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The formation of the c-Li15Si4 phase has well-established detrimental effects on the capacity retention of thin film silicon electrodes. However, the role of this crystalline phase with respect to the loss of capacity is somewhat ambiguous in nanoscale morphologies. In this work, three silicon-based morphologies are examined, including planar films, porous planar films, and silicon nanoparticle composite powder electrodes. The cycling conditions are used as the lever to induce, or not induce, the formation of c-Li15Si4 through application of constant-current (CC) or constant-current constant-voltage (CCCV) steps. In this manner, the role of this phase on capacity retention and Coulombic efficiency can be determined with few other convoluting factors such as alteration of the composition or morphology of the silicon electrodes themselves. The results here confirm that the c-Li15Si4 phase increases the rate of capacity decay in planar films but has no major effect on capacity retention in half-cells based on porous silicon films or silicon nanoparticle composite powder electrodes, although this conclusion is nuanced. Besides using a constant-voltage step, formation of the c-Li15Si4 phase is influenced by the dimensions of the Si material and the lithiation cutoff voltage. Porous Si films, which, in this work, comprise primary Si particle sizes that are smaller than those in the preformed Si nanoparticle slurries, do not undergo the formation of c-Li15Si4 at 50 mV, whereas Si nanoparticle slurries are accompanied by the formation of c-Li15Si4 up to 80 mV. The solid-electrolyte interphase (SEI) formed from reaction of the c-Li15Si4 with the carbonate-based electrolyte causes polarization in both nanoparticle and porous film silicon electrodes and lowers the average Coulombic efficiency. A comparison of the cumulative irreversibilities due to SEI formation between different lithiation cutoff voltages in silicon nanoparticle slurry electrodes confirmed the connection between higher SEI buildup and formation of the c-Li15Si4 phase. This work indicates that concerns about the c-Li15Si4 phase in silicon nanoparticles and porous silicon electrodes should mainly focus on the stability of the SEI and a reduction of irreversible electrolyte reactions.

Self-assembly of block copolymers (BCPs) is an alternative patterning technique that promises high resolution and density multiplication with lower costs. The defectivity of the resulting nanopatterns remains too high for many applications in microelectronics and is exacerbated by small variations of processing parameters, such as film thickness, and fluctuations of solvent vapor pressure and temperature, among others. In this work, a solvent vapor annealing (SVA) flow-controlled system is combined with design of experiments (DOE) and machine learning (ML) approaches. The SVA flow-controlled system enables precise optimization of the conditions of self-assembly of the high Flory-Huggins interaction parameter (χ) hexagonal dot-array forming BCP, poly(styrene-b-dimethylsiloxane) (PS-b-PDMS). The defects within the resulting patterns at various length scales are then characterized and quantified. The results show that the defectivity of the resulting nanopatterned surfaces is highly dependent upon very small variations of the initial film thicknesses of the BCP, as well as the degree of swelling under the SVA conditions. These parameters also significantly contribute to the quality of the resulting pattern with respect to grain coarsening, as well as the formation of different macroscale phases (single and double layers and wetting layers). The results of qualitative and quantitative defect analyses are then compiled into a single figure of merit (FOM) and are mapped across the experimental parameter space using ML approaches, which enable the identification of the narrow region of optimum conditions for SVA for a given BCP. The result of these analyses is a faster and less resource intensive route toward the production of low-defectivity BCP dot arrays via rational determination of the ideal combination of processing factors. The DOE and machine learning-enabled approach is generalizable to the scale-up of self-assembly-based nanopatterning for applications in electronic microfabrication.

Group(IV) of the periodic table is a promising column with respect to high capacity anode materials for sodium-ion batteries (SIBs). Unlike carbon that relies on interlayer defects, pores, and intercalation to store sodium, its heavier cousins, silicon, germanium, and tin, form binary alloys with sodium. Alloying does lead to the formation of high capacity compounds but they are, however, susceptible to large volumetric changes upon expansion that results in pulverization of the electrodes and poor cycling stability. Silicon and tin are particularly intriguing due to their high theoretical reversible capacities of 954 mAh/g (NaSi) and 847 mAh/g (Na15Sn4), respectively, but suffer from poor practical capacity and very short lifetimes, respectively. In order to buffer the detrimental effects of volume expansion and contraction, nanoscale multilayer anodes comprising silicon and tin films were prepared and compared with uniform films composed of atomically mixed silicon and tin, as well as elemental silicon and tin films. The results reveal that the high capacity fade for elemental Sn is associated with detrimental anodic (desodiation) reactions at a high cutoff voltage with a threshold defined as ~0.8 VNa. Binary mixtures of Si and Sn were tested in a number of different architectures, including multilayer films and co-sputtered films with varying volume ratios of both elements. All mixed films showed improved capacity retention compared to the performance of anodes comprising only elemental Sn. A multilayer structure composed of 3 nm-thick silicon and tin layers showed the highest Coulombic efficiency and retained 97% of its initial capacity after 100 cycles, which is vastly improved compared to 7% retention observed for the elemental Sn film. The role of the Si interlayers appears to be one of acting as a buffer during cycling to help preserve Sn particles within the thin Sn interlayers. The alloying element, Si, plays two roles - it stabilizes grain growth/pulverization and also alters the surface chemistry of the anodes, thus affecting the formation of solid electrolyte interphase (SEI).

The covalent functionalization of unoxidized silicon surfaces is of interest for a wide range of applications and for fundamental studies linking surface functionalization and electronic properties. Determination of the level of substitution (yield) of a reaction on a silicon surface is necessary as the number of functional groups bound to the surface is directly linked to properties. X-ray photoelectron spectroscopy, XPS, is the most common analytical method for determining the substitution level of the chemical handle on the silicon surface, typically a Si–H or Si–Cl bond, through which a new stable bond is formed to link the molecule to the surface. Calculations using the atomic ratio of carbon to silicon, as determined by XPS, do not take into account the effect of adventitious hydrocarbons and retained solvent, and the substitution level is typically measured by first assuming 100% substitution of a fictitious hydrocarbon layer with an effective thickness determined by the XPS intensity ratio of C to Si; the actual substitution level is then taken as the ratio of the effective thickness to the theoretical height of the molecule. In this work, we present an alternative and more physically meaningful approach to deriving expressions for the substitution level that is based on the proportionality of the photoelectron attenuation length to the substitution level. For all-hydrocarbon molecules grafted to a silicon surface, this new approach yields the same equations for substitution levels as an earlier effective thickness model. More importantly, unlike the effective thickness models, this method can be extended to include molecules with a heteroatom “tag”, such as fluorine and chalcogenides, for determining coverage by XPS. The use of the heteroatomic tags is shown to provide a greater degree of certainty with respect to calculating the coverage on silicon. We finish with a simple flowchart to guide the reader to the appropriate equation for both Si(111) and Si(100) surfaces.

Redox flow batteries (RFBs) are promising energy storage candidates for grid deployment of intermittent renewable energy sources such as wind power and solar energy. Various new redox-active materials have been introduced to develop cost-effective and high-power-density next-generation RFBs. Electrochemical kinetics play critical roles in influencing RFB performance, notably the overpotential and cell power density. Thus, determining the kinetic parameters for the employed redox-active species is essential. In this Perspective, we provide the background, guidelines, and limitations for a proposed electrochemical protocol to define the kinetics of redox-active species in RFBs.

The formation of c-Li3.75Si is known to be detrimental to silicon anodes in lithium-ion batteries. To suppress the formation of this crystalline phase and improve the electrochemical performance of Si-based anodes, three approaches were amalgamated: addition of a nickel adhesion sublayer, alloying of the silicon with titanium, and addition of either carbon or TiO2 as a capping layer. The silicon-based films were analyzed by a suite of methods, including scanning electron microscopy (SEM) and a variety of electrochemical techniques, as well as X-ray photoelectron spectroscopy (XPS) to provide insights into the composition of the resulting solid-electrolyte interphase (SEI). A nickel adhesion layer decreased the extent of delamination of the silicon from the underlying copper substrate, compared to Si deposited directly on Cu, which resulted in less capacity loss. Alloying of silicon with titanium (85% silicon, 15% titanium) further increased the stability. Finally, capping these multilayer electrodes with ...

A water soluble octahedral Co(ii) complex, BCPIP-Co(ii), with 4 appended carboxylic groups on the ligand periphery is utilized as both posolyte and negolyte in an aqueous, symmetric redox flow battery (RFB). The full RFB demonstrates coulombic efficiencies >99% for up to 100 cycles.

The formation of the

As editors of a materials chemistry journal, we are thrilled at the awarding of the 2019 Nobel Prize in Chemistry to John B. Goodenough, M. Stanley Whittingham, and Akira Yoshino, for their contributions that have led to the modern lithium ion battery (Figure 1). As the Nobel Prize Committee states succinctly, “They created a rechargeable world.”(1) The commercial and societal rewards of experimental research typically require decades to reach fruition, and lithium ion batteries were no different, with crucial leads dating back to the 1960s, and even earlier.(2) Materials chemistry journals only emerged 30 years ago with the advent of Chemistry of Materials, the Journal of Materials Chemistry, and Advanced Materials in 1989. Much of the earlier work in battery materials appeared beforehand in electrochemistry, physics, and solid state journals. The key fundamental discovery underpinning the lithium ion battery was the understanding and application of ion intercalation, in this case,(3) lithium ions inserted between the layers in graphite, metal sulfides, and, eventually, oxides that were commercialized. This Nobel Prize was evenly split three ways because, as the Nobel committee correctly observed, the contributions of all three inventors were essential to the success of the commercialization of the lithium ion battery.

Sn–Sb composites are of great interest for high capacity sodium-ion batteries due to their high stability, but because multiple phases and alloys are formed during cycling, the roles of each are challenging to deduce. In this work, two approaches were taken to investigate the importance of β-SnSb formation on the cycling stability of Sn-rich Sn–Sb composite sodium-ion battery (SIB) anodes. First, to tease out the role of each component, thin layers of amorphous silicon, with thicknesses ranging from 0.5 to 10 nm, were incorporated between Sn and Sb layers, of equal thicknesses. Silicon has low solubility in both tin and antimony, and thus acts as a barrier layer that can interfere with the formation of Sn–Sb alloys. The equivalent composition of this sandwich structure was Sn₅₃Sb₄₇. Upon electrochemical cycling, a clear correlation between capacity retention and Si thickness was observed, and it was found that a 1 nm thick Si layer was sufficient to inhibit the formation of the β-SnSb intermetallic, resulting in loss of the capacity of the tin layer after a few tens of cycles. The second approach involved capping a Sn film with increasingly thicker Sb layers. Thicker antimony layers were found to have a large positive influence on cycling stability with a marked drop-off in the capacity retention when there is not enough Sb to fully convert the bilayer into β-SnSb. These results point to the necessity of the Sn and Sb being in intimate contact prior to cycling for the β-SnSb phase to form in operando, which is necessary for the excellent capacity retention of the Sn–Sb system.

Silicon-based anodes for Li-ion batteries have been gaining a great deal of attention due to their high theoretical gravimetric energy density. Approaches for overcoming the challenge of pulverization associated with Si-based electrodes are required for efficient, reversible, and stable operation of such high energy batteries. This study focuses on addressing the source of pulverization of amorphous silicon films upon cycling, which is typically attributed to the formation of the c-Li3.75Si phase. Cross-sectional samples prepared by focused-ion beam milling revealed fractured sponge-like silicon structures after 150 cycles at a lithiation cutoff voltage of 5 mVLi, at which the c-Li3.75Si phase forms. Cycling at a higher lithiation cutoff voltage, 50 mVLi, however, resulted in a film with a higher degree of integrity, along with the absence of the c-Li3.75Si phase. These results clearly verify and underscore the deleterious effects of the c-Li3.75Si phase. Alternating carbon and silicon layers results in s...

Optically transparent PDMS stamps coated with a layer of gold nanoparticles were employed as plasmonic stamps to drive surface chemistry on silicon surfaces. Illumination of a sandwich of plasmonic stamps, an alkene ink, and hydride-terminated silicon with green light of moderate intensity drives hydrosilylation on the surface. The key to the mechanism of the hydrosilylation is the presence of holes at the Si-H-terminated interface, which is followed by attack by a proximal alkene and formation of the silicon-carbon bond. In this work, detailed kinetic studies of the hydrosilylation on silicon with different doping levels, n++, p++, n, p, and intrinsic were carried out to provide further insight into the role of the metal-insulator-semiconductor (MIS) junction that is set up during the stamping.

In this work, native GaOx is positioned between bulk gallium and degenerately doped p-type silicon (p+-Si) to form Ga/GaOx/SiOx/p+-Si junctions. These junctions show memristive behavior, exhibiting large current-voltage hysteresis. When cycled between -2.5 and 2.5 V, an abrupt insulator-metal transition is observed that is reversible when the polarity is reversed. The ON/OFF ratio between the high and low resistive states in these junctions can reach values on the order of 108 and retain the ON and OFF resistive states for up to 105 s with an endurance exceeding 100 cycles. The presence of a nanoscale layer of gallium oxide is critical to achieving reversible resistive switching by formation and dissolution of the gallium filament across the switching layer.

All-small-molecule organic photovoltaic (OPV) cells based upon the small molecule donor, DRCN5T, and non-fullerene acceptors, ITIC, IT-M, and IT-4F, were optimized using Design of Experiments (DOE) and machine learning (ML) approaches. This combination enables rational sampling of large parameter spaces in a sparse but mathematically deliberate fashion and promises economies of precious resources and time. The work focused upon the optimization of the core layer of the OPV device, the bulk heterojunction (BHJ). Many experimental processing parameters play critical roles in the overall efficiency of a given device and are often correlated, and thus are difficult to parse individually. DOE was applied to the (i) solution concentration of the donor and acceptor ink used for spin-coating, (ii) the donor fraction, and (iii) the temperature and (iv) duration of the annealing of these films. The ML-based approach was then used to derive maps of the PCE landscape for the first and second rounds of optimization to be used as guides to determine the optimal values of experimental processing parameters with respect to device efficiency. This work shows that with little knowledge of a potential combination of components for a given BHJ, a large parameter space can be effectively screened and investigated to rapidly determine its potential for high efficiency OPVs.

Interfaces comprising incommensurate or twisted hexagonal lattices are ubiquitous and of great interest, from adsorbed organic/inorganic interfaces in electronic devices, to superlubricants, and more recently to van der Waals bilayer heterostructures (vdWHs) of graphene and other 2D materials that demonstrate a range of properties such as superconductivity and ferromagnetism. Here we show how growth of 2D crystalline domains of soft block copolymers (BCPs) on patterned hard hexagonal lattices provide fundamental insights into van der Waals heteroepitaxy. At moderate registration forces, it is experimentally found that these BCP-hard lattice vdWHs do not adopt a simple moire superstructure, but instead adopt local structural relaxations known as mass density waves (MDWs). Simulations reveal that MDWs are a primary mechanism of energy minimization and are the origin of the observed preferential twist angle between the lattices.

The following joint Editorial was originally published in ACS Applied Materials & Interfaces (DOI: 10.1021/acsami.0c10979). We confront the terrible reality that systemic racism and discrimination impacts the daily personal and professional lives of many members of the scientific community and broader society. In the U.S., the brutal killing of George Floyd while in police custody is one of the most recent examples of the centuries of systemic violence suffered by Black Americans. This moment and its aftermath lay bare the legacies of racism and its exclusionary practices. Let us be clear: we, the Editors, Staff, and Governance Members of ACS Publications condemn the tragic deaths of Black people and stand in solidarity with Black members of the science and engineering community. Moreover, ACS condemns racism, discrimination, and harassment in all forms. We will not tolerate practices and viewpoints that exclude or demean any member of our community. Despite these good intentions, we recognize that our community has not done enough to provide an environment for Black chemists to thrive. Rep. Eddie Bernice Johnson, Chairwoman of the U.S. House Committee on Science, Space, and Technology said, “So far, we have gotten by with a STEM workforce that does not come close to representing the diversity of our nation. However, if we continue to leave behind so much of our nation’s brainpower, we cannot succeed.”(1) Indeed, the U.S. National Science Foundation notes that Blacks and other under-represented minority groups continue to be under-represented in science and engineering education and employment.(2) What is abundantly clear in this moment is that this lack of representation is a symptom of systemic racism across all levels of education and professional life. We know that supportive words are not enough. We must develop and implement a concrete plan for changing our trajectory. Publications and citations are academic currency, and while we like to think publishing a manuscript is “just about the science”, we know that is not true for everyone. We have seen the biases (largely through the lens of gender and in Western countries because of the limitations in bibliometric analyses) and applaud our colleagues at the RSC for their massive study that explored these gender barriers in the publishing pipeline(3) and their recent Inclusion and Diversity Framework.(4) At the present time, unfortunately, less is known about the effects of race and ethnicity on publishing success. A study published in PeerJ, however, found that unprofessional reviewer comments had a disproportionate effect on authors from under-represented groups.(5) As the world’s leading society publisher, we have a responsibility to aggressively combat bias in all aspects of the publishing process, including systemic under-representation of Blacks in this endeavor (no ACS journal is currently led by a Black Editor-in-Chief). Within ACS Publications, we actively track gender and geographic diversity of editors, advisors, authors, and reviewers, and we anecdotally report on race of editors. Diversity encompasses many more dimensions than these, and we acknowledge that we can do much more than we have. We affirm that diversity and inclusion strengthen the research community and its impact, and we are committed to developing, implementing, tracking, and reporting on our progress to ensure that our editors, advisors, reviewers, and authors are more diverse and that all authors receive the same fair treatment and opportunity to publish in our journals. We acknowledge that we do not have all the answers now, but we seek to hear from and listen to our community on how we can improve our journals to be more diverse and inclusive. As first steps, we commit to the taking the following actions: Gathering and making public our baseline statistics on diversity within our journals, encompassing our editors, advisors, reviewers, and authors; annually reporting on progress Training new and existing editors to recognize and interrupt bias in peer review Including diversity of journal contributors as an explicit measurement of Editor-in-Chief performance Appointing an ombudsperson to serve as a liaison between Editors and our Community Developing an actionable diversity plan for each ACS journal These are only initial plans and the start of a conversation: other ideas are beginning to germinate, and we commit to sharing them with you regularly. We invite you contribute your ideas on how we can do better via our Axial website. We are listening carefully. We encourage you to take immediate action in your own circles. In a recent editorial, JACS Associate Editor Melanie Sanford(6) offered practical steps to take now. Take a moment to find out more about these actions and how to bring them into your work and your life. We all have a responsibility to eradicate racism and discrimination in the science and engineering community; indeed, to make a real difference, we need to be antiracist. The tragic events we have seen in the Black community provide great urgency to this goal. The work will be difficult and will force us to confront hard realities about our beliefs and actions. We fully expect that you, and everyone in the community, will hold us accountable.

In this preprint, we reevaluate the use of X-ray photoelectron spectroscopy (XPS) to determine substitution levels of reactions on non-oxidized silicon surfaces. XPS is the most commonly used method to determine the yields of reactions on surfaces. We go back to the most basic assumptions, and work through the calculations to provide a revised set of calculations that take into account (i) possible adventitious hydrocarbon contamination, (ii) the effect of choosing a different silicon crystal face [Si(100) versus Si(111)], and (iii) the utility of choosing a small heteroatom tag to enable a more accurate measure of substitution levels. We provide a simple algorithm and summary of the equations one can use to make it easy for the reader/researcher.

Most discoveries in materials science have been made empirically, typically through one-variable-at-a-time (Edisonian) experimentation. The characteristics of materials-based systems are, however, neither simple nor uncorrelated. In a device such as an organic photovoltaic, for example, the level of complexity is high due to the sheer number of components and processing conditions, and thus, changing one variable can have multiple unforeseen effects due to their interconnectivity. Design of Experiments (DoE) is ideally suited for such multivariable analyses: by planning one’s experiments as per the principles of DoE, one can test and optimize several variables simultaneously, thus accelerating the process of discovery and optimization while saving time and precious laboratory resources. When combined with machine learning, the consideration of one’s data in this manner provides a different perspective for optimization and discovery, akin to climbing out of a narrow valley of serial (one-variable-at-a-time) experimentation, to a mountain ridge with a 360° view in all directions.

β-SnSb is known to be a highly stable anode for sodium ion batteries during cycling, but its sodiation–desodiation alloying reactions are poorly understood. Combining in situ TEM with electroanalytical methods, we demonstrate that β-SnSb forms Na3Sb and Na15Sn4 in sequence upon sodiation and re-forms as β-SnSb upon desodiation. The negative enthalpy of mixing for Sn and Sb is sufficient to cause sequentially deposited bilayers of Sn/Sb to transform into β-SnSb, resulting in comparable cycling stability. The good cycling stability of β-SnSb results from the complex two-phase amorphous–nanocrystalline microstructure in the partially charged–discharged states, as well as the intrinsic mechanical toughness of the β phase. Per the in situ TEM results, the sequential phase transformation shows minimal fracturing of the β-SnSb, indicating facile buffering of stresses. Extensively cycled specimens eventually show crystalline Sn phase segregation, which may be the source of the ultimate capacity fade in the alloy and bilayers.

In light of the intense recent interest in the methylammonium lead halides, CH3NH3PbX3 (X = Cl, Br, and I) as sensitizers for photovoltaic cells, the dynamics of the methylammonium (MA) cation in these perovskite salts has been reinvestigated as a function of temperature via 2H, 14N, and 207Pb NMR spectroscopy. In the cubic phase of all three salts, the MA cation undergoes pseudoisotropic tumbling (picosecond time scale). For example, the correlation time, τ2, for the C–N axis of the iodide salt is 0.85 ± 0.30 ps at 330 K. The dynamics of the MA cation are essentially continuous across the cubic ↔ tetragonal phase transition; however, 2H and 14N NMR line shapes indicate that subtle ordering of the MA cation occurs in the tetragonal phase. The temperature dependence of the cation ordering is rationalized using a six-site model, with two equivalent sites along the c-axis and four equivalent sites either perpendicular or approximately perpendicular to this axis. As the cubic ↔ tetragonal phase transition temperature is approached, the six sites are nearly equally populated. Below the tetragonal ↔ orthorhombic phase transition, 2H NMR line shapes indicate that the C–N axis is essentially frozen.

Organic solar cells (OSCs) are a complex assembly of disparate materials, each with a precise function within the device. Typically, the electrodes are flat, and the device is fabricated through a layering approach of the interfacial layers and photoactive materials. This work explores the integration of high surface area transparent electrodes to investigate the possible role(s) a three-dimensional electrode could take within an OSC, with a BHJ composed of a donor–acceptor combination with a high degree of electron and hole mobility mismatch. Nanotree indium tin oxide (ITO) electrodes were prepared via glancing angle deposition, structures that were previously demonstrated to be single-crystalline. A thin layer of zinc oxide was deposited on the ITO nanotrees via atomic layer deposition, followed by a self-assembled monolayer of C60-based molecules that was bound to the zinc oxide surface through a carboxylic acid group. Infiltration of these functionalized ITO nanotrees with the photoactive layer, the bulk heterojunction comprising PC71BM and a high hole mobility low band gap polymer (PDPPTT-T-TT), led to families of devices that were analyzed for the effect of nanotree height. When the height was varied from 0 to 50, 75, 100, and 120 nm, statistically significant differences in device performance were noted with the maximum device efficiencies observed with a nanotree height of 75 nm. From analysis of these results, it was found that the intrinsic mobility mismatch between the donor and acceptor phases could be compensated for when the electron collection length was reduced relative to the hole collection length, resulting in more balanced charge extraction and reduced recombination, leading to improved efficiencies. However, as the ITO nanotrees increased in height and branching, the decrease in electron collection length was offset by an increase in hole collection length and potential deleterious electric field redistribution effects, resulting in decreased efficiency.

In this work, the performance and electrochemical charge/discharge behavior of Sn–Bi–Sb alloy films were examined, as well as pure Sn, Bi, and Sb films, as anodes for sodium ion batteries (SIBs). Alloying was utilized as an approach to modify the morphology and active phases in an effort to improve the cycling stability of elemental anodes of Sn or Sb, while maintaining a high capacity. The films were prepared via sputtering, which enabled study of a broad swath of compositional space. The cycling performance of the Sb-rich compositions surpassed that of all other alloys tested as anodes for SIBs. The best performing alloy had a composition of 10 at% Sn, 10 at% Bi, and 80 at% Sb (called Sn10Bi10Sb80, here), and maintained 99% of its maximum capacity during cycling (621 mA h g−1) after 100 cycles. Stability of these anodes dropped as the quantity of Sb decreased; to contrast, Sn20Bi20Sb60, Sn25Bi25Sb50 and Sn33Bi33Sb33 were increasingly less stable as anodes in SIBs as the molar quantity of Sb in the films dropped to 60%, 50%, and 33%, respectively. The Sn10Bi10Sb80 electrode was found to possess a single phase as-deposited microstructure of Sn and Bi in substitutional solid solution with the Sb lattice and the sodiation sequence was found to be significantly different from pure Sb. Numerous possible mechanisms for the improvement in capacity retention were discussed, where modification and material response to internal stresses by changes in the Sb chemical potential and solid solution strengthening were found to be the most likely.

Aqueous symmetric redox flow batteries (RFB) are of great interest due to the non-flammability and high conductivity of the solvent, and avoidance of irreversible anolyte crossover seen in asymmetric cells. In this work, we introduce a simple octahedral Co(II) complex, termed BCPIP-Co(II), that has 4 appended carboxylic groups on the ligand periphery that render it both water-soluble and pH-sensitive in the range of pH 1.5 - 5.5. The complex has reversible BCPIP-Co(II-III) and BCPIP-Co(II-I) redox couples within the water splitting window, as well as fast kinetics. The overall charge of the complex varies from +3 to -3, resulting from the level of deprotonation of the carboxylic acid moieties and the oxidation state of the cobalt metal center, both of which affect the resulting redox properties. BCPIP-Co(II) was then incorporated, as both the posolyte and negolyte, into a symmetric aqueous RFB, demonstrating Coulombic efficiencies >99% for up to 100 cycles.

The formation of c-Li3.75Si is known to be detrimental to silicon anodes in lithium-ion batteries. To suppress the formation of this crystalline phase and improve the electrochemical performance of Sibased anodes, three approaches were amalgamated: addition of a nickel adhesion sublayer, alloying of the silicon with titanium, and the addition of either carbon or TiO2 as a capping layer. The silicon-based films were analyzed by a suite of methods, including scanning electron microscopy (SEM) and a variety of electrochemical methods, as well as X-ray photoelectron spectroscopy (XPS) to provide insights into the composition of the resulting solid electrolyte interphase (SEI). A nickel adhesion layer decreased the extent of delamination of the silicon from the underlying copper substrate, compared to Si deposited directly on Cu, which resulted in less capacity loss. Alloying of silicon with titanium (85% silicon, 15% titanium) further increased the stability. Finally, capping these multilayer electrodes with either a thin 10 nm layer of carbon or TiO2 resulted in the best electrode behavior, and lowest cumulative relative irreversible capacity. TiO2 is slightly more effective in enhancing the capacity retention, most likely due to differences in the resulting solid electrolyte interphase (SEI). The combination of an adhesion layer, alloying, and surface coatings shows a cumulative suppression of the formation of c-Li3.75Si and SEI, resulting in the greatest improvement of capacity retention when all three are incorporated together. However, these strategies appear to only delay the onset of the c-Li3.75Si phase; eventually, the c-Li3.75Si phase will form, and at that point, the rate of capacity degradation of all the electrodes becomes similar.