In-situ pyrolysis based on alkaline medium removes fluorine-containing contaminants from spent lithium-ion batteries

Hanlin Huang; Chunwei Liu; Zhi Sun

doi:10.1016/j.jhazmat.2023.131782

In-situ pyrolysis based on alkaline medium removes fluorine-containing contaminants from spent lithium-ion batteries

J Hazard Mater. 2023 Sep 5:457:131782. doi: 10.1016/j.jhazmat.2023.131782. Epub 2023 Jun 5.

Authors

Hanlin Huang¹, Chunwei Liu², Zhi Sun³

Affiliations

¹ Chemistry and Chemical Engineering Data Center, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China; School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 101407, China; National Engineering Research Center of Green Recycling for Strategic Metal Resources, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China.
² Suzhou Botree Cycling Sci. & Tech Co., Ltd, China.
³ Chemistry and Chemical Engineering Data Center, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China; School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 101407, China; National Engineering Research Center of Green Recycling for Strategic Metal Resources, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China. Electronic address: sunzhi@ipe.ac.cn.

PMID: 37307731
DOI: 10.1016/j.jhazmat.2023.131782

Abstract

Pyrolysis is an effective method for removing organic contaminants (e.g. electrolytes, solid electrolyte interface (SEI), and polyvinylidene fluoride (PVDF) binders) from spent lithium-ion batteries (LIBs). However, during pyrolysis, the metal oxides in black mass (BM) readily react with fluorine-containing contaminants, resulting in a high content of dissociable fluorine in pyrolyzed BM and fluorine-containing wastewater in subsequent hydrometallurgical processes. Herein, an in-situ pyrolysis process is proposed to control the transition pathway of fluorine species in BM using Ca(OH)₂-based materials. Results show that the designed fluorine removal additives (FRA@Ca(OH)₂) can effectively scavenge SEI components (Li_xPOF_y) and PVDF binders from BM. During the in-situ pyrolysis, potential fluorine species (e.g. HF, PF₅, and POF₃) are adsorbed and converted to CaF₂ on the surface of FRA@Ca(OH)₂ additives, thereby inhibiting the fluorination reaction with electrode materials. Under the optimal experimental conditions (temperature = 400 °C, BM: FRA@Ca(OH)₂ = 1: 4, holding time = 1.0 h), the dissociable fluorine content in BM was reduced from 3.84 wt% to 2.54 wt%. The inherent metal fluorides in BM feedstock hinder the further removal of fluorine with pyrolysis treatment. This study provides a potential strategy for source control of fluorine-containing contaminants in the recycling process of spent LIBs.

Keywords: Calcium hydroxide; Defluorination; Pollutant source control; Pretreatment; Spent LIBs.