Mechanical properties of the solid Li-ion conducting electrolyte: Li0.33La0.57TiO3

Abstract

Li 0.33 La 0.57 TiO 3 (LLTO) is a potential Li-ion conducting membrane for use in aqueous Li-air batteries. To be in this configuration its mechanical properties must be determined. Dense LLTO was prepared using a solidstate (SS) or sol-gel (SG) procedure and was hot-pressed to yield a high relative density material ([95 %). Young's modulus, hardness, and fracture toughness of the LLTO-SS and sol-gel LLTO-SG materials was determined and compared to other solid Li-ion conducting electrolytes. The Young's modulus for LLTO-SG and LLTO-SS was 186 ± 4 and 200 ± 3 GPa, respectively. The Vickers hardness of LLTO-SG and LLTO-SS was 9.7 ± 0.7 and 9.2 ± 0.2 GPa, respectively. The fracture toughness, K IC , of both LLTO-SG and LLTO-SS was *1 MPa m 1/2 ; the fracture toughness of LLTO-SG was slightly higher than that of LLTO-SS. Both LLTO-SG and LLTO-SS have a Young's modulus and hardness greater than the other possible solid Li-ion conducting membranes

Mechanical Properties of Hot Isostatically Pressed Li0.35La0.55TiO3

“…A representative hardness load curve for a hipped LLTO sample is given in Figure 3. [11] Since, the microstructure (grain size 1 mm [10] vs. 2.42 mm and relative density 95% [10] vs. 99%) of the LLTO materials tested in this study and those of Cho et al [10] are nearly similar it is highly likely that the variation between the current LLTO hardness values and those of the previous reports is more likely due to the testing method (Knoop vs. Vickers) rather than differences between the LLTO materials. Cho et al [10] measured the hardness for their hot pressed LLTO samples of about 9.2 GPa using a Vickers microhardness indenter, which was consistent with an even earlier report on hot pressed LLTO.…”

“…All values fall within 0.07 g cm À3 of each other, and their average is 4.942 g cm À3 . [10] A higher modulus is expected for the denser hipped LLTO samples since, it is known that Young's modulus increases with reduced porosity. Investigation of the ceramic microstructure with SEM confirms the low occurrence of residual porosity that would be expected for such high density.…”

“…Currently, there is no single electrolytic material, which meets these requirements, but Liion conducting ceramics have the potential to serve as crucial components in potential mixed solid/liquid electrolyte system [5] for a Li-air cell, as well as other electrolytic applications such as in an all-solid state battery. [10,11] In addition, no strength measurements were reported in these studies. [8] Li 3x La (2/3)Àx TiO 3 perovskite (LLTO) is a strong candidate for use as a ceramic electrolyte.…”

Compliant Yet Brittle Mechanical Behavior of Li2S–P2S5 Lithium‐Ion‐Conducting Solid Electrolyte

“…[3][4][5] A key concern in these and other solid electrolytes, however, is their mechanical stability in the presence of strains in the adjacent electrode materials accompanying reversible Li storage (intercalation or alloying) that may vary from a few percent by volume up to a factor of three (e.g., in the case of silicon anodes). [6,7] Sulfide-based electrolytes have remarkably lower Young's modulus (~20 GPa [8] ) than many of these active materials (e.g., 100-200 GPa), as well as oxide-based solid electrolytes such as the garnets (100-200 GPa for Li 7 La 3 Zr 2 O 12 or LLZO and Li 0.33 La 0.57 TiO 3 or LLTO [8][9][10] ), which initially suggested to us that the sulfides might exhibit superior strainaccommodation characteristics in solid state batteries. However, detailed understanding of elastoplastic and fracture properties, which has heretofore been lacking, is required to draw clear conclusions of material design and selection for sulfide solid electrolytes.…”

“…[22] Solid electrolyte garnet-type oxides such as LLTO and LLZO are much stiffer (E ~ 100 GPa), but likewise less brittle (K Ic ~ 0.9 to 1.6 MPa-m 1/2 when measured via Newton-scale indentation as reported herein). [10,23] To confirm the structure and conductivity of the sample, we ground the LPS to a powder form and conducted X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) measurements. Figure 3a shows the XRD pattern of the melt-quenched LPS sample (after grinding to powder), the same material after annealing for stress-relief, and the pattern reported by Minami et al [24] for "glassy" LPS powder obtained via the same melt-quench process.…”