Controllable Construction Of Nano-Antimony/Three-Dimensional Porous Carbon Composite Anode Materials Via Salt-Template And Their Sodium/Potassium Storage Mechanisms

Lithium-ion batteries（LIBs）are widely used in various industries,but face challenges such as resource shortages and rising costs.Sodium/potassium ion batteries（SIBs/PIBs）are considered as important energy storage devices to replace LIBs.The development of efficient SIBs/PIBs anode materials is an important prerequisite to promote their application and development.Antimony（Sb）-based materials are one of the potential candidates due to their high theoretical capacity and suitable operating voltage,but the large-radius sodium/potassium ions（Na⁺/K⁺）will cause their volume to expand dramatically during cycling,thereby resulting in a sharp deterioration in performance.Coupling modified carbon matrix is an effective way to improve the performance of Sb-based materials.However,it is still a great challenge to explore inexpensive and efficient synthesis processes to construct higher-performance antimony/carbon（Sb/C）composite anodes.Herein,we used low-cost and water-soluble sodium chloride（NaCl）as a template,and Sb/C composites with different structures were controllably prepared via freeze-drying,thermal-drying,and spray-drying combined with heat treatment process.The relationship between synthesis process,structure,and energy storage mechanism was systematically investigated to find a new way to obtain Sb/C composites with optimal energy storage performance.The main research contents and results are as follows:1)Based on the Na⁺and Cl^-ionized by raw material to in-situ generate NaCl act as templates.A 3D discontinuous porous N-doped carbon network embedded with solid Sb nanoparticles（Sb-N@3DPC）was constructed by freeze-drying and one-step pyrolysis process.The effect of raw material acidity and alkalinity on the porosity of3D structure was studied;the relationship between porosity and Sb-N-C valence bond and K⁺storage performance was explored;the K-storage capability,mechanism,and practicality of Sb-N@3DPC were investigated.The studies show that HCl（strong acid）is easier to ion exchange with Na₃C₆H₅O₇（strong base and weak acid salt）than NH₄Cl（strong acid and weak base salt）to generate more NaCl,thereby regulating the size and continuity of the porous structure;the Sb-N-C valence bond is beneficial to enhance the stability of F-K in the solid electrolyte interface（SEI）and the interaction with the carbon matrix,so that F-K is enriched in the SEI,thus forming a thin and stable layer of SEI to enhance the electrode conductivity and stability.Therefore,Sb-N@3DPC exhibits excellent K storage performance in both half/full cells.2)NaCl with uniform morphology as a template was prepared via"anti-solvent precipitation".A 3D continuous porous N/S co-doped carbon network embedded with solid Sb nanoparticles（Sb@NS-3DPC）was fabricated through thermal-drying combined with pyrolysis process.The effect of NaCl on the size of Sb nanoparticles was investigated;the structural evolution of the carbon matrix during energy storage was explored;the Na-storage performance,mechanism,and practicality of Sb@NS-3DPC were discussed.The results show that NaCl acts like a"reaction platform"to"pin"Sb（～30 nm）,and Naatoms derived from NaCl can enhance the carbon matrix to inhibit agglomeration and growth of Sb;the carbon matrix occurs graphitization upon cycling,thus improving the electrochemical performance of the electrode during cycling;the Nastorage capacity retention rate of Sb@NS-3DPC is98.9%after 20000 cycles at 10 A g^-1,and the capacity retention rate of its full-cell is97.4%after 200 cycles at 0.2 A g^-1.3)NaCl was added directly to act as a template.A 3D continuous porous N/S co-doped carbon hollow spheres embedded with yolk-shelled Sb@C nanoparticles（Sb@NS-3DPCMSs-120）was synthesized via spray-drying method combined with a"one-pot multi-step"pyrolysis process.The formation mechanism of the yolk-shelled Sb@C structure was investigated;the Na-storage performance,mechanism,and practicality of Sb@NS-3DPCMSs-120 were explored.The studies show that the one-pot multi-step pyrolysis involves a continuous phase transition（Sb O_x→Sb₂S₃→Sb）.Since the volume of Sb is smaller than that of Sb₂S₃,a limited void is generated between carbon and Sb.During the heat preservation process at 600°C,Sb（melting point is 630°C）is easily sublimated and escaped,resulting in the reduction of the particle size of Sb and the increase of the pore space of the yolk shell.Therefore,the Sb structure and content of the sample can be controlled by the graphene content in the carbon matrix and the high temperature holding time;Sb@NS-3DPCMSs-120exhibits～100%Nastorage capacity retention after 10000 cycles at 10 A g^-1,and has a high specific capacity(140 m Ah g^-1)at 5°C,and its full-cell also presents excellent electrochemical performance.4)Adding NaCl as a template,and a 3D continuous porous N-doped carbon hollow spheres embedded with core-shell Sb@Sb₂O₃ nanoparticles（Sb@Sb₂O₃@N-3DCHs）was prepared by spray drying and a two-step heat treatment process.The formation mechanism of the core-shelled Sb@Sb₂O₃ structure was studied;the influence of the heterostructure interface between core-Sb and shell-Sb₂O₃ on Na/K storage was explored;the Na/K storage performance,mechanism,and practicality of Sb@Sb₂O₃@N-3DCHs were investigated.The researches show that the surface of solid Sb can be oxidized into a core-shelled Sb@Sb₂O₃ structure during the low-temperature oxidation treatment,and a heterostructure interface will be spontaneously generated between Sb and Sb₂O₃.Among them,Sb has a faster Na⁺/K⁺migration ability than Sb₂O₃,while Sb₂O₃ has stronger adsorption capacity for Na⁺/K⁺than Sb,so the heterostructure can enhance the Na⁺/K⁺storage capacity through the synergistic effect between Sb and Sb₂O₃;the capacity retention rates of Sb@Sb₂O₃@N-3DCHs are both 100%after 10000 cycles at 5 A g^-1（Nastorage）and 2 A g^-1（K storage）.Meanwhile,the capacity retention rate is close to 99%after 500 charges and discharges.Through the comparison of the above four Sb/C composites with different structures,it is found that the Sb/C composite with heterostructure interface is more conducive to improve the energy storage performance of the electrode and has more practical value.