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.