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We report the use of iron 1s3p resonant X-ray emission processes to conduct spin-selective, high-energy resolution fluorescence detected X-ray absorption near-edge spectroscopy (HERFD-XANES) on an iron-containing, lithium- and manganese-rich, fully earth-abundant cathode material, Li1.3Mn0.5Fe0.2O2(0.7Li2MnO3·0.3LiFeO2). Coupling this technique with conventional Mn K-edge XANES and detailed extended X-ray absorption fine structure (EXAFS) analysis from both the Mn and Fe vantage points, we gain fundamental insights into the redox processes and migration tendencies of transition metals in this cathode material at the bulk level. We show that during the first charge, Fe3+undergoes oxidation to form Fe4+prior to the activation plateau. Toward the end of activation, a significant fraction of the iron is present as tetrahedral Fe3+. This observation reveals that iron migration from octahedral to tetrahedral sites and iron reduction are initiated during activation. Upon first discharge from the activated state, a continuous and overlapping reduction of both Fe and Mn is observed, with Fe largely restored back as an octahedrally coordinated Fe3+. The manganese local environment gradually changes to a distorted cooperative Jahn–Teller Mn3+structure during discharge, with the clear presence of two Mn–O as well as two Mn–Mn correlation distances at 2.0 V. The significant reduction of manganese in the very first discharge is distinctly different from that seen in typical nickel-based lithium-manganese-rich materials but is similar to that observed for pure Li2MnO3. These findings shed light on key structure–property correlations in the cathode material and point to a causative relationship between the redox mechanisms as well as structural changes endured by the material and relatively poor performance during extended electrochemical cycling.

Tailoring the chemical reactivity of nanomaterials at the atomic level is one of the most important challenges in catalysis research. In order to achieve this elusive goal, fundamental understanding of the geometric and electronic structure of these complex systems at the atomic level must be obtained. This article reports the influence of the nanoparticle shape on the reactivity of Pt nanocatalysts supported on γ-Al2O3. Nanoparticles with analogous average size distributions (∼0.8−1 nm), but with different shapes, synthesized by inverse micelle encapsulation, were found to display distinct reactivities for the oxidation of 2-propanol. A correlation between the number of undercoordinated atoms at the nanoparticle surface and the onset temperature for 2-propanol oxidation was observed, demonstrating that catalytic properties can be controlled through shape-selective synthesis.

Embedding a lithiated cobalt oxide spinel (Li2Co2O4, or LiCoO2) component or a nickel-substituted LiCo1–xNixO2analogue in structurally integrated cathodes such as xLi2MnO3·(1–x)LiM′O2(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 LiCoO2synthesized 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(Fd3̅m) vs trigonal-layered HT-LiCoO2(R3̅m), respectively) can be explained by a small difference in the free energy between these two compounds. Additionally, the observed voltage profile of a Li/LiCoO2cell 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 Fd3̅mLT-Li1–xCoO2, has been calculated to help understand the complex electrochemical charge/discharge processes. A search of LiCoxM1–xO2lithiated 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(Fd3̅m), 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.

This personal narrative relates to the discovery in 1981 of stoichiometric LiM2O4spinel electrodes (where M = metal cation) for lithium-ion batteries by the Goodenough group at Oxford University, UK, and the subsequent identification and evolution of stable lithiated-spinel Li2M2O4(or LiMO2) cathodes at the Council for Scientific and Industrial Research in South Africa and Argonne National Laboratory (USA). The competition that occurs between the formation of lithiated-spinel and layered (LiMO2) structures at 400 °C, and recent efforts to design high-capacity, Mn-rich composite cathodes with partial disorder, are discussed. The paper is written in honor of John Goodenough’s 100th birthday.