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

Abstract

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.