Development of a thin flexible Li battery design with a new gel polymer electrolyte operating at room temperature

Abstract In this study, we develop a new Li-metal battery design merging with IoT requirements, mainly the low thickness, the thermal stability and the flexibility. To reach these specifications, we firstly prepared an efficient gel polymer electrolyte (GPE) composed of a PVDF-HFP polymer network, a LiFSI: Pyr13FSI liquid binary solution and a lithium montmorillonite Li-MMT clay. The as-synthesized material exhibits a high ionic conductivity (0.48 mS cm−1 at 25 °C) and a good thermal stability, up to 140 °C. In parallel, a new battery design with an optimized ratio of packaging to active material thickness is developed. In this design, copper foils act both as current collector and as battery casing, decreasing the overall cell thickness. Li metal batteries are realized using the developed GPE material and this new battery design. The cell thickness is 360 and 760 μm for single side and double-sided architectures respectively. These batteries show well functioning under high bending and exhibit a good cycling ability with a remaining capacity higher than 85% after more than 200 cycles at 25 °C. Thanks to the combination of the original Cu packaging and the flexible GPE membrane, developed Li-metal batteries exhibit promising properties to merge with the new IoT requirements.