다공성 복합전극을 이용한 무음극 리튬 금속전지에서의 리튬 증착물 형상 제어에 관한 연구

Abstract

Soaring demand for carbon neutrality for a cleaner future and rapid growth of the electric vehicle (EV) market have led to the development of high energy density batteries. However, the limited energy density of current commercial Li-ion batteries (LIBs) has prevented sufficient driving range from being delivered for EVs. Among the next generation energy storage systems with alternative electrochemistries, Li-free or anodeless all-solid-state batteries (ASSBs) which only use cathode active materials as an exclusive Li source are regarded as optimal battery due to their high energy density. However, unstable interface between anode and solid electrolyte (SE) originated from separation of the interface during Li deposition degrades reversibility in Li deposition/stripping and causes the early failure. Furthermore, in the case of ASSBs with a sulfide SE, the high reactivity of Li metal with SE induces side reactions at the interface. A porous composite anode can enable the Li deposition and stripping without SE/anode separation and limit the direct contact between SE and Li electrodeposits. However, a lack of understanding regarding the Li deposition behavior onto porous architecture makes the composite anode design difficult. This dissertation aims to clarify the Li deposition behavior onto porous architecture in Li-free ASSBs and design the porous composite anode for high-performance batteries. I believe that the clarified Li deposition (movement) behavior and proposed anode design strategy can guide the further development Li-free ASSBs. In Chapter 2, the factors determining the morphology and location of Li electrodeposits in Li-free ASSBs with a porous interlayer coated on current collector are identified based on both the thermodynamics of Li electrodeposition and the kinetics of Li movement through the interlayer. Interfacial adhesion work is pointed out as the key thermodynamic factor that determines the Li deposition location and it is experimentally confirmed that the interface with low adhesion energy is thermodynamically favorable. For kinetic factors, pore size of the porous interlayer, temperature, scaffold materials, and surface modification with Ag nanoparticles are investigated. The pore size dependency of Li deposition indicates that Li moves through the interlayer via diffusional Coble creep, and factors that facilitate this kinetics are identified; smaller pores, higher temperatures, and a lithiophilic surface. In chapter 3, a 3D porous anode which can accommodate Li electrodeposits within the pores of the anode is fabricated for reversible Li-free ASSBs. The anode is designed based on the pore-size and surface property dependent Li deposition behavior. The Li deposition within 3D anode enables the Li deposition and stripping without interface separation between anode and SE. Thus, intimate contact can be maintained during the cycling and a Li-free all-solid-state full cell with a LiNi0.8Mn0.1Co0.1O2 cathode shows an initial areal capacity of 2 mAh cm-2 for retaining a Coulombic efficiency of 99.46% for 100 cycles at 30 ℃. Chapter 4 summarize all the research accomplishments in this dissertation and suggested directions for future research.