In situ electrochemical activation converts carbon disulfide into an organosulfide cathode material for rechargeable lithium-organosulfide batteries

Although carbon disulfide (CS2) exhibits high sulfur content and optimal electrolyte solubility, its intrinsic electrochemical inertness prevents its direct use as an active cathode material, relegating it to a non-capacitive electrolyte additive. In this work, it is found that CS2 can be activated electrochemically to transform into a redox-active cathode material that contributes to reversible capacity in lithium batteries under specific conditions. A coin cell (Li//CS2 battery) using bare carbon paper as the cathode (containing no active material), lithium metal as the anode, and a mixture of commercial liquid electrolyte (1 M LiTFSI in 1,2-dimethoxyethane (DME)/1,3-dioxolane (DOL) (3:1 v/v)) and CS2 as the additive is assembled. When the first-cycle discharge cut-off voltage drops below 1.6 V vs. Li/Li⁺, CS2 can be reduced to form CS2 radicals, which subsequently generate electrochemically active lithium tetrathiooxalate anhydride with thiodicarbonic acid (LTAT) under the present of Li+ ions. And LTAT can serve as a new active material in subsequent battery cycles when the discharge cut-off voltage is restored to the conventional 1.7 V vs. Li/Li⁺ during the following charge–discharge cycles. After CS2 being fully activated, the coin Li//CS2 battery delivers a reversible discharge specific capacity of 163 mAh g-1 (calculated based on the total mass of CS2 initially added in the electrolyte) along with exceptional cycling stability (capacity decay rate of merely 0.0096% per cycle over 6,000 cycles) at a current density of 1.0 mA cm-2 within the voltage range of 1.7 to 3.0 V vs Li/Li⁺. The Li//CS2 flow battery delivers a high reversible capacity of 75.5 Ah L-1 at a current density of 0.3 mA cm-2. And the Li//CS2 pouch cell with CS2 as the cathode material retains a capacity retention rate of 95.7% after 100 cycles at 0.3mA cm-2. This work presents a novel strategy for designing high-performance and high-energy-density storage lithium-organosulfide batteries.