The ORNL team overcame these barriers by first synthesizing a new class of sulfur-rich materials—lithium polysulfidophosphates (LPSPs)—that conduct ions as well as the lithium metal oxides conventionally used in the battery’s cathode.

LPSPs have ionic conductivities of 3.0×10⁻⁵ S cm⁻¹ at 25 °C, which is 8 orders of magnitude higher than that of Li₂S (lithium sulfide). The high lithium ion conductivity imparts excellent cycling performance, the researchers noted.

The researchers then combined the new sulfur-rich cathode and a lithium anode with a solid electrolyte material, also developed at ORNL, to create an energy-dense, all-solid battery.

A paper on their work is published in the journal Angewandte Chemie International Edition.

Our approach is a complete change from the current battery concept of two electrodes joined by a liquid electrolyte, which has been used over the last 150 to 200 years. This game-changing shift from liquid to solid electrolytes eliminates the problem of sulfur dissolution and enables us to deliver on the promise of lithium-sulfur batteries. Our battery design has real potential to reduce cost, increase energy density and improve safety compared with existing lithium-ion technologies

—Chengdu Liang, lead author

The new ionically-conductive cathode enabled the ORNL battery to maintain a capacity of 1,200 mAh/ g after 300 charge-discharge cycles at 60 °C. By comparison, a conventional lithium-ion battery cathode has an average capacity between 140-170 mAh/g. Because lithium-sulfur batteries deliver about half the voltage of lithium-ion versions, this eight-fold increase in capacity demonstrated in the ORNL battery cathode translates into four times the gravimetric energy density of lithium-ion technologies, explained Liang.

The team’s all-solid design also increases battery safety by eliminating flammable liquid electrolytes that can react with lithium metal. Chief among the ORNL battery’s other advantages is its use of elemental sulfur, a plentiful industrial byproduct of petroleum processing.

Although the team's new battery is still in the demonstration stage, Liang and his colleagues hope to see their research move quickly from the laboratory into commercial applications. A patent on the team’s design is pending.

In addition to Liang, coauthors are ORNL’s Zhan Lin, Zengcai Liu, Wujun Fu and Nancy Dudney. The research was sponsored by the US Department of Energy, through the Office of Energy Efficiency and Renewable Energy's Vehicle Technologies Office. The investigation of the ionic conductivity of the new compounds was supported by the Department's Office of Science.

The synthesis and characterization was conducted at the Center for Nanophase Materials Sciences at ORNL. CNMS is one of the five DOE Nanoscale Science Research Centers (NSRCs) supported by the DOE Office of Science, premier national user facilities for interdisciplinary research at the nanoscale.

Together the NSRCs comprise a suite of complementary facilities that provide researchers with advanced capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative.

The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos national laboratories.

Resources

• Lin, Z., Liu, Z., Fu, W., Dudney, N. J. and Liang, C. (2013), Lithium Polysulfidophosphates: A Family of Lithium-Conducting Sulfur-Rich Compounds for Lithium-Sulfur Batteries . Angew. Chem. Int. Ed. doi: 10.1002/anie.201300680