All cells discussed here are 18650 NMC cells.
Balancing Energy Density and Safety
Using silicon-based additives in the anode requires a delicate trade-off in cell design. While silicon increases the energy density, it also brings significant challenges for cell safety.
Why More Space is Needed
Silicon expands and contracts during charge-discharge cycling, a phenomenon far more pronounced than with graphite. To prevent excessive mechanical pressure on the electrodes and the can, additional space must be reserved for jelly roll expansion.
- Graphite expansion: relatively small (≈10%)
- Silicon-based additives expansion: much larger (up to ~300%)
This stark difference explains why cells with silicon-containing anodes demand a larger gap between the jelly roll and the can. However, increasing the gap too much reduces energy density, so optimization is critical.
Experimental Findings
The graph below demonstrates the experimentally observed relationship between silicon additive ratio and the jelly roll-can gap. The correlation is nonlinear at lower silicon contents the required gap increases moderately, but once a critical threshold is passed, expansion accelerates due to particle cracking, repeated SEI formation, and structural instability.
A Multidimensional Design Challenge
Cell design is like playing 3D chess: every parameter energy density, safety margin, electrode porosity, binder system, and SOC window interacts with the others. Without advanced modeling or AI-assisted tools, optimizing this balance quickly becomes a trial-and-error game.
Stay tuned for more information and analysis on cell design!
Kerem Buğra Batuş, Cell Design & Process Development
At AION Engineering, we accelerate lithium-ion cell development using AI-driven design and advanced technologies, delivering innovative, sustainable energy solutions for a better future
See also: Silicon Anode