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 LiFePO 4 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 µ‐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 µm 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.