A Conduction-Nucleation-Competition-Guided 3D Adaptive Gradient Buffer for Dendrite-Free All-Solid-State Lithium Metal Batteries.

The existing designs of buffer for all-solid-state Li-metal batteries (ASSLMBs) are mostly limited to static optimization of single functions and lack systematic regulation of the dynamic competition among ionic conduction, electron distribution, and interfacial lithiophilicity. Herein, a conduction-nucleation competition mechanism is proposed firstly, clarifying that lithium deposition is governed by the synergy of these three factors. Guided by this principle, a self-adaptive gradient buffer layer composed of soft carbon and Mg3N2 (SCMN) is designed. After lithiation, the buffer forms a continuous lithiophobic/lithiophilic gradient and subsequently undergoes in-situ conversion into highly ion-conductive Li3N and highly electron-conductive/ lithiophilic Li-C/Li-Mg alloys during electrochemical activation, enabling dynamic interface self-optimization. The gradient structure creates a fast ion-electron dual conduction network, guiding bottom-top lithium deposition within the buffer layer without volume expansion. Consequently, the symmetric cells achieve stable cycling over 1600 h at 1.5 mA cm- 2 and remain stable even under low stack pressure (15 MPa). The LiCoO2-based full cells deliver ultra-stable cycle with 98.5% capacity retention after 200 cycles at 0.1 C. Additionally, the full cells paired with high-voltage LiNi0.8Co0.1Mn0.1O2 cathodes exhibit exceptional cycling stability at high loading (4.45 mg cm-2). This work demonstrates a mechanism-driven design paradigm toward high-energy, long-life ASSLMBs.