Engineering high-concentration electrolyte with high ionic conductivity and solvation structure regulation enables high-performance Li/CFx primary batteries

Abstract

Lithium/fluorinated carbon (Li/CF_x) batteries have garnered significant interest because of their exceptionally high theoretical energy density compared to other primary energy storage systems. However, the slow ionic transport of the electrolyte during the discharge phase restricts its ability to achieve the theoretical maximum. Herein, a novel high-concentration electrolyte is proposed based on one salt (lithium tetrafluoroborate (LiBF₄)) and two high dielectric constant solvents (propylene carbonate (PC) and N,N-dimethylacetamide (DMAC)). This innovative electrolyte formulation has significantly enhanced a notable improvement in the discharge performance of Li/CF_x batteries. Specifically, Li/CF_x batteries used of the high-concentration electrolyte demonstrate a higher discharge voltage platform of 2.68 V (compared to 2.50 V with a commercial electrolyte) and a higher energy density of 2175 Wh Kg⁻¹ (vs 1928 Wh Kg⁻¹ with a commercial electrolyte) at a current density of 50 mA g⁻¹. Notably, the overall performance improvements are largely due to the utilization of a high-concentration electrolyte with high ionic conductivity and regulated solvation structure (with less coordinated solvents), leading to the superior Li⁺ transport and facilitating more effective participation of Li⁺ and CF_x in the reaction, thereby boosting capacity. This strategy offers valuable insights into electrolyte design for the improvement of electrochemical performance of Li/CF_x batteries.