An Energy-Power Balancing Act:  Balancing the High Capacity and Rate of LiMn₂O₄-Carbon Nanofoam Cathodes with Solution-Processable Conducting Polymer Anodes

As the energy and power demands of current and next-generation devices continually strain the capabilities of present power sources, there is a push to develop materials with high capacity and electrode architectures to facilitate delivering that capacity at high rates. En route to addressing this energy/power issue, we have shown that with the appropriate ultraporous electrode architecture, it is possible to extract full theoretical capacity from LiMn2O4, a nominal battery material, in as little as 18 seconds.[i] While representing a significant advancement at the single-electrode level, the implementation of these advanced electrode materials in practical devices has been hampered by the lack of suitable negative electrode materials with sufficient capacity to balance that of the LiMn2O4. A conducting polymer-based negative electrode would be ideal to pair with the LiMn2O4 in terms rate capability, but issues with solution processability have typically limited these materials to thin film-based electrodes, which will not provide adequate capacity for the LiMn2O4. Recently, the Reynolds group at Georgia Tech has developed synthetic protocols to overcome this roadblock for ProDOT-biEDOT-based polymers.[ii],[iii] This advancement makes it possible to incorporate such conducting polymers as thin, conformal coatings on the interior and exterior surfaces of conductive, porous carbon nanofoam-based electrodes. The nanoscale nature of the coating coupled with the intrinsically fast charge-discharge of the polymer supports high rate and the 3D projection of the conducting polymer via the macroscopically-thick carbon nanofoam provides high area-normalized capacitance to balance that of the LiMn2O4. [i]. Sassin, M.B., Long, J.W., Greenbaum, S.G., Stallworth, P.E., Mansour, A.N., Hahn, B.P., and Pettigrew, K.A., “Achieving electrochemical capacitor functionality from a traditional battery material: Conformal, nanoscale LiMn2O4 coatings on 3-D, device-ready carbon nanoarchitectures,” J. Mater. Chem. 1, 2431 (2013). [ii]. Ponder Jr., J. F.; Österholm, A. M.; Reynolds, J. R. “Designing a Soluble PEDOT Analogue without Surfactants or Dispersants,” Macromolecules 49, 2106 (2016). [iii]. Österholm, A. M.; Ponder Jr., J. F.; Kerszulis, J. A.; Reynolds, J. R., “Solution Processed PEDOT Analogues in Electrochemical Supercapacitors,” ACS Appl. Mater. Interfaces 8, 13492 (2016).