Recycling All-Solid-State Lithium Batteries

open_access
Open Access
Author:
Lan, Yi Chen
Graduate Program:
Chemical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 03, 2024
Committee Members:
Robert Rioux, Professor in Charge/Director of Graduate Studies
Enrique Gomez, Chair & Dissertation Advisor
Bryan Vogt, Major Field Member
Christian Pester, Major Field Member
Clive Randall, Outside Unit & Field Member
Keywords:
all-solid-state lithium battery
recycling
cold-sintering process
polymer electrolyte
lithium metal battery
solid-state electrolyte
Abstract:
All-solid-state lithium batteries (ASSBs) have emerged as a promising alternative to conventional lithium-ion batteries, offering the potential for improved safety, higher energy density, and longer cycle life. Unlike traditional lithium-ion batteries that use liquid electrolytes, ASSBs employ solid-state electrolytes, which eliminate the risk of electrolyte leakage and flammability. The development of ASSBs has gained significant attention in recent years, driven by the increasing demand for safer and more efficient energy storage solutions in applications ranging from portable electronics to electric vehicles. Despite the growing interest in ASSBs as a next-generation energy storage technology, the development of effective recycling methods for these batteries has received relatively little attention. As ASSBs near widespread commercialization, the lack of established recycling processes poses a significant challenge in terms of environmental sustainability and resource conservation. ASSBs present unique complexities due to their diverse materials and intricate architectures, which complicates the recycling process and requires the development of novel separation and recovery techniques. Moreover, the absence of standardized designs and the use of scarce materials further emphasize the urgent need for efficient recycling strategies. Addressing the lack of recycling methods becomes crucial to ensure the sustainable development of this promising technology and to minimize its environmental impact. The cold sintering process (CSP) has emerged as a promising technique for the fabrication of dense ceramic materials at remarkably low temperatures (< 300 °C), offering a more energy-efficient and environmentally friendly alternative to traditional high-temperature sintering methods. By applying the principles of CSP, it is possible to effectively repair and densify fragmented solid-state electrolytes, which often undergo severe mechanical degradation during cycling. The low-temperature nature of CSP allows for the reintegration of composite electrolytes without causing significant changes to the chemical composition or structure, thereby preserving their electrochemical properties. Designing recyclable ASSBs is a vital step towards promoting sustainability and minimizing the environmental impact of energy storage technologies. By incorporating design principles that facilitate the separation process and allow for direct recycling of spent batteries, we can greatly improve the sustainability of ASSB. A promising approach involves introducing polymer interfacial layers between the electrodes and the solid-state electrolyte. These flexible polymer-salt layers serve a dual purpose: they bridge the solid-solid interfaces, enabling lithium-ion conduction across the interfaces, and they act as sacrificial layers that can be easily removed to facilitate the separation process during recycling. While lithium metal anodes in all-solid-state batteries offer enhanced energy density, they introduce challenges related to unstable interfaces. The introduction of fluorine-containing lithium salts in the polymer-salt layers on the anode interfaces leads to the formation of a LiF-rich solid electrolyte interphase (SEI) layer, which serves as a protective barrier. This LiF-rich SEI passivates the Li metal surface, prevents side reactions, minimizes resistive secondary phases, and suppresses lithium dendrite growth, thereby enhancing cycling stability and longevity. This stable SEI also simplifies the recycling process by reducing interfacial chemistry complexity, and its effective removal allows for efficient recovery of valuable electrolyte materials without extensive purification, ultimately improving the battery performance, durability, and recyclability. The occurrence of incongruent dissolution during the cold sintering process can potentially altering the stoichiometric composition and affecting the electrochemical properties of the ceramic materials. By replacing liquid water with water vapor as the transient solvent, the extent of incongruent dissolution can be minimized while maintaining effective densification of the fragmented composite electrolytes. Through careful control of the transient solvent amount, it is possible to tailor the intergranular properties of LATP–LiTFSI electrolytes, promoting lithium-ion transport within the water-in-salt structures formed at the grain boundaries. To improve the cycling performance and recyclability of all-solid-state lithium batteries, optimizing the polymer interfacial layer is crucial. Enhancing the mechanical strength of this layer can prolong battery longevity and facilitate efficient separation during recycling. Adopting green solvents during recycling can contribute to a safer environment and better human health. Further research is necessary to solidify the understanding of intergranular properties and their impact on battery performance, validating the concept and guiding future developments.