Chemical Stability and Degradation Mechanism of Solid Electrolytes/Aqueous Media at a Steady State for Long-Lasting Sodium Batteries

Abstract

Research on the interface between solid electrolytes and electrode materials or catholyte is important to effectively and safely use their high energy densities. However, compared to interfaces with electrode materials, the interface between solid electrolytes and liquid media lacks research. Herein, the stability of NA superionic conductor (NASICON) pellets is studied in various aqueous solutions, including deionized (DI) water and a marine environment, associated with different degradation mechanisms. A representative detrimental hydronium exchange reaction between solid electrolytes and aqueous media is suppressed with increasing concentration and ion types dissolved in the solutions. Results of density functional theory calculation and electron energy loss spectroscopy reveal the different activation energies and chemical bonding states of solid electrolytes based on the aqueous solutions' conditions. NASICON's ionic conductivity decreases to ∼10 −6 S/cm because of severe changes in aqueous solutions with insufficient dissolved ions resulting in inferior chemical stability. Furthermore, chemical stability variations at a steady state can severely affect battery performance. Seawater batteries fabricated with NASICON in immersed DI water for 1 year exhibit a large resistance region from the first cycle; this system breaks down before 200 h, unlike a cell fabricated using NASICON immersed for 1 year in a marine environment.

Investigation on the Structure and Properties of Na3.1Zr1.55Si2.3P0.7O11 as a Solid Electrolyte and Its Application in a Seawater Battery

“…18,20 Since ZrO 2 has no Na + conductivity, the lower amount of ZrO 2 in the vA-NASICON ceramic leads to a smaller value of R g.b compared to H-NASICON. 15 In addition, ZrO 2 causes microcracking (explained in the mechanical section), which can cause grain boundaries to separate, thus increasing R g.b . It can also be observed from Table S1 that the NASICON grain size in the vA-NASICON ceramic (2−6 μm) was larger than that of the H-NASICON ceramic (0.5−3 μm).…”

“…Among them, Na 3 Zr 2 Si 2 PO 12 ( x = 2) [H-NASICON] is the most well-known composition that shows a high ionic conductivity at room temperature. Typical ionic conductivity values are σ bulk (bulk ionic conductivity) = ∼6.8 × 10 –4 S/cm, and σ total (total ionic conductivity) = ∼3 × 10 –4 S/cm as shown in Table , , and some recent studies improved σ total up to ∼1 × 10 –3 S/cm using advanced synthesis methods. , The H-NASICON ceramic was reported to be stable in room-temperature seawater and used in the SWB as a solid electrolyte with a long cycle life . However, H-NASICON always contains a minor secondary phase of ZrO 2 (2–4 wt %), which has been reported to reduce ionic conductivity and mechanical strength. − …”

Strong interfacial energetics between catalysts and current collectors in aqueous sodium–air batteries

“…The overall electrochemical performances of PvdF were unstable because the trapped air resulted from the hydrophobic nature of PvdF. Furthermore, the PvdF cannot form strong bonds with electrodes and metals, 9 resulting in a rapid increase and saturation of overpotential (∼1.05 V at 30 th cycle) (Fig. 4b, S18a†) which is similar to the overpotential of bare HCF (1.02 V).…”

“…1,2 Aqueous metal–air batteries, such as lithium, sodium, potassium, and zinc–air batteries, have emerged as a new type of energy storage belonging to the family 3–6 of alkali metal–air batteries because of their advantages over modern commercial power supplies, such as low cost and eco-friendliness. 7–9 However, such systems have been considerably restricted to high overpotentials because of oxygen evolution and reduction reactions (OER and ORR), which results in a low power owing to the four-electron process and decrease energy efficiency by a large gap of charge and discharge curves. The previous study attempted to minimize the overpotential using electrocatalysts and polymeric binders.…”

Seawater Battery-Based Wireless Marine Buoy System With Battery Degradation Prediction and Multiple Power Optimization Capabilities

“…Marine application devices based on the SWB cells include the power plants [12], [13], the energy storage system (ESS) for boats [14], and the buoy for coastal positioning which is self-powered with other harvesting devices like the photovoltaic (PV) [15]. Especially, the buoy application is interested in its usage time [16], but there are still some issues to be resolved in these previous works. Firstly, it requires proper methods to support the state of charge (SOC) estimation function [17]- [21].…”