Cathode active material for lithium secondary batteries comprising a lithium tetramethylsilyl borate coating layer and manufacturing method thereof

Lithium tetramethylsilyl borate-coated cathode material forming an artificial CEI layer via room-temperature slurry mixing

This technology features a cathode active material with a lithium tetramethylsilyl borate (LTB) coating layer containing silyl borate functional groups on the surface of a Ni-rich NCM lithium composite transition metal oxide core. During the cathode slurry mixing process, LTB chemically reacts with the cathode material to create a nano-thick artificial CEI layer.

While Ni-rich NCM cathodes offer high specific capacity, they suffer from rapid capacity degradation, especially at high temperatures, as unstable Ni4+ species decompose the electrolyte and the resulting fluoride ions erode the transition metals. Conventional inorganic coating methods require complex heat treatment processes at hundreds of degrees Celsius, while electrolyte additive methods are limited by their reliance on additive decomposition.

This technology involves the one-step synthesis of LTB using tris(trimethylsilyl) borate and lithium trimethylsiloxide, which is then mixed into the slurry to form a 1–20 nm coating layer that scavenges fluoride ions via an SN2 reaction without the need for high-temperature heat treatment. This achieves a capacity retention rate of over 69.1% after 100 cycles at 55°C. Furthermore, it can be applied directly to existing electrode manufacturing slurry processes, enhancing interfacial stability without requiring additional investment in coating equipment.

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Key Features:

• Cathode active material with a lithium tetramethylsilyl borate coating layer formed on the surface of a LiNiaCobMncO2 lithium composite transition metal oxide core
• Step of preparing lithium tetramethylsilyl borate by mixing tris(trimethylsilyl) borate and lithium trimethylsiloxide prior to cathode slurry preparation
• A 1–20 nm thick coating layer with fluoride scavenging capability that produces fluorotrimethylsilane and LiB(OH)4 through an SN2 reaction with fluoride ions
• Step of mixing 0.5–3.0 wt% of lithium tetramethylsilyl borate into the cathode slurry—composed of cathode active material, conductive agent, binder, and solvent—while reducing the binder content by the amount of the additive

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This invention was developed with support from the Ministry of Education for the development of blue carbon biomass-based source materials and the establishment of a marine resource recycling platform.

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