## 2 Experimental Materials and Test Methods  
In this study, PVC membrane material was produced by Shanghai Yeli Membrane Structure Co., Ltd. ( Shanghai, China) with the size of 1060 \(\times\) 1060 \(\times\) 0.5 mm. According to China National Standard (GB13022-91), the uniaxial tension mechanical properties of PVC film were obtained, including two categories along the 0-degree direction and 45-degree angle direction of the membrane fiber. Three groups of experiments were carried out for each type. The films were stretched using a model LANDMARK tension and torsion tester manufactured by MTS Corporation of America. The loading method was used as displacement control. The loading speed was 10 mm/min. The test procedure is shown in Figure 1.  
Thin-film batteries (size: 178 \(\times\) 40 \(\times\) 0.5 mm; model: amorphous silicon thin-film solar cells on a 0.5 WCel flexible substrate; manufacturer: United-Solar (Michigan, USA), were combined with PVC membranes to form a composite structure, as shown in Figure 2. The technical specifications of thin-film batteries are shown in Table 1. Film batteries were firmly adhered to the center and corner of the PVC membranes using alpha-cyanoacrylate glue so that no relative slip between the membrane batteries and the PVC membranes occurs during tension. Because PVC membranes and thin-film batteries are orthotropic materials, two types of bidirectional loading were designed. One was loaded along the polyester fiber base fabric direction, which corresponds to Battery A and Battery B. Another way is to load at an angle of 45 degrees between the fibers, which corresponds to battery C and D. Three groups of tests were carried out for each loading mode, with six specimens. To prevent edge tearing, edges were treated according to the China Membrane Structure Technical Regulation (CECS158-2015). That is, the boundary of the PVC membrane was folded and thermally combined to form a 60 mm perimeter sheath. Then, the 5 mm diameter side rope was passed through the sheath and around the PVC membrane's edge. At the corner of the PVC membrane, the specimens were clamped by an arc plate. Figure 1: Uniaxial tension test process: (**a**) uniaxial tension sample size/mm, (**b**) clamping of specimens, and (**c**) test machine loading. A biaxial diagonal tension loading device with variable height difference was designed. With this device, the tension force was not in the same plane, so that the tension film forms a saddle-shaped surface. The schematic diagram of the device is shown in Figure 3. The oil pump and two-way oil cylinder were used to exert tension. In order to ensure high accuracy, the oil pump and two-way oil cylinder are calibrated according to China's Verification Specification for Hydraulic Jacks (JJG621-2012). The supporting steel pipes with a pulley were used to adjust the tension position and direction. The supportive steel pipe's outer and inner diameter is 78 mm and 74 mm, respectively. The length of that is 1200 mm. There was a pin inside the steel pipe, and the plug is a solid steel bar with a diameter of 11 mm. The steel pipe was inserted into the reaction bearing platform's hole, and the tension position was adjusted by adjusting the extension length of the steel pipe. The four steel pipes' diagonal size was 3905 mm, and the height difference of the adjacent steel pipes was 100 mm. \begin{table}
\begin{tabular}{c c} \hline \hline
**Power (Pm)** & **0.5 W** \\ \hline Open circuit voltage (Voc) & 2.2 V \\ short-circuit current (ISC) & 0.4A \\ Peak power voltage (VM) & 1.6 V \\ Peak power current (IM) & 0.31 A \\ Peak power temperature coefficient & \(-\)0.23\%/\({}^{\circ}\)C \\ Temperature coefficient of open-circuit voltage & \(-\)0.38\%/\({}^{\circ}\)C \\ Temperature coefficient of short circuit current & \(+\)0.12\%/\({}^{\circ}\)C \\ Nominal operating temperature condition of the battery cell & 51.5 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical parameter for thin-film batteries.