In solid polymer electrolytes (SPEs) based Li-metal batteries, the inhomogeneous migration of dual-ion in the cell results in large concentration polarization and reduces interfacial stability during cycling. A special molecular-level designed polymer electrolyte (MDPE) is proposed by embedding a special functional group (4-vinylbenzotrifluoride) in the polycarbonate base. In MDPE, the polymer matrix obtained by copolymerization of vinylidene carbonate and 4-vinylbenzotrifluoride is coupled with the anion of lithium-salt by hydrogen bonding and the "σ-hole" effect of the CF bond. This intermolecular interaction limits the migration of the anion and increases the ionic transfer number of MDPE (t Li + = 0.76). The mechanisms of the enhanced t Li + of MDPE are profoundly understood by conducting first-principles density functional theory calculation. Furthermore, MDPE has an electrochemical stability window (4.9 V) and excellent electrochemical stability with Li-metal due to the CO group and trifluoromethylbenzene (ph-CF 3 ) of the polymer matrix. Benefited from these merits, LiNi 0.8 Co 0.1 Mn 0.1 O 2 -based solid-state cells with the MDPE as both the electrolyte host and electrode binder exhibit good rate and cycling performance. This study demonstrates that polymer electrolytes designed at the molecular level can provide a broader platform for the high-performance design needs of lithium batteries.

Solid‐state polymer electrolytes (SPEs) for all‐solid‐state batteries (ASSBs) have received considerable attention owing to excellent processability, good flexibility, high safety levels, and superior thermal stability. However, the practical application of SPEs is currently restricted by their low ionic conductivity, narrow electrochemical oxidation window, and poor long‐term stability of lithium (Li) metal. These challenges are mainly related to the polymer molecular structures, the dynamic of the polymer electrolyte, and the polymer compound stability at the electrode‐electrolyte interface. In this review, we provide recent strategies and discuss strategies of interest for applications to high‐energy‐density ASSB, particularly the molecular design, ion‐transport dynamic mechanisms of solid polymer electrolytes, and organic‐inorganic composite. Based on recent work, perspectives on future research directions are discussed for developing solid polymer electrolytes.

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Utilization of lithium (Li) metal anodes in all‐solid‐state batteries employing sulfide solid electrolytes is hindered by diffusion‐related dendrite growth at high rates of charge. Engineering ex‐situ Li‐intermetallic interlayers derived from a facile solution‐based conversion‐alloy reaction is attractive for bypassing the Li0 self‐diffusion restriction. However, no correlation is established between the properties of conversion‐reaction‐induced (CRI) interlayers and the deposition behavior of Li0 in all‐solid‐state lithium‐metal batteries (ASSLBs). Herein, using a control set of electrochemical characterization experiments with LixAgy as the interlayer in different battery chemistries, this work identifies that dendritic tolerance in ASSLBs is susceptible to the surface roughness and electronic conductivity of the CRI‐alloy interlayer. This work thereby tailors the CRI‐alloy interlayer from the typical mosaic structure to a hierarchical gradient structure by adjusting the pit corrosion kinetics from the (de)solvation mechanism to an adsorption model, yielding a smooth organic‐rich outer layer and a composition‐regulated inorganic‐rich inner layer composed mainly of lithiophilic LixAgy and electron‐insulating LiF. Ultimately, desirable roughness, conductivity, and diffusivity are integrated simultaneously into the tailored CRI‐alloy interlayer, resulting in dendrite‐free and dense Li deposition beneath the interlayer capable of improving battery cycling stability. This work provides a rational protocol for the CRI‐alloy interlayer specialized for ASSLBs.

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