Electrolyte for lithium-ion batteries to improve graphite anode surface stability and lithium-ion batteries containing the same

Lithium-ion electrolyte with silyl phosphate compound to reinforce graphite anode SEI

This technology involves an electrolyte for lithium-ion secondary batteries using graphite anodes, composed of 3 wt% of a silyl phosphate compound with a specific chemical formula, an organic solvent mixture of EMC and EC in a 2:1 ratio, and a lithium salt, which forms an SEI layer containing Si and P components on the anode surface.

The performance of lithium-ion secondary batteries depends heavily on the stability of the SEI layer formed on the anode surface, but not all electrolytes create a stable film. In particular, when used with high-nickel cathodes, impurities have historically caused issues with capacity, cycle life, and high-temperature stability.

This technology uses an electrolyte additive that creates a robust SEI layer containing fluorine, phosphorus, and silicon bonds on the graphite anode surface, preventing further electrolyte decomposition and maintaining 95–99% of specific capacity even after 50 cycles. It can be applied to electrolyte formulations for small cells based on graphite anodes, such as those in smartphones and laptops, allowing for extended battery life simply by replacing the additive without modifying existing production lines.

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Key Features:

• A lithium-ion secondary battery comprising a cathode, a graphite anode, an electrolyte for lithium-ion secondary batteries, and a separator, featuring an electrolyte-derived SEI layer on the anode surface
• An electrolyte containing 3 wt% of a compound represented by Chemical Formula 1 based on the total weight of the electrolyte, along with an organic solvent and a lithium salt
• An electrolyte composition using a mixture of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a 2:1 volume ratio as the organic solvent, with a dissolved lithium salt
• Characteristics where the SEI layer formed on the anode surface exhibits F1s, P2p, and Si2p peaks in XPS analysis and shows a silyl phosphate structure in 31P-NMR

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This invention was developed with support from the Ministry of Science, ICT and Future Planning for the development of residual lithium reduction technology for high-capacity lithium secondary battery cathode materials.

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