Trace Al/Ti co-doping in P2-type layered oxide cathodes toward ultra-stable and fast sodium-ion storage

Layered oxide cathodes for sodium-ion batteries (SIBs) often suffer from structural degradation and increased interfacial resistance during prolonged cycling. In this research, an Al/Ti dual-doping synergistic strategy is employed on P2-type Na_0.8Al_0.02Ti_0.02(Ni_0.4Mn_0.6)_0.96O₂ (NNATM) to simultaneously regulate both the bulk lattice structure and interfacial chemical behavior. Al/Ti co-doping enlarges the c-axis spacing, facilitating Na⁺ migration, while the strengthened Al/Ti-O and TM-O bonding interactions stabilize the layered framework and improve interfacial stability during cycling. Electrochemical impedance spectroscopy characterizations confirm a 40% reduction in charge-transport resistance, verifying the promoted interfacial charge conduction capability of the electrode. The NNATM cathode exhibits outstanding electrochemical performance: it delivers a reversible specific capacity of 111 mAh g^-1 at 0.1C, and a reversible capacity retention of 90.55% is achieved after 500 cycles at 100 mA g^-1. The investigation provides a reliable method to enhance the long-term stability and reversibility of SIBs cathode.