Ferroelectricity-enhanced potassium-ion storage in van der Waals layered CuInP2S6

Abstract

We integrate ferroelectric principles into two-dimensional (2D) van der Waals materials to enhance both charge and potassium ion (K⁺) transport at the electrode interface. CuInP₂S₆ (CIPS) has a distinct room-temperature ferroelectric field effect due to the unique ordering of Cu and In ions in the CIPS lattice, which disrupts its centrosymmetry and causes significant spontaneous polarization. Its natural dipole moment creates a persistent polarizing electric field, facilitating fast carrier transfer from the material's bulk to its surface, boosting ionic conductivity under high electric fields. Utilizing the synergistic effects, layered CIPS coupled with graphene (CIPS@G) exhibits high specific capacity, superior long cycling stability and outstanding rate performance. The CIPS@G composite in a potassium-ion battery (PIB) offers a reversible capacity of 565 mA h g⁻¹ at 50 mA g⁻¹, robust stability over 1000 cycles, and high rate performance (10 A g⁻¹), and a cycle life exceeding 400 cycles was also achieved when assembled in a full battery. In hybrid capacitors, CIPS@G stands out with superior rate performance up to 2.0 A g⁻¹ and high energy density (40 W h kg⁻¹) at 2.0 A g⁻¹, surpassing other PIB phosphide and sulfide anodes reported to date. These results show that high-rate nanochannels between 2D CIPS nanosheets and graphene, paired with CIPS's ferroelectric polarization, improve electronic conductivity, support K⁺ diffusion, relieve CIPS aggregation, and buffer volume changes. The study on enhancing K⁺ performance in 2D materials through the integration of ferroelectric field principles holds promise for pioneering advancements in electrochemical systems.