Due to its low redox potential and high theoretical specific capacity, Li metal has drawn worldwide research attention because of its potential use in next-generation battery technologies such as Li-S and Li-O2. Unfortunately, uncontrollable growth of Li microstructures (LmSs, e.g., dendrites, fibers) during electrochemical Li stripping/plating has prevented their practical commercialization. Despite various strategies proposed to mitigate LmS nucleation and/or block its growth, a fundamental understanding of the underlying evolution mechanisms remains elusive. Herein, synchrotron in-line phase contrast X-ray tomography was employed to investigate the morphological evolution of electrochemically deposited/dissolved LmSs nondestructively. We present a 3D characterization of electrochemically stripped Li electrodes with regard to electrochemically plated LmSs. We clarify fundamentally the origin of the porous lithium interface growing into Li electrodes. Moreover, cleavage of the separator caused by growing LmS was experimentally observed and visualized in 3D. Our systematic investigation provides fundamental insights into LmS evolution and enables us to understand the evolution mechanisms in Li electrodes more profoundly.
Addressing the multitude of electronic phenomena theoretically predicted for confined graphene structures requires appropriate in situ fabrication procedures yielding graphene nanoflakes (GNFs) with well-defined geometries and accessible electronic properties. Here, we present a simple strategy to fabricate quasi-free-standing GNFs of variable sizes, performing temperature programmed growth of graphene flakes on the Ir(111) surface and subsequent intercalation of gold. Using scanning tunneling microscopy (STM), we show that epitaxial GNFs on a perfectly ordered Au(111) surface are formed while maintaining an unreconstructed, singly hydrogen-terminated edge structure, as confirmed by the accompanying density functional theory (DFT) calculations. Using tip-induced lateral displacement of GNFs, we demonstrate that GNFs on Au(111) are to a large extent decoupled from the Au(111) substrate. The direct accessibility of the electronic states of a single GNF is demonstrated upon analysis of the quasiparticle interference patterns obtained by low-temperature STM. These findings open up an interesting playground for diverse investigations of graphene nanostructures with possible implications for device fabrication.
Knowledge about degradation and failure of Li-ion batteries (LIBs) is of paramount importance especially because failure can be accompanied by severe hazards. To contribute to the understanding of such phenomena synchrotron in-line phase contrast Xray tomography was employed to investigate internal cell deformation and degradation caused by an internal short circuit (ISC). The tomographic images taken from an uncycled Li/Li cell and a short-circuited Li/Li cell reveal how lithium microstructures (LmS) develop during electrochemical stripping and plating during discharge and charge and how the three-layer separator used is damaged by growing LmSs and delaminates and melts as a consequence of an ISC. Previously unknown insights into the internal cell degradation and deformation mechanisms caused by an ISC are obtained and provide hints of how the properties of the separator could be modified in order to improve the reliability and safety of current and next-generation LIBs.
FIB-SEM tomography is used to reconstruct the carbon binder domain (CBD) of a LiCoO 2 battery cathode (3.9 µm 5 µm 2.3 µm) with contrast enhancement by ZnO infiltration via atomic layer deposition. We calculate the porosity inside the CBD (57.6%), the cluster-size distribution with a peak at 54 nm and the pore-size distribution with a peak at 64 nm. The tortuosities of the pore space (1.6-2.0) and the CBD (2.3-3.5) show a mild anisotropy, which is attributed to the fabrication process. A comparison to a modeled homogenous CBD reveals that clustering in the CBD decreases its electronic conductivity
Silicon (Si) has been proposed as one of the most promising anode materials for next-generation lithium ion batteries (LIBs). However, unsatisfactory discharge capacity/energy density and inevitable performance worsening prevent their commercialization. Herein, an in-depth investigation on the same Si composite electrode before and after the first discharge by employing in situ synchrotron X-ray tomography is presented. It is found that i) on the electrode level, the Si particles located in the central part of the electrode preferentially experience crack formation; ii) on the individual particle level, heterogeneous electrochemical lithiation behaviour is observed; iii) cavities are formed during the electrode preparation and battery operation. Moreover, the correlation between the electrochemical activities of Si particles and their individual electrical contact to the electron conducting network is investigated. For the first time it is quantified that Si particles will experience lithiation only under the condition that at least 40% of their surface is electrically connected. These novel insights are possible explanations for low discharge capacity/energy of Si electrode LIBs, and would open new design principles and opportunities for high-capacity electrode materials for next-generation energy storage systems.
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