Reinventing the High-rate Energy Storage of Hard Carbon: the Order-degree Governs the Trade-off of Desolvation-Solid Electrolyte Interphase at Interfaces

Abstract

In alkali metal-ion battery systems, the electrolyte enables being decomposed on the electrode surface to form a solid electrolyte interphase (SEI) film. In principle, a thin, uniform SEI film facilitates the enhancement of the performance of the cell. Herein, we successfully distinguish the effects of desolvation behavior and SEI process on the kinetic behavior of hard carbon (HC) electrodes by adopting the strategy of switching the electrolyte interface model to modulate the properties of SEI film. Our findings reveal that although the SEI film is generally responsible for significantly affecting the HC's capacity, the equally crucial desolvation process must not be overlooked. The trade-off between the two factors is found to be determined by the structural features of HCs. Specifically, in the context of a more ordered HC, the desolvation of ions emerges as the rate-limiting step for Na⁺ transport across the electrode/electrolyte interface, exerting a more pronounced effect rather than the SEI. Thus, a close correlation was established between the SEI, solvation structure effects, hard carbon structure, and electrode performance. This linkage is thereof fundamental for the strategic design of electrolytes and the targeted enhancement of cell performance.