The use of extrusion coating for lithium-ion battery electrodes enables the practical possibility of using multilayer coatings to improve battery performance. The use of multilayer coatings of different materials, for example, a LiFePO4
coating next to a LiCoO2
coating, or a NMC coating next to a LiMn2
coating, has been experimentally tested in the literature and modeling approaches to optimize multilayer coatings presented. In this presentation simulation results exploring the effects of particle size and layer thickness are explored in order to minimize the cost of a HEV battery, and some case studies presented for high-energy cells.
To minimize the cost of a HEV battery, bilayer coatings for both positive (NMC) and negative (graphite) electrodes are considered where layer thickness and particle size are adjusted. For very thin coatings (≤ 40 mm), the simulated performance of bilayer coatings containing different particle sizes is comparable to a single-layer coating containing a mixture of particle sizes. In both cases a substantial benefit comes from using a larger fraction small size particles (~ 1 mm radius), but small particles lead to greater impedance growth and capacity fade over time.
For the thicker electrodes typically used in energy cells, simulations indicate that the pulse power capability can be increased by using multilayer electrode coatings. However, for battery electric vehicles, the benefit is not clear as the power requirement is not difficult to meet with conventional single layer electrodes.