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China team proposes paired electrolysis process to recover spent LiCoO2 and LiFePO4

Researchers in China are proposing a paired electrolysis process for the more efficient recovery of spent lithium cobalt oxide (LiCoO2) and lithium iron phosphate (LiFePO4) electrode materials. Their work is presented in an open-access paper in the RSC journal Green Chemistry.

There are three typical methods for recovery of spent batteries. The pyrometallurgy process of using high-temperature calcination benefits from the simplicity of the process and can be used on a large scale, but this method consumes a lot of energy and produces a large amount of greenhouse gases (GHG). The hydrometallurgy process uses chemicals such as mineral acids to selectively leach metal elements from the positive electrode material of LIBs and recover various elements through fractional precipitation. It is widely prevalent because of the high-purity products, but the hydrometallurgy process needs to consume a large amount of chemical reagents and water. The third is the cheap biohydrometallurgy process, but it needs to take a long time to cultivate microorganisms and a more rigorous environment.

As an adjustable and eco-friendly technique, electrochemical technologies have recently been researched. However different electrochemical methods for recycling LIBs have different emphases. Several types of lithium battery cathode materials have been recovered by electric field-driven de-lithium in NaCl solution. There is a recycling strategy of LiNi1/3Co1/3Mn1/3O2 by an electrochemical oxidation method in (NH4)2SO4 solution. Qi et al. used the electrochemical reduction method to leach Li and Co by using 1.25 mol/L of malic acid at 8 V.32 Recently, research demonstrated that the spent cathode and anode materials can be recovered in a low energy consumption method through the strategy of electrochemical oxidation.

However, the strategy only uses a half-reaction in one electrolytic cell while the other half-reaction produces byproducts. The simultaneous utilization of electrochemical reactions at both cathode and anode in one electrolytic cell is beneficial to save chemicals and reduce energy consumption, which is of great interest to explore.

In this paper, we propose a process of paired electrolysis of LCO and LFP in a low-concentration H2SO4 solution.

—Zhao et al.

Zhao

Schematic diagram of the process for the pre-treatment and the paired electrochemical recovery. Zhao et al.


In their process, the team vacuum pyrolyzed spent LCO and LFP cathodes to separate the active materials from the aluminum foils. The resulting powders were coated on titanium mesh to make working electrodes.

The paired electrolysis experiments of LCO and LFP were performed in a low- concentration sulfuric acid solution. A dual electrolysis system was used for constant voltage electrolysis, with the LCO as the cathode and the LFP as the anode.

In this process, LiCoO2 is reduced to release Co2+ and Li+ into the electrolyte through a surface chemical reaction control process. LiFePO4 is oxidized to FePO4 while releasing Li+ through a surface chemical reaction control process.

Through this approach, both leaching efficiencies of Li and Co reach above 98%. Since two electrode reactions simultaneously proceed in one electrolytic cell, the paired electrolysis has the benefit of maximizing energy efficiency, as well as reducing the amount of chemicals and secondary wastes, the researchers said.

Resources

  • J. Zhao, F. Zhou, H. Wang, X. Qu, D. Wang, Z. Zheng, Y. Cai, S. Gao, D. Wang and H. Yin, (2023) “Co-recovery of spent LiCoO2 and LiFePO4 by paired electrolysis”Green Chem. doi: 10.1039/D3GC03322H.

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