Used primarily as a chlorinating agent in organic synthesis, converting alcohols to alkyl chlorides and carboxylic acids to acyl chlorides. Commonly employed in the production of pharmaceuticals, agrochemicals, and specialty chemicals where chlorine introduction is required. Also utilized in the manufacture of lithium-thionyl chloride batteries due to its role as a cathode material, offering high energy density and long shelf life. Handles moisture-sensitive reactions effectively because it reacts vigorously with water, making it useful for drying gases and dehydrating metal chlorides. Requires careful handling due to high reactivity and corrosive by-products.