Recent Progress of Synthetic Polymer-Derived Hard Carbon in Sodium-Ion Batteries

In the past decade, the rapid development of portable electronic devices and electric vehicles has aroused interest in the commercialization of electrochemical energy storage systems. Because of the abundant reserves of sodium on earth, sodium-ion batteries are the most promising alternative to lithium-ion batteries. As an emerging low-cost energy storage technology, sodium-ion batteries have good application prospects in large-scale electrochemical energy storage systems. Carbon materials are the best choice for battery anode materials because of their abundant raw materials, low cost, and low electrochemical potential. Among them, graphite is widely used in commercial lithium-ion batteries because of its excellent chemical stability and high specific capacity. However, because of the limitations of thermodynamics, the interlayer compound between sodium and graphite does not exist, and graphite as the anode of sodium-ion battery shows nearly no sodium storage activity, which leads to considerable loss of capacity. Hard carbon is a battery anode material that is considered to be the most likely to achieve commercial application to sodium-ion batteries anode because of its expandable graphene interlayer, suitable working voltage, and relatively low cost. As an important source of hard carbon precursors, synthetic polymers can have different structures and morphologies when the chemical composition structures and process conditions are adjusted to meet various performance requirements. In this study, the recent progress of synthetic polymer-derived hard carbon for anodes is reviewed, and specific attention is focused on the influence of the types and preparation methods of synthetic polymers on the microstructure and morphology of hard carbon materials, as well as the relationship between morphology and electrochemical properties. Moreover, the key factors, which will help improve the electrochemical performance of hard carbon materials, are discussed, and the main development directions for the future, which will help promote the commercialization of sodium-ion batteries, are proposed. © 2022, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.