| Under the background of energy transformation promoted by"two-carbon strategy",it is urgent to realize efficient energy storage and transformation.Among many energy storage devices,polymer-based flexible dielectric capacitors have the advantages of high power density,high voltage rating and strong machinability.They are widely used in high power density weapons,electromagnetic ejection devices and high voltage flexible DC transmission.Currently,many fields require polymer-based dielectric capacitors to work stably and efficiently at high temperatures(～120°C)and high fields(500 k V/mm).It is of great engineering significance to develop new polymer based composite media with high dielectric constant,high breakdown strength and high temperature and high field application.In this paper,a new type of composite thin film is prepared by using the strategy of coupling the advantages of linear nonlinear polymer with the structural design from microscopic to mesoscopic,so as to realize the optimization of"step"energy storage performance of polymer-based composite dielectric from low field to high field and then to high temperature and high field.The relationship between the structure and properties of the composite media was obtained through the structure characterization,performance testing and mechanism analysis.In order to solve the problem of low permittivity of polymer,one-dimensional titanium oxide nanotubes(TNTs)with large dipole moment,high permittivity and rich OH surface were introduced into linear polymer polyimide(PI)matrix by in-situ polymerization method to prepare PI/TNTs composite films.The structural characterization showed that,under the scraping process,TNTs were slightly oriented spontaneously in the PI matrix,which promoted the orderly arrangement of PI molecular chains and generated strong hydrogen bond interface between TNTs and PI matrix.The performance test shows that 1 wt%PI/TNTs composite film has the same breakdown strength as pure PI,and the dielectric constant is increased by53%.Under 260 k V/mm electric field,energy storage density can reach 2.85 J/cm~3,optimizing low field energy storage performance.In order to optimize the breakdown strength of polymer,ZIF-8 nanoparticles with metal active sites were introduced into PI matrix by in-situ polymerization to prepare PI/ZIF-8 composite films.In situ synchrotron radiation characterization confirmed that the thermal activation induced the"multi-site bonding effect"between the active site of ZIF-8 and the PI molecular chain during the imidization process,which played a role in strengthening the PI molecular chain.The performance test shows that the multi-site bonding network effectively inhibits the dielectric loss of the composite film and significantly increases the breakdown strength.At 500k V/mm,the energy storage density of 1 wt%PI/ZIF-8 composite film reaches 7.7J/cm~3,and the efficiency is maintained at～80%,which optimizes the high field energy storage performance.Aiming at improving dielectric constant,breakdown strength and matrix optimization.By optimizing the electrospinning process,TNTs were introduced into the nonlinear highly polarized P(VDF-HFP)matrix to prepare the horizontally oriented P(VDF-HFP)/TNTs composite films(PT).The dielectric property test shows that PT has higher dielectric constant and breakdown strength based on PI/TNTs.By in-situ polymerization,ZIF-8 was introduced into the linear PEI matrix with more stable dielectric properties at high temperature,and the PEI/ZIF-8 composite film(EZ)with high breakdown strength was prepared.The syntron radiation absorption spectra showed that there was a"bonding network"microstructure between ZIF-8and PEI matrix,which further improved the breakdown strength of EZ composite film.It can reach 664.5 k V/mm.Using EZ linear(L)composite film and PT nonlinear(N)composite film as insulation layer and polarization layer,EZ PT-EZ LNL laminated composite film was prepared by hot pressing process.EZ-PT-EZ combines the advantages of linear and nonlinear polymers,presenting excellent dielectric properties of high dielectric constant,low dielectric loss and high breakdown strength.At high temperature and high field,the"multi-site bonding network"in EZ insulation layer effectively inhibits the insulation performance degradation of EZ-PT-EZ sandwich composite film.At room temperature,the energy storage density of EZ1-PT1-EZ1 composite film can reach 13.68 J/cm~3 at 620k V/mm,and the efficiency is above 85%.At 120°C and 520 k V/mm,the energy storage density is 8.51 J/cm~3 and the efficiency is about 65%.LNL structure heterogeneous interface effectively inhibits charge injection and transport,optimizing energy storage performance at high temperature and high field.In this paper,starting from multiple dimensions such as package-matrix microstructure design,matrix and process optimization,and linear nonlinear mesoscopic structure design,solutions to the key problems of polymer-based composite media such as low dielectric constant,breakdown strength to be improved and high temperature applicability are given.The"step"optimization of polymer based composite dielectric energy storage is realized,and the application of polymer based composite dielectric in the field of new energy is promoted. |
PDF Full Text Request