Rechargeable lithium-ion batteries may be losing access to their full energy-storage potential for a reason hidden inside individual electrode particles. Researchers have now identified a size-dependent mechanism behind a puzzling phenomenon known as activation, in which a battery’s capacity falls during its early cycles before gradually recovering. The discovery could help engineers design high-capacity anodes that deliver more energy sooner, while maintaining stable performance over repeated charging and discharging.
The study focuses on advanced anode materials that store lithium through conversion and alloying reactions. Unlike graphite, the conventional anode material used in many commercial lithium-ion batteries, these materials can accommodate much larger quantities of lithium. That greater storage capacity makes them attractive for electric vehicles, portable electronics and grid-scale energy storage. However, they can also undergo substantial structural and mechanical changes during operation, creating challenges that have limited their practical use.
Activation is one of the most difficult behaviors to understand. In affected electrodes, the measured capacity initially decreases and then increases gradually over subsequent cycles. This delayed recovery prevents the battery from immediately using the full amount of lithium that the active material should theoretically store. It can also expose the electrode to prolonged mechanical and chemical stresses, potentially weakening its structure and reducing long-term reliability. Although activation has been observed in many high-capacity materials, its physical origin has remained uncertain.
A research team led by Fangxi Xie and Mingmei Wu of Sun Yat-sen University in China, working with Shengfu Tong of Jinhua Advanced Research Institute and David Kisailus of the University of California, Irvine, has now connected activation directly to particle size. The researchers compared electrodes made from particles approximately 500 nanometers across with electrodes composed of much smaller particles, about 65 nanometers in size. Their results, published in Nano Research on July 2, 2026, show that large and small particles can follow fundamentally different lithiation pathways.
The larger particles displayed pronounced activation during cycling, while the smaller particles showed little or no comparable behavior. To determine why, the researchers tracked characteristic elements within the electrodes at different stages of operation. Their observations indicated that the electrolyte, the medium through which lithium ions move, could penetrate the small-particle electrode relatively quickly. This rapid access allowed lithium to reach more of the active material without a prolonged delay. In the larger particles, however, electrolyte access to the interior was significantly slower, creating a bottleneck during the early cycles.
The team’s analysis revealed that the delay is not simply a matter of electrolyte diffusion. Instead, it is closely related to the way lithiation advances through a particle. In a core-shell reaction mode, lithium first reacts with the outer region, forming a lithiated shell around an incompletely lithiated core. As this shell develops, it can expand relative to the original material. The surrounding, still-unreacted core constrains that expansion, generating compressive stress within the lithiated outer layer.
That stress acts as a brake on further electrochemical transformation. As lithium attempts to move inward from the shell toward the core, the accumulated compressive stress slows transport and makes continued lithiation increasingly difficult. In a large particle, the lithium must travel through a comparatively thick shell before the reaction reaches the center. The stress-induced resistance therefore persists for a longer period, producing the gradual capacity recovery characteristic of activation. The battery may eventually access more of the particle, but only after repeated cycling relieves or reorganizes the barriers to transport.
For the small particles, the same stress effect is much less influential. Their reduced dimensions shorten the distance that lithium must travel and limit the extent of stress accumulation in the lithiated shell. Faster electrolyte penetration and easier inward lithiation allow a greater fraction of the active material to participate earlier in the battery’s operation. As a result, these electrodes can reach stable cycling behavior without the prolonged activation period observed in their larger-particle counterparts.
To establish this explanation, the researchers combined direct experimental observations with finite-element simulations and electrochemical kinetic analyses. The simulations modeled how stress develops as the reaction front moves through a particle, while the kinetic studies examined how that stress influences lithium transport and reaction rates. Together, the results support a unified picture in which particle size controls the balance between reaction progress, diffusion and mechanical constraint. The work transforms activation from a largely empirical battery symptom into a predictable consequence of coupled electrochemical and mechanical processes.
The findings suggest that particle engineering could become an important strategy for improving high-capacity lithium-ion anodes. Reducing particle size may help suppress stress-induced kinetic retardation, accelerate access to the material’s full capacity and improve early-cycle performance. At the same time, particle size cannot be treated as an isolated design variable, because smaller particles can introduce other challenges, including greater surface reactivity and potentially more extensive side reactions with the electrolyte. Future battery designs will therefore need to balance transport advantages against chemical and structural stability.
By revealing how a core-shell reaction mode produces size-dependent activation, the study offers a new framework for understanding why apparently similar high-capacity materials can behave so differently in a working battery. The researchers’ results point toward a more precise approach to electrode design—one that controls not only composition, but also particle dimensions, reaction pathways and stress evolution. If these factors can be optimized together, advanced anodes may deliver their promised energy density more rapidly and retain it more reliably across the many cycles demanded by next-generation batteries.
Subject of Research: Size-dependent activation and stress-induced kinetic retardation in high-capacity lithium-ion battery anodes
Article Title: Researchers uncover the origin of activation in high-capacity lithium-ion anodes
News Publication Date: 2-Jul-2026
Web References: https://www.sciopen.com/journal/1998-0124; https://doi.org/10.26599/NR.2026.94908669
References: Nano Research, DOI: 10.26599/NR.2026.94908669
Image Credits: Nano Research, Tsinghua University Press
Keywords
Lithium-ion batteries, high-capacity anodes, battery activation, particle size, lithiation, core-shell reaction, stress-induced retardation, lithium transport, electrochemical kinetics, energy storage
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