Effects of P-doping on CO₂-Derived Porous Carbon for the Cathode of Lithium-Sulfur Batteries

To address the sluggish redox kinetics and the polysulfide shuttle effect in lithium-sulfur (Li-S) batteries, phosphorus-doped CO₂-derived carbon (PCDC) was developed to improve their electrochemical performance. The carbon scaffold was derived from CO₂ reduction through sodium borohydride (NaBH₄), enabling the simultaneous incorporation of boron and oxygen. This eco-friendly strategy converts CO₂ into a hierarchically porous structure with the phosphoric acid treatment. The resulting PCDC exhibited a large surface area and pore volume, enabling effective sulfur loading and rapid lithium-ion transport. Structural analyses confirmed the presence of both B and P within the carbon matrix, with B contributing to enhanced electrical conductivity and P forming catalytically active configurations such as C₃PO and C₂PO₂. Electrochemical testing revealed that PCDC accelerates polysulfide redox reactions, reduces charge transfer resistance, facilitates Li₂S nucleation, and outperforms the CO₂-derived carbon (CDC) without phosphorus doping. It delivered a capacity of 800 mAh g^-1 for 100 cycles at 0.2C and showed around 600 mAh g^-1 after 100 cycles at 0.5C. This multi-heteroatom doping approach offers a practical route to high-efficient Li-S batteries.