Probing the Nano-electrocatalyst using Multimodal Operando Techniques
Title: Revealing catalyst restructuring and composition during nitrate electroreduction through correlated operando microscopy and spectroscopy
Authors: Yoon, et al.,
Journal: Nature Materials Link
Direct visualization of dynamic electrochemical processes inside a transmission electron microscope (TEM) is crucial for understanding nanoscale energy systems. This approach becomes even more powerful when complemented by well-established spectroscopic techniques. Electrochemical liquid cell transmission electron microscopy (EC-TEM) has proven to be a valuable tool for observing the electrically driven shape evolution of nanostructures in liquid. However, its limited spectroscopic capability—due to the thickness of the chip window and liquid—has restricted its widespread adoption in the research community.
In this study, the authors developed a method to comprehensively track the evolution of Cu₂O nanocubes during nitrate reduction, a key electrocatalytic reaction. By integrating EC-TEM with transmission X-ray microscopy (TXM), they successfully achieved both imaging and spectroscopic analysis without compromising the reaction environment. This was possible because X-rays experience less attenuation from the electrolyte and window membranes than electrons, better in preserving data quality.
To validate their findings, the authors further employed operando hard X-ray absorption spectroscopy (XAS), which provided bulk-level oxidation state analysis of nanoparticles extracted at the same potential in an electrolyte of identical composition to that used in TEM/TXM. Their results demonstrated how the evolution of Cu₂O nanocubes depends on nitrate reduction conditions, such as applied potential and chemical atmosphere. Additionally, they revealed that chemical heterogeneities arising from phase formation at different reductive potentials significantly impact ammonia selectivity, likely through electrocatalytic conversion reaction activation.
Characterizing Dendrite Formation in the ASSB using Magnetic Resonance Techniques
Title: Dendrite formation in solid-state batteries arising from lithium plating and electrolyte reduction
Authors: Liu, et al.,
Journal: Nature Materials Link
A comprehensive understanding of dendrite formation in all-solid-state batteries (ASSBs), both spatially and temporally, is far from attainable without a proper characterization method. While numerous studies have investigated dendrite formation at the electrode-electrolyte interface, less effort has been dedicated to deciphering electrolyte grain boundaries, which are theoretically favorable sites also for dendrite formation. Transmission electron microscopy techniques provide spatial resolution of these boundaries and electronic insights; however, they are limited to local, two-dimensional structural information that is susceptible to transformation under electron beam irradiation.
In this study, the authors synergistically combined non-invasive techniques such as nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) to offer both temporal and spatial insights into dendrite formation within a moderately cycled ASSB composed of Li/Li7La3Zr2O12/Li. The study identified two distinct formation routes: (1) the electrode-electrolyte interface route, driven by non-uniform Li deposition/stripping, and (2) the electrolyte grain surface/boundary route, involving Li+ reduction facilitated by defect-induced electronic structures. These mechanisms were differentiated by the relative abundance of ⁶Li and ⁷Li isotopes within the electrolyte. Over the course of cycling until shorting, the study demonstrated in-situ the alternating dominance of these mechanisms at different stages, with stalled growth occurring between.
Magnetic resonance techniques hold promise as non-destructive characterization tools for the battery industry, which is increasingly focused on next-generation technologies, particularly ASSBs.
Influence of the Electron Beam Dose on the Battery Material Characterization Using Cryo-TEM
Title: Electron Beam-Induced Artifacts in SEI Characterization: Evidence from Controlled-Dose Diffraction Studies
Authors: Koh et al.,
Journal: ACS Energy Letters Link
The solid electrolyte interphase (SEI) is a critical component in batteries, acting as a charge transport bridge between the electrode and electrolyte, significantly influencing battery performance. While cryogenic transmission electron microscopy (cryo-TEM) has been widely used to evaluate SEI, many studies simply assume and even claim its ability to protect against any electron beam irradiation damage.
This study disproves that assumption by demonstrating the formation of Li₂O under accumulated electron doses by comparing short and prolonged electron exposure of SEI. High-resolution TEM (HRTEM), used quite often in cryo-conditions in previous studies and also in this study, requires a high dose rate (~1000 e⁻/Ų·s), which can immediately induce artifacts. In contrast, scanning electron nanobeam diffraction with a low probe dose of less than 200 e⁻/Ų and small convergence semi-angle reveals the SEI as amorphous, contradicting HRTEM observation. Selected area electron diffraction and electron energy loss spectroscopy indicate that total electron doses of 450 e⁻/Ų and 600 e⁻/Ų are sufficient to induce Li₂O formation in SEI layers of Li metal deposited in LiFSI+LiTFSI/DME and LiPF₆/EC-DEC electrolytes, respectively.
Nanostructure characterization in batteries can be challenging due to electron beam interactions that can lead to erroneous conclusions. The paper suggests the use of scanning TEM, and even more, 4D-STEM for comprehensive yet artifact-free characterization in the cryogenic environment but note that this can certainly be data-intensive and expensive to be considered for routine work.
Comprehensive Characterization Tool for Modeling and Understanding the Behaviors of Li-ion Cells after Heavy Cycles
Title: The Complex and Spatially Heterogeneous Nature of Degradation in Heavily Cycled Li-ion Cells
Authors: Bond et al.,
Journal: Journal of The Electrochemical Society Link
Synchrotron X-ray diffraction (XRD) has become a widely adopted structural characterization technique in the battery research community. However, studies utilizing this technique are often conducted in overly simplified settings with model cells (e.g., single-layer cells subjected to hundreds of cycles), raising questions about the applicability of their conclusions to commercial battery cells.
In this study, the authors characterized commercially manufactured polycrystalline NMC622 and graphite cells (prismatic wound pouch-type) cycled over more than two years using a combination of non-destructive electrochemical and imaging methods. Spatially resolved, in-situ, and operando synchrotron XRD was employed to investigate spatially heterogeneous changes across three differently cycled cells: heavily cycled, lightly cycled, and only with formation cycling.
Static and time-resolved data were obtained under near-equilibrium conditions (CC-CV), non-equilibrium conditions (CC only), and after open-circuit relaxation. The diffraction peaks corresponding to NMC (113) were analyzed using a three-component fitting method to quantify the temporal and spatial lithiation state distribution (i.e., active, inactive, and semi-active regions). The heavily cycled cells exhibited complex, multi-modal, and heterogeneous kinetics during charge, discharge, and after open-circuit relaxation, in contrast to the more uniform behavior of the lightly cycled and formation-only cells. The authors also demonstrated that these behaviors correlated with microcracking and surface reconstruction in the heavily cycled cells could be mitigated by employing single-crystal electrodes, which suppress microcracking, reduce pore growth, and significantly decrease the fraction of inactive material.
This study presents a robust spatial and temporal methodology to characterize the complex behavior of degraded cells through a multi-faceted approach, accounting for the extent of cell degradation, equilibrium states under varied test protocols, and rigorous quantitative analysis. By demonstrating the depth and comprehensiveness of such characterization, the authors highlight the potential for advancing the knowledge of cycle-intensive systems for commercial application.
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November 27, 2024
Electron Backscatter Diffraction for Imaging Solid-state Battery Microstructure
Title: Imaging the microstructure of lithium and sodium metal in anode-free solid-state batteries using electron backscatter diffraction
Authors: Fuchs et al.,
Journal: Nature Materials Link
The battery industry is gradually transitioning to all-solid-state batteries (ASSBs), creating a growing demand for advanced techniques to visualize dissolution and deposition processes within these systems. In this context, the authors’ work is particularly promising, as it employs in-situ electron backscatter diffraction (EBSD) analysis to investigate the evolution of the cross-sectional microstructure of Li and Na metals interfaced with widely studied solid electrolytes. The study effectively demonstrates the grain size and orientation evolution during charge(plating) and highlights pore formation during discharge (stripping).
Characterizing lithium (or sodium) microstructures using EBSD, especially in-situ, is an exceptionally challenging task due to several technical hurdles. Firstly, the sample must be meticulously polished and flat to ensure accurate analysis. Secondly, focused ion beam (FIB) cutting must be performed under cryogenic conditions to prevent artifacts. Thirdly, electron beam intensity and EBSD sensitivity must be precisely optimized to generate meaningful results. Additionally, the sample must be stored and transported under inert gas or vacuum conditions at all times, further complicating the process.
Despite these challenges, this work is an important stepping stone for understanding key phenomena in ASSBs. Future studies could build upon these findings by diversifying testing conditions and conducting comprehensive quantitative analyses to gain deeper insights into the underlying mechanisms driving battery performance.
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November 11, 2024
Scanning Transmission Electron Microscopy Techniques for Cathode Material Analysis
Title: Phase Transitions and Ion Transport in Lithium Iron Phosphate by Atomic-Scale Analysis to Elucidate Insertion and Extraction Processes in Li-Ion Batteries
Authors: Šimic et al.,
Journal: Advanced Energy Materials Link
To fully understand the lithiation dynamics in cathode materials, atomic-scale visualization and quantification are essential. In this study, the authors applied selected area electron diffraction and scanning transmission electron microscopy (STEM) with integrated differential phase contrast imaging (iDPC) to examine the lithiation behavior in LiFePO₄ (LFP), a widely used and commercially relevant cathode material. This approach allowed the researchers to calculate local strain, crystal misfit, and estimate the lithium diffusion coefficient, revealing that lithium diffusion within the LFP lattice is constrained by multiple limiting factors.
The technique holds promise for application to other cathode systems, such as lithium nickel manganese cobalt oxides with varied nickel and manganese ratios, or manganese-doped LFP. It provides critical insights into structural features like phase relationships, strain, and distortion, as well as, to some extent, lithium kinetics—offering valuable guidance for cathode design.
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November 05, 2024
Simple Pulsing Experiment for Thermodynamic, Kinetic, and Transport Analysis of the Battery Cell
Title: Extracting Thermodynamic, Kinetic, and Transport Properties from Batteries Using a Simple Analytical Pulsing Protocol
Authors: Wood et al.,
Journal: Journal of the Electrochemical Society Link
This paper presents a novel, non-invasive pulsing protocol for analyzing lithium-ion battery (LIB) cells. This technique enables the extraction of key parameters for thermodynamic, kinetic, and transport properties through pulse profiles performed at specific C-rates. These parameters include the Gibbs free energy, exchange current density, and lithium-ion diffusion coefficient.
Thermodynamics: The thermodynamic properties are calculated using dQ/dV curves from open-circuit voltage (OCV) values across nine defined pulse cycles, effectively isolating thermodynamic contributions by neglecting overpotentials from kinetic and transport effects. The Gibbs free energy of reaction is then determined using the maximum dQ/dV value, revealing the purely thermodynamic energy associated with the reaction.
Kinetics: The kinetic properties are evaluated by analyzing cell potentials at the beginning of the pulse and at rest. The difference between these potentials represents the kinetic overpotential and the system’s internal resistance. Using the Butler-Volmer model, the exchange current density is then calculated.
Transport: Transport properties are derived from the potential at the beginning (i.e. end of the pulse phase) and end of the rest phase (i.e., equilibrium) following a pulse. This difference, combined with the current density, is applied in Fick’s law to determine the diffusion coefficient, with set boundary conditions.
This technique is reported to have a robust fundamental basis with minimal assumptions, providing accurate, quantifiable metrics for any cell form factor. link
November 04, 2024
Welcome to Battery Park!
We’re excited to announce the launch of Battery Park! Stay tuned for updates — we aim to share one or two pieces of content each week, covering recent papers on material characterization aligned with industry expectations.
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