Phenylphosphonate surface functionalisation of MgMn2O4 with 3D open-channel nanostructures for composite slurry-coated cathodes of rechargeable magnesium batteries operated at room temperature

Koichi Kajihara; Daisuke Takahashi; Hiroaki Kobayashi; Toshihiko Mandai; Hiroaki Imai; Kiyoshi Kanamura

doi:10.1039/d1ra02598h

Phenylphosphonate surface functionalisation of MgMn₂O₄ with 3D open-channel nanostructures for composite slurry-coated cathodes of rechargeable magnesium batteries operated at room temperature

RSC Adv. 2021 May 26;11(31):19076-19082. doi: 10.1039/d1ra02598h. eCollection 2021 May 24.

Authors

Koichi Kajihara¹, Daisuke Takahashi¹, Hiroaki Kobayashi², Toshihiko Mandai³, Hiroaki Imai⁴, Kiyoshi Kanamura¹

Affiliations

¹ Department of Applied Chemistry for Environment, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University 1-1 Minami-Osawa Hachioji Tokyo 192-0397 Japan kkaji@tmu.ac.jp.
² Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 2-1-1 Katahira, Aoba-ku Sendai Miyagi 980-8577 Japan.
³ Center for Green Research on Energy and Environmental Materials, National Institute for Materials Science (NIMS) 1-1 Namiki Tsukuba Ibaraki 305-0044 Japan.
⁴ Department of Applied Chemistry, Faculty of Science and Technology, Keio University 3-14-1 Hiyoshi, Kohoku-ku Yokohama Kanagawa 223-8522 Japan.

Abstract

Spinel-type MgMn₂O₄, prepared by a propylene-oxide-driven sol-gel method, has a high surface area and structured bimodal macro- and mesopores, and exhibits good electrochemical properties as a cathode active material for rechargeable magnesium batteries. However, because of its hydrophilicity and significant water adsorption properties, macroscopic aggregates are formed in composite slurry-coated cathodes when 1-methyl-2-pyrrolidone (NMP) is used as a non-aqueous solvent. Functionalising the surface with phenylphosphonate groups was found to be an easy and effective technique to render the structured MgMn₂O₄ hydrophobic and suppress aggregate formation in NMP-based slurries. This surface functionalisation also reduced side reactions during charging, while maintaining the discharge capacity, and significantly improved the coulombic efficiency. Uniform slurry-coated cathodes with active material fractions as high as 93 wt% can be produced on Al foils by this technique employing carbon nanotubes as an electrically conductive support. A coin-type full cell consisting of this slurry-coated cathode and a magnesium alloy anode delivered an initial discharge capacity of ∼100 mA h g^-1 at 25 °C.