Multi-anionic and multi-cationic high-entropy oxides as electrode materials for lithium-ion batteries

Abstract

High-entropy materials are promising for using as anode materials for energy storage. Here, the possibility of obtaining single-phase multi-anionic and multi-cationic high-entropy oxides Li_x(Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)_2-xO_2-xF_x (0.0 ≤ x ≤ 1.0) with the rock salt structure is investigated. The electrode materials were prepared by the mechanochemically assisted solid-state synthesis and co-precipitation method. The as-prepared anode materials were characterized by X-ray powder diffraction, cyclic voltammetry, galvanostatic cycling, impedance spectroscopy and galvanostatic intermittent titration technique. The maximum x value for obtaining the single-phase materials is 0.5 for two synthesis methods. When used as an anode material for Li⁺ ion batteries, Li_0.5(Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)_1.5O_1.5F_0.5 (x = 0.5) exhibits improved reversibility and kinetics of the electrochemical reactions compared to (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)O (x = 0.0). Li_0.5(Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)_1.5O_1.5F_0.5 obtained by the solid-state synthesis provides the highest reversible capacity of 562.2 mAh g⁻¹ (89 % of the theoretical capacity) with a Coulombic efficiency of 99.5 % during prolonged cycling, while Li_0.5(Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)_1.5O_1.5F_0.5 prepared by co-precipitation method and (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)O prepared by solid-state synthesis and co-precipitation show a reversible capacity of 366.9, 329.9 and 238.7 mAh g⁻¹, respectively.