Tunable Mn Valence in MnO2@SWCNT Enables High-Performance Planar Micro-Supercapacitors for Integrated Energy Storage and Sensing

Abstract

Flexible and miniaturized energy storage devices are essential for emerging wearable and integrated electronic systems; however, their practical utilization is often constrained by insufficient energy density and limited systematic integration. Here, a textile-based planar micro-supercapacitor (MSC) is developed by coupling a single-walled carbon nanotube (SWCNT) conductive scaffold with nano-structured MnO2, followed by an oxygen vacancy strategy to regulate the manganese valence states. Oxygen vacancies introduced through a mild chemical reduction alter the local coordination environment and shift the Mn valence distribution toward lower oxidation states, leading to enhanced electronic conductivity and improved charge-transfer kinetics. The resulting hybrid electrode exhibits efficient electron transport enabled by the interconnected SWCNT network, while the modified MnO2 provides abundant and electrochemically accessible active sites. As a consequence, the optimized MSC delivers an areal capacitance of 95.5 mF cm–2 and retains approximately 92.5% of its initial capacitance after 10,000 cycles. Density functional theory calculations confirm that oxygen vacancies introduce additional electronic states near the Fermi level and improve quantum capacitance. In addition to intrinsic performance, the device demonstrates stable output under integration, reaching ∼4 V through series connection without noticeable degradation in electrochemical behavior. More importantly, by integrating the energy storage unit with a SWCNT-based sensing element on the same textile platform, an MSC combined with the sensor system capable of continuous signal monitoring under mechanical deformation is realized. The stable electrical response during repeated bending highlights the robustness of the conductive network and the reliability of energy supply. This work illustrates how defect-induced electronic modulation combined with hierarchical structural design can achieve both high-performance energy storage and functional system integration, offering a practical route toward compact, wearable, and autonomous electronic devices.