Nickel foam deposited with borophene sheets used as a self-supporting binder-free anode for lithium-ion batteries

Abstract

The facile synthesis of large size borophene is highly desirable, especially in reserving green energy by borophene-based Li-ion batteries (LIBs). In this study, an easy method of synthesizing a series of nickel foam (NF) deposited with borophene sheets without the use of catalysts is reported via an improved chemical vapor deposition (CVD) process. During the CVD process, the B₂O₂ vapor was moved to the heated nickel foam and converted into Ni₃B and crystalline B under an H₂ atmosphere. Numerous micron-sized lamellar borophene with thicknesses of less than 2 nm were deposited on the surface of the nickel foam, and the borophene sheets displayed ultrathin and transparency. Deep microstructural analysis revealed the crystalline nature of pure B in the as-obtained borophene sheets, and the β₁₂-phase is dominant. The β₁₂-borophene holds great potential for designing high-capacity anode material for LIBs. When the nickel foam-supported borophene sheets were directly used as a self-supporting binder-free anode material for LIBs, the NF framework not only hindered the aggregation of borophene sheets and alleviated the strain change during the lithiation/delithiation process but also provided a three-dimensional highway conductive network for fast electron transport. The fabricated electrodes exhibit superior lithium storage capacity and cyclic stability than blank NF electrodes. However, the results suggest that this is still far lower than the theoretical lithium storage capacity of the boron anode. The kinetics analysis combined with density functional theory calculations demonstrated that slow electron and ion transportation in the electrodes is attributed to the existence of the Ni₃B phase and deactivated borophene. This study may provide vital guidance for designing high-performance borophene-based LIBs.