The Li<i>_x</i>VPn₄ Ternary Phases (Pn = P, As): Rigid Networks for Lithium Intercalation/Deintercalation

Abstract

We present the ternary phases LixVPn4 (Pn = P, As) as new materials for the negative electrode in lithium-ion batteries. Associated with a large variation of lithium content per formula unit (3 ≤ x ≤ 7.5 for P and 3 ≤ x ≤ 11 for As), these materials show a higher specific capacities in their first charge/discharge cycle than the graphite (550 mA·h/g for Pn = P and 530 mA·h/g for Pn = As vs 372 m·Ah/g for Cgr) and open new routes for the design of new types of rechargeable Li-ion batteries. High-temperature syntheses, X-ray diffraction analyses, and first-principle electronic structure calculations give evidence of remarkable stability of the LixVPn4 crystal structure upon various lithium compositions. Owing to rather strong covalent V−Pn bonds, the host matrixes behave as structurally stable networks of weakly interacting tetrahedra, able to store (respectively, release) a large number of additional electrons (correlatively with the intercalation (respectively, deintercalation) of Li+ in the host matrix) into a nearly nonbonding Pn−Pn band. This leads to very weak volumetric variations (<1%) of the unit cells upon cycling compared to what is usually observed in the negative electrode materials such as alloy compounds. The cycling performances of the new, promising LixVPn4/Li cells are currently under investigation.