Browsing by Author "Xin, Huolin L."
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- Enhancing surface oxygen retention through theory-guided doping selection in Li1-xNiO2 for next-generation lithium-ion batteriesCheng, Jianli; Mu, Linqin; Wang, Chunyang; Yang, Zhijie; Xin, Huolin L.; Lin, Feng; Persson, Kristin A. (2020-11-28)Layered lithium metal oxides have become the cathode of choice for state-of-the-art Li-ion batteries (LIBs), particularly those with high Ni content. However, the Ni-rich cathode materials suffer from extensive oxygen evolution, which contributes to the formation of surface rocksalt phases as well as thermal instability. Using first-principles calculations, we systematically evaluate the effectiveness of doping elements to enhance surface oxygen retention of Li1-xNiO2. The evaluation process includes (i) choosing the most stable surface facet from the perspective of equilibrium surface stability analysis of as-synthesized LiNiO2, (ii) determining the preferable atomic site and segregation behavior for each dopant, and (iii) evaluating the surface oxygen retention ability of doped-Li1-xNiO2 (0.25 <= x <= 1) compared to the pristine material. We also discuss and rationalize the ability of these elements to enhance surface oxygen retention based on local environment descriptors such as dopant-oxygen bond strength. Overall, W, Sb, Ta and Ti are predicted as the most promising surface dopants due to their strong oxygen bonds and robust surface segregation behavior. Finally, Sb-doped LiNiO2 is synthesized and shown to present a surface enrichment of Sb and a significantly improved electrochemical performance, comparing with pristine LiNiO2. This work provides a generic approach that can lead to the greatly enhanced stabilization of all high-energy cathode materials, particularly the high Ni and low Co oxides.
- Resolving atomic-scale phase transformation and oxygen loss mechanism in ultrahigh-nickel layered cathodes for cobalt-free lithium-ion batteriesWang, Chunyang; Han, Lili; Zhang, Rui; Cheng, Hao; Mu, Linqin; Kisslinger, Kim; Zou, Peichao; Ren, Yang; Cao, Penghui; Lin, Feng; Xin, Huolin L. (2021-06-02)Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes. We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials.
- A spongy nickel-organic CO2 reduction photocatalyst for nearly 100% selective CO productionNiu, Kaiyang; Xu, You; Wang, Haicheng; Ye, Rong; Xin, Huolin L.; Lin, Feng; Tian, Chixia; Lum, Yanwei; Bustillo, Karen C.; Doeff, Marca M.; Koper, Marc T. M.; Ager, Joel; Xu, Rong; Zheng, Haimei (AAAS, 2017-07-28)Solar-driven photocatalytic conversion of CO2 into fuels has attracted a lot of interest; however, developing active catalysts that can selectively convert CO2 to fuels with desirable reaction products remains a grand challenge. For instance, complete suppression of the competing H2 evolution during photocatalytic CO2-to-CO conversion has not been achieved before. We design and synthesize a spongy nickel-organic heterogeneous photocatalyst via a photochemical route. The catalyst has a crystalline network architecture with a high concentration of defects. It is highly active in converting CO2 to CO, with a production rate of ~1.6 × 104 μmol hour−1 g−1. No measurable H2 is generated during the reaction, leading to nearly 100% selective CO production over H2 evolution. When the spongy Ni-organic catalyst is enriched with Rh or Ag nanocrystals, the controlled photocatalytic CO2 reduction reactions generate formic acid and acetic acid. Achieving such a spongy nickel-organic photocatalyst is a critical step toward practical production of high-value multicarbon fuels using solar energy.
- Spontaneous incorporation of gold in palladium-based ternary nanoparticles makes durable electrocatalysts for oxygen reduction reactionWang, Deli; Liu, Sufen; Wang, Jie; Lin, Ruoqian; Kawasaki, Masahiro; Rus, Eric; Silberstein, Katherine E.; Lowe, Michael A.; Lin, Feng; Nordlund, Dennis; Liu, Hongfang; Muller, David A.; Xin, Huolin L.; Abrun, Hector D. (Nature Publishing Group, 2016-06-01)Replacing platinum by a less precious metal such as palladium, is highly desirable for lowering the cost of fuel-cell electrocatalysts. However, the instability of palladium in the harsh environment of fuel-cell cathodes renders its commercial future bleak. Here we show that by incorporating trace amounts of gold in palladium-based ternary (Pd6CoCu) nanocatalysts, the durability of the catalysts improves markedly. Using aberration-corrected analytical transmission electron microscopy in conjunction with synchrotron X-ray absorption spectroscopy, we show that gold not only galvanically replaces cobalt and copper on the surface, but also penetrates through the Pd–Co–Cu lattice and distributes uniformly within the particles. The uniform incorporation of Au provides a stability boost to the entire host particle, from the surface to the interior. The spontaneous replacement method we have developed is scalable and commercially viable. This work may provide new insight for the large-scale production of non-platinum electrocatalysts for fuel-cell applications.
- Structural Degradation of Layered Cathode Materials in Lithium-Ion Batteries Induced by Ball MillingPan, Taijun; Alvarado, Judith; Zhu, Jian; Yue, Yuan; Xin, Huolin L.; Nordlund, Dennis; Lin, Feng; Doeff, Marca M. (2019-06-11)Layered LiNi0.4Mn0.4Co0.18Ti0.02O2 cathode powders were ball-milled for various lengths of time. The structural properties of the pristine and milled powders, which have different particle sizes were examined with X-ray diffraction, soft X-ray absorption spectroscopy, and transmission electron microscopy to determine the effect of milling on structure. Electrochemical testing in half-cells was also carried out and shows that milling plays an important role in the performance of these cathode materials; as milling time increases, there is a decrease in initial discharge capacity. The first cycle irreversible capacity also increases for milled samples, as does capacity loss upon cycling under some regimes. The electrochemical degradation is strongly correlated with damage to the lamellar structure of cathode particles induced by milling, and lithium carbonate formation. (c) The Author(s) 2019. Published by ECS.