Thermoelectric textiles can convert the temperature difference between the human body and the surrounding air into electrical energy, which can be used to power sensors without batteries. Such sensors could track body movements or monitor heartbeat, offering applications that benefit daily life and healthcare. To meet practical demands, these materials need to be safe, flexible, and lightweight, especially when worn close to the skin.

The Chalmers team utilized silk thread coated in a conductive plastic polymer. This particular polymer structure allows it to conduct electricity while maintaining the comfort and flexibility required for wearable textiles. "The polymers that we use are bendable, lightweight, and can be utilized in both liquid and solid forms. They are also non-toxic," explained Mariavittoria Craighero, a doctoral student at Chalmers University and the lead author of the study.

A key improvement from previous research was eliminating metals, which had been used to enhance the material's stability in air. Instead, the new thread uses solely organic, carbon-based polymers to achieve both enhanced conductivity and stability. "We found the missing piece of the puzzle - a newly discovered polymer that provides exceptional stability in air while maintaining high conductivity. Importantly, our approach avoids rare earth metals, which are common in electronics," added Craighero.

To demonstrate its practical use, the researchers produced two thermoelectric generators: a button and a textile piece sewn with the coated threads. When placed between a hot and cold surface, these generators showed an increase in voltage, depending on the temperature difference and the quantity of conductive material.

For example, a larger fabric section produced about 6 millivolts when exposed to a 30-degree Celsius temperature gradient. Theoretically, a voltage converter could utilize this energy to charge portable devices via USB. Notably, the thread retained two-thirds of its electrical properties even after seven machine washes, which Craighero noted was a promising result, though further improvement is needed before commercialization.

Scaling up the production is the current challenge, as the conductive thread is still made by hand in the lab. Creating a textile with the conductive silk took four days of hand stitching. Despite this limitation, Christian Muller, a professor at Chalmers and leader of the research, emphasized the potential of the innovation: "We have demonstrated that conductive organic materials can meet the functional demands of thermoelectric textiles. This is an important advancement, paving the way for future applications with considerable societal benefits."