In Situ Observation of Electrodeposition of Li on Pt and Ni Substrates in Organic Electrolyte
To investigate the effect of current density on Li deposition morphology, potentiodynamic and galvanostatic polarization measurements were conducted. Pt and Ni substrates were mechanically polished with SiC paper through 1500 grit, and then polished down to 1 µm using diamond paste. The counter electrode was a Pt wire. The reference electrode was Li. 1 M LiPF6 EC:DMC(1:1 vol%) was used as the electrolyte. The electrode surface area was around 95mm2. The current density for the galvanostatic experiment was varied from 0.1 to 2.0 mA/cm2, and the electrochemical deposition of Li was performed at constant charge (3.6 C/cm2). Surface observations were conducted by an optical microscope and a laser microscope. All electrochemical measurements were carried out in a glove box filled with argon.
Figure 1 shows the cathodic polarization curves of Pt and Ni substrate. The increases in cathodic current densities were observed at around 0 V(vs.Li/Li+), indicating that the electrodeposition of Li proceeded at the potential range less than 0 V. Figure 2 shows the laser microscope images of the electrode surfaces after the galvanostatic polarization measurements. The surface of Li deposited on Ni was smooth compared with that on Pt. In particular, non-uniform deposition was observed at 0.1 and 2.0 mA/cm2 on the Pt substrate. In the case of the Ni substrate, a more uniform deposition was observed at lower current density.