Electrolyte additives are the leverage point of cell engineering — a few weight-percent of the right molecule rebuilds the SEI, raises the flash point, widens the voltage window, or steers selectivity at a CO2RR cathode without redesigning the electrolyte. This collection groups the small-volume, high-impact compounds we stock for battery, supercapacitor, and aqueous-electrolyzer research, organized by chemical family so you can pick by mechanism rather than by trade name.
Film-forming carbonates and sultones
Fluorinated and cyclic carbonates dominate SEI engineering on silicon, lithium-metal, and high-voltage layered cathodes. FEC is the reference fluorinated cyclic carbonate for accommodating large volume changes on Si and Li-metal anodes; FEMC is its linear analog, used as a co-solvent that lowers flammability and stabilizes high-voltage CEIs. Cyclic sulfur additives — 1,3-propane sultone family members such as 1,4-butane sultone (BS), and the sulfate-ring additive DTD (ethylene sulfate) — reduce preferentially on graphite, LTO, and silicon anodes to build dense, ionically conductive interphases. Succinic anhydride (SA) plays a complementary cathode-side role by passivating reactive surface oxygen on Ni-rich layered and high-voltage spinel chemistries.
Salts, polyelectrolytes, and sodium-ion additives
Borate and sulfonate additives tune interphase chemistry beyond carbonate solvents. NaBOB is the sodium analog of LiBOB, dissolved at low loading to stabilize both the anode SEI and the cathode CEI in sodium-ion cells. PSS (polystyrene sulfonate) appears here as a water-soluble, ionically conductive polyelectrolyte used as a binder/additive that lowers electrode resistance versus PVDF. Phenyl disulfide (PDS) is a redox-mediator additive used in Li-S, Li-CO2, and CO2RR systems to cleave polysulfides and shuttle electrons at the catalyst interface.
Flame retardants and ionic liquids
Phosphate and phosphonate additives such as DMMP scavenge combustion-chain radicals and are blended at single-digit weight-percent to push electrolyte flash points up. Imidazolium ionic liquids — [EMIM][TFSI] and [BMIM][TFSI] — serve as non-flammable, low-vapor-pressure co-solvents for Li-ion, Na-ion, and supercapacitor electrolytes, and as wide-window solvents for fundamental electrochemistry. CTAB is included as a cationic surfactant additive used in CO2RR electrolytes to reorganize interfacial water and suppress the parallel hydrogen evolution reaction.
If you are formulating an SEI for silicon or lithium-metal anodes, start with the fluorinated carbonates and sultones. For high-voltage layered cathodes, pair a sulfate or anhydride with a film-forming co-solvent. For CO2RR or Li-S work, see the redox-mediator and surfactant entries. Browse related sections under Electrolytes and Solvents.
