Single-Void Dynamics Reveal How Solid-State Batteries Quietly Fail

Solid-state batteries have long been heralded as the next great leap in energy storage, promising electric vehicles that charge faster, travel farther, and shrug off the fire risks that haunt conventional lithium-ion cells. Yet a stubborn enemy has kept this technology largely confined to laboratories: the interface where lithium metal meets the solid electrolyte. When the battery discharges and lithium atoms are stripped away from that boundary, tiny voids open up like potholes on a molecular roadway. Each void shrinks the contact area through which current flows, forcing electrons into ever-narrowing channels, heating hot spots, and ultimately seeding the dendrite filaments that can pierce the electrolyte and short-circuit the entire cell. A new study published in Advanced Science now dissects this failure process atom by atom, following the life story of a single void and revealing that its fate hinges on a delicate tug-of-war between surface diffusion, vacancy transport, and electrochemical reaction kinetics.

The stakes could hardly be higher. Lithium metal is the dream anode, packing a theoretical specific capacity of 3860 mAh per gram with a remarkably low mass density of 0.534 g per cubic centimeter and an aggressive reducing potential of −3.04 volts against the standard hydrogen electrode. Paired with nonflammable inorganic solid electrolytes such as garnet-type LLZO, it underpins not only next-generation solid-state cells but also exotic lithium–sulfur and lithium–air chemistries. The problem is that a solid–solid contact is never truly conformal. Unlike the liquid electrolytes that wet every crevice of a conventional electrode, a rigid ceramic pressed against soft lithium leaves microscopic gaps, and those imperfections amplify into spatially heterogeneous deposition and dissolution. Years of experiments, from pressure-dependent stripping tests on Li–LLZO cells to operando synchrotron X-ray tomography, have converged on a single conclusion: contact loss during stripping, not interphase growth, is the primary driver of current constriction and cell failure.

What has been missing is a mechanistic account of how an individual void actually behaves once it forms. Does it simply grow monotonically under stripping, as many models assumed? Or can it shrink, migrate, or even detach from the interface entirely? The research team behind the new work, using a three-dimensional kinetic Monte Carlo framework, simulated a 50-by-50-by-50 cubic lattice representing a 17.5-nanometer cube of lithium against LLZO, and tracked a single hemispherical void through the competing atomic events that shape it. Four mechanisms were woven into the model: bulk migration of lithium vacancies away from the interface, surface diffusion of lithium atoms across the evolving void boundary, electro-dissolution at active contact sites governed by Butler–Volmer kinetics, and transport of lithium ions into the electrolyte bulk. Each event carried an Arrhenius rate constant calibrated to literature values, with activation barriers of 0.3 eV for terrace diffusion, 0.15 eV for step diffusion, and 0.5 eV for interlayer diffusion.

The simulations revealed a strikingly choreographed two-act drama. In the first act, current focusing concentrates the electric field at the sharp circular edge of the hemispherical void, where the electrolyte’s potential distribution distorts around the non-conducting cavity. The enhancement decays with a 1/r-cubed dependence, so dissolution attacks the void rim preferentially, and the void spreads laterally along the interface while its depth barely changes. In the second act, surface diffusion takes over: vacancies redistribute from the interface down along the void surface, the void’s footprint retracts slightly, and its depth increases substantially. The team quantified this morphological ballet with geometric descriptors, including a circularity index that dropped as the footprint elongated and roughened, then recovered as surface diffusion smoothed the shape back toward symmetry, and a vertical shape factor that stayed flat during lateral growth before climbing sharply during the deepening phase.

The most consequential discovery concerns the three distinct modes of surface diffusion, classified through a terrace-step-kink framework that distinguishes atomic hops by their coordination environment. Terrace diffusion, in which adatoms glide across flat crystalline planes, and step diffusion, in which they travel along step edges, both act to keep voids compact and anchored at the interface. Interlayer diffusion, by contrast, shuttles atoms between adjacent atomic layers and directs vacancies into the depth of the electrode. When interlayer diffusion dominates, voids detach from the interface and drift into the lithium bulk, which paradoxically allows the interface to heal as fresh contact is restored. Phase maps sweeping the activation barriers from 0.05 to 0.5 eV showed that suppressing interlayer diffusion while keeping terrace diffusion active produces flat, pancake-shaped voids, whereas strong step diffusion inflates voids in both lateral and depth directions, and combined dominance of interlayer and bulk diffusion can dissolve a void entirely into the electrode.

To unify these observations, the researchers introduced an electrochemical Damköhler number, the ratio of the reaction rate to the bulk vacancy diffusion rate, which compares how fast vacancies are generated at the interface with how fast they can be swept away into the anode interior. When this number is far below unity, vacancy removal outpaces generation, vacancies disperse, and voids shrink or vanish altogether, defining a no-void regime. When it is far above unity, vacancies pile up around the void perimeter, and the resulting morphology is dictated by the surface diffusion ratios. Strong terrace diffusion yields compact but irregular voids; strong step diffusion carves the deepest attached voids; strong interlayer diffusion promotes detachment at moderate Damköhler numbers and complete dissolution when bulk diffusion is also strong. Notably, the analysis showed that bulk diffusion and interlayer diffusion are two independent routes by which a void can effectively disappear into the electrode, a finding with direct implications for how operating conditions might be tuned to favor healing over degradation.

Temperature emerged as a double-edged lever. Sweeping the operating temperature from −10 to 80 degrees Celsius, a range that spans subzero winter starts to sustained elevated-temperature operation in real cells, the model showed that higher temperatures accelerate both surface diffusion and bulk vacancy transport through Arrhenius kinetics, effectively enabling a transport-driven healing mechanism that suppresses void growth. But the authors caution that this benefit is chemistry-dependent. For garnet oxides like LLZO, whose interface with lithium is kinetically passivated, the morphological advantage of warmth is captured directly by the model. Sulfide electrolytes, however, can undergo interfacial reduction and form interphases that grow faster, and sometimes more dangerously, at elevated temperature, so chemical degradation may offset the healing benefit. The optimal operating temperature therefore depends on the balance between morphological recovery and chemical stability, and it will vary with electrolyte chemistry in ways the current framework deliberately leaves for future work.

Perhaps the most dramatic finding is the percolation transition. As stripping proceeds, thousands of single-site vacancy clusters nucleate randomly at the interface and along void edges, where current focusing makes dissolution most aggressive. These point defects act as nuclei that grow through aggregation and coalescence. The team tracked cluster populations across four stages of stripping and watched the original 6-cubic-nanometer void swell to 9 cubic nanometers as neighbors merged into it. Two coupled mechanisms drive the merging: current focusing is strongest in the narrow lithium ligaments separating adjacent voids, so those bridges dissolve preferentially, and curvature-mediated surface diffusion then transports atoms away from the high-curvature necks, lowering surface energy and consolidating each merged pair into a single compact void. At a critical void fraction of 0.0256, the void network suddenly connects across the simulation domain, snapping from an isolated-defect state to a percolated structure composed entirely of one giant cluster.

The electrochemical consequences of that geometric transition are severe. Using a flux-tube formulation, the researchers estimated the interfacial constriction resistance directly from the simulated contact morphology and found that it climbs by roughly two orders of magnitude across the percolation window, peaking at the minimum contact fraction before partially recovering as void detachment restores contact. The percolation threshold itself is tunable: strong terrace diffusion keeps voids as isolated compact clusters and prevents percolation entirely, while strong interlayer diffusion detaches voids before they can link laterally. A connected, contact-destroying network emerges only when both modes are sufficiently weak, and within that regime, step diffusion acts as the controlling mechanism, with strong step diffusion delaying the onset of percolation by carving deeper, more isolated voids instead of shallow lateral ones.

The model’s predictions align qualitatively with a decade of experimental evidence: the lateral-then-deep growth sequence matches operando dilatometry observations, the Damköhler threshold echoes the critical stripping current above which voids accumulate, and the partial healing under enhanced surface diffusion mirrors the recovery of dewetted interfaces after thermal treatment. The framework deliberately excludes mechanical effects such as stack pressure and lithium creep, which would supply material toward the interface and slow void growth, meaning the present results represent a conservative, pressure-free bound on degradation. Even so, the study delivers something solid-state battery engineers have lacked: a theoretical baseline identifying which surface diffusion modes dictate void morphology, and therefore a design compass for selecting electrolyte chemistries, operating temperatures, and current densities that keep lithium’s molecular potholes from connecting into a highway to failure.

Subject of Research: Void formation and percolation dynamics at the lithium metal–solid electrolyte interface during stripping in solid-state batteries

Article Title: Mechanistic Insights Into Instability From Single Void Dynamics at the Lithium Metal‐Solid Electrolyte Interface

Article References: Banerjee, S., Vishnugopi, B. S., Lin, G., & Mukherjee, P. P. (2026). Mechanistic Insights Into Instability From Single Void Dynamics at the Lithium Metal‐Solid Electrolyte Interface. Advanced Science, Article e78028. https://doi.org/10.1002/advs.78028

Image Credits: AI Generated

DOI: 10.1002/advs.78028

Keywords: solid-state batteries, lithium metal anode, solid electrolyte, void formation, kinetic Monte Carlo, surface diffusion, vacancy transport, percolation, LLZO, electrochemical stripping, interfacial stability, dendrite formation