Na₃V₂(PO₄)₃ as the Sole Solid Energy Storage Material for Redox Flow Sodium‐Ion Battery

Abstract

like wind and solar for electricity generation. The growth will go on accelerating to replace the fossil fuels in the future. [1] At the same time, the intermittent nature of these power sources necessitates a durable and cost-effective energy storage system to meet the huge demands for peak shifting and power buffering for GWscale systems. Considering the scalability, operation safety, and flexibility, redox flow battery (RFB) is regarded as one of the most promising electrochemical energy storage technologies which have found their own niche for the large-scale energy storage applications. [2] Unlike other rivals such as lithium ion battery and leadacid battery, RFB stores energy in mobilized electrolyte solutions other than in solid active materials coated on electrode sheets. The design that the redox active compounds circulate between the storage reservoir and cell stack with the aid of pumps, enables decoupled energy storage and power generation.However, the conventional redox flow batteries severely suffer from low energy density (<40 Wh L −1 ) as a result of limited solubility of redox species and low cell voltage, which adds on the footprint and capital cost of the system, impeding its practical deployment. [3] To improve the energy density, various aprotic RFBs have been explored for enhanced cell voltage. [4,5] However, because of the low solubility of aprotic solvents to many redox active compounds, [6] the reported high energy aprotic RFBs are limited to a few systems such as polyiodide, [7] redox-active ionic liquids, [8,9] deep eutectics, [10] and hybrid electrolyte. [11,12] Through molecular engineering, metallocene such as ferrocene derivatives [13,14] and redox-active organic materials [15][16][17][18][19] such as 2,2,6,6-tetramethylpiperidin-1-oxyl derivatives [17] and benzothiadiazole [16] have recently been reported to have good solubility and potentially high energy density. Although the solubility can reach up to 5 m in pure solvent, taking the supporting salts and electrolyte viscosity into consideration, the practical concentration of those molecules remains limited to <2 m.[2] By forming slurry of solid active materials with conducting carbon additives, semisolid flow cells that utilize solid suspensions represent an alternative way to increase the effective concentration. [20] Although the energy density can in theory be increased considerably, these cells may have critical issues on fluid conductivities and Redox flow batteries have considerable advantages of system scalability and operation flexibility over other battery technologies, which makes them promising for large-scale energy storage application. However, they suffer from low energy density and consequently relatively high cost for a nominal energy output. Redox targeting-based flow batteries are employed by incorporating solid energy storage materials in the tank and present energy density far beyond the solubility limit of the electrolytes. The success of this concept relies on paring suitable redox mediators with solid mate...

A Comparative Review of Metal‐Based Charge Carriers in Nonaqueous Flow Batteries

“…This resulted in a demonstrated volumetric energy density of 88 Wh L À 1 and a solid storage capacity of 52 %. [80] The authors also observed an [80] improvement in electron transfer kinetics over previous systems.…”

Bi2S3 spheres coated with MOF-derived Co9S8 and N-doped carbon composite layer for half/full sodium-ion batteries with superior performance

“…6a). The Na 3 V 2 (PO 4 ) 3 /rGO has been widely explored and used as a promising cathode material for SIBs owing to its excellent work voltage and superior cycling stability [53,[58][59][60]. SEM images and XRD pattern of the as-synthesized Na 3 V 2 (PO 4 ) 3 /rGO are shown in Fig.…”

Single‐Molecule Redox‐Targeting Reactions for a pH‐Neutral Aqueous Organic Redox Flow Battery

“…[13] This feature may allow a high SMRT reaction rate since it has been suggested to be limited by the ion diffusion in the solid matrix in the actual working conditions. [39,26] Volume-unbalanced while compositionally symmetric cells were fabricated to evaluate the catholyte performance and NiHCF utilization without crossover interference. As shown in the Supporting Information, Figure S11, the elongated voltage profile was a result of the two-way SMRT reactions of NiHCF-NaI/NaI 3 .…”

“…[21][22][23] The redox-targeting reactions, where solid materials are used as capacity boosters in the energy storage tank (Figure 1 a; Supporting Information, Figure S1), have been demonstrated as an efficient method to considerably improve the effective solubility of redox species in various RFBs such as nonaqueous redox flow lithium or sodium batteries and metal complex-based aqueous RFBs, and so on. [24][25][26][27][28] In this study, the redox targeting reaction of quinone with polyimide was investigated to solve the low-solubility hurdle of 2,7-AQDS in pH-neutral electrolyte system.…”