Research On Design And Performance Of Lithium Metal Anodes Interfacial Layer Based On In-situ Construction

Lithium-ion secondary batteries have been widely used in the fields of portable electronic devices and electric vehicles.However,with the rapid development of the emerging industries such as electric vehicles,aerospace,high-end communication terminals,and large-scale energy storage stations,the requirements for the energy density of energy storage systems are increasing.Existing lithium-ion secondary batteries can not provide the required high energy density.Lithium(Li)metal anode has become one of the most promising anode materials for the next generation of high-energy density lithium secondary batteries because it has an ultrahigh theoretical specific capacity(3860 mAh g-1)and the lowest redox potential(-3.04 V vs.SHE).Unfortunately,commercial application of Li metal anodes is fundamentally limited by low Coulomb efficiency and serious safety hazards caused by uncontrollable growth of Li dendrites.In this paper,two types of interfacial layers,Li-Zn alloy and LiI,are formed in situ on the Li metal anode.The effects of two types of interfacial layers on optimizing the cycling performance of the Li metal anode and suppressing the growth of Li dendrites were investigated.The main research contents and conclusions are as follows:A Li-Zn alloy layer is formed in situ on the surface of the Li metal anode by a simple and effective chemical method.The resulting Li-Zn alloy layer facilitates fast charge transfer and reaction kinetics at the interface,which afford stable homogeneous deposition of Li and thus result in deposition of Li with a smooth morphology and no dendrite growth.In addition,the reactivity of the Li-Zn alloy with the electrolyte is lower than that of Li metal,reducing the side reactions between Li metal and the electrolyte and thereby providing a stable electrode/electrolyte interface for the Li metal anode.Therefore,in the assembled symmetrical cells,the Li metal anode modified with the Li-Zn alloy layer shows stable cycling performance and long cycling lifetime under the testing condition of a current density of 2 mA cm-2 and a deposition capacity of 2 mAh cm-2.In the test of LiFePO4 full cells,the Li metal anode modified with Li-Zn alloy layer exhibits better electrochemical cycling performance,and its capacity retention ratio can reach 98.1%after 500 cycles.A LiI layer as a protective layer for the Li metal anode is constructed in situ on the surface of the Li metal anode by a reaction of iodine vapor with Li metal.The LiI layer has good Li ion transport capability,which realizes the uniform deposition of Li and thereby effectively suppresses the formation of Li dendrites.Meanwhile,the uniform LiI layer can effectively avoid the contact and reduce side reactions between the Li metal and the electrolyte,and thus improve the interfacial stability of the Li metal anode.The experimental results show that the Li metal anode modified with LiI layer exhibits better cycling stability and cycling lifetime in the tests of symmetrical cells.In full cells with NCM523 and LiFePO4 as the cathode,the Li metal anode modified with LiI layer shows better electrochemical cycling performance and better capacity retention ratio.