Ionic Conductivity in Polymer Electrolyte Systems

Ionic conductivity in polymer electrolyte systems underpins the performance of emerging solid-state electrochemical devices, including next-generation lithium-ion batteries, fuel cells and flexible electronics. In these materials, a polymer host dissolves a salt or blends with an ionic liquid to create a medium in which mobile ions migrate under an electric field. Key factors governing conductivity include the degree of crystallinity, the concentration of free ions and the segmental mobility of polymer chains. Amorphous domains typically facilitate faster ion transport by allowing greater chain flexibility, while crystalline regions can impede it. Strategies to enhance conductivity encompass the incorporation of plasticisers or ionic liquids to reduce crystallinity, the addition of inorganic fillers or nanofillers to form continuous ion-conduction pathways, and morphological control via alignment or porosity engineering. Advances in polymer chemistry have produced block copolymers, graft polymers and composite architectures that balance mechanical integrity with high ionic mobility. Understanding the interplay between polymer-salt interactions, microstructure and ion-solvation dynamics remains essential to achieving conductivities on par with or exceeding liquid electrolytes, while maintaining safety, stability and processability for large-scale applications.

Research from Nature Portfolio

Recent studies have reported the development of boronic ionic liquid based ternary gel polymer electrolytes employing novel difluoro(oxalate)borate anions within a poly(vinylidene fluoride-co-hexafluoropropylene) host. An optimised formulation containing approximately 80 wt % ionic liquid achieved ionic conductivities up to 10⁻³ S cm⁻¹ at elevated temperature alongside stable cycling in Li|electrolyte|LiCoO₂ cells, delivering discharge capacities above 140 mAh g⁻¹ with near-unity coulombic efficiency over prolonged operation. Structural characterisation revealed that the boronic anion effectively disrupts polymer crystallinity and enhances segmental flexibility, thereby facilitating continuous lithium-ion transport pathways and improved electrochemical reversibility.

Research from all publishers

A 2024 report demonstrated a composite solid polymer electrolyte comprising hollow silicon nanorods loaded with ionic liquid embedded in a polyethylene oxide matrix. Under a magnetic field, aligned nanorods reduced PEO crystallinity and formed percolating Li⁺ transport channels at the nanorod–polymer interface. This design delivered conductivities of 2.14 × 10⁻⁴ S cm⁻¹ and a Li⁺ transference number of 0.31, with Li|electrolyte|LiFePO₄ cells exhibiting stable cycling for over 2000 h and near-100 % coulombic efficiency.

An investigation into silica-aerogel-reinforced PEO-PMMA-LiClO₄ electrolytes found that adding 8 wt % mesoporous aerogel to an 8:1 PEO:PMMA host enhanced the amorphous content and promoted LiClO₄ dissociation. The resulting solid polymer electrolyte achieved lithium-ion conductivities of 1.35 × 10⁻⁴ S cm⁻¹ at 30 °C, while retaining good thermal and mechanical stability, underscoring the utility of high-surface-area fillers in tuning microstructure and ion transport.

A gel polymer electrolyte composed of PVDF-HFP and PMMA plasticised with propylene carbonate and diethyl carbonate reached maximum ionic conductivities of 3.97 × 10⁻⁴ S cm⁻¹ at optimal plasticiser ratios. Spectroscopic analysis confirmed strong interactions among polymers, salt and plasticisers, and microscopy revealed enhanced porosity. Dielectric measurements and electrochemical stability tests demonstrated the versatility of blended polymer hosts combined with organic solvents to balance conductivity and mechanical robustness.

Ionic Conductivity in Polymer Electrolyte Systems publication trend

The graph below shows the total number of articles in ionic conductivity in polymer electrolyte systems across all publications each year (not limited to Nature Index journals).

Technical terms

Polymer electrolyte: A solid or gel matrix composed of polymer chains that solubilise ionic species and enable ion conduction.

Ionic conductivity: A measure of the ease with which ions move through an electrolyte, expressed in siemens per centimetre (S cm⁻¹).

Amorphous phase: A non-crystalline region of a polymer in which chains are randomly arranged, enhancing segmental mobility and ion transport.

Segmental motion: Localised movement of polymer chain segments that facilitates coordinated transport of solvated ions.

Ionic liquid: A salt in the liquid state at ambient or moderate temperatures, used to improve ion dissociation and suppress polymer crystallinity.

Transference number: The fraction of total ionic current carried by a particular ion species within an electrolyte.

References

1. An enhanced electrochemical and cycling properties of novel boronic Ionic liquid based ternary gel polymer electrolytes for rechargeable Li/LiCoO2 cells. Scientific Reports (2017).
2. Aligned Hollow Silicon Nanorods Containing Ionic Liquid Enhanced Solid Polymer Electrolytes with Superior Cycling and Rate Performance. Advanced Science (2024).
3. Fabrication of PEO-PMMA-LiClO4-Based Solid Polymer Electrolytes Containing Silica Aerogel Particles for All-Solid-State Lithium Batteries. Energies (2018).
4. Gel polymer electrolyte based on PVDF-HFP:PMMA incorporated with propylene carbonate (PC) and diethyl carbonate (DEC) plasticizers : electrical, morphology, structural and electrochemical properties. Materials Research Express (2020).