No abstract

Manganese oxide (Mn3O4) is of great potential for lithium storage based on conversion reactions, but its application in rechargeable lithium batteries is severely hindered by the low electric conductivity and large volume variation during lithiation/delithiation. Herein, a biomimetic ear‐of‐wheat‐like nanocomposite of ultrafine Mn3O4 nanoparticles (MONPs) and multi‐walled carbon nanotubes (MWCNTs) is prepared using a facile solvothermal method. The tightly packed MONP “cereal‐grains” are directly grown and uniformly interspersed on the outer surface of skeleton MWCNT “central stems.” The ultrafine MONPs are favorable to lithium incorporation/extraction while the interconnected MWCNT skeletons provide a highly conducting network for electron transportation. Consequently, a high reversible capacity of 810 mA h g−1 is obtained at the current density of 40 mA g−1. After 50 cycles at 160 mA g−1, the nanocomposite still delivers a capacity up to 796 mA h g−1, which is higher than twice of that of pure Mn3O4 nanopowders. The unique nanostructure and the facile biomimetic method can be widely extended to design and explore various high‐performance energy materials for lithium/sodium ion batteries and fuel cells.

The abundant reserves of sodium resources and its low price make the desire to build energy storage systems on room-temperature rechargeable sodium batteries. The current challenge exists in exploring high-performance key materials, especially cathode materials. Vanadium-based phosphates have attracted extensive attention as a class of promising cathode materials for sodium batteries due to their stable structure, large capacity, and high voltage advantages. In this paper, sodium vanadium oxyfluorophosphate, Na3V2(PO4)2F3–2y O2y (0 ≤ y < 1), is exploited to improve its electrochemical performance through oxygen tuning. The effect of oxygen amount on the structure, morphology, and performance is comprehensively and comparatively investigated. It is found that the optimal electrochemical performance is achieved in Na3V2(PO4)2F2O when y = 0.5. Its specific discharge capacity at 0.1, 0.5, 1, 8, and 20 C is 125, 111, 101, 71, and 58 mA h g–1, respectively. The superior rate performance and good cyclability are ascribed to the low impurity, mixed V3+/V4+ valence state, small particle size, suitable residual carbon coating, low charge transfer resistance, fast Na+ diffusion, and particularly the regulation of charge/discharge potentials as well as polarizations due to proper oxygen tuning.