An Imidazole-Based Electrolyte Additive for Enhancing the Cyclability of Graphite||LiFePO4 Batteries

Abstract

Graphite||LiFePO₄ (Gr||LFP) lithium-ion batteries (LIBs) are extensively utilized in stationary energy storage systems, particularly for photovoltaic and wind power generation. Nevertheless, the lifetime of Gr||LFP batteries remains inadequate for fulfilling long-term energy storage demands. In this study, through molecular structure design, an imidazole-based molecule, N,N′-carbonyldiimidazole (CDI), is applied as an innovative solid electrolyte interphase (SEI)-forming additive for Gr||LFP batteries. This molecular design aims to construct a dense and chemically stable SEI on a graphite anode. CDI is characterized by a low energy level of the lowest unoccupied molecular orbital and strong adsorption energy on the graphite surface, attributed to its dual-ring structure. It can be preferentially reduced at 1.58 V vs Li/Li⁺ to form an SEI enriched with nitrogen-containing species. Additionally, CDI facilitates the decomposition of PF₆^– anions, resulting in increased LiF production, which enhances the interfacial stability. As a result, the capacity retention of Gr||LFP pouch cells improves by 18% after 1000 cycles at 45 °C at a 1 P rate compared to cells with the base electrolyte. This study highlights the significance of designing electrolyte additive molecular structures to manipulate the composition and robustness of the SEI layer, offering an approach for formulating electrolytes to achieve long-lifespan LIBs.