Synthesis and characterization of lithium-ion cathode materials in the system (1-x-y) LiNi0.8Co0.15Al0.05O2.xLi2MnO3.yLiCoO2
Date
2013
Authors
Yerramilli, Anish, author
James, Susan P., advisor
Prieto, Amy, committee member
Wu, Mingzhong, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Energy storage technology has been dominated by lithium ion batteries, which are considered the most promising with higher energy density compared to any other battery technologies. The market for lithium ion batteries has increased rapidly from 2007. Goals set by the U.S Department of Energy for hybrid electric vehicles have not been met by any of the existing cathode materials. The objective of this thesis was to find a material composition that has better cyclability and lower cost than the standard battery materials. A ternary composition with low cost materials like Al, Mn and Ni were used instead of high amounts of Co to reduce the cost of the battery. It was hypothesized that there are cathode compositions in the system (1-x-y) LiNi0.8Co0.15Al0.05O2.xLi2MnO3.yLiCoO2 that when tested for discharge capacities and cyclability will show better properties than the current generation lithium ion cathode materials. The system (1-x-y) LiNi0.8Co0.15Al0.05O2.xLi2MnO3.yLiCoO2 is synthesized using a simple sol-gel synthesis. The materials LiNi0.8Co0.15Al0.05O2, Li2MnO3 and LiCoO2 were used as end points in a ternary composition diagram. Twenty eight cathode compositions spanning the entire ternary composition diagram were synthesized under the same conditions and characterized using X-ray diffraction (XRD) and an Arbin BT2000 battery testing system. XRD results showed α-NaFeO2 structure with a space group of R3m. The results from electrochemical testing revealed a wide range of electrochemical capacities and cyclabilities. The regions close to Li2MnO3 showed high capacities and cyclability. The material with composition Li1.5 Ni0.133Co0.358Al0.008Mn0.5 had an initial discharge capacity of 216.3 mAh/g and retained this capacity even after multiple cycles in the voltage range of 4.6-2 V at a rate of C/15. Statistical analysis was done using SAS/STAT 9.2 with the ADX procedure to fit a general linear model with three linear terms and three two way interactions to map capacities and cyclabilities. This analysis was used to choose the compositions with best capacities and cyclability. Inductively couple plasma (ICP) analysis was carried out on the chosen samples to find the error between calculated composition and the theoretical composition. XPS (X-ray photoelectron spectroscopy) was conducted for the chosen samples and the oxidation states of the elements were determined. The material with composition Li1.5 Ni0.133Co0.358Al0.008Mn0.5 was found to be the promising material for commercialization. Before going into the market additional changes like synthesis conditions and surface treatments should be conducted on the material.