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All Solid State Lithium–Sulfur Battery Using a Glass-Type P2S5–Li2s Electrolyte
Lithium-sulfur battery has attracted great attention since its electrochemical process, i.e. 16Li + S8 = 8Li2S, theoretically provides a specific energy of 2500 Wh Kg-1 much larger than the 650 Wh Kg-1 of the conventional lithium battery presently offered by the market and largely used in the electronic devices. However, to realize the practical battery based on the sulfur cathode, its red-ox shuttle of polysulfide originated in the dissolution into the organic electrolyte is strongly required to prevent for improving the charge/discharge cycle ability. On the contrary, solid state sulfide electrolytes are of considerable practical concern in these days. Application of a solid-state ion conductor is one of promising candidates for avoiding the red-ox shuttle due to the dissolution of polysulfide in Li-S battery. Its applicability of Li2S-P2S5 based solid electrolyte to the sulfur cathode has been reported using Li-In alloy for the anode1). To obtain higher energy density, we adopted pure Li and verified its applicability to the all solid-state Li-S battery.
Experimental
A solid state lithium ion conductor was prepared by using high energy ball milling method. Li2S:P2S5=80:20 mol% (SE) was adopted. A coin cell, 2032 was prepared by stacking and compressing Li foil, SE, and sulfur/MCMB(50:50wt%) mixture. The loading level of net sulfur was approximately 0.9mgcm-2. Another cell configuration, a compression metal cell was also used for verifying the electrochemical performances. The electrochemical measurements were mostly performed at 80 oC. The details are given in our previous paper2).
Results and Discussion
The Li/Li2S–P2S5/S-MCMB cell was prepared and its electrochemical characteristics were evaluated by Galvanostatic charge discharge cycle at 80 °C. The average discharge potential was approximately 2.1 V and a cycling capacity of 400 mAh g−1 at a C/20 rate was observed. The cycling tests show ca.100% Coulombic efficiency and stable capacity. However, only 25% of the theoretical capacity of the sulfur electrode was obtained in this system, because of the high resistance of the solid–solid interface at the cathode side and the associated ohmic polarization during cycling. Nevertheless, the very stable capacity of 400 mAh g−1 at a working voltage of 2.1 V results in a theoretical energy density of 840 Wh kg−1, In addition, the solid cell here reported is characterized by very high safety level, since the cell is completely based on solid-state. The details of the electrochemical characteristics on anode and cathode including recent progress are given in the poster.
1) M. Nagao, A. Hayashi, M. Tatsumisago, J. Mater. Chem. 22 (2012) 10015–10020
2) M. Agostini, Y. Aihara, T. Yamada, B. Scrosati, J. Hassoun, Solid State Ionics 244 (2013) 48–51