Carbon-encapsulated ultrathin MoS₂ nanosheets epitaxially grown on porous metallic TiNb₂O₆ microspheres with unsaturated oxygen atoms for superior potassium storage

Rechargeable potassium-ion batteries (KIBs) have emerged as promising alternatives to lithium-ion batteries (LIBs) in large-scale applications due to the abundant and low-cost potassium resources. To date, only a few suitable potassium storage materials have been reported due to the large-sized potassium ions and sluggish kinetics. Herein, we design a three-layered heterostructure with porous metallic TiNb₂O₆ as the core and carbon-encapsulated MoS₂ nanosheets as the shell (denoted as TiNb₂O₆@MoS₂/C) as an advanced anode for KIBs. This hybrid configuration can significantly enhance the electronic conductivity from the interior to the exterior by virtue of the oxygen-atom-unsaturated metallic TiNb₂O₆ core. Furthermore, the amorphous carbon shell plays a crucial role to inhibit the particle agglomeration, accommodate the volume expansion and protect the active material from pulverization because of the three-layered heterostructure. As a result, impressive electrochemical behavior with high capacity (424 mA h g^-1 at 0.1 A g^-1 after 50 cycles) and high cycling stability (175 mA h g^-1 at 1.0 A g^-1 after 300 cycles) is achieved. This work opens the door for designing highly conductive heterostructures for energy storage devices.