Phosphate-Based "Nanorulers" for Potassium-Ion Battery Cathodes

Phosphate-Based "Nanorulers" for Potassium-Ion Battery Cathodes

Author: Angewandte Chemie International Edition

Potassium-ion batteries (PIBs) could be a useful alternative to commercial lithium-ion batteries in the field of large-scale energy storage due to the abundance of potassium resources and the low electrochemical potential. However, the large ionic radius of K+ results in a large lattice strain and large volume variations, which hampers the practical application of PIBs.

Xiaosi Zhou, Nanjing Normal University, China, and colleagues have developed a one-step solvothermal method for the production of a low-strain, phosphate-based PIB cathode material, i.e., K3(VO)(HV2O3)(PO4)2(HPO4), or KVP, with a “nanoruler” shape (pictured schematically in green). The team mixed VOSO4, K3PO4·3H2O, and K2HPO4·3H2O in ethylene glycol and water and heated the mixture to 160 °C. They tailored the size and morphology of the KVP nanorulers by tuning the volume ratio of ethylene glycol and water in the precursor solution.

X-ray diffraction analysis showed that KVP has a small cell volume change (2.7 %) during repeated K+ extraction/insertion processes. In addition, fast K+ transport kinetics were confirmed by electrochemical tests and density functional theory (DFT) calculations. The KVP nanorulers provide a high average working voltage (4.11 V) and good cyclic performance (92.1 % capacity retention after 2,500 cycles) and rate properties (54.4 mAh g–1 at 5 A g–1).



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