An official website of the United States government
A major challenge for lithium-containing electrochemical systems is the formation of lithium carbonates. Solid-state electrolytes circumvent the use of organic liquids that can generate these species, but they are still susceptible to Li2CO3 formation from exposure to water vapor and carbon dioxide. It is reported here that trace quantities of Li2CO3, which are re-formed following standard mitigation and handling procedures, can decompose at high charging potentials and degrade the electrolyte–cathode interface. Operando electrochemical mass spectrometry (EC–MS) is employed to monitor the outgassing of solid-state batteries containing the garnet electrolyte Li7La3Zr2O12 (LLZO) and using appropriate controls CO2 and O2 are identified to emanate from the electrolyte–cathode interface at charging potentials > 3.8 V (vs Li/Li+). The gas evolution is correlated with a large increase in cathode interfacial resistance observed by potential-resolved impedance spectroscopy. This is the first evidence of electrochemical decomposition of interfacial Li2CO3 in garnet cells and suggests a need to report “time-to-assembly” for cell preparation methods
more »
« less
Surface Reduction of Li2CO3 on LLZTO Solid-State Electrolyte via Scalable Open-Air Plasma Treatment
We report on the use of an atmospheric pressure, open-air plasma treatment to remove Li2CO3 species from the surface of garnet-type tantalum-doped lithium lanthanum zirconium oxide (Li6.4La3Zr1.4Ta0.6O12, LLZTO) solid-state electrolyte pellets. The Li2CO3 layer, which we show forms on the surface of garnets within 3 min of exposure to ambient moisture and CO2, increases the interface (surface) resistance of LLZTO. The plasma treatment is carried out entirely in ambient and is enabled by use of a custom-built metal shroud that is placed around the plasma nozzle to prevent moisture and CO2 from reacting with the sample. After the plasma treatment, N2 compressed gas is flowed through the shroud to cool the sample and prevent atmospheric species from reacting with the LLZTO. We demonstrate that this approach is effective for removing the Li2CO3 from the surface of LLZTO. The surface chemistry is characterized with X-ray photoelectron spectroscopy to evaluate the effect of process parameters (plasma exposure time and shroud gas chemistry) on removal of the surface species. We also show that the open-air plasma treatment can significantly reduce the interface resistance. This platform demonstrates a path towards open-air processed solid-state batteries.
more »
« less
- Award ID(s):
- 2234636
- PAR ID:
- 10580046
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Batteries
- Volume:
- 10
- Issue:
- 7
- ISSN:
- 2313-0105
- Page Range / eLocation ID:
- 249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Dielectric barrier discharges are receiving increasing attention as sampling/ionization sources for ambient mass spectrometry. Nevertheless, the underlying mechanisms are not completely understood, particularly when the plasma plume is exposed to a sample surface. Herein, an atmospheric pressure helium micro-dielectric barrier discharge (μDBD), flowing into open-air and onto a sample surface (floating Cu or LDPE), is studied via optical emission spectroscopy (OES) with radial information extracted through Abel's inversion. Radially resolved optical emission profiles along the axis are shown to shift with respect to the line-of-sight counterparts, for some species. The OES images, as well as vibrational and rotational temperature maps, indicate the energy transfers mainly via Penning ionization of N 2 with He metastables to produce N 2 + , as the plasma plume exits the capillary into open air, while charge transfer with He 2 + is dominant further downstream, as well as toward the periphery of the plume. In addition, the sample surface is shown to play an important role in the energy transfer mechanisms. For the LDPE sample, the spatial distribution sequence of excited species is similar to the free-flowing counterpart but disappears into the surface, which indicates that excited N 2 further downstream/outer periphery is produced from electron recombination with N 2 + . On the other hand, the presence of the floating Cu sample results in an intensity peak at the plasma/surface interface for most species. We propose that the temporal evolution of the half-cycle dynamics have a great effect, where the resulting higher electron temperature and density towards the surface of metallic samples favors electron impact excitation. Furthermore, profilometry of the resulting craters in the floating Cu samples revealed a close correlation between their diameter and the width of the N 2 + emission.more » « less
-
Atmospheric pressure plasma jets (APPJs) are used to improve the adhesive and hydrophilic properties of commodity hydrocarbon polymers such as polypropylene, polyethylene, and polystyrene (PS). These improvements largely result from adding oxygen functional groups to the surface. PS functionalization is of interest to produce high value biocompatible well-plates and dishes, which require precise control over surface properties. In this paper, we discuss results from a computational investigation of APPJ functionalization of PS surfaces using He/O 2 /H 2 O gas mixtures. A newly developed surface reaction mechanism for functionalization of PS upon exposure to these plasmas is discussed. A global plasma model operated in plug-flow mode was used to predict plasma-produced species fluxes onto the PS surface. A surface site balance model was used to predict oxygen-functionalization of the PS following exposure to the plasma and ambient air. We found that O-occupancy on the surface strongly correlates with the O-atom flux to the PS, with alcohol groups and cross-linked products making the largest contributors to total oxygen fraction. Free radical sites, such as alkoxy and peroxy, are quickly consumed in the post-plasma exposure to air through passivation and cross-linking. O-atom fluences approaching 10 17 cm −2 saturate the O-occupancy on the PS surface, creating functionality that is not particularly sensitive to moderate changes in operating conditions.more » « less
-
Nonthermal plasmas in contact with liquids have been shown to generate a variety of reactive species capable of initiating reduction–oxidation (redox) reactions at the electrochemically active plasma–liquid interface. In conventional electrochemical cells, selective redox chemistry is achieved by controlling the reduction potential at the solid electrode–electrolyte interface by applying a bias via an external circuit. In the case of plasma–liquid systems, an analogous means of tuning the reduction potential near the interface has not clearly been identified. When treated as a floating surface, the liquid is expected to adopt a net negative charge to balance the flux of hot electrons and relatively cold positive ions. The reduction potential near the plasma–liquid interface is hypothesized to be proportional to the floating potential, which can be approximated using an analytical model provided the plasma parameters are known. Herein, we present a framework for correlating the electron density and electron temperature of a noble gas plasma jet to the reduction potential near the plasma–liquid interface. The plasma parameters were acquired for an argon atmospheric plasma jet in contact with an aqueous solution by means of laser Thomson scattering. The reduction potential was determined using identical reference electrodes to measure the potential difference between the plasma–liquid interface and bulk solution. Interestingly, the measured reduction potentials near the plasma–liquid interface were found to be in good agreement with the model-predicted values determined using the plasma parameters obtained from the Thomson scattering experiments.more » « less
-
Reforming of methane (CH4) is a process to produce syngas (CO/H2) and other value-added chemicals including oxygenates such as methanol (CH3OH). Atmospheric pressure plasmas have the potential to be more energy efficient than traditional reforming methods as value-added chemicals can be synthesized directly in the plasma without requiring an additional step. In this paper, we discuss the results from a computational investigation of the formation of oxygenates by CH4 oxidation in the presence of Ar, including CH3OH and CH2O, in a nanosecond pulsed dielectric barrier discharge. The plasma is formed in a microfluidic channel whose small dimensions are ideal for plasma formation at atmospheric pressure. The production and consumption mechanisms of dominant radicals and long-lived species are discussed in detail for the base case conditions of Ar/CH4/O2 = 50/25/25. CH3OH is produced primarily by CH3O reacting with CH3O and CH3O2 reacting with OH, while CH2O formation relies on reactions involving CH3O and CH3. The most abundant oxygenate formed is CO (produced by H abstraction from CHO). However, the greenhouse gas CO2 is also formed as a by-product. The effects of gas mixture are examined to maximize the CH3OH and CH2O densities while decreasing the CO2 density. Increasing the Ar percentage from 0% to 95% decreased the CH3OH and CH2O densities. At low Ar percentages, this is due to an increase in consumption of CH3OH and CH2O, while at high Ar percentages (>40% Ar), the production of CH3OH and CH2O is decreased. However, both CO and CO2 reached peak densities at 70%–90% Ar. Changing the CH4/O2 ratio while keeping 50% Ar in the discharge led to increased CH3OH and CH2O production, reaching peak densities at 35%–40% CH4. The CO and CO2 densities decreased beyond 20% CH4, indicating that a CH4 rich discharge is ideal for forming the desired oxygenates.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/batteries10070249
