Study On Tin-based Composites As Anode Materials For Potassium Ion Batteries

Lithium-ion batteries are widely used in various fields due to their inherent advantages.However,the lack of lithium resources and uneven distribution pose challenges to the application of lithium-ion batteries,and it is urgent to develop alternatives energy storage system.Potassium is abundant and has similar properties to lithium,and the electrode potential of potassium is close to that of lithium,which possesses the potassium-ion batteries of a higher energy density.These advantages indicate a broad application prospect of potassium-ion baterries.Alloy-type anodes are favored by researchers because of their high theoretical capacity and suitable voltage platform.Sn-based materials are particularly valuable for its high earth abundance and environmental benignity.However,the radius of potassium ion is so large that it will cause the pulverization of electrode material during the cycle and lead to the rapid capacity decay.Generally,to improve the electrochemical performance,efforts have been put on downsizing the Sn-based materials and combining them with carbon matrix to shorten the electron/ion transmission pathway.Based on the above analysis,we synthesized three kinds of Sn-based materials and used them as the anode of potassium-ion batteries for systematic research.The specific research content is as follows:Firstly,tin sulfur selenium（SnSSe）is synthesized through vacuum solid-phase reaction,and then expanded graphite,carbon nanotubes,and carbon nanoparticles are separately ball-milled with SnSSe to obtain SnSSe/multilayer graphene nanosheets（SnSSe/MGS）,SnSSe/carbon nanotubes（SnSSe/CNT）and SnSSe/carbon nanoparticles（SnSSe/CNP）.Studies have shown that layered SnSSe/MGS nanocomposites have the best potassium storage performance.SnSSe/MGS delivers a high specific capacity(423 mAh g^-1 at 100 mA g^-1),excellent rate capability(218mAh g^-1 at 5 A g^-1),and long cycling stability(271 mAh g^-1 after 500 cycles at 100mA g^-1).More importantly,the full cell composed of the SnSSe/MGS anode and the potassiated 3,4,9,10-perylene-tetracarboxylic aciddianhydride（PTCDA）cathode exhibits a high reversible capacity of 209 mAh g^-1 after 100 cycles at 50 mA g^-1.Secondly,tin telluride（SnTe）is synthesized by vacuum solid-phase reaction,and then high-energy ball milling with expanded graphite（MGS）to obtain SnTe/MGS composite.Compared with pure SnTe,the electrochemical performance of the SnTe/MGS composite has been significantly improved.When used as the negative electrode of potassium-ion batteries,it can provide a reversible capacity of 338 mAh g^-1 in the first cycle,and the corresponding initial coulombic efficiency is 68.4%.After 1000 cycles,the capacity is still 279.4 mAh g^-1,the capacity retention rate is82.7%,and the excellent rate capability is 91.7 mAh g^-1 at a current density of 5 A g^-1.Finally,we prepare nanocomposites of tin phosphide（Sn₄P₃）and expanded graphite by two-step high-energy ball milling,and explore the effects of different carbon contents on the potassium storage performance of Sn₄P₃ active materials.The results show that when the mass ratio of Sn₄P₃ to expanded graphite is 8:2,the electrochemical performance of the composite material is the best.When Sn₄P₃/MGS-80 is used as the electrode material,the initial reversible capacity can reach 345.4 mAh g^-1 at 100 mA g^-1,and the capacity can still maintain 90%after 100cycles,and the good stability is also maintained.