How to Obtain Reproducible Results for Lithium Sulfur Batteries?

Abstract

The basic requirements for getting reproducible Li-S battery data have been discussed in this work. Unlike Li-ion batteries, electrolyterich environment significantly deteriorates the cycling stability of Li-S batteries assembled and tested under the same conditions. The reason has been assigned to the low concentration of polysulfide-containing electrolyte in the cells, which shows profound influences on both sulfur cathode and lithium metal anode. With optimized sulfur/electrolyte (S/E) ratio of 50 g L −1 , a good balance between electrolyte viscosity, wetting ability, diffusion rate of dissolved polysulfide and nucleation/growth of short-chain Li 2 S/Li 2 S 2 has been established along with largely reduced corrosion of the lithium metal anode. Accordingly, good cyclability, high reversible capacity and Coulombic efficiency are achieved in Li-S cell with optimized S/E ratio without any additive. Other factors such as sulfur content in the composite and sulfur loading in the whole electrode also need careful concern in Li-S battery system in order to generate reproducible results and gauge the various methods used to improve Li-S battery technology.Lithium-sulfur (Li-S) batteries have attracted increasing interest because of their high theoretical capacity, natural abundance and environmental benignity. 1-5 Li-S battery operates by reduction of sulfur during discharge to form lithium polysulfides with different chain lengths and finally to insoluble Li 2 S 2 or Li 2 S. The multi-electron conversion reaction generates high capacity and energy of 1675 Ah kg −1 and 2650 Wh kg −1 , respectively, drastically higher than those of state-of-the-art lithium ion batteries. 6-9 Li-S batteries suffer from the soluble intermediate products, a series of polysulfides Li 2 S x (x > 2), which participate in the well documented 'sulfur shuttle mechanism' reactions. 1,10 The undesired shuttle effect not only lowers the Coulombic efficiency, but also causes fast capacity degradation and severe self-discharge. Moreover, the irreversible relocation of polysulfides in the whole cell during "shuttle reactions" is also the reason leading to the quick loss of energy-bearing materials. [11][12][13] The end result is the significantly shortened lifespan of Li-S battery, which plagues its market penetration.In an effort to overcome the hurdles in Li-S battery technology, various approaches have been proposed, spanning from immobilization of sulfur in the different kinds of hosting materials, 10,11,14-17 electrolyte modification 18-20 and anode protection by employing LiNO 3 as the electrolyte additive. 3,21-24 It is known that electrolyte is critical for Li-S battery thus novel electrolyte or electrolyte additives have been explored. 25,26 However, the basic information on the electrolyte composition and the electrolyte amount used in each test are rarely mentioned in literature. 27 For lithium ion batteries, excessive amount of electrolyte always improves the results from half-cell tests, although it is not the case in practical applicatio...

Critical Link between Materials Chemistry and Cell-Level Design for High Energy Density and Low Cost Lithium-Sulfur Transportation Battery

“…In the literature, E/S ratios corresponding to electrolyte vol% in the cathode higher than 90% are suggested for improved cyclability. 50,51 Figure 4a shows the pack-level energy density and specific energy predictions of the model as a function of the electrolyte vol% in the cathode. It is evident from the figure that the systems-level properties decrease significantly at the high electrolyte vol% suggested in the literature.…”

Nucleophilic substitution between polysulfides and binders unexpectedly stabilizing lithium sulfur battery

“…The optimum ratio between solid sulfur and liquid electrolyte was identified to be 50 g L −1 (20 μL/mg-s). [55] This optimum highly depends on sulfur loading, and electrode materials choice. In our work, high loading of sulfur is used in the electrode, 16 µL/mg-s generate best results, and has been consistently used in this study.…”

“…[55] In comparison, cells using PVDF binder suffered from rapid capacity decay, showing capacity retention of 31% after 100 cycles. The PVS also gave initial good performance.…”

Pitfalls in Li–S Rate-Capability Evaluation

“…[9][10][11][12] do affect the extent to which the polysulfide shuttle impacts on the performance of the cell. 8,9,24,25 The aim of the present study is to assess the sensitivity and reliability of rate-capability tests for Li-S systems. We have studied in a systematic way how various cycling conditions and electrolyte-related parameters influence the practical capacity, the coulombic efficiency, and the overpotentials in a model Li-S cell at various rates.…”