MOF-derived, N-doped, hierarchically porous carbon sponges as immobilizers to confine selenium as cathodes for Li-Se batteries with superior storage capacity and perfect cycling stability

Nitrogen-doped carbon sponges (NCS) composed of hierarchical microporous carbon layers are derived from metal organic frameworks (MOFs) via carbonization at high temperatures under Ar and NH3 flow. Se is impregnated into 0.4-0.55 nm micropores by melting-diffusion and infiltration methods. The confinement of Se within small-sized micropores of NCS efficiently prevents Se loss, and mesopores between carbon layers absorb a sufficient amount of electrolyte, as well as serve as cushion spaces for large volume changes during delithiation-lithiation processes. Nitrogen doping improves the electrical conductivity of carbon matrix and facilitates rapid charge transfer, making the carbon sponge a highway for charges involved in redox reactions. When serving as cathode materials for Li-Se batteries, the NCS/Se-50 composite with 50 wt% Se exhibits excellent cycling stability, superior rate capability and high coulombic efficiency. The cathode can exhibit 443.2 mA h g(-1) at the 200th cycle with a coulombic efficiency of up to 99.9% at 0.5C (C = 675 mA h g-1), which leads to 0.031% capacity loss per cycle from 5th to 200th cycles. Even at a high rate of 5C, it can still retain 286.6 mA h g(-1). The unique, large surface rod-like MOF-derived, N-doped carbon sponges with hierarchical porosity could be potential candidates in the related energy-storage systems.