The design and fabrication of lithium secondary batteries with a high energy density and shape flexibility are essential for flexible and wearable electronics. In this study, we fabricated a high-voltage (5 V class) flexible lithium polymer battery using a lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ) cathode. A LiNi 0.5 Mn 1.5 O 4 -hybridized gel polymer cathode (GPC) and a gel polymer electrolyte (GPE) membrane, both containing a sulfolane (SL)-based highly concentrated electrolyte (HCE), enabled the fabrication of a polymer battery by simple lamination with a metallic lithium anode, where the injection of the electrolyte solution was not required. GPC with high flexibility has a hierarchically continuous three-dimensional porous architecture, which is advantageous for forming continuous ion-conduction paths. The GPE membrane has significant ionic conductivity enough for reliable capacity delivery. Therefore, the fabricated lithium polymer pouch cells demonstrated excellent capacity retention under continuous deformation conditions. This study provides a promising strategy for the fabrication of scalable and flexible 5 V class batteries using GPC and GPE containing SL-based HCE.

Lithium−sulfur (Li−S) batteries can theoretically deliver high energy densities exceeding 2500 Wh kg −1 . However, high sulfur loading and lean electrolyte conditions are two major requirements to enhance the actual energy density of the Li−S batteries. Herein, the use of carbon-dispersed highly concentrated electrolyte (HCE) gels with sparingly solvating characteristics as sulfur hosts in Li−S batteries is proposed as a unique approach to construct continuous electron-transport and ion-conduction paths in sulfur cathodes as well as achieve high energy density under lean-electrolyte conditions. The sol−gel behavior of carbondispersed sulfolane-based HCEs was investigated using phase diagrams. The sol-to-gel transition was mainly dependent on the amount of the carbonaceous material and the Li salt content. The gelation was caused by the carbonaceous-material-induced formation of an integrated network. Density functional theory (DFT) calculations revealed that the strong cation−π interactions between Li + and the induced dipole of graphitic carbon were responsible for facilitating the dispersion of the carbonaceous material into the HCEs, thereby permitting gel formation at high Li-salt concentrations. The as-prepared carbon-dispersed sulfolane-based composite gels were employed as efficient sulfur hosts in Li−S batteries. The use of gel-type sulfur hosts eliminates the requirement for excess electrolytes and thus facilitates the practical realization of Li−S batteries under lean-electrolyte conditions. A Li−S pouch cell that achieved a high cell-energy density (up to 253 Wh kg −1 ) at a high sulfur loading (4.1 mg cm −2 ) and low electrolyte/sulfur ratio (4.2 μL mg −1 ) was developed. Furthermore, a Li−S polymer battery was fabricated by combining the composite gel cathode and a polymer gel electrolyte.

Li-S batteries have received much attention as the next-generation secondary batteries because of their extremely high theoretical energy density. A roll-to-roll fabrication method based on continuous laminating and winding of the sheet-like electrodes and electrolyte without an electrolyte injecting process would enable a more efficient manufacturing process for mass production of Li-S batteries. In order to realize such batteries, it is necessary to prepare the sheet-type sulfur cathode electrode in which an electrolyte is incorporated. We recently reported that a less volatile, highly concentrated lithium salt electrolyte could serve as a good dispersing media of carbon nanotube (CNT).[1] In this study, the same method was applied not only to CNT but also to other carbonaceous materials to obtain sheet sulfur cathode electrode containing highly concentrated electrolytes that serve as the dispersing media. As a result, we fabricated a Li-S polymer battery by combining the sheet sulfur cathode and the polymer gel electrolyte membrane.[2] This is a trail to realize polymer Li-S battery fabricated by the roll-to-roll process. The cathode slurry was prepared by adding a dispersion solvent, NMP (N-methyl-2-pyrrolidone), to the mixture (sulfur, Ketjen black (KB), polymer, and highly concentrated electrolyte: [Li(SL)2][TFSA] (SL : sulfolane, [TFSA] = [N(SO2CF3)2])[3]). This slurry was coated to an Al foil current collector and dried to obtain the gel cathode. The gel electrolyte was prepared from PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) and [Li(SL)2][TFSA] by a solvent casting method. The Li-S polymer battery was then prepared using the gel cathode, electrolyte and Li-anode. Figure 1(a) shows a conceptual scheme of roll-to-roll making process for the Li-S polymer battery. By using the sheet-like cathode and gel electrolyte, a battery can be manufactured simply via laminating them with Li-anode. It is worth mentioning that the subsequent electrolyte injecting step can be omitted here because the gel cathode and electrolyte already contain uniformly distributed electrolytes. Figure 1(b) shows the charge-discharge curves of the Li-S polymer battery. The battery delivered the initial discharge capacity of 850 mAh g−1. After 20 cycles, nearly 700 mAh g−1 of capacity could be retained, which indicated reasonable cycling stability. In our previous research,[1] CNT was used as the carbonaceous material for the S gel cathode. However, in this study, we found the amounts of electrolyte could be greatly reduced by using KB. It is considered that CNT requires more electrolyte to disperse the aggregated bundles and to unbundle them by cation-π interaction. Hence, our results would indicate a great potential on designing the sulfur gel cathode by a very simple method with lower cost materials. The detailed electrochemical behavior of the Li-S polymer batteries will be discussed in the presentation. Further, studies on the effects of composition and thickness of the S gel cathode and gel electrolyte on the electrochemical behavior will be presented. References [1] R. Tamate, A. Saruwatari, et al., Electrochem. Commun., 2019, 109, 106598. [2] T. Michot, A. Nishimoto, M. Watanabe, Electrochim. Acta, 2000, 45, 1347. [3] A. Nakanishi, K. Ueno, et al., J. Phys. Chem. C, 2019, 123, 14229. Figure 1