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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Revealing the aging process of solid electrolyte interphase on SiOx anode

Abstract As one of the most promising alternatives to graphite negative electrodes, silicon oxide (SiO x ) has been hindered by its fast capacity fading. Solid electrolyte interphase (SEI) aging on silicon SiO x has been recognized as the most critical yet least understood facet. Herein, leveraging 3D focused ion beam-scanning electron microscopy (FIB-SEM) tomographic imaging, we reveal an exceptionally characteristic SEI microstructure with an incompact inner region and a dense outer region, which overturns the prevailing belief that SEIs are homogeneous structure and reveals the SEI evolution process. Through combining nanoprobe and electron energy loss spectroscopy (EELS), it is also discovered that the electronic conductivity of thick SEI relies on the percolation network within composed of conductive agents (e.g., carbon black particles), which are embedded into the SEI upon its growth. Therefore, the free growth of SEI will gradually attenuate this electron percolation network, thereby causing capacity decay of SiO x . Based on these findings, a proof-of-concept strategy is adopted to mechanically restrict the SEI growth via applying a confining layer on top of the electrode. Through shedding light on the fundamental understanding of SEI aging for SiO x anodes, this work could potentially inspire viable improving strategies in the future.

25 ENERGY STORAGE↗
DOE OSTI2020

Effect of Water Concentration in LiPF 6 -Based Electrolytes on the Formation, Evolution, and Properties of the Solid Electrolyte Interphase on Si Anodes

A trace amount of water in an electrolyte is one of the factors detrimental to the electrochemical performance of silicon (Si)-based lithium-ion batteries that adversely affect the formation and evolution of the solid electrolyte interphase (SEI) on Si-based anodes and change its properties. Thus far, a lack of fundamental and mechanistic understanding of SEI formation, evolution, and properties in the presence of water has inhibited efforts to stabilize the SEI for improved electrochemical performance. As such, we investigated the SEI formed in a Gen2 electrolyte (1.2 M LiPF6 in ethylene carbonate/ethyl methyl carbonate, 3:7 wt %, water content: <10 ppm) with and without additional water (50 ppm) at varying potentials (1.0, 0.5, 0.2, and 0.01 V vs Li/Li + ). The impact of additional water on the morphological, (electro)chemical, and structural properties of SEI was studied using microscopic (atomic force microscopy and scanning spreading resistance microscopy) and spectroscopic (X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform infrared spectroscopy, and time-of-flight secondary ion mass spectrometry) techniques. The SEI exhibits both potential- and water concentration-dependent trends in its morphology and chemical composition. The presence of additional water in the electrolyte causes parasitic reactions, which onset at ~1.0 V, resulting in a reduction of electrolyte components and result in the formation of an insulating, fluorophosphate-rich SEI. In addition, hydrolysis of LiPF 6 creates hydrofluoric acid, which reacts with the surface oxide layer on the Si electrode, leading to a pitted and inhomogeneous SEI structure.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Mass spectral molecular mapping shows benefits of thermal evaporation in prelithiated silicon-based electrodes

Silicon based composites have become increasingly popular as potential anodes for lithium-ion batteries due to their large storage capacity and potential ability to generate batteries with energy densities greater than 350 Wh kg −1 . These anodes often see reduced initial columbic efficiency (ICE) due to disruptive volume expansionup to 300% and continuous solid electrolyte interphase (SEI) layer formation. Prelithiation, where an excess reservoir of Li is added to the electrode to compensate for irreversible SEI formation losses during their sample preparation, has proven to solve the issue of immediate capacity loss. Thermal evaporation is a prelithiation technique with limited studies on its effectiveness. In this study, time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to highlight the benefits of prelithiation via thermal evaporation. ToF-SIMS provides chemical mapping and spatial information in 2D and 3D visualizing the deposition of lithium, identifying Li x Si y alloy and Li x Si y O z silicate formation, and the distribution of lithium passivation into the electrodes. Passivation under different atmospheric conditions, such as inert Argon (Ar) and Ar/ carbon dioxide (CO 2 ), highlights the impact of the environment on the passivation effectiveness and formation of Li x Si y alloy and Li x Si y O z silicate. The ToF-SIMS molecular imaging and depth profiling results indicate that prelithiation via thermal evaporation effectively distributes lithium throughout the depth profile thickness of several hundred nanometers. It induces a greater degree of Li x Si y O z silicate formation over Li x Si y alloy. Our ToF-SIMS characterization results show the effectiveness of thermal evaporation in producing a more stable electrode and an electrode with an effective lithium reserve that can preserve its capacity.

Parker, Gabriel D. [Oak Ridge National Laboratory ↗
DOE OSTI2020

Insights on the cycling behavior of a highly-prelithiated silicon–graphite electrode in lithium-ion cells

Nanosized silicon materials are being developed for use in the anodes of high-energy lithium-ion batteries. However, the high surface areas of these materials increase the rate of parasitic reactions in the electrode, which consume cyclable Li + and degrade battery performance. Prelithiation offers a realistic strategy to compensate for this reactivity, by injecting additional charge into the cell to counterbalance the Li + loss. Interestingly, the benefits offered by prelithiation extend beyond its more obvious purpose. Here, by using a reference electrode in NMC532//Si–Gr cells, we show how prelithiation alters the cycling potentials experienced by the Si-containing anode and how that translates into gains in cycle life. The rate of consumption of the prelithiated charge is lower than that expected from the behavior of non-prelithiated cells. Curiously, the Si particles become partially unresponsive during the C/3 cycling apparently because of kinetic constraints. Electrochemical studies on harvested electrodes in half-cells show that capacities are intact after the long-term cycling and that most of the lithium reservoir is still present in the anode. We conclude that the high capacity retention displayed by the prelithiated cells mainly results from a higher participation of graphite particles during the extended electrochemical cycling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Modeling and Analysis of Polarization Losses in Solid Oxide Fuel Cells with Siloxane Contamination

In this study, the degradation of the solid-oxide fuel cell (SOFC) nickel-yttria stabilized zirconia anode under decamethyltetrasiloxane (L4) contamination is examined with experiments and modeling. A model is developed for the polarization losses based on the charge transfer coefficient,α, and diffusion layer thickness,δ, and fitted to the experimental data to understand how the siloxane degrades the SOFC performance with time. The results of the model indicate that the total polarization losses increase approximately 44% over the course of the 180 min experiment at 350 mA cm −2 . Activation losses dominate the polarization losses initially but decrease in their total contribution while concentration losses increase. Scanning electron microscopy (SEM) with wavelength dispersive X-ray spectroscopy (WDS) elemental mapping indicates that silicon deposition is highest at the outer edge of the anode and forms a barrier layer to fuel diffusion, increasing concentration losses. When the model is applied to other previous D4 and L4 siloxane experiments conducted over a period of 40 h, similar trends in polarization losses are observed. Polarization losses increase more rapidly with D4 compared to L4 siloxane contamination, with concentration losses increasing the fastest with both types of siloxane.

Electrochemistry↗
DOE OSTI2020

Accommodation of Silicon in an Interconnected Copper Network for Robust Li-Ion Storage

Silicon (Si)-based materials are one of the most promising anodes to be applied in rechargeable lithium ion batteries. However, the active Si/electrolyte interface causes continuous side reactions and poor conductivity, which significantly decreases the cycling stability. Cu is the only metallic current collector that has been known to promote electron conduction and lithium-ion transfer without alloying reaction occurrence. However, to the best current knowledge, scalable interface engineering incorporating Cu has not been reported. In this study, this conductive Cu interface (CCI) is constructed through a self-assembly carbothermic reduction method to achieve efficient protection of Si/electrolyte interfaces while allowing for fast Li + diffusion. The energy barrier of lithium-ion diffusion through Cu is calculated to be 0.1965 eV, which is much lower than that through Au, Fe, and Ni films. Benefiting from the enhanced interfacial protection and kinetics of Si with CCI, a fading rate of only 0.068% is maintained for 1000 cycles and an aerial capacity of 4.78 mAh cm -2 is achieved after 280 cycles, which is comparable to the industry standards required for practical application.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electrolyte-phobic Surface for the Next-Generation Nanostructured Battery Electrodes

Nanostructured electrodes are among the most important candidates rationally designed to enable high capacity battery chemistry. Nanostructures can solve issues such as the volume change and mechanical fragmentations. However, the high surface area they usually possess would decrease the Coulombic efficiencies, since the side chemical reactions scale with surface area. Moreover, electrodes comprised of nanomaterials have significant intakes of liquid electrolytes, which reduces the overall energy density and increases the cost of the battery. Here we present a new strategy of limiting effective surface area by introducing an “electrolyte-phobic surface”. In this study, a porous Si anode functions as a model material to demonstrate this concept. Silicon boasts high theoretical capacity, but experiences large volume change during its lithiation and delithiation processes. Porous Si can address this volume change problem with the buffer effect of its inner pores. However, porous silicon shows low initial Coulombic efficiencies and high irreversible lithium loss, owing to its intrinsic high surface area. In this report, a covalently linked perfluorinated surface coating layer on porous Si particles serves as an electrolyte-phobic protection layer, minimizing the accessible surface area for the electrolytes, decreasing the side reactions between the electrolyte and Si surface, and thus significantly enhancing the initial Coulombic efficiencies, up to ~88% compared to ~60% for the pristine porous silicon. Meanwhile, the electrolyte-phobic protection layer of Si particles keeps the silicon surface compatible with the conventional polyvinylidene fluoride (PVDF) binder, which helps to stabilize the Si electrode for long-term battery cycling.

Qian, Chenxi↗
DOE OSTI2021

Effect of cathode on crosstalk in Si-based lithium-ion cells

Crosstalk between the cathode and the anode in Li-ion batteries has a great impact on performance, safety and cycle lifetime. However, a systematic investigation of crosstalk behavior in silicon (Si)-based cells with various cathode materials has not been reported. We investigated the crosstalk behavior of a Si anode coupled with one of the following cathodes—LiCoO 2 (LCO), LiNi 0.5 Mn 0.3 Co 0.2 (NMC532), and LiFePO 4 (LFP)—in a full cell. For each electrochemical couple, we compared electrolyte decomposition products, solid electrolyte interphase (SEI) chemistry, and degradation mechanisms during cycling. From a very early stage of cycling, each couple showed different crosstalk behavior; different electrolyte decomposition products and SEI chemistry on the Si anodes were seen. Specifically, the formation and growth mechanism of Si SEI differ depending on cathode materials. For the LFP system, the Si SEI rich in LiF and inorganic species, which is stable and robust. It forms at an early stage of cycle. As a result, the SEI of Si from the LFP system well tolerates SEI breakage due to mechanical changes of Si and suppresses Li loss, resulting in stable cycle life.

25 ENERGY STORAGE↗
DOE OSTI2024

Elucidating the Role of Carbon Conductive Additive in the Processing and Electrochemical Behavior of Surface-Modified Si Anodes

In the present work, we explore the impact of conducting carbon on the processing of silicon (Si)-rich electrodes, their resulting cycling performance, and parasitic side reactions. We employed three different carbon additives, Super C45 (carbon black), Super C65 (carbon black), and TIMCAL C-NERGY KS 6L (graphite), with varying sizes and morphologies to determine how these parameters influence the structure and the electrochemical behavior of the cast electrodes. Raman mapping indicates that the improved performance achieved using C45 can be explained by the homogeneous distribution of Si and carbon, enabling the formation of continuous electrical pathways throughout the electrode. Further, this finding aligns with the results of ζ potential measurements, which indicate that C45 can maintain more stable dispersions in N-methyl-2-pyrrolidone (NMP) compared with the other carbon additives. However, electrodes with C45 as the conducting agent exhibited increased parasitic side reactions, as evidenced by the leakage current obtained from voltage hold experiments. These side reactions can have adverse effects on the calendar life of the electrode. Furthermore, the Raman maps of the electrodes reveal heterogeneities in Si and carbon distribution with lower carbon content, especially with only 2% carbon. This drastically impacts the cyclability of the electrodes, with portions of the low-carbon electrodes that remain unable to undergo cycling even at slow rates (0.2 Ah g –1 ). Additionally, we found that slower formation rates are favored in the context of parasitic side reactions, although slower formation rates can potentially create thicker passivating films that could hinder Li + -ion transport. Therefore, we emphasize the need for an intricate balance in materials selection and cycling protocol for optimal electrode processing and electrochemical behavior.

25 ENERGY STORAGE↗
DOE OSTI2020

Si-based materials for lithium-ion batteries IV: Surface-modified Si/C/perfluorooctene powder

X-ray photoelectron spectroscopy was used to analyze nano-Si/C/perfluorooctene powder obtained from Paraclete Energy Inc. The spectra were obtained using incident monochromatic Al K α radiation at 1486.6 eV (0.834 01 nm). An initial survey spectrum together with F 1s, O 1s, C 1s, and Si 2p are presented. A final survey spectrum was collected to ascertain the amount of beam-induced damage, which appears to be minimal. Finally, the spectra indicate the principal core level photoelectron and Auger electron signals with only minor nitrogen signal and show the expected silicon-carbon, carbon-fluorine, and silicon-fluorine species related to the surface modification process in addition to oxidized carbon and silicon due to atmospheric exposure.

25 ENERGY STORAGE↗
DOE OSTI2021

High-Performance Li-Ion Battery Anodes from Electrospun Nanoparticle/Conducting Polymer Nanofibers

The project objectives were: (1) Fabricate, characterize, and optimize the composition/morphology of an entirely new class of Si-based nanofiber anodes for Li-ion batteries, with high gravimetric and volumetric energy density and minimal capacity fade during charge/discharge cycling, (2) Improve our understanding of structure/functions correlations in electrospun particle/conducting polymer nanofiber anodes, and (3) Perform pilot-scale-up studies for anode commercialization.

25 ENERGY STORAGE↗
DOE OSTI2022

Failure analysis and design principles of silicon-based lithium-ion batteries using micron-sized porous silicon/carbon composite

Significant progresses have been made to overcome the fundamental challenges in silicon (Si)-based lithium-ion batteries (LIBs). However, much less work have been reported on the design and failure analysis these batteries for practical applications. In this work, we analyzed various cell design parameters affecting the performance of pouch cells using micron-sized porous Si with nano-pore structure and coated by pitch-carbon (p-Si/C). The correlation among particle level, electrode level, and cell level properties, especially the effect of electrode density on the volumetric capacity density of Si anode and full batteries have been systematically investigated. It is found that the corrosion of p-Si/C particle surface is the main failure mechanisms on the eventual capacity loss, while Li plating on anode electrode surface is the main reason for the fast capacity loss in later stage of cycling. The volumetric capacity of Si anode highly depends on both electrode density and the Si content. Moreover, the prelithiation of Si anodes is found to increase energy density while decreasing cycle life of Si-based full cells. Finally, the pathways and strategies for adoption of micron-sized p-Si/C anodes in LIBs have been proposed for their practical applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Understanding the Effect of Cathode Composition on the Interface and Crosstalk in NMC/Si Full Cells

Crosstalk between the cathode and the anode in lithium-ion batteries has a great impact on performance, safety, and cycle lifetime. Still, no report exists for a systematic investigation on crosstalk behavior in silicon (Si)-based cells as a function of transition metal composition in cathodes. We studied the effect of crosstalk on degradation of Si-rich anodes in full cells with different cathodes having the same crystal structure but different transition metal compositions, such as LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NM111), LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532), and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811). We found that the transition metal composition in cathodes, especially Mn ion concentration, significantly affects electrolyte decomposition reactions, even from very early cycles. This change causes differences in the solid electrolyte interphase (SEI) chemistry of each aged Si sample. As a result, each of the aged Si samples has a different electrochemistry, in terms of initial Coulombic efficiency and the mechanism of capacity fade.

25 ENERGY STORAGE↗
DOE OSTI2023

Environmental stability of additively manufactured siliconized silicon carbide for applications in hybrid energy systems

A key consideration for the successful operation of hybrid energy systems will be the environmental stability of materials used for their construction, particularly when experiencing service environments containing water vapor at high temperatures. Here, we report results from the characterization of siliconized silicon carbide (Si-SiC) prepared via binder jet additive manufacturing and reactive silicon melt infiltration after being exposed to environments representative of those in solid oxide fuel cell (SOFC) anodes, and to exhaust gases inside a microturbine operating on natural gas. In both cases, it was found that oxide scales formed on the surface and that these scales were dense, continuous, and well-bonded to the substrates, although there was evidence of transverse and longitudinal cracking most likely as a result of mismatches in the thermal expansion of the scale and the substrate. Measured values of the thickness of the oxide scale were compared to those predicted by parabolic oxidation kinetics of silicon, but the potential effects of silica volatilization induced by water vapor, and silica reduction when exposed to hydrogen are discussed. The overall results showed that the oxide scale is expected to be protective under the conditions of hybrid power generation systems.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Direct Prelithiation of Silicon-Based Composite Electrodes via Island-like Thermal Evaporation

Irreversible losses of Li during solid electrolyte interface (SEI) conditioning is a key contributor to the lower specific capacities observed in silicon-containing Li-ion batteries. Herein, thermal evaporation of between 1 and 20 µm of Li onto Si-based composite anodes has been investigated as a prelithiation method to account for such losses. To account for mechanical strain caused by Li-Si alloying during the deposition, a stainless-steel mesh is applied to the electrodes before prelithiation to form “island-like” deposition on the electrode surface. The open circuit potential was also found to decrease as a function of increased Li evaporation, consistent with the potentials of electrochemically prepared LixSi alloys. Prelithiating to account for irreversible Li losses to SEI formation resulted in full cells with a 15.8% increase in initial coulombic efficiency and a 47.8% reduction in irreversible capacity loss after SEI formation cycling. Subsequent C/3 cycling showed up to a 62.9% increase in specific capacity in prelithiated cells. X-ray photoelectron spectroscopy (XPS) revealed differences in the SEI composition that was formed by electrochemical cycling and reactively formed in prelithiated cells upon exposure to Gen2 + 3% FEC electrolyte. The reactively formed SEI from the spontaneous reaction with lithiated silicon was carbonate-rich while the electrochemical SEI formation showed significantly more LiPFx species, which could play a role in overall cycling performance.

Musgrove, Amanda↗
DOE OSTI2021

Chemical Interplay of Silicon and Graphite in a Composite Electrode in SEI Formation

In this study, we investigated the effect of the Si/graphite weight ratio in half-cells on the solid electrolyte interphase (SEI) layer's chemistry. The nominal concentrations of active materials were (wt % Si/wt % Gr) 15/73, 30/58, 60/28, and 80/0. The electrolyte in the cells consisted of either 1.2 M LiPF 6 in ethylene carbonate/ethyl methyl carbonate (3:7 by wt) or 1.2 M LiPF 6 in ethylene carbonate:ethyl methyl carbonate (3:7 by wt) + 10 wt % fluoroethylene carbonate. These coin cells were cycled five times at the C/10 rate. As expected, the addition of silicon to the electrode significantly increased the measured capacity. Examination of the aged composite material showed that the electrolyte influenced the concentration of chemical environments on the surface. Depth profiling revealed that these concentrations of surface environments changed with sputtering time. A statistics-of-mixtures model was used to deconvolute how silicon and graphite interacted during the formation of these species and how the interaction changed with depth.

25 ENERGY STORAGE↗
DOE OSTI2025

Understanding LIB Battery Electrodes Through Classical Electrochemical Interface Theory

Classical models of the electrochemical interface can be applied to complex and dynamic electrodes to understand important mechanisms that are relevant to device-level phenomena like calendar aging or cycle life. Here, we show that negative alloy electrodes with wide electrochemical windows cannot be assumed to have static interfaces throughout all states of charge. Under high states of charge, the interface -including the solid electrolyte interphase - has characteristics that resemble a highly polarized electrode far from the point of zero charge. Under these conditions, the interface can be understood through the Helmholtz model. At lower states of charge, the interface capacitance decreases and the space charge layer length increases. This transformation resembles a metal electrode approaching the point of zero charge which is understood through the Gouy-Chapman-Stern-Grahame model of the electrochemical interface. This transformation happens at both silicon and carbon-coated silicon interfaces. From voltage-limited cycling experiments, in the limit of the diffuse double layer, the silicon electrode impedance rises significantly in the first few cycles. This rise is related to the continuous electrochemical reduction of electrolyte components from an interface that is not electronically screened from the electrolyte. In other words, an electrode interface for batteries should resemble a 'Helmholtz-like' structure.

anode↗