It is well known that when synthesized at 900°C, LiMn0.5Ni0.5O2 features a layered structure.6 The existence of lithated-spinel like LiMn0.5Ni0.5O2 at low temperature (400°C) immediately raise another question: How does the synthesis temperature affect the structure and electrochemical performance of LiMn0.5Ni0.5O2? We synthesized a series of different temperature of LiMn0.5Ni0.5O2 powders. By collecting high energy X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) data, we confirm that, the LiMn0.5Ni0.5O2 exhibits a lithated spinel → disordered layered → ordered layered structure transformation as temperature increase from 400-900 °C. The Rietveld refinements results also reveals a gradual decrease of the Li/Ni exchange ratio accompanied by the synthesis temperature changes. The evolution of specific discharge capacity for different temperature LiMn0.5Ni0.5O2 shows a parabola-like curve behavior with the lowest discharge capacity at 700 °C. This unique behavior is likely to be related to the diffusion channels reconstruction along with the structure changes. 3D diffusion channels are incorporated with 2D diffusion channels at low temperature (400°C) for lithated-spinel LiMn0.5Ni0.5O2. Within the middle temperature range (500°C-700°C), the 3D channels destroy rapidly while 2D diffusion channels are not well established due to the highly disorder ratio resulting in a decrease of capacity. At higher temperature (800-900°C), the 2D diffusion channels are more well established enabling an increase of the capacity.
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