Good safety, high interfacial compatibility, low cost, and facile processability make polymer‐based solid electrolytes promising materials for next‐generation batteries. Key issues related to polymer‐based solid electrolytes, such as synthesis methods, ionic conductivity, and battery architecture, are investigated in past decades. However, mechanistic understanding of the ionic conduction is still lacking, which impedes the design and optimization of polymer‐based solid electrolytes. In this review, the ionic conduction mechanisms and optimization strategies of polymer‐based solid electrolytes, including solvent‐free polymer electrolytes, composite polymer electrolytes, and quasi‐solid/gel polymer electrolytes, are summarized and evaluated. Challenges and strategies for enhancing the ionic conductivity are elaborated, while the ion‐pair dissociation, ion mobility, polymer relaxation, and interactions at polymer/filler interfaces are highlighted. This comprehensive review is especially pertinent for the targeted enhancement of the Li‐ion conductivity of polymer‐based solid electrolytes.

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Electrolytes with high ionic transference number hold great promise for reducing battery polarizations and achieving safe energy storage. Herein, single-ion electrolytes containing α-LiAlO2@γ-Al2O3 nanosheets as fillers in PVDF-HFP are prepared....

Sodium metal batteries are promising for cost‐effective energy storage, however, the sluggish ion transport in electrolytes and detrimental sodium‐dendrite growth stall their practical applications. Herein, a cross‐linking quasi‐solid electrolyte with a high ionic conductivity of 1.4 mS cm−1 at 25 °C is developed by in‐situ polymerizing poly (ethylene glycol) diacrylate‐based monomer. Benefiting from the refined solvation structure of Na+ with a much lower desolvation barrier, random Na+ diffusion on the Na surface is restrained, so that the Na dendrite formation is suppressed. Consequently, symmetrical Na||Na cells employing the electrolyte can be cycled >2000 h at 0.1 mA cm−2. Na3V2(PO4)3||Na batteries reveal a high discharge specific capacity of 66.1 mAh g−1 at 15 C and demonstrate stable cycling over 1000 cycles with a capacity retention of 83% at a fast rate of 5 C.

Practical applications of polymer electrolytes in lithium (Li) metal batteries with high‐voltage Ni‐rich cathodes have been hindered by the dendrite growth and poor oxidative stability of electrolytes. Herein, a self‐healing polymer electrolyte is developed by in situ copolymerization of 2‐(3‐(6‐methyl4‐oxo‐1,4‐dihydropyrimidin‐2‐yl)ureido)ethyl methacrylate (UPyMA) and ethylene glycol methyl ether acrylate (EGMEA) monomers. With the electrolyte, the dendrite growth is inhibited by spontaneously repairing dendrite‐induced defects, cracks, and voids at the Li/electrolyte interface; the suppressed dendrite growth and associated electro‐chemo behaviors are visualized by the kinetic Mont‐Carlo simulation. Benefitting from the high ionic conductivity, wide electrochemical window and good interfacial stability, the self‐healing polymer electrolyte enables stable cycling of the LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode under 4.7 V, achieving a high specific capacity of ≈228.8 mAh g−1 and capacity retention of 80.4% over 500 cycles. The new electrolyte is very promising for developing highly safe and dendrite‐free Li metal batteries with high energy density.