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PNNL team develops electrolyte for high-voltage sodium-ion battery with extended longevity

Cheap and abundant, sodium is a promising candidate for new battery technology. However, the limited performance of sodium-ion batteries has hindered large-scale application. Now, a research team from the Department of Energy’s Pacific Northwest National Laboratory (PNNL) has developed a new electrolyte enabling a high-voltage sodium-ion battery with greatly extended longevity in laboratory tests. A paper on the work appears in Nature Energy.

Sodium-ion batteries (NIBs) have attracted worldwide attention for next-generation energy storage systems. However, the severe instability of the solid–electrolyte interphase (SEI) formed during repeated cycling hinders the development of NIBs. In particular, the SEI dissolution in NIBs with a high-voltage cathode is more severe than in the case of Li-ion batteries (LIBs) and leads to continuous side reactions, electrolyte depletion and irreversible capacity loss, making NIBs less stable than LIBs.

Here we report a rational electrolyte design to suppress the SEI dissolution and enhance NIB performance. Our electrolyte lowers the solvation ability for SEI components and facilitates the formation of insoluble SEI components, which minimizes the SEI dissolution. In addition to the stable SEI on a hard carbon (HC) anode, we also show a stable interphase formation on a NaNi0.68Mn0.22Co0.1O2 (NaNMC) cathode.

Our HC||NaNMC full cell with this electrolyte demonstrates >90% capacity retention after 300 cycles when charged to 4.2V. This study enables high-voltage NIBs with long cycling performance and provides a guiding principle in electrolyte design for sodium-ion batteries.

—Jin et al.

A battery electrolyte forms by dissolving salts in solvents, resulting in charged ions that flow between the positive and negative electrodes. Over time, the electrochemical reactions that keep the energy flowing get sluggish, and the battery can no longer recharge. In current sodium-ion battery technologies, this process happens much faster than in similar lithium-ion batteries.

The PNNL team, led by scientists Yan Jin and Phung Le, attacked that problem by switching out the liquid solution and the type of salt flowing through it to create a new electrolyte recipe. The new electrolyte consists of 1.5M sodium bis(fluorosulfonyl)imide (NaFSI) salt in a solvent mixture of dimethyl carbonate (DMC) and tris (2,2,2-trifluoroethyl)phosphate (TFP) (1.5:2 in mole or 1.6:8.4 in wt.).

In laboratory tests, the new design proved durable, holding 90% of its cell capacity after 300 cycles at 4.2 V—higher than most sodium-ion batteries previously reported.

The current electrolyte recipe for sodium-ion batteries results in the protective film on the negative end (the anode) dissolving over time. This film is critical because it allows sodium ions to pass through while preserving battery life. The PNNL-designed technology works by stabilizing this protective film. The new electrolyte also generates an ultra-thin protective layer on the positive pole (the cathode) that contributes to additional stability of the entire unit.

The new PNNL-developed sodium-ion technology uses a naturally fire-extinguishing solution that is also impervious to temperature changes and can operate at high voltages. One key to this feature is the ultra-thin protective layer that forms on the anode. This ultra-thin layer remains stable once formed, providing the long cycle life reported in the research paper.

We also measured the production of gas vapor at the cathode. We found very minimal gas production. This provides new insights to develop stable electrolyte for sodium-ion batteries that may operate at elevated temperatures.

—Phung Le

Although sodium-ion technology still lags behind lithium in energy density, it offers advantages, such as imperviousness to temperature changes, stability and long cycle life, which are valuable for applications of certain light-duty electric vehicles and even grid 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—and eventually eliminate—the need to include cobalt, which is toxic and expensive if not recovered or recycled.

The study was supported by the Department of Energy’s Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office. Imaging studies were performed 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.


  • Jin, Y., Le, P.M.L., Gao, P. et al. (2022) “Low-solvation electrolytes for high-voltage sodium-ion batteries.” Nat Energy doi: 10.1038/s41560-022-01055-0



There are a lot of similarities with other recent alternative chemistry breakthroughs, such as recent lithium- sulfur batteries. The use of advanced chemistry to generate protective interface layers is a repeating theme. This is indicative of fundamental advances in our understanding of how batteries work and material and chemical sciences.

Early lithium-ion batteries were almost a matter of happening upon working solution, we didn’t control the fundamental building blocks, we just found something that worked well and continued to refine at a macro level.

We all are fatigued by the years of constant “battery breakthrough” announcements and didn’t pay enough attention to all of the advanced imaging and modeling breakthroughs. That’s all paying off now because we aren’t just kids with a chemistry set now, researchers are targeting and building next generation batteries that will revolutionize the next few decades.

2000-2020 was the era of solar and wind becoming affordable, primarily due to government investment (Germany, USA and China primarily), industry growth and the learning curve as a result. That curve hasn’t really stopped, but we are just really stepping into the era of battery disruption. It builds slow but the S curve is really starting to accelerate and most people will simply look back and say “how did that happen?”


And then there's solid state sodium ion - to read their press releases put out almost two years ago(and posted by GCCongress) you'd think that UK startups Ion Ventures and LiNa(links below) would be close to producing and testing their solid state sodium ion batteries in various devices by now - perhaps even an ebike or escooter. And in the non-solid-state arena Faradion now owned by Reliance(India) seem confident that they've cracked all the problems that this article claims sodium ion batteries still suffer from. Energy density increases will be accelerated once we have established a burgeoning competitive global market in both stationary and motive sodium ion energy storage applications. See:
Paul G

I never get fatigued by the constant “battery breakthrough” announcements, I get energized.

The relentless progress to achieve a substantial portion of the potential energy densities represented by these various chemistries is inspiring.

The high efficiency, long life and simplicity of operation of battery electric cars will be very hard to beat.

Who will want a car powered by liquid fuels when you can get 400-500 miles range, 10,000 cycles, fast charging and powered by cheap, fungible renewable sources like wind, solar, hydro and eventually fusion?


@electric car insider:

If you simply imagine infinite progress in the technologies you fancy, and ignore any possibility of progress in those you don't, you can come up with precisely the results you want.

To name one possible alternative, SOFC or high temperature PEMs can use more or less any hydrocarbon, and production of those would neatly solve storage issues for renewables.

To objections about efficiency, there are umpteen possible pathways for improvement, mostly using currently thrown away energy, or hybrid configurations where batteries cover day to day driving, which we are continually told is most driving, whilst liquid fuels cover distances without needing hundreds of kilos of batteries.

What will the transports system finally look like, with what split between batteries and fuel cells?

I don't know.

And neither do you.

Unfortunately you imagine that you know with absolute certainty.

The first stage in scientific and technological assessment is to realise what you don't really know, and are just guessing or hoping


We need all solutions to slow global warming


Anyone basing progress on hoping and believing should got to church and leave scientific research to those capable of applying math and logical reasoning as the basis for further progress.


An old Scottish Proverb: "If wishes were horses, beggars would ride".
Recently, I have researched many variations of Sodium batteries.
First, let’s look at what is ready today. CATL, the world’s largest battery company released last year a Sodium Ion battery with 160 Wh/kg Energy Density comparable to LFP batteries and suitable for automotive applications. This battery has a Hard Carbon Anode and a Prussian Blue Analog (PBA) Cathode. This PBA Cathode is also called “Prussian White” or Fennac and will be produced in quantity by ALTRIS in Sweden.
This reference describes the CATL Release:
There is also new research in “Hard Carbon “ anodes at Tokyo University of Science, by Shinichi Komaba that shows it is possible to develop high energy density Sodium Ion batteries.
There are many future possibilities, e.g. Sodium Sulfur, Solid State, and Dual Ion batteries. However, those are down the road (latter part of the decade).
UCSD has an in-depth article if you would like to read.



I have been following CATL with great interest, as their sodium technology seems to be 'good enough' to work in light transport, whilst reducing some of the material resource constraints of lithium batteries.

Your third link notes that sodium does not form an alloy with aluminum, which consequently can be used instead of copper.

And solid state using sodium seems to be on the cards, which as I am not too keen on Toyota's sulphur technology, mainly because of the difficulty in assembly due to dry assembly, is promising.

But never bet against Toyota in solving manufacturing problems.

And for all I know sodium batteries, solid state or not, could have comparable or worse assembly issues.


And just in from Deakin University, more progress on boron nitride hydrogen storage:

At up to 8% by weight, it shows that batteries are not the only game in town for even mobile applications.


The PNNL High Voltage Electrolyte would work well with this:
“ Quasi-Solid-State Dual-Ion Sodium Metal Batteries for Low-Cost Energy Storage”
This battery has an energy density of 484 Wh/kg with an operation voltage of 4.4 V. and has two anodes: Hard Carbon and Sodium Metal.

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