ICE optimization strategies of hard carbon anode for sodium-ion batteries:from the perspective of material synthesis

With the continuous exploration of researchers in the field of sodium-ion batteries,the performance of these batteries has been greatly improved,and they have a wide range of application prospects in large-scale energy storage,traffic power and other fields.Hard carbon is the most important anode material for sodium-ion batteries.Although it has the advantages of low cost,stable structure and performance,it still has the problems of low initial Coulombic efficiency(ICE)and poor rate performance in application.In order to solve the problem of low ICE of hard carbon anode in sodium-ion batteries,in recent years the literature about hard carbon anode in sodium-ion batteries has been comprehensively reviewed.Based on the microstructure of hard carbon material,the causes of low ICE of hard carbon are analyzed.At the same time,from the point of view of material structure design and regulation,the current optimization strategies of hard carbon anode ICE are summarized,including the following aspects:optimization and improvement of the carbonization process,precursor screening and design,surface coating strategy,micro-pore structure control,catalytic carbonization strategy.We hope that this review will provide reference for further optimization of hard carbon properties and its large-scale application in sodium-ion batteries.

Recent progress of interface modification of layered oxide cathode material for sodium-ion batteries

With the advantages of similar theoretical basis to lithium batteries,relatively low budget and the abundance of sodium resources,sodium ion batteries(SIBs)are recognized as the most competitive alternative to lithium-ion batteries.Among various types of cathodes for SIBs,advan-tages of high theoretical capacity,nontoxic and facile synthesis are introduced for layered transition metal oxide cathodes and therefore they have attracted huge attention.Nevertheless,layered oxide cathodes suffer from various degradation issues.Among these issues,interface instability including surface residues,phase transitions,loss of active transition metal and oxygen loss takes up the major part of the degra-dation of layered oxides.These degradation mechanisms usually lead to irreversible structure collapse and cracking generation,which signifi-cantly influence the interface stability and electrochemical performance of layered cathodes.This review briefly introduces the background of researches on layered cathodes for SIBs and their basic structure types.Then the origins and effects on layered cathodes of degradation mech-anisms are systematically concluded.Finally,we will summarize various interface modification methods including surface engineering,doping modification and electrolyte composition which are aimed to improve interface stability of layered cathodes,perspectives of future research on layered cathodes are mentioned to provide some theoretical proposals.