A New Method of Improving Electric Storage Efficiency and Heat Tolerance for ElectronicsMay 05, 2020 by Abdulwaliy Oyekunle
Researchers at The Pennsylvania State University have developed a new method of electric storage efficiency for capacitors using nanofillers at low volume content in a high-temperature semi-crystalline polymer.
Dielectrics and Storage Efficiency of Capacitors
Dielectrics determine the charge/discharge efficiency of capacitors. With a high dielectric constant and a high applied electric field, a desirable energy density is provided for capacitors. Dielectric polymers exhibit conduction losses at high temperatures and high electric field which causes heating in dielectric devices.
For instance, biaxially oriented polypropylene (or BOPP) films provide BOPP film capacitors with a relatively high energy density approximately 3 J/cm3. However, heating is attributed to the capacitors when used in applications with hot environments. This leads to installing additional cooling devices in applications using capacitors.
The Use of Dielectric Polymers
In the past, researchers have worked on improving the storage efficiency of capacitors using dielectric polymers. Experiments and researches are being conducted to improve energy density while providing techniques to reduce conduction losses.
The use of polymer capacitors in temperature above 150⁰C is also considered in recent researches. Such researches involve adding nanocomposites of high dielectric constants to the polymer matrix to raise the dielectric constant in an attempt to improve the energy density of the capacitor. This experiment does not improve the charge/discharge efficiency of capacitors as well as raising the operating temperature to 150⁰C.
In another study, nanocomposites of cross-linked high glass transition temperature polymer such as benzocyclobutene with 10% boron nitride nanosheets have proven to reduce conduction loss at high temperatures. This reduction in conduction loss results into having an energy density of 2.2 J/cm3 and 90% charge/discharge efficiency at 150⁰C under an applied electric field of 400MV/m.
Xin Chen, a doctorate candidate in the Dept of Materials Sciences and Engineering, and Qiming Zhang, a professor of electrical engineering from Penn State University, are pictured testing a film capacitor for the research study. Image credited to Penn State College of Engineering
Improving Electric Storage Efficiency in Dielectric Materials
Researchers at Pennsylvania State University adopted a scalable dielectric metamaterial to improve the energy density, charge/discharge efficiency and breakdown field of a high-temperature semi-crystalline dipolar polymer.
In the study, it was found that Poly arylene ether urea (PEEU) has a high dipole moment of 4.56 D which is also a high glass transition temperature polymer. The energy density of the dipolar polymer of the nano-filler loading at charge/discharge efficiency is six times greater than the energy density of the dipolar polymer without the nano-filler loading.
In addition, the performance of a dipolar polymer was compared with the PEEU adopted in the research. PEI with 0.32 percent volume nanofiller loading resulted in an increase in dielectric constant from 3.2 to 5. However, PEI nanofiller loadings did not improve the breakdown field.
Preparation Procedures of PEEU with Alumna Nano-filler
Poly arylene ether urea powder was first dissolved in dimethylformamide (aka DMF) at 60⁰C to form a solution and a weighted percentage of alumina particles which was also dispersed in DMF at about 25⁰C for an hour in order to form a suspension.
The PEEU solution was then added to this suspension and sonicated for six hours. This was then cast onto a silicon plate and kept in a vacuum for hours. The solvent in the solution was removed by drying at 80⁰C for 12 hours. This resulted in a film and further drying was done at 180⁰C for 24 hours to remove the remnants of the solvent. Platinum electrodes of 4 mm in diameters were sputtered on the film to cause the dielectric characterization.
In the end, PEEU with alumina nano-filler with thickness in the range of 2 µm to 3 µm was created.
Impacts of the Study on Electronic Devices
The experiment done in this study has shown that 0.21 percent of alumina nano-filler loading gives improvement to the energy density and the charge/discharge efficiency of capacitors. This makes it possible to have a wide range of applications such as for high voltage electric networks.
The experiment also shows that the dipolar polymer adopted can be used in applications that require high operating temperature, as high as 150⁰C without having to install external cooling devices.