Abstract
Solid-state lithium-ion batteries (SS-LIBs) are a cutting-edge technology that will enhance safety and energy density compared to traditional LIBs. However, the rapid degradation of SS-LIBs upon charge-discharge cycling is a current barrier to commercialization. This degradation primarily stems from the formation of undesirable compounds at the electrode-electrolyte interfaces, which impede Li+ transport and lead to a reduction in charge capacity. Understanding the reactions occurring at the electrode-electrolyte interface is critical to mitigate this degradation and enhance battery performance. Here, we employ cryogenic four-dimensional STEM (4D-STEM) including energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and electron diffraction pair distribution function analysis (ePDF) at ~1 nm spatial resolution to inspect the cathode-electrolyte interfaces in SS-LIBs and study the reaction mechanisms driving interphase formation. For this study we employed Nickel rich LiNi0.6Co0.2Mn0.2O2 (NMC 622) as the cathode electrode material and Li10GeP2S12 (LGPS) as the solid electrolyte. We report a simplified process to measure interphase formation using chemical delithiation of NMC with MoCl5 in ethanol, followed by physical mixing of NMC and LGPS powder before STEM imaging. STEM measurement at the NMC-LGPS interface reveal that anion migration through the interface is a key driver for interphase formation. We also describe the development of a thin-film polyhydroquinone (PHQ) coating formed by oxidative molecular layer deposition (oMLD) as a candidate to encapsulate NMC and mitigate interface formation issues in SS-LIBs. The PHQ coating is expected to act as a selective conductor for cations and electrons, ensuring electrochemical operation of the battery while preventing anion transport. Our latest results showing assembly of SS-LIB cells with and without the oMLD barrier coatings will be discussed to reveal how the oMLD coating influence interface reactions and overall battery performance. Figure 1
Published Version
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