Preparation Method and Application of Sn4P3 Nanoparticle / Carbon Nanotube Composite Material

Abstract

The present invention provides a method for preparing a Sn4P3 nanoparticle / carbon nanotube composite material, including steps such as a directed template method, polydopamine coating, carbonization, and phosphidation. The structure of the obtained composite material includes Sn4P3 nanoparticles encapsulated in carbon nanotubes. The outer diameter of the carbon nanotubes is 100 - 200 nm, the wall thickness is 1 - 25 nm, and the particle size distribution of Sn4P3 is in the range of 2 - 10 nm. The present invention has a reasonable design, a simple preparation method, and low cost. The obtained composite material is suitable for preparing the negative electrode material of a secondary battery. Among them, the carbon nanotube network can provide high electrical conductivity and buffer volume expansion. Monodisperse Sn4P3 nanoparticles can shorten the ion diffusion path. Nitrogen-doped carbon sites help improve electron conductivity, and porous hard carbon materials can maintain mechanical stability. The secondary battery prepared from the composite material has excellent energy storage performance and long cycle stability, which is conducive to future commercial applications.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and particularly to a novel anode material for secondary batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Alkali metal ion batteries (AIBs), such as lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs), exhibit high working voltages due to the high electronegativity of alkali metals and the fast kinetics of monovalent alkali metal ions. Although LIBs have been successfully commercialized due to their high energy density, high working voltage, and long cycle life, the limited lithium resources in the earth's crust restrict their further development. Although the energy densities of SIBs and PIBs are generally lower than those of LIBs, the abundant resources and the low-cost advantages of sodium and potassium make them marketable in special application fields. In addition, sodium and potassium belong to the same group as lithium in the periodic table, so some development experiences of lithium-ion batteries, such as electrode materials, electrolytes, separators, and battery manufacturing technologies, can also be used as references for the development of SIBs and PIBs. AIBs all have their advantages and disadvantages and can be used in various scenarios. For example, LIBs are usually used in consumer electronics and electric vehicles with high energy density requirements, while SIBs and PIBs can be used in large-scale energy storage power grids with strict cost control.

[0003] Although carbon materials with an intercalation mechanism are one of the most commonly used anode materials in AIBs (i.e., graphite for LIBs and PIBs, and hard carbon for SIBs), their low specific capacity limits their energy density. Phosphorus (P) with a multi-electron alloying mechanism shows a high theoretical specific capacity (2590 mAh g -1 , corresponding to A3P as the final discharge product) in AIBs. However, its huge volume change (≈300% for LIBs and ≈400% for SIBs) and low electrical conductivity limit the cycling and rate performance of P in AIBs. Currently, modification strategies mainly include research on nanosizing, carbon coating, alloying, and functional electrolytes and binders. Alloying can not only enhance the volume conductivity of P and buffer volume expansion, but sometimes can also provide additional capacity depending on whether the second-phase metal participates in the formation of the alloy. Several representative metal phosphides, including NiP3, FeP, CoP, Cu3P, Zn3P2, Se4P4, Sn4P3, show excellent electrochemical storage performance.

[0004] Sn4P3 has a relatively high theoretical weight / volume capacity (1132 mAh g -1 / 6650 mAh cm -3), good conductivity, insertion potential and low cost, are becoming a hot research field for diversified energy storage. Compared with P, Sn has a smaller specific capacity, but the volumetric capacity of Sn can make up for this disadvantage, and the conductivity of Sn is better than that of P. However, Sn4P3 anodes show huge volume expansion and low intrinsic conductivity during cycling, leading to the formation of unstable solid electrolyte interface (SEI) and electrode pulverization during cycling, resulting in poor cycling stability. Therefore, it is necessary to study how to adopt effective strategies to simultaneously promote their advantages and overcome their disadvantages to achieve high capacity, high electronic conductivity and excellent anode performance of AIBs. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and provide a Sn4P3 nanoparticle / carbon nanotube composite material and a preparation method thereof. At the same time, the application of the composite material can improve the electrochemical performance of secondary batteries, inhibit electrode volume expansion, and is suitable for large-scale production.

[0006] In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing a Sn4P3 nanoparticle / carbon nanotube composite material, comprising the following steps:

[0008] Step a, subjecting manganese oxide precursor nanowires to a hydrothermal reaction with stannate and urea to prepare a manganese oxide precursor with a SnO2 nanolayer deposited on the surface, denoted as MnO-P@SnO2 nanotubes;

[0009] Step b, fully mixing the MnO-P@SnO2 nanotubes prepared in step a with Tris-HCl buffer and dopamine hydrochloride to obtain polydopamine-coated MnO-P@SnO2 nanotubes, denoted as MnO-P@SnO2@PDA;

[0010] Step c, removing the manganese oxide precursor in the MnO-P@SnO2@PDA prepared in step b, and obtaining polydopamine-coated SnO2 nanotubes, which are recorded as SnO2@PDA precursor;

[0011] Step d, annealing the SnO2@PDA precursor obtained in step c for the first time under an inert atmosphere, then grinding it with a phosphorus source, and annealing the ground mixture for the second time under an inert atmosphere to obtain the Sn4P3 nanoparticle / carbon nanotube composite material, recorded as Sn4P3@CNT.

[0012] In the present invention, the manganese oxide precursor is composed of manganese oxide, which is also represented by the symbol "MnO-P" in the present invention.

[0013] In step a, the manganese oxide precursor nanowires have a solid nanowire structure with a smooth surface, and the diameter is uniformly distributed in the range of 50 - 190 nm.

[0014] In a preferred embodiment, in step a, the mass ratio of the manganese oxide precursor nanowires, stannate, and urea is 1:1 - 2:8 - 13.

[0015] In a preferred embodiment, in step a, the stannate is selected from sodium stannate, potassium stannate, or calcium stannate.

[0016] In a preferred embodiment, in step a, the solvent for the hydrothermal reaction is water or an ethanol aqueous solution.

[0017] In a preferred embodiment, in step a, the temperature of the hydrothermal reaction is 160 - 180 °C, and the time of the hydrothermal reaction is 1 - 2 h.

[0018] In a preferred embodiment, in step a, after the hydrothermal reaction, it is washed with water, dried, and the gray product is collected, thus obtaining MnO-P with a SnO2 nanolayer deposited on its surface, denoted as MnO-P@SnO2 nanotubes.

[0019] In step a, a SnO2 nanolayer is uniformly deposited on the surface of MnO-P by a simple hydrothermal method. The obtained MnO-P@SnO2 nanotubes have a good structure. Compared with the MnO-P nanowires, their surface becomes slightly rough. In addition, due to the deposition of SnO2, the diameter of these MnO-P@SnO2 nanotubes increases to 70 - 210 nm.

[0020] In step b, the "Tris-HCl buffer solution" is prepared by dissolving tris(hydroxymethyl)aminomethane (Tris) in water, and then adding 0.1 mol L -1 of dilute hydrochloric acid dropwise to the Tris solution to adjust the pH value. In a preferred embodiment, the concentration of the Tris-HCl buffer solution is 5 - 15 mmol / L. In a preferred embodiment, the pH value of the Tris-HCl buffer solution is 8.0 - 8.8; more preferably 8.3 - 8.5. In a preferred embodiment, the mass-to-volume ratio of dopamine hydrochloride to the Tris-HCl buffer solution is 1 mg:1.2 - 5.0 mL.

[0021] In a preferred embodiment, in step b, the mass ratio of dopamine hydrochloride to MnO-P@SnO2 nanotubes is 1:1 - 1:8. In a more preferred embodiment, the mass ratio is 1:1 - 1:5.

[0022] In a preferred embodiment, in step b, the thorough mixing is carried out by ultrasonic or stirring means. In the case of stirring, the time for the thorough mixing reaction is 4 - 6 h.

[0023] The post-treatment of the product of step b includes washing with water and drying. The drying temperature is 60-80 °C and the drying time is 12-24 h.

[0024] In a preferred embodiment, in step c, an acid or a salt is added to remove MnO-P in the MnO-P@SnO2@PDA prepared in step b. In a more preferred embodiment, the acid is oxalic acid and the salt is ammonium chloride. The specific operation includes: placing MnO-P@SnO2@PDA in a solution of oxalic acid or ammonium chloride and stirring for 20-40 min to remove MnO-P, where the mass ratio of MnO-P@SnO2@PDA to oxalic acid is 1:60-1:140, or the mass ratio of MnO-P@SnO2@PDA to ammonium chloride is 1:60-1:140.

[0025] The post-treatment of the product of step c includes washing with water and drying. The drying temperature is 60-80 °C and the drying time is 12-24 h.

[0026] In a preferred embodiment, the inert atmosphere in step d is nitrogen or argon.

[0027] In step d, the purpose of the first annealing is to form a nitrogen-doped carbon nanotube coating.

[0028] In a preferred embodiment, the first annealing includes heating to 600-700 °C at a rate of 2-3 °C / min and holding for 4-6 h. The first annealing further includes natural cooling to room temperature after holding.

[0029] The product after the first annealing in step d does not require post-treatment and is directly used for subsequent reactions.

[0030] In a preferred embodiment, the phosphorus source in step d is selected from hypophosphite or elemental phosphorus. In a more preferred embodiment, the hypophosphite includes but is not limited to sodium hypophosphite, calcium hypophosphite, ammonium hypophosphite or their hydrates. In a more preferred embodiment, the elemental phosphorus is red phosphorus. In a more preferred embodiment, the mass ratio of the product of step c to the hypophosphite is 1:4-1:10, or the mass ratio of the product of step c to the elemental phosphorus is 1:0.7-1:1.6. In a more preferred embodiment, the grinding time is 3-5 min.

[0031] In step d, the purpose of the second annealing is phosphorization.

[0032] In a preferred embodiment, the second annealing in step d includes heating to 250-300 °C at a rate of 5 °C / min and holding for 30-50 min. The second annealing further includes natural cooling to room temperature after holding.

[0033] After the second annealing in step d, the post-treatment includes washing and drying. Wash several times with a dilute HCl solution of 0.1 - 0.2 mol / L and water, and the drying temperature is 60 - 80 °C and the drying time is 12 - 24 h. The final product, Sn4P3 nanoparticle / carbon nanotube composite, is denoted as Sn4P3@CNT.

[0034] Furthermore, the raw material MnO-P nanowires of the present invention can be obtained by referring to the literature synthesis method, and are preferably prepared by a hydrothermal reaction using KMnO4 as the raw material. In the hydrothermal reaction using KMnO4 as the raw material: preferably, the hydrothermal reaction is carried out in the presence of PVP; preferably, the mass ratio of KMnO4 to PVP is 1:0.35 - 1:0.8; preferably, the hydrothermal reaction temperature is 150 - 170 °C and the hydrothermal reaction time is 9 - 12 h; after the hydrothermal reaction is completed, a grayish-red product is obtained. The morphology of the product is a solid nanowire structure with a smooth surface, and the diameter is uniformly distributed in 50 - 190 nm, denoted as MnO-P nanowires.

[0035] In the present invention, room temperature refers to 10 - 30 °C; unless otherwise specified, the operations of the present invention are carried out at room temperature.

[0036] In the present invention, the water refers to deionized water.

[0037] The present invention also provides a Sn4P3 nanoparticle / carbon nanotube composite, which is prepared by the preparation method described above. In the Sn4P3 nanoparticle / carbon nanotube composite, the mass content of carbon is 1 - 10%, the structure of the composite includes Sn4P3 nanoparticles encapsulated in carbon nanotubes, the outer diameter of the carbon nanotubes is 100 - 200 nm, the wall thickness of the carbon nanotubes is 1 - 25 nm, and the particle size distribution of the Sn4P3 nanoparticles is 2 - 10 nm.

[0038] In a preferred embodiment, in the Sn4P3 nanoparticle / carbon nanotube composite, the length of the carbon nanotubes is 500 nm - 2 μm.

[0039] In a preferred embodiment, in the Sn4P3 nanoparticle / carbon nanotube composite, the wall thickness of the carbon nanotubes is 10 - 25 nm.

[0040] In a preferred embodiment, in the Sn4P3 nanoparticle / carbon nanotube composite, the particle size distribution of the Sn4P3 nanoparticles is 4 - 7 nm.

[0041] In a preferred embodiment, the specific surface area of the Sn4P3 nanoparticle / carbon nanotube composite is 50 - 300 m 2 g -1 .

[0042] In a preferred embodiment, the Raman spectrum of the Sn4P3 nanoparticle / carbon nanotube composite shows a D peak and a G peak, and the peak intensity ratio I D / I G is 0.85 to 1.10.

[0043] In a preferred embodiment, single crystal detection shows that in the Sn4P3 nanoparticle / carbon nanotube composite, the crystal structure of Sn4P3 is hexagonal, and the space group is No. 166; the unit cell parameters are and (Z = 3); is 481.8(1).

[0044] The present invention also provides the use of the Sn4P3 nanoparticle / carbon nanotube composite obtained by the preparation method of the present invention in the preparation of the negative electrode material of a secondary battery. In a preferred embodiment, the secondary battery is selected from a lithium ion secondary battery, a sodium ion secondary battery or a potassium ion secondary battery.

[0045] The present invention also provides a secondary battery, wherein the negative electrode material of the secondary battery comprises the Sn4P3 nanoparticle / carbon nanotube composite obtained by the preparation method of the present invention. In a preferred embodiment, the secondary battery is selected from a lithium ion secondary battery, a sodium ion secondary battery or a potassium ion secondary battery.

[0046] The Sn4P3 nanoparticle / carbon nanotube composite obtained by the preparation method of the present invention can be used to prepare the negative electrode material of a secondary battery, and then reassembled into a secondary battery to test the electrochemical performance.

[0047] The specific operation for preparing the negative electrode material of the secondary battery is as follows: The working electrode is prepared by mixing the active material (such as the composite material of the present invention, or other negative electrode materials), the conductive material and the binder in a mass percentage ratio of 50 to 99.5 wt%: 0.1 to 40 wt%: 0.1 to 40 wt%. The conductive material is at least one or a mixture of several of carbon black, acetylene black, natural graphite, carbon nanotubes, graphene, and carbon fibers; the binder is at least one or a mixture of several of polytetrafluoroethylene, polyvinylidene fluoride, polyurethane, polyacrylic acid, polyamide, polypropylene, polyvinyl ether, polyimide, styrene-butadiene copolymer, sodium carboxymethyl cellulose, and sodium alginate; N-methylpyrrolidone (NMP) is added to adjust the viscosity, and then it is dispersed evenly using a high-speed disperser and coated on a copper foil; then it is vacuum dried at 60 °C overnight, and the loading amount of the active material of the obtained working electrode is 0.8 to 1.0 mg cm -2 . The charge and discharge current density used for testing the cycle performance is 100 mA g -1 and 200 mA g -1 .

[0048] The specific operation of assembling a lithium-ion secondary battery is as follows: In addition to the negative electrode of the lithium-ion secondary battery, it also includes a positive electrode, a separator, and an electrolyte; among them, the positive electrode is any one of lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMnO2), lithium nickel manganese cobaltate (Li(Ni 0.8 Co 0.1 Mn 0.1 )O2); the separator includes any one of an aramid separator, a non-woven fabric separator, a polyethylene microporous membrane, a polypropylene membrane, a polypropylene-polyethylene double-layer or three-layer composite membrane, and its ceramic-coated separator; the electrolyte contains a lithium salt (electrolyte) and a non-aqueous solvent for dissolving it. As the electrolyte, LiPF6, LiClO4, LiBF4, LiClF4, LiAsF6, LiSbF6, LiAlO4, LiAlCl4, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiCl, LiI, etc. can be cited. As the non-aqueous solvent, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), etc. can be cited.

[0049] The specific operation of assembling a sodium-ion secondary battery is as follows: In addition to the negative electrode of the sodium-ion secondary battery, it also includes a positive electrode, a separator, and an electrolyte; among them, the positive electrode is any one of sodium cobaltate, sodium manganate, sodium nickelate, or a composite metal oxide of sodium; the separator includes any one of an aramid separator, a non-woven fabric separator, a polyethylene microporous membrane, a polypropylene membrane, a polypropylene-polyethylene double-layer or three-layer composite membrane, and its ceramic-coated separator; the electrolyte contains an electrolyte and a solvent; the electrolyte is at least one or a mixture of multiple of NaPF6, NaBF4, NaClO4, NaAsF6, NaCF3SO3, NaN(CF3SO2), NaBOB, NaCl, NaBr, NaI; the solvent includes at least one or a mixture of several of propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, ethylene carbonate, butylene carbonate, diethyl carbonate, ethyl acetate, and vinylene sulfite.

[0050] The specific operation of assembling a potassium-ion secondary battery is as follows: In addition to the negative electrode of the potassium-ion secondary battery, it also includes a positive electrode, a separator, and an electrolyte; among them, the positive electrode material is K2Ti4O9, K2Ti6O 13 、K2Ti8O 17, any one of titanium phosphate (KTi2(PO4)3) and titanium carbide compound (Ti3C2); the separator includes any one of aramid separator, non-woven fabric separator, polyethylene microporous membrane, polypropylene membrane, polypropylene-polyethylene double-layer or three-layer composite membrane and its ceramic-coated separator; the electrolyte contains electrolyte and solvent; the electrolyte is at least one of potassium hexafluorophosphate, potassium perchlorate, potassium fluoroborate and potassium bis(fluorosulfonyl)imide; the solvent is carbonate-based solvent or ether-based solvent. The carbonate-based solvent is at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate and fluorinated carbonate; the ether-based solvent is at least one of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether and ethylene glycol dimethyl ether.

[0051] The secondary battery prepared with the Sn4P3 nanoparticle / carbon nanotube composite material of the present invention shows excellent electrochemical performance, has a high specific capacity and a high initial Coulomb efficiency, as well as good long-term cycling stability.

[0052] The present invention also provides an energy storage and supply device, which includes the Sn4P3 nanoparticle / carbon nanotube composite material prepared by the preparation method of the present invention, or the secondary battery of the present invention. The energy storage and supply device includes but is not limited to energy storage devices, electric devices, electronic products, etc. In a preferred embodiment, the secondary battery is selected from lithium-ion secondary batteries, sodium-ion secondary batteries or potassium-ion secondary batteries.

[0053] The present invention prepares the Sn4P3 nanoparticle / carbon nanotube composite material by a directed template method, polydopamine coating, carbonization and phosphidation, and applies the composite material to a secondary battery. The beneficial effects of the present invention are as follows: (1) The composite material of the present invention adopts a hollow structure design to achieve monodisperse Sn4P3 particles and a strong carbon network structure. The introduction of the carbon nanotube network provides a conductive interconnect network and a buffer layer, with advantages such as excellent electrical conductivity and elastic support. The one-dimensional tubular structure can improve the directional transport efficiency of electrons and ions. The thinner the tube wall, the better its electrical conductivity, and it is beneficial to the full penetration of the electrolyte. The characteristics of monodisperse Sn4P3 nanoparticles shorten the ion diffusion path and maintain the inherent advantages of Sn4P3. Using polydopamine as the carbon source, nitrogen doping is successfully introduced to improve the electronic conductivity, and the nitrogen-doped carbon sites contribute to Li + / Na + / K +

[0054] insertion / extraction process to be fast and reversible, and the porous hard carbon material maintains mechanical stability.

[0055] (2) The composite material of the present invention is applied to prepare the anode material of a secondary battery. Due to the reasonable structural design of the composite material, the prepared tin phosphide / carbon nanoscale composite material can accelerate electron and ion transport, improve the conductivity of the anode material and stabilize the solid electrolyte interface (SEI), and can also adapt to expansion strain. Therefore, the high-performance electrode material effectively improves the electrochemical activity of the secondary battery, and the secondary battery has excellent high capacity and cycle stability, which is conducive to the effective promotion and recognition of the novel phosphorus-based composite material in future commercial applications.

[0056] (3) The preparation method of the present invention is simple, low-cost, has good repeatability, and is environmentally friendly, with broad industrial application prospects. The vapor deposition low-temperature phosphidation used therein is a synthesis method with simple process and high safety, and can prepare composite materials with high purity, monodispersity, and uniform particles. Description of the Drawings

[0057] Figure 1 It is the scanning electron microscope (SEM) image of MnO-P nanowires in Example 1.

[0058] Figure 2 It is the scanning electron microscope (SEM) image of MnO-P / SnO2 nanotubes in Example 1.

[0059] Figure 3 It is the scanning electron microscope (SEM) image of MnO-P / SnO2@PDA in Example 1.

[0060] Figure 4 It is the transmission electron microscope (TEM) image of the composite material Sn4P3@CNT in Example 1. The left figure is the overall view, and the right figure is the cross-sectional view of the carbon nanotube.

[0061] Figure 5 The upper figure is the X-ray diffraction pattern (XRD) of the composite material Sn4P3@CNT in Example 1, and the lower figure is the standard diffraction pattern of Sn4P3 (PDF#73-1820). The abscissa is 2θ (°), and the ordinate is the intensity (a.u.). Figure 6 It is the size distribution histogram of Sn4P3 nanoparticles in the composite material Sn4P3@CNT in Example 1. The abscissa is the nanoparticle size (nm), and the ordinate is the count.

[0062] Figure 7 It is the N2 adsorption-desorption isotherm curve diagram of the composite material Sn4P3@CNT in Example 1 and the material in Comparative Example 1. The abscissa is the relative pressure (P / P0), and the ordinate is the adsorption amount (cm 3 g -1 , STP). The square dots in the figure represent Example 1, and the round dots represent Comparative Example 1.

[0063] Figure 8 Raman spectrum of the composite material Sn4P3@CNT in Example 1, where the abscissa is the Raman shift (cm -1 ), and the ordinate is the intensity (a.u.).

[0064] Figure 9 CV curves of the lithium-ion battery in Example 1 within 0.01 - 3.0 V at a scanning rate of 0.1 mV s -1 , where the abscissa is the voltage (V vs. Li + / Li), and the ordinate is the current (mA).

[0065] Figure 10 Nyquist plots of the lithium-ion battery in Example 1 before cycling (shown as black dots in the figure) and after the 100th cycle (shown as white dots in the figure) in the frequency range of 0.1×10 -1 - 10 6 Hz, where the abscissa is Z′ (ohm) and the ordinate is Z″ (ohm).

[0066] Figure 11 Cycling performance plots of the lithium-ion battery in Example 1, the sodium-ion battery in Example 4, the potassium-ion battery in Example 5, and the sodium-ion battery in Comparative Example 1 at a current density of 100 mA g -1 , where the abscissa is the number of cycles (n) and the ordinate is the capacity (mAh g -1 ), and the hollow dots in the figure represent charging and the solid dots represent discharging.

[0067] Figure 12 Cycling performance plots of the lithium-ion battery in Example 1, the sodium-ion battery in Example 4, the potassium-ion battery in Example 5, and the sodium-ion battery in Comparative Example 1 at a current density of 200 mA g -1 , where the abscissa is the number of cycles (n) and the ordinate is the capacity (mAh g -1 ), and the hollow dots in the figure represent charging and the solid dots represent discharging. Detailed implementation manners

[0068] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following further elaborates on the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0069] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0070] The reagents and materials used in the following examples can all be obtained from commercial sources unless otherwise specified.

[0071] X-ray powder diffraction (XRD) is usually applied to the analysis of crystal structures. It mainly uses X-rays incident on a crystal to generate a periodically varying electromagnetic field in the crystal, enabling a non-destructive in-depth analysis of the material. In this invention, a D8 Advance X-ray diffractometer produced by Bruker in Germany is used. Its target material is a Cu target (incident / receiving slit Rs = 0.15 mm / 0.15 mm, incident slit Ds = 0.05 mm, wavelength is 0.154178 nm). The material to be tested is in powder form, and the 2θ angle range for testing is 20 - 70°.

[0072] The specific surface area pore adsorption analyzer (BET) utilizes the reversible physical adsorption of nitrogen molecules on the surface of a sample. By measuring the equilibrium adsorption amount and combining with a theoretical model, information such as the specific surface area and pore size distribution of the material can be obtained. In this invention, an ASAP 2020M + C device produced by MICROMERITICS in the United States is used to complete the test of automatic specific surface area pore adsorption.

[0073] The field emission scanning electron microscope (SEM) mainly uses a beam of high-energy electrons to bombard the surface of a sample. Through different interactions between electrons and the sample, various signals such as secondary electrons and backscattered electrons are generated, which is a general device for studying the microscopic morphology of materials.

[0074] Raman Spectrum is a method of scattering spectrum analysis, mainly used for the test and analysis of the molecular structure of materials. By analyzing the scattering spectrum formed by the incident light frequency, information related to molecular vibration, rotation, etc. can be obtained.

[0075] The carbon content is obtained through thermogravimetric-differential thermal analysis (TG-DTA). Under programmed temperature control and a certain atmosphere, the mass of the sample and the temperature difference between the sample and the reference material input are measured simultaneously as a function of temperature or time. Steps occur due to the mass loss of the composite material, and the carbon content is calculated by reading the values of the steps.

[0076] Example 1

[0077] 1.1 Preparation of the composite material Sn4P3@CNT in Example 1

[0078] Step 1: KMnO4 (171 mg), PVP (K30, 90 mg) and deionized water (72 mL) are ultrasonically stirred at room temperature for 30 min to form a solution. Then the obtained solution is sealed in a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner and hydrothermally reacted at 160 °C for 9 h. After the hydrothermal reaction ends, it is cooled, and the precipitate is washed several times with deionized water and ethanol and then dried to obtain a grayish-red product, which is a nanowire of a manganese oxide precursor, denoted as MnO-P nanowire.

[0079] Step 2: The prepared MnO-P nanowires (230 mg), ethanol (26 mL), and deionized water (43 mL) in Step 1 were ultrasonically dispersed at room temperature for 20 min to form a homogeneous suspension. K2SnO3·3H2O (0.33 g) and urea (2.07 g) were added to the above suspension, and the mixture was stirred at room temperature for 30 min. Then, the obtained mixture was sealed in a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner and hydrothermally reacted at 170 °C for 1 h. After the hydrothermal reaction was completed, it was cooled, and the precipitate was washed with deionized water and dried overnight. The gray product, which is MnO-P with a SnO2 nanolayer deposited on the surface, was collected and denoted as MnO-P@SnO2 nanotubes.

[0080] Step 3: The prepared MnO-P@SnO2 nanotubes (375 mg) in Step 2 were dispersed in 10 mM Tris-HCl buffer solution (470 mL, pH≈8.5), ultrasonically dispersed for 10 min, and then dopamine hydrochloride (188 mg) was added under vigorous stirring. Stirring was continued for 5 h, and the precipitate was washed with deionized water and dried overnight to obtain a product (320 mg), which is MnO-P@SnO2 nanotubes coated with polydopamine and denoted as MnO-P@SnO2@PDA.

[0081] Step 4: At room temperature, MnO-P@SnO2@PDA (320 mg) prepared in Step 3 was added to an aqueous solution (500 mL) containing oxalic acid (31.5 g), and the mixture was stirred for 30 min to remove MnO-P. Then, the precipitate was washed 4 times with deionized water and dried overnight at 60 °C to obtain a product, which is polydopamine-coated SnO2 nanotubes and denoted as SnO2@PDA precursor.

[0082] Step 5: The SnO2@PDA precursor prepared in Step 4 was annealed for the first time by heating it to 600 °C at a rate of 2 °C / min in an N2 atmosphere and holding for 4 h, and then naturally cooling to room temperature; 0.06 g of the product obtained from the first annealing and NaH2PO2·H2O (0.3 g) were manually ground for 3 min, and the ground mixture was annealed for the second time by heating it to 280 °C at a rate of 5 °C / min - in an N2 atmosphere and holding for 30 min, and then naturally cooling to room temperature; it was washed several times with dilute HCl solution (0.1 mol L -1 ) and deionized water, and dried to obtain the final product, which is Sn4P3 nanoparticle / carbon nanotube composite and denoted as Sn4P3@CNT.

[0083] 1.2 Characterization of the composite material Sn4P3@CNT in Example 1

[0084] The scanning electron microscope (SEM) image of the product MnO-P nanowires in Step 1 is as Figure 1As shown, the morphology is nanowires, which are smooth-surfaced solid structures with a diameter of 50 - 190 nm and uniform dispersion.

[0085] The scanning electron microscope (SEM) image of the product MnO-P@SnO2 nanotubes in Step 2 is as Figure 2 shown. Compared with the MnO-P nanowires, its surface becomes slightly rougher. In addition, due to the deposition of SnO2, the diameter of the MnO-P@SnO2 nanotubes increases to 70 - 210 nm.

[0086] The scanning electron microscope (SEM) image of the product MnO-P / SnO2@PDA in Step 3 is as Figure 3 shown. Compared with the MnO-P@SnO2 nanotubes, it shows a uniform carbon shell and a slightly rough surface. It is confirmed that polydopamine (PDA) has successfully coated the material uniformly.

[0087] The transmission electron microscope (TEM) of the composite material Sn4P3@CNT is as Figure 4 shown. It shows that the structure of the composite material is monodisperse nanoparticles encapsulated in carbon nanotubes. The outer diameter of the carbon nanotubes is about 150 nm, the wall thickness is 15 - 20 nm, and the length of the carbon nanotubes is about 1 μm.

[0088] The X-ray diffraction pattern (XRD) of the composite material Sn4P3@CNT is as Figure 5 shown above. By comparing with the standard diffraction pattern, it can be seen that the main diffraction peaks of the composite material match the standard diffraction pattern of Sn4P3 (PDF#73-1820), indicating that the tin phosphide in the composite material belongs to a single Sn4P3.

[0089] The size distribution histogram of Sn4P3 nanoparticles in the composite material Sn4P3@CNT is as Figure 6 shown. It shows that the particle size distribution of Sn4P3 nanoparticles is in the range of 4 - 7 nm.

[0090] The N2 adsorption - desorption isotherm curves of the composite material Sn4P3@CNT and the material Sn4P3 in Comparative Example 1 are as Figure 7 shown. The curves of the two are different, and the shape of the adsorption - desorption isotherm curve is related to the pore structure of the material. The specific surface area of Sn4P3@CNT is 185.3 m 2 g -1 , which is much larger than the specific surface area of 8.9 m 2 g -1 of the material Sn4P3 in Comparative Example 1. This means that without the carbon layer coating, the microstructure and morphology of the material collapse, resulting in a huge difference in specific surface area.

[0091] The Raman spectrum of the composite material Sn4P3@CNT is asFigure 8 as shown. The two peaks of the sample at 1343 cm -1 and 1573 cm -1 correspond to the disordered carbon form (D peak) and the graphite carbon form (G peak). Generally, the peak intensity ratio I D / I G ratio reflects the crystallinity of carbon. Figure 8 It shows that I D / I G is 1.02, and the D peak is slightly stronger than the G peak, indicating that the Sn4P3@CNT sample is mainly composed of disordered carbon due to the doping of N, Sn, and P elements.

[0092] The carbon content of the composite material Sn4P3@CNT is 5%.

[0093] 1.3 Preparation of Lithium-Ion Batteries from the Composite Material Sn4P3@CNT in Example 1 and Testing of Electrochemical Performance

[0094] A lithium-ion battery was prepared by encapsulating the active material and a lithium foil in a CR2032 coin cell case. The specific operation is as follows: The working electrode was prepared by mixing the active material (the product of Example 1), a conductive material (acetylene black), and a polyvinylidene fluoride binder (PVDF) in a certain mass ratio (7:2:1), adding NMP to adjust the viscosity, then dispersing evenly using a high-speed disperser, and coating it on a copper foil. Subsequently, it was vacuum-dried at 60 °C overnight, and the active material loading of the obtained working electrode was 0.9 mg cm -2 . Using a lithium foil as the counter electrode, with an electrolyte system of 1 M LiPF6 / EC:DEC (1:1) and a microporous polypropylene membrane (Celgard 2400) as the separator, the lithium-ion battery of Example 1 was prepared.

[0095] Figure 9 Figure shows the CV curves of the lithium-ion battery of Example 1 in the initial four cycles at a scanning rate of 0.1 mV s -1 within 0.01 - 3.0 V. The reduction peaks at 0.24 V and 0.30 V correspond to the alloying reaction between tin and lithium and the formation of the solid electrolyte interface (SEI) film. During the first charging process, the negative electrode peaks at 0.53 V and 1.05 V are related to the decomposition of Li x Sn alloy and Li3P. In subsequent cycles, the oxidation peaks do not shift significantly, indicating good reversibility due to the small size and thin layer structure. In addition, the same subsequent CV curves indicate stable electrochemical characteristics.

[0096] Figure 10 Figure shows the lithium-ion battery of Example 1 at 0.1×10 -1 ~10 6Nyquist plots before cycling and after the 100th cycle in the Hz frequency range. The semicircle (charged state) of the electrode in Example 1 after cycling is significantly smaller than that before cycling, indicating that due to the carbon coating in the composite material, the electrochemical contact between the electrode and the electrolyte during cycling is better, promoting the improvement of the electron transfer efficiency during the lithium-ion insertion / extraction reaction.

[0097] The cycling performance graph of the lithium-ion battery in Example 1 at a current density of 100 mA g -1 is as shown in Figure 11 . It shows that it has a high capacity, with a discharge / charge specific capacity reaching 1532 / 1394 mAh g -1 , and the initial efficiency is as high as 90%; it has good cycling stability, with a high capacity retention rate of 85% after 100 cycles at a constant current discharge density of 100 mA g -1 ; at a constant current discharge density of 200 mA g -1 , the reversible capacity still remains at 980 mAh g -1 after 200 cycles, as shown in Figure 12 .

[0098] Example 2

[0099] 2.1 Preparation of the composite material Sn4P3@CNT in Example 2

[0100] Except that the addition amount of dopamine hydrochloride is changed to 375 mg, other preparation steps are the same as those in Example 1.1.

[0101] 2.2 Characterization of the composite material Sn4P3@CNT in Example 2

[0102] Referring to the characterization method of the composite material Sn4P3@CNT in Example 1, the composite material Sn4P3@CNT in Example 2 was tested. The results show that the structure of the composite material Sn4P3@CNT in Example 2 is monodisperse nanoparticles encapsulated in carbon nanotubes. The outer diameter of the carbon nanotubes is 155 nm, the wall thickness is 20 - 25 nm, the particle size distribution of the Sn4P3 nanoparticles is 4 - 7 nm, the length of the carbon nanotubes is about 1 μm, and the specific surface area is 211.3 m 2 g -1 .

[0103] 2.3 Preparation of a lithium-ion battery from the composite material Sn4P3@CNT in Example 2 and testing of its electrochemical performance

[0104] Replacing the composite material in Example 1 with the composite material in Example 2 and keeping other conditions unchanged, according to the preparation method of the lithium-ion battery in Example 1.3, the lithium-ion battery in Example 2 was obtained.

[0105] Example 2 The cycling performance of the lithium-ion battery at a current density of 100 mA g -1 for 100 cycles shows that the initial efficiency of the battery is high, at 85%; the battery has good cycling stability, and at a constant current discharge density of 100 mA g -1 , the capacity retention rate after 100 cycles is 80%.

[0106] Example 3

[0107] 3.1 Preparation of the composite material Sn4P3@CNT in Example 3

[0108] Except that the addition amount of dopamine hydrochloride is changed to 75 mg, other preparation steps are the same as those in Example 1.1.

[0109] 3.2 Characterization of the composite material Sn4P3@CNT in Example 3

[0110] Referring to the characterization method of the composite material Sn4P3@CNT in Example 1, the composite material Sn4P3@CNT in Example 3 was tested. The results show that the structure of the composite material Sn4P3@CNT in Example 3 is monodisperse nanoparticles encapsulated in carbon nanotubes. The outer diameter of the carbon nanotubes is 145 nm, the wall thickness is 10 - 15 nm, the particle size distribution of the Sn4P3 nanoparticles is 4 - 7 nm, the length of the carbon nanotubes is about 1.2 μm, and the specific surface area is 135.8 m 2 g -1 .

[0111] 3.3 Preparation of a lithium-ion battery from the composite material Sn4P3@CNT in Example 3 and testing of its electrochemical performance

[0112] Replace the composite material in Example 1 with the composite material in Example 3, and keep other conditions unchanged. According to the preparation method of the lithium-ion battery in Example 1.3, the lithium-ion battery in Example 3 was obtained.

[0113] The cycling performance of the lithium-ion battery in Example 3 at a current density of 100 mA g -1 for 100 cycles shows that the initial efficiency of the battery is high, at 83%; the battery has good cycling stability, and at a constant current discharge density of 100 mA g -1 , the capacity retention rate after 100 cycles is 78%.

[0114] 3.4 Comparison of the characteristics of the composite materials with different polydopamine coating amounts in Examples 1 - 3 of the present invention and the electrochemical performance of their lithium-ion batteries is shown in Table 1.

[0115] Table 1 Comparison of the characteristics of the composite materials with different polydopamine coating amounts and the electrochemical performance of their lithium-ion batteries

[0116]

[0117] The data in Table 1 show that according to the preparation method of the present invention, the composite material Sn4P3@CNT of the present invention can be prepared under different amounts of polydopamine coating. The carbon nanotube wall is thin, only 10 - 25 nm. The reasonable structural design makes the specific surface area of the composite material relatively large, and the electrochemical activity of the lithium-ion battery prepared from the composite material is high, and the initial efficiency is ≥83%; it has good cycle stability. At a constant current discharge density of 100 mA g -1 , the capacity retention rate after 100 cycles is ≥78%.

[0118] Example 4 Preparation of a sodium-ion battery from the composite material Sn4P3@CNT of Example 1 and testing of its electrochemical performance

[0119] A sodium-ion battery was prepared by encapsulating the active material and a sodium sheet in a CR2032 coin cell case. The specific operation is as follows: The working electrode was prepared by mixing the active material (the product of Example 1), the conductive material (acetylene black), and the polyvinylidene fluoride binder (PVDF) in a certain mass ratio (7:2:1), adding NMP to adjust the viscosity, then dispersing evenly using a high-speed disperser, and coating it on a copper foil. Subsequently, it was vacuum dried at 60 °C overnight, and the active material loading of the obtained working electrode was 0.9 mg cm -2 . Using a sodium sheet as the counter electrode, with an electrolyte system of 1 M NaClO4 / EC:DMC (1:1) and a microporous polypropylene membrane (Celgard 2400) as the separator, the sodium-ion battery of Example 4 was prepared.

[0120] The cycling performance of the sodium-ion battery of Example 4 at a current density of 100 mA g -1 shows that the sodium-ion battery has a high capacity, and the discharge / charge specific capacity reaches 770 / 600 mAh g -1 , and the initial efficiency is 77%; the sodium-ion battery has good cycle stability. At a constant current discharge density of 100 mA g -1 , the capacity retention rate after 100 cycles is high, at 85%, as Figure 11 shown; at a constant current discharge density of 200 mA g -1 , the reversible capacity still remains at 414 mAh g -1 after 200 cycles, as Figure 12 shown.

[0121] Example 5 Preparation of a potassium-ion battery from the composite material Sn4P3@CNT of Example 1 and testing of its electrochemical performance

[0122] A potassium-ion battery was prepared by encapsulating the active material and potassium pieces in a CR2032 button battery case. The specific operation is as follows: The working electrode was prepared by mixing the active material (the product of Example 1), the conductive material (acetylene black), and the polyvinylidene fluoride binder (PVDF) in a certain mass ratio (7:2:1), adding NMP to adjust the viscosity, then dispersing evenly using a high-speed disperser, and coating it on a copper foil. Subsequently, it was vacuum dried at 60 °C overnight, and the active material loading of the obtained working electrode was 0.9 mg cm -2 . Using potassium pieces as the counter electrode, with an electrolyte system of 1 M KPF6 / EC / DEC (1:1) and a microporous polypropylene membrane (Celgard 2400) as the separator, the potassium-ion battery of Example 5 was prepared.

[0123] The cycling performance of the potassium-ion battery of Example 5 at a current density of 100 mA g -1 showed that the potassium-ion battery had a high capacity, and the discharge / charge specific capacity reached 703 / 518 mAh g -1 , and the initial efficiency was 74%; the potassium-ion battery had good cycling stability. At a constant current discharge density of 100 mA g -1 , the capacity retention rate after 100 cycles was 71%, as Figure 11 shown; at a constant current discharge density of 200 mA g -1 , the reversible capacity still remained at 303 mAh g -1 after 200 cycles, as Figure 12 shown.

[0124] Comparative Example 1

[0125] 1. The synthesis of Sn4P3 includes the following steps:

[0126] Step 1: Add K2SnO3·3H2O (0.33 g) and urea (2.07 g) to a mixed solution of ethanol (26 mL) and deionized water (43 mL), stir at room temperature for 30 min, then seal the mixture in a 100 mL stainless steel reaction kettle with a polytetrafluoroethylene lining, and carry out a hydrothermal reaction at 170 °C for 1 h. After cooling, wash with deionized water and dry overnight.

[0127] Step 2: Heat the SnO2 precursor prepared in step (1) to 600 °C at a rate of 2 °C / min under a N2 atmosphere, hold for 4 h, and then cool naturally to room temperature.

[0128] Step 3: Manually grind the product of step (2) (0.06 g) and NaH2PO2·H2O (0.3 g) for 3 min, and heat it to 280 °C at a rate of 5 °C / min under a N2 atmosphere, hold for 30 min, then cool naturally to room temperature, and use dilute HCl solution (0.1 mol L-1 ) and washed several times with deionized water, then dried to obtain the final product Sn4P3.

[0129] 2. Characterization of the material Sn4P3 in Comparative Example 1

[0130] The N2 adsorption - desorption isotherm curve of the material Sn4P3 in Comparative Example 1 is as Figure 7 shown, and the specific surface area is only 8.9 m 2 g -1 , which is much smaller than the specific surface area of the composite material Sn4P3@CNT of the present invention. This means that without the carbon layer coating, the microscopic morphology and structure of the material collapse, resulting in a huge difference in specific surface area.

[0131] 3. Preparation of sodium - ion batteries from the material Sn4P3 in Comparative Example 1

[0132] Replace the product of Example 4 with the material Sn4P3 in Comparative Example 1, and keep other conditions unchanged. According to the preparation method of the sodium - ion battery in Example 4, the sodium - ion battery of Comparative Example 1 is obtained.

[0133] Test Example 1 Comparative test of the electrochemical performance of different secondary batteries

[0134] The lithium - ion battery of Example 1, the sodium - ion battery of Example 4, the potassium - ion battery of Example 5, and the sodium - ion battery of Comparative Example 1 are tested for energy storage cycle performance under the condition of a charge - discharge current density of 100 mA g -1 for 100 cycles. The results are as Figure 11 shown, and the specific data are shown in Table 2.

[0135] Table 2 Comparison table of the energy storage cycle performance of secondary batteries (charge - discharge at 100 mA g -1 for 100 cycles)

[0136]

[0137] The lithium - ion battery of Example 1, the sodium - ion battery of Example 4, the potassium - ion battery of Example 5, and the sodium - ion battery of Comparative Example 1 are tested for energy storage cycle performance under the condition of a charge - discharge current density of 200 mA g -1 for 200 cycles. The results are as Figure 12 shown, and the specific data are shown in Table 3.

[0138] Table 3 Comparison table of the energy storage cycle performance of secondary batteries (charge - discharge at 200 mA g -1 for 200 cycles)

[0139]

[0140] The results in Table 2 and Table 3 show that, compared with the sodium-ion battery of Comparative Example 1, the secondary batteries of Examples 1, 4, and 5 of the present invention all exhibit excellent electrochemical performance:

[0141] (1) The secondary battery has a high specific capacity and a high initial efficiency. The discharge / charge specific capacity of the lithium-ion battery reaches 1532 / 1394 mAh g -1 , with an initial efficiency of 90%, the discharge / charge specific capacity of the sodium-ion battery reaches 770 / 600 mAh g -1 , with an initial efficiency of 77%, and the discharge / charge specific capacity of the potassium-ion battery reaches 703 / 518 mAh g -1 , with an initial efficiency of 74%.

[0142] (2) The secondary battery has a high capacity retention rate. The Li + / Na + / K + batteries of the present invention have capacity retention rates of 85%, 85%, and 71% respectively after 100 cycles at a constant current discharge density of 100 mA g -1 , and capacity retention rates of 70%, 69%, and 58% respectively after 200 cycles at a constant current discharge density of 200 mA g -1 , all showing a long cycle life and good cycle stability.

[0143] The significant improvement in electrochemical performance is conducive to the effective promotion and recognition of the novel phosphorus-based composite material of the present invention in future commercial applications.

Claims

1. A preparation method of Sn4P3 nanoparticle / carbon nanotube composite material, characterized in that, The following steps are involved: Step a, hydrothermally reacting manganese oxide precursor nanowires with stannate and urea, wherein the mass ratio of manganese oxide precursor nanowires, stannate and urea is 1: 1-2: 8-13, to prepare a manganese oxide precursor with a SnO2 nanolayer deposited on the surface, which is recorded as MnO-P@SnO2 nanotubes; Step b, fully mixing the MnO-P@SnO2 nanotubes prepared in step a with Tris-HCl buffer and dopamine hydrochloride to obtain polydopamine-coated MnO-P@SnO2 nanotubes, denoted as MnO-P@SnO2@PDA; Step c, removing the manganese oxide precursor in the MnO-P@SnO2@PDA prepared in step b, and obtaining polydopamine-coated SnO2 nanotubes, which are recorded as SnO2@PDA precursor; Step d, annealing the SnO2@PDA precursor obtained in step c for the first time under an inert atmosphere, then grinding it with a phosphorus source, and annealing the ground mixture for the second time under an inert atmosphere to obtain the Sn4P3 nanoparticle / carbon nanotube composite material, recorded as Sn4P3@CNT.

2. The preparation method according to claim 1, characterized in that, In step b, the concentration of Tris-HCl buffer is 5~15 mmol / L, the pH value of Tris-HCl buffer is 8.0~8.8, the mass volume ratio of dopamine hydrochloride to Tris-HCl buffer is 1 mg:1.2~5.0 mL, and the mass ratio of dopamine hydrochloride to MnO-P@SnO2 nanotubes is 1:1~1:

8.

3. The preparation method according to claim 1, characterized in that, In step c, an acid or a salt is added to remove the manganese oxide precursor in MnO-P@SnO2@PDA.

4. The preparation method according to claim 1, characterized in that, In step d, the first annealing includes heating to 600-700°C at a rate of 2-3°C / min and keeping warm for 4-6 hours, the phosphorus source is selected from hypophosphite or elemental phosphorus, and the second annealing includes heating to 250-300°C at a rate of 5°C / min and keeping warm for 30-50 minutes.

5. A Sn4P3 nanoparticle / carbon nanotube composite material, characterized in that, Prepared by the preparation method according to any one of claims 1 to 4.

6. The Sn4P3 nanoparticle / carbon nanotube composite material according to claim 5, wherein The structure comprises Sn4P3 nanoparticles encapsulated in carbon nanotubes. The mass content of carbon in the Sn4P3 nanoparticle / carbon nanotube composite material is 1-10%, the outer diameter of the carbon nanotube is 100-200 nm, the tube wall thickness is 1-25 nm, and the particle size distribution of the Sn4P3 nanoparticles is 2-10 nm.

7. Use of the Sn4P3 nanoparticle / carbon nanotube composite material according to claim 5 or 6 in preparing negative electrode materials for secondary batteries.

8. A secondary battery, characterized in that, The negative electrode material of the secondary battery comprises the Sn4P3 nanoparticle / carbon nanotube composite material according to claim 5 or 6.

9. An energy storage and supply device, characterized in that, The energy storage and supply device comprises the Sn4P3 nanoparticle / carbon nanotube composite material according to claim 5 or 6 or the secondary battery according to claim 8.

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