Research On Properties Of Gel Polymer Electrolytes And Lithium Ion Batteries

The traditional liquid lithium-ion battery contains low flash point and low ignition point organic electrolyte,so there are serious security risks in the production,transportation and use of lithium-ion batteries.The gel polymer electrolyte is a solvent-swollen polymer network system and does not contain a flowable flammable organic electrolyte,which can effectively improve the safety of the lithium-ion battery and make the battery miniaturized,lightened,and high energy density.It is an important trend to develop safe lithium-ion batteries in the future.This article aims to develop lithium-ion batteries with high-safty,high energy density,high power density and long cycle life.The physicochemical properties of polyvinyl chloride?PVC?gel polymer electrolytes based on different lithium salts were studied.In order to improve the mechanical strength,temperature characteristics,ionic conductivity and interface stability of the gel polymer electrolyte,as well as the cycle,rate characteristic,and safety characteristics of the battery,a new type of blended gel polymer electrolyte was developed,and the physicochemical properties of the gel polymer electrolyte,the battery preparation process,and the battery performance were studied.Finally,the structural stability of the tin-based anode and the cycle and rate characteristics of the battery can be improved by introducing inert element Cu and nano modification,and the performance of the corresponding gel polymer lithium-ion battery was studied.This paper is divided into the following three sections:?a?Research on preparation and properties of PVC gel polymer electrolytes based on LiClO₄,LiTSFI lithium salts.The results showed that the internal pores of LITFSI-PVC gel polymer electrolyte membrane are high connectecd,and with a large specific surface area compared to the LiClO₄-PVC gel polymer electrolyte.The tensile strength of LITFSI-PVC gel polymer electrolyte is 0.95 MPa,elongation at break is229.95%,and the mechanical strength is slightly lower than that of LiClO₄-PVC system.Since the association constant of LITFSI is smaller than LiClO₄,the LITFSI-PVC gel polymer electrolyte has more free lithium ions at the same molar amount lithium salt,which is favorable for the transport of lithium ions and therefore with higher ion conductivity(4.3×10^-4 S/cm),and its electrochemical window is above 5 V?vs Li/Li⁺?,and its lithium-ion transference number is as high as 0.69.It was shown that LITFSI with high dissociation constant,large anion and high temperature resistance is more suitable for PVC gel polymer electrolytes,which is beneficial to the improvement of its physicochemical properties.?b?Research on the preparation and properties of gel polymer electrolytes based on blending PVC,chlorinated polyvinyl chloride?CPVC?,methyl methacrylate,butadiene and styrene terpolymer?MBS?and thermoplastic acrylic resin?B44?and doping nano-SiO₂.The effect of film formation temperature on the morphology of the porous polymer membrane was studied.The effects of different lithium salt concentrations on the physical morphology,pore size distribution,porosity,and electrolyte uptake of the porous bleded polymer membrane were further investigated.When the concentration of LITSFI is 2.9 wt%and at 50°C,the pore structure of the porous polymer membrane is optimal,and the electrolyte uptake reaches the highest value?85%?.The ionic conductivity of the corresponding blended gel polymer electrolyte was 9.6×10^-4 S/cm and the lithium-ion transference number was 0.61.Finally,the porous polymer membrane was coated in situ on the anode by using the dip coating method.LiPF₆electrolyte was used to achieve blended gel polymer electrolyte,and PVC-CPVC-MBS-B44 blended gel polymer soft pack batteries?LiCoO₂/graphite?based on LITFSI-LiPF₆ blended lithium salt were obtained.The battery was cycled at0.5C,after 200 cycles,the discharge capacity was 116 mAh/g,the retention rate was still above 80%.Discharged at 0.2C,0.5C,1C,the discharge capacity of the blended gel polymer battery is basically the same as that of the liquid battery.The discharge capacity at 1C was 129.4 mAh/g,and the retention rate was 93.7%with respect to the0.2C capacity.According to the safety test standard,1Ah gel polymer soft pack batteries were subjected to heavy impact and nail penetration safty test,the batteries did not catch fire,smoke or burn.It was proved that through the selection of polymer matrix,blending modification,optimization of lithium salts,addition of nano-SiO₂ fillers,coating process optimization,the new blended gel polymer batteries have good cycle characteristics,high rate characteristic and high safety characteristic,have wide application prospects.?c?Study on the preparation and electrochemical properties of high theoretical capacity Cu₂SnS₃ nano-anode.The results showed that the annealing treatment at 540°C had an obvious improvement on the electrochemical performance of Cu₂SnS₃nanoparticles.Cu₂SnS₃ gel polymer electrolyte button cell were cycled at a current of100 mA/g from 0.05 V to 2 V.The initial discharge capacity of the cell was 1057 mAh/g,the reversible capacity was 230 mAh/g,and the first Coulomb efficiency was 21.7%.After 50 cycles,the discharge capacity decayed to 41 mAh/g.The first Coulomb efficiency is low and the cycle performance is poor.The mechanism analysis is the formation of amorphous Li₂S for the first charge and discharge,which consumes irreversible Li,micro-agglomeration of nanoparticles,large interface impedance between gel electrolyte and electrode,resulting in the severe polarization,the capacity of the active material can not be normally exerted.The nano-anode material itself and the interface compatibility with the gel polymer electrolyte must be further optimized.