Actual
parallel-plate architecture of lithium-ion batteries consists
of lithium-ion diffusion in one dimension between the electrodes.
To achieve higher performances in terms of specific capacity and power,
configurations enabling lithium-ion diffusion in two or three dimensions
is considered. With a view to build these complex three-dimensional
(3D) battery architectures avoiding the electrodes interpenetration
issues, this work is focused on fused deposition modeling (FDM).
In this study, the formulation and characterization of a 3D-printable
graphite/polylactic acid (PLA) filament, specially designed to be
used as negative electrode in a lithium-ion battery and to feed a
conventional commercially available FDM 3D printer, is reported. The
graphite active material loading in the produced filament is increased
as high as possible to enhance the electrochemical performance, while
the addition of various amounts of plasticizers such as propylene
carbonate, poly(ethylene glycol) dimethyl ether average M
n ∼ 2000, poly(ethylene glycol) dimethyl ether
average M
n ∼ 500, and acetyl tributyl
citrate is investigated to provide the necessary flexibility to the
filament to be printed. Considering the optimized plasticizer composition,
an in-depth study is carried out to identify the electrical and electrochemical
impact of carbon black and carbon nanofibers as conductive additives.
Among the 3D-printing technologies, fused deposition modeling (FDM) represents a promising route to enable direct incorporation of the battery within the final 3D object. Here, the preparation and characterization of lithium iron phosphate/polylactic acid (LFP/PLA) and SiO2/PLA 3D-printable filaments, specifically conceived respectively as positive electrode and separator in a lithium-ion battery is reported. By means of plasticizer addition, the active material loading within the positive electrode is raised as high as possible (up to 52 wt.%) while still providing enough flexibility to the filament to be printed. A thorough analysis is performed to determine the thermal, electrical and electrochemical effect of carbon black as conductive additive in the positive electrode and the electrolyte uptake impact of ceramic additives in the separator. Considering both optimized filaments composition and using our previously reported graphite/PLA filament for the negative electrode, assembled and “printed in one-shot” complete LFP/Graphite battery cells are 3D-printed and characterized. Taking advantage of the new design capabilities conferred by 3D-printing, separator patterns and infill density are discussed with a view to enhance the liquid electrolyte impregnation and avoid short-circuits.
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