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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Reactivity of Carbonate Solvent Electrolytes on Lithium Silicon Anodes

Silicon (Si) is promising for lithium-ion battery (LIB) anodes due to their high theoretical capacity and low electrochemical potential. However, significant challenges remain, including severe volumetric expansion during cycling and the electrochemical instability of electrolytes, which leads to the formation of a nonuniform solid electrolyte interphase (SEI). To investigate SEI formation mechanisms, computational molecular dynamics simulations offer valuable insights. In this work, we examine the trajectories and charge transfer behavior of lithium hexafluorophosphate (LiPF 6 ) salt with various solvent compositions using density functional theory (DFT) and ab initio molecular dynamics (AIMD). Among the tested electrolyte systems, LiPF 6 with vinylene carbonate (VC) added to ethyl methyl carbonate (EMC) exhibits the lowest reactivity with the Si anode. In contrast, the effects of fluoroethylene carbonate (FEC) and VC depend on whether the primary solvent is EMC alone or a mixture of ethylene carbonate (EC) and EMC. Moreover, we show that electrolyte reactivity varies with the degree of lithiation of the Si anode (LiSi vs Li 15 Si 4 ) and under different charge states. To decouple electrolyte reactivity from surface effects, we analyze the dissociation and formation energies of individual species from solvated configurations. Overall, these first-principles-based findings provide a strategic foundation for electrolyte design to improve cycling stability and extend calendar life in LIBs using Si anodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Surprising Relationship between Silicon Anode Calendar Aging and Electrolyte Components in a Localized High-Concentration Electrolyte System

Although localized high-concentration electrolytes (LHCEs) have been shown to improve the calendar lifetime of silicon anodes, the roles of the electrolyte constituents in calendar aging are not well understood. Here, in this work, we utilize a voltage hold protocol and an LHCE with varying molar ratios of lithium bis(fluorosulfonyl)imide (LiFSI), tetramethylene sulfone (TMS), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to probe the component roles during aging. Interestingly, the estimated calendar lifetime and irreversible lithium losses from the V-hold experiments are independent of the electrolyte formulations. Contrarily, the solid electrolyte interphase (SEI) composition depends on the electrolyte formulation. X-ray photoelectron spectroscopy shows that TMS-coordinated species decompose to form insoluble alkanes and lithium hydroxide (LiOH), while lithium fluoride (LiF) originates from the anion-coordination complex. The SEI composition does not appear to play a significant role in the silicon anode passivity, as measured by parasitic current, suggesting that the SEI-electrolyte interactions dictate the calendar aging mechanisms.

Si anode↗
DOE OSTI2025

The Solid Electrolyte Interphase Dispersion Can Predict Cycle and Calendar Lifetimes in Silicon Anodes for Lithium-Ion Batteries

The solid electrolyte interphase (SEI) plays a critical role in lithium-ion battery (LIB) anodes. It is responsible for passivating the reactive surface of lithiated anodes against degradation of the electrolyte which enables long cycle and calendar lifetimes for LIBs. This role is especially important in high energy density anodes like silicon, that undergo massive volumetric changes during electrochemical cycling. The mechanism by which the SEI performs this role, however, is not clear which makes designing an SEI to passivate silicon anodes impossible. Through decades of research, dozens of chemical species have been identified within the SEI ranging from inorganic solids to polymeric coatings all of which simultaneously exist in a 'mosaic' composition at the anode surface. This mosaic creates a highly dispersive environment in which electrostatic screening of the anode surface from the electrolyte is not always complete. Here, we present an electrochemical technique to directly test the dispersion at the anode surface. We use this technique to screen more than 20 different electrolytes against silicon anodes and find correlations between both the cycle life and calendar life. The insights from this study offer a new framework to think about the SEI and a rapid screening method to test novel electrode/electrolyte combinations.

battery↗
DOE OSTI2025

Solid‐State Prealkylation of Electrode Architectures (SPEAR): Direct Control of Prelithiation Levels in Silicon Anodes and Electrochemical Cycling

The Solid-state Prealkylation of Electrode ARchitectures (SPEAR) is different than traditional electrochemical prealkylation processes. Through SPEAR, alkylation is driven by solid-state diffusion without the simultaneous SEI formation concomitant with polarization. Here, we investigate the prelithiation of 80 wt. % Si-based anodes to varying amounts (up to Li 1.38 Si) to understand the trade-off between improved Li capacity and expansion-induced stress. Through dilatometry, we found that solid-state lithiation led to filling of the electrode pores through silicon expansion. This swelling changed the SEI formation process and accessibility of the silicon compared to an electrochemically lithiated electrode. Indeed, optimal prelithiation to Li 0.82 Si increases the initial C/3 cycling capacity post-SEI formation up to 43%, consistent with deeper Si activation through the electrode bulk. Prelithiation and cycling cells prelithiated beyond Li 0.82 Si results in a state of charge (SOC) close to 100% which facilitates parasitic degradation mechanisms and volume expansion of the Si electrode. The results demonstrate a pathway to modify silicon activation/SEI formation to enable high-energy electrodes.

Musgrove, Amanda L. [Oak Ridge National Laboratory↗
DOE OSTI2024

Fracture Dynamics in Silicon Anode Solid-State Batteries

Solid-state batteries (SSBs) with silicon anodes could enable improved safety and energy density compared to lithium-ion batteries. However, degradation arising from the massive volumetric changes of silicon anodes during cycling is not well understood in solid-state systems. Here, we use operando X-ray computed microtomography to reveal micro- to macro-scale chemo-mechanical degradation processes of silicon anodes in SSBs. Mud-type channel cracks driven by biaxial tensile stress form across the electrode during delithiation. We also find detrimental cracks at the silicon/ solid electrolyte interface that form due to local reaction competition between neighboring domains of different sizes. Continuum phase-field damage modeling quantifies stress-driven channel cracking and shows that the lithiated silicon stress state is critical for determining the extent of interfacial fracture. This work reveals the mechanisms that govern SSBs compared to conventional lithium-ion batteries and provides guidelines for engineering chemomechanically resilient electrodes for high-energy batteries.

25 ENERGY STORAGE↗
DOE OSTI2025

Role of Salt Concentration on Interphase Dynamics and Chemistry of Silicon Anodes during Electrochemical Cycling

We investigated the chemistry and structure of the solid electrolyte interphase (SEI) grown over a silicon anode as a function of the lithium salt concentration. In these experiments, in situ neutron reflectivity measurements were performed to measure the thickness and composition of the SEI formed from 1.0 and 5.5 M lithium bis(trifluoromethane)sulfonimide (LiTFSI) in standard ethylene carbonate:dimethyl carbonate electrolytes. These measurements reveal the formation of a 350+ Å thick SEI layer that is predominantly organic (∼80%) and dimensionally stable when using a 1.0 M salt solution. In contrast, increasing the salt concentration to 5.5 M resulted in an SEI that exhibited thickness changes from 100 to 375 Å and became up to 30% inorganic. In conclusion, these compositional and structural changes point to the role of salt speciation on the resulting passivation of silicon electrodes and indicate the need to form more organic-like passivation layers to promote the calendar life of silicon anodes.

Electrodes↗
DOE OSTI2026

Electrode-omics reveals epochs in silicon anode evolution underpinning electrochemomechanical resilience

Here, we advance electrode-omics to identify evolutionary bursts by which ethereal locally superconcentrated electrolytes (LSCEs) mitigate silicon anode degradation through its epochs of electrochemical and chemical reactions. Anode composites form initially at high potential from ethereal solvent and anion [bis(fluorosulfonyl)imide (FSI − )] redox. A first evolutionary burst at lower potential enriches composites with lithium alkoxides (LiO–R) and lithium oxide (Li 2 O) and depletes sulfur oxides (SO x ) species. As the cells are cycled, a second evolutionary burst takes place, where previously extinct SO x species reemerge concurrently with a loss of LiO–R and Li 2 O. This identifies reactions rooted in “SuFEx” chemistry, where oxoanionic LiO–R and Li 2 O species, electrochemically generated in the solid-electrolyte interphase, chemically react with FSI − in the electrolyte to form emergent species. This sequence of evolutionary bursts produces a mechanically resilient composite that reduces silicon anode cracking over hundreds of cycles, leading to overpotential increase of only ~0.01 volts after 200 cycles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Enhanced Performance of Silicon Anodes through Hybrid Surface Engineering

Silicon (Si) is a promising anode material for nextgeneration lithium-ion batteries (LIBs) due to its high theoretical capacity. However, Si-containing anodes typically suffer from unacceptably short lives because of the unrestricted growth of the solid electrolyte interphase (SEI). Here, in this study, hybrid surface coatings are developed to stabilize the SEI in high loading pure Si anodes using atomic and molecular layer deposition. The coatings, consisting of LiF paired with lithicone, create an ionically conductive surface that enhances the capacity retention, rate performance, and longevity. Careful binder selection helps demonstrate the full utility of the coatings by enabling high loading electrodes to cycle continuously at current densities of 1200 mA/g Si . Uncoated controls, in comparison, fail within just 10 cycles at lower loadings. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy are used to provide supporting evidence of the coating composition and efficacy. The data indicate that our lithicone coating is converted to Li 2 CO 3 upon cycling contributing to favorable LiF/Li 2 CO 3 interfaces that enhance the space-charge effect at the active material’s surface. When applied to electrodes made with thermally stable binders and increasingly higher loadings (approaching 5 mAh/cm 2 ), ion transport through the bulk electrode, rather than SEI growth, is shown to be the limiting factor. Furthermore, data suggests a favorable interaction between lithicone precursors and poly(acrylic acid) binders mitigates thermal decomposition at higher temperatures. The work presented here represents the successful realization of composite coatings containing LiF/Li 2 CO 3 components to stabilize high-loading Si anodes. This work helps inform advanced surface engineering strategies to achieve highly reversible, high-capacity Si anodes capable of fast charging for high-performance LIBs.

atomic layer deposition↗
DOE OSTI2025

Multi-phase characterization of pitch-carbon coated nano-silicon anodes for lithium-ion batteries

Silicon (Si) is a leading next-generation Li-ion battery anode candidate that meets rigorous performance demands for portable power including enhanced power and energy density with robust cycling performance. However, a series of complex and interrelated reactions lead to reduced calendar life in Si-containing systems and therefore challenge practical adoption. In the present work, we probe the mechanisms underlying observed performance improvements by adding a pitch-carbon coating onto nano-Si material. We pair solid-phase (X-ray photoemission spectroscopy, Fourier-transform infrared), semi-volatile phase (solid-phase microextraction-gas chromatography-mass spectrometry), and gas-phase (gas chromatography-flame-ionization detector) characterization signals to comprehensively evaluate the impact of pitch-carbon coating on the evolution of the Si solid-electrolyte interphase (SEI) and the associated impacts on electrode/electrolyte reactivity. The pitch-carbon is found to serve as a physicochemical barrier, reducing the electro-active surface area for Si/electrolyte reactivity and preventing Si oxidation. Further, the pitch-carbon coating promotes the evolution of a more-favorable SEI by subsuming substantial functionality typically associated with the fluoroethylene carbonate (FEC) electrolyte additive - such as alkoxide scavenging and suppression of transesterification pathways - and by shifting the competitive electrolyte degradation pathways' favorability. The multi-phase characterization approach enables holistic end-products evaluation from complex (electro)chemical interfacial reactions, which informs a robust interpretation of the carbon coating's role in electrochemical performance improvements. The present mechanistic evaluation aids the rational design for improved nano-Si materials.

25 ENERGY STORAGE↗
DOE OSTI2025

On the dynamics of the fluoroethylene carbonate generated solid electrolyte interphase on silicon anodes during calendar life aging

Here, the widespread use of silicon (Si)-rich anodes in lithium-ion batteries (LIBs) is impeded by an unstable solid electrolyte interphase (SEI) incurring insufficient cell life. Fluoroethylene carbonate (FEC) additive in the electrolyte significantly improves cycle life. However, the gains on calendar life remain unclear; the SEI structure still undergoes detrimental alterations at rest. Thus, elucidating the SEI dynamics during calendar aging is critical to mitigating time-dependent capacity degradation. ATR-FTIR, XPS, and ToF-SIMS are used herein to investigate the SEI structure before and after calendar aging. Si cycled without FEC exhibits no notable SEI chemistry changes Pre- and Post-aging, leaving poor passivation as the main failure pathway. Conversely, the FEC-SEI starts as short oligomeric species from FEC/EC electroreduction prior to aging; after calendar aging, polymerized carbonates become consistently more prominent. Unexpectedly, the deposition of self-polymerized FEC species results from time exposure to the delithiated Si specifically as opposed to the lithiated surface. This unexpected finding is supported by another recent Si calendar-aging research, which albeit not investigating FEC, finds global failure of the SEI upon delithiation resulting in ∼247 fold more reactive surface compared to the lithiated.

Batteries↗
DOE OSTI2026

Mechanistic Understanding of Interphase-driven Aging in Silicon Anodes

Conventional solid electrolyte interphases (SEIs) strongly adhere to micro-silicon (µ-Si) and crack under volume changes, causing poor cycling performance. Nano-silicon improves cycling performance but remains costly with limited calendar life. Here potentiostatic ageing tests demonstrate that both calendar and cycle ageing are governed by SEI cracking and dissolution with different relative contributions. When the system is not dominated by SEI dissolution, the relative calendar life of Si anodes could correlates positively with their cycle life. LiF-rich SEI that enables long cycle life in µ-Si is therefore expected to enhance calendar life as well. Using this framework, we screened electrolytes, SEIs and electrodes and validated them with full-cell storage. LiF-rich SEI minimizes cracking and dissolution, enabling μ-Si to achieve excellent calendar life, whereas nano-silicon suffers from SEI dissolution and needs reduced electrolyte–electrode contact for better calendar life. This work clarifies calendar-ageing behaviour and accelerates electrolytes and SEI development for long-life Si anodes.

Johnson, Christopher S.↗
DOE OSTI2025

Multiscale electro-chemo-mechanical model of high-capacity amorphous silicon anode material in sodium-ion batteries

The growing interest in sodium-ion batteries (SIBs) is fueled by their abundant resources and environmentally friendly nature, with amorphous silicon (a-Si) emerging as a promising anode material for enhancing capacity. However, the key challenge lies in sustaining reversible capacity during cycling. Here, in this work, we developed a multiscale electrochemical model incorporating an a-Si anode to elucidate the performance parameters of SIBs. Additionally, we integrated an electro-chemo-mechanical model at the particle level to capture stress generation, an essential factor in the degradation of high-capacity electrodes. Unlike existing models, our approach accounts for large-deformation chemo-mechanics at the particle scale and includes simulations under varying charge rates to explore multiscale behavior. The results reveal that coupled sodiation significantly prolongs complete cycling times and influences discharge dynamics, indicating that neglecting this coupling leads to an underestimation of actual capacity. Furthermore, we observed pronounced polarization effects at higher charge rates, resulting in heterogeneous stress distributions across the anode. With the identification of critical failure parameters for both active particles and binder materials, offering novel insights for mitigating degradation in high-capacity electrode systems.

Amorphous silicon anode↗
DOE OSTI2026

Experimental considerations and applications for time-resolved impedance on silicon-anode battery systems

Dynamic electrochemical impedance spectroscopy (dEIS) utilizes a superimposed multi-sinusoidal waveform and enables temporally resolved investigations on various electrochemical processes; however, the signal-to-noise ratio must be maximized while retaining linearity and stationarity within the system. In the present work, we probe the impact of the waveform’s total amplitude as well as the waveform and phase profiles. The equal amplitude multi-sinusoidal waveform with 35 mV total amplitude (<1 mV per frequency) and random phase profile exhibits the lowest impedance noise. This input signal is sufficient in avoiding the high frequency signal attenuation from the potentiostat’s low-pass filter. Additionally, we demonstrate the optimized dEIS waveform’s utility in investigating surface passivation within thin-film and composite silicon (Si) anodes. Within a two-electrode Si-lithium metal coin cell, the charge transfer resistance (RCT) associated with alloying kinetics dominates the overall impedance. RCT increases with state of charge indicating a kinetic bottleneck at higher lithiation states. To explore this further, we utilize a three-electrode Si-LiNi0.8Mn0.1Co0.1O2 pouch cell to deconvolute the Si impedance contributions. The evolution of the solid electrolyte interphase (SEI) and charge transfer resistances correlate to specific Li–Si alloy phases. We attribute this to the influence of Si particle volume expansion on SEI instabilities and a kinetic bottleneck at higher lithiation states.

Lam, Steven [ORNL]↗
DOE OSTI2025

Building High-Energy Silicon-Containing Batteries Using Off-The-Shelf Materials

The technology of silicon anodes appears to be reaching maturity, with high-energy Si cells already in pilot-scale production. However, the performance of these systems can be difficult to replicate in academic settings, making it challenging to translate research findings into solutions that can be implemented by the battery industry. Part of this difficulty arises from the lack of access to engineered Si particles and anodes, as electrode formulations and the materials themselves have become valuable intellectual property for emerging companies. Here, we summarize the efforts by Argonne’s Cell Analysis, Modeling, and Prototyping (CAMP) Facility in developing Si-based prototypes made entirely from commercially available materials. We describe the many challenges we encountered when testing high-loading electrodes (>5 mAh cm −2 ) and discuss strategies to mitigate them. With the right electrode and electrolyte design, we show that our pouch cells containing ≥ 70 wt% SiO x can achieve 600–1,000 cycles at C/3 and meet projected energy targets of 700 Wh L −1 and 350 Wh kg −1 . These results provide a practical reference for research teams seeking to advance silicon-anode development using accessible materials.

25 ENERGY STORAGE↗
DOE OSTI2025

The Origin of Improved Performance in Boron‐Alloyed Silicon Nanoparticle‐Based Anodes for Lithium‐Ion Batteries

Stabilizing the solid electrolyte interphase (SEI) remains a key challenge for silicon‐based lithium‐ion battery anodes. Alloying silicon with secondary elements like boron has emerged as a promising strategy to improve the cycle life of silicon anodes, yet the underlying mechanism remains unclear. To address this knowledge gap, how boron concentration influences battery performance is systematically investigated. These results show a near‐monotonic increase in cycle lifetime with higher boron content, with boron‐rich electrodes significantly outperforming pure silicon. Additionally, silicon‐boron alloy anodes exhibit nearly three times longer calendar life than pure silicon. Through detailed mechanistic analysis, alternative contributing factors are systematically ruled out, and it is proposed that improved passivation arises from a strong permanent dipole at the nanoparticle surface. This dipole, formed by undercoordinated and highly Lewis acidic boron, creates a static, ion‐dense layer that stabilizes the electrochemical interface, reducing parasitic electrolyte decomposition and enhancing long‐term stability. These findings suggest that, within the SEI framework, the electric double layer is an important consideration in surface passivation. This insight provides an underexplored parameter space for optimizing silicon anodes in next‐generation lithium‐ion batteries.

25 ENERGY STORAGE↗