Radical Decomposition of Ether-Based Electrolytes for Li-S Batteries

Abstract

In this work, the stability of ether-based electrolytes for Li-S batteries is investigated with particular regard to the effect of dissolved oxygen. Specifically, the performance of two different electrolyte solvents, i.e., 1,2-dimethoxyethane and its mixture with 1,3-dioxolane (DME:DOL, 1:1 v/v), is characterized in cells assembled in dry air environment, which would substantially lower production costs with respect to inert atmosphere (Ar). Although stability of all the components would suggest that Li-S batteries built in both the environments should behave similarly, it is found that cells containing the DME:DOL-based electrolyte are rather unstable in the presence of O 2 in contrast to those employing DME-based electrolyte, which show a relatively good performance. The different sensitivity toward O 2 of these electrolytes is associated to the ring-opening reaction of DOL, which happens to a greater extent when O 2 is present, but occurs also in its absence. Based on these results a mechanism for electrolyte degradation in Li-S cells, and its reaction with dissolved polysulfides is proposed, which rationally explain for the first time the behavior already reported in literature for these kind of batteries. These findings are also relevant to the field of Li-O 2 batteries, where these ether-based electrolytes are also used. Sulfur has been extensively investigated as a new cathode material for secondary batteries, in order to replace metal oxides normally used in lithium-ion batteries (LIBs). The first point of interest is its high theoretical specific capacity, around 1672 mAh g −1 , but, as a raw material sulfur is also non-toxic, readily available, and very inexpensive. It is indeed one of the main side products of crude oil refining, with more than 60 million tons produced annually.1 Even the relatively low operating voltage of sulfur-based cathodes, at around 2 V vs. Li/Li + , can be considered as a potential advantage, making it intrinsically safer. 2 Furthermore, the high specific gravimetric capacity of sulfur enables the remarkable specific energy of about 2600 W h kg −1 . However, Lithium-Sulfur batteries (LSB) still present some specific challenges that need to be solved to enable their commercialization.2 First, sulfur has a very low electrical conductivity, around 5 × 10 −30 S cmat 25• C, requiring the introduction of a conductive matrix, normally carbon-based. The carbon host is generally electrochemically inert, such that it decreases the energy density of the electrode as whole, especially since it is often near to 50 wt% of the total sulfur-composite mass. Secondly, and most importantly, sulfur is a conversion material undergoing several chemical transformations during discharge and forming a variety of different polysulfides with the formal oxidation state of sulfur changing from 0 to −2. Some of these intermediate species are soluble in the electrolyte, and very reactive toward both the electrolyte itself 3,4 and the lithium metal anode. 2,5 Most importantly though, their dissolution cause...

Dandelion-shaped manganese sulfide in ether-based electrolyte for enhanced performance sodium-ion batteries

“…2a) reveal a corresponding dominant anodic peaks at 2 V as well as at 1.6 V. These features are the typical characteristics of similar high temperature α-MnS electrodes with cubic lattice reported for NIBs 38 . Concordantly, as expected, the related oxidation peaks of α-MnS electrode used in LIB applications are observed at slightly higher potentials (~2 and 2.5 V) and these features are attributed to the reformation of the MnS phase 33,39 . Nevertheless, these redox features are completely different from the only one oxidation peak (around 1.5 V) observed during the anodic scan of the low-temperature γ-MnS electrode with hexagonal lattice in a lithium half-cell configuration 40,41 .…”

An electrolyte additive of bromoxoindole enables uniform Li-ion flux and tunable Li2S deposition for high-performance lithium–sulfur batteries

“…5d, in situ FT-IR spectroscopy was performed to monitor changes in organic functional groups of the solvation structures during the discharge of the 0.5 wt% BOD cell from 2.8 to 1.6 V. In the initial stage (2.8–2.4 V), characteristic signals of DOL, DME, TFSI − , and BOD were detected, where the peaks at 1184 cm −1 and 868/1054/1135 cm −1 are vibrational signals of –CH 3 and C–O–C from DOL/DME; the peaks at 1018 and 1355 cm −1 belong to the ν as vibrations of S–N–S and SOS from TFSI − ; and the peaks at 682 and 795/920 cm −1 are assigned to the out-of-plane bending vibrations of C–Br and benzene ring C–H groups of BOD, respectively. 54–59 In the subsequent stage (2.4–2.0 V), the solvation structure changed as the polysulfide chain length decreased. Hence, a red shift (from 1054 to 1040 cm −1 ) and peak intensity increase of C–O–C vibrations were found in DOL/DME solvents, indicating an increase of free solvent molecules.…”

Designing Electrolytes with Steric Hindrance and Film‐Forming Booster for High‐Voltage Potassium Metal Batteries

“…Apart from the C─O bond, there is an essential amount of C═O bond after cycling in DiDBE‐D electrolyte, which may result from the formation of carbonyl groups after the isomerization reaction of the DiDBE solvent with radical species. [ 31 ] Furthermore, the ROSO 2 − peak related to S‐containing organics is outstanding in the S 2p spectrum (Figure 3e) on the surface of the DiDBE‐D sample, whose intensity is over two times that of the EC/DEC one. The pronounced S─F peak in the F 1s spectrum (Figure 3f) further confirms more S‐containing organic species in the CEI formed in DiDBE‐D, which mainly comes from the DTD decomposition.…”