A superatom-assembled B₈N₂ monolayer acting as an electronic sponge for high-capacity anode materials for Na/K-ion...

Rechargeable sodium/potassium-ion batteries (SIBs/PIBs) have emerged as appealing alternatives for lithium-ion batteries due to their earth-abundance and economic benefits. However, exploring high-capacity anode materials for SIBs/PIBs is still challenging. Superatoms with delocalized electronic shells possess high flexibility as electron-acceptors/donors, making them ideal candidates for anode materials. Here, a superatom-assembled boron nitride monolayer (B₈N₂) was theoretically predicted using first principles calculations. The B₈ core is assembled with two B₄ superatoms, and further linked by nitrogen atoms in a graphene-like lattice. The B₈N₂ monolayer has an undirected bandgap (0.82 eV/HSE06) with an ultra-high carrier mobility of 13 × 10⁴ cm² V^-1 s^-1, where Na/K ions can be effectively adsorbed on its surface. The remarkably high theoretical storage capacities (924 mA h g^-1/1115 mA h g^-1), and low open-circuit voltages (0.08 V/0.21 V) are also revealed for the B₈N₂ monolayer with Na/K ions. Intriguingly, adsorption of Na/K ions causes little geometric deformation of the B₈N₂ monolayer, which ensures a promising cell operating cycle during the adsorption of Na/K ions at high concentrations. This work reveals the potential of superatoms as an efficient "electronic sponge", providing impetus for the design of superatomic electrode materials for metal ion batteries.