Halogen-substituted cathode active material for sodium secondary batteries and sodium secondary batteries containing the same

Sodium-ion battery cathode material with a reinforced structure through halogen substitution at oxygen sites and sodium content adjustment

This technology is a cathode active material that enhances structural stability by substituting a portion of the oxygen (O) sites in a layered sodium transition metal oxide (Na-TM-O) lattice with halogen elements (F, Cl, Br, I) and adjusting the sodium (Na) content accordingly.

Due to the large ionic radius of sodium ions, significant lattice volume changes occur during charge and discharge cycles. This leads to irreversible phase transitions and instability in transition metal-oxygen bonds, which limits cycle life and high-rate performance.

This technology primarily uses fluorine to partially substitute oxygen sites to reinforce the crystal structure, while reducing sodium content to maintain a high Mn4+ ratio. The process involves a primary heat treatment of transition metal complex hydroxides and fluorine compounds at 300–500°C, followed by a secondary heat treatment with sodium salts at 700–900°C. Applicable to sodium-ion battery cathodes for residential/industrial energy storage and low-cost electric mobility, it suppresses irreversible phase transitions in O3-type layered structures and mitigates capacity loss during high-rate charging and discharging.

‍

‍

Key Features:

• Halogen element selected from fluorine, chlorine, bromine, or iodine, substituted into a portion of the oxygen sites within a layered sodium transition metal oxide
• O3-structured cathode active material with a composition of Nax-a[TM1-bMnb]O2-aXa, where sodium is reduced by an amount equivalent to the halogen substitution
• Step of mixing a transition metal complex hydroxide with a fluorine compound and performing primary heat treatment to produce a fluorine-substituted transition metal oxide
• Step of mixing the fluorine-substituted transition metal oxide with a sodium salt and performing secondary heat treatment to produce a fluorine-substituted sodium transition metal oxide

‍

This invention was developed with support from the Ministry of Trade, Industry and Energy's GET-Future Laboratory program for next-generation lithium-ion batteries.

‍