Yang Shao-Horn

Lithium–oxygen batteries (LOBs) have emerged as a compelling next-generation energy storage technology for aviation due to their high theoretical energy densities and the use of abundant oxygen as a cathode reactant. Unlike conventional lithium-ion batteries (LIBs), which are limited by the mass of intercalation materials and one-electron redox processes, LOBs leverage multielectron oxygen redox chemistry to achieve gravimetric energy density exceeding 3,500 Wh kgLi2O2–1 based on lithium peroxide and up to 5,200 Wh kgLi2O–1 for lithium oxide. However, practical implementation of LOBs remains constrained by significant challenges including low round-trip efficiency and low system-level energy density, the latter arising from the need for oxygen management in both open and closed architectures. The electrolyte viscosity, oxygen solubility, volatility, and chemical stability toward reactive oxygen species can profoundly influence discharge capacity, rate capability, reversibility, and long-term stability. This review provides a comprehensive assessment of recent progress in LOBs, focusing on electrolyte designs, electrode engineering, and strategies for mitigating parasitic reactions as well as the interplay between material-level properties and system-level constraints, offering a critical perspective on the path toward realizing high-energy, practical LOB systems.

Oxidative degradation of carbonate solvents via C–H activation is observed on late transition metal oxide positive electrodes in Li-ion batteries. However, analogous reactivity of other classes of organic molecules on oxides is not well understood. Here, we used density functional theory calculations to show how C–H activation changes from deprotonation to oxidative hydrogen abstraction as the lattice oxygen activity increases by moving the Fermi level closer to the oxygen 2p-band center. By using a set of 23 small molecules with 50 nonequivalent C–H bonds, spanning a broad range of functional groups and substitutions, we show how relevant energies of the isolated molecules impact the driving force for degradation reactions at the surface of LiNiO2, an oxide with high lattice oxygen activity. We demonstrated that C–H bond oxidation free energy, measured as the free energy to substitute a C–H bond with a C–OH bond for the isolated molecule, is the descriptor with the most predictive power for the C–H activation driving force on an oxide with highly reactive lattice oxygen. Using this descriptor, we identified promising S- and F-containing compounds with enhanced stability toward C–H activation. These results pave the way for a rational design of novel electrolytes that minimize degradation and impedance growth of Ni-rich LiNixMnyCo1–x–yO2 (NMC) electrodes.

Insights into how permanent microporosity influences ion transport in polymer electrolytes could facilitate the design of next‐generation single‐ion conducting (SIC) materials. Intrinsically microporous polymers and conventional polymers are typically regarded as fundamentally distinct electrolyte platforms; direct comparisons between compositionally similar examples are lacking. Here, we introduce a strategy for the synthesis of fluorinated aryl sulfonimide‐based polymers of intrinsic microporosity (FAS‐PIMs) together with flexible polysulfonimide analogs of similar composition that lack permanent microporosity. Although these polymers possess fundamentally different dry‐state architectures, incorporation of a common pore‐filling transport medium, succinonitrile (SN), drives the two systems toward remarkably similar nanostructures with similar bulk conductivities (>10 ⁻⁵ –10 ⁻⁴ S/cm at 40°C–80°C), thermomechanical properties ( G ʹ within 1–10 MPa over the temperature range of 25°C–120°C), and reprocessability. Molecular dynamics simulations and experiments suggest these unusual combinations of properties arise through different conduction mechanisms within the materials, and that sulfonimide anions are particularly advantageous for conduction in microporous matrices relative to strongly binding anions. Overall, this work introduces the first sulfonimide‐based PIM, establishes a comparison between permanently microporous and transiently porous single‐ion conducting polymers, and demonstrates that these two traditionally distinct electrolyte architectures can converge toward similar, useful bulk properties after incorporation of a pore‐filling transport medium.

Insights into how permanent microporosity influences ion transport in polymer electrolytes could facilitate the design of next‐generation single‐ion conducting (SIC) materials. Intrinsically microporous polymers and conventional polymers are typically regarded as fundamentally distinct electrolyte platforms; direct comparisons between compositionally similar examples are lacking. Here, we introduce a strategy for the synthesis of fluorinated aryl sulfonimide‐based polymers of intrinsic microporosity (FAS‐PIMs) together with flexible polysulfonimide analogs of similar composition that lack permanent microporosity. Although these polymers possess fundamentally different dry‐state architectures, incorporation of a common pore‐filling transport medium, succinonitrile (SN), drives the two systems toward remarkably similar nanostructures with similar bulk conductivities (>10 ⁻⁵ –10 ⁻⁴ S/cm at 40°C–80°C), thermomechanical properties ( G ʹ within 1–10 MPa over the temperature range of 25°C–120°C), and reprocessability. Molecular dynamics simulations and experiments suggest these unusual combinations of properties arise through different conduction mechanisms within the materials, and that sulfonimide anions are particularly advantageous for conduction in microporous matrices relative to strongly binding anions. Overall, this work introduces the first sulfonimide‐based PIM, establishes a comparison between permanently microporous and transiently porous single‐ion conducting polymers, and demonstrates that these two traditionally distinct electrolyte architectures can converge toward similar, useful bulk properties after incorporation of a pore‐filling transport medium.

Ruthenium metal nanoparticles are among the most active catalysts for the oxygen evolution reaction (OER) but suffer from poor stability due to Ru dissolution. Anchoring Ru nanoparticles onto functional porous carbon supports is therefore being explored to enhance stability while retaining high catalytic activity. A Ru-based electrocatalyst consisting of Ru nanoparticles decorated on nitrogen-doped functional mesoporous carbon spheres was synthesized via a one-pot nanoemulsion micelle-assembly method followed by pyrolysis. The nitrogen-doped functional porous carbon spheres facilitate coordination, as evidenced by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy mapping. Additionally, defects in the carbon matrix accelerate OER kinetics. Electrochemistry-mass spectrometry (EC-MS) measurements on the annealed sample at 1000 °C (Ru/C@1000) reveal the onset of oxygen evolution at 1.4 V vs. RHE. EC-MS reveals the onset of CO2 evolution at potentials above 1.2 V vs. RHE; however, the faradaic efficiency for oxygen evolution approaches unity above 1.4 V vs. RHE, indicating that the anodic current is predominantly due to OER. However, limited catalytic stability under prolonged testing may be attributed to carbon support instability against oxidation and partial oxidation/dissolution of Ru nanoparticles. This study evaluates the effectiveness of anchoring Ru nanoparticles on carbon supports and provides insights for developing stable, efficient Ru/C-based OER electrocatalysts.

Polymer electrolytes are promising materials to enable practical lithium‐metal batteries for high‐energy‐density energy storage. Yet, parasitic side reactions at the lithium|polymer interface and inhomogeneous lithium deposition, compromising cycling reversibility and safety, remain a challenge. Despite the key role of the interfacial reactivity, there is a lack of quantitative and comparable information on interfacial charge–transfer kinetics with polymer electrolytes, and their impact on the lithium plating/stripping behavior remains unclear. Therefore, in this work, we apply a validated method for quantifying interfacial charge–transfer kinetics via the exchange current density j ₀ to a series of polyethylene oxide (PEO)‐based polymer electrolytes to clarify how the electrolyte composition influences interfacial kinetics. By combining the j ₀ analyses with measurements of the solid electrolyte interphase resistance and lithium cycling reversibility, we identify a consistent trend in which smaller j ₀ and higher R _SEI values correlate with higher Coulombic efficiencies. This indicates that moderated interfacial kinetics and a sufficiently passivating interphase favor higher plating/stripping reversibility. The results provide a coherent dataset of interfacial charge–transfer parameters for polymer electrolytes and highlight the importance of deliberate electrolyte and interphase design for achieving highly reversible lithium‐metal cycling in polymer‐based electrolyte systems.

Understanding solid electrolyte interphase (SEI) formation on Li metal in fluorinated electrolytes is critical for improving Coulombic efficiency (CE). We combined in situ Fourier transform infrared spectroscopy (FTIR), in situ Raman, ex situ X-ray photoelectron spectroscopy (XPS), and electrochemical mass spectrometry (ECMS) to investigate concentration-dependent SEI with lithium bis(fluorosulfonyl)imide (LiFSI) and fluoroethylene carbonate (FEC) electrolytes. In situ Raman and FTIR revealed VC and poly(VC) in FEC-rich electrolyte (50 mM), indicating non-ring-opening polymerization, with poly(VC) decreasing at higher LiFSI concentration. In parallel, FEC underwent multiple ring-opening pathways: at 50 mM, FEC formed Li2CO3 while evolving predominantly H2, as observed by ECMS. Increasing LiFSI concentration favored making CO2 while suppressing Li2CO3. This concentration-dependent mechanism was further supported by depth-resolved (∼40 nm) XPS, where Li2CO3 resided predominately in the outer SEI and decreased with sputter depth and at higher LiFSI concentration. Critically, LiF was the dominant salt-derived species, which increased sharply with LiFSI concentration. These results elucidate how FEC and LiFSI shape the SEI, and identify both SEI fluorination and Li2CO3 suppression as key CE descriptors to guide future electrolyte design.

The discovery of advanced battery electrolytes is challenged by the vast compositional space of multi-component liquid formulations. Here, we introduce the ELectrolyte Laboratory for Integrated Experimentation (ELLIE), an automated platform that combines electrolyte formulation and impedance spectroscopy to map ionic conductivity across high-dimensional sodium electrolytes containing up to five salts and 15 solvents, generating an experimental dataset spanning nearly two orders of magnitude in conductivity. 23Na NMR, Raman spectroscopy, and viscosity measurements on a subset of electrolytes at a fixed salt concentration reveal that conductivity is jointly influenced by Na+ solvation strength, ion association, and solvent dynamics and positively correlates with inverse viscosity. Conductivity estimates based on the Nernst–Einstein relation captures broad concentration and viscosity relationships but do not extrapolate well across compositionally diverse electrolytes. Random forest modeling identifies lower solvent molecular weight as the dominant descriptor of high conductivity. Together, these results establish solvent molecular size as a physically interpretable descriptor of ion transport and demonstrate how automated experimentation can accelerate data-driven electrolyte optimization across complex compositional spaces.

Ion solvation in battery electrolytes involves supramolecular host-guest interactions and is most often enabled by Lewis basic coordination of cations, sometimes at the expense of cation mobility. Here, we investigate anion-centered solvation using Lewis acidic supramolecular hosts. We introduce a class of small-molecule boranes that selectively coordinate anions, enabling systematic interrogation of how anion binding strength governs salt dissociation and ion transport. A family of readily accessible boranes spanning a wide range of Lewis acidities was synthesized and evaluated with Li- and Na-based salts. Increasing borane Lewis acidity strongly correlated with enhanced dissociation and ionic conductivity of otherwise poorly soluble halide salts (Cl^-, F^-), yielding order-of-magnitude conductivity enhancements and, in some cases, performance exceeding that of TFSI-based electrolytes. These results establish anion coordination strength as a powerful and tunable handle for regulating ion transport and expand supramolecular host-guest chemistry to the rational design of electrolyte solvation environments.