Enabling metal substrates for garnet-based composite cathodes by laser sintering

Abstract

In this study, a laser irradiation method developed by Fraunhofer ILT was used to sinter screen-printed cathode layers of LiCoO2 (LCO) and Li7La3Zr2O12 (LLZO) directly on a stainless steel current collector. The laser sintering method was proved to be a promising method to sinter the composite cathode onto steel with greatly reduced side reactions and material degradation. In comparison, conventional sintering and another light-absorption-based sintering method, namely rapid thermal processing (RTP) in a lamp furnace, led to almost complete decomposition of the LLZO phase accompanying with the detrimental formation of LaCoO3 and CoO. Phase and morphology analysis of the laser-sintered cathodes using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy confirmed sintering of LCO and LLZO through the layer with small amounts of secondary phases (LaCoO3, Li0.5La2Co0.5O4 and CoO). The resulting porous matrix of the laser-sintered cathode was infiltrated with a polyethylene oxide (PEO) electrolyte to connect the cathode to an LLZO separator and a Li metal anode without an additional sintering step. This model cell was used to evaluate the electrochemical activity of the laser-sintered composite cathodes, which exhibited a specific discharge capacity of 102 mAh g−1 at 4.0 V in the first electrochemical cycle.