[en] Realizing reversible reduction-oxidation (redox) reactions of lattice oxygen in batteries is a promising way to improve the energy and power density. However, conventional oxygen absorption spectroscopy fails to distinguish the critical oxygen chemistry in oxide-based battery electrodes. Therefore, high-efficiency full-range mapping of resonant inelastic X-ray scattering (mRIXS) has been developed as a reliable probe of oxygen redox reactions. Here, based on mRIXS results collected from a series of Li_1.17Ni_0.21Co_0.08Mn_0.54O₂ electrodes at different electrochemical states and its comparison with peroxides, we provide a comprehensive analysis of five components observed in the mRIXS results. While all the five components evolve upon electrochemical cycling, only two of them correspond to the critical states associated with oxygen redox reactions. One is a specific feature at 531.0 eV excitation and 523.7 eV emission energy, the other is a low-energy loss feature. We show that both features evolve with electrochemical cycling of Li_1.17Ni_0.21Co0.08Mn_0.54O₂ electrodes, and could be used for characterizing oxidized oxygen states in the lattice of battery electrodes. This work provides an important benchmark for a complete assignment of all mRIXS features collected from battery materials, which sets a general foundation for future studies in characterization, analysis, and theoretical calculation for probing and understanding oxygen redox reactions.

[en] Amorphous indium gallium zinc oxide (a-IGZO) is the archetypal transparent amorphous oxide semiconductor. Despite the gains made with a-IGZO over amorphous silicon in the last decade, the presence of deep subgap states in a-IGZO active layers facilitate instabilities in thin film transistor properties under negative bias illumination stress. Several candidates could contribute to the formation of states within the band gap. Here, we present evidence against In⁺ lone pair active electrons as the origin of the deep subgap features. No In⁺ species are observed, only In⁰ nano-crystallites under certain oxygen deficient growth conditions. Our results further support under coordinated oxygen as the source of the deep subgap states. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] This work reports a comprehensive study of a novel polyol method that can successfully synthesize layered LiNi_0.4Mn_0.4Co_0.2O₂, spinel LiNi_0.5Mn_1.5O₄, and olivine LiCoPO₄ cathode materials. When properly designed, polyol method offers many advantages such as low cost, ease of use, and proven scalability for industrial applications. Most importantly, the unique properties of polyol solvent allow for greater morphology control as shown by all the resulting materials exhibiting monodispersed nanoparticles morphology. This morphology contributes to improved lithium ion transport due to short diffusion lengths. Polyol-synthesized LiNi_0.4Mn_0.4Co_0.2O₂ delivers a reversible capacity of 101 and 82 mAh·g⁻¹ using high current rate of 5C and 10C, respectively. It also displays surprisingly high surface structure stability after charge-discharge processes. Each step of the reaction was investigated to understand the underlying polyol synthesis mechanism. A combination of in situ and ex situ studies reveal the structural and chemical transformation of Ni-Co alloy nanocrystals overwrapped by a Mn- and Li-embedded organic matrix to a series of intermediate phases, and then eventually to the desired layered oxide phase with a homogeneous distribution of Ni, Co, and Mn. We envisage that this type of analysis will promote the development of optimized synthesis protocols by establishing links between experimental factors and important structural and chemical properties of the desired product. The insights can open a new direction of research to synthesize high-performance intercalation compounds by allowing unprecedented control of intermediate phases using experimental parameters. .

[en] Full, reversible intercalation of two Li"+ has not yet been achieved in promising VOPO_4 electrodes. A pronounced Li"+ gradient has been reported in the low voltage window (i.e., second lithium reaction) that is thought to originate from disrupted kinetics in the high voltage regime (i.e., first lithium reaction). Here, we employ a combination of hard and soft x–ray photoelectron and absorption spectroscopy techniques to depth profile solid state synthesized LiVOPO_4 cycled within the low voltage window only. Analysis of the vanadium environment revealed no evidence of a Li"+ gradient, which combined with almost full theoretical capacity confirms that disrupted kinetics in the high voltage window are responsible for hindering full two lithium insertion. Furthermore, we argue that the uniform Li"+ intercalation is a prerequisite for the formation of intermediate phases Li_1_._5_0VOPO_4 and Li_1_._7_5VOPO_4. The evolution from LiVOPO_4 to Li_2VOPO_4 via the intermediate phases is confirmed by direct comparison between O K–edge absorption spectroscopy and density functional theory.