Stable nickel-substituted spinel cathode material (LiMn1.9Ni0.1O4) for lithium-ion batteries obtained by using a low temperature aqueous reduction technique

Abstract

A nickel substituted spinel cathode material (LiMn_1.9Ni_0.1O₄) with enhanced electrochemical performance was successfully synthesized by using a locally-sourced, low-cost manganese precursor, electrolytic manganese dioxide (EMD), and NiSO₄·6H₂O as a nickel source by means of a low temperature aqueous reduction synthesis technique. This synthesis protocol is convenient to scale up the production of the spinel cathode material, with minimal nickel content (Ni = 0.1) in the structure, for lithium-ion battery applications. Ni-ions substituting Mn-ions was confirmed using XRD, EDS, XPS and electrochemical performance studies. LiMn_1.9Ni_0.1O₄ materials showed an octahedral shape with clearly exposed (111) facets that enhanced the Li-ion kinetics and improved the cycling performance compared to the pristine spinel sample (LiMn₂O₄). The LiMn_1.9Ni_0.1O₄ sample exhibited superior capacity retention by retaining 84% of its initial capacity (128 mA h g⁻¹) whereas pristine LiMn₂O₄ retained only 52% of its initial capacity (137 mA h g⁻¹). XPS confirmed that the Mn³⁺/Mn⁴⁺ ratio changed with nickel substitution and favored the suppression of capacity fading. The study clearly suggests that the integration of small amounts of Ni into the spinel structure is able to eliminate the disadvantageous Jahn–Teller effects in the LiMn₂O₄.