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.