Browsing by Author "Xu, Zhengrui"

Now showing 1 - 8 of 8
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    Charge distribution guided by grain crystallographic orientations in polycrystalline battery materials
    Xu, Zhengrui; Jiang, Zhisen; Kuai, Chunguang; Xu, Rong; Qin, Changdong; Zhang, Yan; Rahman, Muhammad Mominur; Wei, Chenxi; Nordlund, Dennis; Sun, Cheng-Jun; Xiao, Xianghui; Du, Xi-Wen; Zhao, Kejie; Yan, Pengfei; Liu, Yijin; Lin, Feng (2020-01-08)
    Architecting grain crystallographic orientation can modulate charge distribution and chemomechanical properties for enhancing the performance of polycrystalline battery materials. However, probing the interplay between charge distribution, grain crystallographic orientation, and performance remains a daunting challenge. Herein, we elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic "surface-to-bulk" charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials.
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    Defect and structural evolution under high-energy ion irradiation informs battery materials design for extreme environments
    Rahman, Muhammad Mominur; Chen, Wei-Ying; Mu, Linqin; Xu, Zhengrui; Xiao, Ziqi; Li, Meimei; Bai, Xianming; Lin, Feng (Nature Research, 2020-09-11)
    Understanding defect evolution and structural transformations constitutes a prominent research frontier for ultimately controlling the electrochemical properties of advanced battery materials. Herein, for the first time, we utilize in situ high-energy Kr ion irradiation with transmission electron microscopy to monitor how defects and microstructures evolve in Na- and Li-layered cathodes with 3d transition metals. Our experimental and theoretical analyses reveal that Li-layered cathodes are more resistant to radiation-induced structural transformations, such as amorphization than Na-layered cathodes. The underlying mechanism is the facile formation of Li-transition metal antisite defects in Li-layered cathodes. The quantitative mathematical analysis of the dynamic bright-field imaging shows that defect clusters preferentially align along the Na/Li ion diffusion channels (a-b planes), which is likely governed by the formation of dislocation loops. Our study provides critical insights into designing battery materials for extreme irradiation environments and understanding fundamental defect dynamics in layered oxides.
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    Effect of the grain arrangements on the thermal stability of polycrystalline nickel-rich lithium-based battery cathodes
    Hou, Dong; Xu, Zhengrui; Yang, Zhijie; Kuai, Chunguang; Du, Zhijia; Sun, Cheng-Jun; Ren, Yang; Liu, Jue; Xiao, Xianghui; Lin, Feng (Springer, 2022-06-15)
    One of the most challenging aspects of developing high-energy lithium-based batteries is the structural and (electro)chemical stability of Ni-rich active cathode materials at thermally-abused and prolonged cell cycling conditions. Here, we report in situ physicochemical characterizations to improve the fundamental understanding of the degradation mechanism of charged polycrystalline Ni-rich cathodes at elevated temperatures (e.g., ≥ 40 °C). Using multiple microscopy, scattering, thermal, and electrochemical probes, we decouple the major contributors for the thermal instability from intertwined factors. Our research work demonstrates that the grain microstructures play an essential role in the thermal stability of polycrystalline lithium-based positive battery electrodes. We also show that the oxygen release, a crucial process during battery thermal runaway, can be regulated by engineering grain arrangements. Furthermore, the grain arrangements can also modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered oxide cathode materials.
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    Heterogeneous Redox Chemistries in Layered Oxide Materials for Lithium-Ion Batteries
    Xu, Zhengrui (Virginia Tech, 2022-01-05)
    The invention of the lithium-ion battery has revolutionized the passenger transportation field in recent years, and it has emerged as one of the state-of-the-art solutions to address greenhouse gases emission and air pollution issues. Layered oxide lithium-ion battery cathode materials have become commercially successful in the past few decades due to their high energy density, high power density, long cycle life, and low cost. Yet, with the increasing demand for battery performance, it is crucial to understand the material fading mechanisms further to improve layered oxide materials' performance. A heterogeneous redox reaction is a dominant fading mechanism, which limits the utilization percentage of a battery materials' redox capability and leads to adverse effects such as detrimental interfacial reactions, lattice oxygen release, and chemomechanical breakdown. Crystallographic defects, such as dislocations and grain boundaries, are rich in battery materials. These crystallographic defects change the local lithium-ion diffusivity and have a dramatic effect on the redox reactions. To date, there is still a knowledge gap on how various crystallographic defects affect electrochemistry at the microscopic scale. Herein, we adopted synchrotron-based diffraction, imaging, and spectroscopic techniques to systematically study the correlation between crystallographic defects and redox chemistries in the nanodomain. Our studies shed light on design principles of next-generation battery materials. In Chapter 1, we first provide a comprehensive background introduction on the battery chemistry at various length scales. We then introduce the heterogeneous redox reactions in layered oxide cathode materials, including a discussion on the impacts of heterogeneous redox reactions. Finally, we present the different categories of crystallographic defects in layered oxide materials and how these crystallographic defects affect electrochemical performance. In Chapter 2, we use LiCoO2, a representative layered oxide cathode material, as the material platform to quantify the categories and densities of various crystallographic defects. We then focus on geometrically necessary dislocations as they represent a major class of crystallographic defects in LiCoO2. Combining synchrotron-based X-ray fluorescence mapping, micro-diffraction, and spectroscopic techniques, we reveal that geometrically necessary dislocations can facilitate the charging reactions in LiCoO2 grains. Our study illustrates that the heterogeneous redox chemistries can be potentially mitigated by precisely controlling the defects. In Chapter 3, we systematically investigated how grain boundaries affect redox reactions. We reveal that grain boundaries can guide redox reactions in LiNixMnyCo1-x-yO2 (NMC) materials. Specifically, NMC materials with radially aligned grains have a more uniform charge distribution, less stress mismatch, and better cycling performance. NMC materials with randomly orientated grains have a more heterogeneous redox reaction. These heterogeneous redox reactions are related to the lattice strain mismatch and worse cycling performance. Our study emphasizes the importance of tuning grain orientations to achieve improved performance. Chapter 4 systematically investigated how the grain boundaries and crystallographic orientations affect the thermal stability of layered oxide cathode materials. Combining diffraction, spectroscopic, and imaging techniques, we reveal that a cathode materials' microstructure plays a significant role in determining the lattice oxygen release behavior and, therefore, determines cathode materials' thermal stability. Our study provides a fundamental understanding of how the grain boundaries and crystallographic orientations can be tuned to develop better cathode materials for the next-generation Li-ion batteries. Chapter 5 summarizes the contributions of our work and provides our perspective on future research directions.
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    Investigating Particle Size-Dependent Redox Kinetics and Charge Distribution in Disordered Rocksalt Cathodes
    Zhang, Yuxin; Hu, Anyang; Liu, Jue; Xu, Zhengrui; Mu, Linqin; Sainio, Sami; Nordlund, Dennis; Li, Luxi; Sun, Cheng-Jun; Xiao, Xianghui; Liu, Yijin; Lin, Feng (Wiley-V C H Verlag, 2022-04)
    Understanding how various redox activities evolve and distribute in disordered rocksalt oxides (DRX) can advance insights into manipulating materials properties for achieving stable, high-energy batteries. Herein, the authors present how the reaction kinetics and spatial distribution of redox activities are governed by the particle size of DRX materials. The size-dependent electrochemical performance is attributed to the distinct cationic and anionic reaction kinetics at different sizes, which can be tailored to achieve optimal capacity and stability. Overall, the local charged domains in DRX particles display random heterogeneity caused by the isotropic delithiation pathways. Owing to the kinetic limitation, the micron-sized particles exhibit a holistic "core-shell" charge distribution, whereas sub-micron particles show more uniform redox reactions throughout the particles and ensembles. Sub-micron DRX particles exhibit increasing anionic redox activities yet inferior cycling stability. In summary, engineering particle size can effectively modulate how cationic and anionic redox activities evolve and distribute in DRX materials.
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    Mutual modulation between surface chemistry and bulk microstructure within secondary particles of nickel-rich layered oxides
    Li, Shaofeng; Jiang, Zhisen; Han, Jiaxiu; Xu, Zhengrui; Wang, Chenxu; Huang, Hai; Yu, Chang; Lee, Sang-Jun; Pianetta, Piero; Ohldag, Hendrik; Qiu, Jieshan; Lee, Jun-Sik; Lin, Feng; Zhao, Kejie; Liu, Yijin (2020-09-07)
    Surface lattice reconstruction is commonly observed in nickel-rich layered oxide battery cathode materials, causing unsatisfactory high-voltage cycling performance. However, the interplay of the surface chemistry and the bulk microstructure remains largely unexplored due to the intrinsic structural complexity and the lack of integrated diagnostic tools for a thorough investigation at complementary length scales. Herein, by combining nano-resolution X-ray probes in both soft and hard X-ray regimes, we demonstrate correlative surface chemical mapping and bulk microstructure imaging over a single charged LiNi0.8Mn0.1Co0.1O2 (NMC811) secondary particle. We reveal that the sub-particle regions with more micro cracks are associated with more severe surface degradation. A mechanism of mutual modulation between the surface chemistry and the bulk microstructure is formulated based on our experimental observations and finite element modeling. Such a surface-to-bulk reaction coupling effect is fundamentally important for the design of the next generation battery cathode materials.
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    Rigid registration algorithm based on the minimization of the total variation of the difference map
    Xiao, Xianghui; Xu, Zhengrui; Hou, Dong; Yang, Zhijie; Lin, Feng (International Union of Crystallography, 2022-07)
    Image registration is broadly used in various scenarios in which similar scenes in different images are to be aligned. However, image registration becomes challenging when the contrasts and backgrounds in the images are vastly different. This work proposes using the total variation of the difference map between two images (TVDM) as a dissimilarity metric in rigid registration. A method based on TVDM minimization is implemented for image rigid registration. The method is tested with both synthesized and real experimental data that have various noise and background conditions. The performance of the proposed method is compared with the results of other rigid registration methods. It is demonstrated that the proposed method is highly accurate and robust and outperforms other methods in all of the tests. The new algorithm provides a robust option for image registrations that are critical to many nanoscale X-ray imaging and microscopy applications.
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    TXM-Sandbox: an open-source software for transmission X-ray microscopy data analysis
    Xiao, Xianghui; Xu, Zhengrui; Lin, Feng; Lee, Wah-Keat (International Union of Crystallography, 2022-01)
    A transmission X-ray microscope (TXM) can investigate morphological and chemical information of a tens to hundred micrometre-thick specimen on a length scale of tens to hundreds of nanometres. It has broad applications in material sciences and battery research. TXM data processing is composed of multiple steps. A workflow software has been developed that integrates all the tools required for general TXM data processing and visualization. The software is written in Python and has a graphic user interface in Jupyter Notebook. Users have access to the intermediate analysis results within Jupyter Notebook and have options to insert extra data processing steps in addition to those that are integrated in the software. The software seamlessly integrates ImageJ as its primary image viewer, providing rich image visualization and processing routines. As a guide for users, several TXM specific data analysis issues and examples are also presented.