The Structure Design Of 3D Alkali Metal Anode And Its Application

In order to cope with the increasing demands of the development on energy density of batteries,it is a widely recognized consensus in battery research to apply alkali metal anode(lithium and sodium)to replace the current commercial traditional graphite anode.However,dendrite growth of alkali metal anode and the consequent safety problems restrict its practical application.At present,great progress on alkali metal anode protection has been made by the means of improving electrolyte composition and constructing artificial SEI membrane.These two strategies usually focus on the improvement of the SEI film on alkali metal surface.In order to further enhance the energy density of the cathode,it is necessary to make the metal alkali metal thin as possible and improve the utilization ratio of alkali metal at the same time.However,high utilization of lithium will trigger larger volume change,posing a serious threat to the thin SEI of anode.How to improve the safety of alkali metal anode while taking into account the effect of volume expansion so as to realize the stability of the interface is a problem to be comprehensively considered in the research of lithium anode protection.The theory and the previous experimental results show that the composite structure of metallic lithium and 3D lithiophilic skeleton can not only inhibit dendrite growth,but also effectively alleviate the negative polar volume expansion effect because the 3D skeleton provides sufficient internal space.Therefore,the design of 3D composite lithium negative electrode can jointly improve the stability of lithium negative electrode from two aspects of dendrite inhibition and mitigation of volume expansion,thus playing a role of stabilizing the interface.In this paper,a lithiophilic modification layer was constructed in-situ on the surface of 3D porous conductive materials(copper foam,carbon cloth,etc.).By combining the advantages of micro/macro structure,the composite metal lithium negative electrode with excellent performance was expected to be obtained.The main results are as follows:(1)For the first time,foamed copper was selected as the current collector,and copper nanowires were constructed in-situ on the Cu surface.The nanostructure enhanced the reactive area,alleviated local current concentration,and provided abundant deposition sites in the three-dimensional space through the foamed copper,which effectively restrained the volume changes in the deposition/stripping process.Under ultrahigh areal capacity(12 mAh cm-2),the stable charge-discaharge process can be over 1000 h,and the deposition morphology is uniform and dense.Through the composite structure design of nanowire and 3D skeleton,the system successfully realized the stability under the high areal capacity,which sheds some light on the later work.(2)Carbonized ZIF-67 was first used as a current collector to regulate lithium metal deposition behavior.The ZIF-67 precursor was obtained by liquid phase reaction at room temperature,and then carbonized to break the coordination bond of cobalt ions to form element cobalt.The amino functional group in 2-methylimidazole,was decomposed into pyridine nitrogen and pyrrole nitrogen,thus obtaining cobalt/nitrogen double-doped graphene clusters(Co@N-G).The first principle was used to calculate the binding energy of each component to lithium atom in the material.The results showed that the trend of lithium binding was the strongest at the Co-N-C tri-phase interface,indicating that cobalt and nitrogen as the active sites of lithium affinity could synergistically improve the lithiophilicity of carbon materials.Co@N-G coating on copper foil as a modification layer can significantly improve the deposition process of lithium ions on the surface of the collector,inhibit dendrite growth,and improve the cycling stability.(3)lithiophilic nanorod arrays modified 3D carbon cloth was used as current collector and the electrochemical properties was explored here.By changing the solvent,carbonized ZIF nanorod array was constructed on the carbon cloth(NRA-CC).The battery tests showed that under extreme test conditions such as 12 mA cm-2,12 mAh cm-2,the cell could still cycle stably for more than 200h,which was due to the synergistic effect of excellent lithiophilicity of the carbonized ZIF modification layer and abundance space of 3D skeleton.The 3D composite lithium anode was matched with high voltage positive electrode NCM and solid electrolyte,and a stable solid lithium metal battery was successfully constructed.The next step will focus on the design and synthesis of self-support 3D lithium anode,and explore simple and efficient promotion strategies for the interface problem between 3D lithium anode and solid-state electrolyte.