Introduction: redefining electrolytes for next‑generation energy storage

Ionic liquids (ILs) have emerged as a class of designer solvents and electrolytes with unique properties that align well with the ambitious performance targets of modern energy storage technologies. In 2023, the field continued to move beyond the early promise of ILs as safe, non-volatile media, toward targeted materials design that addresses the trade-offs between electrochemical stability, ionic conductivity, viscosity, and cost. ILs—often composed entirely of bulky organic cations and inorganic or organic anions—offer negligible vapor pressure, broad thermal stability, and the potential for high electrochemical windows. These attributes make them especially attractive for high‑voltage lithium metal batteries, sodium and potassium systems, redox‑active ILs, and ionogels that combine solid‑like mechanics with liquid‑like ion transport.

From a systems perspective, 2023 reinforced a core tenet of energy storage engineering: the electrolyte is not a passive medium but an active component that influences SEI (solid-electrolyte interphase) formation, interfacial kinetics, dendrite suppression, and heat management. For researchers and practitioners, ILs offer a toolkit for tuning solvation environments, suppressing flammability, and enabling safer long‑term operation under a wide temperature range. Yet the same properties that make ILs appealing—high viscosity, synthetic complexity, and, in some cases, cost—also frame the challenges that must be solved to achieve scalable, commercially viable devices. This review synthesizes the 2023 landscape, highlighting advances in electrolyte design, device integration, and the practical considerations that connect laboratory insight to real‑world energy storage systems.

What makes ionic liquids compelling for energy storage in 2023

The key selling points of ILs for energy storage remain consistent, but the emphasis has shifted toward purposeful design and system integration:

• Electrochemical stability window. Many ILs exhibit wide electrochemical windows, enabling operation at higher voltages than conventional organic solvents. In 2023, researchers reported strategies to push windows even further by pairing robust anions with stable cations and by forming stable interphases with electrode materials. The result is potential compatibility with high‑voltage cathodes and with lithium metal anodes, where aggressive solvents often limit performance.
• Thermal stability and safety. The negligible vapor pressure of ILs reduces flammability and volatility concerns—critical factors for large‑format energy storage and electric vehicles. Thermal robustness also translates into broader operating temperature ranges, which helps in cold climates and hot operating environments alike.
• Solvation control and SEI engineering. ILs provide tailored solvation environments for lithium, sodium, and other metal salts. By selecting cations, anions, and functional groups (as in TSILs—task‑specific ionic liquids), researchers can influence SEI formation, ionic conductivity, and oxidative stability at the electrode interface.
• Compatibility with solid and gel architectures. ILs enable ionogels and polymer‑ionic blends that combine electrolyte fluidity with solid‑like mechanical integrity. These formats can damp dendritic growth, improve leak resistance, and enable flexible device geometries in supercapacitors and thin‑film batteries.
• Redox‑active ILs for energy storage integration. Some 2023 studies explored ILs that themselves participate in redox chemistry, offering avenues to augment energy density in certain battery concepts or to act as redox mediators that improve charge transfer during high‑voltage operation.

Across these dimensions, the 2023 literature emphasized not only isolated properties but how ILs interact with electrodes, salts, and separators to shape full‑cell performance. The narrative shifted from “do ILs work?” to “how should ILs be designed, combined, and processed to unlock durable, safe, high‑performance devices?”

2023 highlights: design strategies and practical milestones

The following themes capture representative progress from 2023, reflecting both fundamental understanding and device‑level impact.

1) Task‑specific ionic liquids for tailored solvation and SEI formation

Researchers pursued imidazolium, pyrrolidinium, and other cations paired with fluorinated or difluoro‑sulfonyl imide anions to modulate Li+ solvation and passivation layers. By incorporating functional groups that interact with lithium surfaces or with typical SEI constituents, these TSILs helped form more uniform interphases, reducing dendritic risk and enhancing coulombic efficiency in lithium metal and high‑rate systems.

2) High‑voltage ILs and solvent‑in‑salt strategies

To push energy density while maintaining safety, innovators explored “salt in IL” and “IL in salt” conceptions that balance ionic conductivity with oxidative thresholds. In several 2023 demonstrations, high‑voltage compatible ILs enabled cathodes operating near 4.5–5.0 V vs Li/Li+, with attention to viscosity management and ion transport pathways. These efforts often paired ILs with high‑voltage salts to realize practical rate performance.

3) Ionogels and polymer‑IL electrolytes for mechanical resilience

Ionogels—ILs immobilized within a porous polymer or silica network—gained traction as a path to safer, leak‑proof electrolytes that still provide fast ion transport. 2023 developments highlighted optimized pore architectures and surface chemistries that reduce tortuosity and improve interfacial wetting with electrode materials. The move toward solid‑like formats was especially pronounced for flexible electronics and microbatteries.

4) Redox‑active ionic liquids and dual‑function electrolytes

Beyond acting as inert media, a subset of ILs participated in redox reactions or supported redox mediation. In 2023, such formulations offered subtle gains in energy density or facilitated low‑overpotential charging by stabilizing transient species at the electrode interface. These approaches are nuanced and often device‑specific, but they illustrate the broader trend of ILs as active functional components rather than passive solvents.

5) Safety, lifecycle, and environmental considerations

As ILs move closer to commercial relevance, researchers and industry partners weighed synthesis complexity, feedstock availability, and end‑of‑life considerations. While ILs are non‑volatile, some components can be persistent or toxic, so scope expanded to greener synthesis routes, recyclability, and impact analyses. 2023 work increasingly integrated lifecycle thinking alongside performance metrics to guide practical decisions.

6) Scaling from lab to pilot demonstrations

Despite impressive lab results, scaling IL electrolytes often reveals new bottlenecks in processing, purity control, and long‑term stability. 2023 saw more pilot demonstrations that address manufacturing routes, purification challenges, and integration with standard battery fabrication lines, signaling a maturation toward industrial relevance.

Device‑level implications: from chemistry to performance metrics

To translate electrolyte chemistry into meaningful energy storage gains, researchers linked IL properties to device indicators such as energy density, power density, cycle life, and safety margins. Several common threads emerged in 2023 studies:

• Energy and power trade‑offs. Higher voltage operation improves energy density but can increase interfacial stress and degrade long‑term stability. ILs that maintain a stable SEI at elevated voltages without excessive viscosity helped mitigate these trade‑offs for certain lithium metal and sodium metal cells.
• Rate capability and temperature resilience. Although ILs are often more viscous than conventional solvents, dialing in cation/anion combinations and confining ILs in ionogels can preserve high rate performance across a wide temperature envelope. This is particularly valuable for EVs and grid storage in fluctuating climates.
• Dendrite suppression in metal anodes. Several 2023 reports linked stable SEI formation and interfacial stability with reduced dendrite growth in lithium and sodium metal systems when using specifically designed ILs or IL‑based gels. The practical takeaway is that electrolyte design remains a central lever for safety and lifespan.
• Interfacial engineering with separators and coatings. The choice of IL influenced not only the bulk transport but also how interphases formed on cathodes and anodes interacted with separators. Advanced separators combined with ILs could suppress side reactions and improve cycle life, particularly at high voltages and elevated temperatures.

In practice, many successful demonstrations emphasized a systems approach: selecting the right IL or TSIL for the target electrode chemistry, pairing it with compatible salts, and adopting an electrolyte architecture (liquid, gel, or solidified) that supports manufacturing constraints and safety requirements.

Challenges and practical considerations for deployment

Despite compelling advances, the path to widespread adoption of IL electrolytes in commercial energy storage remains nuanced. The following challenges were underscored in 2023 literature and industry discussions:

• Cost and synthesis complexity. Many ILs rely on multi‑step syntheses and specialized precursors. Cost reductions will require scalable routes, perhaps leveraging bio‑based or readily available starting materials, as well as simplified purification strategies.
• Viscosity and transport properties. The high viscosity of many ILs can limit ion mobility, particularly at low temperatures. Balancing viscosity with electrochemical stability is an active area of design optimization.
• Moisture sensitivity and purity control. Even trace water can alter SEI formation and salt solubility in IL systems. Rigorous moisture control and robust processing protocols are essential for reliable performance.
• Environmental and end‑of‑life considerations. While ILs are non‑volatile, their environmental footprint depends on synthesis and disposal practices. Lifecycle assessments and recycling strategies are increasingly part of the design brief.
• Compatibility with existing manufacturing lines. Transitioning to IL electrolytes requires compatibility with current electrode fabrication, electrolyte filling, and battery assembly workflows. Pilot programs help identify integration bottlenecks early.

From a researcher’s viewpoint, a practical pathway involves prioritizing ILs that deliver the strongest safety gains without sacrificing cycle life and rate capability, while simultaneously pursuing cost reductions and scalable production routes. For engineers, the focus is on device architecture—how to best exploit IL properties in ionogels, gels, and solid‑state formats to meet targeted performance and safety criteria.

Industrial perspectives: cost, manufacturing, and safety as differentiators

As the energy storage market scales, the economics of ILs move from academic curiosity toward practical feasibility. In 2023, several industry voices emphasized:

• Market segmentation by application. High‑energy density niches (like grid‑scale storage and premium automotive segments) may tolerate higher IL costs if the technology delivers meaningful safety, longevity, or performance gains. Lower‑cost applications may require substantial reductions in IL price or the development of simpler IL formulations.
• Process compatibility and supply chain resilience. Access to reliable IL precursors and standardized purification methods are prerequisites for consistent device manufacturing. Partnerships across material suppliers, salt producers, and processing equipment makers became more common in the year.
• Regulatory and environmental stewardship. Regulators and corporate sustainability teams scrutinize solvent choices. Companies that can demonstrate lower lifecycle impact or safer handling protocols with IL‑based electrolytes may gain a competitive edge in markets with strict safety and environmental standards.

Ultimately, the economic viability of IL electrolytes will hinge on achieving a sweet spot where performance, safety, and cost intersect. In 2023, this balance was mapped for several device archetypes, providing a clearer roadmap for where IL‑based electrolytes could outperform incumbent chemistries.

Future directions: where the field is headed post‑2023

Looking forward, several trajectories appear poised to define the next wave of progress in ionic liquids for energy storage:

• Greener and cheaper synthesis. Researchers are pursuing streamlined, scalable routes to ILs, including bio‑derived cations or anions and solvent‑free synthesis pathways that reduce waste and energy input.
• Hybrid electrolyte platforms. The trend toward combining ILs with conventional solvents, polymers, or inorganic fillers aims to blend the best attributes of each component—high voltage stability, better transport, and robust mechanical properties.
• Tailored interfacial chemistry. A deeper mechanistic understanding of SEI and cathode surface interactions with ILs will guide the design of interfaces that endure many cycles under high voltage and high temperature, with minimal degradation.
• Applications beyond lithium chemistry. Sodium, potassium, zinc, and multivalent systems present opportunities where ILs can address specific challenges, such as dendrite suppression and high‑voltage operation, expanding the applicability of ILs to a broader set of energy storage technologies.
• Standardization and performance benchmarking. As more groups publish data, standardized test protocols and benchmarking matrices will help compare IL electrolytes across labs, accelerating the identification of truly scalable solutions.

For researchers entering this field, the recommended focus areas include literacy in interfacial science, an eye for scalable synthesis, and an emphasis on holistic device engineering that aligns electrolyte design with electrode materials and packaging constraints.

What to watch for: guidance for researchers, engineers, and decision makers

The 2023 literacy around ionic liquids in energy storage suggests several practical takeaways for different audiences:

• For researchers: Prioritize robust SEI formation strategies, demonstrate cycle life under representative operating conditions, and present clear stability data at the voltages of interest. Include moisture control methodologies and purification protocols to ensure reproducibility.
• For engineers and product developers: Evaluate ILs and IL‑based formats not only on energy and power metrics but also on manufacturability, safety margins, and integration with existing battery lines. Early pilot tests with scale‑appropriate cells can reveal critical path issues.
• For policy and market strategists: Consider market segments where IL attributes—safety, temperature resilience, and non‑flammability—provide enough added value to justify premium costs, while supporting ongoing R&D for cost reduction and waste management.

Key takeaways for 2023 and beyond

• Ionic liquids offer a compelling combination of wide electrochemical windows, thermal stability, and non‑volatility that can unlock high‑voltage, safe energy storage devices when designed carefully for the electrode chemistry.
• Task‑specific ionic liquids and ionogel platforms emerged as practical routes to optimize interfacial phenomena and mechanical stability, addressing core bottlenecks in metal anode batteries and high‑voltage cathodes.
• Cost, synthesis complexity, and environmental implications remain critical barriers. The 2023 reportage calls for integrated approaches that co‑optimize performance with processing, lifecycle, and sustainability.
• The field is moving toward hybrid electrolyte architectures and broader metal systems (not just lithium), with an emphasis on scalable production, standardized benchmarking, and pilot‑scale demonstrations.
• Successful deployment will depend on cross‑disciplinary collaboration among chemists, materials scientists, process engineers, and supply chain partners to translate laboratory insights into reliable, manufacturable products.

Further reading and references

For readers who want to dive deeper, consider recent reviews, standard‑setting papers, and journal articles from 2023 that discuss ionic liquids in energy storage, electrolyte design, and device integration. Suggested topics include:

• Design principles of TSILs for SEI engineering
• Ionogel and polymer‑IL electrolyte architectures
• Redox‑active ionic liquids and their role in energy storage
• Lifecycle assessment and environmental impact of IL electrolytes

Note: This section provides pointers to themes rather than a curated bibliography. When evaluating sources, prioritize peer‑reviewed articles with clear experimental protocols, active electrochemical windows data, and explicit breakdowns of conductivity and viscosity across temperatures.

Expert note: Researchers new to ionic liquids should balance the allure of wide electrochemical windows with practical considerations of viscosity, moisture sensitivity, and compatibility with electrode materials. A holistic view—covering synthesis, processing, device integration, and lifecycle—will accelerate the path from lab discovery to real‑world impact.