Solid State Batteries

Impact of Lithium Metal Impurities on Lithium Stripping Behavior Lithium metal foils for solid-state batteries typically have impurities, such as sodium, in the 0.1% to 1% range. TOFSIMS and XPS data reveals that for reservoir-free cells, lithium electrodeposited onto the negative current collector is significantly purer than commercial foils because of selective ion transport of Li+ through the solid electrolyte. Electrochemical testing of low-purity and high-purity lithium foils showed that impurities negatively affect accessible discharge capacity by accumulating at the solid electrolyte interphase and causing kinetic hindrance. Sodium-rich layers restrict lithium diffusion and create voids which localize current flow and increase interfacial resistance. This work does contrast with findings from other studies, but this could be explained by samples with different mechanical properties.

Influence of impurity content on accessible lithium capacity during stripping.

The role of microstructure and mechanical properties is therefore a major focus for future work. Although electrodeposited lithium exhibited higher stripping capacity than both foils, the purity relationship does not necessarily extend to deposited lithium films.

Purity of lithium metal plays a critical role on stripping performance for lithium foils in solid-state batteries and should always be specified when reporting cell data.

Source: 1 Nature Communications 16.1 2025 5395. 2 Energy Storage Materials 74 2025 103975.

Measurement of impurity content in various lithium samples. a) XPS spectra and b) calculated sodium content.

Impact of lithium purity in (reservoir-free) solid-state batteries. a) Voltage profile and interface evolution of b) low-purity foil and c) high-purity foil.

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