Tunable LiAlO2/Al2O3 Coating through a Wet-Chemical Method To Improve Cycle Stability of Nano-LiCoO2

A facile wet-chemical method to coat nano-LiCoO2 particles is investigated and established in this study. In this newly developed wet-chemical method, Al(NO3)(3) is used as the Al source to form Al2O3 and LiAlO2, whereas LiNO3 is used as a sacrificial agent to protect nano-LiCoO2 and at the same time to form LiAlO2 by reacting with Al2O3. Addition of LiNO3 into the Al(NO3)(3) coating solution suppresses the unwanted formation of Co3O4 during the coating process and leads to a thin (5-10 nm) and continuous LiAlO2/Al2O3 coating on nano-LiCoO2 particles. The 21 wt %LiAlO2/Al2O3-coated nano-LiCoO2 exhibits an unusually high initial specific capacity of 225 mA h g(-1), while micro-LiCoO2 can only deliver a specific capacity of 145 mA h g(-1) even though the charge/discharge voltage windows are the same. Furthermore, 21 wt % LiAlO2/Al2O3-coated nano-LiCoO2 offers 100% increase in the specific capacity over pristine nano-LiCoO2 after 5 cycles at 0.1C, 20 cycles at 1C, and 20 cycles at 3C. Moreover, 21 wt % LiAlO2/Al2O3-coated nano-LiCoO2 can charge/discharge for 425 cycles at 3C with only 18% capacity loss and maintain a final specific capacity of 128 mA h g(-1). In contrast, the specific capacity of micro-LiCoO2 diminishes to 50 mA h g(-1) after 200 cycles at 3C. The unusually high specific capacity and superior capacity retention for long cycle life at high rates of 21 wt % LiAlO2/Al2O3-coated nano-LiCoO2 are attributed to its huge electrode/electrolyte interfacial area for charge/discharge with small polarization and the effectiveness of LiAlO2/Al2O3 coating in preventing capacity decay during soaking as well as during cycling. The principle and methodology of this newly developed wet-chemical coating method are applicable to other layered transition metal oxide cathodes and can open up new opportunities to obtain superior electrochemical properties from these advanced cathodes in the future.