Synthetic control of crystallite size of silver vanadium phosphorous oxide (Ag_0.50VOPO₄ · 1.9H₂O): Impact on electrochemistry

This report describes a synthetic approach to control the crystallite size of silver vanadium phosphorous oxide, Ag_0.50VOPO₄ · 1.9H₂O, and the impact on electrochemistry in lithium based batteries. Ag_0.50VOPO₄ · 1.9H₂O was synthesized using a stirred hydrothermal method over a range of temperatures. X-ray diffraction (XRD) was used to confirm the crystalline phase and the crystallite size sizes of 11, 22, 38, 40, 49, and 120 nm. Particle shape was plate-like with edges <1 micron to >10 microns. Under galvanostatic reduction the samples with 22 nm crystallites and 880 nm particles produced the highest capacity, ~25% more capacity than the 120 nm sample. Notably, the 11 nm sample resulted in reduced delivered capacity and higher resistance consistent with increased grain boundaries contributing to resistance. Under intermittent pulsing ohmic resistance decreased with increasing crystallite size from 11 nm to 120 nm implying that electrical conduction within a crystal is more facile than between crystallites and across grain boundaries. This systematic study of material dimension shows that crystallite size impacts deliverable capacity as well as cell resistance where both interparticle and intraparticle transport are important.