Micromorphological Studies of Lithium Electrodes in Alkyl Carbonate Solutions Using in Situ Atomic Force Microscopy

The morphology of lithium electrodes in a variety of alkyl carbonate solutions was studied using in situ atomic force microscopy (AFM). We made use of a workstation specially built for the study of highly reactive electrochemical systems by AFM and other scanning probe techniques, based on an evacuable, vibration-protected glovebox. The electrolyte solution used was composed of propylene carbonate (PC), mixtures of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and Li salts from the following list: LiPF6, LiClO4, LiAsF6, LiN(SO2CF3)2, LiN(SO2CF2CF3)2, and LiC(SO2CF3)3. We studied the effect of solution composition, prolonged storage, Li deposition, and dissolution at low and high current densities. The AFM imaging of these systems shows the complicated morphology of the Li electrodes that depend on the solution composition. We were able to clearly follow the nonuniform nature of Li deposition and dissolution in these systems. We were also able to follow by in situ AFM imaging critical events such as the onset of dendrite formation and the breakdown and repair of the surface films on lithium during Li dissolution at high current densities. The basic morphology of Li electrodes in alkyl carbonate solutions and the condition for the reversible behavior of Li electrodes is discussed.