All‐Solid‐State Planar Sodium‐Ion Microcapacitors with Multidirectional Fast Ion Diffusion Pathways

Abstract

With the relentless development of smart and miniaturized electronics, the worldwide thirst for microscale electrochemical energy storage devices with form factors is launching a new era of competition. Herein, the first prototype planar sodium‐ion microcapacitors (NIMCs) are constructed based on the interdigital microelectrodes of urchin‐like sodium titanate as faradaic anode and nanoporous activated graphene as non‐faradaic cathode along with high‐voltage ionogel electrolyte on a single flexible substrate. By effectively coupling with battery‐type anode and capacitor‐type cathode, the resultant all‐solid‐state NIMCs working at 3.5 V exhibit a high volumetric energy density of 37.1 mWh cm−3 and an ultralow self‐discharge rate of 44 h from V max to 0.6 V max, both of which surpass most reported hybrid micro‐supercapacitors. Through tuning graphene layer covered on the top surface of interdigital microelectrodes, the NIMCs unveil remarkably enhanced power density, owing to the establishment of favorable multidirectional fast ion diffusion pathways that significantly reduce the charge transfer resistance. Meanwhile, the as‐fabricated NIMCs present excellent mechanical flexibility without capacitance fade under repeated deformation, and electrochemical stability at a high temperature of 80 °C because of using nonflammable ionogel electrolyte and in‐plane geometry. Therefore, these flexible planar NIMCs with multidirectional ion diffusion pathways hold tremendous potential for microelectronics.

3D printed hybrid-dimensional electrodes for flexible micro-supercapacitors with superior electrochemical behaviours

“…Figure 3h displays the Ragone plot of the Fe 2 O 3-/graphene/Ag MSCs, where the calculated areal energy and power densities were 65.4 μWh cm −2 and 1.07 mW cm −2 , respectively, at the current density of 2 mA cm −2 (Table S1). This Ragone plot is a clear indication that the energy density and power density values of the MSCs are significantly advantageous when compared with previous reported MSCs such as SWCNTs MSCs (Bellani et al 2019), NiCo 2 O 4 MSCs (Lu, Kai Jiang, and Shen 2019), sodium titanate (NTO)//activated graphene (AG) sodium-ion microcapacitors (NIMCs) (Zheng et al 2019) and Ti 3 C 2 T x MSCs (Zhang, McKeon, et al 2019). The exceptional electrochemical performance of the MSC devices was mainly attributed to the optimal 3D printed hybrid-dimensional electrode structure, which allowed for the rapid electron transport and ionic transport during the charge and discharge processes.…”

Substrate‐Free and Shapeless Planar Micro‐Supercapacitors

“…Additionally, with no substrate blocking the bottom surface (e.g., for conventional planar MSCs on a substrate), the flow of electrolyte ions could be unhindered. This in principle should significantly improve the capacitance, especially, at high rates, because of enhanced ion diffusion, as we demonstrated in our previous work about the presence of multiple ionic diffusion pathway in the planar MSCs …”

Recent developments of advanced micro-supercapacitors: design, fabrication and applications

“…4d). Besides, Zheng et al 74 took a maskassisted filtration strategy to make the urchin-like sodium titanate and the nanoporous activated graphene deposited on either side of the MSC, respectively. After applying high-voltage ion gel as the electrolyte, the planar sodium-ion micro-capacitors (NIMCs) were obtained on a flexible substrate, which exhibited a high volumetric energy density, excellent mechanical flexibility as well as good heat resistance at 80°C.…”