Research On The Mass-Energy Transfer Mechanisms And Operating Characteristics Of Lithium Extraction From Brine By Electric-Assisted Adsorption Method

Lithium batteries are widely used in portable electronic devices,electric vehicles and energy storage devices.With the growing consumption of lithium,the existing lithium ore and brine can not meet the future needs.Compared with the traditional lithium extraction method from lithium ore and brine,the lithium can be extracted from low lithium concentration brine through the electric-assisted adsorption lithium extraction method,which only needs the lithium adsorbents and a small amount of electric energy.Using the electric-assisted adsorption lithium extraction method can not only effectively alleviate the shortage of lithium source,but also contribute to the goal of carbon neutralization in 2060.In order to extract lithium from brine more efficiently,this thesis focuses on the new idea of mass transfer mechanism and electric field control optimization of lithium extraction.The specific research contents and main conclusions are as follows:（1）Corresponding theoretical models were constructed for the current four main electric-assisted adsorption lithium extraction systems（ion capture system,rocking chair system,ion exchange system and capacitance system）respectively.The system mass transfer mechanism was revealed.The validity of the model,fast response,etc.were verified,in which the ion transient,ion distribution and potential change during the lithium extraction of electric-assisted adsorption lithium extraction methods process can be shown in detail.Through these systems,the electrode structure,porosity and thickness,the ion concentrations of feed and recovered solution,current densities and other influencing factors can be reasonably studied.The design and research provide theoretical guidance and simulation verification methods in order to effectively design an electric-assisted lithium extraction system.（2）The influences of the external stability of the electrodes were explored,and it was found that LiNi_0.8Co_0.1Mn_0.1O₂（LNCM）had better external environmental stability and lithium extraction performance than the other two kinds of electrodes.Aiming at the kinetic limitation of LNCM electrode during the lithium extraction cycle,the crasping mechanism model was proposed:In the aqueous environment,the primary praticles of LNCM will crack during the first cycle,and the excessively high voltage leads to serious mixing phenomenon during the lithium extraction cycle of LNCM,which causes cracks in the secondary praticles of the electrode,then the electrode is invalid.We proposed a method to optimize the lithium extraction performance and improve the stability of the electrode by adjusting the cut-off voltage during the intercalaction and deintercalaction process.The feasibility of the method is verified by experiments and first-principles calculations.（3）The electrochemical lithium extraction performance of different current densities,frequencies and curves in the brine with Li⁺/Na⁺/Mg²⁺ion ratio of 1:1:1 was investigated.We found that the purity,production and energy consumption can be optimized by the magnitude and the frequency of the discharge profiles.In the initial solution(solution with Li⁺/Na⁺/Mg²⁺ion ratio of 1:1:1),the optimum value was obtained at a current density of 0.5 m A cm^-2 and a frequency of 0.5 Hz.What’s more,for the same average current,a downward trend in the current profiles leaded to higher production,purity,and lower energy consumption.At the same time,through theoretical simulations of dynamic ion diffusion,we investigated the diffusion and reaction of ions on the electrode surface and related the performance differences to the concentration polarization at different current profiles.We found that lower overpotentials can be generated by suppressing the depletion of lithium ions on the electrode surface,leading to better lithium extraction performance.Finally,we used seawater from the Yellow Sea to carry out lithium extraction research and verify the phenomenon.By using the current pulse profiles with a gradual downward trend,the product purity can reach 0.78(7.3×10^-5 in the original solution)and 0.96 for further purification.The total energy consumption was only 62 Wh mol^-1.These results showed the potential of electrochemical lithium extraction for practical applications and the feasibility of optimizing performance by current operation.Therefore,we proposed not only new mechanistic explanations,but also general and practical directions for current optimization to achieve higher lithium extraction performance.Extracting lithium ions from brine with low lithium concentration can effectively alleviate the current shortage of lithium carbonate products,which is crucial for our country’s energy transition.In this thesis,we constructed numerical models,studied the electrode kinetics limitation and the correlation between current and concentration polarization,which are helpful to understand the ion transport process in the lithium extraction system,improve the cycling stability of the adsorption electrode,and design an efficient,energy-saving and stable lithium extraction system.