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Single-atoms (SAs) with atomically coordinated reaction centers are considered the next generation of catalysts that can exhibit exceptional catalytic efficiency. However, the general concern about thermodynamic vulnerabilities of SAs questions their practical value. Moreover, whether the inherent catalytic nature of SAs is superior compared with that of larger nanoparticles is still under debate. Here, we address two controversies by a comparative study using two catalysts: Pt/TiO2 and Pt/CeOx-TiO2. Based on a hierarchical study of density functional theory, time-resolved catalysis performance test, in situ infrared spectroscopy, and operando X-ray absorption spectroscopy, we could unveil the catalytic nature of Pt-SAs and their stability. By utilizing the heterogeneous interface formed between TiO2 supporting particles and CeOx clusters formed on the surface of TiO2, we preferentially synthesized Pt-SAs pinned at the CeOx-TiO2 interfaces on CeOx-TiO2 hybrid-oxide supports. The strong electronic coupling between the Pt-SAs and the Ce ions at the CeOx-TiO2 interfaces enhanced the catalytic activity toward CO oxidation of Pt-SAs and improved the long-term stability under CO oxidation conditions. The CO oxidation activity of Pt-SAs stabilized at CeOx-TiO2 was improved by 13.5 times at 200 °C compared with the Pt-SAs on TiO2. The results present how to easily improve the activity and stability of Pt-SAs using a simple interface control method. Moreover, we demonstrate that the catalytic activity and the stability of Pt-SAs can be monitored through the chemical state of the interfaces. Our study provides comprehensive understanding about the catalytic nature as well as a novel strategy toward applications of Pt-SAs, enabling sustainable use of Pt in heterogeneous catalysts.

The use of oxide cathodes in Mg batteries would unlock a potential energy storage system that delivers high-energy density. However, poor kinetics of Mg diffusion in known solid oxide lattices strongly limits reversible intercalation, which motivates the sustained exploration of new candidates. Herein, nanocrystals of a few-layer phyllomanganate, reminiscent of the mineral vernadite, were shown to have considerable electrochemical activity toward Mg intercalation at room temperature, where it delivered ∼190 mAh g-1 at ∼1.9 V (vs Mg/Mg2+) in batteries paired with a Mg metal anode. Multimodal characterization confirmed the notable degree of reversible intercalation by probing the structural, compositional, and redox changes undertaken by the oxide. Distinct levels of Mg activity were also observed while varying the content of small amounts of lattice water and the temperature of the reaction. The results reaffirm the prospects for operational Mg batteries using oxide cathodes in moderate conditions, overcoming current limits of performance of this prospective technology.

Battery function is determined by the efficiency and reversibility of the electrochemical phase transformations at solid electrodes. The microscopic tools available to study the chemical states of matter with the required spatial resolution and chemical specificity are intrinsically limited when studying complex architectures by their reliance on two-dimensional projections of thick material. Here, we report the development of soft X-ray ptychographic tomography, which resolves chemical states in three dimensions at 11 nm spatial resolution. We study an ensemble of nano-plates of lithium iron phosphate extracted from a battery electrode at 50% state of charge. Using a set of nanoscale tomograms, we quantify the electrochemical state and resolve phase boundaries throughout the volume of individual nanoparticles. These observations reveal multiple reaction points, intra-particle heterogeneity, and size effects that highlight the importance of multi-dimensional analytical tools in providing novel insight to the design of the next generation of high-performance devices.

The development of cathode materials for lithium-ion batteries (LIBs) aims to achieve high energy density, cost-effectiveness, and thermal as well as mechanical stability. It generally proceeds through multidimensional design rules at the atomic, phase, particle, and electrode levels. Recently, new strategies have been proposed to achieve high energy density even in olivine-structured cathodes, which have a relatively lower theoretical capacity compared to layered cathode materials. These strategies involve substituting iron (Fe) with manganese (Mn), controlling particle morphology, and fabricating thick electrodes to simultaneously achieve high energy density and cost-effectiveness. However, comprehensive design guidelines for the material design, particle morphology, and fabrication of thick electrodes for olivine cathodes are still lacking. Herein, we provide detailed insights from well-established prior knowledge on olivine cathodes and share the latest findings related to their particle morphology control and electrode thickening. Additionally, our review closely investigates further considerations related to kinetics, such as low electronic and ionic conductivity, and mechanical instability issues that arise while thickening electrodes. It is emphasized that these issues can be resolved through a comprehensive understanding and strategies from the atomic level to the electrode level. Therefore, this review aims to contribute to achieving high energy density in olivine-based cathodes by understanding their kinetic limitations and mechanical instabilities. [ABSTRACT FROM AUTHOR]

The performance of battery electrode materials is strongly affected by inefficiencies in utilization kinetics and cycle life as well as size effects. Observations of phase transformations in these materials with high chemical and spatial resolution can elucidate the relationship between chemical processes and mechanical degradation. Soft X-ray ptychographic microscopy combined with X-ray absorption spectroscopy and electron microscopy creates a powerful suite of tools that we use to assess the chemical and morphological changes in lithium iron phosphate (LiFePO4) micro- and nanocrystals that occur upon delithiation. All sizes of partly delithiated crystals were found to contain two phases with a complex correlation between crystallographic orientation and phase distribution. However, the lattice mismatch between LiFePO4 and FePO4 led to severe fracturing on microcrystals, whereas no mechanical damage was observed in nanoplates, indicating that mechanics are a principal driver in the outstanding electrode performance of LiFePO4 nanoparticles. These results demonstrate the importance of engineering the active electrode material in next generation electrical energy storage systems, which will achieve theoretical limits of energy density and extended stability. This work establishes soft X-ray ptychographic chemical imaging as an essential tool to build comprehensive relationships between mechanics and chemistry that guide this engineering design.

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The energy density of current batteries is limited by the practical capacity of the positive electrode, which is determined by the properties of the active material and its concentration in the composite electrode architecture. The observation in dynamic conditions of electrochemical transformations creates the opportunity of identifying design rules toward reaching the theoretical limits of battery electrodes. But these observations must occur during operation and at multiple scales. They are particularly critical at the single-particle level, where incomplete reactions and failure are prone to occur. Here, operando full-field transmission X-ray microscopy is coupled with X-ray spectroscopy to follow the chemical and microstructural evolution at the nanoscale of single crystals of Li1+xMn2-xO4, a technologically relevant Li-ion battery electrode material. The onset and crystallographic directionality of a series of complex phase transitions are followed and correlated with particle fracture. The dynamic character of this study reveals the existence of nonequilibrium pathways where phases at substantially different potentials can coexist at short length scales. The results can be used to inform the engineering of particle morphologies and electrode architectures that bypass the issues observed here and lead to optimized battery electrode properties.

Ni‐rich layered oxides are envisioned as the most promising cathode materials for next‐generation lithium‐ion batteries; however, their practical adoption is plagued by fast capacity decay originating from chemo‐mechanical degradation. The intrinsic chemical–mechanical instability, inherited from atomic‐ and nanoscale defects generated during synthesis, is not yet resolved. Here, atomic‐ and nanoscale structural evolution during solid‐state synthesis of Ni‐rich layered cathode, Li[Ni0.92Co0.03Mn0.05]O2, is investigated using combined X‐ray/neutron scattering and electron/X‐ray microscopy. The multiscale analyses demonstrate the intertwined correlation between phase transition and microstructural evolution, with atomic‐scale defects derived from the decomposition of precursors leading to the creation of intra/inter‐granular pores. The nucleation and coalescence mechanism of pore defects during the synthesis of Ni‐rich layered cathodes are quantitatively revealed. Furthermore, a modified synthetic route is proposed to effectively circumvent the formation of nanoscale defects in Ni‐rich layered cathodes by facilitating uniform synthetic reactions, resulting in superior electrochemical and microstructural stability. [ABSTRACT FROM AUTHOR]

Redox-active organic materials have recently drawn significant attention in the development of green and cost-efficient rechargeable batteries. However, their use as a cathode has been practically hampered in part by the relatively low redox potentials that are typically displayed at ∼2 V (vs. Li/Li+). Herein, we report a rationally designed oxygen-containing heterocyclic compound, dibenzo-1,4-dioxin (DD), which undergoes a reversible redox reaction at the highest redox potential (1.1 V vs. Ag/Ag+ or 4.1 V vs. Li/Li+) among organic electrode materials reported thus far. Moreover, DD, a ready-to-charge active material, delivers a flat discharge voltage profile at this high voltage of 4.1 V in a lithium cell with a respectable rate capability. From a combined spectroscopic and computational analysis, it is revealed that the primary redox reaction takes place via the redox activity of the ring-embedded oxygen based on the p-type reaction in a dual-ion battery. We further demonstrate that introducing an iptycene motif to DD substantially suppresses the dissolution of the electrode material, enhancing the cycle stability without compromising the high discharge voltage. This finding suggests that a practically high discharge voltage over 4 V (vs. Li/Li+) can be achievable from the organic materials by the rational molecular tuning of redox-active atoms and the molecular skeleton, opening up a pathway for developing high-voltage organic batteries. [ABSTRACT FROM AUTHOR]