Design, Construction And Potassium Storage Properties Of Anode Materials For Potassium-ion Batteries

Lithium-ion batteries（LIBs）have been widely employed in energy storage and conversion devices,but the lithium resources in the crust are poor and distributed unevenly,which significantly increases the costs of LIBs,thus it is urgently necessary to explore other low-cost and high-performance novel energy devices aim to replacing LIBs.Potassium-ion batteries（PIBs）have attracted extensive attention due to their rich potassium resources and similar electrochemical working mechanism to LIBs.Potassium has lower redox potential（-2.93 V）and can perform wider voltage window.These advantages indicate that PIBs have great potential and important research value in the application of large-scale energy memory devices.Since the working mechanism of PIBs is similar to LIBs,it is inclined to apply the anode materials that have been maturely used in LIBs to PIBs.However,due to the large volume expansion of electrode materials induced by the large size of potassium ions,these materials cannot achieve the comparable performance to LIBs.The volume expansion of electrode materials and the subsequent electrode pulverization are the major challenges during the development of PIBs.Therefore,the research on the electrochemical performance of traditional anode materials,the development and reasonable design of new anode materials are equally important to improve the performance of PIBs.In this paper,biomass-derived carbon material,metallic tin@carbon and cobalt sulfide/carbon were used as the anodes of PIBs,through studying their phase composition,microstructure and electrochemical performance.The research mainly includes:（1）Biomass-derived porous carbon materials have rapidly become the research focus of electrode materials due to their low price,diverse microstructure and low environmental pollution.In this chapter,three-dimensional porous carbon materials were prepared by a simple and universal high temperature calcination using bagasse as carbon source.The obtained materials have mesoporous and microporous structures.This hierarchical porous structure provides numerous channels and active sites for potassium ions,thereby improving the performance of the battery.At the current density of 50 m A g^-1,the initial specific capacity of PIBs based on GZ-700was 282 m Ah g^-1,and the specific capacity retained at 94 m Ah g^-1after 40 cycles.However,electrochemical tests revealed that the potassium storage performance of biomass-derived carbon material is lower than that of sodium storage performance,which can be attributed to the larger ion radius of potassium ions and the induced sluggish reaction kinetics.（2）In order to alleviate the volume change of electrode materials during charge and discharge processes,polydopamine（PDA）was uniformly coated on the surface of Zn Sn O₃nanocubes.After calcination,core-shell Sn@C materials were formed.Sn@C nanomaterials can effectively alleviate the volume expansion of electrode materials,and carbon matrix significantly enhance the conductivity of total electrode.The electrochemical results show that the obtained material calcinated at 750℃possesses the best performance.The initial specific capacity of PIBs was 415 m Ah g^-1at 50 m A g^-1,and the specific capacity retained at 66 m Ah g^-1after 50 cycles.（3）To further solve the volume expansion problem during electrochemical reactions and improve the performance of PIBs,hollow polyhedral carbon structures embedded with polar Co₉S₈nanocrystals were successfully prepared by the template method.The large pore size in Co₉S₈/C hollow polyhedral buffered the volume changes,improved the kinetics of redox reactions,and facilitated the transport and diffusion of potassium ions.The electrochemical results showed that the initial specific capacity was 292 m Ah g^-1at 200 m A g^-1,and the specific capacity retained at79 m Ah g^-1after 70 cycles.