Design and Evaluation of Three Dimensional (3D) Current Collectors for Lithium Metal Batteries: Insights from Meta-Analysis and Experimental Studies

Abstract

As energy demand for mobile applications grows exponentially worldwide, energy storage solutions are becoming increasingly important. Electrochemical storage in the form of batteries is already widespread, but design demands for new applications require novel solutions. Lithium metal batteries (LMBs) are regarded as a promising avenue for significantly boosting the gravimetric energy density of batteries, a property that is particularly important for electric vehicles. However, the instability of the lithium metal anode (LMA) continues to hinder performance. Three-dimensional (3D) current collectors (electrically conductive substrates) have frequently been proposed as a solution, but many questions remain regarding which properties are most critical for performance and how the structures behave in realistic configurations. This thesis addresses these questions to guide the design and implementation of 3D current collectors in high-energy-density LMBs. A vast body of literature already exists surrounding 3D current collectors for LMA. However, few efforts have systematically analyzed the relationships between structural parameters of the current collector and anode performance to inform design. A coupled meta-analysis of published results and machine learning (ML) and data science techniques was undertaken to extract trends between 3D current collector structure and composition and cell performance metrics of Coulombic efficiency (CE) and cycle life (number of charge-discharge cycles before failure). The analysis revealed no correlation between structural pore diameter and performance but showed that a low to moderate specific surface area correlates to higher CE and cycle life than high specific surfaces areas. The analysis also indicated that the presence of oxygen and tin on base structures improves performance. These findings were validated experimentally: a low specific surface area carbon current collector outperformed a high surface area counterpart, and 3D copper structures incorporating oxygen and tin outperformed unmodified structures. The study highlights the value of meta-analysis for uncovering cross-cutting insights across diverse studies. Beyond the lack of clarity on optimal structural properties, few studies have examined the effects of combining 3D current collectors with various electrolytes (ionic conductor between electrodes) or have incorporated a lithium reservoir. Four commercially available copper current collectors were paired with four different electrolytes to assess how these factors influence cycling performance with a 4 mAh/cm2 lithium reservoir. Coulombic efficiency (CE) measurements revealed no statistically significant difference in CE across different current collectors within the same electrolyte. However, significant variation was observed when the electrolyte was changed while using the same current collector. Although polarization, electrochemical impedance, and lithium morphology varied between structures and electrolytes, no consistent patterns emerged to identify a clearly superior current collector structure. These results suggest that when a lithium reservoir is used, the choice of current collector structure becomes less critical, and efforts should instead prioritize electrolyte selection and design.