Micro-scale graded electrodes for improved dynamic and cycling performance of Li-ion batteries

Li-ion battery cathodes based on LiFePO4 are fabricated by a layer-by-layer spray printing method with a continuous through thickness gradient of active material, conductive carbon, and binder. Compared with cathodes with the more usual homogeneous distribution, but with the same average composition, both C-rate and capacity degradation performance of the graded electrodes are significantly improved. For example at 2C, graded cathodes with an optimized material distribution have 15% and 31% higher discharge capacities than sprayed uniform or conventional slurry cast uniform cathodes, and capacity degradation rates are 40-50% slower than uniform cathodes at 2C. The improved performance of graded electrodes is shown to derive from a lower charge transfer resistance and reduced polarization at high C-rates, which suggests a more spatially homogeneous distribution of over-potential that leads to a thinner solid electrolyte interphase formation during cycling and sustains improved C-rate and long-term cycling performance.