Self-powered highly stretchable ferroelectret nanogenerator towards intelligent sports Yiqin Wang a,1 , Xianfa Cai a,1 , Yufeng Guo a,* , Zhi Chen a , Yunqi Cao b , Wangdi Du b , Tian Xia c , Nelson Sepulveda d,* , Wei Li a,c,* a College of Integrated Circuit Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing, Jiangsu 210023, China b College of Control Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China c College of Engineering and Mathematical Sciences, University of Vermont, Burlington, VT 05405, USA d Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, USA ARTICLE INFO Keywords: Nanogenerator Ferroelectret Stretchable Flexible Transverse piezoelectricity Sports training ABSTRACT Ferroelectret nanogenerators (FENGs), recognized for their porous structures that facilitate charge retention, thereby creating giant electric dipoles and exhibiting remarkable piezoelectric properties, are utilized in the development of various flexible transducers. However, despite their flexibility, most developed ferroelectret nanogenerators lack adequate stretchability and satisfactory transverse piezoelectric properties, significantly inhibiting their widespread deployment in wearable or skin-mounted electronics. Here, we introduce a highly stretchable ferroelectret nanogenerator (HS-FENG) built from laser-induced graphene (LIG), Ecoflex and anhy- drous ethanol, demonstrating exceptional flexibility and stretchability, along with longitudinal and transverse piezoelectric effects. The stretchability of HS-FENG can reach a record of 468 %, while the quasi-static piezo- electric coefficients d 33 and d 31 are approximately 120 pC/N and 70 pC/N, respectively. To our knowledge, this is the first demonstration of the developed FENG with remarkably high stretchability. Furthermore, leveraging the performance of the created HS-FENG, we construct a skin-mounted intelligent kinesiology tape capable of effectively monitoring motion signals from human muscles and joints, thereby offering a deeper understanding of movement for users across different levels of physical activity, from professional athletes to individuals under- going rehabilitation. The development of intelligent kinesiology tape exemplifies the potential of HS-FENG technology in enhancing professional athletic training and personalized healthcare. It contributes to the advancement of inconspicuous skin-mounted biomechanical feedback systems and human-machine interfaces, marking progress in the field. 1. Introduction As we delve deeper into the era of artificial intelligence (AI), Big Data, and the Internet of Things (IoT) [1,2], we are witnessing trans- formative changes across numerous facets of life, and sports is no exception [3,4]. This transition into the digital intelligence era has brought about an increasing demand for innovative intelligent sports sensors that can monitor real-time information about body movement and muscle activity status. Such developments are not only guiding sports training [5,6], but they also address people’s health concerns related to sports [7,8]. Traditional sports bracelets, which primarily monitor pulse and heart rate as indirect feedback on sports status, have become inadequate to meet the growing needs of users [9,10]. This has spurred the rapid development of new wearable electronic sensors that offer unique functionalities, high reliability, and precise monitoring [11–21]. However, some sensors require power from traditional energy storage devices (like batteries), which face challenges such as limited lifespan, hazardous chemicals, large size, rigid structure, and heat pro- duction [22–24]. Additionally, some sensors, despite their flexibility, demonstrate limited stretchability and twistability [25], which restricts their applicability to specific scenarios or exercise modes and hinders precise real-time exercise guidance. To tackle these challenges effec- tively, there is a need to develop a skin-mounted electronic sensor [26–29] that integrates selfpowered capabilities, excellent flexibility, * Corresponding authors. E-mail addresses: yfguo@njupt.edu.cn (Y. Guo), nelsons@egr.msu.edu (N. Sepulveda), wei.li@uvm.edu (W. Li). 1 These authors contributed equally. Contents lists available at ScienceDirect Nano Trends journal homepage: www.elsevier.com/locate/nantre https://doi.org/10.1016/j.nwnano.2024.100053 Received 2 August 2024; Received in revised form 12 September 2024; Accepted 23 September 2024 Nano Trends 8 (2024) 100053 Available online 28 September 2024 2666-9781/© 2024 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/).