Electrochemical effects of residual Al in the resynthesis of Li[Ni1/3Mn1/3Co1/3]O2 cathode materials

Abstract

As the demand for various electronic devices using the advantages of lithium ion batteries (LIBs) increases, the disposal of LIBs has also been an important issue. We synthesize Li[Ni1/3Mn1/3Co1/3]O2 (NMC) and Li[Ni1/3Mn1/3Co1/3]AlxO2 (NMCA) cathode active materials with various amounts of Al (NMCA (x%)) via hydroxide coprecipitation and calcination processes, which simulates the resynthesis of NMC in leachate containing Al from spent LIBs. The effects of Al on the physicochemical, thermal and electrochemical (initial charge/discharge capacity, cyclability and rate capability) properties of NMCA are investigated and compared with NMC. An increase in the Al content in NMCA incurs an irregular shape and the uneven distribution of active material particles as confirmed by scanning electron microscope. The initial charge/discharge capacity and cyclability deteriorate as the Al content increases. The capacity retention of NMCA (2.00%) starts to decline rapidly at an earlier cycle than the other NMCA samples. On the other hand, the rate capability of NMCA is enhanced and electrochemical impedance spectroscopy analysis shows that NMCA (2.00%) has a higher lithium ion diffusion coefficient than NMC. Overall, residual Al in the cathode active materials has an adverse effect on capacity and cyclability, which could be tolerated with traces of Al less than 0.05% in NMCA.