What ionic liquid electrolytes are — and why they matter now
Ionic liquid (IL) electrolytes are room-temperature molten salts composed entirely of ions — large organic cations paired with weakly coordinating anions — that remain liquid at or near room temperature without any molecular solvent. Unlike conventional organic carbonate electrolytes, they exhibit negligible vapour pressure, non-flammability, electrochemical stability windows of 4–6 V vs. Li/Li⁺, and thermal stability exceeding 200–300 °C. These properties make them a structurally different answer to the safety failures that have dogged conventional lithium-ion systems.
The urgency behind IL electrolyte research stems from two converging pressures. First, thermal runaway incidents in conventional lithium-ion batteries — driven by the flammability of organic carbonate solvents — are escalating in frequency and consequence across consumer electronics, electric vehicles, and grid storage. Second, post-lithium chemistries (sodium, magnesium, aluminium) demand electrolytes that organic solvents cannot adequately serve. IL electrolytes address both problems simultaneously.
An ionic liquid is a salt with a melting point at or below 100 °C — typically at or near room temperature. IL electrolytes are defined by their all-ionic composition: large organic cations (imidazolium, pyrrolidinium, ammonium, phosphonium, piperidinium) paired with weakly coordinating anions (TFSI⁻, FSI⁻, BF₄⁻, PF₆⁻, Cl⁻). The dominant cation families in the research literature are pyrrolidinium (Pyr14) and imidazolium (EMIM, BMIM), with TFSI⁻ and FSI⁻ as the most widely researched anion counterparts.
The field has expanded well beyond simple drop-in replacements for liquid electrolytes. At least five distinct sub-domains now exist: pure IL electrolytes, IL/polymer hybrid electrolytes (gel and semi-solid), polymerized ionic liquids (PILs), IL@metal-organic framework (MOF) composites, and IL-modified aqueous “water-in-salt” systems. Each sub-domain addresses different trade-offs between safety, ionic conductivity, and operating temperature — and each carries distinct IP implications for R&D strategists. According to WIPO, electrolyte chemistry is among the fastest-growing patent categories within the broader energy storage technology domain.
Ionic liquid electrolytes offer electrochemical stability windows of 4–6 V vs. Li/Li⁺ and thermal stability exceeding 200–300 °C, properties that conventional organic carbonate electrolytes cannot match, making them a primary candidate for safety-critical battery applications in aerospace, military, and electric vehicle sectors.
Three phases of innovation: from foundations to AI-driven design
The IL electrolyte field has moved through three distinct phases between 2011 and 2024, each characterised by a different type of innovation activity — from establishing viability, to diversifying applications, to integrating IL chemistry with computational and materials science tools.
Phase 1 — Early Foundations (2011–2016)
Foundational reviews established IL viability for electric double layer capacitors and lithium-ion batteries, demonstrating non-volatility and non-flammability as core advantages. Tsuruoka National College of Technology’s 2011 work on IL electrolytes for EDLC applications represents an early anchor in the dataset. Zhejiang University’s 2016 review introduced a systematic taxonomy of five electrolyte classes, formally positioning ILs within a broader electrolyte design framework.
Phase 2 — Growth and Diversification (2017–2020)
This period saw intense activity in IL-based electrolytes for high-temperature LIBs, post-lithium systems (Al, Na), and hybrid IL/polymer membranes. Key milestones include demonstration of Pyr14TFSI in Li–air cells at Helmholtz Institute Ulm, pyrrolidinium-based electrolytes for medium-high temperature solid polymer batteries, and the pivot toward high-concentration and functionalized IL formulations exemplified by Helmholtz Institute Ulm’s 2019 work on concentrated IL-based electrolytes for high-voltage lithium batteries.
Phase 3 — Maturation and Integration (2021–2024)
The most recent cluster shows convergence on IL integration with MOFs and polymer matrices, post-lithium battery systems, and co-solvent water-in-salt approaches. Renmin University of China’s 2024 review of electrochemical stability of IL- and deep eutectic solvent-based electrolytes signals growing scrutiny of whether IL electrochemical stability claims hold under real battery conditions — a classic maturity indicator. At the frontier, Asahi Kasei’s 2025 JP patent on AI-driven electrolyte performance prediction represents the industrialisation of computational electrolyte design.
“Renmin University of China’s 2024 review signals growing scrutiny of whether IL electrochemical stability claims hold under real battery conditions — a classic indicator that a technology is transitioning from research optimism to engineering rigour.”
Four technology clusters shaping the IL electrolyte field
The IL electrolyte innovation landscape organises into four distinct technology clusters, each addressing a different aspect of the core challenge: delivering the safety benefits of ionic liquids while overcoming their viscosity, conductivity, or mechanical limitations.
Cluster 1: Pure Ionic Liquid Electrolytes
The core approach employs neat ILs — most commonly Pyr14TFSI or EMIM-based systems — as direct replacements for organic carbonate solvents, with dissolved lithium or sodium salts (LiTFSI, NaTFSI). Uppsala University demonstrated in 2018 that Pyr14TFSI-based cells with TiO₂ nanotube/LFP electrodes maintain capacity retention over 100 cycles at 80 °C, while organic electrolyte cells degrade rapidly under the same conditions. Tyndall National Institute and University College Cork’s 2020 comprehensive review confirmed pyrrolidinium ILs’ high electrochemical stability windows and compatibility with diverse cathode and anode materials including LFP, V₂O₅, Ge, and Sn.
Pyr14TFSI-based lithium-ion cells demonstrated capacity retention over 100 cycles at 80 °C in Uppsala University research (2018), while conventional organic electrolyte cells degraded rapidly at the same temperature — establishing pyrrolidinium TFSI systems as the leading candidate for high-temperature battery applications.
Cluster 2: IL/Polymer Hybrid Electrolytes
This cluster addresses the primary weakness of neat ILs — high viscosity and low room-temperature conductivity — by incorporating ILs into polymer matrices (PEO, PVDF-HFP, epoxy) or polymerizing the IL itself into poly(ionic liquids) (PILs). Helmholtz Institute Ulm’s 2018 work showed PEO membranes incorporating N-butyl-N-methylpyrrolidinium TFSI achieved excellent cycling at 80 °C with no lithium dendrite growth. Université de Lyon demonstrated that phosphonium-based IL (trihexyl(tetradecyl)phosphonium TFSI) confined in an epoxy network achieved thermal stability above 300 °C and ionic conductivity of 0.13 mS/cm at 100 °C. Sun Yat-Sen University’s 2022 PIL-bonded LATP composites achieved ionic conductivity of 1.2 × 10⁻³ S/cm — one order of magnitude above pristine LATP — while maintaining flexibility.
Map the full IL electrolyte patent landscape — assignees, filing dates, and whitespace — with PatSnap Eureka.
Explore IL Patent Data in PatSnap Eureka →Cluster 3: Post-Lithium IL Electrolytes (Al, Na, Mg)
For aluminium-ion batteries, haloaluminate IL systems (AlCl₃/EMIM-Cl) are not merely an alternative — they are frequently the only demonstrated viable electrolyte class, enabling reversible Al plating and stripping. Northeastern University (Shenyang) demonstrated in 2021 that an AlCl₃/[EMIM][TF₂N] IL achieved an oxidation voltage of 2.50 V vs. Al/Al³⁺ and approximately 75 mAh/g stable capacity at near-100% Coulombic efficiency. For sodium-ion systems, ENEA (Italy) showed in 2020 that binary NaTFSI-IL mixtures with EMI-based cations achieved room-temperature conductivities above 10⁻³ S/cm, with stable performance even below −10 °C — a result with direct implications for cold-climate grid storage.
Cluster 4: IL@MOF and Advanced Composite Solid Electrolytes
The most structurally novel cluster integrates ILs into porous host frameworks — metal-organic frameworks, NASICON ceramics, inorganic/polymer composites — to create solid-state or quasi-solid-state electrolytes with improved mechanical integrity and ion transport pathways. PETRONAS Technology University’s 2022 review highlights IL@MOF hybrids as an emerging class combining high ionic conductivity with chemical and mechanical stability, with computational methods used to understand atomistic conduction mechanisms. This sub-domain appears in multiple 2020–2022 records as structurally novel but not yet commercially mature — representing accessible IP whitespace.
Poly(ionic liquid) binders and IL-infiltrated MOF electrolytes appear across multiple 2020–2022 records as structurally novel but not yet commercially mature. Filing activity in these areas — particularly in flexible and wearable device contexts — represents accessible whitespace for IP portfolio development, according to the analysed dataset.
Application domains: where IL electrolytes are gaining ground
Ionic liquid electrolytes are not confined to a single battery chemistry — they span at least six distinct application domains, each with different maturity levels and commercial drivers.
Lithium-Ion Batteries (High-Temperature and Safety-Critical)
The dominant application domain in the dataset. IL electrolytes are positioned primarily for LIBs operating above 40 °C — including aerospace, military, and electric vehicle applications requiring thermal stability beyond the capability of organic solvents. German Aerospace Center (DLR) explicitly frames ILs for aerospace, medical, and electric vehicle energy storage devices. Dalian Institute of Chemical Physics (CAS) demonstrated a non-flammable zwitterionic IL/ethylene carbonate mixed electrolyte with a 1.65–5.10 V window and conductivity of 1.0 × 10⁻³ S/cm at 20 °C — a result that directly addresses the flammability problem without sacrificing performance.
Supercapacitors and Hybrid Energy Storage
ILs enable higher operating voltages in electric double layer capacitors (EDLCs) than aqueous or organic electrolytes, directly increasing energy density. University of Nottingham Ningbo China’s 2019 work and Chalmers University of Technology’s 2017 research cover EMIM Ac and BMIM Cl for high-temperature EDLC integration in microelectronics — an application area where the non-volatility of ILs is particularly valuable.
Post-Lithium Batteries (Al, Na, Mg)
For aluminium-ion batteries, IL electrolytes are not competing against entrenched organic electrolyte incumbents — they are often the only demonstrated solution. Osaka University’s foundational review of haloaluminate ILs for electrochemical surface finishing and energy storage established the AlCl₃/EMIM-Cl system as the baseline architecture. For sodium-ion batteries, ENEA’s 2020 results and Yalova University’s 2023 review together indicate Na-ion IL electrolytes are advancing from curiosity to practical consideration, driven by sodium’s abundance and cost advantage relative to lithium.
For aluminium-ion batteries, haloaluminate ionic liquid systems — specifically AlCl₃/EMIM-Cl formulations — are frequently the only demonstrated viable electrolyte class, enabling reversible aluminium plating and stripping. Northeastern University (Shenyang) demonstrated near-100% Coulombic efficiency and approximately 75 mAh/g stable capacity using an AlCl₃/[EMIM][TF₂N] electrolyte in 2021.
Lithium–Air and Lithium–Sulfur Batteries
IL electrolytes provide the chemical stability required at the oxygen electrode in Li–air systems, where conventional electrolytes degrade. Helmholtz Institute Ulm’s 2014 work established TFSI-based ILs as top candidates for stable SEI formation in Li–air cells. For Li–S batteries, ILs’ wide electrochemical stability window and non-volatility address the polysulfide shuttle problem — Kogakuin University’s 2019 work developed solvate IL-based electrolytes specifically for this application.
Redox Flow Batteries and Grid Storage
Rzeszów University of Technology’s 2022 review identifies ILs as electrolytes, membranes, and redox couples in flow battery architectures — introducing new flexibility for grid-scale applications. This is a relatively early-stage application in the dataset but one with significant scale potential, given the global push toward long-duration energy storage as tracked by organisations including the IEA.
Industrial Lubrication (Non-Energy)
Sinopec Lubricants’ 2021 research and a separate 2021 review of ILs’ path to first industrial application document commercial deployment of ILs as hydraulic and lubricating fluids. This non-battery application confirms manufacturability at scale — a meaningful signal for battery-focused IL developers assessing supply chain feasibility.
Identify uncontested IP positions in post-lithium and IL@MOF electrolyte sub-domains using PatSnap Eureka’s patent analytics.
Analyse IP Whitespace in PatSnap Eureka →Geographic and assignee landscape: who leads and where
Innovation in ionic liquid electrolytes is broadly distributed across academic and national laboratory institutions in at least 15 countries, with limited evidence of dominant corporate patent holders in the IL electrolyte subspace — the exception being Asahi Kasei and Hitachi in Japan at the device-integration level.
China accounts for the largest volume of institutional contributors, spanning the full technology stack from pure IL synthesis to composite solid electrolytes and post-lithium systems. Key institutions include Dalian Institute of Chemical Physics (CAS), Beijing Institute of Technology, Northeastern University (Shenyang), Soochow University, Sun Yat-Sen University, University of Electronic Science and Technology of China, and Renmin University of China.
Germany — led by Helmholtz Institute Ulm and Karlsruhe Institute of Technology (KIT) — is the most prominent single-nation contributor for high-temperature IL electrolyte research, appearing in multiple high-impact studies on Pyr14TFSI electrolytes for Li-air and Li-polymer batteries. German Aerospace Center (DLR) contributes the aerospace application framing. Research published by institutions including Nature and tracked by the OECD consistently identifies Germany and China as co-leaders in advanced battery materials research.
Japan (Osaka University, Kogakuin University, Hitachi R&D, Asahi Kasei) is active across both fundamental IL research and device-level integration. Asahi Kasei’s 2025 JP patent on AI-driven electrolyte performance prediction signals Japanese corporate interest in AI-accelerated electrolyte development — a strategic shift from pure materials research toward computational formulation intelligence.
Europe (Italy — ENEA; Sweden — Uppsala University, Chalmers; France — Université de Lyon; Poland — Rzeszów University of Technology) contributes primarily through academic research on Na-ion IL electrolytes, PIL systems, and flow battery IL applications. South Korea (Kyungpook National University, KAIST, Inha University) and the USA (MIT, Argonne National Laboratory, University of Texas at Austin, Illinois Institute of Technology, Brookhaven National Laboratory) remain active in foundational electrolyte chemistry and concentration-dependent phenomena.
In the ionic liquid electrolyte research dataset analysed (80+ records, 2011–2024), China accounts for the largest volume of institutional contributors spanning the full technology stack, while Germany — led by Helmholtz Institute Ulm and KIT — is the most prominent single-nation contributor for high-temperature device-integration research. Innovation is broadly distributed across academic and national laboratory institutions, with limited evidence of dominant corporate patent holders in the IL electrolyte subspace.
Emerging directions and strategic IP implications
The most recent records (2022–2024) in the dataset point to five converging directions that will shape the IL electrolyte competitive landscape through 2026 and beyond.
Deep Eutectic Solvents as IL Analogues
Renmin University of China’s 2024 review explicitly frames deep eutectic solvents (DES) as a co-equal “green” electrolyte class alongside ILs for lithium-ion, lithium-metal, and post-lithium batteries. This signals an expanding IL conceptual boundary toward hydrogen-bond-donor-based systems — and a potential convergence of two previously separate IP domains.
Gemini-Type and Zwitterionic Ionic Liquids
Uppsala University’s 2023 work on Gemini ionic liquids in water-in-salt electrolytes and Illinois Institute of Technology’s research on di-cationic and zwitterionic IL architectures demonstrate next-generation formulations with superior conductivity profiles. These represent a structural evolution beyond standard imidazolium/pyrrolidinium systems — and an emerging IP frontier.
AI and Machine Learning-Assisted Electrolyte Design
Asahi Kasei’s 2025 JP patent applies predictive modelling to electrolyte composition — including flammability and battery performance metrics — signalling the industrialisation of data-driven IL formulation. NIMS Japan’s 2022 work using Bayesian optimisation for multi-component electrolyte discovery in Li–O₂ batteries represents the academic counterpart to this corporate move. Organisations without computational electrolyte capabilities will face increasing lag-to-market for novel IL systems, according to the strategic analysis in the dataset. Patent offices including the EPO have begun classifying AI-assisted materials discovery as a distinct patent category, further formalising this trend.
“The 2025 Asahi Kasei JP patent on ML-based electrolyte performance prediction signals that the next competitive advantage will be in formulation intelligence — combining multi-component IL mixtures with predictive models. Organisations without computational electrolyte capabilities will face increasing lag-to-market.”
Water-in-Salt Hybrid Architectures
Uppsala University’s 2023 Gemini IL work represents a fusion of two previously separate electrolyte paradigms — water-in-salt and ionic liquid — into ternary co-solvent systems. This direction targets both the safety of aqueous systems and the wide electrochemical stability window of ILs simultaneously, potentially opening a new application domain for grid-scale aqueous storage.
Strategic IP Implications
Four strategic conclusions emerge from the dataset analysis. First, safety differentiation is the primary commercial pull — across the dataset, the dominant motivation for IL electrolyte adoption is non-flammability and thermal stability, not energy density or cost. R&D teams targeting aerospace, military, grid, and EV applications should prioritise pyrrolidinium-TFSI and FSI-based systems with demonstrated 80 °C cycling performance. Second, post-lithium battery markets represent an uncontested IL niche — for aluminium-ion and sodium-ion batteries, IL electrolytes are often the only demonstrated solution, and IP strategists should evaluate whitespace in AlCl₃/EMIM-based systems and NaTFSI/IL binary mixtures in EU and Asian jurisdictions. Third, China’s institutional volume and Germany’s device-integration depth define the competitive frontier — IP strategists should monitor Chinese academic-to-industrial transfer paths (CAS institutes, key laboratories with industry partners) and German KIT/Fraunhofer outputs for near-term licensing opportunities. Fourth, AI-driven electrolyte formulation will compress discovery timelines, making computational capability a prerequisite for competitive IL development by 2026.
For R&D and IP teams seeking to navigate this landscape, platforms that combine patent analytics with scientific literature — such as PatSnap’s IP intelligence platform — provide the cross-domain visibility needed to identify whitespace and monitor competitor activity across the IL electrolyte sub-domains described here.