Molecular-confinement of polysulfides within mesoscale electrodes for the practical application of lithium sulfur batteries

Kuo²,

et al. 2019

Int J Energy Res

Summary Multi‐walled carbon nanotube (MWCNT) protection layers have previously been used to trap polysulfides and suppress the shuttle effect in lithium sulfur (Li‐S) batteries, leading to significant performance improvement. While the MWCNT is inherently highly conductive and mechanically strong, the cost can be significant and in turn hampered wider application of MWCNT protection layers. Here, we employed lignin, a byproduct during high‐quality bleached paper manufacturing, to replace a portion of MWCNT in the protection layer to reduce cost and enhance surface properties of pristine MWCNT protection layers. We found that the protection layer with 25 wt% lignin leads to the best overall electrochemical performance of Li‐S batteries during charging/discharging at 0.5°C and 1C rate (1C = 1,675 mA g−1) among various weight‐ratios of lignin/MWCNT, and a low decay rate (0.20% per cycle) and high initial capacity (1342 mA g−1 and 1437 mA g−1 for 1C and 0.5C, respectively) are demonstrated. Besides, Li‐S cells with 25 wt% lignin/MWCNT composite protection layer also exhibited great rate capability, of which the specific capacities at 0.1C, 0.5C, 1C, and 2C were 1150, 913, 824, and 637 mAh g−1, respectively. The enhanced electrochemical stability and performance of Li‐S batteries can be attributed to strengthened polysulfide trapping and improved lithium ion transport with lignin reinforced MWCNT protection layers. We showcased an economic approach to extend cycle life and improve rate capability of Li‐S batteries.

Section: Resultssupporting

confidence: 87%

Improving lithium‐sulfur battery performance with lignin reinforced MWCNT protection layer

Kuo²,

et al. 2019

Int J Energy Res

Advanced Energy Materials

“…[ 37 ] Elemental sulfur (S 8 , Alfa Aesar) and the MWCNTs (Cheap Tubes Inc.) (80:20 w/w) were mixed together by mechanical ball milling for 5 h. The mixture was then sealed in a polytetrafl uoroethylene (PTFE) container and heated to 155 °C in an oven for 24 h under the protection of inert Ar gas. [ 37 ] Elemental sulfur (S 8 , Alfa Aesar) and the MWCNTs (Cheap Tubes Inc.) (80:20 w/w) were mixed together by mechanical ball milling for 5 h. The mixture was then sealed in a polytetrafl uoroethylene (PTFE) container and heated to 155 °C in an oven for 24 h under the protection of inert Ar gas.…”

Section: Methodsmentioning

confidence: 99%

Restricting the Solubility of Polysulfides in Li‐S Batteries Via Electrolyte Salt Selection

Chen

Han

Henderson

et al. 2016

Self Cite

1 M lithium bis(trifl uoromethanesulfonyl)imide (LiTFSI) in 1,3-dioxolane/1,2-dimethoxyethane (DOL/DME). [ 21 ] Switching to other solvents with high dielectric constant such as dimethyl sulfoxide (DMSO) or dimethylacetamide (DMA) facilitates the production of sulfur radicals and the full utilization of the sulfur, but the cycling stability of the cell is also sacrifi ced and the unstable interface between the reactive DMSO/DMA solvent and Li metal raises other concerns. [ 22,23 ] Alternative cell designs incorporating solid-state electrolytes completely prevent the dissolution of polysulfi des, but the utilization of the sulfur (i.e., the reversible capacity) is also largely reduced. [ 24 ] Therefore, the solubility of the polysulfi des in cells with liquid electrolytes needs to be carefully tuned and well understood. In most studies, a low sulfur loading (less than 1 mg cm -2 ) is used, but a high S loading is desired for high-capacity full cells. [ 25,26 ] In this paper, lithium trifl uoromethyl-4,5-dicyanoimidazole (LiTDI) is studied for Li-S cells. We study the effect of LiTDI on the solubility of polysulfi des. The performance of this electrolyte was investigated with a high sulfur (i.e., practically usable) loading at 3 mg cm -2 under a high current density.A comparison of the physical properties of electrolytes with either 1 M LiTFSI or LiTDI in DOL/DME (1/1, v/v) is shown in Table 1 . Both electrolytes have a comparable conductivity and viscosity, suitable for the electrochemical needs, but an 83% decrease in the Li 2 S 8 solubility is observed in the LiTDI electrolyte. Restricting the polysulfi de solubility to a low level is expected to improve the Li-S cell cycle life because of the suppression of the polysulfi de shuttle mechanism, reduction of anode contamination, and the minimization of the loss of active material from the cathode. [ 22 ] To understand the relationship between the polysulfi de solubility and electrolyte supporting salt, 7 Li and 17 O nuclear magnetic resonance (NMR) spectroscopic measurements were used to aid in understanding the solvation interactions. The δ ( 7 Li) for the LiTDI and LiTFSI-based electrolytes without polysulfi des was -0.8 and -1.2 ppm (relative to Li + cations fully solvated by H 2 O molecules) ( Figure 1 a-c), respectively. The δ ( 17 O) for the DME molecules shifts to ≈ -27.7 and -26.9 ppm in the LiTDI and LiTFSI-based electrolytes, respectively, from -24.3 ppm in a neat DOL/DME solvent mixture. The δ ( 17 O) for the DOL molecules near 35 ppm shifts by 1-2 ppm. The smaller shift of δ ( 17 O) for the DOL molecules relative to the DME molecules and signifi cant broadening of the peaks for the latter suggest that the Li + cations may be preferentially solvated by the DME. [ 27 ] It has been reported that the solvation of Li + cations in the electrolyte affects the short-chain polysulfi de solubility by solvating the Li + ion in the polysulfi des, but it did not affect the

“…Wettability in nanochannels is essential for understanding and conquering many remaining challenging problems in material science and technology, such as mass transport, catalysis, confined chemical reaction, nanofabrication, energy storage and conversion, and liquid separation ( Figure ). Both experimental investigations and molecular dynamic (MD) simulations have been conducted to investigate wettability in nanochannels .…”

Section: Introductionmentioning

confidence: 99%

Wettability and Applications of Nanochannels

2018

Wettability in nanochannels is of great importance for understanding many challenging problems in interface chemistry and fluid mechanics, and presents versatile applications including mass transport, catalysis, chemical reaction, nanofabrication, batteries, and separation. Recently, both molecular dynamic simulations and experimental measurements have been employed to study wettability in nanochannels. Here, wettability in three types of nanochannels comprising 1D nanochannels, 2D nanochannels, and 3D nanochannels is summarized both theoretically and experimentally. The proposed concept of “quantum‐confined superfluid” for ultrafast mass transport in nanochannels is first introduced, and the mostly studied 1D nanochannels are reviewed from molecular simulation to water wettability, followed by reversible switching of water wettability via external stimuli (temperature and voltage). Liquid transport and two confinement strategies in nanochannels of melt wetting and liquid wetting are also included. Then, molecular simulation, water wettability, liquid transport, and confinement in nanochannels are introduced for 2D nanochannels and 3D nanochannels, respectively. Based on the wettability in nanochannels, broad applications of various nanochannels are presented. Finally, the perspective for future challenges in the wettability and applications of nanochannels is discussed.