High-Na-Content Birnessite via P′3-Stacking with Tunable Active Facets for Advanced Aqueous Sodium-Ion Batteries

Layered Na-birnessites are promising cathode materials for aqueous sodium-ion batteries due to their high theoretical capacity, low cost, and environmental benignity. However, the general O′3 Na-birnessites possess low Na content and dominant inactive 001 exposed facets, which compromise their Na storage capability and cycling stability. Herein, we develop a high-Na-content P′3-Na 0. 71 MnO 2 ·0. 15H 2 O with highly enriched 010 active facets by a hydrothermal conversion method. In comparison with the O′3 Na-birnessite, the P′3 Na-birnessite with a high ratio of 010/001 exposed facets provides greatly increased open channels for Na + diffusion, while the P′3 stacking affords a lower Na + diffusion barrier, resulting in improved electrode kinetics with a large specific capacity of 176 mAh g –1 at 0. 2 A g –1. More importantly, the P′3 Na-birnessite manifests solo Na + intercalation/deintercalation with extraordinary cycling stability in an aqueous electrolyte, achieving 90. 5% capacity retention after 60, 000 cycles. When coupled with the NaTi 2 (PO 4) 3 anode, the P′3 Na-birnessite-based full cell delivers both high energy density and long cycle life, demonstrating the potential application in aqueous sodium-ion batteries. This study demonstrates an efficient method to prepare high-Na-content P′3 birnessite with tunable exposed facets and provides important insights into developing highly stable layered cathodes for sustainable aqueous sodium-ion batteries.