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Lee, Jungwoo Z.

Publications and source records attributed to Lee, Jungwoo Z..

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Quantifying inactive lithium in lithium metal batteries

Lithium metal anodes offer high theoretical capacities (3,860 milliampere-hours per gram)1, but rechargeable batteries built with such anodes suffer from dendrite growth and low Coulombic efficiency (the ratio of charge output to charge input), preventing their commercial adoption. The formation of inactive (‘dead’) lithium— which consists of both (electro)chemically formed Li + compounds in the solid electrolyte interphase and electrically isolated unreacted metallic Li 0 —causes capacity loss and safety hazards. Quantitatively distinguishing between Li + in components of the solid electrolyte interphase and unreacted metallic Li 0 has not been possible, owing to the lack of effective diagnostic tools. Optical microscopy, in situ environmental transmission electron microscopy, X-ray microtomography and magnetic resonance imaging provide a morphological perspective with little chemical information. Nuclear magnetic resonance, X-ray photoelectron spectroscopy and cryogenic transmission electron microscopy can distinguish between Li + in the solid electrolyte interphase and metallic Li 0 , but their detection ranges are limited to surfaces or local regions. Here we establish the analytical method of titration gas chromatography to quantify the contribution of unreacted metallic Li 0 to the total amount of inactive lithium. We identify the unreacted metallic Li 0 , not the (electro)chemically formed Li + in the solid electrolyte interphase, as the dominant source of inactive lithium and capacity loss. By coupling the unreacted metallic Li 0 content to observations of its local microstructure and nanostructure by cryogenic electron microscopy (both scanning and transmission), we also establish the formation mechanism of inactive lithium in different types of electrolytes and determine the underlying cause of low Coulombic efficiency in plating and stripping (the charge and discharge processes, respectively, in a full cell) of lithium metal anodes. Here we propose strategies for making lithium plating and stripping more efficient so that lithium metal anodes can be used for next-generation high-energy batteries.

25 ENERGY STORAGE↗
DOE OSTI2019

Cryogenic Focused Ion Beam Characterization of Lithium Metal Anodes

Lithium metal is viewed as the ultimate battery anode because of its high theoretical capacity and low electrode potential, but its implementation has been limited by low Coulombic efficiency and dendrite formation above a critical current density. Determining the fundamental properties dictating lithium metal plating–stripping behavior is challenging because characterization techniques are limited by the sensitivity of lithium metal to damage by external probes, which regularly results in altered morphology and chemistry. Motivated by recent application of cryogenic transmission electron microscopy (cryo-TEM) to characterize lithium metal at the atomic scale, we explore the cryogenic focused ion beam (cryo-FIB) method as a quantitative tool for characterizing the bulk morphology of electrochemically deposited lithium and as a technique that enables TEM observation of Li-metal/solid-state electrolyte interfaces. Lastly, this work highlights the importance of cryo-FIB methodology for preparing sensitive battery materials and elucidates the impact of electrolyte selection on the density and morphology of plated lithium.

25 ENERGY STORAGE↗
DOE OSTI2018

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO 2 /LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

25 ENERGY STORAGE↗
DOE OSTI2016

Amorphous lithium lanthanum titanate for solid-state microbatteries

Lithium lanthanum titanate (LLTO) is a promising solid state electrolyte for solid state batteries due to its demonstrated high bulk ionic conductivity. However, crystalline LLTO has a relatively low grain boundary conductivity, limiting the overall material conductivity. In this work, we investigate amorphous LLTO (a-LLTO) thin films grown by pulsed laser deposition (PLD). By controlling the background pressure and temperature we are able to optimize the ionic conductivity to 3 × 10 –4 S/cm and electronic conductivity to 5 × 10 –11 S/cm. XRD, TEM, and STEM/EELS analysis confirm that the films are amorphous and indicate that oxygen background gas is necessary during the PLD process to decrease the oxygen vacancy concentration, decreasing the electrical conductivity. Amorphous LLTO is deposited onto high voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel cathode thin films and cycled up to 4.8 V vs. Li showing excellent capacity retention. Finally, these results demonstrate that a-LLTO has the potential to be integrated into high voltage thin film batteries.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effects of cathode electrolyte interfacial (CEI) layer on long term cycling of all-solid-state thin-film batteries

All-solid-state lithium-ion batteries have the potential to not only push the current limits of energy density by utilizing Li metal, but also improve safety by avoiding flammable organic electrolyte. However, understanding the role of solid electrolyte – electrode interfaces will be critical to improve performance. In this paper, we conducted long term cycling on commercially available lithium cobalt oxide (LCO)/lithium phosphorus oxynitride (LiPON)/lithium (Li) cells at elevated temperature to investigate the interfacial phenomena that lead to capacity decay. STEM-EELS analysis of samples revealed a previously unreported disordered layer between the LCO cathode and LiPON electrolyte. This electrochemically inactive layer grew in thickness leading to loss of capacity and increase of interfacial resistance when cycled at 80 °C. Finally, the stabilization of this layer through interfacial engineering is crucial to improve the long term performance of thin-film batteries especially under thermal stress.

25 ENERGY STORAGE↗