Nickel hexacyanocobaltate quantum dots embedded in N-doped carbon for aqueous alkaline batteries with ultrahigh...

Nickel-cobalt Prussian blue analogues (Ni-Co PBAs) suffer from structural instability in neural and alkaline electrolytes due to the dissolution of metal cations and cyanide anions caused by external H₂O attack, resulting in capacity degradation and restricted life span. Herein, in this work, Ni-Co PBA quantum dots embedded in N-doped carbon (CC-Ni-Co PBA) were synthesized via a facile coprecipitation method and in situ polymerization followed by calcination under a nitrogen atmosphere. The obtained electrode provided a high specific capacity of 333.7 C g^-1 and still retained 188.8 C g^-1 when the current density increased by 40 times. Remarkably, it exhibited outstanding cycling stability with 82% retention of capacity after 10 000 cycles in an aqueous alkaline electrolyte, which benefited from the inner Ni-Co PBA quantum dots that provided a surrounding space and significantly accommodated the volume change during the repeated charge-discharge process, and the outer carbon layer that served as a protective barrier to hinder the Ni-Co PBA from dissolving into the electrolyte, thus realizing the durability of the electrode. Furthermore, an asymmetric alkaline battery device was assembled which achieved a maximum energy density of 33.2 W h kg^-1 and a power density of 3.1 kW kg^-1. Our work contributed to the development of PBA-based electrode materials with improved cycling stability as battery-type electrodes in aqueous electrolytes.