Pyrrolidinium ionic liquid as a multifunctional additive of electrolytes for superior Li/CFx batteries

Abstract

Lithium/fluorinated carbon (Li/CF_x) batteries have attracted wide attention due to their ultrahigh energy density and low self-discharge rate. However, robust C-F covalent bonds of CF_x and insufficient ionic conductivity of the discharge product lithium fluoride (LiF) limit the discharge platform and energy density of Li/CF_x batteries at high discharge current densities. Herein, 1,1-dimethylpyrrolidinium tetrafluoroborate (DMP.BF₄) is developed as an additive of the LiBF₄/PC/DME electrolyte to substantially promote the energy density and the rate capability of Li/CF_x batteries. The Li/CF_x battery with DMP.BF₄ exhibits high discharge capacity performance at 0.01C (933mAh g⁻¹, 2442 Wh kg⁻¹) and a remarkable high-rate capability at 10C (823mAh g⁻¹, 1722 Wh kg⁻¹), compared to the performance of battery using initial electrolyte (2142 Wh kg⁻¹ at 0.01C and 1288 Wh kg⁻¹ at 10C). It is found that the interaction between DMP⁺ and F weakens the C-F bond and Li-F bond, forms DMP-LiF coordination compound, accelerates the discharge rate and the reaction depth of the CF_x cathode, and finally improves the capacity and kinetics performance of Li/CF_x battery. This work provides an effective and facile strategy for ionic liquid as multifunctional additives to increase the performance of Li/CF_x batteries.