Graphite Porosity Gradient in Li-Ion Anodes for Temperature Stability

The patent applies local quality by creating a gradient distribution of graphite particles with different internal porosities within the negative electrode active material layer. Specifically, particles with 8% to 20% internal porosity are concentrated in the inner region (near the current collector) to enhance electrolyte permeation and low-temperature discharge characteristics, while particles with 5% or less internal porosity are concentrated in the outer region to improve high-temperature storage characteristics. This spatial variation in particle properties resolves the contradiction between high-temperature storage and low-temperature discharge performance.

The patent resolves this contradiction by applying local quality through a controlled gradient distribution. High-porosity particles (8% to 20%) are localized in the inner region of the active material layer where they enhance electrolyte penetration and low-temperature discharge performance, while low-porosity particles (5% or less) are localized in the outer region where they provide thermal stability and improve high-temperature storage characteristics. This localized assignment of different particle types to different regions eliminates the trade-off.

The patent applies local quality by establishing a gradient distribution of graphite particles with different internal porosities across the thickness of the negative electrode active material layer. This gradient structure—where particle porosity varies systematically from the inner region (8% to 20% porosity) to the outer region (5% or less porosity)—simultaneously optimizes both high-temperature storage and low-temperature discharge characteristics while remaining manufacturable through controlled mixing and coating processes.