Transition-Metal Mixing and Redox Potentials in Lix(M1-yM′y)PO4 (M, M′ = Mn, Fe, Ni) Olivine Materials from First-Principles Calculations

David H. Snydacker, Chris Wolverton*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

The performance of olivine cathode materials can be improved using core/shell structures such as LiMnPO4/LiFePO4 and LiMnPO4/LiNiPO4. We use density functional theory to calculate the energetics, phase stability, and voltages of transition-metal mixing for a series of olivine phosphate materials. For LiMn1-yFeyPO4, LiFe1-yNiyPO4, and LiMn1-yNiyPO4, we find phase-separating tendencies with (mean-field) maximum miscibility gap temperatures of 120, 320, and 760 K respectively. At room temperature, we find that Mn is completely miscible in LiFePO4, whereas Mn solubility in LiNiPO4 is just 0.3%. Therefore, we suggest that core/shell LiMnPO4/LiNiPO4 particles could be more effective at containing Mn in the particle core and limiting Mn dissolution into the electrolyte relative to LiMnPO4/LiFePO4 particles. We calculate shifts in redox potentials for dilute transition metals, M, substituted into LixM′PO4 host materials. Unmixed LixMnPO4 exhibits a redox potential of 4.0 V, but we find that dilute Mn in a LiNiPO4 shell exhibits a redox potential of 4.3 V and therefore remains redox inactive at lower cathode potentials. We find that strain plays a large role in the redox potentials of some mixed systems (LixMn1-yFeyPO4) but not others (LixMn1-yNiyPO4).

Original languageEnglish (US)
Pages (from-to)5932-5939
Number of pages8
JournalJournal of Physical Chemistry C
Volume120
Issue number11
DOIs
StatePublished - Mar 24 2016

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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