Sodium-ion batteries have a compelling pitch: sodium is cheap and abundant, the chemistry has attractive safety characteristics, and it sidesteps much of the supply-chain anxiety around lithium. Their weakness has been energy density. A new study from Xi’an Jiaotong University, published in Nature Energy on November 2, 2026, tackles that problem with a radical design choice: remove the anode entirely, and then fix the chemistry that has kept such batteries from lasting.
According to the university’s announcement, a team led by Professor Weijiang Xue at the State Key Laboratory for Mechanical Behavior of Materials, working with Research Professor Yong-Sheng Hu of the Institute of Physics, Chinese Academy of Sciences, built anode-free sodium pouch cells that kept about 80% of their capacity after 1,400 cycles and still delivered about 88% of their room-temperature capacity at a frigid -40 °C.
Why go anode-free?
In a conventional sodium-ion cell, sodium ions shuttle between a cathode and an anode, typically made of hard carbon. That anode adds weight, volume and cost. As the Xi’an Jiaotong announcement explains, an anode-free design skips the pre-installed anode material altogether. During charging, sodium ions from the cathode plate directly onto a bare current collector as metallic sodium; during discharge they strip off again and return to the cathode.
The payoff is a lighter, more compact cell with potentially higher energy density and lower cost. The catch is brutal: because there is no reservoir of extra sodium, every ion lost to side reactions is gone for good. The university describes “irreversible sodium loss during cycling” as the barrier that has severely limited the cycle life of these batteries.
The work builds on a run of electrolyte research from Xue’s group. Since joining Xi’an Jiaotong University in 2022, according to the announcement, Xue has developed a series of molecular-design strategies for electrolytes used in sodium-ion batteries, high-energy lithium-metal batteries, and lithium-ion batteries with silicon-carbon anodes. The new paper’s co-first authors are Shuicen Ding, Xijie Chen and Zhen Yao from Xue’s group, along with Mengdi Hao from the Institute of Physics. Characterization support came from facilities including the Shanghai Synchrotron Radiation Facility, and funding from the National Natural Science Foundation of China, among others.
The fix: an electrolyte that builds its own shield
Most of that sodium loss happens at the interface where metal meets electrolyte. The electrolyte keeps decomposing on the fresh sodium surface, consuming active sodium and forming thick, unstable layers. The Xi’an Jiaotong team’s answer was a molecular redesign of the electrolyte built around a cyclic ether called 1,3-dioxane, abbreviated DOX.
According to the paper’s abstract, the strategy works on two fronts at once:
- Easier, cleaner plating. DOX coordinates only weakly with sodium ions, which helps the ions shed their solvent shell (desolvation) and deposit and strip reversibly.
- A self-built protective layer. Under controlled conditions, DOX molecules link into short chains (oligomers) right at the electrode surface. This “controlled interfacial polymerization,” as the university calls it, forms a thin, robust solid-electrolyte interphase (SEI) that stops the electrolyte from continuously breaking down and stabilizes sodium plating and stripping.
The Nature Energy editors summarize the idea as using a moderate-strain cyclic ether that redirects electrolyte decomposition to form a thin, robust interphase, minimizing sodium consumption. In effect, the decomposition that normally destroys these cells is steered into building the very layer that protects them.
The numbers, in practical cells
Importantly, the team tested the chemistry in pouch cells rather than only in small coin cells, which tend to flatter results. According to the paper’s abstract, the 300 mAh-class anode-free pouch cells, using a high cathode loading of about 20 mg per square centimetre:
- retained about 80% of capacity after 1,400 cycles at a 1C rate;
- operated at charge and discharge rates up to 3C;
- maintained 88% capacity at -40 °C;
- achieved round-trip energy efficiency of up to about 98%.
The study also drew a Nature Energy News & Views commentary, “Directing solvent reactivity,” co-authored by Professor Yong-Mook Kang, which the university highlights as recognition of the approach.
What it means for energy storage
For utilities, EV makers and grid-storage developers, this work matters less as a finished product and more as a signal about where sodium technology is heading. Key takeaways:
- Closing the energy-density gap. Removing the anode is one of the most direct routes to more energy per kilogram for sodium cells. Long cycle life has been the missing piece, and this study shows it can be addressed through electrolyte design alone.
- Cold-climate performance. Holding 88% capacity at -40 °C is notable. Low-temperature weakness is a familiar complaint about lithium-ion batteries in winter, and strong cold performance could make sodium chemistries attractive for outdoor storage and vehicles in harsh climates.
- Cheaper materials. Sodium is abundant, and skipping a hard-carbon anode removes another cost line from the bill of materials.
- A design playbook. The team presents “controlled interfacial polymerization” as a molecular electrolyte design strategy, a principle other groups can apply and extend.
Some perspective is warranted. A 300 mAh pouch cell is a meaningful step beyond lab coin cells, but it is still far from the multi-amp-hour cells used in vehicles or grid racks, and 1,400 cycles at 80% retention, while strong for anode-free sodium, is short of the many thousands of cycles expected from commercial stationary storage. Scaling up manufacturing, safety validation and long-term testing are the obvious next steps.
The bottom line
Anode-free sodium batteries promise lighter, cheaper energy storage built on one of Earth’s most common elements, but they have long been held back by the steady disappearance of their sodium. By designing an electrolyte that forms its own thin protective layer, the Xi’an Jiaotong University and Chinese Academy of Sciences team has shown pouch cells that last well over a thousand cycles and keep working at -40 °C. It is a significant step toward making sodium a serious contender for affordable, high-density storage.