【作者】 陈波；

【导师】 马玉林；

【作者基本信息】 哈尔滨工业大学 ， 材料与化工（专业学位）， 2022， 硕士

【摘要】 近些年随着新能源汽车和便携式移动设备的广泛普及,人们对电化学储能装置的比能量提出了更高的要求。碱金属（锂、钠、钾）作为电池负极材料具有较低的氧化还原电位和较高的理论比容量,是目前研究的热点。然而,碱金属负极材料在充放电过程中枝晶生长问题严重,存在巨大安全隐患。而液态钠钾合金由于其具有金属的本质和液态的物理形态,可以从本质上消除枝晶。但是由于液态钠钾合金具有流动性,需要多孔材料进行固定,降低了其比能量,因此,本文从原位制备液态钠钾合金及枝晶原位液化的角度提高碱金属（钠、钾）电池比能量,同时解决电极/电解液界面枝晶问题。分别探究了液态钠钾合金化学稳定性和电化学稳定性,物理制备的液态钠钾合金其表面覆盖一层高表面活性氧化膜,与液态电解液接触形成液-固-液界面而非液-液接触界面,在无压力的作用下存在枝晶的生长和电解液分解;在压力的作用下通过原位电化学沉积首次实现在金属钠片表面形成一层液态钠钾合金,消除碱金属枝晶,实现自支撑。即使在50 m A cm^-2电流密度下依旧能实现枝晶原位液化。探究了液态钠钾合金负极消除枝晶原理,明晰了液态钠钾合金负极消除枝晶的沉积-溶解过程,即在充放电过程中首先在负极表面生成碱金属枝晶,其在压力的作用下刺破负极表面SEI膜,转化为液态合金,负极表面均匀生成液态合金,最终形成电极-电解液之间液-液接触界面,实现无枝晶电沉积。与钠离子电解液相比,在Na‖Na对称电池中采用钾离子电解液表现出优越的电化学性能,Na‖Na对称电池在5 m A cm^-2(5 m Ah cm^-2)电流密度下稳定循环1000 h以上,极化电压稳定在150 m V左右。在Na‖Cu体系中采用钾离子电解液库伦效率从12%左右提高到67%;在Na‖单晶普鲁士蓝组（PB）体系中1 C倍率循环1000圈后容量保持率从49.8%提升到93.1%,0.1 C倍率下放电比容量为117m Ah g^-1。通过原位光学照片、XPS、SEM、EDS和ICP等物理测试方法,证明了采用钾离子电解液可以在钠片表面原位生成一层微米级液态钠钾合金,在充放电过程中达到无枝晶电沉积,提高电池电化学性能和循环稳定性,从而提高碱金属电池安全性。此外,循环后钠片表面覆盖一层富含KF的SEI膜,阻止金属钠的溶解和析出。这项研究加深了对液态钠钾合金消除碱金属枝晶理论的理解,开辟了一条实现高性能无枝晶碱金属负极的制备方法,为无枝晶碱金属电池奠定理论基础。更多还原

【Abstract】 In recent years,with the widespread popularity of new energy vehicles and portable mobile devices,people have put forward higher requirements for the specific energy of electrochemical energy storage devices.Alkali metals（lithium,sodium,potassium）as battery anode materials have low redox potential and high theoretical specific capacity,which is a hot topic in current research.However,the dendrite growth problem of alkali metal anode materials during charging and discharging is serious,and there are huge safety risks.The liquid sodium-potassium alloy,due to its metallic nature and the physical form of the liquid state,essentially eliminating dendrites.However,due to the fluidity of liquid sodium-potassium alloys,porous materials are required to be fixed,which reduces their specific energy.Therefore,this paper improves the specific energy of alkali metal（sodium,potassium）batteries from the perspective of in situ preparation of liquid sodium-potassium alloys and dendrite in situ liquefaction.And it can solve the dendrite problem at the electrode/electrolyte interface.Respectively explores the liquid sodium-potassium alloy chemical stability and electrochemical stability.Since the surface of the physically prepared liquid sodium-potassium alloy is covered with a layer of high surface activity oxide film,its contact with the liquid electrolyte forms a liquid-solid-liquid interface rather than a liquid-liquid interface,and there is dendrite growth and electrolyte decomposition without pressure.And a layer liquid sodium-potassium alloys was formed on the surface of metal sodium sheets for the first time by in-situ electrochemical deposition under the pressure,so as to eliminate alkali metal dendrites and realize self-support.In situ liquefaction of dendrites even at 50 m A cm^-2.The principle of dendrite elimination of the anode of liquid sodium-potassium alloy is explored,and the deposition-dissolution process of dendrite elimination of the anode of liquid sodium-potassium alloy is clarified.that is,in the process of charging and discharging,the alkali metal dendrite is first generated on the surface of the anode,which pierces the SEI membrane on the surface of the anode under pressure and converts it into a liquid alloy,until the anode indicates that the in situ liquid alloy is uniformly generated,and finally the liquid-liquid contact interface between the electrode and the electrolyte is formed to achieve dendrite-free electrodeposition.Compared with the sodium ion electrolyte,the Na‖Na symmetrical battery with the potassium ion electrolyte showed excellent electrochemical performance.The Na‖Na symmetric battery can be cycled stably for more than 1000 h at 5 m A cm^-2 with 5 m Ah cm^-2,and the polarization voltage is stable at around 150 m V.In Na‖Cu system,coulombic efficiency was increased r fom 12%to 67%by using potassium electrolyte,and the capacity retention rate increased from 49.8%to 93.1%in Na‖PB（single crystal Prussian blue）system after 1000 cycles at 1 C,and the discharge specific capacity was 120.5 m Ah g^-1at 0.1 C.It was found that micron-level liquid Na K alloy was formed on the surface of the sodium sheet by in-situ optical photos,XPS,SEM,EDS and ICP.The surface of the sodium sheet maintained structural integrity and was covered with a KF-rich SEI film,which prevented the dissolution and precipitation of metal sodium.Dendrite-free electrodeposition is achieved in the charging and discharging process,which improves the electrochemical performance and cycle stability of the alkali metal battery.This study deepens the understanding of the theory of alkali dendrite elimination by liquid Na K alloy,opens up a preparation method to achieve high performance dendrite-free alkali metal anode,and lays a theoretical foundation for dendrite-free alkali metal battery.更多还原