Decoding Hard Carbon Microstructure for Fast‐Charging Lithium‐Ion Batteries

Abstract Hard carbon is a promising anode material for fast‐charging lithium‐ion batteries (LIBs) due to its abundant lithium‐ion storage sites, short ion diffusion pathways, and tunable microstructure. However, challenges such as an unclear lithium‐ion storage mechanism, low initial Coulombic efficiency, and poor cycling stability hinder its practical application in high‐rate LIBs. To the end, this review decodes fundamental structure–performance relationships between hard carbon microstructure and its fast‐charging behavior, aiming to elucidate the underlying lithium‐ion storage mechanisms. The influence of precursor materials on microstructure is discussed first and the proposed lithium‐ion storage mechanisms are summarized. Next, the key bottlenecks limiting fast‐charging performance are analyzed and state‐of‐the‐art design strategies, including optimization of active sites, enhancement of ion/electron transport, and solid electrolyte interface engineering are summarized. Furthermore, the unique role of the isotropic and cross‐linked structure of hard carbon in mitigating volume expansion is highlighted, which can also improve the fast‐charging capability of other anode materials. Finally, future research directions to accelerate the commercialization of hard carbon for high‐performance fast‐charging LIBs are outlined. This review offers valuable insights and guidance for advancing hard carbon anodes and next‐generation energy storage technologies.