Reducing charge−discharge overpotential of transition metal oxide catalysts can eventually enhance the cell efficiency and cycle life of Li−O 2 batteries. Here, we propose that crystal phase engineering of transition metal oxides could be an effective way to achieve the above purpose. We establish controllable crystal phase modulation of the binary Mn x Co 1−x O by adopting a cation regulation strategy. Systematic studies reveal an unprecedented relevancy between charge overpotential and crystal phase of Mn x Co 1−x O catalysts, whereas a dramatically reduced charge overpotential (0.48 V) via a rational optimization of Mn/Co molar ratio = 8/2 is achieved. Further computational studies indicate that the different morphologies of Li 2 O 2 should be related to different electronic conductivity and binding of Li 2 O 2 on crystal facets of Mn x Co 1−x O catalysts, finally leading to different charge overpotential. We anticipate that this specific crystal phase engineering would offer good technical support for developing highperformance transition metal oxide catalysts for advanced Li−O 2 batteries.
ZnO is a promising anode material for lithium-ion batteries (LIBs); however, its practical application is hindered primarily by its large volume variation upon lithiation. To overcome this drawback, we synthesized ZnO/graphene composites using the combination of a simple hydrothermal reaction and spray drying. These composites consisted of well-dispersed ZnO nanorods anchored to graphene. The folded three-dimensional graphene spheres provided a high conductivity, high surface area, and abundant defects. LIB with an anode composed of our novel ZnO/graphene material demonstrated a high initial discharge capacity of 1583 mAh g−1 at 200 mA g−1.
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