Yarn-Shaped Batteries Activated By An Ultralow Volume Of Sweat For Self-Powered Sensing Textiles

Electronic textile is a kind of textile that can perform electronic functions such as sensing,computing,display,and communication.It has shown great potentials in the fields of the Internet of Things,human-computer interaction,motion monitoring,and wearable communication.As one of the most important components in electronic textiles,the energy supplying unit has attracted much attention due to its critical role in powering the multiple functions of electronic textiles.Since the electronic textiles are expected to directly contact human skin,its safety issue has always been a concern.Human sweat is a typical biofluid containing various ions such as Na⁺,Cl^-,K⁺,and Ca²⁺.Thus,it can be used as a natural,safe,and reliable electrolyte.Sweat-activated battery（SAB）,as a flexible,multifunctional,and biocompatible energy supplying device,has been considered as one of the ideal solutions for energy supplying units in the electronic textile system.Very recently,a flexible and woven cotton-yarn-based SAB with a segmental structure has been developed,in which carbon-black-modified,pristine yarn and Zn foil-wrapped segments are prepared to serve as the cathode,salt bridge,and anode,respectively.Despite the cotton-yarn-based SABs’success in electronic textiles,their applications may still be constrained by their low power outputs,which are a result of the high internal resistance caused by the cotton-yarn-based salt bridge.Additionally,the uneven distribution of sweat on the skin surface and low-volume secretion at the beginning of perspiration may lead to slow and inefficient activation of the SABs.To address the above issues,we developed a core-sheath-structured sweat-activated yarn battery（SAYB）with conventional spinning technique,in which the Zn-wire core,cotton-yarn sheath,and outermost carbon yarn serve as the anode,sweat-wicking separator,and cathode,respectively.The ultra-low-volume sweat activation and the impact of yarn structures on the battery have been studied in this thesis.The large-scale production and self-powered wearable application have also been explored,demonstrating its potential in the daily lives.The thesis contains the following contents:1.Preparation of yarn-shaped batteries activated by an ultralow volume of sweatAiming at the problems of high internal resistance,limited output power,and large-volume of sweat activation in cotton-yarn-based SAB with a segmental structure,a core-sheath-structured sweat-activated yarn battery（SAYB）was developed with a Zn-wire anode,a cotton-yarn separator,and a carbon-yarn cathode.After absorbing artificial sweat,SAYB can reach an open circuit potential of～1.0 V.The coil number of the carbon yarn,the twist number of the cotton yarn,and the thickness of the cotton layer may all be adjusted to alter the power outputs of the SAYBs.Liquid electrolytes could be rapidly infiltrated and transferred over the separator thanks to the small distance between the electrodes and the great wicking capability of the hydrophilic cotton layer,enabling the fast activation of the battery by an ultra-low volume（1μL）of sweat within 3 seconds.SAYB can maximally absorb～60μL of artificial sweat.Due to the water evaporation-induced volume change of the residual liquid electrolyte,environmental factors including humidity,wind speed and temperature have significant influences on the operation duration of the activated batteries.Under suitable conditions,the battery has a power density of 1.72 m W cm^-2and an energy capacity of 15.3 m Ah,which are much greater than those of the previously reported cotton-yarn-based SAB.The batteries could tolerate 10,000 cycles of bending,2800 cycles of twisting,and 20cycles of washing without significantly reducing their power outputs,indicating excellent flexibility,durability,and washability.2.Sweat-activated energy fabric and its self-powered wearable applicationThe SAYBs could be connected to form a battery pack for higher outputs.When the number of in-series connected SAYBs increases from 1 to 4,the open-circuit voltage of the battery pack rises from 1.0 to 3.99 V.Under an external load of 100Ω,the current output and power density of a single battery are 2.71 m A and 1.56 m W cm^-2,respectively.By connecting four batteries in parallel,the values could increase to 9.36m A and 4.65 m W cm^-2,respectively.Multiple batteries connected in proper configurations could power headlights or charge portable gadgets like a smart watch and a smart phone.With the conventional spinning technique,the continuous manufacture of 60-meter-long SAYB has been achieved.To demonstrate the practical application potential of SAYB,a 5 m×0.5 m a sweat-activated energy fabric（SAEF）was created via the weaving method due to its compatibility with the traditional textile industry.The headband based on SAEF could be used as a self-powered safety warning device for night-time running,jogging,and cycling.The SAEF was further used to tailor a T-shirt with the energy-supplying area on the back.Combined with mini wireless analyzers and strain-sensing yarns,a self-powered sensing T-shirt was prepared.The T-shirt can be triggered to wirelessly monitor the arm swing frequency and breathing rate in real time after wicking up the sweat created by a volunteer while he is jogging.In summary,we have demonstrated the fabrication of a scalable,high-performance,core-sheath SAYB constructed with a Zn-wire anode,a cotton-yarn separator,and a carbon-yarn cathode.With the SAYBs,a sweat-activated energy fabric（SAEF）has been successfully constructed,demonstrating the great potential for self-powered wearable applications.The SAYBs developed in this thesis are expected to contribute to the production of self-powered smart garments for wearable healthcare and exercise monitoring as stable and reliable one-dimensional power sources.