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Li-metal batteries (LMBs) employing conversion cathode materials (e.g., FeF

Achieving synergy between ion-conducting polymers and ceramics in a composite electrolyte has been proven to be difficult as the complicated ceramic/polymer interface presents challenges to understand and control. In this work, we report a strategy to utilize discrete ceramic fillers to form a gel composite electrolyte with enhanced transport properties for lithium metal batteries. The matrix of the composite membrane is crosslinked poly(ethylene oxide) with bis(trifluoromethane)sulfonimide lithium salt (LiTFSI). The membrane is plasticized with tetraethylene glycol dimethyl ether (TEGDME). The incorporation of doped-lithium aluminum titanium phosphate particles (LICGC™) into the membrane greatly improves the membrane's cycling characteristics against the lithium electrode, exhibiting lower interfacial impedance, lower overpotential and higher rate capability. The underpinnings of the superior performance of the gel composite electrolyte are discussed in depth. LICGC™ can immobilize the TFSI− anions in the polymer matrix and simultaneously promote Li+ transport by increasing the plasticizer to Li+ ratio. Further, the transport enhancement is achieved without sacrificing mechanical properties. The composite membrane shows significantly improved handleability and processability. This work sheds light on the design strategy for a safe electrolyte towards stable Li metal batteries.

Single-ion-conducting polymer electrolytes are attractive to use in lithium batteries as the transference number of the lithium cation approaches unity. This helps prevent concentration gradients a...

Battery interfaces help govern rate capability, safety/stability, cycle life, and self-discharge, but significant gaps remain in our understanding at atomic length scales that can be exploited to improve interfacial properties. In particular, Li partially plated on copper current collectors, relevant to the anodeless, lithium metal cell which is a holy grail of high density energy battery research, has recently been reported to undergo galvanic corrosion and exhibit short shelf lives. We apply large scale Density Functional Theory (DFT) calculations and X-ray photoelectron spectroscopy to examine the reaction between the electrolyte and Li|Cu junctions coated with thin, uniform electrolyte interphase (SEI) passivating films at two applied voltages. These novel DFT galvanic corrosion simulations show that electrolyte degradation preferentially occurs on Li-plated regions and should lead to thicker SEI films. Our simulations reveal similarities but also fundamental differences between traditional metal localized pitting and Li-corrosion mechanisms. Furthermore, using the recently proposed, highly reactive lithium hydride (LiH) component SEI as example, we distinguish between electrochemical and chemical degradation pathways which are partially responsible for self-discharge, with the chemical pathway found to exhibit slow kinetics. We also predict that electric fields should in general exist across natural SEI components like LiH, and across artificial SEI films like LiI and LiAlO(2) often applied to improve battery cycling. Underlying and unifying these predictions is a framework of DFT voltage/overpotential definitions which we have derived from electrochemistry disciplines like structural metal corrosion studies; our analysis can only be made using the correct electronic voltage definitions., 41 pages. 8 figures

Battery cells with metal casings are commonly considered incompatible with nuclear magnetic resonance (NMR) spectroscopy because the oscillating radio-frequency magnetic fields (“rf fields”) responsible for excitation and detection of NMR active nuclei do not penetrate metals. Here, we show that rf fields can still efficiently penetrate nonmetallic layers of coin cells with metal casings provided “

Solid-state magnesium-ion conductors are desired for next-generation battery applications. Here we investigate magnesium conducting polymer electrolytes produced through dual cation exchange of a p...

The development of polymer electrolytes for magnesium batteries has been hindered by difficulties related to achieving sufficient magnesium ion conduction and magnesium electrodeposition. The high charge density of the magnesium cation causes it to interact with both the polar polymer matrix and any counteranions, challenging ion transport. Solvents and salts that are known to be incompatible with the magnesium electrode have widely been used in prior reports to increase ionic conductivity. Herein we report the use of a single-ion conducting magnesium gel polymer electrolyte consisting of a poly(ethylene glycol) dimethacrylate (PEGDMA) crosslinker that is copolymerized with an anionic monomer and subsequently swelled in solvents compatible with magnesium metal. Sufficient magnesium ion conductivities (>10–4 S/cm at 25 °C) were able to be achieved with specific solvents and solvent mixtures. Constant potential holds were used to interrogate magnesium electrodeposition from these electrolytes. Small amounts...

Lithium-metal anodes can theoretically enable 10× higher gravimetric capacity than conventional graphite anodes. However, Li-metal anode cycling has proven difficult due to porous and dendritic morphologies, extensive parasitic solid electrolyte interphase reactions, and formation of dead Li. We systematically investigate the effects of applied interfacial pressure on Li-metal anode cycling performance and morphology in the recently developed and highly efficient 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane electrolyte. We present cycling, morphology, and impedance data at a current density of 0.5 mA/cm2 and a capacity of 2 mAh/cm2 at applied interfacial pressures of 0, 0.01, 0.1, 1, and 10 MPa. Cryo-focused ion beam milling and cryo-scanning electron microscopy imaging in cross section reveal that increasing the applied pressure during Li deposition from 0 to 10 MPa leads to greater than a fivefold reduction in thickness (and therefore volume) of the deposited Li. This suggests that pressure during cycling can have a profound impact on the practical volumetric energy density for Li-metal anodes. A "goldilocks zone" of cell performance is observed at intermediate pressures of 0.1-1 MPa. Increasing pressure from 0 to 1 MPa generally improves cell-to-cell reproducibility, cycling stability, and Coulombic efficiency. However, the highest pressure (10 MPa) results in high cell overpotential and evidence of soft short circuits, which likely result from transport limitations associated with increased pressure causing local pore closure in the separator. All cells exhibit at least some signs of cycling instability after 50 cycles when cycled to 2 mAh/cm2 with thin 50 μm Li counter electrodes, though instability decreases with increasing pressure. In contrast, cells cycled to only 1 mAh/cm2 perform well for 50 cycles, indicating that capacity plays an important role in cycling stability.

Author(s): Jungjohann, KL; Gannon, RN; Goriparti, S; Randolph, SJ; Merrill, LC; Johnson, DC; Zavadil, KR; Harris, SJ; Harrison, KL | Abstract: The dramatic 50% improvement in energy density that Li-metal anodes offer in comparison to graphite anodes in conventional lithium (Li)-ion batteries cannot be realized with current cell designs because of cell failure after a few cycles. Often, failure is caused by Li dendrites that grow through the separator, leading to short circuits. Here, we used a new characterization technique, cryogenic femtosecond laser cross sectioning and subsequent scanning electron microscopy, to observe the electroplated Li-metal morphology and the accompanying solid electrolyte interphase (SEI) into and through the intact coin cell battery's separator, gradually opening pathways for soft-short circuits that cause failure. We found that separator penetration by the SEI guided the growth of Li dendrites through the cell. A short-circuit mechanism via SEI growth at high current density within the separator is provided. These results will inform future efforts for separator and electrolyte design for Li-metal anodes.

Li metal anodes are enticing for batteries due to their high theoretical storage capacity, but commercialization is plagued by dendritic Li growth and short circuits when cycled at high currents. Applied pressure has been suggested to improve morphology, and therefore performance. We hypothesized that increasing pressure would suppress dendritic growth at high currents. To test this hypothesis, here we extensively use cryogenic scanning electron microscopy to show that varying the applied pressure from 0.01-1 MPa has little impact on Li morphology after one deposition. We show that pressure improves Li density and preserves Li inventory after 50 cycles. However, contrary to our hypothesis, pressure exacerbates dendritic growth through the separator, promoting short circuits. Therefore, we suspect Li inventory is better preserved in cells cycled at high pressure only because the shorts carry a larger portion of the current, with less being carried by electrochemical reactions that slowly consume Li inventory.

Cross-linked ionomer networks of varying poly(ethylene glycol) diacrylate cross-linker chain length, ionic comonomer chemistry, and comonomer ratio have been studied for their use as polysulfide shuttle inhibiting separators in magnesium–sulfur (Mg–S) batteries. Through the use of X-ray scattering, polysulfide diffusion experiments, conductivity measurements, and Mg–S cell cycling, it was determined that inclusion of tethered anions in polymer networks mitigates the polysulfide shuttle effect. Polysulfide crossover through networks into a bulk electrolyte can be reduced by absorption into the polymer gel, steric rejection, and electrostatic rejection, with the predominance of these mechanisms dictated by polymer composition and structure. The best network composition allowed an initial Mg–S cell discharge capacity of 522 mAh/g compared to a discharge capacity of 365 mAh/g using a literature standard glass fiber separator. The ionomer cell saw 67% capacity retention after three cycles, whereas the glass fi...

We report an investigation of electrochemical properties and speciation of electrolytes composed of magnesium bis(hexamethyldisilazide) (Mg(HMDS)2) and magnesium chloride in sulfone-ether mixtures. The inclusion of sulfones dramatically increased the thermal stability of the electrolytes to 80 °C. The addition of ether was necessary to form an electrochemically active species. Electrochemical reversibility was maintained above 90 % for 50 cycles for equivolume mixtures of butyl sulfone and THF. Sulfolane based solutions demonstrated low reversibilities and mass spectrometry measurements showed the preferential formation of an MgCl+ cation over the Mg2Cl3+ cation. Greater amounts of Mg2Cl2+ compared to MgCl+ is linked with higher performing electrolytes. Spectroscopic measurements showed co-solvation of the active magnesium cation with both solvents.

Magnesium batteries are a promising alternative to lithium-ion batteries due to the widespread abundance of magnesium and its high specific volumetric energy capacity. Ethereal solvents such as tetrahydrofuran (THF) are commonly used for magnesium-ion electrolytes due to their chemical compatibility with magnesium metal, but the volatile nature of THF is a concern for practical application. Herein, we investigate magnesium bis(hexamethyldisilazide) plus aluminum chloride (Mg(HMDS)2-AlCl3) electrolytes in THF, diglyme, and tetraglyme at varying temperature. We find that, despite the higher thermal stability of the glyme-based electrolytes, THF-based electrolytes have better reversibility at room temperature. Deposition/stripping efficiency is found to be a strong function of temperature. Diglyme-based Mg(HMDS)2-AlCl3 electrolytes are found to not exchange as quickly as THF and tetraglyme, stabilizing AlCl2+ and facilitating undesired aluminum deposition. Raman spectroscopy, 27Al NMR, and mass spectrometry ...

Rechargeable magnesium sulfur (Mg/S) batteries suffer from fast capacity fading due to difficulty of reoxidation of MgS and the polysulfide shuttle. Other works have reported that use of Cu current collectors or CuS at the cathode improves cycleability. Here we investigate Cu nanoparticles grown on carbon nanofibers (Cu@CNF) as an additive for the Mg/S battery cathode to test the effects of Cu metal on capacity and rate performance at controlled Cu loading. The Mg/S battery with Cu additives can run at 1 C with a capacity of 452 mAh/g after 100 cycles. It was confirmed via X-ray photoelectron spectroscopy that Cu2S forms during cathode formation and contributes to the high initial capacity, but then converts back to metallic Cu. Upon extending cycling, the Cu additives promote the formation of smaller, more dispersed discharge product particles, thereby enhancing reversibility. Finally, it is found that the loading of S and Cu at the cathode must be low to achieve substantial and sustained benefits of the Cu additives.

Li primary batteries have been used in commercial and military applications for decades due to their unrivaled energy density and long shelf-life. For years, the impressive shelf-life of these batteries has been primarily attributed to a stable solid electrolyte interphase (SEI), which hinders parasitic reactions at the anode/electrolyte interface. However, few published studies have probed electrode/electrolyte composition in commercial cells, and no previous studies have isolated contributions of the cathode and the electrolyte to SEI stability. To fill this knowledge gap, the present study attempts to de-convolute contributions from each entity by determining component compositions and unveiling the effect each constituent has on SEI stability. In this study, we investigate SEI compositions of three common Li primary chemistries - Li/MnO2, Li/FeS2 and Li/CFx, all of which display exceptional shelf-life. Additionally, due to the dynamic nature of the SEI, cells exposed to varying extents of ageing have been investigated to understand how the SEIs physical and chemical characteristics vary with time. Techniques such as X-ray Photoelectron Spectroscopy (XPS) and Energy-Dispersive Spectroscopy (EDS) are used to conduct chemical analysis of the SEI, while Scanning Electron Microscopy (SEM) is used to elucidate morphological changes in anode and SEI behavior as a function of extent of ageing and cathode/electrolyte chemistry. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

A series of crosslinked ionomer networks of varying poly(ethylene glycol) diacrylate crosslinker chain length, ionic co-monomer chemistry, and co-monomer ratio have been studied for their use as polysulfide shuttle inhibiting separators in magnesium-sulfur (Mg-S) batteries. Through the use of X-ray scattering, polysulfide diffusion experiments, conductivity measurements, and Mg-S cell cycling, it was determined that inclusion of tethered anions in polymer networks mitigates the polysulfide shuttle effect. Polysulfide crossover through networks into a bulk electrolyte can be reduced by absorption into the polymer gel, steric rejection, and electrostatic rejection, with the predominance of these mechanisms dictated by polymer composition and structure. The best network composition allowed an initial Mg-S cell discharge capacity of 522 mAh/g compared to a discharge capacity of 365 mAh/g using a literature standard glass fiber separator. The ionomer cell saw 67% capacity retention after three cycles, whereas the glass fiber separator could not complete the first charging cycle due to polysulfide shuttle.

Solvent-free, single-ion conducting electrolytes are sought after for use in electrochemical energy storage devices. Here, we investigate the ionic conductivity and how this property is influenced by segmental mobility and conducting ion number in crosslinked single-ion conducting polyether-based electrolytes with varying tethered anion and counter-cation types. Crosslinked electrolytes are prepared by the polymerization of poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) methyl ether acrylate, and ionic monomers. The ionic conductivity of the electrolytes is measured and interpreted in the context of differential scanning calorimetry and Raman spectroscopy measurements. A lithiated crosslinked electrolyte prepared with PEG31DA and (4-styrenesulfonyl)(trifluoromethanesulfonyl)imide (STFSI) monomers is found to have a lithium ion conductivity of 3.2 &times, 10&minus, 6 and 1.8 &times, 5 S/cm at 55 and 100 &deg, C, respectively. The percentage of unpaired anions for this electrolyte was estimated at about 23% via Raman spectroscopy. Despite the large variances in metal cation&ndash, STFSI binding energies as predicted via density functional theory (DFT) and large variations in ionic conductivity, STFSI-based crosslinked electrolytes with the same charge density and varying cations (Li, Na, K, Mg, and Ca) were estimated to all have unpaired anion populations in the range of 19 to 29%.

Magnesium batteries are a promising alternative to lithium-ion batteries due to the widespread abundance of magnesium and its high specific volumetric energy capacity. Ethereal solvents such as tetrahydrofuran (THF) are commonly used for magnesium-ion electrolytes due to their chemical compatibility with magnesium metal, but the volatile nature of THF is a concern for practical application. Herein, we investigate magnesium bis(hexamethyldisilazide) plus aluminum chloride (Mg(HMDS)

The increased use of electronic devices and electric vehicles over the past decade has led to the development of advanced lithium-ion batteries. However, the intercalation electrode materials used in lithium-ion batteries have inherently low theoretical capacities. The use of metallic anodes provides a pathway to increased energy density. Metallic electrodes suffer from instabilities at the electrode-electrolyte interface, including unstable SEI formation, low coulombic efficiencies, and dendritic growth. This work studies the use of thin film ionomers as a protection layer between the electrolyte and the anode for lithium metal and magnesium metal batteries. The ionomer in use is a crosslinked polymer network with covalently bound anions that is coated onto a traditional microporous separator. We quantify the impact of the ionomer on cation transference number and on coulombic efficiency, overpotential, and cell lifetime while galvanostatic cycling. Post-mortem analysis is completed to evaluate dendrite formation and electrolyte decomposition. We find that the thin ionomeric coatings can influence the metal deposit morphology and that the composition of the coating influences the effectiveness as a protection layer.

Rechargeable batteries with magnesium metal anodes are of recent research interest due to their potential for high energy density and the widespread availability of magnesium. Magnesium electrolytes are complex due to the divalent nature of Mg2+ and hence the multitude of distinct ionic entities that may exist. Characterizing the ion states is crucial for interpreting the observed bulk properties of the electrolytes. In this presentation, characterization of liquid magnesium electrolytes based on ethers and/or sulfones with mixed salts as well as polymeric magnesium electrolytes will be discussed. Electrospray ionization mass spectrometry (ESI MS), nuclear magnetic resonance spectroscopy (NMR), and Raman spectroscopy are used to provide insight into ion complexation.

The metallic Mg anode has a very high theoretical volumetric capacity of 3832 mAh/cm3, in comparison to 2062 mAh/cm3 for Li. Moreover, Mg has widespread natural abundance and is of lower cost. Sulfur is also a cheap and safe material which can be used as cathode for Mg batteries. However, the Mg/S battery has several disadvantages which block its practical application. One of these challenges is the polysulfide shuttle effect which is common in metal-sulfur batteries and results in decreased coulombic efficiency and battery lifespan. To solve this problem, many inorganic compounds have been used as additives to adsorb polysulfides in the Li/S battery cathode. The same method may also be effective in the Mg/S battery. It has been reported that the Mg/S battery with a Cu current collector is able to cycle for more 25 cycles while using other current collectors, the Mg/S cell has much poorer performance. This result suggests that the Cu-S interaction can influence the performance of Mg/S battery and improve the cycling stability. To study the interaction between Cu and S, Cu nanoparticles are synthesized and mixed with the sulfur cathode. It is found that Cu2S forms on the Cu surface and facilitates the reduction of sulfur in the Mg/S battery. The inclusion of Cu nanoparticles enables the battery to charge/discharge at higher current densities and also improves the cycling stability. The Mg/S battery with Cu additives can run at 0.5 C for more than 50 cycles and deliver a significant capacity.

The development of new rechargeable battery systems employing novel chemistries is imperative to meet the increasing energy storage demands of emerging technologies. Magnesium-sulfur (Mg-S) is one promising chemistry for moving beyond lithium-ion, owing to the widespread abundance of both Mg and S and the high theoretical energy density of the Mg-S couple. However, it is well known that similar to other batteries with sulfur cathodes, the Mg-S system suffers dramatic capacity fade as a result of the polysulfide shuttle effect. A series of model crosslinked polymer networks are herein investigated for use as cathode coatings to eliminate or restrict the polysulfide shuttle. Understanding the mechanisms governing ion transport in these systems is critical for engineering materials that balance the need to transport magnesium but restrict polysulfide crossover. The effects of dielectric constant, electrostatic interactions, and steric configurations on magnesium and polysulfide ion transport through the model networks are examined in detail. X-ray scattering, diffusion experiments, and conductivity measurements are used in tandem to relate structural and transport properties of the polymer networks. In general, we find that some characteristics that facilitate magnesium ion conduction likewise facilitate polysulfide crossover. By analyzing the model networks both ex-situ and implemented as cathode coatings, correlations between fundamental materials properties of the ionic polymer networks and performance enhancement of Mg-S cells containing coated cathodes are made. These insights are used to propose design rules for effective sulfur cathode coatings.

Rechargeable magnesium-ion batteries are under investigation as a possible alternative platform to lithium-ion. Magnesium metal serves as a viable anode for post lithium-ion batteries due to its high volumetric charge capacity and widespread abundance. The electrolyte is identified as a limiting factor in magnesium batteries, as many analogous electrolytes to lithium-ion batteries can passivate the magnesium metal surface preventing rechargeability. Both electrolyte salt(s) and solvent(s) must be chosen to ensure chemical compatibility while facilitating desired electrochemical activity. Here we report our recent efforts to understand the effects of speciation and electrochemical performance of magnesium bis(disilizane)-based liquid electrolytes. We find that the solvent and anion types both effect electrolyte equilibration and complexation, resulting in varying conditioning procedures required, the reversibility and facileness of magnesium deposition and stripping, and oxidative stability.

Lithium-ion batteries have dominated the rechargeable battery market since the 1990s when they were first commercialized. Many advanced technologies (portable devices, electric vehicles) are limited by the performance of commercialized lithium-ion batteries. Furthermore, future resource availability is undetermined. Magnesium serves as a viable anode for post lithium-ion batteries due to its high volumetric charge capacity and widespread abundance. Magnesium batteries are under investigation for future applications in electric vehicles due to their potential to have high energy density and reduced cost. The electrolyte is identified as a limiting factor in magnesium batteries, as many analogous electrolytes to lithium-ion batteries can passivate the magnesium metal surface preventing rechargeability. Thus, many new electrolytes are under investigation in the field. Here we report the effect of the anion electronic structure and solvent on the performance of magnesium bis(disilazide) based electrolytes. This includes the electrolytes’ stability window, ability to electrochemically deposit magnesium, and conductivity.