Turning waste paper into Li-ion battery parts

Scientists from Nanyang Technological University, Singapore (NTU Singapore) have developed a technique to convert waste paper from single-use packaging and bags, and cardboard boxes, into a crucial component of lithium-ion batteries.

Through a process called carbonisation that converts paper into pure carbon, the researchers turned the paper’s fibres into electrodes, which can be made into rechargeable batteries that power mobile phones, medical equipment and electric vehicles. To carbonise the paper, the team exposed the paper to high temperatures, which reduces it to pure carbon, water vapour and oils that can be used for biofuel. As carbonisation takes place in the absence of oxygen, this emits negligible amounts of carbon dioxide, and the process is a greener alternative to disposing of kraft paper through incineration, producing large amounts of greenhouse gases.

The carbon anodes produced by the research team demonstrated superior durability, flexibility and electrochemical properties. Laboratory tests showed that the anodes could be charged and discharged up to 1200 times. The batteries that used the NTU-made anodes could also withstand more physical stress than their counterparts, absorbing crushing energy up to five times better. The NTU-developed method uses fewer energy-intensive processes and fewer heavy metals compared to current industrial methods of manufacturing battery anodes. The research findings were published in the scientific journal Additive Manufacturing.

Using waste paper as the raw material to produce battery anodes would ease the reliance on conventional sources for carbon, such as carbonaceous fillers and carbon-yielding binders, which are mined and processed with harsh chemicals and machinery. The current innovation, which presents an opportunity to upcycle waste products and reduce the dependence on fossil fuels, reflects NTU’s commitment to mitigating humanity’s impact on the environment. Assistant Professor Lai Changquan, who led the project, said that while paper is used in many facets of our daily lives, little is done to manage it when it is disposed of, besides incineration, which generates high levels of carbon emissions due to its composition. “Our method to give kraft paper another lease of life, funnelling it into the growing need for devices such as electric vehicles and smartphones, would not only help cut down on carbon emissions but would also ease the reliance on mining and heavy industrial methods,” Changquan said.

To produce the carbon diodes, the researchers joined and laser cut several thin sheets of kraft paper to form different lattice geometries, some resembling a spiky piñata. The paper was then heated to 1200°C in a furnace without the presence of oxygen, to convert it into carbon, forming the anodes. The researchers attribute the anode’s durability, flexibility and electrochemical properties to the arrangement of the paper fibres. The combination of strength and mechanical toughness shown by the NTU-made anodes could allow batteries of phones, laptops and automobiles to better withstand shocks from falls and crashes.

Currently Li-ion battery technology relies on internal carbon electrodes that gradually crack and crumble after physical shocks from being dropped, which is one of the main reasons why battery life gets shorter with time. The researchers said that their anodes, which are hardier than current electrodes used in batteries, will help address this problem and extend the life of batteries in a range of uses, from electronics to electric vehicles. Co-author of the study Lim Guo Yao said the anodes displayed a combination of strengths, such as durability, shock absorption and electrical conductivity, which are not found in current materials. “These properties demonstrate that our kraft paper-based anodes are a sustainable and scalable alternative to current carbon materials and would find economic value in demanding, high-end, multifunctional applications, such as the nascent field of structural batteries,” Yao said.

According to Lai, the NTU method converts a common and ubiquitous material — paper — into another that is durable and in high demand. “We hope that our anodes will serve the world’s quickly growing need for a sustainable and greener material for batteries, whose manufacturing and improper waste management have shown to have a negative impact on our environment,” Lai said.

Professor Juan Hinestroza from Cornell University, US, who was not involved in the research, said that the creative approach pioneered by the researchers at NTU Singapore could have great potential for impact at a global scale, because kraft paper is produced in large quantities and disposed likewise, all over the world. “Any discovery that will allow the use of waste as a raw material for high-value products like electrodes and foams is indeed a great contribution. I think that this work may open a new avenue and motivate other researchers to find pathways for the transformation of other cellulose-based substrates, such as textiles and packaging materials, which are being discarded in large quantities all over the globe,” Hinestroza said.

The NTU researchers will conduct further research to improve the energy storage capacity of their material and minimise the heat energy required to convert the paper into carbon. The research team has filed for a patent with NTUitive and is also working towards commercialising the invention.

Image credit: Nanyang Technological University, Singapore