Sodium superionic conductor NaTi2(PO4)3 surface layer modified P2-type Na2/3Ni1/3Mn2/3O2 as high-performance cathode for sodium-ion batteries

Abstract

The surface modification of P2-type Na2/3Ni1/3Mn2/3O2 (NNMO) with the thin film of solid-state electrolyte of NaTi2(PO4)3 (NTP) using a facile solution-based method is investigated. The coated Na2/3Ni1/3Mn2/3O2 cathode (NNMO/NTP) exhibits enhanced structural and electrochemical stability. This kind of coating layer is uniformly dispersed on the surface of Na2/3Ni1/3Mn2/3O2. The NASICON-type NTP coating layer with excellent ion conductivity effectively prevents the direct contacting of cathode and electrolyte, guarantees stable phase interfaces, and accelerates Na+ diffusion at the interface. NTP coating induces the partial doping of Ti4+ into the crystal structure which enlarges the interlayer spacing and improves the Na+ diffusion and rate capability. In addition, the NTP coating layer suppresses particle exfoliation and the dissolution of Mn2+ over-prolonged cycling. Thus, the NTP-coated NNMO exhibits excellent cycling stability and outstanding rate capability (111.5 mAh g−1 of the initial capacity at a high rate of 5 C compared with only 52.4 mAh g−1 for the bare electrode). More meaningfully, this coating strategy could have a remarkable influence upon further constructing other cathode materials for Na-ion batteries.