Ferroelectricity enhances ion migration in hard carbon anodes for high-performance potassium ion batteries

Hard carbon is a promising candidate for potassium ion batteries due to its large interlayer spacing and abundant closed pores. However, the slow migration and sluggish diffusion kinetics of potassium ions lead to inferior insertion and pore-filling processes, causing severe ion channel blocking, continuous byproduct generation, and poor cycling stability. In this study, we coated hard carbon on top of tetragonal barium titanate particles forming a ferroelectricity-aided anode (t-BTO@C). The t-BTO@C anode exhibits higher interfacial charge density, enhanced insertion-pore filling capacity, and formation of fewer byproducts. The effective interaction between the spontaneous polarization electric field of t-BTO and potassium ions accelerates the potassium ion kinetics and ensures the homogeneous migration of potassium ions, as well as the improvement of t-BTO@C anode potassium storage. After 100 cycles at 0.05 A g^-1, the t-BTO@C anode shows a specific capacity of 374.9 mA h g^-1, higher than those of SiO₂@Carbon (97.2 mA h g^-1) and Pure Carbon (240.1 mA h g^-1). Paired with a Prussian white cathode, the full cell shows a specific capacity of 313.0 mA h g^-1 at 0.1 A g^-1, with 88.9% capacity retention after 40 cycles, much higher than those in recent reports. Our strategy provides a new path to improve the performance of the hard carbon anode in potassium ion batteries.