In Situ Nanoscale Probing of Lithium‐Aluminum Alloying / De‐Alloying Kinetics and Mechanical Failure in All‐Solid‐State Batteries

Alloy anodes with high specific capacity are extensively utilized in all-solid-state batteries (ASSBs). However, they are challenged by interfacial kinetic and mechanical issues. Real-time investigation of interfacial failure mechanisms at the nanoscale is crucial for optimizing the alloy anodes. Utilizing the high spatial resolution and real-time imaging capabilities of electrochemical atomic force microscopy (EC-AFM), we discovered that Li₁Al₁ alloying unevenly, and the delithiated phase Al with its sluggish kinetics hinders the de-alloying processes. Combining the high mechanical modulus of Li₁Al₁ and Al leads to electrode fracture. This kinetic-mechanical coupling failure diminishes the reversibility of the Al anode. To weaken the kinetic-mechanical coupling failure, we employ a co-sintering reaction between Al and Li₆PS₅Cl (LPSCl), introducing Al₂S₃ and P₂S₇ ^4-, followed by Al₂S₃ in situ lithiation to Li₉Al₄. This process improved interfacial charge transfer and mitigated mechanical failure. Consequently, the Li-anode-less ASSBs maintain 90.2% retention rate after 2000 h (420 cycles) and 87.4% retention rate after 3500 h (750 cycles) at an areal capacity of 2.9 mAh cm^- ² and low N/P ratio of 1.8 with a high average coulombic efficiency of 99.98%. Such tracking of the alloy interfacial reaction provides an in-depth understanding of kinetic-mechanical coupled failure and thus benefits the alloy anode optimization.