Enhanced cyclability and reversibility of nickel-rich cathode for lithium-ion batteries via LiH2PO4 assisted saturated Li2CO3 washing

Air humidity sensitivity of LiNi1−x−yCoxAlyO2 (NCA, (1 − x − y) ≥ 0.8) cathode materials deteriorates their safety and electrochemical properties due to the rapid formation of high alkali surface. Water washing is the most used method to remove those residues alkali efficiently, however, excessive loss of Li+ and Al3+ during washing increases the resistance greatly and worsens the reversibility of cathodes eventually. In this paper, saturated Li2CO3 solution is introduced for eliminating toxic LiOH by-products selectively, while inhibiting the dissolution of lattice Li+. As a result of full-cell test, the washed LiNi0.815Co0.15Al0.035O2 exhibited upgraded electrochemical performance with an initial discharge capacity of 184.5 mAh g−1 at 0.2C and an upgraded capacity retention rate of 86.2 % after 500 cycles at 1C rate. In order to further improve the stability of Ni-rich lithium storage structure, LiH2PO4 is introduced as a washing additive to construct a protective phosphate coating layer with high stability instead of Li2CO3 on the outer surface of NCA. The stable phosphate skim improves the electrochemical stability of NCA effectively, and the modified cathode shows an excellent cycle stability with a high capacity retention rate of 90.3 % after 500 cycles at 1C.