

[0094] Example 2

[0095] This embodiment discloses a tin disulfide-doped silicon-carbon anode material, the preparation process of which includes:

[0096] (I) Sodium carbonate and barium chloride were dissolved in deionized water at a molar ratio of 1:1 to prepare sodium carbonate solution and barium chloride solution with a concentration of 0.3 mol / L, respectively. Then, the nano-silicon was uniformly dispersed in the barium chloride solution at a molar ratio of 0.2:1 to obtain a suspension. The suspension was added dropwise to the sodium carbonate solution while stirring. After filtration, washing with deionized water and drying, precursor A of barium carbonate coated nano-silicon was obtained.

[0097] (II) Polyacrylonitrile and precursor A are added to an organic liquid (the organic liquid is a mixture of N,N-dimethylformamide and ethanol in a volume ratio of 3:1) at a mass ratio of 10:1 to obtain a mixture with the content of precursor A in the mixture being 50 g / L. The mixture is then magnetically stirred at 70°C for 18 h to obtain spinning precursor B.

[0098] (III) Precursor B was loaded into a 5 mL syringe for electrospinning. The voltage was controlled at 20 kV and the jet flow rate was 0.4 mL / min. The nanofibers were collected using aluminum foil at a distance of 15 cm from the needle. After drying, the nanofibers were transferred to a tube furnace and carbonized in an inert gas atmosphere (nitrogen or argon) at a temperature of 10 °C / min to 700 °C for 5 h to obtain composite precursor C consisting of carbon nanofibers coating precursor A.

[0099] (IV) The precursor C was washed with hydrochloric acid solution and deionized water (washed 5 times with 3 mol / L hydrochloric acid solution and then 5 times with deionized water) to remove the barium carbonate template coated on the surface of the nano-silicon. After drying, the precursor D of carbon nanofiber coated with nano-silicon with a structure similar to egg yolk shell was obtained (where the nano-silicon has a certain gap around it).

[0100] (V) The precursor D, l-cysteine ​​(sulfur source reagent), tin tetrachloride pentahydrate and deionized water were mixed evenly at a mass ratio of 800:5:1:500. The resulting suspension was then transferred to a polytetrafluoroethylene-lined reactor and reacted at 180°C for 24 hours. After the reaction, the black powder was collected by centrifugation, washed three times with ethanol, then washed three times with deionized water, and then dried in a vacuum drying oven at 60°C for 24 hours to obtain tin disulfide-doped silicon-carbon anode material.

[0101] This embodiment also provides a negative electrode, including the tin disulfide-doped silicon-carbon negative electrode material prepared in this embodiment. The preparation steps and other components of the negative electrode are the same as in Example 1.

[0102] This embodiment also provides a lithium-ion battery, including the negative electrode described in this embodiment. The battery preparation steps and other components are the same as in Embodiment 1.

[0103] Example 3

[0104] This embodiment discloses a tin disulfide-doped silicon-carbon anode material, the preparation process of which includes:

[0105] (I) Sodium carbonate and barium chloride were dissolved in deionized water at a molar ratio of 1:1 to prepare sodium carbonate solution and barium chloride solution with a concentration of 1.0 mol / L, respectively. Then, the nano-silicon was uniformly dispersed in the sodium carbonate solution at a molar ratio of nano-silicon to solute (sodium carbonate) of 0.3:1 to obtain a suspension. The suspension was added dropwise to the barium chloride solution while stirring. After filtration, washing with deionized water and drying, precursor A of barium carbonate coated nano-silicon was obtained.

[0106] (II) Polyacrylonitrile and precursor A are added to an organic liquid (the organic liquid is a mixture of N,N-dimethylformamide and ethanol in a 5:1 mass ratio) at a mass ratio of 20:1 to obtain a mixture with the content of precursor A in the mixture being 80 g / L. The mixture is then magnetically stirred at 80°C for 14 h to obtain spinning precursor B.

[0107] (III) Precursor B was loaded into a 5 mL syringe for electrospinning. The voltage was controlled at 25 kV and the jet flow rate was 1.0 mL / min. The nanofibers were collected using aluminum foil at a distance of 15 cm from the needle tip. After drying, the nanofibers were transferred to a tube furnace and carbonized in an inert gas atmosphere (nitrogen or argon) at a rate of 8 °C / min to 800 °C for 3 h to obtain composite precursor C consisting of carbon nanofibers coating precursor A.

[0108] (IV) The precursor C was washed with hydrochloric acid solution and deionized water (washed 4 times with 5 mol / L hydrochloric acid solution and then 4 times with deionized water) to remove the barium carbonate template coated on the surface of the nano-silicon. After drying, the precursor D of carbon nanofiber coated with nano-silicon with a structure similar to egg yolk shell was obtained (where the nano-silicon has certain gaps around it).

[0109] (V) The precursor D, l-cysteine ​​(sulfur source reagent), tin tetrachloride pentahydrate and deionized water were stirred and mixed evenly in a mass ratio of 1000:5:1:400. The resulting suspension was then transferred to a polytetrafluoroethylene-lined reactor and reacted at 300°C for 18 hours. After the reaction, the black powder was collected by centrifugation, washed three times with ethanol, then washed three times with deionized water, and then dried in a vacuum drying oven at 70°C for 8 hours to obtain tin disulfide-doped silicon-carbon anode material.

[0110] This embodiment also provides a negative electrode, including the tin disulfide-doped silicon-carbon negative electrode material prepared in this embodiment. The preparation steps and other components of the negative electrode are the same as in Example 1.

[0111] This embodiment also provides a lithium-ion battery, including the negative electrode described in this embodiment. The battery preparation steps and other components are the same as in Embodiment 1.

[0112] Example 4

[0113] This embodiment discloses a tin disulfide-doped silicon-carbon anode material, the preparation process of which includes:

[0114] (I) Sodium carbonate and barium chloride were dissolved in deionized water at a molar ratio of 1:1 to prepare sodium carbonate solution and barium chloride solution with a concentration of 0.6 mol / L, respectively. Then, nano-silicon was uniformly dispersed in sodium carbonate solution at a molar ratio of 0.5:1 to solute (sodium carbonate) to obtain suspension. The suspension was added dropwise to barium chloride solution while stirring. After filtration, washing with deionized water and drying, precursor A of barium carbonate coated nano-silicon was obtained.

[0115] (II) Polyacrylonitrile and precursor A are added to an organic liquid (the organic liquid is a mixture of N,N-dimethylformamide and ethanol in a 5:1 ratio) at a mass ratio of 1:1 to obtain a mixture with the content of precursor A in the mixture being 100 g / L. The mixture is then magnetically stirred at 60°C for 20 h to obtain spinning precursor B.

[0116] (III) Precursor B was loaded into a 5 mL syringe and electrospun. The voltage was controlled at 15 kV and the jet flow rate was 0.8 mL / min. The nanofibers were collected using aluminum foil at a distance of 15 cm from the needle. After drying, the nanofibers were transferred to a tube furnace and carbonized in an inert gas atmosphere (nitrogen or argon) at a temperature of 5 °C / min to 600 °C for 3.5 h to obtain composite precursor C consisting of carbon nanofibers coating precursor A.

[0117] (IV) The precursor C was washed with hydrochloric acid solution and deionized water (washed 4 times with 2 mol / L hydrochloric acid solution and then 4 times with deionized water) to remove the barium carbonate template coated on the surface of the nano-silicon. After drying, the precursor D of carbon nanofiber coated with nano-silicon with a structure similar to egg yolk shell was obtained (where the nano-silicon has certain gaps around it).

[0118] (V) The precursor D, l-cysteine ​​(sulfur source reagent), tin tetrachloride pentahydrate and deionized water were stirred and mixed evenly in a mass ratio of 1200:4:1:200. The resulting suspension was then transferred to a polytetrafluoroethylene-lined reactor and reacted at 250°C for 14 hours. After the reaction, the black powder was collected by centrifugation, washed three times with ethanol, then washed three times with deionized water, and then dried in a vacuum drying oven at 100°C for 18 hours to obtain tin disulfide-doped silicon-carbon anode material.

[0119] This embodiment also provides a negative electrode, including the tin disulfide-doped silicon-carbon negative electrode material prepared in this embodiment. The preparation steps and other components of the negative electrode are the same as in Example 1.

[0120] This embodiment also provides a lithium-ion battery, including the negative electrode described in this embodiment. The battery preparation steps and other components are the same as in Embodiment 1.

[0121] In some other embodiments of the present invention, the sulfur source reagent may be selected from at least one of l-cysteine, thioacetamide or thiourea.

[0122] The tin disulfide-doped silicon-carbon anode materials prepared in Examples 1-4 are fibrous materials with a fiber diameter of 250-400 nm. The silicon-carbon anode material consists of, from the inside out, multiple nano-silicon particles, a tubular carbon material (a nanofiber material) encapsulating the multiple nano-silicon particles, and a tin disulfide nanosheet layer grown on the surface of the tubular carbon material. Some or all of the tin disulfide nanosheets have one end connected to the outer surface of the tubular carbon material, and the other end away from the tubular carbon material. The wall thickness of the tubular carbon material is 20-80 nm, the thickness of the tin disulfide nanosheet layer is 50-110 nm, and there is a gap (between 80-200 nm) between the inner wall of the tubular carbon material and the nano-silicon particles. The multiple nano-silicon particles encapsulated within a single tubular carbon material are in a movable stack (adjacent nano-silicon particles can move relative to each other), and there is a certain amount of void space around the nano-silicon particles (the gap between the nano-silicon particles is 1-300 nm).

[0123] Comparative Example 1

[0124] This comparative example discloses a silicon-carbon anode material, the preparation process of which includes:

[0125] (I) Sodium carbonate and barium chloride were dissolved in deionized water at a molar ratio of 1:1 to prepare sodium carbonate solution and barium chloride solution with a concentration of 0.1 mol / L, respectively. Then, the nano-silicon was uniformly dispersed in the barium chloride solution at a molar ratio of 0.1:1 to obtain a suspension. The suspension was added dropwise to the sodium carbonate solution while stirring. After filtration, washing with deionized water and drying, precursor A of barium carbonate coated nano-silicon was obtained.

[0126] (II) Polyacrylonitrile and precursor A are added to an organic liquid (the organic liquid is a mixture of N,N-dimethylformamide and ethanol in a volume ratio of 2:1) at a mass ratio of 5:1 to obtain a mixture. The content of precursor A in the mixture is 20 g / L. The mixture is magnetically stirred at 50°C for 24 h to obtain spinning precursor B.

[0127] (III) Precursor B was loaded into a 5 mL syringe and electrospun. The voltage was controlled at 15 kV and the jet flow rate was 0.2 mL / min. The nanofibers were collected using aluminum foil at a distance of 15 cm from the needle. After drying, the nanofibers were transferred to a tube furnace and carbonized in an inert gas atmosphere (nitrogen or argon) at a temperature of 2 °C / min to 500 °C for 2 h to obtain composite precursor C consisting of carbon nanofibers coating precursor A.

[0128] (IV) The precursor C was washed with hydrochloric acid solution and deionized water (washed three times with 1 mol / L hydrochloric acid solution and then three times with deionized water) to remove the barium carbonate template coated on the surface of the nano-silicon. After drying, the silicon-carbon composite material was obtained.

[0129] This comparative example also provides a negative electrode, comprising the silicon-carbon negative electrode material prepared in this comparative example. The preparation steps and other components of the negative electrode are the same as in Example 1.

[0130] This comparative example also provides a lithium-ion battery, including the negative electrode described in this comparative example. The battery preparation steps and other components are the same as in Example 1.

[0131] Test case

[0132] This experimental example tested the performance of the silicon-carbon anode material and battery obtained in the examples and comparative examples, specifically including:

[0133] The rate performance and cycle stability were tested using the Blue Electric CT2001A battery testing system within a voltage range of 0.01-2.5V. First, rate performance was tested at current densities of 0.1A / g, 0.3A / g, 1.0A / g, 1.5A / g, 3.0A / g, 5.0A / g, and 0.1A / g, with 10 charge-discharge cycles at each current density. For cycle stability testing, 10 charge-discharge cycles were first performed at a current density of 0.1A / g to eliminate the irreversible capacity loss caused by the formation of a solid electrolyte layer. Then, long-term charge-discharge stability was tested at a current density of 1.5A / g.

[0134] For ease of understanding, the button batteries made from the silicon-carbon anode materials prepared according to Example 1, Example 2, Example 3, Example 4 and Comparative Example 1 are named C1, C2, C3, C4 and R1, respectively.

[0135] Table 1 shows the discharge specific capacity (unit: mAh / g) of each button cell battery measured in the experiment at different current densities. The rate performance test results of the button cells in Example 1 are as follows: Figure 2 As shown.

[0136] Table 1

[0137]

[0138]

[0139] Depend on Figure 2As shown in Table 1, the button cell batteries C1 to C4 all exhibited high specific capacity at various current densities. Furthermore, when the current density recovered to 0.1 A / g, the discharge specific capacity could still reach more than 96% of the initial value, indicating that the preparation method proposed in this invention can obtain lithium-ion battery anode materials with excellent specific capacity and rate performance.

[0140] Table 2 shows the capacity (unit: mAh / g) of each button cell after a specific number of cycles in the cycle stability test. The cycle stability test results of the button cells in Example 1 are as follows: Figure 3 As shown.

[0141] Table 2

[0142]

[0143] Depend on Figure 3 As shown in Table 2, when subjected to cyclic charge-discharge tests at 1.5 A / g, the button batteries C1 to C4 all exhibited good capacity retention. In particular, after 500 cycles, the capacity retention rate still reached over 93%, indicating that the preparation method proposed in this invention can obtain lithium-ion battery anode materials with excellent cycle stability.

[0144] As shown in Tables 1-2, the silicon-carbon anode material in battery R1 in Comparative Example 1 does not contain tin disulfide. The rate performance and cycle stability of batteries (C1 to C4) in Examples 1-4 are significantly better than those of R1.

[0145] The silicon-carbon anode material of this invention has a composite structure, comprising tubular carbon nanofibers, on which tin disulfide nanosheets are grown. The carbon nanofibers encapsulate several nano-silicon particles within their cavities, with a certain amount of void space around the silicon nanosheets. Furthermore, this invention uses inorganic barium carbonate as a template, which, after acid washing, leaves no residue on the surface of the silicon nanosheets. This ensures sufficient volume space around the silicon particles to accommodate volume changes, which is beneficial for the long-term stability of the silicon-carbon anode material under operating conditions.

[0146] It should be noted that, unless otherwise specified, "room temperature" or "normal temperature" in this article refers to approximately 25°C; and the word "approximately" in numerical values ​​in this article means an error of ±5%.

[0147] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A tin disulfide-doped silicon-carbon negative electrode material, characterized in that, The tin disulfide-doped silicon-carbon negative electrode material comprises tubular carbon materials and tin disulfide nanosheets on the surface of the tubular carbon materials, each of the tubular carbon materials containing at least one nanosilicon, the tubular carbon material having a wall thickness of 20-80 nm, wherein the tin disulfide nanosheets are grown in situ on the surface of the tubular carbon material, the surface of the tubular carbon material being provided with a plurality of tin disulfide nanosheets, one end of some or all of the tin disulfide nanosheets being connected to the surface of the tubular carbon material and the other end being away from the tubular carbon material. The preparation method of the tin disulfide-doped silicon-carbon negative electrode material comprises the following steps: S1, taking nanosilicon, coating the nanosilicon with a sacrificial layer material to obtain a nanosilicon coated with a sacrificial layer, which is intermediate I; wherein the sacrificial layer material comprises a metal carbonate; S2, mixing intermediate I with a carbon source material, electrospinning, and carbonizing to obtain a composite material of the intermediate I coated with a carbon material layer, which is intermediate II; wherein the carbon source material comprises a polymer carbon source, and the polymer carbon source comprises at least one of polyacrylonitrile or polyvinylpyrrolidone; S3, removing the sacrificial layer to obtain a composite material of the nanosilicon coated with a carbon material layer, which is intermediate III; S4, mixing intermediate III with a sulfur source material and tin tetrachloride, placing them in a reaction kettle, and reacting at 150-300°C for 12-24h to obtain the silicon-carbon negative electrode material, wherein the sulfur source material comprises at least one of l-cysteine, thioacetamide or thiourea.

2. The tin disulfide-doped silicon-carbon anode material of claim 1, wherein, The silicon-carbon negative electrode material is a fibrous material, and the fiber diameter of the silicon-carbon negative electrode material is 250-400 nm.

3. The tin disulfide-doped silicon-carbon anode material of claim 1, wherein, The plurality of nanosilicons in one tubular carbon material can move relative to each other, and there is a gap between the inner wall of the tubular carbon material and the nanosilicon.

4. The tin disulfide-doped silicon-carbon anode material of claim 1, wherein, In step S3, an acidic substance is used to remove the sacrificial layer.

5. A negative electrode characterized by comprising: The negative electrode comprises the tin disulfide-doped silicon-carbon negative electrode material according to any one of claims 1-4.

6. A secondary battery characterized by comprising: The secondary battery comprises the negative electrode according to claim 5.

Images