An In Situ Small-Angle X-Ray Scattering Study of Sodium Insertion into a Nanoporous Carbon Anode Material within an Operating Electrochemical Cell

An electrochemical cell with beryllium X‐ray windows has been designed and used for in situ small‐angle X‐ray‐scattering studies of operating electrodes for the first time. This cell is ideally suited to the study of the filling of nanoscopic pores in solids by electrochemically transported atoms. The mechanism of electrochemical lithium and sodium insertion in nanoporous carbonaceous materials has been the subject of some recent controversy, which is resolved by the studies reported here. We show indisputable evidence that the filling of the pores accounts for all the sodium (and lithium) inserted into these carbons at a chemical potential near that of metallic sodium (or lithium). At lower chemical potential (higher cell voltage), sodium (or lithium) is inserted between graphene layers in an intercalation mechanism. © 2000 The Electrochemical Society. All rights reserved.