Long‐Term Cycling Stability and Dendrite Suppression in Garnet‐Type Solid‐State Lithium Batteries via Plasma‐Induced Artificial SEI Layer Formation

Abstract The garnet‐based solid‐state‐electrolyte Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) faces challenges due to its poor contact with Li‐metal, resulting in high interfacial‐resistance and dendrite growth. To address this, an SnO 2 ‐Al (SA) ultra‐thin film on LLZTO is fabricated using direct‐current/radio‐frequency plasma magnetron co‐sputtering. This modification layer reacts with molten Li in situ to form a dense and continuous artificial solid‐electrolyte‐interphase (SEI) layer, composed of Li 2 O, Li‐Al‐O, Li x Sn, and Li 9 Al 4 alloy. Density‐functional‐theory calculations and in situ optical‐microscopy characterization confirm the effectiveness of this interlayer in improving interfacial‐modification. Consequently, an ultrahigh critical‐current‐density of 5.4 mA cm −2 is achieved, effectively preventing lithium‐metal penetration into the bulk electrolyte. The Li symmetric cell with the SA artificial SEI layer cycles stably for 8700 h without dendrite formation, significantly outperforming the SnO 2 modified layer (only 1350 h) and most interface modification layers reported in literature, demonstrating its excellent interfacial‐stability. Additionally, full cells with LiFePO 4 and LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathodes exhibit stable cycling performance (LiFePO 4 : 88.95% capacity retention at the 400 th cycle at 0.5 C; LiNi 0.8 Co 0.1 Mn 0.1 O 2 : 89.16% capacity retention at the 200 th cycle at 0.5 C). This work underscores the significant potential of the plasma magnetron co‐sputtering method for creating artificial SEI layers, paving the way for the practical application of garnet‐type solid‐state batteries.