Elucidating electrochemical intercalation mechanisms of biomass-derived hard carbon in sodium-/potassium-ion batteries

摘要

Hard carbon materials are characterized by having rich resources,simple processing technology,and low cost,and they are promising as one of the anode electrodes for commercial applications of sodium-/potassium-ion batteries.Simultaneously,exploring the alkali metal ion storage mechanism is particularly important for designing high-performance electrode materials.However,the structure of hard carbon is more complex,and the description of energy storage behavior is quite controversial.In this study,the Magnolia grandiflora Lima leaf is used as a precursor,combined with simple pyrolysis and impurity removal processes,to obtain biomass-derived hard carbon material(carbonized Magnolia grandiflora Lima leaf[CMGL]).When it is used as an anode for sodium-ion batteries,it exhibits a high specific capacity of 315mAh/g,and the capacity retention rate is 90.0%after 100 cycles.For potassium-ion batteries,the charge specific capacity is 263.5mAh/g,with a capacity retention rate of 85.5%at the same cycling.Furthermore,different electrochemical analysis methods and microstructure characterization techniques were used to further elucidate the sodium/potassium storage mechanism of the material.All the results indicate that the high potential slope region represents the adsorption/desorption characteristics on the surface active sites,whereas the low-potential quasiplateau region belongs to the ion insertion/extraction in the graphitic microcrystallites interlayer.It is noteworthy that potassium ion is randomly intercalated between the graphitic microcrystallite layer without forming a segmented intercalation compound structure.