Transitions from Near-Surface to Interior Redox upon Lithiation in Conversion Electrode Materials

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• 作者：Kai He ; Huolin L. Xin ; Kejie Zhao ; Xiqian Yu ; Dennis Nordlund ; Tsu-Chien Weng ; Jing Li ; Yi Jiang ; Christopher A. Cadigan ; Ryan M. Richards ; Marca M. Doeff ; Xiao-Qing Yang ; Eric A. Stach ; Ju Li ; Feng Lin ; Dong Su
• 刊名：Nano Letters
• 出版年：2015
• 出版时间：February 11, 2015
• 年：2015
• 卷：15
• 期：2
• 页码：1437-1444
• 全文大小：559K
• ISSN：1530-6992

文摘

Nanoparticle electrodes in lithium-ion batteries have both near-surface and interior contributions to their redox capacity, each with distinct rate capabilities. Using combined electron microscopy, synchrotron X-ray methods and ab initio calculations, we have investigated the lithiation pathways that occur in NiO electrodes. We find that the near-surface electroactive (Ni²⁺ 鈫?Ni⁰) sites saturated very quickly, and then encounter unexpected difficulty in propagating the phase transition into the electrode (referred to as a 鈥渟hrinking-core鈥?mode). However, the interior capacity for Ni²⁺ 鈫?Ni⁰ can be accessed efficiently following the nucleation of lithiation 鈥渇ingers鈥?that propagate into the sample bulk, but only after a certain incubation time. Our microstructural observations of the transition from a slow shrinking-core mode to a faster lithiation finger mode corroborate with synchrotron characterization of large-format batteries and can be rationalized by stress effects on transport at high-rate discharge. The finite incubation time of the lithiation fingers sets the intrinsic limitation for the rate capability (and thus the power) of NiO for electrochemical energy storage devices. The present work unravels the link between the nanoscale reaction pathways and the C-rate-dependent capacity loss and provides guidance for the further design of battery materials that favors high C-rate charging.