Poly(N-vinylcarbazole) As The New High-Potential Organic Cathode For Sodium-ion Batteries

Sodium element has a high content in the earth’s crust.Thus sodium-ion batteries（SIBs）is one of the very-cheap battery systems.However,the large atomic radius of sodium element makes it difficult to find traditional inorganic electrode materials.Fortunately,organic materials have the advantages of large internal lattice space,designable structure,low cost and controllable synthesis process,indicating that it has great development value as the next-generation electrode materials for SIBs.Therefore,the development of organic compounds with redox activity as the electrode materials for SIBs has become one of the hottest research fields.At present,organic cathode materials exhibiting high potentials are very scarce.For the first time,this paper studies the electrochemical performance of poly（N-vinylcarbazole）((C₁₂H₈NCH:CH₂)_n,PVK)as a new high-potential cathode material for SIBs.In this batteries system,the material has a theoretical specific capacity of 138 mAh/g.This paper demonstrates the electrochemical activity of PVK and explores its behavior in the SIBs systems.Meanwhile,this paper further studies the effect of different conductive additives on the performance of PVK.And the results confirm that the conductive carbon nanotubes can indeed improve the battery performance.Furthermore,the paper also investigates the effect of different electrolytes on the electrochemical performance of PVK.And the results show that the SIBs can show excellent electrochemical performance when the electrolyte is 1M NaPF₆ in EC:DEC with 2%FEC.Afterwards,this paper introduces a small amount of graphene for the electrode compositions.Although the results show that the electrochemical performance of PVK can be greatly improved at low current,but its actual specific capacity quickly decays when the current is increased.To solve this problem,we replaces mesoporous carbon with graphene.And the results demonstrate that PVK can show excellent electrochemical performance under this condition（voltage range is 1.9⁴.6 V）,with the specific capacity reaching up to 119 mAh/g at 100 mA/g and 80 mAh/g after 1000 cycles at 2000 mA/g.Finally,this paper discusses the problems of excessive capacity loss,random jump ponits,and low coulomb efficiency of PVK in SIBs.And the analysis shows that the carbazole group has strong chemical activity at the C3 and C6 positions,which may lead to the dimerization and even multimerization of PVK during the redox processes.