Navigating phase diagram complexity to guide robotic inorganic materials synthesis

Efficient synthesis recipes are needed both to streamline the manufacturing of complex materials and to accelerate the realization of theoretically predicted materials. Oftentimes the solid-state synthesis of multicomponent oxides is impeded by undesired byproduct phases, which can kinetically trap reactions in an incomplete non-equilibrium state. We present a thermodynamic strategy to navigate high-dimensional phase diagrams in search of precursors that circumvent low-energy competing byproducts, while maximizing the reaction energy to drive fast phase transformation kinetics. Using a robotic inorganic materials synthesis laboratory, we perform a large-scale experimental validation of our precursor selection principles. For a set of 35 target quaternary oxides with chemistries representative of intercalation battery cathodes and solid-state electrolytes, we perform 224 reactions spanning 27 elements with 28 unique precursors. Our predicted precursors frequently yield target materials with higher phase purity than when starting from traditional precursors. Robotic laboratories offer an exciting new platform for data-driven experimental science, from which we can develop new insights into materials synthesis for both robot and human chemists

Pliable Lithium Superionic Conductor for AllSolid-State Batteries

The key challenges in all-solid-state batteries (ASSBs) are establishing and maintaining perfect physical contact between rigid components for facile interfacial charge transfer, particularly between the solid electrolyte and cathode, during repeated electrochemical cycling. Here, we introduce inorganic-based pliable solid electrolytes that exhibit extraordinary clay-like mechanical properties (storage and loss moduli <1 MPa) at room temperature, high lithium-ion conductivity (3.6 mS cm(-1)), and a glass transition below -50 degrees C. The unique mechanical features enabled the solid electrolyte to penetrate into the high-loading cathode like liquid, thereby providing complete ionic conduction paths for all cathode particles as well as maintaining the pathway even during cell operation. We propose a design principle in which the complex anion formation including Ga, F, and a different halogen can induce the claylike features. Our findings provide new opportunities in the search for solid electrolytes and suggest a new approach for resolving the issues caused by the solid electrolyte-cathode interface in ASSBs

Interface Stability in Solid-State Batteries

Development of high conductivity solid-state electrolytes for lithium ion batteries has proceeded rapidly in recent years, but incorporating these new materials into high-performing batteries has proven difficult. Interfacial resistance is now the limiting factor in many systems, but the exact mechanisms of this resistance have not been fully explained - in part because experimental evaluation of the interface can be very difficult. In this work, we develop a computational methodology to examine the thermodynamics of formation of resistive interfacial phases. The predicted interfacial phase formation is well correlated with experimental interfacial observations and battery performance. We calculate that thiophosphate electrolytes have especially high reactivity with high voltage cathodes and a narrow electrochemical stability window. We also find that a number of known electrolytes are not inherently stable but react in situ with the electrode to form passivating but ionically conducting barrier layers. As a reference for experimentalists, we tabulate the stability and expected decomposition products for a wide range of electrolyte, coating, and electrode materials including a number of high-performing combinations that have not yet been attempted experimentally.Samsung Advanced Institute of Technolog

Design of Li[subscript 1+2x]Zn[subscript 1−x]PS[subscript 4], a New Lithium Ion Conductor

Recent theoretical work has uncovered that a body-centered-cubic (bcc) anion arrangement leads to high ionic conductivity in a number of fast lithium-ion conducting materials. Using this structural feature as a screening criterion, we find that the I[4 with combining macron] material LiZnPS[subscript 4] contains such a framework and has the potential for very high ionic conductivity. In this work, we apply ab initio computational techniques to investigate in detail the ionic conductivity and defect properties of this material. We find that while the stoichiometric structure has poor ionic conductivity, engineering of its composition to introduce interstitial lithium defects is able to exploit the low migration barrier of the bcc anion framework. Our calculations predict a solid-solution regime extending to x = 0.5 in Li[subscript 1+2x]Zn[subscript 1−x]PS[subscript 4], and yield a new ionic conductor with exceptionally high lithium-ion conductivity, potentially exceeding 50 mS cm[supercript −1] at room temperature.National Science Foundation (U.S.) (ACI-1053575

First-Principles Studies on Cation Dopants and Electrolyte|Cathode Interphases for Lithium Garnets

Lithium garnet with the formula Li₇La₃Zr₂O₁₂ (LLZO) has many properties of an ideal electrolyte in all-solid state lithium batteries. However, internal resistance in batteries utilizing these electrolytes remains high. For widespread adoption, the LLZO’s internal resistance must be lowered by increasing its bulk conductivity, reducing grain boundary resistance, and/or pairing it with an appropriate cathode to minimize interfacial resistance. Cation doping has been shown to be crucial in LLZO to stabilize the higher conductivity cubic structure, yet there is still little understanding about which cations have high solubility in LLZO. In this work, we apply density functional theory (DFT) to calculate the defect energies and site preference of all possible dopants in these materials. Our findings suggest several novel dopants such as Zn²⁺ and Mg²⁺ predicted to be stable on the Li- and Zr-sites, respectively. To understand the source of interfacial resistance between the electrolyte and the cathode, we investigate the thermodynamic stability of the electrolyte|cathode interphase, calculating the reaction energy for LLMO (M = Zr, Ta) against LiCoO₂, LiMnO₂, and LiFePO₄ (LCO, LMO, and LFP, respectively) cathodes over the voltage range seen in lithium-ion battery operation. Our results suggest that, for LLZO, the LLZO|LCO is the most stable, showing only a low driving force for decomposition in the charged state into La₂O₃, La₂Zr₂O₇, and Li₂CoO₃, while the LLZO|LFP appears to be the most reactive, forming Li₃PO₄, La₂Zr₂O₇, LaFeO₃, and Fe₂O₃. These results provide a reference for use by researchers interested in bonding these electrolytes to cathodes

A sinter-free future for solid-state battery designs

The newly developed sequential decomposition synthesis (SDS) method permits the fabrication of ceramic solid electrolytes with thickness close to today's polymer separators and offers opportunities to obtain the desired phase at reduced temperatures.</jats:p

Just Accepted Manuscript •

Abstract In this work, we investigated the effect of Rb and Ta doping on the ionic conductivity and stability of the garnet Li 7+2x-y (La 3-x Rb x )(Zr 2-y Ta y )O 12 (0≤x≤0.375, 0≤y≤1) superionic conductor using first principles calculations. Our results indicate that doping does not greatly alter the topology of the migration pathway, but instead acts primarily to change the lithium concentration. The structure with the lowest activation energy and highest room temperature conductivity is Li 6.75 , has a lower activation energy than c-LLZO, but further Rb doping leads to a dramatic decrease in performance. We also examined the effect of changing the lattice parameter at fixed lithium concentration and found that a decrease in the lattice parameter leads to a rapid decline in Li + conductivity, whereas an expanded lattice offers only marginal improvement. This result suggests that doping with larger cations will not provide a significant enhancement in performance. Our result

Design and synthesis of the superionic conductor Na10SnP2S12

Sodium-ion batteries are emerging as candidates for large-scale energy storage due to their low cost and the wide variety of cathode materials available. As battery size and adoption in critical applications increases, safety concerns are resurfacing due to the inherent flammability of organic electrolytes currently in use in both lithium and sodium battery chemistries. Development of solid-state batteries with ionic electrolytes eliminates this concern, while also allowing novel device architectures and potentially improving cycle life. Here we report the computation-assisted discovery and synthesis of a high-performance solid-state electrolyte material: Na10SnP2S12, with room temperature ionic conductivity of 0.4 mScm_1 rivalling the conductivity of the best sodium sulfide solid electrolytes to date. We also computationally investigate the variants of this compound where tin is substituted by germanium or silicon and find that the latter may achieve even higher conductivity.National Science Foundation (U.S.) (Grant number ACI-1053575

Lithium superionic conductors with corner-sharing frameworks.

Superionic lithium conductivity has only been discovered in a few classes of materials, mostly found in thiophosphates and rarely in oxides. Herein, we reveal that corner-sharing connectivity of the oxide crystal structure framework promotes superionic conductivity, which we rationalize from the distorted lithium environment and reduced interaction between lithium and non-lithium cations. By performing a high-throughput search for materials with this feature, we discover ten new oxide frameworks predicted to exhibit superionic conductivity-from which we experimentally demonstrate LiGa(SeO3)2 with a bulk ionic conductivity of 0.11 mS cm-1 and an activation energy of 0.17 eV. Our findings provide insight into the factors that govern fast lithium mobility in oxide materials and will accelerate the development of new oxide electrolytes for all-solid-state batteries