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In the OPINCHARGE Scientific Publications series, we highlight research that advances our understanding of battery materials, interfaces and degradation processes. This study investigates how ultrathin metal interlayers can control lithium deposition, addressing one of the key challenges facing anode-free solid-state batteries.
The publication “Correlative Electron-Ion Beam Analysis of the Effect of Lithiophilic Interlayers on Regulating the Li+ Flux Distribution in Anode Free Solid-State Batteries” was authored by Sayantan Sharma, Alexander Santiago, Maria Martinez-Ibañez, Athira Suresh Kumar, Olivier De Castro, Jean-Nicolas Audinot and Santhana Eswara.
Read the publication: https://zenodo.org/records/22691305
Anode-free solid-state batteries are a promising route towards higher-energy-density and potentially safer batteries. Unlike conventional lithium-metal batteries, they do not contain a lithium-metal anode when assembled. Instead, lithium ions extracted from the cathode are deposited directly onto the anode-side current collector during the first charge, creating the anode inside the battery.
However, their performance strongly depends on how uniformly lithium deposits on this surface. Uneven lithium plating can lead to dendritic growth, inactive or “dead” lithium, capacity loss and ultimately battery failure.
One strategy is to modify the copper current collector with an ultrathin lithiophilic – or lithium-attracting – interlayer.
The researchers compared bare copper with copper coated with 20 nm layers of silver (Ag) or gold (Au). These metals have a greater affinity for lithium and can therefore change the way lithium initially nucleates and grows on the surface.
The difference was striking. Lithium nucleation on bare copper required an overpotential of approximately 59 mV, while both silver- and gold-coated surfaces reduced it to below 1 mV.
To understand what was happening at the microscopic level, the researchers combined focused ion beam-scanning electron microscopy and secondary ion mass spectrometry (FIB-SEM-SIMS) with lithium isotope tracing.
The cells contained a ⁶Li-enriched electrode, allowing the researchers to distinguish lithium originating from different parts of the cell. SEM revealed the morphology of deposited lithium, while SIMS mapped the spatial distribution of lithium isotopes.
Together, these techniques allowed the team to connect how lithium first nucleates on a surface with how the subsequent Li+ flux is distributed.
On bare copper, lithium formed relatively few, larger and irregularly distributed deposits. The average density was approximately 0.65 lithium deposits per µm².
Adding the lithiophilic layers dramatically changed this behaviour. Deposit density increased to around 3.85 per µm² with gold and 9.87 per µm² with silver, while individual deposits became smaller and more uniformly distributed.
Lithium isotope mapping confirmed the same effect: bare copper produced a heterogeneous Li+ flux, with lithium concentrated in localised regions, whereas the Ag- and Au-coated surfaces showed a much more homogeneous distribution.
These local differences can have major consequences for battery lifetime.
On bare copper, sporadic lithium nucleation creates local current hotspots. These regions concentrate further lithium deposition and can eventually promote filament-like dendrite growth, short circuits and the formation of inactive lithium.
The lithiophilic interlayers reduce the energy barrier for lithium nucleation, creating many more nucleation sites. This distributes the Li+ flux more evenly across the surface and promotes denser and more homogeneous lithium deposition.
The study shows that something as thin as a 20 nm surface coating can fundamentally change how lithium behaves inside a battery.
By connecting interfacial properties, lithium nucleation, deposit morphology and Li+ flux distribution, the research provides new insight into why lithiophilic coatings can help stabilise anode-free solid-state batteries.
These findings can support the systematic design of better current collectors and interlayers, helping reduce degradation and move high-energy-density anode-free batteries closer to practical applications.
