A dynamic polyanion framework with anion/cation co-doping for robust Na/Zn-ion batteries

Among various cathode materials for sodium-ion batteries (SIBs), Na3V2(PO4)3 has an open and stable three-dimensional framework to reversibly (de)intercalate sodium ions (Na+), but its inherently insulated and stiff features originated from VO6 octahedron and PO4 tetrahedron result in limited capacity and poor rate performance. Herein, this work resolves these issues by implementing anion (Cl−) and cation (Mg2+) to respectively substitute a small fraction of O and V elements to expand Na+ migration channel and boost electronic conductivity, which is verified by both experiment and theory calculations. Even with carbon coating less than 1 wt% in content, which is one of the least carbon coating as reported, a dramatically improved capacity (120 mA h g−1 at 0.1 C) and rate performance (65 mA h g−1 at 30 C) are realized for Na3V1.95Mg0.05(PO4)2.9Cl0.1 in contrast to Na3V2(PO4)3 that merely releases 66.7 mA h g−1 at 0.1 C and decrease to 0 mA h g−1 at 30 C. Meanwhile, stable full SIBs and zinc-ion batteries are also demonstrated with this dynamic polyanion framework.