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Updated: Jul 4, 2026

Sulfate Separation by Selective Crystallization with a Bis-iminoguanidinium Ligand
Published on: September 8, 2016
Sodium Humate Chelating Ferrous Ions in the Aqueous Synthesis of High-Purity Sulfate Cathode Materials for
Yi Xiao1, Jingjing Han1, Naik Muhammad1
1College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, China.
Abstract:
Na2Fe2(SO4)3 (NFS) is a promising, low-cost, high-voltage cathode material with elemental abundance for sustainable sodium ion batteries. However, the high-performance application of NFS is haunted by the low conductivity and the FeSO4 impurity. Herein, sodium humate (SH), which acts as a Fe2+ chelating agent, is applied in a facile aqueous synthesis strategy to obtain high-purity NFS. Control samples prepared with nonchelating sodium carboxylic acid salts, such as monosodium glutamate, sodium acetate, or sodium gluconate, are accompanied by significant FeSO4·H2O impurities. SH also avoids the FeSO4·H2O impurity in the synthesis of Na2.5Fe2(SO4)2.5(PO4)0.5 (NFSP). The chelation between SH and Fe2+ has been demonstrated through visual experiments, as well as by X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy characterizations. Furthermore, the integration of NFS or NFSP with graphene enhances the capacity and rate capability. For instance, the initial discharge capacity of NFS/4%G doubles that of NFS (84.77 vs. 40.11 mAh g-1) at 0.1 C. This study paves the way for the development of pure-phase polyanion cathode materials through chelation chemistry.
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