Stabilizing conversion reaction electrodes by MOF derived N-doped carbon shell for highly reversible lithium storage

Surface engineering has been applied to resolve the problem of cycling instability in conversion/alloying reaction electrodes which can have high capacity but suffer from large volumetric change and pulverization in electrochemical cycles. However, due to structural instability, most of the surface coatings are still fragile and unstable in electrochemical cycles. Here, a facile low-temperature melting method has been developed to fabricate a uniform and ultrathin metal-organic framework (MOF) shell on various oxides electrode materials, followed by a gradient heat treatment process. A uniform and ultrathin N-doped carbon (NC) shell is formed as a robust coating to keep the integrity of materials and provide a highly conductive pathway for both electron and ions. This carbon confinement strategy can be easily applied to diverse ternary metal oxides with high bonding energy, such as Zn2SiO4, Zn2WO4 and Zn2TiO4. The obtained carbon-confined Zn2SiO4 (Zn2SiO4@NC) nanowires have achieved enhanced lithium storage performances compared to pure Zn2SiO4 nanowires. As revealed by in situ transmission electron microscopy, in the process of lithiation the Zn2SiO4@NC nanowires have lower radical expansion and faster kinetics than pure Zn2SiO4 nanowires, and the N-doped carbon shell remains stable. This work provides a new approach for the design and construction of carbon-based nanostructures which have great potential in energy-related applications.