A novel retractable spring-like-electrode triboelectric nanogenerator with highly-effective energy harvesting and conversion for sensing road conditions

Integrated multi-layer structural triboelectric nanogenerators (TENGs) have been verified as an effective approach to solving the insufficient energy supply to single-layer devices. Unfortunately, the contact/separation asynchronism between triboelectric materials during the working stage severely hinders promotion of further output performance from TENGs. In this work, based on spring steel as both skeleton and electrode, we demonstrated a novel retractable spring-like-electrode TENG (SL-TENG) for harvesting vibratory energy. Benefiting from the specific elasticity of spring steel and the unique spring structure of the device, the contact/separation synchronism of a SL-TENG is integrally enhanced and further strengthened as vibration frequency increases, which can be used to tandem stack springs to efficiently collect and convert vibration energy in a small volume. A three-layer SL-TENG in a volume of approximate 5 cm(3) can reach a maximum negative current of 9.4 mu A and positive current of 8 mu A at a frequency of 7 Hz, which is 4.09 and 2.29 times that at a frequency of 2 Hz, respectively. Including appropriate frequency, separation distance, and enlarged friction area, it was found that a device's internal resistance is decreased gradually with an increased number of layers. This may be one important reason for the boost in output performance of multi-layer SL-TENGs. In addition, the three-layer SL-TENG was applied to alternately illuminate tens of commercial LEDs, and the results attest that a SL-TENG is promising in the application of a self-powered sensor for monitoring road potholes.