Green Synthesis of Nickel-rich Ni

Nickel-rich layered oxides such as LiNixCoyAl1−x−yO2 (NCA) are attractive cathode materials for lithium-ion batteries because they can deliver high energy density at reduced cobalt content. However, conventional co-precipitation routes typically require external acid/base dosing for pH control, which increases chemical consumption and generates salt-rich effluents. Here, we propose an electrochemical (acid-free) synthesis route using a bipolar-membrane electrolyzer to generate H+ and OH− in situ from water, thereby replacing reagent-based pH adjustment. A mixed Ni–Co–Al sulfate solution (Ni:Co:Al = 89:8:3) was processed at 60 °C and electrolyzed at 0.08 A cm−2 for 60 and 120 min. The resulting deposits were washed and dried, then lithiated with LiOH (Li:cathode precursor=1.05:1) and calcined (500 °C/6 h followed by 800 °C/20 h). SEM revealed hierarchical secondary aggregates with a flower-like morphology that became more consolidated at longer electrolysis time. EDS confirmed the presence of Ni, Co, and Al in the deposits. XRD showed reflections consistent with a layered NCA-type structure when compared with the reference card (JCPDS 87-1562), with the 120 min sample exhibiting sharper and better-resolved peaks; minor secondary phases were also detected, indicating incomplete phase purity under the present conditions. Overall, the bipolar membrane-assisted route demonstrates a feasible pathway to reduce external chemical inputs in Ni-rich cathode precursor synthesis, while highlighting the processing window required to strengthen phase formation toward layered NCA.