New Meta-Weakly Solvating Electrolyte Unlocks Stable High-Voltage Sodium-Ion Battery Operation

RICHLAND, Wash. / LONDON – Researchers at the U.S. Department of Energy's Pacific Northwest National Laboratory (PNNL) have developed a novel electrolyte chemistry that enables high-voltage sodium-ion batteries to operate with unprecedented stability, addressing a long-standing barrier to the technology's commercial competitiveness.

Published in the journal Nano Energy, the work introduces a "meta-weakly solvating electrolyte" - a design philosophy that deliberately loosens the bond between sodium ions and solvent molecules to suppress detrimental side reactions at electrode surfaces. The approach represents a fundamental departure from conventional electrolyte engineering.

 

Commonly used battery electrolyte formulations are generally developed to solvate metal ions sufficiently so that the metal ions can move through liquid and carry charge. However, the metal ion's strong association with the solvent results in the formation of an incredibly stable ionic "shell" surrounding the metal ions hence preventing the breakdown of this shell at the electrode surface and the entrapment of electrolyte molecules in parasitic chemical reactions once this shell breaks. The result is that the electrolyte is consumed in the degradation of the battery and accelerates the capacity fade of the battery.

The PNNL researchers took a different approach and developed a meta-weakly solvating electrolyte where the sodium ions have a much lower binding force to the solvent molecules. The meta-weakly solvating electrolyte has an intermediate solvation structure that allows the sodium ions to occupy this structure and have different ion characteristics at the electrode interface. As a result, the strong solvent-ion interactions do not create overly stable ions' shells at the electrode interface that lead to the degradation of the battery.

"Meta-weakly solvating nature, defined as Na⁺ solvation significantly weaker than that of the single-solvent electrolyte with the weakest solvent component, is confirmed by ²³Na NMR," the researchers wrote. Through complementary spectroscopic analyses - including Raman and FT-IR - the team demonstrated that weakened solvation arises from enhanced solvation dynamics and predominantly affects solvent coordination.

The results demonstrated clear advantages. The proposed battery cell design achieved improved sodium mobility while conventional counterparts exhibited earlier degradation and instability. Leakage current tests confirmed that the cell using the meta-weakly solvating electrolyte delivers the best high-voltage interfacial stability, consistent with reduced free-solvent reactivity and improved cathode–electrolyte interphase (CEI) formation.

Crucially, the full cells retained 80% of their capacity after 500 cycles, substantially outperforming both conventional carbonate-based electrolytes and localized high-concentration electrolytes (LHCEs). Lead author An L. Phan noted that "the new electrolyte represents a new strategy to regulate Na solvation structure that can facilitate favorable reactions and suppress unwanted ones," resulting in reduced irreversible loss and degradation of cell materials under practical conditions.

Sodium-ion batteries have been considered as an option since they have similar chemistries, but also differ in terms of abundance, accessibility, price and stability versus Li-ion. However, sodium-ion batteries are still taking longer to commercially develop compared to lithium, with lakhs of commercial sedans made with Li-ion batteries sold since the 1990s, and an electric vehicle using sodium-ion chemistry was launched in late 2023 at less than 1% of total world's production of lithium-ion batteries as of 2025.

That dynamic is shifting rapidly. CATL, the world's largest battery manufacturer, has confirmed plans for large-scale sodium-ion deployment across multiple sectors beginning in 2026, including a 60 GWh energy storage system order. BYD has begun construction of its first sodium-ion battery plant. The sodium-ion battery market is currently valued at 2.9billionandisprojectedtomorethandoubleto2.9billionandisprojectedtomorethandoubleto6.2 billion by 2031. According to the IEA, an effective anion-rich solvation structure is realized while favorable Na⁺ local mobility and desolvation are maintained.

The PNNL breakthrough arrives at a pivotal moment for sodium-ion technology. By resolving the interfacial instability that has historically limited high-voltage operation, the meta-weakly solvating electrolyte removes a key obstacle to achieving the energy densities required for broader EV adoption. The research is available in full in Nano Energy, Volume 154, July 2026.

With 2026 widely regarded as the commercialization "year one" for sodium-ion batteries, and with major battery manufacturers signing multi-gigawatt-hour supply agreements, the window for sodium-based energy storage technologies to claim a meaningful share of the global battery market has never been wider.