High-pressure synthesis and electrochemical properties of lithium transition metal oxides with layered rock-salt structure

摘要

Li-rich layered transition metal oxides with the nominal composition of Li_(1+x)[Li_(0.2)Mn_αCo_βNi_γ]O_2 with 0.0 ≤ x ≤ 0.7 are synthesized using a high-pressure technique. The chemical compositions are determined using inductively coupled plasma (ICP) spectroscopy and the structure is identified from X-ray diffraction measurements as a mixture of rhombohedral R-3m and cubic Fm-3m phases. Rietveld refinement analysis reveals that the layered to cubic phase ratio increases as x tends towards 0.7, with an almost complete cubic phase present for x ≥ 0.6. Electrochemical charge-discharge experiments performed using coin cells and show capacities of around 200 mAh g~(-1) for 0.0 ≤ x ≤ 0.4 samples, although the capacity quickly decreases for x ≥ 0.5, which is consistent with the trend towards a predominantly cubic phase. The plateau for oxygen generation, which appears at the 4.4 V threshold, is reduced as x increases.