Application Of Water-based Polyurethane Binder In Graphite Anode Of Lithium Ion Battery

Lithium ion batteries have been widely used in various fields due to their high energy density,good cycle stability and no pollution.In the process of preparing lithium-ion batteries,the traditional PVDF binder uses N-methyl-pyrrolidone?NMP?as solvent,which is toxic and harmful to the environment.At the same time,due to its insufficient bonding strength,the active material may be peeled off during the charging and discharging of the battery.Therefore,the development of new environmentally friendly and efficient binders has become one of the focuses of current research.Waterborne polyurethane?WPU?uses water as a dispersant is non-toxic,inexpensive and has good bonding properties.In this paper,the application of waterborne polyurethane in graphite negative electrode of lithium ion battery is studied.In chapter 2,the raw materials as IPDI,PTMG,DMPA,Ymer-N120 and sodium ethylenediamine sulfonate?A-95?were used to synthesize carboxylic acid type,nonionic type and sulfonic acid type waterborne polyurethane.The results show that the WPU synthesized with three different ion types has an initial decomposition temperature above 273?,which meets the requirements of battery binders.The bonding strength and conductivity of WPU-2were better than that of traditional PVDF,th peel strength up to 0.37 N·cm^-1.Three kinds of WPU and PVDF were used as binders to prepare the anode and assembling the battery.According to the test,it can be seen that the battery assembled with WPU2 as binder has the best performance,the initial discharge capacity reached 62 mAh·g^-11 at 0.2C with the coulombic efficiency of 86.61%.The capacity retention was 80.2%after 700 cycles at 1C.In chapter 3,a series of fluorinated sulfonated waterborne polyurethane?FWPU?were synthesized with IPDI,PPG,A-95 and pfoctyl hexanediol as main materials.The effect of FWPU as graphite anode binder on the performance of lithium battery was studied.The results showed that the initial decomposition temperature of fluorine modified WPU emulsion is above 240?,which meets the requirements of battery binder.When the content of organic fluorine is 3%,the bonding strength and conductivity of the fluorine modified waterborne polyurethane?FWPU3?are better,and the peeling strength is 0.56 N·cm^-1.The battery was assembled by the anode prepared by the modified WPU binder with different content of fluorol.The result showed that performance of battery prepared by WPU-3 is best,the initial discharge capacity reached 372 mAh·g^-11 at 0.2C with the coulombic efficiency of 84.47%,and the capacity retention was 82.9%after 700 cycles at 1C.In chapter 4,fluorinated waterborne polyurethane was synthesized from IPDI,PPG,sodium ethylenediamine sulfonate?A-95?and perfluorooctyl hexanediol,using PVP as a protective agent.The organic fluorine modified waterborne polyurethane?PANI-FWPU3?were prepared by synthesizing PANI in FWPU emulsion.The results showed that PANI modified FWPU3 emulsion was successfully synthesized.When the mass fraction of PANI in FWPU3 is 4%,the composite modified emulsion?PANI-FWPU3-4?has the best comprehensive performance.The anode prepared by PANI-FWPU3-4 binder was used to assemble the battery.The initial discharge capacity reached 368 mAh·g^-11 at 0.2C with the coulombic efficiency of 86.81%,and the capacity retention was 88%after 400 cycles at 1C.