Thermally enhanced substrate design for flexible thermoelectric devices via ultrasonic welding

Abstract

Flexible thermoelectric devices (f-TEDs) facilitate direct energy conversion between heat and electricity, presenting significant potential in body heat harvesting and personal thermal management. Conventional f-TEDs employing polyimide (PI) substrates encounter challenges in conforming to the complex curved surfaces of human skin, resulting in air gaps and increased thermal resistance. Here, we present a laminated substrate that integrates a PI film with a thermally conductive silicone gel pad, fabricated using ultrasonic welding under optimized conditions: 30 kHz frequency, 50% amplitude, and a 6 second welding duration. This innovative approach achieves a remarkable 23.2-fold enhancement in thermal conductivity compared to PI film itself. Moreover, the substrate exhibits improved skin conformity and wearability. In contrast to the f-TED without a laminated substrate, the output performance of the optimized f-TED demonstrated a 47% augmentation under the constant heat source condition (0.38–0.56 mW). The optimized f-TED also reached an output power of 5.02 mW (power density 313.7 μW cm⁻²) at a temperature difference of 25 K and demonstrated robust performance, with resistance variation limited to 3.03% after 1000 bending cycles. Additionally, we developed an intelligent thermal management system capable of achieving over 6 °C cooling in environments of 31.4 °C, and over 10 °C heating in environments of 28 °C, exhibiting superior cooling and heating performance across various physical activities. These are of great significance for promoting the application of f-TEDs in smart wearables, personal thermal management, environmental protection and energy conservation.