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Sustainability and electronics do not always go hand in hand. The manufacturing, operation, and limited shelf life of electronic devices such as mobile phones and televisions, for example, are a burden on the environment.
According to the United Nations’ estimates, between 40 and 50 million tons of electrical waste are generated worldwide every year. It’s not surprising given that computer performance doubles every few years, new flat screens and smart phones continually replace older technology — and all these old devices have to be disposed of somehow … somewhere.
The waste from industrialized nations often-times ends up in the dumps of poorer nations, such as those in Africa and Asia. The world’s largest electronic waste disposal site is located in Agbogbloshie, Ghana. Here, 40,000 people live in an area of about 1600 ha, and it is one of the most contaminated places in the world.
Lately, an idea first put forth in 1939 has been gaining traction: The concept is to produce electronic components from cellulose — the main component of plant cell walls — to create sustainable, environmentally-friendly electronics.
In particular, there is a growing interest within the energy research community in cellulose-based energy storage devices, such as supercapacitors and batteries. Several publications have appeared in recent years which explore cellulose as an alternative material in energy storage devices.
Since cellulose can be produced in large quantities at low cost using paper manufacturing techniques, energy storage systems made from the sustainable material would be an important step towards green electronics. Such devices could provide cost-effective alternatives to lithium-based batteries, for example, and facilitate the development of new types of energy storage systems.
In a progress report recently published in Advanced Materials, Dr. Zhaohui Wang and Professor Leif Nyholm of Uppsala University, Sweden, together with Professor Sang-Young Lee and coworkers from Ulsan National Institute of Science and Technology (UNIST), Korea, explored this area of research and assessed the feasibility of cellulose in these types of applications. These include energy storage devices composed of conducting composites and thin layers of electroactive materials, as well as cellulose-based current collectors and functional separators.
Cellulose has been found to be an excellent material in the fabrication of electrodes as well as battery separators through a straightforward approach that deposits a thin layer of a conductive material on the surface of a cellulose sheet, thus converting the insulating paper into a flexible, conductive current collector. Furthermore, cellulose is an attractive substrate for printed energy storage devices due to its superior mechanical flexibility, thermal stability, and recyclability. A particularly interesting study successfully demonstrated a sustainable paper-based micro-supercapacitor.
“The recent development of cellulose-based electrochemical energy storage devices as well as materials for such devices clearly indicate that cellulose has the potential to become a very important material in the realization of new types of inexpensive and sustainable devices,” wrote the authors.
The authors emphasize that close attention should be paid to the properties of the cellulose like porosity, pore distribution, pore-size distribution, and crystallinity, as these properties directly affect the energy storage performance. Cellulose derived from wood conducts differently compared to cellulose from algae or cotton. Further investigations should consider the proper selections of the types of cellulose employed as well as optimized porosities. A too low or a too high porosity would decrease the battery performance, the water content of the cellulose is another important parameter.
According to the team, flexibility and production costs are decisive factors that favor cellulose-based electronics, as well as utilizing various printing techniques, which have long been available.
Thus, research on cellulose-based supercapacitors and batteries is very promising and should therefore be given a higher priority. Considering the properties of cellulose and the possibilities to employ existing large-scale manufacturing methods, they believe that cellulose-based energy storage systems will enable novel devices that will serve as complements to conventional technology.
Reference: Z. Wang, et al. ‘Why Cellulose-Based Electrochemical Energy Storage Devices?’ Advanced Materials (2020). DOI: 10.1002/ adma.202000892