On the stabilizing effect of Zr doping in LiMn1.5Fe0.5O4 spinel cathodes for Lithium-ion Batteries

Abstract

Spinel structures are promising cathodes for Lithium-ion batteries due to good functional performance and sustainability. LiMn₂O₄ is the most investigated composition, despite some drawbacks: i) Jahn-Teller distortion involving Mn (III), and ii) partial dissolution of Mn (II) upon cycling. Here, we report on spinel compositions (LiM_xMn_1-xO₄) where Mn is partially substituted by Fe (III) to decrease the Mn (III) amount. This system was doped with small amounts (<0.05 at.%) of Zr (IV) and decorated with ZrO₂ nanoparticles with a synergistic role: i) to replace electrochemically active cations with pillar ions and stabilize the spinel structure during cycling; ii) to protect the electrode/electrolyte interface and reduce the TMs dissolution upon cycling. Li(Mn_1.5-xFe_0.5 Zr_x)O₄ (LMFZ) was synthesized through solid-state reaction and characterized by multi-technique approach. The best composition (LMFZ2) exhibited very high structural stability with no change in lattice parameters and very low Mn (II) dissolution rate upon prolonged cycling at 0.5C. When cycled at 0.08C at 2.3-4.3V, this cathode delivered stable specific capacity exceeding 140 mAh g^-1. Good capacity retention > 87% was determined after 160 cycles at both low and higher C rates (namely 0.5C and 2C). Superior electrochemical properties were observed for the Zr-doped cathode with respect to LiMn_1.5Fe_0.5O₄.