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NASA NTRS2012

Fundamental Investigation of Silicon Anode in Lithium-Ion Cells

Silicon is a promising and attractive anode material to replace graphite for high capacity lithium ion cells since its theoretical capacity is ~10 times of graphite and it is an abundant element on Earth. However, there are challenges associated with using silicon as Li-ion anode due to the significant first cycle irreversible capacity loss and subsequent rapid capacity fade during cycling. Understanding solid electrolyte interphase (SEI) formation along with the lithium ion insertion/de-insertion kinetics in silicon anodes will provide greater insight into overcoming these issues, thereby lead to better cycle performance. In this paper, cyclic voltammetry and electrochemical impedance spectroscopy are used to build a fundamental understanding of silicon anodes. The results show that it is difficult to form the SEI film on the surface of a Si anode during the first cycle; the lithium ion insertion and de-insertion kinetics for Si are sluggish, and the cell internal resistance changes with the state of lithiation after electrochemical cycling. These results are compared with those for extensively studied graphite anodes. The understanding gained from this study will help to design better Si anodes, and the combination of cyclic voltammetry with impedance spectroscopy provides a useful tool to evaluate the effectiveness of the design modifications on the Si anode performance.

Wu, James J.↗

DOE OSTI2020

Simple, compact, high-resolution monochromatic x-ray source for characterization of x-ray calorimeter arrays

X-ray calorimeters routinely achieve very high spectral resolution, typically a few eV full width at half maximum (FWHM). Measurements of calorimeter line shapes are usually dominated by the natural linewidth of most laboratory calibration sources. This compounds the data acquisition time necessary to statistically sample the instrumental line broadening and can add systematic uncertainty if the intrinsic line shape of the source is not well known. To address these issues, we have built a simple, compact monochromatic x-ray source using channel cut crystals. A commercial x-ray tube illuminates a pair of channel cut crystals that are aligned in a dispersive configuration to select the Kα1 line of the x-ray tube anode material. The entire device, including the x-ray tube, can be easily hand-carried by one person and may be positioned manually or using a mechanical translation stage. The output monochromatic beam provides a collimated image of the anode spot with magnification of unity in the dispersion direction (typically 100 μm–200 μm for the x-ray tubes used here) and is unfocused in the cross-dispersion direction so that the source image in the detector plane appears as a line. We measured output count rates as high as 10 count/s/pixel for the Hitomi soft x-ray spectrometer, which had 819 μm square pixels. We implemented different monochromator designs for energies of 5.4 keV (one design) and 8.0 keV (two designs), which have effective theoretical FWHM energy resolution of 0.125 eV, 0.197 eV, and 0.086 eV, respectively; these are well-suited for optimal calibration measurements of state-of-the art x-ray calorimeters. We measured an upper limit for the energy resolution of our Cr Kα1 monochromator of 0.7 eV FWHM at 5.4 keV, consistent with the theoretical prediction of 0.125 eV.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Understanding trends in lithium binding at two-dimensional materials

Layered structure and peculiar electronic properties of two-dimensional (2D) materials foster the concept of utilizing them as main components of lithium-ion batteries. Understanding basic physical mechanisms governing the interaction of Li with 2D crystals is of key importance to succeeding in a rational design of cathode and anode materials with superior functionalities. In this study density functional theory was applied to reveal the microscopic picture of Li interaction with 15 2D crystals, including several transition metal oxides and dichalcogenides, carbides of Group XIV elements, functionalized graphene, silicene, and germanene, as well as black phosphorus and Ti2C MXene. We found that the general trend in Li binding can be estimated from positions of conduction band minima of 2D materials, since the energy of the lowest empty electronic states shows a nice correlation with the strength of Li adsorption. At variance to the majority of studied surfaces where the electron transferred from Li is spread across the substrate, in monolayers of carbides of Group XIV elements the interaction with Li and the charge transfer are well localized. This gives rise to their capability to accommodate Li structures with a nearly constant binding energy of alkaline atoms over Li coverages ranging from well-separated adatoms to a full monolayer. © 2018 American Physical Society.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2012

Fundamental Investigation of Si Anode in Li-Ion Cells

Silicon is a promising and attractive anode material to replace graphite for high capacity lithium ion cells since its theoretical capacity is approximately 10 times of graphite and it is an abundant element on earth. However, there are challenges associated with using silicon as Li-ion anode due to the significant first cycle irreversible capacity loss and subsequent rapid capacity fade during cycling. In this paper, cyclic voltammetry and electrochemical impedance spectroscopy are used to build a fundamental understanding of silicon anodes. The results show that it is difficult to form the SEI film on the surface of Si anode during the first cycle, the lithium ion insertion and de-insertion kinetics for Si are sluggish, and the cell internal resistance changes with the state of lithiation after electrochemical cycling. These results are compared with those for extensively studied graphite anodes. The understanding gained from this study will help to design better Si anodes.

Wu, James J.↗

NASA NTRS2020

Simple, Compact, High-Resolution Monochromatic X-Ray Source for Characterization of X-Ray Calorimeter Arrays

M A Leutenegger↗

DOE OSTI2017

Influence of the ZnO nanoarchitecture on the electrochemical performances of binder-free anodes for Li storage

Zinc oxide nanoarchitectures may be employed as binder-free, high specific capacity anodes for lithium batteries. By means of simple and low-impact wet chemistry approaches, we synthesized 1D (nanorods), 2D (single- and multi-layered nanosheets), and 3D (nanobrushes) ZnO arrays. These nanoarchitectures were compared as far as concerns their electrochemical properties and the structural modifications upon lithiation/delithiation. The best results were offered by 2D nanosheets, which showed reversible capacity of the order of 400 mAhg{sup −1} after 100 cycles at 1 Ag{sup −1}. This was due to: i) small nanoparticles, with average diameter of about 10 nm, which maximize the array specific surface area and favor the formation of the LiZn alloy; ii) the presence of a mesoporous texture, which allows larger space for accommodating the volume changes upon lithiation/delithiation. However, also these 2D structures showed large irreversible capacity losses. Our work highlights the need for more efficient buffering solutions in ZnO binder-free nanostructured anodes. - Graphical abstract: ZnO nanosheets as anode materials for lithium batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Local ionic transport enables selective PGM-free bipolar membrane electrode assembly

Bipolar membranes in electrochemical CO 2 conversion cells enable different reaction environments in the CO 2 -reduction and O 2 -evolution compartments. Under ideal conditions, water-splitting in the bipolar membrane allows for platinum-group-metal-free anode materials and high CO 2 utilizations. In practice, however, even minor unwanted ion crossover limits stability to short time periods. Here we report the vital role of managing ionic species to improve CO 2 conversion efficiency while preventing acidification of the anodic compartment. Through transport modelling, we identify that an anion-exchange ionomer in the catalyst layer improves local bicarbonate availability and increasing the proton transference number in the bipolar membranes increases CO 2 regeneration and limits K + concentration in the cathode region. Through experiments, we show that a uniform local distribution of bicarbonate ions increases the accessibility of reverted CO 2 to the catalyst surface, improving Faradaic efficiency and limiting current densities by twofold. Using these insights, we demonstrate a fully platinum-group-metal-free bipolar membrane electrode assembly CO 2 conversion system exhibiting <1% CO 2 /cation crossover rates and 80-90% CO 2 -to-CO utilization efficiency over 150 h operation at 100 mA cm -2 without anolyte replenishment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Niobium tungsten oxides for high-rate lithium-ion energy storage

Here, the maximum power output and minimum charging time of a lithium-ion battery – key parameters for its use in, for example, transportation applications – depend on mixed ionic– electronic diffusion. While the discharge/charge rate and capacity can be tuned by varying the composite electrode structure, ionic transport within the active particles represents a fundamental limitation. Thus, to achieve high rates, particles are frequently reduced to nanosize dimensions despite this being disadvantageous in terms of volumetric packing density as well as cost, stability, and sustainability considerations. As an alternative to nanoscaling, we show that complex niobium tungsten oxides with topologically frustrated polyhedral arrangements and dense µm-scale particle morphologies can rapidly and reversibly intercalate large quantities of lithium. Multielectron redox, buffered volume expansion, and extremely fast lithium transport approaching that of a liquid lead to extremely high volumetric capacities and rate performance for both crystallographic shear structure and bronze-like niobium tungsten oxides. The active materials Nb 16 W 5 O 55 and Nb 18 W 16 O 93 offer new strategies toward designing electrodes with advantages in energy density, scalability, electrode architecture/complexity and cost as alternatives to the state-ofthe art high-rate anode material Li 4 Ti 5 O 12 . The direct measurement of solid-state lithium diffusion coefficients (DLi) with pulsed field gradient NMR demonstrates room temperature DLi values of 10–12–10–13 m 2 × s -1 in the niobium tungsten oxides, which is several orders-ofmagnitude faster than typical electrode materials and corresponds to a characteristic diffusion length of ~10 µm for a 1 minute discharge. Materials and mechanisms that enable lithiation of µm particles in minutes have implications for high power applications, fast charging devices, all-solid-state batteries, and general approaches to electrode design and material discovery.

25 ENERGY STORAGE↗

DOE OSTI2019

A new family of cation-disordered Zn(Cu)–Si–P compounds as high-performance anodes for next-generation Li-ion batteries

The development of low-cost, high-performance anode materials for Li-ion batteries (LIBs) is imperative to meet the ever-increasing demands for advanced power sources. In this paper we report our findings on the design, synthesis, and characterization of a new cation-disordered ZnSiP 2 anode. When tested in LIBs, the disordered phase of ZnSiP 2 demonstrates faster reaction kinetics and higher energy efficiency than the cation-ordered phase of ZnSiP 2 . The superior performance is attributed to the greater electronic and ionic conductivity and better tolerance against volume variation during cycling, as confirmed by theoretical calculations and experimental measurements. Moreover, the cation-disordered ZnSiP 2 /C composite exhibits excellent cycle stability and superior rate capability. The performance surpasses all reported multi-phase anodes studied. Further, a number of the cation-disordered phases in the Zn(Cu)–Si–P family with a wide range of cation ratios show similar performance, achieving large specific capacities and high first-cycle coulombic efficiency while maintaining desirable working potentials for enhanced safety.

25 ENERGY STORAGE↗

DOE OSTI2019

Structural Changes in Si–CuSi Films upon Intercalation of Lithium Ions

We studied the possibility of using composite films representing amorphous silicon reinforced with crystalline inclusions of copper silicide as an anode material for lithium-ion batteries with liquid electrolyte. The films were made by layer-by-layer magnetron sputtering of amorphous silicon and copper, followed by low-temperature (100–200°C) annealing of the structure. The tests of the anodes revealed the effect of prolonged intense growth of their reversible capacity. To describe the effect, a phenomenological model based on the multidirectional migration of silicon and copper atoms in an inhomogeneous field of elastic mechanical stresses arising during electrode cycling is proposed.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2016

Highly Reversible Zinc-ion Intercalation with Chevrel Phase Mo6S8 Nanocubes and Applications for Advanced Zinc-ion Batteries

We demonstrate the application of the Chevrel phase Mo6S8 nanocubes as the anode material for rechargeable Zn-ion batteries. Mo6S8 can host Zn2+ ions reversibility both in aqueous and nonaqueous electrolytes with specific capacities around 90 mAh/g and exhibited remarkable intercalation kinetics as well as stability. Furthermore, we assembled full cells by integrating Mo6S8 anode with zinc-polyiodide (I-/I3-) based catholytes, and demonstrated that such fuel cells was also able to deliver outstanding rate performance and cyclic stability. This first demonstration of zinc intercalating anode could inspire the design of advanced Zn ion batteries.

Multivalent↗

DOE OSTI2015

Elucidation of the Local and Long-Range Structural Changes that Occur in Germanium Anodes in Lithium-Ion Batteries

Metallic germanium is a promising anode material in secondary lithium-ion batteries (LIBs) due to its high theoretical capacity (1623 mAh/g) and low operating voltage, coupled with the high lithium-ion diffusivity and electronic conductivity of lithiated Ge. Here, the lithiation mechanism of micron-sized Ge anodes has been investigated with X-ray diffraction (XRD), pair distribution function (PDF) analysis, and in-/ex-situ high-resolution Li-7 solid-state nuclear magnetic resonance (NMR), utilizing the structural information and spectroscopic fingerprints obtained by characterizing a series of relevant Li(x)Gey model compounds. In contrast to previous work, which postulated the formation of Li9Ge4 upon initial lithiation, we show that crystalline Ge first reacts to form a mixture of amorphous and crystalline Li7Ge3 (space group P32(1)2). Although Li7Ge3 was proposed to be stable in a recent theoretical study of the Li-Ge phase diagram (Morris, A. J.; Grey, C. P.; Pickard, C. J. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 90, 054111), it had not been identified in prior experimental studies. Further lithiation results in the transformation of Li7Ge3, via a series of disordered phases with related structural motifs, to form a phase that locally resembles Li7Ge2, a process that involves the gradual breakage of the Ge-Ge bonds in the Ge-Ge dimers (dumbbells) on lithiation. Crystalline Li15Ge4 then grows, with an overlithiated phase, Li15+delta Ge4, being formed at the end of discharge. This study provides comprehensive experimental evidence, by using techniques that probe short-, medium-, and long-range order, for the structural transformations that occur on electrochemical lithiation of Ge; the results are consistent with corresponding theoretical studies regarding stable lithiated LixGey phases.

Jung, Hyeyoung↗

DOE OSTI2019

Sacrificial template synthesis of hollow C@MoS 2 @PPy nanocomposites as anodes for enhanced sodium storage performance

Molybdenum disulfide (MoS 2 ) has become a potential anode material for sodium-ion batteries (SIBs) by showing decent cell performance but it suffers poor electronic conductivity and large volume expansion during sodiation. Here we design a nanocomposite with hollow nitrogen doped carbon and polypyrrole modified MoS 2 for improving the performance for SIBs. The designed nanocomposite shows a much-improved electronic conductivity and the design of the architecture provides sufficient channels for mass transport and accommodates large volume change. This C@MoS 2 @PPy anode delivers a high specific capacity of 713 mAh g -1 at 0.1 A g -1 for 100 cycles, and an excellent rate capacity of 294 mAh g -1 at 5 A g -1 for 500 cycles. This specific architecture of C@MoS2@PPy could guide the future design of the electrode material in SIBs and its superior electrochemical performance indicates the great potential application for SIBs.

25 ENERGY STORAGE↗

DOE OSTI2024

Surface and Bulk Stabilization of Silicon Anodes with Mixed-Multivalent Additives: Ca(TFSI) 2 and Mg(TFSI) 2

Here, silicon is drawing attention as the upcoming anode material for the next generation of lithium-ion batteries due to its higher capacity compared to commercial graphite. However, silicon anions formed during lithiation are highly reactive with binder and electrolyte components creating an unstable SEI layer and limiting the calendar life of silicon anodes. The reactivity of lithium silicide and the formation of an unstable SEI layer is mitigated by utilizing the use of a mixture of Ca and Mg multivalent cations as an electrolyte additive for Si anodes to improve their calendar life. The effect of mixed salts on the bulk and surface of silicon anodes was studied by multiple structural characterization techniques. Ca and Mg ions in the electrolyte formed relatively thermodynamically stable quaternary Li-Ca-Mg-Si Zintl phases in an in-situ fashion and more stable and denser SEI layer on the Si particles. These in turn protect silicon particles against side reactions with electrolytes in a coin cell. The full cell with the mixed cation electrolyte demonstrates enhanced calendar life performance with lower measured current and current leakage than that of the baseline electrolyte due to reduced side reactions. Electron Microscopy, HRXRD, and solid-state NMR results showed that electrodes with mixed cations tended to have less cracking on the electrode surface compared to Si electrodes with Gen2 + FEC and the presence of mixed cations enhances cation migration and formation of quaternary Zintl phases stabilizing bulk and forming a more stable SEI.

25 ENERGY STORAGE↗

DOE OSTI2017

Strong texturing of lithium metal in batteries

Lithium, with its high theoretical specific capacity and lowest electrochemical potential, has been recognized as the ultimate negative electrode material for next-generation lithium-based high-energy-density batteries. However, a key challenge that has yet to be overcome is the inferior reversibility of Li plating and stripping, typically thought to be related to the uncontrollable morphology evolution of the Li anode during cycling. Here we show that Li-metal texturing (preferential crystallographic orientation) occurs during electrochemical deposition, which governs the morphological change of the Li anode. X-ray diffraction pole-figure analysis demonstrates that the texture of Li deposits is primarily dependent on the type of additive or cross-over molecule from the cathode side. With adsorbed additives, like LiNO 3 and polysulfide, the lithium deposits are strongly textured, with Li (110) planes parallel to the substrate, and thus exhibit uniform, rounded morphology. A growth diagram of lithium deposits is given to connect various texture and morphology scenarios for different battery electrolytes. In conclusion, this understanding of lithium electrocrystallization from the crystallographic point of view provides significant insight for future lithium anode materials design in high-energy-density batteries.

25 ENERGY STORAGE↗

NASA NTRS1983

Variable anodic thermal control coating

A process for providing a thermal control solar stable surface coating for aluminum surfaces adapted to be exposed to solar radiation wherein selected values within the range of 0.10 to 0.72 thermal emittance (epsilon sub tau) and 0.2 to 0.4 solar absorptance (alpha subs) are reproducibly obtained by anodizing the surface area in a chromic acid solution for a selected period of time. The rate voltage and time, along with the parameters of initial epsilon sub tau and alpha subs, temperature of the chromic acid solution, acid concentration of the solution and the material anodized determines the final values of epsilon/tau sub and alpha sub S. 9 Claims, 5 Drawing Figures.

Gilliland, C. S.↗

DOE OSTI2019

Elucidating the Limit of Li Insertion into the Spinel Li 4 Ti 5 O 12

Here in this work, we show that the well-known lithium-ion anode material, Li 4 Ti 5 O 12 , exhibits exceptionally high initial capacity of 310 mAh g –1 when it is discharged to 0.01 V. It maintains a reversible capacity of 230 mAh g –1 , far exceeding the “theoretical” capacity of 175 mAh g –1 when this anode is lithiated to the composition Li 7 Ti 5 O 12 . Neutron diffraction analyses identify that additional Li reversibly enters into the Li 7 Ti 5 O 12 to form Li 8 Ti 5 O 12 . density functional theory (DFT) calculations reveal the average potentials of the Li 4 Ti 5 O 12 to Li 7 Ti 5 O 12 step and the Li 7 Ti 5 O 12 to Li 8 Ti 5 O 12 step are 1.57 and 0.19 V, respectively, which are in excellent agreement with experimental results. Transmission electron microscopy (TEM) studies confirm that the irreversible capacity of Li 4 Ti 5 O 12 during its first cycle originates from the formation of a solid electrolyte interface (SEI) layer. This work clarifies the fundamental lithiation mechanism of the Li 4 Ti 5 O 12 , when lithiated to 0.01 V vs L

25 ENERGY STORAGE↗

DOE OSTI2022

Exploring the Promise of Multifunctional “Zintl-Phase-Forming” Electrolytes for Si-Based Full Cells

Li-M-Si ternary Zintl phases have gained attention recently due to their high structural stability, which can improve the cycling stability compared to a bulk Si electrode. Adding multivalent cation salts (such as Mg 2+ and Ca 2+ ) in the electrolyte was proven to be a simple way to form Li-M-Si ternary phases in situ in Si-based Li-ion cells. To explore the promise of Zintl-phaseforming electrolytes, we systematically investigated their application in pouch cells via electrochemical and multiscale postmortem analysis. The introduction of multivalent cations, such as Mg 2+ , during charging can form Li x M y Si ternary phases. They can stabilize Si anions and reduce side reactions with electrolyte, improving the bulk stability. More importantly, Mg 2+ and Ca 2+ incorporate into interfacial side reactions and generate inorganic-rich solid- electrolyte interphase, thus enhancing the interfacial stability. Therefore, the full cells with Zintl-phase-forming electrolytes achieve higher capacity retentions at the C/3 rate after 100 cycles, compared to a baseline electrolyte. Additionally, strategies for mitigating the electrode-level fractures of Si were evaluated to make the best use of Zintl-phase-forming electrolytes. In conclusion, this work highlights the significance of synergistic impact of multifunctional additives to stabilize both bulk and interface chemistry in high-energy Si anode materials for Li-ion batteries.

25 ENERGY STORAGE↗