Probing Electrochemically-Induced Structural Changes and Defects Affecting Li-Ion Intercalation and De-Intercalation in High Capacity Orthosilicate Cathodes

Li-ion batteries (LIBs) have already made tremendous progress supplying power for multiple devices used in our daily life. Now LIBs are gradually entering the plug-hybrid and fully electric vehicles. Safety and high specific capacity enabling long range driving between charges are among industry’s priorities in this domain. One cathode material group that potentially can provide solutions to these priorities is lithium metal silicates. Orthosilicates, Li₂MSiO₄, where M = Fe, Mn, Co, Ni, are characterized by a theoretical specific capacity that is twice that of LiFePO₄, namely 340 vs. 170 mAh/g^1,2. In this presentation, we report on the synthesis and electrochemical/structural evaluation of different phase (monoclinic and orthorhombic) Li₂(Fe,Mn)SiO₄ materials using a combination of organic-assisted hydrothermal and reducing annealing treatment steps. During the electrochemical process, we find that the Li₂FeSiO₄ cathode demonstrates rate- and phase- dependent capacity changes upon lithiation/delithiation³. We have probed these changes by conducting both in-situ/postmortem synchrotron XRD/XANES and first-principle calculations of the structure/phase stabilities and Li ion diffusion properties of monoclinic Li₂FeSiO₄ orthosilicate. It is revealed that formation of Li-Fe antisite defects play a key role in destabilizing the orthosilicate structure and “catalyzing” the monoclinic-to-orthorhombic transition. Furthermore the charge compensation mechanism that is essential in achieving more than one Li extraction is discussed accordingly as well as the Li-ion diffusion properties are analyzed. The rich insight obtained from these Li₂FeSiO₄ studies is invaluable as we move towards the design and testing of stable orthosilicate structures with fully reversible 2-Li intercalation capacity for high-energy next generation LIB cathodes.

References

1. A., Nyten; A., Abouimrane; M., Armand; T., Gustafsson & J. O., Thomas, Electrochemical performance of Li₂FeSiO₄ as a new Li-battery cathode material. Electrochem. Commun. 7, 156-160, (2005).

2. M. Saiful Islam et al., Silicate cathodes for lithium batteries: alternatives to phosphates?  J. Mater. Chem., 2011, 21, 9811.

3. Xia Lu; Huijing Wei; Hsien-Chieh Chiu; Raynald Gauvin; Pierre Hovington; Abdelbast Guerfi; Karim Zaghib and George P. Demopoulos, Rate-dependent phase transitions in Li₂FeSiO₄ cathode nanocrystals, Sci. Rep. 5 (2015) 8599.