3D Printing of Conversion Cathodes for Enhanced Custom-Form Lithium Batteries

Additive manufacturing techniques can enable the fabrication of batteries in nonconventional form factors, enabling higher practical energy densities due to improved power source packing efficiency. Furthermore, energy density can be improved by transitioning from conventional Li-ion materials to lithium metal anodes and conversion cathodes. Iron disulfide (FeS₂) and iron trifluoride (FeF₃) are two promising conversion cathodes of commercial and academic interest, but the 3D direct-ink-write (DIW) printing of inks made from these materials for custom-form battery applications has yet to be demonstrated. In this work, the deposition of FeS₂ and FeF₃ inks are investigated and optimized using DIW 3D printing to produce custom-form batteries. Two distinct custom form-factors, one on wave-shaped current collectors and the other on cylindrical current collectors, are demonstrated and shown to exhibit performance similar to coin cells when conventional Celgard separators are used. Additionally, FeF₃ cells are integrated with a DIW printed separator consisting of an electrolyte exchanged PVDF-HFP based ionogel [1], which resulted in 5-7 stable charge/discharge cycles before degradation occurred. Meanwhile, in FeS₂inks, it was found that cathodes with a ridged surface, produced from the filamentary extrusion of highly concentrated inks (60-70% solids w/w%) exhibited optimal power, uniformity, and stability when cycled at higher rates (in excess of C/10) [2]. Overall, DIW printing of conversion cathodes is demonstrated to be a viable path toward the making of custom-form conversion lithium batteries. More broadly, surface ridging is found to optimize rate capability, a finding that may have broad impact beyond FeS₂, FeF₃ and DIW extrusion.<br/><br/>[1] A.S. Lapp, L.C. Merrill, B.R. Wygant, D.S. Ashby, A.S. Bhandarkar, A. Zhang, E.J. Fuller, K.L. Harrison, T.N. Lambert, and A.A. Talin. Room Temperature Pseudo-Solid State Iron Fluoride Conversion Battery with High Ionic Conductivity and Low Interfacial Resistance. 2022.<br/><br/>[2] J.A. Cardenas, J.P. Bullivant, I.V. Kolesnichenko, D.J. Roach, M.A. Gallegos, E.N. Coker, T.N. Lambert, E. Allcorn, A.A. Talin, A.W. Cook, and K.L. Harrison. 3D Printing of Ridged FeS2 Cathodes for Improved Rate Capability and Custom-Form Lithium Batteries. <i>ACS Applied Materials & Interfaces</i> 14, 45342-45351. 2022.