In Situ Atomic-Scale Observation of Electrochemical (De)potassiation in Te Nanowires

Potassium-ion batteries (PIBs) have great potential in energy storage due to their high abundance and low cost of potassium resources. Tellurium (Te) is a promising PIB cathode due to its high volumetric capacity and good electronic conductivity. However, the electrochemical (de)potassiation mechanism of Te remains elusive due to the lack of an effective method of directly observing the dynamic reaction at atomic resolution. Here, the phase transformations of single crystal Te on (de)potassiation are clearly revealed by in situ high-resolution transmission electron microscopy and electron diffraction. Te undergoes a consecutive phase transformation during potassiation: from Te to K2Te3 in the initial potassiation, and then part of the K2Te3 to K5Te3 on further potassiation. The reaction has extremely high reversibility in the following depotassiation. By atomic-scale observation, an anisotropic reaction mechanism where K+ intercalates into Te crystalline lattice preferentially through the (001) plane (having a large d-spacing) is established during potassiation. While in the depotassiation process, K ions extract from the polycrystalline KxTe along the same diffusion path to form single crystal Te, indicating the potassium storage is highly reversible. The strong orientation-dependent (de)potassiation mechanism revealed by this work provides implications for the future design of nanostructured cathodes for high-performance PIBs.

Automated summary

This study reveals the phase transformations and electrochemical mechanism of tellurium (Te) in potassium-ion batteries (PIBs) using in situ high-resolution transmission electron microscopy and electron diffraction. The results show that the potassium storage in Te is highly reversible, providing implications for the future design of high-performance nanostructured cathodes for PIBs.