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Comparative Studies on the Phase Stability, Electronic Structure, and Topology of the Charge Density in the Li₃XO₄ (X = P, As, V) Lithium Orthosalt Polymorphs

Christine Frayret*^†, Christian Masquelier^†, Antoine Villesuzanne^‡, Mathieu Morcrette^† and Jean-Marie Tarascon^†

LRCS-CNRS, Universit

de Picardie, 33, Rue Saint-Leu, 80039 Amiens Cedex, France, and ICMCB, CNRS, Universit

de Bordeaux 1, 87 Av. Dr. A. Schweitzer, 33608 Pessac Cedex, France

Chem. Mater., 2009, 21 (9), pp 1861–1874

DOI: 10.1021/cm803429s

Publication Date (Web): April 10, 2009

* To whom correspondence should be addressed. Tel: +33 322827586. Fax: +33 322827590. E-mail: christine.frayret@u-picardie.fr., †

Universit de Picardie.

, ‡

Universit de Bordeaux 1.

Abstract

Density functional theory (DFT) calculations within the generalized gradient approximation (GGA) were performed to study phase transitions in lithium orthosalts Li₃XO₄ (X = P, As, V). The equilibrium crystal structure parameters and the total energies of the Li₃XO₄ polymorphs were calculated for the β- and γ-phases. The relative lattice stabilities of the two polymorphs were examined in the light of various peculiarities at atomic scale. The β-polymorph was systematically found to be the most stable one, agreeing well with experimental results. Using an all electron full potential method, we have investigated densities of states and the topology of charge density through the Bader’s quantum theory of “atoms in molecules” (AIM) along with electrostatic energy density maps in order to evaluate factors governing the stability of each polymorph. Higher stability of the β-polymorph or differences in energy between β- and γ-phases according to the nature of X along with the experimental temperatures of phase transitions can be connected to several microscopic features, including differences in constraint within XO₄ tetrahedron or chemical bonding characteristics. This new approach can be applied to other phase stability studies, including the family of Li₂MSiO₄, which is of great interest for cathode materials in lithium batteries.

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