Na2S in‐situ infiltrated in actived carbon as high‐efficiency presodiation additives for sodium ion hybrid capacitors

Abstract Sodium ion hybrid capacitors (SIHC) are emerging as promising next‐generation energy storage devices with high energy/power density. Presodiation is an essential part of SIHC production due to the lack of sodium sources in the cathode and anode. However, in the current presodiation methods, electrochemical presodiation by galvanostatic current charging and discharging requires a temporary half‐cell or a complex reassembling process, which severely hinders the commercialization of SIHC. Herein, in situ synthesized Na2S infiltrated in activated carbon was used as a sodium salt additive for supplying Na+ in SIHC. Due to a low ratio of Na2S additive attributed to high theoretical specific capacity, the fabricated Na2S/activated carbon composite//HC SIHC can show a higher energy density of 129.71 Wh kg−1 than previously reported SIHC on presodiation of cathode additives. Moreover, the designed SIHC shows an excellent cycling performance of 10,000 cycles, which is attributed to the Na2S additive with the advantages of low decomposition potential and no gas generation. This work provides a novel approach for the fabrication of highly efficient Na2S additive composite cathodes for SIHC

Electrospun Core–Shell Carbon Nanofibers as Free-Standing Anode Materials for Sodium-Ion Batteries

The development of wearable devices requires flexible batteries that can be bent and folded. However, deficiencies in material flexibility, conductivity, and other aspects can affect the performance of a flexible electrode. One-dimensional nanofibers possess high specific surface area, high conductivity, and a 3D network structure that enables them to buffer stress and strain. Consequently, they hold significant potential in the field of electrochemical energy storage as flexible electrode materials. In this study, we utilized polyvinylpyrrolidone (PVP) as a template to form a supramolecular polymer (PNDS) through hydrogen bonding between 1,4,5,8-naphthalene tetracarboxylic acid (NTCA) and 3,3′-diaminobenzidine (DAB) monomers. Through core–shell electrospinning and carbonization, PNDS precursors were used to prepare polybis(benzimidazobenzophenanthroline-dione) (BBB)-based carbon nanofibers featuring a core–shell structure. The BBB polymer, featuring a continuous aromatic ring structure, undergoes conversion into a highly graphitic carbon skeleton upon carbonization at 1000 °C. This transformation enhances the conductivity of flexible electrodes, improves the current collection effect under high currents, and ensures stability in the charge–discharge cycle. The iron-containing polymers within the shell layer ultimately transform into iron oxide and iron carbide nanoparticles encapsulated within the carbon fibers, compensating for the lower specific capacity characteristic of pure carbon materials. Serving as a SIB flexible anode, the specific capacity can achieve 250 mAh g–1 after 950 cycles at 0.2 A g–1, with negligible attenuation throughout the cycling process. This study demonstrates that BBB-based carbon nanofibers featuring core–shell structures exhibit excellent electrochemical performance while retaining flexibility, presenting clear advantages over traditional electrodes characterized by complicated processes and limited active substance content