Stress‐Regulated Li Plating in Hybrid Ag–Carbon/Carbon Nanofiber Anodes for Durable All‐Solid‐State Batteries

ABSTRACT

All‐solid‐state batteries (ASSBs) with Li‐metal or Li‐metal‐free anodes enable high energy density, yet high‐loading cathodes induce severe mechanical instability, leading to rapid cell failure. Herein, we identify stress accumulation caused by repetitive Li plating/stripping as a critical degradation origin in ASSBs and propose a mechanically adaptive Ag–carbon/carbon nanofiber (CNF) hybrid anode to address this challenge. Operando pressure analysis and mechanical modeling reveal that increasing cathode areal capacity substantially amplifies pressure fluctuations and dynamic mechanical instability, leading to interfacial disruption and short‐circuiting. To mitigate this behavior, the Ag–C interlayer and porous CNF framework were independently customized to provide complementary electrochemical regulation and mechanical buffering functions. The Ag–C layer promotes uniform Li nucleation through Ag–Li alloy‐assisted interfacial regulation, while the porous CNF host accommodates volumetric changes and dissipates stress. Phase‐field modeling and microstructural analyses reveal sequential Ag–Li alloying within the Ag–C interlayer, CNF lithiation and pore filling, and controlled interfacial Li deposition, thereby spatially redistributing volumetric expansion. Consequently, the Ag–C/CNF architecture significantly reduces pressure fluctuation and enables stable cycling over 250 cycles under high‐loading conditions (∼5 mAh cm ⁻² ). Furthermore, stable pouch‐cell operation is demonstrated under practical stack pressures of 1 and 2 MPa, highlighting a viable strategy for mechanically robust high‐energy‐density ASSBs.