Correlative Electron-Ion Beam Analysis of the Effect of Lithiophilic Interlayers on Regulating the Li+ Flux Distribution in Anode Free Solid-State Batteries.

Anode-free solid-state batteries (AFSSBs) are promising candidates for next-generation high-energy-density batteries, but their widespread use is impeded by nonuniform lithium plating on the anode-side current collector (CC), which compromises stability and cycle life. Although the use of lithiophilic interlayers exhibits uniform Li plating, the underlying mechanisms by which they regulate lithium deposition are not yet fully understood. Here, a correlative focused ion beam-scanning electron microscopy-secondary ion mass spectrometry (FIB-SEM-SIMS) imaging approach combined with lithium isotope tracing is employed to investigate Li plating on different CC substrates. Half-cells with 6Li-enriched counter electrode and gel polymer electrolyte were assembled using bare Cu CC and Cu CC coated with 20 nm Ag and Au interlayers as working electrodes. Chronopotentiometry measurements revealed a nucleation overpotential of 59 mV for bare Cu CC, which decreased to below 1 mV for interlayer-coated substrates. Postmortem FIB-SEM-SIMS analysis was performed to correlate the electrochemical measurements with Li nucleation behavior of these substrates and investigate how differing Li nucleation mechanisms affected the subsequent distribution of Li+ flux. SEM data revealed a pronounced higher areal density of Li electrodeposits on interlayer coated substrates compared to bare Cu CC, while SIMS isotope mapping confirmed more uniform spatial distribution of Li+ flux for the interlayer coated substrates compared with bare Cu CC. Overall, the insights from this study highlight the critical role of CC substrate properties in developing high-performance AFSSBs.