The Predicted Crystal Structure of Metastrengite I FePO4∙2H2o and Its Importance in Li-Ion Battery Systems

The demands for large-scale energy storage devices have increased significantly for the past decade [1].  Olivine structured lithium iron phosphate, LiFePO₄, has been recognized as a promising cathode material for lithium ion batteries because of its advantages of high power capability, low cost, non-toxicity, excellent thermal safety, and high reversibility [2].  In addition to LiFePO₄, various amorphous and crystalline phases of iron phosphates, FePO₄ and FePO₄·nH₂O have been proposed as the cathode materials in lithium ion batteries [3].

Among various phases of iron phosphates, the exact crystal structure of crystalline FePO₄·2H₂O (metastrengite I) is still unknown as first mentioned by Rémy et al. [4].  It was determined that an orthorhombic olivine-type LiFePO₄ (Pnma) and metastrengite I FePO₄·2H₂O (Pbnm) belong to the same space group #62.  Here, we use the recently developed genetic-algorithm-based FPASS method [5] to determine the crystal structure of crystalline FePO₄·2H₂O (metastrengite I) and discuss the possible applications of the crystalline FePO₄·2H₂O (metastrengite I) for the LIBs system.

 

References

[1] J. M Tarascon and M. Armand, Nature, 414, 359 (2001).

[2] A. K. Padhi, K. S. Nanjundaswamy, and J. B Goodenough, J. Electrochem Soc., 144, 1188 (1997).

[3] C. Delacourt, P. Poizot, D. Bonnin, and C. Masquelier, J. Electrochem. Soc., 156, A595 (2009).

[4] P. Rémy, Ph.D. Thesis, University of Paris, France (1971).

[5] B. Meredig and C. Wolverton, Nature Mater., 12, 123 (2013).