Temperature-Induced Activation of Graphite Co-intercalation Reactions for Glymes and Crown Ethers in Sodium-Ion Batteries

• Published in: Journal of physical chemistry. C Vol. 122; no. 47; pp. 26816 - 26824
• Main Authors: Goktas, Mustafa, Akduman, Baris, Huang, Peihua, Balducci, Andrea, Adelhelm, Philipp
• Format: Journal Article
• Language: English
• Published: American Chemical Society 29.11.2018
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b07915

The intercalation of solvated ions into graphite leads to ternary graphite intercalation compounds (t-GICs). Here, we study the impact of temperature on the electrochemical activity of graphite electrodes for co-intercalation reactions between 20 and 80 °C in sodium cells. For this, a range of linear ethers (mono-, di-, tri-, and tetraglyme) are studied. For the first time, pentaglyme and several crown ethers are also investigated. We find that several solvents that appear as unsuitable for the co-intercalation reaction at room temperature provide higher capacities at elevated temperatures. The most evident example is pentaglyme. While poor performance is found at room temperature for this solvent (20 mAhg−1 and large polarization), almost complete utilization (∼110 mAh g−1) and excellent rate capability are obtained at 45 °C. We find that the reactions involving mono-, di-, tetra-, and (at elevated temperatures also) pentaglyme are thermodynamically controlled, whereas the reaction with triglyme is kinetically limited. We also find that the crown ether 18c6 can be used as an electrolyte solvent above its melting point, which, for the first time, demonstrates the synthesis of t-GICs with crown ethers by electrochemical methods. Additionally, parasitic reactions are found to appear at elevated temperatures. Overall, we demonstrate that new co-intercalation reactions can be activated by temperature. The chemistry of these compounds might therefore be much richer than previously thought.