Mixed ionic-electronic conductor enabled effective cathode-electrolyte interface in all solid state batteries

One of the main challenges to develop all solid state lithium (Li) metal batteries is the poor contact and thus the high interfacial resistance between electrodes and solid state electrolytes (SSEs). Recently, significant improvements have been made toward effective Li-garnet interfaces however due to the poor conductivity and rigid granular morphology of cathode materials, the cathode-garnet interface is deficient. In this work, we report an effective cathode-garnet interface using a mixed ionic-electronic (MIE) conductor, which enables cycling of all solid state batteries without a liquid or polymer electrolyte interface. The solution-processed two dimensional (2D) layered TiS2 shows MIE conductivity after slow pre-lithiation, resulting in more than 20 times lower interfacial resistance. In addition, solution-processed carbon nanotubes offer a conformal coating for an efficient cathode-current collector interface with enhanced charge transport kinetics. As a result, we demonstrated the first garnet-based truly all solid state battery using solution processed composite cathode. Given the excellent chemical stability of the Li metal anode, garnet SSE, and TiS2 cathode, the all solid state batteries can work at high temperatures from 100 degrees C to 150 degrees C for 400 cycles at current densities up to 1 mA/cm(2). The demonstrated MIE concept for addressing cathode-electrolyte interface can be further extended to other solid state battery chemistries.