Sulfur And Nitrogen Co-doped Carbon As The Anode For High-performance Potassium-ion Batteries

Potassium ion batteries show great potential due to their abundant raw materials,rapid ion transport kinetics in electrolyte and low cost,and are considered to be the most promising next generation energy storage devices.Potassium is abundant,and the content of potassium in the earth crust is 1.5 wt%,while the reserve of lithium is only 0.0017 wt%.Significantly,potassium,lithium and sodium elements belong to the same main group and have similar physical and chemical properties.The standard electrode potential of K⁺/K（-2.93V vs SHE）is lower than that of Na⁺/Na（-2.71V vs SHE）.The wide electrochemical window enables it to have a higher energy density.Carbon-based materials are considered as ideal anodes for potassium ion batteries because of their stable properties and abundant sources.However,carbon-based materials are restricted by low first coulombic efficiency.The atomic size of potassium ions is large,so when potassium ions are embedded in the anode,they will cause huge volume expansion,resulting in the collapse of the anode structure and a sharp decrease in energy density.Nitrogen-sulfur co-doped carbon electrode（SNC-650）was prepared by simple sulfidation process as anode for potassium ion batteries.Nitrogen doping helps to improve electrical conductivity and surface wettability,while abundant sulfur doping provides more active sites and helps to expand layer spacing and shorten ion diffusion distance,thus optimizing reaction kinetics.These synergistic effects make SNC-650 exhibit high reversible capacity and excellent rate performance in potassium ion batteries.When used in potassium ion batteries,the SNC-650 anode provides a high specific capacity of 311.2 mAh g^-1 at a current density of 0.1A g^-1.At 1 A g^-1,the capacity retention rate is as high as 96%even after 100 cycles.This work opens up a new way to construct heteroatom doped anode to obtain excellent potassium ion storage performance.