Striking impact of Na insertion on structural and electronic properties of the electrode material Na2+xV6O16.
The Na2.55V6O16structure is a promising material for sodium ion batteries due to a significant capacity and stability at high current rates, but its cycle stability for Na application is significantly lower than that obtained with Li (de-)insertion. In this work, we present the results of density functional theory (DFT) calculations on the structural and electronic properties of Na2+xV6O16compounds up to x  =  2. As x increases, we evidence a strong deformation of the tetrahedral sites occupied by sodium ions, leading to new highly stable sites for these inserted ions at x  =  2. Comparing with Li4V6O16, we demonstrate that the stability of these new Na sites can be attributed to the electrostatic interactions between sodium ions and atoms of the host structure, the evolution of the oxidation degree of Vanadium atoms being another indicator of such effects.
Sciences et Ingénierie des Matériaux et Procédés (SIMAP), UMR CNRS 5266, Grenoble Université Alpes, BP 75, 38402 Saint-Martin d'Hères Cedex, France.
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