Kyle Proffitt
September 22, 2025 | Delivering the featured presentation at the 2025 Solid-State and Sodium-Ion Battery Summit, Shirley Meng made a key statement for the sodium-ion community: “Sodium batteries is a long journey, but today I want to say that it is the next terawatt-hour technology; I am absolutely confident.” She continued, “Liquid or solid, sodium batteries have to play an important role in the energy transition.”
Sodium-ion remains a relatively less proven technology, although research in the area dates back over 40 years. As lithium-ion found successes, sodium-ion largely faded from memory. However, the global availability and associated low cost of sodium make it very attractive as an alternative, provided that challenges such as energy density limits can be overcome. Sodium is both heavier and a fundamentally weaker reducing agent than lithium; it less easily gives up its electron, which translates to lower voltages for sodium-ion batteries, and that limits energy density. But sodium also has advantages. The larger cation is less strongly solvated, meaning in principle it can move more quickly through solvent, and this can translate to improved charge/discharge rates and low-temperature performance.
Meng provided an example of how sodium lends itself better to fast charging in an anode-free setup. She first presented the successful creation of an anode-free, solid-state sodium-ion battery at the 2024 International Battery Seminar and Exhibit and published the work shortly after. Now she could explain a fortuitous benefit that made this easier. “In the sodium case, we are very lucky … It’s a critical property of the materials that it will automatically go for the high diffusion rate sodium (101) texture.” Effectively, the (101) crystal packing is less tightly packed than the (100) packing that lithium more naturally adopts, and ions can diffuse more easily. Also, “sodium is softer, and its mobility is higher, so low pressure cycling is possible. Even in the pellet cell, we go below 5 to 10 megapascal,” Meng said. Just last week, her group published a step forward for solid-state sodium-ion batteries. They developed a solid electrolyte that is rapidly cooled to lock in a metastable orientation with greatly improved sodium ion diffusion; that enabled coupling with a thick, high-areal-loading (45 mg/cm2) cathode material with good performance at subzero temperatures.
While academic labs proceed, commercial ventures are accelerating. Chinese companies such as CATL, Farasis, and HiNa Battery have established sodium-ion manufacturing facilities and are including batteries with energy density up to 175 Wh/kg in EVs. The US company Natron Energy was slated to produce 24 GW of sodium-ion batteries annually for grid storage applications, but they ceased operations in early September related to funding issues. At the 2025 Solid-State and Sodium-Ion Battery Summit, we heard from several academic speakers about their fundamental research advancing the technology.
More Manganese and Avoiding Structural Damage
Hui (Claire) Xiong, Professor at Boise State University, presented some of the recent advances with sodium-ion batteries, taking aim at the cathode material with the use of Mn-rich layered oxide materials.
She addressed a refrain being discussed: how are sodium-ion batteries going to compete with lithium-ion batteries? Her answer is that they don’t actually need to win. Sodium-ion, she says, should be considered an alternative that can satisfy some of the existing high demand for lithium-ion. “You can find the niche market … there’s other applications such as large-scale energy storage,” she added.
She showed a graph of source material and lithium-ion battery costs over the last decade, revealing significant “price turbulence” based on global supply chains and announcements such as the recent closure of a CATL lithium mine in Yichun, China. She pointed to LFP dominance in the Chinese market and the difficulty in outperforming it on a cost/kWh basis but reminded the audience that LFP costs have also seen volatility.
While they may not need to outcompete lithium-ion for every use, comparable energy density is certainly desirable, and Xiong believes we need all hands on deck to make this happen. “We need to have this concerted effort in the field, not just in academia—in industry as well as government support—in order for us to have innovation in the sodium field,” she said.
Part of her solution is the inclusion of manganese, which is abundant, cheap, and less susceptible to price turbulence than nickel, cobalt, and lithium. Xiong presented results with a P2-type (prismatic Na coordination with 2 layers of transition metals per unit cell) layered oxide sodium-ion cathode containing 67% Mn and 33% Ni in the transition metal layers. She pointed out that, “You can almost make all the layered structures with the first row of the transition metals in the sodium system, as compared to lithium, you only have limited choice; that means we have a broader choice in terms of materials.”
Unfortunately, the voltage profile for sodium layered oxide cells often looks like a “devil’s staircase” of discrete steps, unlike the smoother and more desirable voltage curve seen with lithium-ion cells. As Na+ ions are inserted and removed, they don’t just fit in uniformly—they order into specific sites between the layers of transition metals, coordinating with oxygen in different arrangements. When sodium is removed during charging, the resulting vacancies make it easier for the metal layers to slide over each other, which can change Na+ coordination geometry from prismatic to octahedral. The combined processes drive phase transitions that appear as steps in the voltage profile.
Researchers also want to push higher voltages with sodium-ion to maximize energy density, but that can create electrolyte incompatibilities, metal dissolution, and oxygen release. Worse, the higher voltage causes structural changes that permanently limit sodium cycling. Xiong’s group discovered that they could perform a heat annealing step with their cathode and induce an “intergrowth framework” with both a “primary layered structure” and “secondary disordered rock-salt-like nano domains”—kind of a hybrid, more stable structure. Most importantly, this treatment allowed them to cycle sodium-ion cells 150 times between 2.0 and 4.3 V with 98% capacity retention and a smooth profile, whereas the untreated cathode only showed 28% retention under the same conditions. The work is not yet published but has been archived. Xiong also showed research published this year, where they specifically varied the sodium content in a Ni0.25Mn0.75O2 material to tailor an intergrowth structure of mixed P2 and P3 types. The mixed intergrowth showed improved cyclability and kinetics relative to P3 alone and improved capacity relative to P2 alone, providing another avenue to tweak these structures and optimize performance.
Electrolyte and Interface Optimization
Arumugam Manthiram, Professor at the University of Texas at Austin, also discussed sodium-ion battery cathodes, interfaces, and the influence of electrolyte.
Manthiram discussed the three primary options for cathode material in sodium-ion cells— polyanion, layered oxide, and Prussian blue—each with pros and cons. The polyanions give good stability and long cycle life, he says, but have lower energy density. Prussian blue analogues have higher energy, but they can release deadly HCN and cyanogens at higher temperatures. Layered oxides also show good energy density, but they often suffer from instability with electrolyte.
He explained a unique advantage for sodium. Because of some intricate details, iron can be incorporated into a layered oxide cathode for sodium-ion, but not for lithium-ion. If iron is used in a lithium-ion cell, a polyanion like LFP must be used, reducing energy density (Manthiram discovered this class of cathode material with John Goodenough). In contrast, sodium has a disadvantage on the anode side. “We have to use hard carbon, not graphite; graphite does not work,” Manthiram said, and that increases cost.
He pointed to LFP at about 200 Wh/kg and said that sodium-ion needs to catch up. However, “At the end of the day, you have to worry about dollar per kilowatt hour,” Manthiram said. LFP sits around $50/kWh, so this is the price to beat, and the path is not trivial. “If the lithium price goes up, then you have a big advantage with sodium ion,” Manthiram added.
Like Xiong, Manthiram focused on layered oxides, but much of the advances he reported involved electrolyte optimization. His general setup is an O3-type (octahedral Na coordination, 3 transition metal layers per unit cell) NaMO2 layered oxide, where M is a combination of Ni, Mn, Fe, Mg, etc. “My goal here is overcoming the surface reactivity and interfacial instability with the electrolyte,” he said. Improving this reactivity can enable higher voltages to be used and provide greater energy density, and Manthiram ran through a series of experimental results with different metal configurations. For example, he showed that an O3-type 1:1 Ni:Mn layered oxide cathode synthesis can be tailored to form either single crystals or polycrystals (many smaller crystals in clusters). The polycrystal arrangement shows many cracks at grain boundaries during cycling, reducing battery life. The single crystals perform better, but they can adopt distinct morphology—polyhedral, with poor cycle life, or octahedral, with greatly improved cycle life. Similar improvement was achieved using a localized high concentration electrolyte (LHCE, 1.1 M NaFSI and 0.3 M NaNO3 in trimethyl phosphate (TMP)).
The idea with an LHCE is that you start with a high salt concentration, which reduces flammability and improves interface properties because anion reactivity (not solvent reactivity) dominates at interfaces. However, high salt concentration electrolyte is more expensive, viscous, and lower conductivity. To get the best of both worlds, one can dilute with a non-solvating diluent, often fluorinated ethers, preserving the local ion solvation environment while reducing cost, viscosity, and resistance. In the first example, the diluent is the sodium salt NaNO3, and this allows Manthiram’s group to use only TMP solvent, avoiding any fluorinated ethers and rendering the electrolyte completely non-flammable.
Combining morphology control (single crystals) and LHCE produced the best results—up to 71% retention after 200 cycles. That work was published earlier this year.
Several other results were shown with different combinations of layered oxide cells, primarily paired with hard carbon anode and using LHCE. Manthiram showed full NaNi1/3Fe1/3Mn1/3O2 pouch cells operating up to 4.2 V for 400 cycles with 70% energy retention, whereas standard carbonate electrolyte controls showed 71% retention at just 200 cycles. Detailed experimental results from SEM, time of flight mass spectrometry, and in-situ gas evolution revealed that the LHCE created dense and thin interphase layers at both cathode and anode and limited gas evolution during high-voltage cycling. This work was published this month.
In one final idea, Manthiram showed that polyamide macromolecules could be added to carbonate solvents, avoiding fluorinated ethers while creating some of the same advantages as LHCEs and enabling cyclability up to 4.4 V. They published on this earlier this year.
Commercial Cells for Uninterrupted Power Supply
Moving beyond the academics, Asmae El Mejdoubi from Tiamat SAS (France) presented data for their commercial sodium-ion cells. These cells (cylindrical and pouch formats available) show only 110 Wh/kg energy density, but they can undergo 20C cycling with 80% capacity retention, they can operate at -30°C (90% capacity with 5C discharge), and they can retain 85% capacity after 17,000 cycles (2C charge, 5C discharge). For their technology, Tiamat uses an NVPF polyanion cathode, liquid carbonate-based electrolyte, and hard carbon anode on aluminum current collector. They take advantage of another sodium-ion perk; cheaper aluminum can be used as the current collector on both electrodes, whereas lithium would react with aluminum at the anode. As such, Tiamat SAS avoids lithium, cobalt, nickel, and copper. However, the cost of these batteries per kWh was not discussed. They report no explosions or fires with thermal stability testing, and El Mejdoubi made a case that the cells are ideally suited for energy grid load balancing and uninterrupted power supply for AI data centers. Stellantis is an investor too, though, and they are targeting hybrid mobility solutions where the rapid power release can supplement other energy sources. Tiamat SAS has plans to open the first European sodium-ion factory gigafactory in 2027 and produce 5 GWh/year.
In summary, it does not appear that sodium-ion batteries will imminently revolutionize the EV and mobility industries, but inroads are continually developing, and they are becoming increasingly viable alternatives. Applications in stationary energy storage are likely to see widespread adoption sooner, and if Shirley Meng is correct, we will only see their influence continue to grow.
