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Exploración de los procesos de redox catión-anión en catodos de iones de magnesio recargables de tetrasulfuro de
Sunita Dey1, Jeongjae Lee1, Sylvia Britto1,2
1Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, U.K.
Journal of the American Chemical Society
|October 27, 2020
Resumen
Las baterías de iones de magnesio requieren nuevos cátodos. VS4 es prometedor, pero su mecanismo de intercalación de Mg involucra redox V y S acoplados, formando una nueva vía intermedia y competidora, limitando la reversibilidad.
Área de la Ciencia:
- Ciencias de los materiales
- La electroquímica
- Tecnología de baterías
Sus antecedentes:
- Las baterías de iones de magnesio (MIB) necesitan materiales de cátodo estables para su viabilidad comercial.
- VS4 es un cátodo MIB prometedor debido a su estructura 1D y su gran espaciado entre cadenas.
- Los procesos redox detallados y los cambios estructurales durante la intercalación / desintercalación de Mg en VS4 siguen sin estar claros.
Objetivo del estudio:
- Para aclarar los mecanismos de reacción de la intercalación y desintercalación de Mg en los cátodos VS4.
- Para identificar cualquier nuevo intermedio formado durante el ciclo electroquímico de VS4.
- Comprender los factores que influyen en la reversibilidad y la capacidad de VS4 en MIB.
Principales métodos:
- Espectroscopia de fotoelectrones de rayos X (XPS) para el análisis químico de superficies.
- Espectroscopia de absorción de rayos X V y S (XANES) para la estructura electrónica.
- V Hahn eco y MATPASS RMN para conocimientos estructurales locales.
- Teoría funcional de la densidad (DFT) con algoritmos evolutivos para la predicción de la estructura.
- Análisis de la función de distribución de pares de rayos X para la verificación experimental de la estructura.
Principales resultados:
- La intercalación de Mg en VS4 implica redox catiónico-aniónico acoplado: V4+ se oxida a V5+ y S2- se reduce a S2.
- Se descubrió y caracterizó estructuralmente un nuevo intermedio, Mg3V2S8, que contiene [VS4]3- unidades tetraédricas.
- Se observaron dos vías de reacción competidoras: formación intermedia y conversión directa a MgS y V metal.
- La carga reforma parcialmente el intermedio V5+/S2, no el VS4 original, lo que indica una reversibilidad limitada.
Conclusiones:
- El mecanismo de reacción en los cátodos VS4 es un proceso complejo de redox acoplado catiónico-aniónico.
- La formación de nuevas vías de reacción intermedias y competidoras tiene un impacto significativo en la reversibilidad.
- Los policalcogenuros de metales de transición ofrecen potencial para MIB de mayor capacidad a través de mecanismos redox similares.
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