Interfacial Lithium-Ion Transfer Between Graphite Negative Electrode and Sulfide Solid Electrolyte

Abstract

Introduction All-solid-state lithium secondary batteries using inorganic solid electrolytes instead of liquid electrolytes have been expected as next-generation secondary batteries with high safety and high reliability. Among the inorganic solid electrolytes, sulfide-based solid electrolyte such as Li2S-P2S5 based glass solid electrolyte has received much attention due to the high lithium-ion conductivities and room temperature pressure sintering [1]. Graphite has been used as the negative electrode materials in commercial lithium-ion batteries, and the improvement in interfacial lithium-ion transfer reaction between graphite and liquid electrolyte is recognized as an important issue and this issue should be considered in all-solid-state lithium secondary batteries. In this study, interfacial reaction between graphite and sulfide solid electrolyte was investigated. Experimental A layered electrolyte consists of 75Li2S-25P2S5 glass pellet and 1 mol dm-3 LiClO4/propylene carbonate (PC) was used in order to use lithium metal electrode as reference electrode. A three-electrode cell was assembled by using graphite sheet as working electrode, lithium metal as counter and reference electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy were carried out. Results Figure 1 shows the cyclic voltammogram of the three-electrode cell using graphite sheet as working electrode. An oxidation-reduction current was observed between 0 – 0.5 V (vs. Li/Li+). Since lithium ion cannot intercalate into graphite sheet in LiClO4/PC, this oxidation-reduction peak indicates that lithium-ion intercalation/de-intercalation proceeded at the interfacial between graphite sheet and 75Li2S-25P2S5 glass pellet. In the Nyquist plot, one semi-circle was observed and assigned to interfacial lithium-ion transfer process. In the meeting, the activation energy for the interfacial lithium-ion transfer process will be discussed. Reference [1] A. Sakuda et al., Sci. Rep., 3, 2261 (2013). Acknowledgement This work was financially supported by ALCA-SPRING of the JST. Figure 1