Penn State and PNNL researchers are investigating a new sodium-based crystalline material which could be a promising solid-state conductor
Researchers at the US’ Penn State University and the Pacific Northwest National Laboratory (PNNL) have used a newly discovered sodium-based material to design and test a solid-state battery.
The material is composed of sodium, phosphorous, tin and sulphur and is structured in a “tetragonal crystal shape, the team said. Its conductive properties come from surface defects in the material – spaces where certain sodium, tin and sulphur atoms would be – which allow for it to transfer ions and enable its use as a solid-state electrolyte.
In addition to reducing the potential for flammability that comes with conventional liquid li-ion packs, sodium is much more abundant than lithium, meaning batteries using sodium salts could be far cheaper to produce.
“Our material has a wide voltage window as well as high thermal stability,” said Penn postdoctoral researcher in mechanical and nuclear engineering Zhaoxin Yu. “When you heat liquid electrolytes up to 150°C (302°F), they will catch fire or release a lot of heat that could damage other battery or electronic components. Our material performs well up to 400°C (752°F).”
Although sodium-ion batteries are unlikely to beat lithium for energy density – some have claimed to have developed liquid sodium cells reaching about 200Wh/kg, compared with an average 250Wh/kg for lithium – but the lower cost of materials could enable the technology to be used in more cost-effective grid-scale applications, or indeed in low-cost EVs.
In a paper published in Nano Energy, the team report that their material has room-temperature ionic conductivity about one-tenth that of liquid electrolytes used in today’s batteries. The important discovery, they said, is the specific configuration of defects within the crystal structure. “Our discovery of this new structure of this material also shows us that there’s a pathway for creating a new family of advanced sodium-ion superionic conductors,” said Penn research professor in materials science and engineering Shun-Li Shang.
The team created and tested this new battery in Wang’s laboratory, which is part of Penn State’s Battery and Energy Storage Technology Center. During the design process, the group has been able to identify how different crystal formations, as well as inconsistencies in the material, have affected its performance
“If you don’t have this set of tools, it would be difficult to make a breakthrough,” said distinguished professor of materials science and engineering Zi-Kui Liu. “Our approach that uses both computation and experiments allows us to analyse the reason why materials perform differently. That will make things faster for the next round of design because we know what we need to control in order to enhance ion transportation.”
The team say they are now fine-tuning the material using an iterative design approach that they hope could reduce the time from research to everyday use.