【作者】 张帆；

【导师】 何平；

【作者基本信息】 南京大学 ， 材料学， 2020， 硕士

【摘要】 在近十几年来,锂电池由于其高的理论能量密度、长使用寿命、低自放电率和绿色环保等优点,得到了飞速的发展,在电动汽车、手机电脑等消费类电子产品中得到广泛应用。然而随着锂电池的不断普及,锂资源的消耗量也日益增加,从而导致锂资源的价格逐年上涨。锂资源的不断消耗导致的锂资源短缺问题将会成为制约锂离子电池发展的一大重要因素。相较于1.4×10⁷t有限的陆地锂储量,富含2.3×10¹¹ t锂储量的海水资源,有望成为新型的锂资源储备,为锂电池的发展提供几乎取之不尽用之不竭的锂资源。研究人员已经开发出了蒸发结晶法、沉淀法、萃取法、吸附法、渗析法和电化学法等各种海水提锂方法,以期望于成功实现海水提锂的实用化。然而由于海水中含有0.17 mg·L^-1极少量的锂和大量其他金属阳离子,目前已有的海水提锂技术受到很大的限制,锂产率和纯度不高。本文主要提出了一种基于组合电解液的电解法海水提锂技术,并对其进行了深入的研究。此项技术通过搭建以Ru基催化剂为阳极,海水为阳极电解液,铜片为阴极,0.5 M的Li Cl O₄的碳酸丙烯酯溶液为阴极电解液,LAGP(Li_1.5Al_0.5Ge_1.5（PO₄）₃)为阴阳极区分隔层的电解体系,实现有选择性地从海水中提取出金属锂单质。在太阳能提供的电能下,阳极发生氧化反应,析出氧气和氯气;阴极发生还原反应,电解液中的锂离子还原生成金属锂单质;海水中的锂离子透过LAGP补充阴极电解液中消耗的锂离子,而其他金属阳离子则被LAGP阻隔留在海水中。此种技术表现出了高的锂产量、锂纯度和能量利用效率,能够实现高效地从海水中提取出锂资源。在相关测试中,在240μA·cm^-2电流密度下,锂产率最高,达到了60μg·h^-1,能量利用效率达到了50 mg·Wh^-1。然而,此项技术仍然不够成熟,Ru基催化剂提高了其成本,LAGP的稳定性也未达到实用要求。通过更换更为廉价的过渡金属氧化物为阳极催化剂,在不影响电化学性能的前提下,降低装置的成本。Ni O@SP（Ni O@Super P）、Co O@SP（Co O@Super P）和Mn O₂@SP（Mn O₂@Super P）均表现出了优秀的电催化活性,电解电位均低于4.7 V,能量利用效率均高于50 mg·Wh^-1。其中Ni O@SP的电解电位为4.54V,能量利用效率达到了57 mg·Wh^-1,表现出了不逊色于贵金属的电催化性能。通过在LAGP海水侧表面原位光聚合一层PMMA（聚甲基丙烯酸甲酯）海水保护层,实现提高电解法海水提锂装置的稳定性和使用寿命。由于PMMA较逊色于LAGP的锂离子电导率和PMMA与LAGP的界面阻抗,PMMA/LAGP表现出了1.58×10^-5 S·cm^-1的低于LAGP一个数量级的锂离子电导率。因此相对于原始装置4.4 V的电解电位,PMMA/LAGP表现出了4.7 V的较高的电解电位。但是PMMA/LAGP表现出了远远优于LAGP的稳定性能和使用寿命。更多还原

【Abstract】 In the past decade,lithium battery has been developed rapidly because of its high theoretical energy density,long service life,low self-discharge rate and environmental protection.It has been widely used in consumer electronics products such as electric vehicles,mobile phones and computers.However,with the continuous popularity of lithium batteries,the consumption of lithium resources is also increasing,which leads to the price increase of the lithium resources.The shortage of lithium resources caused by the continuous consumption of lithium resources will become an important factor restricting the development of lithium-ion batteries.Compared with the limited land lithium reserves of 1.4×10⁷ t,sea water resources with lithium reserves of 2.3×10¹¹ t are expected to become a new type of lithium resource reserve,providing almost inexhaustible lithium resources for the development of lithium batteries.Researchers have developed various methods of lithium extraction from seawater,such as evaporation crystallization,precipitation,extraction,adsorption,dialysis and electrochemical method.However,due to a small amount of lithium of 0.17 mg·L^-1 and a large number of other metal cations in seawater,the existing technology has been greatly limited with low lithium productive rate and purity.In this manuscript,a technology of lithium extraction from seawater by electrolysis based on hybrid electrolyte is proposed and studied in depth.This technology can selectively extract metallic lithium from seawater by electrolytic cell using Ru base catalyst as anode,seawater as anode electrolyte,copper as cathode,propylene carbonate solution of 0.5 M Li Cl O₄ as cathode electrolyte and LAGP as the separation layer of anode electrolyte and cathode electrolyte.With the electric energy powered by solar energy,the anode underwent oxidation reaction with the separation of oxygen and chlorine;lithium ions reduced as metallic lithium on the cathode;the lithium ions passed through LAGP to replenish the consumed lithium ions in cathode electrolyte while other cations were blocked in seawater by LAGP.Under the current density of 240μA·cm^-2,the technology showed the highest lithium productive rate of 60μg·h^-1 and the energy utilization efficiency of 50 mg·Wh^-1.However,this technology is still not mature enough with the high cost caused by Ru based catalyst and the instability of LAGP.The cost could be reduced without sacrificing the electrochemical performance by replacing the cheaper transition metal oxide as anodic catalyst.Ni O@SP,Co O@SP and Mn O₂@SP all showed excellent electrocatalytic activity with the electrolytic potential lower than 4.7 V and the energy utilization efficiency beyond 50 mg·Wh^-1.Ni O@SP showed best electrocatalytic performance no less than noble metals with the electrolysis potential of 4.54 V and the energy utilization efficiency of 57 mg·Wh^-1.The stability and service life of the technology could be improved by in-situ photopolymerization of a PMMA seawater protective layer on the sea water side of LAGP.PMMA/LAGP the Li-ion conductivity of 1.58×10^-5 S·cm^-1 an order of magnitude lower than LAGP due to the inferior Li-ion conductivity of PMMA and the interface impedance.Therefore,PMMA/LAGP showed the higher potential of 4.7 V compared with the pristine of 4.4 V.However,PMMA/LAGP shows much better stability and service life than LAGP.更多还原