Engineering topics
Wolfenstine, Jeff
Publications and source records attributed to Wolfenstine, Jeff.
Mechanical properties of NaSICON: a brief review
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Correlating the effect of dopant type (Al, Ga, Ta) on the mechanical and electrical properties of hot-pressed Li-garnet electrolyte
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Mechanical and physical properties of LiNi0.33Mn0.33Co0.33O2 (NMC)
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Electrochemical Window of the Li-Ion Solid Electrolyte Li 7 La 3 Zr 2 O 12
The recent discovery of fast ion-conducting solid electrolytes could enable solid-state and other advanced battery chemistries with higher energy densities and enhanced safety. In addition to high ionic conductivity, a viable electrolyte should also exhibit an electrochemical window that is wide enough to suppress undesirable electronic transport (i.e., self-discharge and/or short circuiting) arising from charge injection or extraction from the electrodes. Here, direct current chronoamperometry, alternating current electrochemical impedance spectroscopy, and optical absorption band gap measurements are combined with first-principles calculations to systematically characterize the electrochemical window of the promising superionic conductor Li 7 La 3 Zr 2 O 12 (LLZO). Negligible electronic current was measured within LLZO for a wide range of voltages relevant for high-voltage cathodes. This auspicious behavior is consistent with both the large band gap (~6 eV) predicted for LLZO and the absolute positions of its band edges. These features imply that a wide electrochemical window is an intrinsic property of LLZO, facilitating its use in next-generation batteries.
Cr and Si Substituted-LiCo0.9Fe0.1PO4: Structure, full and half Li-ion cell performance
Abstract not provided
Elastic Properties of the Solid Electrolyte Li7La3Zr2O12 (LLZO)
The oxide known as LLZO, with nominal composition Li 7 La 3 Zr 2 O 12 , is a promising solid electrolyte for Li-based batteries due to its high Li-ion conductivity and chemical stability with respect to lithium. Solid electrolytes may also enable the use of metallic Li anodes by serving as a physical barrier that suppresses dendrite initiation and propagation during cycling. Prior linear elasticity models of the Li electrode/solid electrolyte interface suggest that the stability of this interface is highly dependent on the elastic properties of the solid separator. For example, dendritic suppression is predicted to be enhanced as the electrolyte s shear modulus increases. In the present study a combination of first-principles calculations, acoustic impulse excitation measurements, and nanoindentation experiments are used to determine the elastic constants and moduli for highconductivity LLZO compositions based on Al and Ta doping. The calculated and measured isotropic shear moduli are in good agreement and fall within the range of 56-61 GPa. These values are an order of magnitude larger than that for Li metal and far exceed the minimum value ( 8.5 GPa) believed to be necessary to suppress dendrite initiation. These data suggest that LLZO exhibits sufficient stiffness to warrant additional development as a solid electrolyte for Li batteries.
Characterizing the Li–Li 7 La 3 Zr 2 O 12 interface stability and kinetics as a function of temperature and current density
The stability and kinetics of the Li–Li 7 La 3 Zr 2 O 12 (LLZO) interface were characterized as a function of temperature and current density. Polycrystalline LLZO was densified using a rapid hot-pressing technique achieving 97 ± 1% relative density, and <10% grain boundary resistance; effectively consisting of an ensemble of single LLZO crystals. It was determined that by heating to 175 °C, the room temperature Li-LLZO interface resistance decreases dramatically from 5822 (as-assembled) to 514 Ω cm 2 ; a > 10-fold decrease. In characterizing the maximum sustainable current density (or critical current density – CCD) of the Li-LLZO interface, several signs of degradation were observed. In DC cycling tests, significant deviation from Ohmic behavior was observed. In post-cycling tests, regions of metallic Li were observed; propagating parallel to the ionic current. For the cells cycled at 30, 70, 100, 130 and 160 °C, the CCD was determined to be 50, 200, 800, 3500, and 20000 μA cm –2 , respectively. As a result, the relationships and phenomena observed in this work can be used to better understand the Li-LLZO interface stability, enabling the use of batteries employing Li metal anodes.
A Tale of Two Sites: On Defining the Carrier Concentration in Garnet-Based Ionic Conductors for Advanced Li Batteries
Abstract not provided
Structure and Stoichiometry in Supervalent Doped Li[subscript 7]La[subscript 3]Zr[subscript 2]O[subscript 12]
Abstract not provided
Tetragonal vs. cubic phase stability in Al – free Ta doped Li 7 La 3 Zr 2 O 12 (LLZO)
X-ray and neutron diffraction, Raman spectroscopy, complex impedance spectroscopy and electron microscopy were used to characterize the tetragonal vs. cubic phase stability in superionic conducting garnet-oxide electrolyte.
Resolving the grain boundary and lattice impedance of hot-pressed Li 7 La 3 Zr 2 O 12 garnet electrolytes
Here, the cubic-stabilized garnet solid electrolyte with a nominal composition of Li 6.28 Al 0.24 La 3 Zr 2 O 12 is thoroughly characterized by impedance spectroscopy. By varying the frequency of the applied AC signal over 11 orders of magnitude for characterizations from –100 to +60 °C, the relative contributions of grain and grain boundary conduction are unambiguously resolved.