Preparation And Electrochemical Properties Study Of Plastic Crystal Composite Polyacrylate Electrolytes

The liquid electrolyte lithium ion batteries suffer serious safety problems due to the use of flammable carbonate ester organic solvents,and the lithium metal electrode in organic electrolyte is unstable,those prevent the practical application of lithium metal second batteries.Using polymer electrolyte instead of liquid electrolyte can effectively solve above problems.Polymer electrolyte does not contain volatile liquid solvent,and its safety is improved remarkably.Meanwhile,it has advantages of easily forming,good elasticity,light weight and multifunctional application.Nevertheless,the polymer electrolyte has low room-temperature ionic conductivity,poor mechanical strength,large electrode-electrolyte interface impedance and other key issues need to be solved.In this thesis,plastic crystal polymer electrolyte has been prepared by in situ and UV-cured polymerized methods,its physicochemical and electrochemical properties were characterized,and the electrochemical performance of LiFePO₄/polymer electrolyte/Li batteries also had been studied.Using trimethylolpropane ethoxylate triacrylate?TMPETA?as monomer,sulfonated non-woven fabric as supporting substrate,succinonitrile plastic crystal composite polymer electrolyte was prepared by in-situ polymerized method,which can form tight interface contact,effectively reduce interface impedance,non-woven 3D space network provide a good support for polymer electrolyte,and significantly enhance mechanical strength and thermal stability of the polymer electrolyte.The preparared polymer electrolyte has 0⁴.70 V electrochemical stable window,0.89×10^-3 S/cm room-temperature ionic conductivity,2.72×10^-3 S/cm at 55 ?,lithium ion transfer parameter is up to 0.42.The composite polymer electrolyte has good compatibility with lithium metal electrode and can inhibit the growth of lithium dendrites.The assembled LiFePO₄/in-situ polymer electrolyte/Li polymer battery has a 151.0 mAh/g discharge capacity at 0.2 C at room temperature after 200 cycles,and the capacity retention rate is up to 97.4%,and without any capacity attenuation after 150 cycles at 0.5 C.At 55 ?,the battery has 156.5 mAh/g rate capacity at 1 C,and 117.7 mAh/g at 8 C.The other plastic crystal composite semi IPN polymer electrolyte was prepared by UV-cured method by taking TPMETA and poly?ethylene glycol?methyl ether acrylate?PEGMEA?as the monomers.The semi IPN polymer structure enable the electrolyte has good flexibility.The preparaed composite polymer electrolyte has good thermal stability up to 185 ?,0⁴.78 V electrochemical stable window,0.91×10^-3 S/cm room-temperature ionic conductivity,lithium ion transfer parameter of 0.43.LiFePO₄/UV-cured polymer electrolyte/Li polymer batteries were assembled,the battery has a first cycle discharge capacity of 147.1 mAh/g at room temperature at 0.5 C cutternt density,the capacity retention rate is nearly 94% after 100 cycles.At 55 ? and 2 C current density,the discharge capacity is about 150 mAh/g for the first cycle,and without any capacity attenuation after 138 cycles,the capacity retention rate is more than 96% after 150 cycles,the rate discharge capacity is close to 150 mAh/g at 5 C current density,and 137.2 mAh/g at 10 C.It has been found that both the polymer battery and liquid electrolyte battery have almost similar dynamic property during the Li ion intercalation/deintercalation process by analyzing the cyclic voltammetry curves at different scanning speed.