Printed Zinc-Ion Batteries on Hydrogel Reinforced Cellulose Composite for Paper Electronics

Paper electronics provides a low-cost and sustainable option for the ever growing demand of Internet of Things (IoT) devices. Batteries are considered as the heart of those energy-consuming paper electronics.[1] Rapid development of flexible electronics not only poses severe challenges to traditional manufacturing methods, but also raises further concerns on their impact on environment. [2] Deriving from abundant biomass, cellulose paper presents an ideal building block for developing flexible and sustainable electronics.[3] Paper electronics could be the raising star of next-generation functional devices, especially in the field of paper-based flexible batteries, sensors, circuits, and diagnostic equipment.[4] Imagine if these devices can be integrated on a piece of paper, it will greatly facilitate the application scenarios and enhance the commercial values. Meanwhile, the compatibility of paper to printing techniques allows facile ink printing of a wide variety of functional materials. [5] Therefore, facile and scalable fabrication of paper-based batteries is crucial to build paper electronics systems.<br/>In our study, we propose polyacrylamide hydrogel reinforced cellulose paper (HCP) for printable zinc batteries and paper electronics. By combining the characteristics of cellulose paper and hydrogel, the composite paper presents favourable mechanical and ioninc conductivity properties that are suitable to its function as the separator and electrolyte for zinc batteries.We have realized printing of quasi-solid, biodegradable aqueous Zn-Ni and Zn-Mn batteries and demonstrate its possibility of integrating with other paper electronics. In our strategy, HCP serves as the separator and electrolyte while maintaining its printability as a paper substrate, and electrodes are printed on both sides of the HCP to form flexible batteries. The hydrogel significantly improves the mechanical strength of the cellulose fibers and maintains the ion conductivity of the composite. As a result, the printed batteries are cuttable and flexible without the risk of short of contact failure.The printed zinc batteries deliver remarkable volumetric energy density of ~26 mWh cm^–3 (based on total device volume), and feature of cuttability and compatibility with flexible circuits and devices.<br/>Furthermore, The HCP holds great biodegradability as natural cellulose. Polyacrylamide and cellulose are decomposable in the presence of bacteria, fungi, and other microorganisms. When buried in natural soil (roof garden, NTU campus, Singapore), HCP became fractured after two weeks of burial. Hygroscopicity of hydrogel greatly facilitates the growth and reproduction of microorganism. HCP can be completely degraded within four weeks. In addition, the compatibility of the paper batteries with flexible circuits and devices allows the construction of a self-powered paper system that integrates printed battery with solar cells.<br/>In conclusion, we demonstrate the possibility of printed paper batteries and integration with flexible electronics toward the new era of paper electronics.This paper batteries will be an important step to paper electronics when other electronic parts, such as solar cells, can be also printed on the same paper. With the facile synthesis and high performance, the HCP-based printed batteries hold great promise for next-generation sustainable paper electronics.<br/><br/>Abstract original from: <u>Adv. Sci. 2021, 2103894, DOI: 10.1002/advs.202103894</u><br/><br/>[1] Printed Batteries: Materials, Technologies and Applications, John Wiley & Sons Ltd, 2018.<br/>[2] Nat. Commun. 2015, 6, 7170.<br/>[3] Adv. Mater. 2018, 30, 1703453.<br/>[4] Adv. Mater. 2021, 33, 2000892.<br/>[5] Adv. Mater. 2018, 30, 1801588.