Across electric vehicles, drones, robotics, defense, space, and other advanced mobility platforms, batteries are being asked to deliver more power, charge faster, last longer, and fit into increasingly demanding system designs.
But as cells are pushed toward higher rates, larger formats, and more energy-dense materials, a less visible limitation is emerging inside the battery itself.
For years, the industry has engineered around familiar degradation mechanisms, including SEI instability, material stress, and transport limitations inside the cell. These remain critical. Yet a 2024 study published in Energy & Environmental Science defined another mechanism that may play an important role in both high-rate performance and battery lifetime: Electrolyte Motion induced Salt Inhomogeneity, or EMSI.
A New Lens on Battery Degradation
In every lithium-ion battery, efficient movement of ions and electrons is essential during charge and discharge. When that movement becomes limited or uneven, the cell can experience higher resistance, localized stress, lithium plating, and accelerated degradation.
EMSI describes a salt concentration imbalance that forms as electrolyte moves inside the cell during cycling. During charge, the anode expands as lithium is inserted into the active material. This expansion can push low-salt-concentration electrolyte away from the anode and into open spaces within the cell. During discharge, as the anode contracts, that electrolyte can be pulled back in.
Over repeated cycles, especially under fast or continuous operation with limited rest time, this movement can create localized regions with lower salt concentration. These regions may increase the risk of lithium plating, contributing to active lithium loss, capacity fade, and reduced cell lifetime.
Why EMSI Is Becoming Harder to Ignore
This challenge becomes more relevant as the industry moves toward larger formats, including 4680 and 4695 cylindrical cells, as well as large-format pouch and prismatic cells. These formats can reduce inactive materials, simplify pack architecture, and support higher energy density. Yet as cells scale, internal transport paths become longer and more complex, heat becomes harder to dissipate, and electrolyte concentration gradients become more difficult to manage.
Importantly, research published in the Journal of The Electrochemical Society has also shown that EMSI can occur even at relatively modest charge rates, such as C/4, after approximately 100-400 cycles in commercial 18650 cells. This suggests that EMSI is not only a concern for extreme fast-charging scenarios, but a mechanism relevant to commercial cell design and long-term performance.
The challenge is intensified by another major industry trend: silicon-rich anodes. Silicon can significantly increase energy density, but it also undergoes much greater volume change during cycling than graphite. That expansion and contraction can amplify electrolyte movement, making uniform salt distribution harder to maintain.
Cell orientation can also influence EMSI, especially when batteries operate in different physical positions. This makes uniform electrolyte movement increasingly important across real-world applications.
For automotive applications, this matters beyond a single fast-charging event. EV batteries must maintain performance over years of repeated use, and even small internal imbalances can become meaningful when repeated across thousands of charge-discharge cycles.
Current mitigation strategies can help, but each comes with trade-offs:
| Mitigation strategy | Potential benefit | Trade-off |
| Use graphite-only anodes | Minimizes anode volume change | Limits cell energy density |
| Increase electrode porosity | Improves lithium-ion transport | Can limit cell energy density |
| Reduce the overall amount of electrolyte | Can limit the extent of salt imbalance | Can increase ionic resistivity |
| Use high salt concentration electrolytes | Can increase the lower limit of salt concentration | Expensive |
Overcoming EMSI with Addionics’ 3D Current Collectors
In most commercial cells, the current collector is still designed as a flat metal foil: a passive component that supports the active material and conducts electrons. But this conventional design is impermeable to electrolyte, forcing large-scale ion and electrolyte transport to occur mostly across two-dimensional pathways along the electrode plane.
For EMSI, this is a structural limitation. Salt concentration gradients form across long distances inside the cell, while flat, impermeable foils do nothing to shorten the diffusion path or support more uniform electrolyte distribution.
Addionics changes this architecture.
Smart Porous 3D Current Collectors replace traditional flat foils with a conductive, porous, three-dimensional metal structure. This creates more efficient pathways for both electrons and ions and supports more uniform, multidirectional electrolyte movement inside the cell.
In the context of EMSI, uniformity is the key. By reducing diffusion length from centimeters to millimeters or less, Addionics’ 3D Current Collectors can shorten relaxation time significantly – from weeks to hours or less. This directly addresses one of the core conditions behind EMSI: localized salt depletion that contributes to lithium plating and long-term degradation.
The impact becomes even more important in large-format cells, where internal transport and electrolyte uniformity are harder to manage. Addionics addresses these challenges from inside the electrode itself, where transport limitations, resistance, and concentration gradients begin.
Across various tests, Addionics’ technology has shown improvements in both rate capability and cell lifetime – the same performance areas EMSI can affect through transport limitations, lithium plating, and degradation.
As high-performance cells continue to scale, managing electrolyte motion and internal transport will become essential to preserving both power capability and lifetime.