Microstructure and (De)lithiation Front in a 400 μm Thick 3D-Printed LiFePO4 Electrode

Abstract

The progress towards more sustainable practices for the manufacturing of lithium-ion batteries has lagged behind the faster evolution in the Li-insertion materials and electrolyte formulations. 3D printing is a potential alternative coating method that can enable the preparation of high-loading electrodes with a good control over the microstructural details and spatial distribution of the electrode components. Herein, a high loading LiFePO4 electrode with an areal loading of 30 mg cm-2 is reported. This is achieved by 3D printing of an aqueous ink with an optimal formulation including carbon microfiber and carbon black as conductive additives and carboxymethyl cellulose and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate as binders. The electrodes are characterized for the electronic and ionic percolation to substantiate the superior performance of the 3D-printed electrodes compared to their conventionally doctor-blade coated counterparts. The in situ mu -x-ray diffraction (XRD) imaging of the electrodes is performed to visualize the in- and through-plane solid-state Li concentration profiles within the 400 mu m thick 3D-printed electrodes during cycling at C/5 and 1C. The concentration-gradient maps, once analyzed together with the tortuosity data, and physics-based simulations, identify the synergistic effect of an enhanced ionic transport and higher active surface-area of the 3D-printed electrodes to be the cause of their superior performance.