At the 2025 International Battery Seminar & Exhibit in Orlando FL (USA), Prof. Jeff Dahn (Dalhousie University) highlighted how Si-carbon composite active materials prepared through monosilane deposition on carbon matrices exhibit very promising cycling stability.
Prof. Dahn emphasized that the quantity of liquid electrolyte has to be very carefully controlled in such high-energy cells to avoid ‘Electrolyte Motion Induced Salt Inhomogeneity’ (EMSI), which can lead to temporary capacity loss (reversible after letting cells rest for weeks) and lithium plating (risk of irreversible damage).
Prof. Dahn referred to work by Dr. Sophie Solchenbach et al. [1] from BMW, who illustrate that an ‘electrolyte pore filling ratio’ in Si active material-containing cells of slightly below 1 should be targeted (‘sweet spot’, as the presence of too little electrolyte also can cause problems).
New Evidence from AABC Europe 2026
At the recent AABC Europe 2026 in Mainz (Germany), Edwin Knobbe (BMW) presented highly insightful work on the coupling of electrochemistry and mechanics inside battery cells. Two findings stood out. First, the LiPF6 concentration at the edges of the jelly roll dropped to below one fifth of the value at the center of the cell, built up over repeated fast-charge cycling. Second, teardown photos showed metallic lithium plated on the edges of the negative electrodes after repeated fast charging, while the slow-charged reference cells stayed clean.
This matters well beyond cycle life: overcoming such edge plating removes a real barrier on the path towards roughly 5-minute fast charging in high-energy cells.
EMSI as a Long-Range Transport Problem
Taken together with the earlier observations, this additional data points to a more general reading of EMSI: it is fundamentally a long-range transport problem. The electrochemistry only requires ion transport across roughly 100 µm – but the displaced electrolyte travels centimeters, to the edges and into the void spaces of the cell, and that is where the salt piles up or runs low.
As cells push silicon content for higher energy density, the driving force for this long-range migration only grows – more electrode swelling, leaner electrolyte and larger cell formats all add to it. The safe window for a freely mobile liquid narrows accordingly, and the effect can be expected to bite earliest where fast charge and high silicon content collide.
Implications for High-energy Li-ion Battery Cell Development & Up-scaling
It is very easy to underestimate the performance of Si-based active materials, which can depend not only on the electrolyte type, but also on the electrolyte pore filling ratio because of the EMSI phenomenon.
Even if the liquid electrolyte content in cells is very carefully optimized during product development and kept constant during cell production, the ‘electrolyte pore filling ratio’ may vary between cells if there are lot-to-lot differences in terms of negative / positive electrode or separator porosity. As a consequence, the undesired EMSI phenomenon could occur if the ‘electrolyte pore filling ratio’ is too high, or an increase of the internal resistance if it is too low.
Furthermore, the ‘electrolyte pore filling ratio’ can vary across a cell’s lifetime if some of the electrolyte evaporates (a significant risk given the low boiling points for common liquid electrolyte components DMC, EMC and DEC of 90, 107 and 126 °C, respectively).
It is to be watched closely if high-viscosity / high-boiling liquid, semi-solid and/or all-solid electrolytes allow for the avoidance of the undesirable EMSI phenomenon regardless of the exact ‘electrolyte pore filling ratio’. If yes, relaxed specifications in terms of electrode / separator pore size distribution / electrolyte filling ratio could allow for cost-savings at mass production scale and increased performance consistency across cell production lots.
Cell Design Responses and a Reframed Ionic Conductivity Question
High-energy designs are likely to respond to this challenge in different ways – some by immobilizing the electrolyte, moving along the spectrum from gel to solid-liquid hybrid to all-solid, and others by engineering the liquid and the fill window hard enough to live with the phenomenon. For programs moving towards immobilized electrolytes, there is an under-appreciated upside beyond cycle life: a root cause that is designed out no longer has to be managed for the life of a program, validated cell by cell, or simulated at full cell dimensions.
One objection sits underneath this reasoning: higher viscosity has always meant lower conductivity, and therefore worse fast charge – which is precisely why liquid electrolytes have been optimized near the conductivity peak. But that trade-off holds only at the roughly 100 µm scale. EMSI adds a second, long-range cost to a freely mobile liquid, and the depleted edge it creates is itself a low-conductivity zone. The question therefore shifts from “what maximizes bulk conductivity?” to “what keeps conductivity up where the cell actually plates?” – and while those used to share the same answer, they may no longer.
References
- Sophie Solchenbach, Camilla Tacconis, Aurora Gomez Martin, Verena Peters, Lea Wallisch, Anna Stanke, Johanna Hofer,a Diemo Renz, Burkhard Lewerich, Georg Bauer, Moritz Wichmann, Daniel Goldbach, Alexander Adam, Markus Spielbauer, Peter Lamp and Johannes Wandt, Electrolyte motion induced salt inhomogeneity – a novel aging mechanism in large-format lithium-ion cells, Energy & Environmental Science, Issue 19, 2024
- Corresponding LinkedIn Post: https://www.linkedin.com/posts/pirminulmann_lithiumionbattery-batterytechnology-siliconanode-activity-7311074764029136901-e7BQ
- LinkedIn post update: https://www.linkedin.com/posts/pirminulmann_aabceurope-solidstatebatteries-semisolidbatteries-share-7468209160950591489-8mnH/
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See also: Wettability