Extreme Long Life Battery Via Atomic Layer Deposition of Solid Electrolyte on CFx Electrodes
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 CFxelectrodes.
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 CFx chemistry which is believed to result from the low conductivity of fresh CFx materials . The elimination of the voltage delay presents significant performance advantages at start-ups. The ALD solid electrolyte coated CFxcells 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 CFx lead to significantly improved storage stability at extreme temperatures (e.g. 85°C) and superior after-storage discharge performance, compared with CFxwithout coating.
Our results in this study suggest solid electrolyte coating via ALD on CFx is a promising material processing methodology for extreme long life battery power sources with a complete elimination of CFx 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.
Sheng S. Zhang, Donald Foster, Jeff Wolfenstine, Jeffrey Read, Journal of Power Sources 187, 233 (2009).