| HS Code | 200797 |
| Productname | Bis(Fluorosulfonyl)Imide |
| Casnumber | 14984-73-7 |
| Molecularformula | F2HNO4S2 |
| Molecularweight | 181.14 g/mol |
| Appearance | Colorless to pale yellow liquid |
| Physicalstate | Liquid |
| Meltingpoint | 14-17 °C |
| Boilingpoint | 170 °C |
| Density | 1.98 g/cm3 at 25 °C |
| Refractiveindex | 1.36 |
| Solubility | Reacts with water; soluble in polar organic solvents |
| Acidity | Strong acid |
| Vaporpressure | 1.5 mmHg at 25 °C |
| Flashpoint | >100 °C |
| Storageconditions | Store in a dry, inert atmosphere at room temperature |
| Corrosivity | Corrosive to skin, eyes, and metals |
| Hygroscopicity | Moisture sensitive |
| Odor | Pungent |
As an accredited Bis(Fluorosulfonyl)Imide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Supplied in 100 g sealed, PTFE-lined HDPE bottles under dry nitrogen, with corrosive hazard labels and moisture-protective outer packaging. |
| Container Loading (20′ FCL) | Bis(Fluorosulfonyl)Imide securely palletized and loaded into a 20′ FCL container, sealed and labeled for safe chemical transport. |
| Shipping | Bis(fluorosulfonyl)imide is shipped as a corrosive, moisture-sensitive hazardous material in sealed PTFE/PFA-lined containers under dry inert gas. It typically requires UN3265, corrosive labels, UN-approved packaging, and IATA/ADR/IMDG compliance. Transport cool, dry, upright, segregated from water, bases, oxidizers, glass, and heat. Use PPE and documented emergency response. |
| Storage | Store bis(fluorosulfonyl)imide in a cool, dry, well-ventilated, fire-resistant area away from moisture, heat, ignition sources, bases, and oxidizers. Keep containers tightly sealed under dry inert gas in corrosion-resistant, fluorinated plastic or glass-lined vessels. Provide secondary containment, grounding, clear labeling, and restricted access. Use appropriate personal protective equipment and inspect regularly for leaks or degradation. Store separately from incompatible materials. |
| Shelf Life | Typically 24 months when stored sealed under inert gas in a cool, dry place; avoid moisture, which causes hydrolysis. |
In electrolyte salt production, bis(fluorosulfonyl)imide is neutralized under a dry nitrogen blanket in a glass-lined agitated reactor charged with anhydrous acetonitrile or ethyl acetate. The acid feed is controlled to maintain an exotherm between 0 °C and 10 °C; a molar excess of lithium hydroxide monohydrate at 1.01:1 to 1.05:1 relative to the imide acid is used to drive complete conversion and hold the endpoint pH between 7.0 and 7.8. Residual water in the neutralization solvent is controlled below 100 ppm before charging the acid because the sulfonimide acid is susceptible to hydrolysis at elevated temperature. After neutralization, the slurry is passed through a 0.2 µm PTFE depth filter, vacuum-distilled, and crystallized; the wet cake is dried at 110 °C to 120 °C under ≤ 10 mbar vacuum until moisture is ≤ 50 ppm. Battery-grade lithium bis(fluorosulfonyl)imide produced from this route is specified with chloride ≤ 5 ppm, sulfate ≤ 10 ppm, transition metals ≤ 2 ppm, and residual solvent ≤ 20 ppm, with cell-level qualification conducted according to IEC 62619:2022 and transport testing under UN 38.3. In carbonate-based electrolyte formulating, the resulting LiFSI is added at 0.5–3.0 wt% to 1.0 M LiPF6 in ethylene carbonate/ethyl methyl carbonate 3:7 vol%, where the imide anion reduces charge-transfer resistance and improves low-temperature discharge. The downstream production process includes electrolyte blending in a dry room with dew point ≤ -40 °C, addition of film-forming additives such as vinylene carbonate at 0.5–2.0 wt%, filtration through 0.2 µm membranes, and vacuum filling into cylindrical 18650 and 21700 cells or multilayer pouch cells. Finished terminal product types include electric vehicle traction batteries, stationary energy storage modules, and high-rate power tool packs.
Sodium bis(fluorosulfonyl)imide is prepared from the same imide acid by neutralizing with sodium hydroxide or sodium carbonate in anhydrous ethanol or isopropanol. The sodium salt exhibits stronger hygroscopicity than the lithium analogue; therefore, the production line requires lyophilized sodium carbonate metered at 1.03–1.08 molar equivalents to the acid, with addition over 45–90 min to keep the batch below 25 °C. The resulting precipitate is washed with chilled solvent at ≤ 5 °C, filtered under vacuum, and dried at 80–100 °C in a vacuum tray dryer to a final moisture content of ≤ 30 ppm. Compliance testing for sodium-ion cells follows IEC 62619:2022, UL 1973, and UN 38.3, with electrolyte purity verified by ion chromatography and Karl Fischer titration; chloride is maintained ≤ 10 ppm and sulfate ≤ 20 ppm. In electrolyte formulation, NaFSI is dissolved at 1.0 M in ethylene carbonate/diethyl carbonate 1:1 vol% or at 0.8 M in propylene carbonate with 5.0 wt% fluoroethylene carbonate, yielding a sodium-ion conducting electrolyte with lower viscosity at -20 °C than equivalent NaPF6 systems. Downstream production involves hard carbon anode coating with 2.5–3.5 mAh/cm² mass loading, electrolyte filling under vacuum, formation cycling at C/10, and sealing in 32140 cylindrical or 10 Ah pouch formats. Terminal product types include low-speed electric vehicle batteries, grid frequency regulation modules, and industrial backup power cabinets.
Blending of non-aqueous electrolytes for electric double-layer capacitors using the FSI anion starts with high-purity onium FSI ionic liquids, typically 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide or N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide. The bis(fluorosulfonyl)imide acid is converted to the onium salt via metathesis or acid-base neutralization, and the product is dried under ≤ 5 mbar vacuum at 70–90 °C until water content falls below 20 ppm. In capacitor electrolyte formulation, the FSI ionic liquid is blended with acetonitrile at 1.5–1.8 M or with propylene carbonate at 40–60 wt%, giving a room-temperature conductivity between 12 mS/cm and 20 mS/cm and viscosity between 18 mPa·s and 25 mPa·s; blends with acetonitrile are restricted to sealed cells because of the 82 °C boiling point. Electrolyte preparation is performed in stainless steel mixing vessels under dry-air dew point ≤ -50 °C, followed by 0.2 µm PTFE filtration and vacuum degassing before activated carbon electrode impregnation. Compliance is verified under IEC 62391-1:2022 and UL 810A, and fluorinated ionic liquid content is documented for RoHS 2011/65/EU and REACH substance registrations. Terminal capacitor products include 2.7 V and 3.0 V radial and screw-terminal EDLC cells, modules for wind turbine pitch control, and ride-through backup power units.
| Application segment | Standard designation | Scope |
|---|---|---|
| Lithium-ion traction cells | IEC 62619:2022 | Safety requirements for industrial lithium cells and batteries |
| Sodium-ion industrial cells | UL 1973 | Batteries for stationary and motive auxiliary use |
| Electric double-layer capacitors | IEC 62391-1:2022 | Fixed electric double-layer capacitors for power applications |
| Battery transport | UN 38.3 | Lithium metal and lithium-ion battery transport testing |
| Electric vehicle traction cells | IEC 62660-1:2018 | Performance testing for lithium-ion traction cells |
In high-voltage NMC811/graphite electrolyte development, the lithium imide salt is introduced at 0.5–2.5 wt% into a baseline 1.0 M LiPF6 ethylene carbonate/ethyl methyl carbonate 3:7 vol% solution containing 1.0–2.0 wt% vinylene carbonate and 0.5 wt% fluoroethylene carbonate. The imide anion lowers interfacial resistance on nickel-rich cathodes and improves capacity retention at 4.35 V; however, replacement of more than 3.0 wt% LiFSI without auxiliary passivation can raise aluminum current collector dissolution at potentials above 4.0 V, so co-addition of lithium difluoro(oxalato)borate or lithium bis(oxalato)borate at 0.2–1.0 wt% is standard. Electrolyte blending is performed in jacketed 316L stainless steel vessels at 25 °C under dry-room dew point ≤ -40 °C, with low-shear agitation at 100–200 rpm, 0.2 µm polypropylene filtration, and Karl Fischer moisture control ≤ 15 ppm. Formation protocols for high-voltage cells use C/20 to C/10 initial charge steps to stabilize the cathode electrolyte interphase. Cycle-life qualification is performed according to IEC 62660-1:2018; safety qualification follows IEC 62619:2022. Terminal products include 4.35 V pouch cells for drones, high-discharge power tool packs, and portable medical device batteries.
Dissolving the lithium salt in a binary cosolvent of ethylene carbonate and propylene carbonate, then mixing with poly(vinylidene fluoride-co-hexafluoropropylene) dissolved in acetone or N-methyl-2-pyrrolidone, produces a casting solution suitable for phase-inversion gel electrolyte films. The formulation uses 12–18 wt% LiFSI relative to polymer mass and 20–30 wt% carbonate plasticizer, with the balance being PVDF-HFP; the casting solution is applied to a polyester release film using a slot-die coater with wet-film thickness between 150 µm and 300 µm. Phase inversion is induced by immersion in a water bath at 20–25 °C, followed by vacuum drying at 60 °C until residual solvent is ≤ 500 ppm. The resulting free-standing film shows ionic conductivity in the range of 0.1–1.0 mS/cm at 25 °C, suitable for low-rate thin-cell designs. Compliance for assembled cells references UL 1642 for lithium cells, IEC 62619:2022 for industrial battery safety, and ISO 10993-5 when the powered device is skin-contacting. Terminal product types include printed thin-film batteries for smart cards, wearable electrocardiogram patches, and low-power environmental sensor labels.
During dry-room blending of fluorinated ether–carbonate formulations for lithium-metal cells, the imide salt is dissolved at 1.0–1.2 M in 1,2-dimethoxyethane/1,3-dioxolane 1:1 vol%, with lithium nitrate added at 0.1–0.3 M to stabilize the solid electrolyte interphase on lithium foil. The electrolyte is prepared in an argon-filled glovebox with oxygen ≤ 1 ppm and moisture ≤ 1 ppm; all components are dried to ≤ 10 ppm water before mixing. The use of LiFSI in place of LiPF6 reduces hydrolysis-associated HF generation in the presence of trace water, but operational boundaries include lithium electrode cycling at current densities above 3 mA/cm², where dendrite-induced soft-short failure may occur unless the formulation is paired with a fluorinated ether diluent at 20–40 wt%. Cell assembly uses 20–50 µm lithium foil, polyethylene or polypropylene separator, and pouch packaging in a dry room; formation cycling is performed at C/20 with a cutoff of 4.3 V. Compliance testing follows UN 38.3 and IEC 62619:2022, with cycle-life data collected under 0.5 C charge/discharge at 25 °C. Terminal product types include pilot lithium-metal pouch cells for high-altitude aircraft, electric vertical-takeoff-and-landing demonstrators, and satellite battery packs.
Competitive Bis(Fluorosulfonyl)Imide prices that fit your budget—flexible terms and customized quotes for every order.
For samples, pricing, or more information, please contact us at +8615380400285 or mail to sales2@ascent-chem.com.
We will respond to you as soon as possible.
Tel: +8615380400285
Email: sales2@ascent-chem.com
Flexible payment, competitive price, premium service - Inquire now!
Bis(Fluorosulfonyl)Imide, also written bis(fluorosulfonyl)imide and abbreviated HFSI, is the sulfonimide acid registered under CAS 14984-73-7 and described by the condensed formula HN(SO2F)2 with molar mass 181.13 g mol⁻¹. The product is a strongly acidic, moisture-sensitive liquid or low-melting solid supplied predominantly as an electrolyte precursor for lithium bis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide (NaFSI), and pyrrolidinium or imidazolium salts used in non-aqueous electrochemical devices. In this product class, the two terminal S–F groups replace the P–F bonds of lithium hexafluorophosphate or the S–CF₃ groups of lithium bis(trifluoromethanesulfonyl)imide; this structural difference alters anion hydrolysis pathways, aluminium current-collector surface film composition, and low-temperature transport. The free acid itself is not formulated into finished cells but is neutralised under controlled anhydrous conditions to produce the corresponding salts, which are then dried to electrolyte-grade moisture contents.
Water activity is the main constraint for the free sulfonimide acid. In the presence of free moisture, HFSI undergoes hydrolysis at the S–F position to generate fluorosulfonic acid and sulfamide-type intermediates; published kinetic data for the pure acid are limited, but manufacturing lots packaged in fluoropolymer-lined drums show measurable assay loss after repeated partial-container use when ambient relative humidity exceeds 30% RH. Transfer operations are therefore performed in nitrogen or argon dry boxes with a dew point no higher than −40 °C, and process lines use perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), or annealed stainless steel passivated by previous exposure to anhydrous fluorosulfonyl species. Unpassivated carbon steel and 316L stainless steel are unsuitable for concentrated acid service because acid-catalysed fluoride release can initiate pitting at welds and crevices. Glass-lined vessels and PTFE-lined steel drums are the standard contact surfaces for long-term storage.
Drying is a second processing boundary. If crude HFSI is subjected to vacuum at temperatures above 60 °C, low-mass fluorosulfonyl components may volatilise and free fluoride may increase, whereas insufficient vacuum or stripping leaves bound water above the level tolerable in subsequent LiFSI electrolytes. Pilot-scale drying records indicate an operating window between 45 °C and 55 °C at pressures below 5 mbar with dry-nitrogen sparging, although published data for specific supplier configurations is limited. Incoming solvent used for dilution must be dried to below 20 mg kg⁻¹ water by molecular sieves or sparging before contact with the acid.
Electrolyte precursor grades are sold against a release profile that includes assay, water, ionic impurities, and metal residues. The primary anionic impurities are chloride and sulfate carried from sulfonyl chloride or fluorosulfonate intermediates, while sodium, potassium, and iron are the main cationic residues introduced from neutralisation equipment or raw material sources. Acceptance limits vary by producer; the table below represents a typical electrolyte-precursor acid profile and should be checked against the batch certificate of analysis. Test methods are selected from normal laboratory standards for moisture, anion chromatography, and trace-metal measurement.
| Parameter | Test method | Typical acceptance limit |
|---|---|---|
| Assay as HN(SO2F)2 | Non-aqueous acid-base titration or ion chromatography | ≥ 98.0% by mass |
| Water content | Karl Fischer coulometry, ASTM E203-16 | ≤ 0.10% or 1000 mg kg⁻¹ |
| Chloride | Suppressed anion chromatography, ISO 10304-1:2007 | ≤ 50 mg kg⁻¹ |
| Sulfate | Suppressed anion chromatography, ISO 10304-1:2007 | ≤ 100 mg kg⁻¹ |
| Lithium, sodium, potassium | ICP-MS, ISO 17294-2:2016 | ≤ 10 mg kg⁻¹ total |
| Free fluoride | Ion-selective electrode after aqueous hydrolysis | ≤ 20 mg kg⁻¹ |
Conversion to LiFSI is carried out by controlled neutralisation with lithium hydroxide monohydrate or lithium carbonate in a non-aqueous suspension. The reaction is strongly exothermic and the fluorosulfonyl group is sensitive to local pH excursions above 10 when aqueous alkali is used; industrial batches therefore use jacketed glass-lined reactors with PTFE-coated temperature probes, slow acid or base metering, and anchor or retreat-blade agitation at low tip speed, commonly below 2.5 m s⁻¹. Reaction temperature is maintained below 50 °C, and the addition is stopped if the reactor temperature derivative exceeds 2 °C min⁻¹. After neutralisation, the mixture is filtered through a 0.2 μm PTFE or polypropylene membrane to remove insoluble lithium carbonate and metal hydroxides. The clarified LiFSI solution is concentrated and dried at 45–55 °C and 5 mbar to achieve moisture below 20 mg kg⁻¹; batch-to-batch variation in water content is the main release issue when ambient humidity during packaging is not controlled below 0.5% RH in a closed transfer isolator.
The free acid is incompatible with alcohols, primary and secondary amines, and strong aqueous bases; these cause rapid sulfonylation or neutralisation and generate heat. It should not be combined with polyamide or polyurethane seals because acid-catalysed chain scission occurs at stressed sealing surfaces. The operational boundary for routine pump transfer is 25 °C maximum in PTFE-lined gear or magnetically coupled sealless pumps to limit vapour generation and seal embrittlement.
The FSI anion derived from the free acid has a lower formula mass than the TFSI anion: 180.13 g mol⁻¹ versus 280.15 g mol⁻¹. This smaller anion yields lower solution viscosity at equivalent concentration in carbonate solvents and is the basis for its use as a low-temperature additive or primary salt. The PF₆ anion has a lower mass of 144.96 g mol⁻¹ and historically lower cost, but LiPF₆ is hydrolytically unstable and releases HF and phosphorus oxyfluorides on contact with moisture. LiFSI hydrolysis is slower under comparable water exposure and does not generate the POF₃ cascade, but the salt is not unconditionally stable against aluminium at all potentials. Linear sweep voltammetry at 1 mV s⁻¹ on platinum from 0.5 V to 6.0 V versus Li/Li⁺ is used to compare electrochemical windows; carbonate-based electrolyte-grade LiFSI generally shows an oxidation onset above 5.0 V versus Li/Li⁺, although published data for specific cell configurations is limited.
Aluminium current-collector behaviour is the critical difference in full cells. The FSI anion tends to produce a fluorine-containing surface film on aluminium at potentials above 3.8 V versus Li/Li⁺, which suppresses pitting compared with TFSI in many formulations. The protection is formulation-dependent and is affected by water content above 30 mg kg⁻¹; cells with elevated water levels show isolated pitting in coin-cell ageing tests after 200 h at 45 °C. In separator-coated or pouch-cell configurations, corrosion is monitored by chronoamperometry at constant potential using a three-electrode cell with an aluminium working electrode, and the residual current after 48 h is used as a quality gate. These measurements follow internal cell-test protocols because a harmonised ISO or ASTM method for aluminium current-collector stability in non-aqueous electrolytes is not available.
At production scale, in-process control for HFSI purification is performed by Raman spectroscopy or online mid-infrared spectroscopy because the fluorosulfonyl group has characteristic S–F and S–O vibrations in the 800–1200 cm⁻¹ region. Ion chromatography with suppressed conductivity detection is used off-line to quantify chloride and sulfate at limits of quantification near 10 mg kg⁻¹. Water is measured by coulometric Karl Fischer with oven introduction at 150 °C; sample size is adjusted to yield 30–70 µg of titre. These conditions minimise the interference of acid protons and permit batch release within 2 h after sampling from a closed-loop sampling loop.
The pyrrolidinium and imidazolium salts prepared from HFSI are employed in electrochemical capacitors and aluminium deposition electrolytes where the absence of halide is critical. In such applications, the acid is neutralised with anhydrous trialkylamine in acetonitrile at 0–10 °C; the resulting ionic liquid is washed with hexane and dried under vacuum at 60 °C and 1 mbar until water is below 50 mg kg⁻¹. This use differs from battery electrolytes because the final product is a room-temperature ionic liquid or deep eutectic, not a lithium salt solution. The operational limit is amine purity: primary and secondary amines are excluded because they form covalent sulfonamides instead of ionic liquids.
In lithium-ion cell manufacturing, bis(fluorosulfonyl)imide-derived LiFSI is used in two distinct modes: as a primary lithium salt at concentrations from 1.0 mol dm⁻³ to 1.5 mol dm⁻³ in carbonate or carbonate/ester blends, and as an additive at 0.5–2.0 wt% relative to the total electrolyte to reduce interfacial resistance on graphite or silicon-dominant anodes. When used as an additive, mixing is performed in a high-shear mixer under nitrogen until the Karl Fischer value remains below 20 mg kg⁻¹; filtration through a 0.2 μm membrane is standard before cell filling. The low-temperature advantage is typically assessed at −20 °C and −40 °C using impedance spectroscopy from 10 mHz to 100 kHz, and the product is accepted only if the bulk ionic conductivity is stable after 72 h of storage at 60 °C. This application boundary should not be extrapolated to aqueous systems, because the sulfonimide acid and its lithium salt are designed for non-aqueous operations and lose integrity under prolonged aqueous exposure.
