Pyrochlore nanocrystals as versatile quasi-single-source precursors to lithium conducting garnets

Weller, J. Mark; Chan, Candace K.

doi:10.1039/d0ta05842d

Cited by 12 publications

(29 citation statements)

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“…However, there are still substantial variations in the total ionic conductivity between these various samples, even of similar relative density, especially when comparing the HB-MSS and 1Â-SSR 1000 (93.4% and 93.0% relative density, respectively) samples, where the 1Â-SSR 1000 sample has more than double the room temperature ionic conductivity. As all the samples described herein and in our previous works [38,40,41] were sintered in a manner to minimize Li 2 O loss using the same approach, the effect of variation of Li content due to evaporation should be minimal. Furthermore, as many samples were sintered for each method, the samples with the highest room temperature ionic conductivity are considered approximately optimized, such that Li 2 O loss is minimal.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, we have developed several molten salt synthesis (MSS) approaches for Ta-doped LLZO (Scheme 1c). [39][40][41][42] Recently, we investigated [40] the effect of Lux-Flood [43,44] basicity on the formation temperature of LLZTO. The Lux-Flood acidbase theory considers the acidity or basicity of oxides, wherein an acid is a O 2À acceptor, and a base is a O 2À donor.…”

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confidence: 99%

“…We also showed that an extension of this MSS approach could be used to prepare LLZTO from pyrochlore-type lanthanum zirconate nanocrystals, which were doped to contain La, Zr, and Ta with a nominal composition of La 2.4 Zr 1.12 Ta 0.48 O 7.04 . [41] Using this approach (which we call pyrochlore-to-garnet [PG-MSS]), LLZTO powders could be obtained in the mHB-MSS medium at synthesis temperatures as low as 400 C, or blended with a Li source and reactively sintered to form dense garnet electrolyte membranes due to the convenient containment of all cationic species besides Li in the pyrochlore powder. [41] From all of these studies, we found that in each case, garnet electrolytes with high relative density (>90%) and ionic conductivity (>0.5 mS cm À1 ) can be obtained when the processing was optimized.…”

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confidence: 99%

“…[41] Using this approach (which we call pyrochlore-to-garnet [PG-MSS]), LLZTO powders could be obtained in the mHB-MSS medium at synthesis temperatures as low as 400 C, or blended with a Li source and reactively sintered to form dense garnet electrolyte membranes due to the convenient containment of all cationic species besides Li in the pyrochlore powder. [41] From all of these studies, we found that in each case, garnet electrolytes with high relative density (>90%) and ionic conductivity (>0.5 mS cm À1 ) can be obtained when the processing was optimized. On the other hand, a range of values of ionic conductivity were observed, with some samples or synthesis methods apparently able to produce electrolytes with higher conductivity.…”

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confidence: 99%

“…These results provide evidence that in addition to other variables known to affect the ionic conductivity of garnet electrolytes, such as relative density [49] and Li content [9] (or Li 2 O loss [24] ), the compositional homogeneity of the final sintered ceramic can influence the ionic conductivity of solid garnet electrolytes. For comparison with the LLZTO synthesized in our previous works via NAP combustion synthesis, [38] MSS, [40] and PG-MSS, [41] LLZTO of the same nominal composition (Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 ) was prepared via conventional SSR and sintered using the same approach to produce a standard sample set for comparison. Three types of SSR LLZTO were synthesized to explore the effect of synthesis temperature and degree of mixing of the various reactants on the properties of the resultant material.…”

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Observation of Elemental Inhomogeneity and Its Impact on Ionic Conductivity in Li‐Conducting Garnets Prepared with Different Synthesis Methods

Weller

Dopilka

Chan

2021

Adv Energy and Sustain Res

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Garnet-type lithium lanthanum zirconate (Li 7 La 3 Zr 2 O 12 [LLZO]) and its doped derivatives continue to generate interest as solid electrolytes for future solid-state lithium batteries. Most Li-conducting garnets adopt the cubic garnet crystal structure (Ia3d). [1] However, without extrinsic dopants, LLZO adopts a tetragonal structure (I4 1 /acd) due to its uniquely high Li content, which causes a spontaneous ordering of the Li sublattice. [2][3][4] This thermodynamically favorable (at room temperature) tetragonal phase has lower ionic conductivity (%10 À6 S cm À1 at room temperature) compared with the cubic phase (%10 À4 -10 À3 S cm À1 ). [1,5,6] For this reason, an aliovalent dopant is needed to introduce Li vacancies to stabilize the highly conducting cubic phase. [1,3,[7][8][9][10] Many doping schemes have been explored, including Al 3þ [6,7,11] and Ga 3þ [7,12] to dope the Li sublattice, Nb 5þ [13,14] and Ta 5þ [7][8][9][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] to dope the Zr sublattice, Ca 2þ [22,29] and other alkaline earths such as Ba 2þ [30] to dope the La sublattice (often used in conjunction with another site dopant), and even recently F À[31-33] to dope the oxygen sublattice. Of the many possible compositions of LLZO, Ta-doped LLZO (LLZTO) with formula Li 7Àx La 3 Zr 2Àx Ta x O 12 (0.2 < x < 1) combines good electrochemical stability with lithium metal [14] and high ionic conductivity (>1 mS cm À1 ) [23,34,35] and, by virtue of doping the Zr sites in the garnet structure, does not block sites on the Li sublattice [7] unlike other dopants such as Al or Ga.Li-conducting garnets are generally synthesized via conventional solid-state reaction (SSR) methods that require high reaction temperatures (in excess of 900 C) and long reaction times (usually in excess of 8 h) (Scheme 1a). [10,36] Initial blending of oxide precursors is typically accomplished via ball milling for an extended time for mixing, particle size reduction, and to minimize the diffusion distance between individual atomic species. [10,36,37] After the synthesis, further high-energy ball milling is often required to reduce the particle size of the resultant coarse powder to confer greater sinterability. [20] In many cases, multiple milling and calcination steps are used to ensure full intermixing of atomic species. [10] Each of these steps has a large time cost in addition to requiring substantial thermal and

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Section: Resultsmentioning

confidence: 99%

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Observation of Elemental Inhomogeneity and Its Impact on Ionic Conductivity in Li‐Conducting Garnets Prepared with Different Synthesis Methods

Weller

Dopilka

Chan

2021

Adv Energy and Sustain Res

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Processing and Properties of Garnet‐Type Li₇La₃Zr₂O₁₂ Ceramic Electrolytes

Chen

Wang

et al. 2022

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the limited electrochemical window of liquid organic electrolytes, high-voltage cathode materials and Li metal cannot be incorporated in current battery chemistry, thus making it challenge to further improve the energy density. Moreover, the flammability of liquid electrolytes also poses serious safety concerns of LIBs. Under such context, solid-state battery (SSB) using solid state electrolytes (SSEs) have attracted much attention. SSEs are typically nonflammable with wide electrochemical window and high mechanical strength. These merits allow to employ high-voltage cathodes and the "holy-grail" Li metal anode (≈3860 mAh g −1 ), offering drastic improvements in energy density and safety performance. Owing to these promises, SSB has been intensively studies in recent years.Developing a suitable solid electrolyte is critical to realize SSB technology. Substantial efforts have been made on developing various SSE systems, including NASICON (Na Super Ion Conductor)-type, perovskite-type, Garnet-type Li 7 La 3 Zr 2 O 12 (LLZO), sulfide-based, polymer electrolytes, and composite electrolytes. Among these materials, LLZO possesses high ionic (10 −4 -10 −3 S cm −1 ) and low electronic (σ e < 10 −8 S cm −1 ) conductivities at room temperature, [2,3] good mechanical strength, and good electrochemical stability. As such, it has received tremendous attention since its discovery in 2007. [3] Numerous experimental and computational studies have been conducted over the past decades. LLZO-based SSBs have also been demonstrated through various interface engineering strategies.Various formats of LLZO electrolyte have been studied so far. Based on the properties and processing routes, they can be in general categorized into three types, ceramic bulk/tape-based, thin film-based, and single crystal-based electrolytes (Figure 1 and Table 1). Among them, thin film LLZO processing faces the difficulties of Li loss and impurity phase formation during deposition and annealing (Figure 1a). Successful preparation of dense, uniform, and single phase LLZO films is rarely demonstrated. The reported conductivities of thin film LLZO in most studies are between 10 −8 and 10 −4 S cm −1 , which is far behind its ceramic counterpart. In addition, due to geometric limit (≈µm), the capacity of thin film batteries is low, making them only applicable to microelectronic devices. Single crystal growth also faces many processing-related difficulties (Figure 1b). The LLZO single crystal is mostly for the purposes of mechanistic study in LLZO crystal chemistry, which can be investigated without the interference from microstructural defects. [5] From Garnet-type solid electrolyte Li 7 La 3 Zr 2 O 12 (LLZO) is widely considered as one of the most promising candidates for solid state batteries (SSBs) owing to its high ionic conductivity and good electrochemical stability. Since its discovery in 2007, great progress has been made in terms of crystal chemistry, chemical and electrochemical properties, and battery application. Nonetheless, reliable and controll...

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Reactive sintering of garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) from pyrochlore precursors prepared using a non-aqueous sol–gel method

Guo

Weller

Yang

et al. 2022

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Pyrochlore nanocrystals as versatile quasi-single-source precursors to lithium conducting garnets

Abstract: Lithium conducting garnets are attractive solid electrolytes for solid-state lithium batteries but are difficult to process, requiring high reaction and sintering temperatures with long duration. In this work, we demonstrate...

Cited by 12 publications

References 47 publications

Observation of Elemental Inhomogeneity and Its Impact on Ionic Conductivity in Li‐Conducting Garnets Prepared with Different Synthesis Methods

Observation of Elemental Inhomogeneity and Its Impact on Ionic Conductivity in Li‐Conducting Garnets Prepared with Different Synthesis Methods

Processing and Properties of Garnet‐Type Li₇La₃Zr₂O₁₂ Ceramic Electrolytes

Reactive sintering of garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) from pyrochlore precursors prepared using a non-aqueous sol–gel method

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Pyrochlore nanocrystals as versatile quasi-single-source precursors to lithium conducting garnets

Abstract: Lithium conducting garnets are attractive solid electrolytes for solid-state lithium batteries but are difficult to process, requiring high reaction and sintering temperatures with long duration. In this work, we demonstrate...

Cited by 12 publications

References 47 publications

Observation of Elemental Inhomogeneity and Its Impact on Ionic Conductivity in Li‐Conducting Garnets Prepared with Different Synthesis Methods

Observation of Elemental Inhomogeneity and Its Impact on Ionic Conductivity in Li‐Conducting Garnets Prepared with Different Synthesis Methods

Processing and Properties of Garnet‐Type Li7La3Zr2O12 Ceramic Electrolytes

Reactive sintering of garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) from pyrochlore precursors prepared using a non-aqueous sol–gel method

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Processing and Properties of Garnet‐Type Li₇La₃Zr₂O₁₂ Ceramic Electrolytes