Accelerated Degradation in a Quasi-Single-Crystalline Layered Oxide Cathode for Lithium-Ion Batteries Caused by Residual Grain Boundaries

The rapidly growing demand of electrical vehicles (EVs) requires highenergy-density lithium-ion batteries (LIBs) with excellent cycling stability and safety performance. However, conventional polycrystalline high-Ni cathodes severely suffer from intrinsic chemomechanical degradation and fast capacity fade. The emerging single-crystallization strategy offers a promising pathway to improve the cathode's chemomechanical stability; however, the single-crystallinity of the cathode is not always guaranteed, and residual grain boundaries (GBs) could persist in nonideal synthesis conditions, leading to the formation of quasi-single-crystalline (QSC) cathodes. So far, there has been a lack of understanding of the influence of these residual GBs on the electrochemical performance and structural stability. Herein, we investigate the degradation pathway of a QSC high-Ni cathode through transmission electron microscopy and X-ray techniques. The residual GBs caused by insufficient calcination time dramatically exacerbate the cathode's chemomechanical instability and cycling performance. Our work offers important guidance for next-generation cathodes for long-life LIBs

Automated summary

The growing demand for electrical vehicles requires high-energy-density lithium-ion batteries with excellent cycling stability and safety performance. However, conventional polycrystalline high-Ni cathodes suffer from degradation and capacity fade. The single-crystallization strategy improves cathode stability, but residual grain boundaries can persist, forming quasi-single-crystalline cathodes. The influence of these grain boundaries on electrochemical performance and structural stability is not well understood. Here, we investigate the degradation pathway of a quasi-single-crystalline high-Ni cathode and find that residual grain boundaries worsen its instability and cycling performance. This work provides important guidance for next-generation long-life lithium-ion battery cathodes.