V-doping suppressed lattice distortion in MnO2@exfoliated graphene for high-rate and ultrastable micro-supercapacitors

Delta manganese dioxide (δ-MnO 2 ) has emerged as a promising material for electrochemical energy storage due to its layered structure and high theoretical capacity. However, its practical application is hindered by poor rate performance and structural instability caused by low electronic conductivity and Jahn-Teller distortion. In this study, we demonstrate a vanadium-doped δ-MnO 2 composite anchored on exfoliated graphene (V-MnO 2 @EG) via a one-step electrodeposition method for planar micro-supercapacitors (PMSCs). Vanadium doping modulates the micromorphology of δ-MnO 2 from nanoflower to a coral-like architecture, enhancing specific surface area (125.84 m 2  g −1 vs. 95.86 m 2  g −1 for pristine MnO 2 @EG) and electrolyte diffusion kinetics. Density functional theory (DFT) calculations reveal that V-doping introduces oxygen vacancies, suppresses Jahn-Teller distortion, and improves electronic conductivity and Li + adsorption energy. The V-MnO 2 @EG electrode delivers a remarkable areal capacitance of 441.2 mF cm −2 at 1 mA cm −2 and retains 97.67 % capacitance after 100,000 cycles. Ex-situ characterizations confirm reversible Li + intercalation/deintercalation as the charge storage mechanism. This work provides a rational strategy for designing high-performance manganese oxide-based micro-energy storage devices.