Deciphering and Integrating Functionalized Side Chains for High Ion-Conductive Elastic Ternary Copolymer Solid-State Electrolytes for Safe Lithium Metal Batteries.

A critical challenge in solid polymer lithium batteries is developing a polymer matrix that can harmonize ionic transportation, electrochemical stability, and mechanical durability. We introduce a novel polymer matrix design by deciphering the structure-function relationships of polymer side chains. Leveraging the molecular orbital-polarity-spatial freedom design strategy, a high ion-conductive hyperelastic ternary copolymer electrolyte (CPE) is synthesized, incorporating three functionalized side chains of poly-2,2,2-Trifluoroethyl acrylate (PTFEA), poly(vinylene carbonate) (PVC), and polyethylene glycol monomethyl ether acrylate (PEGMEA). It is revealed that fluorine-rich side chain (PTFEA) contributes to improved stability and interfacial compatibility; the highly polar side chain (PVC) facilitates the efficient dissociation and migration of ions; the flexible side chain (PEGMEA) with high spatial freedom promotes segmental motion and interchain ion exchanges. The resulting CPE demonstrates an ionic conductivity of 2.19 × 10-3 S cm-1 (30 °C), oxidation resistance voltage of 4.97 V, excellent elasticity (2700%), and non-flammability. The outer elastic CPE and the inner organic-inorganic hybrid SEI buffer intense volume fluctuation and enable uniform Li+ deposition. As a result, symmetric Li cells realize a high CCD of 2.55 mA cm-2 and the CPE-based Li||NCM811 full cell exhibits a high-capacity retention (~90%, 0.5 C) after 200 cycles.

Enabling an Inorganic-Rich Interface via Cationic Surfactant for High-Performance Lithium Metal Batteries.

An anion-rich electric double layer (EDL) region is favorable for fabricating an inorganic-rich solid-electrolyte interphase (SEI) towards stable lithium metal anode in ester electrolyte. Herein, cetyltrimethylammonium bromide (CTAB), a cationic surfactant, is adopted to draw more anions into EDL by ionic interactions that shield the repelling force on anions during lithium plating. In situ electrochemical surface-enhanced Raman spectroscopy results combined with molecular dynamics simulations validate the enrichment of NO3-/FSI- anions in the EDL region due to the positively charged CTA+. In-depth analysis of SEI structure by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry results confirmed the formation of the inorganic-rich SEI, which helps improve the kinetics of Li+ transfer, lower the charge transfer activation energy, and homogenize Li deposition. As a result, the Li||Li symmetric cell in the designed electrolyte displays a prolongated cycling time from 500 to 1300 h compared to that in the blank electrolyte at 0.5 mA cm-2 with a capacity of 1 mAh cm-2. Moreover, Li||LiFePO4 and Li||LiCoO2 with a high cathode mass loading of > 10 mg cm-2 can be stably cycled over 180 cycles.