Extreme Long Life Battery Via Atomic Layer Deposition of Solid Electrolyte on CFx Electrodes

Modern defense and commercial applications, such as environmental sensors or implantable medical devices, require battery power sources with a wide operating temperature range, excellent reliability, an ability to resist abuse including mechanical vibrations and shock, high energy density and extreme long battery life (20 years). Unfortunately, state-of-the-art (SOA) battery power sources cannot adequately meet the combined energy density and long life requirements.

Here we present a promising method to prepare extreme long life batteries via atomic layer deposition (ALD) of solid electrolyte onto inherently high energy density and stable CF_xelectrodes.             

Figure 1 shows discharge voltage profiles of cells containing ALD solid electrolyte coated electrodes, overlaid with a control cell without oxide coating. The anode was metallic lithium and a conventional Li-ion electrolyte was used. The cells were discharged with a constant, one-year current rate, a relatively fast rate for 20 year service life. The ALD solid electrolyte coated cell showed no voltage delay at the initial discharge which is shown in the control cell, a phenomenon characteristic of CF_x chemistry which is believed to result from the low conductivity of fresh CF_x materials [1]. The elimination of the voltage delay presents significant performance advantages at start-ups. The ALD solid electrolyte coated CF_xcells demonstrated more than 60mV higher discharge running voltage than that of the control cell, resulting in higher energy density and, potentially, longer battery service life. 

Figure 2 shows Nyquist plots of electrochemical impedance spectroscopy (EIS) carried out for ALD solid electrolyte coated and the control cells.  The ALD solid electrolyte coated cell showed a much smaller semi-circle representing a 66% smaller charge transfer resistance (leading to faster charge transfer kinetics) than the control cell. The EIS data strongly support the improved discharge performance presented above.   

We will show that ALD enabled solid electrolyte coatings on CF_x lead to significantly improved storage stability at extreme temperatures (e.g. 85°C) and superior after-storage discharge performance, compared with CF_xwithout coating.  

Our results in this study suggest solid electrolyte coating via ALD on CF_x is a promising material processing methodology for extreme long life battery power sources with a complete elimination of CF_x voltage delay and significantly enhanced charge transfer kinetics, energy density and electrochemical stability at extreme temperatures. Such methodology is potentially scalable economically when high throughput and high volume ALD processes are implemented.

Reference

1. Sheng S. Zhang, Donald Foster, Jeff Wolfenstine, Jeffrey Read, Journal of Power Sources 187, 233 (2009).