Preparation Of Imidazole Multi-arm Polymeric Ionic Liquid All Solid State Electrolyte And Its Application In Lithium Metal Batteries

All-solid-state polymer electrolytes have become a potential alternative to liquid electrolytes due to their high safety,flexibility,processability and adjustable physical and chemical properties.However,the low ionic conductivity and poor interfacial contact between the electrode and electrolyte cause the inferior capacity,rate capacity and cycling performance,severely restricting the practical application of all-solid-state polymer electrolyte in lithium metal batteries.Herein,linear and four-armed polymeric ionic liquid（IMLPIL and IMFPIL）were prepared via the Atom Transfer Radical Polymerization of hydroxyethyl acrylate and ion exchanging reaction.Meanwhile,series and parallel polymeric ionic liquid(S-P（PEGMA-IM and P-P（PEGMA-IM））were obtained from the block copolymerization of PEGMA and hydroxyethyl acrylate.The relationship between the structure and electrochemical properties of the samples were investigated.The preformances of the assembled Li-metal batteries based on these polymer electrolytes were evaluated.The specific work is as follows.（1）Four-armed imidazolium cation-tethered polymeric ionic liquid（IMFPIL）is prepared through atom transfer radical polymerization of hydroxyethyl acrylate and subsequent functionalization.The branching architecture of the organic scaffold endows IMFPIL with high thermal stability,low glass transition temperature and loosely packed polymer backbones.The derived more free paths and volumes for Li-ion migration confer much enhanced ion conductivity on the as-prepared all-solid-state polymer electrolyte（IMFSPE）,which is 22 times that of the linear counterpart with the same composition.High-temperature thermal integration of IMFSPE into the lithium metal battery effectively eliminates the gaps between the electrolyte and the two electrodes,rendering excellent interfacial contact and stability.The volume variation of the electrodes during the charge-discharge can be effectively mediated.As a result,in sharp contrast to the battery failure of the linear counterpart,such an integrated Li Fe PO₄/IMFSPE/Li all-solid-state battery presents a high discharge capacity of 153 m Ah g^-1 at 0.2 C with 99%of coulombic efficiency,and the capacity retention ratio reaches 73%after 150 cycles.Compared with IMLSPE,IMFSPE-2efficiently weakens the formation of dendritic lithium.The branching design combining with the thermal integration strategy and superior electrochemical features of imidazole make IMFSPE behave as an all-solid-state polymer electrolyte,which paves a new way for developing PILs as ideal SPEs in energy storage device.（2）Series polymeric ionic liquid（S-P（PEGMA-IM））was prepared by imidazole functionalization of P（PEGMA）.Meanwhile,parallel polymeric ionic liquid（P-P（PEGMA-IM））was obtained via from the block copolymerization of PEGMA and hydroxyethyl acrylate.Due to the introduction of branched vinyl imidazole,the glass transition temperature of P-P（PEGMA-IM）is effectively decreased,and the introduction of a cross-linked structure makes the thermal stability slightly improved.The special vinyl imidazole branched structure effectively improves the ionic conductivity of P-SPE.The electrochemical windows of S-SPE-2 and P-SPE-2 of the two samples are 4.83 V and 4.87 V,respectively.The lithium ion migration numbers of S-SPE-2 and P-SPE-2 are 0.41 and 0.46.As a result,in contrast to the battery of the S-SPE counterpart,such Li Fe PO₄/P-SPE/Li all-solid-state battery presents a high discharge capacity of 157 m Ah g^-1 at 0.2 C with 99% of coulombic efficiency,and the capacity retention ratio reaches 81%after 100 cycles.The interface impedance of the S-SPE keeps increasing during the cycle,which makes the capacity retention rate of the S-SPE after100 cycles only 75%.Compared with S-SPE,P-SPE effectively reduced the formation of lithium dendrites and dead lithium.The introducing of vinyl imidazole in the PEGMA backbone makes the polymer more efficient in the application of all solid-state lithium metal batteries.