Effect of microstructure and surface impurity segregation on the electrical and electrochemical properties of dense Al-substituted Li7La3Zr2O12

Cheng, Lei; Park, Joong Sun; Hou, Haiyun; Zorba, Vassilia; Chen, Guoying; Richardson, Thomas J.; Cabana, Jordi; Russo, Richard E.; Doeff, Marca M.

doi:10.1039/c3ta13999a

Cited by 177 publications

(228 citation statements)

References 25 publications

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“…In comparison to dilatometry results of cubic LLZO published in literature, the onset of sintering is lowered by about 250 °C. [ 33,34 ] Dilatometry studies performed by the group of Doeff and co-workers [ 34 ] on Al-substituted LLZO synthesized by solid-state methods revealed that a reduction in particle size from 10 to 1 µm by attrition milling lowers the onset temperature for sintering by ≈130 °C and increases the density of sintered pellets. This is attributed to the larger surface and thus larger contact area between crystallites.…”

Section: Resultsmentioning

confidence: 99%

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li⁺ Conductors

Broek

Afyon

Rupp

2016

Advanced Energy Materials

282

187

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with solid electrolytes. [ 3 ] Solid electrolytes offer many advantages and could enable the use of new high capacity electrode materials such as sulfur, [ 4 ] manganese, [5][6][7] and vanadate [ 8,9 ] -based cathodes which may not be stable and safe in the current Li-ion battery technology based on liquid electrolytes. [ 10 ] Furthermore, solid electrolytes have the promise to use directly metallic lithium anodes, i.e., preventing dendritic lithium growth, which enables even higher energy densities. From a practical point of view, one may also highlight that solid electrolytes have much-improved thermal operation windows resulting in a higher chemical and thermal stability, benefi ting the long-term operation and safety when compared to their liquid counterparts. This allows for safe packaging of the cell geometries and enables miniaturized cell architectures while simultaneously reducing the battery weight. [ 11,12 ] Among the oxide solid Li-ionic electrolytes, Li 7 La 3 Zr 2 O 12 (LLZO) garnets and their doped variants show one of the highest Li-ion conductivities in the range of ≈10 −4 S cm −1 at room temperature. [ 13 ] LLZO was fi rst synthesized and characterized in 2007 by Murugan et al. [ 14 ] Not until a few years later Geiger et al. [ 15 ] showed that LLZO appears in two different crystal structures, a cubic and a tetragonal one, with the cubic phase showing a Li-ion conductivity two orders of magnitude higher than the tetragonal phase. Using doping strategies, i.e., by introducing Al 3+ , Ga 3+ , Ta 5+ , Nb 5+ , etc., the high conductive cubic phase can be stabilized at room temperature by introducing vacancies into the Li sublattice of the structures. [16][17][18][19] One of the most commonly used dopants is Al 3+ , which stabilizes the cubic phase by substituting for three Li + , thereby creating two Li vacancies and resulting in the stoichiometry of Li 7−3 x Al x La 3 Zr 2 O 12 for the cubic phase.[ 20 ] Despite the promises, all-solid-state Li-ion batteries based on cubic LLZO solid electrolytes have still challenges in realizing high practical performances due to their high electrode-electrolyte interfacial resistances. For the investigations on all-solid-state batteries based on garnet-type cubic LLZO, most of the current research efforts are concentrated on the cathode material, most prominently on LiCoO 2 . [21][22][23][24][25][26][27] Reasonable electrochemical activities are so far only achieved by vacuum deposition of the cathode as thin fi lms, i.e., by pulsed laser deposition (PLD), because of the resulting good electrolyte-electrode contact. [ 25,26 ] Here, the exact chemical composition of the electrolyte-electrode interface also greatly determines the contact properties, the interfacial

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Section: Resultsmentioning

confidence: 99%

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li⁺ Conductors

Broek

Afyon

Rupp

2016

Advanced Energy Materials

282

187

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“…3,9,10 Al-doped Li 7 La 3 Zr 2 O 12 prepared without adding any excess lithium salts during synthesis, but varying the processing using powder cover condition for sintering, greatly affects the morphology, grain size and density. 11 Attempts have also been made to reduce the sintering temperature and improve the control of stoichiometry via wet chemical synthesis as well as through additives acting as sintering aids. [12][13][14][15][16][17][18] It has been shown that Al migrates from the alumina crucible used for garnet synthesis, causing significant effects in the material including stabilization of the cubic phase.…”

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confidence: 99%

Effect of Excess Li on the Structural and Electrical Properties of Garnet-Type Li₆La₃Ta_1.5Y_0.5O₁₂

Narayanan

Hitz

Wachsman

et al. 2015

J. Electrochem. Soc.

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Volatility of lithium during preparation of lithium-stuffed garnet-type metal oxide solid Li ion electrolytes is a common problem, which affects phase formation, ionic conductivity, mechanical strength and density. Synthesis of Li-stuffed garnets has been performed generally using the conventional solid-state reactions at elevated temperature in air. The present study describes the effect of excess LiNO 3 (2.5 to 15 wt.%) addition during the ceramic synthesis on the structural and electrical properties of garnet-type Li 6 La 3 Ta 1.5 Y 0.5 O 12 . Powder X-ray diffraction (PXRD) confirmed that cubic phase was formed in all tested cases, and there is no significant variation in lattice parameter with amount of excess LiNO 3 used. However, increasing amounts of excess lithium decreased inter-particle contact and increased grain growth during sintering, producing sharply varied microstructures. PXRD showed no secondary phase and scanning electron microscopy (SEM) analysis showed rather uniform morphology and absence of "glassy" materials at the grain-boundaries. The bulk Li ion conductivity was found to increase with amount of excess lithium, reaching a maximum room temperature conductivity of 1.62 × 10 −4 Scm −1 for the sample prepared using 10 wt.% excess LiNO 3 . Raman microscopy study indicated the presence of Li 2 CO 3 in all aged Li 6 La 3 Ta Li-stuffed garnet-type metal oxides have been considered as a potential candidate solid electrolyte material to replace conventional organic liquid based Li ion conducting electrolytes in Li-ion batteries, since members of garnet solid electrolytes exhibit high bulk ion conductivity of 10 −4 -10 −3 Scm −1 at room temperature. Furthermore, some of the garnet-type electrolytes show excellent chemical stability against reaction with elemental Li, Li-ion insertion or intercalation cathodes and high electrochemical stability window.1,2 However, the synthesis of high bulk Li ion conducting garnet-type metal oxidebased lithium ion conductors is a challenging process, very sensitive to preparation conditions used, that are not yet fully characterized. For example, Li 7 La 3 Zr 2 O 12 calcined at 1230• C results in highly conducting (7 × 10 −4 Scm −1 at room temperature) cubic phase with a space group Ia-3d whereas a calcining temperature of 980• C leads to tetragonal phase with a space group I4 1 /acd, which showed 2 orders of magnitude less conductive than cubic phase.3,4 Traditional solid-state techniques are the most commonly used to synthesize garnet-type metal oxides, but usually require the highest sintering temperature resulting in the production of large particles. [5][6][7][8] It is known that volatilization of lithium occurs in the furnace, therefore, several researchers commonly compensate with a 10 wt.% excess lithium precursors.3,9,10 Al-doped Li 7 La 3 Zr 2 O 12 prepared without adding any excess lithium salts during synthesis, but varying the processing using powder cover condition for sintering, greatly affects the morphology, grain size and density. 11Attempts h...

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“…There is, however, significant variation in the impedance of these boundaries with some regions much higher than in others, where it is close in value to that of the grain itself. Several research groups have observed that there is Al enrichment at the grain boundaries of LLZO samples similar to the one in this study (Jin and McGinn, 2011;Li et al, 2012Li et al, , 2014Cheng et al, 2014;Ren et al, 2015). Grain boundary conductivities may also vary in polycrystalline samples due to a distribution of grain misorientation angles.…”

Section: Discussionmentioning

confidence: 49%

“…Li7La3Zr2O12 powders used for preparing dense pellets were synthesized from stoichiometric amounts of Li2CO3, La(OH)3, ZrO2, and Al2O3, as described in Cheng et al (2014). Powders were attrition-milled to an average size of about 1 μm and then compacted into pellets.…”

Section: Materials and Methods Sample Preparation And Characterizationmentioning

confidence: 99%

“…Pellets made from attrition-milled powders, as described in Cheng et al (2014) were 92% dense with a majority of grains about 150-200 μm across. The X-ray diffraction data, energy dispersive X-ray spectroscopy (EDS) mapping, inductively coupled plasma optical emission spectrometry (ICP-OES), and laser-induced breakdown spectroscopy (LIBS) results reported in that paper were consistent with the interpretation of a phase-pure, homogeneous garnet sample, once surface impurities were polished away.…”

Section: Scanning Electrochemical Microscopy Experimentsmentioning

confidence: 99%

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Intermittent Contact Alternating Current Scanning Electrochemical Microscopy: A Method for Mapping Conductivities in Solid Li Ion Conducting Electrolyte Samples

et al. 2016

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Intermittent contact alternating current scanning electrochemical microscopy (ic-ac-SECM) has been used to determine the electrochemical response to an ac signal of several types of materials. A conductive gold foil and insulating Teflon sheet were first used to demonstrate that the intermittent contact function allows the topography and conductivity to be mapped simultaneously and independently in a single experiment. Then, a dense pellet of an electronically insulating but Li ion conducting garnet phase, Al-substituted Li7La3Zr2O12 (LLZO), was characterized using the same technique. The polycrystalline pellet was prepared by classical ceramic sintering techniques and was comprised of large (~150 μm) grains. Critical information regarding the contributions of grain and grain boundary resistances to the total conductivity of the garnet phase was lacking due to ambiguities in the impedance data. In contrast, the use of the ic-ac-SECM technique allowed spatially resolved information regarding local conductivities to be measured directly. Impedance mapping of the pellet showed that the grain boundary resistance, while generally higher than that of grains, varied considerably, revealing the complex nature of the LLZO sample.

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Effect of microstructure and surface impurity segregation on the electrical and electrochemical properties of dense Al-substituted Li₇La₃Zr₂O₁₂

Cited by 177 publications

References 25 publications

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li⁺ Conductors

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li⁺ Conductors

Effect of Excess Li on the Structural and Electrical Properties of Garnet-Type Li₆La₃Ta_1.5Y_0.5O₁₂

Intermittent Contact Alternating Current Scanning Electrochemical Microscopy: A Method for Mapping Conductivities in Solid Li Ion Conducting Electrolyte Samples

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Effect of microstructure and surface impurity segregation on the electrical and electrochemical properties of dense Al-substituted Li7La3Zr2O12

Cited by 177 publications

References 25 publications

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li+ Conductors

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li+ Conductors

Effect of Excess Li on the Structural and Electrical Properties of Garnet-Type Li6La3Ta1.5Y0.5O12

Intermittent Contact Alternating Current Scanning Electrochemical Microscopy: A Method for Mapping Conductivities in Solid Li Ion Conducting Electrolyte Samples

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Effect of microstructure and surface impurity segregation on the electrical and electrochemical properties of dense Al-substituted Li₇La₃Zr₂O₁₂

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li⁺ Conductors

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li⁺ Conductors

Effect of Excess Li on the Structural and Electrical Properties of Garnet-Type Li₆La₃Ta_1.5Y_0.5O₁₂