Electrochemically driven conversion reaction in fluoride electrodes for energy storage devices (用于储能体系的氟化物电极中的电化学驱动转换反应) 
Chilin Li, Keyi Chen, Xuejun Zhou & Joachim Maier
npj Computational Materials 4:22 (2018)
doi:10.1038/s41524-018-0079-6
Published online:23 April 2018
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摘要:探索电化学驱动的转换反应对开发新型储能材料至关重要，因为基于转换反应的材料可提供比目前锂离子电池电极更高的能量密度。氟化物的转换反应涉及又小又轻的氟阴离子，化学键断裂可发生在较低的Li活度（即较高的电池电位），因而可提供特别高的能量密度。基于氟基电极的电池可与其他设想的体系（如锂-硫或锂-空气电池）一较高下，因为这些体系）仍有许多未解决的热力学和动力学问题。氟基电极的转化反应通常是多相参与的氧化还原反应，其成核和生长过程通常伴随着显著的界面和质量传输现象，因此该反应常涉及显著的过电位和非平衡态的反应路径。本文综述了近期基于先进表征技术和计算模拟方法所揭示的（氧）氟化物在不同转化反应阶段中的相演变现象和机理特征。这些结果表明，设计优异的纳米结构体系将有助于改善动力学问题，克服显著的电压滞后现象。在这种情况下，掺杂和开框架策略是有效的。通过调节，那些不允许大量非化学计量比Li嵌入的简单材料有望变成电活性材料。 　　

Abstract:Exploring electrochemically driven conversion reactions for the development of novel energy storage materials is an important topic as they can deliver higher energy densities than current Li-ion battery electrodes. Conversion-type fluorides promise particularly high energy densities by involving the light and small fluoride anion, and bond breaking can occur at relatively low Li activity (i.e., high cell voltage). Cells based on such electrodes may become competitors to other envisaged alternatives such as Li-sulfur or Li-air systems with their many unsolved thermodynamic and kinetic problems. Relevant conversion reactions are typically multiphase redox reactions characterized by nucleation and growth processes along with pronounced interfacial and mass transport phenomena. Relevant conversion reactions are typically multiphase redox reactions characterized by nucleation and growth processes along with pronounced interfacial and mass transport phenomena.Hence significant overpotentials and nonequilibrium reaction pathways are involved.In this review, we summarize recent findings in terms of phase evolution phenomena and mechanistic features of (oxy)fluorides at different redox stages during the conversion process, enabled by advanced characterization technologies and simulation methods.It can be concluded that well-designed nanostructured architectures are helpful in mitigating kinetic problems such as the usually pronounced voltage hysteresis.In this context, doping and open-framework strategies are useful. By these tools, simple materials that are unable to allow for substantial Li nonstoichiometry (e.g., by Li-insertable channels) may be turned into electroactive materials.