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Advances in treatment and diagnosis of human health demand advances in energy storage providing small, adaptable, predictable, and reliable systems. This article summarizes key milestones in the adoption of batteries used for implantable medical applications, provides details about several of the dominant battery chemistries currently powering medical devices, and provides comment on the future impact of advances in the battery field on medical devices.

Silicon (Si) is a promising high-capacity material for lithium-ion batteries; however, its limited reversibility hinders commercial adoption. Approaches such as particle and crystallite size reduction, introduction of conductive carbon, and use of different electrolyte solvents have been explored to overcome these electrochemical limitations. Herein, operando isothermal microcalorimetry (IMC) is used to probe the influence of silicon particle size, electrode composition, and electrolyte additives fluoroethylene carbonate and vinylene carbonate on the heat flow during silicon lithiation. The IMC data are complemented by X-ray photoelectron and Raman spectroscopies to elucidate differences in solid electrolyte interphase (SEI) composition. Nanosized (∼50 nm, n-Si) and micrometer-sized (∼4 μm, μ-Si) silicon electrodes are formulated with and without amorphous carbon and electrochemically lithiated in ethylene carbonate (EC), fluoroethylene carbonate (FEC), or vinylene carbonate (VC) based electrolytes. Notably, n-Si electrodes generate 53-61% more normalized heat relative to their μ-Si counterparts, consistent with increased surface area and electrode/electrolyte reactivity. Introduction of amorphous carbon significantly alters the heat flow profile where multiple exothermic peaks and increased normalized heat dissipation are observed for all electrolyte types. Notably, the VC-containing electrolyte demonstrates the greatest normalized heat dissipation of the electrode compositions tested showing as much as a 50% increase compared to the EC or FEC counterparts. The results are relevant to the understanding of silicon negative electrode function in the presence of electrolyte additives and provide insight relative to silicon containing cell reactivity and safety.

Abstract The global shift to electricity as the main energy carrier will require innovation in electrochemical energy storage (EES). EES systems are the key to the “electron energy economy,” minimizing losses and increasing reliability between energy supply and demand. However, steep challenges such as cost, cycle/calendar life, energy density, material availability, and safety limit widespread adoption of batteries for large-scale grid and vehicle applications. Battery innovation that meets today’s challenges will require new chemistries, which can originate from understanding charge transport phenomena at multiple time and length scales. The advancement of operando characterization can expedite this progress as changes can be observed during battery function. This article highlights progress in bulk and interfacial operando characterization of batteries. Specifically, a case study involving Fe3O4 is provided demonstrating that combining X-ray absorption spectroscopy and isothermal microcalorimetry can provide real-time characterization of productive faradaic redox processes and parasitic interfacial reactions during (de)lithiation. Graphic abstract

A series of V-substituted α-MnO2 (KxMn8-yVyO16·nH2O, y = 0, 0.2, 0.34, 0.75) samples were successfully synthesized without crystalline or amorphous impurities, as evidenced by X-ray diffraction (XRD) and Raman spectroscopy. Transmission electron microscopy (TEM) revealed a morphological evolution from nanorods to nanoplatelets as V-substitution increased, while electron-energy loss spectroscopy (EELS) confirmed uniform distribution of vanadium within the materials. Rietveld refinement of synchrotron XRD showed an increase in bond lengths and a larger range of bond angles with increasing V-substitution. X-ray absorption spectroscopy (XAS) of the as-prepared materials revealed the V valence to be >4+ and the Mn valence to decrease with increasing V content. Upon electrochemical lithiation, increasing amounts of V were found to preserve the Mn-Mnedge relationship at higher depths of discharge, indicating enhanced structural stability. Electrochemical testing showed the y = 0.75 V-substituted sample to deliver the highest capacity and capacity retention after 50 cycles. The experimental findings were consistent with the predictions of density functional theory (DFT), where the V centers impart structural stability to the manganese oxide framework upon lithiation. The enhanced electrochemistry of the y = 0.75 V-substituted sample is also attributed to its smaller crystallite size in the form of a nanoplatelet morphology, which promotes facile ion access via reduced Li-ion diffusion path lengths.

The phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a 1C rate revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated uniform lithiation across the TPE in agreement with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.

Sodium vanadate (Na1+xV3O8 or NVO) has recently attracted significant interest as a potential cathode material for an aqueous Zn ion battery for its unique pillared framework facilitating Zn ion migration. Here, we performed a detailed study on reaction mechanisms of hydrated Na2V6O16·2H2O slabs and nonhydrated Na1.25V3O8 nanorods using transmission electron microscopy. Our initial observation reveals that the thin (30–50 nm) Na2V6O16·2H2O system successfully undergoes discharge with Zn ion insertion into the structure while thick (120–170 nm) Na1.25V3O8 allows Zn ion insertion only at the surface, signifying the importance of both the presence of water and the nanostructure thickness in determining the reaction mechanism of NVO. More in-depth analysis of these two systems revealed the irreversible formation of the stable byproduct phase Zn3Nax(OH2)V2O7 (ZNVO), which likely evolved through a Zn-ion redox reaction, contributing to overall cell performance. Eventually, the entire discharge/charge process ap...

One of the inherent challenges with Li-S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS2 materials as polysulfide trapping agents. Herein the synthesis and thorough characterization of hydrothermally prepared MoS2 nanosheets that vary in layer number, morphology, lateral size, and defect content are reported. The materials were incorporated into composite sulfur-based cathodes and studied in Li-S batteries with environmentally benign ether-based electrolytes. Through directed synthesis of the MoS2 additive, the relationship between synthetically induced defects in 2 D MoS2 materials and resultant electrochemistry was elucidated and described.

As batteries revolutionize all technological areas – from miniaturized electronic devices to electric vehicles and to large-scale energy storage, understanding the complex morphological, chemical and structural evolution and their interplays has been at the forefront of the research. Synchrotron X-ray characterization techniques provide insights into the electrochemical reactions and multiscale, multiphysics environments to address the fundamental mechanisms in these systems. The presentation will highlight the application of synchrotron X-ray analysis in two Li-ion battery systems, including both aqueous and non-aqueous systems. X-ray nano-tomography via transmission X-ray microscopy and spectroscopic imaging, complemented by other diffraction, spectroscopy and microscopy techniques, will be discussed. We will present how synchrotron X-ray nano-tomography and quantitative 3D morphological analysis were instrumental in revealing the dimensionality effect of conductive carbon fillers in LiNi 1/3Mn1/3Co1/3O2 (NMC111) cathode [1]. Additionally, we will discuss how a multimodal characterization approach offered insights when probing kinetics of water-in-salt aqueous batteries with thick, porous LiV3O8-LiMn2O4 electrodes [2, 3]. Through the morphological and chemical analyses, the work aims to facilitate the design of future advanced energy storage materials, as well as provide a novel characterization framework for studying a wider range of electrochemical systems. References: [1] "Dimensionality effect of conductive carbon fillers in LiNi 1/3Mn 1/3Co 1/3O 2 cathode", Cheng-Hung Lin, Zhengyu Ju, Xiaoyin Zheng, Xiao Zhang, Nicole Zmich, Xiaoyang Liu, Kenneth J. Takeuchi, Amy C.Marschilok, Esther S.Takeuchi, Mingyuan Ge, Guihua Yu, Yu-chen Karen Chen-Wiegart, Carbon (2021), DOI: https://doi.org/10.1016/j.carbon.2021.11.014 [2] "Probing Kinetics of Water-in-Salt Aqueous Batteries with Thick Porous Electrodes", Cheng-Hung Lin, Lei Wang, Steven T. King, Jianming Bai, Lisa M. Housel, Alison H. McCarthy, Mallory N. Vila, Hengwei Zhu, Chonghang Zhao, Lijie Zou, Sanjit Ghose, Xianghui Xiao, Wah-Keat Lee, Kenneth J. Takeuchi, Amy C. Marschilok, Esther S. Takeuchi, Mingyuan Ge, and Yu-chen Karen Chen-Wiegart, ACS Central Science (2021), DOI: 10.1021/acscentsci.1c00878 [3] "Systems-Level Investigation of Aqueous Batteries for Understanding the Benefit of Water-In-Salt Electrolyte by Synchrotron Nano-Imaging", Cheng-Hung Lin, Ke Sun, Mingyuan Ge, Lisa Housel, Alison McCarthy, Mallory Vila, Chonghang Zhao, Xianghui Xiao, Wah-Keat Lee, Kenneth J. Takeuchi, Esther S. Takeuchi, Amy C. Marschilok, Yu-chen Karen Chen-Wiegart, Science Advances (2020), DOI: 10.1126/sciadv.aay7129

Mixed transition metal oxides, such as Ni0.8Mn0.1Co0.1O2 (NMC811), are intended to combine the high capacity of nickel oxides, the rate capability of cobalt oxides, and the structural stability of manganese oxides to meet the capacity and power demands of electric vehicles and commercial portable electronics. However, the capacity fade mechanisms in Ni-rich chemistries (x >y+z in NixMnyCozO2) can be elusive due to factors at the crystallographic, particle, or electrode level. In this study, bulk and surface x-ray spectroscopy characterization of NMC cathodes was used to explore cathode degradation mechanisms as influenced by cycling protocol, namely current rate and upper voltage limits. Soft x-ray absorption spectroscopy (sXAS) was used to probe the surface of recovered NMC electrodes via transition metal L-edge and O K-edge spectroscopy. The effect of rate and upper voltage potential under charge will be discussed to illustrate the versatility of sXAS for NMC cathode electrode characterization.

Aqueous electrochemical systems suffer from a low energy density due to a small voltage window of water (1.23 V). Using thicker electrodes to increase the energy density and highly concentrated “water-in-salt” (WIS) electrolytes to extend the voltage range can be a promising solution. However, thicker electrodes produce longer diffusion pathways across the electrode. The highly concentrated salts in WIS electrolytes alter the physicochemical properties which determine the transport behaviors of electrolytes. Understanding how these factors interplay to drive complex transport phenomena in WIS batteries with thick electrodes via deterministic analysis on the rate-limiting factors and kinetics is critical to enhance the rate-performance in these batteries. In this work, a multimodal approach—Raman tomography, operando X-ray diffraction refinement, and synchrotron X-ray 3D spectroscopic imaging—was used to investigate the chemical heterogeneity in LiV3O8–LiMn2O4 WIS batteries with thick porous electrodes cycled under different rates. The multimodal results indicate that the ionic diffusion in the electrolyte is the primary rate-limiting factor. This study highlights the importance of fundamentally understanding the electrochemically coupled transport phenomena in determining the rate-limiting factor of thick porous WIS batteries, thus leading to a design strategy for 3D morphology of thick electrodes for high-rate-performance aqueous batteries., Multimodal Raman and synchrotron X-ray analysis reveals that the rate-limiting factor of thick porous LiMn2O4 electrodes in a water-in-salt electrolyte is the ionic diffusion in the liquid phase. The finding furthers the understanding of kinetics in an aqueous system for electrochemical energy storage with highly concentrated electrolytes, guiding the future design of advanced 3D-architecture electrodes.

A series of V-substituted α-MnO

Molybdenum(IV) sulfide (MoS2) has generated significant interest as an electroactive material for Li-ion batteries because of its high theoretical capacity, good rate capability, and minimal volume...

Battery electrodes are complex mesoscale systems comprising an active material, conductive agent, current collector, and polymeric binder. Although significant research on composite electrode materials for Li-ion batteries focuses on the design, synthesis, and characterization of the active particles, the binder component has been shown to critically impact stability and ensure electrode integrity during volume changes induced upon cycling. Herein, we explore the ability of water-soluble, carboxylated conjugated polymer binders to aid in electron and ion transport in magnetite-based anodes. Specifically, poly[3-(potassium-4-butanoate)thiophene] (PPBT) and a potassium carboxylate functionalized 3,4-propylenedioxythiophene (ProDOT)-based copolymer (WS-PE2) were investigated and evaluated against the control, potassium salt form of poly(acrylic acid) (PAA-K). When used in conjunction with a polyethylene glycol (PEG) surface coating for the magnetite active material, PPBT provided for overall improved electro...

Conversion based transition-metal oxides as a promising class of anode materials, require proper nanostructuring for enhanced Li-ion storage capabilities. However, aggregation is found to be a common issue in nanomaterial systems, and can have detrimental effects on transport properties in composite electrodes. By employing a model transition-metal oxide anode with unique two-dimensional holey nanostructures, we investigated underlying reasons for the limited electrochemical kinetics induced by mesoscale aggregation. Through combined electrochemical and in situ characterization techniques, we demonstrate that aggregation leads to hindered interfacial charge transfer and retarded phase transformation, with the influence on kinetics escalating with more aggregation. These results shed light on more dedicated structural design for effective battery electrodes across multiple length scales.

Fe3O4 nanoparticles (NPs) with an average size of 8-10 nm have been successfully functionalized with various surface-treatment agents to serve as model systems for probing surface chemistry-dependent electrochemistry of the resulting electrodes. The surface-treatment agents used for the functionalization of Fe3O4 anode materials were systematically varied to include aromatic or aliphatic structures: 4-mercaptobenzoic acid, benzoic acid (BA), 3-mercaptopropionic acid, and propionic acid (PA). Both structural and electrochemical characterizations have been used to systematically correlate the electrode functionality with the corresponding surface chemistry. Surface treatment with ligands led to better Fe3O4 dispersion, especially with the aromatic ligands. Electrochemistry was impacted where the PA- and BA-treated Fe3O4 systems without the -SH group demonstrated a higher rate capability than their thiol-containing counterparts and the pristine Fe3O4. Specifically, the PA system delivered the highest capacity and cycling stability among all samples tested. Notably, the aromatic BA system outperformed the aliphatic PA counterpart during extended cycling under high current density, due to the improved charge transfer and ion transport kinetics as well as better dispersion of Fe3O4 NPs, induced by the conjugated system. Our surface engineering of the Fe3O4 electrode presented herein, highlights the importance of modifying the structure and chemistry of surface-treatment agents as a plausible means of enhancing the interfacial charge transfer within metal oxide composite electrodes without hampering the resulting tap density of the resulting electrode.

Magnetite, Fe3O4, holds significant interest as a Li-ion anode material because of its high theoretical capacity (926 mAh/g) associated with multiple electron transfers per cation center. Notably, both crystallite size and agglomeration influence ion transport. This report probes the effects of crystallite size (12 and 29 nm) and agglomeration on the reactions involved with the formation of the surface electrolyte interphase on Fe3O4. Isothermal microcalorimetry (IMC) was used to determine the parasitic heat evolved during lithiation by considering the total heat measured, cell polarization, and entropic contributions. Interestingly, the 29 nm Fe3O4-based electrodes produced more parasitic heat than the 12 nm samples (1346 vs 1155 J/g). This observation was explored using scanning electron microscopy (SEM) and X-ray fluorescence (XRF) mapping in conjunction with spatially resolved X-ray absorption spectroscopy (XAS). SEM imaging of the electrodes revealed more agglomerates for the 12 nm material, affirmed...

This study demonstrates that thermal regeneration is an effective approach to convert degraded phases to functioning electroactive materials, restore functional delivered capacity and recover material crystallinity while retaining the integrity of the parent electrode. V2O5 nanowires were synthesized through a facile hydrothermal method and used to fabricate V2O5/carbon nanotube (CNT) binder free electrodes. Discharge of the V2O5–CNT electrodes coupled with operando energy dispersive X-ray diffraction shows no evidence of phase segregation throughout the 150 μm thick binder free electrodes indicating full utilization of a thick electrode. When V2O5 is highly electrochemically lithiated (x > 2 in LixV2O5), irreversible phase transformation to ω-LixV2O5 was observed, accompanied by a capacity decrease of ∼40% over 100 cycles. A simple thermal treatment of the entire electrode results in a delivered capacity equal to or higher than the original value. Both phase conversion and an increase in material crystallinity as a result of thermal treatment are observed where structural analysis indicates the formation of Li1V3O8. The electrode design approach with thick electrodes and functional thermal regeneration may provide a broader choice of electroactive materials through decreasing the environmental burden by extending the lifetime of energy storage systems.

We report on the design of a battery electrode architecture in which ion and electronic transport pathways are contiguous and span the entire volume of a thick, nonplanar electrode. It is shown tha...

The electrochemical charge storage of sodium vanadate (NaV

Li-ion batteries capable of extreme fast charging (XFC) are in demand to facilitate widespread electric vehicle (EV) adoption. While the impact of fast charge on the negative electrode has been studied, degradation of state-of-the-art NMC811 under XFC conditions has not been studied in detail. Herein, cathode degradation is probed in NMC811/graphite batteries by analysis of structural and chemical changes for recovered samples previously cycled under XFC conditions and during typical cycling. NMC surface reconstruction, as determined by soft X-ray absorption, was not detected for recovered electrodes. However, bulk redox activity from X-ray absorption near edge structure measurements showed more change in the oxidation state of Ni and Co under the 1C charge rate compared to the 4C rate consistent with the electrochemistry. Increased unit cell volume contraction under the 1C rate as determined by operando X-ray diffraction suggests that higher charge rates may provide a protective effect on the cathode by reducing structural distortion due to less delithiation.

The phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a 1C rate revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated uniform lithiation across the TPE in agreement with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.

Synchrotron microscopy visualizes and furthers the understanding of cycling stability of water-in-salt Li-ion batteries., Water-in-salt (WIS) electrolytes provide a promising path toward aqueous battery systems with enlarged operating voltage windows for better safety and environmental sustainability. In this work, a new electrode couple, LiV3O8-LiMn2O4, for aqueous Li-ion batteries is investigated to understand the mechanism by which the WIS electrolyte improves the cycling stability at an extended voltage window. Operando synchrotron transmission x-ray microscopy on the LiMn2O4 cathode reveals that the WIS electrolyte suppresses the mechanical damage to the electrode network and dissolution of the electrode particles, in addition to delaying the water decomposition process. Because the viscosity of WIS is notably higher, the reaction heterogeneity of the electrodes is quantified with x-ray absorption spectroscopic imaging, visualizing the kinetic limitations of the WIS electrolyte. This work furthers the mechanistic understanding of electrode–WIS electrolyte interactions and paves the way to explore the strategy to mitigate their possible kinetic limitations in three-dimensional architectures.

Understanding the current response at an electrode from suspended solid particles in an electrolyte is crucial for developing materials to be used in semi-solid electrodes for energy storage applications. Here, an analytical model is proposed to predict and understand the current response from non-disintegrable solid particles at a rotating disk electrode. The current is shown to be limited by a combination of ion diffusion within the solid particle and the mean residence time of the particle at the rotating disk electrode. This results in a relationship between current and angular frequency of I ∝ ω 3 / 4 , instead of the classical I ∝ ω 1 / 2 predicted by Levich theory. Specifically, the current response of Li4Ti5O12 (LTO) microparticles suspended in a non-aqueous electrolyte of lithium hexafluorophosphate (LiPF6) in ethylene carbonate: diethyl carbonate (EC:DEC) was determined experimentally and compared favorably with predictions from the proposed analytical model using fitting parameters consistent with the experimental conditions.

Vanadium dioxides exist as a variety of polymorphs, each with differing structural and electrochemical capabilities. The monoclinic to rutile transition is an interesting system for study as the transition temperature is easily accessible at moderate temperature and corresponds to an increase in electrical conductivity by 2 orders of magnitude. The transition from monoclinic to rutile is characterized structurally herein using synchrotron-based X-ray diffraction and related to lithium-ion electrochemistry using electrochemical impedance spectroscopy and intermittent pulsatile galvanostatic discharge tests. The experimental results indicate a decrease in ohmic resistance for lithium-based cells tested under higher temperatures. Complementary density functional theory calculations described the experimentally measured intercalation voltages and identified a possible Li-induced LixVO2(M) to LixVO2(R) phase transition during the discharging process rationalizing the favorable impact on the function of a lithi...

One of the inherent challenges with Li-S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS

ConspectusFuture advances in energy storage systems rely on identification of appropriate target materials and deliberate synthesis of the target materials with control of their physiochemical properties in order to disentangle the contributions of distinct properties to the functional electrochemistry. This goal demands systematic inquiry using model materials that provide the opportunity for significant synthetic versatility and control. Ideally, a material family that enables direct manipulation of characteristics including composition, defects, and crystallite size while remaining within the defined structural framework would be necessary. Accomplishing this through direct synthetic methods is desirable to minimize the complicating effects of secondary processing.The structural motif most frequently used for insertion type electrodes is based on layered type structures where ion diffusion in two dimensions can be envisioned. However, lattice expansion and contraction associated with the ion movement a...

In battery systems, a solid electrolyte interphase (SEI) is formed through electrolyte reaction on an electrode surface. The formation of SEI can have both positive and negative effects on electrochemistry. The initial formation of the layer protects the electrode from further reactivity, which can improve both shelf and cycle life. However, if the layer continues to form, it can impede charge transfer, which increases cell resistance and limits cycle life. The role of SEI is particularly important when studying conversion electrodes, since phase transformations which unveil new electroactive surfaces during reduction/oxidation can facilitate electrolyte decomposition. This manuscript highlights recent developments in the understanding and control of SEI formation for magnetite (Fe3O4) conversion electrodes through electrolyte and electrode modification.

Vanadium dioxides exist as different polymorphs, each with unique electrochemical properties. Herein, we investigate the monoclinic to rutile transition of vanadium dioxide using different temperatures. The transition from monoclinic to rutile is characterized using synchrotron-based X-ray diffraction and electrochemical performance is performed using electrochemical impedance spectroscopy and intermittent pulsatile galvanostatic discharge tests in a lithium-ion environment. The experimental results indicate a decrease in ohmic resistance when lithium-ion cells are tested at higher temperatures. Density functional theory calculations also identified a possible LixVO2(M) to LixVO2(R) phase transition during the discharging process. Since the monoclinic to rutile transition corresponds to an increase of electrical conductivity by 2 orders of magnitude this can favorably impact the function of a lithium-based electrochemical cell.

Newer, more demanding energy storage systems require high energy density along with high power and fast charge rates. Conventional battery electrode fabrication techniques are often limited by how much active material they can hold in the case of slurry-cast electrodes and how much of the electrode can be utilized in the case of dense pelletized electrodes. Thick porous electrode fabrication techniques have been developed as a way to obtain a higher active mass loading and an architecture which enables ionic and electronic transport. The homogeneity of the phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a fast rate of 1C revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated homogenous lithiation across the electrode upon discharge at 1C consistent with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. The absence of the beta phase peaks in the EDXRD over extended cycling are consistent with electrochemical accessibility of only part of the active material. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.

Advances in electrochemical energy storage are key for the integration of intermittent wind and solar energy sources into the grid, widespread adoption of electric vehicles, and development of new safe and reliable consumer devices. For grid, transportation, and electronic energy storage markets, each application has distinct needs. Therefore, developing battery technology for emerging and wide-spread applications demands greater understanding of the complex chemical and electrochemical processes that occur within rechargeable batteries. Electron transfer and ion transport are the foundation of battery function where the capacity, loaded voltage and current define the practical energy and power delivery of the system. During operation, repetitive addition and removal of electrons and ions can lead to structural change within the electrode and interfacial formation that can dramatically impact electrochemical outcomes. Thus, structural, chemical, and electrochemical characterization during operation is critically important for next generation electrochemical energy storage technologies. The research efforts highlighted in this talk use multiple advanced characterization techniques, including operando methods, to probe charge transport properties, structural changes, and interfacial evolution in multiple rechargeable battery systems. Specifically, spatiotemporal x-ray fluorescence mapping was used to quantify elemental composition near the electrode and in the electrolyte of operando cells. Isothermal microcalorimetry was used to determine heat evolution due to parasitic or decomposition reactions operando. X-ray absorption spectroscopy enabled structure and oxidation state elucidation in the absence of long-range order. X-ray diffraction was employed to track phase changes of distinct electroactive materials. Using advanced characterization, these research efforts provide insight into electron transfer and ion transport properties and their impact on application relevant outcomes (resistance, cycle life, delivered capacity) of electrochemical energy storage technologies.

The electrochemical charge storage of sodium vanadate (NaV3O8 or NVO) cathodes in aqueous Zn-ion batteries has been hypothesized to be influenced by the inclusion of structural water for facilitating ion transfer in the material. Materials properties considered important (morphology, crystallite and particle size, surface area) are systematically studied herein through investigation of two NVO materials, NaV3O8· 0.34H2O [NVO(300)] and NaV3O8·0.05H2O [NVO(500)], with different water content, acicular morphologies with different size and surface area achieved via post-synthesis heat treatment. The electrochemistry of the two materials was evaluated in aqueous Zn-ion cells with 2 M ZnSO4 electrolyte using cyclic voltammetry, galvanostatic cycling, and rate capability testing. The thinner NVO(300) nanobelts (0.13 mm) demonstrate greater specific capacities and higher effective diffusion coefficients relative to the thicker NVO(500) nanorods. Notably however, while cells containing NVO(500) deliver lower specific capacity, they demonstrate enhanced capacity retention with cycling. The structural changes accompanying oxidation and reduction are elucidated via ex situ X-ray diffraction, transmission electron microscopy, and operando V K-edge X-ray absorption spectroscopy (XAS), where NVO material properties are shown to influence the ion insertion. Operando XAS verified that electron transfer corresponds directly to change in vanadium oxidation state, affirming vanadium redox as the governing electrochemical process.

Developing scalable energy storage systems with high energy and power densities is essential to meeting the ever-growing portable electronics and electric vehicle markets, which calls for development of thick electrode designs to improve the active material loading and greatly enhance the overall energy density. However, rate capabilities in lithium-ion batteries usually fall off rapidly with increasing electrode thickness due to hindered ionic transport kinetics, which is especially the issue for conversion-based electroactive materials. To alleviate the transport constrains, rational design of three-dimensional porous electrodes with aligned channels is critically needed. Herein, magnetite (Fe

Silicon offers high theoretical capacity as a negative electrode material for lithium-ion batteries; however, high irreversible capacity upon initial cycling and poor cycle life have limited commercial adoption. In this work, an operando isothermal microcalorimetry (IMC) study of a model system containing lithium metal and silicon composite film electrodes was reported on the first two cycles of (de)lithiation. The total heat flow data are analyzed in terms of polarization, entropic, and parasitic heat flow contributions to quantify and determine the onset of parasitic reactions. These parasitic reactions, which include solid−electrolyte interphase formation, contribute to electrochemical irreversibility. To complement the calorimetry, operando X-ray diffraction is used to track the phase evolution of silicon. During cycle 1 lithiation, crystalline Si undergoes transformation to amorphous lithiated silicon and ultimately to crystalline Li15Si4. The solid-state amorphization process is correlated to a decrease in entropic heat flow, suggesting that heat associated with the amorphization contributes significantly to the entropic heat flow term. This study effectively uses IMC to probe the parasitic reactions that occur during lithiation of a silicon electrode, demonstrating an approach that can be broadly applied to quantify parasitic reactions in other complex systems.

Fe