Manipulation of the MoO/MoSe Heterointerface Boosting High Rate and Durability for Sodium/Potassium Storage.

The main challenge for sodium/potassium ion storage is to find the suitable host materials to accommodate the larger-sized Na/K and conquer the sluggish chemical kinetics. Herein, by selenation of polyoxometalate in electrospinning fiber, a novel MoO/MoSe heterostructure embedded in one-dimensional (1D) N,P-doped carbon nanofiber (MoO/MoSe@NPC) is rationally constructed to show distinct enhancement of rate performance and cycle life for sodium ion batteries (SIBs) and potassium ion batteries (PIBs). The 1D skeleton of MoO/MoSe@NPC decreases the diffusion pathway of Na/K, and the doping of N/P heteroatoms in carbon fiber creates abundant active sites and provides good reachability for Na/K transportation. MoSe nanosheets grow in the bulk phase of MoO local phase transformation to achieve effective and firm heterointerfaces. Especially, the exposure extent of heterointerfaces can be controlled by treatment temperature during the preparation process, and the optimized heterointerfaces result in an ideal synergic effect between MoO and MoSe. DFT calculations confirm that the internal electric field in the heterogeneous interface guides the electron transfer from MoO to MoSe, combined with strong adsorption capacity toward sodium/potassium, facilitating ion/electron transfer kinetics. It is confirmed that the MoO/MoSe@NPC anode for SIBs delivers 382 mA h g under 0.1 A g upon 200 cycles; meanwhile, a reversible capacity of 266 mA h g is maintained even under 2 A g after 2000 cycles. For PIBs, it can reach up to 216 mA h g in the 200th cycle and still retain 125 mA h g after 2000 cycles under 1 A g. This study opens up a new interface manipulation strategy for the design of anode materials to boost fast Na/K storage kinetics.