(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award Address) Understanding the Mn-Based Oxide Electrode Materials and Beyond from First Principles and Experiment

Abstract

Technology has advanced rapidly, especially in the 21st century, influencing our daily life on unprecedented levels. Most such advances in technology are closely linked to, and often driven by, the discovery and design of new materials. Many researchers have been actively searching for alternative cathode materials for Lithium-ion batteries (LIBs) that can be more clean, efficient, cost-effective, and deliver higher electrochemical performance compared to the already-commercialized electrodes. However, finding new and effective energy storage technologies is a particularly daunting task, even for a very experienced researcher. Computational compilation of battery materials properties such as voltage, diffusivity, and phase stability against irresponsible phase transformations using first-principles density functional theory (DFT) calculations has helped understand the underlying mechanism in many existing and hypothetical compounds that can be used as a part of battery components. By computationally modeling the spinel LiMn2O4 surface structures, we were able to provide a novel strategy to suppress Mn dissolution and the Jahn-Teller distortion associated with Mn3+, particularly at the (001) LiMn2O4 facet, which has been a challenging task to overcome in order to mitigate capacity fading in the Mn-based cathodes [1-3]. In addition, the idea of a multi-faceted high-throughput screening within the Open Quantum Materials Database (OQMD) [4,5] was carried out to discover a number of new Li-rich Li2MO3-type layered compounds (beyond Li2MnO3) to narrow down the list of thousands of candidate composite electrodes to a handful that are the most likely to be synthesized in experiment [6]. We classified the family of discovered Li2MO3 compounds as active cathodes or inactive stabilizer and have suggested the top-30 Li2MIO3-Li2MIIO3 active/inactive pair cathode systems (MI, MII = transition- or post-transition-metal ions) by examining the properties with respect to their operating voltage, stability against oxygen loss and metal migration, and the formation of solid-solution and/or coherent nanocomposites [6]. Our computational predictions have included at least a dozen new Li-rich cathode pairs with higher gravimetric energy densities compared to recently-discovered Ru-based Li2MO3 cathodes, which might have varying degrees of practical vs. purely scientific interest due to cost or toxicity reasons. Currently, there is an on-going investigation in order to verify whether these computational predictions can be realized in experiment and the further details will be discussed at the upcoming meeting. Furthermore, our recent study prompted a re-investigation of lithiated spinel (Li1+x Co2O4; 0 < x ≤ 1) and Li2Co2-y Ni y O4 (0 < y ≤ 0.4) with the argument that a lithiated cobalt-containing oxide spinel component embedded in a layered-layered-spinel composite electrode would benefit in terms of both delivered voltage and cycling stability, when compared to a manganese-based spinel oxide [7,8]. In order to understand the electrochemical performance of Li-Co-O cathodes synthesized at different temperatures, we revisited the phase stability of Fd-3m and R-3m LiCoO2 using DFT calculations [9]. In addition, a structural search of Fd-3m Li2Co z M2-z O4 (0 ≤ z ≤ 2) lithiated-spinel (M' = Ni or Mn) structures and compositions was conducted to extend the exploration of the chemical space of Li-Co-Mn-Ni-O electrode materials, where we have predicted a new lithiated-spinel based composition lying on the convex hull (i.e., thermodynamically-stable) that may have potential for exploitation in structurally-integrated, layered-spinel cathodes for next-generation LIBs [9]. Lastly, our recent alternative synthesis approach to prepare each cathode material separately and to integrate two- or three-component cathode via a high-energy ball-milling process will be presented [10-14], which could be simple, robust, cost effective, rapid, and scalable at industrial scale, as well as it can synthesize a number of new closely-connected nanocomposite systems with the difficulty in preparing phase-pure materials. This simple synthesis method could bring a new perspective on the preparation and use of the high-energy-density cathode material systems, consisting of more than two components.