Suppressing SEI Growth for Al Foil Anode under a Low Stack Pressure with Solid Polymer Electrolytes

Metal foils that alloy with lithium have attracted renewed interest as the issue of continuous solid-electrolyte interphase (SEI) growth can be effectively addressed with solid-state electrolytes (SSEs). However, an impractically high pressure is required to maintain the contact between the foils and inorganic SSEs. Here, we show that a soft polymer solid electrolyte can also alleviate the issue of SEI growth for an Al foil anode at a practically low pressure. Unlike liquid electrolytes, the polymer PVDF-HFP does not infiltrate pits and pores formed during Al lithiation, leading to a more uniform reaction and insignificant SEI growth deep in the anode, as shown by microstructural and compositional analyses of both the surface and the cross section of the anode. It thereby significantly boosts the Coulombic efficiency and the cycling stability of the Al foil anode compared to its liquid counterpart. The work unveils a new path to stabilize alloy anodes for safe, inexpensive solid-state batteries.