An Integrated First Principles and Experimental Approach to Enabling Multi-Electron Lithium-Ion Battery Cathodes

Today’s commercial lithium-ion battery cathodes function on the basis of a single-electron transfer per transition metal. In order to attain significantly higher capacities, particularly in polyanionic compounds with higher voltages, achieving reversible multi-electron transfer per transition metal is necessary. In this talk, we will discuss the efforts of the Northeast Center for Chemical Energy Storage (NECCESS), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001294, to identify crystal structures that can reversibly intercalate two lithium ions and understand the implications to the crystal lattice and its stability of inserting those two lithium ions. Specifically, we will present results from our combined first principles and experimental investigations into the thermodynamics, kinetics and electronic structure of ε-VOPO₄ (theoretical capacity of 318 mAh/g) over two Li insertion. We find that density functional theory, X-ray photoelectron spectroscopy and cyclic voltammetry all provide evidence of two-phase behavior during the first Li insertion and multiple intermediate phases during the second Li insertion. We will also show that ε-VOPO₄ and its lithiated compounds show extremely good thermal stability relative to other well-known cathodes, and discuss our findings on the ionic and electronic limitations in this material.