Solid-state electrolytes are widely considered the "holy grail" for safer, more energy-dense batteries, promising to replace flammable liquid electrolytes in everything from smartphones to electric vehicles. However, a major hurdle remains: achieving high ionic conductivity—the ease with which lithium ions move—while maintaining long-term stability.
Now, a research team from North China Electric Power University and the State Grid Shanxi Electric Power Company has developed a novel Gel Polymer Electrolyte (GPE) that tackles this challenge head-on. By chemically grafting a specialized salt onto a polymer backbone, the researchers have created a material that not only conducts ions efficiently but also forms a protective shield around the battery's anode, significantly extending its lifespan.
The study, published in the journal ENGINEERING Energy, details a new synthesis strategy involving the copolymerization of methyl methacrylate (MMA) with a long-chain quaternary ammonium salt known as C₁₆DMAAC.
The Problem: Trade-offs in Traditional Designs Polymethyl methacrylate (PMMA)-based gel electrolytes are popular due to their good mechanical strength and ease of fabrication. However, they inherently suffer from low ionic conductivity. To fix this, scientists often blend in salts or fillers. "While blending with quaternary ammonium salts offers an effective solution, it often leads to salt deposition during cycling, compromising long-term stability," the authors explain. In simple terms, loose salt additives can clump together over time, clogging the system and degrading performance.
The Solution: Chemical Anchoring Instead of just mixing the salt in, the research team chemically bonded (grafted) the C₁₆DMAAC salt directly onto the PMMA polymer chains. This "in-situ copolymerization" ensures the salt molecules are uniformly distributed and locked in place, preventing them from aggregating.
This molecular engineering achieved three critical improvements:

• Enhanced Conductivity: The bulky grafted salt chains increase the "disorder" of the polymer structure, opening up pathways for faster lithium-ion movement. The electrolyte achieved a high ionic conductivity of 7.23 × 10⁻⁴ S/cm.
• Immobilized Anions: The positively charged ammonium groups on the polymer backbone effectively "trap" anions, allowing lithium ions to move more freely. This resulted in a high Lithium-ion transference number of 0.59.
• Robust Interface: The specific chemistry of the C₁₆DMAAC promotes the formation of a stable, inorganic-rich Solid Electrolyte Interphase (SEI) layer on the lithium metal anode. This protective layer suppresses the growth of lithium dendrites—needle-like structures that can cause short circuits.

Superior Performance in Real Batteries To prove the concept, the team built full battery cells using a high-performance NCM811 cathode. The results were impressive:

• Durability: The cells retained 92% of their initial capacity after 200 cycles at a standard charge rate (0.5 C).
• Fast-Charging Potential: Even at high charging rates (2 C), the battery retained 80% of its capacity after 300 cycles.
• High Voltage Tolerance: The electrolyte remained stable up to 4.9 V, making it compatible with high-energy cathode materials.

"This work presents a promising strategy for designing novel electrolyte structures by grafting quaternary ammonium salts into polymer chains to improve battery stability and lifespan," the researchers conclude. This advancement offers a clear pathway toward safer, longer-lasting batteries for the next generation of energy storage.
DOI: 10.1007/s11708-026-1047-3