Due to their instability under atmospheric conditions, moisture control during the storage and processing of Ni-rich cathode active materials for lithium-ion batteries poses a major challenge in battery development and manufacturing. In a recent study published in the journal Chemistry of Materials, Leonhard Reinschlüssel and Rebecca Wilhelm from the Chair of Technical Electrochemistry at TUM have now shown that the CO₂ content during humid storage is decisive for the surface chemistry and cycle life of Ni-rich cathode materials, while moisture alone has only a minor (self-limiting) influence. The results illustrate that, in addition to the dew point, the CO₂ concentration—particularly during storage, electrode fabrication, or cell assembly—is a decisive factor for the long-term stability of Ni-rich cathode materials.

💡Highlights of the study:

• Storage under controlled conditions: Humid synthetic air (50% relative humidity) with and without CO₂ (0, 500, and 1500 ppm, respectively) as a function of storage duration.
• Moisture alone is self-limiting: Without CO₂, the Li⁺/H⁺ exchange quickly comes to a halt—only small amounts of surface contaminants and HMO₂ are formed.
• CO₂ as a driver of degradation: In the presence of CO₂, HMO₂, Li₂CO₃, and NiCO₃ grow continuously, accompanied by a progressive reduction of Ni³⁺ to Ni²⁺.
• Clear effect on cycle life: Humid but CO₂-free storage has little effect on LiNiO₂|graphite full cells—in contrast, CO₂-containing conditions lead to a noticeable loss of capacity and poorer performance.
• Practical relevance for cell production: Not only the dew point, but above all the CO₂ concentration in the ambient air is critical for the stability of Ni-rich cathode materials during storage, electrode fabrication, and cell assembly.

The full article is available Open Access.