An appropriate amount of new spinel phase induced by control synthesis for the improvement of electrochemical performance of Li-rich layered oxide cathode material

Reconstructing a novel layered-spinel composite structure in Li-rich layered oxides (LLOs) is considered as an efficient method to improve its electrochemical performance, including the initial coulombic efficiency (ICE), rate and cycle performances. Herein, we report the preparation and characterization of the Li_1+xMn_0.54Ni_0·13Co_0·13O₂ (x = 0.08, 0.14, 0.20 and 0.26) samples by a modified sol-gel route with an annealing process. X-ray diffraction (XRD) patterns in combination of their refinement results, Raman spectra, high resolution transmission electron microscopy (HRTEM), selected electron diffraction (SEAD) and electrochemical measurements of the materials indicate the presence of different amounts of novel cobalt-rich spinel phase (LiCoMnO₄) within these materials, which increases with the decrease of relative lithium compositions. It is found that an appropriate amount of new spinel phase induced by the control synthesis process (using reasonable lithium usage and annealing treatment) contributes to the improvement of the electrochemical performance of LLO, specifically, the Li_1·14Mn_0·54Ni_0·13Co_0·13O₂ (Li_1.14) sample delivers a high initial discharge specific capacity and ICE of 303.0 mA h g⁻¹ and 77.0%, respectively at 20 mA g⁻¹, good rate capability (∼200 mA h g⁻¹ at 1.0 C rate; 1.0 C = 200 mA g⁻¹) and capacity retention capability (83.7% after 100 cycles at 1.0 C rate). The results presented herein offer evidence that the incorporation of the novel cobalt-rich spinel phase in LLOs by a simple synthesis route is a feasible way to improve its electrochemical performance.