Preparation And Properties Of Polyionic Liquid Based Solid Electrolyte

Solid electrolyte has advantages such as low leakage,wide electrochemical window,and good thermal stability.Its application in lithium metal batteries can mechanically suppress the growth of lithium dendrites,fundamentally solving the safety issues caused by traditional organic electrolytes in lithium metal batteries.Compared to inorganic solid electrolytes,organic polymer electrolytes have the advantages of low cost,simple preparation method,high safety,and compatibility with deformation during electrode cycling.However,the hindered migration of lithium ions caused by high crystallinity limits the development of organic polymer electrolytes.It is expected to improve the ionic conductivity by adding plasticizers to the polymer substrate.Ionic liquids have the advantages of low vapor pressure,incombustible,nonvolatile and high ionic conductivity.When they are used as plasticizers,they can effectively improve the ionic conductivity and electrochemical stability of polymer electrolytes.It is worth noting that a large number of ionic liquids are used as plasticizers at the cost of sacrificing the mechanical properties of polymer electrolytes.In response to the above issues,this paper grafted ionic liquids onto polymer frameworks,resulting in polyionic liquids with high ionic conductivity and excellent cyclic stability.The specific research work is as follows:（1）This article graft EMIM⁺with high ionic conductivity onto MMA monomers and prepare poly（1-ethyl-3-ethyl acrylate）imidazole bromide through free radical polymerization（ATRP）.By controlling the reaction time,the regulation of polymer molecular weight is achieved.The experimental results show that the polyionic liquid based solid electrolyte（PIL-18）prepared at a reaction time of 18 hours exhibits excellent electrochemical performance,with a room temperature ionic conductivity of up to 0.43 m S·cm^-1.This electrolyte has a wide electrochemical stability window of 5.12 V,and lithium metal batteries using a polyionic liquid based solid electrolyte have excellent cycling stability.At a current density of 0.05 m A·cm^-2,the Li|PIL-18|Li symmetric battery can stably cycle for 1800 hours,with a polarization voltage of 90 m V.At a current density of 0.5 C,the Li|PIL-18|LiFePO₄ all solid-state battery still has a high specific capacity of 110.8 m Ah·g^-1after stable cycling for 250 cycles,At this point,the capacity attenuation is only 8.2%.（2）To solve the problems of limited strength,poor self-supporting performance,difficult packaging and limited shape in practical application of a single polyionic liquid gel,this topic screened the common polymer substrates such as PAN,PVDF,PVDF-HFP,PEGDA and PVC,blended the PVDF-HFP with low crystallinity and high electrochemical window with the PIL prepared in the previous chapter,and optimized the electrolyte composition by adjusting the substrate content.Compared to pure polyionic liquid solid electrolytes,the ion conductivity of this composite solid electrolyte at room temperature is(7.15×10^-4 S·cm^-1)and lithium ion migration number(t_Li⁺=0.77)showed significant improvements.Lithium metal batteries using composite solid electrolytes have excellent cycling stability.At a current density of 0.05 m A·cm^-2,Li|PVDF-HFP@PIL 3:1|Li symmetric battery can stably cycle for 1500 hours,with a polarization voltage of only 50 m V.When the current density is 0.5 C,Li|PVDF-HFP@PIL 3:1|After stable cycling for 300cycles,LiFePO₄ still has a high specific capacity of 128.8 m Ah·g^-1,with a capacity loss rate of only4.1%.