Nanoscale Surface Modification of P2-Type Na0.65[Mn0.70Ni0.16Co0.14]O2 Cathode Material for High-Performance Sodium-Ion Batteries

Abstract P2-type Na0.65[Mn0.70Ni0.16Co0.14]O2 (NMNCO) is a promising cathode material for sodium-ion batteries (SIBs). However, NMNCO faces challenges of inferior rate capability and cycling stability owing to its poor structural stability induced by the P2-O2 phase transition during high voltage charging. In order to improve the performance of NMNCO, surface modification has been identified as one of the most effective approaches. Among various surface modifiers, NASICON-type NaTi2(PO4)3 (NTP) attracts tremendous attention due to its three-dimensional structure with open framework of large interstitial spaces. Nevertheless, the fundamental understanding of the effect of NTP surface modification on the electrochemical performance is still lacking and needs to be further investigated. Here, NMNCO is successfully modified with NTP (NMNCO@NTP) via a wet chemical method. Particularly, the effect of NTP surface modification on the electrochemical performance is unraveled by a combination of in-situ X-ray diffraction (XRD) technique, ex-situ transmission electron microscopy (TEM) analysis and first-principles calculations. When evaluated as a cathode material for SIBs, the NMNCO@NTP composite can deliver a high reversible capacity of 105.1 mA h g-1 with a capacity retention of 84.3% after 500 cycles at 5 C, suggesting significantly improved rate capability and cycling stability. The results revealed that the NTP surface coating and doping can effectively suppress the structural change of NMNCO during sodiation/desodiation process, leading to a highly structural reversibility. In addition, NTP coating layer with exceptional ion conductivity can effectively restrain gradual encroachment, and guarantee stable phase interfaces.