Composite Film Coating for Silicon Anode Expansion and Dendrite Control

The patent embeds silicon particles or silicon oxide within a graphite matrix structure, creating a composite negative electrode where the high-capacity silicon material is nested inside the volume provided by graphite. This nested configuration allows the silicon to expand during alloying while being contained within the graphite framework, thus increasing capacitance per gram while controlling volume expansion.

The patent creates a composite negative electrode material combining silicon particles/silicon oxide with graphite. This composite structure leverages the high theoretical capacitance of silicon (4190 mAh/g for silicon particles, 1970 mAh/g for silicon oxide) while utilizing graphite's structural stability to mitigate volume expansion effects, achieving improved overall capacitance with reduced volume change.

By nesting silicon particles within the graphite matrix, the patent provides a flexible and resilient structural framework that can accommodate the volume expansion of silicon during alloying. The graphite matrix acts as a buffer that prevents structural cracks from forming, maintaining the integrity of the conductive network throughout charge/discharge cycles.

The graphite matrix functions as a flexible shell surrounding the silicon particles, allowing for volume changes during lithium alloying while maintaining structural continuity. This flexible confinement prevents the formation of structural cracks that would otherwise occur with rigid silicon structures, preserving both strength and conductivity.

The composite structure of silicon particles embedded in graphite maintains a continuous conductive network throughout cycling. The graphite matrix provides structural stability and conductivity that persists through multiple charge/discharge cycles, preventing the conductive path breakdown that typically occurs with pure silicon electrodes. This ensures long cycle lifespan while maintaining high capacitance.

The nested configuration of silicon within graphite ensures that the conductive graphite matrix remains intact and functional throughout cycling. Even as silicon expands and contracts, the surrounding graphite framework maintains electrical connectivity, preventing isolation of conductive paths and ensuring sustained performance over many cycles.

The patent introduces a coating layer comprising metal oxide particles (such as aluminum oxide, silicon oxide, or magnesium oxide) dispersed in a binder as an intermediary between the electrodes and electrolyte. This coating layer acts as a mediator that captures divalent metal ions through adsorption or complexation, preventing them from participating in harmful electrochemical reactions that would lead to lithium dendrite formation, while still allowing normal lithium ion transport.

The patent converts the potentially harmful presence of divalent metal ions into a beneficial effect by using the coating layer to selectively capture and immobilize these ions. The divalent metal ions that would otherwise cause dendrite formation are instead trapped by the metal oxide particles in the coating, transforming a harmful factor into a controlled component that enhances battery safety and performance.