Preparation Of Carbon-based Anode Materials For Potassium Ion Batteries And Study On Their Potassium Storage Mechanism

Potassium-ion batteries(KIBs)have recently attracted extensive attention as a potential alternative for the next-generation energy storage systems due to the merits of resource abundance and relatively low redox voltage(-2.93 V vs.SHE)of potassium.However,the larger radius of K+would cause sluggish kinetics of anodes with substantial volume changes upon cycling,which in turn results in a sharp drop in cycle performance.In this thesis,two types of high-performance carbon-based KIB anode materials are designed and prepared,which enable stable accommodatation of potassium ions and theirreversible and rapid deintercalation.Besides,in-situ transmission electron microscopy(In-situ TEM)is employed to systematically investigate their potassium storage mechanisms.The research contents and main results are summurized as follows:(1)A viable anode material composed of hollow porous bowl-like hard carbon dual-doped with nitrogen(N)and phosphorus(P)(N/P-HPCB)is developed for highperformance PIBs.With prominent merits in structure,the as-fabricated N/P-HPCB electrode manifests extraordinary potassium storage performance in terms of high reversible capacity(458.3 mA h g-1 after 100 cycles at 0.1 A g-1),superior rate performance(213.6 mA h g-1 at 4 A g-1),and long-term cyclability(205.2 mA h g-1 after 1000 cycles at 2 A g-1).N/P co-doping is beneficial to promote the adsorption/diffusion of K+ and enhance the electronic conductivity,thereby ensuring improved capacity and rate performance.Moreover,in situ TEM in conjunction with ex situ microscopy and Raman spectroscopy confirms the exceptional cycling stability,which originates from the excellent potassiation/depotassiation reversibility and robust structural integrity of N/P-HPCB electrode during cycling.(2)An anode material composed of nitrogen-rich carbon nanosheets is prepared,in which the introduction of Sb single atoms significantly enhances the potassium storage capacity and reaction kinetics of the material.By adopting a simple and efficient onestep pyrolysis method,we prepare the carbon nanosheets(Sb SA/NC)with high nitrogen doping content(13%)modified by single Sbatoms.The dopant N atoms can provide a good microscopic environment for the coordination/separation of Sb atomic points.A suitable amount of antimony source can alleviate the agglomeration of Sb atoms during the entire synthesis process,thus forming an electrode material with good dispersion and moderate loading.Meanwile,the as-prepared material also has excellent potassium storage performance.After 115 cycles at 0.1 A g-1,it exhibits a high reversible K storage capacity of 593.3 mA h g-1.After 400 cycles at a current density of 2 A g-1,a stable capacity of 246.4 mA h g-1 can still be retained.Ex-situ scanning/transmission electron microscopy studies show that the Sb SA/NC anodes have the capability of uniform potassium storage during cycling and can maintain the structural integrity of the anodes.