Ta-doped Li7La3Zr2O12 Research Articles

Interface engineering enabling thin lithium metal electrodes down to 0.78 μm for garnet-type solid-state batteries

Controllable engineering of thin lithium (Li) metal is essential for increasing the energy density of solid-state batteries and clarifying the interfacial evolution mechanisms of a lithium metal negative electrode. However, fabricating a thin lithium electrode faces significant challenges due to the fragility and high viscosity of Li metal. Herein, through facile treatment of Ta-doped Li7La3Zr2O12 (LLZTO) with trifluoromethanesulfonic acid, its surface Li2CO3 species is converted into a lithiophilic layer with LiCF3SO3 and LiF components. It enables the thickness control of Li metal negative electrodes, ranging from 0.78 μm to 30 μm. Quasi-solid-state lithium-metal battery with an optimized 7.54 μm-thick lithium metal negative electrode, a commercial LiNi0.83Co0.11Mn0.06O2 positive electrode, and a negative/positive electrode capacity ratio of 1.1 shows a 500 cycles lifespan with a final discharge specific capacity of 99 mAh g−1 at 2.35 mA cm−2 and 25 °C. Through multi-scale characterizations of the thin lithium negative electrode, we clarify the multi-dimensional compositional evolution and failure mechanisms of lithium-deficient and -rich regions (0.78 μm and 7.54 μm), on its surface, inside it, or at the Li/LLZTO interface.

Enhanced electrochemical performance of garnet Li7La3Zr2O12 electrolyte by efficient incorporation of LiCl

Garnet-type Ta-doped Li7La3Zr2O12 (LLZO) lithium-ion-conducting ceramic electrolytes has become the promising and critical candidate for developing the high-energy-density all-solid-state lithium batteries, due to the satisfied Li+ conductivity, stability against metallic lithium anode, and the feasible preparation under ambient air. Here, to further increase the lithium-ion conductivity of LLZO comparable to that of the commercial organic liquid electrolytes, lithium chloride (LiCl) is effectively introduced to synthesize the garnet-type ceramic electrolytes with the nominal composition (Li6.5La3Zr1.5Ta0.5O12)1-x–(LiCl)x (x = 0, 5mol%, 10mol%, 15mol%, 20mol%, and 25mol%) via high-temperature calcination process. The cubic structure with highly conductive performance is confirmed from X-ray diffraction measurement as well as Raman spectra analysis. Structural information is observed according to field emission scanning electron microscope equipped with energy dispersive spectrometer and density measurements. Among above investigated ceramic compositions, the prepared (Li6.5La3Zr1.5Ta0.5O12)0.85–(LiCl)0.15 ceramic electrolyte sheet sintered at 1200 °C for 12h presents the room-temperature Li-ion conductivity of 1.22 × 10−3 S·cm−1 by alternating current (AC) impedance analysis along with the corresponding activation energy of 0.262eV through Arrhenius equation calculation. The electronic conductivity measurements are also done by direct-current polarization to confirm the ionic nature for all investigated ceramics. Furthermore, the Li|(Li6.5La3Zr1.5Ta0.5O12)0.85–(LiCl)0.15 |Li symmetric batteries can possess the small interfacial resistance of 92.3 Ω cm2 and stably run for 1000 h at 0.1 mA cm−2 without a short circuit at room temperature. The hybridized lithium-sulfur battery with (Li6.5La3Zr1.5Ta0.5O12)0.85–(LiCl)0.15 electrolyte delivered excellent initial room-temperature discharge capacity of 1204mAh·g−1 and 1152 mAh·g−1 under the current density of 0.1C and 0.2C respectively, large coulombic efficiency, and great cycling stability. Moreover, the lithium-sulfur batteries also can show excellent cycling performances under different current densities and a good capacity recoverability. The above investigation results suggest that the low-melting-point LiCl incorporation in Li6.5La3Zr1.5Ta0.5O12 electrolyte is an effective measurement to synthesize the cubic and dense Li-stuff garnet ceramic sheets for the high-performance rechargeable next-generation solid-state batteries.

The construction of concentration gradient inducing low resistance for Li7La3Zr2O12-based thermal battery

Ta-doped Li7La3Zr2O12 (LLZTO) electrolytes not only show considerable potentials in solid-state Li metal batteries, but also display great possibility in thermal battery working at elevated temperature with high security. However, the great resistance of the single cell has hindered its practical application for the large interfacial resistance and high Li+ transport pressure. Herein, a new effective approach to construct intense interface and distinct concentration gradient of O2– and Cl- through pre-discharge state at small current (PDS) was successfully employed to decline the resistance of the LLZTO-based thermal battery under thermal and electric field. The formed intense interface is conductive under the thermal field than the pristine poor contact at the interface. The obtained significant and distinct concentration gradient of O2– and Cl- under the joint function of thermal and electric field achieves larger effective charge transport after PDS, suggesting lower polarization and resistance of the single cell owing to the relaxing burden of Li+. Consequently, the resistance of the single cell decreases to 2.4 Ω from 3.7 Ω, coming with larger specific energy at 500 °C (from 444 Wh kg−1 to 1038 Wh kg−1). This work provides a facile strategy to decline the resistance of the battery through the construction of concentration gradient, which is also promising to be used for battery whose materials are sensitive to electric or thermal field.

In-Situ Formed Electron Inhibitor Enabling Dendrite-free Garnet Electrolytes: A Case Study of Fumed Silica.

Ta-doped Li7 La3 Zr2 O12 (LLZTO) solid-state electrolytes (SEs) show great promise for solid-state batteries due to its high conductivity and safety. However, one of the challenges it faces is lithium dendrite propagation upon long-term cycling. To address this issue, we propose the incorporation of fumed silica (FS) at the grain boundaries of LLZTO to modify the properties of the garnet pellet, which effectively inhibits the dendrite growth. The introduction of FS has demonstrated several beneficial effects. Firstly, it reduces the migration barrier of lithium ions, which helps prevent dendrite formation and propagation. Additionally, FS reduces the electronic conductivity of the SEs pellet, suppressing the dendrite formation. Moreover, the formed lithium silicates from FS might also be acted as electron inhibitor, thus inhibiting the lithium dendrite growth upon cycling. By investigating the use of FS as a modifier in LLZTO-based electrolytes, our study contributes to advancing dendrite-free solid-state electrolytes and thus the development of high-performance all-solid-state batteries.

Lithium Dendrite Propagation in Ta-Doped Li7La3Zr2O12 (LLZTO): Comparison of Reactively Sintered Pyrochlore-to-Garnet vs LLZTO by Solid-State Reaction and Conventional Sintering.

Ta-doped Li7La3Zr2O12 (LLZTO) garnet is a promising Li-ion-conducting ceramic electrolyte for solid-state batteries. However, it is still challenging to use LLZTO in Li metal batteries operating at high current densities because of the tendency for Li metal to nucleate and propagate along the grain boundaries. In this study, we carry out a detailed investigation to elucidate the effect of microstructure and grain size on the electrochemical properties and short circuit behavior in LLZTO. Pellets were prepared using reactive sintering from pyrochlore precursors (a method called pyrochlore-to-garnet, P2G) and compared with LLZTO synthesized using solid-state reaction (SSR) followed by conventional pressureless sintering. Both preparation methods were controlled to keep the phase and elemental composition, ionic and electronic conductivity, relative density, and area-specific resistance of the pellets constant. Reflection electron energy loss spectroscopy and X-ray photoelectron spectroscopy confirm that both types of LLZTO have similar band gaps and chemical states. Microstructure analysis shows that the P2G method results in LLZTO with an average grain size of around 3 μm, which is much smaller than the grain sizes (as large as 20 μm) seen in SSR LLZTO. Galvanostatic Li stripping/plating and linear sweep voltammetry measurements show that P2G LLZTO can withstand higher critical current densities (up to 0.4 mA/cm2 in bidirectional cycling and >1 mA/cm2 for unidirectional) than those seen in SSR LLZTO. Post-mortem examination reveals much less Li deposition along the grain boundaries of P2G LLZTO, particularly in the bulk of the pellet, compared to SSR LLZTO after cycling. The improved cycling behavior in P2G LLZTO despite the higher grain boundary area could be from more homogeneous current density at the interfaces and different grain boundary properties arising from the liquid-phase, reactive sintering method. These results suggest that the effect of grain size on Li dendrite propagation in LLZO may be highly dependent on the synthesis and sintering method employed.

Highly Efficient Aligned Ion-Conducting Network and Interface Chemistries for Depolarized All-Solid-State Lithium Metal Batteries

HighlightsThis study introduces an innovative 3D-printed electrolyte with vertically aligned ion transport network, which contains well-dispersed nanoscale Ta-doped Li7La3Zr2O12 in a poly(ethylene glycol) diacrylate matrix.The 3DSE architecture enables efficient ion transport across the Li/electrolyte and electrolyte/cathode interfaces, which allows for increased active material mass loading and enhanced interfacial adhesion.The p-3DSE Li symmetric cell displays an impressive critical current density value of 1.92 mA cm−2 and stable operation for 2600 h at room temperature. Full cells using p-3DSE achieve notable areal capacities.

In situ dual-interface layer enabling lower resistance of Ta-doped Li7La3Zr2O12-based thermal battery

Application of Ta-doped Li7La3Zr2O12 (LLZTO) to thermal battery could solve overflow safety hazards caused by molten salt electrolytes. However, the capacity of large current discharge is obstructed by the large interfacial resistance originating from poor solid–solid contact between LLZTO and cathode. In this work, an in-situ dual-interface layer with favorable conductivity and multi-ionic diffusion between LLZTO and cathode is constructed by introducing connection layer in a simple way. The Ni(BrxCl2-x) layer with favorable conductivity would be established at high temperature during discharge for the reaction between the connection layer and NiCl2 cathode; the ionic (Br-,Cl-,O2–) diffusion layer with significant diffused direction among the connection layer, LLZTO layer and cathode layer occurs simultaneously at high temperature during discharge. Besides, the left connection layer with low melting point could form wettable interface as well. Consequently, the internal resistance of the single cell modified by in-situ dual-interface layer is reduced from 3.72 Ω to 1.70 Ω, accompanying with larger discharge current density (from 25 to 100 mA cm−2) and higher specific energy (from 444 to 1050 Wh kg−1) at 500 °C. Comparing with the typical discharge current of LLZTO which is less than 1 mA cm−2, this report provides a new insight to improve the interfacial resistance for the solid–solid contact at ambient temperature and the application for LLZTO on high-temperature battery.

Fusing Ta-doped Li7La3Zr2O12 grains using nanoscale Y2O3 sintering aids for high-performance solid-state lithium batteries.

Solid-state lithium batteries have advantages of high energy density and usage safety and are considered as promising next-generation power sources. Among them, the garnet-type oxide electrolyte has become a widely studied inorganic electrolyte due to its high ionic conductivity and chemical stability. In this paper, nanoscale Y2O3 (NYO) particles are introduced as sintering aids for fabricating Ta-doped Li7La3Zr2O12 (LLZTO) ceramics, and the sintering effects of various NYO ratios on the properties of LLZTO are investigated. Among the samples, the LLZTO-5%NYO sample exhibits the highest ionic conductivity (7.39 × 10-4 S cm-1) and the lowest activation energy (0.17 eV). At various current densities, the polarization voltage of LLZTO-5%NYO is also the lowest without a short circuit. The full cells of LFP|LLZTO-5%NYO|Li exhibit a high capacity of 163.9 mA h g-1 with a high initial coulombic efficiency of 97.4%, and the capacity retention rate is up to 98.1% after 50 cycles. This work may inspire the development of analogous solid-state electrolytes and lithium batteries.

(Digital Presentation) Electrochemical Properties of Ta-Doped Li7La3Zr2O12 Ceramic Electrolyte Sintered with Ga2O3 Additive

A garnet-type oxide with the formula of Li7La3Zr2O12 (LLZO) has attracted much attention because of its high Li ion conductivity at room temperature, excellent thermal performance, and high stability against Li metal.1,2) However, poor interfacial connection causes non-uniform Li plating and intergranular penetration of Li dendrite in polycrystalline LLZO when the cell is cycled particularly at high current densities, resulting in internal short-circuit failure.3,4) It has been pointed out that the tolerance for Li dendrite growth into LLZO is influenced by many factors such as the interfacial resistance between LLZO and Li anode, cell stacking pressure and microstructure (density and grain size) of LLZO. In this study, we fabricated Ta-doped LLZO (Li6.55La3Zr1.55Ta0.45O12) solid electrolytes with Ga2O3 additive and investigated the effects on the microstructure and electrochemical properties.Ta-doped LLZO with Ga2O3 additive were synthesized via a conventional solid-state reaction process. 1-7 mol % Ga2O3 powder was mixed with calcined Ta-doped LLZO powder. The mixture was pelletized and then sintered at different temperatures with an Al-free crucible. In XRD analysis, each sintered sample has a cubic garnet phase and diffraction peaks from other phases were not detected. In SEM observation, microstructure of sintered sample was strongly influenced by sintering temperature and Ga2O3 addition, due to the sintering with liquid Li-Ga-O phase during high temperature sintering.5, 6) The high total (bulk + grain-boundary) ionic conductivity above 1 mS cm-1 at room temperature was obtained in samples composed of large grains with the size of several 10 to 100 µm. However, the tolerance for Li dendrite growth characterized in a symmetric cell is improved remarkably in the samples with uniform microstructure composed of fine grains with the size of below 5 µm. Since the interfacial resistance between Li and solid electrolyte was adjusted to the same level, the difference in tolerance for Li dendrite growth is mainly attributed to the difference in microstructure depending on both the sintering condition and the amounts of Ga2O3 addition.

An advanced 3D gel cathode with continuous ion and electron transport pathway for solid-state lithium batteries

Ta-doped Li7La3Zr2O12 (LLZTO) is known as a garnet-type solid-state electrolyte with high ionic conductivity and good stability against lithium metal anode, which is regarded as one of the most promising electrolytes for the commercialization of solid-state batteries (SSBs). However, the poor electron and ion transport among cathode active material particles, as well as the large interfacial impedance between LLZTO ceramic pellet and cathode, remain major issues for SSBs. In this work, we proposed a novel 3D gel cathode based on the “cation-π” interaction between the organic cations in ionic liquid (IL) and the large electron-rich π-system in single-walled carbon nanotubes (SWNTs). The designed gel cathode, which is composed of SWNTs, IL and LiFePO4 (LFP) without binder, possesses a good wettability with the LLZTO ceramic pellet and affords highly efficient conductive pathways for electrons and ions through the interface and entire cathode. As a consequence, the assembled SSBs with the gel cathode exhibit excellent long-term cycling stability with a high capacity retention of 91.74% after 700 cycles at 0.5C, and a high coulombic efficiency close to 100% can be achieved over the course of cycling at 25 °C.

A novel garnet-type high-entropy oxide as air-stable solid electrolyte for Li-ion batteries

Li-ion batteries are considered prospective candidates for storage systems because of their high energy density and long cycling life. However, the use of organic electrolytes increases the risk of explosion and fire. Hence, all-solid-state Li-ion batteries have attracted considerable attention because the use of solid electrolytes avoids the combustion of electrolytes and explosions, and enhances the performance of batteries. Garnet-type oxides are commonly used solid electrolytes. The common Ta-doped Li7La3Zr2O12 can react easily with CO2 and H2O in air, and its ionic conductivity decays after contact with air. In this study, a novel garnet-type, high-entropy oxide, Li6.4La3Zr0.4Ta0.4Nb0.4Y0.6W0.2O12 (LLZTNYWO), is successfully synthesized as a solid electrolyte for Li-ion batteries,using a conventional solid-state method. Ta, Nb, Y, and W are used as substitutes for Zr, which significantly increase conductivity, have high stability in air, and a lower sintering temperature. LLZTNYWO achieves higher Li-ion conductivity at 1.16 × 10−4 S cm−1 compared to mono-doped Li6.6La3Zr1.6Ta0.4O12 (6.57 × 10−5 S cm−1), Li6.6La3Zr1.6Nb0.4O12 (2.19 × 10−5 S cm−1), and Li6.2La3Zr1.6W0.4O12 (1.16 × 10−4 S cm−1). Additionally, it exhibits higher ionic conductivity compared to equimolar Li5.8La3Zr0.4Ta0.4Nb0.4Y0.4W0.4O12 (1.95 × 10−5 S cm−1). The Li-ion conductivity of LLZTNYWO remains constant for 30 days in the atmosphere without decay, thereby revealing its excellent air stability. Furthermore, LLZTNYWO exhibits a remarkable electrochemical window of up to 6 V vs Li/Li+ and excellent electrochemical stability against Li metal after cycling at 0.1 mA·cm−2 for 2 h, which indicates that it is a promising solid electrolyte for Li-ion batteries.

Lower Interfacial Resistance between a Ta-Doped Li7La3Zr2O12 (LLZTO) Solid Electrolyte and NiCl2 Cathode by a Simple Heat Treatment for a High-Specific Energy Thermal Battery.

Large current discharge is restricted because of the poor conductivity between the Ta-doped Li7La3Zr2O12 (LLZTO) solid electrolyte and electrode. The poor conductivity would be caused by the interfacial reaction between LLZTO and the cathode, which is detrimental to the secondary Li ionic or metal battery. In this case, we studied the interfacial reaction between LLZTO and a haloid cathode (NiCl2) for a thermal battery for the first time, and a lower interfacial resistance could be obtained by a simple heat treatment. Owing to the element interdiffusion of Cl- and O2- at a high temperature of 600 °C, the main reaction products are LaOCl, LiCl, and La2Zr2O7. This reaction reduces the interfacial resistance from 3 Ω to 2 Ω. After a pretreatment at 600 °C, the discharge specific energy could reach 1254 Wh kg-1 from 828 Wh kg-1 at 550 °C with a cut-off voltage of 1.8 V. These results suggest that the interfacial reaction could be significant for the battery by adding interfacial contact. It is an effective approach to decrease the interfacial resistance at high temperature for some specific system, such as a haloid cathode-solid electrolyte.

Enable high reversibility of Fe/Cu based fluoride conversion batteries via interfacial gas release and detergency of garnet electrolytes

Garnet-type Ta-doped Li7La3Zr2O12 (LLZTO) electrolyte suffers from unstable chemical passivation under air exposure, responsible for the poor interfacial wettability and conductivity with Li metal. Instead of conventional methods to remove surface contaminants by mechanical polishing, acid etching and high temperature reduction, herein we propose a simple strategy of interfacial gas release and detergency to smartly convert Li2CO3 passivation layer into ion-conductive Li3PO4 domains at mild temperature (∼200 ℃). The in-situ formation of PH3 vapor and its phosphorization enables a dramatic decrease of Li/garnet interfacial resistance down to 2 Ω cm2 at room temperature (RT). The improved interfacial wettability and conductivity endow the symmetric cells with ultra-stable galvanostatic cycling over 1500 h and high critical current density of 2.6 mA/cm2. The high coulombic efficiency of Li plating enables a high reversibility of solid-state NCM811/Li cells even under a low N/P ratio (∼4) and high cut-off voltage of 4.5 V at RT. The prototype of fluoride-garnet solid-state batteries are successfully driven as rechargeable system (rather than widely known primary battery) with high conversion capacity (400 ∼ 500 mAh/g) and high-rate performance (251.2 mAh/g at 3 C). This interface infiltration-detergency approach provides a practical solution to the achievement of high-energy solid-state Li metal batteries.

Study of graphite interlayer modification on the interfacial stability of solid electrolyte Li7La3Zr2O12 with lithium metal anode

The instability of Ta-doped Li7La3Zr2O12 (LLZTO) solid electrolytes with Li anode has severely restricted the development of all-solid-state lithium batteries. Herein, a simple interlayer of graphite is constructed at the Li/LLZTO interface with pencil, and the electrochemical stability of the battery has been significantly improved. Results show that the internal resistance of battery modified by 2B type graphite interlayer is reduced more than 2 orders of magnitude than that of the unmodified battery. And the battery has good cycling stability at current density of 0.1 mA cm−2 with polarization voltage< 0.01 V after 200 cycles. Besides, it also has excellent high-current discharge performance in the range of 0.1 mA cm−2 ∼ 0.6 mA cm−2 with polarization voltage close to 0 V. SEM showed that before galvanostatic charge-discharge (GCD) cycle, the morphology of the surface graphite is lamellar, while it is irregular granular shape and appeared at the grain boundary of LLZTO solid electrolyte after GCD cycle. Raman and XPS results shows that a LiC6 compound is formed after GCD cycle, which locally form LiC6/LLZTO/LiC6 microbatteries, where Li+ can spontaneously diffuse in the in-situ lithiated graphite layer, thereby enhancing the electrochemical performance of the battery.

Effect of Ga2O3 Addition on the Properties of Garnet-Type Ta-Doped Li7La3Zr2O12 Solid Electrolyte

Garnet-type Ta-doped Li7La3Zr2O12 (LLZO) ceramic solid electrolytes with Ga2O3 additive were synthesized using a conventional solid-state reaction process. When the amounts of Ga2O3 additive were below 2 mol %, the sintered sample has a dense structure composed of grains with an average size of 5 to 10 μm, whereas 3 mol % or more Ga2O3 addition causes a significant increase in grain size above several 10 to 100 μm, due to high-temperature sintering with a large amount of liquid Li-Ga-O phase. At room temperature, the highest total (bulk + grain-boundary) ionic conductivity of 1.1 mS cm−1 was obtained in the sample with 5 mol % Ga2O3 addition. However, this sample was shorted by Li dendrite growth into solid electrolyte at a current density below 0.2 mA cm−2 in galvanostatic testing of the symmetric cell with Li metal electrodes. The tolerance for Li dendrite growth is maximized in the sample sintered with 2 mol % Ga2O3 addition, which was shorted at 0.8 mA cm−2 in the symmetric cell. Since the interfacial resistance between Li metal and solid electrolyte was nearly identical among all samples, the difference in tolerance for Li dendrite growth is primarily attributed to the difference in microstructure of sintered samples depending on the amounts of Ga2O3.

Thermodynamics as a Driving Factor of LiCoO2 Grain Growth on Nanocrystalline Ta-LLZO Thin Films for All-Solid-State Batteries.

All-solid-state batteries primarily focus on macrocrystalline solid electrolyte/cathode interfaces, and little is explored on the growth and stability of nanograined Li-garnet and cathode ones. In this work, a thin (∼500 nm) film of LiCoO2 (LCO) has been grown on top of the polycrystalline layer of Ta-doped Li7La3Zr2O12 (Ta-LLZO) solid electrolyte using the pulsed laser deposition (PLD) technique. Scanning transmission electron microscopy, electron diffraction, and electron tomography demonstrated that the LCO film is formed by columnar elements with the shape of inverted cones. The film appears to be highly textured, with the (003) LCO crystal planes parallel to the LCO/Ta-LLZO interface and with internal pores shaped by the {104} and {102} planes. According to density functional theory (DFT) calculations, this specific microstructure is governed by a competition between free energies of the corresponding crystal planes, which in turn depends on the oxygen and lithium chemical potentials during the deposition, indicating that thermodynamics plays an important role in the resulting LCO microstructure even under nonequilibrium PLD conditions. Based on the thermodynamic estimates, the experimental conditions within the LCO stability domain are proposed for the preferential {104} LCO orientation, which is considered favorable for enhanced Li diffusion in the positive electrode layers of all-solid-state batteries.

High-performance Ta-doped Li7La3Zr2O12 garnet oxides with AlN additive

Garnet-type oxide is one of the most promising solid-state electrolytes (SSEs) for solid-state lithium-metal batteries (SSLMBs). However, the Li dendrite formation in garnet oxides obstructs the further development of the SSLMBs seriously. Here, we report a high-performance garnet oxide by using AlN as a sintering additive and Li as an anode interface layer. AlN with high thermal conductivity can promote the sintering activity of the garnet oxides, resulting in larger particle size and higher relative density. Moreover, Li3N with high ionic conductivity formed at grain boundaries and interface can also improve Li-ion transport kinetics. As a result, the garnet oxide electrolytes with AlN show enhanced thermal conductivity, improved ionic conductivity, reduced electronic conductivity, and increased critical current density (CCD), compared with the counterpart using Al2O3 sintering aid. In addition, Li symmetric cells and Li∣LiFePO4 (Li∣LFP) half cells using the garnet electrolyte with the AlN additive exhibit good electrochemical performances. This work provides a simple and effective strategy for high-performance SSEs.

High Specific Energy Li7La3Zr2O12 Solid Electrolyte Based Thermal Battery

Garnet-type Ta-doped Li7La3Zr2O12 (LLZTO) solid electrolyte has been widely investigated for secondary Li ionic or metal batteries at ambient temperature. Because of the increasing ionic conductivity of LLZTO with temperature, we applied the LLZTO solid electrolyte to thermal battery working at 550 °C. The LLZTO presents ultrahigh specific energy as the discharge specific energy and specific power is 605 W h kg−1 and 2.74 kW kg−1 at 100 mA cm−2 with a cut-off voltage of 1.8 V, respectively. This is larger than the LiF–LiCl-LiBr electrolyte which is commonly used in thermal battery with a specific energy of 514 W h kg−1. The internal resistance of the single cell reaches 0.65 Ω, but the specific energy remains at about 400 W h kg−1 as the current density increases to 400 mA cm−2. We report the application of LLZTO in thermal battery with high specific energy, large current, and high voltage discharge for the first time, broadening the application range of solid electrolytes.

Tailoring grain growth and densification toward a high-performance solid-state electrolyte membrane

The synthesis of dense and uniform solid-state electrolyte membranes for Li batteries is challenging due to the lack of fine control over the grain growth by conventional sintering methods. Using such techniques, abnormal grain growth can often occur, with associated contaminants and voids, often resulting in electrolyte membranes that suffer from high resistivity, poor stability, and the risk of Li dendrite penetration. Herein, we report a new high-temperature (1500 K) and rapid sintering (30 s) process by Joule heating that tailors the grain growth and densification toward high-quality, high-performance solid-state electrolyte membranes. The high temperature contributes to the rapid removal of impurities, leading to a dense and uniform microstructure in seconds. The short sintering time provides controlled grain growth, with nearly unchanged grain size and distribution compared to the solid-state electrolyte powders prior to sintering. Using calcined Ta-doped Li7La3Zr2O12 (LLZTO) garnet powders, we show that the grain size distribution before and after the rapid sintering are nearly identical (∼4 μm for both), while defects (e.g., voids and gaps) and impurities are effectively eliminated. The resulting high-quality membrane features good ionic conductivity (6.4 × 10−4 S cm−1 at room temperature) and excellent stability during lithium striping/plating (>300 h under 0.2 mA cm−2), making it suitable for Li battery applications. This high-temperature rapid sintering approach can be further extended to a variety of ceramic Li+ conductors toward the future development of solid-state batteries.

Tolerance for Li dendrite penetration in Ta-doped Li7La3Zr2O12 solid electrolytes sintered with Li2.3C0.7B0.3O3 additive

We fabricated garnet-type Ta-doped Li7La3Zr2O12 (LLZTO)/Li2.3C0.7B0.3O3 (LCBO) composite ceramic solid electrolytes. By adding the appropriate amount of LCBO to LLZTO, composite solid electrolytes were densified by sintering at 1000 °C without covering the pellet with LLZTO mother powder. LLZTO/LCBO Composites with LCBO volume contents of 20 and 50% showed the ionic conductivity well above 1 × 10−4 S cm−1 at room temperature. Li plating and stripping property for LLZTO/LCBO composites was evaluated using symmetric cells with Li metal electrodes at room temperature. As results, a symmetric cell composed of composite solid electrolyte with low LCBO volume content was stably cycled at the current density up to 0.3 mA cm−2, but increasing the amount of LCBO significantly lowered the current density where the Li dendrite penetration in solid electrolyte occurs. This indicates that LCBO addition is effective for lowering the sintering temperature of LLZTO but the smaller LCBO content is prefer to maintain the tolerance for Li dendrite penetration at high current density.