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

Layered transition metal oxides are attractive cathode materials for sodium-ion batteries (SIBs) 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 Na 1- x Li x Mn 2/3 Ni 1/3 O 2 . It is found that Li doping can provide robust structure benefiting from contracted adjacent transition metal (TM) layers owing to strong bonding property of O-Li-O and incremental inactive Mn 4+ . So it follows that noxious Mn 3+ Jahn-Teller distortion and slabs slipping are mitigated. Also, the presence of “Li pillar” disturbs the Na + /vacancies and TM ordering during Na extraction, preventing phase transformation during deep desodiation process. Consequently, the Na 1- x Li x Mn 2/3 Ni 1/3 O 2 demonstrates high capacity, remarkable rate capability, and long-term cycling life. Among them, Na 0.8 Li 0.2 Mn 2/3 Ni 1/3 O 2 cathode delivers a discharge capacity of 115.3 mA h g -1 , 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. • Intergrowth structure can be carefully designed by Li substitution, where Li occupies both TM and Na sites. Exotic Li disturbs the Na + /vacancy and TM ordering, resulting in the inhibition of phase transformation upon Na + extraction. • Li-doped samples with narrower interlayer space still show fast ion motion, which is ascribed to decreased diffusion barrier rooting from disordered vacancy rearrangement. • In comparison to Li-free sample, Li-substituted materials possess better water resistance and air stability after aging treatment.