Yttrium-preintercalated layered manganese oxide as a durable cathode for aqueous zinc-ion batteries.

Rechargeable aqueous zinc-ion batteries (RAZIBs) are regarded as competitive alternatives for large-scale energy storage on account of cost-effectiveness and inherent safety. In particular, rechargeable Zn-MnO2 batteries have drawn increasing attention due to high manufacturing readiness level. However, obtaining MnO2 with high electrochemical activity and high cyclic stability toward Zn2+/H+ storage still remains challenging. Herein, we reveal that incorporating yttrium ions (Y3+) into layered MnO2 can regulate the electronic structure of the MnO2 cathode by narrowing its band gap (from 3.25 to 2.50 eV), thus boosting the electrochemical performance in RAZIBs. Taking advantage of this feature, the optimized Y-MnO2 (YMO) sample exhibits greater capacity (212 vs. 152 mA h g-1 at 0.5 A g-1), better rate capability (94 vs. 61 mA h g-1 at 8 A g-1), reduced charge-transfer resistance (79 vs. 148 Ω), and promoted mass transfer kinetics (3.13 × 10-11vs. 2.37 × 10-11 cm2 s-1) in comparison with Y-free MnO2 (MO). More importantly, compared to MO, YMO-0.1 exhibits enhanced energy storage capability by nearly 40% (309 vs. 222 W h kg-1) and stable cycle performance (94 vs. 52 mA h g-1 after 3000 cycles). In situ Raman microscopy further reveals that the presence of Y3+ endows MnO2 with remarkable electrochemical reversibility during charge/discharge processes. This work highlights the importance of the Y3+ preintercalation strategy, which can be further developed to obtain better cathode materials for aqueous batteries.