Battery Technology as Applied to Thermal Insulation

Tuesday, 3 October 2017: 09:15
Chesapeake G (Gaylord National Resort and Convention Center)
D. Scherson, A. J. J. Jebaraj, J. Xu (Case Western Reserve University), Z. Feng (Lawrence Berkeley National Laboratory), and N. S. Georgescu (Case Western Reserve University, Department of Chemistry)
The development of cost-effective, high performance thermal insulation (HPTI) is essential to improving the energy efficiency of buildings and appliances. An effective means of meeting this challenge involves the use of vacuum insulated panels (VIPs), which consist of an evacuated sealed enclosure that houses a porous solid core for structural integrity. As VIPs age, gases and moisture, permeate through the envelope and seals, making it necessary to use getters/desiccants to maintain their internal pressure and high R-values. The thermal performance of VIPs (R40/inch) greatly exceeds that of conventional materials, e.g. fiberglass, or foam used in the building industry (R5/inch). This very high R-value is the result of the low pressure within the panel. As pressure decreases from atmospheric conditions (1000 mbar), the R-value increases. For VIPs, pressures less than 1 mbar are desired initially to ensure that even with pressure creep due to leaks, the R-value will remain high during the life of the application. While potential energy savings are possible from HPTI, the current costs of VIPs are prohibitive and their performance can suffer from significant degradation over time. To ensure this technology is effective in building envelopes, extending their service life to several decades is desirable. The on demand getter (ODG) device proposed herein can greatly disrupt the building industry.

The architecture of the ODG, (see Fig. 1), resembles that of a discharged thin film Li battery, which upon applying a negative current to the cathode produces metallic Li or Li alloys that react irreversibly with atmospheric molecular gases. The products of these reactions are solids that display no vapor pressure at ambient temperature. Additional ODG components include a microelectronics board and a battery which powers the device. As envisioned, the ODG incorporates a porous Ni cathode; a non-volatile, thin, Li+-conducting ceramic film, such as LiPON; and a Li-ion counter electrode. Preliminary measurements aimed at demonstrating the overall concept were performed using a Li-ion conducting polymer electrolyte and a Li film as the counter electrode. The assembled ODG was placed in vacuum and the voltage scanned to -0.7 V vs Li+|Li to deposit metallic Li (see insert, Fig. 2). The cell was then disconnected and its open circuit potential (OCP) recorded. As shown in Fig. 2 (black line), the OCP remained at 0.0 V for ca. 10 min., consistent with the presence of metallic Li on the cathode, and later increased to a higher value, as Li reacted with gases in the chamber. In similar experiments, the chamber was opened to air after Li deposition and the OCP was found to jump to a high value indicative of reactions of Li with atmospheric components (blue line, Fig. 2). The efficacy of the ODG is currently being characterized by measuring the thermal conductivity as a function of pressure and imposed degradation conditions. The ODG will be installed in VIPs along with other traditional getter systems, which will then be subjected to various laboratory and field exposures while monitoring their thermal performance either continuously or periodically over an extended service life and its efficacy compared with the present state of the art.