Nonflammable Gel Polymer Electrolyte with Ion-Conductive Polyester Networks for Sodium Metal Cells with Excellent Cycling Stability and Enhanced Safety

Abstract

Sodium metal batteries have received a considerable amount of attention because of the low cost of Na resources and high theoretical capacity of Na metal. However, liquid electrolytes used in batteries cause safety problems such as fires and explosions under abnormal conditions. The uncontrolled dendritic Na growth in the cell also results in poor cycling stability. Herein, we report nonflammable gel polymer electrolytes (GPEs) synthesized by in situ cross-linking of a gel precursor containing ion-conductive polycaprolactone triacrylate. The GPE exhibits a high ionic conductivity of 6.3 mS cm–1 because of the Na+–carbonyl interactions and high segmental motion of polycaprolactone chains despite its three-dimensional network structure. The ion-conductive polymer networks effectively suppress the growth of Na dendrite by inducing uniform Na deposition on the Na electrode, resulting in improved interfacial characteristics of the Na electrode. The Na/Na3V2(PO4)3 cell employing GPE delivers high discharge capacities at high C rates and exhibits excellent cycling stability. Additionally, the superior thermal stability of GPE prevents a short circuit of the cell at high temperature, which allows safe operation of the Na/Na3V2(PO4)3 cells.

Interface chemistry for sodium metal anodes/batteries: a review

“…Electrolyte plays an important role in ion transport and affects the deposition morphology of metal anodes. Different electrolyte types have a major influence on dendrite appearance [20,47,[62][63][64][65][66][67][68][69] . SEI layers will greatly affect dendrite formation.…”

“…A low-cost and cross-linked gel-polymer electrolyte of poly(methyl methacrylate) (PMMA) was compounded, enabling dendrite suppression and excellent cycling stability [117] . In addition to organic crosslinked polymers, Lei et al developed a blended inorganic ionic conductor/GPE composite electrolyte, where a β/β"-Al 2 O 3 nanowire (AN) membrane possessing 78.1% β"-phase was tightly wrapped by PVDF-HFPbased GPE, effectively inhibiting the growth of Na dendrite and successive side reactions of the Na metal anode [Figure 8D] [47] . This study for the first time proved the efficient inorganic solid electrolyte ion conductor/polymer composite gel transmission behavior of sodium ions with inorganic ion conductor in its solid-liquid mixture of sodium ion transport mechanism, and illustrated the high efficient inorganic ion conductor matrix composite gel electrolyte for building an important highly stable solid SMB system.…”

“…(E) Schematic of NVP/Na batteries using ANs-GPE and GFs-GPE electrolytes. (D and E) Reproduced with permission from [47] . Copyright 2016, Nature Publishing Group.…”

“…However, until now, the interaction among electrolyte-SEI-sodium dendrite has rarely been summarized, and reviews about electrolyte regulation strategies in suppressing dendrite growth for SMBs have not been published thus far [41][42][43] . This review summarizes a fundamental understanding of sodium dendrite and then gathers various electrolytes, including the components, concentrations, and additives of liquid electrolytes and solid-state electrolytes technologies, to inhibit dendrite growth and the related SEI for dendrite-suppressed SMAs [Figure 1] [44][45][46][47][48][49][50][51][52] . Finally, this review briefly presents a general conclusion and outlook for constructing high-performance and dendrite-suppressed SMBs.…”

Effects of Flexible Group Length of Phosphonate Monomers on the Performance of Gel Polymer Electrolytes for Sodium-Ion Batteries with Ultralong Cycling Life

“…As a quasi-solid state electrolyte, GPE has relatively high ionic conductivity of up to 1 × 10 –3 S cm –1 , which is far higher than SPE and enough for practical applications. , Moreover, GPEs exhibit good electrochemical stabilities with high voltages and thermal stabilities superior to that of LEs . Currently, scientists are devoted to improving the performances of GPEs through various strategies such as adding nanofillers, adding flame retardant additives, composites with commercial separators, blending, copolymerization, and cross-linking by in situ polymerization, etc. Zhu et al prepared a nonwoven-reinforced PVDF-HFP composite GPE, which improved the mechanical properties as well as the electrochemical properties .…”