X. Lu, H. C. Chiu (McGill University), Z. Arthur (University of Guelph), H. Wei (McGill University), J. Zhou (Canadian Light Source), J. Wang (Canadian Light Source Inc), N. Chen (Canadian Light Source), D. T. Jiang (University of Guelph), K. Zaghib (IREQ), and G. P. Demopoulos (McGill University)
Orthosilicates, Li
2MSiO
4, where
M = Fe, Mn, Co, Ni, are characterized by a theoretical specific capacity that is twice that of LiFePO
4, namely 340
vs. 170 mAh/g. In this presentation, we have probed the structural evolution and charge compensation of Li
2FeSiO
4 cathode using both
in-situ/postmortem synchrotron XRD/XANES and first-principle calculations
1-3. The results demonstrate that the formation of Li-Fe antisite defects play a key role in destabilizing the Li
2FeSiO
4 structure and “catalyzing” the monoclinic-to-orthorhombic transition. Then the charge compensation for the first Li extraction does not come solely from the ferrous to ferric conversion due to the strong electron correlation of Fe 3
d orbitals, but interestingly from prominent participation of lattice oxygen as well that appears to destabilize the cycled structure. Using scanning transmission X-ray microscopy, it is revealed that the electrochemical lithiation/delithiation of Li
2FeSiO
4 electrode does not proceed uniformly but it exhibits an unusual solid solution pattern
4 with the stored Li content varying locally possibly arising from a combination of inherent LFS material and electrode properties like poor conductivities, variable particle size/distribution and extent of electrolyte penetration. All these findings should have a thought-provoking influence on the study of the material itself and the broader Li-ion battery research community as well.
References
1. Lu, X.; Wei, H. J.; Chiu, H. C.; Gauvin, R.; Hovington, P.; Guerfi, A.; Zaghib, K.; Demopoulos, G. P. Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals. Sci Rep-Uk 2015, 5, 8599.
2. Arthur, Z.; Chiu, H.-C.; Lu, X.; Chen, N.; Emond, V.; Zaghib, K.; Jiang, D.-T.; Demopoulos, G. P. Spontaneous reaction between uncharged lithium iron silicate cathode and LiPF6-based electrolyte Chem Commun 2015, accpeted, DOI: 10.1039/C5CC07197F.
3. Lu, X.; Chiu, H.-C.; Bevan, H. K.; Jiang, D.-T.; Zaghib, K.; Demopoulos, P. G. Density functional theory insight into the structure stability and Li diffusion properties of monoclinic and orthorhombic Li2FeSiO4 cathodes. J Power Sources 2015, In revision.
4. Lu, X.; Chiu, H.-C.; Arthur, Z.; Zhou, J. G.; Wang, J.; Chen, N.; Jiang, D.-T.; Zaghib, K.; Demopoulos, G. P. Quasi-equilibrium Li storage in metastable Li2FeSiO4 cathode. 2015, Under review.
