Preparation And Application Of Gel Polymer Electrolyte Films For Lithium Ion Batteries

Lithium ion batteries have many advantages,such as long cycle life,high specific energy and good electrochemical stability.They have good application prospects in the field of portable electronic products and electric vehicle.However,the security problem has been restricted the further development of lithium ion batteries.The reason of its security problem is the organic electrolyte which is easy to break down and burning.Therefore,in recent years,polymer lithium ion batteries have been widely concerned because of its better safety performance.The key to the development of polymer lithium ion batteries lies in the preparation of polymer electrolytes with good comprehensive performance.At present,the polymer electrolyte research is mainly focused on gel polymer electrolyte.In this paper,the polymer PVd F-HFP is used as matrix materials,Li BF₄ is used as adding lithium salt,and the solid polymer electrolyte films are prepared by solution casting.X ray diffraction,scanning electron microscope,universal tensile testing machine,differential scanning calorimetry,frequency analyzer and electrochemical workstation are used to analyzed the polymer electrolyte films.The results show that the 85 PVd F-HFP:15Li BF₄ system has good crystallinity,thermal performance and mechanical properties.However,the ionic conductivity and electrochemical stability window are still relatively low,which cannot be used to assemble polymer lithium ion battery.In order to improve the electrochemical performance of the polymer electrolyte films,ethylene carbonate and propylene carbonate were added to the 85 PVd F-HFP:15Li BF₄ system.It is found that with the addition of plasticizers,the crystallinity of gel polymer electrolyte will decrease,and thu s its electrochemical performance can be significantly improved.When the added plasticizer content is 150%,the polymer electrolyte film has the best microporous structure and relatively lower crystallinity.Therefore,the ionic conductivity of 85 PVd F-HFP:15Li BF₄+150%（EC+PC）gel polymer electrolyte film is the highest,it is up to 8.1×10-4 S cm-1,and the electrochemical stability window also up to 4.4V,which means it can satisfy the practical requirement of polymer lithium ion batteries.In this paper,the gel polymer electrolyte films which have the content of plasticizer was 100%,150% and 200%,respectively,was applied to the assembly of button polymer lithium ion batteries.And then the battery test system is use to test the charge and discharge per formance of these polymer lithium ion batteries.The results show that the polymer lithium ion battery assembled by 85 PVd F-HFP:15Li BF₄+150%（EC+PC）gel polymer electrolyte film,have the best first charge and discharge performance.The first discharge capacity of this battery was 165.1 m Ah g-1,after 100 times cycles,the discharge capacity was 159.4 m Ah g-1,the capacity loss percentage was only 3.45%.In addition,the charging and discharging platform of the polymer lithium ion battery is very flat,the charging platform voltage is 3.48 V,and the discharge platform voltage is 3.38 V.The polymer lithium ion battery is tested under different current intensity,and it also shows a good charge and discharge performance,which means it can meet the requirements of high power charge and discharge.