S.H. Zheng, S. Wang, Y. F. Dong, F. Zhou, J. Qin, X. Wang, F. Su, C. L. Sun, Z.-S. Wu,* H.-M. Cheng, X.H. Bao
Advanced Science, 2019, 6(23), 1902147.
DOI: 10.1002/advs.201902147 [PDF]
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 micro-capacitors (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 high volumetric energy density of 37.1 mWh cm-3 and ultralow self-discharge rate of 44 h from Vmax to 0.6 Vmax, both of which surpass most reported hybrid micro-supercapacitors. Through tunning graphene layer covered on the top surface of interdigital microelectrodes, the NIMCs unveil remarkably enhanced power density, owing to the establishment of favorable multi-directional 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 high temperature of 80 oC because of using non-flammable ionogel electrolyte and in-plane geometry. Therefore, these flexible planar NIMCs with multi-directional ion diffusion pathways hold tremendous potential for microelectronics.
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