Browsing by Autor "Max Vargas"

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NUEVA RUTA DE SÍNTESIS ATRANO/HIDRO-SOLVOTERMAL PARA EL CONTROL DEL TAMAÑO DE NANOPARTÍCULA DE Li4 Ti5 O12 A TRAVÉS DEL USO DE TOHAC's
(2023) Luz J. Pozadas; Cesario Ajpi; Max Vargas; Saúl Cabrera; Gustavo García; Área Ciencia de Materiales, Catálisis y Petroquímica, Instituto de Investigaciones Químicas, Carrera de Ciencias Químicas, Universidad Mayor de San Andrés UMSA, Ciudad Universitaria, Cota Cota, La Paz, Bolívia.; Saúl Cabrera; Área Ciencia de Materiales, Catálisis y Petroquímica, Instituto de Investigaciones Químicas, Carrera de Ciencias Químicas, Universidad Mayor de San Andrés UMSA, Ciudad Universitaria, Cota Cota, La Paz, Bolívia.; Gustavo García; Área Ciencia de Materiales, Catálisis y Petroquímica, Instituto de Investigaciones Químicas, Carrera de Ciencias Químicas, Universidad Mayor de San Andrés UMSA, Ciudad Universitaria, Cota Cota, La Paz, Bolívia.
En el presente trabajo se propone un nuevo método de síntesis por vía húmeda denominada “Atrano/Hidro- Solvotermal”, que permite obtener nanopartículas de Li 4 Ti5 O12 (LTO) con tamaños predefinidos. Estas nanopartículas se obtienen mediante un control de velocidad de crecimiento de los atrano-clúster metálicos formados durante los procesos de hidrólisis y condensación en solución acuosa y solvotermal. Se sintetizaron nanopartículas de LTO a partir de precursores tipo atrano (litiatrano, titanatrano). Éstos forman complejos de especies oligoméricas “Clústers de Titanio-Oxo-Hidroxo-Atrano” (TOHAC’s). Los TOHAC’s con tamaños predefinidos fueron obtenidos mediante un control del tiempo de hidrólisis y condensación. El tamaño promedio de los TOHAC’s formados se caracterizaron mediante la técnica dispersión dinámica de la luz (DLS), obteniéndose tamaños promedio de 2.40, 7.17, 20.13, y 40.00 nm para las muestras (B:0), (B:48), (B:144) y (B:288) respectivamente. Los TOHAC’s fueron utilizados como bloques de construcción (building blocks), seguidos de un tratamiento Hidro-Solvotermal, y un tratamiento térmico a 500°C. Los difractogramas de DRX de los productos obtenidos muestran la presencia mayoritaria de la fase de interés Li 4Ti5 O12 (LTO) con estructura tipo espinela, y β-Li 2 TiO3 monoclínico como fase secundaria. Las imágenes SEM muestran partículas de diámetro promedio de 12.82 ±5 nm (LTO: B:0) 10.03±3 nm (LTO: B:48), 20.03±7.6 nm (LTO: B:144), y 40.0 ±5 nm (LTO:B:288). Estos tamaños de partícula van en correlación con los TOHAC´s (building blocks) empleados.
Synthesis and Characterization of LiFePO4–PANI Hybrid Material as Cathode for Lithium-Ion Batteries
(Multidisciplinary Digital Publishing Institute, 2020) Cesario Ajpi; Naviana Leiva; Max Vargas; Anders Lundblad; Göran Lindbergh; Saúl Cabrera
This work focuses on the synthesis of LiFePO4-PANI hybrid materials and studies their electrochemical properties (capacity, cyclability and rate capability) for use in lithium ion batteries. PANI synthesis and optimization was carried out by chemical oxidation (self-assembly process), using ammonium persulfate (APS) and H3PO4, obtaining a material with a high degree of crystallinity. For the synthesis of the LiFePO4-PANI hybrid, a thermal treatment of LiFePO4 particles was carried out in a furnace with polyaniline (PANI) and lithium acetate (AcOLi)-coated particles, using Ar/H2 atmosphere. The pristine and synthetized powders were characterized by XRD, SEM, IR and TGA. The electrochemical characterizations were carried out by using CV, EIS and galvanostatic methods, obtaining a capacity of 95 mAhg-1 for PANI, 120 mAhg-1 for LiFePO4 and 145 mAhg-1 for LiFePO4-PANI, at a charge/discharge rate of 0.1 C. At a charge/discharge rate of 2 C, the capacities were 70 mAhg-1 for LiFePO4 and 100 mAhg-1 for LiFePO4-PANI, showing that the PANI also had a favorable effect on the rate capability.
Synthesis and spectroscopic characterization of NiII coordination network: Poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)] as material for lithium ion batteries
(Elsevier BV, 2022) Cesario Ajpi; Naviana Leiva; Max Vargas; Anders Lundblad; Göran Lindbergh; Saúl Cabrera
The compound Ni3(C8H4O4)3(C3H7NO)3, poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)], was synthesized by the solvothermal method prepared via reaction between NiCl2•6H2O and terephthalic acid using N,N-dimethylformamide (DMF) as solvent. The structure was characterized by powder X-ray diffraction and infrared spectroscopy analyses. The electrochemical properties as a potential active material in lithium-ion batteries were characterized by electrochemical impedance spectroscopy and galvanostatic charge-discharge curves in a battery half-cell. The characterization results show that the coordination network contains one independent structure in the asymmetric unit. It is constructed from Ni2+ ions, terephthalate bridges and in-situ-generated DMF ligands, forming two similar two-dimensional (2D) layer structures. These similar 2D layers are in an alternating arrangement and are linked with each other by dense H—H interactions (45%) to generate a three-dimensional (3D) supramolecular framework with ordered and disordered DMF molecules. The electrochemical measurements, conducted in the potential range of 0.5–3.5 V vs Li/Li+, show that Ni3(C8H4O4)3(C3H7NO)4 has good electrochemical properties and can work as anode in lithium-ion batteries. The material presents an initial specific capacity of ∼420 mAh g−1, which drops during consecutive scans but stabilizes at ∼50 mAh g−1. However, due to the wide potential range there are indications of a gradual collapse of the structure. The electrochemical impedance spectroscopy shows an increase of charge transfer resistance from 24 to 1190 Ohms after cycling likely due to this collapse.