Influence of Atmosphere on Electrochemical Performance of LiNi_0.8Co_0.1Mn_0.1O₂ Electrodes for Li-Ion Batteries

Ni-rich layered materials have been regarded as competitive candidates for advanced lithium-ion batteries due to their high energy density, relatively low cost and environmentally-friendly nature. However, they suffer from serious degradation of cycling performance after exposing to air during their storage. Here we selected LiNi_0.8Co_0.1Mn_0.1O₂ as a typical Ni-rich positive material to study the influence upon exposure to ambient air on surface chemical composition and electrochemical performance. TEM confirms the existence of amorphous surface layer after contacting with atmosphere and the thickness is about 3-4 nm. The fresh LiNi_0.8Co_0.1Mn_0.1O₂ sample has capacity retention of 94.6% and 93.3% after 50 cycles at 0.2C and 1C, respectively, comparing to the 91.7% and 82.4% of the exposed sample. The charge-discharge curves and electrochemical impedance spectra indicate that exposure to air lead to increased impedance and polarization, which seriously affects LiNi_0.8Co_0.1Mn_0.1O₂ cycling properties. So, it is very important for Ni-rich cathode materials without contacting with atmosphere directly.