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