Pore-Free Single-Crystalline Particles for Durable Na-Ion Battery Cathodes.

The O3-type Na[Ni 1- x - y Co x Mn y ]O 2 cathodes have received significant attention in sodium-ion batteries (SIBs) due to their high energy density. However, challenges such as structural instability and interfacial instability against an electrolyte solution limit their practical use in SIBs. In this study, the single-crystalline O3-type Na[Ni 0.6 Co 0.2 Mn 0.2 ]O 2 (SC-NCM) cathode has been designed and synthesized to effectively relieve the degradation pathways of the polycrystalline O3-type Na[Ni 0.6 Co 0.2 Mn 0.2 ]O 2 (PC-NCM) cathode for SIBs. The mechanically robust SC-NCM due to the absence of pores in the particles enhances tolerance to particle cracking, resulting in stable cycling performance with a cycle retention of 73% over 350 cycles. Moreover, the proposed SC-NCM is synthesized using a simple and cost-effective molten-salt synthetic route without the complex quenching process typically associated with PC-NCM synthesis methods, showing good practical applicability. This study will provide an innovative direction for the development of advanced cathode materials for practical SIBs.