Polymeric nanomaterials emerge as key building blocks for engineering materials in a variety of applications. In particular, the high modulus polymeric nanofibers are suitable to prepare flexible yet strong membrane separators to prevent the growth and penetration of lithium dendrites for safe and reliable high energy lithium metal-based batteries. High ionic conductance, scalability, and low cost are other required attributes of the separator important for practical implementations. Available materials so far are difficult to comply with such stringent criteria. Here, we demonstrate a high-yield exfoliation of ultrastrong poly(p-phenylene benzobisoxazole) nanofibers from the Zylon microfibers. A highly scalable blade casting process is used to assemble these nanofibers into nanoporous membranes. These membranes possess ultimate strengths of 525 MPa, Young's moduli of 20 GPa, thermal stability up to 600 °C, and impressively low ionic resistance, enabling their use as dendrite-suppressing membrane separators in electrochemical cells. With such high-performance separators, reliable lithium-metal based batteries operated at 150 °C are also demonstrated. Those polyoxyzole nanofibers would enrich the existing library of strong nanomaterials and serve as a promising material for large-scale and cost-effective safe energy storage.

The application of lithium−sulfur (Li−S) batteries is severely hampered by the shuttle effect and sluggish redox kinetics. Herein, amorphous cobalt phosphide grown on a reduced graphene oxide-multiwalled carbon nanotube (rGO-CNT-CoP(A)) is designed as the sulfur host to conquer the above bottlenecks. The differences between amorphous cobalt phosphide (CoP) and crystalline CoP on the surface adsorption as well as conversion of lithium polysulfides (LiPSs) are investigated by systematical experiments and densityfunctional theory (DFT) calculations. Specifically, the amorphous CoP not only strengthens the chemical adsorption to LiPSs but also greatly accelerates liquidphase conversions of LiPSs as well as the nucleation and growth of Li 2 S. DFT calculation reveals that the amorphous CoP possesses higher binding energies and lower diffusion energy barriers for LiPSs. In addition, the amorphous CoP features reduced energy gap and the increased electronic concentrations of adsorbed LiPSs near Fermi level. These characteristics contribute to the enhanced chemisorption ability and the accelerated redox kinetics. Simultaneously, the prepared S/rGO-CNT-CoP(A) electrode delivers an impressive initial capacity of 872 mAh g −1 at 2 C and 617 mAh g −1 can be obtained after 200 cycles, exhibiting excellent cycling stability. Especially, it achieves outstanding electrochemical performance even under high sulfur loading (5.3 mg cm −2 ) and lean electrolyte (E/S = 7 μL E mg −1 S ) conditions. This work exploits the application potential for amorphous materials and contributes to the development of highly efficient Li−S batteries.

However, the development of Li-S batteries is still facing many challenges, mainly including the insulating properties of S/Li 2 S 2 /Li 2 S, the huge volume changes during cycles as well as the dissolution and shuttle of lithium polysulfides (LiPSs) in the electrolyte. Additionally, the complex multi-electron and multi-phase reactions of sulfur species cause sluggish redox kinetics, which severely limits the battery performance. [2] Furthermore, for the purpose of taking full advantages of high-energy-density of Li-S batteries in practical applications, high sulfur loadings and low amount of electrolyte are necessary. It further increases the electrochemical polarization and aggravates the loss of LiPSs, leading to the inferior cycling stability and low specific capacity. [3] Nowadays, many researches concentrate on the design and optimization of sulfur host to solve the above problems. [4] Carbon materials and metal compounds are generally combined as the sulfur host to construct channels for transferring electrons and ions, adsorb LiPSs and catalyze the conversions of LiPSs. [5] Among the metal compounds, transition metal phosphides (TMPs) have drawn increasing interests because of their excellent electronic conductivity, easily adjustable electronic structure and high catalytic activity. [6] Some studies have shown that TMPs can chemically immobilize LiPSs through M-S and PLi bonds to restrain the shuttle effect and expedite redox kinetics in electrochemical conversions of LiPSs. Chen et al. found that CoP nanoparticles can effectively capture LiPSs and reduce the overpotential of Li 2 S nucleation. [7] Wang et al. demonstrated that MoP nanoparticles can inhibit the formation of "dead sulfur" under lean electrolyte conditions. [8] Qian et al. revealed the best catalytic behavior of CoP among several cobalt-based metal compounds (Co 3 O 4 , CoS 2 , Co 4 N, and CoP). [9] Although some progress has been made in the application of TMPs in Li-S batteries, it is still a challenge to further restrain the shuttle effect and improve the electrochemical kinetics through regulating its electronic structures.Since defect engineering has been shown to effectively tailor the electronic structure of metal compounds, the possibility of tuning the adsorption and electrochemical conversions of LiPSs on the surface of sulfur hosts through anion vacancy Lithium-sulfur batteries have aroused great interest in the context of rechargeable batteries, while the shuttle effect and sluggish conversion kinetics severely handicap their development. Defect engineering, which can adjust the electronic structures of electrocatalyst, and thus affect the surface adsorption and catalytic process, has been recognized as a good strategy to solve the above problems. However, research on phosphorus vacancies has been rarely reported, and how phosphorus vacancies affect battery performance remains unclear. Herein, CoP with phosphorus vacancies (CoP-Vp) is fabricated to study the enhancement mechanism of phosphorus vacancies in Li-S chemistry...

Mixed oxygen ionic and electronic conduction is a vital function for cathode materials of solid oxide fuel cells (SOFCs), ensuring high efficiency and low-temperature operation. However, Fe-based layered double perovskites, as a classical family of mixed oxygen ionic and electronic conducting (MIEC) oxides, are generally inactive toward the oxygen reduction reaction due to their intrinsic low electronic and oxygen-ion conductivity. Herein, Zn doping is presented as a novel pathway to improve the electrochemical performance of Fe-based layered double perovskite oxides in SOFC applications. The results demonstrate that the incorporation of Zn ions at Fe sites of the PrBaFe2O5+δ (PBF) lattice simultaneously regulates the concentration of holes and oxygen vacancies. Consequently, the oxygen surface exchange coefficient and oxygen-ion bulk diffusion coefficient of Zn-doped PBF are significantly tuned. The enhanced mixed oxygen ionic and electronic conduction is further confirmed by a lower polarization resistance of 0.0615 and 0.231 Ω·cm2 for PrBaFe1.9Zn0.1O5+δ (PBFZ0.1) and PBF, respectively, which is measured using symmetric cells at 750 °C. Moreover, the PBFZ0.1-based single cell demonstrates the highest output performance among the reported Fe-based layered double perovskite cathodes, rendering a peak power density of 1.06 W·cm–2 at 750 °C and outstanding stability over 240 h at 700 °C. The current work provides a highly effective strategy for designing cathode materials for next-generation SOFCs.

Protonic ceramic fuel cells (PCFCs) are receiving increasing attention because of their high energy conversion efficiency. However, traditional mixed oxygen-ionic and electronic conductors (MOECs) show sluggish oxygen reduction kinetics when used in PCFCs because of their intrinsic low protonic conductivity. Herein, it is reported that cooperatively regulating the concentration and basicity of oxygen vacancies can result in fast proton transport in MOECs, which is demonstrated in a Zr 4+ -doped Sr 2 Fe 1.5 Mo 0.5 O 6−δ (SFMZ) perovskite. The so-obtained SFMZ perovskite renders plentiful oxygen vacancies and strong hydration ability, which can boost the formation of protonic defects. Furthermore, the chemical diffusion coefficient of protons (D H,chem ) is established first to determine the proton mobility of the cathode. The results indicate that SFMZ exhibits improved proton diffusion kinetics with a D H,chem value of 8.71 × 10 −7 cm 2 s −1 at 700 °C, comparable to the diffusion coefficient of the commonly used protonic electrolyte BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ of 1.84 × 10 −6 cm 2 s −1 . A low polarization resistance of 0.169 Ω cm 2 and a peak power density as high as 0.79 W cm −2 were achieved at 700 °C with the SFMZ cathode. Such excellent performance suggests that rationally tailoring the oxygen vacancy is a feasible strategy to promote proton diffusion in perovskite-structured electrode materials as efficient PCFC cathodes.

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Ni-Doped ZIF-8 (Ni-ZIF-8) not only restrains the shuttling of LiPSs by chemical adsorption but also facilitates the redox reaction kinetics.

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