Zhao Qing, Liu Xiaotun, Zheng Jingxu, Deng Yue, Warren Alexander, Zhang Qiyuan, Archer Lynden
Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853.
Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853.
Proc Natl Acad Sci U S A. 2020 Oct 20;117(42):26053-26060. doi: 10.1073/pnas.2004576117. Epub 2020 Oct 5.
In the presence of Lewis acid salts, the cyclic ether, dioxolane (DOL), is known to undergo ring-opening polymerization inside electrochemical cells to form solid-state polymer batteries with good interfacial charge-transport properties. Here we report that LiNO, which is unable to ring-open DOL, possesses a previously unknown ability to coordinate with and strain DOL molecules in bulk liquids, completely arresting their crystallization. The strained DOL electrolytes exhibit physical properties analogous to amorphous polymers, including a prominent glass transition, elevated moduli, and low activation entropy for ion transport, but manifest unusually high, liquidlike ionic conductivities (e.g., 1 mS/cm) at temperatures as low as -50 °C. Systematic electrochemical studies reveal that the electrolytes also promote reversible cycling of Li metal anodes with high Coulombic efficiency (CE) on both conventional planar substrates (1 mAh/cm over 1,000 cycles with 99.1% CE; 3 mAh/cm over 300 cycles with 99.2% CE) and unconventional, nonplanar/three-dimensional (3D) substrates (10 mAh/cm over 100 cycles with 99.3% CE). Our finding that LiNO promotes reversibility of Li metal electrodes in liquid DOL electrolytes by a physical mechanism provides a possible solution to a long-standing puzzle in the field about the versatility of LiNO salt additives for enhancing reversibility of Li metal electrodes in essentially any aprotic liquid electrolyte solvent. As a first step toward understanding practical benefits of these findings, we create functional Li||lithium iron phosphate (LFP) batteries in which LFP cathodes with high capacity (5 to 10 mAh/cm) are paired with thin (50 μm) lithium metal anodes, and investigate their galvanostatic electrochemical cycling behaviors.
在路易斯酸盐存在的情况下，环状醚二氧戊环（DOL）已知会在电化学电池内部发生开环聚合反应，以形成具有良好界面电荷传输特性的固态聚合物电池。在此，我们报告，无法使DOL开环的LiNO具有一种此前未知的能力，即在本体液体中与DOL分子配位并使其产生应变，从而完全抑制其结晶。应变的DOL电解质表现出与无定形聚合物类似的物理性质，包括显著的玻璃化转变、提高的模量以及低的离子传输活化熵，但在低至 -50°C的温度下表现出异常高的、类似液体的离子电导率（例如1 mS/cm）。系统的电化学研究表明，这些电解质还能促进锂金属阳极在传统平面基板（1 mAh/cm²，1000次循环，库仑效率99.1%；3 mAh/cm²，300次循环，库仑效率99.2%）和非常规的非平面/三维（3D）基板（10 mAh/cm²，100次循环，库仑效率99.3%）上以高库仑效率（CE）进行可逆循环。我们发现LiNO通过物理机制促进锂金属电极在液态DOL电解质中的可逆性，这为该领域长期存在的一个谜题提供了可能的解决方案，即LiNO盐添加剂在基本上任何非质子液体电解质溶剂中增强锂金属电极可逆性的通用性问题。作为理解这些发现实际益处的第一步，我们制备了功能性锂||磷酸铁锂（LFP）电池，其中高容量（5至10 mAh/cm²）的LFP阴极与薄（50μm）锂金属阳极配对，并研究了它们的恒电流电化学循环行为。
