Scalable All Nanotube Carbon Nanotube–Boron Nitride Nanotube–Carbon Nanotube Supercapacitors for Enhanced Structural Energy Storage

Composite structural supercapacitors (SSCs) seek to offer improved size, weight, and power energy storage to mobile devices or transportation vehicles. This technology, similar to the development cycle of high‐performance batteries, requires significant materials development tailored to the supercapacitors requirements. Several electrode materials have been developed which offer good energy and power performance, but are limited in their effectiveness due to the lack of an advanced separator material suitable for high‐performance composite materials processing. Currently, glass fiber cloths are the only feasible separator material for SSCs. The present research effort examines an alternative to separator materials. Boron nitride nanotube (BNNT) films have been deposited onto a single side of carbon nanotube (CNT) mat electrodes using vacuum filtration. Thin and uniform BNNT films show good coverage, but may exhibit thickness variations due to the flow properties of the underlying CNT mat. BNNT coverage and mechanical robustness are improved at significantly reduced thicknesses by decreasing the amount of BNNT and adding long‐chain polymer binders. Careful selection of polymers and ionic liquid electrolyte enables production of reliable, high‐rate performance supercapacitors with specific energy and power of 11.5 Wh kg − 1 at 0.137 kW kg − 1 and 7.87 Wh kg − 1 at 2.69 kW kg − 1 with higher charge–discharge rates. These CNT–BNNT combined electrode and separator components were integrated into a high‐performance fiber‐reinforced polymer composite and cured using industrial autoclave‐cure techniques. The SSC provided excellent electrochemical performance with specific energy and power of 12.8 Wh kg − 1 at 0.0985 kW kg − 1 and retained 3.57 Wh kg −1 at 1.31 kW kg −1 at higher charge–discharge rates, normalizing the combined electrode mass of the CNT–BNNT cathode and anode. The device also shows reliable long‐term performance with 70% capacity retention after 5000 charge–discharge cycles from 0 to 3.3 V at high rates of 0.5 A g −1 .