Tuesday, 31 May 2022: 09:20
West Meeting Room 110 (Vancouver Convention Center)
Fluorinated graphite (CFx) is a class of cathode materials with the high theoretical capacity (865 mAh g-1 in case of x=1) for primary (non-rechargeable) batteries. When using Li metal as the anode material, the system possesses a very low self-discharge rate (< 0.5% per year at 25 °C) compared to other current alternative chemistries. This system, with the proposed general governing reaction of CFx+Li→LiF+C, is one of the best candidates for a wide range of applications, such as implantable medical devices and equipment for extreme environment.
Although the lithium fluorinated graphite system has been under investigation for a few decades, there is still a lack of fundamental understanding of the reaction mechanism in this system. Here, a multiscale investigation on the CFx discharge mechanism was performed using a novel cathode structure to minimize the carbon and fluorine additives for precise cathode characterizations. Titration gas chromatography (TGC), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), cross-sectional focused ion beam (FIB), high-resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) were utilized to investigate this system.
The results demonstrated that: (i) There is no lithium deposition or intercalation through the entire discharge. (ii) The CFx structure transforms to a hard-carbon like structure with less sp2 content by increasing depth of discharge. (iii) The crystalline LiF particles uniformly covered the layers of CFx structure with a size range of < 10 nm. A three-step discharge reaction mechanism is proposed in agreement with our electrochemical performances. This work deepens the understanding of CFx as a high energy density cathode material and highlights the need for future investigations on primary battery materials to advance performance.
Although the lithium fluorinated graphite system has been under investigation for a few decades, there is still a lack of fundamental understanding of the reaction mechanism in this system. Here, a multiscale investigation on the CFx discharge mechanism was performed using a novel cathode structure to minimize the carbon and fluorine additives for precise cathode characterizations. Titration gas chromatography (TGC), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), cross-sectional focused ion beam (FIB), high-resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) were utilized to investigate this system.
The results demonstrated that: (i) There is no lithium deposition or intercalation through the entire discharge. (ii) The CFx structure transforms to a hard-carbon like structure with less sp2 content by increasing depth of discharge. (iii) The crystalline LiF particles uniformly covered the layers of CFx structure with a size range of < 10 nm. A three-step discharge reaction mechanism is proposed in agreement with our electrochemical performances. This work deepens the understanding of CFx as a high energy density cathode material and highlights the need for future investigations on primary battery materials to advance performance.