Polypyrrole/Graphene Composite Interlayer: High Redox Kinetics of Polysulfides and Electrochemical Performance of Lithium–Sulfur Batteries Enabled by Unique Pyrrolic Nitrogen Sites

Modification and Functionalization of Separators for High Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSB) have been recognized as a prominent potential next-generation energy storage system, owing to their substantial theoretical specific capacity (1675 mAh g-1) and high energy density (2600 Wh kg-1). In addition, sulfur's abundance, low cost, and environmental friendliness make commercializing LSB feasible. However, challenges such as poor cycling stability and reduced capacity, stemming from the formation and diffusion of lithium polysulfides (LiPSs), hinder LSB's practical application. Introducing functional separators represents an effective strategy to surmount these obstacles and enhance the electrochemical performance of LSBs. Here, we have conducted a comprehensive review of recent advancements in functional separators for LSBs about various (i) carbon and metal compound materials, (ii) polymer materials, and (iii) novel separators in recent years. The detailed preparation process, morphology and performance characterization, and advantages and disadvantages are summarized, aiming to fundamentally understand the mechanisms of improving battery performance. Additionally, the development potential and future prospects of advanced separators are also discussed.

Conductive Polymer-Based Interlayers in Restraining the Polysulfide Shuttle of Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are considered a promising candidate for next-generation energy storage devices due to the advantages of high theoretical specific capacity, abundant resources and being environmentally friendly. However, the severe shuttle effect of polysulfides causes the low utilization of active substances and rapid capacity fading, thus seriously limiting their practical application. The introduction of conductive polymer-based interlayers between cathodes and separators is considered to be an effective method to solve this problem because they can largely confine, anchor and convert the soluble polysulfides. In this review, the recent progress of conductive polymer-based interlayers used in LSBs is summarized, including free-standing conductive polymer-based interlayers, conductive polymer-based interlayer modified separators and conductive polymer-based interlayer modified sulfur electrodes. Furthermore, some suggestions on rational design and preparation of conductive polymer-based interlayers are put forward to highlight the future development of LSBs.

Construction of Polypyrrole-Coated CoSe2 Composite Material for Lithium-Sulfur Battery

Lithium-sulfur batteries with high theoretical energy density and cheap cost can meet people's need for efficient energy storage, and have become a focus of the research on lithium-ion batteries. However, owing to their poor conductivity and "shuttle effect", lithium-sulfur batteries are difficult to commercialize. In order to solve this problem, herein a polyhedral hollow structure of cobalt selenide (CoSe₂) was synthesized by a simple one-step carbonization and selenization method using metal-organic bone MOFs (ZIF-67) as template and precursor. CoSe₂ is coated with conductive polymer polypyrrole (PPy) to settle the matter of poor electroconductibility of the composite and limit the outflow of polysulfide compounds. The prepared CoSe₂@PPy-S composite cathode shows reversible capacities of 341 mAh g^-1 at 3 C, and good cycle stability with a small capacity attenuation rate of 0.072% per cycle. The structure of CoSe₂ can have certain adsorption and conversion effects on polysulfide compounds, increase the conductivity after coating PPy, and further enhance the electrochemical property of lithium-sulfur cathode material.