음극 보호 이중층을 적용한 전고체 전지의 Ag 위치 에 따른 Li 증착 거동 및 성능에 관한 연구

Abstract

A Study on Li-deposition Behavior and Performance Depending on the Ag Position in the Protective Double-layer in Anode of an All-solid-state Battery Ji Ho LEE Department of Energy Engineering Graduate School of Hanyang University As the utilization of energy storage and electric vehicles (EV) continues to increase, there is a growing demand for lithium (Li) secondary batteries, which serve as vital resources for these applications. However, despite decades of significant advance in commercial Li-ion batteries, it has been reached by limitations in energy density. Safety problems arise from the flammability of the electrolyte, which can lead to thermal runaway and fire hazards, resulting in significant human and property losses. Consequently, further technological developments is needed. Solid-state batteries employing solid electrolytes (SEs) have emerged as promising next- generation energy storage technologies that can enhance energy density and safety. However, the direct deposition of Li onto the SE makes it more prone to interface detachment, leading to decreased stability and undesirable side-reactions between Li deposits and the SEs. It causes a decrease in the overall battery performance. To overcome these challenges, suitable metal or carbon composite interlayers such as silver-carbon (Ag-C) composites or silver (Ag) particles were applied that function as a protective layer. These interlayer materials have been proposed to facilitate uniform Li-deposition between the SEs and active materials. Nevertheless, the behavior of Ag-C composites and Ag nanoparticles (NPs) during charge and discharge cycles remains inadequately understood, with difficulties in electrode design and performance analysis. Therefore, investigation on mechanism and understanding of phenomena are imperative. This thesis aims to elucidate the effects of Ag-C composites and Ag NPs protective layers on Li-deposition behavior and the performance of solid-state batteries. A double-interlayer was fabricated as an anode protective layer to evaluate the effect of the location of Ag in the double-interlayer. One consists of a carbon (C) layer and an Ag-C composite layer, and the other consists of a C layer and an Ag NPs layer. The electrodes were fabricated with different stacking sequence in the double-interlayer to change the location of Ag in the double- interlayer. The variations in Li-deposition behavior and cell performance were analyzed depending on the location of Ag containing layer in the double-interlayer structure. The results revealed that direct contact between Ag NPs or Ag-C composite layer and the SEs resulted in a fast degradation. In contrast, when the Ag-C composite or Ag Nps layer was not in direct contact with SEs, the battery exhibited a better performance. These results suggests that it is necessary to separate Ag from the SEs by introducing a double-layer structure to harness the beneficial effect of alloying with Ag to enhance battery performance. This phenomenon is presumably originated from the increased interfacial resistance between SE and interlayer owing to the direct contact between Ag and the SEs, hindering the desired Li-Ag nucleation and impeding diffusional Coble creep. It is also attributed to the non-uniform current pathway leading to electrolyte-interlayer interface deterioration. In addition, the double-interlayer with Ag-C composite and that with Ag NPs showed different performance in this study. The anode employing double-interlayer with Ag NPs exhibited an enhanced performance compared to that of the anode with Ag-C. This difference may be caused by different amount of Ag metals in the interlayer, and subsequently, different thermodynamics and kinetics. Based on these findings, this study on Li-deposition behavior and performance depending on the location of Ag in the interlayer can contribute to overcoming the challenges encountered in solid-state batteries and provide potential solutions for their future advancement.