Non aqueous sol-gel synthesis of LiCoPO4 olivines coated with LiFePO4 nano-shell

Yelena Gershinsky, Chemistry, BINA, Bar-Ilan University, Ramat-Gan 5290002, Israel
David Zitoun, Chemistry, BINA, Bar-Ilan University, Ramat-Gan 5290002, Israel

Many studies on the Li-ion Batteries (LIBs) have been carried out to develop new electrode materials with high specific capacity, high power density and good thermal stability. The most desirable positive electrode materials expected to fulfill those requirements belong to the LiMPO₄ (M = Fe, Co, Mn) olivine compounds, with a special interest for the LiCoPO₄ with its high theoretical capacity (167 mAh/g) and operating voltage (~4.8 V vs. Li).

In this work, LiCoPO₄, LiFePO₄, their solid solutions (Co:Fe 1:3, 1:1, 3:1 respectively) and core (LiCoPO₄) shell (LiFePO₄) electrode materials have been successfully synthesized within minutes using a microwave-directed non aqueous sol-gel synthesis approach. It was already confirmed that this process is effective in synthesizing LiFePO₄ [1], and hence, considered to be also promising for the syntheses of LiCoPO₄, LiCo_xFe_1-xPO₄ and LiFePO₄ coated LiCoPO₄/ LiCo_xFe_1-xPO_4.

The morphology of produced powders depends on the nature of precursors and the experimental conditions, which were studied by HR-SEM. From the result of X-ray diffraction pattern, we could confirm single-phase (orthorhombic structure with Pnma space group) for LiCo_xFe_1-xPO₄ and two phases for the core shell syntheses.

Preliminary electrochemical results show expected activity for the single phase synthesized materials. Delithiated CoPO₄ phase is known as unstable; suitable metal substitution in the bulk can help to overcome this problem as well as surface shell should protect from the side reactions with the electrolyte at high voltage [2,3]. The behavior of working potential and cycling stability of solid solution and core shell powders produced by directed synthesis are under continuous study.

[1] Bilecka, I., et al., Efficient microwave-assisted synthesis of LiFePO4 mesocrystals with high cycling stability. Journal of Materials Chemistry, 2009. 19(29): p. 5125-5128.

[2] Sharabi, R., et al., Raman study of structural stability of LiCoPO4 cathodes in LiPF6 containing electrolytes. Journal of Power Sources, 2012. 203(0): p. 109-114.

[3] Sharabi, R., et al., Electrolyte solution for the improved cycling performance of LiCoPO4/C composite cathodes. Electrochemistry Communications, 2013. 28(0): p. 20-23.