Al2O3 Coated Concentration-Gradient Li[Ni0.73Co0.12Mn0.15]O2 Cathode Material by Freeze Drying for Long-Life Lithium Ion Batteries

Abstract

In order to enhance the electrochemical performance of the high capacity layered oxide cathode with a Ni-rich core and a concentration-gradient shell (NRC-CGS), we use a freeze drying method to coat Al2O3 layer onto the surface of NRC-CGS Li[Ni0.73Co0.12Mn0.15]O2 material. The samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, charge-discharge measurements and electrochemical impedance spectroscopy. It is revealed that an amorphous Al2O3 layer of about 5nm in thickness is uniformly formed on the surface of NRC-CGS Li[Ni0.73Co0.12Mn0.15]O2 material by the freeze drying procedure. The freeze drying Al2O3-coated (FD-Al2O3-coated) sample demonstrates similar discharge capacity and significantly enhanced cycling performances, in comparison to the pristine and conventional heating drying Al2O3-coated (HD-Al2O3-coated) samples. The capacity decay rate of FD-Al2O3-coated Li[Ni0.73Co0.12Mn0.15]O2 material is 1.7% after 150 cycles at 55°C, which is 9 and 12 times lower than that of the pristine and HD-Al2O3-coated samples. The superior electrochemical stability of the FD-Al2O3-coated sample is attributed to the synergistic protection of CGS and high-quality Al2O3 coating that effectively protect the active material from electrolyte attack. The freeze drying process provides an effective method to prepare the high performance surface-coated electrode materials.