Tethered molecular sorbents: Enabling metal-sulfur battery cathodes

A rechargeable battery that uses sulfur at the cathode and a metal (e.g., Li, Na, Mg, or Al) at the anode provides perhaps the most promising path to a solid-state, rechargeable electrochemical storage device capable of high charge storage capacity. It is understood that solubilization in the electrolyte and loss of sulfur in the form of long-chain lithium polysulfides (Li₂S_x, 2 < x < 8) has hindered development of the most studied of these devices, the rechargeable Li-S battery. Beginning with density-functional calculations of the structure and interactions of a generic lithium polysulfide species with nitrile containing molecules, it is shown that it is possible to design nitrilerich molecular sorbents that anchor to other components in a sulfur cathode and which exert high-enough binding affinity to Li₂S_x to limit its loss to the electrolyte. It is found that sorbents based on amines and imidazolium chloride present barriers to dissolution of long-chain Li₂S_x and that introduction of as little as 2 wt% of these molecules to a physical sulfur-carbon blend leads to Li-S battery cathodes that exhibit stable long-term cycling behaviors at high and low charge/discharge rates.