Cobalt phosphate-based supercapattery as alternative power source for implantable medical devices

The supercapattery is an ideal energy storage device that combines excellent power density and rate capability of supercapacitors and the greater energy density of batteries. With superior storage capacity and long life, this device can be employed in next-generation artificial cardiac pacemakers as a rechargeable energy source for the lifetime of the pacemaker (at least 15-20 years). However, current hybrid energy storage devices are often limited by less than ideal performance of either the supercapacitor or battery. Here, we develop a low cost and scalable prototype supercapattery with cobalt phosphate as positive and activated carbon as negative electrodes. This positive electrode exhibits a maximum specific capacity of 215.6 mAh g^-1 (≈1990 F g^-1), ever reported in a metal phosphate based electrode. The supercapattery delivers a high energy density of 3.53 mWh cm^-3 (43.2 Wh kg^-1) and a power density of 425 mW cm^-3 (5.8 kW kg^-1). Furthermore, the device can retain 79% voltage even after 4 min self-discharge, enough to provide power during cardiac emergencies. This hybrid device provides excellent performance and stability under physiological temperature range (35-41 °C), retaining 68% of specific capacity after 100 000 cycles at room temperature (25 °C) and up to 81.5% after 20 000 cycles at 38 °C, demonstrating its effectiveness as a potential power source for the next-generation implanted medical devices.