Tunable Interfacial Electric Field‐Mediated Cobalt‐Doped FeSe/Fe₃Se₄ Heterostructure for High‐Efficiency Potassium Storage

Abstract

The interfacial electric field (IEF) in the heterostructure can accelerate electron transport and ion migration, thereby enhancing the electrochemical performance of potassium-ion batteries (PIBs). Nevertheless, the quantification and modulation of the IEF for high-efficiency PIB anodes currently remains a blank slate. Herein, we achieve for the first time the quantification and tuning of IEF via amorphous carbon-coated undifferentiated cobalt-doped FeSe/Fe₃Se₄ heterostructure (denoted UN-CoFe₄Se₅/C) for efficient potassium storage. Co doping can increase the IEF in FeSe/Fe₃Se₄, thereby improving the electron transport, promoting the potassium adsorption capacity, and lowering the diffusion barrier. As expected, the IEF magnitude in UN-CoFe₄Se₅/C is experimentally quantified as 62.84 mV, which is 3.65 times larger than that of amorphous carbon-coated FeSe/Fe₃Se₄ heterostructure (Fe₄Se₅/C). Benefiting from the strong IEF, UN-CoFe₄Se₅/C as a PIB anode exhibits superior rate capability (145.8 mAh g^-1 at 10.0 A g^-1) and long cycle lifespan (capacity retention of 95.1 % over 3000 cycles at 1.0 A g^-1). Furthermore, this undifferentiated doping strategy can universally regulate the IEF magnitude in CoSe₂/Co₉Se₈ and FeS₂/Fe₇S₈ heterostructures. This work can provide fundamental insights into the design of advanced PIB electrodes.