Preparation And Electrochemical Properties Of UIO-66 Modified PEO/PVDF Polymer Electrolytes

As a lightweight,convenient,clean,and efficient energy conversion tool,lithium-ion batteries have greatly promoted the development of the electronic devices,electric transportation,and large-scale energy storage.Commercial lithium batteries using liquid electrolytes frequently face safety issues such as thermal runaway and secondary explosions.In contrast,solid electrolytes offer enhanced safety and reliability,making them a promising choice for future high-performance lithium-ion batteries.Polymer solid electrolytes possess flexibility,enabling good contact with electrode materials,and exhibit high processability.However,their conductivity is relatively low.Uio-66 metal-organic frameworks（MOFs）possess a tunable porous structure that facilitates rapid ion motion.In this study,we utilized Uio-66-modified organic electrolyte PVDF to construct a high-performance composite electrolyte material,aiming to improve the charge distribution density and promote Li⁺ion transport at the interface,thus enhancing the electrochemical performance of the polymer electrolyte.The main research findings are as follows:Commercial lithium batteries using electrolytes have safety issues such as physical and chemical instability,frequent thermal runaway,and secondary explosions.In contrast,solid-state electrolytes are expected to become the preferred choice for future high demand lithium-ion batteries,which are safer and more reliable.Polymer electrolytes have a certain degree of flexibility,can establish good contact with positive and negative electrode materials,and have high processability,but their conductivity is low.Uio-66 is a type of MOFs with an adjustable porous structure that provides rapid ion movement.This article uses Uio-66 to modify organic electrolyte PVDF to construct high-performance composite electrolyte materials,in order to improve the internal charge distribution density of PVDF polymer electrolytes and promote the interface Li⁺ion transport ability.Assemble the battery and conduct a series of electrochemical performance studies.The main research is as follows:（1）The Uio-66 MOF material was modified with imidazole to obtain the modified metal-organic framework material（Muio）,which was then incorporated as a filler into the PVDF polymer electrolyte.The changes in impedance and conductivity of the PVDF/Muio polymer electrolyte were investigated,along with the influence of the Uio-66-to-imidazole mass ratio on the performance of the PVDF polymer electrolyte,and the mechanism of imidazole-modified Uio-66 was analyzed.The results showed that when the Uio-66-to-imidazole mass ratio was 1:1,the impedance of the PVDF/Muio polymer electrolyte decreased to 104.2Ω,the ion conductivity reached 1.853×10^-4 S cm^-1,the activation energy was 0.32 e V,and the Li⁺ion migration number was 0.5398.Furthermore,the electrochemical window was as high as 5.22 V.（2）The PVDF/Muio polymer electrolyte was assembled into a full battery.The battery performance was then tested.At 28℃and 0.1 C rate,the initial discharge specific capacity of the full battery reached 168 mAh·g^-1,with a first-cycle coulombic efficiency of 99.862%.At a discharge rate of 1C,the capacity was 85.6715 mAh·g^-1.After 250 cycles,the capacity retention rate was 80.45%.At 28℃,the battery could cycle for 450 h at 0.1 mA/cm²with a polarization voltage less than 0.5 V.（3）A sandwich-structured solid electrolyte（BMP）was designed,with bacterial cellulose BC loaded Uio-66 as the core layers and PVDF as the surface layer.The effect of different mass ratios of BC to Muio in the sandwich structure on the ion transport capacity of the sandwich solid electrolyte was studied.The experimental results showed that when the BC-to-Muio ratio was 1:2,the ionic conductivity of the obtained electrolyte was 2.58×10^-4 S cm^-1,which was 6times higher than that of the electrolyte without BC and Muio fillers,and 1.4times higher than that of the uniformly added Muio electrolyte.The electrochemical stability window of this electrolyte reached 5.218 V,and the Li⁺migration number was 0.4825.（4）The BMP was assembled into a full battery and then tested.The experimental results showed that at 28℃and 0.1 C rate,the initial discharge specific capacity of the full battery reached 163.96 mAh·g^-1,with a first-cycle coulombic efficiency of 99.85%.Under conditions of 0.1 mA/cm²,the full battery could cycle for 570 h with a polarization voltage less than 0.125 V.The mechanistic analysis suggests that BC-loaded Uio-66 particles in the sandwich structure can establish an anion-capturing layer,reducing Li⁺migration barriers and promoting freer movement of Li⁺in the electrolyte.Furthermore,the sandwich structure prevents excessive accumulation of anions at the electrode interface,facilitating uniform charge distribution within the system and thus improving the electrochemical performance of the battery.