Polysulfide Rejection Layer for High Performance Lithium Sulfur Batteries

Polysulfide (PS) shuttle has been an impediment to the development of lithium-sulfur batteries with high capacity and cycling stability. Previous efforts to mitigate PS shuttle were mainly focused on 1) the suppression of diffusion of dissolved PS out of the cathode by geometrically trapping PS in porous carbons or adsorbing PS on oxides and conducting polymers and 2) protection of the Li anode from reaction with PS by forming a passivation layer on the Li metal surface or a hybrid anode structure.

Here, we report a new strategy to remedy the problem using a polymeric polysulfide rejection layer via in situ or ex situ routes. The key concept of this strategy is to form a thin layer which selectively rejects PS anions but permeates lithium ion, mimicking cell membrane. The in situ formed PS rejection layer, which was developed on the sulfur cathode surface from an electrolyte additive during the first discharge, effectively prevented PS shuttle and consequently enhanced discharge capacity and cycling stability owing to an electrochemical equilibrium between the PS-containing cathode electrolyte and the PS rejection layer. In detail, the discharge capacity at the third cycle was 995 mAh g^-1 for the cell with the in situ PS rejection layer and 829 mAh g^-1 for the reference cell. At the 200th cycle, the PS rejection layer cell delivered a reversible 787 mAh g^-1. In contrast, the discharge capacity of the reference cell dropped to 575 mAh g^-1after 200 cycles, which was 73% of the discharge capacity of the cell with the PS rejection layer.  

Using the ex situ formed layer, which exhibited a similar polysulfide rejection behavior as the in situ layer did, the influence of chemical structure of the layer and battery architecture including the layer were investigated. Battery performances were highly dependent on the chemical nature and physical configuration of the layer. In particular, the layer inserted in the interface of cathode and bulk electrolyte phase improved reversible capacity, whereas, that in the interface of anode and bulk electrolyte phase increased cycling efficiency.