Phase Transformations and Charge Ordering during Li+ Intercalation into Hollandite-Type TiO2 Studied by Operando Synchrotron X-ray Powder Diffractionстатья
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Аннотация:Hollandite‐type TiO2 with uniform submicron‐sized particles was prepared using the treatment of K1.2Ti8O16 by KBrO3 in an H2SO4 solution. The electrode material exhibited a 150 mAh g–1 reversible capacity with an average working potential of 1.75 V vs. Li/Li+. Phase transformations taking place during Li+ (de)intercalation were studied by means of synchrotron X‐ray powder diffraction in operando regime. The lowering of symmetry from tetragonal I4/m to monoclinic I2/m at the beginning of the lithiation was observed. The monoclinic distortion was driven by the Ti3+/Ti4+ charge ordering and the location of the Li+ cations at the hollandite tunnel walls in the five‐fold oxygen coordination. The opposite variation of a and b unit cell parameters during charge‐discharge resulted in a negative overall volume change of –1 % at the lithiated state compared to the initial oxide phase. This value is several times lower than the values for other TiO2 polymorphs such as rutile, anatase or TiO2(B) are.