Microstructure and ionic conductivity of Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte prepared by spark plasma sintering

In this paper, the microstructure and ionic conductivity of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) solid electrolytes prepared by spark plasma sintering (SPS) were investigated by XRD, SEM, TEM and EIS, respectively. The results showed that as the sintering temperature was increased, both the relative density and the ionic conductivity of the sintered LAGP samples first increased and then decreased, achieving a maximum value of 97% and 2.12 × 10⁻⁴ S cm⁻¹ simultaneously at 700 °C. At the same time, the crystallinity of the sintered samples was improved, while a few impurity phases, such as AlPO₄ and GeO₂, appeared in the samples. It was also found that carbon contamination and oxycarbide gas was be brought in during SPS. Carbon contamination could produce an extra grain boundary impedance to the samples and could be removed by annealing at 500 °C in an air atmosphere. Oxycarbide gas could affect the relative density of the sintered LAGP samples and could be mitigated by choosing a suitable SPS process. Moreover, the shear modulus of the sintered LAGP was measured to be 49.6 GPa, which exceeded the minimum value of 8.5 GPa that was necessary to suppress Li dendrite growth.     

Cold sintering process of Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte

The recently developed technique of cold sintering process (CSP) enables densification of ceramics at low temperatures, i.e., <300°C. CSP employs a transient aqueous solvent to enable liquid phase‐assisted densification through mediating the dissolution‐precipitation process under a uniaxial applied pressure. Using CSP in this study, 80% dense Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) electrolytes were obtained at 120°C in 20 minutes. After a 5 minute belt furnace treatment at 650°C, 50°C above the crystallization onset, Li‐ion conductivity was 5.4 × 10^?5 S/cm at 25°C. Another route to high ionic conductivities ~10^?4 S/cm at 25°C is through a composite LAGP ‐ (PVDF‐HFP) co‐sintered system that was soaked in a liquid electrolyte. After soaking 95, 90, 80, 70, and 60 vol% LAGP in 1 M LiPF₆ EC‐DMC (50:50 vol%) at 25°C, Li‐ion conductivities were 1.0 × 10^?4 S/cm at 25°C with 5 to 10 wt% liquid electrolyte. This paper focuses on the microstructural development and impedance contributions within solid electrolytes processed by (i) Crystallization of bulk glasses, (ii) CSP of ceramics, and (iii) CSP of ceramic‐polymer composites. CSP may offer a new route to enable multilayer battery technology by avoiding the detrimental effects of high temperature heat treatments.     

Enhancing purity and ionic conductivity of NASICON-typed Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

Increasing demand for safe energy storage and portable power sources has led to intensive investigation for all-solid state Li-ion batteries and particularly to solid electrolytes for such rechargeable batteries. One of the most promising types of solid electrolytes is NASICON-structured Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) due to its relatively high ionic conductivity and stability towards air and moisture. Here, the work is aimed on implementing the steps to hinder formation of impurity phases reported for various synthesis routes. Consequently, the applied modifications in the preparation strategies alter a crystal shape and size of prepared material. These two parameters have an enormous impact on properties of LATP. Fabrication of larger particles with a cubic shape significantly improves its ionic conductivity. As a result, LATP preparation methods such as a solution chemistry and molten flux resulted in the highest ionic conductivity samples with the value of ~10^?4 S cm^?1 at room temperature. Other LATPs obtained by solid-state reaction, sol-gel and spray drying methods depicted the ionic conductivity of ~10^?5 S cm^?1. The activation energy of lithium ion transfer in LATP varied in a range of 0.25–0.4 eV, which is in well agreement with the previously reported data.     

Ionic conduction,colossal permittivity and dielectric relaxation behavior of solid electrolyte Li3xLa2/3-xTiO3 ceramics

Perovskite-type solid electrolyte lanthanum lithium titanate (LLTO), exhibiting high intrinsic ionic conductivity, has been attracting interests because of its potential use in all solid-state lithium-ion batteries. In this work, we prepared LLTO ceramics by solid state reaction method and studied their conductivity and dielectric properties systematically. It is found that the bulk conductivity of LLTO is several orders of magnitude higher than the grain boundary conductivity. In addition, colossal permittivity was observed in LLTO ceramics in wide frequency/temperature ranges. Two non-Debye type relaxation peaks were observed in the imaginary part of permittivity, resulting from Li⁺ ions motion and accumulation near interfaces of grains/grain boundaries/electrodes. It is suggested that colossal permittivity may originate from the lithium ion dipoles inside the samples and the interfacial polarization of lithium ion accumulation near the grain boundaries. These results clarify the relations among colossal permittivity, relaxation behavior and ionic conduction in solid ion conductor ceramics.     

Li1.3Al0.3Ti1.7(PO4)3 ceramic electrolyte fabricated from bimodal powder precursor

A novel approach is proposed to design high-quality NASICON–type solid-state electrolytes (SSEs) based on Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) by incorporating nanoparticles into a matrix of microparticles, which could efficiently improve densification of LATP SSEs by sintering. Moreover, LATP SSEs with bimodal microstructures are obtained by tuning mass ratio of 60 nm and 600 nm ceramic particles, which are fabricated by sol-polymer and molten quenching methods, respectively. The LATP SSE containing 60 nm and 600 nm particles with the mass ratio of 10%/90% displays a high ionic conductivity of (5.93 ± 0.24)× 10⁻⁴ S/cm at room temperature and relative density of 95.5 ± 1.1% after sintering at 900 °C for 6 h. Besides, the Li||LATP||Li symmetric cell with the mass ratio of 10%/90% exhibits better cyclic stability with a steady polarization voltage of 121.2 mV than that of other ratios. Therefore, SSEs with multimodal microstructures pave a promising venue for practical application of high-energy-density and safe solid-state Li metal battery.     

High temperature electrode‐electrolyte interface formation between LiMn1.5Ni0.5O4 and Li1.4Al0.4Ge1.6(PO4)3

All‐solid‐state lithium‐ion electrolytes offer substantial safety benefits compared to flammable liquid organic electrolytes. However, a great challenge in solid electrolyte batteries is forming a stable and ion conducting interface between the electrolyte and active material. This study investigates and characterizes a possible solid‐state electrode‐electrolyte pair for the high voltage active cathode material LiMn_1.5Ni_0.5O₄ (LMNO) and electrolyte Li_1+xAl_xGe_2‐x(PO₄)₃ (LAGP). In situ X‐ray diffraction measurements were taken on pressed pellets comprised of a blend of LMNO and LAGP during exposure to elevated temperatures to determine the product materials that form at the interface of LMNO and LAGP and the temperatures at which they form. In particular, above 600°C a material consistent with LiMnPO₄ was formed. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy were used to image the morphology and elemental compositions of product materials at the interface, and electrochemical characterization was performed on LMNO‐coated LAGP electrolyte pellet half cells. Although the voltage of Li/LAGP/LMNO assembled batteries was promising, thick interfacial phases resulted in high electrochemical resistance, demonstrating the need for further understanding and control over material processing in the LAGP/LMNO system to reduce interfacial resistance and improve electrochemical performance.     

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.     

Microstructure,ionic conductivity and mechanical properties of tape-cast Li1.5Al0.5Ti1.5P3O12 electrolyte sheets

Free-standing Li_1.5Al_0.5Ti_1.5P₃O₁₂ electrolyte sheets with a thickness of 50–150 μm were prepared by tape casting followed by sintering at 850–1000 °C in air. While a sintering temperature of 850 °C was too low to achieve appreciable densification and grain growth, a peak relative density of 95% was obtained at 920 °C. At higher sintering temperatures, the microstructure changed from a bimodal grain size distribution towards exclusively large grains (> 10 μm), accompanied by a decrease in relative density (down to 86% at 1000 °C). In contrast, ionic conductivity increased with increasing sintering temperature, from 0.1 mS/cm at 920 °C to 0.3 mS/cm at 1000 °C. Sintering behavior was improved by adding 1.5% of amorphous silica to the slurry. In this way, almost full densification (99.8%) and an ionic conductivity of 0.2 mS/cm was achieved at 920 °C.Mechanical characterization was carried out on the almost fully densified material, yielding elastic modulus and hardness values of 109 and 8.7 GPa, respectively. The fracture strength and Weibull modulus were also characterized. The results confirm that densification and reduction of grain size improve the mechanical properties.     

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。     

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.     

Effect of SnO–P2O5–MgO glass addition on the ionic conductivity of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

NASICON-type structured compounds Li_1+xM_xTi_2-x(PO₄)₃ (M = Al, Fe, Y, etc.) have captured much attention due to their air stability, wide electrochemical window and high lithium ion conductivity. Especially, Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) is a potential solid electrolyte due to its high ionic conductivity. However, its actual density usually has a certain gap with the theoretical density, leading the poor ionic conductivity of LATP. Herein, LATP solid electrolyte with series of SnO–P₂O₅–MgO (SPM, 0.4 wt%, 0.7 wt%, 1.0 wt%, 1.3 wt%) glass addition was successfully synthesized to improve the density and ionic conductivity. The SPM addition change Al/Ti–O bond and P–O bond distances, leading to gradual shrinkage of octahedral AlO₆ and tetrahedral PO₄. The bulk conductivity of the samples increases gradually with SPM glass addition from 0.4 wt% to 1.3 wt%. Both SPM and the second-phase LiTiPO₅, caused by glass addition, are conducive to the improvement of compactness. The relative density of LATP samples increases first from 0 wt% to 0.7 wt%, and then decreases from 0.7 wt% to 1.3 wt% with SPM glass addition. The grain boundary conductivity also changes accordingly. Especially, the highest ionic conductivity of 2.45 × 10^?4 S cm^?1, and a relative density of 96.72% with a low activation energy of 0.34 eV is obtained in LATP with 0.7 wt% SPM. Increasing the density of LATP solid electrolyte is crucial to improve the ionic conductivity of electrolytes and SPM glass addition can promote the development of dense oxide ceramic electrolytes.     

Rapid crystallization of Li1.5Al0.5Ge1.5(PO4)3 glass ceramics via ultra-fast high-temperature sintering (UHS)

Lithium aluminum germanium phosphate solid electrolyte is a promising candidate for all-solid-state batteries. The currently available processing techniques based on melting-quenching require a rather lengthy crystallization step lasting up to 8 hours. In this work, the newly emerged ultra-fast high-temperature sintering (UHS) was proposed to achieve in a single step reactive consolidation of powder mixture (GeO₂, Al(PO₃)₃, LiPO₃) and crystallization of the electrolyte within 16 minutes. Samples produced using UHS had a better phase purity, reduced Li loss, and improved ionic conductivity when compared to the counterparts prepared using conventional crystallization at 850°C for 6 h. In fact, specimens prepared by UHS achieved a crystallinity of 90% and ionic conductivity as high as 1.31 × 10⁻⁴ S cm⁻¹.     

Li1.4Al0.4Ge0.4Ti1.4(PO4)3 promising NASICON-structured glass-ceramic electrolyte for all-solid-state Li-based batteries: Unravelling the effect of diboron trioxide

Li-ion batteries (LIBs) are the ubiquitous technology to power portable electronics; however, for the next-generation of high-performing electrochemical energy storage systems for electric vehicles and smart grid facilities, breakthroughs are needed, particularly in the development of solid-state electrolytes, which may allow for enhanced energy density while enabling lithium metal anodes, combined with unrivalled safety and operative reliability. In this respect, here we present the successful synthesis of a glass-ceramic Li_1.4Al_0.4Ge_0.4Ti_1.4(PO₄)₃ NASICON-type solid-state electrolyte (SSE) through a melt-casting technique. Being grain boundaries crucial for the total ionic conductivity of SSEs, the effect of the addition of diboron trioxide (B₂O₃, 0.05 wt.%) to promote their liquefaction and restructuring is investigated, along with the effects on the resulting microstructures and ionic conductivities. By the thorough combination of structural-morphological and electrochemical techniques, we demonstrate that bulk materials show improved performance compared to their powder sintered counterpart, achieving remarkable ion mobility (> 0.1 mS cm^–1 at –10 °C) and anodic oxidation stability (> 4.8 V vs Li⁺/Li). The addition of B₂O₃ positively affects the grain cohesion and growth, thus reducing the extension of the grain boundaries (and the related grain/grain interface resistance) and, therefore, increasing the overall ion mobility. In addition, B₂O₃ is seen to contrast the microcracks formation in the LAGTP system under study which, overall, shows very promising prospects as SSE for the next-generation of high-energy density, safe lithium-based batteries.     

Structure and lithium-ion mobility in Li1.5M0.5Ge1.5(PO4)3 (M = Ga,Sc, Y) NASICON glass-ceramics

This work reports structural and lithium-ion mobility studies in NASICON single- or multiple phase Li_1+xM_xGe_2−x(PO₄)₃ (M = Ga³⁺, Sc³⁺, Y³⁺) glass-ceramics using solid-state NMR techniques, X-ray powder diffraction, and impedance spectroscopy. X-ray powder diffraction data show the successful incorporation of Ga³⁺ and Sc³⁺ into the Ge⁴⁺ octahedral sites of the NASICON structure at the levels of x = 0.5 and 0.4, respectively. The glass-to-crystal transition was further characterized by multinuclear NMR and electrical conductivity measurements. Among the studied samples, the gallium-containing glass-ceramic presented the highest DC conductivity, 1.1 × 10⁻⁴ S/cm at room temperature, whereas for the Sc-containing samples, the maximum room temperature conductivity that could be reached was 4.8 × 10⁻⁶ S/cm. No indications of any substitution of Ge⁴⁺ by Y³⁺ could be found.     

锂离子电池正极材料磷酸钒锂的制备及性能研究

以氢氧化锂、钒酸铵、磷酸二氢铵为原料,通过溶胶-凝胶法制备Li3V2(PO4)3,采用SEM和XRD研究了不同的烧结温度和烧结时间对材料形貌结构的影响。结果表明最佳制备条件为:800℃下样品烧结9 h,0.1 C条件下表现出首次充放电容量分别为129.1和127.2 mAh/g,40个周期后仍能保持在124.7 mAh/g水平。     

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.     

Synthesis,structure and electrochemical properties of Al doped high entropy perovskite Lix(LiLaCaSrBa)Ti1-xAlxO3

In this work, the Al doped high entropy perovskite Li_0.2La_0.2Ca_0.2Sr_0.2Ba_0.2TiO₃ ceramic is synthesized by using a solid state reaction method, and the effect of different doping amount on the crystal structures and conductivity are also studied. The result proves that doping leads to a positive influence on the conductivity of ceramic. The material of Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ (LLCSBTA-0.1) exhibits a high total conductivity with approximately 3.92 × 10^-7 S cm^-1 at 30 °C and an activation energy of 0.39 eV. The beneficial result can be ascribed to the increase of Li ⁺ concentration. The Li_0.2La_0.2Ca_0.2Sr_0.2Ba_0.2TiO₃ presents a pure cubic perovskite structure, but with partial tetragonal structure due to the addition of Al₂O₃. However, these high entropy perovskite ceramics showed porous structures which are unfavourable for lithium ion conduction. The electrochemical property of the Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ as electrode is investigated as well. The results show that the Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ electrode exhibits good cyclability and stability for the insert-extraction of lithium ions with the specific capacity of 58.6 mA h g^?1.     

Structural and electrical properties of ceramic Li-ion conductors based on Li1.3Al0.3Ti1.7(PO4)3-LiF

The work presents the investigations of Li_1.3Al_0.3Ti_1.7(PO₄)₃-xLiF Li-ion conducting ceramics with 0 ≤ x ≤ 0.3 by means of X-ray diffractometry (XRD), ⁷Li, ¹⁹F, ²⁷Al and ³¹P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy, thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density method. It has been shown that the total ionic conductivity of both as-prepared and ceramic Li_1.3Al_0.3Ti_1.7(PO₄)₃ is low due to a grain boundary phase exhibiting high electrical resistance. This phase consists mainly of berlinite crystalline phase as well as some amorphous phase containing Al³⁺ ions. The electrically resistant phases of the grain boundary decompose during sintering with LiF additive. The processes leading to microstructure changes and their effect on the ionic properties of the materials are discussed in the frame of the brick layer model (BLM). The highest total ionic conductivity at room temperature was measured for LATP-0.1LiF ceramic sintered at 800 °C and was equal to σ_tot = 1.1 × 10⁻⁴ S cm⁻¹.     

Characterization of (PEO)LiClO4‐Li1.3Al0.3Ti1.7(PO4)3 composite polymer electrolytes with different molecular weights of PEO

A group of polyethylene oxide (PEO)LiClO₄‐Li_1.3Al_0.3Ti_1.7(PO₄)₃ composite polymer electrolyte (CPE) films was prepared by the solution‐cast method. In each film, EO/Li = 8 and the Li_1.3Al_0.3Ti_1.7(PO₄)₃ content of 15 wt % were fixed, but the number averaged molecular weight of PEO (M_n) was altered from 5 to 7 × 10⁴ to 10⁶, 2.2–2.7 × 10⁶, 3–4 × 10⁶, 4–5 × 10⁶, and 5.5–6 × 10⁶, respectively. Several techniques including X‐ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and electrical impedance spectroscopy (EIS) were used to characterize the CPE films. LiClO₄ was found to have a strong tendency to complex with PEO, but Li_1.3Al_0.3Ti_1.7(PO₄)₃ was rather dispersed in PEO matrix. DSC analysis revealed that the amorphous phase was dominant in the CPE films although the PEOs before‐use was considerably crystalline. SEM study showed smooth and homogeneous morphologies of the films with low molecular weight PEO and a dual phase characteristic for those with high molecular weight PEO. EIS results indicated that the CPE films are all ionic conductor and the conducting behavior obeys Vogel‐Tamman‐Fulcher (VTF) equation. The parameters in VTF equation were obtained and discussed by taking into considerations PEO molecular weights and crystallinities of the CPE films. Of all the films, the one with PEO with the smallest M_n = 5–7 × 10⁴ had the maximum conductivity, i.e., 1.590 × 10^?5 S cm^?1 at room temperature and 1.886 × 10^?3 S cm^?1 at 373 K. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4269–4275, 2006     

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。