However, a team based at Rensselaer Polytechnic Institute, Troy, N.Y., is taking it in another direction—they developed a technique for treating and then using this biomass to create part of rechargeable lithium-sulfur batteries.
“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, the research scientist who developed the technology along with colleagues at the Center for Future Energy Systems (CFES). The details are in their paper “Repurposing paper by-product lignosulfonate as a sulfur donor/acceptor for high performance lithium–sulfur batteries,”published in the journal Sustainable Energy & Fuels, with further information in a supplemental package. Along with former graduate student Rahul Mukherjee, Simmons has patented the process, Patent #9,859,561.
In a lithium-sulfur battery, the cathode is composed of a sulfur-carbon matrix, and a lithium-metal oxide is used for the anode. While elemental sulfur is nonconductive, it can be made highly conductive by combining it with carbon at elevated temperatures, thus making it suitable for battery technologies.
However, there’s a problem as the sulfur can dissolve into a battery’s electrolyte, which causes the cathode and anode electrodes to deteriorate after only a few cycles. To overcome this, batteries typically use carbon-based materials (including nanotubes) to confine the sulfur in its place.
The Rensselaer researchers worked with a nearby paper mill, which provided the lignosulfonate, commonly referred to as “brown liquor” (Fig. 1). This dark, syrupy substance was dried and heated to about 700°C in a quartz-tube furnace. The intense heat drives off most of the sulfur gas but retains some of the sulfur as polysulfides (chains of sulfur atoms) embedded deep within an activated carbon matrix.