Ionics 10 (2004) 443 Improvement of Lithium Battery Performance through Composite Electrode Microstructure Optimization D. Guy a , B. Lestriez a , R. Bouchet b , V. Gaudefroy a and D. Guyomard a a Laboratoire de Chimie des Solides, Institut des Matériaux Jean Rouxel, CNRS, Université de Nantes, B.P. 32229, 44322 Nantes Cedex 3, France b Laboratoire Madirel, Université de Marseille, Centre Sr Jérome, Av. Escadrille Normandie Niemen, 13397 Marseille cedex 20 Abstract. The lithium trivanadate Li 1.2 V 3 O 8 has been investigated during the past decade as a very promising positive electrode material for lithium batteries due to its high theoretical capacity of 360 mAh/g. However, the experimental capacity remains generally much lower than (about half) the theoretical value. 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 Li 1.2 V 3 O 8 display a room-temperature cycling capacity of 280 mAh/g (C/5 rate, 3.3-2 V) instead of 180 mAh/g using a Bellcore-type composite electrode (PLIon™ technology). We have coupled SEM observations, galvanostatic cycling and electrochemical impedance spectroscopy in order to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors that provide efficient charge carrier collection within the composite electrode complex medium will be discussed. Present findings open up new and attractive prospects for electrode performance optimisation. 1 . Introduction 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) or poly(vinylidene fluoride) (PVdF) based polymers. Remarkable improvement resulted however from the use of a copolymer of vinylidene fluoride with hexafluoropropylene (PVdF-HFP) in both electrolyte and composite electrode, which lead to the well-known LiPLIon™ technology [2]. Only very few recent papers give examples of composite electrodes made with other polymers [3-6]. Main goals were to achieve a higher liquid electrolyte uptake by selecting less crystalline polymers thus leading to larger ionic conductivity, or to decrease capacity fading with chemically more stable polymers. 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. This study focuses on the polymeric binder used for lithium trivanadate (Li 1.2 V 3 O 8 ) based composite elec- trodes, and its influence on the battery performance. Li 1.2 V 3 O 8 that offers a theoretical capacity of 360 mAh/g, was investigated as a very promising positive electrode material during the past two decades [7-10]. However, the experimental capacity generally remains much lower than the theoretical value. It is actually of only 180 mAh/g with Bellcore-type composite electrode [2]. Li 1.2 V 3 O 8 is thus a material of choice to investigate the influence of