Revealing Electrochemically Induced Antisite Defects in LiCoPO4: Evolution upon Cycling

This article aims to reveal the formation of antisite defects that are induced in LiCoPO4 crystals upon electrochemical charge/discharge cycles. This is achieved using Cs-corrected high-angle annular dark-field scanning transmission electron microscopy that allows their direct visualization. By comparison with simulated images, their evolution is discussed and their quantification performed. In a sample free of defects, a disordering caused by the exchange between lithium and cobalt atoms is progressively created. It is the first time that evidence of antisite defect creation in an olivine-type compound upon electrochemical cycling has been reported. Their formation is shown to occur during the charging process. While they are heterogeneously distributed after the first charge/discharge cycle because of their concentration, such exchange defects appear to be more homogeneously dispersed in the lattice when their amount is much larger after the 30th charge/discharge cycle. This article provides new insight into the behavior of this compound and contributes to an explanation for the reason why such a high-capacity fading is observed when this material is used in a battery.