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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Access to Ru(IV)–Ru(V) and Ru(V)–Ru(VI) Redox in Layered Li 7 RuO 6 via Intercalation Reactions

The push to increase the capacity of oxides to store charge as Li-ion battery cathodes has challenged our knowledge of the boundaries of redox chemistry and its relationship to the atomic structure. Layered phases with Ru are now classical models in the quest for refined theories. Current understanding dictates that the highest formal state that can be reached in them is Ru(V), after which activity centered at the oxide anions is triggered. Yet, this picture is challenged by this investigation of the intercalation chemistry of Li 7 RuO 6 . Coupling structural and spectroscopic analysis with computational simulations, we show that Li 7 RuO 6 is capable of highly reversible lithiation to Li 8 RuO 6 through the Ru(V)/Ru(IV) redox couple. Further, Li 7 RuO 6 can also undergo anodic Li deintercalation, showing clear evidence of the reversible formation of Ru(VI) with octahedral coordination, an unusual state that is not accessible in other layered oxides. The results highlight the versatility of the Ru-O bond to undergo distinct redox transitions depending on the specific layered arrangements. They enrich our understanding of redox chemistry in solids while underscoring the need for descriptions of charge compensation that reflect the nuance of covalent interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Investigating Ternary Li–Mg–Si Zintl Phase Formation and Evolution for Si Anodes in Li-Ion Batteries with Mg(TFSI) 2 Electrolyte Additive

Improved electrochemical performance of Si was recently reported by adding multivalent cation salts (such as Mg 2+ , Al 3+ , Ca 2+, etc.) in the electrolyte. This is achieved via the formation in an in situ manner of relatively more stable Li-M-Si ternary phases with less chemical reactivity. These phases stabilize Si anions and thus reduce side reactions with electrolytes at the surface and eventually benefit the overall electrochemistry. To understand the mechanism of ternary Zintl phase formation and its dynamics upon lithiation/delithiation, high-resolution solid-state 7 Li and 29 Si nuclear magnetic resonance (NMR) are utilized to directly probe the local Li and Si environments on Si electrodes harvested from coin and pouch cells at various states of (de)lithiation. The NMR spectra along with the electrochemical characterization reveal that lithiation of Si starts from the surface Si-O layer further confirmed by 7 Li– 29 Si cross-polarization NMR. Lithiation progresses with heterogeneous silicon clustering with Si -4 anions at high states of lithiation. At a fully lithiated state, the formation of overlithiated Si species is detected. At a low-voltage region (below 100 mV), direct evidence for Mg-ion insertion is found, postulated by two possible mechanisms: ion exchange with fully or overlithiated binary domains (Li 3.75+x Si) and/or a coinsertion with slightly underlithiated domains (similar to Li 3.55 Si). Upon delithiation, Li extraction starts from overlithiated Si domains. No evidence is found for electrochemical Mg removal. Evidence for a lithium-deficient Li y Mg 0.1 Si phase is found as a result of Li removal during charging. This investigation sheds light on the possible mechanisms of a new Si anode chemistry, which could enable the development of stable Si-based anodes for lithium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Understanding the Roles of the Electrode/Electrolyte Interface for Enabling Stable Li∥Sulfurized Polyacrylonitrile Batteries

Sulfurized polyacrylonitrile (SPAN) is a promising high-capacity cathode material. Here, we use spatially resolved X-ray absorption spectroscopy combined with X-ray fluorescence (XRF) microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy to examine the structural transformation of SPAN and the critical role of a robust cathode–electrolyte interface (CEI) on the electrode. LiS x species forms during the cycling of SPAN. However, in carbonate-based electrolytes and ether-based electrolytes with LiNO 3 additives, these species are well protected by the CEI and do not dissolve into the electrolytes. In contrast, in an ether-based electrolyte without the LiNO 3 additive, LiS x species dissolve into the electrolyte, resulting in the shuttle effect and capacity loss. Examination of the Li anode by XRF and SEM reveals dense spherical Li morphology in ether-based electrolytes, but sulfur is present in the absence of the LiNO 3 additive. In contrast, porous dendritic Li is found in the carbonate electrolyte. These analyses established that an ether-based electrolyte with LiNO 3 is a superior choice that enables stable cycling of both electrodes. Based on these insights, we successfully demonstrate the stable cycling of high areal loading SPAN cathode (>6.5 mA h cm –2 ) with lean electrolyte amounts, showing promising Li∥SPAN cell performance under practical conditions.

25 ENERGY STORAGE↗
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.↗
DOE OSTI2023

Characterization of Annealing-Induced Phase Segregation in Composite Silicon Anodes for Li-ion Batteries

Silicon (Si) anodes present a promising alternative to graphite anodes for lithium-ion batteries (LIBs), as Si has a greater specific capacity. However, one major constraint is the volumetric change of Si during lithiation that results in an unstable solid-electrolyte interphase (SEI), so Si-containing electrodes require the use of various strategies to mitigate these effects and improve performance. One such solution is the use of Si nanoparticles (NPs) that maximize the surface area to volume ratio. Here, we discuss electrodes made with Si NPs treated with polyethylene oxide (PEO) (for improving dispersion during processing), conductive carbon NPs, and P84 polyimide binder which shows significant impacts of annealing treatment on improvements of active material utilization, first cycle efficiency, and capacity retention with extensive cycling . We used air-free argon ion polishing to create electrode cross sections and imaged through the electrode thickness using atomic force microscopy (AFM)-based nano-electrical characterization of scanning spreading resistance microscopy (SSRM), nano-mechanical characterizations of contact resonance and force volume (CR-FV), and scanning electron microscopy-based energy dispersive x-ray spectroscopy (SEM-EDS). Results show that the Si and conductive carbon segregate into phases with a distinctive carbon-rich banded morphology that surrounds the Si-rich phase during annealing. In pristine electrodes, the carbon- and SEI-rich bands exhibit a higher electronic conductivity and a lower elastic modulus than the Si active material phase. These structures, as well as distinct electronic and mechanical properties, remain during cycling, suggesting an improvement of electrical conduction pathways and a mechanical strain buffer for active Si material expansion during cycling. This phase separation may be a major factor in the improvement seen in electrochemical performance due to annealing. Additionally, our nm-scale and multi-mode characterizations provide a novel route for understanding and improving energy storage devices, which is advantageous due to the highly inhomogeneous of composite electrodes in nm-mm scales.

ENERGY STORAGE↗
DOE OSTI2024

A Coordinated-Anion-Enriched Electrolyte for Lean-Electrolyte Li–S Batteries

The solid electrolyte interphase (SEI) on Li and cathode electrolyte interphase (CEI) at sulfurized polyacrylonitrile (SPAN) formed in the commonly used liquid electrolytes cannot accommodate the large volume change of both Li anode and SPAN cathode, resulting in severe electrolyte and Li consumption and fast capacity decay under high mass loading and lean electrolyte condition. Herein, a LiF-rich SEI and a LiF-Li x N y O z co-enriched CEI are simultaneously formed by adding ionic liquid (Py 13 TFSI) in the localized high-concentration electrolyte (LHCE), which forms a coordinated-anion-enriched solvation structure. In this study, the LiF-rich interphase results in less stress/strain during large volume changes of Li and SPAN and therefore achieving obviously improved stability even at a high areal capacity. Consequently, Li (50 μm)||SPAN (6 mg cm -2 ) pouch cells under the lean electrolyte condition (E/S ratio of 5 mL g SPAN -1 ) delivers a stable cycle life of 120 cycles with 79.2% capacity retention, demonstrating great promise for high-energy-density lithium-sulfur batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Hyperconjugation-controlled molecular conformation weakens lithium-ion solvation and stabilizes lithium metal anodes

Tuning the solvation structure of lithium ions via electrolyte engineering has proven effective for lithium metal (Li) anodes. Further advancement that bypasses the trial-and-error practice relies on the establishment of molecular design principles. Expanding the scope of our previous work on solvent fluorination, we report here an alternative design principle for non-fluorinated solvents, which potentially have reduced cost, environmental impact, and toxicity. By studying non-fluorinated ethers systematically, we found that the short-chain acetals favor the [gauche, gauche] molecular conformation due to hyperconjugation, which leads to weakened monodentate coordination with Li + . The dimethoxymethane electrolyte showed fast activation to >99% coulombic efficiency (CE) and high ionic conductivity of 8.03 mS cm -1 . The electrolyte performance was demonstrated in anode-free Cu$∥$LFP pouch cells at current densities up to 4 mA cm -2 (70 to 100 cycles) and thin-Li$∥$high-loading-LFP coin cells (200–300 cycles). Overall, we demonstrated and rationalized the improvement in Li metal cyclability by the acetal structure compared to ethylene glycol ethers. We expect further improvement in performance by tuning the acetal structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Hydrophobic versus Hydrophilic Interfacial Coatings on Silicon Nanoparticles Teach Us How to Design the Solid Electrolyte Interphase in Silicon-Based Li-Ion Battery Anodes

Herein, we evaluate the effect of covalently attached molecular coating hydrophobicity on the surface of the silicon nanoparticle (Si NP) active anode material for Li-ion batteries. The experiments are a means to identify the interfacial properties that help minimize electrochemical side reactions during cycling. Preformed coatings on the Si NP surfaces prior to electrode fabrication mimic the ionically conducting and electronically insulating properties of the solid electrolyte interphase (SEI). Hydrophilic oligomers such as polyethylene oxide (PEO) and other related structures are commonly identified as Li+-conducting components of the SEI. Here, we study the effect of such hydrophilic PEO versus hydrophobic alkyl molecular coatings on Si NP anode electrochemical performance. We also study the effect of the PEO oligomer length and the resulting effective thickness of the interfacial coating on the electrochemical performance. We find that PEO oligomers electrochemically isolate Si NPs when the PEO coating thickness approaches the electron tunneling distance of ~2.5 nm. Surprisingly, the thickness of the PEO-based coatings has a negligible effect on their ability to minimize electrochemical side reactions as measured by Coulombic efficiency. These results reveal how the interfacial coating on silicon anode materials should differ from an operando-formed SEI layer and discuss design strategies for an ideal interfacial active material coating based on these results.

25 ENERGY STORAGE↗
DOE OSTI2021

Dynamic spatial progression of isolated lithium during battery operations

The increasing demand for next-generation energy storage systems necessitates the development of high-performance lithium batteries. Unfortunately, current Li anodes exhibit rapid capacity decay and a short cycle life, owing to the continuous generation of solid electrolyte interface and isolated Li (i-Li). The formation of i-Li during the nonuniform dissolution of Li dendrites leads to a substantial capacity loss in lithium batteries under most testing conditions. Because i-Li loses electrical connection with the current collector, it has been considered electrochemically inactive or ‘dead’ in batteries. In this work, contradicting this commonly accepted presumption, we show that i-Li is highly responsive to battery operations, owing to its dynamic polarization to the electric field in the electrolyte. Simultaneous Li deposition and dissolution occurs on two ends of the i-Li, leading to its spatial progression toward the cathode (anode) during charge (discharge). Revealed by our simulation results, the progression rate of i-Li is mainly affected by its length, orientation and the applied current density. Moreover, we successfully demonstrate the recovery of i-Li in Cu–Li cells with >100% Coulombic efficiency and realize LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC)–Li full cells with extended cycle life.

25 ENERGY STORAGE↗
DOE OSTI2020

Fast-Charging and Ultrahigh-Capacity Lithium Metal Anode Enabled by Surface Alloying

Li metal anodes are going through a great revival but they still encounter grand challenges. One often neglected issue is that most reported Li metal anodes are only cyclable under relatively low current density (<5 mA cm -2 ) and small areal capacity (<5 mAh cm -2 ), which essentially limits their high-power applications and results in ineffective Li utilization (<1%). Herein, it is reported that surface alloyed Li metal anodes can enable reversible cycling with ultrafast rate and ultralarge areal capacity. Low-cost Si wafers are used and are chemically etched down to 20-30 mu m membranes. Simply laminating a Si membrane onto Li foil results in the formation of LixSi alloy film fused onto Li metal with mechanical robustness and high Li-ion conductivity. Symmetric cell measurements show that the surface alloyed Li anode has excellent cycling stability, even under high current density up to 25 mA cm -2 and unprecedented areal capacity up to 100 mAh cm -2 . Furthermore, the surface alloyed Li anode is paired with amorphous MoS 3 cathode and achieves remarkable full-cell performance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multidimensional visualization of the dynamic evolution of Li metal via in situ/operando methods

The growing demands for high-energy density electrical energy storage devices stimulate the coupling of conversion-type cathodes and lithium (Li) metal anodes. While promising, the use of these “Li-free” cathodes brings new challenges to the Li anode interface, as Li needs to be dissolved first during cell operation. In this study, we have achieved a direct visualization and comprehensive analysis of the dynamic evolution of the Li interface. The critical metrics of the interfacial resistance, Li growth, and solid electrolyte interface (SEI) distribution during the initial dissolution/deposition processes were systematically investigated by employing multidimensional analysis methods. They include three-electrode impedance tests, in situ atomic force microscopy, scanning electrochemical microscopy, and cryogenic scanning transmission electron microscopy. The high-resolution imaging and real-time observations show that a loose, diffuse, and unevenly distributed SEI is formed during the initial dissolution process. This leads to the dramatically fast growth of Li during the subsequent deposition, deviating from Fick’s law, which exacerbates the interfacial impedance. The compactness of the interfacial structure and enrichment of electrolyte species at the surface during the initial deposition play critical roles in the long-term stability of Li anodes, as revealed by operando confocal Raman spectroscopic mapping. In conclusion, our observations relate to ion transfer, morphological and structural evolution, and Li (de)solvation at Li interfaces, revealing the underlying pathways influenced by the initial dissolution process, which promotes a reconsideration of anode investigations and effective protection strategies.

25 ENERGY STORAGE↗
DOE OSTI2021

Systematic Evaluation of Carbon Hosts for High-Energy Rechargeable Lithium-Metal Batteries

Rechargeable lithium batteries (RLBs) have attracted wide attention for achieving high energy and low cost, but the poor stability of the Li anode has remained as a large challenge. In the last several years, great efforts have been made to develop carbon anode structures for RLB applications. A wide range of carbon structures as well as many chemical modification strategies have been investigated to improve the Coulombic efficiency and extend the cycle life of the anodes or the cells. However, currently there is no clear conclusion on key factors that determine the performance of such the types of carbon structures due to the wide range of experimental conditions used in such studies. In this study, we systematically evaluated and compared the electrochemical properties of representative carbon anode materials as well as chemically functionalized carbon materials in different electrolytes. We have found that chemical functionalization, metallic loading, and the types of micro or nano-structures all have an effect on Li deposition/stripping process, but by far the most critical factor is the nature of the electrolytes. All carbon materials produced poor Coulombic efficiency and cycle life in conventional carbonate or ether-based electrolytes. However, when a Li metal compatible is used, the average Coulombic efficiency of Li metal deposition on all carbon structures is increased to 99% or higher. This study provides critical lessons on the directions for carbon anodes for RLBs. Based on these findings, we constructed Li metal coin cells using prelithiated hard carbon, LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode, and compatible electrolyte and tested the cells under conditions of lean electrolyte, lean Li metal and high cathode loading required for more than 300 Wh kg-1 specific energy. More than 200 stable cycles were demonstrated with over 80% capacity retention. Furthermore, the existing challenges and potential approaches have been discussed to further extend the cyclability of lithium-metal batteries under practical conditions.

Liu, Yao↗
DOE OSTI2021

Enabling High-Performance NASICON-Based Solid-State Lithium Metal Batteries Towards Practical Conditions

Solid-state lithium metal batteries (SSLMBs) are promising next-generation high-energy rechargeable batteries. However, the practical energy densities of the reported SSLMBs have been significantly overstated due to the use of thick solid-state electrolytes, thick lithium (Li) anodes, and thin cathodes. Here, a high-performance NASICON-based SSLMB using a thin (60 µm) Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) electrolyte, ultrathin (36 µm) Li metal, and high-loading (8 mg cm -2 ) LiFePO 4 (LFP) cathode is reported. The thin and dense LAGP electrolyte prepared by hot-pressing exhibits a high Li ionic conductivity of 1 × 10 -3 S cm -1 at 80 °C. The assembled SSLMB can thus deliver an increased areal capacity of ≈1 mAh cm -2 at C/5 with a high capacity retention of ≈96% after 50 cycles under 80 °C. Furthermore, it is revealed by synchrotron X-ray absorption spectroscopy and in situ high-energy X-ray diffraction that the side reactions between LAGP electrolyte and LFP cathode are significantly suppressed, while rational surface protection is required for Ni-rich layered cathodes. This study provides valuable insights and guidelines for the development of high-energy SSLMBs towards practical conditions.

25 ENERGY STORAGE↗
DOE OSTI2020

Definition of Redox Centers in Reactions of Lithium Intercalation in Li 3 RuO 4 Polymorphs

Cathodes based on layered LiMO 2 are the limiting components in the path toward Li-ion batteries with energy densities suitable for electric vehicles. Introducing an over-stoichiometry of Li increases storage capacity beyond a conventional mechanism of formal transition metal redox. However, the role and fate of the oxide ligands in such intriguing additional capacity remain unclear. This reactivity was predicted in Li 3 RuO 4 , making it a valuable model system. For this study, a comprehensive analysis of the redox activity of both Ru and O under different electrochemical conditions was carried out, and the effect of Li/Ru ordering was evaluated. Li 3 RuO 4 displays highly reversible Li intercalation to Li 4 RuO 4 below 2.5 V vs Li + /Li 0 , with conventional reactivity through the formal Ru 5+ -Ru 4+ couple. In turn, it can also undergo anodic Li extraction at 3.9 V, which involves O states to a much greater extent than Ru. This reaction competes with side processes such as electrolyte decomposition and, to a much lesser extent, oxygen loss. Although the associated capacity is reversible, reintercalation unlocks a different, conventional pathway also involving the formal Ru 5+ -Ru 4+ couple despite operating above 2.5 V, leading to chemical hysteresis. This new pathway is both chemically and electrochemically reversible in subsequent cycles. This work exemplifies both the challenge of stabilizing highly depleted O states, even with 4d metals, and the ability of solids to access the same redox couple at two very different potential windows depending on the underlying structural changes. It highlights the importance of properly defining the covalency of oxides when defining charge compensation in view of the design of materials with high capacity for Li storage.

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

Regenerative Solid Interfaces Enhance High-Performance All- Solid-State Lithium Batteries

All-solid-state Lithium batteries (ASSLBs) have gained widespread attention in recent years. However, their performance is still largely limited by the poor transport properties and stability of the solid-solid interfaces (SSIs). In this study, we report a new strategy for creating a reversible interface with good conductivity and self-adaptive mechanical properties for high-performance all-solid-state lithium batteries (ASSLBs). The interface is formed in situ from nanosized lithium iodide (LiI), a component of the solid-state electrolyte (SSE), which flows plastically along the SSE interfaces under high pressure due to its high ductility. Moreover, LiI segregates and enriches along the Li/SSE interfaces, reversibly enhancing Li plating/stripping due to its lithophilicity and high ionic conductivity. This dynamic LiI interface enables stable operation of metallic Li anode (>1000 h) at high current densities and elevated temperatures, and long-term cycling of all-solid-state Li-sulfur batteries (>250 cycles) with high sulfur utilization rate (>1400 mAh g-1) and areal capacity (>2 mAh cm-2). This study reveals a unique role of LiI in building robust SSIs and provides new insights into the design of novel SSEs and interfaces for high-performance ASSLBs.

Yu, Zhaoxin↗
DOE OSTI2023

Effects of cathode loadings and anode protection on the performance of lithium metal batteries

Abstract While lithium-ion batteries (LIBs) are approaching their energy limits, lithium metal batteries (LMBs) are undergoing intensive investigation for higher energy density. Coupling LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode with lithium (Li) metal anode, the resultant Li||NMC811 LMBs are among the most promising technologies for future transportation electrification, which have the potential to realize an energy density two times higher than that of state-of-the-art LIBs. To maximize their energy density, the Li||NMC811 LMBs are preferred to have their cathode loading as high as possible while their Li anode as thin as possible. To this end, we investigated the effects of different cathode active material loadings (2–14 mg cm −2 ) on the performance of the Li||NMC811 LMBs. Our study revealed that the cathode loadings have remarkably affected the cell performance, in terms of capacity retention and sustainable capacity. Cells with high cathode loadings are more liable to fade in capacity, due to more severe formation of the CEI and more sluggish ion transport. In this study, we also verified that the protection of the Li anode is significant for achieving better cell performance. In this regard, our newly developed Li-containing glycerol (LiGL) via molecular layer deposition (MLD) is promising to help boost the cell performance, which was controllably deposited on the Li anode.

Materials Science↗
DOE OSTI2021

Stress-Dependent Chemo-Mechanical Performance of Amorphous Si Anodes for Li-Ion Batteries upon Lithiation

Alloying-type anodes are significantly governed by their chemo-mechanical performance during the electrochemical cycling. The reaction-induced huge volumetric change of these anodes may cause material degradation and failure under mechanical constraints. Here, we investigate the stress-dependent lithiation behavior of amorphous Si (a-Si) anodes using molecular dynamics simulations. It is indicated that a-Si anodes can sustain higher hydrostatic stress than biaxial/uniaxial ones without the occurrence of mechanical failure. Thermodynamic and electrochemical calculations demonstrate that although the lithiation procedure also affects the thermodynamic stability of a-Si anodes, it is mainly dominated by the external mean stresses. Compressive stress is confirmed to destabilize a-Si anodes and further trigger their capacity fading. Compared with our atomistic simulations, previous continuum models underestimate the open-cell potentials of a-Si anodes, due to their ignored large volumetric deformation at higher stresses and Li concentrations. Finally, this computational study provides the intensive atomic-level understanding of the stress-dependent lithiation behavior of a-Si anodes.

25 ENERGY STORAGE↗