Abstract:  

Supercapacitors are widely used for powering flexible/wearable electronics owing to their excellent charge storage capabilities. In this study, MnO₂ nanosheets were grown on the surface of graphene using a simple water bath method to prepare graphene/MnO₂ composites for fabricating supercapacitors. In addition, two-dimensional black phosphorus was introduced as an additive into the electronic ink based on the as-prepared graphene/MnO₂ composites. The characterization and electrochemical analyses results showed that adding black phosphorus considerably improved the capacitive performance of the material, yielding a high specific capacitance of 241.5 F g^-1 at 0.1 A g^-1 and an impressive rate capability improvement from 52.5% to 80.3%. Then the micro-supercapacitor having an area-specific capacitance of 20.15 mF cm^-2 at a scanning rate of 2 mV s^-1 was utilized to demonstrate the practical applicability of this material. To further evaluate the practical applicability of this micro-supercapacitor, the micro-supercapacitor was integrated with a flexible thin-film pressure sensor on paper and cloth through screen printing.

Background Introduction:

In recent years, portable and wearable electronic devices have become extremely popular, and new products are being created to revolutionize our daily lives. Sports bracelets and heatable jackets are widely used by youngsters. In addition, with aging population around the world, flexible wearable devices that can remotely detect the physical condition of the elderly will also become major products in future. These devices will bring about considerable lifestyle changes. Moreover, these electronic devices often require suitable energy storage devices, such as batteries, for power supply. However, currently available power sources including alkaline batteries, Ni–Zn batteries, and Li-ion batteries are often low charge-discharge rate and low power density, resulting in poor compatibility with flexible and wearable electronic devices.

In this study, a simple water bath method was used to grow MnO₂ nanosheets on the surface of single-layer graphene and prepared a graphene/MnO₂ composite material by introducing two-dimensional black phosphorus during the pulping process. This considerably enhances the performance of the supercapacitor. Concentric circular micro-supercapacitors (CCMSCs) fabricated using this composite material can be integrated with flexible membrane pressure sensors. These CCMSCs are expected to facilitate in-plane system integration and be used in wearable electronic devices.

Article Highlights:

The research paper presents an innovative approach to enhancing the performance of micro-supercapacitors through the fabrication of MnO₂ nanosheet/graphene composites with an added black phosphorus, resulting in significantly improved capacitive performance and rate capability. The study demonstrates a high specific capacitance of 241.5 F g^-1 at 0.1 A g^-1 and an impressive rate capability improvement to 80.3%. The micro-supercapacitors not only exhibit excellent durability with over 50% capacitance retention after 10,000 cycles and 78% after 500 bending cycles at 90 degrees but also showcase practical applicability in flexible and wearable electronics. A key demonstration includes the successful integration with a flexible thin-film pressure sensor and the ability to power an LED in response to pressure changes, illustrating the device's potential for real-world applications.

Summary and Outlook:

The graphene/MnO₂/black phosphorus electrode fabricated by doping black phosphorus into graphene/MnO₂ through a facile water bath process during preparation of the electrode ink is proved to be a high-performance electrode for supercapacitors. Adding black phosphorus not only improves the conductivity of graphene/MnO₂ but also maintains structural stability, thus contributing to enhanced rate capability and cyclic stability. Consequently, the supercapacitor with the graphene/MnO2/black phosphorus electrode exhibits an impressive rate capability (reaching approximately 80.3%) and high specific capacitance values (41.7 F g^-1 at 0.1A g^-1 and 21 F g^-1 at 1 A ​g^-1), as well as decent cycle stability (79% after 5000 cycles at a current density of 1 A g^-1). Finally, the concentric circular micro-supercapacitor (CCMSC) with high specific-area capacitance (20.15 mF cm^-2 at a scan rate of 2 mV s^-1) and excellent flexibility (78% after being bent for 500 cycles at 90°) has been integrated in a flexible wearable device, proving the applicability of the graphene/MnO₂/black phosphorus electrode in flexible wearables.

Article Details:

Flexible micro-supercapacitors fabricated from MnO₂ nanosheet/graphene composites with black phosphorus additive

Baocheng Liu, Zongsheng Cao, Zhengchun Yang, Wen Qi, Jie He, Peng Pan, Huayi Li, Ping Zhang

Article Link: https://doi.org/10.1016/j.pnsc.2021.10.008

Author introduction

This work was mainly finished by Advanced Materials and Printed Electronics Center in Tianjin Key Laboratory of Film Electronic & Communication Devices of Tianjin University of Technology with the collaboration of Tianjin University and China Iron & Steel Research Institute Group. The research group was from Prof. Zhengchun Yang, who is the director of Advanced Materials and Printed Electronics Center. Advanced Materials and Printed Electronics Center was established in 2013. The research center was focused on the study of flexible electronic devices. There is a professional printed electronic device processing platform, including screen printing machines, inkjet printing machines, micro plotters, scanning electron microscopes, electrochemical workstations, electrochemiluminescence testing systems, and more. At present, the center mainly undertakes various scientific research projects with a total funding of over 10 million, has published more than 50 papers, and applied for 10 patents.