Direct recovery of LiCoO2 from the recycled lithium-ion batteries via structure restoration
Introduction
As the consumption of global LIBs continues to increase, the generation of waste LIBs increases, which leads to environmental issues if the waste batteries are disposed of inappropriately. It was estimated that a cumulative output in the range of 0.33 million metric tons to 4 million metric tons of LIBs could be generated between 2015 and 2040 [1]. In fact, waste lithium-ion batteries contain appreciable valuable metal resources and are worthy of recycling and reutilization. The main contents of LIBs include heavy metals, plastics and organic solutions with proportions of approximately 5–20% cobalt, 5–10% nickel, 5–7% lithium, 7% plastics and 15% organic solutions [2]. Casual disposal of them leads to environmental pollution [3,4]. On the other hand, cobalt, nickel and lithium are valuable metals with a high recycling value. Therefore, recycling and reusing waste lithium-ion batteries have become an urgent task in modern society to protect the environment and promote resource reutilization efficiency.
Lithium cobaltate (LiCoO2) is a well-known positive active material for lithium-ion batteries that was first proposed by Goodenough et al. [5]. In 1990, LiCoO2 was commercialized by Sony Corporation in Japan in a LiCoO2/carbon lithium-ion battery system and has been widely applied in various electronic devices that have the characteristics of a high voltage stage, high specific capacity, good cycling performance and poor safety compared to that of other types of batteries. However, there are difficulties with the utilization of LiCoO2 owing to the shortage of cobalt and its heavy metal pollution [6,7]. In recent years, many investigations on the recycling of spent LIBs have focused on the recovery of the valuable metals cobalt and lithium [[8], [9], [10], [11], [12], [13], [14]]. The purposes of these works were aimed at elevating the leaching efficiency of metals and controlling the kinetic process therein. Liu and coworkers adopted a novel method for the sustainable recovery of Li and Co from waste LiCoO2 cathodes based on in situ reductive roasting, which had the advantages of not needing to separate the active materials from Al and no external reductants over traditional processes [8]. It was found that 98% of the cobalt was selectively separated from the leach liquor using ammonium oxalate under proper conditions. The precipitation of cobalt could be controlled by a combination of surface chemical reaction and diffusion in terms of kinetics factors [12]. Li et al. developed an environmentally friendly leaching process for recycling valuable metals from LIBs. In their work, the leaching efficiencies of Li, Ni, Co, and Mn reached 97.7, 98.2, 98.9, and 98.4%, respectively [13]. Without the leaching process, He et al. systematically studied the recovery of LiCoO2 via Fenton reagent-assisted flotation [15], pyrolysis-ultrasonic-assisted flotation technology [16], grinding flotation [17] and mechanical crushing combined with pyrolysis-enhanced flotation technology [18], which provided exceptional methods for the preparation of high purity LiCoO2 powders as substitutes for chemical metallurgy methods. To directly reutilize spent active materials in LIBs without chemical leaching processes, researchers have attempted to recover spent LIBs via separation and heat treatment [[19], [20], [21]], showing a promising approach for facile and economic recovery of LIBs.
In this work, LiCoO2 in spent LIBs was collected by discharge, disassembly, soaking and separation. The structure of spent LiCoO2 powder was restored during a calcination process, with lithium salts as additives to supplement the shortage of lithium in the spent LiCoO2. The structure and surface variations of the LiCoO2 powder were analyzed before and after its recovery. In contrast to the published works on valuable metal recycling [8,11,13], high-purity LiCoO2 powder collection [15,17] and low-temperature recovery processes [19,20], the influences of lithium salts and high-temperature treatment on the recovery of LiCoO2 powder were intensively investigated in the present study, including the species and amount of lithium salt and high recovery temperature. Furthermore, we took advantage of the Al2O3 coating on the improved performance of the recovered LiCoO2 because it was revealed that the surface coating enhanced the electrochemical performance of LiCoO2 [[22], [23], [24], [25]]. The electrochemical properties of our recovered LiCoO2 were investigated and compared with those for commercial LiCoO2, and the comparison indicated that a promising method for the direct recovery of spent LiCoO2 was developed in the present work.
Section snippets
Experimental methods
The recycling and regeneration processes of LiCoO2 are schematically displayed in Fig. 1, including the discharge, disassembly, separation and regeneration processes.
Structure and morphology of the recycled LCO after direct calcination
Before calcination, the structures of the recycled LCO and commercial LCO show no obvious discrepancy, except for the relative intensities of the diffraction peaks in Fig. S2. The intensity ratio of I(003)/I(104) decreased from 3.04 for the commercial LCO to 1.72 for the recycled LCO, which implies that the layered structure in the LCO changed after repeated lithiation and delithiation. The ratio of I(003)/I(104) is considered an indicator of the degree of cation mixing in the LCO structure,
Conclusion
In this work, we successfully separated LiCoO2 materials from the aluminum foil in waste lithium-ion batteries and investigated the impact of various calcination temperatures, different lithium sources and Al2O3 coatings on the recovery of recycled LiCoO2. As a result, the best treatment of the waste LiCoO2 herein involved adding Li2CO3 as a lithium source and mixing and sintering the mixture at 800 °C. This process could guarantee good formation of a layered structure in the LiCoO2 without
CRediT authorship contribution statement
Ying Gao: Investigation. Yang Li: Writing - review & editing, Supervision. Jing Li: Writing - review & editing. Huaqing Xie: Writing - review & editing. Yanping Chen: Data curation, Writing - original draft.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (grant number 51590902), Shanghai Municipal Natural Science Foundation (grant number 18ZR1415800) and Gaoyuan Discipline of Shanghai - Environmental Science and Engineering (Resource Recycling Science and Engineering).
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