Research On Preparation And Electrochemical Performance Of Aluminum Based Oxides Modified Li- Rich Layered Cathode Materials

As the demand for electronics, electric vehicles, medical equipment, aerospace devices increasing, the pursuit of high energy density, high power density of battery has become a hot spot. Due to the layered cathode materials have high discharge capacity, high working voltage, good safety and environmental friendliness. So they have been considered as the ideal next generation cathode material of lithium ion batteries.The Li-rich layered cathode material xLi₂MnO₃· （1-x）LiMO₂ （where M is one or more of Ni、 Co、Mn transition metal elements,0<x<1） has high capacity and the structure is similar to LiCoO₂. In this dissertation, the author mainly focused on the modification and electrochemical properties of Li_1.2Ni_0.2Mn_0.6O₂ and Li_1.15Ni_0.17Co0.11Mn_0.57Mn_0.57O₂ these two Li-rich layered cathode materials, the main contents are as follows:Firstly, layered Li_1.2Ni_0.2Mn_0.6O₂ had been successfully synthesized by a co-precipitation method followed by a simple solid-state reaction. And LiAlO₂ was coated on the surface of Li_1.2Ni_0.2Mn_0.6O₂ using isopropanol aluminum by co-precipitation method. The results showed that LiAlO₂-coated Li_1.2Ni_0.2Mn_0.6O₂ had high coulombic efficiency, good rate capability and cycle performance. The discharge capacity of pristine Li_1.2Ni_0.2Mn_0.6O₂ from 205.6mAh/g droped to 134.2mAh/g with the capacity retention of 65.27% after 100 cycles. However, the initial discharge capacity of the LiAlO₂-coated Li_1.2Ni_0.2Mn_0.6O₂ was 213.2mAh/g, after 100 cycles the discharge capacity was 192.9mAh/g with capacity retention of 90.5%. Compared to pristine Li_1.2Ni_0.2Mn_0.6O₂, LiAlO₂-coated Li_1.2Ni_0.2Mn_0.6O₂ showed better electrochemical performance.Secondly, Al₂O₃ coated Li-rich layered cathode material Li_1.15Ni_0.17Co0.11Mn_0.57Mn_0.57O₂ were prepared by using different aluminum source like aluminum nitrate （Al（NO₃）3）, isopropanol aluminum （C9H21AIO₃） and nano alumina （nano-Al₂O₃） by different methods, and the electrochemical properties of Al₂O₃ coated Li_1.15Ni_0.17Co0.11Mn_0.57Mn_0.57O₂ by different aluminum source samples also had been researched. The results showed that the discharge capacity of pristine sample was 197.9mAh/g and 71.5mAh/g at 0.2C,10.0C rate. Meanwhile, Al（NO₃）3, C₉H21AlO₃ and nano-Al₂O₃ as raw mateial to coat the Li_1.15Ni_0.17Co0.11Mn_0.57Mn_0.57O₂ samples at 0.2C discharge specific capacity were 220.1,203.4, and 194.2mAh/g, respectively. At 10.0C rate, discharge capacity of Al₂O₃ coated Li_1.15Ni_0.17Co0.11Mn_0.57Mn_0.57O₂ were 94.7,77.8 and 72.6mAh/g, respectively.Finally, Al₂O₃ coated Li_1.15Ni_0.17Co_0.11Mn_0.57Mn_0.57O₂ had been prepared by ball-milling combining with different calcination temperature and nano-Al₂O₃ as aluminum source. It showed that at 0.5C the discharge capacity of pristine was 181.5mAh/g, at 2.0C rate capacity only had 142.8mAh/g. The discharge capacity of Al₂O₃-coated Li_1.15Ni_0.17Co0.11Mn_0.57Mn_0.57O₂ materials synthesized at 650℃ and 800℃ temperture were 2O₂.5mAh/g and 201.2mAh/g at 0.5C rate, then at 2C the capacity are 153.6mAh/g and 151.7mAh/g, respectively. The cycle performance of Al₂O₃-coated Li_1.15Ni_0.17Co0.11Mn_0.57Mn_0.57O₂ materials synthesized at 650℃ and 800℃ temperture are superior to pristine sample. At 0.5C rate, after 100 cycles the discharge capacity of samples synthesized at 650℃ and 800℃ temperture were 163.2mAh/g and 167.4mAh/g, while the capacity of pristine sample was only 146.3mAh/g.