Committee:

Matthew McDowell, MSE/ME (advisor)

Christopher Muhlstein, MSE

Seung Woo Lee, ME

Naresh Thadhani, MSE

Meilin Liu, MSE

Aluminum-foil-based alloy anodes for solid-state batteries

Project Summary

The objective of this research is to examine the performance of aluminum-foil-based anodes in solid-state batteries (SSBs) by assessing the effects of metallurgically combining aluminum with high-capacity elements on electrochemical behavior. Among the various alternatives to lithium-ion batteries (LiBs), SSBs stand out as promising contenders, offering increased energy and power densities. The novel cell architecture of SSBs employs a solid-state electrolyte (SSE) to replace the conventional liquid electrolyte that surrounds the anode and cathode. The use of a solid electrolyte potentially enables high-capacity electrode materials to be reliable used, resulting in batteries with higher energy density. Alloy anode materials introduce new chemistries and microstructures that interact with the SSB system. This study concentrates on investigating these interactions and identifying advantageous additives or post-processing methods.

Aluminum has been examined as an anode material since the 1970s1,2, since it can reversibly react with large quantities of lithium within batteries. The use of aluminum foil as an anode offers significant manufacturing advantages, particularly in terms of cost reduction and scalability. These benefits can be attributed to aluminum's inherent properties and the streamlined manufacturing process that comes with using foil-based anodes instead of slurry casting. This simplified method for preparing electrodes enables a smoother transition to large-scale manufacturing operations 3.

While the use of aluminum foil anodes presents several manufacturing benefits, the passivating oxide layer and possible interfacial issues between the anode and electrolyte represent challenges to implementation. The issues with interfacial reactions between the liquid electrolyte and aluminum anodes in lithium-ion batteries are primarily related to the formation and instability of the solid electrolyte interphase (SEI) layer during the large volume changes of the material.

SSBs are expected to have fewer issues related to interfacial reactions because the electrolyte no longer permeates the entire anode.  In previous studies, thick aluminum foils were mechanically alloyed with lithium and employed as SSB anodes 4–7. However, these lithium-aluminum materials contained excess materials and proved to be impractical. In this dissertation, multiphase aluminum foil materials are demonstrated to achieve promising electrochemical behavior for the first time in SSBs, achieving practical areal capacities ranging from 2 to 5 mAh cm-2 without prelithiation. The minor addition of other elements to create multiphase alloys significantly enhanced cell performance. Lithium trapping was substantially reduced, likely due to the dual-phase network promoting effective Li transport.

The proposed work aims to investigate the behavior of other multiphase microstructures with different compositions, characterizing failure mechanisms and devising potential solutions to mitigate cell degradation. Understanding that distinct multiphase compositions give rise to diverse microstructures, the initial study will investigate the impact of varying secondary phase content and particle size on the resulting microstructures and their influence on the cycling behavior of the battery. The behavior of aluminum alloy anodes will be further explored in large-format dry-cast SSB pouch cells, which will be operated with at least an order of magnitude less stack pressure than lab-scale testing cells. Furthermore, I will explore the effects of stack pressure on the material evolution, interface, and interfacial contact with the SSE.