Aqueous MXene inks for inkjet-printing microsupercapacitors with ultrahigh energy densities

Although inkjet-printing technology has achieved significant development in preparing scalable and adaptable energy storage devices for portable and micro devices, searching for additive-free and environmentally friendly aqueous inks is a significant challenge. Hence, an aqueous MXene/sodium alginate-Fe2+ hybrid ink (denoted as MXene/SA-Fe) with solution processability and suitable viscosity is prepared for direct inkjet printing micro-supercapacitors (MSCs). The SA molecules are adsorbed on the surface of MXene nanosheets to construct three-dimensional (3D) structures, thus effectively alleviating the two notorious problems of oxidation and self-restacking of MXene. Concurrently, Fe2+ ions can compress the ineffective macropore volume and make the 3D structure more compact. Moreover, the hydrogen and covalent bonding formed between the MXene nano -sheet, SA, and Fe2+ effectively protects the oxidation of MXene and thus increases its stability. Thus, the MXene/ SA-Fe ink endows the inkjet-printed MSC electrode with abundant active sites for ion storage and a highly conductive network for electron transfer. As a demonstration, the MXene/SA-Fe ink is used to direct inkjet-printed MSCs with an electrode spacing of 310 mu m, which exhibit remarkable capacitances of 123.8 mF cm-2 (@5 mV s- 1), good rate capability, an extraordinary energy density of 8.44 mu Wh cm-2 at a power density of 33.70 mu W cm-2, long-term cycling stability of 91.4 % capacitance retention after 10,000 cycles, and surprising mechanical durability with 90.0 % of its initial capacitance retained after 10,000 bending cycles. Therefore, MXene/SA-Fe inks are expected to create various opportunities for printable electronics.

Automated summary

Although significant development has been achieved in the inkjet-printing technology for scalable and adaptable energy storage devices, the search for additive-free and environmentally friendly aqueous inks remains a challenge. In this study, an aqueous MXene/sodium alginate-Fe2+ hybrid ink is prepared and used for inkjet printing micro-supercapacitors (MSCs). The ink is able to alleviate the oxidation and self-restacking problems of MXene and provides abundant active sites for ion storage and a highly conductive network for electron transfer. The inkjet-printed MSCs exhibit remarkable capacitances, good rate capability, high energy density, and excellent cycling and mechanical durability. Therefore, MXene/SA-Fe inks hold great potential for printable electronics.