# A Review of Fabrication Technologies for Carbon Electrode-Based Micro-Supercapacitors
## 6 Micro-Supercapacitor Challenges and Future Perspectives  
Several challenges in the field of carbon electrode-based micro-supercapacitors are identified. Research efforts are mainly driven by the never ending quest for high-performance micro-supercapacitors with higher energy density, which can work in a wide voltage range, and have high charge and discharge rates. This implies a search for better materials, electrodes, and electrolytes, as well as design and fabrication methods, which can be upscaled and taken to application. Moreover, a recent trend also focuses on the sustainability  
Figure 13: Presentation and photographs of screen printing method (**a**); programming-controlled writing (**b**) and painting, using a writing brush (**c**) to fabricate integrated micro-supercapacitors. Figure reprinted with permission from [PERSON] et al. [196]. Copyright 2021 the Royal Society of Chemistry. aspect with synthesis of biomass-derived carbon. The following aspects are expected to be the focus of further research studies. First, with the increasing demand in wearable electronic devices, there is a high need for flexible micro-supercapacitors. The mechanical properties still need further improvement. Moreover, the substrate preparation procedure needs to be optimized, whereby the electrical response should not change under mechanical loading, so a high performance flexible energy storage device is produced. A better method is needed to measure the mechanical flexibility, and to characterize the physicochemical features of the electrode material and gel electrolyte, during mechanical deformation of flexible micro-supercapacitors. Second, the most promising, simple, cost-effective micro-supercapacitor fabrication methods that can be up-scaled include laser etching, inkjet printing, and 3D printing. Further development is still needed on a fast, large-scale fabrication technology to pave the way to applications. For the printing techniques, more research is required on engineering the formulations of the printing inks and printing protocols for cost-effective fabrication, enhancing the printing resolution, and making the methods more environment friendly. Micro-machining methods, such as laser etching and screen printing, enable efficient construction of active electrode materials with high conductivity and channels for ion diffusion by introducing pores and heteroatoms. Still, a cost-effective, large-scale production method is required for carbon electrode materials with high capacitance performance. The integration of these flexible micro-supercapacitors as power sources for wearable electronics also needs to be investigated. Third, the surface area, pore size distribution, surface properties, and electrical conductivity of the electrode material are important for the performance of the micro-supercapacitor. Suitable porous carbon should have a high surface area with abundant active sites for ion storage, as well as an appropriate pore structure that may facilitate the storage and transport of ions. Graphene is certainly of interest because of its open structure, which provides both a high active surface area and abundant channels for ion diffusion. Further research involves improving the energy density and power density of micro-supercapacitors by preparing or designing novel carbons with a hierarchical interconnected porous microstructure that matches the desolvated ions. The design, synthesis methods, and stability of high surface area electrode materials, and their accessibility to electrolytes, still need to be further improved. Moreover, surface heteroatoms are important as they enhance the wettability and electrical conductivity, and structural defects generate active sites for ion accumulation. More work is also required on novel models of high performance carbon-based micro-supercapacitors and their charge storage mechanism.