Electrochemical Insights, Developing Strategies, and Perspectives toward Advanced Potassium-Sulfur Batteries.

The boosting demand for high-capacity energy storage systems requires innovative battery technologies with low-cost and sustainability. The advancement of potassium-sulfur (K-S) batteries have been triggered recently due to abundant resource and cost effectiveness. However, the functional performance of K-S batteries is fundamentally restricted by the vague understanding of K-S electrochemistry and the imperfect cell components or architectures, facing the issues of low cathode conductivity, intermediate shuttle loss, poor anode stability, electrode volume fluctuation, etc. Inspired by considerable research efforts on rechargeable metal-sulfur batteries, the holistic K-S system can be stabilized and promoted through various strategies on rational physical regulation and chemical engineering. In this review, first an attempt is made to address the electrochemical kinetic concept of K-S system on the basis of the emerging studies. Then, the classification of performance-improving strategies is thoroughly discussed in terms of specific battery component and prospective outlooks in materials optimization, structure innovations, as well as relevant electrochemistry are provided. Finally, the critical perspectives and challenges are discussed to demonstrate the forward-looking developmental directions of K-S batteries. This review not only endeavors to provide a deep understanding of the electrochemistry mechanism and rational designs for high-energy K-S batteries, but also encourages more efforts in their large-scale practical realization.

Feasible Catalytic-Insoluble Strategy Enabled by Sulfurized Polyacrylonitrile with In Situ Built Electrocatalysts for Ultrastable Lithium-Sulfur Batteries.

To date, elemental sulfur has been considered as a prospective cathode material for exploring high-energy power systems with low cost and sustainability. However, its practical commercialization has been impeded by inherent drawbacks of notorious capacity decay, unsatisfied insulating nature, and sluggish conversion chemistry. To address these issues, for the first time, freestanding nanofibrous networks with hierarchical nanostructures are facilely constructed by inlaying electrocatalytic bimetallic chalcogenides (FexMn1-xS nanoparticles) into conductive graphene nanosheet (GN)-doped sulfurized polyacrylonitrile (SPAN) fiber matrices. Covalent-bonded SPAN featuring an insoluble mechanism serves as a reliable cathode substrate with enhanced electrostability and high sulfur utilization, while high-surface-area GN dopants promote conductivity improvement and rapid electron transfer. Meanwhile, the results prove that sulfiphilic FexMn1-xS nanoparticles with abundant electrochemically active sites facilitate construction of uniform deposition interfaces and efficient electrocatalysis conversion toward lithium polysufides. This feasible catalytic-insoluble cathode strategy drives the Li-S battery, which exhibits excellent electrochemical performances with a remarkable reversible discharge capacity of 967 mA h g-1 and a capacity retention of 623 mA h g-1 after 500 cycles. Moreover, the corresponding lithiation/delithiation mechanisms are systematically investigated through complementary morphological and spectral analyses, providing valuable insights into advanced metal-sulfur batteries.

Rapid In Situ Polymerization of Polyacrylonitrile/Graphene Oxide Nanocomposites as Precursors for High-Strength Carbon Nanofibers.

Graphene oxide (GO) has been widely used as an additive of polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) to optimize its crystal structure and improve the mechanical performances of nanofibers. However, the homogeneous dispersion of GO nanosheets among entangled PAN molecular chains is always challenging, and the poor dispersion of GO severely limits its positive effects on both the structure and performances of CNFs. Considering this issue, this paper provides for the first time an effective solution to achieve rapid and uniform introduction of GO in PAN-based nanofibers via in situ polymerization, and the optimization of the nanofiber structure by GO is systematically studied in three consecutive stages (polymerization, electrospinning, and carbonization) of the production process. During in situ polymerization, PAN is tightly attached on GO nanosheets to form PAN/GO nanocomposites, and this interaction is maintained throughout the spinning process. Not only the arrangement of PAN molecular chains but also the crystal size of the final turbostratic structure of CNFs is considerably improved by the interaction between PAN and GO. Besides, the direct proof that GO nanosheets promote the crystallization and orientation of the nanofiber matrix is presented. As a result, the tensile strength of CNFs is remarkably increased by 2.45 times with 0.5 wt % addition of GO. In summary, this paper provides a method for efficiently introducing nanoscale additives into PAN-based nanofibers and gives insights into the production of high-performance CNFs with the addition of GO.