Electrolyte Decomposition and Electrode Thickness Changes in Li-S Cells with Lithium Metal Anodes, Prelithiated Silicon Anodes and Hard Carbon Anodes

Abstract

Li-S cells can have high gravimetric energy densities above 300 Wh kg −1 when the electrodes and cell components are optimized. Low electrolyte/sulfur mass ratios or more generallly, the relative amount of electrolyte in a Li-S cell have an especially high impact on the achievable gravimetric energy density. A negative side effect of low electrolyte/sulfur ratios are low cycle numbers due to electrolyte decomposition and the possibility that electrolyte becomes inaccessible at the lithium metal anode when the lithium becomes more and more porous during cycling. Electrode thickness measurements were performed during cycling for various cell chemistries such as lithium-sulfur (Li-S) with different cathode sulfur loadings and porosities, lithium-hard carbon (Li-HC), lithium-silicon (Li-Si), prelithiated HC-sulfur (LiHC-S), prelithiated Si-sulfur (LiSi-S) and Li-ion. The thickness measurements provided information about mechanical stress and irreversible thickness changes. The thickness measurements also helped to explain different electrolyte decomposition behavior and they can be used to discuss the impact of thickness changes on gas analysis. The electrolyte decomposition of the Li-S standard electrolyte based on lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethoxyethane (DME): dioxolane (DIOX) with LiNO 3 was examined by online mass spectrometry (MS) within Li-S, Li-HC, Li-Si, LiSi-S and LiHC-S cells. Several electrolyte decomposition products were verified by post-mortem gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) of Li-S cells with cycled electrolyte. Li-S prototypes demonstrate that high gravimetric energy densities of 300 Wh/kg and above can be obtained. Possible strategies to optimize future sulfur cells are the reduction of the weight amount of passive components e.g. by decreasing the thickness of separator and current collectors and/or the application of thin perforated current collectors. Additionally with lithium metal being conductive, the copper current collector can be removed completely providing high energy densities despite low sulfur loaded (1-3 mg cm −2 ) cathodes. By utilizing a copper current collector high sulfur load cathodes (>5 mg cm −2 ) are required to compensate for the copper's passive weight.1 Thick, high load sulfur cathodes reduce the electrode and separator coating length in a cell and therefore save costs. However high load sulfur cathodes also have the drawback that high transported capacities during cycling stress the lithium metal anode and increase the chance of lithium induced shorts 2 (next to the costs of the copper). Despite all this, the electrolyte is a major weight source in Li-S cells even if the electrolyte/sulfur weight ratio (E/S) is low. With the Li-S standard electrolyte based on lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethoxyethane (DME): dioxolane (DOL) with LiNO 3 additive, the lowest obtainable E/S ratio is likely >3:1. This is due to the high porosity of the sulfur cathode (usually ∼60-80%) which has ...

Tannic Acid as a Small-Molecule Binder for Silicon Anodes

“…This increase in electrode thickness after cycling is usually observed for silicon electrodes. 59,60 But, as indicated in Figure 3, the electrode maintained a stable capacity over a large number of cycles, which implies that TA was able to anchor to the silicon nanoparticles successfully.…”

Enabling High‐Rate and Safe Lithium Ion–Sulfur Batteries by Effective Combination of Sulfur‐Copolymer Cathode and Hard‐Carbon Anode

“…Earlier work demonstrated the successful fabrication of Li ion–S full‐cells with sulfur/carbon composite cathode and Li‐HC anode, but the capacity decreased at high rates to 591 mAh g −1 at 0.5 C and 365 mAh g −1 at 1 C . In another study, a full cell with HC anode showed negligible change of anode thickness after multiple cycling, which is advantageous for cell performance. However, challenges in attaining good high‐rate performance of the full cell with HC anode still remain.…”

“…[16,17] In this work, we utilized ap relithiated hard-carbon (Li-HC)a node, which exhibits high rate capability and low cost in LIBs, [17,18] to enable a full cell Li ion-S battery (LISB).E arlier work demonstrated the successful fabrication of Li ion-S full-cells with sulfur/carbonc omposite cathode and Li-HC anode,b ut the capacity decreased at high rates to 591 mAh g À1 at 0.5 Ca nd 365mAh g À1 at 1C. [19] In anothers tudy,af ull cell with HC anode showed negligible change of anode thickness after multiple cycling, [20] which is advantageous for cell performance. However,c hallenges in attaining good high-rate performance of the full cell with HC anode still remain.…”

An Ether‐Based Low Density Electrolyte for the Use of Graphite Anodes in Stable Lithium‐Sulfur Batteries

“…[3,16,17] Another concern is the dendritic growth of lithium during deposition, which could cause safety issues. [17] To mitigate this obstacle, various approaches were developed such as new electrolytes, [18] electrolyte additives, [19] surface coatings [20] or the substitution of the anode material with silicon, [21,22] hard carbons [22,23] or graphite. [24][25][26][27][28][29][30][31][32][33][34][35] Graphite is a very interesting anode material for LiÀ S batteries, as it has been the standard anode material of the lithium ion battery for decades and electrode production is well established on industrial scale.…”