Abstract graphic of the process of turning paper into batteries.
To carbonize paper, the team exposed it to high temperatures to produce pure carbon, steam and oil that can be used as biofuel. Because carbonization takes place in the absence of oxygen, it releases negligible amounts of carbon dioxide, making the process a greener alternative to burning kraft paper, which produces large amounts of greenhouse gases. The carbon anodes produced by the team also demonstrated superior durability, flexibility and some electrochemical properties.
A series of lab tests showed that the anodes could be charged and discharged up to 1,200 times, at least twice as long as the anodes in current phone batteries. The batteries using NTU-made anodes are also more resistant to physical stress than comparable batteries, absorbing crushing energy up to five times better.
The method developed by NTU also uses a process that is less energy-intensive and uses fewer heavy metals than current industrial methods of producing battery anodes. Since anodes account for 10% to 15% of the total cost of a lithium-ion battery, this latest method, which uses cheap waste materials, is expected to reduce the cost of producing them as well. Using waste paper as a raw material for battery anodes reduces our reliance on conventional carbon sources – such as carbon fillers and binders that create carbon, which is mined and then processed with harsh machinery and chemicals.
Assistant Professor Lai Changquan, School of Mechanical Engineering & “Paper is used in many aspects of our daily lives – from gift wrapping, arts and crafts, to countless industrial applications, such as heavy-duty packaging, protective coverings and filling voids in construction,” said NTU Aerospace and project leader, Dr. John C. Lee, “However, very little technology is in place to manage it when it is disposed of, other than incineration, which generates high carbon emissions due to its composition. Our method gives kraft paper another lease of life, putting it in growing demand for many devices such as electric vehicles and smartphones, not only helping to cut carbon emissions but also reducing our reliance on mining and heavy industry.”
To create the carbon anode, the NTU team laser-cut several thin sheets of kraft paper into different lattice geometries. The paper is then heated to 1,200°C in an oxygen-free furnace, converting it to carbon, forming the anode. The NTU team attributes the anode’s superior strength, flexibility and electrochemical properties to the arrangement of the paper’s fibers.
The combination of strength and mechanical durability exhibited by NTU-made anodes allows batteries in phones, laptops and cars to better withstand shocks from drops and crashes, they say. Current lithium battery technology relies on internal carbon electrodes that gradually crack and crumble after physical shocks from drops – one of the main reasons why battery life shortens over time.
The team of researchers says their anode, which is harder than current electrodes used in batteries, could help solve this problem and extend battery life in a range of uses, from electronics to electric vehicles. Lim Guo Yao, study co-author and engineer in the School of Mechanical & NTU Aerospace, explains: “Our anodes exhibit a combination of strengths – such as strength, shock absorption, electrical conductivity. Several of these structural and functional properties demonstrate that our kraft paper anodes are a sustainable and scalable alternative to current carbon materials, and will find economic value in many demanding, high-end, multifunctional applications – such as the nascent field of structural batteries. Our method converts a common material into another that is extremely durable and in high demand. We hope our anodes will serve the world’s rapidly growing need for a greener, more sustainable material for batteries.”
Underlining the importance of the work done by the NTU team, Professor Juan Hinestroza, Department of Human-Centered Design, Cornell University (USA) and a person not involved in the research commented: “Since kraft paper is produced in such large quantities and processed similarly all over the world, I believe the innovative approach pioneered by the NTU Singapore team has the potential to have a major impact on a global scale. Any discovery that allows waste to be used as a raw material for new products “The high-value moisture as electrodes is really a great contribution. I think this work can open up a new path and motivate other researchers to find ways to convert other cellulose-based substrates, such as textiles and packaging materials, which are being discarded in large quantities globally.”
The NTU team will conduct further research to improve the energy storage capacity of their material and minimize the thermal energy required to convert paper into carbon.