| dc.description.abstract | The cobalt-free spinel positive electrode LiNi0.5Mn1.5O4 (LNMO) is receiving extensive attention for lithium-ion batteries due to its low cost, high operating voltage (4.7 V vs. Li/Li+), superior energy density (690 Wh/kg), and good thermal stability. However, its high operating voltage hampers its stability with commercial electrolytes, leading to capacity decay during long-term charge-discharge cycling. This makes its practical viability challenging.
To solve these problems, we combined ethanol-assisted hydrothermal and metal−organic frameworks (PTA-based MOFs) as precursors to synthesize high-voltage LNMO composite positive electrode. In this way, the metal ions can be successfully aligned by organic ligands, meanwhile the ethanol-assisted hydrothermal process improves the dispersity of LNMO particles with reduced particle size. Since selecting the appropriate hydrothermal temperature is crucial to achieve optimal electrochemical performance, we used different hydrothermal temperatures (T=100, 120, 140, 160°C) for synthesis. In order to further enhance structural stability, Fe was doped in the Ni-Mn precursors of MOF, and the trimetallic precursor is calcinated to form Fe-doped LNMO (LiNi0.5-xMn1.5-xFe2xO4 (x=0, 0.03, 0.05, 0.1, 0.15)).
The results confirm that the novel synthesis method is a feasible strategy to fabricate high-performance LNMO positive electrodes. Various hydrothermal temperatures give rise to different colors and particle size of the LNMO precursors. In addition, it is confirmed by XPS that an amorphous Li2CO3 layer formed on the surface of the as-synthesized LNMO, which can protect the material from overreaction and effectively assist Li+ diffusion. Among the samples, the LNMO-120°C is the smallest with uniform size distribution and has the best discharge capacity (142.5 mAh/g at 0.2 C) and cycling stability with a capacity retention of 80.1 % after 200 cycles at 1 C. Different from the parent LNMO material, the Fe-doped spinel one has reduced rock-salt-type impurity phase and satisfactory cycling stability and rate performance. Among all the samples, the LiNi0.45Fe0.1Mn1.45O4 sample shows the best cycling stability (capacity retention of 96.7 % after 200 cycles at 1 C) and rate capability with a capacity of 118.9 mAh/g even at 5 C. | en_US |