The Relationship between Ionic Conductivity and Solvation Structures of Localized High-Concentration Fluorinated Electrolytes for Lithium-Ion Batteries.

Localized high-concentration electrolytes (LHCEs) combine a diluent with a high-concentration electrolyte, offering promising properties. The ions, solvent, and diluent interact to form complex heterogeneous liquid structures, where high salt concentration clusters are embedded in the diluent. Optimizing LHCEs for desired electrolyte properties like high ionic conductivity, low viscosity, and effective solid electrolyte interphase (SEI) formation ability within the vast chemical and compositional design space requires deeper understanding and theoretical guidance. We investigated the structures and conductivities of LHCEs based on a fluorinated solvent with two different diluents at varying concentrations. 2,2,3,3-Tetrafluoropropyl trifluoroacetate (TFPTFA) enters the solvation cluster due to its stronger Li-ion interactions, whereas 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFETFE) enters only at extremely high diluent concentrations. The ionic conductivity increases with decreasing diluent concentrations, with a slope change during cluster percolation. Overall, TFETFE demonstrates higher effectiveness than TFPTFA, forming higher local salt concentration clusters and resulting in higher ionic conductivity.

Two-Dimensional Siloxene Nanosheets: Impact of Morphology and Purity on Electrochemistry.

Two-dimensional (2D) siloxene (Si6O3H6) has shown promise as a negative electrode material for Li-ion batteries due to its high gravimetric capacity and superior mechanical properties under (de)lithiation compared to bulk Si. In this work, we prepare purified siloxene nanosheets through the removal of bulk Si contaminants, use ultrasonication to control the lateral size and thickness of the nanosheets, and probe the effects of the resulting morphology and purity on the electrochemistry. The thin siloxene nanosheets formed after 4 h of ultrasonication deliver an average capacity of 810 mA h/g under a 1000 mA/g rate over 200 cycles with a capacity retention of 76%. Interestingly, the purified siloxene shows lower initial capacity but superior capacity retention over extended cycling. The 2D morphology benefit is illustrated where the parent siloxene nanosheet morphology and structure were largely maintained based on operando optoelectrochemistry, in situ Raman, ex situ scanning electron microscopy, and ex situ transmission electron microscopy. Furthermore, the purified siloxene-based electrode free from crystalline Si impurity experiences the least expansion upon (de)lithiation as visualized by cross-section electron microscopy of samples recovered post-cycling.

Electron and Ion Transport in Lithium and Lithium-Ion Battery Negative and Positive Composite Electrodes.

Electrochemical energy storage systems, specifically lithium and lithium-ion batteries, are ubiquitous in contemporary society with the widespread deployment of portable electronic devices. Emerging storage applications such as integration of renewable energy generation and expanded adoption of electric vehicles present an array of functional demands. Critical to battery function are electron and ion transport as they determine the energy output of the battery under application conditions and what portion of the total energy contained in the battery can be utilized. This review considers electron and ion transport processes for active materials as well as positive and negative composite electrodes. Length and time scales over many orders of magnitude are relevant ranging from atomic arrangements of materials and short times for electron conduction to large format batteries and many years of operation. Characterization over this diversity of scales demands multiple methods to obtain a complete view of the transport processes involved. In addition, we offer a perspective on strategies for enabling rational design of electrodes, the role of continuum modeling, and the fundamental science needed for continued advancement of electrochemical energy storage systems with improved energy density, power, and lifetime.

Simultaneous Elucidation of Solid and Solution Manganese Environments via Multiphase Operando Extended X-ray Absorption Fine Structure Spectroscopy in Aqueous Zn/MnO2 Batteries.

Aqueous Zn/MnO2 batteries (AZMOB) with mildly acidic electrolytes hold promise as potential green grid-level energy storage solutions for clean power generation. Mechanistic understanding is critical to advance capacity retention needed by the application but is complex due to the evolution of the cathode solid phases and the presence of dissolved manganese in the electrolyte due to a dissolution-deposition redox process. This work introduces operando multiphase extended X-ray absorption fine structure (EXAFS) analysis enabling simultaneous characterization of both aqueous and solid phases involved in the Mn redox reactions. The methodology was successfully conducted in multiple electrolytes (ZnSO4, Zn(CF3SO3)2, and Zn(CH3COO)2) revealing similar manganese coordination environments but quantitative differences in distribution of Mnn+ species in the solid and solution phases. Complementary Raman spectroscopy was utilized to identify the less crystalline Mn-containing products formed under charge at the cathodes. This was further augmented by transmission electron microscopy (TEM) to reveal the morphology and surface condition of the deposited solids. The results demonstrate an effective approach for bulk-level characterization of poorly crystalline multiphase solids while simultaneously gaining insight into the dissolved transition-metal species in solution. This work provides demonstration of a useful approach toward gaining insight into complex electrochemical mechanisms where both solid state and dissolved active materials are important contributors to redox activity.

Design principles for heterointerfacial alloying kinetics at metallic anodes in rechargeable batteries.

How surface chemistry influences reactions occurring thereupon has been a long-standing question of broad scientific and technological interest. Here, we consider the relation between the surface chemistry at interfaces and the reversibility of electrochemical transformations at rechargeable battery electrodes. Using Zn as a model system, we report that a moderate strength of chemical interaction between the deposit and the substrate-neither too weak nor too strong-enables highest reversibility and stability of the plating/stripping redox processes. Focused ion beam and electron microscopy were used to directly probe the morphology, chemistry, and crystallography of heterointerfaces of distinct natures. Analogous to the empirical Sabatier principle for chemical heterogeneous catalysis, our findings arise from competing interfacial processes. Using full batteries with stringent negative electrode-to-positive electrode capacity (N:P) ratios, we show that such knowledge provides a powerful tool for designing key materials in highly reversible battery systems based on Earth-abundant, low-cost metals such as Zn and Na.

The Dopamine Assisted Synthesis of MoO3/Carbon Electrodes With Enhanced Capacitance in Aqueous Electrolyte.

A capacitance increase phenomenon is observed for MoO3 electrodes synthesized via a sol-gel process in the presence of dopamine hydrochloride (Dopa HCl) as compared to α-MoO3 electrodes in 5M ZnCl2 aqueous electrolyte. The synthesis approach is based on a hydrogen peroxide-initiated sol-gel reaction to which the Dopa HCl is added. The powder precursor (Dopa)xMoOy, is isolated from the metastable gel using freeze-drying. Hydrothermal treatment (HT) of the precursor results in the formation of MoO3 accompanied by carbonization of the organic molecules; designated as HT-MoO3/C. HT of the precipitate formed in the absence of dopamine in the reaction produced α-MoO3, which was used as a reference material in this study (α-MoO3-ref). Scanning electron microscopy (SEM) images show a nanobelt morphology for both HT-MoO3/C and α-MoO3-ref powders, but with distinct differences in the shape of the nanobelts. The presence of carbonaceous content in the structure of HT-MoO3/C is confirmed by FTIR and Raman spectroscopy measurements. X-ray diffraction (XRD) and Rietveld refinement analysis demonstrate the presence of α-MoO3 and h-MoO3 phases in the structure of HT-MoO3/C. The increased specific capacitance delivered by the HT-MoO3/C electrode as compared to the α-MoO3-ref electrode in 5M ZnCl2 electrolyte in a -0.25-0.70 V vs. Ag/AgCl potential window triggered a more detailed study in an expanded potential window. In the 5M ZnCl2 electrolyte at a scan rate of 2 mV s-1, the HT-MoO3/C electrode shows a second cycle capacitance of 347.6 F g-1. The higher electrochemical performance of the HT-MoO3/C electrode can be attributed to the presence of carbon in its structure, which can facilitate electron transport. Our study provides a new route for further development of metal oxides for energy storage applications.

Multimodal electrochemistry coupled microcalorimetric and X-ray probing of the capacity fade mechanisms of Nickel rich NMC - progress and outlook.

Lithium nickel manganese cobalt oxide (NMC) is a commercially successful Li-ion battery cathode due to its high energy density; however, its delivered capacity must be intentionally limited to achieve capacity retention over extended cycling. To design next-generation NMC batteries with longer life and higher capacity the origins of high potential capacity fade must be understood. Operando hard X-ray characterization techniques are critical for this endeavor as they allow the acquisition of information about the evolution of structure, oxidation state, and coordination environment of NMC as the material (de)lithiates in a functional battery. This perspective outlines recent developments in the elucidation of capacity fade mechanisms in NMC through hard X-ray probes, surface sensitive soft X-ray characterization, and isothermal microcalorimetry. A case study on the effect of charging potential on NMC811 over extended cycling is presented to illustrate the benefits of these approaches. The results showed that charging to 4.7 V leads to higher delivered capacity, but much greater fade as compared to charging to 4.3 V. Operando XRD and SEM results indicated that particle fracture from increased structural distortions at >4.3 V was a contributor to capacity fade. Operando hard XAS revealed significant Ni and Co redox during cycling as well as a Jahn-Teller distortion at the discharged state (Ni3+); however, minimal differences were observed between the cells charged to 4.3 and 4.7 V. Additional XAS analyses using soft X-rays revealed significant surface reconstruction after cycling to 4.7 V, revealing another contribution to fade. Operando isothermal microcalorimetry (IMC) indicated that the high voltage charge to 4.7 V resulted in a doubling of the heat dissipation when compared to charging to 4.3 V. A lowered chemical-to-electrical energy conversion efficiency due to thermal energy waste was observed, providing a complementary characterization of electrochemical degradation. The work demonstrates the utility of multi-modal X-ray and microcalorimetric approaches to understand the causes of capacity fade in lithium-ion batteries with Ni-rich NMC.

Interfacial Reactivity of Silicon Electrodes: Impact of Electrolyte Solvent and Presence of Conductive Carbon.

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.

Dry heat sterilization as a method to recycle N95 respirator masks: The importance of fit.

In times of crisis, including the current COVID-19 pandemic, the supply chain of filtering facepiece respirators, such as N95 respirators, are disrupted. To combat shortages of N95 respirators, many institutions were forced to decontaminate and reuse respirators. While several reports have evaluated the impact on filtration as a measurement of preservation of respirator function after decontamination, the equally important fact of maintaining proper fit to the users' face has been understudied. In the current study, we demonstrate the complete inactivation of SARS-CoV-2 and preservation of fit test performance of N95 respirators following treatment with dry heat. We apply scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD) measurements, Raman spectroscopy, and contact angle measurements to analyze filter material changes as a consequence of different decontamination treatments. We further compared the integrity of the respirator after autoclaving versus dry heat treatment via quantitative fit testing and found that autoclaving, but not dry heat, causes the fit of the respirator onto the users face to fail, thereby rendering the decontaminated respirator unusable. Our findings highlight the importance to account for both efficacy of disinfection and mask fit when reprocessing respirators to for clinical redeployment.

Impact of Charge Voltage on Factors Influencing Capacity Fade in Layered NMC622: Multimodal X-ray and Electrochemical Characterization.

Ni-rich NMC is an attractive Li-ion battery cathode due to its combination of energy density, thermal stability, and reversibility. While higher delivered energy density can be achieved with a more positive charge voltage limit, this approach compromises sustained reversibility. Improved understanding of the local and bulk structural transformations as a function of charge voltage, and their associated impacts on capacity fade are critically needed. Through simultaneous operando synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) of cells cycled at 3-4.3 or 3-4.7 V, this study presents an in-depth investigation into the effects of voltage window on local coordination, bulk structure, and oxidation state. These measurements are complemented by ex situ X-ray fluorescence (XRF) mapping and scanning electrochemical microscopy mapping (SECM) of the negative electrode, X-ray photoelectron spectroscopy (XPS) of the positive electrode, and cell level electrochemical impedance spectroscopy (EIS). Initially, cycling between 3 and 4.7 V leads to greater delivered capacity due to greater lithium extraction, accompanied by increased structural distortion, moderately higher Ni oxidation, and substantially higher Co oxidation. Continued cycling at this high voltage results in suppressed Ni and Co redox, greater structural distortion, increased levels of transition metal dissolution, higher cell impedance, and 3× greater capacity fade.

Characterization of Materials Used as Face Coverings for Respiratory Protection.

Use of masks is a primary tool to prevent the spread of the novel COVID-19 virus resulting from unintentional close contact with infected individuals. However, detailed characterization of the chemical properties and physical structure of common mask materials is lacking in the current literature. In this study, a series of commercial masks and potential mask materials, including 3M Particulate Respirator 8210 N95, a material provided by Oak Ridge National Laboratory Carbon Fiber Technology Facility (ORNL/CFTF), and a Filti Face Mask Material, were characterized by a suite of techniques, including scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Wetting properties of the mask materials were quantified by measurements of contact angle with a saliva substitute. Mask pass-through experiments were performed using a dispersed metal oxide nanoparticle suspension to model the SARS-CoV-2 virus, with quantification via spatially resolved X-ray fluorescence mapping. Notably, all mask materials tested provided a strong barrier against respiratory droplet breakthrough. The comparisons and characterizations provided in this study provide useful information when evaluating mask materials for respiratory protection.

Ultrahigh-Capacity and Scalable Architected Battery Electrodes via Tortuosity Modulation.

A thick electrode with high areal capacity is a straightforward approach to maximize the energy density of batteries, but the development of thick electrodes suffers from both fabrication challenges and electron/ion transport limitations. In this work, a low-tortuosity LiFePO4 (LFP) electrode with ultrahigh loadings of active materials and a highly efficient transport network was constructed by a facile and scalable templated phase inversion method. The instant solidification of polymers during phase inversion enables the fabrication of ultrathick yet robust electrodes. The open and aligned microchannels with interconnected porous walls provide direct and short ion transport pathways, while the encapsulation of active materials in the carbon framework offers a continuous pathway for electron transport. Benefiting from the structural advantages, the ultrathick bilayer LiFePO4 electrodes (up to 1.2 mm) demonstrate marked improvements in rate performance and cycling stability under high areal loadings (up to 100 mg cm-2). Simulation and operando structural characterization also reveal fast transport kinetics. Combined with the scalable fabrication, our proposed strategy presents an effective alternative for designing practical high energy/power density electrodes at low cost.

Local and Bulk Probe of Vanadium-Substituted α-Manganese Oxide (α-KxVyMn8-yO16) Lithium Electrochemistry.

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.

Structural and electrochemical investigation of crystallite size controlled zinc ferrite (ZnFe2O4).

Zinc ferrite, ZnFe2O4(ZFO), is a promising electrode material for next generation Li-ion batteries because of its high theoretical capacity and low environmental impact. In this report, synthetic control of crystallite size from the nanometer to submicron scale enabled probing of the relationships between ZFO size and electrochemical behavior. A facile two-step coprecipitation and annealing preparation method was used to prepare ZFO with controlled sizes ranging ∼9 to >200 nm. Complementary synchrotron and electron microscopy techniques were used to characterize the series of materials. Increasing the annealing temperature increased crystallinity and decreased microstrain, while local structural ordering was maintained independent of crystallite size. Electrochemical characterization revealed that the smaller sized materials delivered higher capacities during initial lithiation. Larger sized particles exhibited a lack of distinct electrochemical signatures above 1.0 V, suggesting that the longer diffusion length associated with greater crystallite size causes the lithiation process to proceed via non discrete lithium insertion, cation migration, and conversion processes. Notably, larger particles exhibited enhanced electrochemical reversibility over 50 cycles, with capacity retention improving from <20% to >40% at C/2 cycling rate. This intriguing result was probed through x-ray absorption spectroscopy (XAS) and x-ray photoelectron spectroscopy (XPS) measurements of the cycled electrodes. XAS revealed that the larger crystallite size materials do not completely convert to Fe0during the first lithiation and that independent of size, delithiation results in the formation of nanocrystalline FeO and ZnO phases rather than ZnFe2O4. After 20 cycles, the larger crystallites showed reversibility between partially oxidized FeO in the charged state and Fe0in the discharged state, while the smaller crystallite size material was electrochemically inactive as Fe0. XPS analysis revealed more significant solid electrolyte interphase (SEI) formation on the cycled electrodes utilizing ZFO with smaller crystallite size. This finding suggests that excessive SEI buildup on the smaller sized, higher surface area ZFO particles contributes to their reduced electrochemical reversibility relative to the larger crystallite size materials.

Reusing Face Covering Masks: Probing the Impact of Heat Treatment.

The COVID-19 pandemic resulted in imminent shortages of personal protective equipment such as face masks. To address the shortage, new sterilization or decontamination procedures for masks are quickly being developed and employed. Dry heat and steam sterilization processes are easily scalable and allow treatment of large sample sizes, thus potentially presenting fast and efficient decontamination routes, which could significantly ease the rapidly increasing need for protective masks globally during a pandemic like COVID-19. In this study, a suite of structural and chemical characterization techniques, including scanning electron microscopy (SEM), contact angle, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman were utilized to probe the heat treatment impact on commercially available 3M 8210 N95 Particulate Respirator and VWR Advanced Protection surgical mask. Unique to this study is the use of the synchrotron-based In situ and Operando Soft X-ray Spectroscopy (IOS) beamline (23-ID-2) housed at the National Synchrotron Light Source II at Brookhaven National Laboratory for near-edge X-ray absorption spectroscopy (NEXAFS).

(De)lithiation of spinel ferrites Fe3O4, MgFe2O4, and ZnFe2O4: a combined spectroscopic, diffraction and theory study.

Iron based materials hold promise as next generation battery electrode materials for Li ion batteries due to their earth abundance, low cost, and low environmental impact. The iron oxide, magnetite Fe3O4, adopts the spinel (AB2O4) structure. Other 2+ cation transition metal centers can also occupy both tetrahedral and/or octahedral sites in the spinel structure including MgFe2O4, a partially inverse spinel, and ZnFe2O4, a normal spinel. Though structurally similar to Fe3O4 in the pristine state, previous studies suggest significant differences in structural evolution depending on the 2+ cation in the structure. This investigation involves X-ray absorption spectroscopy and X-ray diffraction affirmed by density functional theory (DFT) to elucidate the role of the 2+ cation on the structural evolution and phase transformations during (de)lithiation of the spinel ferrites Fe3O4, MgFe2O4, and ZnFe2O4. The cation in the inverse, normal and partially inverse spinel structures located in the tetrahedral (8a) site migrates to the previously unoccupied octahedral 16c site by 2 electron equivalents of lithiation, resulting in a disordered [A]16c[B2]16dO4 structure. DFT calculations support the experimental results, predicting full displacement of the 8a cation to the 16c site at 2 electron equivalents. Substitution of the 2+ cation results in segregation of oxidized phases in the charged state. This report provides significant structural insight into the (de)lithiation mechanisms for an intriguing class of iron oxide materials.

Spontaneous and field-induced crystallographic reorientation of metal electrodeposits at battery anodes.

The propensity of metal anodes of contemporary interest (e.g., Li, Al, Na, and Zn) to form non-planar, dendritic morphologies during battery charging is a fundamental barrier to achievement of full reversibility. We experimentally investigate the origins of dendritic electrodeposition of Zn, Cu, and Li in a three-electrode electrochemical cell bounded at one end by a rotating disc electrode. We find that the classical picture of ion depletion-induced growth of dendrites is valid in dilute electrolytes but is essentially irrelevant in the concentrated (≥1 M) electrolytes typically used in rechargeable batteries. Using Zn as an example, we find that ion depletion at the mass transport limit may be overcome by spontaneous reorientation of Zn crystallites from orientations parallel to the electrode surface to dominantly homeotropic orientations, which appear to facilitate contact with cations outside the depletion layer. This chemotaxis-like process causes obvious texturing and increases the porosity of metal electrodeposits.

Vanadium-Substituted Tunnel Structured Silver Hollandite (Ag1.2VxMn8-xO16): Impact on Morphology and Electrochemistry.

A series of tunnel structured V-substituted silver hollandite (Ag1.2VxMn8-xO16, x = 0-1.4) samples is prepared and characterized through a combination of synchrotron X-ray diffraction (XRD), synchrotron X-ray absorption spectroscopy (XAS), laboratory Raman spectroscopy, and electron microscopy measurements. The oxidation states of the individual transition metals are characterized using V and Mn K-edge XAS data indicating the vanadium centers exist as V5+, and the Mn oxidation state decreases with increased V substitution to balance the charge. Scanning transmission electron microscopy of reduced materials shows reduction-displacement of silver metal at high levels of lithiation. In lithium batteries, the V-substituted tunneled manganese oxide materials reveal previously unseen reversible nonaqueous Ag electrochemistry and exhibit up to 2.5× higher Li storage capacity relative to their unsubstituted counterparts. The highest capacity was observed for the Ag1.2(V0.8Mn7.2)O16·0.8H2O material with an intermediate level of V substitution, likely due to a combination of the atomic composition, the morphology of the particle, and the homogeneous distribution of the active material within the electrode structure where factors over multiple length scales contribute to the electrochemistry.

Reversible epitaxial electrodeposition of metals in battery anodes.

The propensity of metals to form irregular and nonplanar electrodeposits at liquid-solid interfaces has emerged as a fundamental barrier to high-energy, rechargeable batteries that use metal anodes. We report an epitaxial mechanism to regulate nucleation, growth, and reversibility of metal anodes. The crystallographic, surface texturing, and electrochemical criteria for reversible epitaxial electrodeposition of metals are defined and their effectiveness demonstrated by using zinc (Zn), a safe, low-cost, and energy-dense battery anode material. Graphene, with a low lattice mismatch for Zn, is shown to be effective in driving deposition of Zn with a locked crystallographic orientation relation. The resultant epitaxial Zn anodes achieve exceptional reversibility over thousands of cycles at moderate and high rates. Reversible electrochemical epitaxy of metals provides a general pathway toward energy-dense batteries with high reversibility.

Anode Overpotential Control via Interfacial Modification: Inhibition of Lithium Plating on Graphite Anodes.

Lithium-metal deposition on graphite anodes limits the cycle life and negatively impacts safety of the current state of the art Li-ion batteries. Herein, deliberate interfacial modification of graphite electrodes via direct current (DC) magnetron sputtering of nanoscale layers of Cu and Ni is employed to increase the overpotential for Li deposition and suppress Li plating under high rate charge conditions. Due to their nanoscale, the deposited surface films have minimal impact (∼0.16% decrease) on cell level theoretical energy density. Interfacial properties of the anodes are thoroughly characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and spatially resolved mapping X-ray absorption near edge structure (XANES) spectroscopy. The spectroscopic measurements indicate that the Cu and Ni coatings form oxide upon exposure to an ambient environment, but they are reduced within the electrochemical cell and remain in a metallic state. Li plating is quantified by X-ray diffraction and associated electrochemistry measurements revealing that the surface treatment effectively reduces the quantity of the plated Li metal by ∼50% compared to untreated electrodes. These results establish an effective method using interfacial modification to achieve deliberate control of Li-metal deposition overpotential and reduction of lithium plating on graphite.