RESUMEN

Current Li-ion battery (LIB) recycling methods exhibit the disadvantages of low metal recovery efficiencies and high levels of pollution and energy consumption. Here, products generated via the in-situ catalytic pyrolysis of bamboo sawdust (BS) were utilized to regulate the crystal phase and nanoscale size of the NCM cathode to enhance the selective Li extraction and leaching efficiencies of other valuable metals from spent LIBs. The catalytic effect of the NCM cathode significantly promoted the release of gases from BS pyrolysis. These gases (H2, CO, and CH4) finally transformed the crystal phase of the NCM cathode from LiNixCoyMnzO2 into (Ni-Co/MnO/Li2CO3)/C. The size of the spent NCM cathode material was reduced approximately 31.7-fold (from 4.1 µm to 129.2 nm) after roasting. This could be ascribed to the in-situ catalytic decomposition of aromatic compounds generated via the primary pyrolysis of BS into C and H2 on the surface of the cathode material, resulting in the formation of the nanoscale composite (Ni-Co/MnO/Li2CO3)/C. This process enabled the targeted control of the crystal phase and nanoscale size of the material. Water leaching studies revealed a remarkable selective Li extraction efficiency of 99.27 %, and sulfuric acid leaching experiments with a concentration of 2 M revealed high extraction efficiencies of 99.15 % (Ni), 93.87 % (Co), and 99.46 % (Mn). Finally, a novel mechanism involving synergistic thermo-reduction and carbon modification for crystal phase regulation and nanoscale control was proposed. This study provides a novel concept for use in enhancing the recycling of valuable metals from spent LIBs utilizing biomass waste and practices the concept of "treating waste with waste".

Asunto(s)

RESUMEN

Full-component pyrolysis has been proven to be a prospective method for the disposal of organic matters and the cathode material reduction of spent LiNixCoyMnzO2 (NCM) lithium-ion batteries (LIBs). However, the kinetics of the full-component pyrolysis of spent NCM LIBs is still unclear. This work represents the first attempt to study the kinetics of different stages of full-component pyrolysis of NCM LIBs based on isoconversional method to guide the recycling of spent LIBs. Pyrolysis process was divided into four stages in accordance to the main weight loss temperature ranges and the classical Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa kinetics models were employed to calculate the activation energy (E) in each stage. The main physicochemical reactions were clarified though in situ analysis, and the average E in the four stages was determined: (I) The volatilization of electrolytes occurred in the temperature range of 100-200 °C with the E of 98.6 kJ/mol. (II) The decomposition of organic matters and the preliminary reduction of cathode material transpired in the temperature range of 400-500 °C with the E of 227.2 kJ/mol. (III) The further reduction of NiO and CoO occurred from 650 to 800 °C with the E of 258.8 kJ/mol. (Ⅳ) The reduction of MnO took place from 850 to 1000 °C with the E of 334.9 kJ/mol. The recycling strategies based on full-component pyrolysis of spent NCM LIBs was accordingly proposed. During pyrolysis, the cathode material was gradually reduced and the pyrolytic products can be controlled through temperature regulation.