Affiliation:
1. Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education) State Key Laboratory of Superhard Materials College of Physics Jilin University Changchun 130012 P. R. China
2. Center for High-Pressure Science and Technology Advanced Research Beijing 100193 P. R. China
3. School of Chemical Engineering and Technology Xi'an Jiaotong University No. 28, West Xianning Road Xi'an 710049 P. R. China
4. School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 P. R. China
Abstract
AbstractMixed‐anion‐group Fe‐based phosphate materials, such as Na4Fe3(PO4)2P2O7, have emerged as promising cathode materials for sodium‐ion batteries (SIBs). However, the synthesis of pure‐phase material has remained a challenge, and the phase evolution during sodium (de)intercalation is debating as well. Herein, a solid‐solution strategy is proposed to partition Na4Fe3(PO4)2P2O7 into 2NaFePO4 ⋅ Na2FeP2O7 from the angle of molecular composition. Via regulating the starting ratio of NaFePO4 and Na2FeP2O7 during the synthesis process, the nonstoichiometric pure‐phase material could be successfully synthesized within a narrow NaFePO4 content between 1.6 and 1.2. Furthermore, the proposed synthesis strategy demonstrates strong applicability that helps to address the impurity issue of Na4Co3(PO4)2P2O7 and nonstoichiometric Na3.4Co2.4(PO4)1.4P2O7 are evidenced to be the pure phase. The model Na3.4Fe2.4(PO4)1.4P2O7 cathode (the content of NaFePO4 equals 1.4) demonstrates exceptional sodium storage performances, including ultrahigh rate capability under 100 C and ultralong cycle life over 14000 cycles. Furthermore, combined measurements of ex situ nuclear magnetic resonance, in situ synchrotron radiation diffraction and X‐ray absorption spectroscopy clearly reveal a two‐phase transition during Na+ extraction/insertion, which provides a new insight into the ionic storage process for such kind of mixed‐anion‐group Fe‐based phosphate materials and pave the way for the development of high‐power sodium‐ion batteries.
Funder
National Natural Science Foundation of China
Subject
General Chemistry,Catalysis