MnO2 Nanosheets on a Carbon Nanofiber Freestanding Film by Electrospinning and In Situ Spraying for Lithium and Sodium Storage

Freestanding electrodes are critical for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) with high energy density and long cycling stability. We fabricated freestanding MnO 2 nanosheet-coated carbon nanofibers by synchronous in situ spraying of MnO 2 nanosheets onto electrospinning polymer nanofibers, which might be a high-voltage electric field-induced assembly process. The designed film is used as anode material for LIBs and SIBs. It demonstrates good cycling stability without capacity loss after long cycling for LIBs, delivers a capacity of 256.4 mAh g –1 at 1.00 A g –1, and has an extremely stable cycle life for over 200 cycles at 0.05 A g –1 . For SIBs, it delivers a capacity of 135.0 mAh g –1 at 1.00 A g –1 and has a stable cycle life for over 500 cycles at 0.50 A g –1 . The capacitive contribution ratio increases from 44.4 to 76.2% (0.2–1.0 mV s –1 ), and the capacitive process plays a major role in the total capacity. The enhancement of the electrochemical performance is attributed to the good conductivity of the carbon nanofiber network and the one-dimensional (1D)/two-dimensional (2D) composite structure of the electrode, in which the high performance of carbon nanofibers and MnO 2 nanosheets is fully exploited. Importantly, the combination of in situ spraying and electrospinning can be extended to two or more materials with different polarities, ζ-potential values, or solubilities, broadening the applications of composites.