Pore-Free\nSingle-Crystalline Particles for Durable\nNa-Ion Battery Cathodes

The O3-type Na[Ni<sub>1–<i>x</i>–<i>y</i></sub>Co<sub><i>x</i></sub>Mn<sub><i>y</i></sub>]O<sub>2</sub> cathodes have\nreceived significant attention\nin sodium-ion batteries (SIBs) due to their high energy density. However,\nchallenges such as structural instability and interfacial instability\nagainst an electrolyte solution limit their practical use in SIBs.\nIn this study, the single-crystalline O3-type Na[Ni<sub>0.6</sub>Co<sub>0.2</sub>Mn<sub>0.2</sub>]O<sub>2</sub> (SC-NCM) cathode has been\ndesigned and synthesized to effectively relieve the degradation pathways\nof the polycrystalline O3-type Na[Ni<sub>0.6</sub>Co<sub>0.2</sub>Mn<sub>0.2</sub>]O<sub>2</sub> (PC-NCM) cathode for SIBs. The mechanically\nrobust SC-NCM due to the absence of pores in the particles enhances\ntolerance to particle cracking, resulting in stable cycling performance\nwith a cycle retention of 73% over 350 cycles. Moreover, the proposed\nSC-NCM is synthesized using a simple and cost-effective molten-salt\nsynthetic route without the complex quenching process typically associated\nwith PC-NCM synthesis methods, showing good practical applicability.\nThis study will provide an innovative direction for the development\nof advanced cathode materials for practical SIBs.