The Role of Sulfide Additives in Achieving Long Cycle Life Rechargeable Iron Electrodes in Alkaline Batteries

Abstract

Iron-based alkaline rechargeable batteries such as nickel-iron and iron-air batteries are promising candidates for large-scale energy storage applications because of their relatively low cost, inherent robustness to cycling, and eco-friendliness. In the present study, we demonstrate iron electrodes containing iron (II) sulfide and bismuth oxide additives that do not exhibit any noticeable capacity loss even after 1200 cycles at 100% depth of discharge in each cycle. In iron electrodes prepared with bismuth sulfide additive, capacity loss occurred during cycling, accompanied by a decrease in discharge rate capability and rapid passivation. The recovery of capacity by adding sulfide ions to the electrolyte confirmed that the electrode that suffered capacity fade did not have an adequate supply of sulfide ions. We also found that the loss of cycleability was accompanied by the steady accumulation of magnetite and loss of iron sulfides at the iron electrode. The use of sparingly soluble iron (II) sulfide as an electrode additive ensured a sustained and steady supply of sulfide preventing the accumulation of magnetite during cycling. Thus, we have gained understanding of the critical role of sulfide additives in achieving long cycle life in rechargeable alkaline iron electrodes. Inexpensive and efficient methods of storing electrical energy are essential for the successful integration of solar and wind-based electricity generation into the grid. Among the various means to store electrical energy at a large scale, batteries are particularly promising because of their advantages of high energy efficiency, modularity and flexibility to siting.1-4 The state-of-art commercially-available lithium-ion, lead-acid, nickel-metal hydride and vanadium redox flow batteries may be rated by the levelized cost of energy delivered (LCOE). LCOE is calculated as the ratio of the cost (including capital and operating costs) to the total amount of energy delivered by the battery over its useful lifetime. The LCOE for commercially-available batteries is at least five to ten times higher than the DoE targets of $0.10 to $0.20/kWh. 5,6 Also, since energy storage will be required at the scale of thousands of gigawatt-hours, we are faced with the challenge of providing a sustainable solution, as the global material reserves are quite limited for these state-of-art batteries.7 Therefore, the development of inexpensive, efficient, robust and sustainable battery systems for grid-scale energy storage is a topic of intense research.3-6 Under an effort funded by ARPA-E, we have been focusing on developing such batteries. 7,[8][9][10][11][12] Iron-based battery systems such as nickel-iron and iron-air batteries are based on raw materials that are relatively inexpensive, globally-abundant, and eco-friendly. The promise of iron-based batteries for large-scale energy storage has spurred renewed interest in their development. 11,[13][14][15][16] The development of iron-based alkaline batteries began several decades ago. [17][18][19][20][21][22] In the U...

In Situ Crystallographic Probing on Ameliorating Effect of Sulfide Additives and Carbon Grafting in Iron Electrodes

“…Recently, Narayanan et al have reported that conductive phase of sparingly soluble iron (II) sulfide prevents rapid passivation of iron electrode during discharge and sulfide ions reduce overpotential for the conversion of magnetite to metallic iron. 13 The present study also reflects that sulfide ions from bismuth sulfide have bi-functional role both in charging and discharging reactions of iron electrodes. Beneficial effects of bismuth sulfide additives are that (a) it promotes the reduction of magnetite to iron and hence capacity of iron electrode is increased, (b) it stabilizes and facilitates precipitation of crystalline ferrous hydroxide, (c) it prevents the formation of magnetite during the first step of discharge reaction, and (d) it enhances the cycle life of iron electrodes.…”

Core/Shell Structure Nano-Iron/Iron Carbide Electrodes for Rechargeable Alkaline Iron Batteries

“…4) and further recombination of these ions with iron hydroxide to form iron sulfide within the electrode structure. [38][39][40] The amount of iron sulfide formation is proportional to the availability of iron (II) hydroxide formed during the forward reaction. After ten cycles, there are three well-developed oxidation peaks (A 0 , observed at −0.966 V, A 1 at −0.70 V and A 2 at −0.44 V), which are related to the adsorption of hydroxide ion, 41 further oxidation of Fe to Fe(II) and Fe(II) to Fe(III) respectively.…”

A High-Performance Sintered Iron Electrode for Rechargeable Alkaline Batteries to Enable Large-Scale Energy Storage

“…The iron (II) sulfide is sparingly soluble in the electrolyte, allowing pressed plate electrodes to be discharged at rates as high as 3C, and sustained charge and discharge cycling for over 1000 cycles. 44,45 We found that a sintered electrode could also be prepared with iron (II) sulfide. The discharge rate capability of such a sintered electrode with iron (II) sulfide was found comparable to that of the pressed plate iron electrode containing iron sulfide.…”

“…17 Our recent efforts with a "pressed-plate" type iron electrode have led to remarkable advances in charging efficiency and rate capability, achieved through electrode re-design and re-formulation. 17,[43][44][45] Such "pressed-plate" electrodes were prepared by hot-pressing of a mixture of the carbonyl iron particles, sulfide-containing additives, a pore-forming additive and a polymeric binder. However, greater mechanical robustness is projected for a "sintered-type" iron electrode when compared to other types of electrodes.…”

“…17,43 The role of sulfides in increasing discharge capacity and the factors affecting the cycle life of iron electrodes have also become better understood. 44,45 As a result, iron electrodes with charging efficiencies as high as 96% and with the ability to sustain discharge rates up to 3C, have now been demonstrated. This performance represents a significant improvement compared to the charging efficiency of 55-70% and the recommended discharge Journal of The Electrochemical Society, 164 (2) A418-A429 (2017) A419 rate of 0.2 C of commercial nickel-iron batteries.…”