Surface Engineering Of Commercial Ni Foams For Li Metal Anodes

Lithium-ion batteries have had a profound impact on our daily life,but the energy density of traditional lithium-ion batteries based on graphite anode is limited.It is difficult to meet the growing demand for portable electronic products,electric vehicles and cascade energy storage markets.Therefore,the next generation of high energy density secondary battery system based on lithium metal anode?such as Li-S,Li-O₂ battery?shows a good space for development.Lithium metal anode has extremely high theoretical specific capacity?3860 mAh/g?and very low standard potential?-3.040 V vs.Standard hydrogen electrode?and low density?0.534 g/cm³?are regarded as the"Holy Grail"in the research field of anode materials.However,the high reaction activity of lithium metal anode and the low Coulombic efficiency,short cycle life and high safety hidden danger caused by lithium dendrite growth seriously restrict the application prospect of lithium metal anode in practical battery system.Therefore,how to effectively inhibit the growth of lithium dendrite and construct lithium metal anode with high safety and long life is a key scientific problem to be solved urgently in the research and development and application of high energy lithium secondary battery system.It is an effective strategy to improve the performance of lithium anode by constructing three-dimensional collector to reduce the effective current density in the process of cyclic charge and discharge so as to delay the growth of lithium dendrite.Commercial metal foam materials?such as Ni foam,Cu foam,etc.?have been widely used as three-dimensional fluid collections in the fields of electrocatalysis and supercapacitors because of their three-dimensional interconnection porous structure and excellent electrical conductivity.However,when it is used as a collector of lithium metal anode,it is easy to lead to lithium dendrite growth and dead lithium formation due to the uneven deposition of lithium due to the large pore size and uneven distribution of current on the surface of the skeleton.In addition,the intrinsic lithium aversion of copper or Ni also makes the nucleation barrier of lithium larger,and it is also easy to induce the growth of lithium dendrite.Considering that lithium deposition/stripping is a surface process,how to modify the surface of metal foam to improve the performance of lithium metal anode is a key problem.In this thesis,we developed a surface engineering strategy for commercial Ni foam:first,a layer of gold nanoparticles was modified on the surface of Ni foam by electrochemical deposition,and then AuLi₃ particles were formed by lithiation.Ni foam?AuLi₃@Ni foam?modified by AuLi₃ particles was formed.The results show that compared with bare Ni foam,AuLi₃@Ni foam has stronger lithium affinity,can significantly reduce lithium nucleation energy barrier,improve the uniformity of lithium deposition,effectively inhibit the growth of lithium dendrite and improve the anode performance of lithium metal.In Li|Li symmetrical battery,the lithium metal anode based on AuLi₃@Ni foam collector can cycle stably for 740 hours.After 500 cycles at 1 C rate,the capacity retention rate and Coulombicic efficiency of Li-AuLi₃@Ni foam||LiFePO₄ full cell are 43.5%and 99.2%,respectively.The results show that the improvement of lithium affinity on the surface of commercial Ni foam collector plays an important role in promoting the uniform deposition of lithium without dendrite.On this basis,we further construct the micro-nano structure of AuLi₃ on the surface of Ni foam framework:firstly,gold and tin alloy is deposited on the surface of Ni foam skeleton by electrochemical deposition?AuSn@Ni foam?,and then tin is removed by chemical de-alloy method.As a result,nanoporous gold?NPG@Ni foam?was formed on the surface of Ni foam framework?NPAuLi₃@Ni foam?.Finally,nanoporous AuLi₃?NPAuLi₃?was formed by lithiation process,and nanoporous AuLi₃ modified Ni foam?NPAuLi₃@Ni foam?was obtained.The results show that compared with bare Ni foam,NPAuLi₃@Ni foam not only has stronger lithium affinity,but also has larger specific surface area,and has the function of reducing lithium nucleation energy barrier and effective current density,and can buffer the volume change during lithium deposition/stripping,so as to effectively improve the performance of lithium metal anode.In Li|Li-NPAuLi₃@Ni foam symmetrical battery,the electrode based on NPAuLi₃@Ni foam collector can run stably for2000 hours without short circuit.After 500 cycles at 1 C rate,the capacity retention rate and Coulombicic efficiency of Li-NPAuLi₃@Ni foam||LiFePO₄ full cell are 74%and 99.53%,respectively.The results show that the construction of micro-nano structure of lithium modified layer on the surface of Ni foam collector framework can further improve the electrochemical performance of lithium metal anode based on it.The research work of this paper can provide guidance and reference for the design and development of high-performance three-dimensional collector for lithium anode,and can promote the development of high-energy lithium secondary battery..