High-energy–density carbon-coated bismuth nanodots on hierarchically porous molybdenum carbide for superior lithium storage

Abstract

The use of carbon-based supports, such as graphene and porous carbon, is a well-established approach to overcome the rapid capacity fading issues associated with alloy-based anode materials in lithium-ion batteries (LIBs). However, adopting carbonaceous materials that typically exhibit a low density eventually diminishes the primary purpose of alloys as high-energy–density anode materials. In this study, we introduce three-dimensional hierarchically porous molybdenum carbide (PMC) with high energy density, robust mechanical strength, and high electronic conductivity, which make it a promising alternative support for suppressing the huge volume expansion of alloying-based materials. Carbon-coated, ultrasmall Bi nanodots with an average size of 6.4 nm are uniformly embedded on the PMC surface (denoted as C-Bi/PMC) by facilitating heterogeneous nucleation. When tested as an anode in an LIB, the C-Bi/PMC electrode exhibits a high reversible capacity of 422 mAh g−1 at 50 mA g−1, high-rate capacity of 268 mAh g−1 at 1000 mA g−1, and long-term stability of 400 mAh g−1 at 250 mA g−1 over 500 cycles followed by 0.002 mAh g−1 decay per cycle at 5000 mA g−1 over subsequent 1000 cycles. When paired with LiNi0.5Co0.2Mn0.3O2 cathode as full-cell LIBs, the C-Bi/PMC anode deliver high gravimetric and volumetric energy densities of 352 Wh kg−1 and 563 Wh L–1, respectively. In-situ X-ray diffraction patterns captured during cycling reveal that the Li+-ion insertion mechanism in the voltage plateau region at 0.7–1.0 V consists of the intercalation between Bi layers followed by the formation of triclinic LiBi phase and the subsequent transition of triclinic LiBi to cubic Li3Bi phase.