August 15, 2024 — A research team led by Dr. Yong-Sheng Hu, a leading scientist at HiNa Battery, has published their latest groundbreaking findings in the prestigious journal Science. The paper, titled "Decoupling the Air Sensitivity of Na-Layered Oxides," provides a crucial solution to a major hurdle in the commercialization of sodium-ion batteries, once again highlighting China's leading position in this advanced technology field.

Layered oxides are key cathode materials for both lithium-ion and sodium-ion batteries. However, unlike their lithium counterparts, sodium layered oxides (NaₓTMO₂, where TM represents transition metals) are highly sensitive to air. They can degrade within hours in humid air, leading to sodium loss and irreversible capacity loss in batteries. This problem has perplexed researchers for over four decades, posing a significant obstacle to commercialization.

A deep understanding of the root cause and the establishment of practical design principles to solve it are critical steps toward making sodium-ion batteries viable. A collaborative team, including Dr. Yong-Sheng Hu (Researcher at the Institute of Physics, Chinese Academy of Sciences; Chairman and Chief Scientist of HiNa Battery), Associate Researcher Yaxiang Lu (IoP CAS), Specially Appointed Researcher Xiaohui Rong (Yangtze River Delta Physics Research Center), and Professor Jianyu Huang (Yanshan University), conducted a detailed study on the interaction mechanisms between various gases and sodium layered oxide cathode materials, clarifying the degradation pathways.

The team innovatively developed a standardized testing method to quantitatively compare the air stability of different materials. They identified the intrinsic factors affecting air stability and proposed rational design principles for material modification. Using the widely studied NaNi₁/₃Fe₁/₃Mn₁/₃O₂ (NFM111) as a model material and extending to its homologues, combined with various advanced in-situ and ex-situ characterization techniques, the study found that water vapor, carbon dioxide, or oxygen alone does not cause significant degradation.

Water vapor plays a pivotal bridging role. When coexisting with CO₂ or O₂, it triggers acidic degradation and oxidative degradation processes, respectively. Acidic degradation induces intense Na⁺/H⁺ exchange, forming sodium carbonate/bicarbonate on the material surface, and leads to subsequent reactions like crack propagation, lattice distortion, dislocation generation, and surface transition metal ion reduction/reconstruction under strong acidic conditions. In oxidative degradation, transition metal ions with lower redox potentials in the bulk are preferentially oxidized, releasing Na⁺ to form NaOH. The oxidized transition metal ions (e.g., Ni³⁺) are often unstable on the surface,容易被还原 leading to surface reconstruction.

Based on these findings, the work points out that decoupling the synergistic effects of gases is the key external factor for achieving stable material storage. To quantify the extent of air degradation, the team developed a standardized air stability test based on titration-gas chromatography to quantitatively evaluate the contribution of different reaction pathways and compare the air stability of various materials. Through quantitative analysis of sodium loss in over 30 materials after degradation, the study defined a new parameter—the cation competition coefficient (η)—which incorporates the weighted average ionic potential of transition metals, initial sodium content, and the ionic potential of sodium, reflecting the difficulty of sodium extraction.

The research found that acidic degradation is the dominant factor in the overall deterioration process. Reducing the cation competition coefficient and increasing particle size can effectively enhance a material's resistance to acidic degradation. Selecting high-potential redox couples can significantly improve resistance to oxidative degradation. Based on this deep understanding, the team's designed modified materials reduced sodium loss from 0.489 in the model material to 0.019—a 96% reduction.

This work elucidates the degradation evolution at the material interface and in the bulk, clarifies the intrinsic factors affecting air stability, and proposes corresponding improvement strategies. It provides technical methods and guiding principles for designing more stable and durable layered oxide cathode materials.

Following their pioneering 2020 Science paper, which garnered high international acclaim for opening new avenues in sodium-ion battery research, Dr. Hu Yong-Sheng's team has honed their work over four years to deliver this latest significant achievement. This not only solidifies China's leading role at the global forefront of sodium-ion battery technology but also lays a solid theoretical and practical foundation for the global commercialization of sodium-ion batteries.

Looking ahead, HiNa Battery will continue to deepen its research and development in sodium-ion battery technology, accelerate its commercialization pace, inject strong momentum into China's new energy industry, and jointly chart a new chapter of green, sustainable development.

Reference:
Yang Yang†, Zaifa Wang†, Congcong Du, Bowen Wang, Xinyan Li, Siyuan Wu, Xiaowei Li, Xiao Zhang, Xubin Wang, Yaoshen Niu, Feixiang Ding, Xiaohui Rong, Yaxiang Lu, Nian Zhang, Juping Xu, Ruijuan Xiao, Qinghua Zhang, Xuefeng Wang, Wen Yin, Junmei Zhao, Liquan Chen, Jianyu Huang, Yong-Sheng Hu, Decoupling the air sensitivity of Na-layered oxides, Science, 2024, 385: 744-752
Link: https://www.science.org/doi/10.1126/science.adm9223