WO3-x@W2N heterogeneous nanorods cross-linked in carbon nanosheets for electrochemical potassium storage

Potassium-ion batteries (PIBs) are highly desirable as large-scale sustainable battery systems due to the high working potential and low-cost potassium resources. However, the large radius of potassium ion inevitably causes huge volume expansions and rapid capacity decay of electrodes, so the development of long-life anodes still remains at its infancy. Herein, the nonstoichiometric heterostructures with bimetallic characteristics (WO3-x@W2N) are rationally constructed on mono-faceted nanorods and in-situ cross-linked in nitrogen-doped carbon nanosheets (WO3-x@W2N/CNSs). The mono-faceted WO3-x nanorods endow oxygen vacancies with abundant unsaturated active sites and dangling bonds in their directional charge-transfer paths. The heterostructures with rich self-built electric fields can regulate electronic structures of oxygen-vacancy/metallic WO3-x and metallic W2N, and notably enhance the efficiency of charge transfer and storage under the protection of highly conductive CNSs. Utilizing the vacancy, phase and interface engineering, the WO3-x@W2N/CNSs deliver a large reversible capacity (366.6 mAh g(-1) at 0.1 A g(-1)), with high-rate capacity and ultralong lifespan (113.2 mAh g(-1) after 12,000 cycles at 10.0 A g(-1)). These findings, storage mechanisms and kinetics behaviors are elucidated in detail via the advanced techniques and first-principles calculations, demonstrating that the nonstoichiometric and metallic heterostructures have promising potentials in high-performance metal ion batteries.