Effects of Ca doping on the electrochemical properties of LiNi0.8Co0.2O2 cathode material

LiNi0.8Co0.2O2 and Ca-doped LiNi0.8Co0.2O2 cathode materials were synthesized via a rheological phase reaction method. It is found that the Ca doping significantly improves reversible capacity, cycling performance, thermal stability and rate capability. The Ca-doped LiNi0.8Co0.2O2 cathode material maintains nearly its initial discharge capacity up to 100 cycles at room temperature. It also delivers an initial discharge capacity of 183 mA h g− 1 and still keeps 131 mA h g− 1 even after 120 cycles at 60 °C. These results, together with the X-ray diffraction and electrochemical impedance spectroscopy analysis, reveal that Ca2+ ions occupy Li+ ion sites to form CaLi defects and lithium vacancies (VLi′), which reduce the resistance and increases conductivity of LiNi0.8Co0.2O2.