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Aging and Direct Recycling of Cathode Active Materials in Commercial Li-ion Cell

thesis
posted on 11.11.2020, 16:33 by Han Wang
Recycling of Lithium-ion battery cathode materials has become increasingly important due to the limited amount of resources of raw materials and the environmental and the economic benefit. Recently, a new process, direct recycling, has been gradually developed with less energy and
cost input. For this process, the aged cathode materials directly react with a Lithium source under certain thermal process to refunctionalize the aged cathode. The process is also appealing in cases where there is a large amount of similar cathode materials in use, such as electric vehicles.
In reality, Li-ion batteries go through many materials changes as they are charged and discharged. As a result of aging mechanism that can occur under different cycling conditions at different regions of the cell, aged cathode materials can differ in both bulk properties1, such as
residual Li content level, as well as surface properties, such as solid-state interface (SEI) and surface reconstruction layer. Because these differences exist in aged cathode materials, there is a likely inconsistency of recycled product unless these effects are understood and corrected.
As such, the two primary objectives of this work are:
1. Investigate relationship between the cycling conditions of 18650 Li-ion batteries and the state and consistency of the Li(NixCoyAlz)O2 (x+y+z=1) (NCA) materials in them after aging. 2. Investigate the relationships between aged NCA materials properties, and recycling processes,
and the resulting products. To achieve the 1st objective, commercial 18650 cells were cycled under 4 different conditions. Full cell cycling data and post-mortem analysis of both electrode materials reveal that aged NCA materials show different properties after being tested under different cell cycling conditions. Moreover, inhomogeneity in electrode properties was observed and analyzed under certain cell
cycling condition. Therefore, the differences in aged NCA materials properties, including the level of residual Li content, SEI thickness, surface reconstruction layer and etc, result from not only the cycling condition of the cell but also the inhomogeneous aging within one cell. To achieve the 2nd objective, solid-state recycling process parameters, including Lithium source, reactants ratio, calcination temperature, calcination time, graphite contamination content and etc, were investigated in order to understand the relationship between the aged NCA materials
properties and process parameters. Optimized process steps were created to deal with difference in some of aged NCA materials properties based on the fundamental understanding of the relithiation steps.

History

Date

14/08/2020

Degree Type

Dissertation

Department

Materials Science and Engineering

Degree Name

  • Doctor of Philosophy (PhD)

Advisor(s)

Jay Whitacre

Exports

Exports