Unveiling Li-/Sr-induced reinforced transition metal-oxygen in P2-type layered oxide cathode for highly stable sodium-ion batteries

Abstract

P2-Na₀.₆₇Ni₀.₃₃Mn₀.₆₇O₂ has emerged as a promising cathode material for sodiumion batteries due to its high theoretical specific capacity and excellent air stability. However, this material suffers from two critical bottlenecks: first, it is prone to undergo an irreversible oxygen evolution reaction at a voltage of 4.2 V; second, it experiences significant specific capacity fade under high current density conditions. This work addresses these issues by using a solid-state reaction method to fabricate the Na 0.66 Sr 0.01 Ni 0.32 Li 0.01 Mn 0.67 O 2 material via codoping modification with trace amounts of Li and Sr. The research results demonstrate that the Li and Sr co-doped material exhibits significantly enhanced spatial structural stability at high voltages and effectively suppresses the P2-O2 phase transition. The modified material shows superior rate capability (delivering a reversible specific capacity of 62 mA h g⁻¹ at 20 C) and cycling stability (achieving a capacity retention of 87% after 1000 cycles at 10 C). In summary, this Li/Sr synergistic doping strategy provides an effective and straightforward approach for designing layered oxide cathode materials that combine high rate capability with long cycling stability.