3D printing of hybrid MoS2-graphene aerogels as highly porous electrode materials for sodium ion battery anodes

This study reports a 3D freeze-printing method that integrates inkjet printing and freeze casting to control both the microstructure and macroporosity via formation of ice microcrystals during printing. A viscous aqueous ink consisting of a molecular MoS2 precursor (ammonium thiomolybdate) mixed with graphene oxide (GO) nanosheets is used in the printing process. Post-treatments by freeze-drying and reductive thermal annealing convert the printed intermediate mixture into a hybrid structure consisting of MoS2 nanoparticles anchored on the surface of 2D rGO nanosheets in a macroporous framework, which is fully characterized with FESEM, TEM, XRD, Raman spectroscopy and TGA. The resulting hybrid MoS2-rGO aerogels are studied as anodes for sodium ion batteries. They present a high initial specific capacity over 429 mAh/g at C/3.3 rate in the potential range of 2.5–0.10 V (vs Na+/Na). The process involves both reversible 2 Na+ insertion and slow irreversible conversion of MoS2 to metallic Mo. At higher rates, the conversion reaction is suppressed and the electrode is dominated by fast Na+ intercalation with good stability. This demonstrates that the 3D printing technology can be used as a processing technique to control the materials properties for energy storage. Keywords: 3D printing, Hybrid MoS2/graphene aerogel, Freeze-casting, Sodium ion battery, Porous electrode materials