Electrodeposition of Lithium in LiPF6-Based Electrolyte with Trace-Amount of Water

Abstract

Lithium metal has been considered as an attractive candidate of the anode material for the next-generation secondary batteries because of its high theoretical capacity and low redox potential. Among a lot of strategies in order to suppress the inhomogeneous or dendritic growth of lithium during deposition have been proposed so far, some reports suggested that the trace-amount of water leads to smooth the morphology of deposited lithium metal. (1, 2) However, the relationship between the morphology of deposited lithium metal and the content of the electrolyte which changes with the time after addition of the water is not clear. In the present study, we investigated the electrodeposition of lithium in LiPF6-based electrolyte with trace-amount of water. Especially, we focused on the change of the morphology and surface state of the deposited lithium metal with the content of the electrolyte. 100 ppm of water was added into 1.0 mol dm–3 LiPF6 in propylene carbonate (PC) in the Ar-filled glove box and temporal change of its water content was checked by Karl-Fischer titration method. The water content was gradually decreased with time due to the reaction of LiPF6 and water. (3) When the electrodeposition of lithium was conducted on the copper electrode in the electrolyte, the morphology of the deposited lithium changed from inhomogeneous to granular and smooth as time passes after addition of water. This result proposed that the decomposed product in the electrolyte was strongly affected to the morphology of the deposit. (4) We also checked the surface state of the deposits by auger electron spectroscopy, X-ray and hard X-ray photoelectron spectroscopy, suggesting that the component of the film greatly influences the morphology of the deposit. Acknowledgement This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) under the “Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2)” References J. Qian, W. Xu, P. Bhattacharya, M. Engelhard, W. A. Henderson, Y. Zhang and J.-G. Zhang, Nano Energy, 15, 135 (2015).H. Koshikawa, S. Matsuda, K. Kamiya, Y. Kubo, K. Uosaki, K. Hashimoto and S. Nakanishi, J. Power Sources, 350, 73 (2017).D. Strmcnik, I. E. Castelli, J. G. Connell, D. Haering, M. Zorko, P. Martins, P. P. Lopes, B. Genorio, T. Østergaard, H. A. Gasteiger, F. Maglia, B. K. Antonopoulos, V. R. Stamenkovic, J. Rossmeisl and N. M. Markovic, Nature Catalysis, 1, 255 (2018).K. Kanamura, S. Shiraishi and Z. Takehara, J. Electrochem. Soc., 143, 2187 (1996).