Composite Solid Electrolytes Inhibit Dendrite Penetration for Stable All-Solid-State Lithium Batteries Revealed by 3D EPR Imaging

The practical application of all-solid-state lithium metal batteries (ASSLBs) based on Li₆PS₅Cl (LPSC) is severely hindered by uncontrolled lithium (Li) dendrite penetration, which ultimately leads to soft short circuits and catastrophic battery failure. To address this critical challenge, this work proposes a Li₁₀GeP₂S₁₂-Li₆PS₅Cl (LGPS-LPSC) composite solid electrolyte interlayer between the composite cathode layer and the LPSC bulk layer, which effectively prevents lithium dendrites from penetrating the electrolyte and then enhances the long-term cycling stability. Electrochemically, Li|Li symmetric cells integrated with this composite electrolyte achieve stable operation for 2000 h at a current density of 0.5 mA cm^-2, while Li|LiCoO₂ full cells with composite electrolyte exhibit excellent cycling stability, retaining 69.51% of their initial capacity after 900 cycles at a rate of 1 C. Via 3D electron paramagnetic resonance (EPR) imaging, in situ 2D EPR imaging, and nanoindentation measurements, it is revealed that the LGPS-LPSC composite electrolyte exerts a dual function: it not only enhances the mechanical strength of the electrolyte system to physically block Li dendrite penetration but also tailors ionic conductivity pathways to facilitate uniform Li plating at the Li metal anode interface.