Co-Fe Prussian blue analogue ultrafine nanocrystal cubes grown in-situ in honeycomb carbon as high-performance anode for lithium-ion batteries

Prussian blue analogues (PBAs) are promising anode materials for lithium-ion batteries due to the unique 3D open frameworks, but inferior cycling performance and poor rate capability restrict their application. Herein, Co-Fe PBA@honeycomb carbon is prepared by means of well-designed solution evaporation assembly and in-situ etching-coordination strategy. K_0.90Co[Fe(CN)₆]_0.97□_0.03⋅0·.44H₂O (□: vacancy defect) cubes with uniform size of 20 nm are grown within every honeycomb carbon pore with a diameter of ∼ 180 nm. The mass content of Co-Fe PBA reaches 78.61 wt%. The small size, low defects and less interstitial/coordinated water improve kinetics properties and robustness of Co-Fe PBA. Honeycomb carbon further enhances the electronic conductivity and structural stability of Co-Fe PBA. Accordingly, Co-Fe PBA@honeycomb carbon exhibits high reversible capacities of 915 mAh/g at 0.5 A/g after 200 cycles, 658 mAh/g at 1 A/g after 1000 cycles, 496 mAh/g at 2 A/g after 450 cycles. Rate performance and kinetics properties are superior. The reversible capacity at 5 A/g is as high as 328 mAh/g. The diffusion coefficient of Li⁺ reaches 10^−10.0 ∼ 10^−11.7 cm² s⁻¹. Ex-situ scanning electron microscopy and Fourier transform infrared spectrometer demonstrate that the cycled Co-Fe PBA@honeycomb carbon is stable.