Conventional solid-state synthesis achieves advanced P'2-type Mn-rich cathodes for sodium-ion batteries with 35 mA·h·g−1 capacity increase and 28.7% stability improvement

P'2-type manganese-rich layered oxides are promising cathodes for sodium-ion batteries. However, their synthesis requires unconventional rapid quenching to prevent O₂ absorption and P'2-P2 phase transformation during cooling, which compromises scalability and safety. Moreover, Jahn-Teller active ion enrichment and irreversible phase transitions during cycling impair structural stability. These synthesis challenges and inadequate electrochemical performance hinder practical applications. Herein, we report for the first time a simple solid-state synthesis of P'2-Na 0.55 Mg 0.05 Mn 0.90 O 2 (Na□MM□) cathode with a 3.78% lattice distortion through a dual-vacancy strategy. The Na□MM□ cathode delivers an ultrahigh energy density of 786 Wh·kg −1 . Na vacancies stabilize P'2 structure and enable a reversible P'2-OP4 transition, delivering 35 mA·h·g⁻¹ extra capacity. TM vacancies further synergize with Na vacancies to stabilize the TM-O framework, suppressing lattice oxygen loss and Mn³⁺ enrichment, which improves 100 cycles capacity retention by 28.7%. This work advances the synthesis and electrochemistry of P'2-type materials, offering a practical path toward application. Download: Download high-res image (286KB) Download: Download full-size image