Preparation And Property Investigation Of The Novel Polycarbonate Based Polymer Electrolyte

Lithium ion batteries(LIBS)is a good choice for energy storage device.It has been widely used in portable mobile devices,electric vehicle and smart grid because of high energy density,high working voltage,long life,environment friendly,and no memory effect.However,there are two problems hindering the further development of lithium ion battery: how to improve the energy density of battery,how to improve the safety performance of the battery.Traditional lithium-ion batteries use organic liquid electrolyte which is flammable,volatile,existing danger of fire,explosion and leakage.Polymer electrolyte is a promising candidate to replace the liquid electrolyte,because they have good ion conductivity,excellent electrochemical performance and excellent machinability,without any leak.Polycarbonate based polymer electrolyte have been received widespread attention because of larger lithium ion transference number and wide electrochemical stability window and favorable compatibility with lithium metal.Therefore,this article design and synthesis of the two kinds of polymer electrolyte based on polycarbonate,and they are used in lithium batteries.The main work is as follows:1.The hydroxyl-terminated poly(diethylene glycol carbonate)was prapared by transesterification,and then methacrylate-terminated poly(diethylene glycol carbonate)dimethacrylate(PDEC-DMA)macromonomers were synthesized by hydroxyl groups from PDEC and methacryloyl chloride.PDEC-DMA macromonomers were used to in situ polymerization prepare gel polymer electrolyte and all solid polymer electrolyte.Polymer electrolyte was tested with various electrochemical performance and applied in lithium batteries.Gel network polymer electrolyte(NET-PDEC)have high ionic conductivity(1.65×10-4 S·cm-1),wide electrochemical window(4.5 V vs Li+/Li)and good compatibility with lithium metal.Gel electrolytes were applied in the Li/LiFePO4 battery and high energy density Li/LiFe0.2Mn0.8PO4 battery,and two types of batteries showed good rate performance and cycle performance at room temperature.All solid state polymer electrolyte was used in Li/LiFePO4 battery with excellent cycle performance at 100 oC.2.Using PDEC,isophorone diisocyanate and chain exterder ethylenediamine as raw materials,polycarbonate based polyurethane was achieved successfully.Gel electrolyte based on polyurethane possessed high electrochemical stability window(up to 5 V vs.Li+/Li),the ionic conductivity of 2.93×10-4 S·cm-1 at 60 oC and lithium ion transference number of 0.53.Polymer electrolyte had good good compatibility with lithium metal anode.Finally gel polyurethane electrolyte was used in Li/LiFePO4 batteries at 60 oC,showing excellent cycle performance,with 97% capacity retention at 0.1 C after 100 cycles.