Preparation and electrochemical properties of Zn-doped LiNi_0.8Co_0.2O₂

Zn-doped LiZn_yNi_0.8-yCo_0.2O₂ (0.0000 ≤ y ≤ 0.0100) compositions were synthesized by a conventional solid-state method. The products were characterized by XRD, galvanostatic cycling, cyclic voltammetry, electrochemical impedance spectroscopy and thermal analysis. For the LiZn_0.0025Ni_0.7975Co_0.2O₂ system cycled between 3.0 and 4.2 V, the discharge capacities in the 1st and 100th cycles were 170 and 138 mAh/g with charge retention of 81%. The corresponding values for the undoped material were 158 and 97 mAh/g, with charge retention of 61.4%. The improved electrochemical properties of the doped system were attributed to the structural stability derived from incorporating the size-invariant Zn²⁺ ions. The Zn-doped system also showed improved capacity and cyclability when the cycling was performed in a voltage wider window (2.5-4.4V) and at a higher temperature (55°C). The structural and electrochemical properties of the doped and undoped materials were correlated.