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.

The grain boundary electrical properties of high purity <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">ZrO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>ZrO2 ceramic materials doped with 2, 3, and 8 mol % <mml:math display="inline"><mml:msub><mml:mo>Y</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mo>O</mml:mo><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo></mml:math>Y2O3, and 8 mol % <mml:math display="inline"><mml:msub><mml:mo>Y</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mo>O</mml:mo><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:math>Y2O3 co-doped with 0.4 mol % <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">Al</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mo>O</mml:mo><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:math>Al2O3 were studied in the temperature range of 200 to 500°C by electrochemical techniques and were theoretically analyzed. Although the presence of a siliceous phase is shown to be a major cause for the grain boundary blocking effect, the grain boundary properties appear to be significantly influenced by space charges, particularly in materials of high purity. The oxygen vacancy distribution and the grain boundary resistivity were calculated for 8 mol % <mml:math display="inline"><mml:msub><mml:mo>Y</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mo>O</mml:mo><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:math>Y2O3 doped <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">ZrO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>ZrO2 by assuming double Schottky barriers, and the results were compared with the experiment. It is shown that reasonable space charge potentials lead to grain boundary effects which are consistent with the experimental features. In contrary to the bulk in which defect associates prevail (at temperatures <560°C), in the boundary regions, association effects can be assumed to be much less pronounced due to the vacancy depletion. © 2001 The Electrochemical Society. All rights reserved.

The stable operation of lithium-based batteries at low temperatures is critical for applications in cold climates. However, low-temperature operations are plagued by insufficient dynamics in the bulk of the electrolyte and at electrode|electrolyte interfaces. Here, we report a quasi-solid-state polymer electrolyte with an ionic conductivity of 2.2 × 10⁻⁴ S cm⁻¹ at −20 °C. The electrolyte is prepared via in situ polymerization using a 1,3,5-trioxane-based precursor. The polymer-based electrolyte enables a dual-layered solid electrolyte interphase formation on the Li metal electrode and stabilizes the LiNi_0.8Co_0.1Mn_0.1O₂-based positive electrode, thus improving interfacial charge-transfer at low temperatures. Consequently, the growth of dendrites at the lithium metal electrode is hindered, thus enabling stable Li||LiNi_0.8Co_0.1Mn_0.1O₂ coin and pouch cell operation even at −30 °C. In particular, we report a Li||LiNi_0.8Co_0.1Mn_0.1O₂ coin cell cycled at −20 °C and 20 mA g⁻¹ capable of retaining more than 75% (i.e., around 151 mAh g⁻¹) of its first discharge capacity cycle at 30 °C and same specific current.