Garnet-type Solid Electrolytes Research Articles

Preparation and electrochemical properties of Li6La3Zr0.7Ti0.3Ta0.5Sb0.5O12 high-entropy Li-garnet solid electrolyte

Garnet-type solid electrolytes stand out as promising Li-ion conductors for the next-generation batteries. It has been demonstrated that the inherent properties of garnets can be tailored by introducing various dopants into their crystal structures. Recently, there has been a growing interest in the concept of high entropy stabilization for materials design. In this study, we synthesized high-entropy garnets denoted as Li6La3Zr0.7Ti0.3Ta0.5Sb0.5O12 (LLZTTSO), wherein Ti, Sb, and Ta occupy the Zr site. The formation of the cubic garnet phase in LLZTTSO was confirmed through X-ray diffraction (XRD), and the resulting lattice parameter agreed with predictions made using computational methods. Despite the substantial porosity (relative density 80.6%) attributed to the low sintering temperature, LLZTTSO exhibits a bulk ionic conductivity of 0.099 mS cm−1 at 25°C, and a total ionic conductivity of 0.088 mS cm−1, accompanied by an activation energy of 0.497 eV. Furthermore, LLZTTSO demonstrates a critical current density of 0.275 mA cm−2 at 25°C, showcasing its potential even without any interfacial modification.

Reasonable design a high-entropy garnet-type solid electrolyte for all-solid-state lithium batteries

Traditional garnet solid electrolyte (Li7La3Zr2O12) suffers from low room temperature ionic conductivity, poor air stability, high sintering temperature and energy consumption. Considering the development prospects of high-entropy materials with high structural disorder and strong component controllability in the field of electrochemical energy storage, herein, a novel high-entropy garnet-type oxide solid electrolyte, Li5.75Ga0.25La3Zr0.5Ti0.5Sn0.5Nb0.5O12 (LGLZTSNO) was constructed by partially replacing the Li and Zr sites in Li7La3Zr2O12 with Ga and Ti/Sn/Nb elements, respectively. The experimental and density functional theory (DFT) calculation results show that the high-entropy LGLZTSNO electrolyte has preferable room temperature ion conductivity, air stability, interface contact performance with lithium anode, and the ability to suppress lithium dendrites. Thanks to the improvement of electrolyte performance, the critical current density of Li/Ag@LGLZTSNO/Li symmetric cell was increased from 0.42 to 1.57 mA cm−2, and the interface area specific impedance (IASR) was reduced from 765.2 to 42.3 Ω cm2. Meanwhile, the Li/Ag@LGLZTSNO/LFP full cell also exhibits excellent rate performance and cycling performance (148 mA h g−1 at 0.1 C and 124 mA h g−1 at 0.5 C, capacity retention up to 84.8% after 100 cycles at 0.1 C), showing the application prospects of high-entropy LGLZTSNO solid electrolyte in high-performance all solid state lithium batteries.

Optimized Lithium Ion Coordination via Chlorine Substitution to Enhance Ionic Conductivity of Garnet-Based Solid Electrolytes.

Garnet-type solid-state electrolytes attract abundant attentions due to the broad electrochemical window and remarkable thermal stability while their poor ionic conductivity obstructs their widespread application in all-solid-state batteries. Herein, the enhanced ionic conductivity of garnet-type solid electrolytes is achieved by partially substituting O2- sites with Cl- anions, which effectively reduce Li+ migration barriers while preserving the highly conductive cubic phase of garnet-type solid-state electrolytes. This substitution not only weakens the anchoring effect of anions on Li+ to widen the size of Li+ diffusion channel but also optimizes the occupancy of Li+ at different sites, resulting in a substantial reduction of the Li+ migration barrier and a notable improvement in ionic conductivity. Leveraging these advantageous properties, the developed Li6.35 La3 Zr1.4 Ta0.6 O11.85 -Cl0.15 (LLZTO-0.15Cl) electrolyte demonstrates high Li+ conductivity of 4.21×10-6 Scm-1 . When integrated with LiFePO4 (LFP) cathode and metallic lithium anode, the LLZTO-0.15Cl electrolyte enables the solid-state battery to operate for more than 100 cycles with a high capacity retention of 76.61% and superior Coulombic efficiency of 99.48%. This work shows a new strategy for modulating anionic framework to enhance the conductivity of garnet-type solid-state electrolytes.

Synthesis of Garnet-type Solid Electrolyte for All-Solid-State Battery Application

The Ga-doped Li7La3Zr2O12 (LLZO) Solid State Electrolyte (SSE) has been synthesized via solid-state reaction. The structural study of the SSE was conducted with the help of X-ray diffraction and the Rietveld method. The SSE crystallizes in the Li6.25Ga0.15La2.90Zr2O12 phase with cubic space group number 220 and unit cell parameter 13.02081 Å, and La2Zr2O7 impurity phase with cubic space group number 227 and unit cell parameter 10.79475 Å. Obtained lattice planes in the refinement were confirmed with the help of TEM. The core of the Li-ion migration channel has been defined as the loop formed by the Li32, Li1, Li2, and Li22 sites with minimal Li...Li distance and occupational disorganization of the Ga-doped LLZO SSE. The electron density plots of the Li6.25Ga0.15La2.90Zr2O12 phase have shown maximum distribution of electrons inside the unit cell for lanthanum atoms. XPS confirmed the presence of all the precursors i.e., Li, La, Zr, Ga, and O in the synthesized compound. The elemental composition was confirmed with the help of EDX. In the direct current charge-discharge behavior of the Li symmetric cell no voltage breakdown was observed even at 6 mAcm‑2 current density and after 400 charge/discharge cycles for over 200 hours.

Interfacial Degradation Processes in Solid-State Batteries during High Temperature Processing and the Mitigation Strategies

Garnet-type solid electrolytes have been extensively investigated in recent times as potential candidates for solid-state batteries. Among them, garnets with nominal composition Li7La3Zr2O12(LLZO) have received particular attention due to their high Li-ion conductivity (10-3 Scm-1) at room temperature and chemical stability against metallic lithium besides possessing a large electrochemical window >5V.[1] Despite of striking properties, LLZO suffers from several challenges such as interfacial instability with cathodes, e.g., LCO, during high temperature processing, resulting in a huge interface resistance, which is one of the fundamental reasons for the failure of solid-state batteries based on LLZO.[2-4] So far, the high interfacial impedance has been related to LLZO|LCO interface decomposition occurring due to diffusion of Co across the cathode-electrolyte interface. Herein, we investigated the hypothesis that interfacial degradation originate from the incorporation of Co into the LLZO lattice. The solubility limit of Co is determined to be 0.16 per formula unit, whilst the concentrations beyond promote phase transition (cubic LLZO-to-tetragonal LLZO). We investigated in detail the temperature-dependent Co diffusion into LLZO and concluded that detrimental cross diffusion could take place at any relevant process condition. Besides, the optimal protective Al2O3 coating thickness for relevant temperatures was studied, which allowed to create a process diagram to provide mitigation strategies towards enabling stable LCO|LLZO interface in all-solid-state batteries. Keywords: Solid-state batteries, Interfaces, cross diffusion, interfacial degradation AcknowledgementsD.R. acknowledges financial support by the Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development and the Christian Doppler Research Association (Christian Doppler Laboratory for Solid-State Batteries). D.R. and J. F. acknowledges financial support by the Austrian Science Fund (FWF) in the frame of the project InterBatt (P 31437). D.K. acknowledges funding by the European Union’s Horizon 2020 Research and Innovation Programme (Grant No. 823717, project “ESTEEM3”) and by the Zukunftsfond Steiermark.Reference[1] Murugan, R., Thangadurai, V. and Weppner, W., 2007. Fast Lithium Ion Conduction in Garnet‐type Li7La3Zr2O12. Angew. Chemie. Int. Edt., 46(41), 7778-7781.[2] Chen, X., Xie, J., Zhao, X., & Zhu, T., 2021. Electrochemical Compatibility of Solid‐State Electrolytes with Cathodes and Anodes for All‐Solid‐State Lithium Batteries: A Review. Adv. Energy Sustain. Res., 2(5), 2000101.[3] Sakuda, A., Hayashi, A., Tatsumisago, M., 2010. Interfacial Observation Between LiCoO2 Electrode and Li2S-P2S5 Solid Electrolytes of All-Solid-State Lithium Secondary Batteries Using Transmission Electron Microscopy. Chem. Mater., 22(3), 949–956.[4] Ihrig, M., Kuo, L.Y., Lobe, S., Laptev, A.M., Lin, C.A., Tu, C.H., Ye, R., Kaghazchi, P., Cressa, L., Eswara, S. and Lin, S.K., 2023. Thermal Recovery of the Electrochemically Degraded LiCoO2/Li7La3Zr2O12: Al, Ta Interface in an All-Solid-State Lithium Battery. ACS Appl. Mater. Interfaces.

High Areal Capacity Cycling of Three-Electrode Sodium/NBA/Sodium Cells

The cycling stability of Li and Na metal electrodes is influenced by the interface with the solid electrolyte. Study of the cycling behavior at areal capacities >>0.5 mAh/cm2 are uncommon, and plating and stripping behaviors remain relatively unknown for the individual electrode/electrolyte interfaces because of the difficulty of separating the individual interfaces in a two-electrode cell configuration. Because areal capacities of practical cells target >5 mAh/cm2, it is important to cycle at much higher areal capacities than typically studied. Here, we utilize a three-electrode symmetric cell of sodium metal with sodium beta alumina (NBA) electrolyte and cycled areal capacities ranging from 0.5 to 5 mAh cm-2 and achieved current densities >10 mA cm-2 at 1.0 mAh cm-2. We find that polarization increases most at the stripping electrode, and that during current density ramps the polarizations are greatly affected by the areal capacity, affecting the maximum current density that can be reached prior to either cell shorting or impedance rise that drives the voltage magnitude to well over 1 V. Additionally, we found resistance rise occurring at the Na/NBA interface during plate (reduction) as well as strip (oxidation) for the same electrode, potentially indicating voiding on plate at sufficiently high current densities and areal capacities (5 mAh cm-2, >2 mA cm-2). For two-electrode studies, the voltage evolution on the plating electrode we observe must be considered for the assumption that the plating electrode is a pseudo reference electrode. We also use our three-electrode cell configuration to study several other experimental conditions, including cycling to failure at a fixed current density and areal capacity, as well as a uni-directional current flow experiment to determine the maximum amount of plating / stripping that can be achieved in the absence of cycling. These findings will help direct future experiments and interpretation of data to quantify the limits and improve the engineering of Li and Na metal / solid electrolytes interfaces.Jolly, D. S.; Ning, Z.; Darnbrough, J. E.; Kasemchainan, J.; Hartley, G. O.; Adamson, P.; Armstrong, D. E. J.; Marrow, J.; Bruce, P. G. Sodium/Na Β″ Alumina Interface: Effect of Pressure on Voids. ACS Appl Mater Interfaces 2019, 12 (1), 678–685. https://doi.org/10.1021/ACSAMI.9B17786.Krauskopf, T.; Hartmann, H.; Zeier, W. G.; Janek, J. Toward a Fundamental Understanding of the Lithium Metal Anode in Solid-State Batteries - An Electrochemo-Mechanical Study on the Garnet-Type Solid Electrolyte Li 6.25 Al 0.25 La 3 Zr 2 O 12. ACS Appl Mater Interfaces 2019, 11 (15), 14463–14477. https://doi.org/10.1021/ACSAMI.9B02537/SUPPL_FILE/AM9B02537_SI_001.PDF.

Experimental and theoretical study on enhanced electrochemical properties of double doped garnet-type solid electrolyte

Garnet-type solid electrolyte (Li7La3Zr2O12, LLZO) is believed as a promising candidate for all-solid-state battery due to its high voltage window and good stability with metallic lithium. However, it exists as tetragonal phase with low ionic conductivity at room temperature, which seriously hinders its practical application. In this paper, the strategy of In/Ga ions was introduced into LLZO, which can be found that double doping can improve the structural stability and the electrochemical properties of the sample compared to single doping. When x = 0.1, the sample Li6.55+xGa0.15La3Zr2-xInxO12 shows the high ionic conductivity of 1.5 × 10−4 S/cm, and activation energy of 0.268 eV. Density functional theory (DFT) calculation show that the introduce of In3+ and Ga3+ can effectively improve the ion transport capacity to reduce the transport energy barrier. In addition, the Li/In/Ga-LLZO/Li cells could cycle stably for 1000 h at 60 °C with the current density of 0.1 mA/cm2.

In Situ and Low-Cost Improvement of the Lithium Anode Interface in Garnet-Type Solid-State Electrolytes.

In recent years, the development of electric vehicles and environmental concerns have made necessary improvements in the energy density and safety of lithium-ion batteries. Therefore, the development of all-solid-state lithium-ion batteries (ASSLIBs) has become imperative. One advantage of ASSLIBs is their potential for downsizing with the use of lithium metal as the anode. However, in this study, a garnet-type solid electrolyte (Li6.75La3Zr1.75Ta0.25O12) was used, which has low reactivity with lithium metal. Thus, interface modification using CaCl2 was employed to form a Li-Ca-Cl composite anode. The interfacial resistance was remarkably reduced to 7 Ω cm2, and the symmetric cell exhibited stable cycling for 1200 h at room temperature and a current density of 0.1 mA cm-2. The voltage ranged from ±15 to ±16 mV. The full cell demonstrated a high initial discharge capacity of 149.2 mA h g-1 and a Coulombic efficiency of 98.0% while maintaining a discharge capacity retention of 91.3% after 100 cycles. These findings lay a solid foundation for future commercial applications as interface modification was achieved through a simple spin-coating process using low-cost CaCl2 (0.7 USD g-1).

Nanostructure of Si-Sn Thick-Film Electrodes to Improve the Energy Density of Oxide-Based All-Solid-State Lithium-Ion Batteries

Charge and discharge characteristics of Si-Sn composite thick-film electrodes on a garnet-type solid electrolyte were studied systematically. Charge/discharge cycle performance of 0.1 μm-thick Si-Sn thin-film electrodes simply depended on the Si:Sn composition ratio, while the thick-film electrodes with a thickness of 1 μm delivered the most outstanding performance at a specific Si/Sn atomic ratio of 7:3. The Si7-Sn3 composite film had a unique nanostructure to promote the charge/discharge reactions of Si and to maintain the interfacial contact with the solid electrolyte. These results can provide a clue to the design of Si-based negative electrodes for all-solid-state lithium ion batteries with high energy density.

Optimizing Li Ion Transport in a Garnet-Type Solid Electrolyte via a Grain Boundary Design

Garnet-type solid electrolytes have gained considerable attention owing to their exceptional ionic conductivity and broad electrochemical stability window, making them highly promising for solid-state batteries (SSBs). However, this polycrystalline ceramic electrolyte contains an abundance of grain boundaries (GBs). During the repetitive electroplating and stripping of Li ions, uncontrolled growth and spreading of lithium dendrites often occur at GBs, posing safety concerns and resulting in a shortened cycle life. Reducing the formation and growth of lithium dendrites can be achieved by rational grain boundary design. Herein, the garnet-type solid electrolyte LLZTO was firstly coated with Al2O3 using the atomic layer deposition (ALD) technique. Subsequently, an annealing treatment was employed to introduce Al2O3 into grain boundaries, effectively modifying them. Compared with the Li/LLZTO/Li cells, the Li/LLZTO@Al2O3-annealed/Li symmetric batteries exhibit a more stable cycling performance with an extended period of 200 h at 1 mA cm−2. After matching with the NMC811 cathode, the capacity retention rate of batteries can reach 96.8% after 50 cycles. The infusion of Al2O3 demonstrates its capability to react with LLZTO particles, creating an ion-conducting interfacial layer of Li-Al-O at the GBs. This interfacial layer effectively inhibits Li nucleation and filament growth within LLZTO, contributing to the suppression of lithium dendrites. Our work provides new suggestions for optimizing the synthesis of solid-state electrolytes, which can help facilitate the commercial application of solid-state batteries.

Quasi-In Situ XPS Insights into the Surface Chemistry of Garnet-Type Li6.4La3Zr1.4Ta0.6O12 Solid-State Electrolytes: The Overlooked Impact of Pretreatments and a Direct Observation of the Formation of LiOH.

Garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is a highly promising solid-state lithium metal battery electrolyte due to its exceptional ionic conductivity and electrochemical stability. However, when exposed to air, a passivation layer can be spontaneously formed on the garnet-type electrolyte, deteriorating its wettability with metallic lithium (Li) and impeding the lithium ion transfer at the Li-garnet electrolyte interface. The passivation layer is considered a critical issue for garnet-type solid electrolytes. Despite intensive research, the formation mechanism of the passivation film remains poorly understood. The key to elucidating the formation mechanism is to obtain a pristine garnet electrolyte surface and study how the pristine garnet electrolyte interacts with air. In this study, different passivation layer removal pretreatments were performed to expose pristine garnet electrolytes, and their impacts on the samples were systematically studied. The results reveal the overlooked negative impacts of vacuum annealing and acid treatment on LLZTO, which are indicated by the severe loss of Li and O and the formation of additional Li-depleted metal oxides. It was confirmed that argon annealing is the only viable approach to remove the passivation layer without introducing concomitant contaminations to LLZTO. Based on this method, we directly evidenced the formation of LiOH on LLZTO under rarefied air using quasi-in situ X-ray photoelectron spectroscopy. It was confirmed that the loss of Li and O ions, rather than Li+/H+ exchange, drives the formation of LiOH in the passivation layer. These results not only provide a better understanding of the surface and interface chemistry of LLZTO but also reveal a reliable surface treatment for the LLZTO sample.

Grain Engineering for High-Performance Garnet-Type Li7La3Zr2O12 Solid Electrolytes

Garnet-type solid electrolytes based on cubic Li7La3Zr2O12 (LLZO) are promising candidates for the development of Li metal solid-state batteries due to their high ionic conductivity and excellent chemical stability against metallic lithium. Unfortunately, the leakage of electron through the interface and grain boundaries leads to the nucleation of Li dendrite inside solid electrolyte, making it easier for the failure of solid-state Li metal batteries. Here, we introduce a promising fluorination strategy to suppress Li dendrite formation by blocking electron transport through the interface and along the grain boundaries. Fluorination not only decreases the electronic conductivity of garnet pellet but also improves its wettability toward Li metal. As a result, the optimized LLZOge pellet demonstrates an outstanding critical current density of 2.7 mA cm‒2 and ensures ultra-long cyclability over 5000 h at 0.2 mA cm‒2 and over 300 h at 1 mA cm‒2 at room temperature. This work demonstrates the efficacy of the fluorination strategy in increasing the electronic resistance of garnet-type electrolyte for the suppression of Li dendrite growth. Figure 1

Enabling high rate capability and stability all-solid-state batteries via cationic surfactant modification of composite electrolyte

The garnet-type solid electrolyte Li6.4La3Zr1.4Ta0.6O12 (LLZTO) was modified with a cationic surfactant Cetyltrimethylammonium Bromide (CTAB) to improve the dispersion of LLZTO inorganic particles in Poly (ethylene oxide) (PEO) electrolyte (PEO-LLZTO@CTAB) by a liquid phase casting method. During fabrication, the cationic modifier CTAB is uniformly adsorbed on the surface of LLZTO particles, which can effectively reduce their surface energy and lead to a thin CTAB surface coating layer. This fabricated PEO-LLZTO@CTAB can avoid the aggregation of LLZTO particles in the composite solid-state electrolyte (CSSE) and improve the interfacial contact at the PEO/LLZTO interface, thus reducing the overall resistance of PEO-LLZTO@CTAB/Li half-cell and inhibiting the dendrite growth during cycling. The all-solid-state batteries (ASSBs) with LiFePO4 (LFP) as the cathode, PEO-LLZTO@CTAB as the electrolyte and Li as the anode exhibit a high initial discharge capacity of 146.6 mAh-g−1, excellent rate performance and high-capacity retention of 91.0 % after 300 cycles at 0.2 C multiplier and 60 °C within the voltage range of 2.7–4.0 V.

Computational and experimental investigation of Li+-ion transport mechanism of Eu-doped garnet solid electrolyte for Li-ion batteries

Garnet-type Li7La3Zr2O12 (LLZO) is one of the most preeminent solid electrolytes in all-solid-state lithium batteries (ASSLBs). To further improve the conductivity of LLZO, we synthesized a novel garnet-type solid electrolyte Li7+xLa3Zr2-xEuxO12 (0 ≤ x ≤ 0.20) in which the low-valence Eu+3 doped at the Zr+4 site. Using density functional theory (DFT) calculation, effect of Eu3+ doping was also investigated. Eu3+ doping normalized Li+-ion transport by enhancing Li+-ion occupancy at 96 h position which reduced the Li+-ion diffusion barrier and enhanced the ionic conductivity. Li7.15La3Zr1.85Eu0.15O12 (LLZEO) solid electrolyte exhibited highest ionic conductivity of 0.415 × 10−4 S/cm and the lowest activation energy of 0.28 eV at 25 °C. Further, a flexible composite electrolyte membrane was also prepared using LLZEO as filler into polyethylene oxide/polyethylene glycol matrix, which exhibited excellent flexibility and high ionic conductivity of 0.15 × 10−4 S/cm at 25 °C will be a promising candidate for ASSLBs.

Improvement of PEO-based composite solid electrolyte sheet using particle-size-controlled Ga-Rb-doped LLZO with high ion conductivity

In this study, a Li6.5Ga0.2La2.95Rb0.05Zr2O12 garnet-type solid electrolyte with high ion conductivity was prepared. The particle size was reduced to the nano size through a ball milling process, and the effect of the change in particle size on the all-solid-state batterie was investigated. As all-solid-state batteries have better stability than liquid electrolytes and serve as separators to help increase energy density, much research has been conducted recently. However, their conductivity is much lower than that of the liquid electrolyte. Therefore, an experiment was conducted on the difference in particle size to improve the ionic conductivity and energy density. Reducing the average particle size of the LLZO samples from approximately 10 to 0.6 μm using a ball milling process increased the ionic conductivity of the pellet from 1.27 × 10–3 to 1.58 × 10–3 S cm-1 at 25 °C. The ionic conductivity of the sheet decreased from 2.96 × 10–4 to 2.60 × 10–4 S cm-1 at 70 °C, but lithium transference number increased from 0.56 to 0.64. Therefore, the structural and electrochemical properties of the LLZO-bare and LLZO-ball-milled were investigated using powder X-ray diffraction analysis, field-emission scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic measurements.

Improved Ga-doped Li7La3Zr2O12 garnet-type solid electrolytes for solid-state Li-ion batteries

Improved Ga-doped Li7La3Zr2O12 garnet-type solid electrolytes for solid-state Li-ion batteries

First-principles calculations and Yb3+ doping effects study of garnet-type solid state electrolytes

Garnet-type solid state electrolyte Li7La3Zr2O12 (LLZO) plays a critical role in enhancing the safety of all solid-state lithium batteries, but its practical applications have been seriously limited by its poor ionic conductivity at room temperature. Elemental doping is an effective strategy to address this issue and the influence of Yb3+ doping on LLZO performance was investigated in this study. The doping site of Yb3+ in LLZO was determined by first-principles calculations based on DFT for the first time, and the results revealed that the Yb3+ doping position was La3+ site. A series of Li7La3-xYbxZr2O12 (x = 0.02, 0.04, 0.06, 0.15,0.30, LLYZO) were successfully produced by solid-state reaction route. It was found that the Yb3+ doping strategy not only enhanced the ion conductivity, but also was beneficial to inhibit the abnormal grain growth by forming LiYbO2 second phase and accelerate the sintering process. The LLYZO (x = 0.15) ceramic sintered at 1200 °C for 15 h shows a highest conductivity of 2.53× 10−4 S·cm−1, the lowest activation energy of 0.294 eV and a relative density of 90.2%.

High Cathode Loading and Low-Temperature Operating Garnet-Based All-Solid-State Lithium Batteries - Material/Process/Architecture Optimization and Understanding of Cell Failure.

All-solid-state lithium batteries (ASSLBs) are prepared using garnet-type solid electrolytes by quick liquid phase sintering (Q-LPS) without applying high pressure during the sintering. The cathode layers are quickly sintered with a heating rate of 50-100 K min-1 and a dwell time of 10min. The battery performance is dramatically improved by simultaneously optimizing materials, processes, and architectures, and the initial discharge capacity of the cell with a LiCoO2 -loading of 8.1mg reaches 1 mAh cm-2 and 130 mAh g-1 at 25 °C. The all-solid-state cell exhibits capacity at a reduced temperature (10 °C) or a relatively high rate (0.1 C) compared to the previous reports. The Q-LPS would be suitable for large-scale manufacturing of ASSLBs. The multiphysics analyses indicate that the internal stress reaches 1GPa during charge/discharge, which would induce several mechanical failures of the cells: broken electron networks, broken ion networks, separation of interfaces, and delamination of layers. The experimental results also support these failures.

Understanding the evolution of lithium dendrites at Li6.25Al0.25La3Zr2O12 grain boundaries via operando microscopy techniques

The growth of lithium dendrites in inorganic solid electrolytes is an essential drawback that hinders the development of reliable all-solid-state lithium metal batteries. Generally, ex situ post mortem measurements of battery components show the presence of lithium dendrites at the grain boundaries of the solid electrolyte. However, the role of grain boundaries in the nucleation and dendritic growth of metallic lithium is not yet fully understood. Here, to shed light on these crucial aspects, we report the use of operando Kelvin probe force microscopy measurements to map locally time-dependent electric potential changes in the Li6.25Al0.25La3Zr2O12 garnet-type solid electrolyte. We find that the Galvani potential drops at grain boundaries near the lithium metal electrode during plating as a response to the preferential accumulation of electrons. Time-resolved electrostatic force microscopy measurements and quantitative analyses of lithium metal formed at the grain boundaries under electron beam irradiation support this finding. Based on these results, we propose a mechanistic model to explain the preferential growth of lithium dendrites at grain boundaries and their penetration in inorganic solid electrolytes.

Co-doping strategy enhanced the ionic conductivity and excellent lithium stability of garnet-type Li7La3Zr2O12 electrolyte in all solid-state lithium batteries

Garnet-type Li7La3Zr2O12 (LLZO) is one of the most promising solid-state electrolytes (SSEs). However, the application of LLZO is limited by structural instability, low ionic conductivity, and poor lithium stability. To obtain a garnet-type solid electrolyte with a stable structure and high ionic conductivity, a series of TaCe co-doping cubic Li6·4La3Zr1.4-xTa0.6CexO12 (LLZTCO, x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.30) electrolytes were successfully synthesized through conventional solid-phase method. The Ta5+ doping can introduce more lithium vacancies and effectively maintain the stability of the cubic phase. The Ce4+ with a larger ionic radius is introduced into the lattice to widen the Li+ migration bottleneck size, which significantly increased the ionic conductivity to 1.05 × 10−3 S/cm. It also shows excellent stability to lithium metal by the optimization of Li+ transport channel. Li||LLZTCO||Li symmetric cells can cycle stably for more than 6 000 h at a current density of 0.1 mA/cm2 without any surface modifications. The commercialization potential of LLZTCO samples in all solid-state lithium batteries (ASSLBs) is confirmed by the prepared LiFePO4||LLZTCO||Li cells with a capacity retention rate of 98% after 100 cycles at 0.5C. This new co-doping method presents a practical solution for the realization of high-performance ASSLBs.