Preparation of Artificial SEI Containing LiNxOy on Lithium Metal Anode By Solid-Gas Interface Reaction for Sulfolane Electrolyte

Abstract

Li-S battery is promising next generation energy storage device, and lithium metal anode is promising electrode due to its low electrochemical potential and high theoretical specific capacity. However, the Li metal anode in Li-S battery has problems such as short circuit by growth of dendrite and low coulombic efficiency by continuous electrolyte decomposition. In past study, it was reported that high concentration sulfolane electrolyte attributed to prevent polysulfide dissolution into electrolyte and suppressed shuttle effect.1) Also, by adding LiNO3 into electrolyte, stable passivation film formed on lithium metal anode, and lithium deposition became rounded shape and dendrite was suppressed, and long life was reported to be achieved.2)3) While LiNO3 does not dissolve much in high concentration sulfolane electrolyte, in this study, in order to achieve the effect of LiNO3 even with high concentration sulfolane electrolyte, artificial SEI including LiNxOy made by solid-gas reaction was examined. Solid-gas reaction is considered to have also the advantage for the mass production.In order to produce artificial SEI containing LiNxOy on Li metal anode, which is LiNO3-derived component, polished Li foil was exposed to NO2 gas for 1 h. For the purpose of reacting fresh Li metal surface with NO2 gas, surface of Li foil was polished until metallic luster appeared.Fig. 1 shows XPS spectra (N1s) of polished Li and NO2 exposed Li. Fig. 1 shows the existence of LiNxOy by an exposure to NO2.Fig. 2 shows charge-discharge curves in Li/Li symmetrical cells. Fig. 2(a) shows charge-discharge curve using the polished Li, and Fig. 2(b) shows the one exposed to NO2. In Fig. 2(a), short circuit was recognized by only 5 cycles of charge and discharge. Contrastingly, analogous voltage profile was obtained for 16 cycles, as shown in Fig. 2(b). In addition, from Fig. 2(b), a larger overvoltage in voltage plateau was confirmed than that in Fig. 2(a). The reason is considered to be that Li electrode surface is covered with artificial SEI composed of inorganic components such as LiNxOy having relatively high ionic resistance. In addition, it was suggested that the artificial SEI improved the morphology of lithium deposition to smoother one from the SEM investigation.With an exposure to NO2 on Li metal anode, it was confirmed that artificial SEI containing LiNxOy was prepared and contributed to a certain improvement in cycle life in Li/Li symmetrical cell. Acknowledgement This work was partly supported by Advanced Low Carbon Technology Research, Development Program Special Priority Research Area “Next-Generation Rechargeable Battery” (ALCA-Spring) from the Japan Science and Technology Agency (JST) (Grant Number JPMJAL1301). Reference 1) Azusa Nakanishi et al, Phys. Chem. C, 2019, 123, 14229-142382) Allen Pei et al, Nano Lett. 2017, 17, 2, 1132-11393) Doron Aurbach et al, J. Electrochem. Soc., 2009, 156, A694 Figure 1