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With the rapid development of medical technology, implantable devices have been invented and widely used in many applications such as physiological monitoring, localized drug delivery, and biosensors. The artificial cardiac pacemaker, as one of the most important implantable medical devices, is used to stimulate the heart with electrical impulses in order to regulate heartbeats. Conventional rechargeable batteries are very expensive with limited cycle life and cannot be used in implantable applications due to their limited life cycle. Supercapattery is a new terminology to define the hybrid energy storage system, which combines the high energy-storage-capability of conventional batteries with the high power-delivery-capability of supercapacitors. With the benefit of combining battery-type material and capacitive material, supercapattery is able to obtain high energy from Faradaic redox reactions and high power from fast electron charge-transfer. Thereby, supercapattery has good electrical conductivity and a good capability to store huge amount of charges with long term stability compared to the conventional batteries. Consequently, supercapattery is an ideal hybrid energy storage device with superior storage capacity and long life, which can be employed in next-generation artificial cardiac pacemakers as a rechargeable energy source for the lifetime of the 20 years or more. The aim of my PhD is to develop a supercapattery device based on novel nanostructured materials to store the energy from heartbeats through a piezoelectric device. Nickel foam with a porosity of 95% was used as substrate due to its high surface area to volume ratio and highly conductive 3D network architecture. By employing different hydrothermal processes, four different nanostructured materials including nickel oxideindium oxide heterostructure, nickel phosphate nano/ microflakes, cobalt phosphate nano/ microflakes and cobalt phosphate nanoflake/ microflowers were synthesized. XRD, Raman, SEM, EDX, TEM, and XPS analysis were performed to characterize the morphology and structure of the materials. The electrochemical properties of the four synthesized electrode materials were investigated in a three electrode configuration in-order to understand the charge-storage mechanism. Among these materials, Co3(PO4)2 nanoflake/ microflower material achieved a highest specific capacity of 215.6 mAh g-1 (equivalent to 1990 F g-1 ) with an excellent retention of 90.5% after 5000 charge-discharge cycles. In terms of complete devices, a symmetric and three asymmetric supercapatteries were assembled using synthesized electrode materials and activated carbon. Hybrid supercapattery assembled using cobalt phosphate as the positive and activated carbon as negative electrodes delivers a highest specific density of 43.2 Wh kg-1 . The initial capacity of the device dropped only 16% after first 20,000 cycles and even after 100,000 cycles, the device retained 68% of its initial capacity, which exhibited a long cyclability of 24 years. This device has been investigated under physiological conditions (25 - 45 °C) and showed stable electrochemical properties. Therefore, supercapattery fabricated from these materials can be a promising energy storage system for next generation pacemaker. |
