The predicted crystal structure of Li_4C_6O_6, an organic cathode material for Li-ion batteries, from first-principles multi-level computational methods

In this communication, we use first-principles based multi-level computational methods to predict the crystal structure of Li_4C_6O_6, the key intermediate material that can be oxidized to Li_2C_6O_6 or reduced to Li_6C_6O_6. This predicted structure leads to an X-ray diffraction (XRD) pattern in good agreement with experiment, validating the predicted structure. With this structure in hand one can proceed to determine details for the electrochemical properties of these organic electrodes (chemical potential for Li ion as a function of loading and the mechanism for the lithiation/delithiation process) useful in designing optimum systems

The interplay between thermodynamics and kinetics in the solid-state synthesis of layered oxides.

In the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase. Understanding the competition between thermodynamics and kinetics is a fundamental step towards the rational synthesis of target materials. Here, we use in situ synchrotron X-ray diffraction to investigate the multistage crystallization pathways of the important two-layer (P2) sodium oxides Na0.67MO2 (M = Co, Mn). We observe a series of fast non-equilibrium phase transformations through metastable three-layer O3, O3' and P3 phases before formation of the equilibrium two-layer P2 polymorph. We present a theoretical framework to rationalize the observed phase progression, demonstrating that even though P2 is the equilibrium phase, compositionally unconstrained reactions between powder precursors favour the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solid-state synthesis of ceramic materials, and constitutes a step forward in unravelling the complex interplay between thermodynamics and kinetics during materials synthesis

The Reaction Mechanism and Capacity Degradation Model in Lithium Insertion Organic Cathodes, Li_2C_6O_6, Using Combined Experimental and First Principle Studies

Herein, we explore the capacity degradation of dilithium rhodizonate salt (Li_2C_6O_6) in lithium rechargeable batteries based on detailed investigations of the lithium de/insertion mechanism in Li_2C_6O_6 using both electrochemical and structural ex situ analyses combined with first-principles calculations. The experimental observations indicate that the Li_xC_6O_6 electrode undergoes multiple two-phase reactions in the composition range of 2 ≤ x ≤ 6; however, the transformations in the range 2 ≤ x ≤ 4 involve a major morphological change that eventually leads to particle exfoliation and the isolation of active material. Through first-principles analysis of Li_xC_6O_6 during de/lithiation, it was revealed that particle exfoliation is closely related to the crystal structural changes with lithium deinsertion from C_6O_6 interlayers of the Li_xC_6O_6. Among the lithium ions found at various sites, the extraction of lithium from C_6O_6 interlayers at 2 ≤ x ≤ 4 decreases the binding force between the C_6O_6 layers, promoting the exfoliation of C_6O_6 layers and pulverization at the electrode, which degrades capacity retention

Hidden structural and chemical order controls lithium transport in cation-disordered oxides for rechargeable batteries

This work was supported by the Robert Bosch Corporation, Umicore Specialty Oxides and Chemicals, and the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 under the Advanced Battery Materials Research (BMR) Program. The research conducted at the NOMAD Beamline at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Sciences, U.S. Department of Energy. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The computational analysis was performed using computational resources sponsored by the Department of Energy’s Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory, as well computational resources provided by Extreme Science and Engineering Discovery Environment (XSEDE), which was supported by the National Science Foundation grant number ACI-1053575.Structure plays a vital role in determining materials properties. In lithium ion cathode materials, the crystal structure defines the dimensionality and connectivity of interstitial sites, thus determining lithium ion diffusion kinetics. In most conventional cathode materials that are well-ordered, the average structure as seen in diffraction dictates the lithium ion diffusion pathways. Here, we show that this is not the case in a class of recently discovered high-capacity lithium-excess rocksalts. An average structure picture is no longer satisfactory to understand the performance of such disordered materials. Cation short-range order, hidden in diffraction, is not only ubiquitous in these long-range disordered materials, but fully controls the local and macroscopic environments for lithium ion transport. Our discovery identifies a crucial property that has previously been overlooked and provides guidelines for designing and engineering cation-disordered cathode materials.Publisher PDFPeer reviewe