Sodium Storage Mechanism and Optimization Strategies for Hard Carbon Anode of Sodium Ion Batteries

Sodium ion batteries (SIBs) have been regarded as a very suitable electrochemical energy storage technology for large-scale energy storage due to its low cost and high safety. Suitable anode material is one of the keys to boosting the commercialization process of SIBs. Significantly, hard carbon (HC) anode is considered as the most practical anode material for SIBs due to its rich natural sources, low cost, non-toxic, environmentally friendly, and low sodium storage voltage. However, hard carbon anode also faces the problems of low initial Columbic efficiency, insufficient long cycle stability and poor rate performance, which restrict its practical application in SIBs. In recent years, extensive investigations have been done to improve the performance of hard carbon anode, herein, this review discusses the recent progress of performance optimization strategies of hard carbon anode from four aspects, including structure control, morphology design, interface manufacture, and electrolyte optimization and conducts an analysis of the merits and demerits of each optimization method. Moreover, this review also discusses the bottlenecks and challenges in the process of practical application of hard carbon anode for sodium ion batteries.