Atomic-scale study of NASICON type electrode material: defects, dopants and sodium-ion migration in Na3V2(PO4)3

Abstract

The polyanion-based NASICON type Sodium-Ion Batteries (SIBs) gained much attention 9 as an alternative source of Lithium-Ion Batteries due to their advantages such as high natural abun- 10 dance, cost-effectiveness, higher capacity, high cyclability, and stable three-dimensional structure. 11 Among various NASICON-type electrode materials, Na3V2(PO4)3 (NVP) has been recognized as a 12 potential cathode for batteries because of its high sodium mobility and firm structural stability. The 13 electrochemical suitability of this material is investigated by inspecting the defect properties, dopant 14 nature, and Na+ ion migration using an orthodox atomic scale simulation method. The study re- 15 vealed that the most favorable intrinsic defect is the Na Frenkel (0.46 eV/defect) which ensures the 16 formation of Na vacancy sites that facilitate the Na migration through the vacancy mechanism. The 17 lowest activation energy (0.70 eV) Na migration pathways further affirm the migration. Looking at 18 the aliovalent dopants on the V sites results in the formation of Na vacancies, which may facilitate 19 the Na ion diffusion more. The tetravalent dopants on the P sites increase the amount of sodium 20 incorporation by creating Na interstitials, which could enhance the capacity of the cell. Doping Sn 21 on the V site and Si on the P site are calculated to be energetically favorable for the formation of Na 22 vacancies and Na interstitials respectively.