Highly Mesoporous Carbon Derived from Silica-Embedded Zeolitic Imidazolate Framework As a Potential Reservoir of Metallic Li

摘要

During the last decade, lithium ion batteries (LIBs) have shown great promise as a potential power source for various applications such as portable electronic devices and electric vehicles (EVs). Responding to the growing demand for high-energy LIBs, it is crucial to develop advanced materials which provides a higher energy density than commercial materials currently available. Li metal has long been considered as a future anode material for LIBs because of its extremely high theoretical capacity (～3,860mAh/g) and low potential for electrochemical reactions (-3.04V vs. standard hydrogen electrode). Despite these advantages, the practical use of Li metal is hindered by several technical issues as follow; i) unavoidable dendritic growth of Li and ii) infinite volume changes during cycling. Such issues are still regarded as main drawbacks of Li metal causing rapid performance fading and safety hazards. Recently, the feasibility of various porous materials with a well-defined pore structure has been examined as potential reservoirs for Li storage to suppress unfavorable dendritic growth as well as volume changes of Li metal. Herein, we design a highly mesoporous carbon (MC) as a potential Li storage material, based on the dual-phase reaction mechanism (i.e. lithiation and metallization). It can be synthesized via a direct carbonization of silica-embedded zeolitic imidazolate frameworks (SiO_2@ZIFs) combined with a chemical etching process. Colloidal silica nanoparticles (～20nm) are employed as a mesopore former during the synthesis of ZIFs and then completely removed by a hydrofluoric acid. The formation of mesopores is effective for accommodating a large amount of metallic Li, showing a stable cycle performance over 100 cycles. It is confirmed that Li can be reversibly stored in the structure without significant dendritic growth of Li and volume changes based on various electrochemical and structural analyses. Furthermore, we thoroughly investigate a correlation between pore structure and Li storage behavior of MC as the next generation anode for high-energy LIBs.