Improved ion adsorption capacities and diffusion dynamics in surface anchored MoS2⊥Mo4/3B2 and MoS2⊥Mo4/3B2O2 heterostructures as anodes for alkaline metal-ion batteries

Abstract

First-principles calculations were performed to analyze the atomic structures and electrochemical energy storage properties of novel MoS₂⊥boridene heterostructures by anchoring MoS₂ nanoflakes on Mo_4/3B₂ and Mo_4/3B₂O₂ monolayers. Both thermodynamic and thermal stabilities of each heterostructure were thoroughly evaluated from the obtained binding energies and through first-principles molecular dynamics simulations at room temperature, confirming the high formability of the heterostructures. The electrochemical properties of MoS₂⊥Mo_4/3B₂ and MoS₂⊥Mo_4/3B₂O₂ heterostructures were investigated for their potential use as anodes for alkaline metal ion batteries (Li⁺, Na⁺ and K⁺). It was revealed that Li⁺ and Na⁺ can form multiple stable full adsorption layers on both heterostructures, while K⁺ forms only a single full adsorption layer. The presence of a negative electron cloud (NEC) contributes to the stabilization of a multi-layer adsorption mechanism. For all investigated alkaline metal ions, the predicted ion diffusion dynamics are relatively sluggish for the adsorbates in the first full adsorption layer on MoS₂⊥boridene heterostructures due the relatively large migration energies (>0.50 eV), compared to those of second or third full adsorption layers (<0.30 eV). MoS₂⊥Mo_4/3B₂O₂ exhibited higher onset and mean open circuit voltages as anodes for alkaline metal-ion batteries than MoS₂⊥Mo_4/3B₂ hybrids because of enhanced interactions between the adsorbate and the Mo_4/3B₂O₂ monolayer with the presence of O-terminations. Tailoring the size and horizontal spacing between two neighboring MoS₂ nano-flakes in heterostructures led to high theoretical capacities for LIBs (531 mA h g⁻¹), SIBs (300 mA h g⁻¹) and PIBs (131 mA h g⁻¹) in the current study.