Stable Cycling of High-Mass Loaded MnO2 Electrodes for Sodium-ion Batteries

Abstract

Achieving cost-effective, sustainable solutions for large-scale energy storage are critical for advancing the global clean energy transition. In view of the challenges posed by limited lithium reserves, low-cost sodium-ion batteries (SIBs) have emerged as a promising direction, especially for grid-level energy storage. Among the various battery electrode materials, manganese dioxide (MnO2) stands out as a favorable choice for such large-scale applications due to its earth abundance, cost-effectiveness, and non-toxic nature. Although MnO2 is known as a pseudocapacitive material with superior cycling stability in aqueous electrolytes, its dissolution in non-aqueous electrolytes has restricted its use in long-lifetime batteries. In this study, we address two issues which have limited the use of MnO2 electrodes in non-aqueous electrolytes. First, using electrochemical quartz crystal microbalance measurements in combination with other electrochemical methods, we demonstrate that diglyme (bis(2-methoxyethyl) ether) electrolyte can achieve stable cycling of electrodeposited ε-MnO2. These results enable us to tackle a second objective, that is increasing the mass loading of the MnO2 electrode, since achieving high areal energy density is a significant factor in reducing manufacturing costs. Using 3D printed graphene aerogel (GA) as a scaffold, our studies show that the electrodeposited MnO2/GA electrodes possess scalable properties with mass loadings from 20 to 80 mg cm-2. The resulting electrodes exhibit areal energy densities as high as 4.4 mAh cm-2 at a current density of 10 mA cm-2. The high mass loaded MnO2 electrodes were incorporated as a cathode in a SIB which used TiO2 as the anode. The SIB device exhibited excellent performance with power densities in excess of 70 mW cm-2. These studies highlight the promise of MnO2 electrodes for use in a low-cost technology for large-scale energy storage.