One of the most important challenges in the application of flexible wearable electronic devices is the lack of batteries that can flex and stretch safely with the electronic device or with fabric it is integrated with. When we refer to "smart" clothing, the use of which is increasingly become popular, we envision garments and accessories equipped with sensors and electronic circuits capable of collecting various physical and biometric data such as body temperature and heart rate. Rapid advancements in flexible, stretchable sensor, transistor, actuator, and integrated circuit technologies are the driving force in the development of energy storage systems that can stretch, bend, fold, wrinkle, and most importantly, maintain their electrochemical performance while being exposed to all these deformations. In this field, efforts are focused on making lithium-ion batteries, which are the most commonly used energy storage system in personal electronics, flexible and stretchable.