Reversible Anion-Cation Relay-Intercalation in a T-MnO₂ Cathode to Boost the Efficiency of Aqueous Dual-Ion Batteries

Benefiting from the merits of intrinsic safety, high power density, environmental friendliness, and high-output voltage, aqueous dual-ion batteries (ADIBs) have shown broad potential applications in future grid-scale energy storage. However, since the ADIBs require the cathodes to undergo the intercalation reactions through different local structures and mechanisms, causing large structural deformation and cathode failure, their reversible cation-anion intercalation in the cathode remains a major challenge. To address this issue, based on a reasonable selection and theoretical simulation, this work finds that Todorokite manganese dioxide (t-MnO₂) cathode with a metal-ion stabilized 3 × 3 large-tunnel structure should be suitable for cation-anion intercalation of ADIBs. The comprehensive characterizations confirm that the unique tunnel structure of the t-MnO₂ cathode can withstand large structural deformation during the sulfate radical anion- zinc/proton cation (SO₄ ^2--Zn²⁺/H⁺) intercalation. Due to the intercalation of SO₄ ^2-, the ADIB delivered a high reversible capacity of 398 mAh g^-1 at 0.2 A g^-1 with an output voltage of ≈1.41 V, which is much higher than the theoretical capacity (308 mAh g^-1) of Zn-MnO₂ based Zinc-ion batteries. This work provides the design principles for ADIBs cathode materials and demonstrates that t-MnO₂ can be a promising cathode material for high-performance ADIBs.