Electrode materials for biomedical patchable and implantable energy storage devices

With the rapid development of biomedical and information technologies, the ever-increasing demands on energy storage devices are driving the development of skin-patchable and implantable energy storage materials for biometric information real-time monitoring, medical diagnosis and prognosis, and therapeutic applications. However, it is very challenging to design energy storage materials because of their unique interface with human skin/tissue and biological dynamic conditions. This paper reviews the recent progress of flexible skin-patchable and implantable energy storage devices, covering key considerations on the electrode materials in terms of energy storage performance and biological features. The electrochemical and biological properties of the electrode materials, including carbon nanomaterials, metals, metal oxides, biopolymers, and composites, are comprehensively addressed. Along with the integration of these materials into the device architecture, the device feature and performance under human motion and in-vitro/in-vivo biological environments are also discussed. Finally, the paper provides perspective into the current challenges and future research directions in this field.