Pitch-derived Soft and Hard Carbon Materials for Practical Sodium-ion Batteries

Sodium-ion battery (SIB) shows great potential for large-scale energy storage, high-power and low-temperature supplies. Pitch is a promising precursor for preparing carbon anode materials for SIBs owing to its low cost, high carbon yield, and structural tunability. In this review, the preparation and application of pitch-derived soft- and hard-carbons for SIBs are discussed from a practical perspective. We first introduce the full-slope sodium storage behavior of soft carbon, mainly focused on the storage mechanism, high-rate feature, modification strategies, application scenario, and existing challenges. Thereafter, we present the preparation of pitch-derived hard carbon mainly through pre-oxidation and carbonization. The crucial influencing factors, including pitch property, pre-oxidation temperature, holding time, heating rate, atmosphere, and carbonization conditions, as well as the underlying mechanisms, are discussed. From scientific and industrial points of view, we also propose the challenges for application of pitch-derived carbon materials. Future efforts should be paid on clarifying the sodium storage mechanisms and electrochemical kinetics of carbon, revealing the screening criteria of pitch and the "preparation-structure-performance" relationships through a combination of experiments, artificial intelligence, and big data techniques. Material design and preparation guidance should be obtained to push forward pitch-based carbon for practical SIBs.