The synthesis of shape-controlled crystals has been a highly attractive research topic in modern materials chemistry. In this work, the growth of Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 (NCM) crystals in molten sulfate or carbonate salts (flux) at 1000 °C was systematically studied under various conditions. In situ X-ray diffraction during the growth and thermogravimetry-differential thermal analysis revealed that the growth of NCM crystals in the flux was controlled by liquid-phase sintering according to the Ostwald ripening principle. We studied the effect of Na + in the flux on the crystal shapes and found that Na + was critical in forming octahedral crystals with well-developed facets. Single crystals with well-developed facets were obtained homogeneously from Na 2 SO 4 , while truncated polyhedral crystals of smaller size were obtained from Li 2 SO 4 . The shape-controlled NCM crystals showed discharge capacities approaching 160 mAh g −1 in the operating voltage range of 2.8−4.4 V vs Li/Li + under a low current density of 0.1 C, independent of flux composition. This suggests that the Li + and transition-metal ions in the individual NCM crystals were highly ordered into hexagonal arrangements belonging to the R3̅ m space group, without cation mixing.
Small amounts of fluorine substituting for oxygen deficiencies could reduce Mn dissolution, enhancing the cyclability in spinel-type lithium nickel manganese oxides (LiNi 0.5 Mn 1.5 O 4). Fluorine anion incorporation simultaneously enhances the Crate capability and specific capacity fading. We used experimental and theoretical approaches to obtain a full picture of the mixedanion effects for LiNi 0.5 Mn 1.5 O 4 − x F x cathode materials. The fluorine anion reduced the activation barrier for lithium-ion hopping along the most energetically preferable 8a-16c-8a route, enhancing the Crate capability. Simultaneously, the coordination bond of the linear F −-Mn 3+-F − (Mn@2F diagonal) arrangement increased the oxidation potential to 5.1 V (vs Li + /Li). This hampered full extraction of Li + from the spinel lattice, which was triggered by the oxidation of Mn 3+ below the cutoff voltage (3.5-4.8 V (vs Li + /Li)), leading to a capacity loss.
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