Asymmetric Rate Behavior of Si Anodes for Lithium‐Ion Batteries: Ultrafast De‐Lithiation versus Sluggish Lithiation at High Current Densities |
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Authors: | Juchuan Li Nancy J Dudney Xingcheng Xiao Yang‐Tse Cheng Chengdu Liang Mark W Verbrugge |
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Affiliation: | 1. Materials Science & Technology Division, Oak Ridge National Laboratory, TN, USA;2. Chemical and Materials Systems Laboratory, General Motors Research and Development Center, Warren, MI, USA;3. Department of Chemical & Materials Engineering, University of Kentucky, Lexington, KY, USA;4. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, TN, USA |
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Abstract: | The combined effect of lithium‐ion diffusion, potential‐concentration gradient, and stress plays a critical role in the rate capability and cycle life of Si‐based anodes of lithium‐ion batteries. In this work, Si nanofilm anodes are shown to exhibit an asymmetric rate performance: around 72% of the total available capacity can be delivered during de‐lithiation under a high current density of 420 A g‐1 (100C where C is the charge‐rate) in 22 s; in striking contrast, only 1% capacity can be delivered during lithiation. A mathematical model of single‐ion diffusion is established to elucidate the asymmetric rate performance, which can be mainly attributed to the potential‐concentration profile associated with the active material and the ohmic voltage shift under high currents; the difference in chemical diffusion coefficients during lithiation and de‐lithiation also plays a role. This clarifies that the charge and discharge rates of lithium‐ion‐battery electrodes should be evaluated separately due to the asymmetric effect in the electrochemical system. |
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Keywords: | lithium‐ion batteries silicon electrodes rate performance kinetics diffusion |
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