Study On Gravure Printing, Graphene Based Electrodes And Their Application In Micro-supercapacitors

With the development of modern electronic technologies, more flexible and miniature supercapacitors were applied to wearable and portable device. On account of the advantages(high charge and discharge rates, long cycle life and high power density) of micro-supercapacitors(MSCs), the modern science and technology make them continuous advanced through synthesizing functional electrode materials, designing novel electrode structures and exploring easy fabrication technology. However, how to employ a scientific, synergetic and efficient method among tremendous alternative materials, structures and technologies is the biggest challenge in MSCs for applications. In this work, we utilize the superiority of interdigital structure, based on graphene with high surface area and superior electric conductivity, for the applications of flexible graphene-based MSCs.Firstly, during the process of synthesizing crumpled graphene ink, Mg(OH)2 nanosheets as nanospacers were inserted into graphite oxide layers, resulting in sufficient crumples in graphene nanosheets to prevent the graphene sheets from restacking for enhancing the ion transport and expose the electrochemical active area with oxygen-containing groups for providing more pseudo-capacitance. Additionally, the crumpled graphene ink was printed for a pattern of interdigital electrodes with investigation in the stability of ink, printing rates and printing numbers, resulting into loaning more electrode materials for increasing the capacitance of MSCs.Secondly, gravure printing technique combined with the crumpled graphene ink was employed to obtain flexible interdigital MSCs, achieving a high energy density(1.41 mWh cm-3 at 25 m W cm-3) and high power density(0.35 mWh cm-3 at 300 mW cm-3), accompanying considerable cycling stability and flexibility respectively. Furthermore, the MSC arrays connected by 2 serially and 2 parallelly have been used to power up a red light emitting diode(LED) and a liquid crystal display(LCD), operating 10 s and 35 s, respectively.In this paper, we demonstrated the easy and environment friendly gravure printing technique of crumpled graphene ink to obtain high performance MSCs on a flexible polyimide substrate. The superior electrochemical performance of this MSCs can be ascribed to three reasons: 1) Mg(OH)2 nanosheets as templates inserted into graphene were resulted in sufficient crumples in graphene nanosheets to prevent the graphene sheets from restacking for enhancing the ion transport and expose the oxygen-containing groups for providing more capacitance. 2) Gravure printing technology is tedious, not cost-effective and compatible with flexible substrates, which endows the fabrication techniques of MSCs with briefness and environment friendly. 3) These MSCs fabricated by using fully gravure printing technique with pure crumpled graphene ink achieved an impressive overall performance, even carrying demonstration of applications. In all, this achievements, meaning an efficient and synergetic route, should have a potential in printed flexible graphene based MSCs for electronic applications.