흑연에서의 용매-리튬 이온 삽입 반응을 이용한 리튬 이온 이차전지 소재 개발

Abstract

The intercalation of lithium ions into graphite electrode is the key underlying mechanism of modern lithium-ion rechargeable batteries. However, co-intercalation of lithium-ions and solvent into graphite is considered undesirable because it can trigger the exfoliation of graphene layers and destroy the graphite crystal, resulting in poor cycle life. Here, we demonstrate that the [lithium–solvent]+ intercalation does not necessarily cause exfoliation of the graphite electrode and can be remarkably reversible with appropriate solvent selection. First-principles calculations suggest that the chemical compatibility of the graphite host and [lithium–solvent]+ complex ion strongly affects the reversibility of the co-intercalation, and comparative experiments confirm this phenomenon. Moreover, it is revealed that [lithium–ether]+ co-intercalation of natural graphite electrode enables much higher power capability than normal lithium intercalation, without the risk of lithium metal plating. To be specific, [lithium-ether]+ co-intercalation shows capacity retention of approximately 87% of the theoretical capacity at current density of 1 A g−1. This unusual high rate capability of the co-intercalation is attributable to the (i) absence of the last desolvation step, (ii) negligible formation of the solid-electrolyte interphase on graphite surface, and (iii) partially capacitive charge-transfer mechanism. This work constitutes the first step toward the utilization of fast and reversible [lithium–solvent]+ complex ion intercalation chemistry in graphite for rechargeable battery technology.