Effect of Na from the leachate of spent Li-ion batteries on the properties of resynthesized Li-ion battery cathodes

Highlights: • Effect of Na during coprecipitation on Na-containing cathode materials is examined. • Na does not affect the particle growth and the formation of a layered structure. • Excessive Na in cathode materials affects electrochemical properties negatively. • Residual Na after washing has beneficial effects on cyclability and rate capability. -- Abstract: The explosion of spent Li-ion batteries (LIBs) during the LIB recycling process is often avoided by the discharging process where spent LIBs are soaked into NaCl solutions. Because Na can be incorporated into resynthesized cathode active materials, we synthesize LiNi_0.8Co_0.1Mn_0.1O₂ active materials with extra Na in the simulated coprecipitation solution whose composition was matched to the actual industrial leachate composition. The morphological, structural, and electrochemical properties of the active materials are investigated. The addition of Na does not affect the precursor particle growth during the coprecipitation and the resulting morphology of active materials. Structural analyses show that Na-containing active materials have a favorable environment for the diffusion of Li ions. Overall, Na from the leachate of spent LIBs could be incorporated into the resynthesized cathode active materials unless they are washed thoroughly. Although excessive Na affects the electrochemical properties of cathode active materials adversely, the residual Na after the thorough washing has a beneficial effect on cyclability and rate performance as confirmed by low charge transfer and surface film resistances and high Li ion coefficients.