Engineering Ferroelectric Interlayer between Li1.3Al0.3Ti1.7(PO4)3 and Lithium Metal for Stable Solid‐State Batteries Operating at Room Temperature

The poor contact and side reactions between Li1.3Al0.3Ti1.7(PO4)3 (LATP) and lithium (Li) anode cause uneven Li plating and high interfacial impendence, which greatly hinder the practical application of LATP in high‐energy density solid‐state Li metal batteries. In this work, a multifunctional ferroelectric BaTiO3 (BTO)/poly(vinylidene fluoride‐co‐trifluoroethylene‐co‐chlorotrifluoroethylene) (P[VDF‐TrFE‐CTFE]) composite interlayer (B‐TERB) is constructed between LATP and Li metal anode, which not only suppresses the Li dendrite growth, but also improves the interfacial stability and maintains the intimate interfacial contact to significantly decrease the interfacial resistance by two orders of magnitude. The B‐TERB interlayer generates a uniform electric field to induce a uniform and lateral Li deposition, and therefore avoids the side reactions between Li metal and LATP achieving excellent interface stability. As a result, the Li/LATP@B‐TERB/Li symmetrical batteries can stably cycle for 1800 h at 0.2 mA cm−2 and 1000 h at 0.5 mA cm−2. The solid‐state LiFePO4/LATP@B‐TERB/Li full batteries also exhibit excellent cycle performance for 250 cycles at 0.5 C and room temperature. This work proposes a novel strategy to design multifunctional ferroelectric interlayer between ceramic electrolytes and Li metal to enable stable room‐temperature cycling performance. We develop a multifunctional ferroelectric interlayer between Li1.3Al0.3Ti1.7(PO4)3 and lithium metal by introducing the strong ferroelectric material BaTiO3 into P(VDF‐TrFE‐CTFE) polymer (B‐TERB), which can reduce the Li/LATP interfacial impendence, suppress side reactions and more importantly can generate an inverse polarized electric field. Uniform electric field and ion concentration distributions is achieved at the interface of B‐TERB with Li metal anode to induce homogeneous Li‐ions plating.