Calcium-doped cathode active material for sodium secondary batteries and sodium secondary battery comprising the same

O3-type sodium battery cathode material with enhanced high-voltage structural stability via calcium doping in the sodium layer

This technology improves cycle performance and suppresses crystal structure instability during high-voltage charging and discharging by doping calcium (Ca) into the sodium layer of layered oxide cathode active materials for sodium secondary batteries.

Layered complex metal oxide cathode active materials for sodium secondary batteries have historically faced issues with capacity retention and lifespan degradation, as the repeated extraction and insertion of sodium ions during high-voltage cycling causes the crystal structure to deform or become unstable.

This technology utilizes a cathode active material with the composition Na1-2xCax[(NiyCozMn1-y-z)]O2 (0.007≤x≤0.02) and stabilizes the crystal structure by doping calcium into the sodium layer, ensuring structural integrity even under high-voltage operating conditions exceeding 4.0V. Applicable to sodium-ion batteries for renewable energy-linked ESS, electric two-wheelers, and low-speed electric vehicles, it is expected to increase energy per cell by raising the operating voltage limit to 4.3V.

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Key Features:

• Cathode active material for sodium secondary batteries represented by the composition Na1-2xCax[(NiyCozMn1-y-z)]O2, where x is between 0.007 and 0.02
• Cathode active material with an O3 structure that maintains its structure at voltages exceeding 4.0V due to Ca doping within the sodium layer
• Step of co-precipitating a metal complex hydroxide by supplying an ammonium ion source and caustic alkali to a mixed aqueous solution of nickel, cobalt, and manganese salts
• Step of manufacturing the cathode active material by mixing the metal complex hydroxide with sodium and calcium salts and performing heat treatment

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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.

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