Newsletter

Interphase heterogeneity, rather than bulk conductivity, now limits rate capability and reversibility across lithium-metal, sodium-ion and solid-state systems. Recent work on lithium negative electrodes shows that dual-additive formulations shift SEI composition toward inorganic-rich layers, yet the spatial distribution of those layers remains difficult to control. Operando spectroscopic ellipsometry on lithium-metal anodes reveals pronounced non-uniform passivation that develops within the first few cycles, directly affecting local current density. Parallel simulation efforts attempt to predict interphase chemistry from electrolyte composition, but still require experimental calibration of solvation and decomposition pathways. Sodium-ion studies add another dimension: scandium incorporation and multi-element nanoscale doping alter electrode durability, yet the link to cathode-electrolyte interphase stability is not yet quantified at the particle surface. These threads converge on the same practical constraint: without spatially resolved interphase data, electrolyte and additive design remain largely empirical. ...

Electrolyte solvation, interphase formation, and solid-electrolyte contact emerge as coupled limits on fast-charge stability and solid-state viability rather than independent optimization targets. Fast charging of lithium-ion cells repeatedly drives lithium plating when the anode-electrolyte interface cannot sustain the required lithium-ion flux without metallic deposition. The supplied reports examine whether changes in solvent coordination or additive behavior can shift the onset of plating by altering the local concentration gradient and the composition of the forming interphase. Parallel work on sodium-metal and zinc systems tests whether the same solvation and corrosion mechanisms appear once the alkali or divalent cation replaces lithium. In solid-state configurations, the question moves from solvent coordination to particle-to-particle contact and the mechanical integrity of the interface under stack pressure. ...

Interface stability under realistic exposure and cycling conditions remains the dominant constraint in solid-state systems, where moisture attack, mechanical ductility, and SEI growth kinetics must be treated as coupled variables rather than isolated material properties. The supplied reports this week converge on two practical questions. First, how does trace moisture under dry-room conditions alter the surface chemistry of sulfide electrolytes such as argyrodite Li6PS5Cl, and what spatial resolution is required to map the resulting degradation products? Second, whether existing models of SEI growth can be made to respect physical rate laws across varying protocols without overfitting to single datasets. ...

Solid-state and quasi-solid electrolytes are being evaluated through the lens of interfacial stability, where composition tuning, coatings, and dynamic interfaces are tested against space-charge layers, moisture sensitivity, and contact loss rather than bulk conductivity alone. The arXiv preprint on Li6+xSixSb1-xS5I argyrodites starts from the known limits of iodide-based sulfides: space-charge layers at the cathode interface, slow ion transport across grain boundaries, and susceptibility to lithium penetration. The work reports a ball-milled Li6.6Si0.6Sb0.4S5I composition that aims to raise room-temperature conductivity while widening the electrochemical window. Whether the measured gains survive full-cell stack pressure, repeated plating, and post-mortem analysis of the space-charge region remains the decisive test. ...

Spray deposition of compositional gradients and immobilized gel electrolytes is being examined as a route to couple ion-transport pathways with interphase stability in silicon, lithium-sulfur, and solid-state cells. Homogeneous slurry casting often produces uniform porosity and composition that cannot simultaneously optimize electron and ion pathways, leading to localized lithium depletion during fast charge. Ultrasonic spray methods now allow deliberate placement of porosity near the separator and carbon enrichment near the current collector, directly addressing the transport asymmetry that accelerates degradation. Parallel work on UV-cured gel films deposited in the same manner replaces free liquid with a thin, pinhole-free polymer layer that can be formed directly on the graded electrode. These approaches shift the design problem from bulk electrolyte properties toward controlled spatial variation of both microstructure and interphase chemistry. ...

Grain boundaries and solid-solid interfaces, rather than bulk conductivity, set the practical limits on dendrite formation, lithiation uniformity, and interphase stability in solid-state and high-voltage systems. Solid-state electrolytes were expected to eliminate liquid-related safety risks while supporting higher energy density. In practice, lithium filaments still appear at internal boundaries where two grains of electrolyte meet. The MIT study isolates these grain boundaries as nucleation sites because they locally alter the electric field and provide fast diffusion paths that concentrate lithium. This shifts attention from electrode-electrolyte contact alone to the polycrystalline microstructure itself. ...

Grain-boundary charge and local mechanical stress now emerge as coupled controls on dendrite initiation and short-circuit endurance in garnet-type solid electrolytes. Solid-state batteries continue to show dendrite-driven failures even when bulk ionic conductivity meets targets. Recent work isolates the electrolyte grain boundaries themselves as the sites where lithium filaments first nucleate, rather than the electrode-electrolyte interface alone. The MIT study traces dendrite seeding to the two-grain junctions where local chemistry and transport differ from the grain interior. Two Nature papers add that these boundaries carry net charge and that applied biaxial stress alters the trajectory of any growing filament. Together the results shift attention from maximizing conductivity to controlling boundary potential and stress state during processing and cycling. ...