Effect of Li+/H+ exchange in water treated Ta-doped Li7La3Zr2O12 (original) (raw)
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In this review work it has been tried to briefly summarize solid state electrolytes conductivity status. As the very essential component for battery efficiency and performance, electrolytes need be given due attention as safety problems could also emanate from it as well. The oxide solid state electrolytes are very promising electrolytes for allsolid-state batteries for large applications. The garnet-structured Li 7 La 3 Zr 2 O 12 has shown high ionic conductivity that is comparable to the liquid electrolytes with large potential windows. At lower temperature Li 7 La 3 Zr 2 O 12 will have high Li-ordered and forms the tetragonal structure which is less ionic conductor as compared to the less Li-ordered cubic structure. A total ionic conductivity of the order of 10 -3 Scm -1 has been achieved by the cubic structures of Li 7 La 3 Zr 2 O 12 which will let it to be applicable in practice.
Angewandte Chemie (International ed. in English), 2015
Batteries with an aqueous catholyte and a Li metal anode have attracted interest owing to their exceptional energy density and high charge/discharge rate. The long-term operation of such batteries requires that the solid electrolyte separator between the anode and aqueous solutions must be compatible with Li and stable over a wide pH range. Unfortunately, no such compound has yet been reported. In this study, an excellent stability in neutral and strongly basic solutions was observed when using the cubic Li7 La3 Zr2 O12 garnet as a Li-stable solid electrolyte. The material underwent a Li(+) /H(+) exchange in aqueous solutions. Nevertheless, its structure remained unchanged even under a high exchange rate of 63.6 %. When treated with a 2 M LiOH solution, the Li(+) /H(+) exchange was reversed without any structural change. These observations suggest that cubic Li7 La3 Zr2 O12 is a promising candidate for the separator in aqueous lithium batteries.
Lithium Ion Conducting Solid Electrolytes for Aqueous Lithium-air Batteries
Electrochemistry, 2014
This article summarizes our research on solid electrolytes for rechargeable aqueous lithium-air batteries. Aqueous lithium-air batteries have potential application as a power source for electric vehicles, because of their high specific energy density. A water-stable lithium ion conducting solid electrolyte is the key material for lithium-air batteries to use lithium metal in aqueous circumstance. In this article, two types of lithium ion conducting solid electrolytes, NASICON-type Li 1+x A x Ti 2−x−y Ge y (PO 4) 3 (A = Al, Fe) and garnet-type Li 7−x La 3 Zr 2−x A x O 12 (A = Nb, Ta) are introduced, and the conductivity behavior of these solid electrolytes by elemental substitution, their chemical stabilities in water and electrochemical stabilities with lithium metal are discussed. Lithium ion conductivities of 1.3 × 10 −3 and 5.2 × 10 −4 S cm −1 at 25°C were observed in Li 1.4 Al 0.4 Ti 1.4 Ge 0.2 (PO 4) 3 and Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 , respectively. These solid electrolytes are unstable in water, but stable in saturated LiOH with saturated LiCl aqueous solution. The former solid electrolyte is unstable in contact with lithium metal, while the latter electrolyte shows stability against lithium metal.
2024
Solid-state batteries have garnered attention due to their potentiality for increasing energy density and enhanced safety. One of the most promising solid electrolytes is garnet-type Li7La3Zr2O12 (LLZO) ceramic electrolyte because of its high conductivity and ease of manufacture in ambient air. The complex gas-liquid-solid sintering mechanism makes it difficult to prepare LLZO with excellent performance and high consistency. In this study, an in-situ Li2O-atmosphere assisted solvent-free route is developed for producing the LLZO ceramics. First, the lithium-rich additive Li6Zr2O7 (LiZO) is applied to in-situ supply Li2O atmosphere at grain boundaries, where its decomposition products (Li2ZrO3) build the bridge between the grain boundaries. Second, comparisons were studied between the effects of dry and wet routes on the crystallinity, surface contamination, and particle size of calcined powders and sintered ceramics. Third, by analyzing the grain boundary composition and the evolution of ceramic microstructure, the impacts of dry and wet routes and lithium-rich additive LiZO on the ceramic sintering process were studied in detail to elucidate the sintering behavior and mechanism. Lastly, exemplary Nb-doped LLZO pellets with 2 wt% LiZO additives sintered at 1,300 °C × 1 min deliver Li+ conductivities of 8.39 × 10-4 S cm-1 at 25 °C, relative densities of 96.8%, and ultra-high consistency. It is believed that our route sheds light on preparing high-performance LLZO ceramics for solid-state batteries.
Chemistry of Materials, 2016
Several "Beyond Li-Ion Battery" concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li 7 La 3 Zr 2 O 12 (LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet (Ia3̅ d, No. 230) to "non-garnet" (I4̅ 3d, No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10 −4 S cm −1 to 1.2 × 10 −3 S cm −1 , which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm 2 , the lowest reported value for LLZO so far. These results illustrate that understanding the structure−properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.
Li1.2Zr1.9Ca0.1(PO4)3, a room-temperature Li-ion solid electrolyte
Journal of Power Sources, 2011
Li-ion solid electrolyte Lithium zirconium phosphate Li-ion battery a b s t r a c t Substitution of 5% of Zr by Ca in LiZr 2 (PO 4 ) 3 transforms the structure to that of rhombohedral NASICON to give a room-temperature bulk Li-ion conductivity Li ≈ 1.2 × 10 −4 S cm −1 , which is comparable to that of Li 1.3 Ti 1.7 Al 0.3 (PO 4 ) 3 now being used as a solid Li-ion separator in test cells of novel Li-ion batteries.
ACS Applied Materials & Interfaces
is a promising solid electrolyte for next-generation solid-state Li batteries. However, sufficiently fast Li-ion mobility required for battery applications only emerges at high temperatures, upon a phase transition to cubic structure. A well-known strategy to stabilize the cubic phase at room temperature relies on aliovalent substitution; in particular, the substitution of Li + by Al 3+ and Ga 3+ ions. Yet, despite having the same formal charge, Ga 3+ substitution yields higher conductivities (10 −3 S/cm) than Al 3+ (10 −4 S/cm). The reason of such difference in ionic conductivity remains a mystery. Here we use molecular dynamic simulations and advanced sampling techniques to precisely unveil the atomistic origin of this phenomenon. Our results show that Li + vacancies generated by Al 3+ and Ga 3+ substitution remain adjacent to Ga 3+ and Al 3+ ions, without contributing to the promotion of Li + mobility. However, while Ga 3+ ions tend to allow limited Li + diffusion within their immediate surroundings, the less repulsive interactions associated with Al 3+ ions lead to a complete blockage of neighboring Li + diffusion paths. This effect is magnified at lower temperatures, and explains the higher conductivities observed for Ga-substituted systems. Overall this study provides a valuable insight into the fundamental ion transport mechanism in the bulk of Ga/Al-substituted Li 7 La 3 Zr 2 O 12 and paves the way for rationalizing aliovalent substitution design strategies for enhancing ionic transport in these materials.
Electrochemical Window of the Li-Ion Solid Electrolyte Li7La3Zr2O12
ACS Energy Letters, 2017
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.
Acta Materialia
is a promising solid electrolyte candidate for solidstate Li-ion batteries, but at room temperature it crystallizes in a poorly Li-ion conductive tetragonal phase. To this end, partial substitution of Li + by Al 3+ ions is an effective way to stabilize the highly conductive cubic phase at room temperature. Yet, fundamental aspects regarding this aliovalent substitution remain poorly understood. In this work, we use molecular dynamics and advanced hybrid Monte Carlo methods for systematic study of the room temperature Li-ion diffusion in tetragonal and cubic LLZO to shed light on important open questions. We find that Al substitution in tetrahedral sites of the tetragonal LLZO allows previously inaccessible sites to become available, which enhances Li-ion conductivity. In contrast, in the cubic phase Li-ion diffusion paths become blocked in the vicinity of Al ions, resulting in a decrease of Li-ion conductivity. Moreover, combining the conductivities of individual phases through an effective medium approximation allowed us to estimate the conductivities of cubic/tetragonal phase mixtures that are in good agreement with those reported in several experimental works. This suggests that phase coexistence (due to phase equilibrium or gradients in Al content within a sample) could have a significant impact on the conductivity of Al-substituted LLZO, particularly at low contents of Al 3+. Overall, by making a thorough comparison with reported experimental data, the theoretical study and simulations of this work advance our current understanding of Li-ion mobility in Al-substituted LLZO garnets and might guide future in-depth characterization experiments of this relevant energy storage material.