Polymer‐based solid electrolytes (PSEs) have attracted tremendous interests for the next‐generation lithium batteries in terms of high safety and energy density along with good flexibility. Remarkable performances have been demonstrated in PSEs, which endowed PSEs with the potential to replace liquid electrolytes to meet the market demands. In this review, polymer matrices, different polymer architectures, and functional filler materials used in PSEs are discussed to explore the design concepts, methodologies, working mechanisms, and pros and cons of various PSEs. In addition, their recent notable applications in all‐solid‐state lithium ion batteries, lithium–sulfur batteries, suppression of lithium dendrites, and flexible lithium batteries are also introduced. Finally, the challenges and future prospects are sketched to provide strategies to explore novel PSEs for high‐performance all‐solid‐state lithium batteries.

Metallic Li is considered the most promising anode material for high‐energy density batteries due to its high theoretical capacity and low electrochemical potential. However, commercialization of the Li anode has been hampered by the safety issue associated with Li‐dendrite growth resulting from uneven Li‐ion deposition and an unstable solid electrolyte interphase (SEI). Herein, an in situ prepared 10 nm thin film of covalent organic framework (COF) uniformly covered on the Li anode (COF‐Li) is used as an artificial SEI layer for Li plating/striping stabilization and Li dendrite inhibition. Abundant microcellular structures in the COF can redistribute the Li‐ion flux and lead to the homogeneous plating/stripping process. Meanwhile, the superhard mechanical properties and mechanical behavior during needling of the ultrathin COF film is studied via the digital pulsed force mode equipped in atomic force microscopy, illustrating a high Young's modulus of 6.8 GPa that is strong enough to resist dendrite growth. As a result, stable cycling for 400 h is achieved in the COF‐Li symmetrical cell at a current density of 1 mA cm−2, and the internal short circuit is effectively blocked by COF‐Li in Li–S batteries.

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Novel hierarchically porous carbon materials with very high surface areas, large pore volumes and high electron conductivities were prepared from silk cocoon by carbonization with KOH activation. The prepared novel porous carbon-encapsulated sulfur composites were fabricated by a simple melting process and used as cathodes for lithium sulfur batteries. Because of the large surface area and hierarchically porous structure of the carbon material, soluble polysulfide intermediates can be trapped within the cathode and the volume expansion can be alleviated effectively. Moreover, the electron transport properties of the carbon materials can provide an electron conductive network and promote the utilization rate of sulfur in cathode. The prepared carbon-sulfur composite exhibited a high specific capacity and excellent cycle stability. The results show a high initial discharge capacity of 1443 mAh g(-1) and retain 804 mAh g(-1) after 80 discharge/charge cycles at a rate of 0.5 C. A Coulombic efficiency retained up to 92% after 80 cycles. The prepared hierarchically porous carbon materials were proven to be an effective host matrix for sulfur encapsulation to improve the sulfur utilization rate and restrain the dissolution of polysulfides into lithium-sulfur battery electrolytes.

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