Microscopy Reveals Lithium Ion Transport Flaws in EV Batteries
Lithium-ion batteries remain the dominant energy storage technology for electric vehicles, prized for their high energy density and proven reliability. Yet, as adoption accelerates, expectations for extended driving range and rapid charging are pushing materials science toward more advanced chemistries. Among these, layered lithium nickel-rich oxides have emerged as a leading choice for high-performance applications, particularly in premium EV models. Their electrochemical behavior, however, is still not fully understood, especially regarding the transport of lithium ions within the cathode material.
Recent research supported by the EU-funded SOLARX, MULTILAT, and BATNMR projects has provided new clarity on this issue. The study focused on nickel-rich manganese cobalt oxide (NMC), a next-generation cathode material. Using operando optical scattering microscopy combined with diffusive modeling, the team observed how light interacted with individual active particles during battery cycling. This approach allowed direct visualization of lithium ion distribution in real time—a capability that had not been achieved before.
PhD student and co-first author Alice Merryweather of the University of Cambridge emphasized the novelty of the findings: “This is the first time that this non-uniformity in lithium storage has been directly observed in individual particles. Real time techniques like ours are essential to capture this while the battery is cycling.” The data revealed that lithium storage across particles is far from uniform, contradicting earlier assumptions of even distribution.
The irregularity stems from changes in the rate of lithium-ion diffusion during the charge-discharge cycle. In fully lithiated NMC particles—near the end of discharge—diffusion is slow, leading to lithium-rich surfaces and lithium-poor cores. Conversely, at the start of charging, partial delithiation triggers a rapid increase in diffusion, producing lithium-deficient surfaces and lithium-rich cores. This dynamic creates significant heterogeneity in lithium content within individual particles.
Dr Shrinidhi Pandurangi, also a co-first author from Cambridge, noted the accuracy of their modeling: “Our model predicted lithium distributions accurately and captured the degree of heterogeneity observed in experiments. These predictions are key to understanding other battery degradation mechanisms such as particle fracture.” The mechanical stresses induced by uneven lithium distribution can contribute to structural damage, further reducing battery performance over time.
One striking consequence of this heterogeneity is the loss of capacity in nickel-rich cathodes. Dr Chao Xu of ShanghaiTech University, who participated in the study while at Cambridge, pointed out: “This is significant, considering one industrial standard that is used to determine whether a battery should be retired or not is when it has lost 20 percent of its capacity.” The team’s observations explain why these cathodes can lose around 10 percent of their capacity after just a single charge-discharge cycle—a substantial degradation that occurs well before the typical retirement threshold.
The implications of these findings extend beyond academic interest. By pinpointing the mechanisms behind uneven lithium transport, researchers can explore strategies to mitigate capacity loss and extend battery life. This could involve tailoring particle morphology, optimizing electrolyte composition, or engineering diffusion pathways to promote uniform ion movement. For electric vehicles, such improvements translate directly into longer range, faster charging, and reduced lifecycle costs.
The study’s success hinged on the integration of advanced optical microscopy with robust computational modeling. Operando methods, which track materials under actual operating conditions, are becoming indispensable in battery research. They provide insights that static, post-mortem analyses cannot capture, revealing transient phenomena that critically influence performance.
Supported by SOLARX, MULTILAT, and BATNMR, this work underscores the importance of interdisciplinary collaboration in tackling complex energy storage challenges. By combining expertise in photon management, lattice materials, and nuclear magnetic resonance techniques, the team was able to uncover subtle yet impactful behaviors within NMC cathodes. Such knowledge lays the groundwork for the next generation of high-performance, durable battery materials.
