锂含量与烧结时间对固体电解质Li7La3Zr2O12电导率的影响

具有石榴石结构的固体电解质Li7La3Zr2O12在室温下即可呈现出较高的离子电导率。采用固相反应法,通过在原料中调控不同的锂源含量,以及经历不同的烧结时间,探索了上述制备工艺条件对样品室温离子电导率的影响规律。结果表明：采用不同的锂含量均可获得立方石榴石结构;当混合原料中的锂源采用–3%Li含量时,可以获得最高电导率(2.11×10–4 S/cm);对于不含锂过量的原料,当烧结时间为30 h时,可以获得最高电导率2.03×10–4 S/cm。这些结果表明Li7La3Zr2O12在全固态锂离子电池中具有广阔的应用前景。     

Microstructure and Li‐Ion Conductivity of Hot‐Pressed Cubic Li7La3Zr2O12

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.     

Effect of Sintering Additives on Relative Density and Li‐ion Conductivity of Nb‐Doped Li7La3ZrO12 Solid Electrolyte

Lithium ion conductors with garnet‐type structure are promising candidates for applications in all solid‐state lithium ion batteries, because these materials present a high chemical stability against Li metal and a rather high Li⁺ conductivity (10^?3–10^?4 S/cm). Producing densified Li‐ion conductors by lowering sintering temperature is an important issue, which can achieve high Li conductivity in garnet oxide by preventing the evaporation of lithium and a good Li‐ion conduction in grain boundary between garnet oxides. In this study, we concentrate on the use of sintering additives to enhance densification and microstructure of Li₇La₃ZrNbO₁₂ at sintering temperature of 900°C. Glasses in the LiO₂‐B₂O₃‐SiO₂‐CaO‐Al₂O₃ (LBSCA) and BaO‐B₂O₃‐SiO₂‐CaO‐Al₂O₃ (BBSCA) system with low softening temperature (<700°C) were used to modify the grain‐boundary resistance during sintering process. Lithium compounds with low melting point (<850°C) such as LiF, Li₂CO₃, and LiOH were also studied to improve the rearrangement of grains during the initial and middle stages of sintering. Among these sintering additives, LBSCA and BBSCA were proved to be better sintering additives at reducing the porosity of the pellets and improving connectivity between the grains. Glass additives produced relative densities of 85–92%, whereas those of lithium compounds were 62–77%. Li₇La₃ZrNbO₁₂ sintered with 4 wt% of LBSCA at 900°C for 10 h achieved a rather high relative density of 85% and total Li‐ion conductivity of 0.8 × 10^?4 S/cm at room temperature (30°C).     

LiOH对Ta掺杂石榴石型Li7La3Zr2O12固体电解质的影响

通过固相法制备Ta掺杂Li₇La₃Zr₂O₁₂（Ta-LLZO）陶瓷,以LiOH为锂源合成Ta-LLZO粉末,并以LiOH为助烧剂制备Ta-LLZO陶瓷,研究了LiOH对Ta-LLZO陶瓷的组织结构和离子电导率的影响。结果表明：以LiOH为锂源可促进立方相Ta-LLZO的生成。同时,以LiOH为助烧剂,可有效促进陶瓷的致密化,在1 200℃烧结5 h可获得致密的立方相Ta-LLZO陶瓷。当助烧剂的添加量为6%（质量分数）时,陶瓷的离子电导率可达6.23×10^-4 S?cm^-1。可见,固相法制备的Li₇La₃Zr₂O₁₂在全固态锂离子电池中具有广阔的应用前景。     

Rapid low‐temperature synthesis of tetragonal single‐phase Li7La3Zr2O12

The formation of Li₇La₃Zr₂O₁₂ (LLZ), a Li ion conducting oxide with a garnet‐type crystal structure, from a powder mixture of Li₂CO₃, La(OH)₃, and ZrO₂ was investigated, and two possible reaction pathways were identified. Based on the obtained results, LLZ was synthesized at low temperatures and short reaction times, using Li₂CO₃, La(OH)₃, and La₂Zr₂O₇ (instead of ZrO₂) as starting materials. According to the proposed method, single‐phase LLZ was obtained by heating the initial mixture to 800°C for 1 hour in air, which eliminated possible Li losses. The produced LLZ species exhibited a tetragonal crystal structure with the lattice parameters a=1.3189(3) nm and c=1.2694(1) nm, while their transmission electron microscopy images confirmed that LLZ formation occurred through the dissolution of La₂Zr₂O₇ and La(OH)₃ in a Li₂CO₃ melt followed by LLZ precipitation from solution.     

The Effect of Relative Density on the Mechanical Properties of Hot‐Pressed Cubic Li7La3Zr2O12

The effect of relative density on the hardness and fracture toughness of Al‐substituted cubic garnet Li_6.19Al_0.27La₃Zr₂O₁₂ (LLZO) was investigated. Polycrystalline LLZO was made using solid‐state synthesis and hot‐pressing. The relative density was controlled by varying the densification time at fixed temperature (1050°C) and pressure (62 MPa). After hot‐pressing, the average grain size varied from approximately 2.7–3.7 μm for the 85% and 98% relative density samples, respectively. Examination of fracture surfaces revealed a transition from inter‐ to intragranular fracture as the relative density increased. The Vickers hardness increased with relative density up to 96%, above which the hardness was constant. At 98% relative density, the Vickers hardness was equal to the hardness measured by nanoindentation 9.1 GPa, which is estimated as the single‐crystal hardness value. An inverse correlation between relative density and fracture toughness was observed. The fracture toughness increased linearly from 0.97 to 2.37 MPa√m for the 98% and 85% relative density samples, respectively. It is suggested that crack deflection along grain boundaries can explain the increase in fracture toughness with decreasing relative density. It was also observed that the total ionic conductivity increased from 0.0094 to 0.34 mS/cm for the 85%–98% relative density samples, respectively. The results of this study suggest that the microstructure of LLZO must be optimized to maximize mechanical integrity and ionic conductivity.     

Synthesis of Ga-doped Li7La3Zr2O12 solid electrolyte with high Li+ ion conductivity

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) Li⁺ ion solid electrolyte is a promising candidate for next generation high-safety solid-state batteries. Ga-doped LLZO exhibits excellent Li⁺ ion conductivity, higher than 1 × 10^?3 S cm^?1. In this research, the doping amount of Ga, the calcination temperature of Ga-LLZO primary powders, the sintering conditions and the evolution of grains are explored to demonstrate the optimum parameters to obtain a highly conductive ceramics reproducibly via conventional solid-state reaction methods under ambient air sintering atmosphere. Cubic LLZO phase is obtained for Li_6.4Ga_0.2La₃Zr₂O₁₂ powder calcined at low temperature 850 °C. In addition, ceramic pellets sintered at 1100 °C for 320 min using this powder have relative densities higher than 94% and conductivities higher than 1.2 × 10^?3 S cm^?1 at 25 °C.     

Conductivity enhancement of Al- and Ta-substituted Li7La3Zr2O7 solid electrolytes by nanoparticles

A nanopowder consisting of La₂Zr₂O₇ particles with lithium containing species on their surface was prepared by spray flame synthesis and subsequently added to Li₇La₃Zr₂O₁₂ powder obtained by a conventional solid-state reaction. The spray flame synthesis method utilized in this work yields nanoparticles with a small size of approximately 5 nm, which is unprecedented within the scope of oxide-based ionic conductors for solid-state batteries. Remarkably, the addition of nanoparticles for sintering at a relatively low temperature of 1000 °C significantly improved the ionic conductivity by 50 %. In contrast, there was no influence of incorporating nanoparticles on the conductivity at sintering temperatures at or above 1100 °C, which is the typical temperature range applied for conventional sintering of Li₇La₃Zr₂O₁₂. Compared to prior published work with analogous materials, a more than twofold improvement in conductivity was demonstrated while the sintering temperature was decreased by 100 °C.     

Phase transformation and grain-boundary segregation in Al-Doped Li7La3Zr2O12 ceramics

Cubic phase garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid electrolyte for highly safe Li-ion batteries. Al-doped LLZO (Al-LLZO) has been widely studied due to the low cost of Al₂O₃. The reported ionic conductivities were variable due to the complicated Al³⁺-Li⁺ substitution and Li_xAlO_y segregation in Al-LLZO ceramics. This work prepared Li_7?3xAl_xLa₃Zr₂O₁₂ (x = 0.00~0.40) ceramics via a conventional solid-state reaction method. The AC impedance and corresponding distribution of relaxation times (DRT) were analyzed combined with phase transformation, cross-sectional microstructure evolution, and grain boundary element mapping results for these Al-LLZO ceramics to understand the various ionic transportation levels in LLZO with different Al-doping amounts. The low conductivity in low Al-doped (0.12~0.28) LLZO originates from the slow Li⁺ ion migration (1.4~0.25 μs) in the cubic-tetragonal mixed phase. On the other hand, LiAlO₂ and LaAlO₃ segregation occur at the grain boundaries of high Al-doped (0.40) LLZO, resulting in a gradual Li⁺ ion jump (6.5 μs) over grain boundaries and low ionic conductivity. The Li_6.04Al_0.32La₃Zr₂O₁₂ ceramic delivers the optimum Li⁺ ion conductivity of 1.7 × 10^?4 S cm^?1 at 25 °C.     

湿化学法制备石榴石型固态电解质Li7La3Zr2O12

锂电池因能量密度高、循环寿命长、绿色清洁等特点被广泛应用,但其液态电解质易泄漏、挥发,且隔膜易被锂枝晶刺穿造成短路,引发危险。固态电解质大多是不具燃烧性的无机材料,室温下离子电导率较高、电化学窗口宽且适用温度范围广。因此,采用固态电解质替代液态电解质具有十分重要的意义。相对于其他类型固态电解质,石榴石型氧化物Li₇La₃Zr₂O₁₂（LLZO）具有离子电导率高、电化学窗口宽（>5V vs. Li/Li⁺）、对锂稳定性好和热稳定性高等特点,是非常具有发展潜力的无机固态电解质。本文采用溶胶-凝胶法和低温燃烧法两种湿化学法合成LLZO粉末,对应的电解质片在40℃时的离子电导率分别为1.22×10^-5S/cm和3.87×10^-6S/cm,活化能分别为0.34eV和0.32eV。从实验结果综合比较,溶胶-凝胶法为最佳制备方法。     

Crystal structure and lithium ionic transport behavior of Li site doped Li7La3Zr2O12

Doping some elements on Li site of LLZO is an effective method to stabilize it as cubic phase and improve Li⁺ conductivity. The reported possible Li site elements calculated by first principle are Be, B, Al, Fe, Zn, Ga and the Ga-doped LLZO shows the a higher conductivity than other LLZO. However, whether these elements all can stable LLZO as cubic phase are needed to be verified and the reason of Ga exhibits higher conductivity is not clear enough. In this work, all these elements are tried to be doped on Li site and the results show that the Al, or Fe, or Ga can stable LLZO as cubic phase while the others does not. The Ga-doped LLZO exhibits the highest conductivity of 1.31×10⁻³ S•cm^-1 due to the transform of group space from Ia-3d to I-43d, shorter distances between different Li⁺, and Ga can improve the grain size.     

石榴石型固态电解质Li7La3Zr2O12的改性研究现状

固态电解质是高安全性、高能量密度的全固态锂电池的核心部件,其典型代表Li₇La₃Zr₂O₁₂(LLZO)具有高离子电导率、高机械强度、高电化学稳定性、低界面阻抗以及对锂金属负极良好的稳定性等优势,是科研人员重点关注的对象之一,但与液态电解质相比,目前LLZO仍存在低离子电导率和与电极固-固界面接触等问题。本文主要简介了LLZO的晶体结构、改性方式等对其离子电导率及界面阻抗的影响,同时对LLZO现存的问题进行了总结,对LLZO的未来发展方向进行了展望,为探索全固态锂电池的实际生产应用提供理论指导。     

Li7La3Zr2O12 solid electrolyte sintered by the ultrafast high-temperature method

All-solid-state Li batteries (ASSLBs) are regarded as the systems of choice for future electrochemical energy storage. Particularly, the garnet Li₇La₃Zr₂O₁₂ (LLZO) is one of the most promising solid electrolytes due to its stability against Li metal. However, its integration into ASSLBs is challenging due to high temperature and long dwell time required for sintering. Advanced sintering techniques, such as Ultrafast High-temperature Sintering, have shown to significantly increase the sintering rate. Direct contact to graphite heaters allows sintering of LLZO within 10 s due to extremely high heating rates (up to 10⁴ K min^?1) and temperatures up to 1500 °C to a density around 80 %. The LLZO sintered in vacuum and Ar atmosphere has good mechanical stability and high phase purity, but kinetic de-mixing at the grain boundaries was observed. Nevertheless, the Li-ion conductivity of 1 mS cm^?1 at 80 °C was comparable to conventional sintering, but lower than for Field-Assisted Sintering Technique/Spark Plasma Sintering.     

固态无机电解质Li7La3Zr2O12的改性研究进展

作为一种固态无机电解质材料,石榴石型立方相Li₇La₃Zr₂O₁₂具有较高的室温锂离子电导率、较宽的电化学窗口和优良的热稳定性等特点,是高安全性、高能量密度固态锂离子电池实现商业化应用的关键。阐述了Li₇La₃Zr₂O₁₂的晶体结构与锂传导机理,综述了元素掺杂、聚合物电解质复合、烧结助剂引入、表面包覆或修饰等方式对Li₇La₃Zr₂O₁₂的物相结构稳定性、界面阻抗与相容性、烧结活性、离子电导率等进行改性的最新研究进展。最后,针对Li₇La₃Zr₂O₁₂在产业化应用中所面临的障碍与挑战,提出了制备新工艺的开发、离子电导率的多重改性以及柔性复合电解质膜的结构设计与优化等应对策略,为推动高性能固态锂离子电池的发展提供依据。     

High Li-ion conductivity of Al-doped Li7La3Zr2O12 synthesized by solid-state reaction

Li₇La₃Zr₂O₁₂ (LLZO) has cubic garnet type structure and is a promising solid electrolyte for next-generation Li-ion batteries. In this work, Al-doped LLZO was prepared via conventional solid-state reaction. The effects of sintering temperature and Al doping content on the structure and Li-ion conductivity of LLZO were investigated. The phase composition of the products was confirmed to be cubic LLZO via XRD. The morphology and chemical composition of calcined powders were investigated with SEM, EDS, and TEM. The Li-ion conductivity was measured by AC impedance. The results indicated the optimum sintering temperature range is 800–950 °C, the appropriate molar ratio of LiOH·H₂O, La(OH)₃, ZrO₂ and Al₂O₃ is 7.7:3:2:(0.2–0.4), and the Li-ion conductivity of LLZO sintered at 900 °C with 0.3 mol of Al-doped was 2.11×10⁻⁴ S cm⁻¹ at 25 °C.     

Ta、Ba共掺杂石榴石型Li7La3Zr2O12电解质的制备及性能研究

传统锂离子电池采用有机电解液体系,能量密度难以进一步提升,同时存在一定的安全隐患。采用无机固体电解质构建全固态锂电池,在提高电池能量密度同时可兼顾安全性问题。在众多无机固体电解质中,Li₇La₃Zr₂O₁₂(LLZO)石榴石电解质具有离子电导率高、与金属锂接触稳定等优势,成为受人关注的材料。为了进一步提高该材料的导电性,采用固相法合成Ta、Ba共掺杂LLZO(Li_7-x+yLa_3-yBa_yZr_2-xTa_xO₁₂)电解质,采用X射线衍射、扫描电子显微镜和电化学阻抗法分析样品的物相结构、微观形貌及离子电导率。结果表明,Ta⁵⁺掺杂能够稳定立方相结构,Ba²⁺作为掺杂剂和烧结剂,促进晶粒生长和陶瓷致密化,从而降低总电阻。其中,Li_6.45La_2.95Ba_0.05Zr_1.4Ta_0.6O₁₂样品在室温下的总电导率为1.07×10^-3 S·cm^-1,活化能为0.378 eV。Ta⁵⁺/Ba²⁺共掺杂有利于制备高致密度和高电导率的石榴石型电解质材料。     

Rapid synthesis of garnet-type Li7La3Zr2O12 solid electrolyte with superior electrochemical performance

Li₇La₃Zr₂O₁₂-based garnet-type solid electrolytes are promising candidates for use in all-solid-state lithium batteries (ASSLBs). However, their potential in large-scale commercial applications is largely hindered by the time/energy-consuming and lithium-wasting synthetic method which typically needs a long-duration high temperature solid state reaction process. Herein we invent a fast preparation route that involves a short-period thermal reaction (1100 °C for 10 min) in laboratory muffle furnaces following by conventional hot pressing technique to get almost fully dense (Al, Ga, Ta, Nb)-doped garnet-type electrolytes with high phase purity (>99.9 %). The large and compact grains, low porosity and high phase purities of garnet ceramic electrolytes synthesized in this study ensure superior electrochemical performance. Particularly, Ga-doped cubic Li₇La₃Zr₂O₁₂ shows extremely low E_a values (0.17?0.18 eV) and record-high lithium ionic conductivities (>2 × 10^?3 S cm^-1 at 25 °C).     

Effect of Li2O excess in Li6.4Ga0.2La3Zr2O12 electrolyte for all-solid-state Li-ion batteries

Li₇La₃Zr₂O₁₂ is a promising material used as solid electrolyte in all-solid-state lithium batteries. However, the lithium ionic conductivity of LLZO is limited, and the cycling stability of lithium symmetric battery based on LLZO is not good. In this research, different Ga-doped LLZO samples were prepared by adding different excess amounts of Li₂O, and the effect of excess amount of Li₂O on the structure and performance of LLZO have been researched. The results show that with the rise of the amount of Li₂O, the lithium ionic concentration increases gradually, and the lithium ionic conductivity and the ratio of grain resistance to total resistance rise first and then drop. When the excess amount of Li₂O is 10 wt.%, the sample exhibits the highest lithium ionic conductivity of 1.36 mS/cm, and the lithium symmetric battery exhibits the most stable operation.     

Effect of Gd Content on Luminescence Properties of Eu3+‐Doped La2−xGdxZr2O7 Transparent Ceramics

3 at.% Eu³⁺‐doped La_2?xGd_xZr₂O₇ (x = 0–2.0) transparent ceramics were fabricated by vacuum sintering. The effect of Gd content on crystal structure, in‐line transmittance, and luminescence property of the ceramics were investigated. The ceramics are all cubic pyrochlore structure with high transparency. The cut‐off edge of the transmittance curve of the ceramics varied with Gd content and was also affected by the annealing process. The luminescence intensity became stronger for the ceramics annealed in air. As Gd content increased, the energy band structure as well as the luminescence behavior of the ceramics was changed; in addition, the symmetry of the crystal lattice reduced, resulting in the shift of the strongest luminescence peak from 585 nm to around 630 nm.     

Preparation of Li6Zr2O7 Nanofibers with High Li‐Ion Conductivity by Electrospinning

Li₆Zr₂O₇ nanofibers were synthesized by a simple electrospinning technique. The thermal decomposition behavior, crystal structure, micromorphology, and electrical conductivity of the as‐prepared Li₆Zr₂O₇ nanofibers were characterized. The results show that Li₆Zr₂O₇ nanofibers were of pure phase after calcined at 750°C for 1 h. In addition, the as‐prepared Li₆Zr₂O₇ nanofibers reveal high conductivity in the measured temperature region, which can be attributed to the huge surface and nanosize effect of the nanofiber electrolyte. Moreover, we provide a general method to improve the conductivity of Li‐ion solid electrolyte.