Stacking Fault Formation in LiNi_0.6Co_0.2Mn_0.2O₂ during Cycling: Fundamental Insights into the Direct Recycling of Spent Lithium-Ion Batteries

Abstract

As the global marketplace for lithium-ion batteries (LIBs) proliferates, technologies for efficient and environmentally friendly recycling, i.e., direct recycling, of spent LIBs are urgently required. In this contribution, we elucidated the mechanisms underlying the degradation that occurs during the cycling of a Li/LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cell. The results provided fundamental insights into the optimum procedures for direct recycling using a recently developed, state-of-the-art positive electrode material. Capacity fade in NCM622 was induced by cycling at high voltages above 4.6 V vs Li + /Li, during which the rhombohedral symmetry approached cubic symmetry. The selective line broadening and peak shifts that appeared in the X-ray diffraction patterns after cycling indicated the formation of stacking faults along the c h -axis. In addition, high-resolution transmission electron microscopy clarified that rock-salt domains were located on the NCM622 surface before and after cycling. These structural analyses confirmed that the NCM622 particles degrade not at their surfaces but rather in the bulk, contradicting previous reports where degradation during cycling is mainly caused by rock-salt domains on the surface. Material regeneration processes involving the restoration of the original stacking sequence are essential for effective direct recycling.

Mechanisms underlying the acid leaching process for LiNi0.6Co0.2Mn0.2O2 with and without H2O2

“…The decrease (increase) in a h ( c h ) resembles the change in a h ( c h ) upon the charge reaction. 18 As listed in Table 1, the ICP-AES analysis confirmed that the Li composition decreased as leaching proceeded. By contrast, the a h and c h values with H 2 O 2 were almost constant, regardless of the leaching time, suggesting that Li + ions are not effectively extracted from the NCM622 lattice.…”

“…The structural and electrochemical properties of pristine NCM622 are similar to those previously reported for NCM622. 17,18…”

“…We selected LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) as a model because of its increasing popularity as a positive electrode material for high-energy-density LIBs. [17][18][19][20][21] Then, we examined the particle morphologies, crystal structures, electronic states, and electrochemical properties of NCM622 during the HNO 3 leaching process with and without H 2 O 2 and compared the reaction schemes between the two conditions. An in-depth understanding of the dissolution of NCM622 into an HNO 3 solution could unveil the appropriate conditions for effective and eco-friendly acid leaching and solvent extraction processes.…”

Molecule and Microstructure Modulations of Cyano‐Containing Electrodes for High‐Performance Fully Organic Batteries

“…[1][2][3] Unfortunately, the traditional inorganic electrode materials (e.g., LiCoO 2 , LiFePO 4 , and LiNixMnyCo 1-x-y O 2 ) used for commercial LIBs rely heavily on the non-renewable metal resources and energy-intensive industries, endowing the existing LIBs unsustainable for the ever-increasing energy storage market. [4][5] As an alternative, organic electrode materials (OEMs) have emerged to tackle the bottlenecks facing inorganic materials due to their inherent merits of abundant resources, low cost, and structural diversity. [6][7][8] Recently, incredible breakthroughs regarding the electrochemical performances of OEMs have been achieved, in particular for their impressive capacity.…”

Molecule and Microstructure Modulations of Cyano‐Containing Electrodes for High‐Performance Fully Organic Batteries

“…The rapid expansion of Li‐ion batteries (LIBs) in large‐scale energy storage systems calls for electrodes featuring cost‐efficiency and environmental friendliness [1–3] . Unfortunately, the traditional inorganic electrode materials (e.g., LiCoO 2 , LiFePO 4 , and LiNixMnyCo 1‐x‐y O 2 ) used for commercial LIBs rely heavily on the non‐renewable metal resources and energy‐intensive industries, endowing the existing LIBs unsustainable for the ever‐increasing energy storage market [4–5] . As an alternative, organic electrode materials (OEMs) have emerged to tackle the bottlenecks facing inorganic materials due to their inherent merits of abundant resources, low cost, and structural diversity [6–8] .…”