Utilization of impurities in resynthesized Ni-rich Li[Ni1-x-yCoxMny]O2 (1-x-y≥0.6) cathode materials from leachate for the effective spent lithium-ion battery recycling process = 효율적인 폐리튬이온배터리 재활용 공정 확립을 위한 침출수로부터 재합성된 Ni-rich Li[Ni1-x-yCoxMny]O2 (1-x-y≥0.6) 양극재 내 불순물 활용 연구

다국어 초록 (Multilingual Abstract)

In the typical hydrometallurgy-based recycling process of spent Li-ion batteries (LIBs), excessive amounts of metallic and nonmetallic impurity ions are incorporated in leachate. These impurities are removed through a precipitation reaction using NaOH to recycle into a cathode material, which has same performance as the cathode of the BOL battery. 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 and 2 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 Al2O3 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. Based on the fact that the impurity ions could be used as a dopant, Ni-rich NCM cathode materials (Re622, Re811, and Re955) are resynthesized by the coprecipitation method and the solid-state reaction. The actual leachate was utilized for the synthesis of various Ni-rich hydroxide precursors without a purification process, and in the case of cobalt, the whole required cobalt ions for synthesis were replaced by the leachate. A cathode active material (Re622) with high leachate usage (72 mol % of transition metals) has heterogeneous secondary particles and poor electrochemical performance. In contrast, the resynthesized Re955 using leachate for 18% of the required transition metals has homogeneous spherical secondary particles like those of a pristine NCM955 sample and shows enhanced cyclability and rate capability compared to the pristine NCM955 sample. This study demonstrates that the electrochemical performance of the resynthesized Ni-rich cathode materials could be improved by utilizing the impurities without purification process.

목차 (Table of Contents)

• Ⅰ. Introduction
• Ⅱ. 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
• Experimental
• Physicochemical characteristics
• Electrochemical characteristics
• III. The enhancement of electrochemical properties of resynthesized Ni-rich Li[Ni1-x-yCoxMny]O2 (1-x-y≥0.6) cathode materials from leachate for the effective spent lithium-ion battery recycling process
• Experimental
• Physicochemical characteristics
• Electrochemical characteristics
• Phase deterioration characteristics
• IV. Conclusions
• V. References