Comparative Study of Li₄Ti₅O₁₂ Composites Prepared withPristine, Oxidized, and Surfactant-Treated Multiwalled Carbon Nanotubes for High-Power Hybrid Supercapacitors

In hybrid supercapacitors, lithium-ion battery (LIB)-type intercalation materials have slower reaction kinetics than electrical double-layer-capacitor-type carbonaceous materials. Thus, it is of prime importance to improve the rate capability of LIB-type intercalation materials to achieve high energy density as well as high power density from hybrid supercapacitors. In this study, we report Li₄Ti₅O₁₂/pristine multiwalled carbon nanotube (LTO/P-MWCNT) composites with high rate capability and demonstrate their anode application for high-power hybrid supercapacitors. For comparison, two additional LTO composites are prepared by using oxidized MWCNTs and surfactant-treated MWCNTs through a similar spray-drying process. The LTO/P-MWCNT composite shows superior rate capability over the other two composites, owing to the high electrical conductivity of pristine MWCNTs. The hybrid supercapacitor composed of a LTO/P-MWCNT anode and an activated carbon cathode delivers an energy density of 70.9 Wh kg⁻¹ at a power density of 0.03 kW kg⁻¹ and a maximum power density of 21.8 kW kg⁻¹ is achieved at an energy density of 24.3 Wh kg⁻¹. Furthermore, the hybrid supercapacitor exhibits excellent cycling stability. These salient results provide further impetus to the use of MWCNTs in the design and synthesis of high-rate oxide-based composites with efficient lithium-ion transport and high electrical conductivity for high-power hybrid supercapacitors and high-power LIBs.