Polymer electrolytes have attracted great interest for next-generation lithium (Li)-based batteries in terms of high energy density and safety. In this review, we summarize the ion-transport mechanisms, fundamental properties, and preparation techniques of various classes of polymer electrolytes, such as solvent-free polymer electrolytes (SPEs), gel polymer electrolytes (GPEs), and composite polymer electrolytes (CPEs). We also introduce the recent advances of non-aqueous Li-based battery systems, in which their performances can be intrinsically enhanced by polymer electrolytes. Those include high-voltage Liion batteries, flexible Li-ion batteries, Li-metal batteries, lithium-sulfur (Li-S) batteries, lithium-oxygen (Li-O 2 ) batteries, and smart Li-ion batteries. Especially, the advantages of polymer electrolytes beyond safety improvement are highlighted. Finally, the remaining challenges and future perspectives are outlined to provide strategies to develop novel polymer electrolytes for high-performance Li-based batteries.

The lowC oulombic efficiency and serious safety issues resulting from uncontrollable dendrite growth have severely impeded the practical applications of lithium (Li) metal anodes.H erein we report as table quasi-solid-state Li metal battery by employingah ierarchical multifunctional polymer electrolyte (HMPE). This hybrid electrolyte was fabricated via in situ copolymerizing lithium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide (LiMTFSI) and pentaerythritol tetraacrylate (PETEA) monomers in traditional liquid electrolyte,w hichi sa bsorbed in ap oly(3,3-dimethylacrylic acid lithium) (PDAALi)-coated glass fiber membrane.T he well-designed HMPE simultaneously exhibits high ionic conductivity (2.24 10 À3 Scm À1 at 25 8 8C), near-single ion conducting behavior (Li ion transference number of 0.75), good mechanical strength and remarkable suppression for Li dendrite growth. More intriguingly,t he cation permselective HMPE efficiently prevents the migration of negatively charged iodine (I) species,w hich provides the as-developed Li-I batteries with high capacity and long cycling stability.

Due to the high theoretical specific energy, the lithium–oxygen battery has been heralded as a promising energy storage system for applications such as electric vehicles. However, its large over-potentials during discharge–charge cycling lead to the formation of side-products, and short cycle life. Herein, we report an ionic liquid bearing the redox active 2,2,6,6-tetramethyl-1-piperidinyloxy moiety, which serves multiple functions as redox mediator, oxygen shuttle, lithium anode protector, as well as electrolyte solvent. The additive contributes a 33-fold increase of the discharge capacity in comparison to a pure ether-based electrolyte and lowers the over-potential to an exceptionally low value of 0.9 V. Meanwhile, its molecule facilitates smooth lithium plating/stripping, and promotes the formation of a stable solid electrolyte interface to suppress side-reactions. Moreover, the proportion of ionic liquid in the electrolyte influences the reaction mechanism, and a high proportion leads to the formation of amorphous lithium peroxide and a long cycling life (> 200 cycles). In particular, it enables an outstanding electrochemical performance when operated in air.

The advancement of lithium-oxygen (Li-O 2 ) batteries has been hindered by challenges including low discharge capacity, poor energy efficiency, severe parasitic reactions, etc. We report an Li-O 2 battery operated via a new quenching/mediating mechanism that relies on the direct chemical reactions between a versatile molecule and superoxide radical/Li 2 O 2 . The battery exhibits a 46-fold increase in discharge capacity, a low charge overpotential of 0.7 V, and an ultralong cycle life >1400 cycles. Featuring redox-active 2,2,6,6-tetramethyl-1-piperidinyloxy moieties bridged by a quenching-active perylene diimide backbone, the tailor-designed molecule acts as a redox mediator to catalyze discharge/charge reactions and serves as a reusable superoxide quencher to chemically react with superoxide species generated during battery operation. The all-in-one molecule can simultaneously tackle issues of parasitic reactions associated with superoxide radicals, singlet oxygen, high overpotentials, and lithium corrosion. The molecular design of multifunctional additives combining various capabilities opens a new avenue for developing high-performance Li-O 2 batteries.

A novel light-induced C─H amination of heteroarenes can be accomplished with preformed iodine(III) reagents as the combined oxidant and nitrogen source. The reaction requires the use of a small amount of molecular iodine, which under photochemical activation generates in situ an iodine(I) reagent as the initiator of the radical amination reaction. A total of 32 examples exemplify the broad scope of the transformation.

The low Coulombic efficiency and serious safety issues resulting from uncontrollable dendrite growth have severely impeded the practical applications of lithium (Li) metal anodes. Herein we report a stable quasi‐solid‐state Li metal battery by employing a hierarchical multifunctional polymer electrolyte (HMPE). This hybrid electrolyte was fabricated via in situ copolymerizing lithium 1‐[3‐(methacryloyloxy)propylsulfonyl]‐1‐(trifluoromethanesulfonyl)imide (LiMTFSI) and pentaerythritol tetraacrylate (PETEA) monomers in traditional liquid electrolyte, which is absorbed in a poly(3,3‐dimethylacrylic acid lithium) (PDAALi)‐coated glass fiber membrane. The well‐designed HMPE simultaneously exhibits high ionic conductivity (2.24×10−3 S cm−1 at 25 °C), near‐single ion conducting behavior (Li ion transference number of 0.75), good mechanical strength and remarkable suppression for Li dendrite growth. More intriguingly, the cation permselective HMPE efficiently prevents the migration of negatively charged iodine (I) species, which provides the as‐developed Li‐I batteries with high capacity and long cycling stability.

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Lithium-oxygen (Li-O2) batteries have drawn intensive attention owing to their exceptionally high theoretical specific energy. However, their further advancement has been significantly hindered by challenges including low discharge capacity, poor energy efficiency, severe parasitic reactions, etc. Here, we report a highly Li-O2 battery operated via a new quenching/mediating mechanism that relies on the direct chemical reactions between a versatile molecule and superoxide radical/Li2O2 nanoparticles. The battery exhibits a 46-fold increase of discharge capacity, a low charge over-potential of 0.7 V, and an ultralong cycle life > 1400 cycles. The tailor-designed organic molecule features two redox mediator-active 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) moieties bridged by a quenching-active perylene diimide (PDI) backbone. The PDI-TEMPO molecule not only acts as a soluble redox mediator to catalyze both discharge and charge reactions, but also serves as a reusable superoxide radical quencher to chemically react with superoxide species generated during the operation of Li-O2 batteries, leading to the formation of Li2O2 nanoparticles which are much easier to decompose than the conventional toroidal-shaped Li2O2. The all-in-one molecule as a multifunctional additive can tackle various issues of parasitic reactions associated with superoxide radicals, singlet oxygen, high over-potentials, and lithium corrosion, beyond the mere combination of PDI and TEMPO moieties’ functionalities. The molecular design of multifunctional additives combining the capabilities of redox mediators, superoxide radical quencher and beyond opens a new avenue for developing high-performance Li-O2 batteries.