Stannic pyrophosphate composite negative electrode material and preparation method thereof

Abstract

The application belongs to the technical field of lithium ion battery electrode materials, and particularly relates to a pyrophosphoric tin composite negative electrode material and a preparation method thereof. The preparation method comprises the following steps: firstly, a precipitant and a tin source are mixed and precipitated by using a precipitation method; the obtained precipitate is centrifuged, washed, dried, ground, mixed with phytic acid and a nitrogen-containing carbon source, and then uniformly mixed; most of the solvent is evaporated by water bath heating until a slurry is obtained; then, drying treatment is performed to obtain a precursor; finally, the precursor is transferred to a tube furnace, calcined under an inert atmosphere, the obtained heat-treated product is cooled to room temperature, and grinding is performed to obtain the product. The molecular formula of the obtained pyrophosphoric tin composite negative electrode material is SnP2O7 / C-P@C-N, the specific discharge capacity is high, the cycle and rate performance are good, the preparation method is simple, fast, high-yield, low-energy-consumption, low-cost, environment-friendly, and has a wide application prospect in the field of lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode material technology, specifically relating to a tin pyrophosphate composite anode material and its preparation method. Background Technology

[0002] With dwindling fossil fuel reserves and increasing environmental pollution, the demand for sustainable and clean energy is growing. Lithium-ion batteries, as an energy storage device, have been widely researched and applied due to their superior performance. Graphite was the first commercially available anode material for lithium-ion batteries, but its poor safety and low theoretical specific capacity limit its application in high-energy-density lithium-ion batteries. SnP2O7, as a novel anode material, possesses a high theoretical specific capacity and lithium insertion / extraction potential, effectively preventing lithium dendrite formation during high-current-density charging and discharging, thus ensuring high safety. Furthermore, its large and stable polyanion structure provides a significant buffer space to mitigate volume changes and prevent structural collapse during cycling. Therefore, SnP2O7 is a promising anode material for lithium-ion batteries.

[0003] The traditional processes for preparing tin pyrophosphate mainly use phosphorus sources such as C2H8O7P2, Na2H2PO2, and C. 16 N3P3, NH4H2PO4, and red / black / yellow phosphorus; organic phosphorus sources C2H8O7P2 and C 16 N3P3 is relatively expensive and easily oxidized upon contact with air; Na2H2PO2 and NH4H2PO4 produce toxic PH3 and NH3 gases upon high-temperature heating; red / black / yellow phosphorus is flammable, easily oxidized, and difficult to store, posing significant obstacles to the large-scale preparation of tin pyrophosphate. Common preparation methods for tin pyrophosphate include hydrothermal, solvothermal, and solid-phase phosphating methods, which suffer from problems such as poor safety, complex processes, and high costs. Furthermore, tin pyrophosphate suffers from low electronic conductivity, and due to alloying and dealloying reactions during lithium insertion / extraction, SnP2O7 still exhibits a large volume shrinkage and expansion rate during lithium insertion / extraction. Therefore, it is necessary to explore a simple, green, and pollution-free method for synthesizing SnP2O7 and further modify it to improve its electrochemical performance.

[0004] Chinese invention patent CN114597406A discloses a method for preparing carbon-coated tin pyrophosphate and its application. The method includes: (1) reacting a mixture containing a tin source, a phosphorus source, and compound A through a complexation reaction to obtain an intermediate product; (2) calcining the intermediate product under an inactive atmosphere to obtain the carbon-coated tin pyrophosphate. However, the phosphorus sources selected in this patent, ammonium dihydrogen phosphate and diammonium hydrogen phosphate, produce toxic ammonia gas when heated to high temperatures, causing environmental pollution; the selected phosphoric acid source is toxic and corrosive, and the subsequent heat treatment time is long (6-24 hours), resulting in high energy consumption and cost.

[0005] Chinese patent CN110357059A discloses a hydrothermal method for preparing self-assembled tin pyrophosphate nanospheres. Using SnCl4·5H2O and phosphoric acid as raw materials, it employs a hydrothermal method and carbon template synthesis technology to self-assemble tin hydrogen phosphate-carbon composite microspheres, which are then calcined at high temperature to obtain the tin pyrophosphate microspheres. However, this patent uses toxic and corrosive phosphoric acid, posing safety hazards. The hydrothermal method has a low yield, a long reaction time of up to 24 hours, high energy consumption, and a complex process. Furthermore, the hydrothermal process generates high pressure, requiring a high-pressure reactor with specific pressure resistance requirements, and presents both safety risks and stringent preparation conditions.

[0006] Xinzhu Guo et al. (DOI: 10.1002 / celc.202100793) disclosed a method using phytic acid, tin chloride pentahydrate, and C 18 N 12 SnP2O7@C / CN anode material was prepared by solvothermal and calcination methods using C as raw material. The preparation method includes the following steps: (1) using C 18 N 12 (1) Disperse the phytic acid in ethanol using ultrasonication; (2) Add phytic acid to the suspension from step (1) and stir continuously for 4 hours; (3) Add 1.5 g of tin chloride pentahydrate to the solution from step (2) and stir for another 1 hour; (4) Transfer the solution obtained in step (3) to the polytetrafluoroethylene liner of a 100 mL reactor and place it in a 180 °C oven for a solvothermal reaction for 10 hours; (5) After the reaction system cools naturally, wash the precipitate from step (4) five times by alternating centrifugation with distilled water and anhydrous ethanol, and then dry it under vacuum at 70 °C; (6) Finally, pre-calcine the precursor at 300 °C for 2 hours in an argon atmosphere and then calcine it at 550 °C for 5 hours to obtain the final product. However, the solvothermal method used in this literature has a low yield, a solvothermal time of up to 10 hours, high energy consumption, and a complex process. Moreover, the solvothermal process generates high pressure, which places certain requirements on the pressure resistance of the high-pressure reactor and poses safety hazards. The preparation conditions are also harsh.

[0007] Wei He et al. (DOI: 10.1021 / acsami.1c04231) disclosed a method for preparing tin pyrophosphate anode material using H3PO4 as a phosphorus source. The preparation method includes the following steps: (1) dissolving H3PO4, sucrose, and SnCl4·5H2O in deionized water; (2) transferring the solution from step (1) to a 100mL hydrothermal reactor lined with polytetrafluoroethylene, heating to 180℃ and holding for 24h; (3) after the reaction system cools naturally, washing the precipitate from step (2) three times with distilled water and anhydrous ethanol by centrifugation to remove impurities; (4) calcining the precursor at 800℃ for 5h in air atmosphere to obtain the final product. However, the hydrothermal method used in this literature has a low yield, long reaction time, high calcination temperature, high energy consumption, and complex process. Moreover, the hydrothermal process generates high pressure, which places certain requirements on the pressure resistance of the high-pressure reactor, and there are also safety hazards. The preparation conditions are harsh. In addition, the selected phosphorus source is toxic and corrosive, posing safety hazards.

[0008] Liu Yukun's master's thesis at Tianjin University of Technology discloses a method for preparing tin pyrophosphate anode material using H3PO2 as a phosphorus source. The preparation method includes the following steps: (1) dissolving stannous chloride in ethylene glycol under stirring at 60°C; (2) adding hypophosphoric acid to the solution in step (1) and adding a certain amount of deionized water while continuing stirring; (3) transferring the solution in step (2) to a 100mL stainless steel reactor, heating it to 160-200°C and holding it at that temperature for 2-8 hours; (4) calcining the precursor at 600-900°C for 4-12 hours to obtain the anode material. However, the solvothermal method used in this thesis has a low yield, a high temperature of 160-200°C, and a heat treatment temperature of 600-900°C, resulting in high energy consumption, complex process, and high pressure generated during the solvothermal process, which places certain requirements on the pressure resistance of the high-pressure reactor and poses safety hazards, making the preparation conditions harsh. In addition, the selected phosphorus source will generate PH3 gas when heated at high temperature, which is harmful to the environment and human body. Summary of the Invention

[0009] To overcome the above-mentioned defects, the present invention aims to provide a tin pyrophosphate composite anode material, wherein the molecular formula of the tin pyrophosphate composite anode material is SnP2O7 / CP@CN, the tin pyrophosphate particles are anchored on the P-doped C framework, and the N-doped C layer is coated on the P-doped C framework. The resulting tin pyrophosphate composite anode material has high discharge specific capacity, good cycle and rate performance, and can be widely used in lithium-ion batteries.

[0010] Another objective of this invention is to provide a method for preparing a tin pyrophosphate composite anode material, using phytic acid as the phosphorus and carbon source, and combining precipitation and calcination methods to prepare a high-performance anode material with high yield, simple and rapid process, low energy consumption, low cost, and environmental friendliness.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A tin pyrophosphate composite anode material, wherein the molecular formula of the tin pyrophosphate composite anode material is SnP2O7 / CP@CN, the tin pyrophosphate particles are anchored on a P-doped C framework, and an N-doped C layer is coated on the P-doped C framework.

[0013] A method for preparing a tin pyrophosphate composite anode material includes the following steps:

[0014] A precipitate is obtained by reacting a precipitant and a tin source through a precipitation method.

[0015] The precipitate, phytic acid, and nitrogen-containing carbon source were heated in a water bath to obtain a precursor.

[0016] The precursor is calcined under an inert atmosphere to obtain the product.

[0017] Preferably, the step of reacting the precipitant and the tin source to obtain the precipitate via a precipitation method includes:

[0018] The precipitant and tin source were dissolved separately in a solvent, then mixed and precipitated. The mixture was then centrifuged, washed, dried, and ground to obtain the precipitate.

[0019] The tin source is one or a mixture of SnCl4·5H2O, SnCl2·2H2O, SnCl4, SnCl2 and tin acetate;

[0020] The precipitant is one or a mixture of several of the following: oxalic acid, oxalic acid dihydrate, ammonium bicarbonate, sodium hydroxide, potassium hydroxide, ammonium carbonate, sodium carbonate, sodium oxalate, ammonium oxalate, ammonia, and urea.

[0021] Preferably, the molar ratio of the precipitant to the tin source is 1:2.2-4.5.

[0022] Preferably, the step of heating the precipitate with phytic acid and a nitrogen-containing carbon source in a water bath to obtain the precursor includes:

[0023] The precipitate was mixed with phytic acid and a nitrogen-containing carbon source until most of the solvent was evaporated by water bath heating until it became a slurry. Then, it was freeze-dried under vacuum for 10-12 hours, followed by vacuum drying at 80-120°C for 8-14 hours to obtain the precursor.

[0024] Preferably, the nitrogen-containing carbon source is one or a mixture of several of the following: 2-methylimidazole, polyvinylpyrrolidone, chitosan, amino acids, urea, dopamine hydrochloride, polyaniline, polypyrrole, ethylenediamine, dicyandiamide, melamine, polyacrylonitrile, folic acid, p-phenylenediamine, levodopa, poly(terephthalamide), and p-phenyldecanoamide.

[0025] Preferably, the mass ratio of the precipitate, the nitrogen-containing carbon source, and phytic acid is 1:1-3.6:1.1-2.1.

[0026] Preferably, the water bath heating temperature is 60-90℃.

[0027] Preferably, the calcination treatment step is as follows:

[0028] The precursor was transferred to a tube furnace and calcined under an inert atmosphere. The resulting heat-treated product was then cooled to room temperature and ground to obtain the final product.

[0029] Preferably, the calcination treatment is: pre-calcination at 200-400℃ for 2-3 hours followed by calcination at 500-700℃ for 3-5 hours.

[0030] The positive and beneficial effects of this invention are:

[0031] 1. This invention uses a precipitant and a tin source to prepare a morphologically well-formed spherical SnC2O4 precipitate. This invention uses phytic acid, a green raw material, as both the phosphorus and carbon source. Phytic acid has a strong chelating effect, coordinating with metallic tin ions to form stable complexes, which can improve the dispersion uniformity of tin metal ions. Furthermore, phytic acid has a high phosphorus content; during high-temperature carbonization, it forms tin pyrophosphate and a phosphorus-doped carbon framework simultaneously. Phytic acid is readily soluble in water, ethanol, acetone, glycerol, etc., broadening the selection of solvent systems for dispersing tin precipitates, phytic acid, and nitrogen-containing carbon sources. Simultaneously, phytic acid is abundant, non-toxic, harmless, and environmentally friendly. This invention uses a nitrogen-containing carbon source as the second carbon source, forming an N-doped C layer during calcination, coating the tin pyrophosphate particles and the P-doped C framework. This invention synthesizes a high-performance N-doped C layer-coated tin pyrophosphate composite anode material anchored on a P-doped C framework. The heteroelement N and P doping of carbon introduces defects into the carbon material, improving its conductivity and effectively suppressing the volume shrinkage and expansion of tin pyrophosphate, thereby enhancing electron and Li conductivity. + The electronic conductivity is increased, the charge transfer resistance is reduced, and thus the electrochemical performance is improved.

[0032] 2. This invention first employs a precipitation method to mix and precipitate a precipitant and a tin source. The resulting precipitate is centrifuged, washed, dried, and ground. The precipitation reaction prepares a spherical SnC2O4 precipitate with good morphology. Then, the ground material is mixed evenly with phytic acid and a nitrogen-containing carbon source. Most of the solvent is evaporated by water bath heating, ensuring uniform mixing of the raw materials. Subsequently, the mixture is freeze-dried and vacuum-dried to obtain a precursor, ensuring thorough solvent removal. The precursor is then transferred to a tube furnace and heat-treated under an inert atmosphere. During calcination, tin pyrophosphate is formed, along with a phosphorus-doped carbon framework. The tin pyrophosphate particles are anchored on the P-doped C framework. The nitrogen-containing carbon source generates an N-doped C layer that coats both the tin pyrophosphate particles and the P-doped C framework. This successfully synthesizes a high-performance tin pyrophosphate composite anode material with an N-doped C layer coated and anchored on a P-doped C framework. Moreover, the preparation method of this invention has high yield, uses water bath heating, is simple and rapid, does not involve high voltage, is highly safe, has low energy consumption, low cost, and is environmentally friendly.

[0033] 3. The tin pyrophosphate composite anode material obtained in this invention exhibits high discharge specific capacity and excellent cycle and rate performance. At a current density of 0.5 A / g, it achieves a discharge specific capacity of 416.6 mAh / g after 200 cycles, making it widely applicable in the lithium-ion battery field. Furthermore, LiNi... 0.5 Mn 1.5 The O4 / / SnP2O7 / CP@CN-1.2 full cell exhibits a discharge specific capacity of up to 206.6 mAh / g after 200 cycles at 1.4-4.4V and 0.5C. The full cell can provide LED bulbs with different colors of light, and can also power LED strings and heart-shaped circuit boards. It also has good application prospects in the field of full cells. Attached Figure Description

[0034] Figure 1 The diagram shows the structure of the tin pyrophosphate composite anode material of the present invention. In the diagram: 1. Tin pyrophosphate particles, 2. P-doped C framework, 3. N-doped C layer;

[0035] Figure 2 The image shown is the XRD pattern of the product prepared in Example 1.

[0036] Figure 3 This is a high-resolution XPS image of the C element in the product prepared in Example 1;

[0037] Figure 4 This is a high-resolution XPS image of the N element in the product prepared in Example 1;

[0038] Figure 5 SEM image of the product prepared in Example 1;

[0039] Figure 6 TEM image of the product prepared in Example 1;

[0040] Figure 7 The rate performance graphs for the product prepared in Example 1 at current densities of 0.1, 0.2, 0.5, 1, 2, and 0.1 A / g are shown.

[0041] Figure 8 The graph shows the cycling performance of the product prepared in Example 1 at a current density of 0.5 A / g.

[0042] Figure 9 This is a comparison chart of the cycle performance of full cells assembled with the product prepared in Example 1 at different N / P ratios (capacity ratio of negative electrode and positive electrode);

[0043] Figure 10 The image shows the XRD pattern of the product prepared in Example 2.

[0044] Figure 11 SEM image of the product prepared in Example 2;

[0045] Figure 12 TEM image of the product prepared in Example 2;

[0046] Figure 13 The graph shows the cycling performance of the product prepared in Example 2 at a current density of 0.5 A / g.

[0047] Figure 14 The image shows the XRD pattern of the product prepared in Example 3.

[0048] Figure 15 SEM image of the product prepared in Example 3;

[0049] Figure 16 TEM image of the product prepared in Example 3;

[0050] Figure 17 The graph shows the cycling performance of the product prepared in Example 3 at a current density of 0.5 A / g.

[0051] Figure 18 The image shows the XRD pattern of the product prepared in Example 4;

[0052] Figure 19 This is a SEM image of the SnC2O4 precipitate prepared in Example 4;

[0053] Figure 20 SEM image of the product prepared in Example 4;

[0054] Figure 21 The graph shows the cycling performance of the product prepared in Example 4 at a current density of 0.5 A / g.

[0055] Figure 22 The image shows the XRD pattern of the product prepared in Example 5.

[0056] Figure 23 The image shown is the XRD pattern of the product prepared in Example 6. Detailed Implementation

[0057] The present invention will be further described below with reference to some specific embodiments.

[0058] See Figure 1 A tin pyrophosphate composite anode material, wherein the molecular formula of the tin pyrophosphate composite anode material is SnP2O7 / CP@CN, is derived from... Figure 1 It is known that the present invention prepares a tin pyrophosphate composite anode material with an N-doped C layer coated and anchored on a P-doped C framework. Tin pyrophosphate particles 1 are anchored on a P-doped C framework 2, and an N-doped C layer 3 is coated on tin pyrophosphate particles 1 and P-doped C framework 2.

[0059] Example 1

[0060] A method for preparing the above-mentioned tin pyrophosphate composite anode material (SnP2O7 / CP@CN) includes the following steps:

[0061] Step A: Dissolve 1.6g SnCl2·2H2O in a mixed solution of 80mL anhydrous ethanol and 20mL polyethylene glycol, and stir the solution at room temperature for 30min. Then weigh 0.2g oxalic acid dihydrate and dissolve it in the above mixed solution. The molar ratio of precipitant to tin source is 1:4.5. Then add 100mL deionized water dropwise, mix well, co-precipitate, centrifuge and wash to obtain stannous oxalate, and dry the obtained stannous oxalate at 60℃ for 12h.

[0062] Step B: Grind the dried material from Step A for 30 minutes;

[0063] Step C: Disperse 0.5g of stannous oxalate and 1.2g of 2-methylimidazole obtained in Step B into 100mL of deionized water to obtain a suspension of stannous oxalate and 2-methylimidazole. Disperse 1.2g of 70wt.% phytic acid aqueous solution into 50mL of deionized water. Then add the phytic acid solution dropwise to the suspension of stannous oxalate and 2-methylimidazole. Sonicate for 20min. Place the above mixture in a 90℃ water bath and heat for 2h to evaporate most of the solvent until it becomes a slurry. Freeze-dry the slurry sample under vacuum at -50℃ for 12h, and then vacuum-dry it at 120℃ for 12h.

[0064] Step D: Transfer the precursor obtained in step C to a tube furnace, pre-calcine at 300°C for 2 hours under a nitrogen atmosphere, and then calcine at 600°C for 4 hours.

[0065] Step E: Cool the heat-treated product obtained in step D to room temperature under flowing nitrogen, grind for 15 minutes, and obtain the product.

[0066] Figure 2 The XRD pattern of the product prepared in this embodiment shows that all diffraction peaks can be attributed to tin pyrophosphate, indicating high purity of the material. High purity is beneficial to the electrochemical performance of the material.

[0067] Figure 3 The high-resolution XPS plot of the carbon element in the product prepared in this embodiment shows four distinct peaks for C, C, CP, CN, and CO. The peaks for CN and CP indicate that nitrogen and phosphorus have been successfully doped into carbon, which not only improves the material's conductivity but also generates many external defects and Li. + The diffusion of active sites will greatly improve the electrochemical performance of the composite material.

[0068] Figure 4 The high-resolution XPS image of the N element in the product prepared in this embodiment shows peaks for pyridine-N, pyrrole-N, and oxide-N. In addition, pyrrole nitrogen and pyridine nitrogen can provide pseudocapacitance, which is beneficial to improving the electrochemical performance of the material.

[0069] Figure 5 This is a SEM image of the product prepared in this embodiment. The image shows that the tin pyrophosphate particles are spherical and well-dispersed, which is beneficial for Li... + The migration of these molecules is beneficial to the material's recycling performance.

[0070] Figure 6 The image shows a TEM image of the product prepared in this embodiment. The thickness of the N-doped carbon layer is 7-8 nm.

[0071] Figure 7 The product prepared in this embodiment was cycled 10 times each at current densities of 0.1, 0.2, 0.5, 1, and 2 A / g, and then restored to the rate performance diagram at a current density of 0.1 A / g. After 40 cycles (current density of 1 A / g), the discharge specific capacity still reached 402.2 mAh / g, and the material exhibited good rate performance.

[0072] Figure 8 The cycling performance of the product prepared in this embodiment is shown in the graph at a current density of 0.5 A / g. After 200 cycles at 0.5 A / g, the discharge specific capacity of the material is 416.6 mAh / g, which shows that the material has a high discharge specific capacity.

[0073] Figure 9 This example shows a comparison of the cycle performance of full cells assembled with different N / P ratios (capacity ratio of negative electrode to positive electrode) in this embodiment, where the N / P ratio is 1:2 for LiNi. 0.5 Mn 1.5After 200 cycles at 1.4-4.4V and 0.5C, the discharge specific capacity of the O4 / / SPO / CP@CN-1.2 full cell is 206.6mAh / g, indicating that its application as a negative electrode in lithium-ion full cells can still enable the full cell to release a high specific capacity.

[0074] Example 2

[0075] A method for preparing the above-mentioned tin pyrophosphate composite anode material (SnP2O7 / CP@CN) includes the following steps:

[0076] Step A: Dissolve 1.6g SnCl2·2H2O in a mixed solution of 80mL anhydrous ethanol and 20mL polyethylene glycol, and stir the solution at room temperature for 30min. Then weigh 0.2g oxalic acid dihydrate and dissolve it in the above mixed solution. The molar ratio of precipitant to tin source is 1:4.5. Then add 100mL deionized water dropwise, mix well, co-precipitate, centrifuge and wash to obtain stannous oxalate, and dry the obtained stannous oxalate at 60℃ for 12h.

[0077] Step B: Grind the dried material from Step A for 30 minutes;

[0078] Step C: Disperse 0.5g of stannous oxalate and 0.6g of 2-methylimidazole obtained in Step B into 100mL of deionized water to obtain a suspension of stannous oxalate and 2-methylimidazole. Disperse 1.2g of 70wt.% phytic acid aqueous solution into 50mL of deionized water. Then add the phytic acid solution dropwise to the suspension of stannous oxalate and 2-methylimidazole. Sonicate for 20min. Place the above mixture in a 90℃ water bath and heat for 2h to evaporate most of the solvent until it becomes a slurry. Freeze-dry the slurry sample under vacuum at -50℃ for 12h, and then vacuum-dry it at 120℃ for 12h.

[0079] Step D: Transfer the precursor obtained in step C to a tube furnace, pre-calcine at 300°C for 2 hours under a nitrogen atmosphere, and then calcine at 600°C for 4 hours.

[0080] Step E: Cool the heat-treated product obtained in step D to room temperature under flowing nitrogen, grind for 10 minutes, and obtain the product.

[0081] Figure 10 The XRD pattern of the product prepared in this embodiment shows that all diffraction peaks can be attributed to tin pyrophosphate, indicating high purity of the material. High purity is beneficial to the electrochemical performance of the material.

[0082] Figure 11 The image shows a SEM image of the product prepared in this embodiment. It can be seen from the image that the tin pyrophosphate particles are spherical.

[0083] Figure 12The image shows a TEM image of the product prepared in this embodiment. The thickness of the N-doped carbon layer is 5-6 nm.

[0084] Figure 13 The cycling performance of the product prepared in this embodiment is shown in the graph at a current density of 0.5 A / g. After 200 cycles at 0.5 A / g, the discharge specific capacity of the material is 344.2 mAh / g, which shows that the material has a high discharge specific capacity.

[0085] Example 3

[0086] A method for preparing the above-mentioned tin pyrophosphate composite anode material (SnP2O7 / CP@CN) includes the following steps:

[0087] Step A: Dissolve 1.6g SnCl2·2H2O in a mixed solution of 80mL anhydrous ethanol and 20mL polyethylene glycol, and stir the solution at room temperature for 30min. Then weigh 0.2g oxalic acid dihydrate and dissolve it in the above mixed solution. The molar ratio of precipitant to tin source is 1:4.5. Then add 100mL deionized water dropwise, mix well, co-precipitate, centrifuge and wash to obtain stannous oxalate, and dry the obtained stannous oxalate at 60℃ for 12h.

[0088] Step B: Grind the dried material from Step A for 30 minutes;

[0089] Step C: Disperse 0.5g of stannous oxalate and 1.8g of 2-methylimidazole obtained in Step B into 100mL of deionized water to obtain a suspension of stannous oxalate and 2-methylimidazole. Disperse 1.2g of 70wt.% phytic acid aqueous solution into 50mL of deionized water. Then add the phytic acid solution dropwise to the suspension of stannous oxalate and 2-methylimidazole. Sonicate for 30min. Place the above mixture in a 90℃ water bath and heat for 2h to evaporate most of the solvent until it becomes a slurry. Freeze-dry the slurry sample under vacuum at -50℃ for 12h, and then vacuum-dry it at 120℃ for 12h.

[0090] Step D: Transfer the precursor obtained in step C to a tube furnace, pre-calcine at 300°C for 2 hours under a nitrogen atmosphere, and then calcine at 600°C for 4 hours.

[0091] Step E: Cool the heat-treated product obtained in step D to room temperature under flowing nitrogen, grind for 15 minutes, and obtain the product.

[0092] Figure 14 The XRD pattern of the product prepared in this embodiment shows that all diffraction peaks can be attributed to tin pyrophosphate, indicating high purity of the material. High purity is beneficial to the electrochemical performance of the material.

[0093] Figure 15The image shows a SEM image of the product prepared in this embodiment. It can be seen from the image that the particles are relatively uniformly dispersed, and some of the disposable particles have undergone secondary accumulation.

[0094] Figure 16 The image shows a TEM image of the product prepared in this embodiment. The thickness of the N-doped carbon layer is 9-10 nm.

[0095] Figure 17 The cycling performance of the product prepared in this embodiment at a current density of 0.5 A / g is shown in the figure. After 200 cycles at 0.5 A / g, the discharge specific capacity of the material is 392.1 mAh / g, which shows that the material has a high discharge specific capacity.

[0096] Example 4

[0097] A method for preparing the above-mentioned tin pyrophosphate composite anode material (SnP2O7 / CP@CN) includes the following steps:

[0098] Step A: Dissolve 1.6g SnCl2·2H2O in a mixed solution of 80mL anhydrous ethanol and 20mL polyethylene glycol, and stir the solution at room temperature for 30min. Then weigh 0.2g oxalic acid dihydrate and dissolve it in the above mixed solution. The molar ratio of precipitant to tin source is 1:4.5. Then add 100mL deionized water dropwise, mix well, co-precipitate, centrifuge and wash to obtain stannous oxalate, and dry the obtained stannous oxalate at 60℃ for 12h.

[0099] Step B: Grind the dried material from Step A for 30 minutes;

[0100] Step C: Disperse 0.5g of stannous oxalate and 0.5g of polyvinylpyrrolidone obtained in Step B into 100mL of deionized water to obtain a suspension of stannous oxalate and polyvinylpyrrolidone. Disperse 1.2g of 70wt.% phytic acid aqueous solution into 50mL of deionized water. Then add the phytic acid solution dropwise to the suspension of stannous oxalate and polyvinylpyrrolidone. Sonicate for 30min. Place the above mixture in a 90℃ water bath and heat for 2h to evaporate most of the solvent until it becomes a slurry. Freeze-dry the slurry sample under vacuum at -50℃ for 10h, and then vacuum-dry it at 120℃ for 12h.

[0101] Step D: Transfer the precursor obtained in step C to a tube furnace, pre-calcine at 300°C for 2 hours under a nitrogen atmosphere, and then calcine at 600°C for 4 hours.

[0102] Step E: Cool the heat-treated product obtained in step D to room temperature under flowing nitrogen, grind for 10 minutes, and obtain the product.

[0103] Figure 18The XRD pattern of the product prepared in this embodiment shows that all diffraction peaks can be attributed to tin pyrophosphate, indicating high purity of the material. High purity is beneficial to the electrochemical performance of the material.

[0104] Figure 19 The image shows an SEM image of the Sn precipitate SnC2O4 prepared in this embodiment. It can be seen that the primary particles of SnC2O4 are spherical.

[0105] Figure 20 The image shown is an SEM image of the product prepared in this embodiment. It can be seen that the primary particles of SnP2O7 are spherical, while the precipitate SnC2O4 retains a spherical shape.

[0106] Figure 21 The cycling performance of the product prepared in this embodiment at a current density of 0.5 A / g is shown in the figure. After 200 cycles at 0.5 A / g, the discharge specific capacity of the material is 329.5 mAh / g, which shows that the material has a high discharge specific capacity.

[0107] Example 5

[0108] A method for preparing the above-mentioned tin pyrophosphate composite anode material (SnP2O7 / CP@CN) includes the following steps:

[0109] Step A: Dissolve 1.0 g SnCl2 in a mixed solution of 80 mL anhydrous ethanol and 20 mL polyethylene glycol, and stir the solution at room temperature for 30 min. Then weigh 0.2 g oxalate dihydrate and dissolve it in the above mixed solution. The molar ratio of precipitant to tin source is 1:3.3. Then add 100 mL deionized water dropwise, mix well, co-precipitate, centrifuge and wash to obtain stannous oxalate, and dry the obtained stannous oxalate at 70 °C for 10 h.

[0110] Step B: Grind the dried material from Step A for 20 minutes;

[0111] Step C: Disperse 0.5g of stannous oxalate and 1.2g of chitosan obtained in Step B into 100mL of deionized water to obtain a suspension of stannous oxalate and chitosan. Disperse 0.8g of 70wt.% phytic acid aqueous solution into 50mL of deionized water. Then add the phytic acid solution dropwise to the suspension of stannous oxalate and chitosan. Sonicate for 30min. Place the above mixture in an 80℃ water bath and heat for 3h to evaporate most of the solvent until it becomes a slurry. Freeze-dry the slurry sample under vacuum at -50℃ for 10h, and then vacuum-dry it at 100℃ for 12h.

[0112] Step D: Transfer the precursor obtained in step C to a tube furnace, pre-calcine at 400°C for 2 hours under a nitrogen atmosphere, and then calcine at 500°C for 5 hours.

[0113] Step E: Cool the heat-treated product obtained in step D to room temperature under flowing nitrogen, grind for 15 minutes, and obtain the product.

[0114] Figure 22 The XRD pattern of the product prepared in this embodiment shows that all diffraction peaks can be attributed to tin pyrophosphate, indicating high purity of the material. High purity is beneficial to the electrochemical performance of the material.

[0115] Example 6

[0116] A method for preparing the above-mentioned tin pyrophosphate composite anode material (SnP2O7 / CP@CN) includes the following steps:

[0117] Step A: Dissolve 0.9g SnCl4 in a mixed solution of 80mL anhydrous ethanol and 20mL polyethylene glycol, and stir the solution at room temperature for 30min. Then weigh 0.2g oxalic acid dihydrate and dissolve it in the above mixed solution. The molar ratio of precipitant to tin source is 1:2.2. Then add 100mL deionized water dropwise, mix well, co-precipitate, centrifuge and wash to obtain stannous oxalate, and dry the obtained stannous oxalate at 80℃ for 8h.

[0118] Step B: Grind the dried material from Step A for 10 minutes;

[0119] Step C: Disperse 0.5g of stannous oxalate and 1.5g of melamine obtained in Step B into 100mL of deionized water to obtain a suspension of stannous oxalate and melamine. Disperse 1.5g of 70wt.% phytic acid aqueous solution into 50mL of deionized water. Then add the phytic acid solution dropwise to the suspension of stannous oxalate and melamine. Sonicate for 30min. Place the above mixture in a 90℃ water bath and heat for 2h to evaporate most of the solvent until it becomes a slurry. Freeze-dry the slurry sample under vacuum at -50℃ for 12h, and then vacuum-dry it at 80℃ for 14h.

[0120] Step D: Transfer the precursor obtained in step C to a tube furnace, pre-calcine at 200°C for 3 hours under a nitrogen atmosphere, and then calcine at 700°C for 3 hours.

[0121] Step E: Cool the heat-treated product obtained in step D to room temperature under flowing nitrogen, grind for 10 minutes, and obtain the product.

[0122] Figure 23 The XRD pattern of the product prepared in this embodiment shows that all diffraction peaks can be attributed to tin pyrophosphate, indicating high purity of the material. High purity is beneficial to the electrochemical performance of the material.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a tin pyrophosphate composite anode material, characterized in that, The steps include the following: The tin source was dissolved in a mixed solution of anhydrous ethanol and polyethylene glycol, and then a precipitating agent was added to carry out a precipitation reaction to obtain a precipitate. The precipitate was heated with phytic acid and a nitrogen-containing carbon source in a water bath to obtain a precursor. The precursor was calcined under an inert atmosphere to obtain the product. The precipitant is one or a mixture of several of the following: oxalic acid, oxalic acid dihydrate, sodium oxalate, and ammonium oxalate.

2. The method for preparing the tin pyrophosphate composite anode material according to claim 1, characterized in that, The tin source is one or a mixture of SnCl4·5H2O, SnCl2·2H2O, SnCl4, SnCl2 and tin acetate.

3. The method for preparing the tin pyrophosphate composite anode material according to claim 2, characterized in that, The molar ratio of the precipitant to the tin source is 1:2.2-4.

5.

4. The method for preparing the tin pyrophosphate composite anode material according to claim 1, characterized in that, The process of heating the precipitate with phytic acid and a nitrogen-containing carbon source in a water bath to obtain the precursor includes: The precipitate was mixed with phytic acid and a nitrogen-containing carbon source until homogeneous. Then, the mixture was heated in a water bath to evaporate most of the solvent until it became a slurry. After vacuum freeze-drying for 10-12 h, it was then vacuum dried at 80-120 °C for 8-14 h to obtain the precursor.

5. The method for preparing the tin pyrophosphate composite anode material according to claim 4, characterized in that, The nitrogen-containing carbon source is one or a mixture of several of the following: 2-methylimidazole, polyvinylpyrrolidone, chitosan, amino acids, urea, dopamine hydrochloride, polyaniline, polypyrrole, ethylenediamine, dicyandiamide, melamine, polyacrylonitrile, folic acid, p-phenylenediamine, levodopa, poly(terephthalamide), and p-phenyldecanoamide.

6. The method for preparing the tin pyrophosphate composite anode material according to claim 4, characterized in that, The mass ratio of the precipitate, nitrogen-containing carbon source, and phytic acid is 1:1-3.6:1.1-2.

1.

7. The method for preparing the tin pyrophosphate composite anode material according to claim 4, characterized in that, The water bath heating temperature is 60-90 ℃.

8. The method for preparing the tin pyrophosphate composite anode material according to claim 1, characterized in that, The calcination process is as follows: The precursor was transferred to a tube furnace and calcined under an inert atmosphere. The resulting heat-treated product was then cooled to room temperature and ground to obtain the final product.

9. The method for preparing the tin pyrophosphate composite anode material according to claim 8, characterized in that, The calcination process is as follows: pre-calcination at 200-400 °C for 2-3 hours, followed by calcination at 500-700 °C for 3-5 hours.

10. A tin pyrophosphate composite anode material prepared by the preparation method according to any one of claims 1-9.

11. The tin pyrophosphate composite anode material according to claim 10, characterized in that, The molecular formula of the tin pyrophosphate composite anode material is SnP2O7 / CP@CN, with tin pyrophosphate particles anchored on a P-doped C framework and an N-doped C layer coating the P-doped C framework.

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