Multiple phases in the epsilon -VPO sub(4)O-LiVPO sub(4)O-Li sub(2)VPO sub(4)O system: a combined solid state electrochemistry and diffraction structural study

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2014-06, Vol.2 (26), p.10182-10192
• Main Authors: Bianchini, M, Ateba-Mba, J M, Dagault, P, Bogdan, E, Carlier, D, Suard, E, Masquelier, C, Croguennec, L
• Format: Article
• Language: English
• Subjects: Diffraction; Energy density; Extraction; Insertion; Neutron diffraction; Phases; Signatures; Sustainability
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c4ta01518e

Polyanionic materials attract great interest in the field of Li-ion battery research thanks to the wide range of possible available compositions, resulting in a great amount of different properties. Tavorite type compositions offer a very rich crystal chemistry, among which LiVPO sub(4)F delivers the highest theoretical energy density. In this work we focus our interest on the homeotypic composition LiVPO sub(4)O. This oxy-phosphate shows the ability to exploit two redox couples, V super(5+)/V super(4+) at 3.95 V vs. Li super(+)/Li super(0) and V super(4+)/V super(3+) at an average potential of 2.3 V vs. Li super(+)/Li super(0) upon Li super(+) extraction and insertion, respectively. The two domains show marked differences both in the electrochemical signature and in the phase diagram. Here we address for the first time both topics with a combination of electrochemical techniques and ex situ/in situ X-ray and neutron diffraction and support of density functional theory (DFT) calculations, to get a deep understanding of the behavior of Li sub(1 plus or minus x)VPO sub(4)O. In the low voltage region, in particular, the formation of intermediate phases and the crystal structure of the end member Li sub(2)VPO sub(4)O are reported for the first time.