With the potential to dramatically increase energy density compared to conventional lithium ion technology, lithium metal solid-state batteries (LMSSB) have attracted significant attention. However, ...little is known about the mechanical properties of Li. The purpose of this study was to characterize the elastic and plastic mechanical properties and creep behavior of Li. Elastic properties were measured using an acoustic technique (pulse-echo). The Young’s modulus, shear modulus, and Poisson’s ratio were determined to be 7.82 GPa, 2.83 GPa, and 0.381, respectively. To characterize the stress–strain behavior of Li in tension and compression, a unique load frame was used inside an inert atmosphere. The yield strength was determined to be between 0.73 and 0.81 MPa. The time-dependent deformation in tension was dramatically different compared to compression. In tension, power law creep was exhibited with a stress exponent of 6.56, suggesting that creep was controlled by dislocation climb. In compression, time-dependent deformation was characterized over a range of stress believed to be germane to LMSSB (0.8–2.4 MPa). At all compressive stresses, significant barreling and a decrease in strain rate with increasing time were observed. The implications of this observation on the charge/discharge behavior of LMSSB will be discussed. We believe the analysis and mechanical properties measured in this work will help in the design and development of LMSSB.
The stability and kinetics of the Li–Li7La3Zr2O12 (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 cm2; 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. 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.
•The Li-LLZO interface kinetics and stability are affected by temperature.•The Li-LLZO interface resistance decreases by >10-fold upon heating to 175 °C.•Reducing the charge-transfer resistance increased the maximum current density.•Exceeding the maximum current density resulted in metallic Li propagation.
Lithium Nickel Manganese Cobalt Oxide (NMC) is one of the most common oxide cathode materials for Li-ion batteries. NMC is also under consideration for use in all solid-state batteries. However, ...differences in the coefficients of thermal expansion (CTE) between NMC and the solid electrolyte during composite electrode fabrication and differential expansion and contraction during electrochemical cycling will cause stresses possibly resulting in electrode fracture and battery capacity fade. As a consequence, we hot-pressed phase-pure polycrystalline NMC with controlled density and accurately measured the mechanical (elastic modulus, shear modulus, Poisson’s ratio and nanoindentation hardness) and physical properties (CTE and thermal conductivity). We believe that this is the first report of the mechanical and physical properties of commercially available NMC and these experimental data are important to predict or increase the cycle life of NMC as a cathode material for state-of-the-art Li-ion and advanced solid-state batteries.
Li-ion-conducting solid electrolytes are receiving considerable attention for use in advanced batteries. These electrolytes would enable use of a Li metal anode, allowing for batteries with higher ...energy densities and enhanced safety compared to current Li-ion systems. One important aspect of these electrolytes that has been overlooked is their mechanical properties. Mechanical properties will play a large role in the processing, assembly, and operation of battery cells. Hence, this paper reviews the elastic, plastic, and fracture properties of crystalline oxide-based Li-ion solid electrolytes for three different crystal structures: Li
6.19
Al
0.27
La
3
Zr
2
O
12
(garnet) LLZO, Li
0.33
La
0.57
TiO
3
(perovskite) LLTO, and Li
1.3
Al
0.3
Ti
1.7
(PO
4
)
3
(NaSICON) LATP. The experimental Young’s modulus value for (1) LLTO is ~ 200 GPa, (2) LLZO is ~ 150 GPa, and (3) for LATP ~ 115 GPa. The experimental values are in good agreement with density functional theory predictions. The fracture toughness value for all three of LLTO, LLZO, and LATP is approximately 1 MPa m
−2
. This low value is expected since, they all exhibit at least some degree of covalent bonding, which limits dislocation mobility leading to brittle behavior.
The effect of hot‐pressing temperature on the microstructure and Li‐ion transport of Al‐doped, cubic Li7La3Zr2O12 (LLZO) was investigated. At fixed pressure (62 MPa), the relative density was 86%, ...97%, and 99% when hot‐pressing at 900°C, 1000°C, and 1100°C, respectively. Electrochemical impedance spectroscopy showed that the percent grain‐boundary resistance decreased with increasing hot‐pressing temperature. Hot pressing at 1100°C resulted in a total conductivity of 0.37 mS/cm at room temperature where the grain boundaries contributed to 8% of the total resistance; one of the lowest grain‐boundary resistances reported. We believe hot pressing is an appealing technique to minimize grain‐boundary resistance and enable correlations between LLZO composition and bulk ionic conductivity.
Ga addition to the garnet Li7La3Zr2O12 (LLZO) can lead to stabilization of the cubic structure, high relative density and high Li-ion conductivity at room temperature. Cubic Li6.25La3Zr2Ga0.25O12 ...powders were prepared from co-precipitated nitrate precursor and consolidated by hot-pressing to a relative density of ∼91%. The total Li-ion conductivity was ∼3.5 ×10−4 Scm−1 while the electronic conductivity was ∼7.1 ×10−8 Scm−1. The Ga substituted LLZO had a slightly higher total Li-ion conductivity compared to Al substituted LLZO of similar composition and relative density. This difference may be related to the larger size of Ga versus Al leading to different site occupancy fractions.
► The Li-ion conductivity of hot-pressed Ga-substituted Li7La3Zr2O12 was ∼3.5 × 10−4 Scm−1. ► The electronic conductivity was ∼7.1 × 10−8 Scm−1. ► Ga-substituted Li7La3Zr2O12 had a higher Li-ion conductivity compared to the more commonly Al-substituted Li7La3Zr2O12.
► Highest relative density (∼98%) tetragonal Li7La3Zr2O12 reported. ► Highest total ionic conductivity of ∼2.3×10−5Scm−1 reported for tetragonal Li7La3Zr2O12. ► Microstructure of dense Li7La3Zr2O12 ...revealed twins within the grains.
Hot-pressing at 1050°C lead to near theoretical density (∼98% relative density) tetragonal LLZO. The total conductivity value for dense tetragonal LLZO is ∼2.3×10−5Scm−1. This is the highest reported value for tetragonal LLZO. This vast improvement in total conductivity is a result of the higher density achieved as a result of hot-pressing compared to conventional solid-state sintering. The value of the Li-ion lattice conductivity for dense tetragonal LLZO is 1.1×10−4Scm−1. The microstructure of dense tetragonal LLZO consist of twins within the grains. It is suggested that the presence of twin boundaries adds a significant contribution to the total resistance.
A variety of rechargeable Na batteries are under development for use in energy storage systems. For these batteries, a Na-ion conducting solid electrolyte is desired. One such electrolyte under ...consideration is NaSICON (Na Super Ionic Conductor). One important aspect of the NaSICON electrolytes that has been overlooked is their mechanical properties. Such information is required if NaSICON has to be used as a solid electrolyte in rechargeable Na batteries that exhibit long life cycle and high power. This paper reviews the elastic, plastic, and fracture properties of NaSICON electrolytes. Young’s modulus values for NaSICON range from ~ 56 to 97 GPa with Poisson’s ratio ~ 0.26. Hardness values determined by micro-indentation for NaSiCON are 4.4–4.9 GPa. The value of the Gilman-Chin parameter suggests the bonding in NaSICON is covalent. As a result of its covalent bonding, NaSICON exhibits a high Peierls which leads to low fracture toughness, with K
IC
values ~ 1–1.5 MPa m
0.5
. The fracture strength of NaSICON is between 50 and 110 MPa and is controlled by the amount and size of the second-phase ZrO
2
particles.
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