Zhang Qiankui, Wang Kang, Wang Xianshu, Zhong Yaotang, Liu Mingzhu, Liu Xiang, Xu Kang, Fan Weizhen, Yu Le, Li Weishan
Electrochemistry Branch, Sensor and Electron Devices Directorate, Power and Energy Division , U.S. Army Research Laboratory , Adelphi , Maryland 20783 , United States.
Guangzhou Tinci Material Technology Co., Ltd , Guangzhou 510760 , China.
ACS Appl Mater Interfaces. 2019 Jun 12;11(23):20854-20863. doi: 10.1021/acsami.9b04898. Epub 2019 May 30.
Li metal provides an ideal anode for the highest energy density batteries, but its reactivity with electrolytes brings poor cycling stability. Electrolyte additives have been employed to effectively improve the cycling stability, often with the underlying mechanism poorly understood. In this work, applying lithium bis(oxalate)borate (LiBOB) as a chemical source for a dense and protective interphase, we investigate this issue with combined techniques of electrochemical/physical characterizations and theoretical calculations. It was revealed that the solid electrolyte interphase (SEI) formed by Li and the carbonate electrolyte is unstable and responsible for the fast deterioration of the Li anode. When LiBOB is present in the electrolyte, a reinforced SEI was formed, enabling significant improvement in cycling stability due to the preferential reduction of the BOB anion over the carbonate molecules and the strong combination of its reduction products with the species from the electrolyte reduction. The effectiveness of such new SEI chemistry on the Li anode supports excellent performance of a Li/LiFePO cell. This approach provides a pathway to rationally design an interphase on the Li anode so that high energy density batteries could be realized.
锂金属是能量密度最高的电池的理想负极，但它与电解质的反应性导致循环稳定性较差。电解质添加剂已被用于有效提高循环稳定性，但其潜在机制往往了解甚少。在这项工作中，我们将双草酸硼酸锂（LiBOB）用作致密且具有保护作用的界面层的化学源，采用电化学/物理表征和理论计算相结合的技术来研究这个问题。结果表明，锂与碳酸盐电解质形成的固体电解质界面（SEI）不稳定，是锂负极快速劣化的原因。当电解质中存在LiBOB时，会形成强化的SEI，由于BOB阴离子比碳酸盐分子优先还原，且其还原产物与电解质还原产生的物质强烈结合，从而使循环稳定性得到显著改善。这种新型SEI化学对锂负极的有效性支持了Li/LiFePO电池的优异性能。这种方法为合理设计锂负极上的界面层提供了一条途径，从而有望实现高能量密度电池。
