Deeply Nesting Zinc Sulfide Dendrites in Tertiary Hierarchical Structure for Potassium Ion Batteries: Enhanced Conductivity from Interior to Exterior.

Transition metal sulfides are deemed as attractive anode materials for potassium-ion batteries (KIBs) due to their high theoretical capacities based on conversion and alloying reaction. However, the main challenges are the low electronic conductivity, huge volume expansion, and consequent formation of unstable solid electrolyte interphase (SEI) upon potassiation/depotassiation. Herein, zinc sulfide dendrites deeply nested in the tertiary hierarchical structure through a solvothermal-pyrolysis process are designed as an anode material for KIBs. The tertiary hierarchical structure is composed of the primary ultrafine ZnS nanorods, the secondary carbon nanosphere, and the tertiary carbon-encapsulated ZnS subunits nanosphere structure. The architectural design of this material provides a stable diffusion path and enhances effective conductivity from the interior to exterior for both K ions and electrons, buffers the volume expansion, and constructs a stable SEI during cycling. A stable specific capacity of 330 mAh g is achieved after 100 cycles at the current density of 50 mA g and 208 mAh g at 500 mA g over 300 cycles. Using density functional theory calculations, we discover the interactions between ZnS and carbon interface can effectively decrease the K ions diffusion barrier and therefore promote the reversibility of K ions storage.