3D printing has attracted much attention in industry and academia because it offers simple, low-cost, versatile and environmentally-friendly manufacturing technologies and has been utilized to fabricate flexible electronics like supercapacitors, batteries and sensors. Finding a suitable printable ink is the most challenging task for 3D printing. Carbon materials have been widely used in 3D printing of flexible electronics due to their high electrical conductivity, chemical stability, non-toxicity, and high surface area with versatile pore structure. However, mostly toxic solvents like NMP and DMF as well as non-biodegradable polymer binders such as PVDF and PTFE were used to fabricate printable inks. Herein, a sustainable carbon ink highly suitable for 3D extrusion printing for well-defined, flexible in-plane all-solid-state micro-supercapacitors (MSC) using only non-toxic and biodegradable ingredients is presented. The MSCs show high areal capacitances of up to 13.41 mF cm⁻² and 35.10 F cm⁻³ for 5 mV s⁻¹ as well as excellent cycle stability even when mechanically stressed. Various suspension additives are explored for tuning the rheological behavior, conductivity, and electrochemical performance of MSCs.