Synergistic effect of Na and Al co-doping on the electrochemical properties of Li[Ni0.8Mn0.1Co0.1]O2 cathode materials for Li-ion batteries

In the typical hydrometallurgy-based recycling process of spent Li-ion batteries (LIBs), excessive amounts of Na ions are inevitably incorporated in leachate through a discharging process with salt solutions and a purification step for impurity removal. In this study, a facile Al3+ doping strategy is realized ranging from impurity level to usual doping levels for improving the LIB performance of Na-incorporated Li[Ni0.8Co0.1Mn0.1]O2 (N-NCM). We synthesize Na-incorporated hydroxide precursor via a coprecipitation reaction using a metal solution containing excess amounts of Na (12.6 mol%), simulating the resynthesis of NCM from purified leachate. The Na and Al co-doped NCM811 (NA-NCM) cathode materials are successfully synthesized by subsequent solid-state reactions with various concentrations of Al. The physicochemical and electrochemical properties of NA-NCM are systematically investigated, with N-NCM as a control sample. Notably, the trace amount of Al (0.05 mol%)-doped cathode material reveals the highest cyclability of 93.9% after 80 cycles at 1 C and more than six times higher discharge capacity (115 mAh g−1) at 20 C than N-NCM. Overall, the small amount of Al doping (0.05 mol%) makes the host structures stable and more favorable for Li+ diffusion, whereas the excessive Al (4 mol%) doping lead to the sluggish kinetics on rate capability due to thick A2O3 film layers formed on the particle surface. This work suggests the rational design for upgrading the resynthesized Ni-rich NCM cathode materials for the sustainable recycling of spent LIBs.