Unraveling the Key Atomic Interactions in Determining the Varying Li/Na/K Storage Mechanism of Hard Carbon Anodes

摘要

Hard carbons have been identified as competitive anodes for Li/Na/K-ionbatteries but their Li/Na/K-ion storage mechanisms significantly vary in differentbatteries. It is fundamental to understand the basic science behind thedifference. Herein, it is theoretically revealed that defects on the carbon layersgenerally have an influential impact on the atomic interactions including themetal–metal (M–M) and metal–carbon (M–C) interactions, thereby determiningwhether the stored alkali-metal atoms are in ionic or quasi-metallicstates. Upon increasing the number of metal atoms on a carbon layercomposed of only hexatomic rings, K tends to be stored in an ionic statesimilar to Li due to the dominant M–C interaction, while on a carbon layerwith defects, K tends to be stored in a quasi-metallic state similar to Na dueto the dominant M–M interaction. For experimental verification, a glassycarbon, the extreme form of hard carbon with dominant sp2 hybridization andonly Stone–Wales defects, is selected as a model anode, and its Li/Na/K-ionstorage mechanisms are exactly consistent with the theoretical prediction.More profoundly, for the first time, the quasi-metallic K cluster information iscaptured by ex situ electron paramagnetic resonance.