Pretreatment Process Before Heat Pyrolysis of Plant‐based Precursors Paving Way for Fabricating High‐Performance Hard Carbon for Sodium‐Ion Batteries

Abstract The increasing demand for sodium‐ion batteries has risen due to sodium resources that are inexpensive and abundant compared with its counterpart of lithium‐ion batteries. Development of anode materials with high performance is central issue for sodium‐ion batteries. Plant‐based hard carbon material is a promising anode material for sodium ion batteries due to its green preparation process, favorable ions transport channel, and special porous structure. Previous studies have not systematically correlated the material's inherent structure limitation with its electrochemical properties, resulting in a complex classification and a lack selection of pretreatment methods. In this review, the intrinsic limitations in the structure of plant‐based precursors are divided into four parts, including impure components, single chemical structure, uncontrollable crystalline texture, and irregular porous structure. The previous pretreatment methods are reclassified, including purification component aiming at plant‐based precursors, optimized structure, and precabornized process aiming at intermediate products. Furthermore, the pretreatment strategies are discussed according to the preferred structures of plant‐based hard carbon and the relationship between structure and performance is systematically expounded. This review provides deep understanding of the mechanism of pretreatment and a guide for selecting appropriate pretreatment strategies to optimize the structure of plant‐based hard carbon for sodium ion batteries.