Garnet-type Solid Electrolytes Research Articles

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.

Spontaneous In Situ Formation of Lithium Metal Nitride in the Interface of Garnet-Type Solid-State Electrolyte by Tuning of Molten Lithium.

All-solid-state lithium-ion batteries (ASSLIBs) have attracted much attention owing to their high energy density and safety and are known as the most promising next-generation LIBs. The biggest advantage of ASSLIBs is that it can use lithium metal as the anode without any safety concerns. This study used a high-conductivity garnet-type solid electrolyte (Li6.75La3Zr1.75Ta0.25O12, LLZTO) and Li-Ga-N composite anode synthesized by mixing melted Li with GaN. The interfacial resistance was reduced from 589 to 21 Ω cm2, the symmetry cell was stably cycled for 1000 h at a current density of 0.1 mA cm-2 at room temperature, and the voltage range only changed from ±30 to ±40 mV. The full cell of Li-Ga-N|LLZTO|LFP exhibited a high first-cycle discharge capacity of 152.2 mAh g-1 and Coulombic efficiency of 96.5% and still maintained a discharge capacity retention of 91.2% after 100 cycles. This study also demonstrated that Li-Ga-N had been shown as two layers. Li3N shows more inclined to be closer to the LLZTO side. This method can help researchers understand what interface improvements can occur to enhance the performance of all-solid-state batteries in the future.

Reactive boride as a multifunctional interface stabilizer for garnet-type solid electrolyte in all-solid-state lithium batteries.

All-solid-state batteries are one of the most important game changers in electrochemical energy storage since they are free from the risk of leakage of hazardous flammable liquid solvents. Among the various types of solid-state electrolytes, Li7-xLa3Zr2-xTaxO12 garnets possess many desirable advantages to be considered a suitable candidate for lithium-ion batteries. However, their practical application has been hindered by premature short-circuits due to lithium dendrite growth, nonnegligible electronic conductivity and interfacial air sensitivity issues. Herein, we propose a multifunctional layer strategy to simultaneously address both the interface and electronic conductivity issues. With the help of a facile chemical process based on reactive cobalt boride, electron leakage was effectively blocked and the electrochemical performance/stability could be well maintained over extended cycles. The cobalt boride-coating layer also possessed an impressive Li metal wetting ability while sustaining a low interfacial resistance. A full cell paired with a commercialized cathode showed satisfactory performance with low overpotentials and a high specific capacity over 150 mA h g-1. Moreover, first-principle calculations further revealed the status of the rearrangement of the electron cloud behind the charge-density difference, and the nature of the low diffusion energy barrier of the reactive cobalt boride protective layer. Our strategy highlights the necessity of designing proper multifunctional layers in the garnet-type solid-state lithium-ion battery system.

Processing and Properties of Garnet-Type Li7 La3 Zr2 O12 Ceramic Electrolytes.

Garnet-type solid electrolyte Li7 La3 Zr2 O12 (LLZO) is widely considered as one of the most promising candidates for solid state batteries (SSBs) owing to its high ionic conductivity and good electrochemical stability. Since its discovery in 2007, great progress has been made in terms of crystal chemistry, chemical and electrochemical properties, and battery application. Nonetheless, reliable and controllable preparation of LLZO ceramics with desirable properties still remains as big challenges. Herein, this review summarizes various synthetic routes of LLZO ceramics and examines the influence of various key processing parameters on the chemical and electrochemical properties. Focusing on correlation of processing parameters and properties, this review aims to provide new insights on a reliable and controllable production of high-quality LLZO ceramic electrolytes for SSB application.

Melt-quenching of artificial metallic interlayer enables a resistance-free garnet/lithium interface for all-solid-state lithium-metal batteries

Garnet-type solid electrolytes are by far one of the most promising candidates for all-solid-state lithium-metal battery (ASSLMB) applications owing to their high electrochemical stability and ionic conductivity, but their practical performance is hindered by a poor interfacial compatibility with metallic lithium. Despite extensive efforts devoted to improving the garnet/lithium interface, inadequate success has been made towards commercializing ASSLMBs owing to the lack of both materials and techniques for efficient interfacial modification. In this work, we report the complete elimination of such interfacial resistance by applying an ultra-thin CuzSnyOx (6/5 < z/y < 3) layer to the garnet-electrolyte surface via a facile and scalable melt-quenching approach. Experimental and computational results show that a strong synergistic effect between Cu and Sn facilitates the formation of a uniform CuzSnyOx coating layer on the garnet electrolyte, resulting in stable lithium plating/stripping at the interface of LLZTO/CuzSnyOx with the lithium metal for 4000 hours without a short-circuit. After the interfacial resistance is eliminated with our approach, the stability of the modified garnet electrolyte is solely dependent on the intrinsic property of the garnet electrolyte itself, which brings about a high critical current density of 15.2 mA cm–2 at 60°C. We demonstrate an all-solid-state full cell containing the modified garnet electrolyte and a LiNi0.8Mn0.1Co0.1O2 cathode that had 94% capacity retention after 1000 stable cycles at room temperature.

The effect of Ti to the crystal structure of Li7-3xMxLa3Zr1.8Ti0.2O12 (M= Ga, In) garnet-type solid electrolytes as a second dopant

ABSTRACT Garnet-type solid-state electrolytes are promising candidates for solid-state lithium batteries, nevertheless their ionic conductivity is still not enough for commercial applications. On the other hand, doping still is the common way to improve the ionic conductivities of these solid electrolytes. In this study, mono and dual-doped garnet-type solid electrolytes were synthesised by substituting indium (In), gallium (Ga), indium-titanium (In-Ti) and gallium-titanium (Ga-Ti) to the Li7La3Zr2O12 structure by a solid-state reaction method. The contribution of substitutions to the formation of crystal phases was investigated by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). On the other hand, morphological analyses were done by scanning electron microscope (SEM) and the ionic conductivities of the solid electrolytes were determined by electrochemical impedance spectroscopy (EIS). The study showed that while Li7-3xInxLa3Zr2O12 (for x = 0.05, 0.10, 0.15, 0.20) and Li7-3xGaxLa3Zr2O12 (for x = 0.05) samples were formed in tetragonal phase with a space group of I41/acd:2, dual substituted Li7-3xInxLa3Zr1.8Ti0.2O12 and Li7-3xGaxLa3Zr1.8Ti0.2O12 solid electrolytes for all x values were formed in cubic phase with a space group of I-43d. The highest conductivity is reached for Li6.85Ga0.05La3Zr1.8Ti0.2O12. The radial distribution function studies showed that when more In and Ga atoms take place in the sites of Li atoms, more O atoms take place in the vicinity of both substituted In and Ga atoms within the Li7La3Zr1.8Ti0.2O12 (LLZTO) crystal framework which can eventuate in a change in the conduction mechanism.

The preliminary exploration of composition origin of garnet-type solid inorganic electrolytes by cluster-plus-glue-atom model

The preliminary exploration of composition origin of garnet-type solid inorganic electrolytes by cluster-plus-glue-atom model

Analyzing void formation and rewetting of thin in situ-formed Li anodes on LLZO

•The stripping behavior of thin Li was correlated with current density and thickness •Two regimes of thin Li stripping behavior were identified •The effect of Li void formation during unstable stripping is not fully recovered •De-wetted Li/solid electrolyte interfaces can be reestablished by a thermal treatment The transition from laboratory-scale thick Li-metal anodes (>500 μm) to thin (∼10–30 μm) Li anodes is necessary for the successful implementation of Li-metal solid-state batteries (LMSSBs). However, the mechanical deformation of Li along an interface depends on its thickness, making it essential to understand the interface mechanics between thin Li layers and solid electrolytes. We investigate the stripping behavior of thin Li electrodes that are formed using in situ plated (anode-free) Li on Li7La3Zr2O12 garnet-type solid electrolytes. We demonstrate that the accessible discharge capacity increases as current density decreases and the Li anode thickness increases. It is shown that two different mechanisms restrict the stripping of thin Li electrodes, depending on the current density. We demonstrate that de-wetted Li/LLZO interfaces during stripping can be reestablished using a thermal treatment. This approach could be integrated into future charging protocols, and the findings provide insight into LMSSB design, implementation, and operation. The transition from laboratory-scale thick Li-metal anodes (>500 μm) to thin (∼10–30 μm) Li anodes is necessary for the successful implementation of Li-metal solid-state batteries (LMSSBs). However, the mechanical deformation of Li along an interface depends on its thickness, making it essential to understand the interface mechanics between thin Li layers and solid electrolytes. We investigate the stripping behavior of thin Li electrodes that are formed using in situ plated (anode-free) Li on Li7La3Zr2O12 garnet-type solid electrolytes. We demonstrate that the accessible discharge capacity increases as current density decreases and the Li anode thickness increases. It is shown that two different mechanisms restrict the stripping of thin Li electrodes, depending on the current density. We demonstrate that de-wetted Li/LLZO interfaces during stripping can be reestablished using a thermal treatment. This approach could be integrated into future charging protocols, and the findings provide insight into LMSSB design, implementation, and operation.

Silver Doped Lithium Metal Thin Films for Solid-State Batteries

Potential use of lithium metal anode is a primary factor behind the high-energy density promise of solid-state batteries. However, large anodic loads lead to void formation and contact loss at the lithium/solid electrolyte interface which, in turn, lead to much higher effective local current densities during the subsequent lithium plating, causing dendrite formation and cell shorting.1, 2 This is due to the slow self-diffusion of Li atoms/vacancies, which is an inherent limitation of lithium metal.3 Modifying the bulk physiochemical properties of lithium metal via doping/alloying (<10 at% dopant) is an attractive approach, as such a small concentration of dopants can alter lithium metal’s bulk properties, without lowering its energy density. As an example, pore formation was effectively eliminated by alloying Li with 10 at% Mg, although chemical diffusion of Li within the alloy still restricted its rate performance.4 In this work, we report the effects of Ag as a dopant on the morphological stability and rate capability of Li-Ag alloy anodes during electrochemical cycling, as its concentration is varied in Li from 0-10 at.%. The alloy samples are prepared as 10 μm thick films, a practical form factor for solid-state batteries, via a combination of sputtering and thermal evaporation. Comparison of performance as a function of Ag content will be presented for both polymeric and inorganic solid-state electrolytes. Structural characterization of the alloy anodes via complementary techniques will also be presented. This research was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL). This abstract has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). References Kasemchainan, J.; Zekoll, S.; Spencer Jolly, D.; Ning, Z.; Hartley, G. O.; Marrow, J.; Bruce, P. G., Critical stripping current leads to dendrite formation on plating in lithium anode solid electrolyte cells. Nature Materials 2019, 18 (10), 1105-1111.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 Li6.25Al0.25La3Zr2O12. ACS Applied Materials & Interfaces 2019, 11 (15), 14463-14477.Jow, T. R.; Liang, C. C., Interface Between Solid Electrode and Solid Electrolyte—A Study of the Li / LiI ( Al2 O 3 ) Solid‐Electrolyte System. Journal of The Electrochemical Society 1983, 130 (4), 737-740.Krauskopf, T.; Mogwitz, B.; Rosenbach, C.; Zeier, W. G.; Janek, J., Diffusion Limitation of Lithium Metal and Li–Mg Alloy Anodes on LLZO Type Solid Electrolytes as a Function of Temperature and Pressure. Advanced Energy Materials 2019, 9 (44), 1902568.

High-Energy and Long-Lasting Lithium Metal Batteries Employing Garnet-Type Solid Electrolytes with Tailored Lithium Metal Compatibility

One of the viable options to significantly augment the energy density of lithium-ion batteries (LIBs) is to adopt lithium metal anode in the cell, which offers the highest theoretical capacity (3,860 mAh g-1) among anode materials.1 However, the practical obstacles such as dendrite growth, low Coulombic efficiency, and safety issues still remain unresolved, despite the extensive efforts to employ the lithium metal anode in LIBs.2 Recent progress in solid-state electrolyte development has granted a new promising opportunity for the utilization of lithium metal anodes, whose mechanical rigidity and non-flammable nature are supposed to effectively suppress lithium dendrite short-circuiting, thereby securing battery safety. Nevertheless, there has been no report thus far that demonstrates acceptable levels of electrochemical performance of solid-state lithium metal batteries for real-world applications.3,4 In our research, a lithium-metal-battery employing tailored garnet-type Li7-xLa3-aZr2-bO12 (LLZO) solid-electrolytes that can meet the lifespan requirements of both electric vehicles and stationary applications has been achieved, affording remarkable stability and energy density over 2,000 cycles. It is demonstrated that the compatibility between LLZO and lithium metal is crucial for the long-term stability, which can be accomplished by regulating bulk dopants and the corresponding dopant-specific interfacial treatment using protonation/etching. The appropriate selection of dopant and dopant-specific protonation/etching agent for LLZO leads to (i) the formation of a stable passivation layer at the interface with lithium metal, (ii) effective release of residual stress in LLZO, and (iii) intact contact at the interface.The lithium-metal cell with 2 mAh cm-2 cathode (12 mg cm-2) delivers a cumulative capacity of over 4,000 mAh cm-2 at 3 mA cm-2, which to the best of our knowledge, is the highest long-term cycle value reported for lithium metal batteries with LLZO electrolytes. Moreover, even with the thin 110-µm-LLZO electrolyte and 20-µm lithium metal, a high-loading-capacity cell (3.2 mAh cm-2) exhibits a superior cycle life (>600 cycles) at 2 mA cm-2 without short-circuiting, affording a basis for the high-energy-cell design with ultra-thin electrolyte. In addition, an all-solid-state-battery, excluding the ionic liquid electrolyte, was successfully demonstrated using the composite cathode, which could cycle over 1,000 times at a high current density of 3 mA cm-2 without short-circuiting. To the best of our knowledge, this is the first all-solid-state battery that can operate over 1,000 cycles, enabled by the garnet-type electrolytes and cathode with a commercially acceptable capacity.These findings are expected to open a new avenue for developing long-lasting solid-state lithium metal batteries by highlighting the efficacy of the coupled bulk and interface doping of solid electrolytes.

(Digital Presentation) Investigation on Reusability of Garnet-Type Ta-Doped Li7La3Zr2O12 Solid Electrolyte Degraded By Li Dendrite Growth

Development of solid inorganic lithium (Li) ion conducting materials for the use as solid electrolytes is indispensable for the realization of next-generation all-solid-state Li batteries with high safety and reliability. Among various oxide-based solid electrolyte materials, 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, the formation of a solid-solid interface between LLZO and the Li metal anode is challenging. 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.3–5) There is no doubt that the establishment of prevention technology for short-circuit failures is a top priority issue for the development of all-solid-state Li metal batteries.5) On the other hand, from the viewpoint of effective use of material resources, the possibility of reusing LLZO extracted from a solid-state battery after a short-circuit failure occurred is worth considering. In this work, we investigated the reusability of a Ta-doped Li6.55La3Zr1.55Ta0.45O12 (Ta-LLZO) solid electrolyte shorted by Li dendrite growth during electrochemical Li plating/stripping testing for a Li/Ta-LLZO/Li symmetric cell. Ta-LLZO was taken out of a tested cell after the degradation by Li dendrite growth occurred, and then annealed at 700 ºC in air. The annealing temperature was set to suppress possible excess Li loss from Ta-LLZO during post-annealing.6) In the first Li plating/stripping test, the cell was shorted at 0.85 mA cm-2 and the dark gray area with possible Li dendrite growth was confirmed on the surface of Ta-LLZO. This dark gray area turned white but slightly different from the original color of Ta-LLZO by post-annealing. The ionic conductivity of as-synthesized and post-annealed Ta-LLZO was measured and compared. Post-annealed Ta-LLZO retained high room temperature ionic conductivity of 0.82 mS cm-1, which is slightly lower than the conductivity of as-synthesized one (= 0.90 mS cm-1). We also prepared a symmetric cell with the post-annealed Ta-LLZO and Li metal electrodes and the second Li plating/stripping test was carried out. Symmetric cell with post-annealed Ta-LLZO showed stable voltage response. This indicates the possibility of reusing the degraded garnet-type solid electrolyte by Li dendrite growth for an another solid-state Li battery.

Agglomeration-Free and Air-Inert Garnet for Upgrading PEO/Garnet Composite Solid State Electrolyte

Due to the intrinsically high ionic conductivity and good interfacial stability towards lithium, garnet-type solid electrolytes are usually introduced into polymer electrolytes as fillers to prepare polymer/garnet composite electrolytes, which can improve the ionic conductivity and enhance the mechanical strength to suppress Li dendrites. However, the surface Li2CO3 and/or LiOH passive layers which form when garnet is exposed to the air greatly reduce the enhancement effect of garnet on the composite electrolyte. Furthermore, compared with micro-size particles, nano-size garnet fillers exhibit a better effect on enhancing the performance of composite solid electrolytes. Nevertheless, inferior organic/inorganic interphase compatibility and high specific surface energy of nanofillers inevitably cause agglomeration, which severely hinders the effect of nanoparticles for promoting composite solid electrolytes. Herein, a cost-effective amphipathic 3-Aminopropyltriethoxysilane coupling agent is introduced to modify garnet fillers, which effectively expands the air stability of garnet and greatly improves the dispersion of garnet fillers in the polymer matrix. The well-dispersed garnet filler/polymer interface is intimate through the bridging effect of the silane coupling agent, resulting in boosted ionic conductivity (0.72 × 10−4 S/cm at room temperature) of the composite electrolyte, enhanced stability against lithium dendrites (critical current density &gt; 0.5 mA/cm2), and prolonged cycling life of LFP/Li full cells.

In situ gel electrolyte network guaranteeing ionic communication between solid electrolyte and cathode

Solid electrolytes are regarded as promising candidates replacing organic liquid electrolyte due to much enhanced safety, which is able to use lithium metal as an anode material for high energy system. Among several solid electroytes, garnet-type solid electrolyte has wide electrochemical window as well as high chemical stability and ionic conductivity at room temperature. However, from an assembled full cell's point of view, high interfacial resistance between electrode and solid electrolyte is a huge obstacle which should be overcome. Herein, we synthesize high ionic conductivy of Gallium-doped garnet-type solid electrolyte (Li6.25Ga0.25La3Zr2O12) having 1.2 mS cm-1 at room temperature and then applied gel polymer electrolyte into cathode by in situ gelation method for a full cell system. The interfacial resistance is reduced by about 260 times and rate capability from 0.05C to 1C was 80%, which is superior to a hybrid of liquid electrolyte and LGLZO cell system. Initial capacity retaines 89% even after 800 cycles at 0.5C.

Probing Structure-Property Relations in Garnet-Type Solid Electrolytes for Next-Generation Electrical Energy Storage with Multimode Analytical Scanning and Transmission Electron Microscopy

Probing Structure-Property Relations in Garnet-Type Solid Electrolytes for Next-Generation Electrical Energy Storage with Multimode Analytical Scanning and Transmission Electron Microscopy - Volume 28 Issue S1

Interplay of Dynamic Constriction and Interface Morphology between Reversible Metal Anode and Solid Electrolyte in Solid State Batteries.

In an all-solid-state battery, the electrical contact between its individual components is of key relevance in addition to the electrochemical stability of its interfaces. Impedance spectroscopy is particularly suited for the non-destructive investigation of interfaces and of their stability under load. Establishing a valid correlation between microscopic processes and the macroscopic impedance signal, however, is challenging and prone to errors. Here, we use a 3D electric network model to systematically investigate the effect of various electrode/sample interface morphologies on the impedance spectrum. It is demonstrated that the interface impedance generally results from a charge transfer step and a geometric constriction contribution. The weights of both signals depend strongly on the material parameters as well as on the interface morphology. Dynamic constriction results from a non-ideal local contact, e.g., from pores or voids, which reduce the electrochemical active surface area only in a certain frequency range. Constriction effects dominate the interface behavior for systems with small charge transfer resistance like garnet-type solid electrolytes in contact with a lithium metal electrode. An in-depth analysis of the origin and the characteristics of the constriction phenomenon and their dependence on the interface morphology is conducted. The discussion of the constriction effect provides further insight into the processes at the microscopic level, which are, e.g., relevant in the case of reversible metal anodes.

Topological control of room temperature conductivity in garnet-type solid electrolytes

Topological control of room temperature conductivity in garnet-type solid electrolytes

Improvement of the Interface between the Lithium Anode and a Garnet-Type Solid Electrolyte of Lithium Batteries Using an Aluminum-Nitride Layer.

The next generation of all-solid-state batteries can feature battery safety that is unparalleled among conventional liquid batteries. The garnet-type solid-state electrolyte Li7La3Zr2O12 (LLZO), in particular, is widely studied because of its high Li-ion conductivity and stability in air. However, the poor interface-contact between Li and the electrolyte (garnet) severely limits the development of solid electrolytes. In this study, we synthesize cubic phase Li6.4La3Zr1.4Ta0.6O12 (LLZTO) using a secondary sintering method. In addition, a thin aluminum nitride (AlN) layer is introduced between the metal (Li) and the solid electrolyte. Theoretical calculations show that AlN has a high affinity for Li. Furthermore, it is shown that the AlN coating can effectively reduce the interface impedance between Li and the solid electrolyte and improve the lithium-ion transport. The assembled symmetric Li cells can operate stably for more than 3600 h, unlike the symmetric cells without AlN coating, which short-circuited after only a few cycles. The hybrid solid-state battery with a modified layer, which is assembled using LiFePO4 (LFP), still has a capacity of 120 mAh g−1 after 200 cycles, with a capacity retention rate of 98%. This shows that the introduction of an AlN interlayer is very helpful to obtain a stable Li/solid-electrolyte interface, which improves the cycling stability of the battery.