Research On The Use Of Porous Carbon-based Materials As Anodes For High-performance Potassium Ion Batteries

With the rapid development of society and technology,high-performance secondary batteries are imminently desired by the high power vehicles.Currently Lithium-ion batteries are are limited by lithium resources with low reserves although it's the most widely used secondary energy storage system,hence alternatives are urgent need to be find.The potassium element has the characteristics of high crustal abundance,environmental friendliness and low cost.Therefore,the potassium-ion batteries are new type of secondary batteries with great application potential.However,the large radius of potassium ions and the slow diffusion rate are the main difficulty when develop high-performance electrode materials,especially anode materials for potassium ion batteries.However,the structure of traditional graphite anode material will be destroyed by repeated potassiation/depotassiation.so they've been suffering low reversible capacity,poor rate and unreliable cycling stability.,Porous carbon materials are the better choice for the anode materials of potassium ion batteries because of their abundant active-sites,stable structure and short ion migration channels.The above two materials show excellent potassium-storage performance.In this paper,we not only used renewable acrylic yarn as raw materials,nano-tin particles as templates,and nitrogen-doped porous carbon nanofibers?NMCNFs?were synthesized by electrospinning technology,but also choose acetylacetonate as the carbon source and prepared porous graphite carbon material by self-template technology through high-temperature carbonization and acid washing.The NMCNFs possess highly nitrogen-doped?7.98%?and internal cross-linked multiple pores can provide abundant active sites and shorten ion diffusion channels.The nitrogen-doped porous carbon nanofibers have a high specific capacity of 351.1 m Ah g^-1after 500 cycles under a current density of 200 m A g^-1.Even at a high current density of 10 A g^-1,the specific capacity of 134 m Ah g^-1can still be released.The most noteworthy is its long-cycle cycling performance.It has a specific capacity of 131.2 m Ah g^-1after up to 21,000 cycles at a current density of 2 A g^-1,and the capacity retention rate after 1000 cycles is 100%.In addition,the potassium storage performance of the porous graphitic carbon?PHC-1-700?was also investigated.It retained the ultra-high specific capacity of 414 m Ah g^-1 after 500 cycles at a current density of 200 m A g^-1.When the current density increased to 5 A g^-1,the released capacity of porous graphitic carbon materials are 149m Ah g^-1.Even at a high current density of 1 A g^-1,the porous graphitic carbon materials still retained the specific capacity of 167 m Ah g^-1after 2000 cycles.In order to further study the potassium storage mechanism and kinetics of nitrogen-doped porous carbon nanofibers,we performed a series of ex-situ characterizations.Through the study of CV curves at different sweep speeds,we find its mixed potassium storage mechanism of surface-controlled pseudocapacitance and redox.With the number of cycles increasing,the values of K⁺diffusion coefficient and activation energy show an increasing and decreasing trend,respectively,represent it has self-increasing kinetic characteristics.And ex-situ Raman spectroscopy,XRD,and FTIR test results show that deintercalated/intercalated of K⁺in nitrogen-doped porous carbon nanofibers are highly reversible.Density functional theory calculation results show that the doping of pyridine nitrogen and pyrrole nitrogen and defects of material can effectively improve the potassium storage performance of the material.