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Lithium-sulfur (Li-S) battery is a promising candidate for the next-generation batteries for electric vehicles due to its high theoretical specific energy and the low cost of sulfur. However, the challenges in the battery performance like low volumetric energy density, poor cycle life, and high self-discharge rate are yet to be resolved. To achieve the better understanding on the root causes behind the numerous technical challenges and to provide the right directions to solve the problems, the development of characterization techniques to understand the reaction mechanisms and the phenomena inside the Li-S cells are highly required. In this study, the morphological changes of S-LVO (LiV3O8) composite were analysed to investigate the reason why S-LVO composite shows better battery performance over the pristine sulfur material [1]. Experimental S-LVO composite was manufactured by a mechano-fusion process using a Nobilta equipment to form the LVO coating on sulfur particles as shown in Figure 1.To analyse the cathode electrode, lithium // Celgard 3501 / LiTFSI 1M in DME/DOL (1:1) // sulfur coin cells were prepared and opened at various values of death of discharge (DOD) in the first cycle. The cathodes were rinsed and dried (at 0.65 atm, 55°C for 1h), then observed in the scanning electron microscope (SEM) using a specially designed transfer chamber to avoid any air/moisture contact between the SEM and the glove box. Secondary electrons (SE) images, backscattered electron (BSE) images and comparative X-ray elemental analysis using an energy dispersive spectrometer (EDS) were performed at 15 keV. Results and discussion Figure 2 shows the discharge profile in the 3rd cycle at 0.1C condition and the cycle performance at 0.5C condition in comparison between the S-LVO composite electrode and the reference sulfur electrode. It can be seen that the S-LVO outperforms the pristine sulfur in the initial capacity and the cycle life. Figure 3(a) demonstrates that, as the DOD increases from 0 to 100%, the sulfur-based cathode undergoes a significant densification and tend to form a severe “mud-crack” morphology as shown in Figure 3(a), while this effect is relatively smaller on the S-LVO composite cathode (Figure 3(b)). This densification process is well seen in the SE image in Figure 3(c). It is believed that the dispersed LVO particles retard the densification of electrode and contribute to preserve the mechanical integrity of electrode. Figure 4 shows the evolution of sulfur-to-carbon ratio (S/C) that was measured at constant values of electron beam current, working distance and collection. It is found that the S-LVO electrode shows a lower variation of the S/C ratio, which indicates that S-LVO electrode has relatively homogeneous sulfur distribution while the concentration of sulfur is more localized on the electrode surface in the case of the reference electrode. Reference [1] C-S Kim et al, ‘Facile dry synthesis of sulfur-LiFePO4 core-shell composite for scalable fabrication of lithium/sulfur batteries’, Electroch. Comm, 32 (2013) 35-38.

Prof. Ogumi is one the leading pioneers of lithium-ion technology in Japan and worldwide. His research studies on battery materials include LiCoO2, graphite, and highly oriented pyrolytic graphite (HOPG), Much of his research involved in situ techniques that utilized X-ray, Raman spectroscopy and atomic force spectroscopy (AFM) to investigate the SEI (passivation layer) and lithium intercalation in graphite and HOPG in propylene carbonate (PC)- and ethylene carbonate (EC)-based electrolytes. In this presentation, we will show data and video movies that were obtained during studies of lithium-ion and solid-state batteries using various In operando studies and in situ techniques involving scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction and ultraviolet-visible absorption spectroscopy (UV-vis). These in situ studies are helpful to understand the mechanisms for volume expansion of anodes consisting of lithium metal (20 %), graphite (10 %) and LTO (0 %). Another example that will be discussed is the dimensional changes of the anode, cathode and electrolyte that occur during charge/discharge. The mechanism of lithium dendrite formation was also studied, and details will be discussed in this presentation.  [Don’t know what is meant by Bleand and deleted because I‘m not sure it is needed.] Lithium/solid polymer electrolyte (SPE)/sulfur cells were studied by two in situ techniques:  SEM and UV-vis. During the operation of the cell, extensive polysulfide dissolution in the solid polymer electrolyte (cross-linked polyethylene oxide) leads to the formation of a catholyte. A clear micrograph was obtained of the thick passivation layer on the sulfur-rich anode and the decreased SPE thickness during cycling confirmed the failure mechanism; the capacity decays by reducing the amount of active material, which contributes to a charge inhibiting mechanism called polysulfide shuttle. The formation of elemental sulfur is clearly visible in real time during the charge process beyond 2.3 V. The non-destructive UV-vis also shows the characteristic absorption peaks that evolve with cycling, demonstrating the accumulation of various polysulfide species, and the predominant formation of S4 2- and of S6 2- during discharge and charge, respectively. This finding implies that the charge and discharge reactions are not completely reversible and proceed along different pathways.