A Full Flexible NH₄⁺ Ion Battery Based on the Concentrated Hydrogel Electrolyte for Enhanced Performance

Abstract

Non-metal ammonium (NH þ 4 ) ions have recently been explored as effective charge carriers in battery systems due to their abundancy, light weight, small hydration shells in water. The research concerning the use of NH þ 4 redox chemistry in batteries, particularly in flexible batteries, is still in its infancy. For the first time, we report a flexible full NH þ 4 ion battery (AIB) composed of a concentrated hydrogel electrolyte sandwiched between NH 4 V 3 O 8 • 2.9H 2 O nanobelts cathode and polyaniline (PANI) anode, for enhanced performance. The hydrogel electrolyte is simply synthesized by using ammonium sulfate, xanthan gum and water. As a reference, the AIB based on the liquid aqueous electrolyte is prepared first, which exhibits a capacity of 121 mAh g À 1 and a capacity retention of 95 % after 400 cycles at a specific current of 0.1 A g À 1 . On the other hand, the simple synthesis of the hydrogel electrolyte allows us to facilely tune and optimize the salt contents in the electrolyte, to maximize the ionic conductivity, transport kinetics, mechanical characteristics, and consequently the battery performance. It is found that the flexible battery based on the hydrogel electrolyte prepared from 3 M ammonium sulfate solution shows the best electrochemical performance, i. e., a capacity of 60 mAh g À 1 while maintaining a capacity retention of 88 % after 250 cycles at a specific current of 0.1 A g À 1 . Moreover, the flexible AIB retains excellent electrochemical performance when bent at different angles, demonstrating remarkable mechanical strength and flexibility. Therefore, this study sheds new light on the utilization of concentrated hydrogel electrolyte in the AIB chemistry, for developments of novel electrochemical energy storage technology with high safety and low cost.

Recent Progress in Aqueous Ammonium-Ion Batteries

“…60 In the other report, Kuchena and Wang presented a fully flexible AIB using a concentrated hydrogel electrolyte sandwiched between an ammonium vanadate cathode and a polyaniline anode. 61 The concentrated hydrogel electrolyte was synthesized by simply mixing (NH 4 ) 2 SO 4 , xanthan gum, and water, as shown in Figure 7 b,c. By varying the amount of salt in the electrolyte (prepared using 1, 2, or 3 m solution), it was found that the battery composed of the gel electrolyte prepared from the 3 m salt solution delivers the best initial capacity of 55 mA g –1 as well as good cyclability over 250 cycles at 0.1 A g –1 , as this electrolyte has the highest ionic conductivity of 6.1 × 10 –3 S cm –1 and the largest tensile strength of 4.36 kPa among the three.…”

“…(f) Photo showing the flexible battery lighting up LED light bulbs. Panels (d,e) are reproduced with permission from ref ( 61 ). Copyright 2021 Wiley.…”

“…Schematics showing the (b) synthesis of the hydrogel electrolyte using xanthan gum and (c) structure of the hydrogel electrolyte using xanthan gum. Panels (b,c) are reproduced with permission from ref ( 61 ). Copyright 2021 Wiley.…”

“…In one report, a flexible ammonium-ion battery was demonstrated utilizing a quasi-solid-state electrolyte made from polyacrylamide (PAM) with a slat concentration of 1 M NH 4 Cl solution, as displayed in Figure a, which had an ionic conductivity of 8.7 × 10 –3 S cm –1 and a tensile strength of 5.84 MPa . In the other report, Kuchena and Wang presented a fully flexible AIB using a concentrated hydrogel electrolyte sandwiched between an ammonium vanadate cathode and a polyaniline anode . The concentrated hydrogel electrolyte was synthesized by simply mixing (NH 4 ) 2 SO 4 , xanthan gum, and water, as shown in Figure b,c.…”

Nickel ferrocyanides for aqueous ammonium ion batteries

“…[2][3][4][5][6][7][8] Consequently, lots of framework materials have been explored extensively and some of them are identified as electroactive materials for ammonium ion batteries, e.g. transition metal oxides, [9][10][11][12] organic compounds, [13][14][15] and metal organic frameworks. 2,16 Among the multitudinous reported compounds, Prussian blue analogues as a member of metal organic frameworks are regarded as conceivable cathode can-didates, partly because of their low cost, eco-friendliness, and easy accessibility.…”