The rapid development of wearable electronic products brings challenges to corresponding power supplies. In this work, a thermally stable and stretchable ionogel-based triboelectric nanogenerator (SI-TENG) for biomechanical energy collection is proposed. The ionic conductivity of the ionogel increased to 0.53 S·m−1 through optimal regulation of the amount of amino-terminated hyperbranched polyamide (NH2-HBP), which also has high strain of 812%, excellent stretch recovery, and wide operating temperature range of −80 to 250 °C. The SI-TENG with this ionogel as electrode and silicone rubber both as the triboelectric layer and encapsulation layer exhibits high temperature stability, stretchability, and washability. By adding appropriate amount of nano SiO2 to triboelectric layer, the output performance is further improved by 93%. Operating in single-electrode mode at 1.5 Hz, the outputs of a SI-TENG with an area of 3 cm × 3 cm are 247 V, 11.7 μA, 78 nC, and 3.2 W·m−2, respectively. It was used as a self-charging power supply to charge a 22 μF capacitor to 1.6 V in 167 s with the palm patting and then to power the electronic calculator. Furthermore, the SI-TENG can also be used as a self-powered motion sensor to detect the amplitude and frequency of finger bending, human swallowing, nodding, and shaking of the head motion changes through the analysis of the output voltage.