Building thermally stable supercapacitors using temperature-responsive separators

Ion-Conducting Thermoresponsive Films Based on Polymer-Grafted Cellulose Nanocrystals

“…CNCs used in this study were isolated from Miscanthus x. Giganteus and oxidized via TEMPO-mediated oxidation to yield carboxylic-acid-functionalized CNCs (MxG-CNC-CO 2 H). 46,47 The MxG-CNC-CO 2 Hs (carboxylic acid content: 870 mmol kg −1 ) were functionalized with the amine-endcapped PPMAs (H 2 N-PPMA) using 4-(4,6-dimethoxy-1,3,5triazin-2-yl)-4-methylmorpholinium tetrafluoroborate (DMTMMBF 4 ) as the coupling agent to yield the PPMAgrafted CNCs (MxG-CNC-g-PPMA(6), MxG-CNC-g-PPMA- (10), MxG-CNC-g-PPMA (20), where the number in parentheses represents the approximate molecular weight of the grafted PPMA in kg/mol). The MxG-CNC-g-PPMAs were thoroughly washed with acetone and THF via a centrifugation/ resuspension process at least eight times to remove any free polymer and other contaminants.…”

“…by changing their physical or chemical properties have been subject to extensive research. , One class of temperature-sensitive polymers are those that exhibit a lower critical solution temperature (LCST). − Such polymers are soluble in a solvent at low temperature but become insoluble as the temperature rises above the polymer’s LCST. This class of responsive polymers has been commonly investigated in water and applied to a variety of smart thermoresponsive hydrogels with potential applications as actuators, − separators, , sensors, etc. In addition, it has been shown that with aqueous-based LCST systems it is possible to inhibit ion transport/conduction as the temperature is raised above the LCST. , …”

Advances in materials and fabrication of separators in supercapacitors

“…183 Jiang et al developed temperature responsive separators by casting poly( N -isopropylacrylamide) (PNIPAM) into thin films of varying thicknesses (20, 40 and 60 μm) which were then sandwiched between polypropylene to form a SC. 184 PNIPAM possesses a lower critical solution temperature (LCST) of 32 °C, below which they are hydrophilic, and shift towards the hydrophobic state at higher temperatures. Due to this property, ions can easily migrate between the electrodes at room temperature but would face higher resistance during migration at temperatures above the LCST due to steric hindrance of solvated ions.…”

“…Jiang et al developed temperature responsive separators by casting poly(N-isopropylacrylamide) (PNIPAM) into thin films of varying thickness(20, 40 and 60 µm) which were then sandwiched between polypropylene to form a SC 184. PNIPAM possesses a lower critical solution temperature (LCST) of 32 o C, below which they are hydrophilic, and shift towards the hydrophobic state at higher temperature.…”

Thermo‐responsive polymers for thermal regulation in electrochemical energy devices

“…Surprisingly, the ionic conductivity only reduced by 1 order of magnitude when the temperature increases from 25 to 60°C, and the zinc ion diffusion coefficient exhibited a slight decrease from 1.2 × 10 −9 to 0.9 × 10 −10 m 2 s −1 , which indicates the ion transport may not the limiting factor responsible for the thermal shutdown. A similar example based on PNIPAM is the PP/PNIPAM/PP sandwiched separator for supercapacitors, which exhibits a 50% capacitance decrease at 70°C with a scan rate of 0.5 V s −1 30 . Although the novel application of hydrogels into separators provides a possible route for avoiding thermal runaway, a practical solution will not be reached unless a rapid response to overheating in a non‐aqueous flammable electrolyte system is demonstrated.…”