A structural battery is defined as being multifunctional; it is a load bearing system with some electrochemical energy storing capability. The electrolyte system is the key enabler for a multifunctional structural battery as it must possess sufficient ionic conductivity (~10 -4 S/cm) and mechanical strength (Youngs’s modulus ~ 600-900 MPa) simultaneously. Polymeric systems offer the best possible scenario for practical realization of multifunctional structural batteries due to a set of favorable properties, such as reasonable ionic conductivity, easy processability etc. In the present work, we focus on the development of a dual-phase structural battery electrolyte to optimize ionic conductivity and mechanical performance simultaneously. An epoxy resin-based system is chosen due to its high mechanical strength and its ability for in-situ polymerization that leads to a unique microstructure promoting multi-functionality. Diglycidyl ether of Bisphenol A (DGEBA) accounts for the epoxy to provide hard segments in the matrix and is cured by an amine compound (Jeffamine T-403). A liquid electrolyte is added to the system for improving ionic conductivity without compromising its mechanical strength substantially. Multiple liquid components consisting of lithium salt and solvents are considered -lithium bis(trifluoromethanesulfonyl)imide (LITFSI) dissolved in a solution of ethylene carbonate (EC) and dimethyl methyl phosphonate (DMMP) and LiTFSI dissolved in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI). Ionic conductivity of the electrolyte systems as a function of temperature is measured utilizing electrochemical impedance spectroscopy. Uniaxial load tests are performed to evaluate the mechanical properties (e.g., Young’s modulus, Yield strength) of the epoxy-based electrolyte systems with and without the addition of the ion conducting liquids. Comparative data on the epoxy-based systems containing varying amounts of liquid components will be presented.

Energy density of LIBs are primarily limited by cathodes and further development of cathode materials requires in-depth understanding of the structural and compositional changes spanning across various length scales involved during electrochemical delithiation/lithiaton. Cathode materials are usually synthesized as secondary particles (∼10 µm) that are sintered agglomerates of smaller primary particles (∼100s µm). Lithium distribution may not necessarily be uniform across the entirety of these particles in typical state-of-the-art layered cathodes during electrochemical cycling. A detailed knowledge of lithium distribution within secondary particles is crucially important for obtaining a comprehensive understanding of the energy storage system. To truly understand the structural changes taking place at the nano and atomic scales, high spatial resolution techniques are of paramount importance for understanding the lithium distribution and optimizing/developing future LIB cathodes. STEM-EELS is ideally suited for obtaining such information at the desired (atomic) spatial resolution. In the present work, nanoscale lithium-ion distribution was investigated among various primary particles within a secondary particle of state-of-the-art Ni-rich layered LIB cathode using identical location scanning transmission electron microscopy with electron energy loss spectroscopy (IL-STEM-EELS) by making use of a specially designed electrochemical cell employing TEM grids. Identical location allows for the imaging of the same location before and after electrochemical testing to evaluate localized changes. Nanoscale lithium-ion distribution along with the electron beam dose effects on the nanoscale/atomic structure of layered NMC532 cathodes at various charge stages will be presented.

The microstructural stability of composite electrodes during electrochemical cycling is critically important as it dictates the performance of Li-ion batteries. The issue becomes even more important for the high capacity alloying anode such as silicon that typically exhibits dramatic lithiation–delithiation-induced volume changes. The solid electrolyte interphase (SEI) layer formed on the active electrode surface has a profound effect on the overall microstructural stability of composite electrodes. An ideal SEI layer allows Li+ ions in and out of the electrode, but is an insulator to electrons, preventing the electrolyte from being further reduced. However, the SEI layers formed during initial lithiation may experience changes or degradation with subsequent cycling, adversely affecting the electrode performance. A combination of hyperpolarized 129Xe and 7Li nuclear magnetic resonance spectroscopies was applied to probe the microstructures of nanocomposite silicon electrodes at various stages of the lithiation–delithiation cycle. The results obtained from this study shed light on the degradation mechanism of nanocomposite Si electrodes upon electrochemical cycling and should prove useful in the effort to design more robust electrodes in the future.

Solid electrolyte interphase (SEI) plays an important role in determining electrochemical performances of Li-ion batteries. The ideal SEI layer protects the electrolyte from being further reduced on the electrode surface and allows Li-ion diffusion in and out of electrodes without any consumption. However, degradation of the SEI layer over time, which contributes to the thickening of the SEI layer, is a leading pathway for gradual capacity fade. In this study, a hyperpolarized (HP) Xe-129 nuclear magnetic resonance (NMR) technique was applied for the first time to probe changes in porosity and connectivity in Si nanoparticle composite electrodes as a result of the SEI formation. Nanopores are present in nanocomposite electrodes as a result of aggregation of the constituting nanoparticles. The connectivity among nanopores greatly affects the ion transport property of the electrode materials, which has a substantial influence on the overall energy output of Li-ion batteries. In this work, information on thickness, uniformity of the SEI layer, and connectivity of the pores in the composite electrodes upon growing SEI was obtained from the analysis of temperature-dependent HP Xe-129 NMR spectra. Such information is useful for gaining a better understanding of the degradation mechanism of SEI. This study demonstrates that HP Xe-129 NMR is a potentially unique tool in probing the porosity and connectivity changes in porous practical electrodes during electrochemical cycling.

Electrochemical cycling induced mechanical damage of electrode materials actively contributes towards the performance degradation of lithium-ion batteries. The correlation between mechanical damage and performance degradation in anode materials that show large volume changes, such as silicon, graphite and tin, has been amply demonstrated. On the hand, typical oxide electrodes undergo only a few % volume changes, and the non-reversible nature of the crystal structure evolution as a function of lithium concentration in such electrodes is, in general, believed to be the limiting factor for performance degradation. For example, cycling in Li x CoO 2 is generally limited to 0≤x≤0.5, mainly, due to the irreversibility associated with the crystal structure changes beyond further Li extraction/re-insertion. However, due to their brittle nature only a few % volume changes can have significant implication on the mechanical damage leading to performance degradation for such ceramic oxide electrodes. Thus, the issue of electrochemical cycling induced mechanical degradation in oxide electrodes is being actively explored in recent years [1-2]. In this work, we present in-situ stress evolution of i) two canonical cathode systems, namely layered LiCoO 2 and spinel LiMn 2 O 4 and ii) one conversion electrode system, Co 3 O 4 in thin film configuration to quantify the driving force leading to the mechanical degradation. In-situ stress evolution in thin film electrodes was measured by monitoring the change in the elastic substrate curvature during electrochemical cycling in a suitably designed beaker cell using multiple-beam optical sensing (MOS) method. Thin films of the electrodes were prepared using solution deposition technique. Structural characterizations using XRD and Raman spectroscopy showed predominant presence of desired (poly)crystalline phases in the as prepared samples. In addition, SEM images also revealed the presence of dense microstructural features in the as prepared films. During Li-extraction from layered Li x CoO 2 , there was almost linear increase in compressive stress up to ~50% Li removal, which is consistent with its lattice parameter evolution during Li removal [3], and a maximum compressive stress of ~0.35 GPa was observed for x~0.5. Upon lithiation there was almost reversible stress evolution in Li x CoO 2 . Similar behavior was also observed for subsequent cycles as well, while limiting the upper charging cut-off voltage to 4.3V. On the other hand, initial delithiation from spinel Li x Mn 2 O 4 induces tensile stress up to ~4.1V, beyond which the induced stress reverses direction (termed as “compressive drop”) with further delithiation (up to 4.3 V). This reversal of stress evolution in the later stages of delithiation from spinel Li x Mn 2 O 4 is in apparent contradiction with the lattice parameter evolution of spinel Li x Mn 2 O 4 during lithium extraction [4]. Upon lithium re-insertion (up to 3.5V), induced compressive stress increases linearly. The subsequent cycles (in the 4V region), however, did not show any “compressive drop” during later stages of delithiation and the induced stress evolved reversibly during delithiation-lithiation. The origin of this first cycle “compressive drop” in spinel LiMn 2 O 4 is not known at present. In an attempt to establish the origin of the observed first cycle “compressive drop” in spinel LiMn 2 O 4 thin films, stress measurement data varying multiple parameters including cathode film thickness, reannealing a cycled electrode will be presented. The effect of stress evolution in these thin film electrodes during cycling as a function of cycling voltage window and current density will also be presented and discussed in the light of their crystal structural changes. References D. J. Miller, C. Proff, J. G. Wen, D. P. Abraham and J. Bareno, Adv. Energy Mater., 3 , 1098 (2013). W. H. Woodford, W. C. Carter and Y. M. Chiang, Energy Environ. Sci., 5 , 8014 (2012). J. N. Reimers and J. R. Dahn, J. Electrochem. Soc., 139 , 2091 (1992). Y. Xia and M. Yoshio, J. Electrochem. Soc., 143 , 825 (1996).

Porosity and interconnectivity of pores play an important role in the performance of composite electrodes in Li ion batteries. Hyperpolarized (HP) Xe-129 nuclear magnetic resonance (NMR) is powerful for probing porosity and interconnectivity of nanopores. This study represents the first time that temperature-dependent HP Xe-129 NMR has been successfully applied to explore the pore structure and interconnectivity in composite electrodes made of nano Si powder, super P carbon, and sodium carboxyl methyl cellulose (CMC) binder. In particular, this work focuses on the influence of the binder content on the porosity and pore interconnectivity in Si composite electrode (Si + C):CMC materials. Our data from HP Xe-129 NMR spectra show that the CMC content has an effect on the porosity and pore interconnectivity of Si nanocomposite electrode materials. We determined parameters, such as pore size, heat of adsorption, and characteristic chemical shift, of (Si + C):CMC samples based on the temperature-dependent HP Xe-129 NMR data. Furthermore, HP Xe-129 NMR data suggest that pore structures are partially collapsed at low temperatures for the electrode materials with a higher CMC content, indicating the potential usefulness of variable-temperature HP Xe-129 MNR for examining the integrity of the electrode. This study demonstrates that HP Xe-129 NMR is a powerful diagnostic tool for probing any changes in porosity and pore connectivity in electrode materials. It provides a better understanding of the mechanical failure as a result of the large volume expansion in Si-based anodes, enabling the design of more robust electrodes in the future.

Real time monitoring of stress evolution in electrodes during electrochemical cycling can help quantify the driving forces that dictate their mechanical degradation. In the present work, in-situ stress evolution in thin films of spinel Li1+xMn2O4 (LMO) was measured by monitoring the change in the elastic substrate curvature during electrochemical cycling in a specially designed beaker cell in the 3.5-4.3 V (vs. Li/Li+) voltage range. The LMO thin films were prepared using a solution deposition technique and their structures and morphologies were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The stress evolution in the early part of the first delithiation cycle (<4.05 V) was consistent with the XRD data. However, stress evolution during later stages of the first delithiation cycle (>4.05 V) was not consistent with the XRD results, and showed irreversible behavior, suggesting irreversible changes in the electrode. Beyond the first delithiation cycle, the stress evolution was reversible, with a steady buildup of compressive and tensile stress during lithium insertion and extraction, respectively. Measurements on LMO films of varying thicknesses suggest that the first cycle irreversibility in stress response arises primarily from the electrode bulk. (C) 2016 The Electrochemical Society. All rights reserved.

The effect of elastic strain on catalytic activity of platinum (Pt) toward oxygen reduction reaction (ORR) is investigated through dealloyed Pt-Cu thin films; stress evolution in the dealloyed layer and the mass of the Cu removed are measured in real-time during electrochemical dealloying of (111)-textured thin-film PtCu (1:1, atomic ratio) electrodes. In situ stress measurements are made using the cantilever-deflection method, and nanogravimetric measurements are made using an electrochemical quartz crystal nanobalance. Upon dealloying via successive voltammetric sweeps between -0.05 and 1.15 V vs standard hydrogen electrode, compressive stress develops in the dealloyed Pt layer at the surface of thin-film PtCu electrodes. The dealloyed films also exhibit enhanced catalytic activity toward ORR compared with polycrystalline Pt. In situ nanogravimetric measurements reveal that the mass of dealloyed Cu is approximately 210 +/- 46 ng/cm(2), which corresponds to a dealloyed layer thickness of 1.2 +/- 0.3 monolayers or 0.16 +/- 0.04 nm. The average biaxial stress in the dealloyed layer is estimated to be 4.95 +/- 1.3 GPa, which corresponds to an elastic strain of 1.47% +/- 0.4%. In addition, density functional theory calculations have been carried out on biaxially strained Pt(111) surface to characterize the effect of strain on its ORR activity; the predicted shift in the limiting potentials due to elastic strain is found to be in good agreement with the experimental shift in the cyclic voltammograms for the dealloyed PtCu thin film electrodes.

Layered sodium-ion cathode material P2-Na0.85Li0.17Ni0.21Mn0.64O2 was investigated using operando XAS to characterize structural changes occurring in the material during electrochemical sodiation/desodiation. Based on XANES data, the primary mode of charge compensation in this material is due to Ni2-3/4+ redox activity, while the Mn remains in the +4 oxidation state, thereby providing stability to this material during extended cycling. Investigation of the initial state of the compound by high resolution synchrotron XRD and Li-6 MAS NMR revealed a significant amount of structural disorder due to integration of a small amount of monoclinic layered Li phase within the overall hexagonal layered Na-structure, which manifests as Li-induced stacking faults. High quality EXAFS data could be obtained using our cell construction and revealed the local structural evolution around the redox active Ni centers. (C) 2014 The Electrochemical Society. All rights reserved.

It has become clear that cycling lithium‐oxygen cells in carbonate electrolytes is impractical, as electrolyte decomposition, triggered by oxygen reduction products, dominates the cell chemistry. This research shows that employing an α ‐MnO 2 /ramsdellite‐MnO 2 electrode/electrocatalyst results in the formation of lithium‐oxide‐like discharge products in propylene carbonate, which has been reported to be extremely susceptible to decomposition. X‐ray photoelectron data have shown that what are likely lithium oxides (Li 2 O 2 and Li 2 O) appear to form and decompose on the air electrode surface, particularly at the MnO 2 surface, while Li 2 CO 3 is also formed. By contrast, cells without α ‐MnO 2 /ramsdellite‐MnO 2 fail rapidly in electrochemical cycling, likely due to the differences in the discharge product. Relatively high electrode capacities, up to 5000 mAh/g (carbon + electrode/electrocatalyst), have been achieved with non‐optimized air electrodes. Insights into reversible insertion reactions of lithium, lithium peroxide (Li 2 O 2 ) and lithium oxide (Li 2 O) in the tunnels of α ‐MnO 2 , and the reaction of lithium with ramsdellite‐MnO 2 , as determined by first principles density functional theory calculations, are used to provide a possible explanation for some of the observed results. It is speculated that a Li 2 O‐stabilized and partially‐lithiated electrode component, 0.15Li 2 O· α ‐Li x MnO 2 , that has Mn 4+/3+ character may facilitate the Li 2 O 2 /Li 2 O discharge/charge chemistries providing dual electrode/electrocatalyst functionality.

Enhanced catalytic activity of de-alloyed PtCu electrodes towards oxygen reduction reaction had been demonstrated in thin-film and core-shell geometries. The enhancement in catalytic activity is typically attributed to strained Pt layer (in thin-film electrodes) and Pt shell (in core-shell electrodes). The magnitude and the nature (compressive/tensile) of the strain on de-alloyed Pt were estimated thus far using lattice-constant measurements (via X-ray diffraction) on de-alloyed electrodes. In this work, we report real-time stress and nano-gravimetric measurements made during de-alloying of thin-film PtCu electrodes. In situ stress measurements were made using cantilever-deflection method, and gravimetric measurements were made using an electrochemical quartz crystal nanobalance.

Understanding the nature of discharged products is critical to identifying suitable electrolyte systems for Li-O-2 batteries. We have employed nonresonant inelastic X-ray scattering (NIXS), which is a hard X-ray photon-in photon-out technique to monitor low energy core shell excitations and to obtain bulk sensitive information on the solid discharged products in Li-O-2 batteries using various electrolyte solvent/salt combinations. NIXS measurements were performed on cathodes after discharging the Li-O-2 cells using low discharge current (similar to 25 mA/g of carbon). NIXS results reveal that, even in cells containing current state-of-the-art electrolytes, the oxygen in the discharged products is bound predominantly to species other than a peroxide or lithia. This finding shows that electrolyte decomposition is a significant pathway during discharge of Li-O-2 batteries using ether and oligoether substituted silane based electrolytes.

Atomically dispersed Fe/N/C composite was synthesized and its role in controlling the oxygen evolution reaction during Li-O(2) battery charging was studied by use of a tetra(ethylene glycol) dimethyl ether-based electrolyte. Li-O(2) cells using Fe/N/C as the cathode catalyst showed lower overpotentials than α-MnO(2)/carbon catalyst and carbon-only material. Gases evolved during the charge step contained only oxygen for Fe/N/C cathode catalyst, whereas CO(2) was also detected in the case of α-MnO(2)/C or carbon-only material; this CO(2) was presumably generated from electrolyte decomposition. Our results reiterate the catalytic effect in reducing overpotentials, which not only enhances battery efficiency but also improves its lifespan by reducing or eliminating electrolyte decomposition. The structure of the Fe/N/C catalyst was characterized by transmission electron microscopy, scanning transmission electron microscopy, inductively coupled plasma optical emission spectroscopy, and X-ray absorption spectroscopy. Iron was found to be uniformly distributed within the carbon matrix, and on average, Fe was coordinated by 3.3 ± 0.6 and 2.2 ± 0.3 low Z elements (C/N/O) at bond distances of ~1.92 and ~2.09 Å, respectively.

The reliable identification of lithium oxide species, especially lithium peroxide (Li2O2), is of vital importance to the study of Li-air batteries. Previous X-ray diffraction studies of Li2O2 resulted in the proposal of two disparate structures by Feher and Foppl. In this Letter, we assess these competing Li2O2 structures using a combination of the following X-ray and first-principles techniques: (i) high-energy X-ray diffraction (XRD), (ii) comparisons of the measured nonresonant inelastic X-ray scattering (NIXS) spectra with those computed from first principles using the Bethe-Salpeter equation (BSE), and (iii) comparison of thermochemistry data with the formation enthalpies obtained from density functional theory (DFT) calculations using a hybrid functional. All three approaches result in the identification of Foppl’s proposal as the more appropriate structure for Li2O2. The measured and computed spectra and data presented in this Letter are useful as benchmarks for future characterization of Li2O2.

layered Li(Mn0.5-xCr2xNi0.5-x)O2 cathode materials N. K. Karan, M. Balasubramanian, D. P. Abraham, M. Furczon, R. Thomas and R. S. Katiyar Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, PR 00931-3343. X-ray Science Division, Advanced Photon Source, Argonne National Laboratory Argonne, IL-60439 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439

Nanostructured Carbon-LiFePO4 composite cathode materials were prepared with conventional solid-state route. The orthorhombic olivine structure without any impurity was obtained at 650{degree sign}C. The average LiFePO4 particle sizes were ~80 nm and were coated with residual carbon. The cyclic voltammograms showed only a pair of peaks corresponding to the anodic and cathodic reactions. The irreversible capacity loss in the first cycle was 5 mAh/gm, and the Coulombic efficiency was 97%. The first discharge capacity was 157 mAh/g, equivalent to 93% of the theoretical capacity (Fe2+/Fe3+ redox efficiency). Capacity retention after 80 cycles was ~98% and hence insignificant capacity fading.

First principle calculations and alloy metal method were used for understanding the behavior of the compounds that can be used as a cathode material for lithium ion battery. From calculations we found that LiNi0.8Co0.1Mn0.1O2, is a promising material. The experimental results showed a single phase material, without any structural transformation during the first cycle of the electrochemical process.