Fluorinated graphite nanoplatelets

The development of graphite nano-platelets is getting better and better, and more and more different graphite nano-platelets have been derived. Fluorinated graphite nano-platelets are one of them, and fluorinated graphite nano-platelets are also important raw materials for batteries.

Background

Lithium fluoride carbon (Li / CFX) battery is the battery system with the highest specific energy in solid electrode chemical power supply. It has attracted much attention due to its high energy density, stable working voltage, long service life, safety and reliability, wide working temperature range, and many other advantages. The F / C limit value of conventional fluorinated carbon materials is 1, the theoretical specific capacity is 865mah · g-1 [2,3], and it is difficult to give full play to it. The specific energy of the prepared lithium fluorinated carbon batteries is usually lower than 700wh · kg-1. Therefore, whether and how to achieve higher specific energy based on the lithium fluoride carbon battery system has become a hot and difficult problem.

Content validity

Recently, researcher Wang Xiwen of Tianjin Lishen Special Power Technology Co., Ltd. published a research article entitled “fluorinated graphite nano-platelets for ultra-high capacity lithium primary batteries” on rare metals. The joint research group has made disruptive technical achievements in the preparation of fluorinated carbon materials and fluorinated carbon electrodes, Breaking through the F / C and specific capacity limits of existing fluorinated carbon materials, a new mechanism of “dual function” electrolyte solid-liquid series discharge is proposed, which provides a new strategy for realizing ultra-high specific energy lithium primary battery.

By adjusting the temperature, the edge defects and the active sites of – CF2, – CF3 perfluorinated functional groups were introduced into graphite nano-platelets (NSS) in the form of covalent bond/semi covalent bond/semi ionic bond, which broke the limit of F / C ratio and achieved high-performance ultra-thin microstructure. At the current density of 10 Ma · g-1, the specific capacity of graphite fluoride nano-platelets reached 921 MAH · g-1.

The research group also innovatively put forward the solid-liquid phase relay discharge theory, and designed a “dual function” electrolyte with lithium-ion conduction and lithium synthesis reaction; A 20Ah grade flexible packaging lithium fluoride carbon battery was developed by optimizing the electrode formulation and constructing a high specific energy fluorinated carbon electrode with fast dynamic response characteristics. The specific energy of 0.01c discharge at room temperature and 60 ℃ reached 1021.5 wh · kg-1 and 1116 wh · kg-1 respectively, which is the highest level reported so far.

Graphic ananlysis

The corresponding GFFs were prepared by heating the graphite nanosheet(GR NSS) to a specific temperature of 400 ℃ in a nitrogen atmosphere, and then fluorinated for 10 hours in the fluorine gas environment. It is found that CFX NSS has been transformed into a granular structure and can not maintain the original lamellar structure. TEM and said also shows that CFX NSS is formed by particles with a size of about 20 nm, The high-resolution transmission electron microscopy (HR TEM) also confirmed that it is a completely disordered amorphous structure on an atomic scale.

The results show that the fluorine carbon ratio of CFX NSS is 1.34 and the fluorine carbon ratio is far more than commercial. The high-resolution XPS C1s spectrum contains a large number of CF2 groups (22.27%), which is because of the strong oxidation of fluorine gas under high temperature, which leads to the formation of a large number of edge structures of carbon materials. These edge structures are easy to form perfluorinated functional groups under the action of a large number of suspended bonds [4]. The discharge specific capacity of GR NSS is 921 MAH g-1 in the constant current discharge curve of 10 Mag-1. It is consistent with the theoretical value calculated based on XPS results [5], which proves that -cf2 also has certain electrochemical activity.

The experimental results show that the electrolyte containing ethylene sulfite (ES) and dimethyl sulfite (DMS) can carry out the electrochemical reduction reaction with the carbon as the carrier after the discharge of the fluorinated carbon material, so as to realize the solid-liquid phase relay discharge. Therefore, in the designed CFX / Li primary battery, the electrolyte containing ES / DMS has two positive functions at the same time: supporting the transport of lithium-ion and providing additional energy.

The research group used the unique three-dimensional structure of light aluminum mesh as the collector to prepare 0.85mm thick carbon fluoride electrode, pure metal lithium as the negative electrode, combined with the laminated electrode group structure, to prepare 24 ah flexible lithium fluoride carbon primary battery. At room temperature and 60 ℃, the specific energy of the battery was 1021.5 wh · kg-1 and 1116 wh · kg-1, respectively.

Summary

1. The high temperature helps to introduce edge defects, – CF2 and – CF3 functional groups, and some nonfluorinated regions into the nanoplatelets, thus forming a covalent bond/semi covalent bond/semi ionic bond hybrid valence bonding environment, which shows superior high specific energy performance in practical applications.

2. Sulfites such as ethylene sulfite (ES) and dimethyl sulfite (DMS) can redox with lithium using carbon as a carrier, and have appropriate potential; By introducing es and DMS as electrolyte solvents, the solid-liquid phase relay discharge can be realized, and the specific energy of the battery can be further improved.

3. By optimizing the fluorination process, modifying electrolytes, adopting a thick electrode process, and controlling the proportion of active substance and electrolyte in the battery, the 24 ah flexible packaging effective battery shows ultra-high specific energy, which is the highest level reported at present.