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Defect engineering is an important approach to enhancing the catalytic activity of a material, but there have been few reported controllable experiments due to the lack of systematic and comprehensive understanding of the effects of defects. For nanocarbon catalysts, it is still a challenge to prepare both atom-doped and defect-engineered catalysts with the desired more effective active centers, which requires an in-depth understanding of both experiment and theory. Herein, a topological rich-vacancy-defect nitrogen-doped nanocarbon (TRNC) material is constructed in situ via a simple magnesiothermic technology. It exhibits remarkable oxygen catalytic performance, which can be compared to the best metal-free bifunctional carbon electrocatalysts reported, even better than that of commercial noble-metal RuO2. Combined with density functional theory (DFT) calculations, the carbon vacancy defects with edge nitrogen doping as intrinsic active sites were found to exhibit excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. When used practically as a catalyst in Li–O2 batteries, with a capacity restriction of 500 mA h g−1, it displays a long cycling and high rate durability of over 300 cycles at 200 mA g−1. This excellent performance arises from the three-dimensional topological rich-vacancy-defect nitrogen-doped nanocarbon. The effects of vacancy sites and nitrogen doping were probed via first-principles simulations to clarify the catalytic mechanisms which contribute to this superior performance. [ABSTRACT FROM AUTHOR]

Current electrode materials for commercial lithium ion batteries (LIBs) suffer from poor low temperature electrochemical performance, which seriously limits their application in winter and cold climate areas. Herein, pure phase LISICON structured Li3V2(PO4)3 (r-LVP) was successfully prepared and investigated for the first time as a low temperature cathode for LIBs. Benefiting from a fast ionic conductive structure and high structural stability, the r-LVP exhibits an outstanding high rate performance in a wide temperature range from 25 °C to −20 °C. Even at −30 °C, a discharge capacity of 90 mA h g−1 at 0.2C can be achieved, corresponding to 80% of the room temperature capacity. After 5000 cycles at a high rate of 10C, 84% of the initial capacity can be retained at −10 °C. Such a high rate capability and long cycle stability promise r-LVP could be a competitive candidate for low temperature LIBs. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) are considered to be a promising alternative to lithium ion batteries because of the high abundance of sodium. However, the scarcities of suitable anode materials severely hamper the development of SIBs. Here, we synthesized a GeP5/C composite with binary sodium-reactive components on a large scale. Theoretically, it can promise a capacity of 1888 mA h g−1 or 6891 mA h cm−3, which is the best record in anodes for SIBs reported so far. In practice, the GeP5/C showed a low potential of ≈0.4 V vs. Na+/Na with a smooth charge/discharge profile. It delivered a large reversible capacity of 1250 mA h g−1 with a first coulombic efficiency of 93%. Electrochemical-mechanism studies suggested that the formation of a GeP5 phase endowed a high first coulombic efficiency and synergetic effect between the sodiation of Ge and P. This effect smoothly leveled the multistep plateaus and effectively reduced the polarization between charge/discharge. When applied to a full cell by coupling a Na3V2(PO4)3/C cathode, the assembled Na3V2(PO4)3//GeP5 full cell showed a large capacity of 800 mA h g−1 with a high average output voltage of 2.65 V. The excellent sodium-storage performances of GeP5/C will ensure commercial utilization in future SIBs. [ABSTRACT FROM AUTHOR]