High-Voltage All-Solid-State Lithium Battery with Sulfide-Based Electrolyte: Challenges for the Construction of a Bipolar Multicell Stack and How to Overcome Them

Solid electrolytes can be the key for the desired goal of increased safety and specific energies of batteries. On a cell and battery pack level, the all-solid nature and the absence of liquid electrolyte leakage are considered to enable safe and effective performance realization of the rechargeable Li metal electrode and bipolar cell stacking, respectively. Well performing Li metal cells with high-energy/voltage positive electrodes such as LiNi0.6Mn0.2Co0.2O2 (NMC622) can already be cycled when using a blend of the sulfidic solid electrolyte such as β-Li3PS4 (LPS) and Li salt in poly(ethylene)oxide (PEO). However, operation of a bipolar stack using these cell materials utilizing the common Al/Cu clad as bipolar plate results in an immediate short circuit, because of an ionic intercell connection via molten LiTFSI/PEO. Oversizing the area of the bipolar plates can prevent such a short circuit and indeed enables a partial charge of the stack, but after a certain time, the next cell failure is observed, consisting of severe, sulfur caused, corrosion of copper which was used as metal substrate for the lithium anode. The exchange of the sulfide incompatible Cu collector by (also area-oversized) stainless steel can finally enable a failure-free performance of the bipolar cell stack, which performs similar to a single cell with regard to cycling stability.