All-Solid-State Lithium-Ion Batteries using Sheet-Type Electrodes and Solid Electrolyte Films and Their Diagnostic Study

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Title
All-Solid-State Lithium-Ion Batteries using Sheet-Type Electrodes and Solid Electrolyte Films and Their Diagnostic Study
Other Titles
시트 타입 전극 및 고체전해질 필름을 이용한 전고체전지 및 이들의 진단 연구
Author
Nam, Young Jin
Advisor
Kim, Youngsik
Issue Date
2019-02
Publisher
Graduate School of UNIST
Abstract
Bulk-type all-solid-state lithium batteries (ASLBs) using sulfide solid electrolytes (SEs) are considered as a promising candidate to solve the safety issues originating from the use of flammable organic electrolytes. Moreover, several state-of-the-art sulfide solid electrolytes shows extremely high ionic conductivity over 10-2 S cm-1, compared to conventional liquid electrolytes. However, to develop bulk-type ASLBs, it encountered many technical challenges such as huge interfacial resistances between active materials and SEs, high contents of SEs in ASLBs, scalable fabrication and reliable test protocol. To fulfill these requirements, sheet-type ASLBs using a scalable wet-slurry process can provide a breakthrough in the architecture and fabrication of composite structure. The first part of my thesis is sheet-type ASLBs using bendable solid electrolyte films and dry-/slurry- mixed electrodes, which are prepared by wet-slurry process. In the first case, the facile and scalable fabrication of bendable solid electrolyte films reinforced with a mechanically compliant NW-scaffold, which enables the fabrication of free-standing and stackable ASLBs with high energy density and high rate capabilities. For the second case, the comparative study for electrodes fabricated by dry- and slurry- mixing process was performed. The information provides insights for a need to develop well-designed electrode with better ionic contacts and to improve the ionic conductivity of SEs. Pouch-type 80 x 60 mm2 all-solid-state LiNi0.6Co0.2Mn0.2O2/graphite full-cells fabricated by the slurry process show high cell-based energy density (184 W h kg-1 and 432 W h L-1). Furthermore, their excellent safety is also demonstrated by simple tests (cutting with scissors and heating at 110oC). The second part is a reliable electrochemical analysis of sheet-type ASLBs. Even though the well-developed sheet-type ASLBs using sulfide SEs have been demonstrated, their reliable electrochemical test protocols have not been developed. In this regard, in this study, from the in-depth study of ASLBs using novel bulk-type all-solid-state three-electrode cells, even for the cells having thin SE layers, kinetic behaviors of Li-In(-SE) CEs and internal short circuits (ISC) by penetrating growth of Li metal during charging at high C-rates are revealed. In addition, unique durability of LiNi0.6Co0.2Mn0.2O2/graphite or LiNi0.6Co0.2Mn0.2O2/Si-C full-cells upon discharge to 0 V was described. In the last study, the pressure monitoring system for sheet-type ASLBs is demonstrated. The state-of-charge (SOC) values were estimated from volume changes of graphite electrodes in LiNi0.6Co0.2Mn0.2O2/graphite full-cells. The behavior of rearrangement of particles in electrode during cycling is also observed. These results hold great promise for practical sheet-type all-solid-state technology in terms of fabrication and battery architecture as well as provision of in-depth insights into developing reliable electrochemical test protocols.
Description
Department of Energy Engineering (Battery Science and Technology)
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