Phase Transitions in the “Spinel-Layered” Li(1+x)Ni(0.5)Mn(1.5)O(4) (x = 0, 0.5, 1) Cathodes upon (De)lithiation Studied with Operando Synchrotron X-ray Powder Diffraction

“Spinel-layered” Li(1+x)Ni(0.5)Mn(1.5)O(4) (x = 0, 0.5, 1) materials are considered as a cobalt-free alternative to currently used positive electrode (cathode) materials for Li-ion batteries. In this work, their electrochemical properties and corresponding phase transitions were studied by means of synchrotron X-ray powder diffraction (SXPD) in operando regime. Within the potential limit of 2.2–4.9 V vs. Li/Li(+) LiNi(0.5)Mn(1.5)O(4) with cubic spinel type structure demonstrates the capacity of 230 mAh·g(−1) associated with three first-order phase transitions with significant total volume change of 8.1%. The Li(2)Ni(0.5)Mn(1.5)O(4) material exhibits similar capacity value and subsequence of the phase transitions of the spinel phase, although the fraction of the spinel-type phase in this material does not exceed 30 wt.%. The main component of Li(2)Ni(0.5)Mn(1.5)O(4) is Li-rich layered oxide Li(Li(0.28)Mn(0.64)Ni(0.08))O(2), which provides nearly half of the capacity with very small unit cell volume change of 0.7%. Lower mechanical stress associated with Li (de)intercalation provides better cycling stability of the spinel-layered complex materials and makes them more perspective for practical applications compared to the single-phase LiNi(0.5)Mn(1.5)O(4) high-voltage cathode material.