Magnesium-Ion Storage Capability of MXenes

Abstract

Rechargeable magnesium-ion batteries (MIBs) with Mg metal anodes have been attracting attention due to their potential safety, low cost, and high theoretical energy densities. Nevertheless, developing a high-energy-density MIB with long cycle life and reasonable rate capability is still a huge challenge due to the lack of high-performance cathodes beyond the Chevrel phases. Here, we investigate the mechanism of Mg-ion uptake and storage by MXenes, that have been theoretically predicted to be promising candidates for MIB cathodes. Flexible and conductive 3D macroporous Ti 3 C 2 T x MXene films were fabricated and tested as MIB cathodes after the incorporation of Mg ions from a Mg 2+containing electrolyte. The 3D MXene cathode exhibited promising cycling stability, accompanied by good rate performance. A 3D Mg 0.21 Ti 3 C 2 T x MXene electrode delivered, at 0.5, 1, and 5 C, capacities of ∼210, ∼140, and ∼55 mA h g −1 , respectively. A reversible intercalation charge-storage mechanism was demonstrated and a possible redox reaction mechanism proposed. Considering the large family of 2D transition metal carbides and nitrides, with over 30 different MXenes synthesized to date, this work suggests the availability of a variety of high-rate cathode candidates for MIBs.

A review on MXene for energy storage application: effect of interlayer distance

“…It was demonstrated by Meng-Qiang Zhao et al regarding the storage of magnesium ions in MXenes. The asfabricated 3D microporous flexible and conductive MXene films were tested as a cathode in magnesium ion battery after the intercalation of magnesium ions from a magnesium-based electrolyte [79,80]. A fabricated composite Mg 0.21 Ti 3 C 2 T x electrode shows capacitance values of 210 mAh g −1 , 140 mAh g −1 and 55 mAh g −1 respectively at capacities of 0.5 C, 1 C, and 5 C. It was shown that after intercalating Mg 2+ ion between the MXene layers the (002) peak shifts from 6.5°to 5.7°.…”

Are MXenes suitable as cathode materials for rechargeable Mg batteries?

“…A similar charge storage mechanism may be postulated for Mg-ions. However, the reported voltage profiles for non-aqueous Mg-electrolytes deviate and the charge-storage mechanism is far from resolved, [39][40][41] which will be discussed in the following.…”

“…Another noteworthy attempt to enable MXene cathodes for RMBs was recently reported by Zhao et al, demonstrating a 3D macroporous Ti3C2Tx paper cathode with clear voltage plateaus and reversible capacities around 200 mA h g -1 . 41 The paper cathode was fabricated through a sacrificial template method, obtaining a porosity of around 90%. The highly porous paper was soaked in APC-THF, which lead to increased MXene d-spacing (from 1.36 to 1.55 nm) and substantial amounts of Mg, Al and Cl observed by EDX.…”

“…38 Recently, several works have reported similar initial capacities for pristine Ti3C2Tx, all tested with APC-THF electrolyte at room temperature. [39][40][41] By pre-incorporation of large organic molecules (e.g. cationic surfactant, 40 phenyl-MgCl from the electrolyte 41 ) or even carbon nanospheres, 39 reversible capacities of 100-200 mA h g -1 have been reported.…”

“…Mg-ion intercalation assisted by cetyltrimethylammonium (CTA + ), phenyl-MgCl intercalation, or a combined intercalation and conversion reaction. [39][40][41] This raises a critical question about the possibility of unsolvated Mg 2+ intercalation in MXene, versus predominantly surface reactions and/or intercalation of complex ions. In order to enable competitive energy-dense Mg batteries, intercalation of unsolvated and noncomplexed Mg 2+ ions is necessary.…”