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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Terminally fluorinated glycol ether electrolyte for lithium metal batteries

Despite being an excellent candidate for lithium metal batteries due to its stability towards lithium metal, ethereal solvent suffers from relatively low anodic stability, rendering it incompatible with high voltage cathode. Although the anodic stability of ethereal solvent can be enhanced by fluorination, the lithium solvating ability of fluorinated ethers is largely reduced. As a result, common hydrofluoroethers, such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) and bis(2,2,2-trifluoroethyl) ether (BTFE) are not able to dissolve any lithium salt, albeit enhanced oxidation potential. Therefore, new fluorinated glycol ethers were synthesized in this research. The diglyme analog, which was terminally fluorinated, demonstrated high anodic stability and excellent capability to facilitate lithium plating/stripping. Unlike its non-fluorinated counterpart, the fluorinated diglyme analog displayed outstanding compatibility with lithium hexafluorophosphate, which is an essential salt in lithium-ion batteries. Here it was shown that the electrolyte based on fluorinated diglyme analog with fluoroethylene carbonate as co-solvent enabled highly stable cycling of Li-metal batteries pairing with layered oxide cathode.

25 ENERGY STORAGE↗
DOE OSTI2025

Delineating the Factors Impacting the Electrochemical Behavior of Single-Crystal High-Nickel Layered Oxide Cathodes

High-nickel (Ni) (≥80%) single-crystal LiNi 1-x-y Mn x Co y O 2 (NMCs) have garnered recent interest as cathodes in lithium (Li)-ion batteries (LIBs). However, capacity fade at high voltages, particularly after the onset of the H2–H3 phase transition, hampers their viability. In this study, single-crystal LiNi 0.8 Mn x Co 0.2-x O 2 (x = 0.2, 0.1, 0) are synthesized and tested in LiPF 6 in ethyl methyl carbonate-based electrolytes, with and without monofluoroethylene carbonate and LiF 2 PO 2 additives, to clarify the effects of Co/Mn ratio and surface stabilization on high-voltage cycling degradation. By imposing a kinetic barrier to the accessible H2–H3 capacity, surface reconstruction is identified as the primary driver of high-voltage capacity loss, being greater in the Co-free cathode and in the absence of fluorinated electrolyte components. This is attributed to a synergy between increased mechanical stress due to worsened bulk and interfacial H2–H3 kinetics and decreased interfacial stability due to the poor passivating capability of the electrolyte. Here, the findings highlight the importance of limiting cathode impedance growth during high-voltage cycling, which can be achieved by tuning bulk dopants and electrolyte chemistry.

25 ENERGY STORAGE↗
DOE OSTI2022

Redox-homogeneous, gel electrolyte-embedded high-mass-loading cathodes for high-energy lithium metal batteries

Lithium metal batteries have higher theoretical energy than their Li-ion counterparts, where graphite is used at the anode. However, one of the main stumbling blocks in developing practical Li metal batteries is the lack of cathodes with high-mass-loading capable of delivering highly reversible redox reactions. To overcome this issue, here we report an electrode structure that incorporates a UV-cured non-aqueous gel electrolyte and a cathode where the LiNi 0.8 Co 0.1 Mn 0.1 O 2 active material is contained in an electron-conductive matrix produced via simultaneous electrospinning and electrospraying. This peculiar structure prevents the solvent-drying-triggered non-uniform distribution of electrode components and shortens the time for cell aging while improving the overall redox homogeneity. Moreover, the electron-conductive matrix eliminates the use of the metal current collector. When a cathode with a mass loading of 60 mg cm -2 is coupled with a 100 µm thick Li metal electrode using additional non-aqueous fluorinated electrolyte solution in lab-scale pouch cell configuration, a specific energy and energy density of 321 Wh kg -1 and 772 Wh L -1 (based on the total mass of the cell), respectively, can be delivered in the initial cycle at 0.1 C (i.e., 1.2 mA cm -2 ) and 25 °C.

25 ENERGY STORAGE↗
DOE OSTI2025

Green Electrode Processing Enabled by Fluoro-Free Multifunctional Binders for Lithium-Ion Batteries

The eco-friendly processing of conjugated polymer binder for lithium-ion batteries demands improved polymer solubility by introducing functional moieties, while this strategy will concurrently sacrifice polymer conductivity. Employing the polyfluorene-based binder poly(2,7-9,9 (di(oxy-2,5,8-trioxadecane))fluorene) (PFO), soluble in water-ethanol mixtures, a novel approach is presented to solve this trade-off, which features integration of aqueous solution processing with subsequent controlled thermal-induced cleavage of solubilizing side chains, to produce hierarchically ordered structures (HOS). The thermal processing can enhance the intermolecular π–π stacking of polyfluorene backbone for better electrochemical performance. Notably, HOS-PFO demonstrated a substantial 6–7 orders of magnitude enhancement in electronic conductivity, showcasing its potential as a functional binder for lithium-ion batteries. As an illustration, HOS-PFO protected SiOx anodes, utilizing in situ side chain decomposition of PFO surrounding SiOx particles after aqueous processing are fabricated. HOS-PFO contributed to the stable cycling and high-capacity retention of practical SiOx anodes (3.0 mAh cm -2 ), without the use of any conducting carbon additives or fluorinated electrolyte additives. It is proposed that this technique represents a universal approach for fabricating electrodes with conjugated polymer binders from aqueous solutions without compromising conductivity.

25 ENERGY STORAGE↗
DOE OSTI2022

Progress Towards Extended Cycle Life Si-based Anodes: Investigation of Fluorinated Local High Concentration Electrolytes

Silicon (Si) anodes are promising candidates for Li-ion batteries due to their high specific capacity and low operating potential. Implementation has been challenged by the significant Si volume changes during (de)lithiation and associated growth/regrowth of the solid electrolyte interphase (SEI). In this report, fluorinated local high concentration electrolytes (FLHCEs) were designed such that each component of the electrolyte (solvent, salt, diluent) is fluorinated to modify the chemistry and stabilize the SEI of high (30%) silicon content anodes. FLHCEs were formulated to probe the electrolyte salt concentration and ratio of the fluorinated carbonate solvents to a hydrofluoroether diluent. Higher salt concentrations led to higher viscosities, conductivities, and contact angles on polyethylene separators. Electrochemical cycling of Si-graphite/NMC622 pouch cells using the FLHCEs delivered up to 67% capacity retention after 100 cycles at a C/3 rate. Post-cycling X-ray photoelectron spectroscopy (XPS) analyses of the Si-graphite anodes indicated the FLHCEs formed a LiF rich solid electrolyte interphase (SEI). The findings show that the fluorinated local high concentration electrolytes contribute to stabilizing the Si-graphite electrode over extended cycling.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Methylation enables the use of fluorine-free ether electrolytes in high-voltage lithium metal batteries

Lithium metal batteries represent a promising technology for next-generation energy storage, but they still suffer from poor cycle life due to lithium dendrite formation and cathode cracking. Fluorinated solvents can improve battery longevity by improving LiF content in the solid-electrolyte interphase; however, the high cost and environmental concerns of fluorinated solvents limit battery viability. Here, for this work, we designed a series of fluorine-free solvents through the methylation of 1,2-dimethoxyethane, which promotes inorganic LiF-rich interphase formation through anion reduction and achieves high oxidation stability. The anion-derived LiF interphases suppress lithium dendrite growth on the lithium anode and minimize cathode cracking under high-voltage operation. The Li + -solvent structure is investigated through in situ techniques and simulations to draw correlations between the interphase compositions and electrochemical performances. The methylation strategy provides an alternative pathway for electrolyte engineering towards high-voltage electrolytes while reducing dependence on expensive fluorinated solvents.

25 ENERGY STORAGE↗
DOE OSTI2024

Fully Fluorinated Local High Concentration Electrolytes Enabling High Energy Density Si Anodes

To develop fluorinated localized high concentration electrolytes as a novel approach for constructing a functional SEI on Si based anodes. The technological approach combines the SEI modification strategies of fluorinated carbonate solvents and local high concentration electrolytes. The resulting synergy of anion and fluorinated solvent decomposition will form a mechanically robust, fluorinated SEI that enables extended cycling with high capacity retention. The electrolytes will enable demonstration of silicon-graphite anodes with high Si content, paired with NMC811 cathodes. Characterization will focus on galvanostatic cycling to evaluate electrochemical performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2002

Improved performance and safety of lithium ion cells with the use of fluorinated carbonate-based electrolytes

There has been increasing interest in developing lithium-ion electrolytes that possess enhanced safety characteristics, while still able to provide the desired stability and performance. Toward this end, our efforts have been focused on the development of lithium-ion electrolytes which contain partially and fully fluorinated carbonate solvents. The advantage of using such solvents is that they possess the requisite stability demonstrated by the hydrocarbon-based carbonates, while also possessing more desirable physical properties imparted by the presence of the fluorine substituents, such as lower melting points, increased stability toward oxidation, and favorable SEI film forming Characteristics on carbon. Specifically, we have demonstrated the beneficial effect of electrolytes which contain the following fluorinated carbonate-based solvents: methyl 2,2,2-trifluoroethyl carbonate (MTFEC), ethyl-2,2,2 trifluoroethyl carbonate (ETFEC), propyl 2,2,2-trifluoroethyl carbonate (PTFEC), methyl-2,2,2,2',2',2' -hexafluoro-i-propyl carbonate (MHFPC), ethyl- 2,2,2,2',2',2' -hexafluoro-i-propyl carbonate (EHFPC), and di-2,2,2-trifluoroethyl carbonate (DTFEC). These solvents have been incorporated into multi-component ternary and quaternary carbonate-based electrolytes and evaluated in lithium-carbon and carbon-LiNio.8Coo.202 cells (equipped with lithium reference electrodes). In addition to determining the charge/discharge behavior of these cells, a number of electrochemical techniques were employed (i.e., Tafel polarization measurements, linear polarization measurements, and electrochemical impedance spectroscopy (EIS)) to further characterize the performance of these electrolytes, including the SEI formation characteristics and lithium intercalatiodde-intercalation kinetics. In addition to their evaluation in experimental cells, cyclic voltammetry (CV) and conductivity measurements were performed on select electrolyte formulations to further our understanding of the trends in stability and ionic mobility imparted by different alkyl substituents in linear carbonates.

li-ion batteries fluorinated carbonate electrolyte↗
DOE OSTI2023

Facile Room-Temperature Electrodeposition of Rare Earth Metals in a Fluorine-Free Task-Specific Electrolyte

Electrochemical deposition of rare earth metals at room temperature has attracted increasing interest due to its advantage in energy efficiency over traditional hydrometallurgical and pyrometallurgical processes. Recent progress has been made with fluorinated electrolyte systems; however, the formation of an electrode-passivating fluoride layer by electrolyte decomposition is often overlooked. Such a passivation layer causes significant and rapid decay of the deposition current and significantly hinders practical application. To address this issue, we demonstrate a fluorine (F)-free task-specific electrolyte utilizing the borohydride anion for the efficient electrodeposition of rare earth metals. By eliminating the passivation effect, the deposition process exhibits a stable current and accumulates a thick neodymium deposit on the electrode. Raman spectroscopy of the electrolyte reveals a synergetic effect between rare earth borohydride and lithium borohydride which promotes the dissociation of both borohydride salts, resulting in significantly increased ionic conductivity and electrochemical performance. Cyclic voltammetry and in-depth X-ray photoelectron spectroscopy of the deposits suggest that the electrodeposition of rare earth metals could undergo a Li-mediated reduction process. Finally, quantitative analysis of the deposits reveals that the overall concentration of the rare earth elements reaches 75% which contains 40–48% metallic phase.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mechanistic understanding of aging behaviors of critical-material-free Li 4 Ti 5 O 12 //LiNi 0.9 Mn 0.1 O 2 cells with fluorinated carbonate-based electrolytes for safe energy storage with ultra-long life span

Behind-the-meter storage (BTMS) systems - a viable method to minimize potential risk of blackout events and stabilize the grid - require a different type of cost-effective energy storage with excellent safety, ultra-long (>20 years) cycle life and reasonable energy density compared that of electric vehicles. To increase the energy density and reduce the cost of a long-term cyclable lithium-titanate-based cell, it is required to employ a critical-material-free high voltage cathode and an electrolyte with good electrochemical and transport properties. In this report the long-term electrochemical performance and behaviors of selected critical-material-free Li 4 Ti 5 O 12 (LTO)//LiNi 0.9 Mn 0.1 O 2 (LNMO) full cells for BTMS applications are evaluated and analyzed in the optimized voltage range of 1.4-2.7 V at 45 degrees C with different fluorinated carbonate-based electrolytes. The fluoroethylene carbonate (FEC)-based electrolyte cell shows the highest capacity retention of 57.9% and Coulombic efficiency (CE) of 99.96% after 1000 cycles, potentially attributed to a dense, homogenous and less resistive LiF-rich solid-electrolyte interphase (SEI) layer formed on the surface of LTO that may mitigate electrolyte decomposition and maintain relatively low cell impedance during cycling. The 3,3,3-fluoroethylmethyl carbonate (F-EMC)-based electrolyte cell, however, presents the worst performance with lower capacity and a sharp decrease of CE, due to unstable and non-uniform SEI formation and continuous oxidative electrolyte decomposition. This mechanistic understanding of cell aging behaviors and failure mechanisms with detailed analysis of surface chemistry and electrode morphology can guide design of new electrode chemistries and electrolyte formulations for the development of BTMS batteries.

25 ENERGY STORAGE↗
DOE OSTI2023

Fluorinated High-Voltage Electrolytes To Stabilize Nickel-Rich Lithium Batteries

As state-of-the-art (SOA) lithium-ion (Li-ion) batteries approach their specific energy limit (~250 Wh kg -1 ), layer-structured, nickel-rich (Ni-rich) lithium transition metal oxide-based cathode materials, e. g., LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811), have attracted great interest owing to their practical high specific capacities (>200 mAhg -1 ). Coupled with their high average discharge voltages (~4 V vs Li/Li + ), Ni-rich cathode-based lithium batteries possess a great potential to achieve much higher specific energies (>350 Wh kg -1 at the cell level) than the SOA Li-ion counterparts. In addition, Ni-rich oxides are low-cost battery cathode materials due to their low cobalt contents. However, Ni-rich cathode-based lithium batteries suffer quick capacity degradations upon cycling, particularly at high upper cutoff voltages (e.g., ≥= 4.5 V vs Li/Li + ), due to crystal structure changes of the active cathode materials and parasitic side reactions at the electrolyte/electrode interfaces. In this study, a fluorinated-solvent-based, high-voltage stable electrolyte (HVE), i.e., 1 M Li bis(trifluoromethanesulfonyl)imide (LiTFSI) in fluoroethylene carbonate (FEC), bis(2,2,2-trifluoroethyl) carbonate (FDEC), and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) with Li difluoro(oxalate)borate (LiDFOB) additive, was formulated and evaluated in Li/NMC811 battery cells. Further, to the best of our knowledge, this class of electrolyte has not been investigated for Ni-rich cathode-based lithium batteries. Li/NMC811 cells with HVE exhibited a superior long-term cycle performance stability, maintaining ~80% capacity after ~500 cycles at a high cutoff voltage of 4.5 V (vs Li/Li + ) than a baseline carbonate-solvent-based electrolyte (BE). The superior cycle stability of the Li/NMC811 cells is attributed to the inherently high-voltage stability of HVE, supported by the physical and electrochemical analyses. This conclusion is supported by our density functional theory (DFT) modeling where HVE shows a less tendency of deprotonation/oxidation than BE, leading to the observed cycle stability. The findings in this study are important to help tackle the technical challenges facing Ni-rich cathode-based lithium batteries to realize their high energy density potentials with a long cycle life.

25 ENERGY STORAGE↗
DOE OSTI2023

Revealing the Mechanism Behind Sudden Capacity Loss in Lithium Metal Batteries

Rechargeable Li-metal batteries (LMBs) are attractive energy storage candidates for electric vehicles (EVs) because they offer higher energy density than batteries built with intercalation electrodes. However, one of the main barriers to the commercial deployment of LMBs has been their relatively short cycle life. Re-designing the electrolyte system shows promise in achieving acceptable cycle life, but even so, the resulting cells display a challenging end-of-life (EOL) behavior: a sudden capacity loss. Herein, we report a new method for analyzing voltage profiles during cycling to distinguish between the capacity loss originating from the loss of cathode capacity vs growth in cell resistance. Further, this analysis reveals that sudden capacity loss was preceded by acceleration in the rate of growth of cell resistance, and cycling of multiple cells showed that this phenomenon is sensitive to the initial quantity of electrolyte in the cells. In contrast, the cathode capacity degraded at a constant rate independent of the electrolyte quantity. Combining this evidence with post-analysis of harvested electrolyte and electrodes, we conclude that neither the loss of active lithium nor the loss of active cathode material was the primary source of sudden capacity loss; instead, consumption and decomposition of electrolyte causes the drastic capacity loss at EOL.

25 ENERGY STORAGE↗
DOE OSTI2022

High voltage stable cycling of all-solid-state lithium metal batteries enabled by top-down direct fluorinated poly (ethylene oxide)-based electrolytes

Poly (ethylene oxide) (PEO)-based solid-state polymer electrolytes (SPEs) show prospects in all-solid-state lithium metal batteries. However, they suffer from low ionic conductivity at room temperature and interfacial instability with high voltage cathodes for long-term cycling. In this work, top-down fluorinated PEOs (F-PEOs) for the all-solid-state electrolytes, which are scalable and cost-effective, are developed to improve the battery performance. We demonstrate, that by enhancing the disordering of the F-PEO matrix, the SPE achieves a maximum Li + conductivity of 1.1 x 10 -4 S cm -1 at 40 °C, which is 20 times higher than the baseline. By forming robust cathode/SPE and Li/SPE interfaces, the F-PEO-based SPEs demonstrate stable cycling in the LiFePO 4 /Li and LiNi 0·8 Mn 0·1 Co 0·1 O 2 /Li (3-4.4 V, 500 cycles, capacity retention of 91.6%) based all-solid-state batteries at 40 °C. Therefore, our work highlights the significance of "disordering engineering" for energy storage materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Enabling high energy lithium metal batteries via single-crystal Ni-rich cathode material co-doping strategy

High-capacity Ni-rich layered oxides are promising cathode materials for secondary lithium-based battery systems. However, their structural instability detrimentally affects the battery performance during cell cycling. Here, we report an Al/Zr co-doped single-crystalline LiNi<:sub>0.88 Co 0.09 Mn 0.03 O 2 (SNCM) cathode material to circumvent the instability issue. We found that soluble Al ions are adequately incorporated in the SNCM lattice while the less soluble Zr ions are prone to aggregate in the outer SNCM surface layer. The synergistic effect of Al/Zr co-doping in SNCM lattice improve the Li-ion mobility, relief the internal strain, and suppress the Li/Ni cation mixing upon cycling at high cut-off voltage. These features improve the cathode rate capability and structural stabilization during prolonged cell cycling. In particular, the Zr-rich surface enables the formation of stable cathode-electrolyte interphase, which prevent SNCM from unwanted reactions with the non-aqueous fluorinated liquid electrolyte solution and avoid Ni dissolution. To prove the practical application of the Al/Zr co-doped SNCM, we assembled a 10.8 Ah pouch cell (using a 100 μm thick Li metal anode) capable of delivering initial specific energy of 504.5 Wh kg- 1 at 0.1 °C and 25 °C.

25 ENERGY STORAGE↗
DOE OSTI2023

Fluorine-Substituted Lithium Chloride Solid Electrolytes for High-Voltage All-Solid-State Lithium-Ion Batteries

Lithium ternary halides are promising solid electrolytes, owing to their high ionic conductivity and reasonably high oxidative and chemical stability. Recently, fluorine substitution in Li 3 MCl 6 has been suggested as a promising approach for further enhancing oxidation stability. Accordingly, this study outlines a material design strategy for F-substituted Li 3 MCl 6 through systematic theoretical analyses. Calculations reveal that the mixing limit of F in Li 3 MCl 6–x F x is in the range of 0.5–1.5, and the resulting Li 3 MCl 6–x F x phases can retain ionic conductivity above 1 mS/cm up to x = 1.0. Additionally, the calculations also predict that the formation of F-containing passivating phases could increase the oxidation potential for Li3MCl5F to ~6.3 V. The proposed material design strategy is validated through the synthesis of Li 3 YCl 5 F, which is confirmed to show both high ionic conductivity and enhanced oxidation stability. The design guidelines presented herein can accelerate the potential use of halide-based electrolyte chemistries in high-voltage all-solid-state batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

A Carboranyl Electrolyte Enabling Highly Reversible Sodium Metal Anodes via a “Fluorine‐Free” SEI

Abstract Realization of practical sodium metal batteries (SMBs) is hindered due to lack of compatible electrolyte components, dendrite propagation, and poor understanding of anodic interphasial chemistries. Chemically robust liquid electrolytes that facilitate both favorable sodium metal deposition and a stable solid‐electrolyte interphase (SEI) are ideal to enable sodium metal and anode‐free cells. Herein we present advanced characterization of a novel fluorine‐free electrolyte utilizing the [HCB 11 H 11 ] 1− anion. Symmetrical Na cells operated with this electrolyte exhibit a remarkably low overpotential of 0.032 V at a current density of 2.0 mA cm −2 and a high coulombic efficiency of 99.5 % in half‐cell configurations. Surface characterization of electrodes post‐operation reveals the absence of dendritic sodium nucleation and a surprisingly stable fluorine‐free SEI. Furthermore, weak ion‐pairing is identified as key towards the successful development of fluorine‐free sodium electrolytes.

Tomich, Anton W.↗