Preparation of Pre-Lithiated Sulfur Cathode By an in Situ Contacting Reaction

There is an increasing demand for the development of a new kind of secondary battery with high capacity and long cycle life. The sulfur cathode with the theoretical capacity of 1672 mAh/g (sulfur) has attracted researchers' attention. 1 However, the Li-S batteries faces huge challenges because of the capacity fading caused by the polysulfide's shuttle effect and the safety issues caused by the lithium metal. Recently, researchers were attracted on the fabrication of metallic lithium free battery with the lithiated sulfur cathode. 2 However, due to the high sensitivity of lithium sulfide (Li 2 S) to the moisture of air, this method have to be taken completely in an inert atmosphere, which raises the manufacturing cost and obstruct the access to commercialization. Consequently, it is urgent to introduce a new way to fabricate the lithiated sulphur cathode to meet the application requirement. Herein, we prepared Li 2 S/KB cathode by an in situ synthesis method under the protection of ion-selective polypyrrole (PPy) layer. The anion doped PPy layer was deposited by electrodeposition method on S/KB cathode. 3 The layer by layer structure of the cathode was proved by SEM analysis of the cross-section image (showed in Figure 1a). A lithium source was used to contact with the cathode in a wet environment and the lithium ions will go to the cathode by diffusion. The product of pre-lithiation was confirmed to be amorphous Li 2 S by XPS and XRD analysis. As Figure 1b shows, the first charge capacity can reach 1153 mAh/g (sulfur) at 0.1C rate after paired with a Li foil anode. This Li 2 S/KB cathode can be coupled with lithium free anode, such as graphite, Si to form a lithium free battery. Figure 1. (a) Cross section FE-SEM image of the S/KB/PPy cathode. Inset is the FE-SEM image of the PPy layer of the S/KB/PPy cathode. (b) The charge and discharge of the pre-lithiated cathode at a charge rate of 0.1C. Furthermore, the thickness of PPy was proved to influence the cyclability and capacity of the coin type cell. With the help of PPy, the shuttle effect will be alleviated by the ion-selective property of the PPy layer. Additionally, the lithiated S/KB cathode can be exposed to air for a short time because of the protection of PPy layer. We believe these properties of the lithiated S/KB cathode will provide possibility to assemble Li 2 S battery in air atmosphere and pave way to commercialization. Acknowledgement This work is supported by Advanced Low Carbon Technology Research and Development Program (JST-ALCA) Special Priority Research Area "Next-generation Rechargeable Battery”. References 1. Manthiram, A.; Fu, Y.; Chung, S. H.; Zu, C.; Su, Y. S. Chem. Rev., 114, 11751-87 (2014). 2. Son, Y.; Lee, J.-S.; Son, Y.; Jang, J.-H.; Cho, J. Adv. Energy Mater., 5, 1500110 (2015). 3. Nakamura, N.; Yokoshima, T.; Nara, H.; Momma, T.; Osaka, T. J. Power. Sources , 274, 1263-1266 (2015). Figure 1