Synthetically Produced Isocubanite as an Anode Material for Sodium-Ion Batteries: Understanding the Reaction Mechanism During Sodium Uptake and Release

Abstract

Bulk isocubanite (CuFe2S3) was synthesized via a multistep high-temperature synthesis and was investigated as an anode material for sodium-ion batteries. CuFe2S3 exhibits an excellent electrochemical performance with a capacity retention of 422 mA h g–1 for more than 1000 cycles at a current rate of 0.5 A g–1 (0.85 C). The complex reaction mechanism of the first cycle was investigated via PXRD and X-ray absorption spectroscopy. At the early stages of Na uptake, CuFe2S3 is converted to form crystalline CuFeS2 and nanocrystalline NaFe1.5S2 simultaneously. By increasing the Na content, Cu+ is reduced to nanocrystalline Cu, followed by the reduction of Fe2+ to amorphous Fe0 while reflections of nanocrystalline Na2S appear. During charging up to −5 Na/f.u., the intermediate NaFe1.5S2 appears again, which transforms in the last step of charging to a new unknown phase. This unknown phase together with NaFe1.5S2 plays a key role in the mechanism for the following cycles, evidenced by the PXRD investigation of the second cycle. Even after 400 cycles, the occurrence of nanocrystalline phases made it possible to gain insights into the alteration of the mechanism, which shows that Cu x S phases play an important role in the region of constant specific capacity.

Influence of the Cation on the Reaction Mechanism of Sodium Uptake and Release in Bivalent Transition Metal Thiophosphate Anodes: A Case Study of Fe2P2S6

“…While such observations can have several reasons, [24,25,36–38] it is most likely that a changing electrochemical reaction during long periods of cycling is responsible in this case. The successive changing of discharge/charge profiles (see ESI; Figure S2) during extended cycling is an obvious indication of a changing long‐term mechanism, which is a common observation for MTP compounds [24–26] as well as for other conversion electrodes [27–29,36,38,39] …”

“…The successive changing of discharge/charge profiles (see ESI; Figure S2) during extended cycling is an obvious indication of a changing long-term mechanism, which is a common observation for MTP compounds [24][25][26] as well as for other conversion electrodes. [27][28][29]36,38,39] For further electrochemical characterization, rate capability experiments (Figure 2c) were conducted applying increasing current rates (0.2, 0.5, 1.0, 2.0, 3.0 and again 0.2 A g À 1 ) for 10 cycles each. Increasing the current rate from 0.2 to 3.0 A g À 1 results in decreased specific capacities in the 10 th cycle (Table 1).…”

“…Besides studying structural and electronic changes during the discharge and charge process, another highly interesting question was how Fe 2 P 2 S 6 performs electrochemically compared to its Ni analogue. While the electrochemical characterization of this anode material was carried out using standard methods, previous studies on the reaction mechanisms of different anode materials have shown that the structural characterization of the ongoing reaction mechanisms usually requires multiple complementary techniques [24,25,27–30] . Accordingly, the reaction mechanism of sodium uptake and release in Fe 2 P 2 S 6 anodes was examined extensively and in a similar way as previously done for Ni 2 P 2 S 6 [24] using X‐ray diffraction (XRD), X‐ray absorption spectroscopy (XAS), pair‐distribution function (PDF) analysis as well as 31 P/ 23 Na magic‐angle‐spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy.…”

Facile Phase Control of Solution-Processed Copper Iron Sulfide Nanocrystals for a Low-Cost Self-Powered NIR Photodetector with Fast Response

“…The isocubanite structure of CuFe 2 S 3 was synthesized, as evidenced by the characteristic diffraction reflections of the (111), (220), and (311) lattice planes of the cubic phase in the XRD pattern as well as the 0.306 nm lattice fringe in HRTEM results. 28 Notably, no impurity phase was observed in the XRD pattern. Furthermore, the clear lattice reveals the single-crystalline nature of each nanoparticle.…”

“…65 The excellent recyclability and phase stability of CuFeS 2 -based devices as photocatalysts, sodium-ion batteries, and electrochemical detectors were also demonstrated, even in 0.1 M KCl solution. 15,28,35,66 We also investigated the air and moisture stability of the CuFeS 2 photodetectors, as shown in Figure 7.…”