Fabrication of attractive Li4SiO4 pebbles with modified powders synthesized via surfactant-assisted hydrothermal method

Li₄SiO₄ pebbles have been widely studied as attractive tritium breeding materials in the fusion reactor blanket of international thermonuclear experimental reactor (ITER). In this work, surfactant-assisted hydrothermal method was first employed to prepare ultrafine ceramic powders for fabricating attractive Li₄SiO₄ pebbles. SEM analysis revealed that the introduction of sodium dodecyl sulfate could eliminate the particle aggregation to prepare monodispersed precursor powders, and thus generated the green bodies of pebble with homogeneous microstructure, which was helpful to eventually obtain high-quality Li₄SiO₄ pebbles. Moreover, the effects of sintering temperature on the grain size, relative density, and crush load of Li₄SiO₄ pebbles were also investigated. Li₄SiO₄ pebbles sintered at 700 °C had a high crush load (average value 27.39 N), small grain size (average value 0.57 μm), satisfactory density (88.13%T.D.) and abundant pore structure, which were expected to show favorable tritium release behavior as a promising tritium breeding material for fusion reactor blanket.     

Mass fabrication of Li2TiO3–Li4SiO4 ceramic pebbles with high strength by facile centrifugal granulation method

The bi-phase Li₂TiO₃–Li₄SiO₄ ceramic pebbles have been considered a promising breeder to realize the tritium self-sustainment in the blanket. However, up to now, the reported ceramic pebbles have the disadvantages of low yield, poor crushing load, and loose internal structure, which cannot meet the practical application requirements. In this work, the Li₂TiO₃–Li₄SiO₄ ceramic pebbles with excellent mechanical properties were fabricated successfully via the centrifugal granulation method with the assistance of introducing a spray-drying process, simulating particle trajectory by discrete element software and improving bonding interface between core and shell with ethylene glycol. The composition, microstructure, and inner structure of the Li₂TiO₃–Li₄SiO₄ ceramic pebbles were investigated, respectively, through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray computed tomography (CT). It can be found that the employment of the ethylene glycol solution on the surface of Li₂TiO₃ can make the core and the shell combine well. Moreover, the effect of the rolling speed of the Li₂TiO₃–Li₄SiO₄ ceramic pebbles was investigated via discrete element method (EDEM) simulation and experiments. The experimental results displayed that the Li₂TiO₃–Li₄SiO₄ ceramic pebbles sintered at 1100°C for 2 h have a uniform diameter of 1 mm, a good sphericity of 0.97, and an excellent crushing load of 82.4 N, which are superior to those pebbles that obtained by using the traditional wet methods. Moreover, the CT results showed that the appropriate porosity of the core was 3.21% and of the shell was 10.73%. Therefore, the simple centrifugal granulation method can be applied to prepare the Li₂TiO₃–Li₄SiO₄ ceramic pebbles in a large scale and shed a light to investigate the relevant advanced biphasic tritium breeder materials in the future.     

A preliminary study on the preparation of nanostructured Ti-doped Li4SiO4 pebbles by two-step sintering process

Li₄SiO₄ has been widely studied as attractive tritium breeding materials due to its innate merits. Considering the potential advantages of nanostructure in tritium breeding materials, a distinctive process was developed to obtain nanostructured Li₄SiO₄ pebbles. In brief, ultrafine precursor powders were synthesized by solvothermal method without using surfactants, and then indirect wet method was adopted to generate the green spheres with homogeneous microstructure. After that, the suitable sintering conditions were defined by studying the effects of sintering parameters on the grain size evolution, and nanostructured Ti-doped Li₄SiO₄ pebbles were first obtained by two-step sintering method. This study will be expected to provide references for fabricating other Li-based tritium breeding materials.     

Fabrication of nanostructured Li2TiO3 ceramic pebbles as tritium breeders using powder particles synthesised via a CTAB-assisted method

Nanostructured Li₂TiO₃ ceramics which may have effective thermal conductivity, excellent tritium release behaviour and good irradiation resistance are regarded as a promising solid tritium breeding material for the fusion reactor blanket of the International Thermonuclear Experimental Reactor (ITER). However, due to the limitations of the preparation technology, reports concerning Li₂TiO₃ nanoceramics have been rare. In this paper, uniform nano-Li₂TiO₃ powder particles which were essential to obtain nanostructured Li₂TiO₃ ceramics pebbles were synthesised via a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method, and then rare, homogeneous nanostructured Li₂TiO₃ ceramic pebbles were fabricated with the as-prepared powder particles. The mechanisms by which CTAB can reduce particle agglomeration and be of assistance in achieving a nanostructured Li₂TiO₃ ceramic were also investigated. In addition, systematic experiments on the relationship between the added amount of CTAB and the mechanical properties of the Li₂TiO₃ ceramic structure were also carried out. The results revealed that the desired Li₂TiO₃ nanoceramic could be fabricated when 3% CTAB was introduced, as the Li₂TiO₃ pebbles obtained had a small grain size (90 nm), high relative density (89.71%T.D.) and crush load (99.93 N), which were expected to show favourable potential as a promising tritium breeder material in the fusion reactor blanket.     

One-step fabrication of Li2TiO3 ceramic pebbles using pulsed YAG laser

A large amount of Li-containing ceramic breeder pebbles is packed in the solid breeding blanket of a nuclear fusion reactor. Several pebble fabrication technologies have been proposed in previous studies, including wet process, emulsion method, extrusion spheronization, additive manufacturing, and melt process. However, a simple, energy-effective, and scalable fabrication technology remains to be developed for the automated mass production and reprocessing of used radioactive pebbles post-operation. Selective laser melting potentially enables the quick and automated fabrication of breeder pebbles. Herein, we employ a high-power density pulse laser to produce ceramic breeder pebbles. A pulsed YAG laser was irradiated over a lithium metatitanate (Li₂TiO₃) powder bed in air, and the corresponding temperature was monitored using fiber-type infrared pyrometers. Spherical Li₂TiO₃ pebbles were successfully fabricated in a single step with an average diameter of 0.78 ± 0.13 μm and the sintering density of 87.4% ± 5.6% (input power: 7.9 J/pulse). The irradiated Li₂TiO₃ powder melted and turned spherical under surface tension and rapidly solidified, resulting in uniaxial fine grains and a decrease in the degree of long-range cation ordering.     

Preparation of Li4SiO4-xLi2O powders and pebbles for advanced tritium breeders

Li₄SiO₄ pebbles and Li₂O pebbles have been considered as the potential candidates for tritium breeders. Li₂O exhibits higher lithium density whereas worse lithium loss and hygroscopicity compared with Li₄SiO₄. It is anticipated to obtain an advanced breeder by combining Li₄SiO₄ with Li₂O. The coexistence of Li₄SiO₄ and Li₂O powders could not be obtained by solid state reaction using Li₂CO₃ as lithium source, while the biphasic Li₄SiO₄-xLi₂O (x=0.1, 0.2, 0.3, 0.4) powders were prepared by sol-gel method in this experiment. Meanwhile, the biphasic Li₄SiO₄-xLi₂O pebbles were fabricated by a wet method for the first time. The Li₂O aggregated at the grain boundaries and promoted the grain growth of the Li₄SiO₄. The grain size and the crush load of the Li₄SiO₄-0.3Li₂O pebbles reached 32.3 µm and 46.5 N, respectively.     

Long-term thermal stability of Li4TiO4–Li2TiO3 core–shell breeding pebbles under continuous heating in H2/Ar atmosphere

The long-term thermal stability of tritium breeding materials during service is a key factor to ensure efficient tritium release. In this study, the long-term thermal stability of advanced Li₄TiO₄–Li₂TiO₃ core–shell breeding pebbles under continuous heating in 1%H₂/Ar at 900°C was investigated for the first time. The results show that this core–shell material loses 3.4% Li mass after heating for 30 days, resulting in a reduction in Li density to .415 g/cm³, which is still significantly higher than other breeding materials. The moisture in the sample bed will determine the form of Li volatilization and thus affect the rate of Li mass loss. The core–shell pebbles maintain favorable phase stability during long-term heating, and the grain sizes of the Li₂TO₃ shell and Li₄TiO₄ core after 30 days of heating are 6.5 ± 1.5 and 6.9 ± 2.5 μm, respectively. Moreover, the samples did not crack or collapse during long-term heating and still had a satisfactory crushing strength of 37.61 ± 7.13 N after 30 days of heating. Overall, the high Li density and good thermal stability during long-term heating demonstrate that the Li₄TiO₄–Li₂TiO₃ core–shell breeding pebbles are a very reliable tritium breeding material for long-term service under harsh operating conditions.     

Study on the chemical compatibility between Li2TiO3 ceramic pebbles and diverse advanced structural materials

The tritium breeder and structural materials are necessary components in the blanket to realize tritium (T) self-sustainment of nuclear fusion. The long-term exposure between tritium breeders and structural materials will cause surface corrosion in irradiation environments and then further affect the tritium release behavior. In this study, chemical compatibility between Li₂TiO₃ ceramic pebbles and advanced structural materials was studied systematically at 700 °C for 300 h under He+0.1 % H₂ environment, respectively. The color of the Li₂TiO₃ ceramic pebbles changes from white to dark grey and black. Moreover, the grain size of Li₂TiO₃ ceramic pebbles increases to more than 5 μm, and the crushing load decreased slightly. For the structural materials, the Al-rich oxide layer with about 188.7 nm of 14Cr-5Al oxide dispersion strengthened (ODS) steel and Cr-Fe rich oxide layer with about 1.04 μm of 14Cr-ODS steel were observed on the cross-section. The effective diffusion coefficient of O element in Li₂TiO₃ ceramic moved into ODS steel at 700 °C was calculated to be 3.3 × 10⁻¹⁶cm²/s and 1.02 × 10⁻¹⁴ cm²/s. Unfortunately, when SiC ceramics were contacted with the pebbles, the crystal phase transformed into SiO₂, which severely limits its application. Therefore, these results will provide guidance for the selection of structural materials in the future.     

Low‐Temperature Sintering and Microwave Dielectric Properties of CaMoO4‐Based Temperature Stable LTCC Material

The CaMoO₄–xY₂O₃–xLi₂O ceramics were prepared by the solid‐state reaction method. The sintering behavior, phase evolution, microstructure, and microwave dielectric properties were investigated. CaMoO₄ solid solution was obtained when x = 0.030, and two‐phase system including tetragonal CaMoO₄ phase and cubic Y₂O₃ phase formed when 0.066 ≤ x ≤ 1.417. A temperature stable CaMoO₄‐based microwave dielectric ceramic with ultralow sintering temperature (775°C) was obtained in the CaMoO₄–xY₂O₃–xLi₂O system when x = 0.306, which showed good microwave dielectric properties with a low permittivity of 9.5, a high Q_f value of 63 240 GHz, and a near‐zero temperature coefficient of resonant frequency of +7.2 ppm/°C.     

High-performance Li4Ti5−xVxO12 (0 ≤ x ≤ 0.3) as an anode material for secondary lithium-ion battery

Powders of spinel Li₄Ti_5−xV_xO₁₂ (0 ≤ x ≤ 0.3) were successfully synthesized by solid-state method. The structure and properties of Li₄Ti_5−xV_xO₁₂ (0 ≤ x ≤ 0.3) were examined by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electronic microscope (SEM), galvanostatic charge–discharge test and cyclic voltammetry (CV). XRD shows that the V⁵⁺ can partially replace Ti⁴⁺ and Li⁺ in the spinel and the doping V⁵⁺ ion does almost not affect the lattice parameter of Li₄Ti₅O₁₂. Raman spectra indicate that the Raman bands corresponding to the Li–O and Ti–O vibrations have a blue shift due to the doping vanadium ions, respectively. SEM exhibits that Li₄Ti_5−xV_xO₁₂ (0.05 ≤ x ≤ 0.25) samples have a relative uniform morphology with narrow size distribution. Charge–discharge test reveals that Li₄Ti_4.95V_0.05O₁₂ has the highest initial discharge capacity and cycling performance among all samples cycled between 1.0 and 2.0 V; Li₄Ti_4.9V_0.1O₁₂ has the highest initial discharge capacity and cycling performance among all samples cycled between 0.0 and 2.0 V or between 0.5 and 2.0 V. This excellent cycling capability is mainly due to the doping vanadium. CV reveals that electrolyte starts to decompose irreversibly below 1.0 V, and SEI film of Li₄Ti₅O₁₂ was formed at 0.7 V in the first discharge process; the Li₄Ti_4.9V_0.1O₁₂ sample has a good reversibility and its structure is very advantageous for the transportation of lithium-ions.     

Microwave dielectric properties,low-temperature sintering mechanism,and defects behaviour of temperature stable (1-x)Li2Zn3Ti4O12-xSr3(VO4)2 ceramics

(1-x)Li₂Zn₃Ti₄O₁₂-xSr₃(VO₄)₂ (0.1 ≤ x ≤ 0.4) microwave dielectric ceramics were fabricated by solid-state sintering technology. The impact of SV addition on the microstructure, dielectric properties, sintering process, and defects behaviour was studied. The formation of SrTiO₃ and the glass phase were observed via XRD and TEM, and the latter resulted in a decrease in the sintering temperature. The variations in microwave dielectric properties were consistent with the empirical mixture rules calculated by XRD refinement, and a near-zero τ_f value was obtained. The Li, Zn and V elements of the glass phase and the liquid phase sintering model were deduced via DSC, TEM and Raman spectroscopy. Then, the defect behaviour, such as oxygen vacancies, Ti³⁺, and V⁴⁺, was investigated by XPS and complex impedance spectroscopy. It was found that the generation and migration of defects occurred much more easily in 0.7LZT-0.3 SV than in LZT, resulting in a higher dielectric loss. Finally, the 0.7Li₂Zn₃Ti₄O₁₂-0.3Sr₃(VO₄)₂ ceramic sintered at 900 °C exhibited excellent microwave dielectric properties of ε_r = 17.8, Q × f = 41,891 GHz, and τ_f = ?4.4 ppm/°C and good compatibility with silver electrode, showing a good potential application for LTCC.     

Preparation of tritium breeding Li2TiO3 ceramic pebbles via newly developed piezoelectric micro-droplet jetting

Wet methods as an emerging technique for the preparation of millimeter-sized tritium breeding ceramic pebbles, but the imposed air pressure as the driving forces to extrude slurry droplets are fluctuating during the reciprocating extrusion process, which caused a slight inconsistency in pebble sizes. In this study, a piezoelectric micro-droplet jetting approach was proposed by introducing a piezo-driven valve and modifying the slurry barrel mechanism to realize the air pressure invariable. A self-developed piezoelectric micro-droplet jetting device was successfully utilized to prepare Li₂TiO₃ green pebbles with coefficients of variation being lower than 2.7%. The size of the green pebbles could be precisely controlled in the range of 0.88–1.37 mm by manipulating the nozzle diameter, the air pressure, and the jetting time. The pebbles sintered at 1000°C for 3 h possessed a small grain size of ∼5.9 μm, a satisfied relative density of ∼84.8% T.D., and a high crush load of ∼25.7 N, implying the prepared pebbles could be used as a promising solid tritium breeding material in fusion reactors. These findings are anticipated to provide new opportunities for the highly efficient preparation of size-controllable tritium breeding ceramic pebbles.     

A novel process for fully automatic mass-production of Li2TiO3 ceramic pebbles with uniform structure and size

As an excellent promising tritium breeding material, Li₂TiO₃ ceramic pebbles will be required in large quantities in the future. For this reason, a fully automatic pneumatic eject device based on an improved wet process was employed in the mass-preparation of Li₂TiO₃ ceramic pebbles. The operating principle of the equipment, the preparation process parameters and the performance of the Li₂TiO₃ ceramic pebbles have been studied. The results showed that the spheroidization and solidification process of slurries droplets in the molding medium were critical to the sphericity of pebbles, and the size of the green pebbles was related to the droplet dropping speed、the control pressure and the nozzle inner diameter. It is revealed that more than 90% of the pebbles had an eccentricity of less than 1.1, and the diameter distribution was concentrated between 0.98 mm and 1.03 mm. The Li₂TiO₃ ceramic pebbles with the average grain size of 3.7 μm, the crushing load of 67 N, the relative density of 85.6%, and the porosity of 19.96% can be obtained after sintered at 1100 °C for 2 h. Also, the average pore size was 1.3 μm and the distribution was relatively concentrated. Therefore, this method is expected to meet the future demands of Li₂TiO₃ ceramic pebbles with excellent performance in bulk quantity.     

Fabrication of high strength Li-rich 2Li2TiO3–Li4SiO4 composite breeding ceramics at low-temperature by two-step sintering

In this study, Li-rich 2Li₂TiO₃–Li₄SiO₄ composite breeding ceramics were prepared for the first time through a two-step low-temperature sintering route to meet the increasingly stringent performance requirements of tritium breeding materials. The effects of excess Li addition and sintering atmosphere on the phase composition, mechanical properties, and microstructure of the composite breeding ceramics were systematically studied. A two-step low-temperature sintering method was proposed to integrate the advantages of different sintering environments. The results show that moderate Li addition can significantly enhance the crushing load of composite ceramics while maintaining the nanostructure. However, further increasing the amount of Li addition does not continue to increase the crushing load, and will even affect the structural uniformity of the composite breeding ceramics. Most importantly, the S2.5 (2Li_2.5TiO₃–Li₄SiO₄, molar ratio) composite breeding ceramics sintered at 750 °C in an air-vacuum environment exhibited a grain size of ～86 nm and a crushing load of ～66.9 N, which has not been achieved by previous studies.     

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.     

Effects of Li2CO3 and Sm2O3 additives on low-temperature sintering and piezoelectric properties of PZN-PZT ceramics

To assist the development of applications for multilayer piezoelectric devices, the low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ with Li₂CO₃ and Sm₂O₃ additives were fabricated by a conventional solid-state reaction, and their structural and piezoelectric properties were studied. With the addition of Li₂CO₃, the minimum sintering temperature of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramics was reduced from 1125 °C to 950 °C through the formation of a liquid phase and its piezoelectric properties showed almost no degradation. When the sintering temperature was below 950 °C, however, the piezoelectric properties degraded obviously. The additional Sm₂O₃ resulted in a significant improvement in the piezoelectric properties of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ ceramic with added Li₂CO₃. When sintered at 900 °C, the optimized properties of the 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramic with 0.3 wt% Li₂CO₃ and 0.3 wt% Sm₂O₃ were obtained as d₃₃ = 483 pC/N, k₃₁ = 0.376, Q_m = 73, ɛ_r = 2524, tan δ = 0.0178.     

Low‐Temperature Preparation of β‐Si3N4 Porous Ceramics with a Small Amount of Li2O–Y2O3

Porous β‐Si₃N₄ ceramics are sintered at 1600°C in N₂ and postheat treated at 1500°C under vacuum using Li₂O and Y₂O₃ as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li₂O. The addition of Y₂O₃ is advantageous for the formation of high aspect ratio β‐Si₃N₄ grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the β‐Si₃N₄ porous ceramic with a porosity of 54.1% and high flexural strength of 110 ± 8.1 MPa can be prepared with a small amount of sintering additives, 0.66 wt% Li₂O and 0.33 wt% Y₂O₃, and it is suitable for high‐temperature applications.     

The structure evolution and microwave dielectric properties of MgAl2-x(Mg0·5Ti0.5)xO4 solid solutions

In the present work, MgAl_2-x(Mg_0·5Ti_0.5)_xO₄ (x = 0.02, 0.04, 0.06, 0.08, 0.10) solid solutions were synthesized via the traditional solid-state reaction route. The valence state of Ti ions, crystal structural characteristics, and microwave dielectric properties were discussed. A solid solution with spinel structure was revealed by the Rietveld refinement results. The partial substitution of (Mg_0·5Ti_0.5)³⁺ for Al³⁺ lowered the sintering temperature and improved the Q × f value of MgAl₂O₄ ceramic. The MgAl_2-x(Mg_0·5Ti_0.5)_xO₄ solid solutions with x = 0.06 can be well sintered at 1425 °C in an oxygen atmosphere for 8 h and exhibits excellent microwave dielectric properties with ε_r = 9.1, Q × f = 98,000 GHz, τ_f = −61.36 ppm/°C. The sintering temperature of MgAl_1·94(Mg_0·5Ti_0.5)_0.06O₄ microwave dielectric ceramics was approximately 200 °C lower than that of conventional MgAl₂O₄ ceramics.     

Preparation and characterization of novel spinel Li4Ti5O12−xBrx anode materials

Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) materials were investigated. The Li₄Ti₅O_12−xBr_x (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂, especially at high current rates. When the discharge rate was 0.5 C, the Li₄Ti₅O_12−xBr_x (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g⁻¹, which was very close to its theoretical capacity (175 mAh g⁻¹), while that of the pristine Li₄Ti₅O₁₂ was 123.2 mAh g⁻¹ only.     

Structural and electrochemical characteristics of Li4−xAlxTi5O12 as anode material for lithium-ion batteries

Al-doped Li₄Ti₅O₁₂ in the form of Li_4−xAl_xTi₅O₁₂ (x = 0, 0.05, 0.1 and 0.2) was synthesized via solid state reaction in an Ar-flowing atmosphere. Al-doping does not change the phase composition and particle morphology, but easily results in the lattice distortion and thus the poor crystallinity of Li₄Ti₅O₁₂. Al-doping decreases the specific capacity of Li₄Ti₅O₁₂, while improves remarkably its cycling stability at high charge/discharge rate. The substitution of Al for Li site can enhance the electronic conductivity of Li₄Ti₅O₁₂ via the generation of mixing Ti⁴⁺/Ti³⁺, whereas impede the Li-ion diffusion in the lattice. Excessive Al causes large electrode polarization due to the lower Li-ion conductivity, and thus leads to low specific capacity at high current densities. Li_3.9Al_0.1Ti₅O₁₂ exhibits a relatively high specific capacity and an excellent cycling stability.