Modern lithium-ion battery performance is governed by complex electrochemical processes that are strongly influenced by geometry. While simplified models remain useful for early-stage screening, they often fail to capture localized behaviors that ultimately determine performance limits in real-world designs.

AltaSim has developed a geometry-first simulation framework using COMSOL Multiphysics^® that enables engineers to evaluate how design decisions influence internal battery behavior before physical prototypes are built. By resolving spatial variations in current density, state of charge, and electrolyte transport, this approach provides actionable insight into performance, scalability, and design risk.

In an anonymized industrial example, two battery geometries were evaluated under identical conditions. Simulations were completed for charging rates up to 5C, while higher-rate cases revealed both physical and numerical limitations.

Geometry is not a secondary modeling detail – it is a primary driver of performance, particularly as operating conditions become more demanding.

Battery engineers increasingly rely on simulation to guide design decisions as performance targets rise and development timelines compress. In many workflows, however, geometric complexity is intentionally reduced to simplify model setup and improve runtime efficiency. While this tradeoff can be acceptable for early-stage evaluation, it introduces a fundamental limitation.

Simplified models inherently assume uniform behavior throughout the cell, yet nonuniformity often governs performance under realistic conditions. As batteries become more compact, more conformal, and more aggressively operated, internal gradients begin to dominate. Current density is redistributed, electrolyte transport becomes limiting, and localized regions of elevated overpotential develop, particularly near current collectors and structural features of the design.

AltaSim addresses this gap by treating geometry not as a refinement, but as a primary modeling decision. Using COMSOL Multiphysics^®, engineers can construct geometry-resolved electrochemical models that preserve spatial fidelity while maintaining consistent assumptions across design variations.

This capability fundamentally changes how simulation is used. Rather than validating a single design, engineers can compare multiple geometries directly in a controlled environment, evaluating how each performs under identical boundary conditions and operating scenarios. This enables a shift from simulation as a verification tool to simulation as a virtual design platform, where tradeoffs can be explored rapidly and systematically before committing to hardware.

The flexibility of the modeling framework also supports evaluation across a wide operating envelope. Designs can be tested under both nominal conditions and more aggressive charging scenarios, providing insight into how performance scales and where limitations begin to emerge.

To demonstrate this approach, AltaSim conducted a simulation study of two distinct lithium-ion cell geometries under a consistent electrochemical framework. The scope of the study was intentionally focused on electrochemical behavior, excluding thermal and mechanical coupling to maintain comparability and enable rapid turnaround.

Both geometries were evaluated under identical assumptions, including material properties drawn from representative library values and a charging window spanning 0.8. Simulations were completed for charging rates ranging from 0.5C through 5C. Additional cases at 10C and 20C were initiated but did not converge within the available project timeframe, reflecting both the increasing physical severity of the problem and the practical limitations of simulation under aggressive conditions.

The models produced spatially resolved fields that provided insight into the cell's internal behavior:

• State of charge
• Current density in both electrodes and electrolyte
• Electrolyte salt concentration
• Interfacial current density
• Overpotential
• Electric potential within the current collectors

Taken together, these outputs enabled a detailed view of how each geometry responded internally as operating demands increased.

At lower charge rates, both geometries exhibited relatively smooth and stable internal behavior. However, as the charge rate increased, the simulations revealed increasingly pronounced spatial variation. Gradients in state of charge and current density became more evident, and the influence of electrolyte transport limitations began to emerge.

Importantly, the two geometries did not respond identically under these conditions. Differences in internal structure influenced how current was distributed and where localized stress developed. Regions of elevated overpotential and concentration gradients appeared in different locations and with differing severity, demonstrating that even subtle geometric variations can lead to meaningful differences in performance.

At higher charge rates, the simulations also highlighted the increasing difficulty of both the physical system and the numerical model. Achieving stable solutions at 5C required targeted adjustments to model formulation and parameters. Beyond this point, the inability to converge solutions at 10C and 20C indicated extreme gradients and transport limitations under such conditions.

The value of geometry-resolved simulation lies not only in accuracy but in its ability to guide better decisions earlier in the design process. By enabling direct comparison between candidate geometries, simulation provides a controlled environment in which design tradeoffs can be evaluated objectively. Engineers can identify where and why performance limitations arise, rather than relying solely on system-level metrics that may obscure underlying issues.

This approach also improves confidence in how a design will perform as operating conditions change. Instead of evaluating performance at a single point, engineers can observe how internal behavior evolves as charge rates increase, revealing whether a design remains robust or begins to exhibit limiting behavior.

Ultimately, geometry-first simulation reduces reliance on trial-and-error iteration. Exposing hidden nonuniformities early allows engineering teams to address potential weaknesses before they propagate into costly redesign cycles or late-stage testing failures.

As battery designs are pushed toward higher power, faster charging, and tighter packaging constraints, geometry plays an increasingly central role in determining performance. Ignoring geometric effects can lead to underestimation of risk and overly optimistic performance projections, particularly under aggressive operating conditions.

In contrast, a geometry-first modeling strategy provides a clearer view of internal behavior, enabling more informed design decisions and more efficient development cycles.

Battery design is no longer driven solely by materials and chemistry. Geometry plays a critical role in shaping how electrochemical processes unfold within the cell, particularly under real-world operating conditions.

By leveraging COMSOL Multiphysics^® as an enabling platform, AltaSim's geometry-first approach allows engineers to reveal internal nonuniformities, evaluate competing designs, and identify performance limitations before physical testing begins. This shifts simulation from a supporting role to a strategic one, accelerating innovation while reducing development risk.