Ex-situ measurement of thermal conductivity and swelling of nanostructured fibrous electrodes in electrochemical energy devices. (1st March 2021) - Wang, Runqi
Highlights: Dry buckypaper's conductivity can be ~ 0.1–0.15 W/m K. Interstitial water increases its conductivity by >10 times. Ionic liquid and oil show similar conductivity enhancement. Liquid addition can increase buckypaper thickness by ~60%. Compression reduces swelling of buckypaper electrodes. Abstract: Nanostructured electrodes are widely used in electrochemical energy devices, such as batteries, fuel cells, and supercapacitors. This paper presents an ex-situ experimental study to measure the thermal conductivity and volume change of nanostructured fibrous electrodes that are based on multiwall carbon nanotube (MWCNT) buckypaper. Two typical interstitial liquids are investigated, including deionic water and ionic liquid (BMIM-PF6), along with oil (HM32 hydraulic oil) for comparison. It is found the buckypaper electrodes can be a poor through-plane thermal conductor with a conductivity around 0.2 W/m K despite of highly-conductive CNTs. External compression enhances the conductivities of wet samples up to 80–90%, and after that, further compression shows no evident impacts. Adding interstitial liquids significantly increases the sample's conductivity by up to about 10 times with liquid water exhibiting the largest enhancement. The results are compared favorably with two popular correlations established for wet soils. In addition, buckypaper swelling is observed upon liquid absorption with a thickness change as much as 70%, comparable to the literature data of cotton and viscose rayon fibers. External compression greatly reduces the swelling. The work is valuable to the thermal management and durability studies of nanostructured fibrous electrodes for fuel cells, batteries, and supercapacitor applications.