An asymmetric gel polymer electrolyte with dual functions of immobilizing polysulfides and promoting uniform Li deposition.

have been found in preventing the pen etration of Li dendrites. [15][16][17] However, the excessive interfacial resistance and the complex processing art of inorganic SSEs limit their practical application. [18][19][20] Solid polymer electrolytes (SPEs), on the other hand, can offer good flexibility and stable contact between the electrodes and electrolytes. [20][21][22][23] Several types of polymer matrices have been developed, such as poly(ethyleneoxide) (PEO), [24][25][26] poly carbonate, [27][28][29] and polysiloxane. [30][31][32] SPEs are prepared by mixing polymer matrices with Li salts. PEO is the most popular and deeply studied polymer matrix, [33] and the ethylene oxide chain segments in PEO can dissolve Li salts as well as form complexes with Li + and dis sociated Li salts. [34] Li + is conducted by repeatedly carrying out a "decomplexa tion-recomplexation" process through the movement of chain segments in an amorphous polymer region. [35] The movement of chain segments in an amorphous polymer region is affected by the glass transition temperature (T g ) and crystallinity. Low T g and crystallinity are beneficial for the move ment of chain segments as well as the ionic conductivity. Due to the high crystallinity of PEO, PEObased SPEs have a low ionic conductivity (10 −8 -10 −7 S cm −1 ) at room temperature, which does not meet the requirement for ionic conductivity (>10 −4 S cm −1 at room temperature) of electrolytes with prom ising applications. [33,36,37] Many strategies, such as adding inorganic nanoparticles, [38][39][40] blending, [41] copolymerization, [42] and crosslinking [43][44][45] have been adopted to effectively sup press the crystallization of PEO and improve the ionic conduc tivity of PEObased SPEs. Coat et al. [46] reported the synthesis of poly(diethylene oxidealtoxymethylene) (P(2EOMO)) as a polymer matrix for SPE, which has higher T g than that of PEO in the electrolyte. They found the P(2EOMO)/LiTFSI electro lyte exhibits a slightly lower ionic conductivity due to higher T g , but much higher Li ion transference number can be obtained in P(2EOMO)/LiTFSI electrolyte (0.36) than that in PEO/ LiTFSI (0.19). So tailoring the main chain structure is the most feasible way to optimize the performance of SPEs.Recently, the strategy of in situ polymerizing SPEs in the batteries has attracted extensive attention due to the ability to construct stable ionic conduction networks inside the electrodes to reduce the interfacial resistance, the biggest challenge faced by most SSEs. Cui et al. [13] in situ prepared A series of copolymers are prepared via cationic ring-opening polymerization with 1,3-dioxolane (DOL) and trioxymethylene (TOM) as monomers. The crystallization behaviors of the copolymers can be suppressed by adjusting the ratio of DOL/TOM. With LiBF 4 as a source for a BF 3 initiator, copolymer electrolytes (CPEs) can be prepared in situ inside cells without needing nonelectrolyte catalysts or initiators. The ionic conductivities and Li + diffusion coefficients (D Li + ) of the CPEs inc...

Solid polymer electrolyte is one of the best choices to improve the safety of lithium metal batteries (LMBs). However, its widespread application is hindered because of the low ionic conductivity at room temperature and large interfacial resistance. Here, a cross-linked polymer is synthesized with an unsaturated polyester and used as a polymer electrolyte membrane (PEM). The PEM has a high ionic conductivity (1.99 × 10–3 S cm–1 at 30 °C) and a low glass transition temperature (−54.2 °C), contributing to decreasing interfacial resistance, promoting more uniform Li deposition, and suppressing Li dendrite penetration. The PEM also has a wide electrochemical stable window (∼4.6 V) and superior thermal stability (>150 °C), showing high potential in LMBs. The LiFePO4–Li coin cells and pouch pack batteries with PEM present very stable cycle performance and high safety, indicating that the PEM can be a promising candidate for future solid-state LMBs.

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