Zinc and aluminium: glutamic acid assisted dual-doped LiMn 2 O 4 spinels via sol–gel method as cathode material for use in lithium rechargeable batteries

LiMn 2 O 4 and LiZn x Al y Mn 2-x-y O 4 (x = 0.07–0.10; y = 0.15–0.18) powders have been synthesized by sol–gel method using glutamic acid as chelating agent. The synthesized samples have been subjected to spectral studies viz., thermo gravimetric and differential thermal analysis to ascertain the phase formation, X-ray diffraction to confirm the formation of single-phase spinel material, scanning electron microscope (SEM) and transmission electron microscope (TEM) to understand the surface morphology of the synthesized materials, energy dispersive X-ray analysis (EDAX) to corroborate the elements in the exact composition of the undoped and doped spinel and electrochemical characterization. SEM images of LiMn 2 O 4 depict majority of spherical particles are of 0.5 μm size. TEM images of spinel LiMn 2 O 4 and LiZn x Al y Mn 2-x-y O 4 confirm the synthesized particles are an ice cube morphology of nano-sized (25–50 nm) with good agglomeration. EDAX peaks of Zn, Al, Mn and O have been confirmed in actual compositions of LiMn 2 O 4 and LiZn x Al y Mn 2-x-y O 4 . Charge–discharge studies of pristine spinel LiMn 2 O 4 delivers maximum discharge capacity of 130 mA h g −1 corresponding to columbic efficiency of 74 % during the first cycle with capacity fade of 0.19 mA h g −1 cycle −1 over the investigated ten cycles. At the end of 10th cycle, it delivers maximum discharge capacity of 105 mA h g −1 with columbic efficiency of 67 % and capacity fade of 0.19 mA h g −1 cycle −1 over the investigated ten cycles. An inter alia, all dopant substitutions, (LiZn 0.10 Al 0.15 Mn 1.75 O 4 ) sample exhibits the better cycling performance with good capacity retention (93 %) during the 10th cycle discharge capacity of 112 mA h g −1 comparing to undoped and other doped spinel with capacity fade of 1 mA h g −1 cycle −1 .