Method for manufacturing nickel hexacyanoferrate cathode active material capable of high-speed charging/discharging, cathode active material, and aqueous sodium-ion battery

High-rate aqueous sodium cathode material with reduced crystalline water via sodium citrate chelate dropwise synthesis

This technology synthesizes nickel hexacyanoferrate (NiHCF) by dropwise adding a first solution containing a nickel (Ni) precursor and sodium citrate as a chelating agent into a second solution containing a hexacyanoferrate (Fe(CN)6) precursor. Citrate is used to control water content and iron vacancies within the crystal, while the dropwise method optimizes particle morphology and physical properties.

Conventional NiHCF cathode active materials suffered from structural instability due to crystalline water and iron (Fe) vacancies within the crystal lattice. This led to a simultaneous decline in electrochemical specific capacity and rate capability.

This technology involves dropwise adding a first solution containing NiNO3 and sodium citrate (C6H5Na3O7) into a K4Fe(CN)6 solution, with the citrate concentration optimized at 0.1 M to inhibit the bonding between Ni2+ and H2O. As a result, coordinated water and Fe vacancies within the lattice are reduced, and crystallinity is enhanced, achieving a specific capacity of over 80 mAh/g and a rate capability exceeding 82%. Applicable to aqueous electrolyte-based sodium-ion batteries, renewable energy-linked stationary storage systems, and frequency regulation facilities requiring instantaneous high power, this technology enables rapid charging and discharging in non-flammable aqueous systems without the need for lithium or cobalt.

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Key Features:

• First solution containing 0.02 to 0.04 M NiNO3 and 0.02 to 0.1 M C6H5Na3O7
• Second solution containing Na4Fe(CN)6 or K4Fe(CN)6 at a concentration of 0.02 to 0.04 M
• Dropwise addition step of adding the first solution into the second solution to synthesize nickel hexacyanoferrate
• Cathode active material with a specific capacity exceeding 80 mAh·g-1 and maintaining over 82% capacity at 10 A·g-1 compared to 0.1 A·g-1

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