Layer-stacking of chalcogenide-terminated MXenes Ti₂CT₂(T = O, S, Se, Te) and their applications in metal-ion batteries

Owning to limited supply of lithium for Li-ion batteries, the development of non-Li-ion batteries (such as Na⁺, K⁺Mg²⁺, Ca²⁺, and Al³⁺ion batteries) has attracted significant research interest. In this work, by means of the first-principles calculations, we systematically investigated the performance of chalcogenide-terminated MXenes Ti₂CT₂(T = O, S, Se, and Te) as electrodes for Li-ion and non-Li-ion batteries, as well as the layer-stacking and electronic properties of Ti₂CT₂. We find that the stacking type of O and Te terminated Ti₂C multilayers with AA stacking differs from that of S and Se terminated Ti₂C multilayers with AB stacking. More importantly, Ti₂CO₂monolayer can be potential anode material for Na- and K-ion batteries with high capacities and very low diffusion barriers (0.03-0.11 eV), while Ti₂CS₂and Ti₂CSe₂are promising anode materials with relatively low average open circuit voltages (OCVs) for Na-, K-, and Ca-ion batteries (0.4-0.87 V). Among these materials, Ti₂CS₂exhibits the largest ion capacity of 616 mAh g^-1. These results of our work may inspire further studies of Ti₂C-MXenes multilayers as electrodes for metal-ion batteries either experimentally or theoretically.