Copper sulfide nanoparticles as high-performance cathode materials for magnesium secondary batteries

Abstract

Magnesium secondary batteries are promising candidates for large-scale energy storage systems with high safety, because of the dendrite-free electrodeposition of the magnesium anode. However, the search for available cathode materials remains a significant challenge, hindering their development. In this work, we report copper sulfide nanoparticles as high-performance cathode materials for magnesium secondary batteries, which deliver a high reversible capacity of 175 mA h g-1 at 50 mA g-1. The cathode also shows an excellent rate capability providing 90 mA h g-1 at 1000 mA g-1 and an outstanding long-term cyclability over 350 cycles. The beneficial properties are ascribed to the small-sized copper sulfide particles which facilitate the solid-state diffusion kinetics. Further investigation on the mechanism demonstrates that the reaction is a typical conversion reaction, and the excellent cycling stability is due to the CuS nanoparticles which are not facile to aggregate during cycling. This work introduces an abundant, low-cost and high-performance cathode material for magnesium secondary batteries, and provides feasibility for the practical application of magnesium secondary battery systems in large-scale energy storage devices.

A High‐Rate Rechargeable Mg Battery Based on AgCl Conversion Cathode with Fast Solid‐State Mg2+ Diffusion Kinetics

“…Subsequently, Mg cells were established with Mg(HMDS) 2 ‐AlCl 3 ‐MgCl 2 or Mg(HMDS) 2 ‐AlCl 3 electrolyte and AgCl cathode. A lab‐made cell was used to prevent corrosion caused by the electrolyte (Figure S1, Supporting Information) . Figure a,b shows the galvanostatic cycling of AgCl cathode in Mg(HMDS) 2 ‐AlCl 3 ‐MgCl 2 electrolyte at 100 mA g −1 .…”

“…A high specific capacity of 90.7 mAh g −1 (99.7% of the initial value) can still be recovered upon a decrease in current density to 50 mA g −1 , indicating the excellent rate performance of the material. Figure b compares the rate performance of AgCl with several traditional layered Mg‐intercalation cathodes as well as conversion‐type CuS . Due to the high activation energy during structure conversion, conversion‐type electrodes usually exhibit inferior performance than intercalation‐type electrodes.…”

“…a) Rate performance of AgCl cathode at different current densities and b) comparison with reported Mg cathode materials . c) Long‐term cycling performance of AgCl electrode in Mg cells at a current density of 500 mA g −1 .…”

“…The reversibility of conversion reaction could be well‐explained by hard and soft acids and bases theory. Since X 2 n − anion is bonded with bivalent Mg 2+ ion (hard acid), using soft X 2 n − anions (such as S 2− and Se 2− ) is expected to weaken the Mg—X bonds, and thus could improve the reversibility of conversion reaction . However, selection of M element is also of great significance.…”

“…A soft acid M 2 m + cation (such as Cu + ) would have a relatively stronger interaction with X n − anion and assist the dissociation of discharge product (Mg n X m ). For example, Cu 2 S and Cu 2 Se, which are combinations of soft‐acid cation (Cu + ) and soft‐base anion (S 2− and Se 2− ), show superior Mg‐storage performances as conversion cathodes . Therefore, a promising conversion cathode could be a combination of soft anions and soft cations.…”