Anion-doped polypyrrole three-dimensional framework enables adsorption and conversion in lithium-sulfur batteries

Inhibiting the shuttle effect and propelling polysulfide conversion by introducing a suitable sulfur container has been proven as a promising strategy to enhance the cycle life of lithium-sulfur (Li-S) batteries. Here, a unique three-dimensional (3D) inter-connected framework assembled with SO₄^2--doped polypyrrole (PPy-SO₄) nanowires is proposed. The doping SO₄^2- anion in a polymer skeleton could confine lithium polysulfides (LiPSs) by polar-polar interaction to inhibit the shuttle effect and enhance the conductivity of PPy to accelerate polysulfide conversion. Moreover, the electrostatic coupling between SO₄^2- anion and Li⁺, as well as between -N⁺- and S_n^2-, at polypyrrole /electrolyte interface can effectively regulate the redox kinetics of polysulfide. Besides, the inter-connected framework creates a large contact surface for sulfur and high-flux paths for electron transport. Consequently, the Li-S batteries assembled with PPy-SO₄/S cathode exhibit a stable capacity of 501 mAh g^-1 after 350 cycles at 1C, showing a low decay rate of 0.09% per cycle. Notably, the efficiency of the anion doping strategy is further verified in the pouch cell, realizing a capacity of 480 mAh g^-1 after 250 cycles. This work illustrates that anion doping with rational structural design is a feasible solution to boost the electrochemical performance of Li-S batteries.