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arxiv: 2605.26727 · v1 · pith:GJAKXQZAnew · submitted 2026-05-26 · ❄️ cond-mat.mtrl-sci · physics.chem-ph· physics.optics

Visualizing Degradation in Anode-Free High-Utilization Aqueous Batteries Across Cell Lifetime

Sofia K. Catalina , Kyle Frohna , Willow Thompson , Katherine J. Harmon , Dasol Yoon , Jianbo Wang , Colin Ophus , Daniel N. Congreve
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William C. Chueh
This is my paper

Pith reviewed 2026-06-29 17:22 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci physics.chem-phphysics.optics
keywords anode-free batteriestin metal anodeoperando microscopyaqueous batteriessubstrate effectelectrodepositionbattery degradationhigh-utilization anode
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The pith

Substrate choice determines whether tin plating remains stable at high capacities in anode-free aqueous batteries.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper develops a custom operando optical microscope to capture through-plane images of tin electrodeposition across hundreds of cycles in optically accessible anode-free pouch cells. It shows that copper substrates produce a multi-stage tin growth mode that drives high overpotentials and irreversible active-material loss at high plated capacities, while graphite substrates produce a single-stage growth mode with slower kinetics. This distinction is then used to construct a porous graphite substrate tin anode that reaches 70 percent utilization, or 630 mAh g^{-1}_Sn, while retaining high efficiency and extended lifetime. A sympathetic reader would care because tin anodes promise high energy density yet their reactivity has so far restricted practical cycle life in aqueous systems.

Core claim

The paper claims that the substrate governs the morphology and stability of plated tin, particularly at high plated capacities. Copper substrates exhibit a multi-stage tin growth mode that produces high overpotentials and irreversible active material loss. Graphite substrates instead display a single-stage growth mode with slower kinetics. Using this insight, the authors construct a high-utilization (70 percent, 630 mAh g^{-1}_Sn) porous graphite substrate Sn anode that combines high efficiency with long lifetime. The observations rest on long-term operando optical imaging of bulk-representative electrodeposition behavior.

What carries the argument

Substrate-dependent tin growth mode (multi-stage on copper versus single-stage on graphite), revealed by custom through-plane operando optical microscopy in pouch cells across full cell lifetime.

If this is right

  • Copper substrates cause high overpotentials and irreversible active material loss at high plated capacities.
  • Graphite substrates enable a single-stage growth mode that improves stability despite slower kinetics.
  • A porous graphite substrate supports a tin anode at 70 percent utilization (630 mAh g^{-1}_Sn) with high efficiency and long lifetime.
  • Long-term operando characterization across device lifetime can guide material and device optimization for other electrochemical systems.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same long-term imaging approach could be applied to other reactive metal anodes to screen substrates that avoid multi-stage failure modes.
  • Substrate engineering that favors single-stage growth may raise the practical energy density ceiling for aqueous batteries beyond what copper current collectors currently allow.
  • Combining the graphite substrate with additional surface treatments not tested here might further increase utilization while preserving the observed stability.

Load-bearing premise

The through-plane optical images captured in the custom pouch-cell setup are representative of bulk electrodeposition behavior without significant optical artifacts, cell geometry effects, or imaging-induced changes to the observed morphology.

What would settle it

If copper and graphite substrates produced identical tin morphologies, overpotentials, and cycle lives under identical high-capacity plating conditions, the claim that substrate governs growth mode and stability would be falsified.

Figures

Figures reproduced from arXiv: 2605.26727 by Colin Ophus, Daniel N. Congreve, Dasol Yoon, Jianbo Wang, Katherine J. Harmon, Kyle Frohna, Sofia K. Catalina, William C. Chueh, Willow Thompson.

Figure 1
Figure 1. Figure 1: (a) Schematic of the operando pouch cell. (b) Galvanostatic cycling curves of a Sn-anode, Cu substrate pouch cell. (c) Schematic of the operando optical microscopy setup and the Sn anode reactions taking place at the Cu substrate. (d) Galvanostatic cycling of Cu foam pouch cell at high (70%) utilization taken during an operando microscopy experiment. (e-i) Optical images of the Cu substrate in discharged s… view at source ↗
Figure 2
Figure 2. Figure 2: (a) Voltage (black) and grayscale optical intensity (red) versus capacity for a porous Cu substrate, Sn anode battery. The grayscale intensity value is extracted from the regions imaged in panels (c)-(g). Shaded regions correspond to the oxidation stage and three growth stages shown in panels (c)-(g). (b) dQ/dV plot extracted from the data in panel (a). Panels (c)-(g) show optical microscopy images of a re… view at source ↗
Figure 3
Figure 3. Figure 3: (a) HAADF STEM image, (b) Cu Kα EDX image and (c) Sn Lα EDX image of a Sn grain grown on a Cu substrate with pixel-size limited resolution of 3.85 nm. (d) Cross sectional SEM image of a Cu substrate after a 70% utilization charge. (e) Line cut of Cu Kα (green) and Sn Lα X-ray intensity extracted from the boxes in panels b and c in the direction of the white arrows. (f) Grazing incidence X-ray diffraction p… view at source ↗
Figure 4
Figure 4. Figure 4: (a) Voltage (black) and grayscale optical intensity (red) versus capacity for a porous graphite substrate, Sn anode battery. (b) dQ/dV plot extracted from the data in panel (a). Panels (c)-(g) show optical microscopy images of a region of the porous graphite during Sn plating along with schematics of the reactions occurring at each stage. Galvanostatic charge-discharge curves of pristine (solid lines) and … view at source ↗
Figure 5
Figure 5. Figure 5: Coulombic efficiency (a) and voltaic efficiency (b) of pouch cell cycling over 500 hours as a function of utilization for both the porous graphite (blue) and porous Cu (red) substrates. Coulombic efficiency (c) and voltaic efficiency (d) of porous (circles) and planar (squares) substrate pouch cells over 500 hours of cycling as a function of plated Sn capacity per real surface area. Each condition is repre… view at source ↗
read the original abstract

Operando microscopy has unveiled key mechanistic insights in battery materials during early cycling, but long-term characterization to unveil material evolution, degradation, and failure remain limited. To address this gap, we develop a custom operando optical microscope that captures images across hundreds of cycles and hours using optically accessible, anode-free pouch cells. We image through-plane, bulk-representative electrodeposition behavior of aqueous tin metal anodes, which are promising due to their high energy density but whose reactivity limits practical cycle life. We show that substrate governs the morphology and stability of plated tin, particularly at high plated capacities. Specifically, copper substrates exhibit a multi-stage tin growth mode, which results in high overpotentials and irreversible active material loss at high plated capacities. In contrast, graphite substrates display a single-stage growth mode with slower kinetics. Using this insight, we balance performance and stability to demonstrate a high-utilization (70%, 630 mAh g$^{-1}_{Sn}$) porous graphite substrate Sn anode with high efficiency and long lifetime. Our results underscore the importance of material and device optimization guided by operando characterization across device lifetime with broad applicability to electrochemical systems.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The paper develops a custom operando optical microscope for imaging through-plane electrodeposition in anode-free aqueous Sn pouch cells over hundreds of cycles. It claims that Cu substrates induce multi-stage Sn growth causing high overpotentials and irreversible active-material loss at high plated capacities, while graphite substrates enable single-stage growth with slower kinetics; this insight is used to demonstrate a 70% utilization (630 mAh g^{-1}_Sn) porous graphite Sn anode with high efficiency and long lifetime.

Significance. If the imaging is representative of bulk behavior, the long-term operando visualization across device lifetime is a clear methodological advance over early-cycle-only studies, and the substrate-dependent growth-mode distinction supplies a concrete design rule for balancing utilization and stability in aqueous metal anodes.

major comments (2)
  1. The central claim that substrate governs morphology and stability (Abstract) rests on the assumption that through-plane optical images in the custom pouch cell are free of optical artifacts, light-induced plating changes, pouch-geometry distortions, and line-of-sight projection effects and accurately reflect 3D bulk electrodeposition. No cross-validation (SEM, X-ray tomography, or electrochemical modeling) or artifact-ruling experiments are described, leaving the Cu multi-stage vs. graphite single-stage distinction unverified.
  2. Abstract and results report clear observational distinctions but supply no quantitative error bars on overpotential or capacity-loss values, no raw-image examples, and no statistical assessment of how representative the imaged regions are of the full electrode area.
minor comments (1)
  1. Methods section should explicitly state the optical resolution, illumination wavelength/intensity, and any controls used to confirm that imaging itself does not alter plating morphology.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thorough review and valuable comments. We address the major comments point-by-point below, providing the strongest honest defense of the work while acknowledging where revisions can strengthen the presentation.

read point-by-point responses

  1. Referee: The central claim that substrate governs morphology and stability (Abstract) rests on the assumption that through-plane optical images in the custom pouch cell are free of optical artifacts, light-induced plating changes, pouch-geometry distortions, and line-of-sight projection effects and accurately reflect 3D bulk electrodeposition. No cross-validation (SEM, X-ray tomography, or electrochemical modeling) or artifact-ruling experiments are described, leaving the Cu multi-stage vs. graphite single-stage distinction unverified.

    Authors: The pouch cell architecture uses a thin electrolyte layer and transparent window specifically to enable direct through-plane imaging of bulk electrodeposition while preserving electrochemical behavior. The morphological distinctions are corroborated by independent electrochemical signatures (overpotential evolution and capacity retention) that differ systematically between Cu and graphite. We will revise the manuscript to add an explicit discussion of potential artifacts, the design choices that mitigate them (low light intensity, cell geometry), and the correlation between optical observations and bulk metrics. Full cross-validation with ex-situ 3D techniques was outside the scope of this study focused on long-term operando optical access. revision: partial

  2. Referee: Abstract and results report clear observational distinctions but supply no quantitative error bars on overpotential or capacity-loss values, no raw-image examples, and no statistical assessment of how representative the imaged regions are of the full electrode area.

    Authors: We agree that these elements improve rigor. The revised manuscript will include error bars on all overpotential and capacity-loss plots (from replicate cells), representative raw images in the SI, and a statistical summary of multiple imaged regions demonstrating consistency across the electrode area. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental imaging study with no equations or fitted derivations

full rationale

The paper reports direct operando through-plane optical microscopy observations of Sn electrodeposition on Cu vs. graphite substrates in custom pouch cells, followed by a practical demonstration of a porous graphite anode achieving 70% utilization. No equations, parameters, or mathematical derivations appear in the provided text. The central claims rest on empirical morphology differences and cycle-life data rather than any reduction of outputs to inputs by construction, self-citation chains, or renamed fits. This is a standard experimental workflow; the imaging method itself is not derived from the results it produces.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental imaging study with no mathematical model, free parameters, or postulated entities; observations derive directly from optical data collected in custom cells.

pith-pipeline@v0.9.1-grok · 5773 in / 1099 out tokens · 46184 ms · 2026-06-29T17:22:39.433741+00:00 · methodology

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Reference graph

Works this paper leans on

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    (13) Xu, D.; Zhang, H.; Xie, J.; Zhou, L.; Yang, F.; Ma, J.; Yu, Y.; Wang, G.; Lu, X. Highly Reversible Tin Film Anode Guided via Interfacial Coordination Effect for High Energy Aqueous Acidic Batteries.Advanced Materials2024,36, 2408067. (14) Zhang, F.; Zhang, X.; Shu, Y.; Xiao, H.; Wang, Q.; Guo, Q.; Wang, Y.; Huang, J.; Xia, Y. Constructing Dense Morph...

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    (47) Zhou, X.; Lin, L.; Lv, Y.; Zhang, X.; Wu, Q. A Sn-Fe flow battery with excellent rate and cycle performance.Journal of Power Sources2018,404, 89–95. (48) Yang, Y.; Xiang, Y.; Yang, Y.; Xie, X.; Mushtaq, F.; Zhang, R.; Daoud, W. A. Urea Induces Uniform Tin Deposition for Long Cycle-Life Tin-based Redox Flow Battery. Advanced Functional Materials2025,3...

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