Sodium methanesulfonate is an organic sodium salt with the chemical formula CH3SO3Na. It is a white crystalline solid that is highly soluble in water and polar organic solvents. This compound is characterized by its strong ionic nature and stability, derived from the methanesulfonate anion. Its primary industrial application is as an electrolyte additive in lithium-ion batteries. It functions to improve the stability of the solid electrolyte interphase (SEI) on the anode, particularly under high-voltage or high-temperature operating conditions. This enhancement contributes to increased battery cycle life and safety. Beyond energy storage, it serves as a versatile intermediate and reagent in organic synthesis, often used in reactions where a non-nucleophilic counterion or a source of the methanesulfonate group is required. While generally stable under normal conditions, it should be handled with standard laboratory precautions to avoid inhalation of dust and contact with eyes and skin. Its role as a functional additive in advanced battery systems represents its most significant and growing market application.