Fluorinated Electrolytes for Li-S Battery: Suppressing the Self-Discharge with an Electrolyte Containing Fluoroether Solvent

Abstract

The fluorinated electrolyte containing a fluoroether 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was investigated as a new electrolyte for lithium-sulfur (Li-S) batteries. The low solubility of lithium polysulfides (LiPS) in the fluorinated electrolyte reduced the parasitic reactions with Li anode and mitigated the self-discharge by limiting their diffusion from the cathode to the anode. The use of fluorinated ether as a co-solvent and LiNO 3 as an additive in the electrolyte shows synergetic effect in suppressing the self-discharge of Li-S battery due to the formation of the solid electrolyte interphase (SEI) on both sulfur cathode and the lithium anode. The Li-S cell with the fluorinated electrolyte showed prolonged shelf life at fully charged state. Lithium-sulfur (Li-S) batteries are considered to be promising candidates which can satisfy the demand for high energy density batteries in electronic and transportation devices due to their high theoretical capacity, intrinsic overcharge protection, low cost and nontoxicity. 1,2 Sulfur, one of the most abundant elements in the earth's crust, has a theoretical capacity value of 1675 mAh/g and is the cheapest solid state cathode material for energy storage devices.Despite the considerable advantages, there are several major issues that impede the practical applications of the Li-S battery.3 Sulfur undergoes a series of structural and morphological changes during charge and discharge, which results in the formation of soluble Li 2 S x (4 < x < 8) and insoluble Li 2 S 2 and Li 2 S. The formation of soluble lithium polysulfides (LiPS) and their chemical reaction with the electrolyte and lithium anode leads to low coulombic efficiency and rapid capacity fading. [4][5][6][7] In addition, Li-S battery suffers from severe self-discharge, which is the biggest hurdle for the commercialization of this battery. 8 A secondary battery will lose charge capacity when stored for a period of time at a certain temperature. This behavior is known as self-discharge and depends on the battery chemistry, electrode composition, choice of current collector, electrolyte formulation, and the storage temperature. For Li-S batteries, the self-discharge is a well-known issue due to the severe corrosion of lithium metal anode in the presence of the LiPS in the electrolyte. 5,6,8 Many attempts have been made to overcome the poor cycle life and low sulfur utilization of Li-S batteries.7-14 However, there are only a few publications focused on solving the self-discharge issue of the Li-S battery. Kazazi et al. have reported that the corrosion of the aluminum current collector and the shuttle mechanism play a significant role in the self-discharge of Li-S cells; therefore, LiNO 3 is a suitable electrolyte additive candidate to prevent self-discharge due to its effect on shuttle prevention.8 Mikhaylik and Akridge reported that self-discharge mainly attributed from the high plateau polysulfides. Electrolytes with higher salt concentration also showed lower rates of Li corrosion wit...

Towards Next Generation Lithium-Sulfur Batteries: Non-Conventional Carbon Compartments/Sulfur Electrodes and Multi-Scale Analysis

“…Redistribution subject to ECS terms of use (see 34.213.178. 48 Downloaded on 2018-05-09 to IP Figure 3. X-Ray Powder Diffraction demonstrates that the CCs/S composite contains nano-size orthorhombic sulfur.…”

Towards Stable Lithium–Sulfur Batteries with a Low Self‐Discharge Rate: Ion Diffusion Modulation and Anode Protection

“…[9][10][11][12] Great achievements have been made to obtain ap ractical cathode with an areal sulfur loading of more than 4.0mgcm À2 with high sulfur utilization and extraordinary stability.…”

“…[6,[10][11][12][15][16][17] In al ithium-sulfur cell, both corrosion of the current collector by an electrolyte and shuttling of intermediate polysulfidesc ontributet os elfdischarge. Mikhaylik andA kridge proposed am athematic model to correlate self-discharge to polysulfide shuttle pheThe self-dischargeo falithium-sulfur cell decreases the shelflife of the battery and is one of the bottlenecks that hinders its practical applications.…”

Electrolytes for Lithium and Lithium-Ion Batteries

“…Copyright 2013 Elsevier to mitigate self-discharge of Li-S cells having both low-and high-sulfur loading sulfur cathodes [13,38]. This electrolyte significantly decreased self-discharge at elevated temperature, though differences in behavior of cells with high-and low-sulfur loading were also noted.…”