Structural stability and superior electrochemical performance of Sc-doped LiMn2O4 spinel as cathode for lithium ion batteries

Scandium doped LiScxMn2-xO4 compounds are synthesized by solid-state method, which show single phase with rod-like polyhedron morphology. The Sc-doping decreases the lattice parameter 'a' marginally due to the change in the inter-atomic distance of the metal oxide bonds as confirm by Rietveld refinement. In addition, the expansion of LiO4 tetrahedron and contraction of MnO6 octahedron by similar to 0.01 A upon doping are observed. The Sc2p(3/2) peak at 402.5 eV and Snc2p(1/2) peak at 407.2 eV in the XPS spectrum of LiSc0.06Mn1.94O4 confirms the presence of Sc in the spinel structure. The symmetric stretching of Mn-O bond of LiSc0.06Mn1.94O4 shifts lower value (similar to 4 cm(-1)) than that of LiMn2O4 indicating the occupancy of Sc3+ ion in the octahedral site. The diffusion coefficient value of LiSc0.06Mn1.94O4 (1 x 10(-12) cm(2) s(-1)) is one-order higher than that of undoped LiMn2O4 (1 x 10(-13) cm(2) s(-1)). LiMn2O4 delivers a discharge capacity of 117 mAhg(-1) at 1C with a capacity retention of 74% after 500 cycles, whereas under similar condition LiSc0.06Mn1.94O4 delivers a discharge capacity of 114 mAhg(-1) with a capacity retention of >90%. LiSc0.06Mn1.94O4 also delivers excellent rate capability due to high diffusion coefficient and less charge transfer resistance compared to the parent compound. The structure and morphology of the Sc-doped electrode after 500 cycles remains intact without any formation of Mn-rich agglomeration suggest that the reduction of Mn2+ ion dissolution as well as Jahn-Teller distortion. Hence LiSc0.06Mn1.94O4 can be a potential cathode material for lithium ion batteries. (C) 2019 Elsevier Ltd. All rights reserved.