Solid-state polymer electrolytes are outstanding candidates for next-generation lithium metal batteries in the realm of high specific energy densities , high safeties and tight contact with electrodes. However, their applications are still hindered by the limitations that no single polymer is electrochemically stable with the oxidizing high-voltage cathode and the highly reductive Li anode, simultaneously. Herein, a bilayer asymmetric polymer electrolyte (SL-SPE) without accessional interface resistance that using poly (ethylene glycol) diacrylate (PEGDA) as a “bridge” to connect the sulfonyl (O S = O)-contained oxidation-tolerated layer and polyether-derived reduction-tolerated layer (SPE), is proposed and synthesized by sequential two-step UV polymerizations. SL-SPE can provide widened electrochemical stability window up to 5 V, while simultaneously deploying a stable Janus interface property . Eventually, the superior high-voltage (4.4 V) cycling durability can be displayed in LiNi 0.6 Co 0.2 Mn 0.2 O 2 |SL-SPE|Li batteries . This finding provides a bran-new idea for designing multifunctional polymer electrolytes in the application of solid-state batteries.
Fanglin Xu,Shungui Deng,Qingya Guo,Dong Zhou,Xiayin Yao
Poly(vinylidene fluoride)-based polymer electrolytes are being intensely investigated for solid-state lithium metal batteries. However, phase separation and porous structures are still pronounced issues in traditional preparing procedure. Herein, a bottom-to-up strategy is employed to design single-phase and densified polymer electrolytes via incorporating quasi-ionic liquid with poly(vinylidene fluoride- co -hexafluoropropylene). Due to strong ion/dipole–dipole interaction, the optimized polymer electrolyte delivers high room-temperature ionic conductivity of 1.55 × 10 −3 S cm −1 , superior thermal and oxidation stability of 4.97 V, excellent stretchability of over 1500% and toughness of 43 MJ cm −3 as well as desirable self-extinguishing ability. Furthermore, the superb compatibility toward Li anode enables over 3000 h cycling of Li plating/stripping and ≈98% Coulombic efficiency in Li||Cu test at 0.1 mA cm −2 . In particular, lithium metal battery Li||LiNi 0.6 Co 0.2 Mn 0.2 O 2 exhibits a room-temperature discharge retention rate of 96% after 500 cycles under a rate of 0.1 C, which is associated with the rigid-flexible coupling electrodes/electrolytes interphase. This investigation demonstrates the potential application of quasi-ionic liquid/polymer electrolytes in safe lithium metal batteries.
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