Paper biomass to build lithium-sulfur batteries

　　Researchers at Rensselaer have developed a patented method to use cheap and abundant paper biomass to make lithium-sulfur batteries.

　　A major by-product in the papermaking industry is lignosulfonate – a sulfonated carbon waste material, which is typically combusted on site, releasing CO2 into the atmosphere after sulfur has been captured for reuse.

　　Using this cheap and abundant paper biomass, a team of researchers from Rensselaer Polytechnic Institute said they can build a rechargeable lithium-sulfur battery.

　　The team believe this could be used to power big data centres and provide a more affordable energy-storage option for microgrids and the electric grid.

　　“Our research demonstrates the potential of using industrial paper-mill by-products to design sustainable, low-cost electrode materials for lithium-sulfur batteries,” said Trevor Simmons of Rensselaer.

　　Sulfur is nonconductive, but when combined with carbon at elevated temperatures this changes, allowing it to be used in battery technologies. The challenge is that sulfur can easily dissolve into a battery’s electrolyte, causing the electrodes on either side to deteriorate after only a few cycles.

　　The team explain that, so far, researchers have used different forms of carbon, like nanotubes and complex carbon foams, to confine the sulfur in place, but with limited success. “Our method provides a simple way to create an optimal sulfur-based cathode from a single raw material,” Simmons said.

　　To develop their method, the Rensselaer researchers partnered with Finch Paper in Glens Falls, which provided the lignosulfonate. This ‘brown liquor’ was dried and heated to about 700°Cin a quartz tube furnace.

　　The high heat drives off most of the sulfur gas, the team explained, but retains some of the sulfur as polysulfides that are embedded deep within an activated carbon matrix.

　　The team repeated this process until the right amount of sulfur was trapped in the carbon matrix. The researchers then ground the material and mixed it with an inert polymer binder to create a cathode coating on aluminium foil.

　　The research team said it has managed to create a lithium-sulfur battery prototype that is the size of a watch battery, which can cycle about 200 times. The next step is to scale up the prototype to markedly increase the discharge rate and the battery’s cycle life.