4. Experimental Section
Materials and electrode preparation: the acrylic acid derivative terpolymer (LA136D, Chengdu Indigo, China), polyvinylidene fluoride (PVDF) binder (Arkema, HSV900), butadiene-styrene rubber (SBR) emulsion (JSR, 104A), Fe0.5Co0.5S2, LiCl-KCl molten electrolyte and LiB alloy were commercially available and used as received. The LA136D-based cathode slurry was prepared by mixing LA136D and Fe0.5Co0.5S2 cathode materials in a planetary centrifugal mixer and stirred for 1.5 h, the mass ratio of LA136D and Fe0.5Co0.5S2 is controlled at 1:99.The same procedure and material ratio are applied in PVDF and SBR cathode slurry. The slurry was coated on graphite paper current collector (100 μm) by blade casting. The electrode mass loading was controlled at 35 mg cm-2 by adjusting the casting thickness and solid content of the slurry. The thin film electrode thickness after the calendar is about 100 μm. The contrast pellet electrode was prepared by pressed-pellet technology with a thickness of 400 μm (including 100 μm graphite paper current collector).
Binder and thin film electrode characterization: the thermal properties testing was conducted on a thermal analysis system with a heating rate of 10 °C min−1 from 30 °C to 1000 °C in N2. The Fourier Transform Infrared (FTIR) spectroscopy test of LA136D before and after 550 °C treatment is conducted by using Attenuated Total Reflection (ATR) model. The gaseous products of LA136D were conducted on TG-FTIR with a heating rate of 10 °C min−1 from 30 °C to 600 °C in N2. The electrode peeling test was conducted. The microstructure morphology was observed by SEM.
Electrochemical performance characterization: the thermal battery single cells were assembled by using a pellet cathode and thin film cathode respectively. The cathode material is Fe0.5Co0.5S2, the molten electrolyte is LiCl-KCl, and the anode material is LiB alloy. The compressed pressure used for cell construction is about 0.5 t cm−2. The single cells discharge test was conducted in an Ar2 atmosphere environment, with a temperature of 500 °C and with a compress of 20 N cm−2. The discharge was conducted by a LAND battery test system (Wuhan LAND, China). The current used for single cells capacity characterization is controlled at 0.2 A cm−2 and the cut-off voltage is 1.6 V. The pulse discharge was conducted with a consistent current density of 0.1 A cm−2 and a pulse current density of 1 A cm−2. The thermal battery stacks was assembled in a dry air room and a pulse discharge pattern of 0.05 A cm−2 (15s)-0.2 A cm−2(5s)-0.05 A cm−2(5s)-0.5 A cm−2(5s)-0.05 A cm−2 (5s)-0.2 A cm−2(5s).
Thermal battery inner temperature and pressure characterization:the column thermal battery stainless steel shell was pre-processed with two holes on the ends for signal transfer. The temperature sensor was set on the thermal battery stack surface and can work normally at 600 °C. The pressure sensor was put at the ends of the column thermal battery, outside the insulation layer. The holes were sealed by a high-temperature ceramic binder after the battery assembly.