NML: Reasonably design high sulfur loading MXene nanosheets for lithium-sulfur batteries

【Research Background】

As the demand for portable electronic devices, electric vehicles, and renewable energy sources continues to increase, people need energy storage devices with lower costs, higher energy density, and longer service life. The Li-S battery combines a high-capacity sulfur positive electrode and a lithium negative electrode with abundant reserves on the earth, and is considered to be the most promising candidate. It has a high theoretical special capacity (1675 mAh g ⁻¹ ) and a high theoretical energy density (2600 Wh kg ⁻¹ ). However, the obstacles that hinder the application of lithium-sulfur batteries are rapid capacity decay, poor rate performance, and low actual energy density. The polysulfide shuttle, the low conductivity of sulfur / Li 2 S and the high electrolyte / sulfur ratio (E / S) of the low sulfur area load are the root causes of these challenges. In the past few decades, people have been working hard to develop Li-S batteries with stable performance and high energy density. Among them, functional sulfur matrix materials with different microstructures and surface properties are expected to capture polysulfides in the positive electrode. The physical / chemical adsorption strategy of polysulfides is expected to suppress harmful shuttle effects. These methods shorten the gap between Li-S battery research and application.

【Achievement Introduction】

Recently, the research team of Professor Xuelin Yang of China Three Gorges University and Professor Xiao Liang of Hunan University published an article in the internationally renowned academic journal Nano-Micro Letters : Comprehensive Design of the High-Sulfur-Loading Li–S Battery Based on MXene Nanosheets The research paper, based on MXene phase (Ti 3 C 2 T x nanosheets), carried out a comprehensive material design and battery structure construction, aiming to achieve stable cycling performance of Li-S battery with high sulfur surface load. The inherently negatively charged MXene nanosheets were assembled on positively charged Ketjen black / sulfur (KB / S) particles to construct an interwoven KB / S @ Ti 3 C 2 T x composite material. The Ketjen black core improves the conductivity of sulfur, while Ti 3 C 2 T x ensures the physical / chemical adsorption of soluble polysulfides and further improves the in-plane conductivity. More importantly, the self-assembled secondary particle structure is beneficial to the structural integrity of the volume expansion / contraction of the sulfur electrode.

【Graphic introduction】

Fig. 1 Schematic diagram of the manufacture of a KB / S @ Ti 3 C 2 T x composite material b Zeta potential of the corresponding material c Digital photos of the corresponding material aqueous suspension (d, e) KB / S and (f, g) KB / S SEM image of @Ti 3 C 2 T x

Figure 2 Comparison of sulfur electrode scanning electron microscope

Figure 3 Electrochemical performance of KB / S @ Ti 3 C 2 T x

Figure 4 SEM image of a KB @ Ti 3 C 2 T x . KB @ Ti 3 C 2 T x coated separator b SEM image c SEM cross-sectional view and d photo. e Use original PP membrane and KB @Ti 3 C 2 T x coated membrane polysulfide permeability

Figure 5 Electrochemical performance of corresponding samples

【Summary of this article】

This article demonstrates a comprehensive design of materials and battery structures aimed at achieving improved Li-S batteries with high sulfur surface loads. The material is based on the MXene phase with affinity for polysulfides. Material engineering was carried out on the main body of sulfur and the intermediate layer coated on the separator by means of electrostatic self-assembly. The prepared KB / S @ Ti 3 C 2 T x has an interwoven structure in which the KB carbon core improves electrical conductivity, while the MXene nanosheets ensure physical / chemical adsorption of soluble sulfides. More importantly, the interwoven structure is beneficial to the structural integrity and thus the volume expansion / contraction of the sulfur electrode. To further prevent polysulfides that may escape from the positive electrode, KB @ Ti 3 C 2 T x was coated on the separator to serve as an intermediate layer (about 3 μm). Due to the minimum thickness and weight ratio, the intermediate layer does not sacrifice volume / weight energy density. However, it will delay and activate the dissolved polysulfide, thereby increasing the utilization rate of total sulfur. By combining a robust KB / S @ Ti 3 C 2 T x negative electrode and an effective KB @ Ti 3 C 2 T x modified separator, we obtained a stable Li-S battery with a relatively poor electrolyte High sulfur surface load.

Literature link:

https://doi.org/10.1007/s40820-020-00449-7

Source: MXene Frontier