Electrochemical Properties of Three Li₂Ni₂TeO₆ Structural Polymorphs

Abstract

Three different structures\nof the composition Li₂Ni₂TeO₆ have\nbeen synthesized and their electrochemical\nproperties characterized: a disordered orthorhombic phase with tellurium\nordering and strong Li/Ni cation mixing, a T^#2-layered\nphase, and an O3-layered phase; each have a distinct cycling performance.\nThe disordered orthorhombic structure is the most stable at room temperature\nand has the highest capacity with the lowest overpotential. The T^#2 phase is the least stable and undergoes a phase transformation\nonce lithium is extracted. Density functional theory calculations\nreconcile the relative structural stabilities and physical properties\nof each phase with their electrochemical performances. Calculations\nalso confirmed experimental observations regarding the synthesis of\neach structure and indicated the mechanism for capacity fade of each\nLi₂Ni₂TeO₆ cathode. Strong tellurium–oxygen\ncovalent bonding increases the voltage of the Ni^2+/3+ redox\ncouple in each of these materials over what is normally observed in\nlayered oxides.