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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Carbon Materials Embedded with Metal Nanoparticles as Anode in Lithium-Ion Batteries

Carbon materials containing metal nanoparticles that can form an alloy with lithium were tested for their capacity and cycle life to store and release lithium electrochemically. Metal nanoparticles may provide the additional lithium storage capacity as well as additional channels to conduct lithium in carbon. The cycle life of this carbon-metal composite can be long because the solid-electrolyte interface (SEI) on the carbon surface may protect both lithium and the metal particles in the carbon interior. In addition, the voids in the carbon interior may accommodate the nanoparticle's volume change, and such volume change may not cause much internal stress due to small sizes of the nanoparticles. This concept of improving carbon's performance to store and release lithium was demonstrated using experimental cells of C(Pd)/0.5M Lil-50/50 (vol.%) EC and DMC/Li, where C(Pd) was graphitized carbon fibers containing palladium nanoparticles, EC was ethylene carbonate, and DMC was dimethyl carbonate. However, such improvement was not observed if the Pd nanoparticles are replaced by aluminum, possibly because the aluminum nanoparticles were oxidized in air during storage, resulting in an inert oxide of aluminum. Further studies are needed to use this concept for practical applications.

Hung, Ching-cheh↗
DOE OSTI2021

The Impact of Different Substituents in Fluorinated Cyclic Carbonates in the Performance of High Voltage Lithium-Ion Battery Electrolyte

Ethylene carbonate (EC) has been used as the Solid-Electrolyte Interphase (SEI) former in the conventional electrolyte for decades. However, its low anodic stability leads to severe capacity decay during cycling under high voltage operation. Therefore, finding a viable electrolyte with high anodic stability and the ability to form robust SEI for high voltage lithium-ion batteries is of primary importance. In this study, a series of electrolytes containing various fluorinated cyclic carbonates as the SEI former have been designed, synthesized and evaluated. Linear sweep voltammetry study suggested that fluorinated cyclic carbonates generally possess higher anodic stability than EC. Based on the cycling performance of LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NMC532)/ graphite full cells, the electrolyte with DFEC/FEMC (1.0 M LiPF 6 ) inhibited the oxidation side reaction on the cathode and forms a vigorous SEI on the anode. The high voltage NMC532/Graphite cell utilizing the novel electrolyte exhibits excellent cycling durability under both room and elevated temperature. The superior performance of the DFEC based electrolyte was further unveiled by SEM, EDAX and XRD. Both the anode and cathode of the full cell employing DFEC based electrolyte retained their intrinsic structures after cycling while the electrodes cycled in conventional electrolyte showed severe degradation.

25 ENERGY STORAGE↗
NASA NTRS2012

Electrolytes with Improved Safety Developed for High Specific Energy Li-Ion Cells with Si-Based Anodes

A number of electrolyte formulations that have improved safety characteristics have been developed for use with high capacity silicon-based anodes. To improve the compatibility with Si-based anodes, a number of technical approaches have been employed, including: (1) the use of mono-fluoroethylene carbonate (FEC) in conjunction with, or in lieu of, ethylene carbonate (EC), (2) the use of high proportions of fluorinated co-solvents, (3) the use of vinylene carbonate (VC) to stabilize the Si/C electrode, and (4) the use of lithium bis(oxalato)borate (LiBOB) to improve the compatibility of the electrolyte when Si/C electrodes are used in conjunction with high voltage cathodes. Candidate electrolytes were studied in Li/Si-C and Si-C/ Li(MnNiCo)O2 (NMC) coin cells, as well as in larger Si-C/NMC three-electrode cells equipped with lithium reference electrodes. In summary, many electrolytes that contain triphenyl phosphate (TPP), which is used as a flame retardant additive up to concentrations of 15 volume percent, and possess FEC as a co-solvent have been demonstrated to outperform the all-carbonate baseline electrolytes when evaluated in Si-C/ Li(MnNiCo)O2 cells.

Silicon-Based Anode↗
NASA NTRS2011

Optimized Li-Ion Electrolytes Containing Triphenyl Phosphate as a Flame-Retardant Additive

A number of future NASA missions involving the exploration of the Moon and Mars will be human-rated and thus require high-specific-energy rechargeable batteries that possess enhanced safety characteristics. Given that Li-ion technology is the most viable rechargeable energy storage device for near-term applications, effort has been devoted to improving the safety characteristics of this system. There is also a strong desire to develop Li-ion batteries with improved safety characteristics for terrestrial applications, most notably for hybrid electric vehicle (HEV) and plug-in hybrid electric vehicle (PHEV) automotive applications. Therefore, extensive effort has been devoted recently to developing non-flammable electrolytes to reduce the flammability of the cells/battery. A number of electrolyte formulations have been developed, including systems that (1) incorporate greater concentrations of the flame-retardant additive (FRA); (2) use di-2,2,2-trifluoroethyl carbonate (DTFEC) as a co-solvent; (3) use 2,2,2- trifluoroethyl methyl carbonate (TFEMC); (4) use mono-fluoroethylene carbonate (FEC) as a co-solvent and/or a replacement for ethylene carbonate in the electrolyte mixture; and (5) utilize vinylene carbonate as a "SEI promoting" electrolyte additive, to build on the favorable results previously obtained. To extend the family of electrolytes developed under previous work, a number of additional electrolyte formulations containing FRAs, most notably triphenyl phosphate (TPP), were investigated and demonstrated in experimental MCMB (mesocarbon micro beads) carbon- LiNi(0.8)Co(0.2)O2 cells. The use of higher concentrations of the FRA is known to reduce the flammability of the electrolyte solution, thus, a concentration range was investigated (i.e., 5 to 20 percent by volume). The desired concentration of the FRA is the highest amount tolerable without adversely affecting the performance in terms of reversibility, ability to operate over a wide temperature range, and the discharge rate capability. The use of fluorinated carbonates, much in the same manner as the incorporation of fluorinated ester-based solvents, was employed to reduce the inherent flammability of mixtures. Thus, electrolyte formulations that embody both approaches are anticipated to have much lower flammability, resulting in enhanced safety.

Smart, Marshall C.↗
DOE OSTI2022

Evaluating the roles of electrolyte components on the passivation of silicon anodes

A protocol was recently developed to compare calendar life using a constant potential while monitoring the electrical current required to maintain the potential. Here, this calendar life protocol is used with electrolyte formulations containing various mole fractions of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and LiPF 6 to elucidate the role each component plays in passivation for high silicon anodes. Together, EC and LiPF 6 lead to higher currents, and thus poorer passivation, whereas EMC acts as a spectator. The variation of the components' mole fraction also changes the solid-electrolyte interphase (SEI) composition, as measured by x-ray photoelectron spectroscopy. Importantly, higher LiPF 6 content leads to increased LiF as well as increased current, indicating that higher LiF content does not enhance the passivation of the silicon surface. Finding that EC did not yield a passivating SEI, instead ethylene sulfite, sulfolane, and propylene carbonate (PC) were used in place of EC. Using ethylene sulfite and sulfolane resulted in poorer passivation compared to EC, whereas PC resulted in superior passivation. As a result, the superior passivation may be related to more stable lithium-solvent complexes.

25 ENERGY STORAGE↗
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 OSTI2021

A new cyclic carbonate enables high power/ low temperature lithium-ion batteries

The modern lithium-ion battery (LIB) configuration was enabled by the "magic chemistry" between ethylene carbonate (EC) and graphitic carbon anode. Despite the constant changes of cathode chemistries with improved energy densities, EC-graphite combination remained static during the last three decades. While the interphase generated by EC protects the fragile graphitic structure, the intrinsic disadvantages of EC (high viscosity, high melting point, excessive interphase growth) lead to mediocre power density and poor performances of LIB at sub-zero temperatures, where lithium depositions form upon charging. Such performance compromises arise from the fundamental dilemma between requiring effective interphase protection and high impedance from excessive growth of interphase. In this work, we designed and synthesized a "double EC" molecule as electrolyte additive to resolve the above dilemma. Erythritol bis(carbonate) (EBC) possesses lower LUMO energy level than EC and hence tends to decompose prior to EC reduction, but its weak solvation toward Li + restricts the extent of its reduction, thus minimizing the interphase thickness and the corresponding impedances. Electrolytes containing EBC enables both the charging and discharging of ampere-size LIB pouch cells at sub-zero temperatures from 0 to -20°C, demonstrating that the key approach to improve low temperature performances lies in how to tailor interphasial chemistry rather than the bulk electrolyte composition.

25 ENERGY STORAGE↗
DOE OSTI2021

Highly Concentrated Electrolytes: Electrochemical and Physicochemical Characteristics of LiPF 6 in Propylene Carbonate Solutions

Highly concentrated electrolytes (HCEs) based on LiPF 6 in propylene carbonate (PC) have been examined as lithium-ion battery electrolytes. These HCEs have lower ionic conductivities and higher viscosities than ethylene carbonate (EC) electrolytes with 1.2 M LiPF 6 , but they have higher Li + ion transference numbers. Electrochemical cycling behaviour of LiNi 0.8 Co 0.015 Al 0.05 O 2 //graphite cells with 3.2 M LiPF 6 in PC resembles that of cells with EC-based electrolytes; the HCE cells have higher impedance, which can be lowered by increasing test temperature. By employing Raman and infrared spectroscopy, combined with density functional theory and ab initio molecular dynamics simulations, we reveal that the Li + solvation structure and speciation are key factors that determine cell performance. Two distinct regimes are observed as a function of salt concentration—in the conventional regime, the solvation number (SN) is mostly constant, while in the HCE regime it decreases linearly. Graphite exfoliation is suppressed only at very high salt concentrations ( > 2.4 M), where [ PC ] free /[Li + ] < 1 and P F 6 − f r e e > P C f r e e . Results from the Advanced Electrolyte Model indicate that Li + desolvation improves at higher LiPF 6 concentrations, thereby mitigating PC co-intercalation into the graphite. However, Li + ion transport is hindered in the HCEs, which increases impedance at both the oxide-positive and graphite-negative electrodes.

25 ENERGY STORAGE↗
NASA NTRS2003

Low-EC-Content Electrolytes for Low-Temperature Li-Ion Cells

Electrolytes comprising LiPF6 dissolved at a concentration of 1.0 M in three different mixtures of alkyl carbonates have been found well suited for use in rechargeable lithium-ion electrochemical cells at low temperatures. These and other electrolytes have been investigated in continuing research directed toward extending the lower limit of practical operating temperatures of Li-ion cells down to -60 C. This research at earlier stages was reported in numerous previous NASA Tech Briefs articles, the three most recent being "Ethyl Methyl Carbonate as a Cosolvent for Lithium-Ion Cells" (NPO-20605), Vol. 25, Low-EC-Content Electrolytes for Low-Temperature Li-Ion Cells No. 6 (June 2001), page 53; "Alkyl Pyrocarbonate Electrolyte Additives for Li-Ion Cells" (NPO-20775), Vol. 26, No. 5 (May 2002), page 37; and "Fluorinated Alkyl Carbonates as Cosolvents in Li-Ion Cells (NPO-21076), Vol. 26, No. 5 (May 2002), page 38. The present solvent mixtures, in terms of volume proportions of their ingredients, are 1 ethylene carbonate (EC) + 1 diethyl carbonate (DEC) + 1 dimethyl carbonate (DMC) + 3 ethyl methyl carbonate (EMC); 3EC + 3DMC + 14EMC; and 1EC + 1DEC + 1DMC + 4EMC. Relative to similar mixtures reported previously, the present mixtures, which contain smaller proportions of EC, have been found to afford better performance in experimental Li-ion cells at temperatures < -20 C.

Smart, Marshall↗
DOE OSTI2022

Mechanically and thermally robust microporous copolymer separators for lithium ion batteries

Next generation, multifunctional separators can enhance energy storage, power, and safety performance of lithium ion batteries but must be simple to fabricate and incorporate with existing roll-to-roll manufacturing. Here, this study presents a strategy to facilely prepare these separators using UV-initiated polymerization-induced phase separation (PIPS), wherein microporous polymer separators are fabricated directly from constituent monomers and ethylene carbonate (EC) porogen. This enables a wide compositional design space as co-monomers with specific chemical functionality can be readily incorporated into the PIPS precursor mixture. Herein, 1,4-butanediol diacrylate (BDDA) was copolymerized with poly(ethylene glycol) diacrylate (PEGDA) to increase the acrylate conversion in the photopolymerization and improve mechanical properties. By tuning the ratio of PEGDA and EC, separators with high porosity (41.3%) and effective ionic conductivity (2.09 mS cm –1 ) were prepared. Inclusion of PEGDA was essential to increasing the elastic modulus to > 345 MPa, which is required for cell assembly by roll-to-roll manufacturing. All separators prepared were shown to enable reversible cycling of lithium metal/LiNi 0.5 Mn 0.3 Co 0.2 O 2 half-cells for 100 cycles. Unlike conventional polyolefin separators, which were shown to melt at 160 °C and shrink by up to 29.8% at elevated temperatures, the PIPS separators possess exceptional, safety-enhancing thermomechanical properties, undergoing no phase transitions or thermal shrinkage.

25 ENERGY STORAGE↗
DOE OSTI2024

Extending Calendar Life of Si-Based Lithium-Ion Batteries by a Localized High Concentration Electrolyte

Silicon (Si) is one of the most promising anode materials for the next generation lithium-ion batteries (LIBs). Although significant progresses have been made on the cycle life of Si-based LIBs, their calendar-life is still far less than those required for electrical vehicle applications. Here, in this work, the fundamental mechanisms behind the limited calendar life of Si-LIBs have been investigated. It is found that the unstable interphase layers formed on electrodes during the formation/cycling of batteries using conventional electrolyte with fluoroethylene carbonate (FEC) additive are responsible for the rapid impedance-increase of Si-LIBs during storage at elevated temperature (55°C). By using an FEC-free localized high concentration electrolyte (lithium bis(fluorosulfonyl)imide:ethyl propionate:ethylene carbonate:1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (1:2.8:0.2:1 by mol.) with 1 wt.% lithium difluorophosphate), stable interphase layers formed on electrodes can effectively block the crosstalk between cathode and anode, minimize the impedance increase of Si||LiNi 0.6 Mn 0.2 Co 0.2 (NMC622) batteries during storage at elevated temperature (55°C), therefore largely improve their calendar life. Si||NMC622 batteries using this electrolyte also demonstrated a high-capacity retention of ~92.4% after 500 cycles at 45°C with well-preserved electrode structure. Hence, this novel electrolyte is a good candidate to extend the cycling life and calendar life of Si-LIBs.

25 ENERGY STORAGE↗
DOE OSTI2026

Unraveling interphase-driven failure pathways in LiMn0.6Fe0.4PO4/graphite pouch cells

LiMnxFe1−xPO4 (LMFP) is a promising high-voltage, thermally stable, and earth-abundant cathode material, yet its practical application is limited by interphase instability and Mn dissolution. In this work, we systematically evaluate LiMn0.6Fe0.4PO4/graphite pouch cells using three electrolyte formulations including control carbonate electrolyte, control + 2 wt% vinylene carbonate (VC), and control + 2 wt% VC + 1 wt% 1,3,2-dioxathiolane 2,2-dioxide (DTD), to establish how electrolyte composition governs interphase chemistry and long-term degradation. Electrochemical testing shows that both additives are preferentially reduced prior to ethylene carbonate (EC) during cell formation, generating robust cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI) layers that suppress gas evolution and raise the first-cycle coulombic efficiency to 89.3%. Additionally, the dual-additive electrolyte delivers the most stable performance, retaining over 85% capacity after 600 cycles while minimizing impedance growth under long-term cycling at C/3 and 40 °C. Soft X-ray absorption spectroscopy confirms that VC + DTD effectively suppresses electrolyte oxidation at the cathode surface, and micro-X-ray fluorescence shows substantially reduced Mn dissolution and deposition on the graphite anode. Density functional theory simulations further provided insights into the structural and energetic influences of alkoxide species on the cathode surface, proposing a Mn2+ extraction mechanism. The combined experimental and computational findings establish a mechanistic link between electrolyte composition and interphase evolution, highlighting the effectiveness of electrolyte engineering for extending the operational lifetime of LMFP-based lithium-ion batteries.

Chak, Chanmonirath Michael↗
DOE OSTI2020

Solvent oligomerization pathways facilitated by electrolyte additives during solid-electrolyte interphase formation

The solid–electrolyte interphase (SEI) layer formation is known to play an important role in determining the lifetime of lithium-ion batteries. A thin, stable SEI layer is linked to overall improved battery performance and longevity, however, the factors and mechanisms that lead to optimal SEI morphology and composition are not well understood. Inclusion of electrolyte additives (fluoroethylene carbonate, FEC; and vinylene carbonate, VC) is often necessary for improving SEI characteristics. To understand how these electrolyte additives impact SEI formation, we employed molecular dynamics (MD) and density functional theory (DFT) simulations to study the reaction networks and oligomerization pathways, respectively, for three systems containing ethylene carbonate (EC), a lithium ion, and FEC or VC. MD simulations suggest radical oligomerization pathways analogous to traditional oligomerization with nucleophilic alkoxide species via SN1 reaction mechanisms. Both S N 1 and S N 2 mechanisms were studied for all three systems using DFT. Oligomerization reactions were studied with both a standard alkoxide species and a ring-opened EC radical as the nucleophiles and EC, FEC, and VC as the electrophiles. For all cases, FEC and VC exhibited lower free energy barriers and more stable adducts when compared with EC. We conclude that one of the role of additives is to modify the oligomerization process of EC by introducing branching points (FEC) or termination points (VC).

25 ENERGY STORAGE↗
NASA NTRS2010

Improved Low-Temperature Performance of Li-Ion Cells Using New Electrolytes

As part of the continuing efforts to develop advanced electrolytes to improve the performance of lithium-ion cells, especially at low temperatures, a number of electrolyte formulations have been developed that result in improved low-temperature performance (down to 60 C) of 26650 A123Systems commercial lithium-ion cells. The cell type/design, in which the new technology has been demonstrated, has found wide application in the commercial sector (i.e., these cells are currently being used in commercial portable power tools). In addition, the technology is actively being considered for hybrid electric vehicle (HEV) and electric vehicle (EV) applications. In current work, a number of low-temperature electrolytes have been developed based on advances involving lithium hexafluorophosphate-based solutions in carbonate and carbonate + ester solvent blends, which have been further optimized in the context of the technology and targeted applications. The approaches employed, which include the use of ternary mixtures of carbonates, the use of ester co-solvents [e.g., methyl butyrate (MB)], and optimized lithium salt concentrations (e.g., LiPF6), were compared with the commercial baseline electrolyte, as well as an electrolyte being actively considered for DoE HEV applications and previously developed by a commercial enterprise, namely LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC)(30:70%).

Smart, Marshall C.↗
NASA NTRS2012

Wide Operating Temperature Range Electrolytes for High Voltage and High Specific Energy Li-Ion Cells

A number of electrolyte formulations that have been designed to operate over a wide temperature range have been investigated in conjunction with layered-layered metal oxide cathode materials developed at Argonne. In this study, we have evaluated a number of electrolytes in Li-ion cells consisting of Conoco Phillips A12 graphite anodes and Toda HE5050 Li(1.2)Ni(0.15)Co(0.10)Mn(0.55)O2 cathodes. The electrolytes studied consisted of LiPF6 in carbonate-based electrolytes that contain ester co-solvents with various solid electrolyte interphase (SEI) promoting additives, many of which have been demonstrated to perform well in 4V systems. More specifically, we have investigated the performance of a number of methyl butyrate (MB) containing electrolytes (i.e., LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + MB (20:20:60 v/v %) that contain various additives, including vinylene carbonate, lithium oxalate, and lithium bis(oxalato)borate (LiBOB). When these systems were evaluated at various rates at low temperatures, the methyl butyrate-based electrolytes resulted in improved rate capability compared to cells with all carbonate-based formulations. It was also ascertained that the slow cathode kinetics govern the generally poor rate capability at low temperature in contrast to traditionally used LiNi(0.80)Co(0.15)Al(0.05)O2-based systems, rather than being influenced strongly by the electrolyte type.

Li-ion Battery↗
NASA NTRS2000

Effects of Carbon Structure and Surface Oxygen on the Carbon's Performance as the Anode in Lithium-Ion Battery Determined

Four carbon materials (C1, C2, C3, and C4) were tested electrochemically at the NASA Glenn Research Center at Lewis Field to determine their performance in lithium-ion batteries. They were formed as shown in the figure. This process caused very little carbon loss. Products C1 and C3 contained very little oxygen because of the final overnight heating at 540 C. Products C2 and C4, on the other hand, contained small amounts of basic oxide. The electrochemical test involved cycles of lithium intercalation and deintercalation using C/saturated LiI-50/50 (vol %) ethylene carbonate (EC) and dimethyl carbonate (DMC)/Li half cell. The cycling test, which is summarized in the table, resulted in three major conclusions. The capacity of the carbon with a basic oxide surface converges to a constant 1. value quickly (within 4 cycles), possibly because the oxide prevents solvent from entering the carbon structure and, therefore, prolongs the carbon s cycle life. Under certain conditions, the disordered carbon can store more lithium than its 2. precursor. These samples and their precursor can intercalate at 200 mA/g and deintercalate at 3. a rate of 2000 mA/g without significant capacity loss.

Hung, Ching-Cheh↗
DOE OSTI2021

Understanding extreme fast charge limitations in carbonate mixtures

Charging large format lithium ion batteries within ten to fifteen minutes requires changes to the electrolyte composition in addition to modification of electrode and cell architectures. Several approaches to address this need have been proposed; but there is not a lot of clarity on understanding which factors limit the performance of existing electrolytes. Furthermore, this work takes a closer look at the solvated components of a mixture of LiPF 6 in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in the context of extreme fast charging and relates these findings to cell-level requirements. Molecular dynamics studies of the Gen-2 electrolyte compositions with increasing salt concentrations, have been performed to estimate transport properties like diffusivity, transference number and conductivity. Molecular-level differences in the structure of solvation shells under extreme LiPF 6 concentrations are probed here and some key aspects on solvent structure that help overcome barriers to Li + transport under extreme fast charge are discussed.

25 ENERGY STORAGE↗