The role of the polymeric binder nature and composition on the electronic transport properties of composite electrodes based on Li1.2V3O8, carbon black (CB), and poly(ethylene oxide) (PEO)/poly(vinylidene difluoride)-co-hexafluoropropylene/ethylene carbonate-propylene carbonate (EC-PC)/Li bis(trifluoromethansulfon)imide binders were examined. The variation of the electrical conductivity vs CB volume fraction is typical of tunneling-percolation systems. Lower percolation threshold phi(c) found for preplasticized binders is related to a more efficient CB dispersion due to the presence of EC-PC in the liquid suspension at the time of the composite processing. Above phi(c) the conductivity is a unique function of the PEO to CB concentration ratio in the suspension, log sigma=log(sigma(CB))-a phi(PEO)/phi(CB). This ratio controls the amount of polymer that adsorbs at the surface of the CB particles before the CB conducting network forms. The Li+/e(-) insertion behavior was studied at low current rate, for which ionic conductivity is not a limiting factor. The electrochemical capacity sharply increases at phi(c). However, for CB content typical of practical composite electrodes, the electronic conductivity of the CB network is not the only parameter that governs the electrode performance. It depends also on the electronic wiring at the CB/Li1.2V3O8 interface, which is improved when adding EC-PC and lithium salt in the formulation.

We show that the polymeric binder of the composite electrode may have an important role on the lithium trivanadate Li1.2V3O8 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−1 (C/5 rate, 3.3–2 V) instead of 150 mAh g−1 using a standard-type (poly(vinylidene fluoride)–hexafluoropropylene (PVdF–HFP) binder) composite electrode. We have coupled scanning electron microscopy (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 are discussed.

To increase electrode cycling performance in lithium batteries, most researchers generally play on the active material optimization. In this paper, it is shown that there is also a need for fundamental studies in the field of nonactive components of the composite electrode. Optimization of the environment of Li1.2V3O8 active material within the composite electrode leads to a room-temperature cycling capacity of 280 mAh/g instead of 180 mAh/g with Bellcore-type electrode. Well performing composite electrode was achieved with efficient electronic conduction network, good carbon black/Li1.2V3O8 interface, and total collection of active material grains. The key role of the homogeneous and efficient carbon black (CB) distribution, due to good interactions between pre-plastifed polyethylene oxide binder and CB, and optimized PEO/CB ratio, has been determined. (C) 2004 The Electrochemical Society.

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.

The lithium trivanadate Li1.2V3O8 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 Li1.2V3O8 display a room-temperature cycling capacity of 280 mAh/g (C/5 rate, 3.3-2V) instead of 180 mAh/g using a Bellcore-type composite electrode (PLIonTM 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.

In the field of electrodes for lithium batteries, the most important present advances deal with new families of active materials and new principles of energy storage in these materials. Very scarce research is devoted to the composite electrode as a whole however. The electrode is in fact a very complex medium that needs to bring efficiently the ionic reactants (Li+ ions) and the electrons to the surface of the active material (AM) particles. Such a complex medium is generally obtained by mixing together the AM grains with non-electroactive additives such as a very fine powder of carbon black (CB) and a polymeric binder (B). The CB additive is supposed to ensure electronic percolation within the composite electrode. The binder additive has multiple roles. It brings its mechanical strength to the electrode, it allows for a good electric contact between the electrode and the current collector, and it ensures the electrode a sufficient liquid electrolyte uptake to provide internal ionic percolation. For long-lasting battery operation, the composite electrode complex medium needs to be chemically and electrochemically stable. It also needs to maintain a good mechanical cohesion in the presence of the liquid electrolyte and during the volume changes which occurs when inserting and extracting Li within the AM grains. For battery optimum energy density, the amounts per unit of mass and volume of the non-electroactive additives need to be minimized. In most studies, the nature of the CB and B and their mass amount are chosen almost always the same. B is generally selected as either PTFE or PVDF-HFP, CB is chosen as an acetylene black or its mixture with graphite, and the AM:CB:B mass ratio is generally close to 85:10:5. While polymers have been thoroughly investigated for a while for their use as a component of the electrolyte, their utilization as the electrode binder has not been studied. It seems quite obvious that the organization of the CB and B dispersion and/or morphology within the composite electrode should have an influence on the electrode performance. However, such an issue is a research area, which has never been carefully studied yet, so that the literature is very scarce on that subject. Many studies have been done probably in industry in this field, but such knowledge is not published. The purpose of the present work is to get some understanding of the role of the morphology and organization of the different components inside the composite electrode on the electrode performance, in order to be able to further optimize it. Various composite electrodes have been prepared in which the surrounding of the same active material (LiV3O8) is changed by playing with the type of binder (PMMA, PEO, PVdF-HFP)) and its plasticization by ethylene carbonate and propylene carbonate (EC-PC). We have also varied the quantity and the nature of the solvent used for the binder dissolution, as well as the dispersion tool. In this presentation we will compare the morphological, electrical, and electrochemical characteristics of various composite electrodes studied by a combination of techniques (SEM, BET, DSC, EIS, and electrochemical response).