Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Abstract Electrochemical and thermal properties of Co 3 (PO 4 ) 2 - and AlPO 4 -coated LiNi 0.8 Co 0.2 O 2 cathode materials were compared. AlPO 4 -coated LiNi 0.8 Co 0.2 O 2 cathodes exhibited an original specific capacity of 170.8 mAh g −1 and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g −1 . Co 3 (PO 4 ) 2 -coated LiNi 0.8 Co 0.2 O 2 cathodes exhibited an original specific capacity of 177.6 mAh g −1 and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co 3 (PO 4 ) 2 coating. The Co 3 (PO 4 ) 2 coating material could react with LiOH and Li 2 CO 3 impurities during annealing to form an olivine Li x CoPO 4 phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni 4+ ions compared to the AlPO 4 -coated cathode. Differential scanning calorimetry results showed Co 3 (PO 4 ) 2 -coated LiNi 0.8 Co 0.2 O 2 cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO 4 -coated sample.