Hard Carbon Anodes for Next-Generation Li-Ion Batteries: Review and Perspective

Carbonaceous materials have been accepted as a promising family of anode materials for lithium-ion batteries (LIBs) owing to optimal overall performance. Among various emerging carbonaceous anode materials, hard carbons have recently gained significant attention for high-energy LIBs. The most attractive features of hard carbons are the enriched microcrystalline structure, which not only benefits the uptake of more Li⁺ ions but also facilitates the Li⁺ ions intercalation and deintercalation. However, the booming application of hard carbons is significantly slowed by the low initial Coulombic efficiency, large initial irreversible capacity, and voltage hysteresis. Many efforts have been devoted to address these challenges toward practical applications. This paper focuses on an up-to-date overview of hard carbons, with an emphasis on the lithium storage fundamentals and material classification of hard carbons as well as present challenges and potential solutions. The future prospects and perspectives on hard carbons to enable practical application in next-generation batteries are also highlighted.