Interfacial Chemistry Enables Highly Reversible Na Extraction/Intercalation in Layered‐Oxide Cathode Materials†

Abstract

Comprehensive SummaryLayered transition‐metal oxides are promising cathode candidates for sodium‐ion batteries. However, the inferior interphase formation and particulate fracture during sodiation/desodiation result in structure degradation and poor stability. Herein, the interface chemistry of P2‐Na0.640Ni0.343Mn0.657O2 in an electrolyte of 1.0 mol/L NaPF6 in diglyme is unveiled to enable highly reversible Na extraction and intercalation. The uniform and robust cathode‐electrolyte interphase layer is in situ formed with decomposition of diglyme molecules and anions in initial cycles. The NaF‐ and CO‐rich CEI film exhibits high mechanical strength and ionic conductivity, which suppresses the reconstruction of its electrode interphase from P2 phase to spinel‐like structure and reinforces its structure integrity without cracks. This favours facile Na+ transport and stable bulk redox reactions. It is demonstrated to show long cycling stability with capacity retention of 94.4% for 180 cycles and superior rate capability. This investigation highlights the cathode interphase chemistry in sodium‐ion batteries.