Silicon Negative Electrode Coating for Battery Cycle Life

The patent employs a multi-layer nested coating structure where an inner carbon coating layer is applied first to the silicon particle surface, followed by an outer coating layer containing boron-fluorine or phosphorous-fluorine bonds. This nested structure provides progressive protection: the inner carbon layer prevents direct electrolyte contact and accommodates volume expansion, while the outer layer reinforces surface strength and prevents particle breakage during charging-discharging cycles.

The patent creates a composite coating system combining carbon material with compounds containing boron-fluorine or phosphorous-fluorine bonds. This composite structure leverages the electrical conductivity and expansion accommodation properties of carbon while incorporating the high surface strength and electrolyte resistance of boron/phosphorous fluorides, achieving both capacity retention and particle integrity.

The patent introduces a dual-layer coating as an intermediary between the silicon active material and the electrolyte. The inner carbon layer serves as the primary interface that accommodates expansion while the outer boron/phosphorous fluoride layer acts as a protective mediator that prevents direct electrolyte decomposition. This intermediary structure maintains stable solid-electrolyte interface (SEI) formation without continuous electrolyte consumption.

The patent applies protective coatings to the silicon particle surface before battery operation begins. These pre-applied layers prevent the harmful electrolyte decomposition that would otherwise occur when fresh silicon surfaces are exposed during initial charging-discharging cycles. The preliminary coating establishes a stable protective barrier that prevents subsequent electrolyte consumption and maintains cycle performance.