Chemomechanical study of silicon composite anodes for lithium-ion batteries
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Date
2021-12-15
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Pontificia Universidad Católica del Perú
Abstract
El sillico (Si) es considerado uno de los candidatos que puede reemplazar al grafito
en ánodos de baterías de ion litio debido a su capacidad para almacenar mayor
energía y, por ende, de mejorar sus rendimientos. No obstante, el alto estrés
mecánico causado por su alta variación volumétrica durante los ciclos de carga y
descarga sumado a su baja conductividad eléctrica viene siendo un impedimento
para su amplio uso. Por tal motivo, los composites a base de silicio son estudiados
en esta tesis con el fin de mejorar su viabilidad comercial.
Este trabajo de investigación se enfoca en la síntesis de composites MXeno Ti3C2 -
silicio como ánodos para baterías de iones de litio así como su caracterización
electroquímica. El MXeno Ti3C2 es un material dos dimensional cuya buena
resistencia mecánica y conductividad pueden aportar a solucionar los problemas de
los ánodos de Si. La caracterización de los materiales de partida (partículas de Si y
MXeno Ti3C2) consistió en el estudio de su morfología por microscopía electrónica
de barrido (SEM), distribución de tamaños por dispersión dinámica de luz (DLS),
composición química por espectroscopia de energía dispersiva (EDS) y
microestructura por difracción de rayos X (XRD). Distintas composiciones de
materiales de electrodo fueron preparados mediante una suspensión aplicada sobre
una lámina de cobre por la técnica del recubrimiento con cuchilla y caracterizados
mediante microscopia óptica y SEM. Asimismo, se prepararon semiceldas con
dichos electrodos para ser sometidos a ciclos de carga y descarga a distintas
corrientes. Los procesos electroquímicos fueron estudiados mediante
espectroscopia de impedancia electroquímica (EIS).
Los resultados revelaron que la adición de partículas de Ti3C2 promueve que los
electrodos puedan alcanzar el 80% y 89% de su capacidad teórica cuando el Ti3C2
representa el 20% y 40% de la masa del material activo del electrodo,
respectivamente, en comparación al 56% alcanzado por el electrodo de Si puro.
Esta mejora es explicada por una reducción de la resistencia a la transferencia de
carga observada en los resultados de EIS. Finalmente, el electrodo con 20 % en
peso de Ti3C2 (640 mAh/g) obtuvo la mejor capacidad específica tras 100 ciclos de
carga y descarga, por encima de lo obtenido por el electrodo de Si puro (572 mAh/g).
Silicon (Si) is considered one of the candidates to replace graphite in lithium-ion battery anodes due to its ability to store more energy and thus improve their performance. However, the high mechanical stress of pure silicon, caused by its high volumetric change during charge and discharge cycles, together with its low electrical conductivity have been an impediment to its wide use. Silicon-based composites are, therefore, studied in this thesis to improve their commercial viability. This research work focuses on the synthesis of Ti3C2 MXene-silicon composites as anodes for lithium-ion batteries and their electrochemical characterization. Ti3C2 MXene is a two-dimensional material whose good mechanical strength and conductivity can contribute to solving the problems of Si anodes. The characterization of the starting materials (Si and Ti3C2 MXene particles) consisted of the study of their morphology by scanning electron microscopy (SEM), size distribution by dynamic light scattering (DLS), chemical composition by energy dispersive spectroscopy (EDS) and microstructure by X-ray diffraction (XRD). Electrodes of different compositions were prepared using a slurry mixture deposited by blade coating technique onto a copper foil and characterized by optical microscopy and SEM. Also, half cells were prepared with these electrodes and subjected to charge-discharge cycles at different currents. Additionally, the electrochemical processes were studied by electrochemical impedance spectroscopy (EIS). The results revealed that the addition of Ti3C2 promotes that the electrodes can reach 80% and 89% of their theoretical capacity when Ti3C2 represents 20% and 40% of active material mass, respectively, compared to 56% achieved by the pure Si electrode. This improvement is explained by a reduction of the charge transfer resistance observed in the EIS results. Finally, the electrode with 80 wt.% Si and 20 wt.% Ti3C2 (640 mAh/g) obtained the best specific capacity after 100 charge/discharge cycles, above that obtained by the pure Si electrode (572 mAh/g).
Silicon (Si) is considered one of the candidates to replace graphite in lithium-ion battery anodes due to its ability to store more energy and thus improve their performance. However, the high mechanical stress of pure silicon, caused by its high volumetric change during charge and discharge cycles, together with its low electrical conductivity have been an impediment to its wide use. Silicon-based composites are, therefore, studied in this thesis to improve their commercial viability. This research work focuses on the synthesis of Ti3C2 MXene-silicon composites as anodes for lithium-ion batteries and their electrochemical characterization. Ti3C2 MXene is a two-dimensional material whose good mechanical strength and conductivity can contribute to solving the problems of Si anodes. The characterization of the starting materials (Si and Ti3C2 MXene particles) consisted of the study of their morphology by scanning electron microscopy (SEM), size distribution by dynamic light scattering (DLS), chemical composition by energy dispersive spectroscopy (EDS) and microstructure by X-ray diffraction (XRD). Electrodes of different compositions were prepared using a slurry mixture deposited by blade coating technique onto a copper foil and characterized by optical microscopy and SEM. Also, half cells were prepared with these electrodes and subjected to charge-discharge cycles at different currents. Additionally, the electrochemical processes were studied by electrochemical impedance spectroscopy (EIS). The results revealed that the addition of Ti3C2 promotes that the electrodes can reach 80% and 89% of their theoretical capacity when Ti3C2 represents 20% and 40% of active material mass, respectively, compared to 56% achieved by the pure Si electrode. This improvement is explained by a reduction of the charge transfer resistance observed in the EIS results. Finally, the electrode with 80 wt.% Si and 20 wt.% Ti3C2 (640 mAh/g) obtained the best specific capacity after 100 charge/discharge cycles, above that obtained by the pure Si electrode (572 mAh/g).
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Litio--Baterías, Silicio--Propiedades eléctricas
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