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.

The strongest mechanistic signal this week is the repeated observation that uniform inorganic SEI formation is hindered by local variations in solvation structure and surface reactivity. Operando ellipsometry supplies direct evidence of thickness and optical-property gradients across the lithium surface, while dual-additive papers report changes in SEI inorganic fraction without equivalent spatial maps. Simulation work highlights the absence of transferable force fields that capture both anion coordination and decomposition kinetics at realistic electrode potentials. Until these measurements are combined on the same electrolyte systems, claims that a given additive produces a “stable” interphase stay provisional.

The essentials

Dual-additive SEI engineering. A dual-additive approach produces an inorganic-rich solid electrolyte interphase on lithium negative electrodes, with the mechanism tied to altered solvation and selective decomposition. The evidence centers on surface analysis showing increased inorganic content, yet the paper does not resolve whether the layer remains uniform under high-rate conditions or across different current collectors.

Operando passivation mapping. Spectroscopic ellipsometry performed during lithium-metal cycling detects non-uniform growth of the passivation layer from the earliest cycles. This spatial variation directly influences local charge-transfer resistance and is not captured by average-thickness measurements or ex-situ spectroscopy.

Interphase prediction via simulation. A combined polarizable force-field and machine-learning approach is used to forecast interphase products on lithium metal from electrolyte composition. The unresolved step is experimental validation against operando data for the same solvent-salt-additive combinations, limiting immediate transfer to electrolyte design.

Scandium-modified sodium electrodes. Scandium addition is shown to improve durability of sodium-ion battery electrodes through changes in transport kinetics and surface stability. The mechanistic connection to cathode-electrolyte interphase formation or transition-metal dissolution remains unexamined in the reported experiments.

Nonflammable potassium electrolytes. Anion-reinforced solvation structures enable nonflammable electrolytes for potassium-ion cells while maintaining strong cation coordination. The open question is whether the same solvation motif produces a stable, inorganic-rich interphase on potassium metal or only on the cathode side.

Mechanism and evidence

The clearest mechanistic advance lies in the demonstration that SEI spatial uniformity is governed by local solvation heterogeneity rather than average coordination strength. Operando ellipsometry supplies the first direct, time-resolved map of thickness gradients on lithium metal, linking early-cycle non-uniformity to subsequent current constriction. Dual-additive studies show that targeted anion decomposition can increase the inorganic fraction, but without spatially resolved follow-up the functional benefit at high rate stays correlative. Simulation frameworks now attempt to close the prediction gap, yet they still lack validated decomposition pathways at the potentials and concentrations used in the experimental papers. The combined evidence points to a need for coupled operando and modeling studies on identical electrolyte formulations.

Materials and interfaces

Cathode and anode interface work this week centers on surface modification and solvation control. Surface-fluorinated conductive carbon is examined for coupled electron-ion transport at graphite, while gel-polymer and polymer electrolytes incorporating fluorine and phosphorus are tested for selective ion transport in lithium-metal cells. On the sodium side, multi-element nanoscale doping of iron-rich layered oxides and scandium incorporation aim at electrode-level durability. Solid-state sulfide electrolytes synthesized via liquid-phase routes are reported for lithium-sulfur cells, but interfacial contact and chemo-mechanical stability data are not yet linked to the interphase heterogeneity observed in liquid systems.

Scale-up, safety and manufacturing

Safety-related studies emphasize design-level constraints over material claims. Replaceable covers combined with oil cooling are explored to improve thermal management and post-accident handling of EV battery packs, addressing both mechanical access and heat extraction. Calendar-aging investigations highlight that most cells spend the majority of their life at rest, yet few datasets quantify how interphase evolution during storage affects subsequent cycle life. Nonflammable electrolyte formulations for potassium systems offer a route to reduced fire risk, but the translation to large-format cells requires stack-pressure and separator compatibility data that remain outside the current reports.

Quick Radar

  • Liquid-phase synthesis of superionic sulfide electrolytes: Targets all-solid-state lithium-sulfur cells, yet critical current density and interfacial void formation under stack pressure are not addressed.
  • Ambient-stable cathode-level solid electrolyte: Achieved via wetting-controlled surface modification, raising the question of compatibility with dry-electrode processing routes.
  • Semi-solid anode-free Cu-Li2S cell: Combines Li6PS5Cl with a solvate ionic liquid; the effect of the liquid component on interfacial contact resistance over cycling is unresolved.
  • Cation-polymer coordination in gel polymer electrolytes: Tuned for sodium metal batteries, but sodium plating morphology and dead-sodium accumulation data are absent.
  • Predictive frequency-domain sampling methods: Proposed for spatiotemporal battery modeling, yet their accuracy for interphase growth kinetics has not been benchmarked against operando measurements.

Closing

The practical question for the coming week is whether any of the reported additive or doping strategies can be shown to reduce spatial gradients in interphase thickness when tested under identical current-density and temperature conditions.

Sources

  1. Nature Portfolio - Batteries: Dual-additive enabled inorganic-rich solid electrolyte interphase for high-rate lithium negative electrodes - https://www.nature.com/articles/s41467-026-76653-7
  2. EKL Batteries: Reveal Non-Uniform Passivation on Lithium Metal Anode With Operando Spectroscopic Ellipsometry - https://advanced.onlinelibrary.wiley.com/doi/10.1002/aenm.71434?af=R
  3. arXiv - Battery interphase query: Predictive Simulation of Interphases on Li Metal Surface - https://arxiv.org/abs/2608.09791v1
  4. Tech Xplore - Energy & Green Tech: How scandium can improve the durability of sodium-ion battery electrodes - https://techxplore.com/news/2026-08-scandium-durability-sodium-ion-battery.html
  5. Nature Portfolio - Batteries: Multi-element nanoscale doping of iron-rich sodium layered oxides enables ampere-hour-level Na-ion batteries - https://www.nature.com/articles/s41565-026-02257-3
  6. EKL Batteries: Surface-Fluorinated Conductive Carbon for Coupled Electron/Ion Transport Through the Graphite Anode - https://advanced.onlinelibrary.wiley.com/doi/10.1002/aenm.71436?af=R
  7. Nature Portfolio - Batteries: Reconciling strong coordination and anion-reinforced solvation structure enables nonflammable electrolytes for potassium-ion batteries - https://www.nature.com/articles/s41467-026-76791-y
  8. Tech Xplore - Energy & Green Tech: New engineering studies aim to slow battery aging while idle - https://techxplore.com/news/2026-08-aim-battery-aging-idle.html
  9. Tech Xplore - Energy & Green Tech: Replaceable covers and oil cooling could make EV batteries safer and easier to repair - https://techxplore.com/news/2026-08-oil-cooling-ev-batteries-safer.html