The Evolution of Pore Volume during Stripping of Lithium, Sodium, and Potassium Metal Electrodes in Solid-State Batteries

Alkali metal solid-state batteries (Li, Na, K) suffer from contact loss at the metal|solid electrolyte interface during stripping (discharge), driven by vacancy accumulation and pore formation. This reduces contact area, increases resistance, and promotes dendrite growth during subsequent plating, eventually leading to battery failure. While lithium has been studied extensively, sodium and potassium remain comparatively underexplored despite their high abundance. Their lower yield strength, larger molar volume, and higher homologous temperature strongly affect interfacial contact evolution. Operando electrochemical dilatometry is used to determine the formed pore volume in sodium and potassium metal anodes, enabling evaluation of the vacancy injection ratio (VIR) and comparison with lithium. At low stack pressure, pores form immediately upon stripping for all three metals. The formed pore volume scales with the molar volume across lithium, sodium, and potassium. Increasing current density enhances contact loss and leads to a weaker increase in the formed pore volume in sodium and potassium, with a fraction of the formed pore volume in potassium located inside the metal bulk. ... mehrIn contrast, lithium shows an initial reduction in the formed pore volume (partial pore collapse), followed by a stronger increase at higher current densities. These findings reveal systematic trends among lithium, sodium, and potassium, suggesting lower yield strengths and smaller molar volumes as favorable material properties. Based on these results, a generalized mechanism for pore formation in alkali metal anodes is proposed.