| HS Code | 176307 |
| Product Name | Trimethylsilyl Phosphate |
| Chemical Formula | C9H27O4PSi3 |
| Cas Number | 10497-05-9 |
| Molecular Weight | 314.55 g/mol |
| Appearance | Colorless liquid |
| Density | 0.954 g/mL at 25°C |
| Boiling Point | 228-229°C |
| Refractive Index | 1.412 |
| Solubility | Soluble in organic solvents; hydrolyzes in water |
| Flash Point | 107°C |
As an accredited Trimethylsilyl Phosphate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Trimethylsilyl phosphate is packaged in a 25 g amber glass bottle with a PTFE-lined cap, sealed under nitrogen. |
| Container Loading (20′ FCL) | Load 20′ FCL with tightly sealed drums of Trimethylsilyl Phosphate; use dry container, secure cargo, follow hazardous chemical regulations. |
| Shipping | Trimethylsilyl Phosphate is moisture-sensitive and must ship in airtight, anhydrous containers under inert gas, such as nitrogen. Use glass or PTFE-lined bottles with tight seals, packed in outer drums with desiccant. Protect from water, humidity, and physical damage. Follow applicable dangerous goods regulations and display required hazard labels. |
| Storage | Trimethylsilyl phosphate is moisture-sensitive and should be stored under an inert atmosphere (e.g., nitrogen or argon) in a tightly sealed container. Keep it in a cool, dry, well-ventilated area away from water, humidity, and strong oxidizers. Use proper labeling and ensure containment to prevent hydrolysis and degradation. |
| Shelf Life | Trimethylsilyl phosphate is moisture-sensitive; shelf life is best preserved under dry, inert conditions, typically lasting several months when refrigerated. |
In 4.95 V LiNi0.5Mn1.5O4/graphite pouch cells, tris(trimethylsilyl) phosphate (CAS 10497-05-9) is used as a high-voltage cathode-electrolyte interphase modifier at 0.5–2.0 wt% in 1.0 mol/L LiPF6 dissolved in ethylene carbonate/ethyl methyl carbonate (3:7 w/w). The electrolyte is blended in a jacketed stainless-steel reactor with mechanically coupled agitation under nitrogen at a dew point below −50°C; after the LiPF6 addition exotherm is controlled at 10–25°C, the additive is fed through a mass-flow meter and the batch is recirculated through a 0.2 μm PTFE filter until Karl Fischer moisture is ≤ 20 mg/kg. Filling is performed in a dry room at dew point ≤ −40°C. During formation, a C/20 constant-current step to 4.95 V is followed by a constant-voltage taper to 0.05C; the resulting CEI contains P–O and Si–O fragments that limit oxidative decomposition of carbonate solvent and reduce nickel/manganese dissolution from the spinel. The operational boundary is strict: electrolytes with free alcohol content above 2,000 mg/kg or amine-bearing silane impurities cause premature hydrolysis of the trimethylsilyl ester and must be rejected before additive feeding. Compliance for finished cells is established under UN 38.3 T3 vibration, T4 shock, T5 external short circuit, IEC 62619:2022, and EU Regulation 2023/1542 Article 39 due diligence. Terminal product types include high-voltage pouch and cylindrical lithium-ion cells for specialty portable instrumentation, medical carts, and unmanned aerial systems.
Residual water in LiPF6-carbonate electrolytes converts to HF during float charging, which attacks the LiFePO4 cathode and degrades the graphite solid-electrolyte interphase. Tris(trimethylsilyl) phosphate is added at 0.5–1.5 wt% to a 1.0 mol/L LiPF6 electrolyte in ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (1:1:1 v/v/v) to scavenge free HF and slow the autocatalytic degradation of the electrolyte. The mixing procedure uses a sealed stainless-steel vessel with argon sparging at 15–25°C; the additive is introduced after the LiPF6 dissolving exotherm has dissipated, and Karl Fischer moisture is held at ≤ 15 mg/kg before drumming. Pouch, prismatic, and 18650 cells filled with this electrolyte undergo formation at C/20 to 3.65 V, followed by 55°C aging for 7–10 days to strip volatile radical initiators from the SEI before capacity grading. Compliance for stationary-storage packs is established under IEC 62619:2022, UL 1973:2022, UL 9540A, and UN 38.3. Terminal products include cabinet-type energy storage systems, telecom backup batteries, and industrial forklift packs.
When UL 9540A thermal runaway propagation testing is part of the design qualification, tris(trimethylsilyl) phosphate may be introduced as a flame-retardant co-additive in alkyl carbonate electrolytes at 5.0–10.0 wt%, typically replacing an equal mass fraction of ethyl methyl carbonate to maintain LiPF6 solvation. The addition is performed under nitrogen at 20–30°C in a recirculating mixing loop; viscosity rises measurably above 10.0 wt%, and three-port sampling is required to confirm constant refractive index and density before electrolyte release. Because trimethylsilyl phosphate scavenges HF and participates in anode solid-electrolyte interphase formation, the high-loading window is restricted to cells with moderate C-rate requirements; charge-transfer impedance increases at the anode when the additive fraction exceeds the upper threshold, so pulse-power validation on production cells is mandatory. Flammability performance is judged at the cell and module level under UL 9540A thermal runaway propagation protocols; published data for raw electrolyte self-extinguishing time with TMSP are limited and must be regenerated for each solvent matrix rather than transferred from other phosphate esters. Compliance for finished high-safety packs is anchored to UN 38.3, IEC 62619:2022, UL 9540A, and EU Regulation 2023/1542. Terminal product types include fire-hardened battery modules for automated guided vehicles, hospital grade uninterruptible power supplies, and marine auxiliary power packs.
Bioactive sol-gel processing uses tris(trimethylsilyl) phosphate as a phosphorus precursor in 58S-like compositions where the final oxide ratio is 60 mol% SiO₂, 36 mol% CaO, and 4–6 mol% P₂O₅; the addition is calculated to deliver 4–6 mol% P₂O₅ without introducing triethyl phosphate alcohol fragments that disrupt network homogeneity. Tetraethyl orthosilicate is first hydrolyzed in ethanol-water at pH 2–3 with dilute HNO₃, then Ca(NO₃)₂·4H₂O and the phosphorus precursor are added sequentially under high-shear dispersion at 25–35°C. The sol is cast or spray-dried, aged for 24–48 h, dried at 120°C, and calcined at 650–700°C for 3 h to remove residual nitrate and silyl organic fragments. Compliance for implant-grade output is evaluated under ISO 10993-1:2018, ISO 23317:2014, and ASTM F1538-17; dental remineralization formulations require separate oral care regulatory review. Terminal products include bioactive glass powders for bone void fillers, injectable particulate composites, and dental proximal polishing agents.
At pH 3.5–4.5, phosphate-functionalized sol-gel pretreatment of AA2024-T3 aluminium alloy combines tris(trimethylsilyl) phosphate with 3-glycidyloxypropyltrimethoxysilane at a P/Si molar ratio of 0.05–0.15. Water stoichiometry is controlled to avoid hydrolysis of the P–O–Si bridge to free phosphoric acid before film application; amine-containing silanes are omitted because amine catalysis accelerates condensation before dip application and destabilizes the phosphate-silane network. Panels are dip-coated at withdrawal speeds of 10–30 cm/min, flash-dried at 25°C, and cured at 120–150°C for 60–90 min to condense silanol and phosphate groups into a continuous hybrid network. Published data for TMSP-specific long-term filiform corrosion performance are limited; substrate-specific validation is required before replacing chromate conversion coatings. Compliance for aerospace and architectural substrates is established under ASTM B117-19, ASTM D3359-17, ISO 2409:2013, and relevant OEM chromate-free conversion coating specifications. Terminal product types include pretreated AA2024-T3 skins for aerospace component repair, aluminium architectural extrusions, and electronic enclosure substrates.
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Trimethylsilyl phosphate is supplied as a clear, colourless to pale-yellow liquid in which a central phosphate centre is masked by three trimethylsilyl substituents. The structure is reported under CAS 10497-05-9 as tris(trimethylsilyl) phosphate, formula C₉H₂₇O₄PSi₃, relative molecular mass 314.53 g mol⁻¹. Commercial designations include TMSP-99, TMSP-99.5, and electronic-grade TMSP; the numeric suffix indicates minimum gas-chromatography area purity. Standard lots specified at ≥99.0% are acceptable for general electrolyte blending, while ≥99.5% lots are commonly selected for LiNi₀.₈Mn₀.₁Co₀.₁O₂ and other nickel-rich cathode formulations where chloride and sodium residues become more critical. At 20 °C, the liquid density determined by ASTM D4052 is typically between 0.950 g cm⁻³ and 0.965 g cm⁻³. The product functions as a cathode-electrolyte interphase-forming additive in lithium-ion electrolytes, as an in-situ hydrogen fluoride scavenger, and as a silylating agent in phosphate ester synthesis where a stable P(V) centre is required.
In production-scale electrolyte blending, residual water distribution determines how rapidly the trimethylsilyl groups hydrolyse. The hydrolysis sequence releases trimethylsilanol and hexamethyldisiloxane and eventually converts the phosphate centre to acidic species. The additive is therefore received in nitrogen-blanketed containers and transferred through closed lines in dry-room conditions. Supplier certificates for TMSP-99 typically report moisture by Karl Fischer coulometry using ISO 760:1978; the specification ceiling is set at 150 mg kg⁻¹, while TMSP-99.5 is controlled at no more than 100 mg kg⁻¹ and electronic-grade material at no more than 50 mg kg⁻¹. Carbonate solvents are pre-dried below 20 mg kg⁻¹ water before addition of LiPF₆, and blend hold times are commonly kept below 48 h at 15–30 °C. If residual moisture in the final electrolyte exceeds 150 mg kg⁻¹, acid drift can increase during storage and accelerate aluminium current-collector corrosion during formation, as indicated by electrochemical impedance and post-mortem fluoride analysis. The moisture specification is therefore not a storage convenience but a composition limit that determines the additive’s remaining acid-scavenging capacity.
| Parameter | TMSP-99 | TMSP-99.5 | Electronic grade | Test method |
|---|---|---|---|---|
| Purity, GC-FID normalized area | ≥99.0% | ≥99.5% | ≥99.5% | Area normalization |
| Moisture | ≤150 mg kg⁻¹ | ≤100 mg kg⁻¹ | ≤50 mg kg⁻¹ | ISO 760:1978 |
| Chloride | ≤20 mg kg⁻¹ | ≤10 mg kg⁻¹ | ≤5 mg kg⁻¹ | ASTM D4327-17 |
| Colour, APHA | ≤30 | ≤20 | ≤10 | ASTM D1209-05(2019) |
| Density at 20 °C | 0.950–0.965 g cm⁻³ | 0.950–0.965 g cm⁻³ | 0.950–0.965 g cm⁻³ | ASTM D4052 |
Chloride and sodium levels are not passive quality descriptors. In high-nickel cathode systems, residual chloride can contribute to pitting corrosion of aluminium current collectors at elevated potentials, while sodium can migrate through separator pores and concentrate at negative-electrode surfaces under repeated cycling. The difference between TMSP-99 and TMSP-99.5 is therefore most visible in cells cycled above 4.30 V, where the lower chloride ceiling of the higher-grade product is specified to reduce the probability of localised cell failure.
During formation cycling of LiNi₀.₈Mn₀.₁Co₀.₁O₂/graphite cells, trimethylsilyl phosphate at 0.5–2.0 wt% is oxidatively decomposed on the cathode surface to generate phosphate-rich, silicon-containing films. The resulting interphase attenuates solvent oxidation, but the film resistance is not negligible. Electrochemical impedance spectroscopy with a 10 mV sinusoidal perturbation from 100 kHz to 10 mHz is commonly used to track area-specific impedance; loadings above 2.0 wt% generally increase initial interfacial impedance before the film becomes fully formed. In high-voltage NMC cells cycled to 4.35 V versus Li/Li⁺, X-ray photoelectron spectroscopy shows increased P 2p and Si 2p intensity on aged cathodes, although quantitative depth profiles vary with formation current, temperature, and electrolyte fluorination. Published data for this specific configuration is limited; qualification therefore requires identical coin-cell and pouch-cell protocols rather than extrapolation from low-nickel cathode chemistries.
Cycle-life verification is typically performed with constant-current/constant-voltage profiles patterned after IEC 62660-1. Upper cutoff voltage and cell stack pressure must be recorded because the additive can alter gas evolution during formation. The interphase improvement is not equivalent across all cathode materials: lithium-rich manganese-based oxides and high-voltage spinels may require a modified concentration range, and direct comparative data generated on the intended electrode pair is preferred.
At loadings between 0.5 wt% and 2.0 wt%, trimethylsilyl phosphate is differentiated from tris(trimethylsilyl) phosphite primarily by phosphorus oxidation state. Both materials carry trimethylsilyl groups, but the phosphate is a P(V) compound, CAS 10497-05-9, whereas the phosphite is P(III), CAS 1795-31-9. The phosphite is more oxygen-sensitive and may act as a reducing additive during thermal stress, while the phosphate is preferred where a non-reducing phosphorus centre is required. The two additives are not interchangeable in high-voltage lithium-ion electrolytes because the phosphite-derived interphase can evolve differently at potentials above 4.3 V. A direct substitution of trimethylsilyl phosphate for vinylene carbonate, CAS 872-36-6, is equally invalid as a like-for-like formulation change: vinylene carbonate is primarily an anode SEI former, whereas trimethylsilyl phosphate is primarily active at the cathode. Formulations that add trimethylsilyl phosphate for cathode stability usually retain vinylene carbonate or fluoroethylene carbonate for anode passivation.
In a jacketed 2,000 L electrolyte blending vessel, the additive is introduced through a dip leg below the liquid surface to minimize vapour contact. The addition zone is maintained at 15 °C to 30 °C; below 10 °C, local viscosity increase can delay homogeneous distribution. When LiPF₆ is present, the blend must be handled under a dry nitrogen atmosphere with a supply dew point below -40 °C. Metering is performed with a magnetically coupled gear pump calibrated using mass-flow references traceable to ISO 17025; typical precision for additive delivery is within ±0.05 wt% at a target loading of 1.0 wt%. After incorporation, the final blend is passed through a 0.2 µm hydrophobic polytetrafluoroethylene membrane to remove particulates and any hydrolysis haze. Open handling at ambient humidity above 60% is not permitted; if a container is opened under such conditions, the residue is re-tested or discarded. Observed production-line failure modes include pressure rise in unvented containers and swelling of ethylene-propylene elastomer seals; perfluoroelastomer and polytetrafluoroethylene wetted parts are specified.
The trimethylsilyl group reacts with hydrogen fluoride to form fluorotrimethylsilane, a volatile species that can be monitored by headspace gas chromatography. In a sealed LiPF₆ electrolyte, this reaction shifts fluoride speciation and reduces free HF activity, but it consumes the additive. The acid-scavenging effect is stoichiometric rather than catalytic: one mole of trimethylsilyl phosphate can consume up to three moles of HF if all Si–O bonds are cleaved. This boundary condition matters because heavily degraded LiPF₆ stock solutions can exhaust the additive before cathode interphase formation is complete. In such cases, the remaining phosphate ester concentration should be confirmed by gas chromatography before the electrolyte is released for cell filling, otherwise the intended high-voltage passivation may be underdosed.
Storage of sealed TMSP-99.5 drums under nitrogen at or below 25 °C preserves the specified moisture and colour for a producer-defined shelf life, commonly 12 months from the certificate date. The material is incompatible with water, alcohols, amines, aqueous acids, and strong bases; hydrolysis by-products include phosphoric acid and hexamethyldisiloxane, which can raise acidity and form haze. Waste handling follows the same procedures as for phosphate ester solvents: collection in closed, dry containers, segregation from aqueous waste, and disposal through licensed incineration with flue-gas scrubbing. For battery electrolyte use, the additive is never blended with protic co-solvents or with electrode slurries containing residual moisture above the electrolyte specification, because premature hydrolysis alters the target interphase chemistry and defeats the acid-scavenging function.
