Preparation Of N/O/S Co-Doped Hard Carbon Anode Material And Its Energy Storage In Sodium/Potassium Ion Batteries

The fierce growth in demand for lithium-ion batteries has promoted the rapid development of sodium/potassium-ion batteries with higher resource abundance.Based on the mature working principle of lithium-ion batteries,choosing a reasonable electrode material is the key to breaking through the bottleneck of the development of sodium/potassium-ion batteries.Compared with commercial graphite anodes,hard carbon can provide abundant adsorption and insertion sites for Na⁺and K⁺due to its disordered structure.However,the large ionic radii of Na⁺and K⁺easily induce material volume expansion,which hinders the improvement of rate performance and cycle life.This paper aims to develop low-cost,high-performance hard carbon anode materials which are suitable for sodium/potassium ion batteries,and the research is as follows:N,O,S triple-doped hard carbons（NOS-HCs）with hierarchical micro/mesoporous structures were prepared by carbonizing waste tires through a one-step synthesis method,and used as negative electrode active materials for sodium-ion batteries.The in situ generated NOS-HC900 has a nanostructure of graphitic turbine layers.Based on the synergistic adjustment between crystal parameters and heteroatoms,an initial charge specific capacity of 425.3 m Ah g^-1 and a reversible specific capacity of 402.5 m Ah g^-1 after 1000 cycles were obtained at a current density of 100 m A g^-1,and it has a stable charging specific capacity of 315.1 m Ah g^-1at 2000 m A g^-1.In particular,the sodium storage mechanism of NOS-HC900 is discussed in detail:the adsorption of N and O in NOS-HC900 can be synergistically weakened by S doping,thereby enhancing the migration rate of solvated molecules on the electrode surface.Furthermore,XPS etching confirmed that Na storage did not occur in the form of pore filling,but was first adsorbed at the edge of the defect and further intercalated between carbon layers adjacent to the defect,inducing a fast kinetic process for the formation of Na storage.NOS-HC900@4 was obtained by modifying NOS-HC900 with a mechanical ball milling method,and the reason for the improvement of electrochemical performance was explained in detail from the difference in microstructure after modification.On the premise of maintaining the original interlayer spacing of NOS-HC900@4,the ball milling modification reduced the abundance of ordered nano-microcrystalline domains,so that the concentrated mesopores with larger specific surface area and larger pore size are obtained.Therefore,the sample disorder is increased.Thanks to the abundant defects brought about by the ball milling and the doped heteroatoms,the surface adsorption dominates the potassium storage and the ion migration can be accelerated.At the same time,the volume change caused by interlayer intercalation is reduced,and the performance stability during the long cycle is enhanced.NOS-HC900@4showed more excellent rate performance and cycle performance overall.At a current density of100 m A g^-1,the initial charge-specific capacity was 314.3 m Ah g^-1 and the stable reversible specific capacity was 308.3 m Ah g^-1,a charge-specific capacity of 207.6 mAh g^-1 can be obtained at a current density of 1000 mA g^-1.