Jason R. Croy

First-charge instabilities of layered-layered lithium-ion-battery materials.

Li- and Mn-rich layered oxides with composition xLi2MnO3·(1 -x)LiMO2 enable high capacity and energy density Li-ion batteries, but suffer from degradation with cycling. Evidence of atomic instabilities during the first charge are addressed in this work with X-ray absorption spectroscopy, first principles simulation at the GGA+U level, and existing literature. The pristine material of composition xLi2MnO3·(1 -x)LiMn0.5Ni0.5O2 is assumed in the simulations to have the form of LiMn2 stripes, alternating with NiMn stripes, in the metal layers. The charged state is simulated by removing Li from the Li layer, relaxing the resultant system by steepest descents, then allowing the structure to evolve by molecular dynamics at 1000 K, and finally relaxing the evolved system by steepest descents. The simulations show that about ¼ of the oxygen ions in the Li2MnO3 domains are displaced from their original lattice sites, and form oxygen-oxygen bonds, which significantly lowers the energy, relative to that of the starting structure in which the oxygen sublattice is intact. An important consequence of the displacement of the oxygen is that it enables about ⅓ of the (Li2MnO3 domain) Mn ions to migrate to the delithiated Li layers. The decrease in the coordination of the Mn ions is about twice that of the Ni ions. The approximate agreement of simulated coordination number deficits for Mn and Ni following the first charge with analysis of EXAFS measurements on 0.3Li2MnO3·0.7LiMn0.5Ni0.5O2 suggests that the simulation captures significant features of the real material.

Material design of high-capacity Li-rich layered-oxide electrodes: Li2MnO3 and beyond

Lithium-ion batteries (LIBs) have been used widely in portable electronics, and hybrid-electric and all-electric vehicles for many years. However, there is a growing need to develop new cathode materials that will provide higher cell energy densities for advanced applications. Several candidates, including Li2MnO3-stabilized LiM′O2 (M′ = Mn/Ni/Co) structures, Li2Ru0.75Sn0.25O3 (i.e., 3Li2RuO3–Li2SnO3), and disordered Li2MoO3–LiCrO2 compounds can yield capacities exceeding 200 mA h g−1, alluding to the constructive role that Li2MO3 (M4+) end-member compounds play in the electrochemistry of these systems. Here, we catalog the family of Li2MO3 compounds as active cathodes or inactive stabilizing agents using high-throughput density functional theory (HT-DFT). With an exhaustive search based on design rules that include phase stability, cell potential, resistance to oxygen evolution, and metal migration, we predict a number of new Li2MIO3–Li2MIIO3 active/inactive electrode pairs, in which MI and MII are transition- or post-transition metal ions, that can be tested experimentally for high-energy-density LIBs.

Pristine-state structure of lithium-ion-battery cathode material Li1.2Mn0.4Co0.4O2 derived from NMR bond pathway analysis

Layered lithium ion battery cathode materials have been extensively investigated, of which layered–layered composites xLi2MnO3·(1 − x)LiMO2 (M = Mn, Co, Ni) are of particular interest, owing to their high energy density. Before the structural transformations that occur in these materials with cycling can be understood, the structure of the pristine material must be established. In this work, NMR spectra are measured for the model layered–layered system xLi2MnO3·(1 − x)LiCoO2 and Bond-Pathway-model analysis is applied to elucidate the atomic arrangement and domain structure of this material in its pristine state, before electrochemical cycling. The simplest structural element of an Li2MnO3 domain consists of a stripe of composition LiMn2 parallel to a crystallographic axis in a metal layer of the composite. A simple model of the composite structure may be constructed by a superposition of such stripes in an LiCoO2 background. We show that such a model can account for most of the features of the observed NMR spectra.

Exploring Lithium-Cobalt-Nickel Oxide Spinel Electrodes for ≥3.5 V Li-Ion Cells

Recent reports have indicated that a manganese oxide spinel component, when embedded in a relatively small concentration in layered xLi2MnO3·(1-x)LiMO2 (M = Ni, Mn, or Co) electrode systems, can act as a stabilizer that increases their capacity, rate capability, cycle life, and first-cycle efficiency. These findings prompted us to explore the possibility of exploiting lithiated cobalt oxide spinel stabilizers by taking advantage of (1) the low mobility of cobalt ions relative to that of manganese and nickel ions in close-packed oxides and (2) their higher potential (∼3.6 V vs Li0) relative to manganese oxide spinels (∼2.9 V vs Li0) for the spinel-to-lithiated spinel electrochemical reaction. In particular, we revisited the structural and electrochemical properties of lithiated spinels in the LiCo1-xNixO2 (0 ≤ x ≤ 0.2) system, first reported almost 25 years ago, by means of high-resolution (synchrotron) X-ray diffraction, transmission electron microscopy, nuclear magnetic resonance spectroscopy, electrochemical cell tests, and theoretical calculations. The results provide a deeper understanding of the complexity of intergrown layered/lithiated spinel LiCo1-xNixO2 structures when prepared in air between 400 and 800 °C and the impact of structural variations on their electrochemical behavior. These structures, when used in low concentrations, offer the possibility of improving the cycling stability, energy, and power of high energy (≥3.5 V) lithium-ion cells.

The quest for manganese-rich electrodes for lithium batteries: strategic design and electrochemical behavior

Manganese oxides, notably γ-MnO2 and modified derivatives, have played a major role in electrochemical energy storage for well over a century. They have been used as the positive electrode in primary (single discharge) Leclanche dry cells and alkaline cells, as well as in primary and secondary (rechargeable) lithium cells with non-aqueous electrolytes. Lithiated manganese oxides, such as LiMn2O4 (spinel) and layered lithium–nickel–manganese–cobalt (NMC) oxide systems, are playing an increasing role in the development of advanced rechargeable lithium-ion batteries. These manganese-rich electrodes have both cost and environmental advantages over their nickel counterpart, NiOOH, the dominant cathode material for rechargeable nickel–cadmium and nickel–metal hydride batteries, and their cobalt counterpart, LiCoO2, the dominant cathode material in lithium-ion batteries that power cell phones. An additional benefit is that tetravalent manganese can be used as a redox-active and/or stabilizing ‘spectator’ ion in lithiated mixed-metal oxide electrodes. This paper provides an overview of the historical development of manganese-based oxide electrode materials and structures, leading to advanced systems for lithium-ion battery technology; it updates a twenty-year old review of manganese oxides for lithium batteries. The narrative emanates largely from strategies used to design manganese oxide electrode structures at the Council for Scientific and Industrial Research, South Africa (1980–1994), Oxford University, UK (1981–1982), and Argonne National Laboratory, USA (1994–2017); it highlights the worldwide evolution of ideas and recent trends to improve the design, stability, and electrochemical capacity of structurally integrated, manganese-rich electrode materials.

First-Principles Study of Lithium Cobalt Spinel Oxides: Correlating Structure and Electrochemistry

Embedding a lithiated cobalt oxide spinel (Li2Co2O4, or LiCoO2) component or a nickel-substituted LiCo1- xNi xO2 analogue in structurally integrated cathodes such as xLi2MnO3·(1- x)LiMO2 (M = Ni/Co/Mn) has been recently proposed as an approach to advance the performance of lithium-ion batteries. Here, we first revisit the phase stability and electrochemical performance of LiCoO2 synthesized at different temperatures using density functional theory calculations. Consistent with previous studies, we find that the occurrence of low- and high-temperature structures (i.e., cubic lithiated spinel LT-LiCoO2; or Li2Co2O4 ( Fd3̅ m) vs trigonal-layered HT-LiCoO2 ( R3̅ m), respectively) can be explained by a small difference in the free energy between these two compounds. Additionally, the observed voltage profile of a Li/LiCoO2 cell for both cubic and trigonal phases of LiCoO2, as well as the migration barrier for lithium diffusion from an octahedral (Oh) site to a tetrahedral site (Td) in Fd3̅ m LT-Li1- xCoO2, has been calculated to help understand the complex electrochemical charge/discharge processes. A search of LiCo xM1- xO2 lithiated spinel (M = Ni or Mn) structures and compositions is conducted to extend the exploration of the chemical space of Li-Co-Mn-Ni-O electrode materials. We predict a new lithiated spinel material, LiNi0.8125Co0.1875O2 ( Fd3̅ m), with a composition close to that of commercial, layered LiNi0.8Co0.15Al0.05O2, which may have the potential for exploitation in structurally integrated, layered spinel cathodes for next-generation lithium-ion batteries.