en.Wedoany.com Reported - A team led by Professor Pan Feng from the School of Advanced Materials at Peking University Shenzhen Graduate School, in collaboration with other researchers, has proposed a "strain delocalization" strategy to develop a highly safe, long-cycle aqueous magnesium-ion energy storage battery, achieving 75,000 cycles. The team introduced tantalum doping into molybdenum trioxide nanotube arrays to fabricate molybdenum tantalum oxide (MoTaOx) electrode materials. The related research findings were recently published in the Journal of the American Chemical Society.
Aqueous batteries utilize water-based electrolytes and possess inherent flame-retardant properties, making them a widely studied technological direction in the field of safe energy storage. Traditional aqueous batteries represented by lead-acid and nickel-metal hydride systems have already been applied in automotive starting and civilian devices, but their energy storage density is extremely low. Among emerging aqueous energy storage systems, aqueous magnesium-ion batteries hold potential for constructing high volumetric energy density systems while maintaining lattice stability, owing to magnesium's high crustal abundance, low cost, and small ionic radius. However, their commercialization has long been hindered by severe cycling degradation and actual energy densities far below theoretical values. Although various cathode materials have been explored, alleviating strain accumulation caused by ion intercalation and achieving long-life cycling remain persistent challenges in this field.
The research team discovered that tantalum atom doping introduces oxygen vacancies near terminal oxygen sites. These oxygen vacancies can adsorb and dissociate interlayer water molecules, enabling tantalum hydroxyl groups and water molecules to form complexes through hydrogen bonding, thereby lowering the kinetic energy barrier for hydrated magnesium-ion diffusion. Meanwhile, the ordered arrangement and dissociation of interlayer water molecules can mitigate interlayer expansion and internal strain induced by the co-intercalation of hydrated magnesium ions. These mechanisms collectively form the energy storage foundation of the MoTaOx electrode.
Benefiting from optimized ion transport channels and effective strain delocalization capability, the MoTaOx electrode delivers a capacity of 300 mAh g⁻¹ at a current density of 0.15 A g⁻¹, and maintains high electrochemical stability after 75,000 cycles, with a cumulative capacity reaching 7.2 Ah g⁻¹, far surpassing the best levels previously reported. The joint team also assembled all-aqueous magnesium-ion pouch cells and integrated magnesium-ion microbatteries, validating the material's potential for practical applications.
This study provides a high-capacity cathode material with ultra-long cycling life and elucidates, from a mechanistic perspective, the pathway to achieving ion-intercalation strain delocalization through modulating the local coordination environment, offering both theoretical and practical support for designing next-generation aqueous batteries that combine high energy density with long cycling life.
