Synthesis And Application Of Fluoropolvmer Electrolyte

With the increasing demand for targeted drugs,implantable drug delivery systems have become more and more widely used in various target organs.In order to meet the needs of various target organs and solve the power supply problem of implantable electronic systems,the development of new high-energy-density batteries is essential.Solid polymer electrolytes(SPEs)have emerged as promising alternatives for conventional liquid electrolytes(LE)to access high safety and high energy density all-solid-state batteries(ASSBs),owing to their flexible processability,highly tunable chemical functionality and cost effectiveness.Unfortunately,it is well recognized that the uneven lithium deposition at the surface of metallic lithium would generate electrically disconnected dendrites during repeated charge-discharge cycles,which would lead to large interfacial resistance,low coulombic efficiency,internal short-circuit and therefore premature cell failure,severely hindering the development of lithium-metal based batteries.The unstable solid electrolyte interface(SEI)between the lithium metal negative electrode and the electrolyte is considered to be one of the main causes of lithium dendrites in lithium metal batteries.The most common polyethylene glycol(PEG)SPE has an oxidation stability of less than 4 V vs.Li/Li⁺,which limits its application in high-voltage batteries.Therefore,it is important to develop a multifunctional SPE capable of uniform lithium deposition and a high electrochemical window.Fluorine-containing materials have great potential in the development of new electrolytes due to their high oxidation stability and non-flammability.According to recent reports,it is found that fluorine-containing materials help to form a stable SEI rich in Li-F,and can achieve uniform lithium deposition during charge and discharge cycles.Due to the high crystallinity and low Li⁺solubility of conventional fluoropolymers,these fluoromaterials are mostly used in small molecule liquid electrolytes.Therefore,it is urgent to develop practical solid fluoropolymer electrolytes to stabilize lithium electrodeposition and inhibit lithium dendrites growth.In this article,we use polyethylene glycol methyl ether methacrylate(PEGMA)and methacrylic acid-2.2.3.4.4.4-hexafluorobutyl(HFBMA)as raw materials,via photo-controlled radical polymerizations(photo-CRPs)method synthesized bifunctional fluorinated SPE(BF-SPE)which significantly enhanced the stability of lithium deposition in ASSB.In BF-SPE,the flexible side chain of polyether maintains the solvation of Li⁺and provides high ion conductivity.The fluorine-containing side chain promotes Li⁺from the strong Li-O interaction through the formation of potential Li-F interactions.It dissociates during the action and participates in Li⁺solvation with anions,which is conducive to stabilizing the formation of SEI.The existence of Li-F interaction is proved by ¹⁹F Nuclear magnetic resonance(NMR)and Fourier transform infrared spectroscopy(FTIR).In the lithium deposition/stripping test of Li||Li batteries,BF-SPE has a stable cycle of more than 1500 h at different current densities of 0.05 m A cm^-2,0.1m A cm^-2 and 0.2 m A cm^-2.And a thin and uniform lithium deposition and a stable SEI rich in Li F were observed.In the Li||Cu battery,the Coulombic efficiency(CE)was as high as 87%and it was cycled stably for 80 cycles.BF-SPE also has an electrochemical window of up to 5.0V,and the ASSB assembled with lithium iron phosphate(Li Fe PO4,LFP)and ternary cathode material(Li Ni0.5 Co0.2Mn0.3O2,NCM523)with a current rate of0.1 C at 70?C.,it can circulate stably with high CE,and show capacity reversibility under different magnifications.It embodies the safe and stable electrochemical performance of BF-SPE in high temperature and high voltage batteries.In conclusion,the BF-SPE system demonstrated the prominent influence of introducing fluorine functionality in solid polymer electrolytes to impede lithium dendrites formation and provided a promising way to develop practical ASSBs with highly improved safety.It also is promising to be applied to the ocular implantable drug delivery system to solve the problem of long-term stable power supply,which provides the possibility for the development of a smaller-volume drug delivery system.