Cu3PS4: a sulfur-rich metal phosphosulfide with superior ionic diffusion channel for high-performance potassium ion batteries/hybrid capacitors

The emerging conversion-type chalcogenide anode materials for potassium ion storage may propose high theoretical specific capacity (>600 mA h g−1) and high compatibility with electrolytes, but currently the reported performance falls behind this goal due to severe material pulverization, polysulfide shuttle effect, and slow potassium ion diffusion during a charge/discharge process. Here, we report that Cu3PS4, a sulfur-rich orthorhombic metal phosphosulfide, can achieve highly reversible multiple conversion reactions, including the formation of KP and K2S along with 9 electrons transfer and efficient diffusion of potassium ions. Moreover, we introduce a layer graphite surface coating to enhance the overall conductivity of the electrodes, decrease the internal resistance, and render specific electronic channel with fast kinetic diffusion. During cycling, a tightly connected K-CuPS junctions were formed to establish an ultra-stable heterostructure to entrap polysulfides in materials via an appropriate and uniform affinity. In electrochemical tests, Cu3PS4 potassium ion anodes exhibit the highest capacity of 649.3 mA h g−1 at a current density of 0.05 A/g, reaching 94.4 % of its theoretical capacity (687.3 mA h g−1), and showed an ultra-stable 3000 cycle life and high-rate capability up to 8 A/g. Furthermore, the full battery and hybrid capacitor show attractive energy density and long cycle life of 82.5 W h kg−1 for 800 cycles and 80.3 W h kg−1 for 5000 cycles, respectively. This work provides promising results for metal phosphosulfide applications in high-efficiency potassium-ion storage devices, and may also be instructive for material advancements in related energy fields.