Preparation And Performance Study Of Composite Separators And Gel Electrolytes For Lithium Metal Batteries

Lithium metal batteries have attracted widespread attention due to their ultra-high energy density,but their further development is limited by significant safety hazards in the process,such as overgrowth of lithium dendrites and leakage of organic electrolytes.Coating ceramic particles on the surface of the separator can suppress the growth of lithium dendrites to a certain extent,while using gel electrolytes instead of organic electrolytes can solve the leakage problem.However,currently used ceramic coatings and gel electrolytes have certain drawbacks,such as poor lithium ion conductivity or low mechanical strength.In this work,Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）with high ion conductivity was selected and modified to obtain a high-performance ceramic material.And the high-performance composite separator and gel electrolyte were prepared through rational design.Firstly,LLZTO nanoparticles coated with polydopamine（LLZTO@PDA）were prepared using a solution oxidation method.The environmental stability of PDA coating prevented the formation of lithium carbonate（Li₂CO₃）on the surface of LLZTO after storage in the air for more than 30 days,avoiding damage to battery performance.The commercial polyolefin separator（PP）was further modified by the coating method to obtain PP-LLZTO@PDA composite separator with a tensile strength of 103 MPa.The synergistic effect of PDA and LLZTO effectively inhibits the growth of lithium dendrites.The battery assembled with this composite separator could cycle stably for more than 600 hours at 0.5 mA cm^-2.In addition,the Li//Li Fe PO₄ battery assembled using this composite separator showed the capacity retention rate of 81%after100 cycles at 1 C.After charging and discharging at a higher current density of2 C,the capacity of the battery could recover to 95%of the initial capacity,demonstrating excellent cycle and rate performance.Secondly,a composite nanofiber membrane（LLZTO@PDA-PAN）with polyacrylonitrile（PAN）and LLZTO@PDA nanoparticles as components was prepared by electrospinning and used as the supporting skeleton,in which 1,3-dioxolane（DOL）was used to induce in-situ polymerization to obtain a PDOL gel polymer electrolyte.The electrolyte had a room temperature ionic conductivity of 0.9 mS cm^-1,a low migration activation energy of 0.043 eV,a lithium ion migration number of 0.86,and a high electrochemical stability window of 5.9 V,showing excellent basic electrochemical performance.At the same time,the electrolyte showed good cycling and rate performance.A Li//LiNi_0.8Co_0.1Mn_0.1O₂ battery assembled with this electrolyte had an initial discharge specific capacity of 193.9 mAh g^-1 at 0.1 C and the coulomb efficiency was closed to 100%.After charging and discharging at a higher current density of 2 C,the capacity of battery could recover to 91.5%of the initial capacity.