Recent advances in extremely low power subthreshold electronic circuits [1] benefit greatly military and commercial wireless, event-driven sensing applications, such as, dormant-yet-aware unattended sensors and sensor radio networks used industrial commercial and residential buildings, agricultural settings, and urban areas, serving to improve manufacturing efficiency, safety, reliability, automation, and security. These subthreshold electronics consume extremely low power (£ sub µW) and operate on supply voltages below 1 V with a lower voltage threshold ≥ 0.2V. The diminished power consumption increases sensor lifetime and practical use by assuaging the need for power sources to be replaced or recharged. Since commercial battery power sources are limited to output voltages greater than 1.2 V, they require external components such as regulators to produce stable supply voltages less than 1 V. Unfortunately voltage regulators are energy inefficient and can easily dominate the total power consumption. There is a need to develop novel power sources to provide a sustained, stable requisite voltage for subthreshold electronic circuits; this will increase the unattended sensors’ mission lifetime.

Here we present ADA effort to develop a low voltage, high capacity and long life battery technology based on high specific capacity cathode materials, which are typically used as Li-ion battery anodes, and high specific capacity alkali metal anode. We will show low voltage battery cathode development efforts based on metal alloy materials which have high theoretical specific capacities in the low voltage range, are low in cost, non-toxic, dense, abundant, and readily available from commercial sources and, therefore, ideal for low voltage battery to power near zero power electronics.

Figure 1 shows ADA low voltage cell voltage profiles using different conductive additives in the cathode. Cells including conductive additive #2 delivered 5% higher specific capacity than the conductive additive #1, in the low voltage range. We speculate that the use of conductive additive #2 provided much more effective connectivity among the cathode particles during discharge when the cathode particles expand and pulverize upon the alkali metal alloying with the cathode, compared with the conductive additive #1.

We used atomic-level functional coatings on the cathode electrodes as a means to enhance discharge performance and to stabilize the cathode active particles for battery longevity (low self-discharge). Figure 2 shows voltage profiles of an ADA low voltage battery control cell and cells with atomic-level functional coatings with various coating film thicknesses. It is interesting to note that the coated cathode electrodes demonstrated significantly increased specific capacities, up to 35% higher, compared with the control cell. The increased specific capacities are contributed mainly from the prolonged voltage plateaus which is very desirable. We speculate that the atomic-level functional coatings infiltrated the nano or micro pores within the porous cathode electrodes, which increased electrolyte accessibility and alkali ion diffusivity resulting in much more effective utilization of the cathode active material.

Our low voltage battery technology enhanced by atomic-level coatings represents an ideal power source for near-zero-power electronic applications.

References

1. Mohsen Radfar, Kriyang Shah, and Jugdutt Singh, Active and Passive Electronic Components, Vol. 2012, Article ID 926753, 11 pages.