Breaking the Barrier: Strategies for Mitigating Shuttle Effect in Lithium-Sulfur Batteries Using Advanced Separators

Mitigation of Polysulfide Shuttling in Lithium-Sulfur Batteries Utilizing Vanadium Pentoxide/Polypyrrole Nanocomposite Separators

Lithium-sulfur (Li-S) batteries are promising energy storage devices due to their high theoretical energy density and cost-effectiveness. However, the shuttle effect of polysulfides during the charging and discharging processes leads to a rapid decline in capacity, thereby restricting their application in energy storage. The separator, a crucial component of Li-S batteries, facilitates the transport of Li+ ions. However, the large pores present on the surface of the separator are insufficient to prevent the shuttling effect of polysulfides. This paper proposes a straightforward coating method to introduce a vanadium pentoxide (V2O5) /polypyrrole (PPy) functional coating on the surface of a conventional polymer separator. The unique composition of the V2O5/PPy layer plays an essential role in effectively preventing the bidirectional movement of polysulfides and the subsequent formation of inactive sulfur. Compared to those using polypyrrole separators,when equipped with a V2O5/PPy separator, the capacity retention after 100 cycles was recorded at 98 %, with a measured rate of capacity degradation at just 0.016 %, despite the sulfur content being as high as 1.84 mg cm-2. Furthermore, after 400 cycles at 1 C, the capacity retention rate reached 57.6 %. The thoughtful design of this modified separator represents an effective strategy for improving the performance of Li-S batteries.

2D P-doped carbon nitride as an effective artificial solid electrolyte interphase for the protection of Li anodes

Metallic lithium plays an important role in the development of next-generation lithium metal-based batteries. However, the uncontrolled growth of lithium dendrites limits the use of lithium metal as an anode. In this context, a stable solid electrolyte interphase (SEI) is crucial for regulating dendrite formation, stability, and cyclability of lithium metal anodes. This article proposes an artificial protective layer of P-doped carbon nitride on the lithium anode surface to address these issues. A thin film of P-doped carbon nitride (CNP) was created through a simple drop-casting method using synthesized CNP powder, forming an artificial SEI on the lithium electrode. The resulting symmetric CNP-modified Li/Li cells exhibited remarkable cyclability with low overpotentials of around 40 mV over 500 cycles at a current density of 3 mA cm-2. Anode degradation and SEI composition were thoroughly studied for cycled electrodes to gain insight into the mechanisms underlying this modified surface. Furthermore, these CNP-modified anodes were successfully utilized in a Li-S coin cell battery, achieving high capacity and capacity retention at a high current density (1C). First-principles calculations indicate that P-doping in the carbon nitride structure significantly enhances the surface diffusion of lithium and promotes more homogeneous lithium plating.

Diffusion and thermodynamic properties of lithium polysulfides in different solvents: a molecular dynamics approach

Li-S batteries are promising alternatives due to their proven increased gravimetric capacity compared to Li-ion batteries. However, their development is hindered by many technical issues, one of the most challenging being the dissolution and shuttle of polysulfide species, which causes irreversible loss of cathode material leading to rapid capacity fading. Among the possible strategies to mitigate this effect, the choice of suitable solvents is easy to implement and has large room for improvement. To guide this quest, computationally-aided optimization is a powerful tool, provided that suitable descriptors are used to screen possible solvents. In this work, molecular dynamics simulations were performed for a typical lithium polysulfide Li2S6 dissolved in different solvents. Diffusion coefficients and their related activation energies were calculated, and thermodynamic properties like solvation energies and entropies were also evaluated. Additionally, a theoretical framework for computing the relative solubilities of lithium polysulfide is provided. For the set of solvents considered, we found that the system's viscosity appears as an important descriptor to correlate with different system properties. The donor number of the solvent also appears as a valid descriptor, for low-viscosity solvents. In general, it was found that higher viscosity solvents lead to lower diffusion rates and higher polysulfide solubility. These results suggest that the optimal choice to reduce the shuttle is a trade-off between high-viscosity solvents to reduce polysulfide diffusion and low-viscosity solvents to reduce its solubility, which could be further improved by properly tuning the donor number.

Advanced Separator Materials for Enhanced Electrochemical Performance of Lithium-Sulfur Batteries: Progress and Prospects

Lithium-sulfur (Li-S) batteries are promising energy storage devices owing to their high theoretical specific capacity and energy density. However, several challenges, including volume expansion, slow reaction kinetics, polysulfide shuttle effect and lithium dendrite formation, hinder their commercialization. Separators are a key component of Li-S batteries. Traditional separators, made of polypropylene and polyethylene, have certain limitations that should be addressed. Therefore, this review discusses the basic properties and mechanisms of Li-S battery separators, focuses on preparing different functionalized separators to mitigate the shuttle effect of polysulfides. This review also introduces future research trends, emphasizing the potential of separator functionalization in advancing the Li-S battery technology.

Electrospun MoS2-CNTs-PVA/PVA Hybrid Separator for High-Performance Li/FeS2 Batteries

As a promising candidate for high-energy-density rechargeable lithium metal batteries, Li/FeS2 batteries still suffer from the large volume change and severe shuttle effect of lithium polysulfides during cycling. To improve the electrochemical performance, great efforts have been made to modify FeS2 cathodes by constructing various nanocomposites. However, energy density is sacrificed, and these materials are not applicable at a large scale. Herein, we report that the electrochemical performance of commercial FeS2 can be greatly enhanced with the application of a double-layer MoS2-CNTs-PVA (MCP)/PVA separator fabricated by electrospinning. The assembled Li/FeS2 batteries can still deliver a high discharge capacity of 400 mAh/g after 200 cycles at a current density of 0.5 C. The improved cycling stability can be attributed to the strong affinity towards lithium polysulfides (LiPSs) of the hydroxyl-rich PVA matrix and the unique double-layer structure, in which the bottom layer acts as an electrical insulation layer and the top layer coupled with MoS2/CNTs provides catalytic sites for LiPS conversion.