Configuring Optimal FeS₂@Carbon Nanoreactor Anodes: Toward Insights into Pyrite Phase Change/Failure Mechanism in Rechargeable Ni–Fe Cells

Abstract

Pyrite FeS2 has long been a research focus as the alternative anode of rechargeable Ni–Fe cells owing to its eye-catching merits of great earth-abundance, attractive electrical conductivity, and output capacity. However, its further progress is impeded by unsatisfactory cyclic behaviors due to still “ill-defined” phase changes. To gain insights into the pyrite working principles/failure factors, we herein design a core–shell hybrid of a FeS2@carbon nanoreactor, an optimal anode configuration approaching the practical usage state. The resultant electrodes exhibit a Max. specific capacity of ∼272.89 mAh g–1 (at ∼0.81 A g–1), remarkably improved cyclic longevity/stability (beyond ∼80% capacity retention after 103 cycles) and superior rate capability (∼146.18 mAh g–1 is remained at ∼20.01 A g–1) in contrast to bare FeS2 counterparts. The as-built Ni–Fe full cells can also output impressive specific energy/power densities of ∼87.38 Wh kg–1/ ∼ 11.54 kW kg–1. Moreover, a refreshed redox reaction working mechanism of “FeS2OH ↔FeS2↔Fe0 (in pyrite domains)” is redefined based on real-time electrode characterizations at distinct operation stages. In a total cyclic period, the configured pyrite-based anodes would stepwise undergo three critical stages nominally named “retention”, “phase transition/coexistence”, and “degradation”, each of which is closely related to variations on anodic compositions/structures. Combined with optimal electrode configurations and in-depth clarifications on inherent phase conversions, this focus study may guide us to maximize the utilization efficiency of pyrite for all other aqueous electrochemical devices.

High‐Capacity Iron‐Based Anodes for Aqueous Secondary Nickel−Iron Batteries: Recent Progress and Prospects

“…Particularly, amorphous frameworks can not only provide more exposed ion channels, accelerate rapid charge transfer across the electrode/electrolyte interface, and further facilitate fast ion intercalation, but also offer low internal energy and outstanding chemical stability. Thus, it is critically Metallic iron Fe nanoparticles À 0.6 V 208 mAh/g (1 mA/g) [50] Iron oxides Fe 2 O 3 nanorods À 0.7 V 278 mAh/g (1 A/g) [25] Fe 3 O 4 nanowire À 0.8 V 207.6 mAh/g (5 mA/cm 2 ) [26] FeOx nanocrystals À 1.0 V 370.2 mAh/g (2 A/g) [33] Iron hydroxides Fe(OH) 2 nanorsheets À 1.0 V 300.2 mAh/g (1 A/g) [63] Iron sulfides FeS 2 nanospheres À 0.7 V 272.89 mAh/g (0.81 A/g) [64] FeS nanparticles À 0.9 V 531.2 mAh/g (1C) [65] Iron phosphides FeP nanowires À 0.9 V 0.634 mAh/cm 2 (2 mA/cm 2 ) [66] Iron selenides FeSe 2 nanorods À 0.8 V 124 mAh/g (1 mA/cm 2 ) [30] important to explore innovative synthesis of amorphous Febased anodes for next-generation NiÀ Fe batteries. To date, the underlying energy storage mechanism of Fe-based anodes in aqueous NiÀ Fe batteries is still uncertain.…”

“…Yao et al. designed a low‐cost and novel method to fabricate the core‐shell hybrid FeS 2 @carbon nanoreactor as the anode material [64] . Figure 12a depicted the charging and discharging process of FeS 2 @C, and it was a reversible process with valence change of Fe 2+ and Fe 0 .…”

“…Yao et al designed a low-cost and novel method to fabricate the core-shell hybrid FeS 2 @carbon nanoreactor as the anode material. [64] Figure 12a depicted the charging and discharging process of FeS 2 @C, and it was a reversible process with valence change of Fe 2 + and Fe 0 . TEM in Figure 12b clearly exhibited the well-defined spherical structure of FeS 2 , which is homogeneously wrapped with the carbon nanoreactor with the diacritical size of around 70 nm.…”

Mesoporous Fe3O4@C nanoarrays as high-performance anode for rechargeable Ni/Fe battery

“…Compared with the large capacitive and superior stable Ni-based cathode materials, Fe-based anode materials in Ni/Fe battery usually show poor stability, and the exploration of Fe-based anode electrodes is still unsatisfactory [18]. Iron owns multiple valence states and rich redox chemistry, enabling its high theoretical specific capacity within a wide potential range [19].…”

Rational construction of self-standing fiber-shaped aqueous rechargeable batteries

“…Although the significant progress achieved for Ni-based cathode materials, the lack of high-capacity Fe-based anode materials remains a stumbling block preventing further improvements of the energy density of aqueous rechargeable Ni-Fe batteries. Moreover, with the evergrowing consumer usage of portable and wearable electronics, small, flexible and lightweight fiber-shaped Ni-Fe batteries are regarded as promising energy supply devices [155][156][157][158][159]. Therefore, the exploration of high-performance fibrous Fe-based anodes is still highly valuable and significant for the use in high-energy-density wearable Ni-Fe batteries.…”