2022-03-23 アルゴンヌ国立研究所
・この発見の鍵は、CNMの透過型電子顕微鏡とAPSの放射光X線ビーム（ビームライン11-ID-Cと20-BM）を利用して観察できたことです。材料合成時の温度を急激に下げると、正極粒子の表面の平滑性が低下し、歪みを示す領域が大きくなっていることがわかった。また、正極のサイクル中にこの部分のプッシュプル効果が起こり、正極粒子にクラックが発生し、性能が低下していることもわかった。
・電池開発者は合成条件を調整して、カソード合成中、カソード混合物を空気中で非常に高温にゆっくりと加熱し、設定された時間そこに保持してから、温度を急速に室温まで下げ、はるかに優れたナトリウムイオンカソードを製造できるようになります。
＜関連情報＞
- https://www.anl.gov/article/pivotal-battery-discovery-could-impact-transportation-and-the-grid
- https://www.nature.com/articles/s41467-022-28052-x
ナトリウム系層状酸化物カソードにおける固有格子歪による構造地震の発生 Native lattice strain induced structural earthquake in sodium layered oxide cathodes
Gui-Liang Xu,Xiang Liu,Xinwei Zhou,Chen Zhao,Inhui Hwang,Amine Daali,Zhenzhen Yang,Yang Ren,Cheng-Jun Sun,Zonghai Chen,Yuzi Liu &Khalil Amine
Nature Communications volume 13, Article number: 436 (2022) Published: 27 January 2022
Fig. 1: Solid-state synthesis of O3 NaNi0.4Mn0.4Co0.2O2.
Abstract
High-voltage operation is essential for the energy and power densities of battery cathode materials, but its stabilization remains a universal challenge. To date, the degradation origin has been mostly attributed to cycling-initiated structural deformation while the effect of native crystallographic defects induced during the sophisticated synthesis process has been significantly overlooked. Here, using in situ synchrotron X-ray probes and advanced transmission electron microscopy to probe the solid-state synthesis and charge/discharge process of sodium layered oxide cathodes, we reveal that quenching-induced native lattice strain plays an overwhelming role in the catastrophic capacity degradation of sodium layered cathodes, which runs counter to conventional perception—phase transition and cathode interfacial reactions. We observe that the spontaneous relaxation of native lattice strain is responsible for the structural earthquake (e.g., dislocation, stacking faults and fragmentation) of sodium layered cathodes during cycling, which is unexpectedly not regulated by the voltage window but is strongly coupled with charge/discharge temperature and rate. Our findings resolve the controversial understanding on the degradation origin of cathode materials and highlight the importance of eliminating intrinsic crystallographic defects to guarantee superior cycling stability at high voltages.
