Development of a high particle loading novel copper ink for the fabrication of a three-dimensional hierarchical porous structure using direct ink writing and sintering

Abstract

Recently, the direct ink writing (DIW) of hierarchical porous copper $(Cu)$ (HP-${\text{Cu}}$) for lithium metal battery applications has attracted significant attention. To achieve this, $Cu$ ink with ideal rheological properties and high particle loading is necessary. However, to date, no work focusing on systematic $Cu$ ink development with $Cu$ particle loading more than 95 $wt\%$ has been reported. Hence, in the present work, a novel $Cu$ ink with a particle loading of more than 95 $wt\%,$ and polylactic acid (PLA) as a binder has been developed. The rheological behavior of the $Cu$ ink with different amounts of $Cu$ loading i.e. 93, 95 and 97 $wt\%$ respectively were investigated. Moreover, the modelling using the Herschel-Bulkey equation was done to establish the rheology. All the prepared inks showed viscoelastic and shear thinning behaviour. Moreover, the ink having 97$wt\%$ $Cu$ loading exhibited optimum rheology with a shear elastic modulus of around ${10}^{5} Pa$ in the linear viscoelastic area. Subsequently, DIW using the prepared $Cu$ inks followed by sintering was performed. The morphological study of the 3D printed $Cu$ green samples and sintered samples was performed and it was found that the variation in $Cu$ particle loading significantly affected the density and volumetric shrinkage. Finally, an HP-${\text{Cu}}$ sample having a pore size less than 200 $\mu m$ was fabricated using DIW and sintering to validate the efficacy of the developed $Cu$ ink. Proper interparticle bonding between the $Cu$ particles was observed indicating that the developed ink is suitable for the fabrication of complex $Cu$ parts for lithium metal battery application.