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.

电解质对高压锂 (Li) 金属电池 (LMB) 的性能非常关键，它是下一代高密度储能系统最有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特性及其在电极表面上的界面化学。由于其独特的溶剂化结构，局部高浓度电解质 (LHCE) 在 LMB 的许多方面都优于最先进的碳酸盐电解质。这里研究了 LHCE 中使用的氟化助溶剂的类型，以寻找最适合高浓度电解质 (HCE) 的稀释剂。非溶剂化溶剂（包括氟化醚、氟化硼酸盐、和氟化原甲酸酯）添加到 HCE 中，可以形成具有高浓度溶剂化结构的 LHCE。然而，低溶剂化的氟化碳酸酯会与锂配位⁺离子并形成第二个溶剂化壳或伪 LHCE，这会降低 LHCE 的好处。此外，很明显，除了保留高浓度溶剂化结构之外，稀释剂对电极/电解质界面 (EEIs) 还具有显着影响。高浓度簇周围的稀释剂分子可以通过稀释剂分解共同参与 EEI 形成来加速或减速阴离子分解。不同的相间特征导致显着不同的电池性能。该研究指出了稀释剂及其与导电盐和溶剂化溶剂在设计 LHCE 中的协同作用的重要性。