Zinc–Air Batteries with an Efficient and Stable MnCo₂O₄/Carbon Fiber Bifunctional Electrocatalyst and a Poly(acrylic Acid)-Based Gel Electrolyte

Abstract

Efficient and high-performance zinc–air batteries (ZABs) with gel polymer electrolytes (GPEs) were prepared. Cubic spinel-type MnCo2O4-coated carbon fibers (MnCo2O4/CF) were used to prepare air electrodes, and poly(acrylic acid) was used to prepare alkaline GPEs. Materials characterization, including electron microscopy and X-ray photoelectron spectroscopy, confirmed the formation of MnCo2O4 on the CFs. The optimum composition of the GPE was determined by rheological measurements and battery testing; using GPE with a crosslinker concentration of 30 mM led to the best performing battery. Full-cell battery tests and cycling tests showed that this ZAB cell had outstanding performance with an initial efficiency of 62.6% at 10 mA cm–2, which degraded by only 6.5% after 200 cycles (100 h). The power output of this cell was 240 mW cm–2, which is superior to the power outputs reported in the recent literature for ZABs.

Efficient Low Temperature Performance of All Solid‐State Zinc‐Air Batteries with MnCo2O4/Carbon Fiber Bifunctional Electrocatalyst and Poly(Acrylic Acid) (PAA) Gel Polymer Electrolyte

“…The effect of ion species diffusion becomes more significant at higher current densities (e. g., 50 mA cm −2 ) as the diffusion rates are not fast enough to respond to the higher ORR/OER rates. As such battery performance degrades at 0 °C at current densities greater than ∼20 mA cm −2 [27,32] . At 0 °C, the maximum current density applicable to the cell without causing failure is ∼180 mA cm −2 while at room temperature the battery does fail even at 350 mA cm −2 (Figure 5a and b).…”

“…2) The use of cost‐effective carbon fibers as a conductive substrate for MnCo 2 O 4 improved charge transfer at the air electrode. 3) The hydrogel electrolyte chemistry was optimized [27] …”

“…As such battery performance degrades at 0 °C at current densities greater than ~20 mA cm À 2 . [27,32] At 0 °C, the maximum current density applicable to the cell without causing failure is ~180 mA cm À 2 while at room temperature the battery does fail even at 350 mA cm À 2 (Figure 5a and b). Furthermore, the battery voltage drops more rapidly with increasing current density as the temperature decreases.…”

“…Previous work has shown that when all the other components are the same, the use of a hydrogel electrolyte can lead to higher power densities and better battery performance. This was attributed to the higher viscosity of the hydrogel electrolyte compared with aqueous electrolytes, which resulted in less clogging of porosity and larger electrocatalyst/air/electrolyte contact area [27] . In addition, some recent studies have shown that the use of an effective gel polymer electrolyte can enhance the stability of the battery compared with aqueous electrolytes [28,29] …”

“…This was attributed to the higher viscosity of the hydrogel electrolyte compared with aqueous electrolytes, which resulted in less clogging of porosity and larger electrocatalyst/air/electrolyte contact area. [27] In addition, some recent studies have shown that the use of an effective gel polymer electrolyte can enhance the stability of the battery compared with aqueous electrolytes. [28,29] The purpose of this work is to study the all solid state battery performance, at sub-zero temperatures, of ZABs made with MnCo 2 O 4 /CF as the air electrode material and alkaline poly(acrylic acid) hydrogel electrolyte.…”