Effects of fluorinated solvents on electrolyte solvation structures and electrode/electrolyte interphases for lithium metal batteries

Abstract

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.

Fluorinated ether electrolyte with controlled solvation structure for high voltage lithium metal batteries

“…In the case of Li metal anode (LMA), however, low concentration carbonate electrolytes (i.e., 1 M salt) usually suffer from serious side reactions, which are linked to whisker shape Li dendrite growth and significantly short cycle life. On the contrary, ether-based electrolytes tend to form relatively large and flat Li grains, which decrease the contact surface of LMA with electrolyte and exhibits high Coulombic efficiency (CE) 13 , 14 . However, ethers such as 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) are unstable in the high voltage range (i.e., >4V vs .…”

Enhanced Sodium Metal/Electrolyte Interface by a Localized High-Concentration Electrolyte for Sodium Metal Batteries: First-Principles Calculations and Experimental Studies

“…Recently, high-concentration electrolytes (HCEs) for Li-based batteries exhibited outstanding properties along with the suppression for Li dendrite growth and stable high-voltage performance, which stimulated scientists’ interest. − Meanwhile, in SMBs, analogous superiority of properties could also achieved by using HCEs. , However, the high viscosity and cost of salt and the poor wettability toward the separator of HCEs hinder its wide applications. To address this issue, localized high-concentration electrolytes (LHCEs) have been proposed via adding a diluent into the HCE to lower the concentration of electrolyte and overcome the shortcomings above. − It is highly recognized that the excellent cell performance enabled by the LHCE is mainly attributed to the unique solvation structure in the electrolyte, and in Li-based batteries, the solvation structure and cell performance have been systematically investigated combining the experimental methods and first-principles calculations. − The conclusion of these studies demonstrates that the solvation structure in LHCE shows almost no alteration compared with that in HCE. In Na-based batteries, the exploration of cells using LHCE, e.g., NaFSI/DME-BTFE and NaFSI/TEP-TTE, is also conducted by various experimental methods.…”

Electrolyte Design Enabling a High‐Safety and High‐Performance Si Anode with a Tailored Electrode–Electrolyte Interphase

“…Such cluster separation caused by the nonsolvating HFE enhances the interaction between Li + and the solvation species, resulting in the increased peak intensity of the Li‐O DME , Li‐O FEC , and Li‐O FSI − pairs. [ 28 ] Moreover, chances of the DFOB − participation into the primary solvation sheath have also been increased, which is favorable in promoting its decomposition. [ 25,29,30 ] The LUMO and the highest occupied molecular orbital (HOMO) energy levels of the dominant Li + solvation structures in the N‐DHF electrolyte are further calculated in Figure 2g, where the solvation structures were retrieved from the above MD simulations (Figure S4, Supporting Information).…”