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To accommodate the decreasing lithium resource and ensure continuous development of energy storage industry, sodium-based batteries are widely studied to inherit the next generation of energy storage devices. In this work, a novel Na super ionic conductor type KTi2(PO4)3/carbon nanocomposite is designed and fabricated as sodium storage electrode materials, which exhibits considerable reversible capacity (104 mAh g−1 under the rate of 1 C with flat voltage plateaus at ≈2.1 V), high-rate cycling stability (74.2% capacity retention after 5000 cycles at 20 C), and ultrahigh rate capability (76 mAh g−1 at 100 C) in sodium ion batteries. Besides, the maximum ability for sodium storage is deeply excavated by further investigations about different voltage windows in half and full sodium ion cells. Meanwhile, as cathode material in sodium-magnesium hybrid batteries, the KTi2(PO4)3/carbon nanocomposite also displays good electrochemical performances (63 mAh g−1 at the 230th cycle under the voltage window of 1.0-1.9 V). The results demonstrate that the KTi2(PO4)3/carbon nanocomposite is a promising electrode material for sodium ion storage, and lay theoretical foundations for the development of new type of batteries. [ABSTRACT FROM AUTHOR]

Na3V2(PO4)3 (NVP) is regarded as a promising cathode for advanced sodium-ion batteries (SIBs) due to its high theoretical capacity and stable sodium (Na) super ion conductor (NASICON) structure. However, strongly impeded by its low electronic conductivity, the general NVP delivers undesirable rate capacity and fails to meet the demands for quick charge. Herein, a novel and facile synthesis of layer-by-layer NVP@reduced graphene oxide (rGO) nanocomposite is presented through modifying the surface charge of NVP gel precursor. The well-designed layered NVP@rGO with confined NVP nanocrystal in between rGO layers offers high electronic and ionic conductivity as well as stable structure. The NVP@rGO nanocomposite with merely ≈3.0 wt% rGO and 0.5 wt% amorphous carbon, yet exhibits extraordinary electrochemical performance: a high capacity (118 mA h g−1 at 0.5 C attaining the theoretical value), a superior rate capability (73 mA h g−1 at 100 C and even up to 41 mA h g−1 at 200 C), ultralong cyclability (70.0% capacity retention after 15 000 cycles at 50 C), and stable cycling performance and excellent rate capability at both low and high operating temperatures. The proposed method and designed layer-by-layer active nanocrystal@rGO strategy provide a new avenue to create nanostructures for advanced energy storage applications. [ABSTRACT FROM AUTHOR]