When an electric vehicle pulls up to a fast-charging station and its battery level climbs back up in just ten-odd minutes, intense chemical reactions and physical deformation are occurring simultaneously inside the electrodes. The charger's display shows a smoothly rising percentage, but even when the visible charging behavior looks flawless, serious damage may be progressing in the microscopic world within the electrode.
A research team led by Professor Kang Taek Lee and Professor EunAe Cho at the Korea Advanced Institute of Science and Technology (KAIST) has conducted numerical analysis of localized degradation processes occurring inside electrodes during fast charging, using a 3D digital twin built from the microstructure specifications of a commercial graphite anode. The paper, co-authored with Yejin Kang, Seungsoo Jang, and Jung Hyeon Moon, was selected for the back cover of the journal InfoMat (published July 2026, DOI: 10.1002/inf2.70141). The central finding is that macro-level averages—such as total binder content or average porosity across the entire electrode—are insufficient to capture the degradation behavior that occurs inside electrodes during fast charging.
Three microscopic degradation mechanisms occurring simultaneously inside the battery
During fast charging of a lithium-ion battery, lithium ions that have migrated from the cathode travel through fine, electrolyte-filled pores and burrow into the graphite particles of the anode. A polymer material called a binder holds the graphite particles together and bonds them to the current collector. When charging speed is pushed to an extreme, three interrelated physicochemical phenomena tend to occur inside the electrode, degrading battery performance.
The first phenomenon is metallic lithium deposition. When the rate at which lithium ions insert into the graphite particle surface falls behind the rate at which ions are supplied from the electrolyte, excess ions that cannot enter the graphite lattice instead deposit as metallic lithium on the particle surface. This deposited lithium becomes inactive and no longer contributes to charge or discharge, permanently robbing the cell of capacity—and it can also grow into dendrites that pierce the separator, risking an internal short circuit.
The second phenomenon is uneven growth of the solid electrolyte interphase (SEI). At the interface where graphite meets the electrolyte, decomposition of the electrolyte forms a protective SEI layer. Under the steep potential gradients created by fast charging, this layer can become excessively thick or form unevenly in localized spots, blocking ion pathways and increasing internal resistance.
The third phenomenon is the concentration of internal stress caused by particle volume change. Graphite particles expand by up to about 10% in volume as they absorb lithium. As particles expand, they press against neighboring particles and the binder, generating microscopic mechanical stress. When this stress becomes locally concentrated, it can lead to collapse of the electrode structure or isolation of individual particles.
Conventional physical experiments and standard one-dimensional electrochemical models have struggled to separate how these three phenomena interact with one another at the microscopic scale. Commercial electrode evaluations typically rely on macro-level indicators such as the binder's weight ratio to total electrode volume or average porosity. Even when these average values are identical, the spatial arrangement of the constituent materials can cause large variation in internal ion transport pathways and reaction distribution.
Reconstructing 3D structure and analyzing parameters based on measured data
The research team built a 3D digital twin reproducing the three phases of an actual commercial graphite anode's microstructure—graphite particles, binder, and the electrolyte-filled pore network—based on real specifications. In earlier work (Kang et al., Chemical Engineering Journal, 2025, DOI: 10.1016/j.cej.2025.164524), the same group had established an integrated electro-chemo-mechanical modeling framework combining volume expansion and SEI formation; the current paper extends that framework to analyze microstructural heterogeneity under fast-charging conditions.
The simulation model's validity was verified against measured charging profile data. However, it should be noted that individual degradation outputs from the model—such as the amount of lithium plating, the local distribution of SEI film thickness, and internal stress distribution—represent predictions from computational simulation.
In the analysis, the following parameters were systematically varied as electrode design variables:
- Electrode thickness (a standard 50 μm and an 83 μm thickness assumed for higher capacity)
- Porosity distribution within the electrode
- Spatial arrangement of the binder (a steep gradient concentrated toward the separator side, versus a uniform or gentle gradient)
Through the simulations, the flow of lithium ions along the electrode depth, the locations where overpotential arises, localized lithium plating risk, and stress distribution caused by graphite expansion were visualized at the microscale.
Binder placement effects become more pronounced as thickness increases
The key insight from the computational results is that looking only at the electrode's overall charging capacity can cause localized degradation occurring inside the electrode to go unnoticed.
In the standard 50 μm-thick electrode model, when a case with binder heavily concentrated toward the separator side was compared with a case where binder was uniformly distributed throughout the electrode, the difference in apparent overall charging capacity was less than 4% (the absolute charging capacity values for both cases were not disclosed in the published materials). At first glance, binder distribution appears to have almost no effect on charging behavior.
Looking inside the electrode at the microscale, however, the picture was very different. When binder was concentrated near the separator, the pore pathways available for lithium ions to reach deeper into the electrode narrowed. As a result, the simulation showed that lithium plating near the current collector increased by more than 10% compared with the uniformly distributed binder model (again, the absolute values of local plating amounts were not disclosed in the published materials).
The impact of this internal heterogeneity became clearly apparent in the model where the electrode was thickened to 83 μm to achieve higher energy density. In thick electrodes, where ions must travel farther, increased transport resistance from pore blockage directly limits the capacity the electrode as a whole can deliver. Compared with the model featuring a steep binder concentration, the model with uniformly distributed binder showed roughly 18% higher charging capacity (the corresponding absolute capacity values were not disclosed; this is a relative comparison from the published materials).
| Evaluation Parameter | 50 μm-thick anode (steep binder concentration vs. uniform distribution) | 83 μm-thick anode (steep binder concentration vs. uniform distribution) |
|---|---|---|
| Difference in apparent total charging capacity | Minor difference of less than 4% (internal damage remains hidden); absolute values not disclosed | Uniform distribution maintains ~18% higher charging capacity; absolute values not disclosed |
| Lithium plating near the current collector | Increases by more than 10% with binder concentration; absolute values not disclosed | Plating risk increases across a wider area due to delayed ion transport |
| Role of the pore network | Source of localized ionic resistance | Buffer that relieves stress from particle expansion |
| Primary degradation constraint | Localized overpotential and uneven lithium deposition | Compounded effect of delayed ion diffusion along electrode depth and stress concentration |
The spatial arrangement of pores is also directly involved in relieving mechanical stress. When graphite particles expand during charging, adequate pore space surrounding the particles can absorb the deformation, acting as a buffer zone. In areas where pores are narrow or filled with binder, there is nowhere for the particle's volume change to be released, causing localized mechanical stress to build up. The study confirmed that designs with appropriately arranged high porosity simultaneously reduce ion diffusion resistance and substantially relieve localized stress concentration.
What simulation opens up for electrode design—and the challenges ahead
The conclusion presented by this research points toward a shift, in the design of fast-charging-capable batteries, away from a total-quantity-management mindset—"what to mix in and how much"—and toward a microstructural control perspective focused on how constituent materials are spatially arranged.
In the official announcement, KAIST's Professor Kang Taek Lee noted that the significance of this research lies in having used a 3D digital twin to visualize problems inside the battery that would have been difficult to detect from overall charging performance figures alone. Conventional battery development has relied mainly on building prototype cells, repeating charge-discharge cycle tests, and then performing teardown analysis after degradation has occurred. Using digital twin analysis makes it possible to evaluate ion transport properties and stress concentration risk inside the electrode in a virtual space before prototyping, enabling structural optimization ahead of physical fabrication.
Some academic caveats apply to the interpretation of these results. This research is a theoretical prediction based on computational simulation; it did not involve manufacturing actual cells with the proposed binder arrangement and subjecting them to long-term cycle life testing or physical verification of suppressed lithium plating. The model used is based on the structure of a specific commercial graphite anode, and it remains unverified whether the same numerical results would apply directly to different material systems, such as silicon-doped graphite anodes or all-solid-state batteries.
On the manufacturing floor, precisely controlling the depth-wise distribution of binder to within tens of micrometers as intended, during coating and drying processes, remains a significant manufacturing challenge. Future follow-up research will need to focus on how to reproduce the ideal spatial arrangements indicated by the simulation on actual electrode production lines, and on verifying through physical experiments whether such electrodes actually deliver the predicted long cycle life and fast-charging tolerance.