Image: Leibniz Institute for Photonic Technologies

Next-gen­er­a­tion tex­tiles: smart mate­ri­als gen­er­ate elec­tric­i­ty and help reg­u­late temperature

Researchers at the Leib­niz Insti­tute for Pho­ton­ic Tech­nolo­gies in Jena are devel­op­ing a self-suf­fi­cient ener­gy sup­ply based on tex­tiles. In the future, it will be even eas­i­er to sup­ply pow­er to mobile elec­tron­ic devices worn close to the body, even when no exter­nal pow­er sup­ply is avail­able. For this pur­pose, smart tex­tiles use the emit­ted human body heat and con­vert it into elec­tric­i­ty. Their addi­tion­al cool­ing prop­er­ties make the nov­el mate­ri­als inter­est­ing for safe­ty-rel­e­vant appli­ca­tions and at the same time ensure increased wear­ing com­fort and enhanced well-being.

Minia­tur­ized elec­tron­ic devices worn on the body, so-called wear­ables, check vital func­tions, count steps or pro­vide infor­ma­tion about traf­fic and weath­er. In order to con­tin­u­ous­ly sup­ply these tech­ni­cal com­pan­ions with elec­tric­i­ty, researchers at the Leib­niz Insti­tute of Pho­ton­ic Tech­nolo­gies (Leib­niz-IPHT), togeth­er with a team from ITP GmbH in Weimar and the tex­tile man­u­fac­tur­er E. CIMA in Spain, have devel­oped a mate­r­i­al that sup­plies the required ener­gy inde­pen­dent­ly of exter­nal pow­er sources: Mod­ern, intel­li­gent tex­tiles con­vert body heat into elec­tric­i­ty using ther­mo­elec­tric effects, which can be stored in a battery.

Pow­er sup­ply becomes independent
“Our vision is to use tex­tile mate­ri­als for ener­gy gen­er­a­tion. These smart fab­rics can sup­ply mobile devices for con­sumer elec­tron­ics or health appli­ca­tions with ener­gy in a flex­i­ble, demand-ori­ent­ed and envi­ron­men­tal­ly friend­ly man­ner. Smart­watch­es or fit­ness bracelets are worn direct­ly on the body and can thus be sup­plied with pow­er at any time. Vital para­me­ters, for exam­ple, can be con­tin­u­ous­ly mea­sured and mon­i­tored,” explains Dr. Jonathan Plentz, head of the Pho­ton­ic Thin Film Sys­tems research group at Leibniz-IPHT.

Peo­ple in focus for ener­gy generation
To gen­er­ate ener­gy, the Jena researchers use ther­mo­elec­tric gen­er­a­tors that con­vert the body’s own heat into elec­tri­cal ener­gy (See­beck effect). For this pur­pose, thin-film coat­ings in the form of alu­minum-doped zinc oxide (Al:ZnO) are applied to tex­tile fab­rics as a ther­mo­elec­tric func­tion­al lay­er. Using tem­per­a­ture dif­fer­ences between the user’s skin sur­face and the ambi­ent tem­per­a­ture or indus­tri­al waste heat, the researchers were able to mea­sure ther­mo­elec­tric effects with pow­ers of up to 0.2 μW. The elec­tric­i­ty gen­er­at­ed could be stored in a bat­tery to meet the ener­gy needs of elec­tron­ic devices for health or sports. “This makes the ener­gy sup­ply of devices self-suf­fi­cient,” says Dr. Gabriele Schmid, project man­ag­er at Leibniz-IPHT.

Ther­mo­elec­tric cool­ing for more safe­ty and well-being
The smart tex­tiles can do much more: The ther­mo­elec­tric effect can also be used for cool­ing by means of elec­tri­cal ener­gy and thus be used for cool­ing appli­ca­tions and tem­per­a­ture reg­u­la­tion (Pel-tier effect). Plentz sees a pos­si­ble area of appli­ca­tion in the steel indus­try, for exam­ple: “Work­ers at blast fur­naces are exposed to high lev­els of heat. Even after a short time, the body tem­per­a­ture ris­es sig­nif­i­cant­ly due to the sur­round­ing heat. Intel­li­gent cool­ing fab­rics inte­grat­ed into pro­tec­tive cloth­ing can help to bet­ter reg­u­late body tem­per­a­ture. In addi­tion, the tex­tile mate­ri­als are char­ac­ter­ized in par­tic­u­lar by their air per­me­abil­i­ty, light­ness and flex­i­bil­i­ty, which not only has a pos­i­tive effect on ther­mal man­age­ment, but also pro­vides addi­tion­al com­fort in chal­leng­ing work­ing environments.”

In tests, Pelti­er cool­ing demon­strat­ed a tem­per­a­ture dif­fer­ence of up to 12 °C, which is unique for tex­tile ther­mo­elec­tric ele­ments. In the future, not only could process-crit­i­cal areas in indus­try be tem­per­a­ture-con­trolled, but the smart tex­tiles with their cool­ing prop­er­ties would also pro­vide even bet­ter pro­tec­tion for police and fire­fight­ers. Active reg­u­la­tion of body tem­per­a­ture with high tex­tile com­fort is also very impor­tant in the field of well-being and in the med­ical envi­ron­ment (for exam­ple, to reduce fever). The cool­ing of trans­port goods by means of func­tion­al­ized tex­tiles opens up fur­ther fields of application.

The projects were fund­ed by the Ger­man Fed­er­al Min­istry of Eco­nom­ics and Cli­mate Pro­tec­tion (BMWi) as part of the Cen­tral Inno­va­tion Pro­gram for SMEs (ZIM).

Sci­en­tif­ic publications
G. Schmidl et al: 3D spac­er fab­rics for ther­mo­elec­tric tex­tile cool­ing and ener­gy gen­er­a­tion based on alu­minum doped zinc oxide. Smart Mate­ri­als and Struc­tures 29, (2020) 125003, https://doi.org/10.1088/1361–665X/abbdb5

G. Schmidl et al: Alu­minum-doped zinc oxide-coat­ed 3D spac­er fab­rics with elec­tro­less plat­ed cop­per con­tacts for tex­tile ther­mo­elec­tric gen­er­a­tors. Mate­ri­als Today Ener­gy 21 (2021) 100811, https://doi.org/10.1016/j.mtener.2021.100811