Improving the stability of P2-type NaMn2/3Ni1/3O2 via phasic intergrowth induced by Li-ion substitution

Abstract

Layered transition metal oxides are attractive cathode materials for sodium-ion batteries but are largely hindered by the low capacity and poor cycling stability. Herein, Na is substituted by Li to enhance the capacity and stability of Na1-xLixMn2/3Ni1/3O2. It is found that Li substitution can provide robust structure benefiting from contracted adjacent transition metal layers owing to strong bonding property of O–Li–O and incremental inactive Mn4+. So it follows that noxious Mn3+ Jahn-Teller distortion and slabs slipping are mitigated. Also, the presence of “Li pillar” disturbs the Na+/vacancies and transition metal ordering during Na extraction, preventing phase transformation during deep desodiation process. Consequently, the Na1-xLixMn2/3Ni1/3O2 demonstrates high capacity, remarkable rate capability, and long-term cycling life. Among them, Na0.8Li0.2Mn2/3Ni1/3O2 cathode delivers a discharge capacity of 115.3 mA h/g, with a capacity retention of 86.0% after 100 cycles. This simple strategy to stabilize the layered structure oxides is inspiring to design high-performance cathode materials for sodium-ion batteries.