Abstract: Based on low cost and earth abundance potassium resources, potassium-ion batteries have been regarded as the potential candidate for large-scale energy storage applications for renewable energy and smart grid. Although some earlier works have proposed reversible insertion/extraction of K⁺ ions in K cells, their cycle instability is insufficient for the further application of potassium-ion batteries. Herein, we report a symmetric potassium-ion battery with ultralong life employing a bipolar Cr/Ti based layered oxide, which contains two electrochemically active transition metals with the redox couples of Cr⁴⁺/Cr³⁺ and Ti⁴⁺/Ti³⁺ working on the ca-thode and anode side, respectively. Moreover, the (de)intercalation process in the structure and the in-situ electrochemical exchange process are investigated by ex-situ XRD. As a result, the symmetric cell based on the obtained K-based bipolar layered material exhibits a reversible capacity of 102 mA·h/g between 0.5 V and 3.5 V at 20 mA/g, an ultralong cycle life of 2000 cycles with a capacity retention of 80% and high rate capabilities. The outstanding cycling stability and rate performance endow this work with promising advantages for the future development of the novel energy storage system.

Key words: Layered oxide, Potassium-ion battery, Symmetric electrode, Ultralong life