Study Of The Preparation And Repair Of FePO₄ Electrode For Lithium Extraction From Salt Lake Via Electrochemical Deintercalation/Intercalation Method

The global energy transition leads to sharp increases in the demands for lithium-salt products,and extracting lithium from salt-lake brine efficiently and economically is important to the sustainable development of the lithium industry and the promotion of cleaner energy.The electrochemical de-intercalation/intercalation lithium extraction method has attached wide attention in industrial applications due to its high selectivity and environment friendly,and the efficient preparation of highly selective electrodes is crucial for the application of this method.In response to the shortcomings of the traditional electrochemical method for the FePO₄ electrode preparation,such as long treating time and complicated supporting equipment,this paper proposes a chemical oxidation method for FePO₄ electrode preparation used in the electrochemical lithium extraction method;especially for the characteristics of high Na/Li ratio in the raw salt-lake brine,and the targeted preparation process of Li_0.3FePO₄ electrode with high selectivity is proposed,which realizes the efficient separation of lithium and sodium in the raw brine.In addition,the chemical oxidation-reduction electrode repairment method is proposed to aim at the adsorption capacity fading during the lithium extraction process,which effectively improves the service life of electrode materials in the electrochemical deintercalation/intercalation method.The main researches of this paper are presented as follows.（1）The chemical oxidation method is developed for the efficient preparation of FePO₄ electrode material.The de-lithiation process of the Li FePO₄ electrode and the performance of the prepared FePO₄ electrode is identified through the investigations of the influence including sodium persulfate concentration,temperature,and time,and the optimal process window for the FePO₄ electrode preparation process is established.It reveals the relationship between the solution redox potential and the de-lithiation amount of Li FePO₄electrode during the preparation process of FePO₄ electrode and establishes that the criterion of solution redox potential and FePO₄ electrode performance,which provided a theoretical basis for the online monitoring of FePO₄ electrode preparation process.（2）FePO₄ electrode exhibits good adaptability to salt-lake brine.The electrochemical behavior in different solutions of the FePO₄ electrode prepared by chemical oxidation and its applicability to salt-lake brines were investigated.Cyclic voltammetry curves show the differences in the deintercalation and intercalation performance of different cations(Li⁺,Na⁺,K⁺,Mg²⁺)on the prepared FePO₄ electrode,indicating that the selective extraction of Li⁺from impurity ions in brine can be achieved by adjusting the electrode potential.The prepared FePO₄ electrode exhibits good adaptability to salt-lake brines,and its current efficiency exceeds 70%during lithium extraction from different types of salt-lake brines.（3）Li_0.3FePO₄ electrode materials with high selectivity is prepared.In response to the problem that the high concentration of sodium ions in brine will intercalate into the material lattice and affects the cycling stability of the electrode material,based on the differences in diffusion migration properties of Li and Na on Li_1-xFePO₄ electrode materials,the Li_0.3FePO₄ electrode material with better Li/Na separation performance was prepared to reduce the structural damage of the electrode material and the fading of the adsorption capacity due to the intercalation of sodium ions.The cycling and extraction performance of the Li_0.3FePO₄ electrode in artificial brine was investigated,and the results showed that the electrode adsorption capacity retention was 89.29%after 100 cycles,and the current efficiency reached more than 90%.（4）The performance of electrode material is efficiently repaired by chemical oxidation-chemical reduction method.The electrode performance is repaired by the chemical oxidation-reduction method for the problem that the cycling stability of the electrode material was significantly decreased by the presence of vacant adsorption sites or intercalation of impurity ions.Identified the effects of sodium ascorbate concentration,temperature,and Li concentration on the repair process of the Li FePO₄ electrode,as well as the performance of the repaired Li FePO₄electrode,and determined the optimal operating conditions for the repairment process of the Li FePO₄ electrode.The adsorption capacity of the repaired electrode would increase from 29 mg·g^-1 to 34 mg·g^-1,and the cyclic adsorption capacity retention rate was over 90%.（5）The preparation of Li_0.3FePO₄ electrodes by chemical oxidation method indicated good prospects for industrial applications.The feasibility of using the chemical oxidation method to prepare Li_0.3FePO₄ electrodes for industrial-scale application by controlling the redox potential of the solution was investigated.To clarify the performance of the prepared Li_0.3FePO₄ electrode,the industrial-scale lithium extraction device was built to investigate the lithium extraction effect on different types of brine,and the results showed that the lithium extraction performance was consistent with the laboratory experimental effect.The results of pilot experiments laid the foundation for the efficient and rapid preparation of industrialized Li_0.3FePO₄ electrodes.