Cheap and plentiful, sodium is a promising candidate for new battery technology. But the limited performance of sodium ion batteries has hindered their large-scale applications.
Now, a Department of Energy’s research team Pacific Northwest National Laboratory has developed a sodium-ion battery with a greatly extended life in laboratory tests. An ingenious shift in the ingredients that make up the battery’s liquid core prevents the performance issues that sodium-based batteries have caused. The findings, described in the news Nature Energyoffer a promising recipe for a battery that could one day power electric vehicles and store energy from the sun.
“Here we basically showed that sodium ion batteries have the potential to be a sustainable and environmentally friendly battery technology,” said PNNL lead author Jiguang (Jason) Zhang, a battery technology pioneer with over 23 patented inventions in energy storage technology.
The right salt
In batteries, electrolyte is the circulating “blood” that keeps the energy flowing. The electrolyte forms by dissolving salts in solvents, resulting in charged ions flowing between the positive and negative electrodes. Over time, the electrochemical reactions that keep the energy flowing slow and the battery can no longer be charged. In current sodium-ion battery technologies, this process happens much faster than in comparable lithium-ion batteries.
As a battery goes through repeated cycles of charging and discharging, it loses its ability to hold a charge. A new sodium ion battery technology developed by the Pacific Northwest National Laboratory maintains its ability to charge for longer than previously described sodium ion batteries. (Animation by Sara Levine | Pacific Northwest National Laboratory)
The PNNL team, led by scientists Yan Jin and Phung Le, attacked that problem by switching off the liquid solution and the type of salt flowing through it to create an entirely new electrolyte recipe. In lab tests, the new design proved to be durable, with 90 percent of its cell capacity after 300 cycles at 4.2V, which is higher than most sodium-ion batteries previously reported.
The current electrolyte recipe for sodium ion batteries causes the protective film on the negative end (the anode) to dissolve over time. This film is critical as it allows sodium ions to pass through while preserving battery life. The technology designed by PNNL works by stabilizing this protective film. The new electrolyte also generates an ultra-thin protective layer on the positive terminal (the cathode) which contributes to additional stability of the entire unit.
Non-flammable technology
The new sodium ion technology developed by PNNL uses a natural fire extinguishing solution that is also insensitive to temperature changes and can operate at high voltages. A key to this feature is the ultra-thin protective layer that forms on the anode. This ultra-thin layer remains stable once formed, ensuring the longevity noted in the research paper.
This vial of clear sodium ion electrolyte provides the circulating “blood” that allows the energy to flow through an experimental battery technology. (Photo by Andrea Starr | Pacific Northwest National Laboratory)
“We also measured gas vapor production at the cathode,” said Phung Le, a PNNL battery chemist and one of the lead authors of the study. “We found very minimal gas production. This provides new insights to develop stable electrolyte for sodium-ion batteries that can operate at elevated temperatures.”
For now, sodium ion technology still lags behind lithium in energy density. But it has its own advantages, such as insensitivity to temperature changes, stability and longevity, which are valuable for certain light electric vehicle applications and even energy storage in the future.
The research team continues to refine their design. Le noted that the team is experimenting with other designs in an effort to reduce, reduce and ultimately eliminate the need to incorporate cobalt, which is toxic and expensive if not recovered or recycled.
In addition to Jin, Le and Zhang, PNNL’s entire research team consisted of Peiyuan Gao, Yaobin Xu, Biwei Xiao, Mark H. Engelhard, Xia Cao, Thanh D. Vo, Jiangtao Hu, Lirong Zhong, Bethany E. Matthews, Ran Yi, Chongmin Wang, Xiaolin Li and Jun Liu.
The study was supported by the Department of Energy’s Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office. Imaging studies were conducted at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility at PNNL, sponsored by the Office of Biological and Environmental Research.
Thanks to Pacific Northwest National Laboratory (PNNL)
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