冷烧结工艺制备石榴石固态电解质及其性能

以LiNO_3、Al(NO_3)_3·9H_2O、La(NO_3)3·6H_2O、Zr O(NO_3)_2·5H_2O为原料,采用溶胶-凝胶法制备了Li_(5.95)Al_(0.35)La_3Zr_2O_(12)粉体,随后加入聚乙烯醇(PVA)水溶液作为液相介质,通过冷烧结工艺制备了Li_(5.95)Al_(0.35)La_3Zr_2O_(12)石榴石固态电解质。冷烧结工艺后采用后续热处理改善离子传导性能。采用质量体积法和电化学阻抗谱对Li_(5.95)Al_(0.35)La_3Zr_2O_(12)石榴石固态电解质的体积密度和离子电导率进行了测试,采用XRD与SEM进行晶体结构与形貌表征。结果表明,冷烧结时间和压力对样品的晶体结构几乎没有影响。冷烧结时间过长会导致样品开裂,在15～30min时,冷烧结时间对样品的体积密度和离子电导率影响不大,在烧结时间较短的样品中发现了杂相。提高冷烧结压力可明显提高样品的体积密度和离子电导率,在200℃、510 MPa、30 min的冷烧结条件下可以获得具有较高离子电导率(2.66×10~(–6)S/cm)的Li_(5.95)Al_(0.35)La_3Zr_2O_(12)石榴石固态电解质,其晶界电阻较小。但继续增加冷烧结压力,导致热处理过程中第二相的分解和晶粒生长受到抑制,样品的体积密度和离子电导率反而下降。     

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。     

石榴石型固体电解质体系：离子输运性能调控及其全固态电池研究进展

全固态锂电池采用固体电解质取代液态电解质，使其具有更高安全性，且有望进 一步提高电池的能量密度。而在众多固体电解质中，具有石榴石型结构的立方相 Li7La3Zr2O12 (LLZO) 及其元素掺杂产物由于室温离子电导率较高、电化学窗口较宽、与锂金属稳定等优点， 最有可能应用于全固态锂电池中。本文对 LLZO 的物相及晶体结构、制备方法、锂离子电导率 的提升策略以及其所组装的全固态锂电池等方面进行了详细介绍，并预测了 LLZO 固体电解质 材料进一步提升锂离子电导率的潜在可能以及 LLZO 所装配的全固态锂电池的发展方向。     

Al稳定立方相Li_7La_3Zr_2O_(12)固态电解质的场助烧结制备

石榴石型结构的固态电解质Li_7La_3Zr-2O_(12)(LLZO)因其良好的力学性能、化学稳定性、高离子电导率等特点有着广阔的应用前景。Li_7La_3Zr-2O_(12)(LLZO)具有四方相和立方相两相,其中立方相比四方相有更高的离子电导率(~10~(-3) S/cm)。本文利用场助烧结的制备方法,通过在Li_7La_3Zr-2O_(12)(LLZO)体系中掺杂Al~(3+)来稳定立方相的生成,制备了高离子电导、高致密的立方相Li_7La_3Zr-2O_(12)(LLZO)电解质,探究了Al~(3+)在立方相LLZO中的存在形式。实验采用FESEM、XRD、NMR和交流阻抗等方法研究了固体电解质的表面形貌、物相、Al~(3+)的存在形式及离子电导率。实验结果表明,在1150℃烧结温度下,Al2O3含量为1.5wt.%时,LLZO在室温下具有最高的离子电导率5.7×10~(-4) S/cm,Al位于LLZO晶粒中取代四面体中的Li,且相对密度约为99.8%。     

溶胶-凝胶法制备NASICON型Li_(1.15)Y_(0.15)Zr_(1.85)(PO_4)_3固态电解质

以碳酸锂、硝酸锆、磷酸氢二铵和硝酸钇为原料,柠檬酸为络合剂,采用溶胶–凝胶法制备了NASICON型Li1.15Y0.15Zr1.85(PO4)3固态电解质材料,通过无压烧结和放电等离子烧结(SPS)得到固态电解质片。结果表明:采用无压烧结在1 150℃制备的电解质密度可以达到理论密度的95.2%,在室温下晶粒电导率和总电导率分别为2.19×10–4 S/cm和0.86×10–4 S/cm;采用SPS在1 150℃烧结得到的电解质片密度可达到理论密度的96.8%,在室温下样品总电导为0.97×10–4S/cm,激活能为0.44 e V。四方相Zr O2的存在是样品激活能升高的主要原因。     

Li3PO4助熔剂添加对Li1.3Al0.3Ti1.7(PO4)3性质的影响研究

采用溶胶-凝胶法合成Li1.3Al0.3Ti1.7(PO4)3粉末,向Li1.3Al0.3Ti1.7(PO4)3粉末中添加不同摩尔分数的Li3PO4助熔剂烧结制备锂离子固体电解质Li1.3Al0.3Ti1.7(PO4)3烧结片。通过X射线衍射仪、扫描电子显微镜研究合成产物的结构与形貌,采用循环伏安及交流阻抗技术研究合成产物的氧化-还原电位、离子电导率和活化能。结果表明,添加与未添加Li3PO4助熔剂的Li1.3Al0.3Ti1.7(PO4)3烧结片具有相似的X射线衍射结果。添加Li3PO4的Li1.3Al0.3Ti1.7(PO4)3烧结片空隙率较小,更为致密。添加Li3PO4对Li1.3Al0.3Ti1.7(PO4)3的氧化-还原电位影响不大。在所有添加Li3PO4助熔剂的Li1.3Al0.3Ti1.7(PO4)3烧结片中,添加摩尔分数1%Li3PO4的烧结片具有最高的离子电导率6.15×10-4S.cm-1和最低的活化能0.314 2 eV。     

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。     

烧结温度对陶瓷体氧化铝固体电解质性能的影响

在Al2O3电解质体系中,利用X射线衍射分析仪、扫描电子显微镜和交流阻抗谱仪考察了烧结温度对陶瓷体Al2O3固体电解质(BASE)的β″/β相的形成、体密度和离子电导率的影响。研究表明:固相法合成BASE时,陶瓷体的最佳的陶瓷烧结温度为1 600℃。离子电导率、β″含量、体积密度随烧结温度的升高先上升后下降。离子电导率不仅与相结构有关,还与材料的致密性有关。导电过程在温度升高过程中,会由晶界控制转变为晶粒控制。随着烧结温度的升高,晶界控制的温度范围逐渐减小。     

添加Li_2O对YSZ电解质性能影响

8%（摩尔分数,下同）Y2O3稳定的ZrO2（8YSZ）是固体氧化物燃料电池（SOFC）中最常用的电解质材料,本文研究了在8YSZ基体中加入n%Li2O（n=0,0.25,0.50,1.00,1.50,1.70,2.00,2.50,3.00）后（记为n%Li2OYSZ）对其晶相结构、晶格常数、烧结性能、微观形貌、电导率及其作为SOFC电解质性能的影响。结果表明,Li2O中的Li＋可以固溶到YSZ的晶格内使其晶格常数减小;Li2O的加入量n〈1.70时,瓷体在烧结过程中不会发生相变。加入少量的Li2O（n=0.25,0.50）可以提高YSZ的致密度和电导率,0.25%Li2OYSZ和0.50%Li2OYSZ样品800℃的电导率分别高达0.030 2 S/cm和0.027 6 S/cm,分别是纯YSZ的1.35和1.24倍;当Li2O含量n≥1.00时,相同条件下烧结体致密度随Li2O加入量的增大而逐渐减小;当n≥1.70时,样品在烧结过程中虽然出现相变,但在高于1400℃可以烧结致密,并得到纯立方相YSZ。将1250℃烧结制得的0.25%Li2OYSZ和0.50%Li2OYSZ作为SOFC电解质的单电池,800℃时的开路电压高于1.0V,说明YSZ中没有出现电子电导,具有比纯YSZ为电解质的单电池更高的性能输出,表现出了良好的应用前景。     

固体电解质Li_(1.3)Al_(0.3)Ti_(1.7)(PO_4)_3烧结片的制备与表征

以固相法合成固体电解质Li1.3Al0.3Ti1.7(PO4)3(LATP)粉末。研究了烧结温度以及烧结时间对LATP离子电导率的影响。采用X射线衍射、扫描电子显微镜和交流阻抗技术对材料粉末以及烧结片相组成、结构和离子导电性进行表征。结果表明,900℃条件下合成的粉末为纯相LATP,颗粒均匀,当LATP电解质基片在900℃下烧结4 h,得到的LATP烧结片表面致密光滑,而且离子电导率较高,为3.03×10-4S/cm。     

Rapid preparation and performances of garnet electrolyte with sintering aids for solid-state Li–S battery

Lithium-sulfur (Li–S) batteries are attractive due to their high theoretical energy density. However, conventional Li–S batteries with liquid electrolytes undergo polysulfide shuttle-effect and lithium dendrite formation during charge/discharge process, leading to poor electrochemical performance and safety issues. Garnet type Li₇La₃Zr₂O₁₂ (LLZO) solid-state electrolyte (SSE) restricts the penetration of polysulfides and exhibits high ionic conductivity at room temperature (RT). Herein, Li_6.5La₃Zr_1.5Nb_0.5O₁₂ (LLZNO) ceramic electrolyte using Li₃PO₄ (LPO) as sintering aids (LLZNO-LPO) is prepared by the rapid sintering method and is applied to construct a shuttle-effect free solid-state Li–S battery. The SSE displays high conductive pure cubic-LLZO phase; during the rapid sintering, LPO melts and junctions the voids between the grains, thus improves Li⁺ conductivity. As a result, the LLZNO-LPO ceramic electrolyte with Li⁺ conductivity of 4.3 × 10^?4 S cm^?1 and high critical current density (CCD) of 1.2 mA cm^?2 is obtained at RT. The Li–S solid-state battery which utilizes LLZNO-LPO ceramic electrolyte can deliver an initial discharge capacity of 943 mA h·g^?1 and 602 mA h·g^?1 retention after 60 cycles. In the same time, the initial coulombic efficiency is as high as 99.5%, indicating that the SSE can effectively block the polysulfide shuttle towards the Li anode and fulfill a shuttle-free Li–S battery.     

Enhanced electrochemical performance of garnet-based solid-state lithium metal battery with modified anodic and cathodic interfaces

Due to high ionic conductivity and wide electrochemical window, the garnet solid electrolyte is considered as the most promising candidate electrolyte for solid-state lithium metal batteries. However, the high contact impedance between metallic lithium and the garnet solid electrolyte surface seriously hampers its further application. In this work, a Li-(ZnO)_x anode is prepared by the reaction of zinc oxide with metallic lithium and in situ coated on the surface of Li_6.8La₃Zr_1.8Ta_0.2O₁₂(LLZTO). The anode can be perfectly bound to the surface of LLZTO solid electrolyte, and the anode/electrolyte interfacial resistance was reduced from 2319 to 33.75 Ω·cm². The Li-(ZnO)_0.15|LLZTO|Li-(ZnO)_0.15 symmetric battery exhibits a stable Li striping/plating process during charge-discharging at a constant current density of 0.1 mA·cm^-2 for 100 h at room temperature. Moreover, a Li-(ZnO)_0.15|LLZTO-SPE|LFP full battery, comprised of a polyethylene oxide-based solid polymer electrolyte (SPE) film as an interlayer between LiFePO₄ (LFP) cathode and LLZTO solid electrolyte, presents an excellent performance at 60 ℃. The discharge capacity of the full battery reaches 140 mA·h·g^-1 at 0.1 C and the capacity attenuation is less than 3% after 50 cycles.     

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.     

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。     

Overcoming the abnormal grain growth in Ga-doped Li7La3Zr2O12 to enhance the electrochemical stability against Li metal

Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte is a promising candidate for next generation batteries. In the LLZO family with various doping elements, Ga-doped LLZO (Ga-LLZO) delivers the highest Li-ion conductivity of higher than 1 × 10⁻³ S cm⁻¹. However, Ga-LLZO ceramics always contain lots of overgrown huge grains after sintering, resulting in short-circuiting as applied with Li anode in batteries. Hence a simple two-step sintering strategy is developed to prepare fine-grained Ga-LLZO ceramics with good electrochemical properties. Pellets with the composition of Li_6.4Ga_0.2La₃Zr₂O₁₂ deliver pure garnet phase, uniform fine grains, high relative density of 97.3% and conductivity of 1.24 × 10⁻³ S cm⁻¹ at 27 °C after sintering at 1150 °C for 1 min and 1000 °C for 3 h. In addition, those fine-grained Ga-LLZO exhibit improved stability against molten Li. The Li/Ga-LLZO/Li symmetric cells show a critical current density of 0.7 mA cm⁻², and a stable cycling of over 600 h at 0.4 mA cm⁻² at 27 °C. The Li/Ga-LLZO/LiFePO₄ full cells deliver reversible capacity of 150 mAh g⁻¹, showing negligible decay after 50 cycles. These results bring the Ga-LLZO electrolytes one step closer to practical application in solid-state batteries.     

混合电解质水溶液固液平衡计算

用Lu-Maurer活度系数模型在不增加任何模型参数的前提下回归出18种晶体的溶度积,在此基础上预测了H~+、Mg~(2+)、K~+、Na~+、NH_4~+、Ca~(2+)、Cl~-、SO_4~(2-)、NO_3~-等离子所组合的13种体系在不同温度(最低温度为273.15 K,最高温度为378.15 K)及最高离子强度为34.55 mol·kg~(-1)下的固液平衡.预测结果较为满意.从而说明了该模型的良好普适性和可靠的温度外推性.可以为工业结晶过程提供相平衡的预测估计.     

Influence of cold sintering process on the structure and properties of garnet-type solid electrolytes

Li-stuffed garnet oxides are one of the most promising solid electrolytes for Li batteries, but their development is impeded by the overly high sintering temperature (above 1000 °C), which causes uncontrollable Li evaporation and poor repeatability of synthesis. The present study evaluates the possibility of addressing this issue using a recently developed technique called cold sintering process (CSP). We demonstrates that CSP can easily realize a high density of 87.7% at an extremely low temperature of 350 °C. However, the material becomes air sensitive after CSP, and the conductivity is degraded. Detailed structural and chemical analyses reveal that such detrimental effects arise from the inter-granular phase induced by the preferential dissolution of Al and Li. Therefore, in order to take full advantage of CSP during solid-electrolyte fabrication, the incongruent dissolution issue must be the focal point of improvement. Our results suggest that CSP is a promising solution to the overly high sintering temperature of garnet electrolytes, and deserves more attention in future studies.     

Effect of sintering and annealing on electrochemical and mechanical characteristics of Na3Zr2Si2PO12 solid electrolyte

NASICON (Sodium superionic conductor) type Na₃Zr₂Si₂PO₁₂ (NZSP) has received a lot of interest as the solid electrolyte for all-solid-state sodium-ion batteries (ASSIBs). The electrolyte has superior interfacial characteristics, high thermal stability, and good ionic conductivity. Because of their higher energy density, improved mechanical stability, no liquid leakage problem, and higher operating voltages, All solid-state batteries are expected to replace liquid electrolyte-based batteries in many applications. The solid electrolyte also acts as a separator, and hence additional separator is not required for cell operations. Because of its 3D open architecture and continuous diffusion channels, NZSP is considered a better solid electrolyte. The NZSP solid electrolyte has been synthesized by spark plasma sintering (SPS) followed by annealing the sintered materials. The SPS method leads the material to have higher density and ionic conductivity. Conventional sintering of the materials requires a temperature as high as 1225°C; however, the temperature required for the SPS is as low as 1050°C. Moreover, conventional sintering yields samples of relative density up to 91%, while SPSed samples have achieved a maximum density of around 98%. The ionic conductivity of solid electrolyte SPSed at 1050°C for 10 min is found to be 3.5 × 10⁻⁴ S/cm with an activation energy of 0.27 eV. The annealing of the SPSed samples improves the ionic conductivity of the SPS1050-20mins sample to roughly double the value obtained from the as-prepared SPS sample because there are fewer secondary phases and a structural change from a rhombohedral to a monoclinic system. To ascertain the samples' crystal structure, particle shape, and ionic conductivity, materials were characterized using X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy. The samples' mechanical characteristics, for example, the hardness and fracture toughness of the samples, were also determined.     

Tailoring solid-state synthesis routes for high confidence production of phase pure,low impedance Al-LLZO

Lithium lanthanum zirconium oxide (LLZO) garnet is a solid-state lithium ion conducting electrolyte promising all-solid-state batteries (ASSB) with high charge rates and good energy density due to its chemical stability against lithium metal anodes. LLZO has a high room temperature Li ion conductivity of ∼0.1–1 mS/cm in its cubic phase, but the stability of the cubic phase and ionic conductivity are highly sensitive to lithium stoichiometry. Stabilizing agents such as aluminum oxide and excess lithium are needed to preserve the cubic phase and compensate for lithium volatility. With the range of the end LLZO products spanning powders, porous membranes to dense membranes combined with sintering/calcination that often exceeds 1000°C, it is challenging to maintain an ideal lithium content given its high volatility from a single base powder. This study was designed to elucidate the sensitivities of aluminum doped LLZO powder synthesis and processing along its path to being utilized in a ceramic-manufacturing optimized ASSB. By utilizing thermogravimetric analysis in conjunction with in situ X-ray diffraction analysis of solid-state LLZO synthesis, it was discovered that the sensitivity of the LLZO cubic phase to lithium volatility can be reduced via early incorporation of excess lithium carbonate during initial phase formation in direct combination with controlled surface-to-volume ratios of the powders. Isostatically pressed powders of our LLZO sintered at 1100°C for 2 h showed RT ionic conductivity of 0.3–0.4 mS/cm measured via electrochemical impedance spectroscopy, and an improvement in microstructural uniformity with lowered porosity. The improved suppression of lithium volatilization has important implications for the scalable production of LLZO powders and assembly of ASSBs.