Tremella-like Mo and N Codoped Graphitic Nanosheets by In Situ Carbonization of Phthalocyanine for Potassium-Ion Battery

A tremella-like Mo and N codoped graphitic nanosheet array supported on activated carbon (Mo2C-MoC/AC-N) is prepared via in situ carbonization of nitrogen-rich cobalt phthalocyanine nanoparticulates anchored on activated carbon as a high-performance anode for potassium-ion batteries. The nanosheets about 5 nm thick are uniformly distributed on the surface of activated carbon for fast K-ion intercalation, and the abundant micropores in activated carbon provide additional adsorption sites of potassium ions, forming a three-dimensional architecture for potassium storage. The 3.9 atom % Mo in Mo2C-MoC/AC-N is in the form of Mo2C and MoC flakes (around 1:1) attached to the graphitic nanosheets. X-ray diffraction (XRD) analysis revealed that the reaction with Mo2C (forming K2C) happens mainly at 0.8–0.4 V, while the reaction with MoC (forming K2C) occurs primarily at 0.4–0.01 V. The N doping (9.6 atom %) causes an interlayer spacing expansion of 0.3 Å in the graphitic nanosheets, beneficial to the potassium-ion insertion reaction to form KC8 at 0.4–0.01 V. The Mo2C-MoC/AC-N anode exhibits a capacity of 457.5 mA h g–1 at a current density of 0.05 A g–1 and an excellent capacity of 144.4 mA h g–1 at a high current of 5 A g–1 with a capacity loss rate of 0.49‰ per cycle.