Chemical lithiation methodology enabled Prussian blue as a Li-rich cathode material for secondary Li-ion batteries

Prussian blue analogues (PBAs) have been attracting intense attention owing to its two-electron storage capability and considerable cost advantage, especially in Na-ion and K-ion batteries. However, things are quite different when it comes to Li-ion batteries, because lithium-containing Li4Fe(CN)6 precursor is not commercially available and thus the traditionally prepared Li-deficient FeFe(CN)6 products fail to couple with commercial graphite anode for full cells. Herein, we put forward a potential matching principle to guide the chemical pre-lithiation of FeFe(CN)6 into a Li-rich LixFeFe(CN)6 (x varies from 0 to 2) cathode. The potential matching principle was convincingly confirmed by theoretical analysis and over-lithiation experiments. Perylene-Li reagent was elaborately screened to serve as both Li+ and electron donor for controllable chemical lithiation reaction while preserving the host framework stable. Our work provided a general guiding principle and effective methodology for controllable synthesis of Prussian blue analogues in gradient lithiation depth, which could be served as a platform for in-depth, systematic and comprehensive research on the properties of PBAs materials.