Construction Of Multifunctional Composite Separator And Its Application In Lithium-ion Batteries

In recent years,with the rapid development of 5G mobile phones and electric vehicles,the energy density of lithium-ion batteries is facing greater challenges.Using lithium metal with a high specific capacity（3860 m Ah/g）to replace traditional graphite as the anode can greatly improve the energy density of the battery,which has become a research hotspot.However,the problems of lithium dendrite growth and the irreversible loss of lithium caused by lithium metal in the cycling process hinder the practical application of lithium metal anode.As an important way to stabilize lithium anode,the design of functional separator has been widely studied.Therefore,in this paper,a novel composite separator based on anodic aluminum oxide（AAO）film with high hardness and non-flammability is used as the framework to inhibit the growth of lithium dendrite and improve the electrochemical performance of lithium battery.The main research is as follows:1.AAO film with ordered channels was prepared by two-step anodic oxidation method using self-made electrolytic tank device.The metal-organic framework（MOF）was grown in situ in the channel of AAO film at room temperature,and the AAO@MOF composite separator was prepared.MOF particles with small pore can block the passage of electrolyte anions with large volume to ensure the rapid transport of lithium ions,and its abundant polar bonds can also promote the complexation and dissociation of lithium salts.In the cycling test of Li-Li symmetric cells,the cell with AAO@MOF separator has a smaller and more stable overvoltage than the cell with Celgard and bare AAO separator cells.The discharge capacity of Li/Li Fe PO₄full battery constructed by AAO@MOF separator can still maintain at about 110 m Ah/g after 200 cycles,and the capacity retention rate can reach 86%.This work provides a new solution for the long stable cycling of lithium anode and a new idea for the preparation of ordered MOF arrays.2.The AAO template was prepared by anodic oxidation method,and the polymer PVDF-HFP was filled in the channel of AAO channel in the molten state,so as to complete the preparation of the AAO@PVDF-HFP composite separator.PVDF-HFP with high dielectric constant has great advantages in the dissociation of lithium salts and the concentration of carrier,in which the interaction between the polar atom fluorine atom and lithium ion can guide the transport of lithium ion.At a current density of 2 m A/cm²,Li-Li cells with AAO@PVDF-HFP composite separator have a long cycling life more than 1600 hours.The composition analysis on the surface of the lithium anode after a long cycle confirmed that the stable and strong SEI film was formed during the cycling process.In addition,the AAO@PVDF-HFP composite separator has a good compatibility with Li/Li Fe PO₄battery.After 360 cycles,the discharge capacity can still maintain at 140 m Ah/g,and the capacity retention rate is close to 100%.The results show that reasonable structure design and composition matching of the membrane is an effective way to restrain lithium dendrite and improve the performance of the battery.