Atomic-Layer-Deposition Functionalized Carbonized Mesoporous Wood Fiber for High Sulfur Loading Lithium Sulfur Batteries

Lithium-sulfur battery (LSB) as one of the most promising energy storage devices suffers from poor conductivity of sulfur and fast capacity decay triggered by the dissolution of polysulfides. In this work, functionalized carbonized mesoporous wood fiber (f-CMWF) is employed as a host to accommodate sulfur for the first time. Natural wood microfiber has unique hierarchical and mesoporous structure, which is well-maintained after carbonization. With such a hierarchical mesoporous structure, a high sulfur loading of 76 wt % is achieved in CMWF electrodes. The pore size of CMWF is tunable by atomic layer deposition (ALD) of a 5 nm Al₂O₃ coating to form the f-CMWF. Such a thin layer slightly decreases the sulfur loading to 70%, but it remarkably promotes the cyclic stability of sulfur cathode, which delivers an initial capacity of 1115 mAh g^-1, and maintains a reversible capacity of 859 mAh g^-1 for 450 cycles, corresponding to a slow capacity decay rate of 0.046% per cycle. More importantly, natural wood microfiber is first used as a raw material for sulfur encapsulating. This work is also critical for using low cost and mesoporous biomass carbon as bifunctional scaffold for LSB.