Structural supercapacitor electrodes for energy storage by electroless deposition of MnO2 on carbon nanotube mats

Structural supercapacitors have great potential for the future of electric-powered vehicles and mobile robots, as they can serve a dual purpose of providing structural integrity and storing electric energy. However, a significant challenge in the development of these energy storage structures is the creation of electrodes that are mechanically strong and stiff. Herein, we report an electroless technique for depositing pseudocapacitive manganese dioxide (MnO2) uniformly throughout carbon nanotube (CNT) mats, resulting in multifunctional supercapacitor electrodes with simultaneously enhanced mechanical and electrochemical properties. The deposited MnO2 nanoporous material acts as a structural matrix supporting the CNTs, thus improving the strength and stiffness. Furthermore, the uniform distribution of MnO2 nanoparticles throughout the substrate reduces the through-thickness electrical resistance and achieves outstanding rate capability. With the optimum loading of MnO2 95 wt%, which gives the highest strength, the total capacitance of the electrode material increased by nine times compared to the baseline material, while the tensile strength and stiffness were improved by 110% and 430%, respectively. Employing these high-performance electrodes in supercapacitors results in improved device-level performance. Specifically, the optimum loading of MnO2 increased the device's energy density by around 100 times without compromising the power density. These new high-performance structural electrodes represent a promising technology that could accelerate the practical application of energy storage composite structures.