An Ultra-Thin Wearable Thermoelectric Paster Based on Structured Organic Ion Gel Electrolyte

Abstract

Thermoelectric technology that utilizes thermodynamic effects to convert thermal energy into electrical energy has greatly expanded wearable health monitoring, personalized detecting, and communicating applications. Encouragingly, thermoelectric technology assisted by artificial intelligence exerts great development potential in wearable electronic devices that rely on the self-sustainable operation of human body heat. Ionic thermoelectric (i-TE) devices that possess high Seebeck coefficients and a constant and stable electrical output are expected to achieve an effective conversation of thermal energy harvesting. Herein, we developed an i-TE paster for thermal chargeable energy storage, temperature-triggered material recognition, contact/non-contact temperature detection, and photo thermoelectric conversion applications. An all-solid-state organic ionic gel electrolyte (PVDF-HFP-PEO gel) with onion epidermal cells-like structure was sandwiched between two electrodes, which take full advantage of a synergy between the Soret effect and the polymer thermal expansion effect, thus achieving the enhanced ZT value up to 900% compared with the PEO-free electrolyte. The i-TE device delivers a Seebeck coefficient of 28 mV K−1, a maximum energy conversion efficiency of 1.3% in performance, and ultra-thin and skin-attachable properties in wearability, which demonstrate the great potential and application prospect of the i-TE paster in self-sustainable wearable electronics.

1. Introduction

Thermoelectric technology with the design of advanced, flexible, and miniaturized properties has shown a modern and diversified trend as wearable electronic devices, making a big splash in the field of smart healthcare as well as artificial intelligence such as human–computer interaction [1–3]. Different from the previous thermoelectric devices applied in power generation to respond to the persistently harsh global energy landscape, the optimized thermoelectric electronic could provide efficient heat conversion and communication for mechanical devices and human body heat [4, 5]. Great efforts have been devoted to fabricating thermoelectric devices for application in self-driven human temperature acquisition, image recognition, neural simulation, VR/AR interactive haptic sensing, and passive integrated system building [6]. For example, Li et al. proposed a self-powered material identification ring (MIR) based on the thermoelectric effect of the prepared dual-network ionic hydrogel, which can actively infer the type of material without an external power connection by analyzing the voltage signals related to interfacial heat transfer generated in contact with different materials [7]. Luo and co-workers fabricated a self-driven hemispherical retinotopic eye relying on the photothermoelectric effect of photosensitizer-ionic gel heterojunction, which converts incident photons into neuroelectrical signals with retina-like tunable plasticity, achieving the restoration of intrinsic perceptual functions [8].

High-efficient thermoelectric devices require specific materials to directly convert heat and electric energy into each other. Traditional electron-type thermoelectric materials based on the Seebeck effect are mostly concentrated in materials with high conductivity, carrier mobility, and outstanding energy filtering effects, including inorganic semiconductors composed of alloys, ceramics, and metal oxides, and conductive polymers, such as polyaniline and polythiophene, which suffers very low thermal power less than 10 µV K−1 [9, 10]. As a result, ionic thermoelectric (i-TE) materials with ions as carriers are developed, which rely on two kinds of REDOX effect and Soret effect to realize the collection of low-grade heat (LGH), and especially enrich the thermal energy management system [11–13]. Hydrogel electrolyte as a highly hydrophilic three-dimensional mesh material is widely used in the fabrication of a variety of solid-state i-TE devices [14]. However, the poor dehydration and thermal tolerance capability of the hydrogel makes it difficult to apply in long-life and stable i-TE devices [15, 16]. Therefore, developing an i-TE device based on solid-state organic ion gel electrolytes is crucial for overcoming these limitations.