Pushing capacities and energy densities beyond theoretical limits of lithium primary batteries using active CFx nanocapsules with x > 1

Abstract

The high theoretical capacity and long shelf-life of a Li–CF_x system make it most promising for portable electronics. However, the inactivation ideology of –CF₃ groups in CF_x hinders the development of the Li–CF_x system to realize ultra-high energy density. Here, we developed a unique carbon fluoride nanocapsule (CFNC) with x > 1 using a simple thermal-assisted chemical reaction in a controlled environment. The high curvature 3D hollow structure and rich interfaces generated by the engineered wall structure of the CFNC enable activation of –CF and –CF₂ groups. The resulting structure bears high mass and rich charge transfer channels which deliver a cathode capacity of 1056 mA h g⁻¹ and energy density up to 2487 W h kg⁻¹ beyond the theoretical limits of the Li–CF_x system without compromising the cell voltage. To understand the role of structural engineering, density functional theory (DFT) calculations were carried out to confirm active CF₂ components and the effects of various fragment sizes on the voltage plateau, where a higher discharge plateau voltage is obtained with the larger fragment. The materials design presented in this study is an effective and alternative approach to realizing primary batteries with ultra-high energy densities.