Conductive Surface Modification with Aluminum of High Capacity Layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 Cathodes

The electrode films fabricated with the high capacity layered oxide Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 have been surface modified with metallic aluminum by a thermal evaporation process. The morphology and electrochemical performances of the bare and the Al-coated cathodes have been investigated by scanning electron microscopy (SEM) and charge-discharge measurements. Compared to the bare Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 cathode, the Al-coated cathodes (coating time <= 30 s) exhibit higher discharge capacity with lower irreversible capacity loss, better cyclability, and higher rate capability. Specifically, the 20 s Al-coated cathode exhibits the highest capacity (278 mAh/g at C/20 rate) and the best rate capability (157 mAh/g at 5C rate), while the 30 s Al-coated cathode displays the best cyclability (268 mAh/g with a capacity retention of 98% in 50 cycles). An analysis of the charge-discharge capacity values, surface conductivity evaluation, and electrochemical impedance spectroscopy (EIS) measurements reveal that the improved electrochemical performances are due to the suppression of both the oxygen vacancy elimination at the end of the first charge and side reactions with the electrolyte and the decrease in charge transfer polarization by the Al-modification layer.