Enhanced lithium battery cathode performance via mechanical grinding of CFx_MnO2 hybrid materials for space-grade applications: Unveiling synergistic effects

Abstract

CFx_MnO₂ hybrid cathode materials are prepared from a (C₂F)n-type graphite fluoride (CFx) and industrial MnO₂. Because of its physicochemical (insulating behavior, low content of CF₂ and CF₃ groups, no or a few remaining sp² carbon atoms) and electrochemical properties (flat plateau on galvanostatic curve and theoretical capacity of 623 mAh/g, higher than other conventional cathodes for primary lithium battery), graphite fluoride of (C₂F)n-type is selected to evidence synergetic effects with MnO₂ that occur at the fluoride/oxide and electrolyte/ electrode interfaces. Both materials are mixed by mechanical ball-milling using different sets of parameters. The hybrid material presents very good electrochemical properties with a maximum energy density of about 1600 Wh per kg of active material. Notably, it shows a considerable improvement in voltage plateau and voltage delay compared to CFx. The parameters applied during ball-milling also shape the electrochemical performance of the new hybrid material. Ball milling increases the average discharge voltage plateau, and the power density of the battery, and avoids ohmic drop which may cause a battery to be eliminated as soon as it begins to discharge. More finely, electrochemical impedance spectroscopy shows that pushed grinding leads to more homogeneous but more polarized material-electrolyte interfaces so better diffusion and capacity but lower discharge potential.