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

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.