Abstract

Rechargeable divalent batteries employing Ca or Mg metal negative electrodes have attracted considerable interest due to their low cost and potentially high energy density. However, the development of high-energy Ca and Mg batteries remains limited by the lack of oxide positive electrodes capable of reversibly accommodating divalent ions at room temperature. Here, we demonstrate a new positive electrode material, a nano-sized hexagonal tunnel-structured MoO₃ (nano-h-MoO₃), as a structurally robust host for both Ca²⁺ and Mg²⁺ storage, exhibiting markedly improved reversibility and capacities. Comprehensive structural analyses, supported by computational modeling, reveal a unique charge–discharge mechanism in which divalent-ion (de)insertion occurs through reversible modulation of host metal–oxygen bond lengths while retaining an intact host framework, resulting in minimal lattice expansion (<2%). This structurally resilient tunnel-oxide design provides a promising pathway for developing high-energy, practical divalent metal battery systems.

Credit: Iimura, R., Peiris, M. D. H. C., Yabu, T. et al. Advanced Energy Materials 16(25), e71006 (2026). https://doi.org/10.1002/aenm.71006. Licensed under CC BY 4.0.