AgI Electrolytes for Printable Solid-State Thermal Batteries

Abstract

Thermal batteries are used as power sources in safety-critical electrical systems that require stability during long-term storage and reliability during high current operation when activated. AgI is an attractive material for a solid-state electrolyte for thermal batteries because of its low ionic conductivity near room temperature. It then undergoes a phase transition to a high conductivity phase above 150C. [1, 2] We have investigated the development of AgI batteries using I2 loaded carbon or PVP as a cathode material and Ag as an anode material. The electrochemical reactions for solid-state batteries in this configuration are as follows: Ag+ + e- + ½ I2 => AgI (Cathode)Ag => Ag+ + e- (Anode)Overall: 2Ag + ½ I2 => AgI (DE = 0.95 V) The batteries were first investigated as pressed pellets of Ag powder prepared by electrolysis, AgI powder, and Cabot Norit SX-Ultra activated carbon soaked in an ethanol I2 solution. Pressed pellets yielded an maximum power of 4.9 μW at room temperature and 0.6 mW above 150C, confirming the ability to extract higher power out of the cell when heated. Additive manufacturing of this electrolyte would enable the printing of thermal batteries in custom geometries for integration into small electronics devices. Pastes and processing conditions were developed for the printing of Ag, PVP loaded I2, and AgI. Additive manufacturing would also enable the printing of the higher conductivity AgI/Al2O3 composites which are difficult to fabricate by traditional clean room deposition technologies. This project was supported by Sandia Laboratory Directed Research and Development Grant 209285. SAND2020-4499 A.References.[1] K. Lehovec, J. Broder, Journal of The Electrochemical Society, 101, 208 (1954).[2] J. S. Lee, S. Adams, and J. Maier, Journal of The Electrochemical Society 147, 2407 (2000).Figure 1. Power curves for Ag/AgI/I2 battery operated between room temperature and 160C. Figure 1