Sulfur‐Rich Sustainable Copolymers for Enhancing Redox Kinetics and Alleviating Cathode Passivation in Lithium‐Sulfur Batteries

Lithium‐sulfur (Li‐S) batteries are promising candidates for advanced energy storage systems. However, their performance is hindered by uncontrolled cathode passivation due to the formation of electronically insulating lithium sulfide (Li 2 S). Here, we report a sulfur‐rich copolymer, poly(sulfur‐ random ‐cardanol cystamine) [poly(S‐ r ‐Ccys)], as an efficient cathode material that enables spatially regulated Li 2 S growth and improved redox kinetics. The nitrogen and oxygen functionalities in the Ccys moiety facilitate electrostatic interactions with lithium polysulfides, enhancing their dissolution and redistribution. Pulsed‐field gradient nuclear magnetic resonance measurements confirm improved Li + ion diffusion, while galvanostatic intermittent titration technique analysis reveals faster reaction kinetics in the poly(S‐ r ‐Ccys) cathode. The poly(S‐ r ‐Ccys) cathodes exhibit superior cycling stability compared to conventional elemental sulfur cathodes, maintaining 76.7% of their initial capacity after 300 cycles at 1 C, with a low average capacity fade of just 0.077% per cycle. This work demonstrates that poly(S‐ r ‐Ccys) offers a viable strategy to overcome Li 2 S deposition challenges and improve the cycle life of Li‐S batteries without altering the conventional ether‐based electrolyte system.