Substantially Promoted Energy Density of Li||CF_<i>x</i> Primary Battery Enabled by Li⁺-DMP Coordinated Structure

Abstract

Carbon fluoride (CFx) has attracted worldwide attention due to its high theoretical energy density (over 2000 Wh kg–1). However, the large electrochemical overpotential as resulted from the strong C–F covalent bond limits the full utilization of the intrinsic energy from CFx. In this work, a N,N-dimethylpropionamide (DMP) (along with propylene carbonate (PC) cosolvent)-based electrolyte is designed to boost the discharge plateau of lithium (Li)||CFx batteries. It is revealed that DMP molecules have powerful nucleophilicity and a strong solvating ability with Li+ ions by its high donor number (DN), which significantly weakens the C–F covalent bond and thus promotes the discharge voltage plateau and energy density. The optimized electrolyte, 1 M lithium tetrafluoroborate (LiBF4) dissolved in DMP and PC (8:2 in volume), achieves largely elevated discharge voltage plateau of 2.64 V (vs 2.41 V for carbonate-based electrolyte) and the superior energy density up to 2085 Wh kg–1 (vs 1888 Wh kg–1 for carbonate-based electrolyte) at a current density of 10 mA g–1. The superior electrochemical performance of CFx in the optimized electrolyte is further confirmed in pouch-type cells. Meanwhile, the CFx shows less electrode volume expansion, and good calendar life during storage at 60 °C in the optimized electrolyte, which holds great promise for practical applications.