Cathode active material, method for manufacturing the same, and lithium secondary battery comprising the same

High-nickel cathode material with a fluorine concentration gradient, featuring reduced residual lithium through dry fluorine coating and heat treatment

This technology involves dry-mixing high-nickel cathode active material precursor particles (with a nickel content of 60 mol% or higher) with a fluorine source, such as NH4F or NH4HF2, followed by heat treatment at 300°C or above. This process forms a LiF film or particles on the surface and induces a concentration gradient where the fluorine content gradually decreases toward the interior.

Lithium by-products, such as LiOH and Li2CO3, remaining on the surface of high-nickel cathode active materials have historically reacted with electrolytes, degrading battery performance. These issues, including thermal instability and metal leaching into the electrolyte, become particularly severe as the nickel content increases.

This technology utilizes a dry coating process with a fluorine source, followed by heat treatment at a specific temperature range of 300°C or higher—where the particle's crystal structure remains stable—to allow residual lithium to react with fluorine and form LiF compounds. This process reduces surface residual lithium and introduces fluorine into the particle interior, effectively suppressing HF generation and metal leaching. It is applicable to long-range electric vehicle batteries using high-nickel NCM chemistries and energy storage cells exposed to high-temperature environments, offering the process advantage of managing surface residual lithium through a solvent-free dry process.

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Key Features:

• A step of preparing cathode active material precursor particles by mixing and calcining a transition metal-containing cathode active material precursor with a lithium salt
• A step of forming a fluorine-containing coating material by dry-mixing the precursor particles with a fluorine source containing NH4F or NH4HF2
• A step of heat-treating the coated precursor particles at a temperature of 300°C or higher, while remaining below the crystal structure transition temperature
• Fluorine-containing cathode active material particles where fluorine exists as a LiF film or particles on the surface and is distributed such that its content gradually decreases toward the interior

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