Improved electrochemical properties of solvothermally synthesized Li2FeSiO4/C nanocomposites: A comparison between solvothermal and sol-gel methods

We have synthesized porous Li2FeSiO4/C nanocomposites by two different routes such as sol-gel (Li2FeSiO4/C-SG) and solvothermal (Li2FeSiO4/C-ST) using block copolymer pluronic (P123) as both in-situ carbon source and structure directing agent. Various techniques, like, powder x-ray diffraction, BET nitrogen adsorption-desorption measurement, scanning electron microscopy, transmission electron microscopy, galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the nanocomposites. A comparative study of their structural, electronic and electrochemical properties show that the solvothermally synthesized nanocomposite sample Li2FeSiO4/C-ST-600 (annealed at 600 °C) shows better electrochemical performance compared to the corresponding sol-gel synthesized (Li2FeSiO4/C-SG-600) sample. At a rate of C/30, Li2FeSiO4/C-ST-600 nanocomposite delivered a discharge capacity of ~ 276 mA h g− 1 (84% of theoretical capacity) and also exhibited excellent stability at high rates. It retained 95% of its initial discharge capacity (140 mA h g− 1) after 100 cycles at 1C, comparable to the recently published data on Mg-doped Li2FeSiO4/C composites. We attribute this enhanced electrochemical behavior of Li2FeSiO4/C-ST-600 due to the formation of porous nanocrystalline (~ 15 nm) composite material with a large BET surface area (~ 100 m2 g− 1) resulting in a lower charge transfer resistance (~ 30 Ω) and a higher Li-ion diffusion coefficient (~ 5 × 10− 14 cm2 s− 1). The present study demonstrates that solvothermal synthesis of Li2FeSiO4/C nanocomposites using P123 as a carbon source is an effective method for improving its electrochemical properties.