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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[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 (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 A 2 O 3 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. [Display omitted] • Na can be introduced in leachate during Li-ion battery recycling using salt water. • Strong bond strength of Al-O retards rapid structural degradation during cycling. • Na+ and Al3+ ions in bulk structure have a synergistic effect on rate performance. • Excessive Al doping forms A 2 O 3 layers on the surface of layered cathode materials. • Na and Al co-doping can shed light on upgrading the resynthesized cathode materials. [ABSTRACT FROM AUTHOR]