Nano-Active Electrode Materials

摘要

Nano-active materials are produced by a novel flash calcination process from precursor materials that become mesoporous, with a porosity approaching 50%, with strong necking between grains, so that the materials are intrinsically strong. The flash calcination process has been proven at an industrial scale of 30,000 tpa for oxide materials such as nano-active MgO to produce materials with a surface area in excess of 250 m2/g. This work described the first application of the process to produce electrode materials for batteries. Agricultural grade Manganese Carbonate, without any pre-processing, with a particle size around 15 microns, was flash calcined in a pilot plant reactor in air or steam with a 3 seconds residence time in the heating zone, to give a mesoporous Mn3O4, comprised of grains of about 10-20 nm in size in which the particle size was similar to that of the input material. The Youngs Modulus of the powder particles were measured by nano-indentation, and the modulus was less than 8% of the Mn3O4 crystal value, and characteristic of a fused aggregate of nano-grains. The Mn3O4 power was then heated under argon with Li2O powder to produce either mesoporous LiMn2O4 or Li2MnO3 powder, depending on the molar ratio of Li/Mn. The intercalation process to produce these cathode materials maintained the mesoporous materials structure. Coin cell batteries were fabricated from these materials, and tested over multiple charge discharge cycles. The charge capacity was similar to that of conventional materials, indicating that the small grains enabled an efficient thermal intercalation process, and the cycles showed only a small degradation of performance for the LiMn2O4 or Li2MnO3 materials. With suitable modifications of the production process, it is anticipated that fast charge/discharge batteries suitable for electric vehicle applications can be produced. The stabilisation of the material with nickel and/or cobalt will enhance the electrical conductivity, and enable a comparison of performance with standard lithium ion batteries. The flash calcination process by-passes expensive nano-technology routes to production of nano- electrode materials that generally fail because the binding between aggregates of nano- particles is too weak to resist material restructuring over many cycles. The fusion of the nano-grains during the flash calcination process is the important feature of the flash calcination process. The flash calcination process is a very simple process for production of strong materials that have a mesoporous structure for fast ion and electron transport, and small grains that enable fast, non-destructive intercalation during many cycles using powder materials that can be dropped into existing battery production processes.