Flexible graphene–nickel thiophosphate hybrids enabling fast kinetics and ultrahigh capacity for potassium-ion storage

Exploring high-performance electrode materials are indispensable for the commercialization of potassium-ion batteries (PIBs). Nickel thiophosphate (NPS), a representative ternary metal thiophosphate, holds great promise as an anode due to its high theoretical capacity and distinctive layered structure, yet still facing critical challenges such as rapid capacity decay and sluggish rate performance. Herein, we developed a flexible, self-supporting composite film anode by integrating high-purity NPS nanosheets within a three-dimensional (3D) conductive scaffold composed of nitrogen-doped graphene (NG) and single-wall carbon nanotube (SWNT) via simple vacuum filtration method. The resulting hybrid film features abundant heterointerfaces, which enhance electron/ion transport, accommodate volume changes, and stabilize the electrode structure. As a result, the anode delivers high potassium storage capacity of 643.5 mAh g⁻¹ at 0.1 A g⁻¹ and maintains 163.9 mAh g⁻¹ at 10 A g⁻¹, showcasing excellent rate performance. Full cell assemblies exhibit stable cycling performance with a reversible capacity of 207.8 mAh g⁻¹ after 100 cycles. Combined crystallography and valence state analyses reveal a disordered phase transition in crystalline NPS during potassiation, indicating a dual mechanism involving both conversion and alloying reactions. This study offers valuable insights into the rational design of advanced anode materials for next-generation PIBs.