Spray-drying synthesis and vanadium-catalyzed graphitization of a nanocrystalline γ-Li3.2V0.8Si0.2O4/C anode material with a unique double capsule structure

Abstract

By means of a simple spray-drying method, a unique double capsule structure of nanocrystalline lithium superionic conductor (LISICON)-type γ-Li_3.2V_0.8Si_0.2O₄ (γ-LVSiO) has been obtained for the first time for anodes of hybrid supercapacitors as well as lithium ion batteries. The synthetic procedure involves simultaneous carbonization on crystals which brings about fine control of morphologies of the whole entity of composites depending upon some critical conditions like dispersion diluteness and sucrose concentration as a carbon source. Fine control of these parameters brings about the highest possible rate performance with minimal carbon content without sacrificing the specific energy density of the electrode materials. A significantly efficient network of electrons/ions is constructed across the interphase of embedded γ-LVSiO nanoparticles (ϕ = 50 nm) whereby vanadium(IV) catalytically induced graphitization selectively in the vicinity of nano-γ-LVSiO surfaces: such graphitization occurs at a surprisingly low temperature (700 °C); the graphitization normally occurs at over 1000 °C as elsewhere reported. The authors revealed an unexpectedly efficient interconnection of two different carbons, viz., graphitic and amorphous carbons formed by this method. Such a unique dual-carbon network facilitates an excellent rate performance of γ-LVSiO with a modest total carbon content (12.4 wt%) within the γ-LVSiO composites. A vanadium-based 0.4 mA h class full cell consisting of this γ-LVSiO anode and the Li₃V₂(PO₄)₃ cathode has been assembled for any possible application as a future hybrid supercapacitor or a high-power superbattery. In fact, the cell exhibited outstanding electrochemical performances, maintaining 50% of capacity at a high C-rates of 30 (charge) and 100C-rate (discharge), and almost 100% of initial capacity during the 10C/10C-rate cycle test over 1000 cycles.