Synthesis of stretchable triboelectric material with strain-compensating ability using gradient interpenetrating polymer networks

Abstract

Unlike conventional rigid triboelectric nanogenerators (TENGs), elastic TENGs are considered attractive for energy harvesting and sensing applications in mechanically harsh conditions. However, the practicality of elastic TENGs has been limited by the lack of elastic materials that simultaneously possess the desired mechanical and triboelectric properties. This paper introduces a complementary material synthesis strategy that uses a gradient interpenetrating polymer network (g-IPN) to address this issue. A sub-micron thick g-IPN was formed on a host elastomer (Ecoflex-CNT) that has high contact conformity using a highly chargeable guest polymer (pVP) with a low work function, through initiated chemical vapor deposition (iCVD) process. This complementary material synthesis effectively leveraged only the strengths of each component and resulted in a synergistic enhancement in output performance, with a short-circuit charge density (Q_SC) and an open-circuit voltage (V_OC) up to 445 μC m^-2 and 1335 V, respectively. These values were achieved without affecting bulk mechanical properties of the host elastomer, such as high stretchability and low bulk elastic modulus. Moreover, the depth-directional gradient profile of the g-IPN effectively prevented degradation in output performance under a severely stretched state (up to 100% strain), through a so-called strain-compensating ability. The effectiveness of the g-IPN in three-dimensional (3D)-structured elastic TENGs was successfully demonstrated by applying the g-IPN to a sponge-structured 3D elastic TENG (3D-IPN-TENG), which benefited from the exceptional deposition conformity of the iCVD process. The fabricated 3D-IPN-TENG showed stable operation with a short-circuit volume charge density (Q_SC,vol) of up to 267.2 mC m^-3, which is a record-high value among 3D-structured TENGs that utilize contact electrification (CE) between solids. This work not only overcomes the limitations of existing material strategies for elastic TENGs, but also suggests a new universal material design principle for synthesizing high-performance triboelectric materials.