{"id":"8cc841c2-e54c-4ca6-b547-3f684e1e438c","arxiv_id":"2411.16741","paper_version":3,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"During fast dissolution of Zn anodes in concentrated electrolytes, salt precipitates as a transient interphase (T-SEI) that relaxes quickly and promotes compact, grain-coherent redeposition.","lead":"This paper reports a new, temporary solid layer that forms on battery metal anodes during fast discharging, made of precipitated salt, and shows that this layer changes how metal redeposits, leading to smoother surfaces. The finding suggests a new way to engineer battery cycling by deliberately triggering this transient interphase.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claim that T-SEI causes compact redeposition is confounded: Fig. 6 high-rate controls differ in overpotential/current and surface cleaning; a no-T-SEI control (forced convection or interrupted current) is required.","rationale":"I read the manuscript as an honest attempt to establish a new interfacial phenomenon in metal anodes. The evidence for a transient, transport-induced passivating layer is strong: the voltage-spike behavior in chronopotentiometry, the deviation from ohmic behavior in LSV, the suppression by forced convection in Fig. 2B/C, the rest-time recovery of t_inc,2, and the EIS jump in Rct/Cdl all converge on a supersaturation/precipitation mechanism. The Sand-style scaling Qc ∝ 1/J is a reasonable rationalization, though the slope is not checked against known D and csat values—this is a secondary weakness. However, the paper's most surprising and impactful assertion—that a fully relaxed T-SEI changes the next deposition step—is not isolated from the other consequences of high-rate dissolution. A high-rate dissolution at 5 V is an aggressive anodic treatment that can clean and smooth the surface by electropolishing regardless of any salt film. The SEM/EBSD evidence for compact growth is compelling but only reported for T-SEI conditions; the low-rate control has a different dissolution overpotential and surface chemistry. The reader's identified weakest assumption is therefore correct and is the most load-bearing concern. The proposed forced-convection control would directly test it. Because the manuscript otherwise presents a coherent and multi-technique case, a CONDITIONAL verdict is appropriate, with the condition being this control.","tokens_in":14179,"tokens_out":7293,"duration_ms":70954,"concrete_test":"Repeat the high-rate dissolution step (e.g., 100 mA/cm2 to 1 mAh/cm2 in 3 M ZnSO4) under strong forced convection—using the RDE at ≥3000 rpm or a high-velocity impinging jet—so that the interfacial Zn2+ concentration stays below the ZnSO4 saturation limit. Verify the absence of T-SEI by (i) no voltage spike / no precipitous current drop and (ii) no optically visible film. After a 3-minute rest, redeposit under the exact Fig. 6 conditions (0.5 mAh/cm2 at -1 V vs Zn2+/Zn) and characterize with SEM/EBSD. If the compact, terrace-like grain growth is still observed, the T-SEI is not the causal agent; if particulate nuclei appear, the T-SEI is confirmed. A second check: quantify the 42% roughness reduction with n≥3 independent cells and report error bars.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim has three parts: T-SEI forms by salt supersaturation, relaxes completely, and alters subsequent deposition morphology. The first two are reasonably supported by the electrochemical signatures (voltage spike at t_inc, current decay, rest-time-dependent t_inc2, post-relaxation FIB-SEM absence). The third part is the load-bearing and least controlled claim. Fig. 6 compares low-rate discharge at 0.1 V vs high-rate discharge at 5 V (vs Zn2+/Zn). These conditions differ not only in T-SEI presence but in applied overpotential, current density, total charge passed (same 1 mAh/cm2 but different time), and extent of anodic surface cleaning/electropolishing. The paper attributes the subsequent compact, grain-growth morphology to the 'cleaning' effect of T-SEI (reduced C/S/O EDX signals), but high anodic polarization alone can remove adventitious carbon and produce a smooth, activated surface. The RDE available in the study would allow a forced-convection control: rotating at high rpm during dissolution should suppress supersaturation and T-SEI while retaining a high dissolution current/overpotential. No such control is reported. Without it, the observed redeposition difference could be caused by the high-rate dissolution history (current, overpotential, or electropolishing) rather than by the transient precipitate specifically. The 42% roughness reduction in the proof-of-concept cell also lacks error bars or replicate statistics, so the headline quantitative benefit is not firmly established.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the discovery of a Transient Solid-Electrolyte Interphase (T-SEI) formed during fast anodic dissolution of Zn in concentrated ZnSO4 and ZnCl2 electrolytes. The authors argue that rapid dissolution produces local supersaturation, causing salt precipitation that passivates the electrode, leads to a self-limiting flat dissolution morphology, and fully dissolves upon rest. They further claim that, after relaxation, the T-SEI-modified surface promotes compact, grain-growth-dominated redeposition instead of the isolated particulate nucleation seen on pristine or low-rate-discharged electrodes. Evidence includes J-V deviations under stagnant vs. rotating conditions, constant-current chronopotentiometry voltage spikes and in-operando optical imaging, EIS showing increased charge-transfer resistance and decreased double-layer capacitance, post-mortem FIB-SEM/EDX showing no residual interphase, and SEM/EBSD/profilometry of dissolution and redeposition morphologies. The paper also derives a Sand-type relation Q_c ∝ J^-1 and demonstrates a proof-of-concept cycling protocol with periodic T-SEI formation.","tokens_in":14417,"tokens_out":5733,"duration_ms":54168,"significance":"If the central claim holds, the paper identifies a previously overlooked, purely transient passivating phase that controls both dissolution kinetics and the morphology of the subsequent plating step in concentrated battery electrolytes. The study's strength is its multi-modal approach: RDE voltammetry, chronopotentiometry, operando optical visualization, EIS, FIB-SEM/EDX, EBSD, and profilometry all point consistently toward the existence of a transient interfacial precipitate. The relaxation experiments and post-mortem absence of the interphase are particularly convincing for the transient character. The derivation of Eq. (3) is parameter-free in that it contains no fitted constants, and it yields a falsifiable linear relation; however, the predicted slope is not tested against measured transport properties. The main weakness is that the causal link between T-SEI formation and the improved redeposition morphology is not isolated from other consequences of high-rate anodic polarization, so the third pillar of the central claim is not yet fully established.","major_comments":[{"comment":"The central causal claim—that T-SEI formation, rather than the high-rate dissolution history itself, causes the subsequent compact, grain-growth redeposition—is not isolated in the reported experiments. In Fig. 6, the low-rate (0.1 V vs. Zn2+/Zn) and high-rate (5 V) discharge conditions differ in applied overpotential, current density, total charge time, and extent of anodic cleaning/electropolishing, so the observed differences in redeposition morphology could in principle be produced by the high dissolution current or overpotential alone. The paper's 'cleaning' argument based on reduced C/S/O EDX signals (Fig. 5D-F) is similarly consistent with high anodic polarization removing adventitious carbon. Because the RDE setup enables forced convection, a control experiment with high rotation during dissolution (suppressing supersaturation and T-SEI while retaining a high dissolution current/overpotential) would directly test the attribution; without such a control, the third pillar of the paper's central claim remains confounded. The paper's own observation that the compact-growth mode is not self-sustainable over cycling (Fig. S22) further indicates that the long-term benefit rests on the periodic-enforcement protocol, making the control experiment necessary rather than cosmetic.","section":"Fig. 6 and 'Unusual morphological evolution promoted by T-SEI'"},{"comment":"The linear Q_c-versus-J^-1 relation in Eq. (3) is a direct rearrangement of the modified Sand equation with no fitted parameter; consequently, the good linear fit in Fig. 3B does not by itself validate the T-SEI mechanism or the assumption that the voltage spike is set by saturation. The predicted slope, πD_i[(c_sat - c_infty)nF]^2/4, is not compared with independently measured diffusion coefficients and saturation concentrations, and the application of a binary, dilute-solution Sand equation to 3 M ZnSO4 is questionable given migration, non-ideal activity, and speciation in concentrated electrolytes. A quantitative test using literature or measured transport parameters, or a direct measurement of the precipitate composition, is needed to confirm that the spike corresponds specifically to salt precipitation rather than to another transport-limited process.","section":"Eqs. (1)-(3) and Fig. 3B"},{"comment":"The headline quantitative benefit—a 42% reduction in surface roughness—is reported without error bars, replicate numbers, or statistical analysis, and the proof-of-concept protocol differs from the control not only by the periodic potentiostatic 5 V stripping step but also by the sequence of stripping capacities and rest times. As presented, this result supports only a qualitative proof of concept, not the quantitative claim in the abstract. Please provide replicate statistics or soften the quantitative claim accordingly.","section":"Fig. S23 and proof-of-concept cycling"}],"minor_comments":[{"comment":"The number (4) is used twice, once for Laplace's equation in the text and once for the S_dr formula in Materials and Methods; please renumber to avoid ambiguity.","section":"Equation numbering throughout"},{"comment":"The caption uses panel label 'I' twice, once for the redeposition SEM image and once for the EBSD image; the panel references in the text and caption should be aligned.","section":"Figure 6 caption"},{"comment":"The text refers to 'Table 2' for definitions of t_inc, t_inc,2, τ_R,SEI, and τ_R,conc, but no Table 2 appears in the manuscript body or in the captured supporting information; please include the table or move the definitions into the text.","section":"Main text, paragraph on relaxation times"},{"comment":"In the electrolyte preparation paragraph, 'by weighting certain amounts of salts' should read 'by weighing', and the sentence 'the total counts from the resulting Zn peak were compared' has a subject-verb agreement issue.","section":"Materials and Methods"},{"comment":"The term 'T -SEI' is typeset with inconsistent spacing in several places; please use a consistent unspaced 'T-SEI' throughout the manuscript.","section":"Abstract and main text"}],"recommendation":"major_revision","confidential_remarks":"The paper reports a potentially significant phenomenon and the experimental evidence for the transient interphase is reasonably strong. The main gap is the absence of a no-T-SEI control for the redeposition-morphology claim, which is the load-bearing part of the paper's significance. The Sand-type analysis would also benefit from quantitative validation against independently measured transport properties. I see no grounds for rejection; both concerns are addressable with experiments and analysis that fit within the scope of a revision. There is no obvious novelty disclosure issue, and the prior work on salt films in electropolishing is cited appropriately."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this paper has a genuine observation — a transient salt film forms on a Zn anode dissolving in concentrated ZnSO4/ZnCl2, and it relaxes quickly when the current stops. The weaker link is the claim that this film is what changes the next electrodeposition; that part is confounded and needs a control. Keep the core idea, push for better isolation.\n\nWhat's new: salt-film formation during anodic dissolution is known from electropolishing, but applying it to battery-relevant Zn anodes and showing it happens at practical current densities (~20–60 mA/cm²) is a useful transfer. The in-situ optical imaging showing edge-to-center propagation, the EIS jump in Rct and drop in Cdl, and the rest-time dependence of the second incubation time all point consistently to a transient precipitate. The Sand-based derivation is just a rearrangement, not a fitted model, so it avoids the circularity trap; but it also isn't validated against a known diffusion coefficient, so it stays a consistency check rather than a quantitative test.\n\nThe soft spots are in the morphological claim. Figure 6 compares low-rate discharge at 0.1 V vs high-rate at 5 V. Those conditions differ in overpotential, current density, and extent of surface cleaning — any of which could produce the smoother, 'grain-growth' deposition. The authors attribute the effect to the T-SEI's cleaning action, but high anodic polarization alone can strip adventitious carbon. They have an RDE; a forced-convection control (high rotation during dissolution, which should suppress supersaturation while keeping a high dissolution current) would isolate the T-SEI's role. Without it, the causal story is under-supported. Also, the headline 42% roughness reduction comes from a single proof-of-concept run with no error bars or replicates.\n\nMinor points: the T-SEI composition is inferred as ZnSO4 rather than directly confirmed, and the relaxation time is measured indirectly. These are addressable.\n\nOverall, the paper is honest about its limitations — it even notes the effect degrades over cycling — and the central formation/relaxation story holds up. It deserves a serious referee, but the referee should insist on the convection control and replicate statistics before the morphological claim is accepted. I'd bring it to a reading group and would cite the T-SEI concept if I worked on concentrated metal-anode electrolytes.","headline":"Worth a serious look: the transient salt film on dissolving Zn is real and well-evidenced, but the claim that it controls redeposition morphology needs a cleaner control experiment.","tokens_in":14993,"tokens_out":1682,"would_cite":true,"duration_ms":18181,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A transient salt skin that forms during fast discharge changes how metal anodes re-grow on the next charge.","keywords":["transient solid-electrolyte interphase","metal anode","zinc dissolution","electrodeposition","supersaturation","sand equation","rotating disk electrode","battery interphase"],"falsifier":"Run the same high-rate dissolution on a rotating-disk electrode at high rotation speed, which suppresses local supersaturation (and thus T-SEI) while maintaining high overpotential; then redeposit and check whether the deposit still shows compact grain growth, which would show the effect is not specific to T-SEI.","tokens_in":13916,"feed_emoji":"⚡","tokens_out":4079,"duration_ms":37444,"temperature":0.7,"pith_summary":"The paper claims that a previously overlooked solid layer forms on metal anodes during fast discharge: when dissolution releases cations faster than they can diffuse away, the salt concentration at the surface exceeds saturation and a salt film precipitates. This Transient Solid-Electrolyte Interphase (T-SEI) passivates the electrode, self-limits dissolution, and leaves a flat, clean surface after it fully dissolves. The authors further claim that this brief event changes the next charging step: metal redeposited onto the relaxed surface grows by extending the original grains rather than forming new nuclei, reducing surface roughness by 42% in a proof-of-concept cycling test. The broader claim is that this dynamic precipitation—not only permanent, decomposition-derived SEI—governs electrochemical interfaces in concentrated and water-in-salt electrolytes.","feed_headline":"A transient salt film rewires the next metal deposit","feed_subtitle":"Dissolving zinc at high rate builds an interphase that vanishes in under a second but makes redeposition grow flat and coarse-grained.","key_machinery":"The central object is the Transient Solid-Electrolyte Interphase (T-SEI), a salt precipitate (e.g., ZnSO$_4$) formed at the electrode surface when the local cation concentration exceeds the salt solubility limit during fast dissolution. The modified Sand equation (eq. 2) governs its incubation time, relating the critical discharged capacity to the inverse current density; the interphase relaxes with a characteristic timescale $\\tau_{R,SEI}$ once the current stops. It does the work of creating a self-limiting dissolution front and a clean, flat surface whose subsequent redeposition is epitaxial-like.","core_discovery":"In its own terms: fast electro-dissolution of a metal anode in concentrated electrolyte drives the local salt concentration past saturation, precipitating a salt-based interphase (T-SEI) that is distinct from classical SEI. The T-SEI forms almost instantly once supersaturation is reached (incubation time follows a modified Sand equation, $J\\sqrt{t_{inc}} \\propto (c_{sat} - c_{\\infty})$), and dissolves completely within roughly 300 milliseconds of current removal. Its presence is marked by a voltage spike in chronopotentiometry, a sharp rise in charge-transfer resistance, and a drop in double-layer capacitance consistent with a thicker salt film. Once relaxed, the electrode is chemically cleaned and, on subsequent recharge, metal deposition proceeds by compact growth of existing coarse grains (~15–20 µm) rather than independent particulate nucleation, a regime that can be re-armed periodically by deliberate fast-discharge pulses.","pith_inferences":["Extension: the same supersaturation argument should apply to other cation-releasing interfaces, such as alkali-metal stripping in localized high-concentration electrolytes, where the solubility limit is closer to operating concentrations; the paper demonstrates the effect in zinc but does not test these cases.","Extension: the ~300 ms relaxation time implies that a practical diagnostic for T-SEI could be the linear $Q_c$ versus $J^{-1}$ signature and the accompanying voltage spike, which might be recognized in full-cell cycling data without special instrumentation.","Extension: the paper shows the improved morphology degrades at large capacities, so a natural follow-up is to test whether an optimal frequency and intensity of T-SEI pulses can sustain epitaxial growth over hundreds of cycles."],"forward_implications":["Rapid discharge in concentrated electrolytes will routinely hit a T-SEI regime, so voltage spikes during battery cycling at high rates may be caused by transient salt precipitation rather than by classical ion-depletion effects.","A fully relaxed T-SEI surface changes the subsequent redeposition from independent nucleation to compact grain growth, which is a step toward flat, rechargeable metal anodes.","Because T-SEI relaxes on a sub-second timescale, ordinary post-mortem characterization will miss it; detecting it requires in-operando electroanalytical and optical methods with higher temporal resolution.","Periodic fast-discharge pulses can re-establish the T-SEI 'cleaning' effect, reducing surface roughness by 42% in a proof-of-concept symmetric-cell test, suggesting a practical protocol knob for battery management.","Any electrode process that produces cations at a high rate, such as fast cathode charging, is in principle susceptible to T-SEI formation, extending the relevance beyond metal anodes."],"supporting_citations":[{"why":"Supplies the Sand equation that the paper adapts to predict T-SEI incubation time from supersaturation.","marker":"[20]"},{"why":"Provides a mechanistic model for copper electropolishing where local supersaturation causes salt precipitation, the direct analog for T-SEI formation.","marker":"[37]"},{"why":"Shows that anodically formed salt films on iron have compact and porous sublayers, informing the EIS interpretation of T-SEI as a thicker capacitive layer.","marker":"[44]"},{"why":"Demonstrates that stripping creates voids beneath the SEI, motivating the study of dissolution-side interphases.","marker":"[17]"},{"why":"Reports compact homo-epitaxial deposition when a passivation layer is removed, supporting the claim that T-SEI's cleaning effect enables grain growth.","marker":"[54]"},{"why":"Establishes a linear relation between critical capacity and reciprocal current for deposition, which the paper parallels for dissolution-side T-SEI.","marker":"[43]"}],"fun_headline_variants":["Fast metal stripping builds a vanishing salt film that guides redeposition","Transient salt interphase from fast discharge resets the metal surface","High-rate dissolution creates a self-limiting salt layer that vanishes in milliseconds","A transient salt film from fast stripping makes the next plating grow flat","Fast discharge creates a salt shield that dissolves to control the next metal deposit"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The causal claim that T-SEI formation, rather than the high current or overpotential itself, is responsible for the improved redeposition morphology is not isolated by a control experiment that suppresses T-SEI while keeping the high dissolution rate.","fun_headline_variants_meta":{"raw":{"variants":["Fast metal stripping builds a vanishing salt film that guides redeposition","Transient salt interphase from fast discharge resets the metal surface","High-rate dissolution creates a self-limiting salt layer that vanishes in milliseconds","A transient salt film from fast stripping makes the next plating grow flat","Fast discharge creates a salt shield that dissolves to control the next metal deposit"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00056,"raw_usage":{"total_tokens":2710,"prompt_tokens":1047,"completion_tokens":1663,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":663,"completion_tokens_details":{"reasoning_tokens":1571}},"tokens_in":663,"tokens_out":1663,"duration_ms":11766,"temperature":1.0,"reasoning_tokens":1571,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T14:06:35.176184+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run the same high-rate dissolution on a rotating-disk electrode at high rotation speed, which suppresses local supersaturation (and thus T-SEI) while maintaining high overpotential; then redeposit and check whether the deposit still shows compact grain growth, which would show the effect is not specific to T-SEI.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the Sand equation that the paper adapts to predict T-SEI incubation time from supersaturation."},{"cited_title":"Mendez, R","cited_arxiv_id":null,"evidence_quote":"Provides a mechanistic model for copper electropolishing where local supersaturation causes salt precipitation, the direct analog for T-SEI formation."},{"cited_title":"Grimm, A","cited_arxiv_id":null,"evidence_quote":"Shows that anodically formed salt films on iron have compact and porous sublayers, informing the EIS interpretation of T-SEI as a thicker capacitive layer."},{"cited_title":"Shi et al., Lithium metal stripping beneath the solid electrolyte interphase","cited_arxiv_id":null,"evidence_quote":"Demonstrates that stripping creates voids beneath the SEI, motivating the study of dissolution-side interphases."},{"cited_title":"Baek et al., Naked metallic skin for homo-epitaxial deposition in lithium metal batteries","cited_arxiv_id":null,"evidence_quote":"Reports compact homo-epitaxial deposition when a passivation layer is removed, supporting the claim that T-SEI's cleaning effect enables grain growth."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes a linear relation between critical capacity and reciprocal current for deposition, which the paper parallels for dissolution-side T-SEI."}],"review_version":1}