Predict Long-Term Stability in Ni-Rich Lithium-Ion Batteries Using Formaldehyde Generation

Nickel-rich layered oxide cathodes (e.g., NCA90) are considered some of the most advanced materials for high-energy lithium-ion batteries. Yet, under high-stress conditions, they remain unstable, posing a significant barrier to long-term use in electric vehicles and energy storage.

Because the chemistry of these materials is susceptible to severe electrolyte decomposition, capacity fade accelerates and poses a number of safety hazards.

Figure 1. HPR-40 DEMS, Hiden Analytical. Image Credit: Hiden Analytical

This study determines whether formaldehyde (CH2O) produced during the initial cycle can serve as a reliable diagnostic of long-term battery stability. Herein, it is demonstrated how the baseline CH₂O that first forms under any stress strongly correlates with future capacity retention, voltage hysteresis, and energy efficiency over extended cycling.

Taking 18650-format NCA90/graphite cells manufactured under pilot-line conditions, a systematic evaluation of overcharge, over-discharge, and rapid-charging scenarios was conducted. Ny also applied Hiden’s HPR-40 DEMS system; gas evolution was monitored in real time and aided with 1H NMR spectroscopy of the electrolyte. The findings revealed:

• Overcharge results in exponential increases in CH₂O with voltage escalation (4.5–4.9 V), signifying severe oxidative decomposition.
• While over-discharge gradually generates CH₂O, it is still linked to long-term degradation.
• Rapid charging (2C), even without lithium plating, results in detectable CH2O in the electrolyte, indicating interfacial instability.

Computational free-energy analyses demonstrated that CH₂O was spontaneously yielded via CO₂ reduction at lithiated graphite (LiC₆) surfaces.

Experimentally, it was confirmed that lithiated graphite catalyzes CO₂ conversion to CH₂O, exhibiting how pivotal electrode cross-talk can be.

Most crucially, cells exhibiting lower initial CH₂O generation delivered superior cycle life consistently. CH₂O formation was minimized using optimized electrode designs, in contrast to thin or thick counterparts, which in turn demonstrated the best long-term stability across 1000 cycles.

Figure 2. Postdoctoral researcher, Dr. Nattanon Joraleechanchai. Image Credit: Hiden Analytical

Key Contributions of This Work:

1. Early diagnostic marker – Initial CH₂O levels help predict performance and safety in the long-term, limiting dependence on time- and cost-intensive cycling tests.
2. Mechanistic insight – CH₂O derives from CO₂ reduction at lithiated graphite, associating gas-phase and liquid-phase degradation pathways.
3. Practical screening tool – A combination of Hiden DEMS and NMR puts in place a workflow relevant for electrolyte development, formation optimization, and quality control.
4. Industrial relevance – CH₂O detection, already possible with affordable sensors, can be incorporated into EV or ESS systems as a state-of-health monitoring tool.

This study offers a fundamental and practical framework for degradation reduction in Ni-rich cathodes through the development of electrolytes and interfaces that control CH₂O formation. It also underscores how state-of-the-art analytical tools, such as those from Hiden, facilitate rapid and predictive evaluation of cell chemistry under real-world stress conditions.

References

1. Sangsanit, T., et al. (2024). Initial formaldehyde generation as a predictive marker for long-term stability of Ni-rich Li-ion batteries under abusive conditions. Journal of Power Sources, 611, p.234770. DOI: 10.1016/j.jpowsour.2024.234770. https://www.sciencedirect.com/science/article/abs/pii/S0378775324007225?via%3Dihub.

Hiden Product: HPR-40 DEMS.

This information has been sourced, reviewed and adapted from materials provided by Hiden Analytical.

For more information on this source, please visit Hiden Analytical.