Improved composite electrode and lithium battery performance From smart use of the polymers and their properties
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Improved composite electrode and lithium battery performance From smart use of the polymers and their properties Vincent Gaudefroy, Delphine Guy, Bernard Lestriez, Renaud Bouchet1 and Dominique Guyomard Institut des Matériaux Jean Rouxel, CNRS, Université de Nantes, B.P. 32229, 44322 Nantes Cedex 3, France 1 Laboratoire Madirel, Université de Marseille, Centre St Jérome, Av. Escadrille Normandie Niemen, 13397 Marseille cedex 20 ABSTRACT To increase electrode cycling performance in batteries, most researchers generally focus their work on the active material optimisation. Here we show that the polymeric binder of the composite electrode may have an important role on the electrode performance. We describe a new tailored polymeric binder combination with controlled polymer-filler (carbon black) interactions that allows the preparation of new and more efficient electrode architecture. Using this polymeric binder, composite electrodes based on Li1.2V3O8 display a room-temperature cycling capacity of 280 mAh/g (C/5 rate, 3.3-2 V) instead of 150 mAh/g using a standard-type (PVdF-HFP binder) composite electrode. We have coupled SEM observations, galvanostatic cycling and electronic conductivity measurements in order to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance.
INTRODUCTION This study focuses on the polymeric binder used for lithium trivanadate (Li1.2V3O8) based composite electrodes, and its influence on the battery performance. Polymers are mostly studied for their application as the electrolyte solvent of lithium batteries [1], rather than for their application as the binder of composite electrodes. As a result, for composite electrodes in liquid or gelled electrolyte, the binder used is almost systematically Poly(tetrafluoro ethylene) (PTFE), poly(vinylidene fluoride) (PVdF), or a copolymer of vinylidene fluoride with hexafluoropropylene (PVdF-HFP). In fact, little is known on the exact role of the polymer binder on composite electrode performance and we think there is a need for fundamental researches on model systems. Li1.2V3O8 that offers a theoretical capacity of 330 mAh/g, was investigated as a very promising positive electrode material during the past two decades. However, the experimental capacity generally remains much lower than the theoretical value. It is actually of only 150 mAh/g with standard-type (PVdF-HFP binder) composite electrode. In this paper, the Li insertion and cycling behaviors of a given Li1.2V3O8 compound are studied in the same experimental conditions when varying only the polymeric binder of the composite electrode. Our approach to tailor new polymeric binders is detailed in reference [2]. Carbon black (CB) has a weak self-ability to form a conductive network around active material particles, which is detrimental to the obtained capacity. Good polymer-filler interactions are needed to obtain homogeneous dispersion of colloidal CB powder into a polymer matrix, either in the melt or in
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