New Materials for High-Energy, Long-Life Rechargeable Batteries

Using sulfur-rich, highly ionic compounds as cathodes and electrolytes enables solid-state lithium-sulfur rechargeable batteries.

Scanning electron micrograph of a new solid electrolyte material (lithium thiophosphate) showing its surface morphology and the nanoscale porosity which are responsible for its high ionic conductivity; Inset shows its crystal structure. — Image courtesy of Oak Ridge National Laboratory

The Science

Introduction of nanoscale porosity in a bulk electrolyte material (lithium thiophosphate) was found to promote surface conduction of lithium ions, thereby enhancing the ionic conductivity in the nanostructured material by three orders of magnitude over the normal bulk phase.

The Impact

The high ionic conductivities in these new, nanoporous electrolytes coupled with sulfur-rich, nanostructured cathode materials have led to the development of a new type of solid-state, rechargeable lithium-sulfur battery that is potentially safer and more reliable than today’s commercial Li ion batteries.

Summary

The high ionic conductivities found in a new, nanoporous form of lithium thiophosphate has enabled the development of a new high-performance, solid-state lithium-sulfur (Li-S) battery. Li-S batteries have a high theoretical energy density of 2600 Wh/kg, which is about 5 times higher than that of the state-of-the-art lithium-ion batteries. Conventional Li-S batteries use liquid electrolytes, which can lead to an intrinsically short lifespan of the batteries because of the loss of dissolved sulfur through the so-called “polysulfide shuttle” phenomenon. The use of a solid electrolyte can efficiently prevent the loss of sulfur, thus extending the battery’s lifespan. The nanoporous form of lithium thiophosphate developed in this basic research investigation displays unusually high ionic conductivity–about thousand-times that of the bulk form–and thus is an excellent solid electrolyte that is compatible with Li-metal anode. Additionally, in associated applied research lithium thiophosphate was found to form a new family of lithium-conducting sulfur-rich compounds by reaction with elemental sulfur, called lithium polysulfidophosphates (LPSP). These LPSP compounds are also good Li-ion conductors with excellent cyclability, and therefore can function as superior cathode materials. Collectively, these two parallel advances have paved the way to prototype all-solid-state, rechargeable Li-S batteries that may be safer, more reliable, and have longer lifespans than conventional designs. In initial testing, the prototype Li-S batteries made with these materials exhibited high capacities (700mA hg^-1 at 25oC and 1200mA hg^-1 at 60°C) which are maintained even after 300 charge-discharge cycles.

Contact

Chengdu Liang
Oak Ridge National Laboratory
liangcn@ornl.gov

Funding

DOE Office of Science, Basic Energy Sciences program supported the development of the high conductivity compounds and the synthesis/characterization studies at the Center for Nanophase Materials Sciences User Facility. The development of the batteries and demonstration of the battery properties was supported by the DOE Office of Energy Efficiency and Renewable Energy Vehicle Technologies program.

Publications

Z. Lin, Z. Liu, W. Fu, N. Dudney and C. Liang, “Lithium Polysulfidophosphates: A Family of Lithium-Conducting Sulfur-Rich Compounds for Lithium-Sulfur Batteries”, Angew. Chem. Int. Ed., 52, (2013). [DOI: 10.1002/anie.201300680].

Z. Liu, W. Fu, E. Andrew Payzant, X. Yu, Z. Wu, N. J. Dudney, J. Kiggans, K. Hong, A. J. Rondinone, and C. Liang, “Anomalous High Ionic Conductivity of Nanoporous b-Li3PS4”, J. Am. Chem. Soc., 135, 975, (2013). [DOI: 10.1021/ja3110895].