Immersion precipitation route towards high performance thick and flexible electrodes for Li-ion batteries

Abstract

Enabling the transition to renewable power sources requires further optimization of batteries in terms of energy/power density and cost-effectiveness. Increasing the practical thickness of Li ion battery electrodes not only can improve energy density on cell level but reduces manufacturing cost. However, thick electrodes exhibit sluggish charge-transport kinetics and are mechanically less stable, typically resulting in substandard battery performance compared to the current commercial standards (~50 μm). Here we disclose a novel method based on immersion precipitation by employing a non-solvent to solidify the battery binder, instead of solvent evaporation. This method allows for the fabrication of thick and suitable density electrodes (>100 μm with ultra-high mass loading) offering excellent electrochemical performance and mechanical stability. Using commercial electrode active materials at a remarkable mass-loading of 24 mg cm⁻², the electrodes processed via immersion method are shown to deliver 3.5 mAh cm⁻² at a rate of 2C and operate at rates up to 10C. As additional figure of merit, this method produces electrodes that are both stand-alone and highly flexible, which have been evaluated in flexible full-cells. Furthermore, via immersion precipitation the commonly used more toxic N-Methyl-2-pyrrolidone can be supplanted by environmentally benign dimethyl sulfoxide as solvent for processing electrode layers.