Mechanistic insight into calendar aging of anode-less all-solid-state batteries

Anode-less all-solid-state batteries (ASSBs) with thin interlayers have emerged as a promising solution capable of addressing the dendrite issues of Li metal anodes and considerably enhancing the energy density. However, only a few studies have investigated the calendar life of anode-free ASSBs. Herein, we reveal the degradation of an anode-less ASSB with a LiNi_0.88Co_0.09Al_0.03O₂ (NCA) cathode, a Li₆PS₅Cl (LPSCl) electrolyte, and an Ag-C interlayer during storage and provide mechanistic insights into the possible calendar aging process. The cell shows a decline in discharge capacity after long-term storage, depending on the storage conditions and, more importantly, exhibits the reduced capacity retention upon subsequent cycling. No microstructural and electrochemical degradation is observed on the anode side; however, the composite cathode stored at a high state of charge (SOC) suffers from severe degradation upon storage. In-depth chemical and structural analyses, coupled with impedance decoupling, reveal that the high-SOC storage facilitates the detrimental interfacial side reactions between NCA and LPSCl, which are accelerated at elevated temperatures. As a strategy to address this issue, we further demonstrate that increasing the external pressure to tens of MPa during storage facilitates the chemical lithiation of NCA, which can effectively alleviate the calendar aging of anode-less ASSBs.