Flexible Electronics Directly Written with an Ultrastable Ballpoint Pen Based on a Graphene Nanosheets/MWCNTs/Carbon Black Nanocomposite

A writable ultrafine water-based conductive ink with excellent stability and no harmful gas emission was prepared. The mass fraction of carbon conductive particles was 4.95%, and the mean median particle size (D50) was as low as 5 μm. The size of conductive carbon particles in the ink was analyzed with continuous milling, and the phenomenon of reagglomeration of conductive particles with a small particle size and large specific surface area was explained. Moreover, the sheet resistance of the writable graphene nanosheets/multiwalled carbon nanotubes (MWCNTs)/carbon black nanocomposite conductive ink was 11.1 Ω·sq–1. With a centrifugal speed of 3000 r/min for 15 min, the performance of the ink remained stable. Additionally, a stable conductive ballpoint pen was developed based on the writable conductive ink, and the excellent electrical and mechanical properties of the directly handwritten paper-based flexible circuit and the electrochemical properties of the directly handwritten paper-based chemical battery were tested.