Origin of Outstanding Stability in the Lithium Solid Electrolyte Materials: Insights from Thermodynamic Analyses Based on First-Principles Calculations

First-principles calculations were performed to investigate the electrochemical stability of lithium solid electrolyte materials in all-solid-state Li-ion batteries. The common solid electrolytes were found to have a limited electrochemical window. Our results suggest that the outstanding stability of the solid electrolyte materials is not thermodynamically intrinsic but is originated from kinetic stabilizations. The sluggish kinetics of the decomposition reactions cause a high overpotential leading to a nominally wide electrochemical window observed in many experiments. The decomposition products, similar to the solid-electrolyte-interphases, mitigate the extreme chemical potential from the electrodes and protect the solid electrolyte from further decompositions. With the aid of the first-principles calculations, we revealed the passivation mechanism of these decomposition interphases and quantified the extensions of the electrochemical window from the interphases. We also found that the artificial coating layers applied at the solid electrolyte and electrode interfaces have a similar effect of passivating the solid electrolyte. Our newly gained understanding provided general principles for developing solid electrolyte materials with enhanced stability and for engineering interfaces in all-solid-state Li-ion batteries

Solid-State Chemistries Stable with High-Energy Cathodes for Lithium-Ion Batteries

In the pursuit of higher-energy-density lithium-ion batteries, one major challenge is the stability of high-capacity or high-voltage cathodes with electrolytes. An understanding of how different chemistries interact with high-energy cathodes is required to enable the rational design of coatings or solid electrolyte materials that offer long-term stability with the cathode. Here, we systematically evaluated the thermodynamic stability among a broad range of solid-state chemistries with common cathodes. Our thermodynamic analyses confirmed that the strong reactivity of lithiated and delithiated cathodes greatly limits the possible choice of materials that are stable with the cathode under voltage cycling. Our computation reaffirmed previously demonstrated coating and solid electrolyte chemistries and suggested several new stable chemistries. In particular, the lithium phosphates and lithium ternary fluorides, which have high oxidation limits, are promising solid-state chemistries stable with high-voltage cathodes. Our study provides guiding principles for selecting materials with long-term stability with high-energy cathodes for next-generation lithium-ion batteries

First Principles Study of the Li₁₀GeP₂S₁₂ Lithium Super Ionic Conductor Material

First Principles Study of the Li₁₀GeP₂S₁₂ Lithium Super Ionic Conductor Materia

Solid-State Chemistries Stable with High-Energy Cathodes for Lithium-Ion Batteries

In the pursuit of higher-energy-density lithium-ion batteries, one major challenge is the stability of high-capacity or high-voltage cathodes with electrolytes. An understanding of how different chemistries interact with high-energy cathodes is required to enable the rational design of coatings or solid electrolyte materials that offer long-term stability with the cathode. Here, we systematically evaluated the thermodynamic stability among a broad range of solid-state chemistries with common cathodes. Our thermodynamic analyses confirmed that the strong reactivity of lithiated and delithiated cathodes greatly limits the possible choice of materials that are stable with the cathode under voltage cycling. Our computation reaffirmed previously demonstrated coating and solid electrolyte chemistries and suggested several new stable chemistries. In particular, the lithium phosphates and lithium ternary fluorides, which have high oxidation limits, are promising solid-state chemistries stable with high-voltage cathodes. Our study provides guiding principles for selecting materials with long-term stability with high-energy cathodes for next-generation lithium-ion batteries

A Facile Mechanism for Recharging Li₂O₂ in Li–O₂ Batteries

Li–air is a novel battery technology with the potential to offer very high specific energy, but which currently suffers from a large charging overpotential and low power density. In this work, we use ab initio calculations to demonstrate that a facile mechanism for recharging Li₂O₂ exists. Rather than the direct decomposition pathway of Li₂O₂ into Li and O₂ suggested by equilibrium thermodynamics, we find an alternative reaction pathway based on topotactic delithiation of Li₂O₂ to form off-stoichiometric Li_2–<i>x</i>O₂ compounds akin to the charging mechanism in typical Li-ion intercalation electrodes. The low formation energy of bulk Li_2–<i>x</i>O₂ phases confirms that this topotactic delithiation mechanism is rendered accessible at relatively small overpotentials of ∼0.3–0.4 V and is likely to be kinetically favored over Li₂O₂ decomposition. Our findings indicate that at the Li₂O₂ particle level there are no obstacles to increase the current density, and point to an exciting opportunity to create fast charging Li–air systems

Nanoscale Stabilization of Sodium Oxides: Implications for Na–O₂ Batteries

The thermodynamic stability of materials can depend on particle size due to the competition between surface and bulk energy. In this Letter, we show that, while sodium peroxide (Na₂O₂) is the stable bulk phase of Na in an oxygen environment at standard conditions, sodium superoxide (NaO₂) is considerably more stable at the nanoscale. As a consequence, the superoxide requires a much lower nucleation energy than the peroxide, explaining why it can be observed as the discharge product in some Na–O₂ batteries. As the superoxide can be recharged (decomposed) at much lower overpotentials than the peroxide, these findings are important to create highly reversible Na–O₂ batteries. We derive the specific electrochemical conditions to nucleate and retain Na-superoxides and comment on the importance of considering the nanophase thermodynamics when optimizing an electrochemical system

First-Principles Study of Oxyhydride H^– Ion Conductors: Toward Facile Anion Conduction in Oxide-Based Materials

H^– ion conductor materials have the great potential to enable high-energy density electrochemical storage based on hydrogen. Fast H^– conduction has been recently demonstrated in the La_{2–<i>x</i>–<i>y</i>}Sr_{<i>x</i>+<i>y</i>}LiH_{1–<i>x</i>+<i>y</i>}O_3–<i>y</i> oxyhydride materials. However, little is known about the H^– diffusion mechanism in this new material and its unique structure. The origin of such exceptional H^– conduction in the oxide-based materials is of great interest. Using first-principles calculations, we studied the energetics and diffusion mechanisms of H^– ions as a function of structures and compositions in this oxyhydride system. Our study identified that fast H^– diffusion is mediated by H^– vacancies and that the fast two-dimensional or three-dimensional H^– diffusion is activated by different anion sublattices in different compositions. In addition, novel doping was predicted from ab initio computation to increase H^– conductivity in these materials. The unique two-anion-site feature in this structural framework enables highly tunable lattice and minimizes the blocking of anion diffusion by oxygen sublattice, allowing high mobile-carrier concentration and good diffusion network. This conclusion offers general guidance for future design and discovery of novel oxide-based anion conductors

First-Principles Computational Design and Discovery of Novel Double-Perovskite Proton Conductors

Solid ceramic proton conductors are a crucial component for hydrogen-based energy devices, such as solid oxide fuel cells, electrolyzers, hydrogen separation membranes, and novel electronic computing devices. Perovskite oxide materials in a wide range of cation combinations, especially those with mixed cations, have been developed as solid proton conductors. To rationally guide the future development of these perovskite proton conductors, we perform first-principles computation to systematically investigate a wide range of perovskite and double-perovskite materials and to reveal the effects of different cations and their combinations on proton diffusion and hydrogen incorporation. We observe that lower barrier proton migration can be achieved in perovskites with B-site cations with a lower oxidation state and smaller ionic radii. By studying different mixing of B-site cations, we find that double perovskites with certain B-cations in the layered B-site ordering can simultaneously achieve high proton incorporation and fast proton diffusion without a proton-trapping effect. Our high-throughput computation discovers a number of layered double-perovskite materials with good proton incorporation capability and fast proton diffusion. Our results provide design principles for cation mixing in perovskite proton conductors and provide new research directions for novel double-perovskite proton conductors for novel energy or electronic devices

First-Principles Computational Design and Discovery of Solid-Oxide Proton Conductors

Solid-oxide proton-conducting materials are key components for hydrogen-based energy devices, including solid-oxide fuel cells, electrolyzers, hydrogen separation membranes, and novel electronic computing devices. The further development of these devices requires proton-conducting materials with high proton conductivity and good stability with hydrogen and water under the device-operating environment. In this study, we perform a systematic first-principles computational study on a wide range of ternary oxide materials to identify new proton conductor materials and to understand the role of both cations and compositions on material stability and proton conductivity. By analyzing the computational results of over 5000 oxide materials, we reveal how the cation species and mole fraction affect water stability and hydrogen insertion capability. By studying proton diffusion in many different materials, our analyses show that oxide materials with connected BO6 octahedra are optimal for fast proton diffusion. Following the understanding, a high-throughput computation identifies a dozen oxide materials with good water stability, good proton incorporation capability, and fast proton diffusion. This study provides fundamental understanding and design principles to develop oxide materials with fast proton diffusion and good stability

First-Principles Computational Design and Discovery of Solid-Oxide Proton Conductors

Solid-oxide proton-conducting materials are key components for hydrogen-based energy devices, including solid-oxide fuel cells, electrolyzers, hydrogen separation membranes, and novel electronic computing devices. The further development of these devices requires proton-conducting materials with high proton conductivity and good stability with hydrogen and water under the device-operating environment. In this study, we perform a systematic first-principles computational study on a wide range of ternary oxide materials to identify new proton conductor materials and to understand the role of both cations and compositions on material stability and proton conductivity. By analyzing the computational results of over 5000 oxide materials, we reveal how the cation species and mole fraction affect water stability and hydrogen insertion capability. By studying proton diffusion in many different materials, our analyses show that oxide materials with connected BO6 octahedra are optimal for fast proton diffusion. Following the understanding, a high-throughput computation identifies a dozen oxide materials with good water stability, good proton incorporation capability, and fast proton diffusion. This study provides fundamental understanding and design principles to develop oxide materials with fast proton diffusion and good stability