Smart cell engineering: how electrospun scaffolds and ultra-thin separators simultaneously boost energy density and lifespan in "anode-free" batteries introduction

"Anode-free" (or "anodeless") lithium metal batteries are a critical path toward next-generation energy storage, promising higher energy densities. However, their practical application is severely limited by the low Coulombic efficiency and irreversible capacity loss associated with repeatedly plating and stripping lithium metal on a current collector. While introducing a porous host scaffold is a promising solution, it presents a difficult trade-off: the scaffold itself occupies volume and adds thickness, potentially negating the energy density gains of the anode-free design.

A recent study published in Advanced Functional Materials cleverly resolves this conflict. By combining an electrospun PVDF-HFP porous scaffold with an ultra-thin separator, the research team not only extended the battery's cycle life but also boosted its practical energy density by over 10%, while using advanced techniques like quantitative ⁷Li NMR to reveal the underlying mechanisms.

Scaffold Fabrication and a "Smart" Cell Design

The study begins by fabricating a PVDF-HFP nanofiber scaffold with a high porosity of 91%–96% via an optimized electrospinning process. This process not only creates a uniform fiber network but also increases the proportion of the high-dielectric β-phase in the material from 46% to 80%, which is beneficial for guiding a uniform Li-ion flux.

SEM images and fiber diameter distributions of electrospun fibers

Schematic of the α- and β-phases of PVDF-HFP

However, initial tests showed that while the 20 µm-thick scaffold extended cycle life, it also reduced the cell's energy density by 7% due to its added thickness. To solve this, the team introduced a "Gen 1" smart cell design: replacing the conventional 25 µm separator with an ultra-thin 5 µm version, thereby compensating for and even exceeding the thickness added by the scaffold.

Energy density comparison for bare Cu and two scaffold cell generations

Contact angle images and mechanical properties of different separators

Ultimately, this "electrospun scaffold + ultra-thin separator" combination surpassed the conventional anode-free design in both cycle life and energy density.

Electrochemical performance comparison for bare Cu vs. scaffold-modified Cu anodes

Deep Dive into Mechanisms: From Volumetric "Breathing" to "Dead" Lithium Quantification

To uncover the root cause of the performance improvement, the study employed a range of in-situ and ex-situ characterization techniques:

In-situ Volume Monitoring: Using a capacitive sensor to track the cell's "breathing effect" in real-time, the study found that although the scaffold caused slightly higher initial expansion, it effectively suppressed the continuous, irreversible volume growth caused by "dead" lithium accumulation over long-term cycling.

Relative displacement (volumetric expansion) of pouch cells during cycling

Quantitative ⁷Li NMR Spectroscopy: This was the key to revealing the mechanism. Non-destructive analysis of cycled cells quantitatively confirmed for the first time that the electrospun scaffold significantly suppresses the formation of inactive "dead" lithium (reducing its contribution to capacity loss by ~40%) and reduces the proportion of high-surface-area dendritic lithium (by ~9%).

⁷Li NMR analysis of cycled cells, distinguishing between active Li, SEI, and dead Li

Interfacial Chemistry (XPS): The study also found that the scaffold's presence alters the SEI composition, mitigating the deep decomposition of the electrolyte salt and helping to form a more stable passivation interface.

XPS analysis of the SEI composition on bare and scaffold-modified Cu anodes

Conclusion & Implications: Beyond Materials to Systems Engineering

This paper demonstrates that an electrospun PVDF-HFP scaffold is an effective host for "anode-free" batteries. Its core insight is that through smart cell systems engineering—namely, using an ultra-thin separator to offset the scaffold's thickness—one can unlock the full potential of a porous host to extend cycle life without sacrificing, and in fact even enhancing, energy density.

Comparison of the scaffold design in this work to others reported

A schematic summary of the main findings

The quantitative ⁷Li NMR analysis clearly shows that the performance boost is primarily due to the scaffold's effective suppression of "dead" and dendritic lithium. This work provides an invaluable engineering-based solution for designing practical "anode-free" lithium metal batteries with both high energy density and long cycle life.

The exploration of next-generation anodes involves not only structural design but also innovation in the material system itself. In this arena, LIMX Power has achieved a key breakthrough, having now mass-produced and commenced bulk deliveries of the industry's first all-silicon-carbon anode battery.

Literature Information

L. Wichmann, B. Tengen, P. Yan, et al. “Boosting the Energy Density of “Anode-Free” Lithium Metal Batteries via Electrospun Polymeric Scaffolds.” Adv. Funct. Mater. (2025): e11672. https://doi.org/10.1002/adfm.202511672