Cathode active material for sodium secondary batteries with a tunnel structure and sodium secondary batteries containing the same

Long-life sodium-manganese oxide cathode material with a mixed spinel phase via lithium substitution

This technology features a heterostructured cathode active material that builds upon a tunnel structure while incorporating a spinel structure within the crystal lattice by substituting lithium into sodium or manganese sites. This suppresses the Jahn-Teller effect of manganese and stabilizes the electronic structure.

Conventional sodium-manganese oxide (NMO) faces structural collapse due to crystal structure transitions and Jahn-Teller distortion caused by changes in the oxidation state of transition metals during charge and discharge. Additionally, it has been limited by low discharge capacity and poor cycle life due to inactive sodium content.

This technology controls the amount of lithium substitution in sodium-manganese oxide to form a spinel structure within the crystal, which oxidizes Mn3+ to Mn4+ to stabilize the electronic structure. Furthermore, the secondary particle structure, composed of nanorod-shaped primary particles, secures a specific surface area of 1.3㎡/g or more, improving ion diffusion paths. Applicable to low-cost sodium batteries for energy storage systems (ESS) and power grid auxiliary batteries, it enables cathode designs that reduce reliance on rare metals while withstanding over 1,000 long-term cycles.

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Key Features:

• A cathode active material for a tunnel-structured sodium-transition metal oxide in which at least one of the sodium or transition metals is substituted with lithium
• A cathode active material containing a spinel structure, where Mn3+ accounts for less than 50% of the total Mn3+ and Mn4+ concentration
• Secondary particles where primary particles contain both tunnel and spinel structures, with the spinel structure increasing as lithium substitution increases
• Secondary particles composed of nanorod-shaped primary particles with longer C-axis lengths, resulting in a specific surface area of 1.3㎡/g or more

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This invention was developed with support from the Ministry of Science and ICT for the development of core and commercialization technologies for interface-optimized, rod-shaped secondary battery materials.

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