Cao Xia, Gao Peiyuan, Ren Xiaodi, Zou Lianfeng, Engelhard Mark H, Matthews Bethany E, Hu Jiangtao, Niu Chaojiang, Liu Dianying, Arey Bruce W, Wang Chongmin, Xiao Jie, Liu Jun, Xu Wu, Zhang Ji-Guang
Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA 99354.
Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99354.
Proc Natl Acad Sci U S A. 2021 Mar 2;118(9). doi: 10.1073/pnas.2020357118.
Electrolyte is very critical to the performance of the high-voltage lithium (Li) metal battery (LMB), which is one of the most attractive candidates for the next-generation high-density energy-storage systems. Electrolyte formulation and structure determine the physical properties of the electrolytes and their interfacial chemistries on the electrode surfaces. Localized high-concentration electrolytes (LHCEs) outperform state-of-the-art carbonate electrolytes in many aspects in LMBs due to their unique solvation structures. Types of fluorinated cosolvents used in LHCEs are investigated here in searching for the most suitable diluent for high-concentration electrolytes (HCEs). Nonsolvating solvents (including fluorinated ethers, fluorinated borate, and fluorinated orthoformate) added in HCEs enable the formation of LHCEs with high-concentration solvation structures. However, low-solvating fluorinated carbonate will coordinate with Li ions and form a second solvation shell or a pseudo-LHCE which diminishes the benefits of LHCE. In addition, it is evident that the diluent has significant influence on the electrode/electrolyte interphases (EEIs) beyond retaining the high-concentration solvation structures. Diluent molecules surrounding the high-concentration clusters could accelerate or decelerate the anion decomposition through coparticipation of diluent decomposition in the EEI formation. The varied interphase features lead to significantly different battery performance. This study points out the importance of diluents and their synergetic effects with the conductive salt and the solvating solvent in designing LHCEs. These systematic comparisons and fundamental insights into LHCEs using different types of fluorinated solvents can guide further development of advanced electrolytes for high-voltage LMBs.
电解质对于高压锂金属电池（LMB）的性能至关重要，LMB是下一代高密度储能系统中最具吸引力的候选者之一。电解质的配方和结构决定了电解质的物理性质及其在电极表面的界面化学性质。局部高浓度电解质（LHCEs）由于其独特的溶剂化结构，在LMB的许多方面优于目前最先进的碳酸盐电解质。本文研究了LHCEs中使用的氟化共溶剂类型，以寻找最适合高浓度电解质（HCEs）的稀释剂。添加到HCEs中的非溶剂化溶剂（包括氟化醚、氟化硼酸盐和氟化原甲酸酯）能够形成具有高浓度溶剂化结构的LHCEs。然而，低溶剂化的氟化碳酸酯会与锂离子配位并形成第二溶剂化层或假LHCE，这会削弱LHCE的优势。此外，很明显，稀释剂不仅对保持高浓度溶剂化结构有重要影响，而且对电极/电解质界面（EEIs）也有显著影响。围绕高浓度簇的稀释剂分子可以通过参与EEI形成过程中的稀释剂分解来加速或减速阴离子分解。不同的界面特征导致电池性能有显著差异。本研究指出了稀释剂及其与导电盐和溶剂化溶剂的协同效应在设计LHCEs中的重要性。这些对使用不同类型氟化溶剂的LHCEs的系统比较和基本见解可以指导高压LMBs先进电解质的进一步发展。
