One Pot Synthesis and Characterizations of Nanosize Lithium Metal Silicates and Lithium Metal Flurophosphates for Lithium Ion Battery Applications

Recently, orthosilicates and flurophosphates have been investigating for the cathode applications in lithium ion battery. Orthoslicate materials are built of abundant elements such as Si, Fe and Mn, which makes them cheap cathode materials for large scale high capacity batteries that can operate at higher temperatures^1,2. Fluorophosphates have been considered as potential lithium insertion/ extraction cathodes^3,4. Both, silicates and fluorophosphates have the ability of delivering two lithium ion discharge capacity (290-333 mAhg^-1).

     Herein, we present a supercritical fluid process to synthesize Li₂MSiO₄ and Li₂MPO₄F (M= Fe, Mn and Co) nanoparticles ranging from 5-50 nm and their electrode properties have been investigated. These cathode materials are synthesized via supercritical fluid process by controlling the size and shape. The supercritical synthesis was carried out at 300-450 ^oC for 5 min-30 min of reaction time using mixed solution of water, ethanol, EG as solvents and ascorbic acid, oleic acid and oleylamine as surfactants. The as-synthesized Li₂MSiO₄ and Li₂MPO₄F (M= Fe, Mn and Co) nanoparticles were characterized by XRD, TEM, TG-DTA and FTIR analysis. Further, the electrochemical property of Li₂MSiO₄ and Li₂MPO₄F (M= Fe, Mn and Co) cathode materials have been investigated by galvanostatic charge-discharge method.

    Fig. 1 shows the TEM images of Li₂FeSiO₄ and Li₂FePO₄F nanoparticles synthesized by supercritical method at 300-450 ^oC for 5-30 min. The particles exhibited 5-50 nm in diameter with sphere like morphology. The different kind of morphology with variable size can be synthesized at supercritical conditions. The flower like morphology, rod like morphology and ultrafine particles were successfully synthesized and their electrochemical property was investigated. The charge-discharge curve of carbon coated Li₂FeSiO₄ and Li₂FePO₄F nanoparticles showed 180 mAhg^-1 and 150 mAhg^-1, respectively at 0.05C as shown in fig 1.

References

 1)     A. Nyten, et al. Electrochem.Commun., 2005, 7, 156.2) Y.X. Li, et al. J. Power Sources. 2007, 174, 528. 3) R. Dominko,.et al, J. Electrochem. Commun., 2006, 8, 217. 4) B.L. Ellis, et al. Nature   Mater.,  2007, 6, 749.

Fig.1 TEM image and charge discharge profile of Li₂FeSiO₄ and  Li₂FePO₄F cathode nanomaterials