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Title:Materials development for multicomponent systems with variable oxidation states
Author(s):Ribero-Rodriguez, Daniel
Director of Research:Kriven, Waltraud M.
Doctoral Committee Chair(s):Kriven, Waltraud M.
Doctoral Committee Member(s):Dillon, Shen; Yang, Hong; Shoemaker, Daniel P.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Low temperature synthesis
Polymeric steric entrapment method
Electrochemical caracterization
Negative thermal expansion
Lithium ion batteries
Near zero thermal expansion
Abstract:In this work, the synthesis by the polymeric steric entrapment method of materials that belong to the M1MnOx and M1Ti2(PO3)4 (M1= Li, Na, K,) families was evaluated. Furthermore, the influence on the physico-chemical characteristics of the powders by processing variables such as the dissolution conditions, pH of the solution, mixing conditions, drying procedures, HNO3 addition, amount of polymer (cation:organic ratio), characteristics of the exothermic reaction (C/N ratio), calcination/crystallization atmosphere and temperature, were investigated. Additionally, the electrochemical performance of the LiMn2O4 (LMO4) composition was evaluated and compared against commercial LiMn2O4 powders. Moreover, for powders in the M1Ti2(PO3)4 (M1= Li, Na, K,) family, their thermal expansion behavior were studied by means of high resolution (synchrotron radiation) in-situ high temperature X-ray diffraction, Rietveld refinement and the coefficient of thermal expansion analysis suite (CTEAS) software developed at UIUC. Specifically, powders in the family M1MnOx (LiMn3+O2, LiMn23+/4+O4, Li2Mn4+O3) could be synthesized at low temperature (~300°C) in a single step by taking advantage of the highly exothermic reaction produce by the nitrate and organic decompositions. In order to fully take advantage of the exothermic reactions and control the oxidation state, the precursor solutions had to be dried at low temperature (~70°C - 80°C) to avoid early nitrate/organic decompositions and the micro and macro atmospheres in the process had to be controlled. The micro atmosphere was controlled by the cation:organic ratio which additionally controlled the steric entrapment and the exothermic reaction. Moreover, the macro atmosphere was controlled by the furnace atmosphere. It was found that LiMn3+O2 can be produced at 700°C in flowing forming gas and using cation:organic ratio 6 to 1, whereas LiMn23+/4+O4 and Li2Mn4+O3 were produced in air, calcined at 300°C, and using a cation:organic ratio of 4:1. When powders were synthesized at low temperature (300°C – 500°C) high surface areas (14.6 m2/g for LMO4 at 300°C) and porous secondary particles composed by nanocrystals were produced, while at higher temperature (600°C – 800°C) crystals grew (micron range) and showed necking. This suggested the onset of the sintering process and exhibited a reduction of specific surface area (6.4 m2/g for LMO4 at 700°C). On the other hand, LMO4 produced in this work, exhibited similar or even better electrochemical performance than did LMO4 commercial powders (99.8 mAh/g and 90.1 mAh/g at C/10 and C/5, respectively). In contrast, 93.3 mAh/g, 110 mAh/g 131.8 mAh/g were the specific capacities obtained at C/10 for LMO4 synthesized at 300°C, 500°C and 700°C, respectively. Likewise, the specific capacities obtained at C/5 for LMO4 produced at 300°C, 500°C and 700°C were 88.9 mAh/g, 107 mAh/g and 128.3 mAh/g, respectively. The compounds LiTi2(PO4)3 (LTP), Li1.3Al0.3Ti1.7(PO4)3 (LATP), NaTi2(PO4)3 (NTP) and KTi2(PO4)3 (KTP) were produced by the polymeric steric entrapment method in air and using cation:organic ratio 4:1. It was found that the proper dissolution and mixing of the reagents was even more important than the cation:organic ratio. A pH modification (below 4.4) during the synthesis of LTP and LATP was necessary in order to keep Li + P and Li + Al + P solutions clear and stable. Furthermore, it was found that mechanical re-dispersion of the gel (formed after water soluble solutions (nitrates and P source) and alcohol soluble solutions (TISO + EG)), as well as HNO3 addition and excess of isopropyl alcohol enabled the production of single phase powders. In all cases for powders in the M1Ti(PO4)3 family, single phase powders were obtained at a calcining temperature of 700°C in one step without falling into any undesirable intermediate phase. In general, powders at low calcining temperatures were in the nano range with high specific surface area (500°C – 700°C) with rapid crystal growth. However, reduction in the specific surface area as well as pre-sintering were notice at high temperature (1000°C). The thermal expansion behavior of LTP, LATP, NTP and KTP were measured by in situ, high temperature, synchrotron powder diffraction. It was demonstrated that the CTEs were neither constant nor linear. LTP and LATP exhibited a positive but decreasing thermal expansion along the a-axis in the 25°C - 1000°C range, NTP displayed a negative but increasing thermal expansion in the 25°C - 1200°C range. KTP revealed a negative but increasing behavior up to ~500°C which then became positive and increasing up to ~1300°C. In conclusion, this research work has shed light on how to use the polymeric steric entrapment method to produce materials that contain intermetallic elements which can adopt different oxidation states. Additionally, it has demonstrated a method on how to deal with compositions where their starting reagents do not dissolve or decompose in a specific solvent. Furthermore, it has been demonstrated that in some compositions, advantage of the highly exothermic reaction can be taken in order to synthesize materials at temperatures as low as 300°C which provides a technological advantage for future industrialization. Finally, the electrochemical performance and thermal expansion behavior of some of the produced powders were evaluated in order to verify that the synthesis method was effective.
Issue Date:2017-09-11
Rights Information:Copyright 2017 Daniel Ribero Rodriguez
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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