Effects of lithium excess and SnO2 surface coating on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 cathode material for Li-ion batteries

Abstract

Four LiNi0.8Co0.15Al0.05-based Li-ion-battery cathode materials, i.e., the pristine LiNi0.8Co0.15Al0.05, Li-excess Li1+xNi0.8Co0.15Al0.05, SnO2-coated LiNi0.8Co0.15Al0.05 and SnO2-coated Li-excess Li1+xNi0.8Co0.15Al0.05 are prepared via a facile oxalate coprecipitation route, and are studied with respect to the effects of Li excess and SnO2 coating on the structure and electrochemical properties. X-ray diffraction and X-ray photoelectric spectroscopy demonstrate that a small amount of Li+ and/or Sn2+ ions are incorporated into the transition-metal slabs of the modified materials, and hence reduce the cationic disorder of Li+/Ni2+. High-resolution transmission electron microscopy and scanning electron microscopy confirm the formation of a SnO2 surface layer that prevents the growth and aggregation of the primary particles during high-temperature solid reaction, and therefore results in formation of the SnO2-coated materials with nano/submicron sphere-like morphology. Lithium excess and SnO2 coating enhance the electrochemical performance. The SnO2-coated Li-excess Li1+xNi0.8Co0.15Al0.05 exhibits not only higher specific capacity and better rate capability but also excellent cycling stability. After 400 cycles at 1C rate, the capacity is decreased from 123.7 to 86.7 mAh g−1, giving capacity retention of 70.1%. Li excess is believed to decrease the cationic mixing and SnO2 modification is deemed to restrict the undesirable side reaction between the active material and electrolyte.