Tailoring Local Superstructure Units to Mitigate Voltage Decay in Na-Ion Batteries

The practical application of high-energy-density P2-type cathodes is hindered by severe voltage decay upon high-potential cycling. This voltage decay primarily originates from irreversible interlayer cation migration and detrimental structural degradation, which can be notably suppressed by regulating the arrangement of superstructure units. Herein, we incorporate LiTiMn₅ superstructure units in P2-Na_0.7K_0.04Li_0.1Ni_0.22Mn_0.6Ti_0.08O₂ (NaKLNMT) to construct the long-range in-plane ordered arrangement within transition metal slabs, creating a stable oxygen coordination environment and high energy barriers along the migration path. Furthermore, the circumscribed P-type to O-type stacking evolution and restricted Li/TM migration restrain the formation of vacancy clusters, prohibiting consequential overoxidation of lattice oxygen and inhomogeneous lattice strain accumulation under high-voltage. Therefore, the target NaKLNMT compound exhibits a negligible voltage decay of 0.15 mV/cycle and 96.3% capacity retention over 100 cycles at 1 C. Our findings demonstrate that regulating cation migration through local superstructure control helps steer strategies to address the issues of voltage decay in sodium-layered oxide cathodes.