Mechanistic investigations of N-doped graphene/2H(1T)-MoS2 for Li/K-ions batteries

N-doped graphene (NGr) incorporated with 2H-MoS2 and 1T-MoS2 (NGr/2H(1T)-MoS2) composites have been explored as anode materials for Li/K-ions batteries (LIBs/PIBs), however, the electrochemical mechanisms of their performance have not been well probed. In this work, we use first-principles calculations to investigate the atomic mechanisms associated with their high performance and cycling stability. Graphitic N (grN) is found to play a vital role in improving the structural stability of NGr/2H(1T)-MoS2 and the electronic conductivity of NGr/2H-MoS2, while pyridinic N and pyrrolic N are detrimental to the structural integrity of hybrids. Due to small and stable adsorption energies, fast Li+/K+ adsorption can be achieved in grNGr/2H(1T)-MoS2 hybrids at high Li+/K+ contents. Besides, grNGr/2H(1T)-MoS2 composites have low Li+/K+ diffusion energy barriers and large diffusion coefficients. Especially, grNGr/1T-MoS2 displays superior Li+/K+ adsorption and diffusion capabilities as well as high electronic conductivity, making it a promising anode material for LIBs/PIBs. Based on the lattice expansion during K+ insertion, an optimal range of interlayer distance (6.0-6.5 angstrom) is found. These findings provide an in-depth understanding on the microscale Li+/K+ storage behaviour and are also instructive for optimising NGr/2H-MoS2 composite and designing NGr/1T-MoS2 anode material of LIBs/PIBs.