Potassium Ion Electrolytes Enable High Rate Performance of Li/CFx Primary Batteries

Combining the cathode and anode materials both possessing the highest theoretical energy density among their category, the Li/CFx primary battery represents advance power sources for versatile applications. However, this technology has long been plagued by poor rate performance and limited the range of its wider applications. Here, the electrochemical behavior of Li/CFx batteries using K-ion electrolyte is systematically investigated and compared with these using Li/Na-ion electrolytes. In comparison with 955 Wh kg(-1) (based on the cathode material) and 1104 Wh kg(-1) using electrolytes of LiPF6 and NaPF6, respectively, the Li/CFx battery provides superior energy density of 1232 Wh kg(-1) at 5C using KPF6, because of the higher discharge voltage and specific capacity. Mechanistic studies reveal that this substantial improvement of the K-ion electrolyte originates from faster ion diffusion coefficient and facile nucleation, in which the initial generation of KF crystals facilitates ion diffusion, as well as changes nucleation and growth of subsequent discharge products. This research provides a new avenue for designing electrolytes to improve electrochemical performance of primary Li metal batteries.