In Situ TEM Studies of Sodium Polysulfides Electrochemistry in High Temperature Na-S Nanobatteries

In Situ Device-Level TEM Characterization Based on Ultra-Flexible Multilayer MoS2 Micro-Cantilever

Current state-of-the-art in situ transmission electron microscopy (TEM) characterization technology has been capable of statically or dynamically nanorobotic manipulating specimens, affording abundant atom-level material attributes. However, an insurmountable barrier between material attributes investigations and device-level application explorations exists due to immature in situ TEM manufacturing technology and sufficient external coupled stimulus. These limitations seriously prevent the development of in situ device-level TEM characterization. Herein, a representative in situ opto-electromechanical TEM characterization platform is put forward by integrating an ultra-flexible micro-cantilever chip with optical, mechanical, and electrical coupling fields for the first time. On this platform, static and dynamic in situ device-level TEM characterizations are implemented by utilizing molybdenum disulfide (MoS₂ ) nanoflake as channel material. E-beam modulation behavior in MoS₂  transistors is demonstrated at ultra-high e-beam acceleration voltage (300 kV), stemming from inelastic scattering electron doping into MoS₂  nanoflakes. Moreover, in situ dynamic bending MoS₂  nanodevices without/with laser irradiation reveals asymmetric piezoresistive properties based on electromechanical effects and secondary enhanced photocurrent based on opto-electromechanical coupling effects, accompanied by real-time monitoring atom-level characterization. This approach provides a step toward advanced in situ device-level TEM characterization technology with excellent perception ability and inspires in situ TEM characterization with ultra-sensitive force feedback and light sensing.

Recent Progress in Rechargeable Sodium Metal Batteries: A Review

Sodium metal batteries (SMBs) have been widely studied owing to their relatively high energy density and abundant resources. However, they still need systematic improvement to fulfill the harsh operating conditions for their commercialization. In this review, we summarize the recent progress in SMBs in terms of sodium anode modification, electrolyte exploration, and cathode design. Firstly, we give an overview of the current challenges facing Na metal anodes and the corresponding solutions. Then, the traditional liquid electrolytes and the prospective solid electrolytes for SMBs are summarized. In addition, insertion- and conversion-type cathode materials are introduced. Finally, an outlook for the future of practical SMBs is provided.

A Review on the Construction of Carbon-Based Metal Compound Composite Cathode Materials for Room Temperature Sodium-Sulfur Batteries

Room temperature sodium-sulfur batteries are one of the most attractive energy storage systems due to their low cost, environmental friendliness, and ultra-high energy density. However, due to the inherent slow redox kinetics and the shuttle of polysulfides, the road of room temperature sodium-sulfur batteries to practical application is still full of difficulties. As a sulfur cathode, which is directly related to battery performance, a lot of research efforts have been devoted to it and many strategies have been proposed to solve the shuttle effect problem of sulfur cathodes. This paper analyzes the existing problems and solutions of sodium-sulfur batteries, mainly discusses and summarizes the research progress of constructing carbon-based cathode materials for sodium-sulfur batteries, and expounds the current research popular from two main directions. That is to construct advanced cathode materials based on two mechanisms of adsorption and electrocatalysis. Finally, the research direction of advanced sodium-sulfur batteries is prospected.

Unraveling the Conversion Evolution on Solid-State Na-SeS2 Battery via In Situ TEM

All-solid-state (ASS) Na-S batteries are promising for a large-scale energy-storage system owing to numerous merits. However, the high conversion reaction barrier impedes their practical application. In this work, the basic mechanism on how Se catalyzes the conversion reaction in the Na-S batteries is unraveled. The sodiation/desodiation of Na-SeS2 nanobatteries are systematically evaluated via in situ transmission electron microscopy (in situ TEM) with a microheating device. The real-time analyses reveal an amorphous Na-Sex Sy intermediate phase appears during the direct conversion from SeS2 to Na2 S, and a reverse reaction succeeds at 100 °C with a prior formation of Se. The absence of polysulfides and a much lower desodiation temperature in contrast to Na-S nanobatteries demonstrate that the Se incorporation significantly lowers the conversion reaction barrier. According to these findings, the ASS SeS2 batteries using a Na3 SbS4 solid electrolyte (SE) are assembled using various SE:C ratios in the composite cathodes to investigate the effect of the ion and electron transport on the electrochemical properties, including the effective transport properties, MacMullin number, and the tortuosity factor. The obtained results in turn confirm the findings from the in situ TEM. These findings are applicable to optimize other S-based active materials and improve their utilization.