Lithium Isotope Distribution Acts as Fingerprint for Battery Aging, BAM Researchers Find

Battery Research: Distribution of Lithium Isotopes Serves as a Fingerprint for Aging Processes

The service life of lithium-ion batteries is limited by complex aging processes, the causes of which are often difficult to distinguish from one another. Researchers at the Federal Institute for Materials Research and Testing (BAM) have now shown that the distribution of two lithium isotopes within the cells acts like a fingerprint directly linked to the degradation processes. This correlation opens new possibilities for better understanding aging mechanisms and optimizing batteries in a more targeted manner.

Lithium-ion batteries are a key technology for the energy transition. Despite continuous advances in performance and service life, however, one central problem remains unsolved: cells age with every charge and discharge cycle. Their capacity decreases and their performance declines.

Several complex processes inside the battery are responsible for this. To date, the challenge of clearly identifying these aging mechanisms and distinguishing them from one another remains unresolved. While conventional diagnostic methods show that a battery is aging, they often provide only limited information about when, where, and by what mechanism degradation is triggered.

A BAM team led by Carlos Abad and Beatrice Battistella has developed a new approach, which was published in the journal ACS Energy Letters. The researchers use the distribution of two lithium isotopes within a cell as a diagnostic tool for aging processes. Their characteristic traces and patterns provide a fingerprint of the underlying degradation mechanisms.

The method takes advantage of the fact that natural lithium consists of two isotopes: lithium-6 and the slightly heavier lithium-7. These are variants of the same chemical element with different numbers of neutrons in their nuclei. In new batteries, the two lithium isotopes occur in the same proportions as in natural deposits of the alkali metal, namely 2.4% lithium-6 and 97.6% lithium-7.

The researchers investigated lithium-ion batteries with a lithium nickel manganese cobalt oxide (NMC) cathode and a graphite anode. Measurements on these systems showed that, after the first few charging cycles, lithium-6 began to accumulate preferentially at the anode. Following another 280 cycles, this effect intensified, while the cathode exhibited significantly higher levels of lithium-7. At the same time, the cells’ capacity decreased.

This discovery was made possible by a high-resolution form of mass spectrometry that allowed researchers to determine the distribution of lithium isotopes layer by layer across the entire depth of the electrodes. The research was conducted in collaboration with Nu Instruments Ltd. in the United Kingdom and the Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden).

Beatrice Battistella, said:

The distribution of lithium isotopes thus provides direct information about aging processes in lithium-ion batteries.

”The isotopes act as natural markers. Their distribution provides insight into the mechanisms that controls lithium movement during battery operation and where changes occur. The researchers were also able to demonstrate that these traces are closely linked to the batteries’ capacity loss.”

For Beatrice Battistella and Carlos Abad, the significance of the results lies primarily in their potential applications for precise measurements: instead of detecting aging solely based on capacity loss, it could be tracked much earlier in the future using the traces left by lithium isotopes in the battery cell. This enables a more precise understanding of aging mechanisms and is ultimately crucial for improving batteries in a more targeted manner and predicting their service life more accurately.

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