Extended Plateau Capacity of Hard Carbon Anode for High Energy Lithium-Ion Batteries

Hard carbon materials have shown promising potential for sodium-ion storage due to accommodating larger sodium ions. However, as for lithium-ion storage, the challenge lies in tuning the high lithiation plateau capacities, which impacts the overall energy density. Here, hard carbon microspheres (HCM) are prepared by tailoring the cross-linked polysaccharide, establishing a comprehensive methodology to obtain high-performance lithium-ion batteries (LIBs) with long plateau capacities. The "adsorption-intercalation mechanism" for lithium storage is revealed combining in situ Raman characterization and ex situ nuclear magnetic resonance spectroscopy. The optimized HCM possesses reduced defect content, enriched graphitic microcrystalline, and low specific surface area, which is beneficial for fast lithium storage. Therefore, HCM demonstrates a high reversible capacity of 537 mAh g^-1 with a significant low-voltage plateau capacity ratio of 55%, high initial Coulombic efficiency, and outstanding rate performance (152 mAh g^-1 at 10 A g^-1). Moreover, the full cell (HCM||LiCoO₂) delivers outstanding fast-charging capability (4 min charge to 80% at 10 C) and impressive energy density of 393 Wh kg^-1. Additionally, 80% reversible capacity can be delivered under -40 °C with competitive cycling stability. This work provides in-depth insights into the rational design of hard carbon structures with extended low-voltage plateau capacity for high energy LIBs.