Failure Mechanisms of Aluminum Alloy Foil Anodes in Lithium-ion Batteries Governed by Composition and Cell Design

Abstract

Aluminum alloy foil anodes have emerged as a promising class of material for enabling increased energy density in lithiumion batteries. However, the complex degradation mechanisms are not fully understood. In this work, aluminum alloyed with 1 wt% alloying elements (Si, Cu, or Mg) in LiFePO4 || Al alloy full cells are investigated to uncover the relationship between composition, negative/positive (N/P) ratio, and the mode of degradation. We show that the alloying element and N/P ratio dictate cycle life performance and the dominant mode of failure. Regardless of alloy composition, at a high N/P ratio (> 4), diffusional trapping serves as the primary mode of degradation. Conversely, with a low N/P ratio (< 4), the mode of degradation varies based on the alloying element. Diffusional trapping dominated degradation can be characterized by a low first-cycle efficiency (FCE), capacity gain through cycling, improved cycling stability, and structural stability. Pulverization dominated failure is defined by a higher FCE, improved capacity retention at the expense of cycle life, and severe fracturing that results in a porous structure. Understanding these structure-performance relationships provides a roadmap for the rational design of Al foil anodes with improved performance in practical cells.