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

Abstract

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 Zn 2 SiO 4 , Zn 2 WO 4 and Zn 2 TiO 4. The obtained carbon-confined Zn 2 SiO 4 (Zn 2 SiO 4 @NC) nanowires have achieved enhanced lithium storage performances compared to pure Zn 2 SiO 4 nanowires. As revealed by in situ transmission electron microscopy, in the process of lithiation the Zn 2 SiO 4 @NC nanowires have lower radical expansion and faster kinetics than pure Zn 2 SiO 4 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. A general method for fabricating a strong coating layer of N-doped-carbon to confine target nanostructures has been developed via a facile and efficient low temperature melting method of forming metal-organic framework (MOF) and subsequent controlled pyrolysis, to boost the cycling stability of electrode materials run on conversion/alloying reactions for lithium-ion battery. • A low-temperature melting method is developed to fabricate a robust MOF derived N-doped carbon shell as a uniform coating for oxides. • The carbon-confined Zn2SiO4 nanowires exhibit enhanced lithium storage performance compared to pure Zn2SiO4 nanowires. • In situ transmission electron microscopy has revealed that the N-doped carbon shell remains intact in lithiation. • The carbon-confined Zn2SiO4 nanowires have lower radical expansion and faster kinetics than pure Zn2SiO4 nanowires.