ABSTRACT
The composite cathode material of the conductive polymer polyaniline (PANI)-coated spinel structural LiNi0.5Mn1.5O4 (LNMO) for high-voltage lithium-ion batteries has been successfully synthesized by an in situ chemical oxidation polymerization method. The electrode of the LNMO-PANI composite material shows superior rate capability and excellent cycling stability. A capacity of 123.4 mAh g-1 with the capacity retention of 99.7% can be maintained at 0.5C after 200 cycles in the voltage range of 3.0-4.95 V (vs Li/Li+) at room temperature. Even with cycling at 5C, a capacity of 65.5 mAh g-1 can still be achieved. The PANI coating layer can not only reduce the dissolution of Ni and Mn from the LNMO cubic framework into the electrolyte during cycling, but also significantly improve the undesirable interfacial reactions between the cathode and electrolyte, and markedly increase the electrical conductivity of the electrode. At 55 °C, the LNMO-PANI composite material exhibits more superior cyclic performance than pristine, that is, the capacity retention of 94.5% at 0.5C after 100 cycles vs that of 13.0%. This study offers an effective strategy for suppressing the decomposition of an electrolyte under the highly oxidizing (>4.5 V) and elevated temperature conditions.
ABSTRACT
A layered nanosphere structured NiO catalyst was successfully synthesized by a simple and efficient hydrothermal method as a cathode material for lithium-oxygen (Li-O2) batteries. Cyclic voltammetry (CV), dual electrode voltammetry (DECV) and chronoamperometry (CA) by rotating ring-disk electrode (RRDE) were carried out to investigate the catalytic activity of this catalyst for the oxygen evolution reaction (OER). The results revealed that the layered nanosphere NiO exhibited excellent electrochemical performance, stability and a typical four-electron reaction as a cathode electrocatalyst for rechargeable nonaqueous Li-O2 batteries. The overpotential of the NiO is only up to 0.61 V. X-ray photoelectron spectroscopy (XPS) characterization shows that the Li2O2 and Li2CO3 formed during the discharge process and decomposed after charging. Moreover, the cut-off voltage of discharging is about 2.0 V in the NiO-based Li-O2 batteries, while the specific capacity is up to 3040 mA h g-1. There is no obvious performance decline of the battery after 50 cycles at a current density of 0.1 mA cm-2 with a superior limited specific capacity of 800 mA h g-1. Herein, the layered nanosphere structured NiO catalyst is considered a promising cathode electrocatalyst for Li-O2 batteries.
