In Stockholm, Arfwedson knew the chemist Jöns Jakob Berzelius and received access to his private laboratory, where he discovered the element lithium in 1817, during analysis of the mineral petalite.
U Stockholmu je Arfwedson poznavao Jönsa Jakoba Berzeliusa te je dobio pristup njegovom privatnom laboratoriju, gdje je 1817., tijekom analize minerala petalita, otkrio kemijski element litij.