The experiments of Li electrodeposition and stripping on single crystal Cu current collectors were conducted in a three-pole cell. The orientation of Cu are (111), (101), and (001). Counter and reference electrodes are both Li metal. Prior to experiments, the crystal orientation of collectors was analyzed by electron backscatter diffraction (EBSD). An electrolyte is consisted of 1 M LiPF6 in EC:EMC=5:5. Li was deposited at a current density of 0.5 mA/cm2 with charge capacity of 0.1 mA/cm2. Subsequently, the Li was stripped at same current density with 0.05 mA/cm2. Cyclic voltammetry was performed at a scan rate of 5.0 mV/s. SEM analysis was also conducted to examine Li morphology.
Figure 1 shows cyclic voltammograms of Li deposition and stripping on various Cu collectors. Negative and positive peaks represent Li deposition and stripping respectively. Each peak current decreases substantially as cycle proceeds, probably because of the development of the resistive SEI layer. The smallest overpotential for the first Li deposition was observed in Cu(111), followed by Cu(101) and Cu(001). Uniform formation of the resistive layer expectedly causes this since the SEM analysis revealed that Li morphology on Cu(111) is the most homogeneous. Moreover, Cu(111) delivered the lowest and the most stable overpotential over 10 cycle, while those in the other cases are larger and increase as the cycle progress. Therefore, it can we concluded that crystal orientation of collectors is an important factor for Li metal batteries and Cu(111) is effective for high cycle stability.
References
[1] B. J. Neudecker, et. al., J. Electrochem. Soc. 2000, 147(2), 517-523.
[2] J. Qian, et. al., Adv. Funct. Mater. 2016, 26, 7094-7102.
[3] K.Ishikawa, et. al., Cryst. Growth Des. 2017, 5, 2379-2385.