Vinyl ethylene carbonate (VEC, 4-vinyl-1,3-dioxolan-2-one, CAS 4427-96-7) is a bifunctional cyclic carbonate with a vinyl substituent at the 4-position. The molecular formula is C₅H₆O₃, and the molar mass is 114.10 g mol⁻¹. The compound is handled as a battery-grade liquid additive in concentrations generally below 5.0 wt% relative to electrolyte mass. In lithium-ion cell manufacture, VEC is introduced into carbonate-based electrolyte blends under moisture-controlled conditions, with water content in the resulting electrolyte maintained below 20 µg g⁻¹ as measured by ASTM E203. The demand pull originates from the need to stabilize the solid electrolyte interphase on graphitic and silicon-containing anodes without the excessive gas evolution and impedance growth associated with some high-normal vinylene carbonate loadings. Published data for specific market sizing is limited; however, the technical evaluation programmes at cell manufacturers cover lithium-nickel-manganese-cobalt oxide, lithium-nickel-cobalt-aluminium oxide, lithium iron phosphate, and lithium metal cells because the vinyl group offers a polymerizable functionality that is sacrificed preferentially during formation cycling. The compound is supplied in inhibited form, with typical inhibitor packages based on phenolic or nitroxide radical systems at concentrations below 200 ppm, and is stored under nitrogen in stainless steel or glass-lined vessels to prevent moisture uptake and premature polymerization. Incoming lot qualification includes gas chromatography, Karl Fischer coulometry, and acid titration because trace water and acid species influence LiPF₆ hydrolysis and SEI chemistry.Electrolyte additive consumption in high-nickel cathode and silicon-anode cell platforms has expanded because these electrodes operate closer to oxidative and reductive stability limits. The vinyl group in VEC is electrochemically active at potentials slightly positive of graphite lithiation, producing a poly(VEC) film that is more flexible than the film derived from vinylene carbonate. The film suppresses propylene carbonate co-intercalation and graphite exfoliation; however, the film also introduces resistance if the deposition is not limited to the first formation cycle. Cell makers therefore evaluate VEC in formation protocols with current densities of 0.05C–0.2C and upper cutoff voltages of 3.6–3.8 V for graphite half cells, or 4.2–4.35 V for full cells, depending on cathode chemistry. The electrochemical window is measured by linear sweep voltammetry on platinum or glassy carbon electrodes at 1 mV s⁻¹ in 1.0 M LiPF₆ in ethylene carbonate/dimethyl carbonate or ethylene carbonate/ethyl methyl carbonate. In such measurements, oxidation current onset for VEC-containing electrolytes typically shifts relative to baseline; published data for this specific configuration is limited, but the shift is generally interpreted as formation of a cathode-electrolyte interphase rather than bulk electrolyte degradation. The market relevance of VEC therefore rests less on bulk solvent properties and more on its ability to alter interfacial architecture at both electrodes during the first cycles.The formation efficiency of VEC-derived SEI is governed by the interplay of additive diffusion, electrochemical reduction potential, and radical polymerisation kinetics at the anode surface. In a graphitic anode with a potential of 0.2–0.8 V vs Li/Li⁺ during the first formation cycle, the vinyl group is reduced and initiates polymerisation before the bulk carbonate solvents undergo reductive decomposition. The resulting polymer network incorporates carbonate and lithium alkyl carbonate species, producing a mixed organic-inorganic deposit. The thickness of this deposit is typically controlled by the formation current density and the VEC concentration. At 0.5–1.5 wt%, the deposit is thin enough to provide passivation while maintaining interfacial impedance below 10 Ω cm² in coin cells with lithium reference electrodes. At 3.0 wt% and above, the polymer film thickens, charge-transfer resistance increases, and low-temperature discharge capacity may decline because lithium-ion transport through the film becomes rate-limiting. The standard methods used to track this behaviour include electrochemical impedance spectroscopy at 10 mHz–1 MHz with a perturbation amplitude of 5–10 mV, differential capacity analysis at C/20, and post-mortem X-ray photoelectron spectroscopy with depth profiling. Production-scale formation equipment is configured with dV/dt and dI/dt controls to terminate the first charge if the cell voltage deviates by more than ±2 mV from the formation curve, preventing lithium plating and non-uniform SEI growth. Batch-to-batch variance in VEC purity, particularly in residual vinyl carbonate oligomers, can shift the reduction peak by 20–40 mV and alter the SEI thickness; this is why cell manufacturers require purity above 99.5% and peroxide values below 10 mg kg⁻¹.In a typical electrolyte blending skid, VEC is added after the bulk carbonate solvents and LiPF₆ have been cooled to 5–15 °C to minimize thermal decomposition of the salt. The addition sequence is critical because VEC contains a vinyl group that can oligomerize in the presence of acidic degradation products generated when LiPF₆ hydrolyzes. Blending vessels are constructed from 316L stainless steel or fluoropolymer-lined carbon steel, fitted with polished surfaces to Ra ≤ 0.4 µm and sealed to exclude atmospheric moisture down to 10 ppm water in the headspace. The batch is circulated through a 0.2 µm PTFE filter and a molecular sieve drying loop until Karl Fischer titration per ASTM E203 reads ≤ 20 µg g⁻¹. At that point, viscosity is checked using a rotational viscometer per ASTM D7042; the target kinematic viscosity for a 1.0 M LiPF₆ in ethylene carbonate/ethyl methyl carbonate 3:7 wt% electrolyte with 1.0 wt% VEC is typically 2–4 mm² s⁻¹ at 25 °C, though the exact value shifts with solvent ratio and water content. The addition of VEC at 1 wt% does not materially alter the bulk viscosity, but at 5 wt% the viscosity may increase by 0.2–0.5 mm² s⁻¹, and cold-filling into cylindrical cells becomes more difficult because the electrolyte wetting rate of polyolefin separators follows Washburn kinetics. A production-scale filling line using vacuum pressure differentials of 50–90 kPa and a hold time of 10–30 min must be requalified if the VEC content is changed by more than 0.5 wt%, because the change affects the time constant for separator wetting and the onset of SEI formation during the first charge.In a blended carbonate electrolyte, the lithium cation solvation sheath is dominated by ethylene carbonate, with linear carbonates occupying the outer shell. The insertion of VEC, even at 1 wt%, modifies the shell only locally because the vinyl carbonate dipole competes for Li⁺ coordination. Nuclear magnetic resonance diffusion-ordered spectroscopy and electrochemical impedance measurements show that the bulk ionic conductivity at 25 °C remains within 8–12 mS cm⁻¹ for a 1.0 M LiPF₆ ethylene carbonate/ethyl methyl carbonate electrolyte, but the cation transference number can shift by 0.01–0.03. Pouch cells with 250 µm thick separators and 0.5 g of electrolyte per Ah require a minimum conductivity of 7 mS cm⁻¹ at 0 °C to avoid voltage sag during 2C discharge. The impact of VEC on low-temperature performance is therefore measured by impedance spectroscopy at -10 °C and -30 °C, with the charge-transfer resistance arc remaining below 50 Ω cm² for acceptable cold-cranking performance in automotive cells. In production-scale cells, the electrolyte fill amount is calculated from porosity measured by mercury intrusion porosimetry according to ISO 15901-1, and the electrolyte mass is controlled to ±0.5 g per cell. The VEC addition is confirmed by gas chromatography after filling, with a retention tolerance of ±0.1 wt% relative to the target formulation.When VEC concentrations exceed 3 wt% in electrolytes for LiNi₀.₈Mn₀.₁Co₀.₁O₂ based cells, several failure modes converge within a narrow processing window. The oxidation current at the cathode rises because the vinyl group is electrochemically active; cyclic voltammetry on aluminium current collectors shows an onset at 4.4–4.6 V vs Li/Li⁺, and the resulting polymerisation products deposit on the cathode surface, increasing impedance. In full cells with a capacity of 2–10 Ah, the voltage drop during discharge at 1C increases by 5–15 mV relative to 1 wt% formulations, and the low-temperature discharge capacity at -20 °C falls below 70% of the 25 °C capacity. The processing window for the formation cycle narrows to ±5 °C around 25 °C; at 30 °C, excessive SEI growth occurs, while at 20 °C the film formation is incomplete. Differential scanning calorimetry on the electrolyte with 3.5 wt% VEC shows a broad exotherm starting near 150 °C when the mixture is sealed in stainless steel pans, indicating that the additive contributes to the thermal runaway energy balance. Battery safety tests per IEC 62660-1:2018 and UL 1642 require that such exotherms remain below a cell-level onset temperature threshold, and formulations with excessive additive may fail nail penetration or overcharge tests. Lithium plating on graphite anodes is also observed at charging rates above 1C when the SEI is too thick and the anode surface overpotential shifts by 30–50 mV. Manufacturers therefore limit VEC to 2–3 wt% and blend it with fluoroethylene carbonate or vinylene carbonate at 0.5–1.5 wt% to achieve a passivation balance. Batch-to-batch tolerance in the additive weight percentage is held to ±0.05 wt% because the property cliff-edge is steep.The specification sheet for battery-grade vinyl ethylene carbonate typically lists purity, water, acidity, inhibitor content, and color as release parameters. The gas chromatographic purity is measured on a 30 m capillary column with a polyethylene glycol stationary phase and a flame ionization detector, with an area normalization method. Battery cell manufacturers generally require purity greater than 99.5%, but high-nickel cathode programmes often tighten the requirement to 99.9% for total unknown peaks. Water content is determined by coulometric Karl Fischer titration using ASTM E203 or ISO 760; the limit is typically ≤ 100 µg g⁻¹, and values above 200 µg g⁻¹ are rejected because water converts LiPF₆ to HF and POF₃. Acidity, expressed as HF equivalent, is measured by acid-base titration after extraction into ice-cold water and is limited to ≤ 20 µg g⁻¹. The inhibitor package is controlled to maintain storage stability, but excess inhibitor can interfere with electrochemical reduction at the anode and must be screened. The additive is supplied under the classification and labelling rules of EU Regulation (EC) No 1272/2008; REACH registration obligations apply by tonnage band, and battery electrolyte components fall under the operational scope of Directive 2006/66/EC for batteries and accumulators. A representative compliance checklist is shown below.ParameterTest methodTypical battery-grade limitUnitPurity by gas chromatographyGC-FID internal method under ISO 17025≥ 99.5%Water contentASTM E203≤ 100µg g⁻¹Density at 20 °CASTM D40521.18–1.20g cm⁻³Kinematic viscosity at 25 °CASTM D70424–8mm² s⁻¹ColorASTM D1209≤ 20APHABulk storage of vinyl ethylene carbonate presents a polymerisation risk that is managed through inhibitor concentration, temperature control, and inert headspace. The vinyl group can undergo radical polymerisation initiated by heat, light, or accidental contamination with peroxides. Inhibited grades are typically stabilised with 50–200 ppm of a phenolic inhibitor such as 4-methoxyphenol or 2,6-di-tert-butyl-4-methylphenol; some suppliers use nitroxide-based inhibitors to extend shelf life at elevated temperatures. The storage temperature is maintained below 25 °C, and the headspace oxygen concentration is kept below 5 vol% in nitrogen-blanketed tanks. Under these conditions, the shelf life is generally 6–12 months from the date of packaging. At temperatures above 35 °C, inhibitor consumption accelerates, and the hazard increases when the inhibitor is depleted to below 10% of the original concentration. Production-scale chemical plants monitor inhibitor content by UV-Vis spectroscopy or gas chromatography at monthly intervals and re-inhibit the tank if the concentration falls below the supplier-recommended minimum. The addition of VEC to electrolyte must occur after the bulk solvent has been dried, because water and acidic species can abstract the stabilizer and promote cationic oligomerisation. The exothermic polymerisation of vinyl ethylene carbonate can occur in a runaway scenario if the stabilizer fails; published data for this specific configuration is limited, and each storage facility must conduct accelerating rate calorimetry on the as-received lot to establish a site-specific emergency relief basis. Storage areas are therefore equipped with temperature alarms set at 25 °C, spill containment sized for 110% of the largest tank volume, and deluge systems designed for monomer fire exposure.In silicon-dominant anode evaluation programmes, VEC is typically assessed as a co-additive with fluoroethylene carbonate because the volume expansion of silicon particles demands a more elastic SEI than graphite. Silicon-based anodes can undergo 150–300% volumetric expansion during lithiation, and a brittle SEI fractures, exposing fresh surface and consuming electrolyte. The poly(VEC) layer is thought to provide some mechanical compliance, but the film formed by VEC alone is not sufficient to suppress continuous electrolyte reduction when the silicon content exceeds 20 wt% in the anode. Coin-cell cycling with 0.5 mA cm⁻² lithium-limited half-cells shows that the addition of 1 wt% VEC to 10 wt% fluoroethylene carbonate in 1.0 M LiPF₆ ethylene carbonate/ethyl methyl carbonate improves capacity retention at cycle 100 by a few percentage points relative to fluoroethylene carbonate alone, but the benefit is sensitive to binder chemistry. In water-based polyacrylic acid binder systems, the VEC-derived SEI interacts with the binder at the particle surface, and too much VEC can increase the first-cycle irreversible capacity because the reduction of the vinyl group consumes lithium from the cathode. The formation protocol for silicon-containing anodes often uses a constant voltage hold at 0.05 V vs Li/Li⁺ for 2–4 h to complete the SEI without plating lithium. In this process, the addition of VEC shifts the voltage plateau of the first lithiation by 10–20 mV, which must be compensated in the charge controller. Production-scale electrode lines with slot-die coaters and calender temperatures of 80–120 °C do not expose the electrolyte to the anode; however, the residual carbonate in the electrode film can react with the electrolyte during cell filling, and this boundary condition is not routinely characterized. Published data for this specific configuration is limited, particularly for large-format cells above 50 Ah.Thermal degradation pathways in LiPF₆-carbonate electrolytes containing vinyl ethylene carbonate are dominated by the hydrolysis products of the conducting salt and the ring-opening chemistry of the cyclic carbonate. The addition of VEC does not eliminate the steady generation of HF and POF₃ in the presence of trace water; rather, the vinyl group provides a sacrificial reaction site that can intercept radical species and acidic degradation products before they attack the cathode surface. In sealed ampoule tests at 60 °C for 7 days, the color of a 1.0 M LiPF₆ ethylene carbonate/ethyl methyl carbonate electrolyte containing 2 wt% VEC shifts from clear to pale yellow, and the acid number increases from ≤ 10 µg g⁻¹ to 30–50 µg g⁻¹. At 85 °C, the same composition develops brown discolouration and the total gas volume increases, requiring pressure-rated storage containers. Differential scanning calorimetry on the electrolyte in stainless steel pans shows that the onset of the main decomposition exotherm shifts with VEC concentration; formulations with 0.5 wt% VEC tend to show an onset near 200 °C, while formulations with 3 wt% VEC may show an onset near 180 °C, subject to scan rate and pan conditions. The kinetic parameters reported in academic studies vary widely, with apparent activation energies for the first exothermic event in the range 80–120 kJ mol⁻¹; however, published data for this specific configuration is limited. In cell-level safety tests, the presence of VEC at 1–2 wt% does not eliminate the risk of thermal runaway, and the cell design must still include current interrupt devices, positive temperature coefficient elements, and ceramic-coated separators. The additive is therefore evaluated in conjunction with UN 38.3 transport tests, IEC 62619:2022 safety requirements for industrial applications, and GB 38031-2020 for electric vehicle traction battery safety, with thermal abuse testing at 130 °C.Under production-scale qualification, LFP/graphite cells containing VEC are subjected to a formation protocol that differs materially from that used for lithium-nickel-manganese-cobalt oxide cells because the upper cutoff voltage is lower. In LFP cells, the formation upper voltage is commonly set at 3.65–3.80 V, and the VEC reduction occurs on graphite during the first charge with minimal cathode oxidation interference. The cell manufacturer may therefore qualify a single VEC concentration at 1.0 wt% for LFP/graphite packs destined for energy storage systems, whereas electric vehicle cells with high-nickel cathodes require a blend of VEC with other film-forming additives. The test sequence for a fixed VEC lot includes cycle life testing at 25 °C and 45 °C with charge rates of 0.5C–1C, direct current internal resistance measurement at 50% state of charge, and self-discharge monitoring over 28 days. Production-scale cell assembly equipment with winding mandrels of 2–4 mm diameter and enclosure welding under dew point ≤ -40 °C is particularly sensitive to electrolyte viscosity drift, which is why the blend is held at 20±2 °C during filling. The final cell acceptance criteria follow IEC 62660-1:2018 for capacity, energy, and internal resistance, with destructive analysis reserved for first-article qualification. For gel polymer electrolyte membranes that incorporate VEC, tensile properties are measured after conditioning at 23 °C and 50% relative humidity using ASTM D638-14 Type V specimens; however, published data for this specific membrane configuration is limited, and the migration of VEC within the polymer matrix remains an operational boundary that must be characterized for each cell design.

Vinyl ethylene carbonate (VEC, CAS 4427-96-7; 4-vinyl-1,3-dioxolan-2-one, molar mass 114.10 g/mol) is introduced into carbonate-based non-aqueous electrolytes as a solid electrolyte interphase (SEI) precursor in high-nickel LiNi0.8Mn0.1Co0.1O2 (NMC811)/graphite pouch cells and cylindrical cells. In production-scale electrolyte blending, VEC is typically dissolved at mass fractions of 1–5 wt% into a 1 M LiPF6 EC:DMC (3:7 w/w) base electrolyte that has been dehydrated to a water content below 10 ppm, as determined by coulometric Karl Fischer titration per ASTM E1064. The compound is added after LiPF6 dissolution and after the bulk temperature has been reduced to 20±5 °C, because the vinyl substituent is susceptible to thermally and free-radically initiated polymerization during high-shear mixing. In NMC811/graphite full cells, the primary performance requirement is suppression of transition-metal dissolution at the cathode and stabilization of the anode SEI during high-temperature storage and cycling. Full-cell capacity retention is assessed according to IEC 62660-1:2018 performance testing, with cells cycled at 1 C between 3.0 V and 4.2 V at 45 °C. Published data for VEC in this exact cathode configuration is limited; however, analogous vinylene carbonate systems indicate that SEI-forming additives reduce capacity fade by 5–15 percentage points over 500 cycles when added at 2 wt%, provided formation current density is held below 0.1 C for the first cycle. The operational boundary is that VEC loadings above 3 wt% commonly increase the post-formation charge-transfer resistance, as measured by electrochemical impedance spectroscopy at 1 kHz, and may reduce 10 C discharge rate capability below 80% of the 0.2 C capacity under ISO 12405-4 test profiles.Linear sweep voltammetry on platinum working electrodes at a scan rate of 1 mV/s in 1 M LiPF6 EC:EMC (3:7 w/w) containing 2 wt% VEC shows an oxidation onset that is influenced by residual water, LiPF6 hydrolysis products, and electrode surface condition; published data for this specific configuration is limited. The reductive decomposition of VEC occurs at potentials positive of graphite intercalation, producing a poly(vinyl ethylene carbonate)-based organic layer mixed with LiF, Li2CO3, and lithium alkoxides. This interphase is characterized by X-ray photoelectron spectroscopy using monochromatic Al Kα radiation at 1486.7 eV with argon ion sputtering. In graphite full cells, the electrochemical window of the VEC-derived interphase is not defined by a single potential but by the rate of charge consumption and gas evolution during formation. Pouch cells with headspace gas sampling analyzed by gas chromatography with thermal conductivity detection show that VEC can suppress H2 and CO2 evolution compared with additive-free electrolyte when formation is conducted at 0.05 C and 25 °C; published data for exact gas volumes is limited. The limitation is that VEC-derived poly(vinyl ethylene carbonate) is less thermally stable than inorganic LiF-rich SEI components. High-temperature storage at 60 °C for 7 days under IEC 62660-2:2018 storage testing can induce decomposition and increase cell impedance by 10–25% relative to post-formation values, depending on the base electrolyte and moisture content. The operational boundary is that cells containing VEC should not be exposed to open-circuit voltages above 4.35 V for prolonged periods in high-nickel systems unless the base electrolyte contains a suitable oxidation-stable co-solvent such as fluoroethylene carbonate or adiponitrile; otherwise VEC decomposes on the cathode side and generates CO2.In silicon monoxide (SiOx)/graphite composite anodes with a silicon content of 5–15 wt%, volume expansion during lithiation generates mechanical stress that fractures a rigid LiF-rich SEI, exposing fresh silicon surfaces and consuming electrolyte. VEC is introduced into the baseline 1 M LiPF6 EC:EMC electrolyte at 2 wt% to form a polymeric SEI with higher strain-to-failure than LiF-rich interphases. Cyclic voltammetry on SiOx working electrodes at 0.05 mV/s in half cells with lithium counter electrodes shows that VEC reduction begins before 0.8 V versus Li/Li+ and generates a polymer-like deposit. Pouch cells with 10 wt% SiOx/90 wt% graphite anodes and NMC811 cathodes are cycled under IEC 62660-1:2018 at 1 C between 2.8 V and 4.2 V at 25 °C. Published data for VEC in this configuration is limited; analogous vinylene carbonate and fluoroethylene carbonate systems show that 2 wt% additive can reduce capacity fade by 8–12 percentage points after 300 cycles compared with additive-free electrolyte. The practical limitation is that VEC alone is insufficient for silicon loadings above 10 wt%, and gas evolution during the initial charge increases when VEC is combined with LiFSI-based salts because of aluminum current collector corrosion at high potential. In production-scale pouch cell assembly, electrolyte filling with VEC-containing formulations requires a vacuum pulse profile of −80 kPa for 90 s followed by a 30 s atmospheric dwell to achieve uniform wetting of silicon-containing electrodes; incomplete wetting is detected by post-formation electrochemical impedance spectroscopy at 1 kHz showing impedance variance greater than 10% across 10 cells.Application configurationVEC mass fractionBase electrolyteAnode / cathodeTest designationHigh-nickel NMC pouch cell2 wt%1 M LiPF6 EC:EMC (3:7 w/w)Graphite / NMC811IEC 62660-1:2018SiOx/graphite pouch cell2 wt%1 M LiPF6 EC:EMC (3:7 w/w)10 wt% SiOx-graphite / NMC811IEC 62660-1:2018LiFSI high-voltage system2 wt%1 M LiFSI EC:EMC (3:7 w/w)Graphite / NMC811IEC 62660-2:2018, ASTM G31-21Lithium metal half-cell2 wt%1 M LiFSI DME/TTELi / CuISO 12405-4Production-scale electrolyte blending of VEC requires strict control of temperature, moisture, and free-radical initiation. VEC is a vinyl monomer and can undergo thermal radical polymerization if the inhibitor package is depleted or if the bulk temperature exceeds the supplier-stated maximum handling temperature. Safety data sheets commonly specify refrigerated storage at 2–8 °C under inert atmosphere and avoid contact with peroxides, azo compounds, and strong oxidizers. In a 500 L glass-lined jacketed blending vessel equipped with a PTFE-coated anchor agitator, VEC is introduced at a rate not exceeding 0.5 L/min into a pre-cooled carbonate solvent blend at 15–20 °C; the addition rate is limited by the heat of mixing and the potential for localized hot spots. The process window for neat VEC addition is typically 15–25 °C; excursions above 30 °C may initiate polymerization, particularly if the inhibitor content is below 100 ppm. Viscosity increase is measured during blending by an inline rotational viscometer with a shear rate of 10 s−1; a viscosity rise greater than 5% from baseline indicates oligomerization. Kinematic viscosity of the finished electrolyte at 25 °C is determined by ASTM D445; values above 4.2 mm²/s may indicate oligomer formation. Peroxide content is monitored by iodometric titration; values above 5 ppm in the final electrolyte are considered unacceptable for NMC811/graphite cells. Batch-to-batch variance in inhibitor concentration is a known production bottleneck; two batches with identical mass fraction can exhibit different formation behavior if the inhibitor level differs by more than 25 ppm. The electrolyte is typically filtered through a 0.2 µm PTFE membrane after blending to remove any microgel particles; a pressure drop increase across the filter above 0.3 bar at a flow rate of 20 L/min triggers a batch rejection. Published data for exact polymerization onset temperatures of VEC in carbonate solutions is limited, but the practical processing window is narrow because the vinyl group is inherently reactive. Electrolyte stability during storage is assessed by high-performance liquid chromatography with ultraviolet detection at 254 nm; a decrease in VEC peak area greater than 2% after 30 days at 25 °C indicates premature polymerization. The operational boundary is that VEC-containing electrolytes should not be heated above 30 °C during vacuum degassing or filling, and storage at elevated temperature is not recommended unless the electrolyte is continuously sampled for viscosity and peroxide content.Lithium bis(fluorosulfonyl)imide (LiFSI) is increasingly specified in next-generation electrolytes because of lower impedance and improved low-temperature performance compared with LiPF6, but LiFSI corrodes aluminum current collectors at potentials above 3.9 V vs Li/Li+. VEC is evaluated as a film-forming additive to passivate the aluminum surface and to reduce the corrosion current density. Linear sweep voltammetry on aluminum working electrodes at 1 mV/s in 1 M LiFSI EC:EMC (3:7 w/w) with 2 wt% VEC shows a corrosion current density that depends on water content and scan rate; published data for VEC in this exact configuration is limited. The passivation mechanism involves oxidative polymerization of the vinyl group on the aluminum surface, forming an organic film that blocks continued electrolyte decomposition. In NMC811/graphite pouch cells with LiFSI electrolyte, VEC at 2 wt% is reported to reduce high-temperature storage impedance growth at 60 °C for 7 days under IEC 62660-2:2018, but the effect is concentration-dependent and cliff-edged: at 3 wt% the impedance can increase rather than decrease due to excessive film thickness. The processing boundary is that LiFSI and VEC should not be pre-mixed as neat liquids because the highly polar LiFSI can accelerate vinyl polymerization; VEC is always added after LiFSI is fully dissolved and cooled. The combination also requires moisture control below 10 ppm because LiFSI hydrolysis produces fluorosulfonic acid, which can attack the poly(vinyl ethylene carbonate) film. Equipment compatibility testing is conducted according to ASTM G31-21 for static immersion corrosion; aluminum samples show negligible pitting when the electrolyte contains 2 wt% VEC and 1 M LiFSI, but published data for longer than 30 days is limited.Lithium metal and anode-free cells impose the most demanding SEI requirements because the anode undergoes infinite volume change during plating and stripping, and any SEI fracture consumes active lithium and solvent. VEC is under evaluation as a diluent or co-solvent in localized high-concentration electrolytes for lithium-metal cells because the vinyl group can form a polymer network within the SEI that resists crack propagation. Cyclic voltammetry with lithium symmetric cells in 1 M LiFSI DME/TTE (1:1.2 by weight) containing 2 wt% VEC at 0.5 mV/s shows that VEC shifts the nucleation overpotential by less than 5 mV; published data for Coulombic efficiency in anode-free configurations is limited. The practical limitation is that VEC is not compatible with lithium metal anodes if the electrolyte contains unreacted vinyl groups because continued reduction at low potential forms oligomers that increase interfacial resistance. Copper half-cells for Coulombic efficiency testing are assembled with 50 µL of electrolyte, a lithium counter electrode, and a copper working electrode; the test protocol consists of 20 cycles of plating at 1 mA/cm² and stripping to 1 V at 25 °C, following ISO 12405-4 cycle test conditions. The turnover condition is that VEC loadings above 3 wt% cause a rapid increase in interfacial resistance and reduce the average Coulombic efficiency below 98% due to continuous SEI formation, whereas the target for lithium metal is above 99.5% over 100 cycles. Published data for VEC in anode-free cells is insufficient to specify a universal concentration; cell developers should validate each electrolyte using a fixed-current protocol with a lithium inventory of 4 mAh/cm² and a cathode areal capacity of 4.2 mAh/cm².