Lanterna Rally

Author: Laurence Danis

Publisher:

Published: 2017

Total Pages:

ISBN-13:

"Lithium ion batteries (LIBs) have become a common power source for most portable home electronic devices including cellular phones, computers, tablets, power tools, and, recently, electric vehicles. Despite their success, the commercial market demands portable energy storage which offers more charge/discharge cycles, shorter recharge times, and higher power densities. Therefore, LIB materials research aims to improve key electrochemical properties. The cubic spinel lithium manganese oxide (LixMn2O4) is an alternative to LiCoO2 and is one of the most investigated positive electrode materials for LIBs. LixMn2O4 is of particular interest due to its advantageous electrochemical performance at room temperature (i.e. high capacity and stable operating voltage), significant natural abundance, low cost, and low toxicity. Regardless of these advantages, LixMn2O4 experiences a fast capacity fade with charge/discharge cycling and poor storage performance, particularly at elevated temperatures. This hinders its widespread commercial use, especially for large-scale automotive applications. This capacity-fading phenomenon is believed to be due to numerous factors, such as the Jahn-Teller distortion, the decomposition of electrolyte solution on the negative electrode, and the dissolution of Mn2+ from the positive electrode into the electrolyte. Most research groups agree that dissolution of Mn2+ cations is the leading mechanisms for the decreased capacity and is primarily caused by the hydrogen fluoride (HF) contained in the electrolyte.In-depth understanding of the mechanism of Mn dissolution could provide insights for new methods to inhibit the dissolution pathway. However, standard manganese detection techniques are performed ex-situ, post cell disassembly and have potential risk of data alterations due to air sensitivity of these materials, creating a need for in-situ analysis techniques of battery materials. The presented dissertation investigates the use of scanning probe microscopy (SPM) analysis methods to provide localized information on the fundamental mechanisms, processes and degradation of LIBs. Herein, we present the step-by-step development of a high resolution scanning electrochemical microscopy (SECM) technique for the quantitative detection of Mn2+ cations. More precisely, we describe the development and characterization of Hg/Pt hemispherical micro- and nano- SECM probes used with anodic stripping voltammetry (ASV), for the quantitative detection of Mn2+ cations. We have successfully developed a simple, fast, and reproducible method for the fabrication of disk microelectrodes with controlled geometry. A second fabrication technique is presented for the production of well-defined Pt disk electrodes with the electroactive core in the nanometer scale. Both of these fabrication techniques produce electrodes that are are ideal backbones for the production of Hg-based hemispherical ASV sensors. Also presented is a systematic study of the shear force (SF) characteristics of these nanoelectrodes and a new methodology to identify SF sensitive frequencies. SF is used in SECM to maintain a constant tip-to-substrate distance for the deconvolution of the kinetic and topographic information received in SECM. The Hg/Pt hemispherical nanoelectrodes were used for the quantitative detection of manganese cations. The ASV technique has been used to evaluate the impact of using polymeric chelating macrocyles, such as crown ethers, as separator coatings. The coated separators would serve for the sequestration of Mn2+ cations, thus preventing their migration to negative electrodes, and therefore mitigating the undesirable consequences of manganese dissolution in LIBs. A transition from an aqueous environment to a more representative oxygen and water-free environment in propylene carbonate (PC) LiClO4, a typical a non-aqueous electrolyte for LIBs, has also been performed. " --