biostudies-literatureKobayashi HAdvanced Low Carbon Technology Research and Development ProgramJapan Society for the Promotion of Science3135-3142https://www.ebi.ac.uk/biostudies/studies/S-EPMC9933879biostudies-literatureUnknown17(3)Magnesium rechargeable batteries (MRBs) promise to be the next post lithium-ion batteries that can help meet the increasing demand for high-energy, cost-effective, high-safety energy storage devices. Early prototype MRBs that use molybdenum-sulfide cathodes have low terminal voltages, requiring the development of oxide-based cathodes capable of overcoming the sulfide's low Mg²⁺ conductivity. Here, we fabricate an ultraporous (>500 m² g^-1) and ultrasmall (<2.5 nm) cubic spinel MgMn₂O₄ (MMO) by a freeze-dry assisted room-temperature alcohol reduction process. While the as-fabricated MMO exhibits a discharge capacity of 160 mAh g^-1, the removal of its surface hydroxy groups by heat-treatment activates it without structural change, improving its discharge capacity to 270 mAh g^-1─the theoretical capacity at room temperature. These results are made possible by the ultraporous, ultrasmall particles that stabilize the metastable cubic spinel phase, promoting both the Mg²⁺ insertion/deintercalation in the MMO and the reversible transformation between the cubic spinel and cubic rock-salt phases.ACS nanoUltraporous, Ultrasmall MgMn₂O₄ Spinel Cathode for a Room-Temperature Magnesium Rechargeable Battery.PMC9933879JPMJAL1301JP20H02436Tominaga YIimura RNishimura NWatanabe HIchitsubo TKobayashi HFukumi YImai HMandai TNakayama MHonma IfalseUltraporous, Ultrasmall MgMn₂O₄ Spinel Cathode for a Room-Temperature Magnesium Rechargeable Battery.Magnesium rechargeable batteries (MRBs) promise to be the next post lithium-ion batteries that can help meet the increasing demand for high-energy, cost-effective, high-safety energy storage devices. Early prototype MRBs that use molybdenum-sulfide cathodes have low terminal voltages, requiring the development of oxide-based cathodes capable of overcoming the sulfide's low Mg²⁺ conductivity. Here, we fabricate an ultraporous (>500 m² g^-1) and ultrasmall (<2.5 nm) cubic spinel MgMn₂O₄ (MMO) by a freeze-dry assisted room-temperature alcohol reduction process. While the as-fabricated MMO exhibits a discharge capacity of 160 mAh g^-1, the removal of its surface hydroxy groups by heat-treatment activates it without structural change, improving its discharge capacity to 270 mAh g^-1─the theoretical capacity at room temperature. These results are made possible by the ultraporous, ultrasmall particles that stabilize the metastable cubic spinel phase, promoting both the Mg²⁺ insertion/deintercalation in the MMO and the reversible transformation between the cubic spinel and cubic rock-salt phases.2023-01-01T00:00:00Z2023 Feb2026-03-27T16:37:12.029Z2025-04-04T10:36:11.983ZS-EPMC99338793666909410.1021/acsnano.2c12392