Contradictory Structure Design with Li₂CO₃ Retention for Garnet-Based Solid-State Lithium Metal Batteries

Garnet Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) has emerged as a promising candidate for solid-state lithium-metal batteries (SSLMBs). However, the air susceptibility with Li₂CO₃ impurity and severe electron leakage lead to inferior cycling performance, remaining a critical challenge. Herein, a contradictory interface chemistry has been proposed in which normally undesired Li₂CO₃ is deliberately retained and delicately adopted, which can effectively enhance the interfacial stability of Li|LLZTO. The growth behavior of Li₂CO₃ on LLZTO is systematically investigated, while its formation of residual Li₂CO₃ is controllable, which serves as an insulating layer and blocks the electron leakage. Moreover, the porous lithiophilic Li₃PW₁₂O₄₀ (POMs) ensures enhanced interfacial contact and provides three-dimensional Li⁺-channels to accelerate Li⁺ migration. This contradictory structure can efficiently inhibit Li-dendrite penetration at grain boundaries. Therefore, the Li|POMs-LLZTO|NCM full-cell can achieve 97.7% capacity retention after 100 cycles. This facile strategy innovatively repurposes undesired Li₂CO₃ into a functional interlayer, offering prospects to develop large-scale garnet-based SSLMBs.