Abstract
This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi0.33Mn0.33Co0.33O2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 μm spatial resolution to determine the change in unit cell dimensions as a result of electrochemical cycling. The nature of the technique permits the spatial localization of the diffraction information in 3D and mapping of heterogeneities from the electrode to the particle level. An overall decrease of 0.4% and 0.6% was observed for the unit cell volume after 100 cycles for the electrodes cycled to 4.2 and 4.7 V. Additionally, focused ion beam-scanning electron microscope cross-sections indicate extensive particle cracking as a function of upper cut-off voltage, further confirming that severe cycling stresses exacerbate degradation. Finally, the technique facilitates the detection of parts of the electrode that have inhomogeneous lattice parameters that deviate from the bulk of the sample, further highlighting the effectiveness of the technique as a diagnostic tool, bridging the gap between crystal structure and electrochemical performance.
Highlights
This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi0.33Mn0.33Co0.33O2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 mm spatial resolution to determine the change in unit cell dimensions as a result of electrochemical cycling
High cobalt costs and its inherent toxicity have driven the exploration of other chemistries with reduced Co content, such as lithium nickel manganese cobalt oxide (NMC), where the slightly lower capacity is compensated by excellent power and low self-heating during cycling.[4]
Li-ions to participate in the electrochemical process by cycling to a higher upper cut-off voltage, which corresponds to a greater fraction of Li removal from the transition metal oxide crystal structure at higher voltages
Summary
This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi0.33Mn0.33Co0.33O2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 mm spatial resolution to determine the change in unit cell dimensions as a result of electrochemical cycling. Li-ions to participate in the electrochemical process by cycling to a higher upper cut-off voltage, which corresponds to a greater fraction of Li removal from the transition metal oxide crystal structure at higher voltages This accentuates the aforementioned phenomena, but is likely to affect the stability of the electrolyte over extended cycling.[7] cycling at high voltages can cause the release of oxygen from the cathode lattice, which reacts with the electrolyte, and transition metal dissolution, which can subsequently deposit onto the anode increasing its resistivity and reducing the utilizable capacity.[8,9] A previous study, by Mao et al, uses a combination of X-ray spectroscopic and crystallographic techniques to highlight how different regions with increased oxidation or reduction states are present within a particle as a function of the upper cycling voltage.[10]
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