Carbons‐to‐SiO_x Contact Ratio for Faster Graphite/SiO_x Electrode Formulation Optimization

Abstract

The optimization of composite electrodes based on a silicon/graphite mixture is essential for battery performance, but is complex due to the multiplicity of parameters that come into play. In this direction, we propose to adjust the amount of surface area developed by all the graphitic carbons, including the conductive additive to that of the silicon phase. This concept, introduced here as graphite and carbon‐to‐silicon contact ratio, is based on the importance of contacts on the mechanical, electrical and electrochemical properties of composite electrodes. The validity of this new formulation parameter is studied here for SiOx/Graphite composite electrodes, which differ in the proportions of two types of graphite (spherical or platelet form) and for different types of conductive additives (carbon black and carbon nanotubes). An optimal contact ratio is determined, allowing at the same time the best gravimetric and volumetric capacities, the best cyclability, and the best power performance.

SiOx-Rich Electrode Directly Optimized Using Key Formulation Parameters

“…There are even optimal values, 17 mg binder m −2 SiOx+Gr+C and 20 m 2 Gr+C m −2 SiOx , for electrodes with a porosity around 35%, to maximize both gravimetric and volumetric capacities, and behaviour at high current regime (power). 15,16 The objective of this new work was to study the predictive value of these parameters. Namely, is it possible, based on the optimal values of these parameters for a state-of-the-art electrode, to identify a priori the formulation of an electrode comprising a novel element?…”

“…Indeed, the latter is affected by the formulation of the electrode, namely the quantity of binder which affects the mechanical strength, and the composition of the mixture of graphite and conductive additive which affects, together with the porosity, the number of contacts between the carbon and the SiO x phases. 15,16 Fading mechanism in Li||SiO x Gr half cells.-In order to study the fading mechanism, the incremental capacity curves were used to calculate the capacity delivered by each material (more precisely the capacity resulting from the potential ranges which are characteristic of them) throughout cycling, following the same methodology than above, except that the specific capacity of SiO x was not back corrected. The results are shown in Fig.…”

“…While the SiO x does display a fading, in agreement with the already observed mechanism where some particles are mechanically and therefore electrically disconnected, leading to their electrochemical inactivation. 15,16 Figure 3c shows the variation of the internal resistance of the cell. This one is measured with a short pulse of current to evaluate the electrical resistance of the electrodes without being affected by diffusion limitations of electrolyte species.…”

“…In our previous works, we observed that electrodes with high content of SFG6L graphite are more subject to exfoliation parallel to the current collector due to the orientation of the SF6L platelets. 16 It is important to note that these observations are carried out on electrodes free of any mechanical constraint, whereas in electrochemical cells (button cell in this case), a pressure is exerted, of the order of 0.1-0.5 MPa, 39 which can counteract the opening of these cracks and maintain more or less electrical contact between the electrode layers on either side of these cracks.…”

“…With this dual objective of optimizing and rationalizing the formulation of negative electrodes based on silicon and graphite, we recently proposed using two parameters fixing the proportions of the constituents of the electrode relative to each other. 15,16 The first parameter makes it possible to determine the quantity of binder relative to the quantity of the other powdery constituents, namely the active material(s) and the conductive additive(s). This parameter is given by the following equation,…”