Search

Metal-support interactions have been widely utilized for optimizing the catalytic reactivity of oxide-supported Au nanoparticles. Optimized reactivity was mainly detected with small (1-5 nm) oxide-supported Au nanoparticles and correlated to highly reactive sites at the oxide-metal interface. However, catalytically active sites are not necessarily restricted to the interface but reside as well on the Au surface. Uncovering the interconnection between reactive sites located at the interface and those situated at the metal surface is of crucial importance for understanding the reaction mechanism on Au nanoparticles. Herein, high-spatial-resolution IR nanospectroscopy measurements were conducted to map the localized reactivity in hydrogenation reactions on oxide-supported Au particles while using nitro-functionalized ligands as probes molecules. Comparative analysis of the reactivity pattern on single particles supported on various oxides revealed that oxide-dependent reactivity enhancement was not limited to the oxide-metal interface but was detected throughout the Au particle, leading to site-independent reactivity. These results indicate that reactive Au sites on both the oxide-metal interface and metal surface can activate the nitro groups toward hydrogenation reactions. The observed influence of oxide support (TiO2 > SiO2 > Al2O3) on the overall reactivity pattern specified that hydrogen dissociation occurred at the oxide-metal interface, followed by highly efficient intraparticle hydrogen atom diffusion to the interior parts of the Au particle. In contrast to Au particles, the oxide-metal interface had only a minor impact on the reactivity of supported Pt particles in which hydrogen dissociation and nitro group reduction were effectively activated on Pt sites. Single-particle measurements provided insights into the relative reactivity pattern of oxide-supported Au particles, revealing that the less-reactive Au metal sites can activate hydrogenation reactions in the presence of hydrogen atoms that diffuse from the Au/oxide boundary.

The practical realization of Nickel‐rich layered oxide cathode materials such as LiNi0.8Mn0.1Co0.1O2 (NMC811) is hampered by several structural and interfacial instabilities over prolonged cycling. Several reports have proposed surface passivation via an artificial cathode electrolyte interphase (ACEI) as a promising method for mitigating the parasitic reactions affecting NMC811 while simultaneously improving its electrochemical performance over prolonged cycling. Herein, we report an in‐house designed (tBuMe2Si)2Zn single source precursor for developing SixZnyOz ternary CEI thin films on NMC811 via molecular layer deposition (MLD) in combination with O3 or H2O as oxidizing agent. We demonstrate that the single precursor (tBuMe2Si)2Zn avoids the need for two different precursors (Si & Zn). In‐depth spectroscopic studies reveal the mechanism of the formation of organosiloxane/zinc‐oxide composite thin film, via intermediates of unprecedented organo‐silicon‐zinc compounds. Understanding the reaction mechanism paved the path for a successful deposition of ACEI on NMC811. Rate capability studies shows the ACEI protected cathodes exhibit higher discharge capacity at 4 C than pristine NMC811. Furthermore, studies on full cells with graphite anode were conducted to evaluate the practical viability of SixZnyOz ACEI thin films on NMC811. After prolonged cycling the ACEI‐coated NMC811 full cells significantly improved the electrochemical performance than pristine NMC811 by ~12%. [ABSTRACT FROM AUTHOR]

Tunnel-type Na0.44MnO2 (tt-NMO) is a promising cathode for sodium ion battery having excellent structural stability, diffusion kinetics, and low cost. However, this cathode is reported to suffer from low initial charge capacity (e.g., ≤60 mA h g−1) due to the limited accessibility of sodium ion extraction (0.22–0.24 Na+ per formula unit) from the structure, which hinders the practical viability of this material in a full battery cell. In this study, we report a tailored tt-NMO structure, synthesized using a two-step facile and scalable process, with >95% yield. Our tt-NMO demonstrated a 1st charge capacity of 110 mA h g−1, followed by a discharge capacity of 115 mA h g−1 within the potential window of 4–1.7 V versus Na/Na+. The long-term cycling performance at 0.5C rate and 1C rate (1C = 120 mA h g−1) shows excellent structural integrity for over 400 cycles with >75% capacity retention. We show experimentally and support it with DFT (density functional theory) calculations that the unique microstructure of this tt-NMO, with modulated Na–O bond length and Na–O–Na bond angle, results in open channels along the c-axis in the ab plane, providing a wide pathway for ion diffusion. The Na+ migration barriers (Em) along the two pathways of the c-tunnel are calculated to be within the threshold limit of Na+ migration energy barrier, which renders more sites electrochemically active, enabling the high 1st charge capacity. This novel study opens possibilities to use this unique tt-NMO as an efficient SIB (sodium ion battery) cathode by harnessing the modified structure. [ABSTRACT FROM AUTHOR]

Nickel‐rich cathode materials such as LiNi0.9Co0.05Mn0.05O2 (NMC90) have gained attention due to their ability to deliver high energy densities while being cost‐effective for Lithium‐ion battery manufacturing. However, NMC90 cathodes suffer irreversible parasitic reactions such as electrolyte decomposition, severe capacity fading and impedance build‐up upon prolonged cycling. Herein, we synthesize a conformal ultrathin, surface protection layer on NMC90 powder using ZnxOyvia atomic layer deposition technique (ZnxOy@NMC90). Prolonged electrochemical investigation of full cells at high discharge rates of 2 C shows that ZnxOy@NMC90 cells yielded ~31 % improvement in discharge capacity compared to pristine NMC90. Furthermore, operando electrochemical mass spectroscopy studies show that the ZnxOy@NMC90 cells have significantly suppressed electrolyte decomposition as compared to pristine NMC90 cells. Post‐cycling electrochemical impedance spectroscopy studies show that the ZnxOy@NMC90 full cells have significantly reduced impedance compared with pristine NMC90 cells. Additionally, post cycling manganese dissolution studies show that ZnxOy@NMC90 cells have greatly enhanced chemo‐mechanical integrity thereby contributing to improved electrochemical performances. Our results underscore the potential of tailored ZnxOy surface coatings on nickel‐rich cathode materials to address critical challenges in advanced energy storage systems, offering promising prospects for the development of high‐energy‐density lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

The realization of lithium–oxygen (Li–O2) batteries has been impeded by parasitic reactions that cause cell component degradation, often accompanied by the release of CO2 gas during oxidation reactions. The use of halide-based redox mediators (RMs) like LiBr and LiI has been proposed as a strategy to reduce overpotentials during oxygen evolution reactions and thus suppress the subsequent evolution of CO2. However, there is a scarcity of research examining the effectiveness of these RMs in the direct mitigation of parasitic reactions. In this study, we investigated the evolution of CO2 during the oxidation processes using an online electrochemical mass spectrometer. The results show that cells without RMs exhibited high overpotentials and significant CO2 evolution from the first charging cycle. In contrast, the addition of 50 mM LiI to the electrolyte resulted in a delay in CO2 evolution, observed only after several cycles. Notably, no CO2 evolution was observed in cells containing 50 mM LiBr in 0.5 M LiTFSI during the cell cycling. Our findings demonstrate that while the mechanism of halide-based RMs may be similar, their chemical properties and electrochemical behaviour can greatly influence their ability to effectively mediate the oxygen evolution process. [ABSTRACT FROM AUTHOR]

Oxidative decomposition of organic-solvent-based liquid electrolytes at cathode material interfaces has been identified as the main reason for rapid capacity fade in high-voltage lithium ion batteries. The evolution of "cathode electrolyte interphase" (CEI) films, partly or completely consisting of electrolyte decomposition products, has also recently been demonstrated to correlate with battery cycling behavior at high potentials. Using density functional theory calculations, the hybrid PBE0 functional, and the (001) surfaces of spinel oxides as models, we examine these two interrelated processes. Consistent with previous calculations, ethylene carbonate (EC) solvent molecules are predicted to be readily oxidized on the LixMn2O4 (001) surface at modest operational voltages, forming adsorbed organic fragments. Further oxidative decomposition of such CEI fragments to release CO2 gas is however predicted to require higher voltages consistent with LixNi0.5Mn1.5O4 (LNMO) at smaller x values. We argue that multistep reactions, involving first formation of CEI films and then further oxidization of CEI at higher potentials, are most relevant to capacity fade. Mechanisms associated with dissolution or oxidation of native Li2CO3 films, which are removed before the electrolyte is in contact with oxide surfaces, are also explored. [ABSTRACT FROM AUTHOR]