Design Of Ion-conducting Units In Metal-organic Frameworks And Its Application In Solid-state Lithium Metal Batteries

Lithium metal battery with high energy density is regarded as one of the nextgeneration candidate energy storage battery systems.But lithium metal batteries using traditional liquid electrolytes have non-negligible safety problems,which limit the development and application of lithium metal batteries.Replacing the liquid electrolytes with safer solid electrolytes can effectively improve the safety of lithium metal batteries.However,the current mainstream organic and inorganic solid-state electrolytes each have serious defects: organic solid-state electrolytes have low electrical conductivity and cannot achieve rapid ion conduction;inorganic solid-state electrolytes have poor interface contact and poor stability,which cannot meet the needs of practical applications.As porous materials that have attracted much attention in recent years,metal-organic frameworks(MOFs)have the potential to become high-performance solid-state electrolytes due to their electronic insulating properties and high designability.In this thesis,organic ligands and guest molecules are used as ion-conducting functional motifs for designing the functional motifs in MOFs,so that the nanopores of MOFs can be transformed into channels capable of fast ion transport,and systematically study their applicability in solid-state lithium metal batteries(SSBs).First,the ordered arrangement of halogen groups on the MOFs framework is achieved by using the halogen-bearing ligands by taking advantage of the structural order of the MOFs framework.The combination of DFT calculations and experimental results proves that the ordered halogen groups can change the electron distribution in the MOFs channel,so that electrons are enriched at the wall of channel,thereby forming an electronegativity environment in the channel and promoting the conduction of lithium ions.At the same time,the halogen group can also regulate the composition of the solid-electrolyte interphase(SEI),participate in the formation of a dense and stable SEI layer,and optimize the deposition of lithium ions.Solid-state electrolytes prepared by using this bifunctional halogen-ordered MOFs ionic conductor have shown high rate performance and excellent cycle stability in a variety of Li-metal battery systems,and they even perform well in Li-metal full batteries that assembled with limited lithium.Secondly,the open metal sites of MOFs are used to coordinate and anchor ionic liquids orderly with high ionic conductivity to prepare MOFs solid-state ionic conductors with good ionic conductivity.Among them,the ordered coordination-anchored ionic liquid forms a high-efficiency ion-conducting network in the MOFs channels to facilitate the conduction of ions,reach the same level of ionic conductivity as the MOFs-loaded ionic liquid ionic conductor.And compared with the supported ionic liquid,this ionic liquid ordering method greatly improves the ion transport number and realizes single ion conduction.The all-solidstate lithium metal battery assembled with this material also shows a good performance,with high discharge capacity and good capacity retention rate,and can be cycled for hundreds of cycles at 0.5 C stably.