Cobalt-free spinel–layered structurally integrated Li0.8Mn0.64Ni0.183Fe0.091O2 cathodes for lithium-ion batteries

Cobalt-free, Li-rich layered-spinel structurally integrated positive electrode (cathode) materials for lithium-ion batteries (LIBs), with nominal composition 0.6(Li1.2Mn0.56Fe0.08Ni0.16O2)∙0.4(LiFe0.2Mn1.4Ni0.4O4) which can otherwise be written as Li0.8Mn0.64Ni0.183Fe0.091O2 (FeSL) are synthesized via simple citric acid-assisted sol-gel route. Four different final annealing temperatures (550 °C, 650 °C, 750 °C, and 850 °C) were chosen to investigate their influence on electrochemical performance. The obtained composite materials contain spinel (space group Fd3¯m) as well as Li-rich layered phases (space group C2/m) as revealed by X-ray diffraction (XRD), HRTEM and cyclic voltammetry investigations. The excellent electrochemical performance of the composite material could be attributed to the structural stability achieved by the integration of spinel and layered components. Selected synthesized composite materials exhibit high discharge capacities close to 200 mAh g‐1. The FeSL750 shows better capacity retention (92(3)% at the 50th cycle and 82(5)% at the 70th cycle) and rate capability than the FeSL550 and FeSL650 samples. However, the FeSL850 sample shows different charge-discharge behaviour. The charge capacity corresponding to FeSL850 is found to increase up to the 20th cycle, then stabilizes and displays a capacity retention of almost 100 % at the 50th cycle and 91(1)% at the 70th cycle. The electrochemical mechanism of FeSL750 was elucidated via in operando XAS investigations, which reveal electrochemical activity from all transition metals. [Display omitted] •Synthesized Cobalt free Li-rich layered-Spinel structurally integrated 0.6(Li1.2Mn0.56Fe0.08Ni0.16O2) · 0.4(LiFe0.2Mn1.4Ni0.4O4) material (overall composition Li0.8Mn0.64Ni0.183Fe0.091O2) at various annealing temperatures.•In-depth X-ray Diffraction (Rietveld refinement) analysis confirms the co-existence of Li-rich layered and spinel components. The corresponding phase fractions are quantified.•The co-existence of the Li-rich layered and spinel components in the material is further confirmed from the high-resolution transmission electron microscopy (HRTEM) investigations.•The oxidation state distribution of transition metals present in the material bulk are revealed using ex situ XAS and the electrochemical mechanism was elucidated using in operando XAS.•The material annealed at 750 °C show a specific capacity of ~200 mAh g-1 with a capacity retention of 92% after 50 cycles.