Through a process called carbonisation which converts paper into pure carbon, the researchers turned the paper's fibres into a carbon foam that could be used for the electrodes used in the rechargeable batteries that power mobile phones, medical equipment, and electric vehicles.
To produce the carbon anodes, the researchers joined and laser-cut several thin sheets of kraft paper to form different lattice geometries, both 3D open-cell honeycombs and closed-cell plate lattices, using a sheet lamination process. The paper was then heated to 1200°C in a furnace without the presence of oxygen, to convert it into carbon by pyrolisation.
As carbonisation takes place in the absence of oxygen, negligible amounts of carbon dioxide are emitted, making the process a greener alternative to incineration.
The carbon anodes produced by the research team also demonstrated excellent durability, flexibility, and electrochemical properties. Laboratory tests showed that the anodes could be charged and discharged up to 1,200 times, which is at least twice as durable as anodes in current phone batteries. 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 also uses less energy-intensive processes and heavy metals compared to current industrial methods of manufacturing battery anodes.
As the anode is worth 10 to 15 per cent of the total cost of a lithium-ion battery, this latest method, which uses a low-cost waste material, is expected to also bring down the cost of manufacturing.
Using waste paper as the raw material to produce battery anodes would also ease the reliance on conventional sources for carbon, such as carbonaceous fillers and carbon-yielding binders, which are mined and later processed with harsh chemicals and machinery.
The Singapore researchers said that paper waste, which comprises disposed paper bags, cardboard, newspaper, and other paper packaging, accounted for nearly a fifth of the waste generated by their country in 2020, but could be a feedstock for economically viable carbon materials.
Kraft paper bags, which make up the bulk of Singapore's paper waste, were also found to have large environmental footprints compared to their counterparts made of cotton and plastic, due to their greater contribution to global warming when incinerated and the eco-toxicity potential in producing them.
Assistant professor Lai Changquan, from NTU's School of Mechanical & Aerospace Engineering, who led the project, said: "Paper is used in many facets in our daily lives, from gift wrapping and arts and crafts, to a myriad of industrial uses, such as heavy-duty packaging, protective wrapping, and the filling of voids in construction.
"However, little is done to manage it when it is disposed of, besides incineration, which generates high levels of carbon emissions due to their 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."
The research has been published in Additive Manufacturing.
