Browsing by Author "Longo, Roberto C."
Now showing 1 - 6 of 6
- Results Per Page
- Sort Options
Item Chemical Properties of Metal-Silicates Rendered by Metal Exchange Reaction(American Chemical Society, 2019-04-11) Longo, Roberto C.; Königer, F.; Nefedov, A.; Thissen, Peter; 0000-0003-4353-841X (Longo, RC); 0000-0001-7072-4109 (Thissen, P); Longo, Roberto C.; Thissen, PeterCalcium-silicates and calcium-silicate-hydrates (CS and CSH) are well-known as the most important building material, cement. Both CS and CSH phases react fast with CO₂ from the atmosphere. Due to the porosity of cement and concrete, such reaction goes deep into the material, producing phase transformations, crack formation and propagation. The aim of this work is 2-fold. In the first part, we compare the reaction of CO₂ with CSH phases and with magnesium-silicate-hydrates (MSH). Surprisingly, MSH did not show any contamination of carbonates in the infrared spectra. While the reaction of CO₂ with CSH has been well studied and explained, there is currently no explanation about the resilience of MSH to the interaction with CO₂. For the first time, the atomistic details of the reaction of CO₂ with MgSiO₃ are shown, and the chemical resistance of MgSiO₃ against CO₂ and other relevant chemicals for corrosion of cement and concrete is explained. Second, we demonstrate that Mg and other metals can undergo an exchange in situ process in CS and CSH phases. Depending on the type of metal exchanged, a completely new platform for rendering the properties of cement and concrete surfaces against corrosion is developed. ©2019 American Chemical Society.Item Electrode-Electrolyte Interface for Solid State Li-Ion Batteries: Point Defects and Mechanical StrainSantosh, KC; Longo, Roberto C.; Xiong, Ka; Cho, Kyeongjae; 0000-0003-2698-7774 (Cho, K)In this work, we present an ab-initio investigation of point defects in solid electrolyte γ-Li₃PO₄ and in negative electrode-electrolyte interface (Li/γ-Li₃PO₄). Our results on Li defects on γ-Li₃PO₄ exhibit that Li interstitial defects dominate over vacancy defects, and that Li vacancy-interstitial pair defect formation energy in-the-interface is comparable to the sum of-Li vacancy defect in the electrode and Li ion interstitial defects in the electrolyte region. Our study reveals that the high Li ion defect formation energy is the determining factor for the low ionic conductivity across Li metal/electrolyte interface. Moreover, in a realistic interface, the mechanical strain at the interface increases with the concentration of the impurities produced as a result of the cycling of the battery or due to surface impurities, also affecting the electrostatic potential and charge distribution. Thus, the study of the Li metal/electrolyte interface provides information on the defect formation and mechanical stability and, hence, it helps to understand the realistic modeling of the interface-as a way to-improve the ionic conductivity and stability of future solid state Li-ion batteries.Item Kinetic Stability of Bulk LiNiO₂ and Surface Degradation by Oxygen Evolution in LiNiO₂-Based Cathode Materials(Wiley-VCH Verlag Gmbh, 2018-11-02) Kong, Fantai; Liang, Chaoping; Wang, Luhua; Zheng, Yongping; Perananthan, Sahila; Longo, Roberto C.; Ferraris, John P.; Kim, Moon J.; Cho, Kyeongjae; Kong, Fantai; Liang, Chaoping; Wang, Luhua; Zheng, Yongping; Perananthan, Sahila; Longo, Roberto C.; Ferraris, John P.; Kim, Moon J.; Cho, KyeongjaeCapacity degradation by phase changes and oxygen evolution has been the largest obstacle for the ultimate commercialization of high-capacity LiNiO₂-based cathode materials. The ultimate thermodynamic and kinetic reasons of these limitations are not yet systematically studied, and the fundamental mechanisms are still poorly understood. In this work, both phenomena are studied by density functional theory simulations and validation experiments. It is found that during delithiation of LiNiO₂, decreased oxygen reduction induces a strong thermodynamic driving force for oxygen evolution in bulk. However, oxygen evolution is kinetically prohibited in the bulk phase due to a large oxygen migration kinetic barrier (2.4 eV). In contrast, surface regions provide a larger space for oxygen migration leading to facile oxygen evolution. These theoretical results are validated by experimental studies, and the kinetic stability of bulk LiNiO₂ is clearly confirmed. Based on these findings, a rational design strategy for protective surface coating is proposed.Item Multicomponent Silicate Cathode Materials for Rechargeable Li-ion Batteries: An Ab Initio StudyLongo, Roberto C.; Xiong, Ka; Cho, KyeongjaeA first principles investigation is performed to study the structural and electrochemical properties of new multicomponent silicate materials that can be suitable for the cathode of rechargeable Li-ion batteries. The distribution of different transition metals in the silicate structure alters the structural and electronic properties of the crystal, affecting its kinetics, redox potentials and both ionic and electronic conductivities. We also explain the effect of the multiple interactions between Li ions and the transition metals. These multicomponent structures represent a very powerful strategy to control the electrochemical performance of the silicates. In this work, we finally address the implications of such strategy on the design of Li-ion batteries.Item Selectivity of Metal Oxide Atomic Layer Deposition on Hydrogen Terminated and Oxidized Si(001)-(2x1) Surface(A V S Amer Inst Physics, 2014-02-10) Longo, Roberto C.; McDonnell, Stephen; Dick, D.; Wallace, Robert M.; Chabal, Yves J.; Owen, James H. G.; Ballard, Josh B.; Randall, John N.; Cho, Kyeongjae; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ)In this work, the authors used density-functional theory methods and x-ray photoelectron spectroscopy to study the chemical composition and growth rate of HfO₂, Al₂O₃, and TiO₂ thin films grown by in-situ atomic layer deposition on both oxidized and hydrogen-terminated Si(001) surfaces. The growth rate of all films is found to be lower on hydrogen-terminated Si with respect to the oxidized Si surface. However, the degree of selectivity is found to be dependent of the deposition material. TiO₂ is found to be highly selective with depositions on the hydrogen terminated silicon having growth rates up to 180 times lower than those on oxidized Si, while similar depositions of HfO₂ and Al₂O₃ resulted in growth rates more than half that on oxidized silicon. By means of density-functional theory methods, the authors elucidate the origin of the different growth rates obtained for the three different precursors, from both energetic and kinetic points of view.Item Spurious Dangling Bond Formation During Atomically Precise Hydrogen Depassivation Lithography on Si(100): The Role of Liberated Hydrogen(A V S Amer Inst Physics) Ballard, Joshua B.; Owen, James H. G.; Alexander, Justin D.; Owen, William R.; Fuchs, Ehud; Randall, John N.; Longo, Roberto C.; Cho, KyeongjaeThe production of spurious dangling bonds during the hydrogen depassivation lithography process on Si(100)-H is studied. It is shown that the number of spurious dangling bonds produced depends on the size of the primary pattern on the surface, not on the electron dose, indicating that the spurious dangling bonds are formed via an interaction of the liberated hydrogen with the surface. It is also shown that repassivation may occur if hydrogen depassivation lithography is performed near an already patterned area. Finally, it is argued that the product of the interaction is a single dangling bond next to a monohydride silicon on a silicon dimer, with a reaction probability much in excess of that previously observed.