Pushing the theoretical limit of Li-CF(x) batteries: a tale of bifunctional electrolyte.

In a typical battery, the inert electrolyte functions solely as the ionic conductor without contribution to the cell capacity. Here we demonstrate that the most energy-dense Li-CF(x) battery delivers a capacity exceeding the theoretical maximum of CF(x) with a solid electrolyte of Li3PS4 (LPS) that has dual functions: as the inert electrolyte at the anode and the active component at the cathode. Such a bifunctional electrolyte reconciles both inert and active characteristics through a synergistic discharge mechanism of CF(x) and LPS. The synergy at the cathode is through LiF, the discharge product of CF(x), which activates the electrochemical discharge of LPS at a close electrochemical potential of CF(x). Therefore, the solid-state Li-CF(x) batteries output 126.6% energy beyond their theoretic limits without compromising the stability of the cell voltage. The additional energy comes from the electrochemical discharge of LPS, the inert electrolyte. This bifunctional electrolyte revolutionizes the concept of conventional batteries and opens a new avenue for the design of batteries with unprecedented energy density.