Reappraisal of hard carbon anodes for practical lithium/sodium-ion batteries from the perspective of full-cell matters

Hard carbon (HC) has the potential to be a viable commercial anode material in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, current battery performance evaluation methods based on half-cells are insufficient for accurately assessing the performance of HC anodes due to their ultra-low discharge voltage windows. To develop the next-generation of large-scale rechargeable batteries, it is necessary to examine reported HC materials from a full-cell perspective. This review emphasizes the importance of full-cell validation and provides a comprehensive overview of HC anodes - including their history, fundamentals, carbon chemistry induced by temperature, microstructure correlation with electrochemical performance, and debates surrounding lithium/sodium-ion storage mechanisms. Additionally, this review highlights various optimization strategies and suggests potential areas for future application of HC-based lithium-ion batteries (HC-LIBs) and HC-based sodium-ion batteries (HC-SIBs). Furthermore, different challenges and strategies that need to be addressed are presented in the hope of providing inspiration and guidance for the commercialization of HC anodes. Hard carbon shows promise in LIBs and SIBs, but limited understanding and an incomplete assessment system hinder its progress. This review aims to raise awareness among researchers about these challenges.