Cobalt-free spinel-layered structurally integrated Li 0.8 Mn 0.64 Ni 0.183 Fe 0.091 O 2 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)center dot 0.4(LiFe0.2Mn1.4Ni0.4O4) which can otherwise be written as Li 0.8 Mn 0.64 Ni 0.183 Fe 0.091 O 2 (FeSL) are synthesized via simple citric acid-assisted sol-gel route. Four different final annealing temperatures (550 degrees C, 650 degrees C, 750 degrees C, and 850 degrees C) were chosen to investigate their influence on electrochemical performance. The obtained composite materials contain spinel (space group Fd 3 m ) as well as Li-rich layered phases (space group C 2/ 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.