(Invited) Investigations on Sulfide Solid-Electrolyte Cathode Interfaces

Advances in solid electrolytes (SEs) with superionic conductivity and stabilized electrode-electrolyte interfaces are key enablers for all solid-state batteries (SSBs) to meet the energy density and cost targets for next generation batteries for electric vehicles. Compared to their ceramic counterparts, sulfide- and thiophosphate-based electrolytes offer several key advantages, including (i) exceptionally high ionic conductivities up to 10-2 S/cm (comparable to non-aqueous liquid electrolytes) as reported for Li10GeP2S12 and Li9.54Si1.74P1.44S11.7Cl0.3, (ii) availability of low temperature and inexpensive synthesis routes to produce glass, glass-ceramic, and crystalline structures, and (iii) soft mechanical properties, which facilitates material processing. Among the drawbacks, sulfides have a narrow electrochemical window, hence limited electrochemical stability against Li-metal and cathodes and poor chemical stability including high sensitivity to moisture. Despite an intrinsic narrow thermodynamic range, most SEs rely on kinetic stability based on slow growth of the interfacial layer that has reasonable ionic conductivity and very low electronic conductivity. In addition to the thermodynamical instability, significant mechanical stresses develop in SE due to (i) volume changes of the electrode material during repeated lithiation (delithiation) and (ii) interface roughening from side reactions upon extended cycling. This effect often termed as “chemo-mechanical effect” results in poor interfacial contact between the SE and cathode. The talk will highlight a few material based approaches towards addressing the interfacial stabilities (as mentioned above) between Li3PS4 SE and lithium-ion cathodes such as NMC. The area specific resistance (ASR) between SE-Cathode interfaces were optimized by coating cathode particles, varying stack pressure and doping the SE compositions. Acknowledgment - This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program