A material with ultra-high-efficiency thermoelectric properties has been developed that self-heals and stretches like human skin. This material can be recharged solely by the body's own heat, eliminating the need for batteries, and is expected to bring wearable technology a step closer to commercialization.

Professor Jang Seong-yeon's research team from the Department of Energy and Chemical Engineering at UNIST (President Yong-Hoon Lee) recently announced that they have developed a 'high-performance ionic polymer thermoelectric material' with self-healing capabilities for mechanical and electrical errors and problems in collaboration with Professor Jeon Ju-won's research team from the Department of Applied Chemistry at Kookmin University (President Hong-Jae Lim).

Thermoelectric materials are eco-friendly energy sources that convert thermal energy into electricity. The research team utilized a "self-healing thermoelectric material," which maintains both mechanical properties and electrical performance by repairing itself after being torn or cut through the strong attractive forces between its molecules.

In addition, we precisely analyzed and optimized the variables that determine the thermoelectric performance of ionic thermoelectric materials that were not covered in previous studies. Based on this, a material with ultra-high efficiency thermoelectric conversion performance, excellent mechanical properties, and self-healing ability was developed.

Wearable electronic devices, such as Bluetooth earphones and smartwatches, are now a common sight. Most electronic devices use lithium-ion batteries with liquid electrolytes. However, these liquid-containing batteries limit device design due to issues like leakage, and their reliance on external power for charging presents clear limitations.

In contrast, ionic polymer thermoelectric materials are highly anticipated as next-generation independent power sources due to their unique flexibility and ability to generate electricity using surrounding thermal energy.

On the other hand, thermoelectric materials have lower thermal energy conversion performance than conventional lithium-ion batteries, requiring significant improvements for commercialization. Furthermore, systematic scientific analysis for performance improvement is still lacking.

The research team, for the first time in the world, analyzed the ionic thermoelectric effect within a material thermodynamically to optimize its heat energy conversion performance. The developed material achieved an ionic thermoelectric figure of merit of 12.3, exceeding the previous record by over 70%. It also boasted excellent physical properties, including self-healing capabilities, allowing it to stretch to over 10 times its original length and maintaining its mechanical and electrical properties without loss of performance even after over 50 cycles of durability testing.

“We were able to achieve record-breaking performance by maximizing the energy change of ions that diffuse through heat within the material,” said Dong-Hoo Kim, a researcher in the Department of Energy and Chemical Engineering and the first author. “Since it has excellent self-healing and elasticity, it can be applied to self-power generation for wearable electronic devices in the future.”

The research team used the developed material to manufacture ionic thermoelectric supercapacitor elements and even manufactured modules that amplified output by connecting multiple elements in series. The fabricated module demonstrated a very high voltage output (0.37 V/K), demonstrating that the developed thermoelectric material can generate sufficient voltage to power various electronic devices in everyday life. This suggests that if body temperature can be as low as 10 degrees Celsius above room temperature, it can produce a voltage output similar to that of a conventional lithium-ion battery (approximately 3.7 V).

Professor Jang Seong-yeon of the Department of Energy and Chemical Engineering emphasized, “This study presents all the necessary processes, from material design considering mechanical and electrical properties to commercialization demonstration through modules,” and “This is an important study that will serve as a guide for many researchers developing ionic thermoelectric materials in the future.”

This study was published in Nature Communications on June 5th. The research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT.