Conduction in Multiphase Particulate/Fibrous Networks

Abstract

Several promising Li-ion battery technologies incorporate nanoarchitectured carbon networks, typically in the form of whisker/ particle blends bonded with thermoplastic binders to form the anodes. Degradation of these materials is currently a persistent problem, with damage presenting as blistering and/or delamination of the electrode. Both material composition and morphology play a role in these critical failure modes, and are explored in the present work as they affect conduction in practical battery materials. Lawrence Berkeley National Laboratories and the Institut de Recherche d'Hydro-Quebec supplied the materials studied in this work. Our present approach builds on our previous numerical work, incorporating real material morphology and careful selection of boundary conditions to reduce the numerical difficulties posed by singularities in the field solution, due to phase contrast, sharp corners, etc. In order to allow use of these models for various shapes of particles, we provide a few simple geometrical relations for calculation of total surface area for various morphologies of electrode materials. A four-point-probe technique was employed to obtain the experimental conductivities. Although the existence of contact resistance is well known, there is little literature regarding a technique to measure its value; here, we also present a method for quantifying it, assuming that the anode layer is comprised of two layers. Voltage functions for each layer are determined by enforcement of voltage continuity at the interfaces, current intensities at the inlet and outlet on both sides of interface, and assumption of zero voltage in the second layer as z → ϱ. The four-point-probe technique is suitable for the electrode materials tested, offering reasonable experimental precision in a simple setup. The results of this study offer some insight into the design of active materials. The model shows applicability to a wide variety of materials, including those comprised of fibers, particles, and flakes. Comparisons among simulation predictions and real material conductivities showed very good agreement. An obvious subject of future work is combined electrochemical, conduction, and mechanical modeling of these materials.

Materials Challenges Facing Electrical Energy Storage

“…Mesoscale modeling has allowed the simulation of transport and mechanics in complex architectures of packed agglomerates, 26 but a full predictive theory of chemical energy storage systems still requires fundamental research and methodological developments in several key areas. Progress in these key areas will eventually allow higher energy and power at lower cost and will dramatically accelerate innovation in new materials.…”

Development of carbon conductive additives for advanced lithium ion batteries

“…Also parameters of the electrode manufacturing process are affected by the nature of the conductive additive. Particle size and shape are important properties of the electrochemically active electrode material when combining it with the ideal conductive additive [15][16][17][18][19]. In addition, Wang et al showed that part of the conductive carbon black is incorporated in the polymer binder used in the electrode and that the resulting highly conductive polymer electronically connects the electrode particles [20].…”

“…As the specific energy and energy density of the cell is optimized by keeping the respective amount and volume fraction of conductive carbon as low as possible, there is bound to be a trade-off between cell energy and power. With increasing amount of conductive carbon the electrical electrode resistivity decreases by following more or less distinct percolation curves whose shapes depend on both the type of electrochemically active material and the conductive carbon [14,19]. When increasing the volume fraction of the conductive carbon in the electrode, the electrical electrode resistivity remains at a high constant level until the critical volume fraction is reached where the electrical resistivity of the electrode sharply drops to a lower resistivity level.…”

Performance of carbon-fiber-containing LiFePO4 cathodes for high-power applications

“…Mandal et al [14] showed that both the electronic conductivity and the discharge capacity of LiMn 2 O 4 cathodes depended on conductive-additive content. Sastry and coworkers [15,16] have shown theoretically that the shape of the conductive material has a substantial effect on the conductivity of the network formed. In particular, an increase in the aspect ratio of the filler improves the conductivity of the network for a given volume fraction of additive.…”