Mechanical characterization of electrode material
Gelatin powder was soaked in distilled water and left at room temperature (23℃) for 10 min. The amount of gelatin powder and distilled water were 30 g and 120 g, respectively. Then, glycerol and NaCl were added. The amount of glycerol was 15 g. The amount of NaCl was 0, 1.25, 2.5, 3.75, and 5 g, which corresponded to the mass fraction relative to the amount of gelatin and glycerol of 0, 2.7, 5.3, 7.7, and 10 wt%, respectively. The mixed materials were dissolved at 80°C and stirred at 200 rpm for 1 h using a hot stirrer (AS ONE, CHPS-170DF). The solution was poured into a mold and cured at room temperature for 1 h. The cured sample was demolded and placed in a humidity chamber (Tolihan, WET-297-AHU) at 23°C (67% RH) for at least 24 h until testing. The diameter and thickness of the samples were 29 mm and 12.5 mm, respectively. Three samples were used for each material composition (mass fraction of NaCl 0, 2.7, 5.3, 7.7, and 10 wt%). The testing procedure followed was ISO 7743. Each sample was compressed at a speed of 10 mm/min using a universal testing machine (Shimadzu, AGS-20NX) from which the stress-strain curve was obtained. The testing machine performed four reciprocating motions compressing from 0% to 25% of strain and rebounding from 25% to 0%. The measured force under 20% compressive strain of the fourth round was used to determine the Young’s modulus. It was calculated by dividing the force by the cross-sectional area and strain of the specimen before compression.