Nowadays lithium-ion batteries represent the state-of-the-art of energy storage devices. Within this context the work herein presented deals with the investigation and the improvement of the electrochemical behavior of anode materials for lithium-ion batteries. Conductive agents play a fundamental role in determining the electrochemical performance of electrodes for lithium-ion batteries. Super-P carbon is often used in the electrode formulations in order to increase the electrical conductivity and to improve the contact between particles. In this work we synthesized a copper-modified Super-Pbased conductive agent, in which copper nanoparticles supported on the carbon matrix have been obtained by a microwave-assisted reduction of Cu (II) ions. The obtained copper/Super-P composite showed good dispersion of the nanoscaled copper particles on the carbon matrix. The synthesized conductive agent has been used instead of pristine Super-P during the manufacturing process of graphite and Li4Ti5O12 electrodes. Graphite is at the moment the most commonly used anode material in lithium-ion batteries. Unfortunately when graphite anodes are forced to work at low temperature and/or at high charge/discharge rate, the electrochemical performance drastically decreases. In this work electrodes made of oxidized KS-15 graphite (Timcal) have been tested at low temperature and high charge/discharge rate. Two different anodic formulations have been tested. Unmodified electrodes have been prepared using pristine Super-P as conductive agent. On the other hand, copper-modified ones have been manufactured with the synthesized copper/Super-P composite. It has been demonstrated that the use of the copper/Super-P composite in the electrode formulation leads to improved performances at low temperature (down to -30°C) and at increased charge/discharge rate. Furthermore, we propose a detailed study of the differential capacity curves dQ dE-1 vs. V and a set of experiments to investigate the electrical properties of the tested samples. The obtained results showed decreased polarization and increased electrical conductivity for copper-modified electrodes. The effect of both pristine Super-P and Cu/Super-P on anodes electrochemical behavior is explained by DC- and AC -electrical studies. The results show decreased electrical resistance and metallic-like behavior of the electronic conductivity as a function of the temperature on samples containing Cu/Super-P. It implies that when the temperature is decreased, the electrical conductivity linearly increases. Conversely, the sample containing pure Super-P follows a classical semi-conductor behavior, with the electrical conductivity decreasing with the decreasing temperature. Li4Ti5O12 is considered a safer alternative to carbonaceous anodes. The main disadvantages of LTO-based electrodes are related to the poor ionic and electronic conductivity of this compound, which determine poor rate capability and poor electrochemical performances at low-temperature. In this thesis we demonstrate that the use of the copper/Super-P composite instead of pristine Super-P positively affects the electrochemical behavior of the tested anodes. Electrodes manufactured starting from commercial LTO purchased from Aldrich, have been tested in the temperature range of -30≤ T≤ 20°C. The results demonstrate excellent performances of the copper-modified electrodes. Moreover, the rate capability and the cycling stability of the LTO electrodes have been remarkably improved by the use of copper/Super-P in the electrode composition. Rutile-TiO2 has been considered for a long time as almost inactive towards lithium insertion. Lately it has been proven that by controlling the particles size during its synthesis it is possible to reversibly insert a relevant amount of lithium ions into the rutile structure. In this work, nanoscaled rutile-TiO2 has been synthesized following a sol-gel procedure. The electrochemical tests performed on rutile electrode demonstrated the excellent electrochemical behavior at low temperature. Moreover, it has been demonstrated that rutile-TiO2 electrodes can be cycled within an enlarged potential window (0.1-3 Volts) in addition to the classical 1-3 Volts window of TiO2 system. The results obtained in this thesis have been the subject of the following publications and proceedings of congress: M. Marinaro, M. Pfanzelt, P. Kubiak, R. Marassi, M. Wohlfahrt-Mehrens, Journal of Power Sources, 196 (2011) 9825. M. Marinaro, M. Pfanzelt, P. Kubiak, R. Marassi, M. Wohlfahrt-Mehrens, 219th ECS meeting Montreal, QC, Canada 1-6. May 2011 Abs. 641. The results reported in this thesis about the electrochemical behavior of graphite and LTO electrodes will be subject of further communications.

Investigation of the electrochemical behavior at low temperature and fast charge/discharge rate of anodic materials for lithium-ion batteries

MARINARO, Mario
2012-03-08

Abstract

Nowadays lithium-ion batteries represent the state-of-the-art of energy storage devices. Within this context the work herein presented deals with the investigation and the improvement of the electrochemical behavior of anode materials for lithium-ion batteries. Conductive agents play a fundamental role in determining the electrochemical performance of electrodes for lithium-ion batteries. Super-P carbon is often used in the electrode formulations in order to increase the electrical conductivity and to improve the contact between particles. In this work we synthesized a copper-modified Super-Pbased conductive agent, in which copper nanoparticles supported on the carbon matrix have been obtained by a microwave-assisted reduction of Cu (II) ions. The obtained copper/Super-P composite showed good dispersion of the nanoscaled copper particles on the carbon matrix. The synthesized conductive agent has been used instead of pristine Super-P during the manufacturing process of graphite and Li4Ti5O12 electrodes. Graphite is at the moment the most commonly used anode material in lithium-ion batteries. Unfortunately when graphite anodes are forced to work at low temperature and/or at high charge/discharge rate, the electrochemical performance drastically decreases. In this work electrodes made of oxidized KS-15 graphite (Timcal) have been tested at low temperature and high charge/discharge rate. Two different anodic formulations have been tested. Unmodified electrodes have been prepared using pristine Super-P as conductive agent. On the other hand, copper-modified ones have been manufactured with the synthesized copper/Super-P composite. It has been demonstrated that the use of the copper/Super-P composite in the electrode formulation leads to improved performances at low temperature (down to -30°C) and at increased charge/discharge rate. Furthermore, we propose a detailed study of the differential capacity curves dQ dE-1 vs. V and a set of experiments to investigate the electrical properties of the tested samples. The obtained results showed decreased polarization and increased electrical conductivity for copper-modified electrodes. The effect of both pristine Super-P and Cu/Super-P on anodes electrochemical behavior is explained by DC- and AC -electrical studies. The results show decreased electrical resistance and metallic-like behavior of the electronic conductivity as a function of the temperature on samples containing Cu/Super-P. It implies that when the temperature is decreased, the electrical conductivity linearly increases. Conversely, the sample containing pure Super-P follows a classical semi-conductor behavior, with the electrical conductivity decreasing with the decreasing temperature. Li4Ti5O12 is considered a safer alternative to carbonaceous anodes. The main disadvantages of LTO-based electrodes are related to the poor ionic and electronic conductivity of this compound, which determine poor rate capability and poor electrochemical performances at low-temperature. In this thesis we demonstrate that the use of the copper/Super-P composite instead of pristine Super-P positively affects the electrochemical behavior of the tested anodes. Electrodes manufactured starting from commercial LTO purchased from Aldrich, have been tested in the temperature range of -30≤ T≤ 20°C. The results demonstrate excellent performances of the copper-modified electrodes. Moreover, the rate capability and the cycling stability of the LTO electrodes have been remarkably improved by the use of copper/Super-P in the electrode composition. Rutile-TiO2 has been considered for a long time as almost inactive towards lithium insertion. Lately it has been proven that by controlling the particles size during its synthesis it is possible to reversibly insert a relevant amount of lithium ions into the rutile structure. In this work, nanoscaled rutile-TiO2 has been synthesized following a sol-gel procedure. The electrochemical tests performed on rutile electrode demonstrated the excellent electrochemical behavior at low temperature. Moreover, it has been demonstrated that rutile-TiO2 electrodes can be cycled within an enlarged potential window (0.1-3 Volts) in addition to the classical 1-3 Volts window of TiO2 system. The results obtained in this thesis have been the subject of the following publications and proceedings of congress: M. Marinaro, M. Pfanzelt, P. Kubiak, R. Marassi, M. Wohlfahrt-Mehrens, Journal of Power Sources, 196 (2011) 9825. M. Marinaro, M. Pfanzelt, P. Kubiak, R. Marassi, M. Wohlfahrt-Mehrens, 219th ECS meeting Montreal, QC, Canada 1-6. May 2011 Abs. 641. The results reported in this thesis about the electrochemical behavior of graphite and LTO electrodes will be subject of further communications.
8-mar-2012
Settore CHIM/01 - Chimica Analitica
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11581/401803
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