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。     

Influence of sintering atmosphere on the phase,microstructure, and lithium-ion conductivity of the Al-doped Li7La3Zr2O12 solid electrolyte

Al-doped Li₇La₃Zr₂O₁₂ (Al–LLZO) solid electrolytes were sintered at 1150 ^°C for 8 h in atmosphere of oxygen, argon and air (named as Al–LLZO–O₂, Al–LLZO–Ar and Al–LLZO–Air, respectively). All the Al–LLZO samples exhibited a single cubic garnet-type structure. The sample of Al–LLZO–O₂ possessed the highest relative density (95.60%) and the largest average grain size among the three Al–LLZO samples. Furthermore, owing to its high relative density and small number of grain boundaries, Al–LLZO–O₂ demonstrated a higher lithium-ion conductivity than Al–LLZO–Ar and Al–LLZO–Air.     

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.     

Improving the Li-ion conductivity and air stability of cubic Li7La3Zr2O12 by the co-doping of Nb,Y on the Zr site

The elements Nb and Y were simultaneously substituted to the Zr sites of an Li₇La₃Zr₂O₁₂ (LLZO) electrolyte to improve its Li-ion conductivity and air stability. Samples of Li₇La₃Zr_2-2xNb_xY_xO₁₂ were fabricated using a solid-state reaction method. The results show that the introduction of Nb and Y can stabilise cubic-phase LLZO. The total conductivity of Li₇La₃ZrNb_0.5Y_0.5O₁₂ electrolyte can reach 8.29 × 10^?4 S cm^?1 at 30 °C when sintered at 1230 °C for only 15 h. Surprisingly, the conductivity of Li₇La₃ZrNb_0.5Y_0.5O₁₂ can be maintained at 6.91 × 10^?4 S cm^?1 after exposure to air for 1.5 months, indicating excellent air stability. Furthermore, a LiFePO₄/Li₇La₃ZrNb_0.5Y_0.5O₁₂/Li cell displayed stable charge/discharge and cycling performance at ambient temperature, suggesting there is potential to use Li₇La₃ZrNb_0.5Y_0.5O₁₂ electrolyte in Li-ion batteries. Additionally, the effects of varying the co-doping amount and dwelling time on the Li-ion conductivity of Li₇La₃Zr_2-2xNb_xY_xO₁₂ were investigated.     

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.     

Enhanced Li-ion conductivity of strontium doped Li-excess garnet-type Li7+xLa3-xSrxZr2O12

The mechanism underlying the enhancement of the conductivity of Li₇La₃Zr₂O₁₂ (LLZO), an oxide-based solid electrolyte that contains excess Li, was experimentally investigated through subvalent cation substitution. We prepared Sr-substituted Li-rich LLZO with high conductivity of the order of 10⁻⁴ S/cm by using a solid-state method. We investigated the mechanism underlying the conductivity enhancement via detailed structural analysis through Sr K-edge X-ray absorption near edge spectroscopy and X-ray diffraction and neutron powder diffraction analyses. The results suggested that the conductivity enhancement is due to the change in Li⁺ arrangement caused by the incorporation of excess Li into the LLZO lattice.     

Electrical conductivity of Al-doped Li2ZrO3 ceramics for Li-ion conductor electrolytes

All-solid-state Li-ion batteries (LIBs) have recently attracted widespread attention for their high energy density and safety. Some research have conducted on the Li₂ZrO₃-based Li-ion conductor electrolytes, while there is little work on the conductivity below 100 °C, although it is very important for LIBs work around room temperature. Here, monoclinic Li₂ZrO₃-based ceramics are prepared via a wet chemistry method, and the conductivities of Li₂ZrO₃ ceramics are tuned by defect engineering of Al³⁺ ions introduction. The conductivity of Al-doped Li₂ZrO₃ reaches up to 3.06 × 10^-4 S cm^-1 at 25 °C, the related activation energy of conduction is less than 0.1 eV. Simulation calculation using bond valence site energy reveals that there is a two-dimensional Li-ion migration network in the crystal structure of Li₂ZrO₃.     

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.     

Effects of B2O3 on microstructure and ionic conductivity of Li6.5La3Zr1.5Nb0.5O12 solid electrolyte

Li_6.5La₃Zr_1.5Nb_0.5O₁₂ (LLZN) garnet-type structure was synthesized at low temperature with B₂O₃ addition by solid state reaction method. The effects of B₂O₃ content on the formation, microstructure, ionic conductivity and activation energy of the LLZN solid electrolytes have been investigated by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and alternate current (AC) impedance spectroscopy. The cubic LLZN phase was obtained after calcining at 850 °C for 6 h and no phase evolution was observed after sintering at 1100 °C for 6 h. The relative density and lithium ion conductivity increased first and then decreased with increasing B₂O₃ content, reaching the maximum value of 92.4% and 1.86×10⁻⁴ S cm⁻¹ respectively in the sample with 1.4 wt% B₂O₃. By contrast, the activation energy reached a minimum value of ~31.5 kJ mol⁻¹.     

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。     

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。     

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).     

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。     

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.     

Influence of sintering aids and excess Lithium on the conductivity of perovskite-type Li3/8Sr7/16Zr1/4Nb3/4O3 solid electrolyte

Perovskite-structured Li_3/8Sr_7/16Zr_1/4Nb_3/4O₃ solid-state Lithium-conductors were prepared by conventional solid-state reaction method. Influence of sintering aids (Al₂O₃, B₂O₃) and excess Lithium on structure and electrical properties of Li_3/8Sr_7/16Zr_1/4Nb_3/4O₃ (LSNZ) has been investigated. Their crystal structure and microstructure were characterized by X-ray diffraction analysis and scanning electron microscope, respectively. The conductivity and electronic conductivity were evaluated by AC-impedance spectra and potentiostatic polarization experiment. All sintered compounds are cubic perovskite structure. Optimal amount of excess Li₂CO₃ was chosen as 20 wt% because of the total conductivity of LSNZ-20% was as high as 1.6×10⁻⁵ S cm⁻¹ at 30 °C and 1.1×10⁻⁴ S cm⁻¹ at 100 °C, respectively. Electronic conductivity of LSNZ-20% is 2.93×10⁻⁸ S cm⁻¹, nearly 3 orders of magnitude lower than ionic conductivity. The density of solid electrolytes appears to be increased by the addition of sintering aids. The addition of B₂O₃ leads to a considerable increase of the total conductivity and the enhancement of conductivity is attributed to the decrease of grain-boundary resistance. Among these compounds, LSNZ-1 wt%B₂O₃ has lower activation energy of 0.34 eV and the highest conductivity of 1.98×10⁻⁵ S cm⁻¹ at 30 °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.     

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.     

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。     

Crystal structure of cubic Li7-3xGaxLa3Zr2O12 with space group of I-43d

Cubic Li_7-3xGa_xLa₃Zr₂O₁₂ is a cubic phase with a space group of I-43d instead of Ia-3d. This structure is more conducive to the migration of lithium ions. However, the effect of Ga on the size and environment of lithium ion transport channels has not been researched. In this work, Li_7-3xGa_xLa₃Zr₂O₁₂ (x = 0–0.25) was formulated, and the crystal structure was obtained by neutron diffraction. The results indicated that the minimum channel size to control Li⁺ migration in LLZO was the bottleneck size between the Li2 and Li3 sites (bottleneck size 2), and compared with lanthanum ions, the zirconium ions were closer to lithium ions. As the Ga content increased, bottleneck size 2 levelled off, while the lithium concentration and the distance between skeleton ions and lithium ions decreased. As a result, the lithium ionic conductivity primarily increased and then decreased. When doping 0.2 pfu of Ga, LLZO exhibited the highest lithium ionic conductivity of 1.45 mS/cm at 25 °C due to the coordinated regulation of Li⁺ concentration, bottleneck size, and the distance between skeleton ions and lithium ions.