Selection of high rate capability and cycling stability MnO anode material for lithium-ion capacitors: Effect of the carbon source

Abstract

The N-doped carbon modified MnO composites were successfully prepared using K₂MnO₄ as the manganese source, CH₄N₂O as the nitrogen source, and glucose, sucrose, or reduced graphene oxide as the carbon sources. Among them, the composite (MPN) prepared using glucose as the carbon source exhibited excellent electrochemical performance, attributed to its relatively small particle size (6.4 nm), high specific surface area of 199.4 m²·g⁻¹, and a high I_D/I_G ratio of 0.86. The MnO in MPN contained a significant amount of Mn³⁺, ∼16.8 %, which is ascribed to the incomplete reduction of high valence Mn during the process of synthesis. With the formation of Mn³⁺, a large number of cationic vacancies were generated, which increased the diffusion coefficient of Li⁺ from 2.12 × 10⁻¹⁴ cm² s ⁻¹ to 5.94 × 10⁻¹³ cm² s⁻¹. The carbon layer with appropriate thickness, doped N and mesoporous structure suitable for electrolyte transport provide a fast ion/electron transport channels for MnO, and ensure a stable interface structure in the electrochemical reactions. Consequently, the MPN anode material exhibited remarkable high current discharge capacity (769.5 mAh·g⁻¹ at a high current density of 2 A·g⁻¹) and excellent cycling performance (882.2 mAh·g⁻¹ after 200 cycles at 1 A·g⁻¹), indicating its exceptional rate performance and cycle stability. Furthermore, the lithium ion capacitor constructed with MPN as anode and activated carbon as cathode demonstrated a high specific energy of 190 Wh·kg⁻¹, a high specific power of 205.3 W·kg⁻¹, and an impressive cycling lifespan of up to 3000 cycles without obvious degradation.