Biotreatment for the spent lithium-ion battery in a three-module integrated microbial-fuel-cell recycling system

Highlights

• An BE recycling platform was designed to recover Li and Co from the spent LIBs.

• Three sequential subsystems were consorted based on the kinetic adjustment.

• Central composite design was used to optimize maximize the recovery of Co.

• The effect of (NH₄)₂CO₃ concentrations on the Li recovery was investigated.

• The study supplies the green recycling for the solid waste without recovery loss.

Abstract

A bio-electrochemically (BE) recycling platform was assembled to recover Li and Co from the cathodic materials of spent LIBs in one integrated system. The BE platform consists of three microbial-fuel-cell (MFC) subsystems, including MFC-A, MFC-B, and MFC-C. Co and Li were smoothly recovered from the cathodic materials in the assembled platform. The initial pH and the loading ratios of LiCoO₂ both significantly influenced the leaching efficiencies of Li and Co in MFC-A. Approximately 45% Li and 93% Co were simultaneously released through the reduction of LiCoO₂ at the initial pH of 1 and the loading ratios of LiCoO₂ of 0.2 g/L. The (NH₄)₂C₂O₄-modified granular activated carbons (GAC) with a thickness of 1.5 cm was favorably stacked adjacent to the cathode of the MFC-B system. About 98% of removal efficiency (${\text{RE}}_{\text{Co1}}$) and 96% of recovery efficiency (${\text{RE}}_{\text{Co2}}$) of Co were achieved in MFC-B under optimum conditions. The dosing concentration of Li⁺ lower than 2 mg/L and the (NH₄)₂CO₃ of 0.01–0.02 M were conducive to enhancing the recovery of Li from raffinate and guaranteed the higher power output and coulombic efficiencies in MFC-C. The continuous release of CO₂ caused by exoelectrogenic microorganisms on the biofilm facilitated the precipitation of Li₂CO₃.

Introduction

In recent decades, LIBs have been widely used in many fields, such as mobile electronics, aerospace, and medical care, etc., due to its some instinct advantages including high energy density, large working voltage, long cycle life, and minor memory effect(Chen et al., 2019, Huang et al., 2019a, Sattar et al., 2019, Zhang et al., 2019). The vigorous development of the new-energy vehicles has expanded the demanding production of LIBs and further irritated the increases in the price of raw materials (Guo et al., 2018, Yang et al., 2018). Commonly, LIBs would suffer the inactivation process after about 3 to 5 years. LIBs scrapped from the commercial vehicles and passenger cars will reach 84 GWh and 17.5 GWh, respectively, with around 1.16 million tons in total in 2023(Ku et al., 2016, Zeng et al., 2015, Zhang et al., 2014). Co and Li coming from the mineral resources of raw materials have been rapidly consumed in many countries, especially in China. The relative shortage in the resources and the imbalance between the supply and demand have restricted the healthy development of the power industry (Huang et al., 2019c, Zhang et al., 2018a). In this perspective, recycling Co and Li from the spent LIBs not only solves the potential environmental problems also eases the constraining status caused by the shortage of regeneration resources (Boxall et al., 2018, Dutta et al., 2018, Nascimento et al., 2018, Omelchuk and Chagnes, 2018).

The pretreatment and the chemical recycling for the spent LIBs have been systemically developed until now (Meng et al., 2017, Meng et al., 2018a, Meng et al., 2018b, Meng et al., 2018c). Some traditional pyrometallurgy and hydrometallurgy techniques, such as (bio)leaching, adsorption, ion exchange, chemical precipitation, and solvent extraction, etc. have been applied to the recycling of LIBs(Chagnes and Pospiech, 2013, Gratz et al., 2014, Horeh et al., 2016, Jha et al., 2013, Joulie et al., 2014, Pospiech, 2014, Swain, 2017, Zhang et al., 2018b). However, some drawbacks including high energy consumption, strong reliance on the chemical reagents, and cumbersome route have explicitly hindered the application of these methods (Golmohammadzadeh et al., 2018, Swain, 2017, Yao et al., 2018). Microbial electrolysis cells (MECs) have been proposed as a promising and innovative technology for the recovery of Co and Li from the spent LIBs in overcoming the conventional bottlenecks (Jadhav et al., 2017, Yu et al., 2018). MEC can reduce Co from cathodes, separate Co and Li, and simplify the recovery of Li in the downstream process. However, the consumption of precious metal catalysts and the additional voltage needed to compensate the thermodynamic cap potentially limit the application of MECs in the scale and scope (Hasany et al., 2016, Kadier et al., 2016, Kadier et al., 2014). Correspondingly, the biocathode and self-driven MFCs have been proposed as some improved steps to reduce the cost of some noble catalysts, to lower the overpotentials of MEC systems, and to increase the collateral electricity output without external voltage(Huang et al., 2014a, Huang et al., 2014b, Shen et al., 2015, Wu et al., 2015). However, these researches were dwarfed by the obvious decreases in the removal and recovery rates of Co and Li (Huang et al., 2019c).

In this study, a complete bio-electrochemical (BE) recycling platform was constructed to achieve the recovery of Li and Co from the cathodic material of the spent LIBs. The BE platform consisted of three indispensable and sequential subsystems, MFC-A, MFC-B, and MFC-C. To achieve the maximum recoveries of Li and Co from the cathodic materials, the running performance of each subsystem was consorted and improved based on the adjustment of parameters. The effects of the initial pH in the catholyte and the loading ratios of LiCoO₂ attached to the carbon brush in the MFC-A system were fully studied. The combination of parameters in the MFC-B system was quantitatively optimized to maximize the removal and recovery of Co-based on the analysis results of the individual and synergetic influences of four variables towards the responses in the central composite design (CCD). The effects of the dosing concentrations of Li⁺ and the concentrations of (NH₄)₂CO₃ on the recovery of Li and power generation were comprehensively investigated in the MFC-C system. To better integrate the three subsystems and expand the application scale of the BE platform, the reaction mechanisms of each subsystem were discussed in depth by overviewing the experimental results of indicators and analyzing the morphological and spectra results. The research not only provides a novel method in guiding the step recovery of Co and Li from the cathodic material of spent LIBs in a compacted BE platform and supplies the feasibility of green recycling for the solid waste based on ensuring high recovery rates.