Nitrogen-doped carbon (CN x ) nanostructures are appealing metal-free electrocatalysts for some key electrochemical processes such as oxygen reduction reaction (ORR), due to their low cost, exceptional stability, and desirable selectivity. However, the precise configuration engineering of N-related active sites still remains a big challenge. Herein, we report a concept of monovacancy coupled pyridinic N (MV-c-PN) active site, which is designed and successfully fabricated by the pyrolysis of welldesigned precursor. This unique active site couples the features of pyridinic N and topological monovacancy defect, synergistically tuning the electronic properties of CN x moiety. This tuning induces stronger adsorption of oxygen-containing intermediates on the MV-c-PN sites and alters the ORR kinetics pathway. Additionally, the hierarchical porous nature of CN x nanostructure facilitates the penetration of electrolyte and the transportation of O 2 . Accordingly, the CN x nanomaterial with such MV-c-PN sites shows outstanding ORR activity in alkaline solution, surpassing most of the reported metal-free catalysts, with its intrinsic turnover frequency (TOF) 7.26 times higher than conventional pyridinic N. The assembled zinc-air battery reaches a maximum power density even 40.3% higher than that with the benchmark Pt/C. Our fine configuration engineering of CN x active sites provides a novel strategy for developing efficient carbon-based metal-free ORR catalysts.

A widely adopted strategy to enhance the electronic conductivity of lithium transition metal phosphates is to form a phosphate/C composite by introducing reagents (carbon sources) that can transform to carbon during calcination. In the present work, a systematic study combining X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, solid-state nuclear magnetic resonance, and electrochemical measurements was conducted to investigate how the electrostatic interaction between the functional groups (carboxyl, hydroxyl, etc.) of a carbon source and the building units of Li3V2(PO4)3 (Li+, VO2+, PO4 3–, etc.) in the original precursor affects the structure of a Li3V2(PO4)3–carbon interface in the final composite. It was demonstrated that the types and concentrations of electronegative functional groups in a carbon source play an important role in controlling not only the morphology of the product but also the composition, crystallinity and microstructure of the Li3V2(PO4)3–carbon interface and, in turn, the electrochemical behavior of the Li3V2(PO4)3/C composite. This study provides guidance on carbon–lithium transition metal phosphate interface design and control.

Combining XRD with 31P NMR, it is demonstrated that the Mg and Cl atoms of the new Mg and Cl co-doped Li3V2(PO4)3/C material occupy V and O sites in its structure, respectively.

Supreme high rate cycling performance can be achieved by optimizing the composition of LVP electrode.

The electrochemical properties of Li3V2(PO4)3 (LVP) cathode of lithium ion batteries are often improved by ion doping. Nevertheless, the mechanism of ion doping has not been fully understood. Here, Ti4+ has been chosen as a typical dopant with similar atomic radius to the six-coordinated V3+. A series of Li3Ti x V(2–x)(PO4)3/C samples are successfully synthesized by a sol–gel route. The 7Li MAS NMR spectra of the LT x VP/C demonstrate that the doping of Ti4+ can enhance the mobility of Li ions. The results of electrochemical properties tests show that moderate Ti4+ doping is able to improve the high rate capability of the materials by increasing the electronic conductivity and Li-ion diffusion coefficient. The optimal sample (LT0.08VP/C) exhibits the best cycling behavior and rate capability, which can deliver 110.85 mAh/g and capacity retention of 99.36% at 10 C after 100 cycles. Electrochemical impedance spectroscopy results indicate that LT0.08VP/C possesses the minimum charge transfer resistance. The calculation results of cyclic voltammetry illustrate that the Li-ion diffusion coefficient of LT0.08VP/C has been improved. By combining the information extracted from a series of electrochemical characterizations and NMR tests, a structural model of Li+ vacancy is proposed to explain the improving of Li+ mobility.

In the present paper, the physicochemical properties of a novel composite fibrous membrane, based on a mixture of poly(aryl ether sulfone) (PES) and poly(vinylidene fluoride) (PVDF), as separators for lithium‐ion batteries are reported and discussed. Compared with the pure PVDF fibrous membrane, the introduction of PES can decrease the PVDF crystallinity while increasing the proportion of α‐phase. Meanwhile, the initial thermal decomposition temperature is enhanced by 24°C. Heat shrinkage tests and thermomechanical analyzers indicate the composite membrane has significantly improved thermal‐dimensional stability. The shrinkage rate of the composite membrane after heat‐treated at 180°C for 2 hr is only 4.8%, which is far below the Celgard separator (82%) and the pure PVDF fibrous membrane (75%). The composite membrane with excellent wettability demonstrates a high ionic conductivity (1.69 × 10−3 S cm−1) at room temperature as well as high electrolyte uptake (595%). The cells assembled with the composite membrane exhibit more stable cycle performance, capacity retention, and C‐rate capability than that with polyolefin separator. These results suggest that PES/PVDF composite fibrous membrane is an effective separator for high‐performance Lithium‐ion batteries.

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A polyetherimide/polyvinylidene fluoride (PEI/PVDF) coaxial fiber membrane coated with polyethylene (PE) porous microspheres with thermal shutdown function was prepared. The PE porous microspheres created by the suspension dispersion method are composed of a large number of pleated petal structures, which contain abundant pore structures and have a melting point of 108°C. Ionic conductivity test, scanning electron microscope test, open circuit voltage test, and cycle performance test show that the composite membrane with PE microspheres layer can effectively close the pore structure at 110°C and stop the battery reaction. The thermal stability test shows that the composite membrane does not shrink at 210°C, the thermal shutdown temperature window is as high as 100°C, and the PE coating can significantly improve the high temperature thermal dimensional stability of the membrane. Thanks to the porous microstructure of PE microspheres and the good electrolyte affinity of the PVDF skin layer, the PE composite membrane has good electrolyte wetting and uptake capabilities. The battery assembled by the PE composite membrane has a capacity retention rate of 88.6% after 100 cycles at 0.5 C and has excellent C‐rate capability.