Preparation Of Polymer Nanocomposite Solid Electrolyte And Application In High Temperature Batteries

Secondary batteries have long occupied a dominant position in the market.Traditional commercial ion batteries have attracted much attention due to the safety problems of organic liquid electrolytes,such as leakage,volatilization and high temperature explosion.In order to improve the safety performance of secondary batteries,polymer electrolyte with excellent safety and thermal performance can be used to replace flammable and explosive organic liquid electrolyte.Polymer electrolytes have many advantages,including nonvolatility,low flammability,low cost,machining flexibility,and good interface compatibility compared to ceramic solid electrolytes.However,the practical application of lithium/sodium secondary solid-state batteries is restricted by the low ionic conductivity,narrow electrochemical window,and dendrite growth of lithium/sodium anode materials.Based on the above problems,in this paper,from the perspective of polymer matrix modification,ZIF-8 nanoparticles were introduced into different polymer substrates by in-situ polymerization method,prepared several high-performance solid electrolytes,and studied its impact on various performance.The main research contents are as follows:(1)Poly(ethylene glycol)methyl ether methacrylate-co-4-vinylbenzenesulfonic acid sodium salt(PEGMEM-co-SSS)copolymers were synthesized by a simple free radical polymerization method.The introduction of SSS monomer is attached to the polymer backbone,and provides a single sodium source.Then,we develop a MOF-based single sodium-ion conducting solid electrolyte by in-situ dispersing ZIF-8 nanoparticles into the copolymer matrix.The Zn²⁺acidic sites in ZIF-8 framework preferentially coordinate with the sulfonic acid groups of the copolymer segment by electrostatic interactions,which effectively increases the dissociation of sodium ion.Meanwhile,the well-defined crystalline pore structure of MOFs provides transport channels for ionic migration,realizing the domain-limited efficient transmission of sodium ions.As a result,the nanocomposite electrolytes show a high ion transference number of 0.89 and an ionic conductivity of 4.01×10^-4 S cm^-1 at 80°C.The Na/Na₃V₂(PO₄)₃ cells with such nanocomposite solid electrolytes demonstrate decent rate capability,as well as excellent cycling stability with an initial discharge capacity of 76.6 mAhg^-1 and a capacity retention of 97%after 200 cycles at 0.5 C(80°C).(2)The nanocomposites electrolytes of ZIF-8@PEGMEM-co-AMPS were developed via free radical polymerization reaction,using AMPS and PEGMEM as polymeric monomers,ZIF-8 nanoparticles of 2-methylimidazole(2-MI)and Zn(NO₃)₂ synthesized as a filler.Among them,grafting segments of AMPS and ZIF-8 nanoparticles could effectively inhibit the crystallization of EO chain segments in PEGMEM.In addition,the AMPS with polar groups and ZIF-8nanoparticles with acidic surface are conducive to the dissociation of lithium salts,and improves the ionic conductivity of lithium ions.As a result,the ion conductivity of the composite electrolytes is 1.63×10^-3 S cm^-1 at 80°C.The Li/LiFePO₄ cells exhibit good long cycle performance at 80°C,and the surface of the lithium electrode after the cycle is relatively flat and there is no obvious lithium dendrite.