Gel Polymer Electrolytes Design for Na‐Ion Batteries

Abstract

Na‐ion battery has the potential to be one of the best types of next‐generation energy storage devices by virtue of their cost and sustainability advantages. With the demand for high safety, the replacement of traditional organic electrolytes with polymer electrolytes can avoid electrolyte leakage and thermal instability. Polymer electrolytes, however, suffer from low ionic conductivity and large interfacial impedance. Gel polymer electrolytes (GPEs) represent an excellent balance that combines the advantages of high ionic conductivity, low interfacial impedance, high thermal stability, and flexibility. This short review summarizes the recent progress on gel polymer Na‐ion batteries, focusing on different preparation approaches and the resultant physical and electrochemical properties. Reasons for the differences in ionic conductivity, mechanical properties, interfacial properties, and thermal stability are discussed at the molecular level. This Review may offer a deep understanding of sodium‐ion GPEs and may guide the design of intermolecular interactions for high‐performance gel polymer Na‐ion batteries.

Inert Filler Selection Strategies in Li-Ion Gel Polymer Electrolytes

“…To determine the optimum ratio of fillers, different contents (0, 5, 10, 15, 20%) of silica are used as examples (LiTFSI-PVDF-HFP-SiO 2 ). XRD patterns show that the crystallinity of the polymer decreases with the increase of the amount of SiO 2 , indicating that the filler affects the structure of the polymer chain . When the proportion of filler reaches 15% (0.075 g), the ionic conductivity reaches the maximum.…”

“…XRD patterns show that the crystallinity of the polymer decreases with the increase of the amount of SiO 2 , indicating that the filler affects the structure of the polymer chain. 32 When the proportion of filler reaches 15% (0.075 g), the ionic conductivity reaches the maximum. A continued increase in filler content may cause agglomeration and compromise the conductivity (Figure S1).…”

Optimization Strategies Toward Functional Sodium‐Ion Batteries

“…[ 75 ] Polymer solid‐state electrolytes based on polyethylene oxide (PEO), polyacrylonitrile (PAN), poly‐methylmethacrylate (PMMA), and polyvinylidene fluoride (PVDF) are flexible and have better interfacial contact, but their low ionic conductivity limits their uses. [ 77 ] Inorganic solid electrolytes typically consist of crystalline ceramics and amorphous glasses and are commonly metal based, for example, β″‐Al 2 O 3 , Na 3 PS 4 , and NASICON (Na 1+ x Zr 2 Si x P 3− x O 12 ). [ 78 ] Consequently, they are usually quite brittle and costly.…”

“…Compared to conventional solvents, ionic liquids comprised only of ions that exhibit favorable features, including reduced flammability and excellent thermal and chemical stability. [ 77 ] Ionogel electrolyte composed of NaBF 4 , 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF4), and poly(vinylidene difluoride‐co‐hexafluoropropylene) (PVDF‐HFP) shows remarkable ionic conductivity of 8.1 mS cm −1 at room temperature for micro‐SIBs. [ 87 ] The NaBF 4 ‐IE displayed larger (sodium‐ion transference number) = 0.49 due to smaller sodium clusters facilitating high mobility.…”

Boosting Cycling Stability of Polymer Sodium Battery by “Rigid-Flexible” Coupled Interfacial Stress Modulation

“…Since the interfacial contact between the electrode and the polymer electrolyte (PE) is the rate-limiting step that determines the overall ionic conductivity of the battery, it is crucial to develop good interfacial contact for high-performance PSMBs. It is well-known that in situ polymerization electrolyte and interfacial film design, including cathode–electrolyte interface (CEI) films and solid electrolyte interface (SEI) films, are common strategies to increase interfacial contacts. − Besides forming stable electrode–electrolyte interfaces through polymer electrolyte engineering, modifying cathode materials to possess high mechanical strength is another effective strategy to achieve stable interfaces. Cho et al proposed that the severe stress field during cycling is due to the phase separation caused by the high phase transition barrier and large Na + ions, which is based on first-principles calculations and a phase-field method. , Moreover, Aurbach et al used a bond valence model to calculate strain in layered Mn–Ni–Co oxides, predicting that lattice strain could be relieved by substituting the size and level of cations to form a solid solution. , Given the importance of interfacial stress regulation on the cycling performance of PMSB and the lack of in-depth research at present.…”