One approach to address the low electrical conductivity of cathode materials is to utilize composite electrodes that contain conductive media, most often carbon. While commonly employed, this strategy is imperfect, as inhomogeneous dispersion of the active material in the conductive additive results in incomplete electrical contact to all particles in the electrode. Encapsulation of individual active material particles with a carbon coating can be more effective for providing electrical contact to each particle, however have the disadvantages of additional synthesis steps and increased production cost. An alternative strategy to approach an ideal electrode that we have been exploring is the use of bimetallic material systems. In this approach, the active material particles are electrically connected as they generate a conductive network in-situ on initiation of reduction. Bimetallic cathode materials offer the opportunity for conductive matrix formation via reduction displacement reactions that result in the formation of metal nanoparticles providing the electrical connections.
The investigation of bimetallic materials and the formation of electrically conductive pathways has included exploration of metal oxide and metal polyanion type structures including phosphate and diphosphate moieties. Additionally, composites containing bimetallic materials have been explored. The impact of this strategy on delivered capacity and capacity retention will be discussed.