On the Way to Rechargeable Mg Batteries: The Challenge of New Cathode Materials

Abstract

To initiate wider discussion about promising research directions, this paper highlights a number of challenges in the development of rechargeable Mg batteries, especially those related to the slow solid-state Mg diffusion in common hosts. With a focus on the intercalation mechanism, we compare for the first time different strategies proposed in the literature for developing Mg battery cathodes, like the use of (i) nanoscale cathode materials; (ii) hybrid intercalation compounds containing bound water or other additional anion groups that can presumably screen the charge of the inserted cations, (iii) cluster-containing compounds with efficient attainment of local electroneutrality. This comparative analysis shows that cathodes whose function is based on a combination of the two first strategies, e.g., V2O5 gels and their hybrids, can exhibit relatively high voltage and capacity upon Mg insertion, but their kinetics is insufficiently fast. A proper intercalation mechanism for such materials is still unknown, but their relatively slow cation transport seems to be intrinsic: The paradox is that the high capacity testifies Mg insertion into crystal sites with incomplete charge screening. In contrast, the high rate capability and exclusively stable cycling of cathodes based on Chevrel phases (Mo6-cluster- containing compounds) are appropriate for Mg battery design, but they offer low energy density because of the low voltage. On the basis of the knowledge of the intercalation mechanism in these phases, we believe that the future search for cathode materials in rechargeable Mg batteries should be focused on new cluster-containing intercalation compounds with higher capacity and working potential.

Sponge-Like Porous Manganese(II,III) Oxide as a Highly Efficient Cathode Material for Rechargeable Magnesium Ion Batteries

“…[1][2][3] In particular, MIB has been regarded as the most promising candidate owing to magnesium's rich content in the Earth's crust (20,000 times more than Li), as well as its chemical stability. 4 Compared to Li, Mg is inherently much safer due to higher stability in contact with air in addition to the absence of dendritic formation during electrochemical cycling. 4,5 Also, compared to Li, Mg has a theoretical volumetric capacity of 3833 mAh cm -3 , nearly twice that of Li (2061 mAh cm -3 ), indicating that MIB has a good potential for reaching a high volumetric energy density.…”

Status and challenge of Mg battery cathode

“…Especially the Mo 6 clusters is speculated as a critical factor to ensure high Mg 2+ diffusivity in solid state host because they can easily compensate the chargeunbalance due to the introduction of bivalent Mg 2+ ions. 20 The synthesis of CPs typically starts with the preparation of Cu 2 Mo 6 S 8 followed by leaching out Cu 2+ ions. Cu 2 Mo 6 S 8 , chemically leached in I 2 /acetonitrile or in HCl/H 2 O, was able to accommodate the theoretical amount of Mg 2+ ions upon the fi rst discharge of the electrode (2 Mg atoms per formula unit).…”

“…Levi et al argued that the existence of a cluster-like redox center enables the fast electron re-distribution during the migration of guest Mg 2+ ions. 20 The local electron neutralization requests the distribution of two electrons simultaneously with the migration of Mg 2+ , which in classical intercalation-type cathode is kinetically sluggish. For CPs, however, the electron re-distribution only changes the formal charge of individual Mo ions by 1/3 e .…”

Surface stability of spinel MgNi0.5Mn1.5O4 and MgMn2O4 as cathode materials for magnesium ion batteries

“…The research is now focused on finding suitable electrode materials with a good electrochemical performance for magnesium ion batteries (MIBs) in order to achieve high energy capacity and safety rechargeable ion batteries for electric vehicles [4][5][6][7][8][9][10][11]. Oxides with a spinel structure such as spinel-type Mn 2 O 4 are widely used as cathode materials for lithium ion batteries (LIBs) [12,13].…”