Article

Effect of Defects on Diffusion Behaviors of Lithium-Ion Battery Electrodes: In Situ Optical Observation and Simulation

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Abstract

Lithium-ion batteries (LIBs) with high energy efficiency are urgently needed in various fields. For the LIBs electrodes, defects would be generated during manufacture processes and mechanical degradation, and the defects significantly impact the stability and performance of LIBs. However, the effects of electrode defects on the electrochemical processes are still not clear. Herein, an in situ optical observation system is developed for monitoring the Li diffusion around the pre-introduced defects in the commercial graphite electrodes. The experiments show the gas-filled defects vertical to the direction of the Li diffusion would obviously decelerate Li diffusion, while the electrolyte-filled defects parallel to the direction of the Li diffusion would accelerate Li diffusion. In addition, finite element analysis (FEA) suggests consistent with the experiments, showing nonuniform distribution of local Li concentration around the defect. The equivalent diffusivity obtained by FEA is also dependent on the configuration of the defects. The diffusivities of electrolyte-filled parallel defect and gas-filled vertical defect are 12.6 % and 11.0 %, respectively. For the gas-filled defects, the size-effect calculation manifests that equivalent diffusivity would decrease with the enlarged defect size, and the shape of the defects would substantially impact the decrease rate. The results directly reveal the mechanisms of defect induced diffusion behavior change in the electrodes by the new equivalent 2D experiments, and the equivalent diffusivity would be useful for optimizing electrode designs in LIBs.

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There are growing concerns over the environmental, climate, and health impacts caused by using non-renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium-ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid-electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described.
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A new method for the determination of apparent diffusion coefficients of lithium ions in graphite electrodes was developed. In situ colorimetry – a technique relating the color of an electrode to its state of charge – was used to measure the distribution of lithium ions in model battery electrodes with good local and temporal resolution. Diffusion kinetics data are obtained from the rate of equilibration of a deliberately induced heterogeneous lithium distribution. An apparent activation energy of ca. 17kJ/mol was measured for the diffusion of lithium in a porous graphite electrode.
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a b s t r a c t We describe the first direct in situ measurements of Li transport in an operating cell. Motion of the lith-iation front in the graphite electrode suggests that transport could be controlled by liquid-phase diffu-sion. The electrochemical (current–voltage) data are successfully modeled with a diffusion equation that contains no material or microstructural information. The model is only qualitatively successful in predicting observed Li transport rate data, suggesting that microstructural information is required and that the actual process is more complex than simply diffusion. The technique can provide data for study-ing Li plating and Li dendrite growth, both of which can cause battery degradation.
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Graphites, as well as other intercalation materials used in lithium-ion batteries, change their color upon electrochemical insertion of lithium ions. In this study, in situ colorimetry was developed as a straightforward technical method to measure the local state of charge of lithium-ion battery electrodes. A laboratory cell with a glass window was built for in situ characterization of intercalation materials. Calibration curves of red, green, and blue color values vs state of charge were acquired and used for mapping of lithium distribution in battery electrodes. The lithium distribution in anodes of aged lithium-ion batteries was found to be highly heterogeneous. (c) 2008 The Electrochemical Society.
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Lithium ion batteries have revolutionized the portable electronics market, and they are being intensively pursued now for transportation and stationary storage of renewable energies like solar and wind. The success of lithium ion technology for the latter applications will depend largely on the cost, safety cycle life, energy, and power, which are in turn controlled by the component materials used. Accordingly, this Perspective focuses on the challenges and prospects associated with the electrode materials. Specifically, the issues associated with high-voltage and high-capacity cathodes as well as high capacity anodes and the approaches to overcome them are presented.
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The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.