Single-crystal cathode materials for lithium-ion batteries have attracted increasing interest in providing greater capacity retention than their polycrystalline counterparts. However, after being ...cycled at high voltages, these single-crystal materials exhibit severe structural instability and capacity fade. Understanding how the surface structural changes determine the performance degradation over cycling is crucial, but remains elusive. Here, we investigate the correlation of the surface structure, internal strain, and capacity deterioration by using operando X-ray spectroscopy imaging and nano-tomography. We directly observe a close correlation between surface chemistry and phase distribution from homogeneity to heterogeneity, which induces heterogeneous internal strain within the particle and the resulting structural/performance degradation during cycling. We also discover that surface chemistry can significantly enhance the cyclic performance. Our modified process effectively regulates the performance fade issue of single-crystal cathode and provides new insights for improved design of high-capacity battery materials.
Abstract
Interfacial issues commonly exist in solid-state batteries, and the microstructural complexity combines with the chemical heterogeneity to govern the local interfacial chemistry. The ...conventional wisdom suggests that “point-to-point” ion diffusion at the interface determines the ion transport kinetics. Here, we show that solid-solid ion transport kinetics are not only impacted by the physical interfacial contact but are also closely associated with the interior local environments within polycrystalline particles. In spite of the initial discrete interfacial contact, solid-state batteries may still display homogeneous lithium-ion transportation owing to the chemical potential force to achieve an ionic-electronic equilibrium. Nevertheless, once the interior local environment within secondary particle is disrupted upon cycling, it triggers charge distribution from homogeneity to heterogeneity and leads to fast capacity fading. Our work highlights the importance of interior local environment within polycrystalline particles for electrochemical reactions in solid-state batteries and provides crucial insights into underlying mechanism in interfacial transport.
Mechanical integrity issues such as particle cracking are considered one of the leading causes of structural deterioration and limited long-term cycle stability for Ni-rich cathode materials of ...Li-ion batteries. Indeed, the detrimental effects generated from the crack formation are not yet entirely addressed. Here, applying physicochemical and electrochemical ex situ and in situ characterizations, the effect of Co and Mn on the mechanical properties of the Ni-rich material are thoroughly investigated. As a result, we successfully mitigate the particle cracking issue in Ni-rich cathodes via rational concentration gradient design without sacrificing the electrode capacity. Our result reveals that the Co-enriched surface design in Ni-rich particles benefits from its low stiffness, which can effectively suppress the formation of particle cracking. Meanwhile, the Mn-enriched core limits internal expansion and improve structural integrity. The concentration gradient design also promotes morphological stability and cycling performances in Li metal coin cell configuration.
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.
Analysis of tomographic datasets at synchrotron light sources (including X‐ray transmission tomography, X‐ray fluorescence microscopy and X‐ray diffraction tomography) is becoming progressively more ...challenging due to the increasing data acquisition rates that new technologies in X‐ray sources and detectors enable. The next generation of synchrotron facilities that are currently under design or construction throughout the world will provide diffraction‐limited X‐ray sources and are expected to boost the current data rates by several orders of magnitude, stressing the need for the development and integration of efficient analysis tools. Here an attempt to provide a collaborative framework for the analysis of synchrotron tomographic data that has the potential to unify the effort of different facilities and beamlines performing similar tasks is described in detail. The proposed Python‐based framework is open‐source, platform‐ and data‐format‐independent, has multiprocessing capability and supports procedural programming that many researchers prefer. This collaborative platform could affect all major synchrotron facilities where new effort is now dedicated to developing new tools that can be deployed at the facility for real‐time processing, as well as distributed to users for off‐site data processing.
Laser powder bed fusion (LPBF) is a 3D printing technology that can print metal parts with complex geometries without the design constraints of traditional manufacturing routes. However, the parts ...printed by LPBF normally contain many more pores than those made by conventional methods, which severely deteriorates their properties. Here, by combining in-situ high-speed high-resolution synchrotron x-ray imaging experiments and multi-physics modeling, we unveil the dynamics and mechanisms of pore motion and elimination in the LPBF process. We find that the high thermocapillary force, induced by the high temperature gradient in the laser interaction region, can rapidly eliminate pores from the melt pool during the LPBF process. The thermocapillary force driven pore elimination mechanism revealed here may guide the development of 3D printing approaches to achieve pore-free 3D printing of metals.
The effect of laser power on defect characteristics, microstructure development, constituent phases, and crystallographic texture was studied on a laser powder bed fusion (L-PBF) processed 316L ...stainless steel. A series of specimens was additively manufactured as a function of laser power ranging from 380 to 200 W with a fixed scan speed of 300 mm/s. The density, size, shape, and orientation of pores in as-printed L-PBF cylinders were characterized using high-resolution synchrotron X-ray computed microtomography with a 0.65 μm resolution. The changes in the texture and phases were investigated using high-energy synchrotron X-ray diffraction. The melt pool shape and grain size/orientation were also analyzed using metallography. The results show that the porosity increases linearly from 0.13 to 0.88% with the decrease in laser power. However, even with a decrease in laser power by about half and corresponding seven-fold increase in porosity, the 200 W case can still be considered as nearly fully dense. On the other hand, with the same decrease in the laser power, the cellular spacing was refined from 1.5 to 0.75 μm and the texture changed from strong (200) to random. Therefore, within an optimal porosity range, it is feasible to manipulate microstructure significantly using the control of laser power.
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•Decrease in laser power by half within optimal processing regime results in about seven-fold increase in porosity.•The melt pool shape changes from flat-and-wide to fish-scale morphology with the same decrease in laser power.•At the same time, the preferred orientation changes from strong (200) to random texture.
Lithium-rich nickel-manganese-cobalt (LirNMC) layered material is a promising cathode for lithium-ion batteries thanks to its large energy density enabled by coexisting cation and anion redox ...activities. It however suffers from a voltage decay upon cycling, urging for an in-depth understanding of the particle-level structure and chemical complexity. In this work, we investigate the Li
Ni
Mn
Co
O
particles morphologically, compositionally, and chemically in three-dimensions. While the composition is generally uniform throughout the particle, the charging induces a strong depth dependency in transition metal valence. Such a valence stratification phenomenon is attributed to the nature of oxygen redox which is very likely mostly associated with Mn. The depth-dependent chemistry could be modulated by the particles' core-multi-shell morphology, suggesting a structural-chemical interplay. These findings highlight the possibility of introducing a chemical gradient to address the oxygen-loss-induced voltage fade in LirNMC layered materials.
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