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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Phase instability-coupled fracture behavior in garnet LLZO solid electrolytes: a machine learning-enabled atomistic study

Fracture in the garnet-type solid electrolyte Li 7 La 3 Zr 2 O 12 (LLZO) poses a critical threat to both the performance and safety of solid-state batteries. To unravel the coupled chemomechanical processes that govern fracture in LLZO under external loading, we carry out large-scale molecular-dynamics simulations with a validated machine-learning force field. Our results demonstrate that triaxial stresses at crack flanks trigger a localized cubic-to-tetragonal phase transformation, which is accompanied by Li-ion rearrangement. The emergent tetragonal domains feature lattice contraction normal to the fracture plane, imposing coherent misfit strains that provide an additional driving force for further crack propagation. Crucially, introducing Li deficiencies stabilizes the cubic phase, postponing the phase transition and thereby delaying fracture initiation. These findings highlight the role of intrinsic phase instability in dictating LLZO's fracture resistance and its critical connection to local Li concentration. This chemomechanical coupling points toward targeted strategies to enhance the mechanical robustness of garnet electrolytes, including tuning Li content, ensuring dopant homogeneity, and refining processing protocols.

Materials science↗
DOE OSTI2025

Ultrafast Sintering and Dopant Effects in Garnet LLZO Solid Electrolytes

High-throughput, low-cost manufacturing, and optimization of solid electrolytes are necessary for the adoption of solid-state batteries. In this work, garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) with different aliovalent dopants, 𝑇𝑎$_{^·_{𝑍𝑟}}$, 𝐴𝑙$^{··}_{𝐿𝑖}$, and 𝐺𝑎$^{··}_{𝐿𝑖}$, have been ultrafast-sintered with different temperature ramping rates. The densification behavior, phases, their evolution, and surface chemistry of different LLZO have been investigated and linked to their electrochemical performances. It has been shown that LLZO with 𝑇𝑎$_{^·_{𝑍𝑟}}$ dopant demonstrates the highest garnet phase purity and overall best electrochemical performances, and ultrafast sintering further improves densification, ionic conductivity, and electrochemical stability. On the other hand, LLZO doped with 𝐴𝑙$^{··}_{𝐿𝑖}$ and 𝐺𝑎$^{··}_{𝐿𝑖}$ are reaching higher cubic phase purities and ionic conductivities via conventional sintering, indicating undesirable dopant migration and segregation during the ultrafast sintering process. In conclusion, these findings provide insights into the manufacturing of solid electrolyte materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Working Principle of an Ionic Liquid Interlayer During Pressureless Lithium Stripping on Li 6.25 Al 0.25 La 3 Zr 2 O 12 (LLZO) Garnet‐Type Solid Electrolyte

Abstract Solid‐state‐batteries employing lithium metal anodes promise high theoretical energy and power densities. However, morphological instability occurring at the lithium/solid–electrolyte interface when stripping and plating lithium during cell cycling needs to be mitigated. Vacancy diffusion in lithium metal is not sufficiently fast to prevent pore formation at the interface above a certain current density during stripping. Applied pressure of several MPa can prevent pore formation, but this is not conducive to practical application. This work investigates the concept of ionic liquids as “self‐adjusting” interlayers to compensate morphological changes of the lithium anode while avoiding the use of external pressure. A clear improvement of the lithium dissolution process is observed as it is possible to continuously strip more than 70 μm lithium (i. e., 15 mAh cm −2 charge) without the need for external pressure during assembly and electrochemical testing of the system. The impedance of the investigated electrodes is analyzed in detail, and contributions of the different interfaces are evaluated. The conclusions are corroborated with morphology studies using cryo‐FIB‐SEM and chemical analysis using XPS. This improves the understanding of the impedance response and lithium stripping in electrodes employing liquid interlayers, acting as a stepping‐stone for future optimization.

Fuchs, Till↗
DOE OSTI2021

3D Printed, Low Tortuosity Garnet Framework For Beyond 500 Wh/kg Batteries

In this project, we developed LLZO garnet ink recipes and processes for 3D-printing highly ordered ionically conductive garnet porous structures on dense garnet separators. Using this technique, we are able to fabricate controlled architecture LLZO garnet solid-state electrolyte (SSE) trilayers for application in solid-state lithium batteries. The trilayer comprises a thin dense center layer sandwiched between a 3D-printed patterned porous layer and a random porous layer. The dense layer functions as the ionic separator between the anode and cathode. The random porous layer hosts the lithium-metal anode and provides the structural support. The 3D-printed SSE patterned porous layer hosts the cathode, providing continuous, low tortuosity pathways for fast 3D Li+ transport through the cell while increasing the electrode/electrolyte interface area to decrease the interfacial resistance. Compared to the random porous structure, this ordered patterned structure possesses more vacant space for higher cathode loading without sacrificing ionically conducting capability, thus potentially greatly increasing the cell energy density. For demonstration purposes, we developed two patterns for the 3D-printed porous layer: grids and columns, for hosting sulfur and NMC cathode, respectively. The corresponding two types of cells were fabricated and tested, and have demonstrated achievement of theoretical discharge capacity without cathode calendaring. In addition, we developed a fundamental solid-state ionic and electronic transport model to optimize the 3D-printed structures for maximum energy and power density. The model was validated by experiment and provides the critical design criteria for achieving the >500 Wh/kg energy goal as function of C-rate.

25 ENERGY STORAGE↗
DOE OSTI2021

Microstructural impacts on ionic conductivity of oxide solid electrolytes from a combined atomistic-mesoscale approach

Abstract Although multiple oxide-based solid electrolyte materials with intrinsically high ionic conductivities have emerged, practical processing and synthesis routes introduce grain boundaries and other interfaces that can perturb primary conduction channels. To directly probe these effects, we demonstrate an efficient and general mesoscopic computational method capable of predicting effective ionic conductivity through a complex polycrystalline oxide-based solid electrolyte microstructure without relying on simplified equivalent circuit description. We parameterize the framework for Li 7- x La 3 Zr 2 O 12 (LLZO) garnet solid electrolyte by combining synthetic microstructures from phase-field simulations with diffusivities from molecular dynamics simulations of ordered and disordered systems. Systematically designed simulations reveal an interdependence between atomistic and mesoscopic microstructural impacts on the effective ionic conductivity of polycrystalline LLZO, quantified by newly defined metrics that characterize the complex ionic transport mechanism. Our results provide fundamental understanding of the physical origins of the reported variability in ionic conductivities based on an extensive analysis of literature data, while simultaneously outlining practical design guidance for achieving desired ionic transport properties based on conditions for which sensitivity to microstructural features is highest. Additional implications of our results are discussed, including a possible connection between ion conduction behavior and dendrite formation.

25 ENERGY STORAGE↗
DOE OSTI2022

The effects of aluminum concentration on the microstructural and electrochemical properties of lithium lanthanum zirconium oxide

Cubic lithium lanthanum zirconium oxide (Li 7-x Al x La 3 Zr 2 O 12 , LLZO) garnet has gained attention as a promising next-generation electrolyte for lithium batteries due to its high ionic conductivity and chemical stability with lithium metal. The high conductivity can be achieved through doping over a range of aluminum concentrations. In this study, we hot-pressed samples to achieve <2% nominal porosity with aluminum concentrations from x = 0.25–0.55 mol to understand the effect of aluminum on microstructure and electrochemistry. It was observed that beyond the aluminum solubility limit (x = ~0.40), resistive secondary phases formed at the grain boundaries. As a result, the percent grain boundary resistance increased from 17.6 to 41.2% for x = 0.25 and x = 0.55, respectively. Both the grain boundary and bulk activation energies remained relatively constant as the aluminum concentrations increased (~0.44 eV and ~0.39 eV, respectively). It was, therefore, surmised that the mobility term of the Nernst–Einstein equation was roughly independent of aluminum concentration and the major variable controlling bulk conductivity was the number of lithium charge carriers. As a result, as the aluminum concentration increased from x = 0.25 to x = 0.55 the bulk conductivity decreased from 0.56 to 0.15 mS cm -1 . Following these trends of increasing grain boundary resistance and decreasing bulk conductivity with increasing aluminum concentration, x = 0.25 had the highest total conductivity (0.46 mS cm -1 ). We demonstrated that aluminum concentration has a significant effect on the microstructure and electrochemical properties of LLZO. In conclusion, we believe this work could help understand how to link processing, microstructure, and electrochemical properties to guide the manufacturing of LLZO for use in solid-state batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Optimization of Lithium Content and Sintering Additives in Tape Cast Lithium Garnet Electrolyte Sheets

The lithium garnet (LLZO) remains one of the most promising electrolyte materials for producing solid state batteries. Tape casting is one method for producing the thin ceramic electrolyte layer required for a high-performance solid state battery. Processing of LLZO is complicated by several factors including lithium volatilization, abnormal grain growth and phase instability. Many of these issues are exacerbated in tape cast sheets by the sheets' higher surface area to volume ratio, when compared to pellet processing methods. Here, we report on an environmentally friendly aqueous tape casting process for LLZO using methylcellulose as a binder and compare final sheet properties to other, solvent-based, options. Solids loading, binder content, dispersant composition, and wetting agent type are varied to improve ease of casting and enhance properties of the as-cast tape. Lithium content in sintered LLZO sheets is controlled by the inclusion of excess Li 2 CO 3 as lithium source in the ceramic tape itself and by a novel method of producing a lithium-saturated furnace atmosphere. Sintering time and temperature are optimized, and rapid thermal processing is investigated as a method of reducing lithium loss. Al 2 O 3 and MgO are examined for use as sintering additives. Characterization of LLZO sheets is performed with XRD, EIS and SEM. Li 2 CO 3 and sintering additive levels are optimized for ionic conductivity and density. The optimization effort improved the conductivity and density of 100µm thick sintered sheets to greater than 3x10 -4 S/cm conductivity and 90% density.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The Riddle of Dark LLZO: Cobalt Diffusion in Garnet Separators of Solid‐State Lithium Batteries

Abstract Solid‐state batteries (SSBs) with a Li 7 La 3 Zr 2 O 12 (LLZO) garnet electrolyte are attracting much attention as robust and safe alternative to conventional lithium‐ion batteries. Technical challenges in the practical implementation of garnet SSBs are related to the need for high‐temperature sintering, which often leads to undesirable chemical reactions with the cathode material. While these reactions are well understood for composite cathodes, very little is known about similar processes between cathode and separator during battery fabrication. This work focuses on understanding the processes between the composite LiCoO 2 ‐LLZO cathode and the LLZO separator and how they affect the battery performance. The extensive diffusion of Co‐ions within LLZO, which leads to the often‐observed LLZO darkening, is shown to have a significant impact on ionic conductivity, electronic conductivity, and dendrite stability of the separator. Experimental data coupled with large‐scale molecular dynamics simulations uncover the diffusion mechanism for Co‐ions and identify secondary phases that form during these interactions. In addition to extensive Co‐ion diffusion within the grains, a non‐uniform segregation of Co‐ions at grain boundaries is found leading to the formation of three distinct Co‐containing phases. This work offers a general approach to studying the fundamental ion diffusion processes that occur during the fabrication of oxide SSBs.

electrochemical properties↗
DOE OSTI2022

All Solid-State Li/LLZO/LCO Battery Enabled by Alumina Interfacial Coating

Li 7 La 3 Zr 2 O 12 (LLZO) garnet-type lithium-ion conductors are being investigated as a promising solid electrolyte for solid-state lithium batteries. To enable a functional all-solid-state configuration intensive investigations are needed to reduce the cathode/electrolyte interfacial resistance which contributes the most to cell performance loss. Among the commercial cathode materials investigated so far, LiCoO 2 (LCO) is one of the most stable with garnet electrolytes as only a superficial reaction has been detected between the two materials. However, even this minor reaction would block the Li-ion transport through the interface, resulting in deteriorated cell performance. In this work, we demonstrate that a thin aluminum oxide layer (5 nm) can be an effective interlayer to impede the formation of a harmful interphase and enable facile Li-ion transfer between LCO and the LLZO garnet. Room-temperature-sputtered LCO thin films were employed to form an interface with the garnet electrolyte and annealed at 800 °C to reveal the effect of the interfacial reaction on the Li-ion transfer across the interface. An aluminum oxide layer was then introduced between LCO and the garnet electrolyte by sputtering a metallic aluminum layer which is then annealed together with the upper LCO layer in oxygen, or by direct atomic layer deposition of the oxide. Compared to the LCO/LLZO/Li cells without an aluminum oxide interlayer, those with the interlayer exhibited improved performance, i.e., a stable discharge capacity of up to 90 mAh/(g LCO) at a C/10 rate, a rate capability up to 1.68C and a stable galvanostatic cycling at 0.1C for over 100 cycles with a discharge capacity fade rate of 0.15% per cycle. It was determined that aluminum diffused into the LCO layer after preventing the initial detrimental reaction between LCO and the LLZO garnet from happening during high temperature annealing, suggesting that the coating does not have to remain a physically blocking layer during cycling to function.

Electrochemistry↗
DOE OSTI2022

Compositional and structural control in LLZO solid electrolytes

Garnet-based solid-state electrolytes (SSEs) represent a promising class of materials for next-generation batteries with improved safety and performance. However, lack of control over the composition and crystal structure of the well-known Li 7 La 3 Zr 2 O 12 (LLZO) garnet material has led to poor reproducibility with a wide range of ionic conductivities reported in the literature. In this study, the role of precursor homogeneity in controlling the compositional and structural evolution of Al-doped LLZO is explored. A novel solution-based synthesis approach is employed to demonstrate enhanced atomic-scale mixing of the starting materials in comparison to conventional solid-state preparation methods. Through this technique, it is shown that the stability and formation temperature of the highly conductive cubic phase is directly impacted by the spatial distribution of the doping element and reactant species in the precursor mixture. Precursor homogeneity was also an important factor in mitigating the formation of unwanted secondary impurities. These findings can be used to guide the synthesis of SSEs with reproducible material characteristics and enhanced electrolytic performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Kinetic versus Thermodynamic Stability of LLZO in Contact with Lithium Metal

Li 7 La 3 Zr 2 O 12 (LLZO) garnet-based oxides are a promising class of solid electrolytes used as the separator in all-solid-state batteries (ASSBs). While LLZO is considered to have a wide electrochemical stability window, its intrinsic stability in contact with lithium metal is not sufficiently well understood, and there is still a debate on the key question of whether LLZO does or does not form passivation layers before and during cycling. Utilizing both in situ and operando X-ray photoelectron spectroscopy techniques, in this work we reveal the presence of a kinetic barrier to the reduction of LLZO by Li metal, with the extent of oxygen-deficient interphase (ODI) formation depending sensitively on the energetics of Li metal arriving at the Li vertical bar LLZO interface. Despite the clear presence of a kinetic barrier to reduction, the electrochemical response of the Li vertical bar LLZO interface is unchanged by the presence of the ODI, indicating that ODI formation during electrochemical cycling does not hinder charge transfer across the Li vertical bar LLZO interface. Overall, these results reveal that the reactivity of LLZO with Li metal depends not only on the material properties of the adjoining phases (i.e., surface purity and active contact) and their resulting thermodynamic stability but also on the energy input at the interface and the resulting reaction kinetics. Furthermore, the presence of a kinetic barrier to reduction highlights the additional complexities governing the reactivity of solid-state interfaces in ASSBs and underscores the importance of operando characterization of interfacial stability to design more robust, high-performance protection strategies for solid electrolytes in contact with reactive electrodes.

25 ENERGY STORAGE↗
DOE OSTI2019

All-Solid-State Batteries Using Rationally Designed Garnet Electrolyte Frameworks

Functioning bulk-type all-solid-state batteries in a practical form factor with composite positive electrodes, using Al-substituted Li 7 La 3 Zr 2 O 12 (LLZO) as the solid electrolyte, have been demonstrated for the first time. The devices incorporate bilayers composed of dense LLZO membranes and porous LLZO scaffolds infiltrated with LiNi 0.6 Mn 0.2 Co 0.2 O 2 and other components as positive electrodes, combined with lithium anodes. The porous scaffolds are prepared using an easily scaled freeze-tape-casting method. The unidirectional pores of the scaffold facilitate infiltration of cathode components and shorten lithium ion diffusion path lengths, while the addition of a soft ionically conductive solid to the scaffold ensures good contact among the components.

25 ENERGY STORAGE↗
DOE OSTI2025

Pristine Interface between Lithium Lanthanum Zirconate and Lithium Manganese Oxide by Pulsed Laser Deposition

Solid state lithium-ion batteries have garnered increasing interest in recent years due to several potential advantages over liquid-electrolyte based systems. The possibility of integrating the lithium garnet oxide, Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 (LLZTO), with the high voltage cathode, spinel Li x Mn 2 O 4 (LMO), is evaluated here. Thin film bilayer structures are prepared by pulsed laser deposition on MgO (001) substrates and characterized by x-ray diffraction and transmission electron microscopy. The LLZTO is grown by an alternating layer-by-layer deposition of LLZTO and Li 3 N and subsequently annealed for several hours at 575 °C to promote crystallinity. Growth of crystalline LMO with a pristine interface to LLZTO is achieved by gentle heat treatment (500 °C) to remove surface carbonate from the electrolyte and by cathode growth at a low temperature of 250 °C. Higher temperature depositions (330 – 450 °C) result in reaction between the two materials and the appearance of Li 2 MnO 3 , which may be in part due to the presence of excess lithium in the electrolyte layer. Because fully lithiated LiMn 2 O 4 has a voltage of ≈3.7 V versus Li+/Li, the observation of a well-defined interface, free of impurity phases and with no interdiffusion of elements, indicates LLZTO is stable to at least 3.7 V.

Garnet LLZO↗
DOE OSTI2022

An Investigation of Chemo-Mechanical Phenomena and Li Metal Penetration in All-Solid-State Lithium Metal Batteries Using In Situ Optical Curvature Measurements

Solid-electrolytes (SEs) can provide a pathway to increase energy-density in lithium metal batteries. However, lithium metal penetration through garnet based LLZO solid electrolytes has been identified as a critical failure process. This phenomenon is related to chemo-mechanical processes which are difficult to probe. In particular, characterizing the dynamic mechanical deformations that occur in electrode-SE structures is very challenging. Here study reports in situ curvature measurements that are thus designed to probe chemo-mechanical phenomena that occur during lithium plating. The novel experimental cell configuration created for this work shows that pressure builds up in the Li metal during plating, up until the point where short circuits occur. The resulting data are analyzed with a detailed finite element model (FEM) to quantitatively evaluate stress evolution. The results show that Li metal plating within a surface flaw can produce stress build-up prior to short-circuiting. The combined results from both the experiments and the FEM suggest that it is critical to minimize surface defects and flaws during the manufacturing processes.

25 ENERGY STORAGE↗
DOE OSTI2022

Digestion processes and elemental analysis of oxide and sulfide solid electrolytes

Detailed elemental analysis is essential for a successful development and optimization of material systems and synthesis methods. This is especially relevant for Li- and Na-containing compounds, found in state-of-the-art and next-generation battery systems. Their materials’ properties and thus the final device performance strongly depend on the crystal structure, the stoichiometry, and defect chemistry, e.g., influencing charge carrier concentration and activation energies for vacancy transport. However, a detailed quantitative analysis of light elements in a heavy matrix, featuring a broad range of solubilities and vapor pressures, is often difficult and associated with large uncertainties and thus neglected in favor of just reporting the stoichiometry as “weighed in.” Here, in this work, we report several approaches to digest and dissolve various oxide and sulfide-based materials, used in next-generation Li batteries, for elemental analysis via optical emission spectroscopy. These include the most common solid electrolytes Li-La-Ti–O, a perovskite material (LLTO), and Li-La-Zr-O which has garnet structure (LLZO). Additionally, a facile thermal digestion process is reported for a surrogate sulfide solid electrolyte (Na 2 S). The digestion procedures reported here are suitable for almost any laboratory environment and, when applied, will improve understanding of the synthesis-structure–property correlations needed to advanced batteries with all solid-state configurations.

Malkowski, Thomas F.↗
DOE OSTI2021

Optimization of Tape Casting for Fabrication of Li 6.25 Al 0.25 La 3 Zr 2 O 12 Sheets

Tape casting is an attractive technology for the scalable manufacturing of thin lithium garnet electrolyte (LLZO) layers for solid state battery applications. Processing of LLZO is complicated by many factors including lithium volatilization, abnormal grain growth, and phase instability, which are exacerbated by high surface area to volume ratios. In this work a sintering protocol for commercially available Li 6.25 Al 0.25 La 3 Zr 2 O 12 Sheets (Al-LLZO) powder was developed that requires no mother-powder covering or externally applied pressure. MgO was investigated as a sintering additive to improve density and ionic conductivity of the Al-LLZO sheets and produce a fine-grained microstructure. Al-LLZO sheets with 5 wt % MgO had densities of > 90% and ionic conductivity > 2 × 10 -4 S/cm. The optimized ceramic composition and sintering protocol were used to compare several tape casting binder systems. A "green"water-based system using methylcellulose as a binder was developed with green and final properties comparable to those obtained with solvent-based systems.

25 ENERGY STORAGE↗
DOE OSTI2021

Computation-guided discovery of coating materials to stabilize the interface between lithium garnet solid electrolyte and high-energy cathodes for all-solid-state lithium batteries

All-solid-state batteries with a lithium metal anode, enabled by lithium garnet solid electrolytes such as Li 7 La 3 Zr 2 O 12 (LLZO), are a promising next-generation energy-storage technology. The further development of all-solid-state battery requires the integration of high-energy cathodes such as LiNi 1-x-y Mn x Co y O 2 (NMC) with the garnet solid electrolyte with stable and low-resistance interfaces, which requires a coating layer to stabilize the interface during high-temperature sintering and electrochemical cycling. In order to guide the future development of interfacial coatings, we perform high-throughput thermodynamic analyses based on first-principles computation to investigate the stability of LLZO garnet and high-energy NMC cathodes with a wide range of materials chemistries. Here our study reveals the factors governing the materials stability with LLZO garnet and NMC cathodes, and identifies the mechanisms of good coating layers stable with LLZO and NMC. In addition to classifying known coating layers, our study provides detailed guiding charts and multiple new materials systems as promising coatings for stabilizing LLZO—NMC interfaces to enable high-energy-density garnet-based all-solid-state batteries. Our demonstrated computation scheme and high-throughput analyses are generally applicable to investigate and screen coating materials for stabilizing interfaces in energy-related applications.

25 ENERGY STORAGE↗