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Garnet‐based solid‐state Li‐metal batteries (GSSBs) have the merits of high energy density and high safety. However, the realization of a stable and well‐matched Li|garnet interface for GSSBs remains challenging due to electron leakage and lithiophobic Li2CO3 impurity. To address these issues, herein, new surface chemistry is reported that converts the undesired Li2CO3 contaminant into an ultra‐thin lithium polyphosphate (Li‐PPA) layer through anhydrous polyphosphoric acid ‐induced in situ substitution reaction without damaging the water‐sensitive garnet electrolyte. In particular, the Li‐PPA interlayer not only facilitates the homogenous spreading of molten Li but also creates a robust electron‐blocking shield to suppress Li dendrite formation. As a result, the assembled Li symmetric cell exhibits a low interfacial impedance (4 Ω cm2) and high critical current density (1.8 mA cm−2) at 25 °C, which enables the cell to continuously cycle over 2500 h at 0.2 mA cm−2. Furthermore, the GSSBs paired with LiFePO4 deliver a high capacity of 149.3 mAh g−1 at 1 C and maintain 92.3% of the initial capacity after 500 cycles and can be used for solar energy storage, suggesting the feasibility of this interfacial engineering strategy for GSSBs. [ABSTRACT FROM AUTHOR]

All‐solid‐state lithium batteries (ASSBs) have the potential to trigger a battery revolution for electric vehicles due to their advantages in safety and energy density. Screening of various possible solid electrolytes for ASSBs has revealed that garnet electrolytes are promising due to their high ionic conductivity and superior (electro)chemical stabilities. However, a major challenge of garnet electrolytes is poor contact with Li‐metal anodes, resulting in an extremely large interfacial impedance and severe Li dendrite propagation. Herein, an innovative surface tension modification method is proposed to create an intimate Li | garnet interface by tuning molten Li with a trace amount of Si3N4 (1 wt%). The resultant Li‐Si‐N melt can not only convert the Li | garnet interface from point‐to‐point contact to consecutive face‐to‐face contact but also homogenize the electric‐field distribution during the Li stripping/depositing process, thereby significantly decreasing its interfacial impedance (1 Ω cm2 at 25 °C) and improving its cycle stability (1000 h at 0.4 mA cm−2) and critical current density (1.8 mA cm−2). Specifically, the all‐solid‐state full cell paired with a LiFePO4 cathode delivered a high capacity of 145 mAh g−1 at 2 C and maintained 97% of the initial capacity after 100 cycles at 1 C. [ABSTRACT FROM AUTHOR]

Rigid‐flexible coupled composite polymer electrolytes (CPEs, e.g., polyethylene oxide/Li6.4La3Zr1.4Ta0.6O12, PEO/LLZTO) hold the promise of integrating the respective merits of organic polymer electrolyte and inorganic ceramic fillers to achieve better all‐solid‐state batteries (ASSBs), but commonly suffer from poor synergistic effect owing to the ionically/electronically resistive layer on the ceramic surface. Representatively, the Li2CO3 passivation layer‐isolated LLZTO not only contributes minimally to the Li+ conduction in PEO/LLZTO CPE, but also narrows the available electrochemical window. Herein, an interfacial reconstruction strategy is disclosed based on mild liquid‐phase chemical reaction and subsequent self‐assembly, allowing the detrimental Li2CO3 to fully react with succinic anhydride (SA), and simultaneously constructing a robust ultra‐thin lithium succinate (SALi) ionic conductor shell to eradicate its regeneration. Accordingly, the obtained PEO/LLZTO@SALi (PLS) CPE shows a high room‐temperature ionic conductivity (1.2 × 10−4 S cm−1), a wide electrochemical window (4.8 V), a notable Li+ transference number (0.37), as well as nonflammability and exceptional compatibility with Li metal in Li/Li symmetric cells (2000 h at 0.2 mA cm−2). More encouragingly, the Li/PLS CPE/LiFePO4 full ASSB maintains an ultrahigh capacity retention of 84.3% after 1400 cycles at room temperature. This work propels the design of high‐performance CPEs through the interfacial modulation of inorganic ceramic fillers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Contact issue of the anode-electrolyte interface was tackled by a Li-Mo composite. • Lower cohesive energy and higher binding energy are beneficial to better contact. • Symmetric cell shows a high critical current density and a stable 1200-h cycling. • A full cell with a LiFePO 4 cathode presented stable performance for 200 cycles. • The work provides a facile and feasible way to overcome interface problems. Interface issues are the biggest challenges that hindering the commercialization of solid-state lithium metal batteries (SSLMBs). Here, we propose a novel strategy targeting for effectively resolving the tedious lithium-garnet solid electrolyte interface problem from the lithium side. We intentionally introduce α-MoO 3 nanobelts into the molten metallic lithium, forming a Li-Mo composite. Compared to molten lithium, the composite improves wettability on the garnet electrolyte. As revealed by density functional theory calculations, such improvement could be ascribed to the reduced cohesive energy and the improved interface binding energy to the LLZTO. Intimate surface contact can be easily achieved without complicated surface treatment, which not only significantly reduces the interface resistance to ~ 1 Ω cm2, but could also effectively inhibits the generation of lithium dendrites. These features ensure a significant critical current density of 1700 µA cm−2 and a stable electrochemical Li plating/stripping process for more than 1200 h. A full cell with the Li-Mo composite anode and LiFePO 4 cathode also presents a fairly stable cycling performance at room temperature. Different from most previous strategies that try to tackle the interface issues from the electrolyte side, our research results suggest that designing lithium composite anodes with low cohesive energy and high interface binding energy to the solid electrolyte is an attractive and feasible solution to overcome interface problems. [ABSTRACT FROM AUTHOR]